Preparation And Interface Structure Evolution Of Polymer-Based Composite Electrolytes For All-Solid-State Batteries

Compared with traditional lithium-ion batteries,all solid state lithium-ion batteries have the advantages of good security and high energy density.Solid-state electrolytes as the main components of all-solid-state lithium-ion batteries have attracted wide attention.At present,the composite electrolyte material composed of polyethylene oxide?PEO?and garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂?LLZTO?is one of the most promising solid-state electrolytes.In this paper,the preparation,performance optimization,interface structure and evolution mechanism of LLZTO-PEO-LiClO₄?LPL?composite electrolyte were studied.Composite electrolytes with high ionic conductivity and good mechanical properties were obtained by adding LLZTO to PEO-LiClO₄.All-solid-state lithium-ion batteries were prepared by LPL composite electrolyte,lithium iron phosphate and lithium metal negative electrode,and their performance was studied.The interface structure and evolution of composite electrolytes were studied by solid-state nuclear magnetic resonance?SS NMR?.In this paper,the composite electrolyte was prepared by solution casting method.Firstly,by exploring the optimum effect of different garnet fillers on composite electrolyte,LLZTO was determined to be the best filler.When LLZTO content reached40 mass%,LPL composite electrolyte achieved the highest ionic conductivity,and its ionic conductivity could reach 8.2×10^-5S/cm at room temperature.The electrochemical stability window of LPL composite electrolyte can be increased to more than 5V,and the interface with lithium metal has excellent stability.Performance tests performed at room temperature and 60°C show that batteries using LPL composite electrolyte have higher capacity and more stable cycling performance than those using PEO-LiClO₄electrolyte.The discharge capacity of LFP/LPL?20 mass%LLZTO?/Li battery can reach 153 mAh/g at room temperature.At 60°C,the discharge capacity of LFP/LPL?20mass%LLZTO?/Li battery can reach 160 mAh/g,and the capacity of 200 cycles at 1 C remains at 85%.The LPL composite electrolyte was studied by ¹H,⁶Li,⁷Li,¹³C single pulse NMR experiment and ¹H-⁶Li CP,¹H-⁷Li CP,¹H-¹³C CP NMR experiment.Research results show that the addition of LLZTO not only reduced the crystallinity of PEO,but also catalyzed the addition reaction between PEO and acetonitrile?ACN?to form less mobile PEO-ACN at the interface of oxide and polymer.Solid evidence for the existence of interface in LPL composite electrolyte was obtained,and the Li⁺in the interface originated from LiClO₄.The study of LPL composite electrolyte after charging and discharging shows that the composite electrolyte needs activation just like liquid electrolyte.By comparing and analyzing ⁶Li single pulse and 2D-EXSY NMR experiments of ⁶Li isotope labeled samples,we have reached the conclusion that LLZTO,PEO-LiClO₄ and interface are all involved in Li⁺migration,and the interface plays a key role.