| Lithium-ion batteries(LIBs)are widely used in portable electronics,electric vehicles,grid storage,space exploration and national defense due to their high energy density,long cycle life,low self-discharge and high battery cycle-life.However,its low safety and energy density disadvantage are still huge challenges hindering its development and application.As a new generation of lithium-ion battery technology,the application of solid electrolytes in solid-state batteries not only avoids the flammability and leakage of traditional organic electrolytes,but also effectively inhibits the growth of lithium dendrites,making the application of lithium metal anode possible.Therefore,high-voltage solid-state lithium metal batteries are considered to be the next-generation power battery system with both safety and high energy density.However,in the development of high energy density solid-state lithium metal batteries,the solid-solid interface between the high-voltage cathode and the solid electrolyte limits the performance of the battery.Cathode Electrolyte Interphase(CEI)construction technology is currently one of the most promising processes in cathode interface engineering.In the traditional interface buffer layer construction technology,the lamination method is the most common.However,due to the independence of the manufacturing process,the secondary contact during the assembly process will lead to an increase in the interface impedance.The emergence of in-situ polymerization has solved this problem.However,in the existing in-situ polymerization technology that uses light and heat as the initiation conditions,the addition of initiators increases the complexity of the interface components and may lead to side reactions.To solve the above problems,this work proposes an in-situ electrochemical polymerization method to construct a high-voltage resistant buffer layer interface modification technology.This method does not need to use an initiator.The polymerization reaction is initiated inside the battery to realize the in-situ construction of the buffer layer.The main research contents of this work include:1.Based on the solid-state battery positive electrode interface high-nickel ternary positive electrode LiNi0.8Co0.1Mn0.1O2(NCM811)/polyethylene oxide(PEO)based electrolyte/Li was studied by in-situ electrochemical polymerization to build a high voltage durable Polytrifluoroethyl methacrylate-based gel(Gel-PTFEMA)cathode electrolyte interphase.The electrochemical performance of the battery was tested and characterized,and the interface optimization mechanism was initially discussed.The results shown that the introduction of the gel polytrifluoroethyl methacrylate(Gel-PTFEMA)buffer layer is beneficial to reduce the cathode electrode-electrolyte interface impedance and improve the ionic conductivity.The ionic conductivity of the modified Gel-PTFEMA-PEO electrolyte at room temperature can reach 0.65×10-4 S cm-1 at room temperature and 3.91×10-4 S cm-1at 60?.At the same time,Gel-PTFEMA widens the electrochemical window of the PEO-based solid electrolyte to 5.0 V,and improves the cycle stability of the battery under high voltage.The interface-optimized NCM811-Li battery has a discharge capacity of 212.6 m A h g-1 at the first cycle at 60°C and 0.1C.After 50 charge and discharge cycles,the capacity retention rate is 74.0%.2.In order to further reduce the overall battery safety problems,described further by electrochemical bulk polymerization,without the addition of a solvent and an electrolyte,in situ NCM811/PEO/Li cell employing the cathode interface to build a polymethacrylate Fluoroethyl(PTFEMA)all-solid buffer layer.The results show that the bulk polymerization method without solvent participation and electrochemically initiated can also form a continuous high-voltage-durable ion conductive network,which provides an effective transmission channel for lithium ions.The ionic conductivity of the PTFEMA-PEO electrolyte is 1.02×10-4 S cm-1 at room temperature and 4.72×10-4 S cm-1 at 60°C.The electrochemical window is widened to 5.1V.NCM811/PTFEMA-PEO/Li battery has excellent cycle stability under high voltage.The first discharge capacity reached 179.8 m A h g-1 at 0.1C and 60?.After 50 charge-discharge cycles,the capacity retention rate was66.6%.This shows that the construction of the PTFEMA all-solid interface layer effectively improves the stability of the interface between the high-voltage positive electrode and the all-solid PEO electrolyteIn this work,electrochemical solution polymerization and electrochemical bulk polymerization were used to in situ build a high-voltage-resistant polymer interface buffer layer in the NCM811/PEO/Li battery system,which reduces the interface impedance and improves the interface stability under high voltage.This work provides a new design idea for the optimization of the cathode interface in high specific energy solid-state lithium batteries.On the other hand,adding liquid monomers in the battery preparation process to in situ construct the polymer interface layer by electrochemical initiation is a simple and low cost interface modification method.This method of interface construction can be matched with a conventional battery manufacturing processes,having a potential commercial application. |
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