Investigation On Performance Of PEO-Based Polymer Electrolyte/Lithium Metal Anode

With the development of society,energy storage batteries are becoming more and more important in people's lives and production.However,the current commercial battery energy density has insufficient endurance.The energy density of batteries has become a bottleneck restricting the development of the battery industry.Therefore,there is an urgent need to develop a new high-energy battery system.Lithium metal as an anode material has a theoretical specific capacity as high as3860 m Ah g^-1 and its potential has a super-negative electrode potential of-3.04 V(relative to the standard hydrogen electrode),so lithium metal is an ideal anode material used to construct high energy density batteries.Therefore,lithium metal is an ideal anode material for constructing high-energy density batteries.However,the high activity of lithium causes side reactions with organic electrolytes and dendritic growth of lithium metal.These shortcomings hinder the development of lithium metal batteries.Exploring new battery electrolyte systems and developing efficient lithium negative electrode protection technologies can improve the performance of lithium metal batteries.In this paper,a series of polyethylene oxide(PEO)-based polymer electrolytes were prepared,and their performance in lithium metal batteries was systematically studied.The succinonitrile additives with different contents were prepared in PEO/Li TFSI polymer electrolytes and applied to lithium metal batteries at room temperature.Studies have found that the additive succinonitrile can greatly improve the ionic conductivity of PEO-based polymer electrolytes.When the succinonitrile content is 50%,the room temperature ionic conductivity can reach 10^-3 S cm^-1.However,the addition of a large amount of succinonitrile has a side reaction with the Li anode.In order to ensure that the battery runs well at room temperature,we use Li-Hg alloy anode to protect the Li anode.Experiments show that Li-Hg|PEO-Li TFSI-50%SN|Li-Hg can circulate stably for more than 500 h at 25?and current density of 0.05 m A cm^-2.LFP|PEO-Li TFSI-50%SN|Li-Hg battery can be cycled for more than 200 cycles,and the coulombic efficiency remains above 95%.In order to solve the contact problem between the solid polymer electrolyte and the lithium negative electrode interface,we adopted a gelation strategy.The gel electrolyte is generated in situ by the method of combining commercial Li PF₆liquid electrolyte and PEO-based polymer electrolyte.The in-situ gel polymer electrolyte not only reduces the interface resistance between the electrolyte and the electrode,but also effectively prevents the side reaction products between Li and the carbonate-based electrolyte from shuttle to the cathode electrode.Gel polymer electrolyte adopts double lithium salt system,so the Li⁺migration number is as high as 0.67,which is higher than that of ordinary electrolytes.This also allows it to run well at room temperature.When matched with the commercial high-capacity LFP cathode electrode,the LFP|GPE|Li full battery also showed good performance.Its first lap specific capacity is 152 m Ah g^-1,and its specific capacity is still as high as 110 m Ah g^-1 after 160 cycles.Coulomb efficiency is above 95%.However,the specific capacity of the LFP|Li PF₆|Li full battery decreases severely after 70 cycles,and the specific capacity is only 40 m Ah g^-1 after100 cycles.In order to explore the failure mechanism of the full battery under a high-load cathode electrode,we disassembled the battery and performed related tests.It was found that the cathode electrode of the carbonate-based Li PF₆ battery was severely corroded after cycling,while the cathode electrode of the battery using the gel electrolyte was intact.This also shows that the gel polymer electrolyte can well protect the cathode material and improve the battery performance,providing a new idea for high-performance lithium metal batteries.