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.

Structure characterization and electrochemical properties of new lithium salt LiODFB for electrolyte of lithium ion batteries

Lithium difluoro(axalato)borate (LiODFB) was synthesized in dimethyl carbonate (DMC) solvent and purified by the method of solventing-out crystallization. The structure characterization of the purified LiODFB was performed by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance (NMR) spectrometry. The electrochemical properties of the cells using 1 mol/L LiPF6 and 1 mol/L LiODFB in ethylene carbonate (EC)/DMC were investigated, respectively. The results indicate that LiODFB can be reduced at about 1.5 V and form a robust protective solid electrolyte interface (SEI) film on the graphite surface in the first cycle. The graphite/LiNi1/3Mn1/3Co1/3O2 cells with LiODFB-based electrolyte have very good capacity retention at 55 ℃, and show very good rate capability at 0.5C and 1C charge/discharge rate. Therefore, as a new salt, LiODFB is a most promising alternative lithium salt to replace LiPF6 for lithium ion battery electrolytes in the future.

A new review of single-ion conducting polymer electrolytes in the light of ion transport mechanisms

With the depletion of fossil fuels and the demand for high-performance energy storage devices,solidstate lithium metal batteries have received widespread attention due to their high energy density and safety advantages.Among them,the earliest developed organic solid-state polymer electrolyte has a promising future due to its advantages such as good mechanical flexibility,but its poor ion transport performance dramatically limits its performance improvement.Therefore,single-ion conducting polymer electrolytes(SICPEs)with high lithium-ion transport number,capable of improving the concentration polarization and inhibiting the growth of lithium dendrites,have been proposed,which provide a new direction for the further development of high-performance organic polymer electrolytes.In view of this,lithium ions transport mechanisms and design principles in SICPEs are summarized and discussed in this paper.The modification principles currently used can be categorized into the following three types:enhancement of lithium salt anion-polymer interactions,weakening of lithium salt anion-cation interactions,and modulation of lithium ion-polymer interactions.In addition,the advances in single-ion conductors of conventional and novel polymer electrolytes are summarized,and several typical highperformance single-ion conductors are enumerated and analyzed in what way they improve ionic conductivity,lithium ions mobility,and the ability to inhibit lithium dendrites.Finally,the advantages and design methodology of SICPEs are summarized again and the future directions are outlined.

Improving ionic conductivity of polymer-based solid electrolytes for lithium metal batteries

Because of its superior safety and excellent processability,solid polymer electrolytes(SPEs)have attracted widespread attention.In lithium based batteries,SPEs have great prospects in replacing leaky and flammable liquid electrolytes.However,the low ionic conductivity of SPEs cannot meet the requirements of high energy density systems,which is also an important obstacle to its practical application.In this respect,escalating charge carriers(i.e.Li^(+))and Li^(+)transport paths are two major aspects of improving the ionic conductivity of SPEs.This article reviews recent advances from the two perspectives,and the underlying mechanism of these proposed strategies is discussed,including increasing the Li^(+)number and optimizing the Li^(+)transport paths through increasing the types and shortening the distance of Li^(+)transport path.It is hoped that this article can enlighten profound thinking and open up new ways to improve the ionic conductivity of SPEs.

Semi-interpenetrating-network all-solid-state polymer electrolyte with liquid crystal constructing efficient ion transport channels for flexible solid lithium-metal batteries

The development of the solid-state polymer electrolytes (SPEs) for Li-ion batteries (LIBs) can effectively address the hidden safety issues of commercially used liquid electrolytes.Nevertheless,the unsatisfactory room temperature ion conductivity and inferior mechanical strength for linear PEO-based SPEs are still the immense obstacles impeding the further applications of SPEs for large-scale commercialization.Herein,we fabricate a series of semi-interpenetrating-network (semi-IPN) polymer electrolytes based on a novel liquid crystal (C6M LC) and poly(ethylene glycol) diglycidyl ether (PEGDE) via UV-irradiation at the first time.The LCs not only highly improve the mechanical properties of electrolyte membranes via the construction of network structure with PEGDE,but also create stable ion transport channels for ion conduction.As a result,a free-standing flexible SPE shows outstanding ionic conductivity(5.93×10^(-5) S cm^(-1) at 30℃),a very wide electrochemical stability window of 5.5 V,and excellent thermal stability at thermal decomposition temperatures above 360℃ as well as the capacity of suppressing lithium dendrite growth.Moreover,the LiFePO_(4)/Li battery assembled with the semi-IPN electrolyte membranes exhibits good cycle performance and admirable reversible specific capacity.This work highlights the obvious advantages of LCs applied to the electrolyte for the advanced solid lithium battery.

Rational design on separators and liquid electrolytes for safer lithium-ion batteries

As the energy density of lithium-ion batteries (LIBs) continues to increase,their safety has become a great concern for further practical large-scale applications.One of the ultimate solution of the safety issue is to develop intrinsically safe battery components,where the battery separators and liquid electrolytes are critical for the battery thermal runaway process.In this review,we summarize recent progress in the rational materials design on battery separators and liquid electrolyte towards the goal of improving the safety of LIBs.Also,some strategies for further improving safety of LIBs are also briefly outlooked.

Thermal stability of LiPF_6/EC+DMC+EMC electrolyte for lithium ion batteries

The thermal stability of lithium-ion battery electrolyte could substantially affect the safety of lithium-ion battery. In order to disclose the thermal stability of 1.0 mol·L-1 LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC)+ethylmethyl carbonate (EMC) electrolyte, a micro calorimeter C80 micro calorimeter was used in this paper. The electrolyte samples were heated in argon atmosphere, and the heat flow and pressure performances were detected. It is found that LiPF6 influences the thermal behavior remarkably, with more heat generation and lower onset temperature. LiPF6/EC shows an exothermic peak at 212 ℃ with a heat of reaction -355.4 J·g-1. DMC based LiPF6 solution shows two endothermic peak temperatures at 68.5 and 187 ℃ in argon filled vessel at elevated temperature. EMC based LiPF6 solution shows two endothermic peak temperatures at 191 and 258 ℃ in argon filled vessel. 1.0 mol·L-1 LiPF6/EC+DMC+ EMC electrolyte shows an endothermic and exothermic process one after the other at elevated temperature. By comparing with the thermal behavior of single solvent based LiPF6 solution, it can be speculated that LiPF6 may react with EC, DMC and EMC separately in 1.0 mol·L-1 LiPF6/EC+DMC+EMC electrolyte, but the exothermic peak is lower than that of 1.0 mol·L-1 LiPF6/EC solution. Furthermore, The 1.0 mol·L-1 LiPF6/EC+DMC+EMC electrolyte decomposition reaction order was calculated based on the pressure data, its value is n=1.83, and the pressure rate constants kp=6.49×10-2 kPa·-0.83·min-1.

Review:Natural Polymer Electrolytes for Lithium Ion Batteries

Polymer electrolytes are attractive materials towards achieving safe,flexible and high-performance energy storage devices( ESDs) such as lithium ion batteries( LIBs). Conventional polymer electrolytes are confronted with big challenges to achieve high ionic conductivity,good mechanical properties,excellent biocompatibility and environmental friendliness. In this context,natural polymeric materials have appealing merits of multi-functionality,ease of accessibility,good mechanical strength,etc. making them promising candidates to substitute conventional polymer electrolytes. Recently,the rational design and fabrication of advanced natural bio-based polymer electrolytes have made important progresses. In this review, we summarize recent developments in terms of polymer electrolytes using natural polymers for several application purposes. This review also involves the merits and demerits of the different natural polymers that have been investigated thus far. The insights on state-of-the-art for natural polymer electrolytes and possible solutions for further improvement of them are discussed as well in this review.

Syntheses and Application of All-lithium Salts of Heteropolyacid as Electrolyte of Lithium-ion Battery

The all-lithium salts of heteropoly acid Li_xXM_ 12O_ 40(HPA-Li)(X=P, Si; M=Mo, W) were obtained via ion exchange and characterized by means of IR and UV spectroscopies, TG and elemental analyses. The conductivity of the electrolytic solution consisting of Li_3PW_ 12O_ 40 and PC/DME mixing solvent(1/2.5, volume ratio) is up to 7.2×10 -2 S/cm, being higher than that of LiClO_4 as the electrolyte. The all-lithium salts were used as electrolytes in secondary lithium-ion batteries. The discharge capacity of the PAS/Li batteries with Li_3PW_ 12O_ 40 electrolyte solutions reaches to 148 (mA·h)/g and the cyclic life is up to 380 times, much better than those of commercialized products with LiClO_4 and LiAsF_6 as electrolytes.

Non-flammable electrolytes based on trimethyl phosphate solvent for lithium-ion batteries

The properties of trimethyl phosphate（TMP）-based nonflammable electrolytes with LiPF6 as solute were investigated using graphite anode and LiCoO2 cathode. The effect of TMP on non-flammability of electrolytes was also evaluated. It is found that the TMP reduction decomposition on graphite electrode at the potential of 1.3V （vs Li/Li+） is suppressed with ethylene carbonate（EC）, dimethyl carbonate（DMC） and ethylmethyl carbonate（EMC） cosolvents and vinylene carbonate（VC） additives. The results show that the non-flammable electrolyte of 1mol/L LiPF6 61%（EC1.5-DMC1.0-EMC1.0）-39% TMP has good electrochemical properties. The discharge capacities of half-cells after 20 cycles are 254.8mA·h/g for Li/graphite and 144.1mA·h/g for Li/LiCoO2. The （graphite/）（LiCoO2） prismatic lithium-ion cell delivers a discharge capacity of 131mA·h/g at first cycle. With an addition of 4%VC to this non-flammable electrolyte, a discharge capacity of 134mA·h/g at first cycle and a capacity ratio of （84.3%） after 50 cycles are obtained for prismatic lithium-ion batteries. Furthermore, a nail penetration test demonstrates that the safety of prismatic lithium-ion batteries is dramatically improved by using TMP-containing （non-）（flammable） electrolytes.

Lithium-ion transport in inorganic solid state electrolyte

An overview of ion transport in lithium-ion inorganic solid state electrolytes is presented, aimed at exploring and de signing better electrolyte materials. Ionic conductivity is one of the most important indices of the performance of inorganic solid state electrolytes. The general definition of solid state electrolytes is presented in terms of their role in a working cell （to convey ions while isolate electrons）, and the history of solid electrolyte development is briefly summarized. Ways of using the available theoretical models and experimental methods to characterize lithium-ion transport in solid state elec- trolytes are systematically introduced. Then the various factors that affect ionic conductivity are itemized, including mainly structural disorder, composite materials and interface effects between a solid electrolyte and an electrode. Finally, strategies for future material systems, for synthesis and characterization methods, and for theory and calculation are proposed, aiming to help accelerate the design and development of new solid electrolytes.

Recent advances in gel polymer electrolyte for high-performance lithium batteries

Lithium batteries (LBs) have become increasingly important energy storage systems in our daily life. However, their practical applications are still severely plagued by the safety issues from liquid electrolyte, especially when the batteries are exposed to mechanical, thermal, or electrical abuse conditions. Gel polymer electrolytes (GPEs) are being considered as an effective solution to replace currently available organic liquid electrolyte for building safer LBs. This review provides recent advancements in GPEs applied for high-performance LBs. On the one hand, from the environmental and economic point of view, the skeletons of GPEs changed from traditional polymer to renewable and degradable polymer. On the other hand, in addition to being as a component with good electrochemical and physical characterizations, the GPEs also need to provide some functions for addressing the concerns of lithium (Li) dendrites, unstable cathode electrolyte interface, dissolution and migration of transition metal ions,"shuttle effect" of polysulfides, and so on. Finally, to synchronously meet the challenges from the advanced cathode and Li metal anode, the bio-based GPEs with multi-functionality are proposed to develop high-energy/powerdensity batteries in the future.

Exploring high-voltage fluorinated carbonate electrolytes for LiNi0.5Mn1.5O4 cathode in Li-ion batteries

Ethyl-(2,2,2-trifluoroethyl)carbonate(ETFEC)is investigated as a solvent component in high-voltage electrolytes for LiNi0.5Mn1.5O4(LNMO).Our results show that the self-discharge behavior and the high temperature cycle performance can be significantly improved by the addition of 10%ETFEC into the normal carbonate electrolytes,e.g.,the capacity retention improved from 65.3%to 77.1%after 200 cycles at 60℃.The main reason can be ascribed to the high stability of ETFEC which prevents large oxidation of the electrolyte on the cathode surface.In addition,we also explore the feasibility of electrolytes using single fluoriated-solvents with and without additives.Our results show that the cycle performance of LNMO material can be greatly improved in 1 MLiPF6+pure ETFEC-solvent system with 2 wt%ethylene carbonate(EC)or ethylene sulfate(DTD).The capacity retention of the LNMO materials is 93%after 300 cycles,even better than that of carbonate-based electrolytes.It is shown that the additives are oxidized on the surface of LNMO particles and contribute to the formation of cathode/electrolyte interphase(CEI)films.This composite CEI film plays a crucial role in suppressing the serious decomposition of the electrolyte at high voltage.

Electrolyte-dependent formation of solid electrolyte interphase and ion intercalation revealed by in situ surface characterizations

The formation of solid electrolyte interphase(SEI) and ion intercalation are two key processes in rechargeable batteries, which need to be explored under dynamic operating conditions. In this work, both planar and sandwich model lithium batteries consisting of Li metal | ionic liquid electrolyte | graphite electrode have been constructed and investigated by a series of in situ surface analysis platforms including atomic force microscopy, Raman and X-ray photoelectron spectroscopy. It is found that the choice of electrolyte, including the concentration and contents, has a profound effect on the SEI formation and evolution, and the subsequent ion intercalation. A smooth and compact SEI is preferably produced in highconcentration electrolytes, with FSI^(-) salt superior to TFSI^(-) salt, facilitating the lithiation/delithiation to achieve high capacity and excellent cycle stability, while suppressing the co-intercalation of electrolyte solvent ions. The innovative research scenario of well-defined model batteries in combination with multiple genuinely in situ surface analysis methods presented herein leads to insightful results, which provide valuable strategies for the rational design and optimization of practical batteries, and energy storage devices in general.

Challenges in the Development of Film-Forming Additives for Lithium Ion Battery: A Review

Electrolytes additives are ubiquitous and indispensable in all electrochemical devices. In this sense, the principle and the classification of film-forming additives for lithium ion secondary batteries are described. The film formation mechanism and research progress of the pyrazole derivatives, organic halogenide, esters and derivatives, boron compounds and inorganic compounds are introduced. Emphasis is focused on the principles and film-forming mechanisms of each additive. The development of film-forming additives is forecasted and prospected.

Elaboration of Amorphous-Clay Hybrid: (Al₂Si₂O₇·1/2Li₂O) Designed as a Single Ion Conducting Solid Electrolyte for Li-Ion Batteries

Keying of lithium chloride alkali halide salt into the interlamellar space of nacrite clay mineral leads to a stable hybrid material that after calcination under inert atmosphere at 723 - 873 K induces an amorphous metahybrid. The electrochemical impedance spectroscopy (EIS) was performed to investigate the electric/dielectric properties of the hybrid with various parameters: frequency and temperature. Equivalent circuit was proposed to fit the EIS data. The experiment results show that the ionic conduction mechanism is related to the motion of Li+ cations which are thermally activated, named the hopping model. Furthermore, the resulting metahybrid obtained from dehydroxylation of the formal hybrid shows a superionic behavior with high ionic conductivity up to 10﹣2 S·m﹣1, good electrochemical stability and can be used as a solid electrolyte material for Li-ion batteries.

The feasibility for natural graphite to replace artificial graphite in organic electrolyte with different film-forming additives

The feasibility for natural graphite(NG)to replace artificial graphite(AG)in organic electrolytes with different additives are investigated.Although the strong film-forming additives contributes to form robust solid electrolyte interphase(SEI)film on graphite particle surface,great differences in gas evolution,lithium inventory loss and other side reactions are observed.Lithium bis(oxalato)borate(Li BOB)and fluoroethylene carbonate(FEC)are found more effective and the combination shows to be more promising.In the optimized electrolyte,natural graphite anode exhibits excellent long-term cycling capability.After 800 cycles at high temperature,the capacity retention is comparable to that using artificial graphite.The mechanisms for the capacity-fading of the full cells with AG and NG anode are investigated by ICP,SEM and polarization studies.The results shows that NG electrode consumes more active lithium due to the rough surface and larger volume expansion.The rapid capacity-fading in the initial 100 cycles is related to the instability of the SEI film aroused from large volume expansion.The systematic analysis is inspiriting for the development of high performance lithium ion batteries with reduced cost.

PREPARATION AND ELECTROCHEMICAL CHARACTERISTICS OF POLYMER ELECTROLYTE MEMBRANES BASED ON SAN/PVDF-HFP BLENDS

A copolymer of poly（acrylonitrile-co-styrene） （SAN） was synthesized via an emulsion polymerization method. Novel polymer electrolyte membranes cast from the blends of poly（vinylidene fluoride-co-hexafluoropropylene） （PVDF- HFP）, SAN and fumed silica （SIO2） are microporous and can be used in polymer lithium-ion batteries. The membrane shows excellent characteristics such as high ionic conductivity and good mechanical strength when the mass ratio between SAN and PVDF-HFP and SiO2 is 3.5/31.5/5. The ionic conductivity of the membrane soaked in a liquid electrolyte of 1 mol/L LiPF6/EC/DMC/DEC is 4.9 × 10^-3 S cm^-1 at 25℃. The membrane is electrochemical stable up to 5.5 V versus Li^＋/Li in the liquid electrolyte. The influences of SiO2 content on the porosity and mechanical strength of the membranes were studied. Polymer lithium-ion batteries based on the membranes were assembled and their performances were also studied.

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.