Trend of Developing Aqueous Liquid and Gel Electrolytes for Sustainable,Safe,and High‑Performance Li‑Ion Batteries

Current lithium-ion batteries(LIBs)rely on organic liquid electrolytes that pose significant risks due to their flammability and toxicity.The potential for environmental pollution and explosions resulting from battery damage or fracture is a critical concern.Water-based(aqueous)electrolytes have been receiving attention as an alternative to organic electrolytes.However,a narrow electrochemicalstability window,water decomposition,and the consequent low battery operating voltage and energy density hinder the practical use of aqueous electrolytes.Therefore,developing novel aqueous electrolytes for sustainable,safe,high-performance LIBs remains challenging.This Review first commences by summarizing the roles and requirements of electrolytes–separators and then delineates the progression of aqueous electrolytes for LIBs,encompassing aqueous liquid and gel electrolyte development trends along with detailed principles of the electrolytes.These aqueous electrolytes are progressed based on strategies using superconcentrated salts,concentrated diluents,polymer additives,polymer networks,and artificial passivation layers,which are used for suppressing water decomposition and widening the electrochemical stability window of water of the electrolytes.In addition,this Review discusses potential strategies for the implementation of aqueous Li-metal batteries with improved electrolyte–electrode interfaces.A comprehensive understanding of each strategy in the aqueous system will assist in the design of an aqueous electrolyte and the development of sustainable and safe high-performance batteries.

Gel electrolytes containing several kinds of particles used in quasi-solid-state dye-sensitized solar cells

Composite gel electrolytes containing several kinds of particles used as the quasi-solid-state electrolytes in dye-sensitized solar cells(DSSCs)were reported.Mesoporous particles(MCM-41)with unique structures composed of ordered nanochannels were served as a new kind of gelator for quasi-solid-state electrolytes.MCM-41,hydrophobic fumed silica Aerosil R972 and TiO_(2)nanopatricles P25 were dispersed into gel electrolytes respectively.The solar energy-to-electricity conversion efficiency of these cells is 4.65%,6.85%and 5.05%respectively under 30 mW·cm^(-2)illumination.The preparation methods and the particles sizes exert an influence on the performance of corresponding solar cells.Owing to unique pore structures and high specific BET surface area,mesoporous silica MCM-41 was expected to have the potential to afford conducting nanochannels for redox couple diffusion.

A series of conducting gel electrolytes for quasi-solid-state quantum dot-sensitized solar cells with boosted electron transfer processes

To pursue electron-generation stability with no sacrifice of photovoltaic performance has been a persistent objective for all kinds of solar cells. Here, we demonstrate the experimental realization of this objective by quasi-solid-state quantum dot-sensitized solar cells from a series of conducting gel electrolytes composed of polyacrylamide（PAAm） matrix and conductive polymers [polyaniline（PANi）, polypyrrole（PPy） or polythiophene（PT）]. The reduction of Sx2- occurred in both interface and three dimensional framework of conducting gel electrolyte as a result of the electrical conduction of PANi, PPy and PT toward refluxed electrons from external circuit to Pt electrode. The resulting solar cells can yield the solarto-electrical conversion efficiency of 2.33%, 2.25% and 1.80% for PANi, PPy and PT based gel electrolytes,respectively. Those solar cells possessed much higher efficiency than that of 1.74% based on pure PAAm gel electrolyte owing to the enhanced kinetics for Sx2- ？ S2- conversion. More importantly, the stability of quasi-solid-state solar cell is significantly advanced, arising from the localization of liquid electrolyte into the three dimensional framework and therefore reduced leakage and volatilization.

Experimental and computational analysis of the structure-activity relationship of ionic gel electrolytes based on bistrifluoromethanesulfonimide salts for supercapacitors

Ionic gel(IG)electrolytes are emerging as promising components for the development of next-generation supercapacitors(SCs),offering benefits in terms of safety,cost-effectiveness,and flexibility.The ionic conductivity,stability,and mechanical properties of the gel electrolyte are relevant factors to be considered and the key to improving the performance of the SC.However,the structure–activity relationship between the internal structure of IGs and their SC properties is not fully understood.In the current study,the intuitive and regular structure–activity relationship between the structure and properties of IGs was revealed via combining computational simulation and experiment.In terms of conductivity,the ionic liquid(IL)([EMIM][TFSI])in the IG has a high self-diffusion coefficient calculated by molecular dynamics simulation(MDS),which is conductive to transfer and then improves the conductivity.The radial distribution function of the MDS shows that the larger the g(r)between the particles in the polymer network,the stronger the interaction.For stability,IGs based on[EMIM][TFSI]and[EOMIM][TFSI]ILs have higher density functional theory calculated binding energy,which is reflected in the excellent thermal stability and excellent capacitor cycle stability.Based on the internal pore size distribution and stress-strain characterization of the gel network([ME3MePy][TFSI]and[BMIM][TFSI]as additives),the highly crosslinked aggregate network significantly reduces the internal mesoporous distribution and plays a leading role in improving the mechanical properties of the network.By using this strategy,it will be possible to design the ideal structure of the IG and achieve excellent performance.

Bacterial Cellulose/Zwitterionic Dual-network Porous Gel Polymer Electrolytes with High Ionic Conductivity

Bacterial cellulose(BC)was innovatively combined with zwitterionic copolymer acrylamide and sulfobetaine methacrylic acid ester[P(AM-co-SBMA)]to build a dual-network porous structure gel polymer electrolytes(GPEs)with high ionic conductivity.The dual network structure BC/P(AM-co-SBMA)gels were formed by a simple one-step polymerization method.The results show that ionic conductivity of BC/P(AM-co-SBMA)GPEs at the room temperature are 3.2×10^(-2) S/cm@1 M H_(2)SO_(4),4.5×10^(-2) S/cm@4 M KOH,and 3.6×10^(-2) S/cm@1 M NaCl,respectively.Using active carbon(AC)as the electrodes,BC/P(AM-co-SBMA)GPEs as both separator and electrolyte matrix,and 4 M KOH as the electrolyte,a symmetric solid supercapacitors(SSC)(AC-GPE-KOH)was assembled and testified.The specific capacitance of AC electrode is 173 F/g and remains 95.0%of the initial value after 5000 cycles and 86.2%after 10,000 cycles.

In Situ Polymer Gel Electrolyte in Boosting Scalable Fibre Lithium Battery Applications

The poor interfacial stability not only deteriorates fibre lithium-ion batteries(FLBs)performance but also impacts their scalable applications.To efficiently address these challenges,Prof.Huisheng Peng team proposed a generalized channel structures strategy with optimized in situ polymerization technology in their recent study.The resultant FLBs can be woven into different-sized powering textiles,providing a high energy density output of 128 Wh kg^(-1) and simultaneously demonstrating good durability even under harsh conditions.Such a promising strategy expands the horizon in developing FLB with particular polymer gel electrolytes,and significantly ever-deepening understanding of the scaled wearable energy textile system toward a sustainable future.

Bifunctional TiO_(2-x)nanofibers enhanced gel polymer electrolyte for high performance lithium metal batteries

Exploration of advanced gel polymer electrolytes(GPEs)represents a viable strategy for mitigating dendritic lithium(Li)growth,which is crucial in ensuring the safe operation of high energy density Li metal batteries(LMBs).Despite this,the application of GPEs is still hindered by inadequate ionic conductivity,low Li^(+)transference number,and subpar physicochemical properties.Herein,Ti O_(2-x)nanofibers(NF)with oxygen vacancy defects were synthesized by a one-step process as inorganic fillers to enhance the thermal/mechanical/ionic-transportation performances of composite GPEs.Various characterizations and theoretical calculations reveal that the oxygen vacancies on the surface of Ti O_(2-x)NF accelerate the dissociation of Li PF_6,promote the rapid transfer of free Li^(+),and influence the formation of Li F-enriched solid electrolyte interphase.Consequently,the composite GPEs demonstrate enhanced ionic conductivity(1.90m S cm^(-1)at room temperature),higher lithium-ion transference number(0.70),wider electrochemical stability window(5.50 V),superior mechanical strength,excellent thermal stability(210℃),and improved compatibility with lithium,resulting in superior cycling stability and rate performance in both Li||Li,Li||Li Fe PO_(4),and Li||Li Ni_(0.8)Co_(0.1)Mn_(0.1)O_(2)cells.Overall,the synergistic influence of nanofiber morphology and enriched oxygen vacancy structure of fillers on electrochemical properties of composite GPEs is comprehensively investigated,thus,it is anticipated to shed new light on designing high-performance GPEs LMBs.

Progress in Gel Polymer Electrolytes for Sodium-Ion Batteries

Sodium-ion battery is a potential application system for large-scale energy storage due to the advantage of higher nature abundance and lower production cost of sodium-based materials.However,there exist inevitably the safety problems such as flammability due to the use of the same type of organic liquid electrolyte with lithium-ion battery.Gel polymer electrolytes are being considered as an effective solution to replace conventional organic liquid electrolytes for building safer sodium-ion batteries.In this review paper,the authors present a comprehensive overview of the research progress in electrochemical and physical properties of the gel polymer electrolyte-based sodium batteries.The gel polymer electrolytes based on different polymer hosts namely poly(ethylene oxide),poly(acrylonitrile),poly(methyl methacrylate),poly(vinylidene fluoride),poly(vinylidene fluoride-hexafluoro propylene),and other new polymer networks are summarized.The ionic conductivity,ion transference number,electrochemical window,thermal stability,mechanical property,and interfacial issue with electrodes of gel polymer electrolytes,and the corresponding influence factors are described in detail.Furthermore,the ion transport pathway and ion conduction mechanism are analyzed and discussed.In addition,the advanced gel polymer electrolyte systems including flame-retardant polymer electrolytes,composite gel polymer electrolytes,copolymerization,single-ion conducting polymer electrolytes,etc.with more superior and functional performance are classified and summarized.Finally,the application prospects,development opportunities,remaining challenges,and possible solutions are discussed.

Molecule‑Level Multiscale Design of Nonflammable Gel Polymer Electrolyte to Build Stable SEI/CEI for Lithium Metal Battery

The risk of flammability is an unavoidable issue for gel polymer electrolytes(GPEs).Usually,flameretardant solvents are necessary to be used,but most of them would react with anode/cathode easily and cause serious interfacial instability,which is a big challenge for design and application of nonflammable GPEs.Here,a nonflammable GPE(SGPE)is developed by in situ polymerizing trifluoroethyl methacrylate(TFMA)monomers with flame-retardant triethyl phosphate(TEP)solvents and LiTFSI–LiDFOB dual lithium salts.TEP is strongly anchored to PTFMA matrix via polarity interaction between-P=O and-CH_(2)CF_(3).It reduces free TEP molecules,which obviously mitigates interfacial reactions,and enhances flame-retardant performance of TEP surprisingly.Anchored TEP molecules are also inhibited in solvation of Li^(+),leading to anion-dominated solvation sheath,which creates inorganic-rich solid electrolyte interface/cathode electrolyte interface layers.Such coordination structure changes Li^(+)transport from sluggish vehicular to fast structural transport,raising ionic conductivity to 1.03 mS cm^(-1) and transfer number to 0.41 at 30℃.The Li|SGPE|Li cell presents highly reversible Li stripping/plating performance for over 1000 h at 0.1 mA cm^(−2),and 4.2 V LiCoO_(2)|SGPE|Li battery delivers high average specific capacity>120 mAh g^(−1) over 200 cycles.This study paves a new way to make nonflammable GPE that is compatible with Li metal anode.

Interpenetrating network-reinforced gel polymer electrolyte for ultra-stable lithium−iodine batteries

Li-I_(2) batteries have attracted much interest due to their high capacity,exceptional rate performance,and low cost.Even so,the problems of unstable Li anode/electrolyte interface and severe polyiodide shuttle in Li-I_(2) batteries need to be tackled.Herein,the interfacial reactions on the Li anode and I_(2) cathode have been effectively optimized by employing a well-designed gel polymer electrolyte strengthened by cross-linked Ti-O/Si-O(GPETS).The interpenetrating network-reinforced GPETS with high ionic conductivity(1.88×10^(-3)S cm^(-1)at 25℃)and high mechanical strength endows uniform Li deposition/stripping over 1800 h(at 1.0mA cm^(-2),with a plating capacity of 3.0mAh cm^(-2)).Moreover,the GPETS abundant in surface hydroxyls is capable of capturing soluble polyiodides at the interface and accelerating their conversion kinetics,thus synergistically mitigating the shuttle effect.Benefiting from these properties,the use of GPETS results in a high capacity of 207 mAh g^(-1)(1 C)and an ultra-low fading rate of 0.013%per cycle over 2000 cycles(5 C).The current study provides new insights into advanced electrolytes for Li-I_(2) batteries.

In Situ High-performance Gel Polymer Electrolyte with Dual-reactive Cross-linking for Lithium Metal Batteries

Lithium metal batteries have been considered as one of the most promising next-generation power-support devices due to their high specific energy and output voltage.However,the uncontrollable side-reaction and lithium dendrite growth lead to the limited serving life and hinder the practical application of lithium metal batteries.Here,a tri-monomer copolymerized gel polymer electrolyte(TGPE)with a cross-linked reticulation structure was prepared by introducing a cross-linker(polyurethane group)into the acrylate-based in situ polymerization system.The soft segment of polyurethane in TGPE enables the far migration of lithium ions,and the-NH forms hydrogen bonds in the hard segment to build a stable cross-linked framework.This system hinders anion migration and leads to a high Li^(+)migration number(t_(Li^(+))=0.65),which achieves uniform lithium deposition and effectively inhibits lithium dendrite growth.As a result,the assembled symmetric cell shows robust reversibility over 5500 h at a current density of 1 mA cm^(-2).The LFP∷TGPE∷Li cell has a capacity retention of 89.8%after cycling 800 times at a rate of 1C.In summary,in situ polymerization of TGPE electrolytes is expected to be a candidate material for high-energy-density lithium metal batteries.

Interfacial fusion-enhanced 11 μm-thick gel polymer electrolyte for high-performance lithium metal batteries

In the pursuit of ultrathin polymer electrolyte(<20 μm) for lithium metal batteries, achieving a balance between mechanical strength and interfacial stability is crucial for the longevity of the electrolytes.Herein, 11 μm-thick gel polymer electrolyte is designed via an integrated electrode/electrolyte structure supported by lithium metal anode. Benefiting from an exemplary superiority of excellent mechanical property, high ionic conductivity, and robust interfacial adhesion, the in-situ formed polymer electrolyte reinforced by titanosiloxane networks(ISPTS) embodies multifunctional roles of physical barrier, ionic carrier, and artificial protective layer at the interface. The potent interfacial interactions foster a seamless fusion of the electrode/electrolyte interfaces and enable continuous ion transport. Moreover, the built-in ISPTS electrolyte participates in the formation of gradient solid-electrolyte interphase(SEI) layer, which enhances the SEI's structural integrity against the strain induced by volume fluctuations of lithium anode.Consequently, the resultant 11 μm-thick ISPTS electrolyte enables lithium symmetric cells with cycling stability over 600 h and LiFePO_(4) cells with remarkable capacity retention of 96.6% after 800 cycles.This study provides a new avenue for designing ultrathin polymer electrolytes towards stable, safe,and high-energy–density lithium metal batteries.

Carboxylic bacterial cellulose fiber-based hydrogel electrolyte with imidazole-type ionic liquid for dendrite-free zinc metal batteries

Aqueous zinc metal batteries are regarded as the most promising energy storage system due to their advantages of high safety,low cost,and high theoretical capacity.However,the growth of dendrites and the occurrence of side reactions hinder the development of zinc metal batteries.Despite previous attempts to design advanced hydrogel electrolytes,achieving high mechanical performance and ionic conductivity of hydrogel electrolytes has remained challenging.In this work,a hydrogel electrolyte with an ionic crosslinked network is prepared by carboxylic bacterial cellulose fiber and imidazole-type ionic liquid,following by a covalent network of polyacrylamide.The hydrogel electrolyte possesses a superior ionic conductivity of 43.76 mS cm^(−1),leading to a Zn^(2+)migration number of 0.45,and high mechanical performance with an elastic modulus of 3.48 GPa and an elongation at breaking of 38.36%.More importantly,under the anion-coordination effect of the carboxyl group in bacterial cellulose and[BF4]−in imidazole-type ionic liquid,the solvation sheath of hydrated Zn^(2+)ions and the nucleation overpotential of Zn plating are regulated.The results of cycled testing show that the growth of zinc dendrites is effectively inhibited and the generation of irreversible by-products is reduced.With the carboxylic bacterial cellulose-based hydrogel electrolyte,the Zn||Zn symmetric batteries offer good cyclability as well as Zn||Ti batteries.

Research progress on gel polymer electrolytes for lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries have become a promising candidate for advanced energy storage system owing to low cost and high theoretical specific energy.In the last decade,in pursuit of Li-S batteries with enhanced safety and energy density,the investigation on the electrolytes has leaped form liquid organic electrolytes to solid polymer ones.However,such solid-state Li-S battery system is greatly limited by unfavorable ionic conductivity,poor interfacial contact and narrow electrochemical windows on account of the absence of any liquid components.To address these issues,gel polymer electrolytes(GPEs),the incorporation of liquid electrolytes into solid polymer matrixes,have been newly developed.Although the excellent ionic transport and low interfacial resistance provided by GPEs have prompted numerous researchers to make certain progress on high-performance Li-S coins,a comprehensive review on GPEs for Li-S batteries remains vacant.Herein,this review focuses on recent development and progress on GPEs in view of their physical and chemical properties for the applications in Li-S batteries.Studies on the components including solid hosts,liquid solutions and fillers of GPEs are systematically summarized with particular emphasis on the relationship between components and performance.Finally,current challenges and directional outlook for fabricating GPEs-based Li-S batteries with outstanding performance are outlined.

A self-standing,UV-cured semi-interpenetrating polymer network reinforced composite gel electrolytes for dendrite-suppressing lithium ion batteries

A self-standing,flexible and lithium dendrite growth-suppressing composite gel polymer electrolyte membrane was designed for the use of room-temperature lithium ion batteries.The multi-functional composite semi-interpenetrating polymer network(referred to as“Cs-IPN”)electrolyte membrane was fabricated by combining a UV-cured ethoxylated trimethylolpropane triacrylate(ETPTA)macromer with alumina nanoparticles in the presence of liquid electrolyte and thermoplastic linear poly(ethylene oxide)(PEO).The polymer electrolyte membrane exhibits a semi-interpenetrating polymer network structure and a higher room temperature ionic conductivity,which impart the electrolyte with a significant cycling(120 mAh g^(-1)after 200 cycles)and a remarkable rate(137 mAh g^(-1)at 0.1℃,130 mAh g^(-1)at 0.5℃,119 mAh g^(-1)at 1℃ and 100 mAh g^(-1)at 2℃)performance in Li/LiFePO4 battery.More importantly,the polymer electrolyte possesses superior ability to inhibit the growth of lithium dendrites,which makes it promising for next generation lithium ion batteries.

All-Climate Stretchable Dendrite-Free Zn-Ion Hybrid Supercapacitors Enabled by Hydrogel Electrolyte Engineering

Hybrid supercapacitors have shown great potentials to fulfill the demand of future diverse applications such as electric vehicles and portable/wearable electronics.In particular,aqueous zinc-ion hybrid supercapacitors(ZHSCs)have gained much attention due to their low-cost,high energy density,and environmental friendliness.Nevertheless,typical ZHSCs use Zn metal anode and normal liquid electrolyte,causing the dendrite issue,restricted working temperature,and inferior device flexibility.Herein,a novel flexible Zn-ion hybrid supercapacitor(FZHSC)is developed by using activated carbon(AC)anode,δ-MnO_(2) cathode,and innovative PVA-based gel electrolyte.In this design,heavy Zn anode and its dendrite issue are avoided and layered cathode with large interlayer spacing is employed.In addition,flexible electrodes are prepared and integrated with an anti-freezing,stretchable,and compressible hydrogel electrolyte,which is attained by simultaneously using glycerol additive and freezing/thawing technique to regulate the hydrogen bond and microstructure.The resulting FZHSC exhibits good rate capability,high energy density(47.86 Wh kg^(−1);3.94 mWh cm^(−3)),high power density(5.81 kW kg^(−1);480 mW cm^(−3)),and excellent cycling stability(~91%capacity retention after 30000 cycles).Furthermore,our FZHSC demonstrates outstanding flexibility with capacitance almost unchanged even after various continuous shape deformations.The hydrogel electrolyte still maintains high ionic conductivity at ultralow temperatures(≤−30℃),enabling the FZHSC cycled well,and powering electronic timer robustly within an all-climate temperature range of−30~80℃.This work highlights that the promising Zn metal-free aqueous ZHSCs can be designed with great multifunctionality for more practical application scenarios.

A gel polymer electrolyte with IL@UiO-66-NH_(2) as fillers for high-performance all-solid-state lithium metal batteries

All solid-state electrolytes have the advantages of good mechanical and thermal properties for safer energy storage,but their energy density has been limited by low ionic conductivity and large interfacial resistance caused by the poor Li~+transport kinetics due to the solid-solid contacts between the electrodes and the solid-state electrolytes.Herein,a novel gel polymer electrolyte(UPP-5)composed of ionic liquid incorporated metal-organic frameworks nanoparticles(IL@MOFs)is designed,it exhibits satisfying electrochemical performances,consisting of an excellent electrochemical stability window(5.5 V)and an improved Li^(+)transference number of 0.52.Moreover,the Li/UPP-5/LiFePO_(4) full cells present an ultra-stable cycling performance at 0.2C for over 100 cycles almost without any decay in capacities.This study might provide new insight to create an effective Li^(+)conductive network for the development of all-solid-state lithium-ion batteries.

Molecular Reactivity and Interface Stability Modification in In-Situ Gel Electrolyte for High Performance Quasi-Solid-State Lithium Metal Batteries

Quasi-solid-state lithium metal battery is a promising candidate for next generation high energy density and high safety power supply.Despite intensive efforts on electrolytes,uncontrolled interfacial reactions on lithium with electrolyte and patchy interfacial contacts still hinder its practical process.Herein,we bring in rationally designed F contained groups into polymer skeleton via in-situ gelation for the first time to establish quasi-solid-state battery.This method achieves a capacity retention of 90%after 1000 cycles at 0.5C with LiFePO_(4)cathodes.The interface constructed by polymer skeleton and reaction with–CF_(3)lead to the predicted solid electrolyte interface species with high stability.Furthermore,we optimize molecular reactivity and interface stability with regulating F contained end groups in the polymer.Comparisons on different structures reveal that high performance solid stable lithium metal batteries rely on chemical modification as well as stable polymer skeleton,which is more critical to construct robust and steady SEI with uniform lithium deposition.New approach with functional groups regulation proposes a more stable cycling process with a capacity retention of 94.2%at 0.5C and 87.6%at 1C after 1000 cycles with LiFePO_(4) cathodes,providing new insights for the practical development of quasi-solid-state lithium metal battery.

A UV cross-linked gel polymer electrolyte enabling high-rate and high voltage window for quasi-solid-state supercapacitors

Serving as a promising alternative to liquid electrolyte in the application of portable and wearable devices,gel polymer electrolytes(GPEs)are expected to obtain more preferable properties rather than just be satisfied with the merits of high safety and deformability.Here,an easy-operated method is employed to fabricate cross-linked composite polymer membranes used for GPEs assisted by UV irradiation,in which N-doped carbon quantum dots(N-CQDs)and TiO2are introduced as photocatalysts and additives to improve the performances of GPEs.Specifically,N-CQDs participate as a cross-linker to construct the inner porous structure,and TiO2nanoparticles serve as a stabilizer to improve the electrochemical stability of GPEs under high voltage(3.5 V).The excellent thermal and mechanical stability of the membrane fabricated in this work guarantee the safety of the supercapacitors(SCs).This GPE based SC not only exhibits prominent rate performance(105%capacitance retention at the current density of 40A g^(-1))and cyclic stability(85%at 1 A g^(-1)under 3.5 V after 20,000 cycles),but also displays remarkable energy density(42.88 Wh kg^(-1))with high power density(19.3 k W kg^(-1)).Moreover,the superior rate and cycling performances of the as-prepared GPE based flexible SCs under flat and bending state confirm the feasibility of its application in flexible energy storage devices.

Novel Amphiphilic Polymer Gel Electrolytes Based on PEG-b-GMA-co-MMA

1 Results Gel polymer electrolytes for lithium battery have been widely investigated recently because of their high ion conductivity at room temperature. We synthesized and characterized novel gel electrolytes based on amphiphilic copolymethacrylates containing different lengths of ethylene oxide (EO) chain as ionophilic units and methyl methacrylate (MMA) chain as ionophobic units[1]. Their electrochemical properties were also measured.1H NMR and FTIR analysis results elucidated that PEG-b-glycidyl met...