Preparation,interfacial Modification And Electrochemical Properties Of PDOL-YSZ Composite Solid Electrolyte Thin Membrane

Replacing liquid electrolyte with solid electrolyte is one of the main development directions of lithium ion batteries.It is a hot and difficult point in the field of solid-state lithium battery to develop solid-state electrolyte with high ionic conductivity at room temperature and friendly to lithium metal,and to solve the interface bonding problem between electrolyte and electrode.In this article,1,3-dioxolane（DOL）was compounded with yttria-stabilized zirconia（YSZ）nano-ceramic filler,and an environment-friendly PDOL-YSZ composite solid electrolyte membrane was prepared.By adjusting the polymerization degree of PDOL,a gel interface was formed between the electrode and electrolyte,and the interface compatibility of the battery was improved.The main research contents and achievements of this article are as follows:（1）PDOL-YSZ composite solid electrolyte membrane（CSEM）with high ionic conductivity and stability to lithium was prepared for the first time.The polymerization process of PDOL and the effects of different YSZ addition on the physicochemical and electrochemical properties of the electrolyte were studied.The results show that the thickness of PDOL-YSZ CSEM is about 20μm,the surface is smooth,and YSZ filler is evenly distributed in the electrolyte.When 0.3%YSZ filler is added,the electrolyte has an electrochemical stability window of more than 5.0 V and an ionic conductivity of 5.86×10^-4 S·cm^-1 at room temperature.Li/CSEM/Li symmetrical battery can be stably cycled for 1500 hours at the current density of 0.5m A·cm^-2,showing good stability to lithium.By wetting the electrode/electrolyte interface with a small amount of liquid electrolyte,the initial specific discharge capacity of the assembled LiCoO₂/CSEM/Li battery reached 165 m Ah/g at a current density of 0.5 C,and the capacity retention rate reached 90%after 200 stable cycles.（2）In order to improve the interfacial bonding between electrode and solid electrolyte and reduce the liquid component,a solid PDOL-YSZ film+PDOL gel（“PDOL SE+PDOL Gel”）composite electrolyte was designed and prepared.The effect of the ratio of LiTFSI to LiPF₆ on the performance of gel electrolyte was studied,and the electrochemical performance of solid battery composed of composite electrolyte was analyzed and characterized.It was found that the PDOL gel with the ratio of 2.5 M LiTFSI+1 M LiPF₆ achieved the best gelation effect,with the polymerization degree of 82.65%,the ionic conductivity of the corresponding composite electrolyte reaching 5.96×10^-4S·cm^-1 and the electrochemical stability window reaching 5.0 V.The LiCoO₂/PDOL SE+PDOL Gel/Li battery was assembled,under the condition of no liquid electrolyte wetting,its initial discharge specific capacity reached 165 m Ah/g at the rate of 0.5 C,which could be stably cycled for 250cycles,and the capacity retention rate was above 80%.In addition,Li/PDOL SE+PDOL Gel/Li symmetrical battery can be stably cycled for more than 400 hours at the current density of 1.0 m A·cm^-2,and has good stability to lithium.（3）The function of YSZ filler in PDOL solid electrolyte was analyzed.YSZ filler not only promoted the polymerization of PDOL,but also could be used as Lewis acid to promote the dissociation of lithium salt,release more Li⁺and improve the ionic conductivity of the electrolyte.The“PDOL SE+PDOL Gel”composite electrolyte not only improves the interface bonding between electrode and electrolyte and reduces the interface impedance,but also improves the interface stability of lithium metal and electrolyte by forming a Li-Zr-O+Li F composite transition layer on the negative electrode side,and inhibits the growth of lithium dendrites,thus improving the comprehensive performance of the battery.The above results show that PDOL-YSZ solid electrolyte film and solid/gel composite electrolyte developed in this article not only show high ionic conductivity and stability to lithium,but also provide an effective interface modification method.The preparation process has no pollutant emission,is green and environmentally friendly,and is expected to be popularized and applied to high-performance solid-state lithium batteries.