Preparation Of Poly (Ethylene Oxide) Based Polymer/ceramic Hybrid Solid Electrolyte And Its High Voltage Protection Strategy

Solid electrolyte is the key to develop solid-state lithium metal batteries with high energy density and long cycle life.However,both solid polymer electrolytes and ceramic electrolytes have their own defects,which cannot meet the needs of solid-state batteries.It is expected that ceramic/polymer hybrid solid electrolytes(HSE)will make best use of their advantages and bypass their disadvantages simultaneously.However,there are still great challenges in how to achieve composite efficiently without phase separation,and how to match PEO-based electrolytes with high-voltage cathodes.In this dissertation,a series of PEO-based solid electrolytes were prepared by a in situ coupling reaction,and their compatibility with high voltage cathodes was studied.The main conclusions are as follows:(1)A HSE membrane was prepared by in situ coupling reaction.It demonstrates an ionic conductivity of more than 0.9 ms cm-1 at room temperature,an activation energy of 0.26 eV,and a high Li+transference numbers of 0.68,which can inhibit the growth of lithium dendrite effectively.The LFP‖PEO/PEG-3LGPS‖Li cell runs stable for quite a long time,the capacity retention was still around 91%(143 mAh g-1)after 150 cycles at 0.5 C.After a series of characterization and test,it is found that(3chloropropyl)trimethoxysilane(CTMS)was used as a bridge builder to realize the chemical bonding between ceramic and polymer,which eliminates the phase boundary of them,so that the ceramic can be dispersed in the polymer evenly and the agglomeration issue of ceramic particles caused by mechanical mixing method can be solved.Moreover,the HSE membrane prepared by this method can be exposed to air,and does not react with lithium metal.The assembly process of the battery is simple and convenient for industrialization.(2)An optimized dual-salt electrolyte membrane,SE-5D-20T,was obtained by adjusting the ratio between LiTFSI and LiDFOB along with the method of in situ coupling reaction.It demonstrates an ionic conductivity of 5.69×10-4 S cm-1 at room temperature,an activation energy of 0.41 eV,and a Li+ transference numbers of 0.65,which can inhibit the growth of lithium dendrite effectively.Although the conductivity of dual-salt electrolyte is lower than that of the single salt LiTFSI system,while it can react with cathode to form a high-voltage resistant protective layer,so it can be used with LCO and other 4 V class cathodes.The LCO|SE-5D-20T|Li and NCM622|SE-5D20T|Li cells can run smoothly over 200 cycles at 4.3 V,which has a significant improvement compared with single salt electrolyte.(3)The introduction of succinonitrile into cathode can form a high-voltage resistant protective layer in situ,which can avoid the decomposition of PEO-based electrolyte and make the solid-state lithium batteries run smoothly with 4.3 V LCO as cathode.The initial coulombic efficiency of LCO-15SN|PEO/PEG-3LGPS|Li cell is 49.65%,while the discharge capacity is 133 mAh g-1 after 40 cycles and 103.8 mAh g1 after 80 cycles.This method further proved that the regulation of electrode/electrode interface is an effective strategy to broaden the application area of PEO-based electrolytes.In summary,solid polymer electrolytes and ceramic electrolytes are integrated through strong chemical bonds,and this flexible solid electrolyte demonstrates high ionic conductivity and Li+transference numbers.Through the modification of lithium salt or cathode/electrolyte interface,the application of PEO-based solid electrolytes in 4 V-class cathode materials such as LCO and NCM was preliminarily realized.Therefore,it provides a feasible way for the development of high energy density lithium metal batteries.