Preparation Of Plastic Crystal Composite Polymer Electrolyte And Application In All-Solid-state Lithium-ion Batteries

Traditional commercial lithium-ion batteries are limited by organic liquid electrolytes that are easy to leak and burn,and cannot meet the requirements of high safety and high energy density of next-generation lithium-ion batteries.All-solid polymer electrolytes are widely regarded as the key materials for next-generation lithium-ion batteries due to their many advantages such as non-combustibility,no risk of leakage,and the ability to replace liquid electrolytes and separators to achieve high energy density.However,polymer electrolytes currently have many problems,such as low room-temperature ionic conductivity,high crystalline phase content,and poor mechanical strength,which seriously hinder their practical application.In order to solve the above problems,a three-dimensional cross-linked network structured all-solid polymer electrolyte(SN-SPE)is prepared by UV crosslinking.In this cross-linked structure,the main chain is the crosslinked polyacrylate that provides mechanical strength,and the side chain is ion-conducting oligomeric ethylene oxide.Main chain cross-linking and side-chain ion-conducting design not only effectively solve the problem of linear polyethylene oxide crystallization,but also reduce the impact of cross-linking on chain activity,and increase mechanical strength without sacrificing ion conductivity.In addition,the small molecule succinonitrile is evenly distributed in the cross-linked network,which not only effectively improves the ionic conductivity,but also plays a role of plasticization,and promotes the movement of ion-conducting side chain segments.By adjusting the composition ratio of each monomer and the content of succinonitrile,SN-SPE with room temperature ion conductivity up to 4.56 X 10-4 S cm-1 was successfully prepared,and SN-SPE shows good thermal/electrochemical stability(the thermal decomposition temperature reaches 136?,and the electrochemical stability window reaches 5.1 V vs.Li+/Li).The application of SN-SPE in LiFePO4/SN-SPE/Li all-solid-state half-cells found that due to the poor stability between succinonitrile and lithium metal,the capacity of LiFePO4/SN-SPE/Li all-solid-state half-cell decay rapidly during cycling,and the capacity retention after 50 cycles is only 23.05%.The introduction of 3 wt%LiNO3(based on the SN content)can effectively improve the compatibility between succinonitrile and lithium metal.The modified LiFePO4/LiNO3-SN-SPE/Li solid-state half-cell has an initial discharge specific capacity of 163.34 mAh g'1 at the rate of 0.2 C at 30? and slightly reduce to 145.31 mAh g-1 after 50 cycles.The capacity retention is as high as 88.96%,showing excellent cycle stability.In order to improve the contact between the electrode and electrolyte in the all-solid-state battery,we propose a method of in-situ UV-cured polymer electrolyte on the electrode.The results show that this method can significantly reduce the interfacial resistance between electrode and electrolyte compared with the traditional lamination process(Before cycle,the interface resistance of the cathode-electrolyte integrated LiFePO4/Li4Ti5O12 is only 70?,while the traditional laminated cell is 200 ?),which can promote lithium-ion transfer at the interface and improve battery performance(The capacity retention of the traditional LiFePO4/Li4Ti5O2 cell after 100 cycles is only 68.84%,while the cathode-electrolyte integrated LiFePO4/Li4Ti5O12 cell shows the initial discharge specific capacity of 155.88 mAh g-1 at the rate of 0.2 C at 30? and the capacity retention after 100 cycles is as high as 93.62%).In order to further verify the applicability of the in-situ cross-linking process,the cathode-electrolyte integrated NCM523/Li4Ti5O12 all-solid-state batteries prepared by using a high-voltage ternary LiNi0.5Co0.2Mn0.302 as cathode active material has the initial discharge specific capacity of 147.39 mAh g-1 at the rate of 0.2 C at 30?.After 150 cycles,the capacity retention is as high as 82.67%.In addition,the LiFePO4/SN-SPE/Li4Ti5O12 all-solid-state soft-package cell prepared with SN-SPE electrolyte shows exceptionally excellent safety performance.After undergoing a series of destructive experiments(such as:cutting the soft-package cell in half,bent and naked),and the LED lamp can still running at room temperature.