Rational Design of F-Modified Polyester Electrolytes for Sustainable All-Solid-State Lithium Metal Batteries

Abstract

Solid polymer electrolytes (SPEs) are one of the most practical candidates for solid-state batteries owing to their high flexibility and low production cost, but their application is limited by low Li + conductivity and a narrow electrochemical window. To improve performance, it is necessary to reveal the structure−property relationship of SPEs. Here, 23 fluorinated linear polyesters were prepared by editing the coordination units, flexible linkage segments, and interface passivating groups. Besides the traditionally demonstrated coordinating capability and flexibility of polymer chains, the molecular asymmetry and resulting interchain aggregation are observed critical for Li + conductivity. By tailoring the molecular asymmetry and coordination ability of polyesters, the Li + conductivity can be raised by 10 times. Among these polyesters, solvent-free poly(pentanediol adipate) delivers the highest room-temperature Li + conductivity of 0.59 × 10 −4 S cm −1 . The chelating coordination of oxalate and Li + leads to an electron delocalization of alkoxy oxygen, enhancing the antioxidation capability of SPEs. To lower the cost, high-value LiTFSI in SPEs is recycled at 90%, and polyesters can be regenerated at 86%. This work elucidates the structure−property relationship of polyester-based SPEs, displays the design principles of SPEs, and provides a way for the development of sustainable solid-state batteries.

Effect of LiTFSI Solvation on Ionic Conductivity of Polyester-Based Solid Electrolytes

“…Considering the effect of the folding chain on the coordination mode of – CO and Li + , we simulated the folding configuration of four repeat units, especially for four consecutive carbonyl oxygens in HSH and SHS coordinated with and without Li + , and the HOMO–LUMO energies in Figures c and d. Compared with the coordination energy of Li + –(HS) 4 corresponding to multichain bindings, the single-chain bindings of HSH and SHS with Li + show close and lower energy, proving the less stable coordination states due to the disordered sequence of active groups. , The difference in coordination energy between single-chain and multichain bindings was responsible for the backwardness of T g , as higher coordination interaction had more restriction on the segment motion. Interestingly, the Li + –HSH coordination state shows a lower HOMO energy, indicating better antioxidation of ester groups.…”

“…After cycling for 124 h, short circuits occur, probably due to the decomposition of PHS and inhomogeneous passivation of LiF layer on Li surface as shown in Figures S17 and S18. It has been proved that the reduction of ester groups by Li led to the decomposition of polymer chains and resulted in the appearance of the RCOOLi FTIR absorption peak in Figure S19 . To improve the SPE compatibility with high-voltage cathodes and low-voltage Li metal anodes, the end groups of polyesters are required to be modified for higher interfacial stability. , …”

“…The number of calculated repeat units has a negligible effect on the coordination energy, especially compared with the effect of coordination numbers on the coordination energy. We use one repeat unit (HS) to simulate the binding energy of different coordination numbers. , The coordination energy and the HOMO–LUMO energies of Li ions and carbonyl oxygen at different coordination numbers (Li + –(HS) n , n = 1–4) were simulated by DFT simulation in Figure a,b. The deepest free-energy minimum elucidates the Li + –(HS) 4 has a relatively higher stability in four coordination states .…”

Environmental Aspects and Recycling of Solid-State Batteries: A Comprehensive Review

“…Different new investigations are developed to optimize recycling processes, minimizing the environmental problems that these processes may cause. The use of solid polymer electrolytes (SPEs) are promising for SSBs due to their flexibility and low cost, but face challenges like low Li + conductivity and a narrow electrochemical window [153]. Xie et al [153] studied 23 fluorinated linear polyesters with varied coordination units and flexible linkage segments.…”

“…The use of solid polymer electrolytes (SPEs) are promising for SSBs due to their flexibility and low cost, but face challenges like low Li + conductivity and a narrow electrochemical window [153]. Xie et al [153] studied 23 fluorinated linear polyesters with varied coordination units and flexible linkage segments. They found a molecular asymmetry crucial for Li + conductivity enhancement, with tailored polyesters exhibiting a 10-fold increase in conductivity.…”