Low-cost Anode Materials For Potassium-Ion Batteries

Due to the rapid development of portable electronic devices,the demand for power storage in the lithium-ion battery(LIB)industry continues to grow.However,the continued shortage and uneven distribution of global lithium resources have limited the future application of LIBs.Therefore,potassium-ion batteries(PIBs)have attracted great attention as the secondary batteries with widely distributed resources,low cost,and high energy density.Compared with LIBs,the anode material system of PIBs is under developed and needs constant innovations.At the same time,it is necessary to optimize the structure and morphology of the material system.This thesis aims to prepare the nano-sheet self-assembled flower-type oxychloride bismuth(BiOCl)by a simple hydrothermal method.It is the first time as the anode material of potassium ion battery for studying its electrochemical performance in organic selectrolyte and exploring its energy storage mechanism.At the same time,tin sulfide coated graphene oxide(SnS@GO)was prepared by hydrothermal and annealing.It is the first time as the anode material of potassium ion battery for revealing the effect of GO coating and the electrical conductivity on the electrochemical performance of the anode material.The thesis provides insights into the future research of PIB electrode materials.The thesis includes the following aspects:1.BiOCl synthesized by a hydrothermal method was used to test the electrochemical performance as an anode material of PIBs in organic electrolytes.The choice of the electrolytes and carbon coating optimized the phase,morphology and electrochemical performance of the BiOCl product.It was finally determined that uncoated BiOCl provided a high capacity of 366.6 mAh/g at a current density of50 mA/g in the electrolyte containing KFSI and maintained a specific capacity of58% after 50 cycles.At a current density of 1 A/g,the specific capacity reached175.6 mAh/g,showing high rate performance.The phase,structure and morphologyof the electrode material were analyzed by ex-situ XRD,XPS and SEM tests to study the energy storage mechanism.2.SnS@GO composite synthesized by a hydrothermal method and a subsequent annealing process was used to test the electrochemical performance as an anode material of PIBs in organic electrolytes.By changing the temperature and time,GO coating amount,and electrolytes,the phase,composition,structure,morphology and electrochemical properties of the anode were optimized.It was finally determined that SnS@GO-30 mg,40mg,and 50 mg had the best performance under the condition of the electrolyte containing KFSI.When the current density was 50mA/g,the high capacities of 476,507.8 and 514.2 mAh/g were obtained for different amount of GO,respectively.After the 50 th cycle,the discharge specific capacity was still high,i.e.,304.6,65.2,and 116.3 mAh/g,respectively.The difference of the performance of SnS@GO-30 mg,40mg and 50 mg was demonstrated by long-term cycle and rate capability at different current densities.