Preparation And Modification Of Silicon Oxide Anode Materials For Lithium Ion Batteries

Lithium-ion batteries(LIBs)have served a crucial role in the development of electronic devices because of their merits of high energy density and high power density.Graphite is commonly used as the anode in LIBs.However,graphite has a limited theoretical capacity of only 372 m Ah/g.Thus,when graphite is used as the anode material in LIBs that are used in electric vehicles,the power requirements of these vehicles cannot be met.Therefore,a novel anode material that provides high capacity,high power,and stable performance,such as alloy and silicon,should be used in LIBs.Siis regarded as a potential candidate as anode material because of its high theoretical capacity of 4200 m Ah/g.Serious pulverization and electrode peeling due to its large volume expansion(about 300%)during cycling.Compared with silicon,silicon monoxide shows less volume expansion rate(about 200%)and stable cycle performance,which is the best choice for the next generation of anode materials.In this thesis,the porous SiO_x/C composites are prepared by high temperature disproportionation methods and acidic or alkaline modification treatment with silicon monoxide and phenolic resin as raw materials.Material analysis methods such as SEM,XRD,and TGA are used to explore material composition from the microstructural perspective.Electrochemical methods such as CV and EIS are used to study the electrochemical properties of materials.This thesis is composed of the following two parts:Part one:SiO_x/C composites with pore structures are prepared by high temperature disproportionation and sodium hydroxide modification treatment.The cycle performance of NaOH-SiO_x/C composites is significantly improved compared with untreated SiO_x/C materials.At the current density of 100 m A/g,the discharge capacities of NaOH-SiO_x/C-900? is 1448.1 m Ah/g.The reversible capacity remains at 855.1 m Ah/g after 50 cycles,which is higher than unmodified SiO_x/C composites.The results show that the pore structure can effectively inhibit volume expansion of SiO_xand improve the cycle performance of the battery.Part two:In order to further confirm a better modification treatment method,hydrofluoric acid is used to modify the high-temperature disproportioned material.The results showed that the discharge capacities of the HF-SiO_x/C-900?composites is 1472.3 m Ah/g,at the current density of 100 m A/g.The reversible capacity remains at 880.0 m Ah/g after 100 cycles,which is higher than NaOH-SiO_x/C-900?composites.The above results confirm that the cyclic performance of SiO can be improved significantly through modification treatment.