Unraveling the incompatibility mechanism of ethylene carbonate-based electrolytes in sodium metal anodes

Ethylene carbonate(EC)is widely used in lithium-ion batteries due to its optimal overall performance with satisfactory conductivity,relatively stable solid electrolyte interphase(SEI),and wide electrochemical window.EC is also the most widely used electrolyte solvent in sodium ion batteries.However,compared to lithium metal,sodium metal(Na)shows higher activity and reacts violently with EC-based electrolyte(NaPF_(6)as solute),which leads to the failure of sodium metal batteries(SMBs).Herein,we reveal the electrochemical instability mechanism of EC on sodium metal battery,and find that the com-bination of EC and NaPF_(6) is electrically reduced in sodium metal anode during charging,resulting in the reduction of the first coulombic efficiency,and the continuous consumption of electrolyte leads to the cell failure.To address the above issues,an additive modified linear carbonate-based electrolyte is provided as a substitute for EC based electrolytes.Specifically,ethyl methyl carbonate(EMC)and dimethyl carbon-ate(DMC)as solvents and fluoroethylene carbonate(FEC)as SEI-forming additive have been identified as the optimal solvent for NaFP_(6)based electrolyte and used in Na_(4)Fe_(3)(PO_(4))_(2)(P_(2)O_(7))/Na batteries.The batter-ies exhibit excellent capacity retention rate of about 80%over 1000 cycles at a cut-off voltage of 4.3 V.

Novel sandwich structured glass fiber Cloth/Poly(ethylene oxide)-MXene composite electrolyte

Recently,poly(ethylene oxide)(PEO)-based solid polymer electrolytes have been attracting great attention,and efforts are currently underway to develop PEO-based composite electrolytes for next generation high performance all-solid-state lithium metal batteries.In this article,a novel sandwich structured solid-state PEO composite electrolyte is developed for high performance all-solid-state lithium metal batteries.The PEO-based composite electrolyte is fabricated by hot-pressing PEO,LiTFSI and Ti_(3)C_(2)T_(x) MXene nanosheets into glass fiber cloth(GFC).The as-prepared GFC@PEO-MXene electrolyte shows high mechanical properties,good electrochemical stability,and high lithium-ion migration number,which indicates an obvious synergistic effect from the microscale GFC and the nanoscale MXene.Such as,the GFC@PEO-1 wt%MXene electrolyte shows a high tensile strength of 43.43 MPa and an impressive Young's modulus of 496 MPa,which are increased by 1205%and 6048%over those of PEO.Meanwhile,the ionic conductivity of GFC@PEO-1 wt%MXene at 60℃ reaches 5.01×10^(-2) S m^(-1),which is increased by around 200%compared with that of GFC@PEO electrolyte.In addition,the Li/Li symmetric battery based on GFC@PEO-1 wt%MXene electrolyte shows an excellent cycling stability over 800 h(0.3 mA cm^(-2),0.3 mAh cm^(-2)),which is obviously longer than that based on PEO and GFC@PEO electrolytes due to the better compatibility of GFC@PEO-1 wt%MXene electrolyte with Li anode.Furthermore,the solid-state Li/LiFePO_(4) battery with GFC@PEO-1 wt%MXene as electrolyte demonstrates a high capacity of 110.2–166.1 mAh g^(-1) in a wide temperature range of 25–60C,and an excellent capacity retention rate.The developed sandwich structured GFC@PEO-1 wt%MXene electrolyte with the excellent overall performance is promising for next generation high performance all-solid-state lithium metal batteries.

Enhanced Electrochemical Performance of Poly(ethylene oxide)Composite Polymer Electrolyte via Incorporating Lithiated Covalent Organic Framework

The lithiated covalent organic framework(named TpPa-SO_(3) Li),which was prepared by a mild chemical lithiation strategy,was introduced in poly(ethylene oxide)(PEO)to produce the composite polymer electrolytes(CPEs).Li-ion can transfer along the PEO chain or across the layer of TpPa-SO_(3) Li within the nanochannels,resulting in a high Li-ion conductivity of3.01×10^(-4)S/cm at 60℃.When the CPE with 0.75 wt.%TpPa-SO_(3) Li was used in the LiFePO_(4)‖Li solid-state battery,the cell delivered a stable capacity of 125 mA·h/g after 250 cycles at 0.5 C,60℃.In comparison,the cell using the CPE without TpPa-SO_(3) Li exhibited a capacity of only 118 mA·h/g.

Ag-modified hydrogen titanate nanowire arrays for stable lithium metal anode in a carbonate-based electrolyte

In the investigation of the next-generation battery anode,Li metal has attracted increasing attention owing to its ultrahigh specific capacity and low reduction potential.However,its low columbic efficiency,limited cycling life,and serious safety hazards have hindered the practical application of rechargeable Li metal batteries.Although several strategies have been proposed to enhance the electrochemical performance of Li metal anodes,most are centered around ether-based electrolytes,which are volatile and do not provide a sufficiently large voltage window.Therefore,we aimed to attain stable Li deposition/stripping in a commercial carbonate-based electrolyte.Herein,we have successfully synthesized hydrogen titanate(HTO)nanowire arrays decorated with homogenous Ag nanoparticles(NPs)(Ag@HTO)via simple hydrothermal and silver mirror reactions.The 3 D cross-linked array structure with Ag NPs provides preferable nucleation sites for uniform Li deposition,and most importantly,when assembled with the commercial LiNi_(0.5)Co0.2Mn_(0.3)O_(2) cathode material,the Ag@HTO could maintain a capacity retention ratio of 81.2% at 1 C after 200 cycles,however the pristine Ti foil failed to do so after only 60 cycles.Our research therefore reveals a new way of designing current collectors paired with commercial high voltage cathodes that can create high energy density Li metal batteries.

Laminar Composite Solid Electrolyte with Poly(Ethylene Oxide)-Threaded Metal-Organic Framework Nanosheets for High-Performance All-Solid-State Lithium Battery

Developing laminar composite solid electrolyte with ultrathin thickness and continuous conduction channels in vertical direction holds great promise for all-solid-state lithium batteries.Herein,a thin,laminar solid electrolyte is synthesized by filtrating–NH 2 functionalized metal-organic framework nanosheets and then being threaded with poly(ethylene oxide)chains induced by the hydrogen-bonding interaction from–NH_(2) groups.It is demonstrated that the threaded poly(ethylene oxide)chains lock the adjacent metal-organic framework nanosheets,giving highly enhanced structural stability(Young’s modulus,1.3 GPa)to 7.5-μm-thick laminar composite solid electrolyte.Importantly,these poly(ethylene oxide)chains with stretching structure serve as continuous conduction pathways along the chains in pores.It makes the non-conduction laminar metal-organic framework electrolyte highly conductive:3.97×10^(−5) S cm^(−1) at 25℃,which is even over 25 times higher than that of pure poly(ethylene oxide)electrolyte.The assembled lithium cell,thus,acquires superior cycling stability,initial discharge capacity(148 mAh g^(−1) at 0.5 C and 60℃),and retention(94% after 150 cycles).Besides,the pore size of nanosheet is tailored(24.5–40.9˚A)to evaluate the mechanisms of chain conformation and ion transport in confined space.It shows that the confined pore only with proper size could facilitate the stretching of poly(ethylene oxide)chains,and meanwhile inhibit their disorder degree.Specifically,the pore size of 33.8˚A shows optimized confinement effect with trans-poly(ethylene oxide)and cis-poly(ethylene oxide)conformation,which offers great significance in ion conduction.Our design of poly(ethylene oxide)-threaded architecture provides a platform and paves a way to the rational design of next-generation high-performance porous electrolytes.

ETHYLENE OXIDE-ETHYLENE TEREPHTHALATE SEGMENTED COPOLYMER SOLID ELECTROLYTE

A series of ethylene oxide-ethylene terephthalate segmented copolymers (EOET) weresynthesized and complexed with LiClO_4 to form some new polymer electrolytes. The EOET-LiClO_4 electrolytes exhibit not only high ionic conductivity, but also good mechanical strengthand toughness. The EOET 3400--25--LiClO_4 complex possesses the highest conductivity (4. 65×10^(-5)s·cm^(-1) at room temperature when the ratio [Li^+]/[EO] equals 1/16. The structures of these electrolytes were examined with FTIR analysis, X-ray diffractionand DSC thermograms, and the results of high ionic conductivity of the segmented copolymerswere discussed.

Thermotolerant and fireproof gel polymer electrolyte toward high-performance and safe lithium-ion battery

Poly(ethylene oxide)(PEO)and its derivatives based gel polymer electrolytes(GPEs)are severely limited in advanced and safe lithium-ion batteries(LIBs)owing to the intrinsically high flammability of liquid electrolytes and PEO.Directly adding flame retardants to the GPEs can suppress their flammability and thus improve the safety of LIBs,but results in deteriorative electrochemical performance.Herein,a novel GPE with chemically bonded flame retardant(i.e.diethyl vinylphosphonate)in cross-linked polyethylene glycol diacrylate matrix,featuring both high-safety and high-performance,is designed.This as-prepared GPE storing the commercial 1 mol L^(-1) LiPF6 electrolyte resists high temperature of 200℃and cannot be ignited as well as possesses a high ionic conductivity(0.60 m S cm^(-1))and good compatibility with lithium.Notably,the LiFePO_(4)/Li battery with this GPE delivers a satisfactory capacity of 142.2 m A h g^(-1) and a superior cycling performance with a capacity retention of 96.3%and a coulombic efficiency of close to 100%for 350 cycles at 0.2 C under ambient temperature.Furthermore,the battery can achieve steady charge–discharge for 100 cycles with a coulombic efficiency of 99.5%at 1 C under 80℃and run normally even at a high temperature of 150℃or under the exposure to butane flame.Differential scanning calorimetry manifests significantly improved battery safety compared to commercial battery systems.This work provides a new pathway for developing next-generation advanced LIBs with enhanced performance and high safety.

High-Performance Quasi-Solid-State Pouch Cells Enabled by in situ Solidification of a Novel Polymer Electrolyte

Conventional lithium-ion batteries(LIBs)with liquid electrolytes are challenged by their big safety concerns,particularly used in electric vehicles.All-solid-state batteries using solid-state electrolytes have been proposed to significantly improve safety yet are impeded by poor interfacial solid–solid contact and fast interface degradation.As a compromising strategy,in situ solidification has been proposed in recent years to fabricate quasi-solid-state batteries,which have great advantages in constructing intimate interfaces and cost-effective mass manufacturing.In this work,quasi-solid-state pouch cells with high loading electrodes(≥3 m Ah cm^(-2))were fabricated via in situ solidification of poly(ethylene glycol)diacrylate-based polymer electrolytes(PEGDA-PEs).Both single-layer and multilayer quasi-solid-state pouch cells(2.0 Ah)have demonstrated stable electrochemical performance over500 cycles.The superb electrochemical stability is closely related to the formation of robust and compatible interphase,which successfully inhibits interfacial side reactions and prevents interfacial structural degradation.This work demonstrates that in situ solidification is a facile and cost-effective approach to fabricate quasi-solid-state pouch cells with both excellent electrochemical performance and safety.

Structural regulation chemistry of lithium-ion solvation in nonflammable phosphate-based electrolytes for high interfacial compatibility with graphite anode

With the booming development of lithium-ion batteries,safety has become one of the most primary focuses of current researches.Although there are various approaches to enhance the safety of lithiumion batteries,phosphate-based electrolyte holds the greatest potential for practical application due to their non-flammability.Nonetheless,its compatibility issue with the graphite anode remains a significant obstacle to its widespread use.Herein,an effective method is proposed to improve the compatibility of electrolyte with graphite(Gr)anode by rationally adjusting the proportion of lithium salt and solvent components to optimize the Li^(+)solvation structure.By slightly increasing the Li^(+)/triethyl phosphate(TEP)ratio,TEP alone cannot fully occupy the inner solvation sheath and therefore less polar ethylene carbonate(EC)has to be recruited,and the solvation structure gradually changes from Li^(+)–[TEP]_(4)to Li^(+)–[TEP]_(3)[EC]with the coexistence of EC and TEP.Simultaneously,EC molecules in the Li^(+)–[TEP]_(3)[EC]could be preferentially reduced on graphite compared to the TEP molecules,resulting in the formation of a uniform and durable solid-electrolyte interphase(SEI)layer.Benefiting from the optimized phosphate-based electrolyte,the Gr|Li battery exhibits a capacity retention rate of 96.8%after stable cycling at 0.5 C for 470 cycles which shows a longer cycle life than the battery with carbonate electrolyte(cycling at 0.5 C for 450 cycles).Therefore,this work provides the guidance for designing a non-flammable phosphate-based electrolyte for high-safety and long cycling-life lithium-ion batteries.

Synthesis and Ionic Conductivity of Network Polymer Electrolytes with Internal Plasticizers

Network polymer electrolytes with free oligo(oxyethylene) chains as internal plasticizers were prepared by cross-linking poly(ethylene glycol) acrylates. The effects of salt concentration and properties of internal plasticizers on ionic conductivity were studied.

One dimensional CeO_(2) nanorods/poly(ethylene oxide) solid composite electrolyte for all-solid-state lithium-ion batteries

The research of poly(ethylene oxide)(PEO)-based solid composite electrolyte with high ionic conductivity and excellent interfacial stability is the key to the development of all-solid-state lithium-ion batteries(ASSLIBs). Herein, uniform nanorod structured CeO_(2) fillers were controllably synthesized by electrospinning, which were subsequently filled into PEO polymer to prepare CeO_(2)/PEO solid composite electrolyte. The addition of CeO_(2) nanorods can reduce both the glass transition temperature and the melting point of PEO polymer, and also interact with PEO and lithium bis(trifluoromethanesulphonyl)imide(LITFSI) by Lewis acid—base reaction. Therefore, the solid composite electrolyte exhibits a high ionic conductivity of 4.52 × 10^(-4)S/cm, a wide electrochemical stability window of about 4.8 V, and a good interfacial stability with Li at 55℃. Moreover, the LiFePO_4/Li ASSLIB divulges the discharging specific capacity of 165, 162, 156 and 146 mA,h/g at 0.2, 0.5, 1 and 2 C, respectively, and achieves the capacity retention of 90.3% after 150 cycles at 0.5 C. Consequently, one dimensional CeO_(2) nanorods can be considered as an alternative filler for polymeric solid electrolyte.

Metal Salt and Non-Electrolyte Separation by Means of Dialysis through the Composite Membranes

To separate salts of metals and non-electrolytes, the approach of dialysis through the composite membranes (CMs) is proposed. CM is a combination of cation and anion exchange areas. In the composite membrane, cations and anions are transferred through the respective exchange areas simultaneously without violation of macroscopic electro-neutrality. This provides a better transfer of salts than conventional ion exchange membranes (IEMs). The dialysis of the ethylene glycol aqueous salt solutions through the CMs was investigated. We have shown that the transport of salts through the composite membranes is more intensive (unlike IEM providing no transfer of salts from weakly mineralized aqueous solutions due to the Donnan exclusion) and the ethylene glycol transfer is not very significant, that is the basis of effective separation. The possibility to use of composite membranes for metal salt and other electrolyte separation is discussed.

IONIC CONDUCTIVITY IN CROSSLINKED POLY (METHYLSILOXANE-g-ETHYLENE OXIDE) NETWORK FILMS CONTAINING LITHIUM PERCHLORATE

Polymer electrolytes based on poly (methylsiloxane-g-ethylene oxide) and LiClO_4 have been prepared. The network films crosslinked by a crosslinking agent are found to exhibit a considerably high ionic conductivity of about 10^(-4) Scm^(-1) at room temperature and have good flexibility.

Poly(ethylene carbonate)-based electrolytes with high concentration Li salt for all-solid-state lithium batteries

High-performance solid polymer electrolyte （SPE） has long been desired for the next-generation high energy density and safe rechargeable lithium batteries. A SPE composed of 80 wt% lithium bis（trifluo-romethanesulfonyl）imide （LiTFSI）, 20% poly（ethylene carbonate） （PEC） and a polyamide （PA） fiber membrane backbone was prepared by solution-casting method. This solid electrolyte exhibits quite high ionic conductivity and lithium ion transference number （t＋）, and excellent mechanical strength. The as-prepared solid electrolyte shows good wettability to porous electrodes during cycles, which is beneficial to form ionically conductive phase throughout porous electrodes. All-solid-state LiFePO4lLi cells assembled with the as-prepared solid electrolyte deliver a high initial discharge specific capacity of 125.7 mAh·g^-1 and good cycling stability at 55 ℃ （93.4% retention at 1C after 200 cycles）, and superior cycle performance. Outstanding electrochemical performance can be mainly ascribed to the improved ionic conductivity in the entire porous electrodes due to the good wettability of SPE.

Additives to propylene carbonate-based electrolytes for lithium-ion capacitors

Nowadays,lithium-ion capacitors(LICs) have become a type of important electrochemical energy storage devices due to their high power and long cycle life characteristics with fast response time.As one of the essential components of LICs,the electrolytes not only provide the anions and cations required during charge and discharge processes,but also supply the liquid environment for ions to migrate between anodes and cathodes in LIC cells.It is well accepted that propylene carbonate(PC) cannot be used as a single solvent for Li-ion electrolyte due to the failure to form stable SEI film on graphite surface.In this work,the compatibility of PC-based electrolyte with commercial soft carbon anode and activated carbon cathode has been validated by using the laminated pouch LIC cells.The effects of additives on the electrochemical properties of PC-based LICs have been systematically investigated.Ethylene sulfite(ES) was proved to be an effective additive to promote capacity retention at high C-rate,which is superior to vinylene carbonate and fluoroethylene carbonate.The addition of 5 wt% ES plays an important role in reducing internal resistance,as well as improving electrochemical stability and low-temperature performances.This study is expected to be beneficial to explore robust electrolyte/additive combinations for LICs to reduce the internal resistance and to improve the lowtemperature performances.

Ethylene sulfite based electrolyte for non-aqueous lithium oxygen batteries

Non-aqueous lithium-oxygen （Li-O2） batteries have been considered as the superior energy storage system due to their high-energy density, however, some challenges limit the practical application of Li- O2 batteries. One of them is the lack of stable electrolyte. In this communication, a novel electrolyte with ethylene sulfite （ES） used as solvent for Li-O2 batteries was reported. ES solvent showed low volatility and high electrochemical stability. Without a catalyst in the air-electrode of Li-O2 batteries, the batteries showed high specific capacity, good round-trip efficiency and cycling stability.

Novel fast lithium-ion conductor LiTa_(2)PO_(8)enhances the performance of poly(ethylene oxide)-based polymer electrolytes in all-solid-state lithium metal batteries

At present,replacing the liquid electrolyte in a lithium metal battery with a solid electrolyte is considered to be one of the most powerful strategies to avoid potential safety hazards.Composite solid electrolytes(CPEs)have excellent ionic conductivity and flexibility owing to the combination of functional inorganic materials and polymer solid electrolytes(SPEs).Nevertheless,the ionic conductivity of CPEs is still lower than those of commercial liquid electrolytes,so the development of high-performance CPEs has important practical significance.Herein,a novel fast lithium-ion conductor material LiTa_(2)PO_(8) was first filled into poly(ethylene oxide)(PEO)-based SPE,and the optimal ionic conductivity was achieved by filling different concentrations(the ionic conductivity is 4.61×10^(-4)S/cm with a filling content of 15 wt%at 60℃).The enhancement in ionic conductivity is due to the improvement of PEO chain movement and the promotion of LiTFSI dissociation by LiTa_(2)PO_(8).In addition,LiTa_(2)PO_(8) also takes the key in enhancing the mechanical strength and thermal stability of CPEs.The assembled LiFePO_(4) solid-state lithium metal battery displays better rate performance(the specific capacities are as high as 157.3,152,142.6,105 and 53.1 mAh/g under0.1,0.2,0.5,1 and 2 C at 60℃,respectively)and higher cycle performance(the capacity retention rate is86.5%after 200 cycles at 0.5 C and 60℃).This research demonstrates the feasibility of LiTa_(2)PO_(8) as a filler to improve the performance of CPEs,which may provide a fresh platform for developing more advanced solid-state electrolytes.

Block Copolymer Solid Electrolytes Based on Comb-Like Poly(ethylene glycol)Plasticized Poly(ionic liquid)s for Lithium-Ion Batteries

Electrolytes based on poly(ionic liquid)s(PILs)have attracted great attention in the fields of next-generation solid lithium-ion batteries.However,the low ionic conductivity prevents their practical applications.Herein,we report novel solid electrolytes based on block copolymers composed of PILs and comb-like poly(ethylene glycol)(PEG),which were synthesized via ring-opening metathesis polymerization of 3-(2-(bicyclo[2.2.1]hept-5-en-2-yl)ethyl)-1-butyl-1H-imidazol-3-ium bis((trifluoromethyl)sulfonyl)amide and poly(ethylene glycol monomethyl ether)bicyclo[2.2.1]hept-5-ene-2-carboxylate.Comb-like PEG acts as plasticizers in block copolymers dominated by PILs to promote the mobility of PILs segments.Effects of the copolymer composition and length of the comb-like PEG chain on ionic conductivity were investigated.The optimized electrolyte delivers the highest ionic conductivity of 1.5×10^(–5)S·cm^(–1)at 30℃,and robust electrochemical stability up to 4.6 V.A solid-state Li/LiFePO4 cell using the optimized electrolyte demonstrates good cycle performance at 0.2 C with high capacity retention of 92%after 70 cycles at 50℃.

碳酸亚乙烯酯合成研究进展

碳酸亚乙烯酯(VC)作为一种重要的锂电池电解液添加剂,可以改善电池的高低温性能、降低电池的内阻、改善电池的循环性能等,其合成工艺一直是众多学者关注的焦点。本文着重对VC的合成路线和合成工艺进行综述,包括传统的两步法合成路线,即碳酸乙烯酯(EC)经过氯取代反应生成氯代碳酸乙烯酯(CEC),再经脱氯反应得到VC,以及由EC直接一步脱氢法合成VC的路线。同时,对目前VC的合成工艺进行了归纳总结,分类讨论了不同方法的特点,并对未来的发展趋势进行了展望。传统的两步法路线尽管存在环境和安全问题,但仍然是目前工业化合成VC的主要方法,而一步法合成路线仍需要对催化剂的开发、反应过程和机理等进行深入研究。

杂多酸离子液体催化剂的制备及其合成可降解聚酯PES的催化性能

为了分析杂多酸离子液体催化剂的催化性能,以Fe为中心杂原子、Mo为配位原子,制备了杂多酸阴离子,并将其与1-羟丙基-3-甲基咪唑溴盐通过离子交换反应制备功能化杂多酸离子液体催化剂([HO-(CH_(2))_(2)-mim]_(5)[Ti(H_(2)O)FeMo_(11)O_(39)])。利用FT-IR、UV、XRD和TGA对所制催化剂进行结构表征与性能测试,通过正交试验优化工艺参数,探讨投料比、催化剂用量、酯交换反应温度和时间对其催化性能的影响。结果表明:所制催化剂结构正确,热性能良好,并具有较好催化效果。最佳工艺条件为:投料比2,催化剂质量分数1.0%,反应温度220℃,反应时间5 h,该条件下PES收率为75.32%。