Preparation And Properties Research Of Polycarbonate-Based/LLZTO Composite Solid Electrolyte

Lithium metal batteries have become a key research direction for next-generation lithium batteries due to their high theoretical specific capacity and low chemical potential.However,lithium metal batteries are prone to side reactions with liquid organic electrolytes,resulting in issues such as uncontrollable lithium dendrite growth,easy puncture of the separator,and electrolyte leakage.Solid-state electrolytes（SSEs）are expected to fundamentally solve the above problems due to the absence of liquid organic components.Among them,the carbonate electrolyte in the polymer system has the advantages of good electrochemical stability and easy polymerization to form a film,which can solve the safety problems existing in lithium metal batteries.However,owing to the low ionic conductivity and poor interfacial properties of the carbonate-based electrolyte,this paper proposes using a polyimide（PI）separator as a support,two carbonate monomers as a matrix,PEG as a solvent to dissolve lithium salts,and garnet-type oxide LLZTO particles to prepare a composite solid electrolyte,the specific content of which is as follows:1.Using the polyimide（PI）diaphragm as support,two types of acrylate monomers（HDDA-TMPTMA）as the polymer matrix,and polyvinyl alcohol（PEG）to dissolve lithium salt,the PHTL electrolyte was synthesized through the in-situ polymerization technique.In order to increase the cycle stability of the battery,fluoroethylene carbonate（FEC）was added to the PHTL precursor solution to prepare the PHTL-FEC electrolyte.The effects of various FEC additions on the electrolyte’s ionic conductivity,electrochemical window,and lithium ion migration number were investigated.The electrolyte（PHTL-10%FEC）with 10%FEC addition has the best performance,the ionic conductivity is 1.67×10^-5 S·cm^-1,the electrochemical window is 5.46 V,and the lithium-ion migration number is 0.52.It can be cycled stably for 260 h at a current density of 0.2 m A·cm^-2 without short circuit.2.To further study the adaptability of the optimized polymer electrolyte to different electrode materials,the polymer electrolyte PHTL-FEC was assembled into batteries with Li Fe PO₄（LFP）,Li Co O₂（LCO）,NCM622 as positive electrode,and metal lithium as negative electrode,respectively.After 180 cycles of LFP|PHTL-FEC|Li at 0.2 C rate,the discharge specific capacity is 120.3 m Ah·g^-1,and the capacity retention rate is as high as90.52%.The LCO|PHTL-10%FEC|Li battery after positive electrode interface modification has a discharge specific capacity of 122.8 m Ah·g^-1 in the first cycle at a rate of 0.2 C,and the discharge specific capacity after 100 cycles can be maintained at about 120 m Ah·g^-1,the cycle retention rate can reach 97.7%.3.In follow-up research,a composite solid electrolyte was prepared by adding Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）and FEC based on the matrix electrolyte to further improve the rate performance,and the effects of LLZTO addition on the ionic conductivity,electrochemical window and lithium-ion transfer number of composite electrolytes were investigated.The results show that when the addition amount of LLZTO is 15%,the composite solid electrolyte has good ionic conductivity(1.2×10^-4 S·cm^-1),the highest electrochemical window（5.26 V）,and lithium-ion transfer number（0.62）.A lithium symmetric battery was assembled with PHTL-FEC-15%LLZTO as the electrolyte.The Li|PHTL-FEC-15%LLZTO|Li battery can operate in the voltage range of–15～15 m V at a current density of 0.2 m A·cm^–2.The internal stable cycle is 500 h,indicating that it has a stable and long cycle life,which is mainly due to the reaction between PHTL-FEC-15%LLZTO and the Li electrode,forming a Li F-rich SEI layer at the negative electrode interface,which improves the interface compatibility.