| In recent years,all-solid-state lithium batteries?ASSLBs?have become a hot research topic due to their advantages of high safety performance,simple structure and high energy density.As a key component,solid electrolytes will greatly affect the electrochemical performance and practical application of ASSLBs.In this paper,LLZO/PEO composite solid electrolytes with high ionic conductivity and high electrochemical stability were obtained by compounding different contents of Li7La3Zr2O12?LLZO?in polyethylene oxide?PEO?.The crystallization behavior,microscopic morphology,ionic conductivity,electrochemical stability and lithium contact stability of 7.5%LLZO/PEO,60%LLZO/PEO and 90%LLZO/PEO composite solid electrolytes were systematically studied.At the same time,these LLZO/PEO composite solid electrolytes were applied to the ASSLBs,and the performance of the battery at different temperatures and different rates was systematically assessed.The self-standing LLZO/PEO composite solid electrolytes were prepared by solution casting method.Among them,7.5%LLZO/PEO and 60%LLZO/PEO composite electrolytes have the highest ionic conductivity.It was found that adding a small amount of SN to the LLZO/PEO composite electrolyte can greatly improve the ion mobility and reduce the interfacial resistance between the electrolyte and the electrodes.The mechanism of SN on the electrochemical properties of LLZO/PEO composite solid electrolytes was systematically studied.Among these solid electrolytes,7.5%LLZO/PEO/SN presented a highest ionic conductivity of of 3.61×10-4 S·cm-1 at30°C and a highest Li+transference number of 0.41.The ASSLBs?Li/LiFePO4?assembled with this type of electrolyte had good rate,cycling and low-temperature performance.The initial discharge specific capacities at 0.2C,0.5C,1C,2C were 157.9mAh·g-1,145.6 mAh·g-1,130.2 mAh·g-1,and 122.1 mAh·g-1,respectively.Notably,this ASSLB exhibited excellent cycling stability at 1 C,and 80.0%capacity was retained after 500 cycles.When operated at 45°C and 30°C,the ASSLBs also delivered relatively high specific capacity of 145.3 mAh·g-1 and 104.2 mAh·g-1.At the same time,60%LLZO/PEO/SN presented an ionic conductivity of of 1.22×10-4 S·cm-1 at 30°C and a highest Li+transference number of 0.41.The ASSLBs?Li/LiFePO4?assembled with this type of electrolyte had good rate,cycling and low-temperature performance.The initial discharge specific capacities at 0.1C,0.2C,0.5C,1C were 151.9 mAh·g-1,150.8 mAh·g-1,147.3 mAh·g-1,and 126.1 mAh·g-1,respectively.Moreover,this ASSLB exhibited excellent cycling stability at 0.5 C,and 98%capacity was retained after 200 cycles.When operated at 45°C and 30°C,the ASSLBs also delivered relatively high specific capacity of 125.0 mAh·g-1 and 100.0 mAh·g-1.The flexible 90% LLZO/PEO solid electrolyte was obtained by wet coating and hot pressing method,which has a wide electrochemical window of 5.5V and can be easily mass-produced due to its good flexibility.It was found that the hot pressing process can increase the ionic conductivity of 90%LLZO/PEO electrolyte from6.39×10-7 S·cm-1 to 4.26×10-6 S·cm-1 at 30°C,and reduce the interfacial resistance between the cathode and the electrolyte was reduced from 248?·cm-2 to 62?·cm-2.After the hot pressing treatment,the cycling stability of the Li/LiFePO4 ASSLBs was significantly improved,and the capacity was 148.3 mAh·g-1 after 50 cycles at 0.2 C. |
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