The development of new high-performance binders is an effective strategy for lithium-ion batteries to cope with the volume expansion of SiOx anodes during cycling. In this study, a strategy is adopted for utilizing pre-lithiated sodium alginate (SA-LiCl40) as a high-performance SiOx anode binder. The addition of LiCl not only enables the linear SA binder to link into a three-dimensional network structure but also enriches a large number of lithium carboxylate groups, improving the Li+ transport rate within the anode. As a result, the mechanical properties of the binder increase, and interfacial adhesion between the copper current collector and the SiOx anode stabilizes, efficiently inhibiting volume expansion while enhancing cycling stability and initial Coulombic efficiency (ICE). When SA-LiCl40 serves as the binder for the SiOx anode, the ICE significantly improves by 13.5 %. A discharge capacity of 918.2 mA h g- 1 is obtained after 100 cycles, and a high reversible capacity of 791.9 mA h g- 1 is achieved after 300 cycles at 1 A g-1. Therefore, this work provides novel insights into developing new binders for high-performance SiOx anodes in lithium-ion batteries.

B3+ is an attractive and resource-abundant dopant for Ni-rich layered oxides. It can incorporate into the lattice, alter primary-particle morphology, and generate in-situ borate surface coatings. Prior studies attributed an improvement on cycling stability of boron-modified Ni-rich layered oxides to its radially aligned primaryparticle. However, boron also introduces bulk doping and forms surface borates coating that influence H2-H3 reversibility, lithium consumption, and interfacial reactivity. The relative contributions of B3+ in the bulk and on the surface of Ni-rich layered oxides to electrolyte-driven CEI evolution have not been systematically clarified. In this work, operando FTIR, XPS, and operando XAS are used to reveal the interfacial interactions of B3+-modified Ni-rich layered oxides. It is revealed that the surface borates coating intensifies carbonate deprotonation and promotes PF6- adsorption which favors the formation of an inorganic-rich CEI. In parallel, the borate surface coating avoids direct contact with electrolyte, while boron incorporation reduces Ni-O covalency. Simultaneously, these lower the organic based CEI formation. As a result, boron-modified cathode exhibits slower impedance growth, higher H2-H3 reversibility, and substantial enhancement on cycle stability over pristine sample.

Ni‐rich layered Li(Ni, Co, Mn)O 2 (NCM) oxides are important cathode materials for high‐energy large‐format Li‐ion batteries (LIBs). The urge for higher energy densities at a lower cost has continuously driven the use of NCM with higher Ni contents exceeding 80%. This work presents a coupling strategy of Ni‐rich layered oxide cathodes, consisting of large NCM (LNCM; LiNi 0.83 Co 0.12 Mn 0.05 O 2 , d 50 = 9.4 µm) particles having a relatively lower Ni but a higher Co content than the small NCM (SNCM, LiNi 0.88 Co 0.06 Mn 0.05 Al 0.01 O 2 , d 50 = 3.5 µm), to balance the intrinsic trade‐offs in lithium‐ion battery performance. The LNCM particles enhance structural stability and lithium‐ion diffusion, while SNCM particles provide high specific capacity and mitigate cracking issues associated with large particles. By strategically coupling particle size with transition‐metal composition, this approach achieves more than conventional packing‐density optimization. Optimized large‐to‐small ratios (70/30 and 50/50) deliver up to 38% higher volumetric capacity, >20% enhancement in capacity retention after 200 cycles, and a 32.7% improvement in fast‐charging capability. Importantly, using the coupling strategies can significantly suppress both surface side reactions and mechanical degradation, offering a mechanistic pathway to simultaneously improve energy density, rate performance, and cycling stability.

Silicon has emerged as a high-capacity anode for next-generation solid-state lithium-ion batteries (SSLIBs), although its practical application is constrained by volume expansion, interfacial degradation, and conductivity loss. Polymer electrolytes, offer safety, flexibility, and scalable processing advantages however require careful design to overcome limited conductivity and weak interfacial stability. Conspicuously, despite extensive progress in silicon anodes and polymer electrolytes individually, their direct integration has only been addressed in very few dedicated publications in recent years, emphasizing the infancy of this field. This review highlights progress in silicon-based anode and polymer electrolyte integration, including carbon-engineered composites, stress-buffering coatings, and ceramic and polymer hybrids. Interfacial chemistry such as LiF-rich SEIs, self-healing or elastic polymers, and nitrogen-bonded frameworks have allowed to long-life cycling stability and room temperature conductivities of 10−5–10−3 S cm−1. These advances validate clear pathways for translating laboratory-scale silicon-polymer electrolyte systems into commercial SSLIBs with high energy density, safety, and durability for electric vehicles and grid storage.

Energy density and safety are two crucial parameters when evaluating lithium-metal batteries (LMBs). Herein, we present an ultralight polymer-based current collector, incorporating flame-retardant materials, designed specifically for thin lithium-metal anodes. Compared to the traditional copper current collector (8.96 mg cm-2 , 10 mu m thick), the polymer-based current collector (12 mu m thick) has a significantly lower areal density of 1.41 mg cm-2 , i.e., only one-sixth of the copper collector, thus enabling substantially higher energy densities. Accordingly, when employed in Li||NMC622 full-cells, the polymer-based current collector enables a specific energy of 449 Wh kg-1, representing a notable improvement of about 14.5% compared to cells employing a classic copper current collector. The inclusion of Al(OH)3 as a flame retardant into the current collector suppresses flammability and, thereby, significantly improves the safety of the resulting LMBs. (c) 2025 The Authors. Published by Published by Elsevier B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Ni-rich Li(Ni,Co,Mn)O2 (NCM)-based lithium-ion batteries (LIBs) offer high capacity and energy density but suffer from significant thermal runaway risks, primarily associated with oxygen release from the cathode and subsequent reactions with the anode and electrolyte that can lead to combustion. Herein, we demonstrate a polymer-based surface-shielding strategy for graphite anodes by constructing a protective interphase designed to reduce the severity of thermal runaway. A nanometer-scale (∼2 nm) cross-linked lithium sulfonated chitosan (LiSCS) layer is employed as an artificial solid electrolyte interphase (A-SEI), leveraging its high lithium-ion conductivity and transference number, together with enhanced thermal robustness and low oxygen permeability. In addition to improving the cycling stability and rate capability of graphite anodes, differential scanning calorimetry analyses reveal that the LiSCS coating substantially reduces heat release associated with SEI decomposition and reactions involving lithiated graphite and oxygen released during LiNi0.83Co0.12Mn0.05O2 (NCM83) decomposition or present in the environment. Large-scale safety validation using 1 Ah NCM83∥graphite pouch cells further shows that LiSCS-coated cells exhibit no ignition during nail-penetration tests, in contrast to the violent combustion observed in cells with bare graphite anodes. We propose a surface-shielding effect of the LiSCS coating to mitigate oxygen-assisted exothermic reactions at the anode interface, thereby reducing the progression toward catastrophic thermal runaway. This straightforward and scalable polymer surface-shielding strategy provides a practical pathway toward safer, high-energy-density LIBs.

Silicon/graphite (Si/Gr) composites, promising high-capacity anodes for next-generation lithium-ion batteries, suffer from instability due to silicon's large volume expansion and deleterious interfacial degradation. This work introduces a synergistic composite coating of poly(vinylidene fluoride) (PVDF) and magnesium oxide (MgO) nanoparticles, applied via facile immersion to Si/Gr electrodes, to stabilize the electrode structure and the critical electrode-electrolyte interface. Compared to pristine and PVDF-only controls, the PVDF-MgO coating significantly enhanced long-term cycling, achieving over 760 cycles with 77 % capacity retention, high Coulombic efficiencies (>99.9 %), and improved rate capability. Post-mortem analysis confirmed the PVDF-MgO coatings preserved electrode integrity, dramatically suppressing thickness expansion (from similar to 137 % for pristine to similar to 49 % for optimized PVDF-MgO) after hundreds of cycles. Significantly, the PVDF-MgO coating suppressed lithium dendrite formation under high-rate (5C) and capacity-driven (20 % over-lithiation) conditions, promoting uniform, non-dendritic Li deposition. This suppression is attributed primarily to MgO's beneficial lithiophilicity and Lewis acid-base characteristics guiding Li nucleation and homogenizing ion flux, enabled by the composite structure. Crucially, the processing sequence was found to be paramount; applying the coating before electrode calendering, rather than after, unlocks the material's full potential and yields optimal performance. This discovery of a non-obvious process-structure-property relationship, where process engineering dictates interfacial stability, establishes the synergistic PVDF-MgO composite coating as an effective, scalable strategy for enhancing the durability, efficiency, and safety of high-energy Si/Gr anodes.

The interface between solid electrolyte (SE) and cathode active material in all-solid-state Li-ion batteries (ASSLIBs) is vulnerable to debonding during charge-discharge because of the different chemo-mechanical responses of the two components. Maintaining its close contact, vital to long-term cycle stability, currently relies mainly on applying extraordinary stacking pressures, which hinders practical applications of ASSLIBs. We herein report the development of free-standing-type composite cathodes containing Ni-rich Li(Ni, Co, Mn)O-2 (NCM; Ni stoichiometries >= 0.83) active materials and Li3InCl6 (LIC) SE with chemically fused robust interfaces that enable long-term cycle stability under a stacking pressure as low as nearly 2 MPa. The strong interface is realized via a novel in-situ recrystallization (ISR) process of LIC, which not only enhances close contact between the two solid components but also induces a chemically bonded interface, as revealed by synchrotron X-ray analyses. The bonded interface, while maintaining Li ion diffusion, exhibits extraordinary mechanical robustness against interfacial debonding even under low operating stacking pressures. A free-standing composite cathode containing LiNi0.88Co0.06Mn0.05Al0.01O2 (NCM88) and LIC, having a high specific capacity of similar to 200 mAh g(-1), is demonstrated to sustain 1500 charge-discharge cycles under similar to 2 MPa. This work points to the new strategy of chemically fused interface for achieving prolonged cycle stability of ASSLIBs under low stacking pressures.

Solid polymer membranes/electrolytes (SPEs) can mitigate the threats of commercial lithium-ion batteries (LIBs) that use organic fluid electrolytes. Current SPEs show an inadequate ionic conductivity (at environmental temperature) and exhibit unsatisfactory mechanical strength, restricting their large-scale application. In this study, SPEs are prepared from a solvent-free method and consist of poly(ethylene oxide) (PEO), poly(vinylidene fluoride) (PVDF), lithium bis(trifluoromethane sulfonyl) imide (LiTFSI), and the solid-plasticizer succinonitrile (SN) with superior ionic conductivity, greater durability, and better electrochemical performance. Taguchi composition optimization leads to an optimized film ((PEO)(10)-LiTFSI)(50)-SN30-PVdF(20), which demonstrates an ionic conductivity (at 303 K) of 1.04 x 10(-3) S cm(-1), which is two orders superior to bare ((PEO)(10)-LiTFSI)(100) film made without SN. Besides, thanks to PVDF, the optimized ((PEO)(10)-LiTFSI)(50)-SN30-PVdF(20) membranes exhibit a compressive modulus of 56.8 MPa, which is a five-fold increase when compared to without PVDF-added film (similar to 10 MPa). The solid-state coin cell is fabricated with LiFePO4/((PEO)(10)-LiTFSI)(50)-SN30-PVdF(20)/Li, exhibits a discharge capacity of 129 mAh g(-1), and achieves 84 % capacity maintenance at the end of 300 cycles at 30 degrees C, indicating the potential of as-prepared SPEs for the posterity of solid-state LIBs, which offer higher energy density and better safety.

LiNi0.8Mn0.1Co0.1O2 (NMC811) exceeding a high specific discharge capacity of 200 mAh g(-1). However, this cathode, distinct parasitic reactions with electrolyte are induced by the nucleophilic site on its surface. Here, electron-withdrawing cis-isomerism oligomers are synthesized from phenylenedimaleimide positional isomers to prevent these parasitic reactions. The para and meta substituent oligomerize through a vinyl radical mechanism, which is followed by the C-OH formation. Meanwhile, the oligomerization of ortho substituent (o-OC) gives a more electron-withdrawing carbonyl functional group due to the propagation radical polymerization pathway. This electron-withdrawing group increases the hybridization of NiO according to soft X-ray absorption spectroscopy to further catalyze the polymerization of the oligomer as an artificial cathode electrolyte interphase. Interestingly, due to a smaller angular distance (similar to 60 degrees) between the two maleimide groups of o-CI, leading to the formation of porous organic coverage on NCM811. These unique properties of o-CI and its interaction with NCM811 lead to the entropy-driven ethylene carbonate (EC) to vinylene carbonate (VC) reaction through a direct second deprotonation mechanism. Consequently, the cycle stability is enhanced compared to pristine NCM811 after prolonged cycling. This work demonstrates a coating layer strategy to grant a beneficial conversing of EC to VC.

LiNiO2 (LNO) offers the highest specific capacity among Ni-rich cathodes at a reduced cost. To address its safety concerns and poor cycle life in liquid-electrolyte (LE) applications, we investigate the performance of a free-standing composite cathode membrane integrating LNO with Li3InCl6 (LIC) solid electrolyte (SE) in an all-solid-state Li-metal battery (ASSLMB) operating under a high-capacity (>200 mAh g(-1)) and low-stack pressure (similar to 2 MPa) mode- a more commercially relevant but underexplored operating condition. The LNO composite cathode exhibited significantly enhanced cycle stability compared to LNO in the reference LE cells. We analyzed the dynamics of the LNO ASSLMB using systematic synchrotron operando X-ray characterizations, including absorption, diffraction, and microscopy. Our findings reveal that, while the LNO-LIC interfaces remain strongly bonded upon cycling, thanks to a solvent-mediated synthesis process, LNO crystal-structural disordering, particle cracking, and LNO-LIC interfacial side reactions persist as the three key challenges for cycle stability. The structural-disordering induced fading is predominant and highly dependent on the cut-off voltage above 4.1 V, while the severity of cracking and LNO-LIC interfacial side reactions are less dependent. The results underscore LIC's high-voltage stability, establishing 4.1 V as a critical threshold for achieving long-term cycle stability of LNO in the ASSLMB. This study provides novel solutions and significant insights regarding the applications of LNO in halide-based ASSLMBs.

Ni-rich (Ni content > 60%) layered cathodes are currently the most promising materials for lithium-ion batteries due to their high capacity and elevated voltage plateau compared to LiFePO4. However, Ni-rich cathodes face significant challenges, such as Jahn-Teller distortion, cation mixing, electrolyte deprotonation, and the presence of residual lithium compounds. These issues impede the widespread use of high-energy-density lithium-ion batteries employing Ni-rich cathodes. Ni-rich cathodes, containing a high concentration of Ni3+, encounter another problem known as the oxygen ligand hole effect, which affects the hybridization of O 2p and Ni 3d orbitals. Anionic redox occurs at the oxygen site with Ni3+, leading to a decrease in electron density, making the formation of Ni4+ at high states of charge (SOC) difficult. Consequently, battery capacity is primarily derived from anionic redox reactions. This study presents an organic coating (OC) designed to enhance the stability of the oxygen ligand hole, enabling greater capacity through enhanced Li+ interaction. Additionally, Ni-rich cathodes often suffer from gas evolution when charged to a high SOC, primarily due to the instability of the Ni-O bond. The OC is hypothesized to support the chemical reduction of Ni 2p53dn+2L̲ back to Ni 2p63dn+1L̲, where the L̲ represents O 1s12px+1 → O 1s22px on the surface of NMC811, thereby strengthening the oxygen ligand hole and stabilizing covalent Ni3+. This improvement results in the OC-modified NMC811 exhibiting outstanding cycle performance under high-rate tests and excellent stability at high temperatures.

Electrolyte composition strongly affects the performance of Li-ion batteries in terms of their general electrochemical properties, electrode stability, cycle life, long-term stability (especially at elevated temperatures), and safety. Additives are essential constituents of efficient electrolyte systems for advanced batteries. Their nature and chemical identity are highly diverse, and their modes of action are sometimes not fully understood, seemingly related to “alchemy”. Additives play a crucial role in stabilizing interfaces, enhancing cycle life, and significantly improving safety. Here, a wide scope of additives used in rechargeable Li batteries is examined. Various additives are surveyed emphasizing the importance of their functional groups. We examine routes for judicious optimization of electrolyte solutions by selecting suitable additives for improved rechargeable batteries. As there are many types of additives, their judicious classification is very challenging. We suggest herein the classification and specification of important and representative additives by their central elements. A first classification is based on additives with central atoms other than carbon, hydrogen, and oxygen. Then, we mention additives based on unsaturated bonds and/or unstable ring organic molecules. Dual salt systems are also briefly discussed. Finally, we briefly discussed modelling efforts related to additives.

Ni-rich (Ni content > 60%) layered cathodes are currently the most promising materials for lithium-ion batteries due to their high capacity and elevated voltage plateau compared to LiFePO4. However, Ni-rich cathodes face significant challenges, such as Jahn-Teller distortion, cation mixing, electrolyte deprotonation, and the presence of residual lithium compounds. These issues impede the widespread use of high-energy-density lithium-ion batteries employing Ni-rich cathodes. Ni-rich cathodes, containing a high concentration of Ni3+, encounter another problem known as the oxygen ligand hole effect, which affects the hybridization of O 2p and Ni 3d orbitals. Anionic redox occurs at the oxygen site with Ni3+, leading to a decrease in electron density, making the formation of Ni4+ at high states of charge (SOC) difficult. Consequently, battery capacity is primarily derived from anionic redox reactions. This study presents an organic coating (OC) designed to enhance the stability of the oxygen ligand hole, enabling greater capacity through enhanced Li+ interaction. Additionally, Ni-rich cathodes often suffer from gas evolution when charged to a high SOC, primarily due to the instability of the Ni-O bond. The OC is hypothesized to support the chemical reduction of Ni 2p53dn+2L̲ back to Ni 2p63dn+1L̲, where the L̲ represents O 1s12px+1 → O 1s22px on the surface of NMC811, thereby strengthening the oxygen ligand hole and stabilizing covalent Ni3+. This improvement results in the OC-modified NMC811 exhibiting outstanding cycle performance under high-rate tests and excellent stability at high temperatures.

Possessing high electronic conductivity and the nature of chemical inertness, the Magn & eacute;li phase titanium oxide Ti 4 O 7 is a promising material for various electrochemical applications. Herein, the Ti 4 O 7 electrode in aqueous Li 2 SO 4 electrolyte is characterized for its supercapacitor applications. The oxide electrode exhibits pseudocapacitive behavior over a wide potential range of + 1.0 V ( vs . Ag/AgCl), showing a speci fi c capacitance of 105 F g - 1 , equivalent to 85 mu F cm - 2 - oxide, along with outstanding high -rate performance and cycle stability (96% capacitance retention after 5000 cycles). In situ X-ray absorption near -edge spectroscopy analysis on the Ti K -edge absorption reveals that the pseudocapacitance does not involve the redox reaction of the oxide electrode material. A pseudocapacitance mechanism attributed to the reversible redox reactions of the hydrogen and oxygen atoms adsorbed on the oxide surface is proposed. (c) The Author(s) 2024. Published by ECSJ. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium provided the original work is properly cited. [DOI: 10.5796/electrochemistry.24-70030].

Ovarian cancer (OC) is associated with high late mortality owing to hidden symptoms in the early stages and limited screening measurements. Therefore, it is urgent to develop a highly efficient label-free immunosensor for targeting cancer antigens. In this study, we developed a gold-loaded iron-doped nanoporous carbon (denoted as Au@Fe-NC) as an ideal substrate for cancer antigen detection with high specificity and sensitivity. First, an Fe, N-doped nanoporous carbon (Fe-NC) material was synthesized by carbonizing a Fe-doped metal-organic framework at 900°C under continuous nitrogen flow. The resultant Fe-NC contains pyrrolic-N, which facilitates the auto-reduction of Au³⁺ to Au⁰ without requiring an external reducing agent. Thus, the Au@Fe-NC was spontaneously formed by mixing an aqueous HAuCl₄ solution with Fe-NC. The immunosensor developed using Au@Fe-NC exhibits outstanding stability as well as high sensitivity to carbohydrate antigen 125 (CA-125), a tumor marker, presenting a linear dynamic range of 0.1 pg mL⁻¹ to 1 µg mL⁻¹ and a detection limit of 0.1 pg mL⁻¹. The proposed Au@Fe-NC-based immunosensor has the ability to detect CA-125 in human serum samples and is a promising material for OC diagnosis.

The performance of traditional Li-ion batteries deteriorates when operating at sub-zero temperatures mainly due to the slow diffusion of Li-ions in commercial negative electrode materials. Various alternative anodes have been explored, but complex fabrication methods hinder practical implementation. This work proposes a cost-effective anode material, a porous structured nitrogen-doped hard carbon synthesized from date seeds with further LiF modification to achieve an artificial LiF-rich solid electrolyte interphase (SEI) layer. The resulting anode material showcases promising characteristics, achieving a specific capacity of 525 mAh g- 1 after 50 cycles at room temperature. Furthermore, it maintains a substantial capacity of 280 mAh g- 1 after 100 cycles at-20 degrees C. Notably, even when subjected to a high current of 2C at-20 degrees C, the electrode still provides a remarkable capacity of 72 mAh g- 1 after 500 cycles. The outstanding charge storage performance at low temperatures is attributed to the predominance of capacitance-controlled charge storage mechanisms in the prepared anode. Post-mortem analysis confirms structural stability and formation of a uniform LiF-rich SEI layer. This novel approach presents a practical solution to the difficulties encountered by LIBs in cold environments, paving the way for improved battery performance and longevity.

Herein, we demonstrate a novel and feasible strategy to stabilize the LiNi0.83Co0.12Mn0.05O2 (NCM) structure via the in-situ formation of a superficial spinel layer with potassium (K) doping. While K+ doped NCM is not new, the formation of the protective spinel layer gives surprising results with even a trace amount of doping, which is unique and novel, and nowhere reported. The structural transformation from layered to spinel on the surface region of NCM is achieved with a K-doping level of 0.05 mol% (NCM-0.05K) and the formed spinel layer acted as a protective pillar for stabilizing the host structure, leading to substantially improved electrochemical performance. The X-ray photoelectron spectra demonstrate a large increase in nickel (Ni2+) distribution after cycling for pristine but almost no change for the NCM-0.05K, suggesting a stable preformed spinel layer. The above results reveal that the K+ doping can strongly reduce the Ni4+ to stable Ni2+ under the spinel phase formation and improves cell performances in terms of specific capacity, capacity retention, rate capability, and Li+ diffusivity. The internal micro-cracking of host NCM is also effectively suppressed by the low amount of K doping. Excessive K-doping, in contrast, leads to a reduction in (de)lithiation rate and greater polarization.

Ni-rich cathodes inherit surface residual lithium compounds (SRLCs) for several reasons, such as cation mixing, oxygen vacancies, and the spontaneous reduction of high-Ni valence ions. Consequently, Ni-rich compounds must be treated before use to maximize their performance. This study describes the development of an organic coverage (OC) that can be directly utilized with a deteriorated Ni-rich cathode. The OC is synthesized from 5,5-dimethylbarbituric acid and polyethylene glycol diacrylate to provide two functions for the deteriorated Ni-rich cathode surface: spontaneous ion exchange and the self-electrochemical oxidation of Ni ions. SRLCs, such as Li2CO3 and LiOH, decompose through a transformation reaction from the trioxo to the dioxo form of the OC structure. Then this lithiated OC forms an organic artificial cathode electrolyte interface on the cathode surface, which further reduces the effects of chemical crossover on the anode side. It is also believed that the dioxo form promotes Ni2+ self-oxidation on the surface of Ni-rich cathodes and recovers the original Ni3+ valence state by Li+ re-intercalation. Thus, the capacities of the deteriorated LiNiO2 and LiNi0.8Mn0.1Co0.1O2 recover almost to their original values and retain the same excellent cycle performance as that of the fresh compounds.

Electrochemical capacitors are known for their high power density and cyclability, and various redox reactions can be utilized to improve their energy density. A great variety of redox materials have been investigated recently for use in electrochemical capacitors, not only transition metal oxides, which have been studied for many years. In this review, we provide a comprehensive explanation of redox materials for electrochemical capacitors. Manganese oxides and ruthenium oxides, which are typical metal oxides exhibiting pseudocapacitance, are first discussed. Nickel oxides used in hybrid capacitors are also covered. Various 0D and 2D nanomaterials are highlighted. Pseudo-capacitance using nanosized complex materials and metal-organic frameworks is also presented. Furthermore, electrolyte systems that exhibit redox characteristics for electrochemical capacitors are also reviewed.