Polyether Solid Electrolyte/Electrodes Interfacial Regulation And Electrochemical Behavior

Solid-state lithium batteries using solid electrolytes have attracted great attentionowing to their high safety and increased energy density,and are considered the most promising next generation energy storage systems.Among types of solid electrolytes,polyether electrolytes represented by polyethylene oxide（PEO）have the advantages of light weight,low cost,excellent processability and are considered to the most promising method for industry producing.However,the narrow electrochemical window and high interfacial impedance of polyether solid electrolyte and electrode materials still restrict the performance of solid-state batteries.In order to realize lithium-ion batteries with high safety,high energy density and sustainable development,the interface mechanism and regulation strategy between polyether electrolytes and electrodes were studied.This paper includes three parts:1)PEO based solid electrolyte was modified by triphenyl phosphite（TPPi）in high voltage cathode system to achieve interface stability.2)Perfluoropolyether alcohol was used to modify the interface of low potential lithium negative and applied in solid-state lithium-sulfur batteries.3)Low interfacial impedance of polyether solid electrolyte was realized in organic anthraquinone electrode system though in-situ polymerization.The specific research contents are as follows:1.In order to broaden the electrochemical window of PEO-based solid electrolyte to match with high voltage lithium nickel cobalt manganate(Li Ni_0.8Co_0.1Mn_0.1O₂,NCM),the evolution of the interfacial structure and failure mechanism of PEO-based solid electrolytes and NCM were investigated.It was shown that the high-valent Ni⁴⁺has strong oxidation to the electrolyte under high voltage,leading to the interfacial instability and electrolyte deterioration.To improve the interface stability of the NCM and PEO based electrolyte,TPPi was added in the PEO-based solid electrolyte as a chelating agent to directionally chelate Ni⁴⁺to enhance the cycling stability of PEO-based polymer electrolyte in the NCM battery.Theoretical calculations revealed that TPPi with high HOMO energy level preferentially oxidizes over PEO during charging,which forms a phosphate-rich cathode electrolyte interface film on NCM interface.The stable cathode electrolyte interface film prevented further oxidation of the PEO-based electrolyte.In addition,the solid electrolyte with TPPi reduced the Li-Ni mixing in the NCM electrode and enhanced the structural stability.The Li|T-SPE|NCM battery still has a capacity of111.5 m Ah g^–1 at 0.1 m A cm^–2 for 200 cycles at 45°C,and the coulombic efficiency is still as high as 99.6%.2.Lithium metal has been considered as promising negative material with the low redox potential of-3.04 V（vs.SHE）and ultrahigh theoretical capacity of 3862 m Ah g^-1.However,Li metal negative electrode has been suffering from interfacial side reactions,dendritic problems,volume change and low Coulombic efficiency.In this paper,fluoride-rich perfluoropolyether alcohol（PFA）was used as an interface modifier to improve interface stability in PEO-based solid lithium metal batteries.PFA-modified lithium negative electrode was further applied in solid-state lithium-sulfur batteries.Experiments and density functional theory calculations revealed the different mechanisms of the two polyethers in solid-state lithium-sulfur batteries.In PEO-based solid-state lithium-sulfur battery,lithium polysulfides（Li PSs）were tend to couple with PEO rather than self-aggregated,which caused the penetration of Li PSs into PEO-based electrolyte and the consequent“shuttle effect”.The“coupling”between electrolyte and Li PSs also reduced the reduction stability of PEO at the lithium interface.The fluoride-rich PFA,which decoupled from Li PSs because of the shielding effect of F in PFA on the electron cloud of O and the spatial effect.The PFA-modifed lithium can inhibit the consumption of Li PSs on the lithium interface and prevented the reduction of PEO-based solid electrolyte,thus improving the stability of lithium interface.The results showed that the fading mechanism of PEO-based solid-state lithium-sulfur battery lied in the coupling of SPEs with Li PSs and emphasized the significance of SPE decoupling from Li PSs on solid-state lithium-sulfur battery.This work provided offered guidance for the design of high performance solid-state lithium-sulfur battery.3.Polyether-based solid electrolytes suffer from poor interfacial contact and low interfacial ion flux with general inorganic electrode materials.Organic electrode materials,on the other hand,are highly designable and are promising to enhance the interfacial affinity with polyether electrolytes in terms of structure and functional group design.Compared to inorganic electrode materials,organic electrode materials are highly designable in structure and easy to tune the functional groups,which means that the combination of organic electrode materials with SPEs has greater possibilities in designing high performance batteries.An integrated organic active material aminoanthraquinone-solid polymer electrolyte（AQ-SPE）configuration was prepared based on in-situ polymerisation and used in solid-state battery.The in-situ growth strategy allows the solid electrolyte to be covalently connected to organic electrode material aminoanthraquinone through the naphthacrylate bond.This type of connection is completely different from the physical contact between electrode and SPE and reduces the activation energy of charge transfer process.The problem of dissolution of aminoanthraquinone in liquid electrolytes had also been solved.The amidoanthraquinone electrode material based on the integrated AQ-SPE exhibited excellent cycling performance.In addition,the pouch battery assembled with the integrated AQ-SPE also showed an excellent safety performance even under harsh conditions such as cutting and punching.The integrated electrode/SPE configuration provides a new and scalable design idea for an efficient,safe and environmentally friendly battery.