batterydata/battery-device-data-qa huggingface dataset:
Up to now, owing to the tremendous work done by different research groups, there have been several new types of electrolysers proposed for decoupled H2/O2 generation through the utilization of redox mediators, and a list of these new electrolysers has been provided in Table S1 in the ESI.† For example, a new PEM electrolyser is proposed with polyoxometalates (POMs) used as the redox relay, and the H2/O2 generation can be decoupled both in time and in space (Scheme 1b). Such a design requires three electrodes (OER electrode, carbon electrode for reduction of the soluble POM redox mediator, and Pt catalyst for spontaneous hydrogen evolution), one soluble redox mediator (POMs), one membrane (Nafion membrane) and two cells, which potentially increases the cost for the electrolysers. A solid redox mediator, such as Ni(OH)2, has also been successfully used as the relay for decoupled water splitting (Scheme 1c). This kind of design needs no separator between the cathode and the anode; however, an auxiliary relay electrode has been used and the whole cell is still a three-component system, and the overall cost for the electrolyser may not be effectively reduced. Also, among all these designs, since the HER and OER are decoupled in time, there is always an electrode (either the HER or the OER electrode) in an idle state when the cell is in operation. For decoupled water splitting in time, the integration of the HER and OER in one electrode can effectively reduce the cost and space for the electrolyser, which is more practical for scale-up applications; however, a rational design toward this direction has not been proposed.

Question: What's the cathode?

Question: What's the anode?
Numerous studies reported core–shell 3D-nanostructured Li-ion electrodes with active components such as Si, Sn, TiO2, Nb2O5, Co3O4 or iron oxides, mostly applicable as negative electrodes (anodes). On the other hand, nanostructured 3D positive electrodes (cathodes) based on active materials with a desirable high redox potential vs. Li+/Li (e.g. lithiated manganese oxides, V2O5 or LiCoO2 have been reported in comparatively fewer publications. For such cathodes, a big difficulty lies in inherent oxidation of the 3D current collector during the synthesis of high voltage cathode materials – the latter typically requiring temperatures above 700 °C. By lowering the synthesis temperature to 300 °C, Zhang et al. and Pikul et al. successfully demonstrated both core–shell cathodes and full 3D Li-ion microbatteries which employed lithiated manganese oxides coated on inverse nickel opal current collectors. Impressively, the devices were operational at C-rates above 1000 (where the rate of 1C corresponds to the current required for 1 hour of a complete charge or discharge). The same group also demonstrated other high-performance 3D cathodes, such as a carbon foam coated with dense LiCoO2 or inverted opals doubly-filled with V2O5 and Li2MnSiO4. Currently, however, the electrode design based on regular inverse opal current collectors is difficult to envision for large scale battery manufacturing, as the fabrication of these current collectors is time consuming (e.g. >24 h for a 20 μm-thick structure), involves difficult to handle colloidal templates and is limited to small surfaces (∼1 cm2). Importantly, the application of a current collector with yet a higher volumetric surface area may allow further reducing the thickness of the active material and gaining access to its full theoretical capacity.

Question: What's the cathode?
Answer: a carbon foam coated with dense LiCoO2

Question: What's the cathode?
Answer: inverted opals doubly-filled with V2O5 and Li2MnSiO4
In summary, we report novel free-standing DBHF nanofibers as a highly efficient and high-performance cathode for hybrid Zn batteries. Their unique structure with a fiber-in-tube hierarchical configuration, defect-rich crystals, carbon based network and hollow spherical basic units facilitates fast electron/ion transport and ORR/OER reaction kinetics. Benefitting from the advantages of the DBHF structure and the self-supporting character, the fabricated flexible hybrid Zn battery with the DBHF cathode achieves high operating voltage, high rate capability, high energy/power density and good adaptability under different working conditions. Furthermore, its outstanding stability and high efficiency are demonstrated by five-thousand high-rate cycling. More impressively, the excellent air charging capability makes it an outstanding power source for uninterrupted power supply while altering the working environment. Therefore, this work not only provides a novel strategy to synergistically improve the efficiency and performance of hybrid Zn batteries with both Zn-ion and Zn–air modes, but also opens a new avenue to fabricate high-performance flexible batteries for different electronics under various working conditions.

Question: What's the cathode?
Answer: DBHF nanofibers

Question: What's the cathode?
Answer: DBHF
For more than a decade, researchers have known that layered oxide cathodes, particularly NMC and NCA materials, have fragile surfaces. Thus, it allows various chemical/electrochemical reactions with gases (e.g., storing environments) or liquids (e.g., organic electrolytes) at the surfaces. As the urgent demand for commercialization of the Co-free, Ni-rich layered cathodes, the shelf life of active powders is considered as an important characteristic due to the uncertain delay from powder production to electrode processing and to battery manufacturing. In addition, with the nickel concentration approaching 100%, and the pursuit towards Co-free materials, surface stability against the organic electrolyte is vital in the commercialization. LiNiO2-based materials are more unstable than their cobalt-containing analogs because of the increased magnetic frustration of Ni3+ than Co3+. Therefore, surface degradation is more severe in Ni-rich oxide cathodes due to the high oxidation state of nickel. We previously discovered that the electrochemical performance of LiNiO2 cathode can be improved by incorporating dual dopants through the surface and bulk properties enhancement. Herein, we exploit the platform of LiNiO2-based materials to study the surface fragility under various practical conditions. Moreover, we will further discuss advantages of doping chemistry through the post-mortem characterizations. Lastly, we are aiming to provide insights into developing low-cost, high-energy Co-free Ni-rich cathode materials.

Question: What's the cathode?
Answer: LiNiO2

Question: What's the cathode?
Answer: Ni-rich oxide
The electrode pastes were composed of active materials/carbon black/gel electrolyte precursor whose composition ratios were 60/8.5/31.5 (w/w/w) for the LiCoO2 (LCO) cathode and 52/7.5/40.5 (w/w/w) for the Li4Ti5O12 (LTO) anode, respectively. The gel polymer electrolyte precursor was prepared by mixing a UV-curable ethoxylated trimethylolpropane tri-acrylate (ETPTA) monomer (Aldrich) (including 1.0 wt% 2-hydroxy-2-methl-1-phenyl-1-1propanone (HMPP) as a photo-initiator) and high boiling point electrolyte (1 M LiPF6 in ethylene carbonate(EC)/propylene carbonate(PC) 1/1 (v/v)) in a composition ratio of 15/85 (w/w). To fabricate the bQSSB with cSiPV, the LTO anode paste was directly stencil-printed onto an Al current collector of the cSiPV module without any processing solvents and then exposed to UV irradiation. UV irradiation was performed using an Hg UV-lamp (Lichtzen) with an irradiation peak intensity of approximately 1260 mW cm−2. Subsequently, on the LTO anode (thickness = 50 μm and mass loading = 5.9 mg cm−2), a composite polymer electrolyte (CPE, gel electrolyte precursor/Al2O3 nanoparticles (average particle size ∼300 nm) = 56/44 (w/w)) was introduced through the UV curing-assisted printing process. Then, the LCO cathode paste was stencil-printed directly on the CPE/LTO anode and solidified by UV irradiation, yielding the printed LCO cathode (thickness = 30 μm and mass loading = 6.2 mg cm−2). After placing an Al current collector on top of the printed LCO cathode/printed CPE/printed LTO anode, the QSSB unit cell was obtained. Another QSSB unit cell was introduced, using the same printing process, on the top of the pre-fabricated QSSB unit cell, leading to the bQSSB with a bipolar structure. The number of QSSB unit cells on the cSiPV module was determined from the Vmax of the module concerning the voltage matching between the cSiPV and the bQSSB. Finally, the encapsulation of the bQSSB was conducted with Al pouch packaging substances and a UV-curable hydrophobic polymer (PRO-001, Novacentrix). All assembly steps of the cells were performed in a dry room.

Question: What's the cathode?
Answer:  LiCoO2 (LCO)

Question: What's the cathode?
Answer: LCO
To investigate the electrochemical Na ion storage mechanism to predict the theoretical properties of Nax[Ni0.5Mn0.5]O2, we performed first-principles calculations based on the structural information verified through the Rietveld refinement analysis. At this stage, even though 0.01 mol of Ca2+ ions was incorporated into the bulk Na sites, Na0.98Ca0.01[Ni0.5Mn0.5]O2 showed a nearly identical crystal structure with Na[Ni0.5Mn0.5]O2; hence, we assumed that Na0.98Ca0.01[Ni0.5Mn0.5]O2 experienced the same O3–P3 phase transformation during the Na+ extraction/insertion process. Various Na/vacancy configurations on O3-Nax[Ni0.5Mn0.5]O2 compositions (0 ≤ x ≤ 1) were generated through the cluster assisted statistical mechanics (CASM) code and then, we predicted the theoretical formation energies of the O3-Nax[Ni0.5Mn0.5]O2 composition. Based on information of the formation energies, we calculated the redox potentials of O3-Nax[Ni0.5Mn0.5]O2 during Na+ extraction/insertion using the following equation where E(x) indicates the formation energy on the most stable Na/vacancy configuration of x species. By considering the typical O3–P3 phase transition in the O3-type layered oxide cathode in SIBs, we calculated the formation energies of P3-Nax[Ni0.5Mn0.5]O2 and then applied this information to compare the thermodynamic stability between O3- and P3-phases. As presented in Fig. 4a, we predicted that the O3–P3 phase transition occurred after extraction of 0.25 mol of Na ions from O3-Na1[Ni0.5Mn0.5]O2, and then, when the Na content in P3-Nax[Ni0.5Mn0.5]O2 was reduced to less than 0.25 mol, the O3–P3 phase transition re-occurred. Moreover, we verified that in the case of O3-/P3-Nax[Ni0.5Mn0.5]O2, the redox potentials required for Na+ extraction/insertion were less than ∼4.11 V (vs. Na+/Na) and more than ∼2.48 V, which indicates that 1 mol of Na ions can be reversibly extracted/inserted from/into the O3-Na1[Ni0.5Mn0.5]O2 structure despite the O3–P3 phase transition. Fig. 4b illustrates the predicted redox potential range of the O3/P3-Nax[Ni0.5Mn0.5]O2 cathode as a function of the Na content (0 ≤ x ≤ 1) with experimentally measured galvanostatic intermittent titration technique (GITT) profiles in the voltage range of 2.0–4.3 V. To confirm our hypothesis that the Ca-substituted cathode would undergo a similar O3–P3 phase transformation during the sodiation/de-sodiation process, we checked the GITT profiles of the Na0.98Ca0.01[Ni0.5Mn0.5]O2 cathode and overlaid the results with the predicted theoretical redox potential of the Nax[Ni0.5Mn0.5]O2 cathode. Interestingly, we confirmed that the slope of the charge/discharge curve of O3-Na0.98Ca0.01[Ni0.5Mn0.5]O2 matched the predicted redox potential of the Nax[Ni0.5Mn0.5]O2 cathode well within the wide voltage window of 2.0–4.3 V; this clearly verified our hypothesis and confirmed that ∼1.0 mol of Na+ ions could be extracted/inserted from/into Na0.98Ca0.01[Ni0.5Mn0.5]O2.

Question: What's the cathode?
Answer: O3-type layered oxide

Question: What's the cathode?
Answer: O3/P3-Nax[Ni0.5Mn0.5]O2
Another critical property of an electrode material toward practical application is the ease of handling against a moist environment. Most of the O3-type transition metal oxide cathodes reported so far are moisture sensitive because of the low redox potential associated with 3d-metals. Once the cathode is exposed to air or moisture, water oxidizes the transition metal ions with the concomitant removal of Na+ ions, which further react with CO2 and H2O in air to form Na2CO3 or NaOH. Such undesirable reactions usually cause structural degradation and poor electrochemical performances and thus make them difficult to handle. As revealed in Fig. 7, after exposure to air with a relative humidity of ≈55%, the Na[Ni0.5Mn0.5]O2 exhibited an apparent structural change to a Na-deficient monoclinic O′3 phase together with formation of Na2CO3·nH2O on the surface. In contrast, Na0.98Ca0.01[Ni0.5Mn0.5]O2 remarkably retarded spontaneous phase transition and retained the original O3 structure. To confirm in detail the structural stability against a humid atmosphere, a comparative study of the XRD evolution of the Na0.98Ca0.01[Ni0.5Mn0.5]O2 and Na[Ni0.5Mn0.5]O2 cathodes was conducted as a function of exposure time (1, 3, and 5 days and 1 week) (Fig. S16†). After 1 day, there were no significant structural changes in either cathode. However, after three days, the Na[Ni0.5Mn0.5]O2 cathode was readily oxidized in the presence of moisture, and subsequently, the intensity of (003)hex. and (104)hex. peaks decreased in the XRD patterns. After 5 days, splitting of the (003)hex. and (006)hex. diffraction lines was observed, indicating a slightly enlarged interslab distance for the new monoclinic O3 phase. Finally, after 1 week, the phase transformation from the hexagonal O3 to the monoclinic O′3 phase occurred in the Na[Ni0.5Mn0.5]O2 cathode. This monoclinic O′3 phase transformation can be observed in the sodium deficient structure when the sodium ions are extracted down to 20 mol% in the original O3 structure. In contrast, throughout the week, the intensified peaks, (003)hex., (006)hex., (101)hex., (102)hex., and (104)hex., in the O3 phase were well retained persistently for the Na0.98Ca0.01[Ni0.5Mn0.5]O2 cathode, indicating less reactivity against moisture. These results suggest that the Ca2+ ions on the Na sites with strong Ca–O bonding prevent the removal of Na+ ions from the structure when exposed to air. As expected, in Fig. S17,† the Na0.98Ca0.01[Ni0.5Mn0.5]O2 cathode demonstrated higher reversible capacity with lower voltage polarization and better cycling stability after prolonged exposure, while the Na[Ni0.5Mn0.5]O2 cathode showed poor electrochemical performance and even exhibited an irreversible reaction during charging, due to the decomposition of Na2CO3 which is a by-product of removed Na+ ions and CO2 in air. Such a comparison of the thermal properties and air-stability strengthens the merits of Ca-substituted cathodes in practical application.

Question: What's the cathode?
Answer: Na0.98Ca0.01[Ni0.5Mn0.5]O2 and Na[Ni0.5Mn0.5]O2

Question: What's the cathode?
Answer: Na[Ni0.5Mn0.5]O2
Unlike DC voltage exfoliation, square-wave voltage uses bulk antimony, bismuth and their compounds as the anode and platinum wire or foil as the cathode, and changes the voltage direction to perform electrochemical exfoliation in an electrolytic solution of Na2SO4 or Li2SO4. This process mainly uses oxygen-containing free radicals produced by electrolysed water to assault large pieces of antimony or bismuth or their compounds in the anode, and SO42− intercalates into the interlayer. Subsequently, the gas generated between the layers of the bulk layered material further expands, and finally 2D antimony or bismuth or its compound is obtained in the electrolyte. In 2020, Marzo et al. elucidated the possible mechanism of changing the voltage exfoliation of 2D Sb and Sb2Te3. As shown in Fig. 4b, this exfoliation process comprises four different stages. In the first stage, oxygen-containing free radicals produced by the electrolysis of water on the anode bulk 2D material react with the edges and boundaries, creating bumps, cracks and holes in the bulk 2D material. Next, the small cations (H+, Li+ and Na+) intercalate into the gaps and holes formed in the previous bulk 2D material, initializing a slight and preliminary expansion of the 2D sandwich. When the conversion voltage is −5 V, the SO42− intercalation layer enters the interlayer of the bulk 2D material. Finally, the gases (H2, O2 and SO2 formed in these redox processes) generated by the insertion of ions between the 2D bulk material layers promote the exfoliation of the 2D material and disperses it into the electrolyte (Fig. 4b).

Question: What's the cathode?
Answer:  platinum wire or foil

Question: What's the anode?
Answer:  bulk antimony, bismuth and their compounds
The development of high-capacity rechargeable lithium–sulfur batteries is an ongoing challenge because of the shuttle effect, which causes rapid capacity fade, limited rate capability, and slow kinetics. Herein, conductive hollow cobalt nitride/carbon (Co5.47Nx–C) spheres with nitrogen vacancies are developed as a high-performance cathode material for use in lithium–sulfur batteries. Nitrogen vacancies are formed by annealing a zeolite imidazole framework (ZIF-67) precursor in ammonia. Benefiting from its Co–N bonds and nitrogen-vacancy sites, the Co5.47Nx–C composite achieves strong anchoring of polysulfides, fast polysulfide conversion, and accelerated lithium-ion transport. The strong anchoring effect of Co5.47Nx is confirmed by experimental measurements and density functional theory (DFT) calculations. Because of its high conductivity and nitrogen vacancies, the Co5.47Nx cathode exhibits faster redox reaction kinetics and lower polarization than a Co5.47N cathode without nitrogen vacancies, thus realizing promising rate and cycling performance. The optimized Co5.47Nx–C electrode delivers a capacity of 850 mA h g−1 at 0.5C and a rate performance of 320 mA h g−1 at 10C. This high-performance, high-rate lithium–sulfur battery is promising for widespread application in electric vehicles and intelligent devices.

Question: What's the cathode?
Answer: Co5.47Nx

Question: What's the cathode?
Answer: Co5.47N
Polymers. Using polymeric analogs of small molecules might be an effective strategy to circumvent the solubility issue of organic redox-active materials. The first polymeric cathode material for potassium batteries was poly(anthraquinonyl sulfide) (PAQS, P1). With an ether-based electrolyte (0.5 M KTFSI in DME:DOL) it showed a reversible Qm of 200 mA h g−1 at 20 mA g−1. A capacity fading of 25% was observed after 50 cycles, while the cyclability with a carbonate-based electrolyte was inferior.

Question: What's the cathode?
Answer: polymeric

Question: What's the electrolyte?
Answer: (0.5 M KTFSI in DME:DOL)
Electrospun CNFs/Nb2O5 composite nanofibers were prepared by electrospinning a solution containing the precursors of Nb(C2O4H)5, PAN and TEOS, followed by carbonization and SiO2-etching.Fig. 7f and g show the structural features of the prepared CNFs/Nb2O5 nanocomposites, which reveal a continuous mesoporous network architecture. Compared with solid CNFs/Nb2O5 composites without using TEOS in spinnable solution and bulk C/Nb2O5 prepared via directly annealing the Nb(C2O4H)5, the mesoporous CNFs/Nb2O5 composites revealed much superior electrochemical reactivity. In detail, the mesoporous Nb2O5/CNF showed outstanding cyclability (94% retention after 10000 cycles at 100C, 1C = 200 mA g−1), and superior rate capability with specific capacities of 287 mA h g−1 at 0.5C and 172 mA h g−1 at 150C, which was much higher than that of pure CNFs (159.1 mA h g−1 at 0.5C and 64.9 mA h g−1 at 100C). In addition, a hybrid Na-ion capacitor was fabricated by employing mesoporous CNFs/Nb2O5 as the anode and CNFs/graphene as the cathode. This device showed both large energy densities (124 W h kg−1, 11.2 mW h cm−3) and impressive power densities (60 kW kg−1, 5.4 W h cm−3), indicating that both the introducing of Nb2O5 and the unique continuous mesoporous network architecture played a crucial role in the enhancement of the electrochemical properties.

Question: What's the cathode?
Answer:  CNFs/graphene

Question: What's the anode?
Answer: CNFs/Nb2O5
Although STEM-HAADF imaging has become the most widely used imaging mode in STEM, the strong atomic number dependency of STEM-HAADF contrast also means that the imaging contrast of light atoms is easily submerged by the adjacent heavy atoms. In contrast, STEM-ABF phase-contrast imaging based on wave interference provides better visualization of light elements with the presence of heavy elements, such as oxygen in the SrTiO3 crystal, lithium in LiCoO2 and even hydrogen in metal hydrides. An elegant example was reported by Gu et al., in which aberration-corrected STEM-ABF imaging was applied to directly visualize lithium columns in LiFePO4 and identify an intriguing lithium staging structure in the partially delithiated LixFePO4 (x ≈ 0.5) crystal. Fig. 6(a–c) present the atomic-resolution STEM-ABF images of the LiFePO4 cathode at different charging states. Compared with the pristine and fully-charged structures of LiFePO4 in Fig. 6(a and b), half-delithiated LiFePO4 in Fig. 6(c) demonstrated that part of the lithium remains in the lattice (yellow circles) at every other row of Li-extracted sites (orange circles). This ordered structure contradicted the previous model of LiFePO4/FePO4 two-phase separation, but was analogous to the stage-II phase in some layer compounds, and contributed to minimizing the Li–Li repulsive interaction to stabilize this intermediate phase. This result indicated that a continuous phase transition occurred in partially delithiated LixFePO4 through a metastable phase and helped to understand the high-rate capability of LiFePO4 cathode.

Question: What's the cathode?
Answer:  LiFePO4

Question: What's the cathode?
Answer: LiFePO4
By comparing the C 1s, Li 1s, and O 1s XPS spectra and the corresponding area proportions, we found corroborative results. Firstly, a great amount of residual carbonate on the pristine LiNiO2 surface illustrates the continued challenge in avoiding carbonate formation during calcination and quick transferal. There was a clear increase in inorganic carbonates (C 1s, Li 1s, and O 1s XPS spectra) concurrent with the decrease of lattice Li and O proportions after exposure to ambient environment, which was amplified under continuous human exhalation (lattice Li and O are almost negligible on the surface) (Fig. 1). This is indicative of the continuous formation of inorganic carbonates, which strongly attenuates the photoelectron signals from underneath LiNiO2 layers. Our observation is consistent with previous studies suggesting that dense concentration of water and CO2 on the oxide cathode surface facilitates chemical reactions to yield increased amounts of surface inorganic carbonates. Previous studies have shown the surface chemical bonding and structure of NMC materials are readily transformed by certain environments, including CO2, H2O, O2, and other reactive gases in a glove box. These gases react with layered oxides by extracting lithium from the lattice, further generating LiOH and/or Li2CO3 as well as oxygen vacancies. Lithium residuals on NMC and NCA materials also have been confirmed by infrared spectroscopy, Raman spectroscopy, and TEM. It is a consensus that surface instability is one of the common challenges for many battery materials. Other materials, such as sodium-containing layered cathode materials and Li-rich materials, also encounter surface-air instability, which leads to Na/Li residual formation and elevated pH on the particle surfaces. For sodium-containing layered cathode materials, water intercalation or Na+/H+ exchange also takes place, which can disrupt the layered structure. These changes would trigger slurry alkalization, degassing problem, and electrolyte decomposition. Based on our results and previous findings, we recommend that the details about sample handling should be specified in the journal publications, especially those involving delicate surface chemical analysis.

Question: What's the cathode?
Answer: sodium-containing layered

Question: What's the cathode?
Answer: oxide