Influencing Factors on Li‐ion Conductivity and Interfacial Stability of Solid Polymer Electrolytes, Exampled by Polycarbonates, Polyoxalates and Polymalonates

Abstract

The application of solid polymer electrolytes (SPEs) in all‐solid‐state(ASS) batteries is hindered by lower Li+‐conductivity and narrower electrochemical window. Here, three families of ester‐based F‐modified SPEs of poly‐carbonate (PCE), poly‐oxalate (POE) and poly‐malonate (PME) were investigated. The Li+‐conductivity of these SPEs prepared from pentanediol are all higher than the counterparts made of butanediol, owing to the enhanced asymmetry and flexibility. Because of stronger chelating coordination with Li+, the Li+‐conductivity of PME and POE is around 10 and 5 times of PCE. The trifluoroacetyl‐units are observed more effective than −O−CH2−CF2−CF2−CH2−O− during the in situ passivation of Li‐metal. Using trifluoroacetyl terminated POE and PCE as SPE, the interfaces with Li‐metal and high‐voltage‐cathode are stabilized simultaneously, endowing stable cycling of ASS Li/LiNi0.6Co0.2Mn0.2O2 (NCM622) cells. Owing to an enol isomerization of malonate, the cycling stability of Li/PME/NCM622 is deteriorated, which is recovered with the introduce of dimethyl‐group in malonate and the suppression of enol isomerization. The coordinating capability with Li+, molecular asymmetry and existing modes of elemental F, are all critical for the molecular design of SPEs.

Gel polymer electrolytes for rechargeable batteries toward wide-temperature applications

“…For achieving stable and reversible redox reactions in batteries, a desirable electrolyte must have a sufficient electrochemical stability window against electroreduction and electrooxidation over a wide range of operating temperatures and working voltages without causing detrimental side reactions. 97–99 The electrochemical stability window is typically defined as the gap between the HOMO and LUMO of the electrolyte. However, recent research suggests that the widening of electrochemical stability window requires the consideration of chemical/electrochemical interfacial compatibility beyond just the HOMO and LUMO of electrolyte components.…”

The Fluorine Toolbox: from Molecular Design to Advanced Batteries

“…As shown in FIG. 2b, a series of fluorinated polymer electrolytes have been reported to improve the electrochemical stability window, such as trifluoroacetylterminated polycarbonate, polyoxalate and polymalonate (>4.4 V) 32 , PFEC (>5.5 V) 22 ) 23 . This further leads to an overall improvement in ionic conductivity.…”

Preparation of Main-Chain Fluorinated Alternating Polymer by START Polymerization for All-Solid-State Electrolytes

“…7−9 SPEs own many advantages such as good interface contact, high electrochemical stability, excellent processability, and low cost due to which SPEs have garnered widespread research attention. 10 Among all of the polymer electrolytes studied, poly(ethylene oxide) (PEO) was the most used due to its excellent solvation effect toward Li + and electrode interface compatibility. 11−15 However, it generally exhibited poor oxidative and thermal stability, limited Li + transference number (t Li + ) due to its high crystallinity, and low conductivity at room temperature.…”