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.

Quantum Spin Exchange Interactions to Accelerate the Redox Kinetics in Li–S Batteries

Spin-engineering with electrocatalysts have been exploited to suppress the“shuttle effect”in Li–S batteries.Spin selec-tion,spin-dependent electron mobility and spin potentials in activation barriers can be optimized as quantum spin exchange interactions lead-ing to a significant reduction of the electronic repulsions in the orbitals of catalysts.Herein,we anchor the MgPc molecules on fluorinated carbon nanotubes(MgPc@FCNT),which exhibits the single active Mg sites with axial displacement.According to the density functional theory calculations,the electronic spin polarization in MgPc@FCNT not only increases the adsorption energy toward LiPSs intermediates but also facilitates the tunneling process of electron in Li–S batter-ies.As a result,the MgPc@FCNT provides an initial capacity of 6.1 mAh cm^(-2) even when the high sulfur loading is 4.5 mg cm^(-2),and still maintains 5.1 mAh cm^(-2) after 100 cycles.This work provides a new perspective to extend the main group single-atom catalysts enabling high-performance Li–S batteries.

Smart materials for safe lithium-ion batteries against thermal runaway

In recent years,the new energy storage system,such as lithium ion batteries(LIBs),has attracted much attention.In order to meet the demand of industrial progress for longer cycle life,higher energy density and cost efficiency,a quantity of research has been conducted on the commercial application of LIBs.However,it is difficult to achieve satisfying safety and cycling performance simultaneously.There may be thermal runaway(TR),external impact,overcharge and overdischarge in the process of battery abuse,which makes the safety problem of LIBs more prominent.In this review,we summarize recent progress in the smart safety materials design towards the goal of preventing TR of LIBs reversibly from different abuse conditions.Benefiting from smart responsive materials and novel structural design,the safety of LIBs can be improved a lot.We expect to provide a comprehensive reference for the development of smart and safe lithium-based battery materials.

Access to advanced sodium-ion batteries by presodiation:Principles and applications

Sodium-ion batteries(SIBs)are expected to offer affordability and high energy density for large-scale energy storage system.However,the commercial application of SIBs is hurdled by low initial coulombic efficiency(ICE),continuous Na loss during long-term operation,and low sodium-content of cathode materials.In this scenario,presodiation strategy by introducing an external sodium reservoir has been rationally proposed,which could supplement additional sodium ions into the system and thereby markedly improve both the cycling performance and energy density of SIBs.In this review,the significance of presodiation is initially introduced,followed by comprehensive interpretation on technological properties,underlying principles,and associated approaches,as well as our perspectives on present inferiorities and future research directions.Overall,this contribution outlines a distinct pathway towards the presodiation methodology,of significance but still in its nascent phase,which may inspire the targeted guidelines to explore new chemistry in this field.

Atomistic understanding of capacity loss in LiNiO_(2)for high-nickel Li-ion batteries:First-principles study

Combining the first-principles calculations and structural enumeration with recognition,the delithiation process of LiNiO_(2)is investigated,where various supercell shapes are considered in order to obtain the formation energy of Li_(x)NiO_(2).Meanwhile,the voltage profile is simulated and the ordered phases of lithium vacancies corresponding to concentrations of 1/4,2/5,3/7,1/2,2/3,3/4,5/6,and 6/7 are predicted.To understand the capacity decay in the experiment during the charge/discharge cycles,deoxygenation and Li/Ni antisite defects are calculated,revealing that the chains of oxygen vacancies will be energetically preferrable.It can be inferred that in the absence of oxygen atom in high delithiate state,the diffusion of Ni atoms is facilitated and the formation of Li/Ni antisite is induced.

Design of multifunctional polymeric binders in silicon anodes for lithium‐ion batteries

Silicon(Si)is a promising anode material for lithium‐ion batteries(LIBs)owing to its tremendously high theoretical storage capacity(4200 mAh g−1),which has the potential to elevate the energy of LIBs.However,Si anodes exhibit severe volume change during lithiation/delithiation processes,resulting in anode pulverization and delamination with detrimental growth of solid electrolyte interface layers.As a result,the cycling stability of Si anodes is insufficient for commercialization in LIBs.Polymeric binders can play critical roles in Si anodes by affecting their cycling stability,although they occupy a small portion of the electrodes.This review introduces crucial factors influencing polymeric binders'properties and the electrochemical performance of Si anodes.In particular,we emphasize the structure–property relationships of binders in the context of molecular design strategy,functional groups,types of interactions,and functionalities of binders.Furthermore,binders with additional functionalities,such as electrical conductivity and self‐healability,are extensively discussed,with an emphasis on the binder design principle.

Solid-state synthesis and ion transport characteristics of the β-KSbF_(4) for all-solid-state fluoride-ion batteries

All-solid-state fluoride ion batteries(FIBs)have been recently considered as a post-lithium-ion battery system due to their high safety and high energy density.Just like all solid-state lithium batteries,the key to the development of FIBs lies in room-temperature electrolytes with high ionic conductivity.β-KSbF_(4) is a kind of promising solid-state electrolyte for FIBs owing to its rational ionic conductivity and relatively wide electrochemical stability window at room temperature.However,the previous synthesis routes ofβ-KSbF_(4) required the use of highly toxic hydrofluoric acid and the ionic conductivity of as-prepared product needs to be further improved.Herein,the β-KSbF_(4) sample with an ionic conductivity of 1.04×10^(-4)s cm^(-1)(30°C)is synthesized through the simple solid-state route.In order to account for the high ionic conductivity of the as-synthesizedβ-KSbF_(4),X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive X-ray spectroscopy(EDS)are used to characterize the physic-ochemical properties.The results show that the as-synthesizedβ-KSbF_(4) exhibits higher carrier concentra-tion of 1.0×10^(-6)S cm-Hz^(-1)K and hopping frequency of 1.31×10^(6)Hz at 30°C due to the formation of the fluorine vacancies.Meanwhile,the hopping frequency shows the same trend as the changes of ionic conductivity with the changes of temperature,while the carrier concentration is found to be almost con-stant.The two different trends indicate the hopping frequency is mainly responsible for the ionic conduc-tion behavior withinβ-KSbF_(4).Furthermore,the all-solid-state FIBs,in which Ag and Pb+PbF_(2) are adopted as cathode and anode,andβ-KSbF_(4) as fluoride ion conductor,are capable of reversible charge and discharge.The assembled FIBs show a discharge capacity of 108.4 mA h g^(-1) at 1st cycle and 74.2 mA h g^(-1) at 50th cycle.Based on an examination of the capacity decay mechanism,it has been found that deterioration of the electrolyte/electrode interface is an important reason for hindering the commer-cial application of FIBs.Hence,the in-depth comprehension of the ion transport characteristics inβ-KSbF_(4) and the interpretation of the capacity fading mechanism will be conducive to promoting development of high-performanceFIBs.

The safety aspect of sodium ion batteries for practical applications

Sodium-ion batteries(SIBs)with advantages of abundant resource and low cost have emerged as promising candidates for the next-generation energy storage systems.However,safety issues existing in electrolytes,anodes,and cathodes bring about frequent accidents regarding battery fires and explosions and impede the development of high-performance SIBs.Therefore,safety analysis and high-safety battery design have become prerequisites for the development of advanced energy storage systems.The reported reviews that only focus on a specific issue are difficult to provide overall guidance for building high-safety SIBs.To overcome the limitation,this review summarizes the recent research progress from the perspective of key components of SIBs for the first time and evaluates the characteristics of various improvement strategies.By orderly analyzing the root causes of safety problems associated with different components in SIBs(including electrolytes,anodes,and cathodes),corresponding improvement strategies for each component were discussed systematically.In addition,some noteworthy points and perspectives including the chain reaction between security issues and the selection of improvement strategies tailored to different needs have also been proposed.In brief,this review is designed to deepen our understanding of the SIBs safety issues and provide guidance and assistance for designing high-safety SIBs.

Novel high-voltage cathode for aqueous zinc ion batteries:Porous K_(0.5)VOPO_(4)·1.5H_(2)O with reversible solid-solution intercalation and conversion storage mechanism

Cathode materials that possess high output voltage,as well as those that can be mass-produced using facile techniques,are crucial for the advancement of aqueous zinc-ion battery(ZIBs)applications,Herein,we present for the first time a new porous K_(0.5)VOPO_(4)·1.5H_(2)O polyanionic cathode(P-KIVP)with high output voltage(above 1.2 V)that can be manufactured at room temperature using straightforward coprecipitation and etching techniques.The P-KVP cathode experiences anisotropic crystal plane expansion via a sequential solid-solution intercalation and phase co nversion pathway throughout the Zn^(2+)storage process,as confirmed by in-situ synchrotron X-ray diffraction and ex-situ X-ray photoelectron spectroscopy.Similar to other layered vanadium-based polyanionic materials,the P-KVP cathode experiences a progressive decline in voltage during the cycle,which is demonstrated to be caused by the irreversible conversion into amorphous VO_(x).By introducing a new electrolyte containing Zn(OTF)_(2) to a mixed triethyl phosphate and water solution,it is possible to impede this irreversible conversion and obtain a high output voltage and longer cycle life by forming a P-rich cathode electrolyte interface layer.As a proof-of-concept,the flexible fiber-shaped ZIBs based on modified electrolyte woven into a fabric watch band can power an electronic watch,highlighting the application potential of P-KVP cathode.

Multilevel carbon architecture of subnanoscopic silicon for fast‐charging high‐energy‐density lithium‐ion batteries

Silicon(Si)is widely used as a lithium‐ion‐battery anode owing to its high capacity and abundant crustal reserves.However,large volume change upon cycling and poor conductivity of Si cause rapid capacity decay and poor fast‐charging capability limiting its commercial applications.Here,we propose a multilevel carbon architecture with vertical graphene sheets(VGSs)grown on surfaces of subnanoscopically and homogeneously dispersed Si–C composite nanospheres,which are subsequently embedded into a carbon matrix(C/VGSs@Si–C).Subnanoscopic C in the Si–C nanospheres,VGSs,and carbon matrix form a three‐dimensional conductive and robust network,which significantly improves the conductivity and suppresses the volume expansion of Si,thereby boosting charge transport and improving electrode stability.The VGSs with vast exposed edges considerably increase the contact area with the carbon matrix and supply directional transport channels through the entire material,which boosts charge transport.The carbon matrix encapsulates VGSs@Si–C to decrease the specific surface area and increase tap density,thus yielding high first Coulombic efficiency and electrode compaction density.Consequently,C/VGSs@Si–C delivers excellent Li‐ion storage performances under industrial electrode conditions.In particular,the full cells show high energy densities of 603.5 Wh kg^(−1)and 1685.5 Wh L^(−1)at 0.1 C and maintain 80.7%of the energy density at 3 C.

Thin polymer electrolyte with MXene functional layer for uniform Li^(+) deposition in all-solid-state lithium battery

Solid polymer electrolyte(SPE) shows great potential for all-solid-state batteries because of the inherent safety and flexibility;however, the unfavourable Li+deposition and large thickness hamper its development and application. Herein, a laminar MXene functional layer-thin SPE layer-cathode integration(MXene-PEO-LFP) is designed and fabricated. The MXene functional layer formed by stacking rigid MXene nanosheets imparts higher compressive strength relative to PEO electrolyte layer. And the abundant negatively-charged groups on MXene functional layer effectively repel anions and attract cations to adjust the charge distribution behavior at electrolyte–anode interface. Furthermore,the functional layer with rich lithiophilic groups and outstanding electronic conductivity results in low Li nucleation overpotential and nucleation energy barrier. In consequence, the cell assembled with MXene-PEO-LFP, where the PEO electrolyte layer is only 12 μm, much thinner than most solid electrolytes, exhibits uniform, dendrite-free Li+deposition and excellent cycling stability. High capacity(142.8 mAh g-1), stable operation of 140 cycles(capacity decay per cycle, 0.065%), and low polarization potential(0.5 C) are obtained in this Li|MXene-PEO-LFP cell,which is superior to most PEO-based electrolytes under identical condition. This integrated design may provide a strategy for the large-scale application of thin polymer electrolytes in all-solid-state battery.

Extending the solid solution range of sodium ferric pyrophosphate:Off‐stoichiometric Na_(3)Fe(2.5)(P_(2)O_(7))_(2)as a novel cathode for sodium‐ion batteries

Iron‐based pyrophosphates are attractive cathodes for sodium‐ion batteries due to their large framework,cost‐effectiveness,and high energy density.However,the understanding of the crystal structure is scarce and only a limited candidates have been reported so far.In this work,we found for the first time that a continuous solid solution,Na_(4−α)Fe_(2+α)_(2)(P_(2)O_(7))_(2)(0≤α≤1,could be obtained by mutual substitution of cations at center‐symmetric Na3 and Na4 sites while keeping the crystal building blocks of anionic P_(2)O_(7) unchanged.In particular,a novel off‐stoichiometric Na_(3)Fe(2.5)(P_(2)O_(7))_(2)is thus proposed,and its structure,energy storage mechanism,and electrochemical performance are extensively investigated to unveil the structure–function relationship.The as‐prepared off‐stoichiometric electrode delivers appealing performance with a reversible discharge capacity of 83 mAh g^(−1),a working voltage of 2.9 V(vs.Na^(+)/Na),the retention of 89.2%of the initial capacity after 500 cycles,and enhanced rate capability of 51 mAh g^(−1)at a current density of 1600 mA g^(−1).This research shows that sodium ferric pyrophosphate could form extended solid solution composition and promising phase is concealed in the range of Na_(4−α)Fe_(2+α)_(2)(P_(2)O_(7))_(2),offering more chances for exploration of new cathode materials for the construction of high‐performance SIBs.

Empowering the Future: Exploring the Construction and Characteristics of Lithium-Ion Batteries

Lithium element has attracted remarkable attraction for energy storage devices, over the past 30 years. Lithium is a light element and exhibits the low atomic number 3, just after hydrogen and helium in the periodic table. The lithium atom has a strong tendency to release one electron and constitute a positive charge, as Li . Initially, lithium metal was employed as a negative electrode, which released electrons. However, it was observed that its structure changed after the repetition of charge-discharge cycles. To remedy this, the cathode mainly consisted of layer metal oxide and olive, e.g., cobalt oxide, LiFePO4, etc., along with some contents of lithium, while the anode was assembled by graphite and silicon, etc. Moreover, the electrolyte was prepared using the lithium salt in a suitable solvent to attain a greater concentration of lithium ions. Owing to the lithium ions’ role, the battery’s name was mentioned as a lithium-ion battery. Herein, the presented work describes the working and operational mechanism of the lithium-ion battery. Further, the lithium-ion batteries’ general view and future prospects have also been elaborated.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes(CSEs)with poly(ethylene oxide)(PEO)have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li~+solvating capability,flexible processability and low cost.However,unsatisfactory room-temperature ionic conductivity,weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress.Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture,spatial distribution and content,which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes.Unfortunately,a comprehensive review exclusively discussing the design,preparation and application of PEO/ceramic-based CSEs is largely lacking,in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics.Consequently,this review targets recent advances in PEO/ceramicbased CSEs,starting with a brief introduction,followed by their ionic conduction mechanism,preparation methods,and then an emphasis on resolving ionic conductivity and interfacial compatibility.Afterward,their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized.Finally,a summary and outlook on existing challenges and future research directions are proposed.

Insights on advanced g‐C_(3)N_(4)in energy storage:Applications,challenges,and future

Graphitic carbon nitride(g‐C_(3)N_(4))is a highly recognized two‐dimensional semiconductor material known for its exceptional chemical and physical stability,environmental friendliness,and pollution‐free advantages.These remarkable properties have sparked extensive research in the field of energy storage.This review paper presents the latest advances in the utilization of g‐C_(3)N_(4)in various energy storage technologies,including lithium‐ion batteries,lithium‐sulfur batteries,sodium‐ion batteries,potassium‐ion batteries,and supercapacitors.One of the key strengths of g‐C_(3)N_(4)lies in its simple preparation process along with the ease of optimizing its material structure.It possesses abundant amino and Lewis basic groups,as well as a high density of nitrogen,enabling efficient charge transfer and electrolyte solution penetration.Moreover,the graphite‐like layered structure and the presence of largeπbonds in g‐C_(3)N_(4)contribute to its versatility in preparing multifunctional materials with different dimensions,element and group doping,and conjugated systems.These characteristics open up possibilities for expanding its application in energy storage devices.This article comprehensively reviews the research progress on g‐C_(3)N_(4)in energy storage and highlights its potential for future applications in this field.By exploring the advantages and unique features of g‐C_(3)N_(4),this paper provides valuable insights into harnessing the full potential of this material for energy storage applications.

From Liquid to Solid‑State Lithium Metal Batteries:Fundamental Issues and Recent Developments

The widespread adoption of lithium-ion batteries has been driven by the proliferation of portable electronic devices and electric vehicles,which have increasingly stringent energy density requirements.Lithium metal batteries(LMBs),with their ultralow reduction potential and high theoretical capacity,are widely regarded as the most promising technical pathway for achieving high energy density batteries.In this review,we provide a comprehensive overview of fundamental issues related to high reactivity and migrated interfaces in LMBs.Furthermore,we propose improved strategies involving interface engineering,3D current collector design,electrolyte optimization,separator modification,application of alloyed anodes,and external field regulation to address these challenges.The utilization of solid-state electrolytes can significantly enhance the safety of LMBs and represents the only viable approach for advancing them.This review also encompasses the variation in fundamental issues and design strategies for the transition from liquid to solid electrolytes.Particularly noteworthy is that the introduction of SSEs will exacerbate differences in electrochemical and mechanical properties at the interface,leading to increased interface inhomogeneity—a critical factor contributing to failure in all-solidstate lithium metal batteries.Based on recent research works,this perspective highlights the current status of research on developing high-performance LMBs.

Anode surface engineering of zinc-ion batteries using tellurium nanobelt as a protective layer for enhancing energy storage performance

Over the years,zinc-ion batteries(ZIBs)have attracted attention as a promising next-generation energy storage technology because of their excellent safety,long cycling performance,eco-friendliness,and high-power density.However,issues,such as the corrosion and dissolution of the Zn anode,limited wet-tability,and lack of sufficient nucleation sites for Zn plating,have limited their practical application.The introduction of a protective layer comprising of tellurium(Te)nanobelts onto the surface of Zn anode has emerged as a promising approach to overcome these limitations and improve the electrochemical behav-ior by enhancing the safety and wettability of ZIBs,as well as providing numerous nucleation sites for Zn plating.In the presence of a Te-based protective layer,the energy power density of the surface-engineered Zn anode improved significantly(ranging from 310 to 144 W h kg^(-1),over a power density range of 270 to 1,800 W kg^(-1)),and the lifespan capability was extended.These results demonstrate that the proposed strategy of employing Te nanobelts as a protective layer holds great promise for enhancing the energy storage performance of zIBs,making them even more attractive as a viable energy storage solution forthefuture.

Bifunctional flame retardant solid-state electrolyte toward safe Li metal batteries

Solid polymer electrolytes(SPEs)are one of the most promising alternatives to flammable liquid electrolytes for building safe Li metal batteries.Nevertheless,the poor ionic conductivity at room temperature(RT)and low resistance to Li dendrites seriously hinder the commercialization of SPEs.Herein,we design a bifunctional flame retardant SPE by combining hydroxyapatite(HAP)nanomaterials with Nmethyl pyrrolidone(NMP)in the PVDF-HFP matrix.The addition of HAP generates a hydrogen bond network with the PVDF-HFP matrix and cooperates with NMP to facilitate the dissociation of Li TFSI in the PVDF-HFP matrix.Consequently,the prepared SPE demonstrates superior ionic conductivity at RT,excellent fireproof properties,and strong resistance to Li dendrites.The assembled Li symmetric cell with prepared SPE exhibits a stable cycling performance of over 1200 h at 0.2 m A cm^(-2),and the solid-state LiFePO_4||Li cell shows excellent capacity retention of 85.3%over 600 cycles at 0.5 C.

Lithium-Ion Charged Polymer Channels Flattening Lithium Metal Anode

The concentration difference in the near-surface region of lithium metal is the main cause of lithium dendrite growth.Resolving this issue will be key to achieving high-performance lithium metal batteries(LMBs).Herein,we construct a lithium nitrate(LiNO_(3))-implanted electroactiveβphase polyvinylidene fluoride-co-hexafluoropropylene(PVDF-HFP)crystalline polymorph layer(PHL).The electronegatively charged polymer chains attain lithium ions on the surface to form lithium-ion charged channels.These channels act as reservoirs to sustainably release Li ions to recompense the ionic flux of electrolytes,decreasing the growth of lithium dendrites.The stretched molecular channels can also accelerate the transport of Li ions.The combined effects enable a high Coulombic efficiency of 97.0%for 250 cycles in lithium(Li)||copper(Cu)cell and a stable symmetric plating/stripping behavior over 2000 h at 3 mA cm^(-2)with ultrahigh Li utilization of 50%.Furthermore,the full cell coupled with PHL-Cu@Li anode and Li Fe PO_(4) cathode exhibits long-term cycle stability with high-capacity retention of 95.9%after 900 cycles.Impressively,the full cell paired with LiNi_(0.87)Co_(0.1)Mn_(0.03)O_(2)maintains a discharge capacity of 170.0 mAh g^(-1)with a capacity retention of 84.3%after 100 cycles even under harsh condition of ultralow N/P ratio of 0.83.This facile strategy will widen the potential application of LiNO_(3)in ester-based electrolyte for practical high-voltage LMBs.

Boosting the cycling stability of all-solid-state lithium metal batteries through MOF-based polymeric protective layers

Solid-state electrolytes(SSEs)play a pivotal role in advancing next-generation lithium metal battery technology.However,they commonly encounter substantial interfacial resistance and poor stability when interfacing with lithium metal,hindering practical applications.Herein,we introduce a flexible metal-organic framework(MOF:NUS-6)-incorporated polymeric layer,denoted as NP,designed to protect the sodium superionic conductor(NASICON)-type Li_(1.3)Al_(0.3)Ti_(1.7)(PO_(4))_(3)(LATP)electrolyte from Li metal anodes.The NP matrix establishes a soft interface with the LATP surface,effectively reducing voids and gaps that may arise between the LATP electrolyte and Li metal.Moreover,the MOF component in NP enhances ionic conductivity,offers abundant Li^(+)transport sites,and provides hierarchical ion channels,ensuring a homogeneous Li^(+)flow and thus effectively inhibiting Li dendrite formation.Utilizing NP,we fabricate Li symmetrical cells cycled for over 1600 h at 0.2 mA cm^(-2)and all-solid-state LiINP-LATPI LiFePO_(4)batteries,achieving a remarkable 99.3%capacity retention after 200 cycles at 0.2 C.This work outlines a general strategy for designing long-lasting and stable solid-state Li metal batteries.