Preparation And Performance Of SiO₂-embedded All-solid Cross-linked Polymer Electrolytes

Liquid electrolytes（LEs）with highly volatile and flammable carbonates as solvents severely deteriorate the safety of lithium metal batteries.In addition,poor stability of electrolyte/electrode interface caused by severe parasitic reactions between carbonate solvent and lithium metal anode accelerates the uneven deposition of lithium ions,leading to short charge/discharge cycle life of the battery.Due to excellent safety and high energy density,all-solid polymer electrolytes（ASPEs）have shown great potential in the next generation of lithium metal batteries（LMBs）as an alternative to traditional liquid electrolytes,avoiding serious safety issues such as leakage and flammability.However,the inherent problems with all-solid polymer electrolytes,such as low ionic conductivity of conventional PEO and the agglomeration of inorganic nanoparticles in composite polymer electrolytes leading to poor electrolyte/electrode interfacial stability,which inhibit the development of ASPEs.In view of the above problems,this paper focuses on ether oxygen based and polycarbonate based polymer solid electrolytes.Based on the composite idea of organic polymer and inorganic ceramic,functional inorganic fillers are used to uniformly dispersed in polymer electrolyte matrix in the way of chemical bond,thus improving the ion conductivity,electrochemical window and ion migration number of CPEs.By introducing polycarbonate groups and utilizing the synergistic effect between carbonate and polyethoxy groups,the ion conductivity of polymer electrolytes and battery cycling performance are further improved.Details of the study are as follows.Firstly,a new organic/inorganic composite ASPEs（called SGPP-ASPE）is synthesised by ring-opening and polymerisation reaction between3-glycidoxypropyltrimethoxysilane grafted silica nanoparticles（Si O₂-γ-GPS）,polyethylene glycol diglycidyl ether（PEGDE）and the amino/epoxy groups in polyetheramines（PEA）.The presence of Si O₂particles inhibit the crystallisation of polymer matrix,while the formation of Si-O-Si chains allows SGPP-ASPE exhibit good flexibility,facilitating the rapid migration of lithium ions.In contrast to simple physical mixing,the covalent bonds formed between the monomer and the grafted silica nanoparticles are expected to build a three-dimensional cross-linked matrix,in which the silica particles acting as cross-linking points and can be homogeneously and firmly immobilised,maintaining the structural stability of SGPP during charging and discharging.As a result,a high ionic conductivity of2.4×10^-4can be obtained and the assembled Li Fe PO₄/Li（LFP/Li）cells show good cycling stability with a capacity retention of 93.8%after 100 cycles at 0.2C.Secondly,organic/inorganic composite polymer electrolytes coexisting with polycarbonate and polyether groups are designed and synthesised,polycarbonate groups are introduced utilizing the esterification reaction between diethyl oxalate and amino groups.Ultimately,the synergistic effect of polycarbonate and polyether groups enhances the ion conductivity of polymer electrolytes.Diethyl oxalate grafted with 3-glycidoxypropyltrimethoxysilane nanosilica（Si O₂-γ-GPS）and polyetheramines（PEA）are added to construct a three-dimensional cross-linked composite polymer electrolyte.The SGPD-ASPE electrolyte possesses a high ionic conductivity of 3.8×10^-4.The assembled LFP/Li cell achieves a high discharge specific capacity of 167.7 m Ah/g at 60°C and 0.1 C,then an excellent cycling performance with a capacity retention of over 90%is obtained after long-term cycling.The application of the composite polymer electrolyte with synergistic carbonate group and polyether group can effectively enhance the ionic conductivity of polymer electrolyte,which provides a new idea for the design of solid-state electrolyte.