Li2 SO4 Research Articles

Enabling Aqueous Processing of Ni-Rich Layered Oxide Cathode Materials by Addition of Lithium Sulfate.

Aqueous processing of Ni-rich layered oxide cathode materials is a promising approach to simultaneously decrease electrode manufacturing costs, while bringing environmental benefits by substituting the state-of-the-art (often toxic and costly) organic processing solvents. However, an aqueous environment remains challenging due to the high reactivity of Ni-rich layered oxides towards moisture, leading to lithium leaching and Al current collector corrosion because of the resulting high pH value of the aqueous electrode paste. Herein, a facile method was developed to enable aqueous processing of LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) by the addition of lithium sulfate (Li2 SO4 ) during electrode paste dispersion. The aqueously processed electrodes retained 80 % of their initial capacity after 400 cycles in NCM811||graphite full cells, while electrodes processed without the addition of Li2 SO4 reached 80 % of their capacity after only 200 cycles. Furthermore, with regard to electrochemical performance, aqueously processed electrodes using carbon-coated Al current collector outperformed reference electrodes based on state-of-the-art production processes involving N-methyl-2-pyrrolidone as processing solvent and fluorinated binders. The positive impact on cycle life by the addition of Li2 SO4 stemmed from a formed sulfate coating as well as different surface species, protecting the NCM811 surface against degradation. Results reported herein open a new avenue for the processing of Ni-rich NCM electrodes using more sustainable aqueous routes.

Fe‐VS2 Electrocatalyst with Organic Matrix‐Mediated Electron Transfer for Highly Efficient Nitrogen Fixation

Electrochemical N2 fixation is considered to be a promising alternative to Haber-Bosch technology. Inspired by the composition and structure of natural nitrogenase, Fe-doped VS2 nanosheets were prepared via one-step solvothermal method. The electron transfer system mediated by organic conductive polymer (1-AAQ-PA) was constructed to promote the electron transfer between Fe-VS2 nanosheets and the electrode in electrocatalytic N2 reduction reaction (NRR). The obtained 1-AAQ-PA-Fe-VS2 electrode converted N2 to NH3 with a yield of 31.6 μg h-1 mg-1 at -0.35 V vs. reversible hydrogen electrode and high faradaic efficiency of 23.5 %. The introduction of Fe dopants favored N2 adsorption and activation, while the Li-S bond between Fe-VS2 and Li2 SO4 effectively inhibited hydrogen evolution. The highly efficient electron utilization in the electrocatalytic NRR process was realized using the 1-AAQ-PA as the electron transfer medium. Density functional theory calculations showed that N2 was preferentially adsorbed on Fe and reduced to NH3 via both distal and alternating mechanism.

Electrochemical Performance and Behavior Mechanism for Zn/LiFePO4 Battery in a Slightly Acidic Aqueous Electrolyte.

The electrochemical performances and process mechanisms of Zn/LiFePO4 cells in a slightly acidic 1.9 m Li2 SO4 -0.5 m ZnSO4 aqueous solution were investigated. The results showed that the hydrogen depletion side reaction on the surface of the zinc sheet led to an increase in pH of the electrolyte and fluctuations in specific capacity of the cells, and that the dissolution of Fe2+ ions and the lamination of LiFePO4 particles resulted in a decrease in the specific capacity of the cells. At pH 5.0, the initial discharge specific capacity of the Zn/LiFePO4 cell was about 120.0 mAh g-1 at 0.25 C, about 64.4 mAh g-1 at 3 C, with about 60.9 % capacity retention rate after 200 cycles at 1 C, and the Li+ ions diffusion coefficient was about 7.75×10-12 cm2 s-1 .

The Role of Alkali Cation Intercalates on the Electrochemical Characteristics of Nb2 CTX MXene for Energy Storage.

The intercalation of cations into layered-structure electrode materials has long been studied in depth for energy storage applications. In particular, Li+ -, Na+ -, and K+ -based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb2 CTx electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li2 SO4 , Na2 SO4 , and K2 SO4 electrolytes with d-spacing. Additionally, our results showed that the Nb2 CTx electrode exhibited higher electrochemical performance in the presence of Li2 SO4 than in that of Na2 SO4 and K2 SO4 . This is partly because the smaller-sized Li+ transports quickly and intercalates between the layers of Nb2 CTx easily. Poor ion transport in the Na2 SO4 electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li+ >Na+ >K+ . Our experimental studies provide direct evidence for the intercalation mechanism of Li+ , Na+ , and K+ on the 2D layered Nb2 CTx electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes.

(NH4 )2 V7 O16 Microbricks as a Novel Anode for Aqueous Lithium-Ion Battery with Good Cyclability.

Searching for novel anode materials to address the issues of poor cycle stability in the aqueous lithium-ion battery system is highly desirable. In this work, ammonium vanadium bronze (NH4 )2 V7 O16 with brick-like morphology has been investigated as an anode material for aqueous lithium-ion batteries and Li+ /Na+ hybrid ion batteries. The two novel full cell systems (NH4 )2 V7 O16 ||Li2 SO4 ||LiMn2 O4 and (NH4 )2 V7 O16 ||Na2 SO4 ||LiMn2 O4 both demonstrate good rate capability and excellent cycling performance. A capacity retention of 78.61 % after 500 cycles at 300 mA g-1 was demonstrated in the (NH4 )2 V7 O16 ||Li2 SO4 ||LiMn2 O4 system, whereas no capacity attenuation is observed in the (NH4 )2 V7 O16 ||Na2 SO4 ||LiMn2 O4 system. The reaction mechanisms of the (NH4 )2 V7 O16 electrode and impedance variation of the two full cells were also researched. The excellent cycling stability suggests that layered (NH4 )2 V7 O16 can be a promising anode material for aqueous rechargeable lithium-ion batteries.

Poor Stability of Li2 CO3 in the Solid Electrolyte Interphase of a Lithium-Metal Anode Revealed by Cryo-Electron Microscopy.

The solid electrolyte interphase (SEI) dictates the cycling stability of lithium-metal batteries. Here, direct atomic imaging of the SEI's phase components and their spatial arrangement is achieved, using ultralow-dosage cryogenic transmission electron microscopy. The results show that, surprisingly, a lot of the deposited Li metal has amorphous atomic structure, likely due to carbon and oxygen impurities, and that crystalline lithium carbonate is not stable and readily decomposes when contacting the lithium metal. Lithium carbonate distributed in the outer SEI also continuously reacts with the electrolyte to produce gas, resulting in a dynamically evolving and porous SEI. Sulfur-containing additives cause the SEI to preferentially generate Li2 SO4 and overlithiated lithium sulfate and lithium oxide, which encapsulate lithium carbonate in the middle, limiting SEI thickening and enhancing battery life by a factor of ten. The spatial mapping of the SEI gradient amorphous (polymeric → inorganic → metallic) and crystalline phase components provides guidance for designing electrolyte additives.

Electrochemical Capacitor Performance of Nanotextured Carbon/Transition Metal Dichalcogenides Composites.

Transition metal dichalcogenides (TMDs) are emerging low-dimensional materials with potential applications for electrochemical capacitors (EC). Here, physicochemical and electrochemical characterizations of carbon composites with two sulfides ReS2 and FeS2 are reported. To enhance conductivity, multiwalled carbon nanotubes (NTs) serve as a support for ReS2 while 3D graphene-like network (3DG) is utilized for FeS2 deposition. Unique structure of carbon/TMDs composites allows a faradaic contribution of sulfides to be exploited. Capacitance values, charge/discharge efficiency, capacitance retention, charge propagation, cyclabilty, and voltage limits of EC with carbon/sulfide composites in aqueous neutral solutions (Li2 SO4 , Na2 SO4 ) are analyzed. Special attention is devoted to energetic efficiency of capacitive charge/discharge processes. Structure-to-capacitance correlation for the composites with various TMDs loading is thoroughly emphasized. The more defected structure of layered NTs/ReS2 composite is responsible for the lower capacitor voltage (0.8 V)owing to quicker electrolyte decomposition. Additionally, the catalytic effect of Re for hydrogen evolution reaction plays a crucial role in EC voltage restriction. Contrary, the operating voltage of capacitor based on 3DG/FeS2 is able to be extended until 1.5V in sodium sulfate electrolytic solution.

A Quinone Anode for Lithium-Ion Batteries in Mild Aqueous Electrolytes.

Aqueous batteries could be potentially used for grid-scale energy storage owing to the use of nonflammable electrolytes and long cycle life. Recently, quinones have shown examples as redox-active materials in aqueous batteries under either strong acidic or basic conditions. However, a quinone-based battery with a less corrosive electrolyte is still rare. Given that quinone-based batteries are heavily influenced by the pH of electrolytes, we studied the influence of acid dissociation constants (pKa) of hydroquinones on their performance as solid electrode materials. We measured the pKa of anthracene-9,10-diol (AQH2 ) and benzo[1,2-b:4,5-b']dithiophene-4,8-diol (BDTDH2 ) from the Pourbaix diagrams of two para-quinone monomers [i.e., anthracene-9,10-dione (AQ) and benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BDTD)]. Subsequently, their polymeric forms [i.e., poly(anthraquinonyl sulfide) (PAQS) and poly(benzo[1,2-b:4,5-b']dithiophene-4,8-dione-2,6-diyl sulfide) (PBDTDS)] were investigated as electrodes in aqueous lithium-ion cells. At pH 13, PAQS demonstrates a low capacity and poor cycle life, whereas PBDTDS shows a capacity of 196 mAh g-1 and fade rates of 0.0038 % per cycle over 4200 cycles, 0.77 % per day over 21 days. The differences in capacity and cycle stability can be explained by the difference of corresponding pKa values. A full cell with the configuration of (-)PBDTDS|2.5 m Li2 SO4 (pH 13)|LiCoO2 (+) shows a voltage of 1.08 V, a capacity of 72 mAh g-1 and ≈99.9 % of Coulombic efficiency for 500 stable cycles.

Towards Antimonene and 2D Antimony Telluride through Electrochemical Exfoliation.

Two-dimensional (2D) layered antimony (Sb) and antimony telluride (Sb2 Te3 ) are two valuable materials for optoelectronic devices and thermoelectric applications. Preparing high-quality sheets of these materials is the initial phase to promote their expected issues. Herein, micrometer-sized few-to-multilayered sheets of Sb and Sb2 Te3 have been obtained by electrochemical exfoliation. The layered rhombohedral Sb was exfoliated in Na2 SO4 and Li2 SO4 electrolytes by anodic-cationic intercalation, and Sb2 Te3 was exfoliated in Na2 SO4 . These findings are important contributions for the solution-based room-temperature electrochemical exfoliation, which is stable under glove-box-free conditions, to further improve the production of high-quality exfoliated sheets.

Mechanistic Investigation of a Hybrid Zn/V2 O5 Rechargeable Battery with a Binary Li+ /Zn2+ Aqueous Electrolyte.

Low-cost, easily processable, and environmentally friendly rechargeable aqueous zinc batteries have great potential for large-scale energy storage, which justifies their receiving extensive attention in recent years. An original concept based on the use of a binary Li+ /Zn2+ aqueous electrolyte is described herein for the case of the Zn/V2 O5 system. In this hybrid, the positive side involves mainly the Li+ insertion/deinsertion reaction of V2 O5 , whereas the negative electrode operates according to zinc dissolution-deposition cycles. The Zn//3 mol L-1 Li2 SO4 -4 mol L-1 ZnSO4/ //V2 O5 cell worked in the narrow voltage range of 1.6-0.8 V with capacities of approximately 136-125 mA h g-1 at rates of C/20-C/5, respectively. At 1 C, the capacity of 80 mA h g-1 was outstandingly stable for more than 300 cycles with a capacity retention of 100 %. A detailed structural study by XRD and Raman spectroscopy allowed the peculiar response of the V2 O5 layered host lattice on discharge-charge and cycling to be unraveled. Strong similarities with the well-known structural changes reported in nonaqueous lithiated electrolytes were highlighted, although the emergence of the usual distorted δ-LiV2 O5 phase was not detected on discharge to 0.8 V. The pristine host structure was restored and maintained during cycling with mitigated structural changes leading to high capacity retention. The present electrochemical and structural findings reveal a reaction mechanism mainly based on Li+ intercalation, but co-intercalation of a few Zn2+ ions between the oxide layers cannot be completely dismissed. The presence of zinc cations between the oxide layers is thought to relieve the structural stress induced in V2 O5 under operation, and this resulted in a limited volume expansion of 4 %. This fundamental investigation of a reaction mechanism operating in an environmentally friendly aqueous medium has not been reported before.

Quantification of the Charge Consuming Phenomena under High-Voltage Hold of Carbon/Carbon Supercapacitors by Coupling Operando and Post-Mortem Analyses.

Enhancing the operating voltage of supercapacitors (SCs), hence their specific energy, is important. However, long-term hold at high voltage entails loss of capacitance, increase of resistance and internal pressure. Such detrimental effects could be reduced by obtaining quantitative information on the relative impact of the various mechanisms leading to the worsening of the SCs performance. Now, for a carbon/carbon supercapacitor in aqueous Li2 SO4 , a self-consistent approach is used to assign leaking charge during high voltage hold to the charge: 1) distributed throughout the electrochemical cell (steady-state leakage current measurements), 2) spent at each electrode for gases production (operando electrochemical mass spectrometry (EMS) analysis and pressure records), 3) utilized to oxidize the electrodes surface (from post-mortem surface functionality determination by temperature programmed desorption (TPD)), and 4) used for other parasitic reactions.

Li+ -Containing, Continuous Silica Nanofibers for High Li+ Conductivity in Composite Polymer Electrolyte.

Solid-state electrolytes have recently attracted significant attention toward safe and high-energy lithium chemistries. In particular, polyethylene oxide (PEO)-based composite polymer electrolytes (CPEs) have shown outstanding mechanical flexibility and manufacturing feasibility. However, their limited ionic conductivity, poor electrochemical stability, and insufficient mechanical strength are yet to be addressed. In this work, a novel CPE supported by Li+ -containing SiO2 nanofibers is developed. The nanofibers are obtained via sol-gel electrospinning, during which lithium sulfate is in situ introduced into the nanofibers. The uniform doping of Li2 SO4 in SiO2 nanofibers increases the Li+ conductivity of SiO2 , generates mesopores on the surface of SiO2 nanofibers, and improves the wettability between SiO2 and PEO. As a result, the obtained SiO2 /Li2 SO4 /PEO CPE yields high Li+ conductivity (1.3 × 10-4 S cm-1 at 60 °C, ≈4.9 times the Li2 SO4 -free CPE) and electrochemical stability. Furthermore, the all-solid-state LiFePO4 -Li full cell demonstrates stable cycling with high capacities (over 80 mAh g-1 , 50 cycles at C/2 at 60 °C). The Li+ -containing mesoporous SiO2 nanofibers show great potential as the filler for CPEs. Similar methods can be used to incorporate Li salts into other filler materials for CPEs.

Revisiting a Historical Concept by Using Quantum Crystallography: Are Phosphate, Sulfate and Perchlorate Anions Hypervalent?

There are many examples of atoms in molecules that violate Lewis' octet rule, because they have more than four electron pairs assigned to their valence. These atoms are referred to as hypervalent. However, hypervalency may be regarded as an artifact arising from Lewis' description of molecules, which is based on the assumption that electrons are localized in two-center two-electron bonds and lone pairs. In the present paper, the isoelectronic phosphate (PO4 3- ), sulfate (SO4 2- ) and perchlorate (ClO4 - ) anions were examined with respect to the concept of hypervalency. Lewis formulas containing a hypervalent central atom exist for all three anions. Based on X-ray wavefunction refinements of high-resolution X-ray diffraction data of representative crystal structures (MgNH4 PO4 ⋅6 H2 O, Li2 SO4 ⋅H2 O, and KClO4 ), complementary bonding analyses were performed. In this way, experimental information from the new field of quantum crystallography validate long-known facts, or refute long-standing misunderstandings. It is shown that the P-O and S-O bonds are highly polarized covalent bonds and, thus, the increase in the valence population following three-center four-electron bonding is not sufficient to yield hypervalent phosphorus or sulfur atoms, respectively. However, for the highly covalent Cl-O bond, most bonding indicators imply a hypervalent chlorine atom.

Green-light emission through energy transfer from Ce3+ to Tb3+ ions in the Li2 SO4 -Al2 (SO4 )3 system.

An energy transfer process from Ce3+ to Tb3+ ions was successfully achieved in a Li2 SO4 -Al2 (SO4 )3 mixed-sulphate system. A wet-chemical synthesis was employed to prepare the Li2 SO4 -Al2 (SO4 )3 system by doping Ce3+ and Tb3+ ions individually as well as collectively. The phases were identified using X-ray diffraction studies. The as-prepared samples were characterized by FT-IR and photoluminescence measurements. Green-light emission was exhibited by Ce3+ , Tb3+ co-doped Li2 SO4 -Al2 (SO4 )3 system, thus, indicating its potential as a material for display devices or in the lamp industry.

RGO Functionalized with a Highly Electronegative Keplerate-Type Polyoxometalate for High-Energy-Density Aqueous Asymmetric Supercapacitors.

Keplerate-type polyoxometalates represent a large series of high nuclear molecular clusters; for example, (NH4 )42 [MoVI 72 MoV 60 O372 (CH3 COO)30 (H2 O)72 ] ({Mo132 }) is a kind of spherical heteropoly blue with a large overall negative charge and an electron density and topological structure similar to C60 . {Mo132 } is a good bifunctional material that can be used as an electron acceptor or donor, which is advantageous to accelerate electron transmission in supercapacitors. Herein, a nanocomposite of rGO functionalized with a Keplerate-type polyoxometalate {Mo132 } was prepared by a facile chemical reduction method and used to construct supercapacitors for the first time. The electrochemical performance of the supercapacitors can be significantly improved due to the excellent redox properties, high electronegativity, and hollow porous structures of {Mo132 }, in addition to the outstanding conductivity of rGO. The {Mo132 }-rGO nanocomposite electrode exhibited an excellent gravimetric specific capacitance of 617.3 F g-1 at a current density of 5 A g-1 in 1 m Li2 SO4 electrolyte. An aqueous asymmetric supercapacitor with a voltage range of 2.1 V, with the {Mo132 }-rGO nanocomposite as the negative electrode and modified activated carbon as the positive electrode, exhibited a high energy density of 31.6 Wh kg-1 with a power density of 207.7 W kg-1 and favorable cycling stability.

Biowaste-Derived Hierarchical Porous Carbon Nanosheets for Ultrahigh Power Density Supercapacitors.

Low-cost activated carbons with high capacitive properties remain desirable for supercapacitor applications. Herein, a three-dimensional scaffolding framework of porous carbon nanosheets (PCNSs) has been produced from a typical biowaste, namely, ground cherry calyces, the specific composition and natural structures of which have contributed to the PCNSs having a very large specific surface area of 1612 m2 g-1 , a hierarchical pore size distribution, a turbostratic carbon structure with a high degree graphitization, and about 10 % oxygen and nitrogen heteroatoms. A high specific capacitance of 350 F g-1 at 0.1 A g-1 has been achieved in a two-electrode system with 6 m KOH; this value is among the highest specific capacitance of biomass-derived carbon materials. More inspiringly, a high energy density of 22.8 Wh kg-1 at a power density of 198.8 W kg-1 can be obtained with 1 m aqueous solution of Li2 SO4 , and an ultrahigh energy density of 81.4 Wh kg-1 at a power density of 446.3 W kg-1 is realized with 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte.

Robust Production of Ultrahigh Surface Area Carbon Sheets for Energy Storage.

Nanostructured carbon materials play essential roles in electrochemical energy storage devices. However, scalable production of high surface area carbon with a cost-effective process while controlling the morphology is challenging. Herein, a one-step procedure to produce carbon sheets with very high specific surface area up to 3411 m2 g-1 by direct pyrolysis of dipotassium ethylene diamine tetraacetate is reported. Unlike that of biomass-pyrolyzed carbons, the surface area of prepared carbon sheets is not sensitive to pyrolysis conditions (e.g., heating temperature and time), which makes the production robust and scalable. Moreover, the pore structure is stable against posttreatments, including solvent washing, which are detrimental to that of graphene-based soft sheet assemblies. When used as supercapacitor electrodes, the ultrahigh surface area carbon sheets (HSACS) show a high specific capacitance of 268 F g-1 at 5 mV s-1 , and retain 70% of the capacitance at 100 times higher scan rate in 6 m KOH aqueous electrolyte. Furthermore, the HSACS also exhibit a high specific capacitance of 266 F g-1 within a 1.6 V symmetric supercapacitor potential window in 2 m Li2 SO4 aqueous electrolyte. The symmetric supercapacitor delivers a maximum specific energy of 23.6 W h kg-1 and high power density of 6.4 kW kg-1 .

Achieving High Capacitance of Paper-Like Graphene Films by Adsorbing Molecules from Hydrolyzed Polyimide.

To date, graphene-based electric double layer supercapacitors have not shown the remarkable specific capacitance as theoretically predicted. An efficient strategy toward boosting the overall capacitance is to endow graphene with pseudocapacitance. Herein, molecules of hydrolyzed polyimide (HPI) are used to functionalize N-doped graphene (NG) via π-π interaction and the resulting enhanced electrochemical energy storage is reported. These aromatic molecules in monolayer form on graphene contribute strong pseudocapacitance. Paper-like NG films with different areal mass loadings ranging from 0.5 to 4.8 mg cm-2 are prepared for supercapacitor electrodes. It is shown that the gravimetric capacitance can be increased by 50-60% after the surface functionalization by HPI molecules. A high specific capacitance of 553 F g-1 at 5 mV s-1 is achieved by the HPI-NG film with a graphene mass loading of 0.5 mg cm-2 in H2 SO4 aqueous electrolyte. For the HPI-NG film with highest mass loading, the gravimetric specific capacitance drops to 340 F g-1 while the areal specific capacitance reaches a high value of 1.7 F cm-2 . HPI-NG films are also tested in Li2 SO4 aqueous electrolyte, over an extended voltage window of 1.6 V. High specific energy densities up to 40 Wh kg-1 are achieved with the Li2 SO4 electrolyte.

Corrigendum: Sustainable Gel Electrolyte Containing Pyrazole as Corrosion Inhibitor and Dendrite Suppressor for Aqueous Zn/LiMn2 O4 Battery.

The Zn anode in secondary aqueous batteries suffers from dendrite formation and corrosion. In this work, dendrite formation was suppressed by using a simple but new gel electrolyte containing fumed silica and an additive. The dendrite suppression was evidenced by chronoamperometry and ex situ scanning electron microscopy examinations. Pyrazole was implemented as the additive in the electrolyte. It was found that the presence of 0.2 wt % pyrazole in the electrolyte helped minimize both corrosion and dendrite formation. The Zn/LiMn2 O4 battery using pyrazole-containing gel electrolytes exhibited high cyclability up to 85 % capacity retention after 500 charge-discharge cycles at 4C. This was 8 % higher than the performance of the reference battery (using aqueous electrolyte containing 2 m Li2 SO4 and 1 m ZnSO4 ). Furthermore, self-discharge of the battery with the pyrazole-containing gel electrolyte was suppressed, as evidenced by an open-circuit voltage loss that was 20 % lower than for the reference battery after 24 h monitoring. Float-charge current density under constant voltage (2.1 V) also significantly decreased from approximately 8.0 to 3-6 μA.

Sustainable Gel Electrolyte Containing Pyrazole as Corrosion Inhibitor and Dendrite Suppressor for Aqueous Zn/LiMn2 O4 Battery.

The Zn anode in secondary aqueous batteries suffers from dendrite formation and corrosion. In this work, dendrite formation was suppressed by using a simple but new gel electrolyte containing fumed silica and an additive. The dendrite suppression was evidenced by chronoamperometry and ex situ scanning electron microscopy examinations. Pyrazole was implemented as the additive in the electrolyte. It was found that the presence of 0.2 wt % pyrazole in the electrolyte helped minimize both corrosion and dendrite formation. The Zn/LiMn2 O4 battery using pyrazole-containing gel electrolytes exhibited high cyclability up to 85 % capacity retention after 500 charge-discharge cycles at 4C. This was 8 % higher than the performance of the reference battery (using aqueous electrolyte containing 2 m Li2 SO4 and 1 m ZnSO4 ). Furthermore, self-discharge of the battery with the pyrazole-containing gel electrolyte was suppressed, as evidenced by an open-circuit voltage loss that was 20 % lower than for the reference battery after 24 h monitoring. Float-charge current density under constant voltage (2.1 V) also significantly decreased from approximately 8.0 to 3-6 μA.