Preparation Of Silicon-based Nanomaterials By Ball Milling And Its Charging And Discharging Performance

With the development of electronic products and electric vehicle technology,the requirements for energy density and cycle performance of lithium ion batteries are increasing.The lithium storage capacity of silicon is currently the highest among all negative electrode materials,and has the advantages of abundant reserves and low discharge potential,and is the most potential negative electrode material today.However,there are problems such as volume expansion and cycle performance of the silicon-based anode material,and nanocrystallization and compounding can effectively alleviate the above problems of the silicon anode material.In this paper,nano-silicon-based materials were prepared by ball milling method.The effects of heat treatment and silicon-carbon composite treatment on the specific capacity and cycle performance of silicon anode materials were investigated by charge and discharge performance tests.Nano-silica powder was prepared by ball milling using micron-sized silicon powder as raw material.Studies have shown that both anhydrous ethanol and deionized water can improve the milling efficiency,improve the agglomeration of nano-silica powder,and prepare nano-silica powder with a median diameter of 70 nm.The nano-silica powder prepared by ball milling in deionized water has a significant oxidation phenomenon,while the nano-silica powder prepared by ball milling in anhydrous ethanol has a weak oxidation phenomenon.The morphology of the nano-silica powder can be changed by controlling the rotation speed of the ball mill.The nano-silica powder is spherical at a lower rotational speed,and the nano-silica powder is a spindle-shaped shape at a high rotational speed.This is because the silicon powder peels off along the cleavage surface at low rotation speed and transforms into a surface passivated sphere;at high rotation speed,the silicon powder transforms into a rough surface spindle shape under the combined action of impact and friction.In order to test the charge-discharge performance of the prepared nano-silica powder,the charge-discharge rate of 0.2 C was tested.The first charge-discharge specific capacity of nano-silica powder could reach 2700 m Ah/g,but after 20 cycles,the specific capacity decreased rapidly.Zero,poor cycle performance.The Si@SiO₂/SiO_x core-shell structure material was prepared by using nano-silica powder as raw material and heat treatment under argon atmosphere,and the charge-discharge performance test was carried out.The results show that when the heat treatment temperature is 1000°C and 1200°C,the nano-oxide layer on the surface of the nano-silica powder has a disproportionation reaction with the silicon core,forming a Si@SiO₂/SiO_x core-shell structure.After the heat treatment of the nano-silica powder,the inert product formed by the introduction of oxygen atoms in the SiO₂ and SiO_xlayers reduces the amount of lithium intercalation in the Li_xSi alloy,and thus inhibits the volume expansion of the nano-silica powder.In order to test the charge and discharge performance of the prepared Si@SiO₂/SiO_x core-shell structure mater ial,the test was carried out under the condition of charge-discharge rate of 0.2 C.The first reversible charge-discharge specific capacity was 1200 m Ah/g and 1000 m Ah/g,respectively,and the cycle was 100 cycles.After that,the reversible charge-discharge specific capacity was maintained at 400 m Ah/g and 700 m Ah/g,respectively.Using nano-silica powder as raw material,glucose and graphene as carbon source,silicon-carbon composite treatment under 600°C nitrogen atmosphere,and charging and discharging performance test.The research shows that the Si/C composite can improve the electrical conductivity,maintain good electrical contact inside the conductive network,and reduce the volume expansion of the silicon powder,effectively alleviating the structural collapse of the negative electrode material.In order to test the charge-discharge performance of the prepared Si/C composite,the test was carried out under the condition of charge-discharge rate of 0.2 C.The first reversible charge-discharge specific capacity was 1400 m Ah/g,and the reversible charge-discharge specific capacity remained after 100 cycles at 2000 mAh/g.