milerssliu/battery-device-data-qa huggingface dataset:
In 2015, unique graphene-like Co9S8 with a high surface area and hierarchical porosity was first proposed by Nazar's group to afford superior LiPS adsorptivity for high-performance Li–S batteries. The Co9S8/S composite cathode not only manifests up to a factor of 10 increase of cycling stability (0.045% fading per cycle over 1500 cycles at C/2 at a sulfur loading of 1.5 mg cm−2) compared to standard porous carbons but also, more importantly, enables a high-loading sulfur electrode with up to 75 wt% sulfur and up to 4.5 mg cm−2 areal sulfur loading. First-principles calculations and spectroscopic studies consistently demonstrate that a synergistic dual interaction based on Sn2− → Coδ+ and Li+ → Sδ− exists between the metal sulfide-based host material and LiPSs. In particular, it is revealed that the nature of the crystallographic surface plays a very crucial role. The binding energy of 2.22 eV for Li2S2 on the (002) surface (Co/S = 1:4) increases to 3.24 eV for the (202) surface (Co/S = 5:4) and further to 6.06 eV for the purely Co-terminated (008) plane. This finding enables a better understanding of the interaction mechanism for metal sulfides and provides guidance for fabricating host materials with preferred crystal faces, but unfortunately, the mechanism by which the polar surface accelerates LiPS redox has not been clearly revealed yet. Soon after, Yuan et al. demonstrated that simply introducing half-metallic CoS2 microparticles into graphene electrodes largely amplified the electrochemical current response and reduced charge transfer resistance in LiPS symmetrical cells. More importantly, it is found that CoS2 serves as a mediator to provide strong CoS2–polysulfide interaction and to facilitate the liquid–liquid redox of polysulfides, further affecting the correlated liquid–solid transformation, viz., the prior formation of Li2S nuclei. With a sulfur loading of 0.4 mg cm−2, a high initial capacity of 1368 mA h g−1 at 0.5C, an increase of 10% in energy efficiency, and a low decay rate of 0.034% per cycle for 2000 cycles at 2.0C are realized through the incorporation of mechanically milled CoS2 with a low specific surface area. These observations suggest that manipulating the redox reactivity of polysulfides upon a conducting surface is a more effective strategy for improving the Li–S battery performance, in comparison to tuning the dissolvability and transport behavior of polysulfides in aprotic electrolytes. Given that the metal sulfide herein employed is in the bulk form, therefore, the performance enhancement can be further achieved by optimizing its structure and properties, including engineering the crystal facets to mediate the adsorbate–adsorbent interaction, reducing the dimension to maximize the exposed polar surface and introducing a strong coupling effect between substrates and supported metal sulfides for intriguing modulation of material properties.

Question: What's the cathode?
Answer: Co9S8/S composite
In 2015, unique graphene-like Co9S8 with a high surface area and hierarchical porosity was first proposed by Nazar's group to afford superior LiPS adsorptivity for high-performance Li–S batteries. The Co9S8/S composite cathode not only manifests up to a factor of 10 increase of cycling stability (0.045% fading per cycle over 1500 cycles at C/2 at a sulfur loading of 1.5 mg cm−2) compared to standard porous carbons but also, more importantly, enables a high-loading sulfur electrode with up to 75 wt% sulfur and up to 4.5 mg cm−2 areal sulfur loading. First-principles calculations and spectroscopic studies consistently demonstrate that a synergistic dual interaction based on Sn2− → Coδ+ and Li+ → Sδ− exists between the metal sulfide-based host material and LiPSs. In particular, it is revealed that the nature of the crystallographic surface plays a very crucial role. The binding energy of 2.22 eV for Li2S2 on the (002) surface (Co/S = 1:4) increases to 3.24 eV for the (202) surface (Co/S = 5:4) and further to 6.06 eV for the purely Co-terminated (008) plane. This finding enables a better understanding of the interaction mechanism for metal sulfides and provides guidance for fabricating host materials with preferred crystal faces, but unfortunately, the mechanism by which the polar surface accelerates LiPS redox has not been clearly revealed yet. Soon after, Yuan et al. demonstrated that simply introducing half-metallic CoS2 microparticles into graphene electrodes largely amplified the electrochemical current response and reduced charge transfer resistance in LiPS symmetrical cells. More importantly, it is found that CoS2 serves as a mediator to provide strong CoS2–polysulfide interaction and to facilitate the liquid–liquid redox of polysulfides, further affecting the correlated liquid–solid transformation, viz., the prior formation of Li2S nuclei. With a sulfur loading of 0.4 mg cm−2, a high initial capacity of 1368 mA h g−1 at 0.5C, an increase of 10% in energy efficiency, and a low decay rate of 0.034% per cycle for 2000 cycles at 2.0C are realized through the incorporation of mechanically milled CoS2 with a low specific surface area. These observations suggest that manipulating the redox reactivity of polysulfides upon a conducting surface is a more effective strategy for improving the Li–S battery performance, in comparison to tuning the dissolvability and transport behavior of polysulfides in aprotic electrolytes. Given that the metal sulfide herein employed is in the bulk form, therefore, the performance enhancement can be further achieved by optimizing its structure and properties, including engineering the crystal facets to mediate the adsorbate–adsorbent interaction, reducing the dimension to maximize the exposed polar surface and introducing a strong coupling effect between substrates and supported metal sulfides for intriguing modulation of material properties.

Question: What's the anode?
The Mg/Ti dual dopants also enhance the surface stability even upon deep electrochemical delithiation. Here we found that ex situ soft XAS surface analysis may provide misleading results if the charged electrodes are not handled properly. In principle, Ni should experience oxidation during charging and reduction during discharging. However, due to the cathode–electrolyte parasitic reaction, the surface nickel oxidation state at various charge/discharge states were lower than that of the bulk (Fig. S9†). Another phenomenon that we constantly observe is that the Ni oxidation states for the charged samples were lower than that at the pristine state in both the TEY and FY modes (Fig. S9†), which is counterintuitive. We believe that this might be due to the thermodynamically unstable Ni4+ continually reacting with the electrolyte during the cell teardown and subsequent sample handling. Thus, eliminating the cell resting time and removing the residual electrolyte are critical for maintaining the true Ni oxidation states for soft XAS analysis. We found that the best practice is to dissemble the cell and rinse the electrode immediately after the cell has reached the designated state of charge. This practice is particularly important for the charged electrodes. Here we rinsed the cycled electrode in an Ar filled glove box immediately after the cells were charged to 4.4 V vs. Li/Li+. The LiNiO2 delivered a higher charge capacity at this upper cutoff voltage than the Mg/Ti–LiNiO2 (Fig. S10†). If the surface was stable at the charged state, the Ni oxidation state at the surface should not exhibit significant difference in these two electrodes, because the charge capacity only differed by 22 mA h g−1 (i.e., the Ni oxidation state differed by 0.08). However, we found drastic differences between these electrodes, as explained below. The Ni L3-right/left peak ratios were averaged from three electrodes at the charged state. A significantly higher L3-right/left peak ratio in both FY and TEY modes was found in the Mg/Ti–LiNiO2 sample than that in the LiNiO2 sample (Fig. 4d), indicating enhanced surface stability of the Mg/Ti–LiNiO2 sample in the charged state. Moreover, the low L3-right/left peak ratio in the FY mode of the LiNiO2 electrodes also suggests that the surface reaction induced Ni reduction extended to the deep subsurface. The direct comparison between NMC622 and NMC811 (Fig. S11†) further supports that a higher nickel content results in more surface instability, which can potentially complicate the state of charge assessment using the surface sensitive soft XAS technique. As more studies have made use of the soft XAS technique for analyzing the surface chemistry of battery materials, our results clearly demonstrate that caution is needed when interpreting the data. Although the synchrotron characterization is not highly accessible, other surface-sensitive characterization methods, e.g., XPS, IR, Raman, TEM, ToF-SIMS, also encounter the similar challenges when preparing/handling samples. To improve the data representativeness, the effective error analysis, based on repeated measurements, is recommended.

Question: What's the cathode?
As benchmark inorganic cathodes, we selected a number of materials for non-aqueous cells which, according to the reviews and to the best of our knowledge, are superior in terms of voltage, specific energy/power or cycling stability and are attributed to various material families (hexacyanoferrates, layered oxides, polyanionic compounds, and conversion-type cathodes). The list of benchmarks includes KVPO4F, K2[(VOHPO4)2(C2O4)] (KVPCO), K1.75Mn[Fe(CN)6]·0.16H2O (KMHCF), Fe[Fe(CN)6] (FeHCF), K1.81Ni[Fe(CN)6]0.97·0.086H2O (KNHCF), K0.7Mn0.5Fe0.5O2 (KMFO), K0.51V2O5 and K0.42V2O5·0.25H2O (KVO), and sulfur (S).

Question: What's the cathode?
Answer: hexacyanoferrates, layered oxides, polyanionic compounds, and conversion-type
As benchmark inorganic cathodes, we selected a number of materials for non-aqueous cells which, according to the reviews and to the best of our knowledge, are superior in terms of voltage, specific energy/power or cycling stability and are attributed to various material families (hexacyanoferrates, layered oxides, polyanionic compounds, and conversion-type cathodes). The list of benchmarks includes KVPO4F, K2[(VOHPO4)2(C2O4)] (KVPCO), K1.75Mn[Fe(CN)6]·0.16H2O (KMHCF), Fe[Fe(CN)6] (FeHCF), K1.81Ni[Fe(CN)6]0.97·0.086H2O (KNHCF), K0.7Mn0.5Fe0.5O2 (KMFO), K0.51V2O5 and K0.42V2O5·0.25H2O (KVO), and sulfur (S).

Question: What's the anode?
The cathodes were prepared by mixing 80 wt% active materials, 10 wt% acetylene black and 10 wt% polyvinylidene fluoride (PVDF) binder with N-methyl-2-pyrrolidone (NMP) as the solvent. The mixture was coated on aluminum foil, pressed at 20 MPa, and dried at 120 °C in air for 2 h. The 2025 coin-type cells, consisting of the as-prepared cathode, Li metal as the anode and Celgard 2325 as the separator, were assembled in an argon-filled glove box. The electrolyte was 1 M LiPF6 dissolved in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 3:7). All cells were cycled between 2.0 and 4.8 V (versus Li/Li+) at a current density of 20 mA g−1 at room temperature on Land CT 2001A battery testers unless otherwise defined. The electrochemical impedance spectroscopy (EIS) measurements were performed from 100 kHz to 10 mHz with an amplitude of 10 mV using a multichannel potentiostat (PARSTAT MC).

Question: What's the cathode?
In the context of voltage hysteresis, ‘charge-averaged’ discharge (Vdischarge), charge (Vcharge), and net-average (viz., further average of Vdischarge and Vcharge) voltages (as true average voltages) for the ‘control’ and fully Ti-substituted (for Mn-ion) Na-TM-oxide cathodes were estimated, as per the following relations, and presented in Fig. 4 as variations with cycle number.

Question: What's the cathode?
Answer: Na-TM-oxide
In terms of anode fabrication, TiO2/C@NPSC-x was mixed sufficiently with conductive carbon and sodium carboxymethylated cellulose (CMC-Na) to form a uniform slurry (weight ratio: 7:2:1). Then, the Cu foil coated by the slurry was dried in a vacuum oven at 110 °C overnight. The anode electrodes for ex situ XRD tests were fabricated by coating the active materials/CMC-Na (weight ratio: 9:1) slurry on an Al current collector. For cathode electrodes, the home-made activated carbon (ZDPC), conductive carbon and PTFE were blended evenly in deionized water (weight ratio: 90:5:5) and painted on carbon-coated Al foil. The loading weight of each electrode was about 1.0 mg cm−2. Then, coin-type CR2032 cells were constructed inside a glove box filled with Ar gas. The electrolyte was 0.8 M KPF6 in DEC and EC (1:1, v/v). The separator was glass fibers. Fresh potassium foil served as the counter electrode. Before construction of the PIHC device, the TiO2/C@NPSC-700 anode was pre-activated at 0.1 A g−1 for 10 cycles.

Question: What's the cathode?
Answer:  carbon (ZDPC)
Fig. 4d shows the comparison of the rate performances and coulombic efficiencies of the three types of cathodes under different current densities (0.1, 0.2, 0.5, 1.0, and 2.0C). All three cathodes show a coulombic efficiency over 98%, which could be due to the highly conductive CNF skeletons. And, with increasing the current density from 0.1C to 2.0C, the CNF@V2S3/S cathodes can retain a specific capacitance of 922 mA h g−1 (78.9% of the initial value), which is much higher than those of VS2-based LSBs. However, the CNF@VO0.9/S and CNF/S cathodes can retain 390 mA h g−1 (55.1%) and 592 mA h g−1 (68.8%). Here, to gain better understanding of the effect of V2S3 on the rate performances of cathodes, the in situ reaction resistances were first derived from the charge/discharge curves (see the ESI for details†). As shown in Fig. 4e, the reaction resistances of all three cathodes increase with the increasing specific capacity, which is caused by the low conductivity of intermediate LiPSs. Compared to the CNF@VO0.9/S and CNF/S cathodes, the CNF@V2S3/S ones show a much lower reaction resistance along the whole electrochemical processes. And similar results can also be obtained from Electrochemical Impedance Spectroscopy (EIS) spectra (Fig. S14†). This decrease in resistances often leads to fast redox kinetics on the CNF@V2S3/S cathodes. Besides, galvanostatic intermittent titration technique (GITT) tests were further carried out to further study the origins for fast transfer kinetics of CNF@V2S3/S cathodes (Fig. S15†). The diffusivities of Li ions between the cathode and electrolyte were estimated, as listed in Table S2.† The diffusion coefficient of Li+ ions in the CNF@V2S3/S/electrolyte system is 2.857 × 10−6 cm2 s−1, which is much higher than those of CNF@VO0.9/S and CNF/S ones (1.554 × 10−7 and 1.645 × 10−7 cm2 s−1) in this work. This greatly improved diffusivities of Li ions would result in the high specific capacity and the high rate capability of CNF@V2S3/S cathodes. Also, a similar conclusion can be obtained from EIS spectra in the low-frequency region (Fig. S14†). It can be seen that the curve slope of CNF@V2S3/S cathodes is much larger than those of the CNF@VO0.9/S and CNF/S ones (Table S3†).

Question: What's the cathode?
Answer: CNF@V2S3/S
Fig. 4d shows the comparison of the rate performances and coulombic efficiencies of the three types of cathodes under different current densities (0.1, 0.2, 0.5, 1.0, and 2.0C). All three cathodes show a coulombic efficiency over 98%, which could be due to the highly conductive CNF skeletons. And, with increasing the current density from 0.1C to 2.0C, the CNF@V2S3/S cathodes can retain a specific capacitance of 922 mA h g−1 (78.9% of the initial value), which is much higher than those of VS2-based LSBs. However, the CNF@VO0.9/S and CNF/S cathodes can retain 390 mA h g−1 (55.1%) and 592 mA h g−1 (68.8%). Here, to gain better understanding of the effect of V2S3 on the rate performances of cathodes, the in situ reaction resistances were first derived from the charge/discharge curves (see the ESI for details†). As shown in Fig. 4e, the reaction resistances of all three cathodes increase with the increasing specific capacity, which is caused by the low conductivity of intermediate LiPSs. Compared to the CNF@VO0.9/S and CNF/S cathodes, the CNF@V2S3/S ones show a much lower reaction resistance along the whole electrochemical processes. And similar results can also be obtained from Electrochemical Impedance Spectroscopy (EIS) spectra (Fig. S14†). This decrease in resistances often leads to fast redox kinetics on the CNF@V2S3/S cathodes. Besides, galvanostatic intermittent titration technique (GITT) tests were further carried out to further study the origins for fast transfer kinetics of CNF@V2S3/S cathodes (Fig. S15†). The diffusivities of Li ions between the cathode and electrolyte were estimated, as listed in Table S2.† The diffusion coefficient of Li+ ions in the CNF@V2S3/S/electrolyte system is 2.857 × 10−6 cm2 s−1, which is much higher than those of CNF@VO0.9/S and CNF/S ones (1.554 × 10−7 and 1.645 × 10−7 cm2 s−1) in this work. This greatly improved diffusivities of Li ions would result in the high specific capacity and the high rate capability of CNF@V2S3/S cathodes. Also, a similar conclusion can be obtained from EIS spectra in the low-frequency region (Fig. S14†). It can be seen that the curve slope of CNF@V2S3/S cathodes is much larger than those of the CNF@VO0.9/S and CNF/S ones (Table S3†).

Question: What's the electrolyte?
Fig. 4d shows the comparison of the rate performances and coulombic efficiencies of the three types of cathodes under different current densities (0.1, 0.2, 0.5, 1.0, and 2.0C). All three cathodes show a coulombic efficiency over 98%, which could be due to the highly conductive CNF skeletons. And, with increasing the current density from 0.1C to 2.0C, the CNF@V2S3/S cathodes can retain a specific capacitance of 922 mA h g−1 (78.9% of the initial value), which is much higher than those of VS2-based LSBs. However, the CNF@VO0.9/S and CNF/S cathodes can retain 390 mA h g−1 (55.1%) and 592 mA h g−1 (68.8%). Here, to gain better understanding of the effect of V2S3 on the rate performances of cathodes, the in situ reaction resistances were first derived from the charge/discharge curves (see the ESI for details†). As shown in Fig. 4e, the reaction resistances of all three cathodes increase with the increasing specific capacity, which is caused by the low conductivity of intermediate LiPSs. Compared to the CNF@VO0.9/S and CNF/S cathodes, the CNF@V2S3/S ones show a much lower reaction resistance along the whole electrochemical processes. And similar results can also be obtained from Electrochemical Impedance Spectroscopy (EIS) spectra (Fig. S14†). This decrease in resistances often leads to fast redox kinetics on the CNF@V2S3/S cathodes. Besides, galvanostatic intermittent titration technique (GITT) tests were further carried out to further study the origins for fast transfer kinetics of CNF@V2S3/S cathodes (Fig. S15†). The diffusivities of Li ions between the cathode and electrolyte were estimated, as listed in Table S2.† The diffusion coefficient of Li+ ions in the CNF@V2S3/S/electrolyte system is 2.857 × 10−6 cm2 s−1, which is much higher than those of CNF@VO0.9/S and CNF/S ones (1.554 × 10−7 and 1.645 × 10−7 cm2 s−1) in this work. This greatly improved diffusivities of Li ions would result in the high specific capacity and the high rate capability of CNF@V2S3/S cathodes. Also, a similar conclusion can be obtained from EIS spectra in the low-frequency region (Fig. S14†). It can be seen that the curve slope of CNF@V2S3/S cathodes is much larger than those of the CNF@VO0.9/S and CNF/S ones (Table S3†).

Question: What's the cathode?
Answer: CNF@VO0.9/S and CNF/S
Gas diffusion electrodes (GDEs) were fabricated by spraying a catalyst ink made from polynorbonene tetrablock copolymer powder ionomers (GT32 and GT73) and Pt-based electrocatalysts onto Toray TGP-H-060 gas diffusion layers (GDLs) with 5% PTFE. Commercially available 40% Pt/C (Alfa Aesar HiSPEC 4000, Pt nominally 40% wt, supported on Vulcan XC-72R carbon) was used at the cathode and 60% Pt–Ru/C (Alfa Aesar HiSPEC 10000, Pt nominally 40 wt%, and Ru, nominally 20 wt%, supported on Vulcan XC-72R carbon) was used as the anode. The detailed procedure for ink formulation and GDE fabrication has been previously reported, though a brief description is provided below.

Question: What's the cathode?
Surface modification using some metal oxides is an appropriate approach to overcome such critical drawbacks of LMO. Metal oxides, such as Ta2O5, ZrO2, Al2O3, ZnO, MgO, and TiO2, have been used as coating layers for LMO cathode material powders. The coating layer minimizes direct contact between the cathode and the electrolyte solution, avoids unwanted interfacial reactions, and thus improves the structural stability and phase transitions. To some extent, these coating films can also improve the cycling performance of the material. Nevertheless, the reported high surface coating using metal oxides usually results in agglomerated nanoparticles and leads to increased resistance. Furthermore, the modest improvement could be a result of increased interfacial resistance due to the insulating nature of surface coating layers.

Question: What's the cathode?
Answer: LMO
Moreover, the formation of metal sulfides with a non-crystalline structure also reveals enhanced adsorption/bonding of LiPSs owing to abundant defects and dangling bonds. For example, amorphous TiS4 has been successfully prepared by Sakuda et al. through a mechanical milling process using crystalline TiS2, sulfur, and acetylene black. When used as the cathode in a Li–S battery, the dissolution of LiPSs into the electrolyte is significantly suppressed because amorphization reduces the symmetry of the lattice, leading to the possibility of overlapping electron clouds between sulfur and titanium atoms, resulting in chemical bonding between the elements. Liu et al. reported the synthesis of a S@amorphous NiS2 composite via a coprecipitation reaction using Na2S8 and NiCl2 ethanol solution. Here the soluble sulfide ions can permeate into the loose amorphous structure, and thus the S particle would nucleate and grow in the inner space of NiS2, ensuing the high immobilization of S species. Very recently, Yu et al. meticulously designed hollow-amorphous N-doped carbon/MoS3 nanoboxes (NC/MoS3 NBs) as an advanced sulfur host for Li–S batteries. In a typical synthesis, crystalline α-Fe2O3 nanocubes are first coated with a layer of polydopamine, which are then calcined in a N2 atmosphere and etched in HCl solution to obtain N-doped carbon (NC) shells and hollow NC nanoboxes, respectively. Finally, the NC/MoS3 NB host is prepared through heterogeneous nucleation using CTAB as the surfactant and (NH4)2MoS4 as the precursor. Here, the amorphous MoS3 with unsaturated coordination Mo and electron-rich S not only has strong binding capability to LiPSs but also exhibits a catalytic effect on polysulfide conversion, which are verified by both experimental investigations and theoretical calculations. More interestingly, this synthesis strategy can be generalized to fabricate other amorphous metal chalcogenides nanoboxes such as CoSx and WSx, which is also promising to be applied in the fields of energy storage and conversion.

Question: What's the cathode?
Answer: LiPSs