Study On The Structure And Properties Of Cellulose Based Composite Membranes For Lithium Sulfur Batteries

The scale of energy storage in the world is increasing rapidly,and the traditional lithiumion battery cannot meet this requirement because of its performance limitations.Therefore,researchers turn to explore the development of new batteries.Lithium-sulfur battery is better than lithium-ion battery in terms of its specific capacity and energy density,and it has lower cost,so it is widely concerned.However,the process of lithium-sulfur battery from laboratory to commercial is very difficult,and one of the key factors is the shuttle effect.Polypropylene(PP)diaphragm is often used in lithium-sulfur batteries.Its large pore size has poor inhibition effect on shuttle effect,and its non-natural degradation is harmful to the environment.Therefore,it is necessary to develop a diaphragm that can well inhibit the shuttle effect,and the diaphragm has the characteristics of green environmental protection and degradability.In this thesis,bacterial cellulose(BC)is selected as the raw material and prepared as the substrate,and then the coating of Koqin black(KB)or Koqin black-titanium dioxide(KB-TiO2)is constructed on its surface to prepare the cellulosic composite membrane,and the battery is assembled with the membrane.The thesis mainly includes the following aspects:(1)In this chapter,BC wet membrane was purified and dried to prepare BC substrate,and KB coating was constructed on its surface to obtain BK composite separator.The diaphragm has good wettability to the electrolyte,excellent thermal stability of the diaphragm,and good mechanical properties.In addition,the separator has good electrochemical stability in the 1.7 V-2.8 V charge-discharge range of lithium sulfur battery,and its ionic conductivity value is 0.119 m·S cm-1.(2)In this chapter,KB-TiO2 composite material is obtained by ultrasonic mixing and freeze-drying of KB and TiO2,and then coated on BC substrate to construct BKT composite separator.The diaphragm has good wettability to the electrolyte,excellent thermal stability and good mechanical properties,and it is found that the diaphragm has a good limit on the diffusion of lithium polysulfide through the H-type electrolytic cell experiment.BKT composite separator has good electrochemical stability in the 1.7 V-2.8 V charge-discharge window of lithium sulfur battery,and its ionic conductivity value is 0.14 m·S cm-1.(3)In this chapter,the prepared BK and BKT composite membranes were used for battery assembly,and electrochemical measurement instruments were used to test them.The 0.5 C first discharge specific capacity of lithium sulfur batteries using BK or BKT composite membranes is 1159.4 mAh g-1 and 1180.8 mAh g-1,both of which are superior to 780.7 mAh g-1 lithium sulfur batteries using PP membranes.At the same time,BK and BKT composite membranes still have good performance under the condition of high sulfur carrying surface density of the electrode.