milerssliu/battery-device-data-qa huggingface dataset:
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 electrolyte?
To further analyze the electrochemical difference between the pristine and treated LMO, the initial cycle curves for the two samples are plotted together in Fig. 2a. For pristine LMO, the plateau above 4.5 V appears as the typical behavior of the Li-rich cathode, which corresponds to the delithiation, charge compensation and oxygen release process. Upon discharge, an S-shaped curve was observed with a discharge capacity of around 200 mA h g−1. Interestingly, the characteristic charge plateau (above 4.5 V) was shortened in the T-LMO sample. Simultaneously, plateaus appeared at around 4.1 V for the charged state and 4.0 V/2.8 V for the discharged state, which can be seen clearly in the dQ/dV plots (Fig. 2b), indicating that the spinel phase may exist in T-LMO.

Question: What's the cathode?
Answer: Li-rich
Metal–air batteries with high energy density have emerged as key players in the energy storage sector. They operate on two underlying processes, namely, the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). It provides the impetus to design efficient, earth-abundant and economic bifunctional electrocatalysts vis-à-vis precious metal-based catalysts. In this perspective, a few polyanionic battery insertion materials have been reported as potential electrocatalysts. In the current work, metal fluorophosphate (Na2MPO4F, M = Fe/Co/Mn) family of sodium insertion materials have been shown as a new class of bifunctional electrocatalysts with robust structural stability. In particular, Na2CoPO4F was found to exhibit superior catalytic performance with an onset potential of 0.903 V (vs. RHE) for the ORR and an overpotential of 380 mV (vs. RHE) for the OER. The underlying mechanism and kinetics were explored using ab initio computational studies. Overall, polyanionic transition metal fluorophosphates were explored for the first time as bifunctional electrocatalysts capable of working as potential cathode materials in hybrid metal–air batteries.

Question: What's the cathode?
Imide-functionalized small molecules are represented by 3,4,9,10-perylene-tetracarboxylic diimide (PTCDI 10), recently proposed by Fan et al. It has lower solubility compared to PTCDA, which should have improved its cycling stability. Nevertheless, with 1 M and 3 M KFSI solutions in EC:DMC, rapid capacity fading associated with the material dissolution was observed. The cathode dissolution was suppressed by using 5 M KFSI in EC:DMC, which ensured ∼0% capacity decay over 100 cycles at 100 mA g−1 and ∼90% retention after 600 cycles at 4 A g−1. The reported Qm at 100 mA g−1 was 157 mA h g−1, which is higher than the theoretical value of 137 mA h g−1; the additional capacity (∼27 mA h g−1) originated from the carbon additive. Impressive capacities of 137 and 80 mA h g−1 were observed at 1 and 10 A g−1, respectively. The rate performance of PTCDI was reported to be superior compared to PTCDA under the same conditions. PTCDI-based full cells, which had pre-potassiated graphite as the anode, delivered a Qm of 140 and 80 mA h g−1 at 50 and 500 mA g−1, respectively. The output voltage was 2 V and ∼50% of the capacity retained after 500 cycles at 500 mA g−1.

Question: What's the cathode?
Later, Wang et al. published a similar study, using annealed PTCDA as the anode material and 30 M KFSI aqueous solution as the electrolyte. The reversible capacity of PTCDA reached 134 mA h g−1 at 0.2 A g−1. Decent rate and cycling capabilities were demonstrated. A full cell with potassium iron(II) hexacyanoferrate as the cathode delivered 39 mA h g−1 based on the combined mass of the electrodes, and it was almost constant up to 4 A g−1 current density. The capacity retention of the full cell was 89% after 1000 cycles at 2 A g−1.

Question: What's the cathode?
Answer: potassium iron(II) hexacyanoferrate
Later, Wang et al. published a similar study, using annealed PTCDA as the anode material and 30 M KFSI aqueous solution as the electrolyte. The reversible capacity of PTCDA reached 134 mA h g−1 at 0.2 A g−1. Decent rate and cycling capabilities were demonstrated. A full cell with potassium iron(II) hexacyanoferrate as the cathode delivered 39 mA h g−1 based on the combined mass of the electrodes, and it was almost constant up to 4 A g−1 current density. The capacity retention of the full cell was 89% after 1000 cycles at 2 A g−1.

Question: What's the anode?
Answer: PTCDA
Later, Wang et al. published a similar study, using annealed PTCDA as the anode material and 30 M KFSI aqueous solution as the electrolyte. The reversible capacity of PTCDA reached 134 mA h g−1 at 0.2 A g−1. Decent rate and cycling capabilities were demonstrated. A full cell with potassium iron(II) hexacyanoferrate as the cathode delivered 39 mA h g−1 based on the combined mass of the electrodes, and it was almost constant up to 4 A g−1 current density. The capacity retention of the full cell was 89% after 1000 cycles at 2 A g−1.

Question: What's the electrolyte?
Answer: 30 M KFSI aqueous solution
Determined by a continuous discharging test over 27 h, the recorded specific capacity of the battery with the CNT@CNP catalyst is 846.7 mA h gZn−1, and the relative energy density is 1059.92 mW h gZn−1 at an average voltage of 1.2 V, as shown in Fig. 7(d). These outcomes are better than those of most current Fe–N–C catalysts shown in Table 2. Moreover, the rechargeable performance of the battery, equipped with the CNT@CNP catalyst and commercial 20 wt% IrO2 on carbon paper as an air cathode, has been tested by us. As observed in Fig. 7(e), the novel battery shows remarkably improved ORR and OER properties, compared with the reference of the battery equipped with the commercial Pt/C and IrO2 counterpart. At a constant current density of 20 mA cm−2 for 10 h, the cycling of charge and discharge reaches 2 times with respect to the reference battery, as shown in Fig. 7(f). The battery almost maintains a stable discharge potential of 0.83 V and a recharge voltage of 2.25 V even after 60 cycles, which is much better than that of the reference battery shown in Fig. 7(f). So, the synthesized catalyst shows a very good power density in comparison with the corresponding results available in the literature shown in Table 2. Therefore, the optimal catalytic performance of the carbon interpenetrating networks may be attributed to the formation of abundant edge Fe–Nx moieties as active sites at the boundaries and interfaces in the CNT@CNP composites with a smart structure. If so, developing Fe–N–C with interpenetrating network structures may be major breakthroughs of non-PGM materials serving as next-generation catalysts for the ORR.

Question: What's the cathode?
Answer: air
Fig. 1c shows the main fabrication processes of high-performance LSBs based on CNF@V2S3/S composite cathodes. Electrospun nanoscale fibrous skeletons were often used as conductive substrates for active materials in energy-storage devices. During the annealing under Ar, many V atoms were forced out to the surface of electrospun nanofibers under the Kirkendall effect, and formed into VO0.9 nanocrystals. Then, the formed VO0.9 nanocrystals will further be vulcanized into V2S3 nanocrystals with an ultralow rate during the vulcanization reaction in a S/Ar environment. As a result, many V2S3 nanocrystals are stably connected to the surface of CNFs, which benefit the transport of electrons through the CNF/V2S3 composites. And these tiny V2S3 nanocrystals can also show a high specific surface area and a high catalytic activity, which can benefit the chemisorption and the transformation of sulfur species during the charge/discharge processes in LSBs.

Question: What's the cathode?
Answer: CNF@V2S3/S composite
F-doped h-BNNS were used as the cathode material for magnesium batteries, a potential alternative to Li-ion batteries due to their higher safety and lower cost. It was reported that fluorine can be grafted via a reaction between h-BNNS and fluoroboric acid. Fluorination effectively improves the electrical conductivity of h-BNNS and their electrochemical performance for Mg batteries.

Question: What's the cathode?
Answer: F-doped h-BNNS
Recently, a high energy density (97.6 W h kg−1) along with impressive cycling steadiness (73% retention after 5000 cycles at 1 A g−1) was reported by Yang et al. for a lithium-ion capacitor fabricated by using PAN/hydrothermal-made V3O7·H2O nanowire derived CNFs/V2O3 hybrids as the anode and commercial activated carbon (AC) as the cathode. Additionally, the prepared CNFs/V2O3 nanocomposites with internal void spaces displayed a high capacity of 569.1 mA h g−1 at 0.1 A g−1 as well as unexpected rate capability (238.5 mA hg−1 at 10.0 A g−1) in half-cell tests. By electrospinning a PAN/VO(acac)2 precursor solution, followed by calcination, V–O–C nanocomposites with a specific surface area of 587.9 m2 g−1 were obtained. An atomic level dispersion of vanadium within the composite nanofibers enabled the resultant V–O–C nanocomposites to deliver a specific capacitance of 463 F g−1 at 1 A g−1 with good electronic conductivity and electrolyte penetration. Moreover, the electrochemical properties of V5+ are superior to those of V3+ and V4+ when vanadium oxide-embedded carbon fibers are applied in a supercapacitor. Bai et al. produced CNFs/V2O3, CNFs/VO2–V2O5 and CNFs/V2O5via electrospinning a PAN/VO(acac)2 precursor solution, followed by different calcination processes. The results showed that the electrochemical performance of CNFs/V2O5 is better than that of CNFs/V2O3 and CNFs/VO2–V2O5 when they were applied to SCs. In Tang's work, CNFs/VO/VOx web-like nanocomposites were obtained by electrospinning a polymer-based solution containing PAN, PVP, hybrid vanadium precursors (VO2, V2O5, and VO(acac)2) and DMF, followed by carbonization treatment. The formation of quasi-metallic VO (∼102 Ω−1 cm−1) in the CNF enhanced the rate of electron transfer in the web-like electrode. Besides, the well-developed pore structure and rich vanadium redox couples also promoted the rapid ion transfer rate. As a consequence, the SC equipped with symmetric CNFs/VO/VOx electrodes exhibited a specific capacitance of 325.7 F g−1 at 1 A g−1 with 92% retention at 4 A g−1 after 5000 cycles.

Question: What's the cathode?
Answer: activated carbon (AC)
Second, the electrode capacity was calculated (eqn (4)) to be 453 mA h g−1 and third, by integrating the potential profile (eqn (5)), the gravimetric electrode energy density was estimated to be 570 W h kg−1. Both values are here for the organic redox-active part (AQ4), while if we take into account the entire electrode (AQnC72), we arrive at significantly more modest values: 222 mA h g−1 and 279 W h kg−1 (Table S8†). Neither of these measures are totally fair to be compared with traditional electrodes as we also assume a role as current collector for the graphene. With this caveat, the former measure provides twice the experimentally measured capacity of pure AQ, reported to be 217 mA h g−1 ( ) and a theoretical gravimetric energy density comparable to the cathode active materials LiFePO4 (544 W h kg−1) and LiMn2O4 (548 W h kg−1).

Question: What's the cathode?
Answer: LiFePO4
During the initial discharge on the cathode:

Question: What's the cathode?
In the last few decades, the demand for batteries has rapidly increased in various application fields. Although rechargeable batteries (such as lithium-ion batteries) have become a focus of attention, primary batteries still occupy a large market share in many civilizations and military applications such as portable power sources, signal lights, and space and ocean exploration. As a result, efforts to develop primary batteries with high energy density, high power density, and low cost have never stopped ever since the invention of volt batteries in 18th century. Especially in recent years, large number of batteries with high energy density have been developed, such as the Zn–O2, Mg–O2, Al–O2, Na–O2, and Li–O2 systems. In addition, primary batteries, such as the currently developed Li–SO2, Li–SOCl2, Li–MnO2, and Li-CFx systems, have also been developed under isolated conditions for applications such as ocean and out space. Primary batteries are usually required to have high energy density, long shelf life, stable discharge voltage, and low self-discharge rate and should be readily available for use. Currently, the Li/MnO2 batteries account for more than 80% share of the lithium primary battery market due to their low cost, high safety, and natural abundance of Li and Mn. Moreover, the Li/MnO2 batteries possess a high practical specific energy of 308 W h kg−1 and a long shelf life of about 10 years. However, the application of Li/MnO2 batteries is limited by their poor electrochemical performance at high power output and low temperature, which is ascribed to several issues including low electronic conductivity, low lithium diffusion coefficient, and structural susceptibility of the MnO2 cathode. To address these issues, numerous methods, such as structural design and composite, coating, and metal cation doping, have been studied to optimize the performance of the MnO2 cathode. In addition, to overcome the intrinsic limitations of the current cathode materials, exploring novel cathode materials is a potential strategy for promoting the performance of lithium primary batteries.

Question: What's the cathode?
Answer: MnO2
In order to further study the chemisorption of LiPSs on the electrodes, we carried out the visual adsorption experiment of Li2S6 on the CNF@V2S3 cathodes. As shown in Fig. 3g, the dark-yellow colour of Li2S6 solution containing CNF@V2S3 fades in the visible region obviously after 24 h; while the solution containing CNFs, by contrast, almost shows no change in its colour, directly demonstrating that CNF@V2S3 cathodes can anchor LiPSs strongly. Moreover, we also compare the colour change of the polypropylene separators used in the assembled LSBs. As shown in Fig. S6,† after 100 cycles, the separator in the LSBs based on CNF@V2S3 composites almost retains its own white colour; while that based on CNF@V2S3 and CNFs cathodes show an apparent change in colour from white to light yellow, especially that based on CNFs. These visual comparisons of the change in colour again indicate that the CNF@V2S3 composites could greatly inhibit the shuttling of LiPSs between the electrodes. Furthermore, first-principles simulations based on density functional theory (DFT) have been applied to theoretically study the chemisorption behaviours of LiPSs. Fig. 2h shows the adsorption conformation of LiPSs (Li2Sn: n = 2, 4 and 6) on the (204) plane of V2S3. And the Eads between V2S3 and Li2S/Li2S4/Li2S6 were estimated to be 1.29, 0.81 and 1.02 eV, which are much higher than those values of the Eads between C and LiPSs.

Question: What's the cathode?
Answer: CNF@V2S3
In order to understand the relationship between self-discharge and electrolyte composition, the Li/LiV2(PO4)3 batteries were disassembled after one-week storage. The images of the Al current collectors and metallic Li of the disassembled battery are shown in Fig. 2. As shown in Fig. 2a and j, the Al current collector was obviously corroded, and many black precipitates were formed at the edge of the metallic Li electrode with the LPE-EC electrolyte. However, the appearances of the Al current collector and metallic Li electrode of the batteries with the LPE-PC and LPE-PC–LiBOB electrolytes were significantly better, as displayed in Fig. 2b, c, k and l, showing smooth Al current collectors and clean metallic Li surfaces. SEM was performed in order to verify the actual condition of the Al surface. As shown in the SEM images of the Al current collectors (Fig. 2d and g), the surface morphologies of the corroded Al current collector of the battery with the LPE-EC electrolyte displayed a high pit density, whereas those in the case of the batteries with the LPE-PC and LPE-PC–LiBOB electrolytes were smoother. The pits on the Al current collector were probably caused by the electrochemical oxidation of EC at high potentials generates a proton and triggers the chemical corrosion of aluminum foils. Pitting corrosion of the Al current collector can cause serious problems: passivation of cathode materials, increase of electrical resistance, contamination of the electrolyte, and reduction reactions of dissolved Al3+ on the anode side. Thus, the observed black precipitates on the metallic Li electrode could be the Li–Al alloy (LixAl) or a mixture of metallic Li and Li–Al alloy (cathodic: Al → Al3+ + 3e−; anodic: Al3+ + 3e− + Li → LixAl). The growth of precipitates can lead to separator piercing and internal short circuit of a battery, which is responsible for the rapid voltage drop and self-discharge of the Li/LiV2(PO4)3 batteries with the LPE-EC electrolyte (Fig. 1b). SEM images of the surface of the Al current collector of a battery with the LPE-PC and LPE-PC–LiBOB electrolytes after one-week storage are shown in Fig. 2e and h and Fig. 2f and i, respectively. Almost no obvious pitting corrosion was observed on the surfaces of the Al current collectors, confirming the better shelf stabilities of the Li/LiV2(PO4)3 batteries with the LPE-PC and LPE-PC–LiBOB electrolytes than that of the Li/LiV2(PO4)3 battery with the LPE-EC electrolyte (Fig. 1c and d), respectively. Therefore, the electrolyte composition can affect the stability of the current collector. The corrosion of the current collectors is a key reason for the self-discharge behavior of batteries.

Question: What's the cathode?
The FIB-SEM tomography and electrochemical testing results together strongly suggest that the severe mechanical degradation is the main cause of the rapid capacity fade in the SSB composite electrode, particularly in later cycles. In current study, the crack development is mostly observed near the cathode/solid electrolyte interface, which suggests that the cathode particle volume change is the origin of the mechanical failure during cycling. Thus, minimizing this mechanical degradation is critical to extending the cycle life of SSBs.

Question: What's the cathode?
When used as cathode materials, anhydrides and imides of tetracarboxylic aromatic acids undergo two-electron reversible reduction, as depicted in Scheme 2. The reduction of the remaining carbonyls occurs at low voltages; it is generally considered irreversible, although some data on using these structures as anode materials indicate the opposite (see Section 3.3).

Question: What's the cathode?
Answer: anhydrides and imides of tetracarboxylic aromatic acids
Nowadays, a variety of multifunctional electrocatalysts are being developed while there is still a lack of suitable design to fully realize their multifunctionalities. Here, we propose a general, simple, two-component design of an electrolyser to replace the traditional three-component design for decoupled water splitting. Trifunctional (OER, HER and ORR) electrocatalysts (such as nickel sulfide foams with surface grown N-doped carbon nanotube arrays) are used as the gas evolution electrode to replace both the cathode and the anode, while materials with suitable redox activities (NaTi2(PO4)3 or commercial Ni(OH)2) are used as the relay electrode. In such a design, the H2/O2 evolution can be switched by reversing the current polarity, and the ORR before the HER consumes the residual O2 left in the electrolyser, guaranteeing the high purity (∼99.9%) of the as-obtained H2. With NaTi2(PO4)3 as the relay electrode and the nickel sulfide foam as the gas evolution electrode, owing to the high decoupling efficiency of the NaTi2(PO4)3 relay (97%) and the low HER/OER overpotentials of the trifunctional nickel sulfide foam, an energy conversion efficiency of up to 94.3% can be obtained for the as-assembled electrolyser at a current density of 10 mA cm−2. When combined with a commercial Si PV module with an efficiency of 14.4%, the as-designed PV-electrolysis system showed a solar-to-hydrogen conversion efficiency of up to 10.4%. Utilization of trifunctional electrocatalysts greatly reduces the complexity of the electrolyser and the overall cost for electrochemical H2 production, and these electrolysers may potentially be used to construct highly competitive water splitting systems for continuous H2 production and green energy harvesting. Our research may also bring new insights into the utilization of multifunctional electrocatalysts in other devices, such as metal–air batteries and fuel cells.

Question: What's the cathode?