Structure Design,interface Modification And Electrochemical Properties Of Polyacrylate Based Solid Electrolyte

Solid state lithium battery is considered as the most promising development direction of the next generation battery to replace liquid lithium-ion battery because of its high energy density and high safety.However,the low conductivity of solid electrolyte at room temperature,poor contact with electrode interface and weak ability to inhibit the growth of lithium dendrite in lithium negative electrode have restricted the popularization and application of solid-state lithium battery.In view of the problems mentioned above,a polyacrylate based composite solid electrolyte membrane was proposed which is prepared by UV initiated cross-linking polymerization with porous polyethylene membrane（PE）as the framework.According to the characteristics of the electrolyte,the ultra-thin electrolyte,electrode/electrolyte interface integration and gelation design were proposed to improve the interface between electrodes and electrolytes,and increase the battery rate and cycle stability.The main research contents and achievements include:（1）Poly（ether-acrylate）（PEA）electrolyte membrane（EM）with double-layer structure was prepared by UV initiated crosslinking polymerization.The effects of different formulations and processes on the electrochemical properties of the electrolyte membrane were studied.It is found that the surface of PEA electrolyte membrane is porous and the membrane thickness is about 30μm.The tensile strength is 53.7 MPa and the ionic conductivity at room temperature is 1.5×10^-4S/cm,the ion migration number is 0.81,and the electrochemical window is 4.8 V.Because the PEA electrolyte membrane is thick and the surface is porous,the contact with the electrode is poor,and the cycle performance of the battery is not good.The specific capacity retention rate of NCM622/Li battery is 46%after 150 cycles at 0.5 C.The battery is severely polarized and cannot work at 2 C.（2）In view of the problem of large thickness and porous surface of PEA solid electrolyte membrane,which increases the transmission distance of lithium ions and aggravates the uneven deposition of lithium ions,a single-layer ultra-thin PEA solid electrolyte membrane（UT-PEA）was proposed.The study found that:UT-PEA has compact and dense inside,and the surface has no holes.The ultra thin structure improves the interface contact and reduces the interface impedance of the battery.The skeleton provides support for electrolyte shrinkage,prevents the generation of pores,and doubles the tensile strength.The electrolyte membrane with a thickness of only10μm provides a shorter path for ion transport.Although the ionic conductivity is1.11×10^-4S/cm,the ionic conductance was doubled to 218 m S,and the ion mobility number was 0.93.In addition,the UT-PEA electrolyte membrane exhibits better lithium dendrite suppression ability than PEA EM,and the composed NCM622/Li battery has a specific capacity retention rate of 73%at 0.5 C for 150 cycles and a specific capacity of up to 120 m Ah/g Li at 2 C.（3）In view of the problems of the cathode/electrolyte interface contact problem and the shrinkage of the polymer after polymerization,the rough cathode was used instead of the PE skeleton to play a supporting role,and the PEA electrolyte layer（IEEM）was in-situ polymerized on the surface of the cathode.The relationship between the structure of in-situ polymerization and the electrochemical performance of battery was studied,and the applicability of positive electrodes in-situ process to batteries with different positive and negative electrodes was also studied.It was found that the electrolyte penetrated into the cathode,and the rough cathode inhibited the shrinkage of the electrolyte.The specific capacity retention rate of NCM622/Li battery is 81%under 0.5 C for 200 cycles,and the specific capacity of the battery is as high as 131.2 m Ah/g at 2 C.After 5 cycles at 4 C and 200 cycles at 0.5 C,the retention rate of specific capacity still reaches 80%,showing good interfacial stability and cycling performance.In addition,the study also found that the cathode in-situ process also has good applicability to Li Co O₂,Li Fe PO₄cathodes and graphite,silicon carbon anode batteries.（4）In view of several problems of PEA electrolyte such as easy shrinkage in the process of polymerization and drying,slightly lower electrochemical window,complicated and time-consuming preparation process.A gel electrolyte membrane（PASN）was prepared by cross-linking polymerization of succinonitrile with ethoxylated trimethylolpropane triacrylate,and the effects of different formulation and process on the electrochemical performance of electrolyte membrane were studied.It is found that the electrolyte has a smooth surface and the ionic conductivity is1.5×10^-4S/cm,lithium ion transfer number is 0.77,electrochemical window>5 V,which has good electrochemical stability with lithium metal.The specific capacity retention rate of NCM622/Li battery after 200 cycles at 0.5 C is 93%,which is much higher than that of PEA electrolyte modified in（1～3）.After 600 cycles,the capacity retention rate is 55%,and the specific capacity of the battery at 2 C is 95.7 m Ah/g.The PASN gel electrolyte exhibited good cycling stability.