Capacity Cathode Research Articles

Mitigating Li-Rich Layered Cathode Capacity Loss by Using a Siloxane Electrolyte Additive.

The instability of the electrode-electrolyte interface in high-voltage cathode materials significantly hinders the development of high-energy-density lithium-ion batteries (LIBs). In this study, 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane (DTS) is employed as an electrolyte additive to enhance the cycling stability and capacity retention for Li||LLO (Li-rich layered oxide) batteries operating at 4.8 V. Theoretical calculations show that DTS can preferentially oxidize on the surface of the cathode. The oxidation forms a robust cathode electrolyte interface (CEI) on the LLO surface, significantly mitigating cracking, regeneration, and irreversible phase transitions of the LLO cathode. As anticipated, the Li||LLO batteries with the DTS electrolyte exhibit a capacity retention of 85.4% after 100 cycles at 4.8 V compared to the baseline electrolyte (45.2%). Furthermore, these batteries demonstrate superior capacity retention after 100 cycles at 4.8 V, even with the presence of 1000 ppm of H2O.

Effect of Carbon Morphology and Slurry Formulation in Sulfur Cathode for Li-S Batteries

The performance of Lithium-Sulfur (Li-S) batteries is significantly influenced by material selection and manufacturing processes, with conductive carbon and slurry formulation playing crucial roles. In this study, the impact of carbon morphology and solvent/solid ratio in slurry preparation on microstructure and electrochemical performance of sulfur cathodes was investigated. Various carbon structures, such as nanotubes, sheets, and particles, were explored, and the solvent volume was adjusted to assess their effects on electrode architecture and electrochemical performance. Our findings demonstrate that the binder dissolution process and consequent electrode architecture and performance are highly influenced by both the carbon structure and slurry solvent volume. Furthermore, it was observed that, contrary to common assumption, advanced carbon structures are not necessary for enhanced capacity and durability of Li-S cathodes. Accordingly, the best cycling durability was achieved by optimizing the slurry with 300 μL/mgPVDF of NMP solvent and using Ketjen black as the conductive carbon, resulting in an initial capacity of 1029 mAh gS −1, with a retention of 830 mAh gS −1 after 500 cycles. These results, obtained at a high areal loading of 4.5 mgS cm−2, demonstrate the commercial potential of the proposed electrode formulation and processing method without reliance on advanced materials or techniques.

Fabrication of Free‐Standing Hybrid Composite High Capacity Cathodes for Li−S Batteries with Nickel Oxide Polysulfide Adsorbent

AbstractThis study focuses on enhancing lithium‐sulfur (Li−S) battery performance by using nickel(II) oxide (NiO), as polysulfide adsorbent to mitigate the shuttle effect. Polysulfides have been shown to effectively adsorb onto the hydrophilic surfaces of polar metal oxides and thus suppress this effect. In this work, a NiO – reduced Graphene Oxide/Sulfur (NiO‐rGO/S) hybrid composite paper was developed for use as a binder‐free, flexible cathode. The characterization of the composite films was done through Fourier transform infrared spectroscopy (FT‐IR), Raman spectroscopy, thermogravimetric analysis (TG), field emission gun scanning electron microscopy (FEG‐SEM), energy dispersive x‐ray spectroscopy (EDS) and x‐ray diffraction (XRD). To test adsorption of polysulfides by NiO, ultraviolet‐visible (UV‐Vis) spectroscopy was applied. Electrochemical performance tests of CR2032 cells were also conducted by cyclic voltammetry (CV), charge‐discharge tests, electrochemical impedance spectroscopy (EIS). The NiO‐rGO/S cathode, particularly the one containing 2 % NiO, exhibited remarkable performance. It delivered an initial discharge capacity of 1230 mAh g−1, maintaining 1029 mAh g−1 after 300 cycles, with a high capacity retention of 83.1 %. This suggests that the NiO‐rGO/S hybrid composite is a promising candidate for improving the efficiency and lifespan of Li−S batteries.

Engineering Molecule‐Designed In Situ Polymerization on Al‐Doped Molecular‐Sieve Framework Enables Robust Quasi‐Solid‐State Lithium Batteries

AbstractAchieving fast Li+ transport kinetics and stable electrode/electrolyte interfaces is of paramount importance, yet extremely challenging for the practical success of solid‐state lithium metal batteries, which requires the rational design of the structure and composition of solid‐state electrolytes. Herein, a composite quasi‐solid‐state electrolyte is fabricated through in situ polymerization of a molecule‐designed polymer chain within the functionalized molecular sieve framework (Al‐MCM41). In this design, the robust Brønsted/Lewis acid–base interactions between Al‐MCM41 and TFSI− facilitate the dissociation of lithium salt, leading to a Li+ transference number as high as 0.81. Meanwhile, the well‐ordered mesopores of Al‐MCM41 act as the “reservoir” of the polymer chain, creating continuous ionic migration pathways to offer an excellent Li+ conductivity of 1.09 × 10−3 S cm−1 at 30 °C. Furthermore, the polymer with fluorinated and nitrided functional groups guarantees a dual‐reinforced anode and cathode interface. Such an integrated electrolyte with simultaneous unimpeded Li+ transport and robust interfaces delivers extraordinary capacity retention of 84.6% over 600 cycles at 5 C when coupled with LiFePO4 cathode and remarkable reversible capacity of 129.0 mAh g−1 after 200 cycles with high‐voltage NCM622 cathode. This work provides a significant avenue for enhancing the practical feasibility of solid‐state lithium metal batteries.

Customized Nano‐Confinement Effects of Metal‐Organic Frameworks for High‐Performance Lithium‐Sulfur Batteries

AbstractLithium‐sulfur batteries (LSBs) are considered one of the most promising next‐generation energy storage devices due to their significant theoretical energy density and high specific capacity of sulfur cathode. However, several critical challenges still must be addressed for practical application. The shuttle effect and sluggish redox kinetics severely impact their performance. Metal‐organic frameworks (MOFs) have garnered significant interest attributed to their high structural tunability. Their ability to nano‐confine lithium polysulfides (LiPSs) can be precisely controlled at the molecular level by regulating metal centers and organic ligands, thereby suppressing the shuttle effect and improving the electrochemical performance of LSBs. This review summarizes the nano‐confinement effects of MOFs in LSBs, and the discussion is divided into the selective confinement, repulsion, and nano‐confined adsorption by inert MOFs, as well as nano‐confined catalysis facilitated by catalytically active MOFs. Furthermore, the existing challenges and future prospects for application of MOFs in LSBs are proposed.

Boosting the Charge Storage Capability of Bi2TeO5 Cathode Using Iodide Ions in Aqueous Zinc-Based Batteries System.

As insertion-type cathode materials of aqueous Zn-based batteries (ABs), bismuth chalcogenides/oxychalcogenides exhibits relatively limited capacities in ZnSO4 baseline electrolyte. This work finds that Bi2TeO5 (BTO) cathode with pre-added I- electrolyte additive can simultaneously achieve conversion and insertion chemistries, which enables aqueous BTO-Zn batteries to deliver an extraordinary electrochemical performance. As shown in the experiment results, the BTO cathode showcases an ultrahigh specific capacity of 534.9mA h g-1 at 0.5 A g-1, excellent rate capability (237.3mA h g-1 at 10 A g-1). In the estimation of cyclic durability, the capacity of the BTO cathode decreases from 271.2 to 171.1mA h g-1 during 2000 cycles at 10 A g-1.

Evaluating the Intrinsic Zinc Storage Capacity of Cation-Preintercalated Cathode with Electrochemically Active Surface Area.

The guest cation preintercalation strategy has been widely adopted to improve the performance of zinc-vanadium batteries. However, existing studies always ignore the deintercalation of guest cations. This work focuses on the severe and universal deintercalation phenomenon and confirms the unaltered capacity after deintercalation, indicating that the capacity improvement mechanism cannot be attributed to the role of guest cations. Therefore, after excluding all of the previously researched factors for capacity improvement, the decisive factor is identified as the morphology (surface area). Based on the electrochemically active surface area (ECSA), a quantitative relationship with intrinsic capacity is established for the first time. This guides us to enhance battery capacity via enhancing ECSA through liquid-phase ultrasonic crushing to achieve the highest capacity of cation-preintercalated V2O5·nH2O (333.7 mAh g-1 at 10 A g-1). We believe that the enhanced ECSA is a plausible explanation for the improved performance of hydrated vanadium oxides.

Surface coating engineering of titanate anodes based on tannic acid-formaldehyde polymer chelating bismuth ions for advanced sodium-ion capacitors

As a battery-type anode material for sodium ion capacitors (SICs), titanate (H2Ti2O5·H2O, HTO) exhibits good rate capability due to its layered structure, easy to insert Na+ ions and low potential during sodium-ion storage. However, the structure is unstable due to the lattice distortion resulting from the irreversible embedment of Na+ in the process of sodium storage. So there is a significant mismatch between the dynamic reaction of the HTO anode and the capacitive cathode. Surface coating engineering is a useful strategy for stabilizing the HTO structure, which is critical for improving the kinetic response. In this work, a surface coating technique is designed to enhance the surface of HTO nanoarrays on titanium foil by using the oligomers of tannic acid formaldehyde polymer (TAF) chelated Bi3+ ions (Bi-TAF). As a binder-free anode, HTO coated with Bi-TAF (HTO@Bi-TAF) exhibits more excellent capacity (335.2 mA h g−1, 0.1 A g−1), rate capability (212.3 mA h g−1, 2.0 A g−1), and cycle stability (97 % capacity maintenance following 2000 cycles at 1.0 A g−1) than HTO and HTO coated with TAF (HTO@TAF). At the sweep rate of 1.0 mV s−1, the kinetic investigation reveals that the capacitance contribution of HTO@Bi-TAF is 86 %. The SICs exhibit a significant energy/power density (89.4 Wh kg−1/250 W kg−1). This work shows that the Bi-TAF polymer coating has a dual effect of rate capability improvement and structural protection on the prepared HTO. This results in a reasonable and effective surface coating strategy that provides outstanding rate capability and extended cycle performance of titanium-based anode materials for SICs.

Local electronic structure modulation via S substitution enables fast-discharging capability for Li-rich Mn-based oxides cathodes

Anionic and cationic redox reaction contribute to the ultrahigh specific capacities of Li-rich Mn-based oxides cathodes (LMNC). However, the irreversible oxygen evolution and sluggish kinetics result in the continuous capacity decay and poor rate performance, which limited its application as cathode material in lithium-ion batteries. Herein, the local electronic structure of LMNC is appropriately modulated via S2− doping to alleviate oxygen release, stabilize the crystal structure stability, and facilitate Li+ diffusion via facile surface defect engineering. The effect of S2− doping site on the systematically energy is investigated by DFT. Under the guidance of this result, LNMC-S is prepared by co-precipitation and high-temperature solid-phase reaction method. The effect of doping concentration on electrochemical property of LMNC was systematically investigated. The results exhibit that S2− doping can effectively suppress the electronic insulation of Li2MnO3, enhance the transport dynamics of lithium ion and inhibit the phase transition of LMNC sample during charge-discharge process. Thereby, the modified sample exhibits superior electrochemical property, such as the 200th discharge capacity is 184.3 mAh·g−1 under 1C, with a capacity retention rate of 87.6 %. This paper is beneficial for enriching the existing theoretical findings and discoveries, providing theoretical guidance for the preparation of high-performance material.

Effect of annealing on the MnO2 cathodes for high-performance aqueous Zn-ion batteries

Zinc ion batteries (ZIBs) are increasingly prominent due to their cost-effectiveness, abundance, environmental safety, mature processing methods, high volumetric energy density, and compatibility with aqueous electrolytes. However, a significant challenge lies in finding a suitable cathode material with high capacity and structural stability. Manganese dioxide (MnO2) is a promising candidate for ZIB cathodes in aqueous systems, surpassing other metal oxides in potential. However, MnO2 cathodes encounter challenges, including rapid capacity degradation and limited cyclic stability. Enhancing the structural stability of host materials during intercalation presents a significant avenue for increasing cathode capacity. In this study, we employed a hydrothermal method to synthesize MnO2, followed by annealing in an argon atmosphere at 300 °C for 4 h for MnO2-300 and 400 °C for 2 h for MnO2-400 to bolster its structural integrity. The properties of annealed samples MnO2-300 and MnO2-400 are compared with pristine samples (MnO2-P). Initially, XRD analysis is conducted to compare their structures, followed by a comparison of electrochemical properties, including Cyclic Voltammetry (CV) and charge-discharge analysis. MnO2-400 exhibits a higher initial capacity (149.3 mAhg−1 at 0.1 Ag-1) than MnO2-300 (129.0 mAhg−1 at 0.1 Ag-1) and MnO2-P (107.9 mAhg−1 at 0.1 Ag-1). An extended cycling test of up to 500 cycles also indicates that annealing MnO2 in an Ar atmosphere enhances structural stability and capacity compared to the unannealed sample.

Interlayer Space Engineering-Induced Pseudocapacitive Zinc-Ion Storage in Holey Graphene Oxide-Bearing Vertically Oriented MoS2 Nano-Wall Array Cathode for Aqueous Rechargeable Zn Metal Batteries.

Transition metal dichalcogenides, particularly MoS2, are acknowledged as a promising cathode material for aqueous rechargeable zinc metal batteries (ARZMBs). Nevertheless, its lack of hydrophilicity, poor electrical conductivity, significant restacking, and restricted interlayer spacing translate into inadequate capacity and rate performance. Herein, the unique porous structure and additional functional groups present in holey graphene oxide (hGO) are taken advantage of to dictate the vertical growth pattern of oxygen-doped MoS2 nanowalls (O-MoS2/NW) over the hGO surface. Compared to conventional graphene oxide (GO), the presence of nano-pores in hGO facilitates the homogeneous dispersion of Mo precursors and provides stronger interaction sites, promoting the uniform vertical alignment of O-MoS2/NW. The synergistic interaction between O-MoS2-NW and hGO translates to enhanced electron conductivity, efficient electrolyte penetration, enhanced interlayer spacing, reduced restacking, and enhanced surface area. As a consequence of precise control of various factors that decide the overall battery performance, a high discharge capacity (227mAhg-1 at 100mAg-1) cathode material with significantly lower charge transfer resistance (66Ω) compared to pristine O-MoS2 (153Ω) is developed. These findings underscore the potential of hGO as a multifunctional platform for nanoengineering high-performance cathode materials for the next generation of efficient and durable ARZMBs.

Control of N/P ratios and cut-off voltage for Silicon-Based Li-ion batteries

High-energy density and unwavering safety standards form the cornerstone of new energy vehicle development, necessitating the design of power batteries that seamlessly integrate these critical qualities. Key to this endeavor is the enhancement of energy density at the architectural level, focusing on the optimization of the N/P ratio—a move that demands a holistic evaluation extending beyond mere comparisons of cathode and anode capacities to include initial efficiency, and both reversible and irreversible capacities. Departing from traditional N/P ratio designs requires meticulous optimization. This research introduces a novel N/P ratio design methodology, termed the “Water Cup Model”, for lithium-ion batteries (LIBs), effectively addressing capacity loss issues endemic to conventional designs. This approach, under consistent cathode material and areal capacity conditions, increases the batteries’ specific energy by approximately 5 Wh/kg, without compromising safety. Further innovation is achieved by incorporating a voltage regulation coefficient, λ, allowing for precise adjustment of the cut-off discharge voltage and facilitating the selection of high-performance silicon-based anode materials. Comparative assessments of energy density and cycling performance affirm the superiority of our optimized N/P ratio strategy against conventional methods. This strategy’s core lies in its capacity to significantly boost energy density without extensive modifications to the battery’s internal makeup, relying solely on the precise management of the N/P ratio to ensure safety is not compromised by energy density enhancements. This seminal work lays down a cost-effective, robust framework for advancing high-performance LIB technology, contributing pivotal insights to the field.

Improved Stability of Single‐Crystal LiCoO2 Cathodes at 4.8 V through Solvation Structure Regulation

AbstractIncreasing the charging cut‐off voltage can significantly improve the capacity of LiCoO2 cathode. However, when the cut‐off voltage exceeds 4.5 V (vs Li/Li+), LiCoO2 undergoes irreversible phase transitions, leading to particle cracking and structural failure. Additionally, the decomposition of the electrolyte compromises the stability of the cathode/electrolyte interface, resulting in diminished battery capacity. Herein, the elements Al, Mg, and Zr are doped into single‐crystal LiCoO2 to enhance the structural stability of LiCoO2. Moreover, a 3 Å zeolite film is used to regulate the solvation structure to enhance the oxidation resistance of the electrolyte. This design enables a more stable cathode/electrolyte interface during high‐voltage cycling. At a cut‐off voltage of 4.8 V, the Li||LiCoO2 battery exhibits an initial discharge capacity of 236.2 mAh g−1 at 0.1 C and maintains 86.6% capacity retention after 100 cycles at 1 C. The pouch full cell, which utilizes a graphite anode and LiCoO2 cathode, operating within a charge–discharge range of 2.8–4.65 V, achieves a specific energy of 276 Wh kg−1 with 81% capacity retention after 200 cycles. This work introduces a desolvated electrolyte into the LiCoO2 battery system, providing a professional approach to addressing the challenges of high‐voltage LiCoO2.

Efficient synthesis of LiV2O5 as the cathode materials for high specific energy thermal batteries

LiV2O5 is considered an ideal cathode material for high specific energy thermal batteries due to its high voltage and high thermal stability. However, pure LiV2O5 is difficult to synthesize due to the multivalent nature of vanadium. In this paper, LiV2O5 powders in bulk were synthesized by using commercial V2O5 and LiBr as raw materials, followed by a simple ball milling and a sintering at 600 ℃ for 20 min. The discharge specific capacity of LiV2O5 cathode can reach 360.67 mAh g−1 at 0.05 A cm−2. Furthermore, LiV2O5/CFx cathode shows a specific capacity with 795 mAh g-1 at a cut-off voltage of 1.5 V, demonstrating significant potential for practical applications and providing a new approach for using CFx as a cathode material for thermal batteries. This article not only provides a method for mass-producing pure LiV2O5 cathode materials, but also explores a feasible strategy for using CFx with high-voltage and high specific capacity as cathode materials for thermal batteries.

Hierarchical nanostructure engineering endows ammonium vanadate as high capacity and ultra-long cycle cathode for wide-temperature aqueous zinc-ion batteries

Vanadium-based materials are the most promising cathode materials for Zinc-Ion batteries (ZIBs) due to their rich crystal structures and variable valence states. However, the structural collapse during multiple cycles leads to poor cycle life. Therefore, this work develops a 3-dimensional (3D) hierarchical nanostructure NH4V4O10 microspheres composed of nanosheets by a simple hydrothermal method, which are composed of nanosheets, this hierarchical nanostructure can promote the diffusion kinetics of Zn2+ and effectively mitigate the volume change of NH4V4O10 during the charging and discharging processes. As a result, the ZIBs assembled by the NH4V4O10 cathode exhibits high specific capacity of 522.9 mAh g−1 at 0.1 A g−1 and energy density of 348.96 Wh kg−1 at 215.12 W kg−1. At 20 A g−1, the NH4V4O10//Zn aqueous ZIB has 87.2 % capacity retention after 20,000 cycles. In addition, it exhibits excellent specific capacity and cycling performance over a wide-temperature range. At 10 A g−1, the NH4V4O10//Zn aqueous ZIB only loses 5.1 % capacity after 3500 cycles at −20 °C. Even at a high temperature of 50 °C, the capacity of NH4V4O10 battery is able to maintain 95.8 % after 450 cycles. This work informs the development of aqueous ZIBs for long cycle stability in a wide temperature range.

Electrochemical Activation Inducing Rocksalt-to-Spinel Transformation for Prolonged Service Life of LiMn2O4 Cathodes.

LiMn2O4 spinel is emerging as a promising cathode material for lithium-ion batteries, largely due to its open framework that facilitates Li+ diffusion and excellent rate performance. However, the charge-discharge cycling of the LiMn2O4 cathode leads to severe structural degradation and rapid capacity decay. Here, an electrochemical activation strategy is introduced, employing a facile galvano-potentiostatic charging operation, to restore the lost capacity of LiMn2O4 cathode without damaging the battery configuration. With an electrochemical activation strategy, the cycle life of the LiMn2O4 cathode is extended from an initial 1500 to an impressive 14 000 cycles at a 5C rate with Li metal as the anode, while increasing the total discharge energy by ten times. Remarkably, the electrochemical activation enhances the diffusion kinetics of Li+, with the diffusion coefficient experiencing a 37.2% increase. Further investigation reveals that this improvement in capacity and diffusion kinetics results from a transformation of the redox-inert LiMnO2 rocksalt layer on the surface of degraded cathodes back into active spinel. This transformation is confirmed through electron microscopy and corroborated by density functional theory simulations. Moreover, the viability of this electrochemical activation strategy has been demonstrated in pouch cell configurations with Li metal as the anode, underscoring its potential for broader application.

Zn/Co bimetallic metal-organic framework derived carbon anode with enchanted rate capability for lithium-ion capacitors

Lithium-ion capacitors (LICs) combine the advantages of lithium-ion batteries and supercapacitors, demonstrating great application prospects in the fields of large-scale renewable energy, and have been attracting increasing attention. Regrettably, the power capability of LICs is significantly hindered by the incongruent kinetics between battery-type anodes and capacitive cathodes. To address this challenge, in this study, a carbon anode derived from Zn/Co bimetallic metal-organic framework (MOF), specifically the Zn80Co20-PC, is synthesized through a direct carbonization process. Benefitting from the optimal degree of graphitization, substantial specific surface area, and comprehensive porous structure, the incongruent behaviour is effectively alleviated. As a result, the battery assembled with Zn80Co20-PC yielded an impressive capacity of 397.1 mAh g−1 at a current density of 0.1 A g−1 and a commendable rate capability of 109.6 mAh g−1 at 1.6 A g−1. Moreover, the LICs crafted with a pre-lithiated Zn80Co20-PC anode and an activated carbon (AC) cathode (designated as Zn80Co20-PC//AC LICs) exhibit a notable energy density of 123 Wh kg−1 and an elevated power density of 7150.3 W kg−1, maintaining exceptional durability through 5000 cycles. This study introduces innovative strategies for integrating advanced anode materials into lithium-ion capacitors.

Ternary intermediate phase mediated high energy density and kinetically accelerated Sb-Cd electrode for liquid metal batteries

Liquid metal battery (LMB) is an attractive technology that can address the big challenge of efficient utilization of renewable energies, ascribed to its potential ultralong service lifetime, ideal cost-efficiency, and high safety. However, breaking through the energy density bottleneck remains a persistent challenge, due to the limited lithiation voltage and specific capacity of cathodes. Herein, we design a novel dual-active Sb-Cd cathode, which shows a new ternary alloying discharge mechanism with reversible formation of ternary intermediate phase LiCdSb, accompanied by a high discharge voltage of 1.0 V. Coupled with the excellent Li storage capability of Cd, the Sb80Cd20 cathode attains an attractive capacity (> 500 mAh g-1), outperforming all reported LMB cathodes. More importantly, upon deep lithiation, the conversion reaction of ternary LiCdSb to Li3Sb mediates the regeneration and dispersion of Cd melt in the cathode, which constructs in situ fast electron and lithium diffusion networks for the subsequent discharge, significantly accelerating the electrode reaction kinetics. Thus, the Sb80Cd20 electrode achieves an exceptional combination of high energy density (398.4 Wh kg-1 at 200 mA cm-2) and superior rate capability (542.5 W kg-1 at 2400 mA cm-2). Additionally, the Li||Sb-Cd battery exhibits an outstanding tolerance and self-healing ability towards thermal runaway.

Polyaniline/graphene oxide nanocomposite as an innovative cathode for high energy density aqueous zinc-ion batteries

In order to resolve hard processability, poor conductive and lower capacity of polyaniline(PANI), We design and obtain a nanofiber network polyaniline/graphene oxide(PGO) and polyaniline/graphene oxide/manganese dioxide(PMGO) composite cathode. They are synthesized by electrochemical in-situ intercalative polymerization on oxidized graphite paper and assembled with the zinc anode into aqueous Zn-ion batteries(AZIBs). The initial discharged specific capacity of the PGO cathode is 224 mAh·g-1, and it is lower than that of the PMGO electrode when it discharges at 200mA·g-1. However, the capacity can reach 345 mAh·g-1 with better stability and reversibility compared to the PMGO under the same discharge/charge conditions. Characterization analysis and electrochemical studies show that the PGO composite cathode provides a large specific surface and charge/discharge channel, which optimizes the electrochemical performance of the battery. We also propose a new energy storage mechanism for intercalating PANI into graphene oxide(GO) layers to construct a nano-three-dimensional(3D) network for AZIBs and a proton pool with a hydrogen bond network of the PGO electrode. It is profitable for hindering the polarization, facilitating the electrode reaction, and enhancing the capacity and stability. For these reasons, the storage performance of the PGO electrode is superior to the polyaniline cathode reported at present.

The significant enhancement of energy density by redox and molecular crowding synergistic effects for aqueous zinc-ion hybrid capacitors

Aqueous zinc-ion hybrid capacitors (ZHCs) combine the high energy density of metal-ion batteries with the advantages of fast charging and discharging, high power density and long cycle life of capacitors, and are considered to be one of the most promising next-generation energy storage devices. However, the low operating voltage of aqueous electrolyte and the capacity mismatch between the capacitive cathode and the zinc anode lead to the unsatisfactory energy density of ZHCs. To improve the energy output for ZHCs, we designed an active aqueous electrolyte with high working voltage window by utilizing molecular crowding effect of polyethylene glycol (PEG) and the effect between redox-active ions (3I−/I3−). This high-voltage active aqueous electrolyte exhibits a wide voltage window of 2.2 V by inhibiting the hydrogen evolution in HER. The specific capacity of optimal ZHCs is boosted to 469 F g1 by the additional psedocapacitance from ZnI2 redox additive. The energy density of ZHCs reaches 287.3 Wh kg−1 and the capacity retention remains at 91.6 % after 7000 cycles. These results indicate that the proposed high-voltage active aqueous electrolyte is not only facile and effective for ZHCs, but also can be applied to other aqueous device for high energy density and practical application.