Tuning desolvation kinetics of in-situ weakly solvating polyacetal electrolytes for dendrite-free lithium metal batteries

The host structure of polymers significantly influences ion transport and interfacial stability of electrolytes,dictating battery cycle life and safety for solid-state lithium metal batteries.Despite promising properties of ethylene oxide-based electrolytes,their typical clamp-like coordination geometry leads to crowd solvation sheath and overly strong interactions between Li^(+)and electrolytes,rendering difficult dissociation of Li+and unfavorable solid electrolyte interface(SEI).Herein,we explore weakly solvating characteristics of polyacetal electrolytes owing to their alternately changing intervals between–O–coordinating sites in the main chain.Such structural asymmetry leads to unique distorted helical solvation sheath,and can effectively reduce Li^(+)-electrolyte binding and tune Li^(+)desolvation kinetics in the insitu formed polymer electrolytes,yielding anion-derived SEI and dendrite-free Li electrodeposition.Combining with photoinitiated cationic ring-opening polymerization,polyacetal electrolytes can be instantly formed within 5 min at the surface of electrode,with high segmental chain motion and well adapted interfaces.Such in-situ polyacetal electrolytes enabled more than 1300-h of stable lithium electrodeposition and prolonged cyclability over 200 cycles in solid-state batteries at ambient temperatures,demonstrating the vital role of molecular structure in changing solvating behavior and Li deposition stability for high-performance electrolytes.

Anion-Regulated Weakly Solvating Electrolytes for High-Voltage Lithium Metal Batteries

Development of advanced high-voltage electrolytes is key to achieving high-energy-density lithium metal batteries(LMBs).Weakly solvating electrolytes(WSE)can produce unique anion-driven interphasial chemistry via altering the solvating power of the solvent,but it is difficult to dissolve the majority of Li salts and fail to cycle at a cut-off voltage above 4.5 V.Herein,we present a new-type WSE that is regulated by the anion rather than the solvent,and the first realize stable cycling of dimethoxyethane(DME)at 4.6 V without the use of the“solvent-in-salt”strategy.The relationships between the degree of dissociation of salts,the solvation structure of electrolytes,and the electrochemical performance of LMBs were systematically investigated.We found that LiBF_(4),which has the lowest degree of dissociation,can construct an anion-rich inner solvation shell,resulting in anion-derived anode/cathode interphases.Thanks to such unusual solvation structure and interphasial chemistry,the Li-LiCoO_(2)full cell with LiBF_(4)-based WSE could deliver excellent rate performance(115 mAh g^(-1)at 10 C)and outstanding cycling stability even under practical conditions,including high loading(10.7 mg cm^(-2)),thin Li(50μm),and limited electrolyte(1.2μL mg^(-1)).

Non-solvating fluorosulfonyl carboxylate enables temperature-tolerant lithium metal batteries

Advanced electrolyte engineering is an important strategy for developing high-efficacy lithium(Li)metal batteries(LMBs).Unfortunately,the current electrolytes limit the scope for creating batteries that perform well over temperature ranges.Here,we present a new electrolyte design that uses fluorosulfonyl carboxylate as a non-solvating solvent to form difluoroxalate borate(DFOB-)anion-rich solvation sheath,to realize high-performance working of temperature-tolerant LMBs.With this optimized electrolyte,favorable SEI and CEI chemistries on Li metal anode and nickel-rich cathode are achieved,respectively,leading to fast Li^(+)transfer kinetics,dendrite-free Li deposition and suppressed electrolyte deterioration.Therefore,Li||LiNi_(0.80)Co_(0.15)Al_(0.05)O_(2)batteries with a thin Li foil(50μm)show a long-term cycling lifespan over 400 cycles at 1C and a superior capacity retention of 90%after 200 cycles at 0.5C under 25℃.Moreover,this electrolyte extends the operating temperature from-10 to 30℃and significantly improve the capacity retention and Coulombic efficiency of batteries are improved at high temperature(60℃).Fluorosulfonyl carboxylates thus have considerable potential for use in high-performance and allweather LMBs,which broadens the new exploring of electrolyte design.

Designing weakly and strongly solvating polymer electrolytes:Systematically boosting high-voltage lithium metal batteries

Practical high-voltage lithium metal batteries hold promise for high energy density applications,but face stability challenges in electrolytes for both 4 V-class cathodes and lithium anode.To address this,we delve into the positive impacts of two crucial moieties in electrolyte chemistry:fluorine atom(-F)and cyano group(-CN)on the electrochemical performance of polyether electrolytes and lithium metal batteries.Cyano-bearing polyether electrolytes possess strong solvation,accelerating Li^(+)desolvation with minimal SEI impact.Fluorinated polyether electrolytes possess weak solvation,and stabilize the lithium anode via preferential decomposition of F-segment,exhibiting nearly 6000-h stable cycling of lithium symmetric cell.Furthermore,the electron-withdrawing prop-erties of-F and-CN groups significantly bolster the high-voltage tolerance of copolymer electrolyte,extending its operational range up to 5 V.This advance-ment enables the development of 4 V-class lithium metal batteries compatible with various cathodes,including 4.45 V LiCoO_(2),4.5 V LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2),and 4.2 V LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2).These findings provide insights into design prin-ciples centered around polymer components for high-performance polymer electrolytes.

Regulating the electrolyte solvation structure by weakening the solvating power of solvents for stable lithium metal batteries

Rational electrolyte design is essential for stabilizing high-energy-density lithium(Li)metal batteries but is plagued by poor understanding on the effect of electrolyte component properties on solvation structure and interfacial chemistry.Herein,regulating the solvation structure in localized high-concentration electrolytes(LHCE)by weakening the solvating power of solvents is proposed for high-performance LHCE.1,3-dimethoxypropane(DMP)solvent has relatively weak solvating power but maintains the high solubility of Li salts,thus impelling the formation of nanometric aggregates where an anion coordinates to more than two Li-ions(referred to AGG-n)in LHCE.The decomposition of AGG-n increases the Li F content in solid electrolyte interphase(SEI),further enabling uniform Li deposition.The cycle life of Li metal batteries with DMP-based LHCE is 2.1 times(386 cycles)as that of advanced ether-based LHCE under demanding conditions.Furthermore,a Li metal pouch cell of 462Wh kg^(-1)undergoes 58 cycles with the DMP-based LHCE pioneeringly.This work inspires ingenious solvating power regulation to design high-performance electrolytes for practical Li metal batteries.

Weakly-solvating electrolytes enable ultralow-temperature (-80°C) and high-power CF_(x)/Li primary batteries

Fluorinated carbons(CF_(x))/Li primary batteries with high theoretical energy density have been applied as indispensable energy storage devices with no need for rechargeability,yet plagued by poor rate capability and narrow temperature adaptability in actual scenarios.Herein,benefiting from precise solvation engineering for synergistic coordination of anions and low-affinity solvents,the optimized cyclic ether-based electrolyte is elaborated to significantly facilitate overall reaction dynamics closely correlated to lower desolvation barrier.As a result,the excellent rate(15 C,650 mAh g^(-1))at room-temperature and ultra-lowtemperature performance dropping to-80°C(495 mAh g^(-1)at average output voltage of 2.11 V)is delivered by the end of 1.5 V cut-off voltage,far superior to other organic liquid electrolytes.Furthermore,the CF_(x)/Li cell employing the high-loading electrode(18-22 mg cm^(-2))still yields 1,683 and 1,395 Wh kg^(-1)in the case of-40°C and-60°C,respectively.In short,the novel design strategy for cyclic ethers as basic solvents is proposed to enable the CF_(x)/Li battery with superb subzero performances,which shows great potential in practical application for extreme environments.

Towards practical lean-electrolyte Li-S batteries:Highly solvating electrolytes or sparingly solvating electrolytes?

Lithium-sulfur(Li-S)batteries hold great promise to be the next-generation candidate for high-energy-density secondary batteries but in the prerequisite of using low electrolyte-to-sulfur(E/S)ratios.Highly solvating electrolytes(HSEs)and sparingly solvating electrolytes(SSEs),with opposite nature towards the dissolution of polysulfides,have recently emerged as two effective solutions to decrease the E/S ratio and increase the overall practical energy density of Li-S batteries.HSEs featuring with high polysulfide solvation ability have the potential to reduce the E/S ratio by dissolving more polysulfides with less electrolyte,while SSEs alter the sulfur reaction pathway from a dissolution-precipitation mechanism to a quasi-solid mechanism,thereby independent on the use of electrolyte amount.Both HSEs and SSEs show respective effectiveness in lean-electrolyte Li-S batteries,but encounter different challenges to bring Li-S batteries into practical application.This review aims to present a comparative discussion on their unique features and basic electrochemical reaction mechanisms in practical lean-electrolyte Li-S batteries.Emphasis is focused on the current technical challenges and possible solutions for their future development.

Dilute Aqueous-Aprotic Electrolyte Towards Robust Zn-Ion Hybrid Supercapacitor with High Operation Voltage and Long Lifespan

With the merits of the high energy density of batteries and power density of supercapacitors,the aqueous Zn-ion hybrid supercapacitors emerge as a promising candidate for applications where both rapid energy delivery and moderate energy storage are required.However,the narrow electrochemical window of aqueous electrolytes induces severe side reactions on the Zn metal anode and shortens its lifespan.It also limits the operation voltage and energy density of the Zn-ion hybrid supercapacitors.Using'water in salt'electrolytes can effectively broaden their electrochemical windows,but this is at the expense of high cost,low ionic conductivity,and narrow temperature compatibility,compromising the electrochemical performance of the Zn-ion hybrid supercapacitors.Thus,designing a new electrolyte to balance these factors towards high-performance Zn-ion hybrid supercapacitors is urgent and necessary.We developed a dilute water/acetonitrile electrolyte(0.5 m Zn(CF_(3)SO_(3))_(2)+1 m LiTFSI-H_(2)O/AN)for Zn-ion hybrid supercapacitors,which simultaneously exhibited expanded electrochemical window,decent ionic conductivity,and broad temperature compatibility.In this electrolyte,the hydration shells and hydrogen bonds are significantly modulated by the acetonitrile and TFSI-anions.As a result,a Zn-ion hybrid supercapacitor with such an electrolyte demonstrates a high operating voltage up to 2.2 V and long lifespan beyond 120,000 cycles.

Amphipathic Phenylalanine-Induced Nucleophilic-Hydrophobic Interface Toward Highly Reversible Zn Anode

Aqueous Zn^(2+)-ion batteries(AZIBs),recognized for their high security,reliability,and cost efficiency,have garnered considerable attention.However,the prevalent issues of dendrite growth and parasitic reactions at the Zn electrode interface significantly impede their practical application.In this study,we introduced a ubiquitous biomolecule of phenylalanine(Phe)into the electrolyte as a multifunctional additive to improve the reversibility of the Zn anode.Leveraging its exceptional nucleophilic characteristics,Phe molecules tend to coordinate with Zn^(2+)ions for optimizing the solvation environment.Simultaneously,the distinctive lipophilicity of aromatic amino acids empowers Phe with a higher adsorption energy,enabling the construction of a multifunctional protective interphase.The hydrophobic benzene ring ligands act as cleaners for repelling H_(2)O molecules,while the hydrophilic hydroxyl and carboxyl groups attract Zn^(2+)ions for homogenizing Zn^(2+)flux.Moreover,the preferential reduction of Phe molecules prior to H_(2)O facilitates the in situ formation of an organic-inorganic hybrid solid electrolyte interphase,enhancing the interfacial stability of the Zn anode.Consequently,Zn||Zn cells display improved reversibility,achieving an extended cycle life of 5250 h.Additionally,Zn||LMO full cells exhibit enhanced cyclability of retaining 77.3%capacity after 300 cycles,demonstrating substantial potential in advancing the commercialization of AZIBs.

Solvating power regulation enabled low concentration electrolyte for lithium batteries

Li^(+) solvation structures have a decisive influence on the electrode/electrolyte interfacial properties and battery performances.Reduced salt concentration may result in an organic rich solid electrolyte interface(SEI)and catastrophic cycle stability,which makes low concentration electrolytes(LCEs)rather challenging.Solvents with low solvating power bring in new chances to LCEs due to the weak salt-solvent interactions.Herein,an LCE with only 0.25 mol L^(-1) salt is prepared with fluoroethylene carbonate(FEC)and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether(D_(2)).Molecular dynamics simulations and experiments prove that the low solvating power solvent FEC not only renders reduced desolvation energy to Li^(+) and improves the battery kinetics,but also promotes the formation of a LiF-rich SEI that hinders the electrolyte consumption.Li||Cu cell using the LCE shows a high coulombic efficiency of 99.20%,and LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)||Li cell also exhibits satisfying capacity retention of 89.93%in 200 cycles,which demonstrates the great potential of solvating power regulation in LCEs development.

Coordination structure regulation in non-flammable electrolyte enabling high voltage lithium electrochemistry

High-voltage battery systems bring significant increases in energy density but are also accompanied by fast degradation of electrochemical performance and serious safety issues.Herein,Li^(+)coordination structure regulation was conducted to formulate a non-flammable electrolyte,which consists of 1.5 M lithium bis(fluor sulfonyl)imide(LiFSI)in triethyl phosphate and methyl 2,2,2-trifluoromethyl carbonate(FEMC).The renamed TEP-FEMC-FEC(TFF)electrolyte exhibits an FSI^(−)-dominated solvation structure contributed by the weakly-solvating ability of FEMC.The generated inorganic-rich interfacial layers are conducive to stabilizing the phase transition of high-voltage cathodes while suppressing the dendritic growth on lithium metal or co-intercalation behavior in graphite anode.This TFF electrolyte enables LiCoO_(2)||Li batteries to achieve capacity maintenance over 79%after 400 cycles with high-rate of 5 C at an ultra-high voltage of 4.6 V,and an outstanding capacity exceeding 100 mA h g^(−1)even at a super-high current density of 20 C.Additionally,the Ah-level LiCoO_(2)||graphite pouch cells also exhibit high capacity retention and satisfactory safety performance even under fast charging.This work provides a novel research direction for the pursuit of high energy density non-flammable electrolytes.

Solvation Engineering via Fluorosurfactant Additive Toward Boosted Lithium-Ion Thermoelectrochemical Cells

Lithium-ion thermoelectrochemical cell(LTEC), featuring simultaneous energy conversion and storage, has emerged as promising candidate for low-grade heat harvesting. However, relatively poor thermosensitivity and heat-to-current behavior limit the application of LTECs using LiPF_6 electrolyte. Introducing additives into bulk electrolyte is a reasonable strategy to solve such problem by modifying the solvation structure of electrolyte ions. In this work, we develop a dual-salt electrolyte with fluorosurfactant(FS) additive to achieve high thermopower and durability of LTECs during the conversion of low-grade heat into electricity. The addition of FS induces a unique Li~+ solvation with the aggregated double anions through a crowded electrolyte environment,resulting in an enhanced mobility kinetics of Li~+ as well as boosted thermoelectrochemical performances. By coupling optimized electrolyte with graphite electrode, a high thermopower of 13.8 mV K^(-1) and a normalized output power density of 3.99 mW m^(–2) K^(–2) as well as an outstanding output energy density of 607.96 J m^(-2) can be obtained.These results demonstrate that the optimization of electrolyte by regulating solvation structure will inject new vitality into the construction of thermoelectrochemical devices with attractive properties.

Branch-Chain-Rich Diisopropyl Ether with Steric Hindrance Facilitates Stable Cycling of Lithium Batteries at-20℃

Li metal batteries(LMBs)offer signifi-cant potential as high energy density alternatives;nev-ertheless,their performance is hindered by the slow desolvation process of electrolytes,particularly at low temperatures(LT),leading to low coulombic efficiency and limited cycle stability.Thus,it is essential to opti-mize the solvation structure thereby achieving a rapid desolvation process in LMBs at LT.Herein,we introduce branch chain-rich diisopropyl ether(DIPE)into a 2.5 M Li bis(fluorosulfonyl)imide dipropyl ether(DPE)elec-trolyte as a co-solvent for high-performance LMBs at-20℃.The incorporation of DIPE not only enhances the disorder within the electrolyte,but also induces a steric hindrance effect form DIPE’s branch chain,excluding other solvent molecules from Li+solvation sheath.Both of these factors contribute to the weak interactions between Li^(+)and solvent molecules,effectively reducing the desolvation energy of the electrolyte.Consequently,Li(50μm)||LFP(mass loading~10 mg cm^(-2))cells in DPE/DIPE based electrolyte demonstrate stable performance over 650 cycles at-20℃,delivering 87.2 mAh g^(-1),and over 255 cycles at 25℃ with 124.8 mAh g^(-1).DIPE broadens the electrolyte design from molecular structure considera-tions,offering a promising avenue for highly stable LMBs at LT.

Solvation strategies in various electrolytes for advanced zinc metal anode

Aqueous zinc-ion batteries(AZIBs),known for their high safety,low cost,and environmental friendliness,have a wide range of potential applications in large-scale energy storage systems.However,the notorious dendrite growth and severe side reactions on the anode have significantly hindered their further practical development.Recent studies have shown that the solvation chemistry in the electrolyte is not only closely related to the barriers to the commercialization of AZIBs,but have also sparked a number of valuable ideas to address the challenges of AZIBs.Therefore,we systematically summarize and discuss the regulatory mechanisms of solvation chemistry in various types of electrolytes and the influence of the solvation environment on battery performance.The challenges and future directions for solvation strategies based on the electrolyte environment are proposed to improve their performance and expand their application in AZIBs.

Non-flammable long chain phosphate ester based electrolyte via competitive solventized structures for high-performance lithium metal batteries

Safety remains a persistent challenge for high-energy-density lithium metal batteries(LMBs).The development of safe and non-flammable electrolytes is especially important in harsh conditions such as high temperatures.Herein,a flame-retardant,low-cost and thermally stable long chain phosphate ester based(tributyl phosphate,TBP)electrolyte is reported,which can effectively enhance the cycling stability of highly loaded high-nickel LMBs with high safety through co-solvation strategy.The interfacial compatibility between TBP and electrode is effectively improved using a short-chain ether(glycol dimethyl ether,DME),and a specially competitive solvation structure is further constructed using lithium borate difluorooxalate(LiDFOB)to form the stable and inorganic-rich electrode interphases.Benefiting from the presence of the cathode electrolyte interphase(CEI)and solid electrolyte interphase(SEI)enriched with LiF and Li_(x)PO_(y)F_(z),the electrolyte demonstrates excellent cycling stability assembled using a 50μm lithium foil anode in combination with a high loading NMC811(15.4 mg cm^(-2))cathode,with 88%capacity retention after 120 cycles.Furthermore,the electrolyte exhibits excellent high-temperature characteristics when used in a 1-Ah pouch cell(N/P=0.26),and higher thermal runaway temperature(238℃)in the ARC(accelerating rate calorimeter)demonstrating high safety.This novel electrolyte adopts long-chain phosphate as the main solvent for the first time,and would provide a new idea for the development of extremely high safety and high-temperature electrolytes.

Reversible aqueous aluminum metal batteries enabled by a water-in-salt electrolyte

Aluminum(Al),the most abundant metallic element on the earth crust,has been reckoned as a promising battery material for its the highest theoretical volume capacity(8046 mAh cm^(-3)).Being rechargeable in ionic liquid electrolytes,however,the Al anode and battery case suffer from corrosion.On the other hand,Al is irreversible in aqueous electrolyte with severe hydrogen evolution reaction.Here,we demonstrate a water-in-salt aluminum ion electrolyte(WISE)based on Al and lithium salts to tackle the above challenges.In the WISE system,water molecules can be confined within the Li^(+)solvation structures.This diminished Al^(3+)-H_(2)O interaction essentially eliminates the hydrolysis effect,effectively protecting Al anode from corrosion.Therefore,long-term Al plating/stripping can be realized.Furthermore,two types of high-performance full batteries have been demonstrated using copper hexacyanoferrate(CuHCF,a Prussian Blue Analogues)and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM)as cathodes.The reversibility of Al anode laid the foundation for low cost rechargeable batteries suffering for large-scale energy storage.Broader context:Al batteries are expected to become a safe and sustainable alternative to lithium batteries.For decades,chase for a feasible Al secondary battery has not been successful.The key challenge is to find suitable cathode and electrolyte materials,together with which Al anode battery can function reversibly.Currently,fatal drawbacks have impeded the practical application of Al metal batteries(AMBs),such as sustained corrosion of Al anode and battery case in ionic liquid electrolytes,irreversibility issues as well as severe hydrogen evolution reaction during cycling in aqueous electrolyte.Therefore,electrolyte and their electrochemical kinetics play a vital role in the performance and environmental operating limitations of high-energy Al metal batteries.In this work,we demonstrate a nearly neutral Al ion water-in-salt electrolyte(WISE)to tackle the above challenges.The WISE shows excellent stability in the open atmosphere.The distinct solvation-sheath structure of Al^(3+)in the WISE system would protect Al metal anodes from corrosion and eliminate hydrogen evolution reaction effectively,further promoting the reversibility of Al metal anodes with dendrite-free morphology.Moreover,such a WISE exhibits superior compatibility with LiNi_(0.3)Co_(0.3)Mn_(0.3)O_(2)(NCM)and copper hexacyanoferrate(CuHCF)cathodes and long-term stabilities with high coulombic efficiency(CE)can be attained for full batteries with the WISE.The approach in this study can furnish an opportunity to develop reversible AMBs and lay the foundation for other potential multivalent-metalbased secondary batteries suffering from interface passivation and poor reversibility,which suggest the promise of multivalent metal batteries and their applications in large-scale energy storage.

Critical Solvation Structures Arrested Active Molecules for Reversible Zn Electrochemistry

Aqueous Zn-ion batteries(AZIBs)have attracted increasing attention in next-generation energy storage systems due to their high safety and economic.Unfortunately,the side reactions,dendrites and hydrogen evolution effects at the zinc anode interface in aqueous electrolytes seriously hinder the application of aqueous zinc-ion batteries.Here,we report a critical solvation strategy to achieve reversible zinc electrochemistry by introducing a small polar molecule acetonitrile to form a“catcher”to arrest active molecules(bound water molecules).The stable solvation structure of[Zn(H_(2)O)_(6)]^(2+)is capable of maintaining and completely inhibiting free water molecules.When[Zn(H_(2)O)_(6)]^(2+)is partially desolvated in the Helmholtz outer layer,the separated active molecules will be arrested by the“catcher”formed by the strong hydrogen bond N-H bond,ensuring the stable desolvation of Zn^(2+).The Zn||Zn symmetric battery can stably cycle for 2250 h at 1 mAh cm^(-2),Zn||V_(6)O_(13) full battery achieved a capacity retention rate of 99.2%after 10,000 cycles at 10 A g^(-1).This paper proposes a novel critical solvation strategy that paves the route for the construction of high-performance AZIBs.

Regulating zinc ion transport behavior and solvated structure towards stable aqueous Zn metal batteries

Aqueous Zn metal batteries(AZMBs)with intrinsic safety,high energy density and low cost have been regarded as promising electrochemical energy storage devices.However,the parasitic reaction on metallic Zn anode and the incompatibility between electrode and electrolytes lead to the deterioration of electrochemical performance of AZMBs during the cycling.The critical point to achieve the stable cycling of AZMBs is to properly regulate the zinc ion solvated structure and transfer behavior between metallic Zn anode and electrolyte.In recent years,numerous achievements have been made to resolve the formation of Zn dendrite and interface incompatible issues faced by AZMBs via optimizing the sheath structure and transport capability of zinc ions at electrode-electrolyte interface.In this review,the challenges for metallic Zn anode and electrode-electrolyte interface in AZMBs including dendrite formation and interface characteristics are presented.Following the influences of different strategies involving designing advanced electrode structu re,artificial solid electrolyte interphase(SEI)on Zn anode and electrolyte engineering to regulate zinc ion solvated sheath structure and transport behavior are summarized and discussed.Finally,the perspectives for the future development of design strategies for dendrite-free Zn metal anode and long lifespan AZMBs are also given.

Long‐life lithium batteries enabled by a pseudo‐oversaturated electrolyte

The specific energy of Li metal batteries(LMBs)can be improved by using high‐voltage cathode materials;however,achieving long‐term stable cycling performance in the corresponding system is particularly challenging for the liquid electrolyte.Herein,a novel pseudo‐oversaturated electrolyte(POSE)is prepared by introducing 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether(TTE)to adjust the coordination structure between diglyme(G2)and lithium bis(trifluoromethanesulfonyl)imide(LiTFSI).Surprisingly,although TTE shows little solubility to LiTFSI,the molar ratio between LiTFSI and G2 in the POSE can be increased to 1:1,which is much higher than that of the saturation state,1:2.8.Simulation and experimental results prove that TTE promotes closer contact of the G2 molecular with Li^(+)in the POSE.Moreover,it also participates in the formation of electrolyte/electrode interphases.The electrolyte shows outstanding compatibility with both the Li metal anode and typical high‐voltage cathodes.Li||Li symmetric cells show a long life of more than 2000 h at 1 mA cm^(−2),1 mAh cm^(−2).In the meantime,Li||LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)cell with the POSE shows a high reversible capacity of 134.8 mAh g^(−1 )after 900 cycles at 4.5 V,1 C rate.The concept of POSE can provide new insight into the Li^(+)solvation structure and in the design of advanced electrolytes for LMBs.

Tailoring Electrode–Electrolyte Interface Using an Electron-Deficient Borate-Based Additive in MgTFSI_(2)-MgCl_(2)/DME Electrolyte for Rechargeable Magnesium Batteries

Rechargeable magnesium metal batteries need an electrolyte that forms a stable and ionically conductive solid electrolyte interphase(SEI)on the anodes.Here,we used molecular dynamic simulation,density functional theory calculation,and X-ray photoelectron spectroscopy analysis to investigate the solvation structures and SEI compositions in electrolytes consisting of dual-salts,magnesium bis(trifluoromethanesulfonyl)imide(MgTFSI_(2)),and MgCl_(2),with different additives in 1,2-dimethoxyethane(DME)solvent.We found that the formed[Mg_(3)(μ-Cl)_(4)(DME)mTFSI_(2)](m=3,5)inner-shell solvation clusters in MgTFSI_(2)-MgCl_(2)/DME electrolyte could easily decompose and form a MgO-and MgF_(2)-rich SEI.Such electron-rich inorganic species in the SEI,especially MgF_(2),turned out to be detrimental for Mg plating/stripping.To reduce the MgF_(2)and MgO contents in SEI,we introduce an electron-deficient tri(2,2,2-trifluoroethyl)borate(TFEB)additive in the electrolyte.Mg//Mg cells using the MgTFSI_(2)-MgCl_(2)/DME-TFEB electrolyte could cycle stably for over 400 h with a small polarization voltage of~150 mV.Even with the presence of 800 ppm H_(2)O,the electrolyte with TFEB additive could still preserve its good electrochemical performance.The optimized electrolyte also enabled stable cycling and high-rate capability for Mg//Mo6S8 and Mg//CuS full cells,showing great potential for future applications.