Deciphering the liquid-solid interactions in dealkalization of O3 layered oxides

Domain: biology
Published: 2026-03-19
Editorial outcome: major_revision

Abstract
O3-phase layered oxides are among the mainstream positive electrode active materials for advanced batteries due to stable topological lattice framework and potential for tunability. However, surface residual alkali due to sensitivity hinder their large-scale application. Water washing, an industrial surface residual alkali removal method in lithium-based positive electrode materials, brings about severe issues in sodium-based materials such as lattice collapse and extensive active alkali metal ion leaching. Here, we propose an interaction mechanism between host solid-phase positive electrode materials and guest liquid-phase solvents, which elucidates the dependent structural degradation on the molecular configuration of dispersed solvents and the alkali metal–oxygen bond covalency during dealkalization. For H2O (H3O+), self-propagating molecule intercalation into Na slabs and subsequent protonation induces the leakage of Na ions, leading to lattice destabilization. In contrast, the efficient dealkalizing agent—ethylene glycol, prevents further structural degradation due to the constraint of size effect. Based on time-dependent deterioration of extended scope of positive electrode materials, adaptable analytical framework is established for stability assessment against liquid phase. Our work provides fundamental theoretical guidance for liquid-phase engineering of O3-phase layered oxides.

Introduction
Driven by the rapid advancement of high-performance rechargeable battery technologies, the transition to clean energy has significantly developed. Owing to the open two-dimensional diffusion channels, layered oxides have become prominent positive electrode active materials (PEAMs) for high power and specific energy rechargeable batteries. O3-phase transition metal oxides (TMOs) have emerged as commercially viable positive electrode materials for advanced lithium-ion batteries. In contrast to the limited availability and uneven geographical distribution of lithium resources, the progressive advancement of sodium-based batteries facilitates development of clean energy technologies which are not subject to regional disparities.

Nevertheless, the scaled application of O3 phase materials is hindered by challenges associated with the harsh alkaline synthesis conditions and the unstable framework. The resulting surface residual alkali (SRA), which subsequently causes cradle-to-grave issues have become the shackles in its large-scale application1. Compared with Li-based transition metal oxides (LiTMO2), Na-based transition metal oxides (NaTMO2) tend to be more reactive with ambient air due to the wider alkali metal (AM) layer space for the larger ionic size (1.02 Å for Na+ vs. 0.76 Å for Li+), as evidenced by higher SRAs content2. In particular, the O3-type NaTMO2 are highly susceptible to induced increased SRAs, active Na loss and structural degradation3. This sensitivity restricts their mature applications in several ways: (1) contamination of powder surface4; (2) gelation of electrode slurry5; (3) performance deterioration6; and (4) electrically-driven gas release at high voltage7.

Passive prevention strategies (chemical property tuning8 & inert coating layers9) and active removal strategies (dealkalization) are commonly used to address SRAs issue. Liquid-phase washing dealkalization (as shown in Fig. 1a), which is synergistically applied with secondary sintering, has become a widely used industrialization strategy of Li-based Ni-rich PEAMs10. The aqueous dealkalizing solvents, featured by high efficiency but potential destruction, include water or weakly acidic solutions such as boric acid11, nitric acid12, hydrochloric acid13, NH4H2PO414, LiH2PO415, etc.16, 17 The organic solvents mainly include methanol18, ethanol19, N-methylpyrrolidone20, etc. Unfortunately, O3-NaTMO2 encounter challenges in dealkalization due to their sensitivity to aqueous media (Fig. 1a). Researchers noted that NaTMO2 undergo substantial active Na leaching and layered structures degradation when treated with moisture/water, reflected in a sudden drop in specific capacity21, 22, 23, 24, 25. This failure is often attributed to Na+/H+ exchange (analogous to LiTMO2)26, 27, yet lacks explanation for profound structural degradation over time. The scientific issue of liquid-solid contact involved in the liquid-phase dealkalization process has impeded the further scale-up application of O3-NaTMO2 materials.

In this work, we target the coupling liquid-solid interactions during the dealkalization of O3-NaNi1/3Fe1/3Mn1/3O2 (NFM for short, a typical O3-NaTMO2 which has been put into small-scale industrial application in HiNa Battery, NATRIUM, etc.), employing comprehensive characterizations to comparatively investigate the dealkalization effect of two typical solvents, water and ethylene glycol. The effectiveness of the ethylene glycol is confirmed through evaluations of processability, electrochemical performance and safety. A forward/reverse structure profiling is conducted to reveal interdependent failure behavior. Furthermore, a mechanism of liquid-solid interactions, facilitated by solvent molecular intercalation, is proposed to elucidate the coupling interaction process. Based on the established analytical framework, we convert variable to host O3 layered oxide: extending the scope to more NaTMO2 and Li-based Ni-rich oxides, employing water as reference solvent, to verify the generalizability of this mechanism. “AM loss” is defined to quantify the extent of structural damage, thereby assessing stability tolerance of PEAMs against liquid-phase. This work contributes to the optimization and innovation of dealkalization technology. Moreover, it facilitates the scaled application of highly sensitive oxide PEAMs, further enhancing the potential of cheap and widely distributed sodium-based energy storage technology for future clean energy storage applications.

Results
Dealkalization efficacy of ethylene glycol

In this study, the fresh NFM PEAMs was exposed to air (25℃ and 50% relative humidity) for 24 hours28. These treated materials, referred to as A-NFM, were subsequently utilized for implementing liquid-phase dealkalization. To achieve efficient and minimally invasive dealkalization, the selection of solvents necessitates two key criteria: (1) effectiveness in dissolving SRAs, (2) ability to minimize the structure damage of the PEAMs. In response to this, we evaluated several potential solvents based on solubility and viscosity properties (Supplementary Fig. 1). Polyhydric alcohols, rich in hydroxyl groups, generally enhance SRA solubility. We favor those without long alkyl chains to avoid steric hindrance and maintain high polarity. Glycerol exhibits relatively better solubility for Na2CO3, while high viscosity renders it impractical for application. Ethylene glycol (EG), commonly used as automotive coolant, combine favorable fluidity and considerable solubility. In this work, EG is selected as a candidate solvent for comparison analysis with water. The samples dealkalized using EG were designated as EG-NFM.

A comprehensive evaluation was conducted on the processability, electrochemical properties, and gas release of NFM materials both before and after dealkalization, as shown in Fig. 1. The results of the rheology tests on the electrode slurry demonstrated a significant reduction in viscosity after dealkalization with EG (2.76 Pa·s → 2.22 Pa·s at a shear rate of ~50 s-1 ). Both the storage modulus (G′) and loss modulus (G″) as functions of shear stress exhibit a leftward shift of the thixotropic point, indicating enhanced fluidity of the slurry29, 30. Simulation tests of slurry calendering further illustrating the enhanced processability of EG-NFM (Supplementary Fig. 2). Scale-up validation of the electrode manufacturing process indicated that materials with high alkalinity surface encounter conundrums due to severe slurry gelation. The jelly-like slurry poses challenges for coating the collector, while the dealkalized positive electrode slurry achieves a uniform coating (Fig. 1b). The scanning electron microscopy (SEM) images of the electrode cross-section also illustrates that the binder failure in the high alkalinity slurry leads to warping and peeling, while the dealkalized sample exhibits strong adhesion (Supplementary Fig. 3).

The electrochemical performance of the EG-NFM was evaluated using half cells with sodium metal as referenced and countered electrode, with air-exposed material employed as a control sample. Fig. 1c shows the discharge curves of the NFM positive electrode before and after dealkalization within the voltage range of 2.0–4.0 V at 0.1 C and 1 C (1 C = 150 mA/g). The initial discharge capacity of A-NFM and EG-NFM were measured to be 98.1 and 115.6 mAh/g, respectively, demonstrating the effective capacity recovery through EG dealkalization. Additionally, capacity retention improved from 67.1% to 73.1% after 200 cycles at 1 C. The comparison of rate capabilities shows a similar trend in cycling stability (Supplementary Fig. 4). Na ion diffusion kinetics were analyzed separately by galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV) at different scan rates. Benefiting from the efficient removal of SRAs, EG-NFM exhibits a higher Na+ diffusion coefficient (Supplementary Note 2 and Fig. 5 and 6). Water dealkalized samples (W-NFM) were similarly investigated for further comparison. The drastically declining capacity (62.5 mAh/g), combined with the poor Na+ diffusivity is attributed to the reduction of active Na+ available for reversible extraction/insertion and severe structural degradation. The above results demonstrated the effectiveness of EG for dealkalization in sensitive PEAM while excluding water, given its detrimental effects. It is noteworthy that the specific capacity of dealkalized NFM material remains lower than that of fresh material due to aging treatment. Following actual industrial production, we conducted secondary heat treatment on EG-NFM and performed electrochemical testing (see Supplementary table 1 and Fig. 7 for details). The results indicate that after liquid-phase dealkalization, sodium replenishment and subsequent re-sintering, the performance of A-NFM is restored to industrial application standards. Furthermore, the dealkalizing agent can be recovered and reused under vacuum fractionation, which confirms the practicality of liquid-phase dealkalization.

To evaluate the thermal safety of batteries, differential electrochemical mass spectrometry (DEMS) measurements were conducted on the A-NFM and EG-NFM electrodes to monitor the evolution of carbon dioxide, which reflect the dealkalization efficacy on SRAs31, 32. The A-NFM electrode exhibited a sustained CO2 signal at ~4.0 V and a significant release >4.25 V (decomposition potential for Na2CO3). In comparison, the EG-NFM electrode exhibit weak CO2 signals throughout, suggesting the mitigated gas production in batteries, as demonstrated in the model pouch without swelling in Fig. 1d. Interestingly, due to the sodium ions replenished by the electrochemical decomposition of Na2CO3, A-NFM exhibits higher capacity during the charging (shown as the additional charging platform in Fig. 1d and Supplementary Fig. 8). This corroborates the rapid gas production observed within this potential range. Obviously, efficient dealkalization is essential for the entire manufacturing process of the PEAMs as well as safe operation of batteries.

Surface species and structures of dealkalized NFM materials

The variability of dealkalization solvents result in distinct surface conditions and bulk phase structures of the positive electrode particles. SEM images exhibit air-exposed NFM particles concomitant with nanoscale impurity substances (shown in Fig. 2a). Initially, surface residual sodium compounds, primarily Na2CO3 and NaOH, were quantitatively analyzed using acid-base titration methods (Supplementary Note 3)23. As shown in Fig. 2b, the surface residual Na content of air-exposed samples was up to 43106 ppm, predominantly consisting of Na2CO3 (15.23 wt.%, versus 1.75% for NaOH). Conversely, the dealkalized samples demonstrated a substantial residual Na reduction (10776 ppm for W-NFM, 7902 ppm for EG-NFM), indicating the highly effective SRAs removal capability of both solvents. Similarly, efficient dealkalization is evident in the X-ray photoelectron spectroscopy (XPS) results (detailed in Supplementary Fig. 9).

To further elucidate the characteristics of EG dealkalization, time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was performed to precisely characterize the species near the surface of A-NFM and EG-NFM samples. The depth profiling curves of selected fragments showed that the signals of SRA-related products were significantly weakened after EG dealkalization (Supplementary Fig. 10 and 11). Intensity of NaO2– fragments, initially decreased followed by an increase, is influenced by the bulk particle (Fig. 2c). The abnormal increase in HCO3– fragments intensity for dealkalized samples is further corroborated by Fourier Transform Infrared (FT-IR) spectroscopy results (Supplementary Fig. 12). Based on the results above, we have summarized the mechanism of EG dealkalization as a synergistic process: 1) the dissolution and liquid phase scouring of SRAs; 2) the tuning of particle surface alkalinity by the weak proton liquid phase environment. The intramolecular hydrogen bond formed between adjacent hydroxyl groups in EG stabilizes the deprotonated conjugate base, thereby enhancing its acidity (pKa: 14.2). This enables the tuning of alkalinity on the oxide particles surface. This process can be described as an enhanced dealkalization process, as illustrated in Eqs. (1). The simulated heat of reaction and quantitative analysis of the product water corroborate this process (shown in Supplementary Fig. 13, Tables 3-4 and Supplementary Data 12-15).

NaOH + (CH2OH)2 → CH2OH-CH2ONa + H2O (1)

The morphology and bulk structure of dealkalized NFM particles are illustrated in Figs. 2d-e. The particles exhibit smooth surfaces, indicative of effective SRAs removal by both solvents. However, notable cracks are observed to be parallel to (001) plane in the W-NFM particles (Fig. 2e-i and Supplementary Fig.14). Cross section polisher (CP) and electron probe microanalysis (EPMA) were employed in tandem to analyze the structural integrity and elemental composition within the positive electrode particles along different orientations33. The EG-NFM sample exhibit an intact internal structure, as evidenced by the elemental mapping and line scanning scatter plots of Na in both cross-sectional directions, which displayed a uniform Na distribution. In contrast, the W-NFM sample exhibit severe cracks and significant reduction in Na concentration in both directions (Figs. 2d,e-ii,iii and Supplementary Figs.15-16). Results above suggest that liquid-solid mass transfer in W-NFM occurs continuously and follows a specific path. Transmission electron microscopy (TEM) was further conducted for crystal structure analysis. Fast fourier transform (FFT) patterns of high resolution transmission electron microscopy (HR-TEM) images confirm the intact layered phase of EG-NFM sample even for surface region (Fig. 2d-iv and Supplementary Fig.18)21. Conversely, W-NFM displays dislocations and stacking faults along (003) planes in surface region24 (regions Ⅰ and Ⅱ in Fig. 2e-iv). The decreased (003) spacing (5.24 Å→ 5.10 Å) reflects the contraction of Na slabs due to AM ions loss. Based on the results in this section, disparities in the physical and chemical properties of liquid solvents dictate distinctly different mechanism for the liquid-solid interactions that takes place between them and the highly sensitive O3-phase oxides.

Reverse analysis of solvent invasion-induced structural degradation

In-depth structural profiling of the dealkalized material is crucial for investigating the mechanism of liquid-solid interactions. The limitations of X-ray diffraction (XRD) in the structural analysis of water-sensitive O3-phase layered oxides have been shown in numerous studies23, 24, 25, 34, 35, 36. In line with this, the XRD patterns in Supplementary Fig. 19 just display the presence of hydration peaks and partial derived phases without significant features indicative of structural transitions. Conventional characterization techniques encounter difficulties in revealing the occupation of protons within the ACM layer. Therefore, time-of-flight neutron powder diffraction (NPD) data were collected on the NFM materials before and after dealkalization to achieve precise crystal structure resolution (Figs. 3a-c). According to the Rietveld refinement results (Supplementary Tables 5-8), both A-NFM and EG-NFM samples exhibit main O3 structure and minor rock-salt NiO phase caused by the weak protonic solvent (Fig. 3a,c). The uncalibrated peaks at high d-spacing (>2.25 Å) in A-NFM is attributed to the effect of SRAs that are not observed in EG-NFM. In contrast, the degradation of the primary peak of the O3 phase (2.17 Å) in W-NFM sample, accompanied by the emergence of a derived peak (2.20 Å), typically signify the undesirable phase transition (Fig. 3b). Refinement analysis matches the derived peaks with those of the monoclinic O'3 phase, which is calculated to constitute 41.68%, while the O3 phase reduced to 54.03% (Supplementary Table 8). Indeed, the O'3 phase originates from in-plane distortions caused by Na extraction and alterations in the valence states of TM ions37, 38. The aqueous phase induced sodium extraction elucidates the frequent observed O'3 phase in studies focused on water stability. Limited by the delocalization of intruding substance (weak non-covalent interactions), the monoclinic phase ratios obtained from the refinement can serve as an indirect descriptor to assess the degradation. In addition, the lattice parameter c of W-NFM exhibits a significant increase, suggesting the enhanced repulsive forces between the oxygen layers attributable to sodium depletion.

To reveal the mass transfer in NFM material during liquid phase treatment, thermogravimetric analysis (TGA) was conducted on all samples (Supplementary Fig. 20). Initially, desorption of adsorbed water occurs within 30–150℃ (Point 1 before 100℃). The delayed inflection point of W-NFM (Point 2) is attributed to the higher thermal energy required for the decomposition of intercalated water molecules23, 39. Weight loss between 150-365℃ is primarily due to the removal of proton (H), which distinguish W-NFM samples with substantial proton occupancy40. Decomposition of bicarbonate species also occurs at these two stages4, 23. Decomposition of Na2CO3 occursbetween 365℃-540℃23, 39. Only A-NFM samples continue to lose weight as the temperature further rises, resulting from more SRAs. In contrast, EG-NFM samples present a minimal weight loss (2.49%), suggesting limited mass transfer with the dealkalizing solvent.

For in-depth analysis of structural changes, the reverse structural analysis of dealkalized samples were conducted by in situ variable-temperature XRD technique. The TGA curves were refined according to the evolution of the main peaks in the XRD patterns and divided into five stages, as labeled in Fig. 3d. For Stage Ⅰ (50–130℃), the irregular peak can be attributed to the hydrated phase (consistent with Supplementary Fig. 20 and reference24). In Stage Ⅱ (130–245℃), the derived peak to the right of the (003) peak indicates the formation of the proton phase in the transition state, given that the main peak is not shifted (detailed in Supplementary Fig. 21). The weight loss at this stage measures 1.82%, corresponding to the partial removal of protons. For Stage III (245–364℃), the peaks associated with the layered phase exhibit a shift, signifying the complete O3→O'3 phase transition41. The structure at this stage is analyzed as a mixture of proton phase and O'3 phase for continuous deprotonation (1.68% weight loss). In Stage Ⅳ (>364℃), complete deprotonation leads to more pronounced shift of characteristic peaks associated with formation of P3 phase (Na-deficient state). Additionally, cleavage of the main peak at ~520℃ indicates the initial formation of P'3 phase. In contrast, the in situ XRD results of EG-NFM exhibit a consistent phase structure, which suggests that the material maintains its stability during EG liquid-phase treatment and avoids damaging interactions. A subtle shift of the (003) peak was observed at >200°C, consistent with the temperature interval of deprotonation in the TGA curve. This laterally corroborates the slight EG proton attack.

The structure evolution from Stage Ⅰ to Stage Ⅳ is depicted in Fig. 3e. It is important to note that the vacancies caused by internal Na loss are occupied by H2O molecular (and possibly H3O+) and protons, thus maintaining metastable structures. The proton phase can be discerned in the reverse resolution here, thereby distinguishing it from the derived phase. As the temperature rises, substances which embedded within the layered structure due to liquid-solid interactions are removed, consequently leading to disruption of the charge balance and AM occupancy as following: (1) Na site vacancies emerge inducing lattice distortion that triggers O3→O'3 phase transition; (2) Na vacancies further accumulate with deep deprotonation, causing interlayer slip and O'3→P3 phase transition38, 42. The reverse structure analysis presented in this section confirms the objective existence of liquid-solid interactions (including proton and water erosion, Na leaching), and also predicts potential structural evolution. These findings provide valuable insights and robust support for the subsequent mechanistic studies.

Mechanism of liquid-solid interactions

In O3-phase layered oxides, the Na layer is known to undergo Na+ insertion-extraction (electrochemical). This layer is also susceptible to the intrusion of foreign substances under external driving forces (aqueous phase), which can lead to its expansion/contraction. Existing research frequently interprets the interaction as an exchange of AM ions with protons (e.g. Li+/H+ exchange)10, 43, 44. This perspective is deficient in the intrinsic driving forces and the pathways through which "exchange" transpires. Specifically, in dealkalization applications, the mass transfer between liquid and solid phases constitutes a complex, time-dependent and coupled process, distinct from exposure to air. In this section, first-principles density functional theory (DFT) calculations are performed to clarify the liquid-solid interaction mechanism.

First, the insertion formation energy of the two solvents is presented in Fig. 4a. The insertion of water molecules into the layered structure occurs spontaneously (-1.72 eV), corresponding to the expansion of the layer spacing. Conversely, EG molecules are unable to spontaneously intercalate (0.261 eV). This is attributed to the difference in size effect of the two solvent molecules: H2O molecules have the potential to intercalate into Na layer for the transition state H3O+ is comparable to bare Na+ (1.0 ± 0.1 Å versus 1.02 Å)45; EG molecules with larger size experience spatial site resistance which hinders their intercalation. Furthermore, the deprotonation free energies of the embedded solvent molecules were calculated (Fig. 4b). Embedded H2O undergoes spontaneous deprotonation with the H captured by O slabs (hydrogen bonding dominated), while deprotonation of the embedded EG is less likely to occur. This suggests that H2O induces a time-dependent continuum of structural damage akin to a "domino effect". In contrast, EG affects only the near-surface region of the material due to the low free proton concentration. The atomic coordinates of the optimized computational models are provided in Supplementary Data 1–5.

The structural and compositional characterizations were also employed to verify the time-dependent nature of liquid-solid interactions in aqueous solvents. Fig. 4c shows the structure evolution with the accumulating immersion time. The intensity of the characteristic peaks in the XRD pattern decreases immediately upon exposure to water, stemming from the reduced lattice integrity (Supplementary Fig. 23). It is necessary to clarify that in XRD analysis, only derived phases can be used to calibrate the structure, rather than the more precise mixed phase mentioned earlier. As the immersion time increases (>5 min), (003)L and (104)L peaks concurrently decline with the proton phase developing (marked with gray dotted line at 17.38°). The derived O'3/P3 phase peaks emerge sequentially. The two primary peaks completely disappeared after 2 hours, indicating a thorough degradation of the layered structure. As a crucial aspect of the interaction, the Na loss content over water immersion times was monitored using inductively coupled plasma optical emission spectrometer (ICP-OES). As shown in Fig. 4d, the Na content in NFM material decreases rapidly upon exposure to water. This trend began to decelerate after 15 min, reaching 59% after 40 min. Indeed, sustained Na leaching drives protonation of NaTMO2 following charge balance. Conversely, the inert nature of ethylene glycol (EG) significantly limits its impact on the NFM structure (detailed in Supplementary Fig. 24 and Table 9). Excessive immersion presented a trace amount of leached Na content (1.65% versus full occupancy), indicating a weak ion exchange, which imply its absence of possible competitive reaction with the dealkalization.

Based on the thermodynamic predictions above, the correlation underlying the liquid-solid interactions behaviors (molecular intercalation, protonation, Na leaching) require to be analyzed. Given the challenges in real-time monitoring of the interaction process, models of NFM in various hydration states are established to calculate the free energy of Na leaching (Supplementary Fig. 25 and Supplementary Data 6–7). As shown in Fig. 4e, Na exhibits non-spontaneous leaching at low hydration state (0%, 6.25%). With the intercalated H2O content increases, there is a pronounced tendency for Na to leach from the site (14.5%, 25%). This spontaneous leaching tendency terminates when the hydration state get higher (35.4%, 50%, 75%). Result above substantiates the correlation between solvent molecular intercalation and Na loss46, 47. Aiming to further elucidate the root cause of Na leaching, we comprehend the electronic origin of NFM structure in a specific hydration state. Crystal orbital Hamilton populations (COHP) analysis was employed to investigate the bonding nature in Fig. 4f. We conduct a comparative analysis of the Na–O bond orbitals in both pristine NFM and that with 14.5%H2O intercalation. The reduced integrated crystal orbital hamilton population values (-ICOHP) (0.5528 eV versus 0.7388 eV) indicating that H2O intercalation significantly weakened the strength of Na–O bonds48. This conclusion aligns with the layer spacing simulations in Fig. 4a, given that the expansion of Na layer weakens its O–Na–O binding. Furthermore, this rapid Na leaching may stem from the electrostatic shielding of water molecules for bonding and the rapid interfacial transfer of hydrated sodium ions49, 50.

In summary, for the highly sensitive O3-type layered NFM oxides undergoing dealkalization, we have delineated a mechanism of liquid-solid interactions facilitated by the intercalation of solvent molecular, as shown in Figs. 4g-4h. The interactions transpire continuously between layered structure and aqueous media due to the spontaneous intercalation and deprotonation of H2O molecules, as well as the susceptibility of Na leaching in this context. Therefore, structural degradation in aqueous phase commences on the surface and spreads to the interior of particles as duration increases (depicted by gradient blue blocks in Fig. 4g), which is consistent with earlier findings (Fig. 2e). Conversely, minimal damage to NFM particles by EG can be attributed to blocked molecular intercalation. The potential trace damage is due to the nature of protic solvent (suggested by the dark blue surface in Fig. 4h). Obviously, for specific host material, the significant difference in the guest solvents is the decisive factor for the marked disparity in interactions.

Mechanism Adaptation—from NaNi1/3Fe1/3Mn1/3O2 to O3-type layered oxides

Liquid-solid interactions during the liquid-phase treatment of sensitive O3-type layered oxide poses a prevalent challenge for both researchers and industry practitioners. In this section, we extend the proposed analytical framework for liquid-solid interactions to a wider spectrum of O3-type oxides and demonstrate their compatibility. By integrating time-dependent structural analysis with hydration simulations, we aim to elucidate the interaction intensity between the host material and the guest solvent during the dealkalization. Here, water is selected as the guest solvent, for the failure of more positive electrode materials (Li/Na-based) in water is distinguishable and worthy of investigation.

For the host material, Li-based Ni-rich oxides (water washed in large-scale production) and TM-substituted Na-based oxides (frequently employed to enhance water stability) are considered. We select three representative positive electrode materials, LiNi0.8Co0.1Mn0.1O2 (LNCM), NaNi0.2Fe0.3Mn0.4Cu0.1O2 (NNFMC) and NaNi0.33Fe0.33Mn0.33O2 (NNFM) for structural/compositional analysis under water immersion, in order to elucidate the essential difference between the liquid-solid interaction process.

Time-dependent study of active AM ion loss and the evolution of XRD characteristic peaks are conducted as shown in Figs. 5a-b. The AM ion leaching content from the three materials are measured after different durations in the aqueous phase (Fig. 5a). The data was fitted as a curve to compare the effects of the host material on the interaction intensity (detailed in Supplementary Table 10). The interaction between the LNCM host and water is primarily driven by Li⁺/H⁺ exchange. This process is confined to the surface of the particles and results in only minimal Li loss, even under prolonged liquid-solid contact. Even exposed up to 24 hours, the main characteristic peaks in XRD patterns exhibit only slight intensity changes (Fig. 5b). This also explains why the washing-sintering strategy can be applied to the large-scale production of Ni-rich positive electrode powder. In contrast, sodium-based hosts undergo significant Na leaching upon liquid-solid contact, a trend that gradually moderates after ~20 min. The self-propagating degradation of host with poor water stability accounts for this behavior. NNFM samples undergo rapid structural degradation upon immersion in water: (1) Immediate shifted peaks from O3→O'3 phase transition; (2) Heterogeneous peaks derived after 10 min due to irreversible liquid-solid interactions: (3) Declining diffraction peak intensities from reduced crystallinity. The NNFMC samples exhibited marginally less pronounced deterioration upon water immersion: (1) Retarded decline of peak intensities; (2) Suppressed adverse phase transitions (Supplementary Note 4 and Fig. 26). Apparently, the distinction in AM and TM elements allows the O3-type layered oxides above to demonstrate disparate stability tolerance against liquid-phase, stemming from different interactions between guest solvent molecules and the host oxide lattice.

Furthermore, we extend the analytical framework of the interactions mechanism to encompass multiple positive electrode categories, analyzing it from the perspective of the host material. The free energy of water intercalation in LNCM, NNFMC, and NNFM oxides are simulated in Fig. 5c, coupled with the potential stability against aqueous phase. The atomic coordinates of the optimized computational models are provided in Supplementary Data 8–11. The LNCM is located in the non-spontaneous water intercalation zone (6.56 eV), whereas the Na-based oxides are both situated in the spontaneous water intercalation zone (-0.38 eV for NNFMC and -1.72 eV for NNFM). This result underscores the critical influence of AM with the functionality of TM doping on structure evolution in liquid-solid interactions. The simulated results are also consistent with the interactions mechanism mediated by solvent molecular intercalation. First, the AM element plays a crucial role in determining the intercalation of water molecules. The narrow AM layer spacing in Li-based oxide, owing to the smaller size of Li+, significantly impedes the intercalation of water molecules, thus confining phase transition and Li dissolution primarily to the surface layer. Conversely, Na-based oxides, characterized by broader layer spacing, are susceptible to continuous erosion from water molecules. Furthermore, the electrostatic force of TM–O–Na can be modulated through TM substitution, which can strengthen local structure against water attack and limit active Na leaching 4, 25, 51. In conclusion, the variation in AM dictates the distinct performance of Li/Na-based oxides under aqueous treatment, which count on the AM–O bonding strength. For NaTMO2, tuning the TM–O covalency to enhance the Na–O bonding (higher Na–O bond energy) is a suitable approach.

As is evident from the preceding discussion, PEAMs exhibit diverse and complex behaviors when exposed to liquid phases. It is crucial to establish a unified standard for evaluating their stability during liquid-phase processing. In this section, considering the general damage water inflicts upon PEAMs, we define the battery reversible capacity degradation as “AM loss” (which mean active AM available for electrochemical reaction in layered oxides) to quantify the extent of structural damage, thereby assessing stability tolerance of PEAMs against liquid-phase. Through an extensive review of water treatment studies on the aforementioned positive electrode categories, we have compiled representative data, as illustrated in Fig. 5d. Water-treated Ni-rich LiTMO2 positive electrodes experience less than 5% AM loss. In comparison, Ni/Fe/Mn based NaTMO2 positive electrodes experience drastic AM loss (almost halved) that renders water-treated positive electrodes unavailable. The introduction of water-stabilizing elements (Cu, Ti et. al) can improve the resistance of NaTMO2 to water-induced structural damage despite unavoidable AM loss.

Within the context of O3-type layered oxides examined in this work, “AM loss” serve as a concrete standard for stability tolerance evaluation, which demonstrated its utility for the specific Li/NaTMO2-H2O pair. Obviously, the development of this criterion requires more comprehensive database regarding the diversity of host materials and guest solvents in liquid-solid pairs.

In summary, we have developed a comprehensive evaluation system for liquid-solid interactions of active layered positive electrode materials in liquid-phase media. From the perspective of the O3-TMO host, both AM and TM collectively determine the AM–O bond covalency, which serves as a crucial determinant of lattice stability. From the perspective of the guest solvent, the characteristics of the molecule (such as molecular weight, binding force, polarity, etc.) determines the exchange tendency between the liquid-phase and TMOs. Furthermore, iterative optimization of studies on the liquid-solid interactions for more active materials and solvent can facilitate refinement of analytical models and the expansion of databases.

Methods
Dealkalization of O3-NaTMO2

The O3-NaNi1/3Fe1/3Mn1/3O2 positive electrode materials (Guangdong Canrd New Energy Technology Co.) were treated separately with dealkalizing solvents. Methods of aging the pristine material are mentioned in the text. Deionized water and ethylene glycol (98%, ShangHai HUSHI Co.) were selected as dealkalizing solvents. NFM powder and solvent (1/50, mass ratio) were placed in a closed container at room temperature at 550 rpm and stirred for 5 min. After immediately solid-liquid separation, the positive electrode powder was dried at 70℃ in a vacuum oven for 12 h. The NFM powder was stored in an argon filled glove box (Shanghai MIKROUNA Mech. Tech. Co.) throughout, except for the liquid phase treatment process. In addition, NFMC was synthesized by high-temperature sintering of precursors (Wuhan Jiana Energy Technology Co.). An excess of 2% Na2CO3 (stoichiometric ratio: Na2CO3/precursors=1.02) was added to replenish the loss of Na volatilization at high temperatures. The mixture was calcined at 900℃ for 16 h and cooled to 200℃ with the furnace. The dealkalization step is the same as above.

Electrolytes and electrode preparation

Electrolyte contained 1 M NaClO4 in propylene carbonate/ethylene carbonate (1:1, by volume ratio) with 5.0 wt% fluoroethylene carbonate (DoDoChem) as additive. The slurry comprised NFM active material, Super P and polyvinylidene fluoride (8:1:1, by weight ratio). The slurry (N-methylpyrrolidone, NMP (purity > 99.9%) as dissolving solvent for the binder) was coated onto aluminium (Al) foil current collector using stainless steel scraper and dried at 110℃ for 12 h in a vacuum oven. Super P, polyvinylidene fluoride (5130, molecular weight: 1.1 million) and NMP were provided by Guangdong Canrd New Energy Technology Co. Al foil purity > 99.6%, thickness 18 μm. All electrodes were fabricated in air (26 ± 3°C, 30 ± 5 %RH). As-prepared electrode samples were stored in an Ar-filled glove box with oxygen and moisture below 1 ppm. Electrode cutting equipment (MSK-T10-S) was supplied by MTI Shenzhen Co. The loading mass of the active materials for each NFM electrode is 2.5–3 mg/cm2.

In-situ DEMS measurements

The gas evolution analysis during the initial charge/discharge process was carried out by differential electrochemical mass spectrometry (DEMS, QAS100 Li) with a pouch cell model. The pouch cell model was assembled with hard carbon negative electrode (HC, MTI Shenzhen Co.), carbonate electrolyte (1M NaPF6 in DMC:EC:EMC=1:1:1 Vol% with 5% FEC, from DoDoChem), multi-layer ceramic composition separator, and O3-NaNi1/3Fe1/3Mn1/3O2 positive electrode as described above. The area weight (single side) of positive electrodes is 14.65 mg/cm2. Each pouch was assembled by Z-stacking multiple pieces of 2 negative electrode sheets (coated on single side) and 1 positive electrode sheet (coated on both sides). The clamping pressure exerted by the fixture on the battery is 0.1–0.3 MPa. During the gas detection, the cells were cycled at 0.1 C (17.58 mA/mm2) within 2.0–4.5 V and the flow rate of carrier gas Argon was controlled as 1.2 mL/min (ion source: EI, 70ev; detector: SEM, 1100v). The entire test was performed under a vacuum of 4.6E-6 Pa at room temperature. The full spectrum was scanned based on the expected mass number of the gas products and the mass number m/z = 32, 44 was selected as the analyzed fragment for oxygen and carbon dioxide, respectively.

Electrode slurry rheological properties measurements

The rheological properties of the electrode slurry (composed of NFM materials before and after dealkalization) were investigated using a rotational rheometer (Haake MARS Ⅲ, ThermoElectron). In positive electrode slurry, the mass ratios of PEAMs: Super P: polyvinylidene fluoride were 8:1:1 with a total solid material concentration of 34.5%. The mixed slurry was placed in a thermostatic test chamber at 50℃ for 5 minutes until steady state. The apparent viscosities of the slurry decreased with the decreasing shear rate from 0.01 to 4500 s-1, exhibiting typical shear-thinning. The viscosity value was selected for comparative analysis at a shear rate of 50 s-1. The storage modulus (G′) and loss modulus (G″) of the slurry as a function of shear stress was collected in the range of 10-2–104 Pa. The thixotropic points were observed according to the intersection of G' and G'', for storage modulus described the solid response of the slurry at low shear stress conditions, and the loss modulus reflected the liquid response of the slurry at high shear stress conditions.

Cell assembly and electrochemical measurements

For half-cell fabrication, O3-NaNi1/3Fe1/3Mn1/3O2 (Guangdong Canrd New Energy Technology Co.) served as the working electrode, sodium foil as the counter electrode, and a glass fibre membrane (Whatman GF/D) as the separator. These components were assembled into 2032-type coin cells (Guangdong Canrd New Energy Technology Co.) within an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm). The glass fibre separator was pre-cut into circular discs with a diameter of 14 mm, thickness of 675 μm, porosity of ~80%, and an average pore size of 2.7 μm. Sodium foil was prepared by rolling sodium ingots (99.5%, ShangHai HUSHI Co.) to a thickness of 0.3–0.5 mm and punching into 14 mm diameter discs for immediate use. 60 μl electrolyte was added dropwise to each side of the separator. The assembled cell was then compacted under a pressure of 50 kg/cm² for 10 s to ensure adequate sealing. Galvanostatic measurements were conducted using a Land battery test system (CT2001A, Wuhan LAND Electronic Co.) housed in an environmental chamber maintained at 26°C. Charge/discharge cycling was performed at a current density of 1 C = 150 mA/g over a voltage window of 2.0–4.0 V. Long-term cycling was carried out at 1 C following 2 cycles at 0.1 C for activation. All other electrochemical tests were conducted at 26 ± 3°C.

Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) measurements

TOF-SIMS were performed on PHI nanoTOF II Time-of-Flight SIMS. The depth profile were conducted at the high mass resolution mode (2–1850 u) with a pulsed Bi3+ ion beam (30 keV, 2 nA ion current). The sputtering phase was conducted by a Ar ion gun (3 kv, 100 nA) with the area of 400 μm ×400 μm at ~10 nm/min on SiO2 (sputtering rate), and the analyzed areas are typically 20 μm × 20 μm with the depth of 150 μm.

Neutron powder diffraction (NPD) measurements and Rietveld refinement

NPD characterization was carried out using a deep-penetrating neutron beam with high intensity and spatial resolution for complex phases analysis. Time-of-flight (TOF) NPD data were collected at the beamline of the General Purpose Powder Diffractometer (GPPD) with a 360° rotation stage at the China Spallation Neutron Source (CSNS). The mass of each set of powder samples was not less than 15 g to ensure sufficiently high diffraction intensity. The TOF method was used to collect data over a total scanning time of at least 12 hours. All the diffraction data were refined by the Rietveld method using the Z-code software.

Ex situ and in situ variable-temperature XRD measurements

Ex situ XRD measurement was performed on a Rigaku Ultima IV diffractometer. XRD patterns of NFM powder after different solvent dealkalization treatments were collected over a 2θ range of 5–90° at a scan rate of 5°/min (Cu-Kα radiation source, λ= 1.54 Å). The XRD Rietveld analysis was performed by the FullProf suite. The structural transitions of W-NFM and EG-NFM samples at the temperature range of 25–550℃ were investigated by in situ variable-temperature XRD technique. The in situ test was performed at a ramp rate of 5℃/min and XRD patterns were scanned at a rate of 10°/min. Data of W-NFM were collected at nodes 50℃, 100℃, 125℃, 150℃, 175℃, 200℃, 225℃, 300℃, 400℃, and 550℃, respectively. Data of EG-NFM were collected at nodes 50℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃ , 400℃, 450℃, and 550℃, respectively.

DFT calculations

Density functional theory (DFT) computations based on first principles were carried out using the Vienna Ab initio Simulation Package (VASP)56, incorporating the projector augmented wave (PAW) method57. For the exchange-correlation energy, the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) functional was adopted58. A plane wave basis set with an energy cutoff of 500 eV was employed, and the geometry relaxation was performed until the forces on each atom converged below 0.03 eV/Å. The Brillouin zone was sampled using a 1×1×1 k-point grid. Self-consistent iterations were continued until the energy difference between successive steps fell below 10⁻⁵ eV. To prevent interactions between periodic structures, a vacuum region of 15 Å was added along the z direction. A simplified NaNi1/3Fe1/3Mn1/3O2 model is adopted to focus on solvent molecular intercalation, protonation and leaching of Na. The model was established by expanding the cell to 4*4 and inserting 16 water molecules and 6 ethylene glycol for the simulated W-NFM model and EG-NFM model, respectively, after removing 67% Na. In the calculation of the leaching energy, different amounts of Na are removed and the corresponding water molecules are introduced. In the subsequent calculations of the water intercalation energy barriers for LNCM and NNFMC materials, we adaptively optimized the Li/Na atoms removed from the model based on experimental results. The computation of COHP is performed via LOBSTER software59.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The work by Zhang et al. represent a significant effort to address the surface residual alkali (SRAs) on layered oxide cathode materials for lithium-ion and sodium-ion batteries by investigating liquid-solid interactions. Through a variety of advanced characterizations and modeling, the authors systematically investigated the effects of two representative solvents— water and ethylene glycol on the structural evolution and battery performance of NaNi1/3Fe1/3Mn1/3O2 (NFM111) cathode. Specifically, they have revealed the role of AM-O bonding and solvent properties as well as a quantifiable metric—Stability Tolerance against Liquid Phase (STLP), and further extended the scope to various layered oxide cathodes. The findings are valuable for the mass production and practical application of layered oxide cathodes. A few comments for further improvement of this work:\n1. The structural information and electrochemical performance of pristine NFM cathode are significantly lacking. To my understanding, the performance of EG-NFM cathode (Fig. S4) is still below the industrial level of NFM cathodes. So, it is important to clearly show the comparison between NFM111 and EG-NFM.\n2. Gas release is a big issue for long-term cycling of pouch cells. It is interesting to see that the gas release of EG-NFM is significantly lower than A-NFM (Fig. 1d). However, the specific capacity of EG-NFM pouch cell is much lower than A-NFM, indicating much lower SOC and making the comparison results not fair. In addition, the behavior is also conflict with the results in Fig. 1c, where EG-NFM delivered higher capacity. Please provide an explanation for the discrepancy and re-check the gas release results.\n3. In addition, the authors did provide any experimental details about the gas release measurement of pouch cells.\n4. In situ XRD of EG-NFM cathodes during heating is needed to consolidate the impact of protonation.", "reviewer_2": "The paper demonstrates the interaction mechanism between host solid-phase particles and guest liquid-phase solvents, elucidating how structural degradation depends on the molecular configuration of dispersed solvents and the alkali metal-oxygen bond covalency during dealkalization. In contrast to the water washing process, ethylene glycol (EG) as a dealkalizing agent mitigates structural degradation, owing to the size effect constraint. This work provides fundamental theoretical insights for liquid-phase engineering of O3-phase layered oxides, a critical aspect in the development of oxide cathode materials for Na-ion batteries. Therefore, the paper is suitable for publication in Nature Communications after major revisions.\n1. Ethylene glycol (EG) is a protic compound. Is there any possibility of ion exchange between Na+ from O3-NaNi1/3Fe1/3Mn1/3O2 (NFM) and H+ from EG? Could it be that the dealkalization process and the ion exchange between Na⁺ and H⁺ are competitive?\n2. Can the alkyl chain length of glycol influence the effectiveness of the dealkalization process? For instance, how does ethylene glycol compare to propylene glycol in this regard?\n3. Could ethanol be used as an alternative in the dealkalization process?\n4. The dealkalization process of EG involves an irreversible reaction, converting (CH2OH)2 to CH2OH-CH2ONa. How can EG be reused in industrial applications after this transformation?\n5. Only O3-NaNi1/3Fe1/3Mn1/3O2 (NFM) was examined for EG-mediated dealkalization. Could this process be applicable to other layered cathode materials, such as NaMnO2 or NaNi1-xMnxO2?\n6. Can a mixture of EG and H2O be used in the dealkalization process?", "reviewer_3": "Surface residual alkali significantly influence the processing and performance of layered oxide materials. The authors propose that ethylene glycol effectively removes surface residual alkali while preserving the structural degradation, highlighting potential significance. However, some studies have previously addressed alcohol-mediated surface impurity removal in layered oxides (e.g., ACS Appl. Mater. Interfaces 10, 38246−38254 (2018)) and water-induced liquid-solid interactions in dealkalization processes (Nat. Commun. 11, 3544−3556 (2020); Science 385, 744−752 (2024)). The key discussions and conclusions appear predominantly based on literature references or speculative reasoning rather than reliable experimental validation. Presently, I have major reservations about this manuscript, and I do not recommend its publication in Nature Communications.\n1、The manuscript predominantly emphasizes the role of ethylene glycol in exploring liquid-solid interactions during dealkalization, asserting that using water as a solvent leads to excessive dealkalization and consequent structural damage. However, when the discussion extends to general O3-phase layered materials, water is employed as the solvent, despite the earlier claim regarding the significant impact of transition metals on AM-O interactions. This inconsistency introduces a clear logical contradiction. Additionally, the introduced \"STLP\" concept appears directly borrowed from terminology in lithium-ion battery cathode research, lacking substantial scientific justification and relying primarily on subjective claims regarding its potential practical significance. These issues collectively diminish the scientific merit of the manuscript and necessitate comprehensive reconsideration and revision.\n2、Water intercalation, protonation, reactive sodium extraction, and lattice distortion have been widely reported in the literature. Could the authors explicitly highlight and clarify the innovation and novel aspects of the present study compared to existing reports?\n3、How do the authors confirm that the gas produced during the reaction between ethylene glycol and the alkali is indeed CO2? If this conclusion is correct, the fundamental reaction should essentially involve interactions between OH- and H+ ions; however, breaking O-H bonds in alcohols typically requires additional external conditions, which is not clearly explained. Therefore, a more detailed mechanistic explanation is needed. Additionally, it appears that simple solid–liquid separation would be insufficient to effectively remove CH2OH–CH2ONa salts.\n4、In pouch cell tests, the charging capacity of A-NFM significantly exceeds that of EG-NFM, whereas in half-cell measurements, the capacity of A-NFM is lower compared to EG-NFM. Could the authors explain this discrepancy in detail?\n5、Why does the capacity of W-NFM increase during the cycle?\n6、Fig. 2e-i clearly illustrates significant surface cracking after water-based dealkalization, which typically corresponds to a distinct hydrate-phase diffraction peak around 14°in XRD measurements. However, this expected characteristic peak is not prominent in the manuscript's XRD results (Supplementary Fig. 16). The authors should provide clarification and explain this discrepancy.\n7、For the in situ XRD results, the contour map is not very clear in describing the details, instead, the stacking diagram should be given.\n8、The manuscript contains several noticeable formatting errors, including incorrect terminology such as \"Bi3++ ion beam\" and \"FullProf_suite.\" Additionally, there are inconsistencies in unit formatting (e.g., \"mA g-1\" versus \"mA/g\") and a lack of proper spacing between numbers and units (e.g., \"10nm/min\"). These formatting issues should be carefully corrected for clarity and compliance with journal standards.\n9、The manuscript is significantly redundant and lacks conciseness, detracting from a clear focus on the primary points of discussion. Additionally, both the abstract and main text currently exceed the word limits set by Nature Communications, necessitating substantial revision to comply with journal guidelines."}, "author_response": "Reply: Thank you very much for your comments. Reviewers' comments have been responded to and answered individually.\nSpecific comments:\n1. The structural information and electrochemical performance of pristine NFM cathode are significantly lacking. To my understanding, the performance of EG-NFM cathode (Fig. S4) is still below the industrial level of NFM cathodes. So, it is important to clearly show the comparison between NFM111 and EG-NFM.\nReply & Revision: We acknowledge the oversight in not including comparative data in the initial submission. To address this, we have supplemented the XRD data and TEM images of the pristine NFM material (Supplementary Fig. 16, 18). Additionally, a comparative analysis of the electrochemical performance between NFM111 and EG-NFM is provided (Supplementary Fig. 7).\nThis study primarily investigates the underlying mechanism, selecting aged rather than fresh materials for dealkalization process. It is important to note that exposure to air leads to irreversible capacity loss in the cathode, as active sodium is converted into SRAs. Consequently, the specific capacity of EG-NFM is observed to be lower than that of the original NFM111.\nIn industrial production, washing is typically applied concurrently with secondary heat treatment. Consequently, we subjected EG-NFM to secondary heat treatment (named as EG-NFM-heating) and conducted electrochemical testing. The results indicate that EG-NFM-heating exhibits a specific capacity comparable to fresh NFM111, with improved capacity retention (Table R1). This demonstrates that the performance of the dealkalized material after secondary heat treatment can reach industrial level.\nWe have supplemented the relevant content on Page 5, Lines 142-148 of the main text. Experimental details and analysis are supplemented in Supplementary Fig. 7 and Table 1.\nTable R1 Comparison of electrochemical performance of pristine-NFM, A-NFM, EG-NFM and EG-NFM\nPristine NFM A-NFM EG-NFM EG-NFM-heating\nInitial discharge capacity (mAh/g) 124.8 98.1 115.6 124.4\nDischarge capacity, 1 C (mAh/g) 102.0 77.2 94.6 99.9\nCapacity retention, 1 C (%) 78.5 67.1 73.1 84.1\n2. Gas release is a big issue for long-term cycling of pouch cells. It is interesting to see that the gas release of EG-NFM is significantly lower than A-NFM (Fig. 1d). However, the specific capacity of EG-NFM pouch cell is much lower than A-NFM, indicating much lower SOC and making the comparison results not fair. In addition, the behavior is also conflict with the results in Fig. 1c, where EG-NFM delivered higher capacity. Please provide an explanation for the discrepancy and re-check the gas release results.\nReply & Revision: Thank you for the comment. We apologize for the lack of necessary explanations. The presodiation of residual Na CO on the cathode surface result in the abnormal higher specific capacity of A-NFM pouch cell in Fig. 1d. Specific explanation is as follows:\n(1) Electrochemical oxidation of Na CO at high potential. In comparison to the 2-4 V voltage range in the charge-discharge test depicted in Fig. 1c, the gas release test illustrated in Fig. 1d encompasses a broader voltage range of 2-4.5 V. The substantial residual Na CO (decomposition potential ~4.25 V) on the A-NFM surface undergoes electrochemical oxidation at high potential. This process contributes to a capacity that surpasses that of EG-NFM. This presodiation effect can be demonstrated in the dQ/dV curve of this battery (Supplementary Fig. 8), consistent with the additional references, as shown in Fig. R1. (Ref: Batteries Supercaps 7, e202400009 (2024); Chem. Mater. 29, 5948-5956 (2017))\nFig. R1 a, Additional charging platforms of Na CO decomposition in Fig.1d. b, The dQ/dV curve of the A-NFM sample. The oxidation peak of Na CO is observed at 4.25 V. c, Na CO as a sacrificial additive provides additional charging capacity, Ref. Batteries Supercaps 7, e202400009 (2024). d, Cyclic voltammograms of the cathode with Na CO , the oxidation peak at 4.25 V represents the decomposition of Na CO .\n(2) Different counter electrodes in batteries. The charge-discharge test in Fig. 1c employs half coin cells with a Na metal anode, ensuring an abundant supply of active Na+. Conversely, gas release test shown in Fig. 1d employs full pouch cells with a hard carbon anode, indicating that the cathode is the sole source of the limited Na+. The irreversible loss of Na⁺ during cycle, attributed to the formation of SEI, leads to a reduced specific capacity for EG-NFM compared to A-NFM under presodiation.\nIn response to your comments, we have revised Fig. 1d and provided supplementary explanation for this discrepancy on Page 5, Lines 154-161, Supplementary Fig. 8.\n3. In addition, the authors did provide any experimental details about the gas release measurement of pouch cells.\nReply & Revision: We apologize for the lack of measurement details. We have supplemented main details of the gas release measurement in Methods (Page 20, Lines 580-594). Additionally, specific design parameters of the model pouch cells have been presented in Supplementary Table 10.\n4. In situ XRD of EG-NFM cathodes during heating is needed to consolidate the impact of protonation.\nReply & Revision: Thank you for the constructive comment. We supplemented the in situ XRD of EG-NFM cathodes, as shown in Fig. 3d and Supplementary Fig. 21. Relevant content has also been provided on Page 10, Lines 295-299. As expected, no phase transitions are observed in this XRD patterns, consistent with the low weight loss in the TGA analysis.\nReviewer #2 (Remarks to the Author):\nThe paper demonstrates the interaction mechanism between host solid-phase particles and guest liquid-phase solvents, elucidating how structural degradation depends on the molecular configuration of dispersed solvents and the alkali metal-oxygen bond covalency during dealkalization. In contrast to the water washing process, ethylene glycol (EG) as a dealkalizing agent mitigates structural degradation, owing to the size effect constraint. This work provides fundamental theoretical insights for liquid-phase engineering of O3-phase layered oxides, a critical aspect in the development of oxide cathode materials for Na-ion batteries. Therefore, the paper is suitable for publication in Nature Communications after major revisions.\nReply: Thank you very much for your comments. Reviewers' comments have been responded to and answered individually, and the necessary data has been supplemented.\nSpecific comments:\n1. Ethylene glycol (EG) is a protic compound. Is there any possibility of ion exchange between Na+ from O3-NaNi Fe Mn O (NFM) and H+ from EG? Could it be that the dealkalization process and the ion exchange between Na⁺ and H⁺ are competitive?\nReply & Revision: Thank you for the comment. During liquid-phase processing in EG, H+/Na+ exchange does occur on the surface of NFM materials. However, this process is characterized by slow kinetics and a low degree of reaction, resulting in a minimal impact on the material. The specific analysis is as follows:\n(1) The negligible effect of H+/Na+ exchange on materials during the dealkalization process. Thermogravimetric analysis of EG-NFM confirmed the occurrence of H+/Na+ exchange (Supplementary Fig. 19). Additionally, we supplemented the Na element loss test in NFM after immersion in EG for varying durations (Table R2), revealing that ion exchange induces only minor damage to the material. Detailed analysis in Supplementary Table 7 and Fig. 23.\nTable R2 Na leaching of NFM materials after different duration of immersion in EG\nDissolved metal ions\nStirring 20 minutes Stirring 2 hours Stirring 24 hours\nin filtrate\nNa (mg/L) 7.825 (1.14% loss) 9.769 (1.42% loss) 11.341 (1.65% loss)\nNi (mg/L) 0.041 0.067 0.078\nFe (mg/L) 0.087 0.095 0.099\nMn (mg/L) 0.011 0.021 0.065\n(2) The dealkalization process does not compete with H+/Na+ ion exchange. As illustrated in Fig. 2b, dealkalization process is characterized by a relatively short operational duration, demonstrates the high dealkalization efficiency of EG in this context. In contrast, the rate of H+/Na+ exchange is extremely slow, leading to minimal Na loss even after 24 hours of immersion. This indicates that the kinetically slow ion exchange has a negligible impact on the dealkalization process, indicating that the two processes do not compete directly.\nBased on your comment, we have added relevant discussion on Page 10, Lines 277-279 and 295-299.\n2. Can the alkyl chain length of glycol influence the effectiveness of the dealkalization process? For instance, how does ethylene glycol compare to propylene glycol in this regard?\nReply & Revision: Thank you for the constructive comment. The alkyl chain length in alcohols affects their solubility of Na CO , thereby influencing the efficiency of dealkalization.\nBased on our research and related literature, we identified the key factors influencing the solubility of Na CO in alcohol solvents, specifically the presence of hydroxyl groups and alkyl groups within the alcohol molecule. The dissolution of Na CO in alcohols originates from ionic-dipole interactions. Due to the high electronegativity of the O atom, alcohol molecules exhibit an asymmetric charge distribution, rendering them dipolar. This dipolar nature facilitates electrostatic interactions with Na+ (supported by Ref. J. Phys. Chem. C 123, 15513-15522 (2019)).\n(1) Increased hydroxyl density enhances dealkalization efficiency. The solvation of Na CO in alcohols relies on the ion-dipole interactions between the highly polar hydroxyl groups and alkali ions. For alcohols with same carbon chain lengths, diols are superior to monohydric alcohols. Typically, ethylene glycol (EG) demonstrates higher efficiency than ethanol (EtOH). Glycerol surpasses propylene glycol (PG) in dealkalization but excluded due to high viscosity (Supplementary Fig. 1).\n(2) Increased alkyl chain length reduces the dealkalization efficiency. For alcohol, the steric hindrance of alkyl groups impedes its solvation effect on Na CO . Increased alkyl groups reduce the polarity of alcohol molecules, diminishing the available polar sites within the solvent. For example, the dealkalization efficiency of propylene glycol (PG) is lower than that of EG.\nTo validate the conclusions above, we compared the dealkalization efficiency of EtOH/EG/PG. Solubility test (Na CO ) results showed: EG (3.34 g/100 g) > PG (0.42 g/100 g) > EtOH (0.3 g/100 g), as depicted in Fig. R2a. Titration analysis of SRAs on cathode revealed consistency with solubility data: PG exhibited reduced dealkalization efficiency compared to EG due to additional alkyl effects (Fig. R2b).\nWe have made revisions based on your comment: emphasizing the impact of solvent molecular configuration on dealkalization efficiency, such as Page 4 Lines 101-108 and Supplementary Note 1.\nFig. R2 a, Viscosity-solubility (versus Na CO ) statistics of potential dealkalization solvents. b, Concentration of the residual Na on the A-NFM, EtOH-NFM, EG-NFM and PG-NFM cathode materials measured by acid-base titration.\n3. Could ethanol be used as an alternative in the dealkalization process?\nReply & Revision: Thank you for the comment. Ethanol is not a preferred solvent due to its poor solubility for Na CO (as shown in Fig. R2a). This renders it incapable of effectively removing surface residual alkaline. The above statements can be corroborated in the Ref. Nano Lett. 19, 182−188 (2019); J. Chem. Eng. Data 52, 1213-1216 (2007).\n4. The dealkalization process of EG involves an irreversible reaction, converting (CH OH) to CH OH-CH ONa. How can EG be reused in industrial applications after this transformation?\nReply & Revision: We appreciate this valuable suggestion. Through mature industrial distillation techniques (such as vacuum distillation), effective separation of the solvent EG can be achieved for reuse.\nDealkalization primarily relies on the dissolution of SRAs by EG, meaning that the EG component (boiling point: 197℃) in the dealkalization solvent can be recovered through distillation. To prevent thermal decomposition of small amounts of CH₂OH-CH₂ONa (>180°C for sodium alcoholate), which could reduce distillation efficiency and product purity, vacuum distillation—widely employed in industrial settings—can be utilized (Ref. New Chem. Mater. 43, 40-42 (2015); Vogel's Text book of practical organic chemistry including qualitative organic analysis). By applying negative pressure (-0.1 MPa), the boiling point of EG could be reduced to 110-130℃ for distillation. The distillate can subsequently be dehydrated using molecular sieves for reuse.\nAccording to your comment, we have added relevant content regarding the recycling of dealkalization solvents on Page 5, Lines 148-150.\n5. Only O3-NaNi Fe Mn O (NFM) was examined for EG-mediated dealkalization. Could this process be applicable to other layered cathode materials, such as NaMnO or NaNi Mn O ?\nReply & Revision: Thank you for the valuable comment. Based on comprehensive comparative experimental data, it can be demonstrated that dealkalization possesses technological universality.\n(1) For Na-based oxides, the residual alkali formed by air-sensitive degradation exists predominantly as Na CO , which dissolves efficiently in EG. Therefore, EG solvent is universally applicable to Na-based layered oxides in dealkalization efficiency.\n(2) This study concludes that EG avoids intercalation and further deep damage to O3-NFM due to its interlayer size shielding effect. Na-based layered oxide cathodes exhibit similar structures and layer spacings. Therefore, EG is also applicable to other materials with low damage potential.\nNotably, the NaMnO reviewer mentioned is a metastable O'3 phase cathode (with Mn (III)). Here, we selected O3-NaNi Mn O , O3-NaNi Fe Mn Zn O and P2-Na Ni Mn O as proof of the universality of EG dealkalization. Quantitative analysis of SRAs and electrochemical performance data are compiled in Table R3. Evidently, the substantial SRAs of the three Na-based oxides can be effectively removed by EG. Electrochemical performance indicates that the capacity of cathodes recover after dealkalization, and the capacity retention rate improve after cycling. In summary, owing to its high efficiency and low damage, EG is suitable for liquid-phase dealkalization of various Na-based layered oxides.\nTable R3 Residual Na content measured by acid-base titration, and electrochemical performance of O3-NaNi Mn O , O3-NaNi Fe Mn Zn O and P2-Na Ni Mn O A-Na TMO and EG-Na TMO represent exposed cathode and dealkalized cathode respectively.\nResidual Na Removal Discharge specific Capacity retention,\nSamples content rate capacity, 0.1 C 200 cycle, 1 C\n(ppm) (%) (mAh/g) (%)\nA-NaNi Mn O 44418.7 104.8 80.2\n0.5 0.5 2\n66.3\nEG-NaNi Mn O 14956.2 135.4 89.6\n0.5 0.5 2\nA-NaNi Fe Mn Zn O 15812.5 109.5 70.2\n0.31 0.33 0.33 0.02 2\n45.5\nEG-NaNi Fe Mn Zn O 8625.3 127.0 93.4\n0.31 0.33 0.33 0.02 2\nA-Na Ni Mn O 14087.5 100.3 79.2\n0.67 0.33 0.66 2\n45.3\nEG-Na Ni Mn O 7705 118.9 89.5\n0.67 0.33 0.66 2\n6. Can a mixture of EG and H O be used in the dealkalization process?\nReply & Revision: Thank you for the comment. The mixture of EG and H O cannot be used for dealkalization, as even trace amounts of water molecules exert a significant structural degradation effect on layered oxide materials. Relevant experiments were supplemented for demonstration (Fig. R3 and Table R4).\nWe prepared mixtures at ratios of 90:10, 95:5 and 98:2 (EG wt%:H₂O wt%), employing the same dealkalization procedure as described in the text. The structure and Na loss of dealkalized NFM material are shown in Fig. R3a. Once water is added, NFM cathode experience significant Na loss and structural degradation (decline in layered phase peaks). The discharge specific capacity of dealkalized NFM cathode by the mixture also indicates that water in the dealkalization solvent causes non-negligible damage (Table R4). Therefore, a mixture of EG and H O cannot be used for dealkalization of Na-based layered oxides.\nTable R4 Na loss content and specific capacity loss caused by EG/H O mixture\nNa loss content Specific capacity, 0.1 C Capacity loss vs. EG\nEG wt%:H₂O wt%\n(%) (mAh/g) (mAh/g)\n90:10 28.67 63.55 52.05\n95:5 23.76 68.95 46.65\n98:2 20.24 78.58 37.02\nFig. R3 Structural characterization and electrochemical performance of NFM materials dealkalized with EG/H O mixtures in different proportions (90:10, 95:5, 98:2). a, XRD patterns and Na loss content. b, Charge–discharge curves at 0.1 C rate between 2–4 V, compared with pure EG sample.\nReviewer #3 (Remarks to the Author):\nSurface residual alkali significantly influence the processing and performance of layered oxide materials. The authors propose that ethylene glycol effectively removes surface residual alkali while preserving the structural degradation, highlighting potential significance. However, some studies have previously addressed alcohol-mediated surface impurity removal in layered oxides (e.g., ACS Appl. Mater. Interfaces 10, 38246−38254 (2018)) and water-induced liquid-solid interactions in dealkalization processes (Nat. Commun. 11, 3544−3556 (2020); Science 385, 744−752 (2024)). The key discussions and conclusions appear predominantly based on literature references or speculative reasoning rather than reliable experimental validation. Presently, I have major reservations about this manuscript, and I do not recommend its publication in Nature Communications.\nReply: Thank you very much for your comments. As you mentioned, the air stability of layered oxides has garnered considerable attention in recent years, particularly concerning the gas-solid phase reaction mechanisms involved in material storage process. However, our research focuses on another critical process step—liquid-phase dealkalization, which involves unique liquid-solid reactions. By investigating the complex interactions between various liquid-phase solvents and active cathode materials, we have systematically elucidated the mechanisms that clarify the interplay of degradation phenomena. This holds practical value for the development of liquid-phase engineering of highly active materials. Additionally, it should be noted that the data collected from the literature primarily served to validate the accuracy of the proposed mechanism, which originated from the experiments in this work. In summary, our research offers innovations that distinguish it from the aforementioned studies.\nWe have highlighted the innovation in the text (detailed in Comment 2) and made corresponding revisions based on your comments. Specific details will be elaborated as follows.\nSpecific comments:\n1. The manuscript predominantly emphasizes the role of ethylene glycol in exploring liquid-solid interactions during dealkalization, asserting that using water as a solvent leads to excessive dealkalization and consequent structural damage. However, when the discussion extends to general O3-phase layered materials, water is employed as the solvent, despite the earlier claim regarding the significant impact of transition metals on AM-O interactions. This inconsistency introduces a clear logical contradiction. Additionally, the introduced \"STLP\" concept appears directly borrowed from terminology in lithium-ion battery cathode research, lacking substantial scientific justification and relying primarily on subjective claims regarding its potential practical significance. These issues collectively diminish the scientific merit of the manuscript and necessitate comprehensive reconsideration and revision.\nReply & Revision: Thank you for the constructive comment. The logical transition within the article is emphasized; the concept lacking precision has been revised. Details are as follows.\n(1) The key focus of this work lies in the interactions between the host material and the guest solvent, rather than solely on the solvent's dealkalization effect. The first part is based on a specific host cathode (NFM), comparing the effects of different solvents. The second part examines a specific guest solvent, comparing its interaction with various cathodes. Water was selected here because the degradation of more cathodes in water exhibits significantly different behavior.\n(i) The first part of this article emphasizes the practical value of dealkaliation solvents and investigates the liquid-solid interaction mechanisms between solvents and cathodes. Using NFM as the host material, we studied the liquid-phase treatment effects of water and ethylene glycol. Ethylene glycol was identified as the more valuable solvent for application in this section.\n(ii) The second part aims to expand the liquid-solid interaction mechanisms. In this section, we use water to investigate multiple oxide cathodes. Water was selected as the representative guest solvent because: the failure behavior of more cathode materials (Li/Na-based) in water is significantly distinguishable and investigable, facilitating the mechanism extensions. Clearly, we cannot differentiate the liquid-solid interaction of more cathodes in ethylene glycol, given its stability toward the host materials.\nWe have made corresponding revisions based on your comment: emphasizing the research approach and clarifying logical transitions, such as Page 3, Lines 82-86; Page 13, Lines 390-392; Page 14, Lines 409-415.\n(2) To ensure rigorousness and avoid conceptual confusion, we have uniformly revised “STLP” to “Stability tolerance against liquid-phase” in the article. A more rational explanation is provided, emphasizing that it serves as a guideline for evaluating the stability of active materials in liquid phases, rather than a quantitative metric. Specifically for this article, we propose that the tolerance of O3-type oxides in aqueous solutions can be quantitatively analyzed based on the loss of active AM ions. Based on the conducted experiments and statistical data validation, the liquid-phase stability of various cathode materials can be comprehensively evaluated. Revisions are detailed in the Abstract, Fig. 5d, Page 3, Lines 87-88; Page 16, Lines 467-473; Page 17, 480-484.\nThank you for the constructive suggestion. We aim to propose a foundational, universal concept that can be widely applied. However, this study found that it is currently unfeasible to describe “STLP” through a quantifiable metric, meaning that targeted analysis must be conducted for specific cathode/solvent. In addition, thorough research indicate that this concept has not yet been proposed in the lithium-ion battery cathode. We believe this concept holds significant scientific importance for the liquid-phase processing of highly reactive materials, hence we highlight its development potential in the outlook, Page 19, 538-544.\n2. Water intercalation, protonation, reactive sodium extraction, and lattice distortion have been widely reported in the literature. Could the authors explicitly highlight and clarify the innovation and novel aspects of the present study compared to existing reports?\nReply & Revision: Thank you for the comment. The innovation of this study is discussed from two perspectives below.\n(1) Significantly different material production processes and mechanisms involved.\nPrevious studies have conducted insightful investigations into the degradation mechanisms of gas-solid phase contact involved in the vital storage aging process of Na-based oxides (Science 385, 744−752 (2024); Nat. Commun. 11, 3544−3556 (2020)).\nIn contrast, our work focuses on another critical step, washing dealkalization process (post treatment), in which material degradation involves liquid-solid phase contact. This process exhibits a more profound degree of water-induced structural damage to the active cathode compared to gas-solid interactions. For instance, time-dependent phase degradation (Fig. 3b, Fig. 4c); active Na loss following a specific pathway dependent on water intercalation (Fig. 2e, Fig. 4e,g). Therefore, based on the principle of selecting solvents with high efficiency and low damage, we chose ethylene glycol as an alternative dealkalizing agent (considering viscosity and solubility for sodium carbonate) for subsequent research. These findings significantly distinguish this study from other research concerning gas-solid contact, thereby conferring its innovative value.\n(2) A systematic mechanism clarifying the distinct liquid-solid phase interaction between dealkalizing solvents and Na-based layered oxides.\nBased on the first systematic investigation into the degradation behaviors between solvents with different configurations (water/ethylene glycol) and O3-type oxides, we propose a degradation mechanism facilitated by self-propagation solvent molecular intercalation. Therefore, the distinct interaction between water/EG and O3-phase layered oxides can be summarized (Figs. 4g-h). (i) In aqueous media, structural degradation transpire continuously into layered structure driven by the spontaneous intercalation and deprotonation of H O molecules (Figs. 4a-b). Na leaching exhibits a nonlinear relationship with the duration of aqueous phase treatment, controlled by the hydration state of layered oxides (Figs. 4d-e). (ii) For ethylene glycol, minimal damage to NFM particles is attributed to blocked molecular intercalation, with trace near-surface degradation due to protic solvent. This mechanism addresses the inadequacies of the Na+/H+ exchange effect that was frequently employed in explanation for liquid-phase damage in different solvents and materials. We also generalize the proposed liquid-solid interaction mechanism to more O3-type CAMs, and demonstrated its compatibility through extensive experiments and simulations. This provides guidance for optimizing the liquid-phase processing of CAMs, making our work innovative compared to existing research.\n3. How do the authors confirm that the gas produced during the reaction between ethylene glycol and the alkali is indeed CO ? If this conclusion is correct, the fundamental reaction should essentially involve interactions between OH- and H+ ions; however, breaking O-H bonds in alcohols typically requires additional external conditions, which is not clearly explained. Therefore, a more detailed mechanistic explanation is needed. Additionally, it appears that simple solid–liquid separation would be insufficient to effectively remove CH OH–CH ONa salts.\nReply & Revision: Thank you for the significant comment. Based on supplementary experiments and research, we correct the equations concerning the reaction between ethylene glycol and alkali. Additionally, we provide a solution for CH OH–CH ONa salts that cannot be removed by liquid-solid separation.\n(1) We collected the gas produced by mixing ethylene glycol with alkaline NFM material and conduct Gas Chromatograph (GC) testing (Fig. R4). The results exhibit only N within the sealed reaction vessel, demonstrating that the bubbles released from liquid-solid mixture are adsorbed air in powders, rather than products resulting from the reaction between alkaline substances and alcohol. Therefore, we delete Eqs. 2 and relevant content on Page 7.\nAdditionally, we corrected the reaction described in Eqs. 1 based on the protonic properties of ethylene glycol. Intramolecular hydrogen bonds formed between adjacent hydroxyl groups in ethylene glycol stabilize the deprotonated conjugate base, enhancing its acidity (pKa=14.2, Bordwell pKa Table from ACS Division of Organic Chemistry). Therefore, ethylene glycol can react with NaOH in the SRAs (pKa (conjugate acid H O) =15.7) as shown in Eqs. 1. NaHCO formed from Na CO hydrolyzed by trace water product remain during liquid-solid separation, which accounts for the slight increase in NaHCO detected in the text. In summary, we revise the description corresponding on Page 7, Lines 198-203.\n10000\nDectector: TCD\nCarrier gas: Ar\n120℃\nKit1: H , N , CO, CO , CH\n2 2 2 4\nu.) N 2\na. 5000\ny\n(\nsit\nn\ne\nnt\nI\n0\n0 5 10 15 20\nTime (min)\nFig. R4 Gas Chromatograph test. The gas generated by mixing ethylene glycol with highly alkaline cathode materials is collected via an aluminum foil gas collection bag. The gas collection process is conducted using Aluminium foil bag in an argon-filled glove box to eliminate the air.\n(2) Solid-liquid separation cannot completely remove CH OH–CH ONa salts on surface. Our original intent in this article focused on analyzing the dealkalization mechanism, hence performing only a simple dealkalization-separation step. In practical engineering applications, liquid-phase dealkalization is typically employed with secondary heat treatment to achieve material regeneration, thereby resolving the residual organic salt. We conduct secondary heat treatment of dealkalized material for validation. Simultaneous thermal analysis confirmed the decomposition of alcohol-based sodium; electrochemical testing demonstrated the recovery of NFM cathode performance following heat treatment. Relevant content is provided on Page 5, Lines 142–148 and Supplementary Fig. 7.\n4. In pouch cell tests, the charging capacity of A-NFM significantly exceeds that of EG-NFM, whereas in half-cell measurements, the capacity of A-NFM is lower compared to EG-NFM. Could the authors explain this discrepancy in detail?\nReply & Revision: Thank you for the comment. We apologize for the lack of necessary explanations. The presodiation of residual Na CO on the cathode surface result in the abnormal higher specific capacity of A-NFM pouch cell. Specific explanation is as follows:\n(1) Electrochemical oxidation of Na CO at high potential. In comparison to the 2-4 V voltage range in the charge-discharge test depicted in Fig. 1c, the gas release test illustrated in Fig. 1d encompasses a broader voltage range of 2-4.5 V. The substantial residual Na CO (decomposition potential ~4.25 V) on the A-NFM surface undergoes electrochemical oxidation at high potential. This process contributes to a capacity that surpasses that of EG-NFM. This presodiation effect can be demonstrated in the dQ/dV curve of this battery (Supplementary Fig. 8), consistent with the additional references, as shown in Fig. R5. (Ref: Batteries Supercaps 7, e202400009 (2024); Chem. Mater. 29, 5948-5956 (2017))\nFig. R5 a, Additional charging platforms of Na CO decomposition in Fig.1d. b, The dQ/dV curve of the A-NFM sample. The oxidation peak of Na CO is observed at 4.25 V. c, Na CO as a sacrificial additive provides additional charging capacity, Ref. Batteries Supercaps 7, e202400009 (2024). d, Cyclic voltammograms of the cathode with Na CO , the oxidation peak at 4.25 V represents the decomposition of Na CO .\n(2) Different counter electrodes in batteries. The charge-discharge test in Fig. 1c employs half coin cells with a Na metal anode, ensuring an abundant supply of active Na+. Conversely, gas release test shown in Fig. 1d employs full pouch cells with a hard carbon anode, indicating that the cathode is the sole source of the limited Na+. The irreversible loss of Na⁺ during cycle, attributed to the formation of SEI, leads to a reduced specific capacity for EG-NFM compared to A-NFM under presodiation.\nAccording to your comments, we have revised Fig. 1d and provided supplementary explanation for this discrepancy on Page 5, Lines 154-161, Supplementary Fig. 8.\n5. Why does the capacity of W-NFM increase during the cycle?\nReply & Revision: Thank you for the comment. Due to the interlayer water molecules and protons occupying the Na sites in W-NFM, the initial specific capacity is relatively low. As cycling continues, interlayer substances gradually desorb under the influence of the electric field, releasing a few active sites and causing the specific capacity to recover. After a certain number of cycles, the capacity exhibits a normal decay trend. This is demonstrated as follows.\nBased on the TGA curve in Supplementary Fig. 19, we subjected W-NFM to heat treatment at 200°C for 5 hours (named as W-NFM-H) and conducted electrochemical testing. The results revealed a sustained capacity decay in subsequent cycles following a slight initial increase (Fig. R6a). This indicates that heat treatment, by removing intercalated substances, alleviates the capacity increase phenomenon.\nFurther XRD testing of W-NFM and W-NFM-H electrodes after cycling is shown in Fig. R6b. Due to the desorption of intercalated substances during cycling, a complete O'3→P3 phase transformation occurs in W-NFM, indicating significant increased Na vacancies. In contrast, W-NFM-H exhibits only partial Na vacancy formation during cycling due to the partial desorption of intercalated substances during heat treatment, resulting in an incomplete O'3 phase transformation. The phase analysis results are corroborated by the Ref. Inorg. Chem. 51, 6211−6220 (2012); Adv. Sci. 12, 2501649 (2025). In fact, the original NFM material does not undergo significant phase transformation after recycling.\nFig. R6 a, Cycling performance of W-NFM-H compared to W-NFM at 1 C. b, XRD pattern of W-NFM, W-NFM-H electrode before and after cycle.\n6. Fig. 2e-i clearly illustrates significant surface cracking after water-based dealkalization, which typically corresponds to a distinct hydrate-phase diffraction peak around 14° in XRD measurements. However, this expected characteristic peak is not prominent in the manuscript's XRD results (Supplementary Fig. 16). The authors should provide clarification and explain this discrepancy.\nReply & Revision: Thank you for the comment. The signals of hydrated phase crystallization in O3-type oxide cathodes are generally weak. In numerous studies investigating the aging of materials during moisture storage, the XRD diffraction peaks of hydrated phases remain undetectable. However, the cathode particles exhibit cracking in their morphology. Ref. J. Mater. Chem. A 24, 14074-14084 (2021); ACS Appl. Mater. Interfaces 14, 5338-5345 (2022); Science 385, 744−752 (2024).\nIn our study, the amplified XRD pattern clearly reveals signals of the hydrated phase due to aqueous phase treatment (Supplementary Fig. 18). Following your suggestion, we provide further explanation on Page 8, Lines 236-240 and in Supplementary Fig. 18.\n7. For the in situ XRD results, the contour map is not very clear in describing the details, instead, the stacking diagram should be given.\nReply & Revision: Thank you for the comment. The original stacking diagram for Fig. 3d has been provided in Supplementary Fig. 20, with clear phase information labeled. We chose to present the contour map in the main text to illustrate the temperature nodes at which W-NFM undergoes structural transformation at high temperatures, and to delineate different stages. This is crucial for reversely analyzing the failure mechanisms of NFM materials in aqueous environments.\nWe have refined the description of the stacking diagram in the notes for Supplementary Figure 20. Additionally, the in situ XRD data for EG-NFM has been added in Fig. 3d and Supplementary Figure 21.\n8. The manuscript contains several noticeable formatting errors, including incorrect terminology such as \"Bi3++ ion beam\" and \"FullProf_suite.\" Additionally, there are inconsistencies in unit formatting (e.g., \"mA g-1\" versus \"mA/g\") and a lack of proper spacing between numbers and units (e.g., \"10nm/min\"). These formatting issues should be carefully corrected for clarity and compliance with journal standards.\nReply & Revision: Thank you for your thorough review. We apologize for the formatting errors and have corrected all instances mentioned on Page 21, Line 619, 625, 627 and Line 644. Additionally, we have thoroughly reviewed the entire document to ensure the accuracy and rigor of its content.\n9. The manuscript is significantly redundant and lacks conciseness, detracting from a clear focus on the primary points of discussion. Additionally, both the abstract and main text currently exceed the word limits set by Nature Communications, necessitating substantial revision to comply with journal guidelines.\nReply & Revision: Thank you for your insightful comment. We apologize for the redundancy and inaccuracies in the article. We have made further revisions to the article based on your suggestions.\n(1) Simplify expressions and eliminate redundancy. We have reduced the total word count from ~7000 words in the original draft to ~5000 words (in compliance with journal requirements). The abstract was also revised to under 180 words.\n(2) Clarify the logic and enhance innovation. The discussion of the innovative aspects of this work has been strengthened, and necessary logical transitions have been added, such as on Page 3, Lines 82-86; Page 14, Lines 409-415; Page 18, Lines 521-525.\n(3) Supplement data and enhance the scientific rigor and standardization. The necessary experimental data and analysis have been supplemented, such as Fig. 1d, Fig. 3d, Supplementary Figs. 7, 8, 16, etc."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I appreciate the authors for addressing the comments. I recommend publicaton of this manuscript.", "reviewer_2": "The authors have addressed essentially all of my previous concerns, and their revisions have substantially improved the manuscript. I have no further comments.", "reviewer_3": "The author has adequately addressed the routine errors present in the manuscript, and no further concerns remain in this regard. However, significant doubts persist regarding the novelty of the work. The author has acknowledged the inadequacy of the originally proposed core mechanism (Na2CO3 + (CH2OH)2 → CH2OH-CH2ONa + H2O +CO2), but the alternative explanation put forward appears somewhat arbitrary and lacks robust supporting data (NaOH + (CH2OH)2 → CH2OH-CH2ONa + H2O). No compelling evidence has been provided to demonstrate that this reaction genuinely occurs under the reported conditions. Therefore, in my assessment, the manuscript does not meet the publication standards for Nature Communications."}, "author_response": "Reply: We sincerely appreciate the reviewer’s rigorous review and insightful comments, which prompted us to verify and correct the characterization regarding the dispersion state of sodium carbonate in the ethylene glycol (EG) liquid environment in the initial manuscript. According to your comments, we have further corroborated the accuracy of the revised reaction equation through experimental results and theoretical calculations.\nFirst, the simulated heat of reaction for [OH— + (CH OH) → CH OH-CH O— + H O] is presented in Figure R1 and Table R1. We comprehensively considered both the gauche-conformation and trans-conformation of ethylene glycol, calculating the heat of reaction for all four possible pathways. The results demonstrate that the reaction proceeds spontaneously (with negative heat of reaction) under all conditions.\nRelevant details have been added to the text on Page 7, Lines 201-204 and Supplementary Figure 13 and Table 3.\nFigure R1 Schematic diagram of the reaction pathway between NaOH and ethylene glycol.\nTable R1 Calculated heat of reaction results for the four pathways of the NaOH-EG reaction. EG- (reactant-product) denotes the conformation (gauche/trans) of the reactant and product.\nType Reaction pathway Heat of reaction (eV)\nFurthermore, supplementary experiments demonstrated the objective presence of water as a product in the revised reaction within the NaOH-EG system. Karl Fischer titration results indicated an increase in H O content (531 ppm → 805 ppm) within the system following complete reaction between EG and NaOH, as shown in Table R2. This confirms the forward proceeding of the reaction [NaOH + (CH OH) → CH OH-CH ONa + H O]. Relevant details have been added to the text on Page 7, Lines 201-204 and Supplementary Table 4.\nTable R2 Evolution of moisture content in the EG-NaOH reaction system. EG was pre-treated with molecular sieves to remove water. The filtrate after reaction was tested to exclude interference from powder residues. The entire reaction process was conducted within an argon-filled glove box to prevent contamination from ambient air.\nSamples H O concentration (ppm)\nEG 531\nEG + NaOH (12 hours duration) 605\nEG + Na CO (12 hours duration) 805\nIt is important to note that the aforementioned formula does not constitute the core mechanism conclusion of our work and is not directly related to the novelty. Since liquid-phase dealkalization primarily depends on the dissolution of residual alkali, the reaction between NaOH and ethylene glycol proceeds at a slow rate with a negligible extent. This merely indicates a weak interaction between the solvent environment and surface residual alkali on cathode powder, as mentioned on Page 4, Lines 101-107, and Page 7, Lines 196-201 in the text.\nIn fact, the core of our work lies in the complex interactions between various liquid-phase solvents and active cathode materials in liquid-phase dealkalization. The innovative aspects of this research comprise: (i) the first investigation to systematically link solvent-molecule configuration to the structural degradation of O3 phase layered oxides; (ii) an in-depth revelation of the interplay between multiple structural/performance degradation phenomena within this process; (iii) the insightful extension of the summarized liquid-solid reaction mechanism to additional oxides of the same structure, thereby conferring its universal applicability. These insights offer fundamental theoretical and technical guidance for the scalable liquid-phase engineering of functional powder materials, particularly in dealkalization routes, coating compatibility, etc."}]

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