Preparation And Properties Analysis Of Silicon Anode Active Materials

With lithium-ion battery increasingly widely used in mobile power, electric vehicles and smart grids, the industry’s demand for superior electrochemical performance of the electrode active materials is also increasingly urgent. When silicon to be used as the negative electrode active material, its theoretical specific capacity exceeds 4000 mAh/g, which is far better than the conventional graphite anode, therefore it attracts the attention of enormous researchers. However, two main factors restrict the development of silicon anode: First, silicon is a kind of semiconductor materials, thus it have poor conductivity; Second, silicon produced nearly 300% volume change during discharge and charge process, which could destruct the electrode structure seriously. In order to reduce the damage of volume change to silicon anodes, this paper tried to prepare silicon nanomaterials. Low temperature solution synthesis, the reduction of silica, the etching of acid/base, these three methods that are rapid, low-cost and have simple process, were used to prepare silicon nanoparticles, silicon nanospheres and silicon micro/nanochips, respectively. In addition, synthesis mechanisms, physical properties and electrochemical performance of these materials were included.(1) Kauzlarich method was improved: magnesium was used to reduce silicon tetrachloride to prepare silicon nanoparticle precursors at first, then these precursors were passivated by amines or amides to finally produce silicon nanoparticles having high reducibility whose average particle sizes were under 50 nm. With different passivants used, the materials’ microscopic morphology became different. When N-methyl-2- pyrrolidone was used as passivants, the produced silicon nanoparticles resemble grapes. Discharge capacities of 1688 mAh/g in first cycle and 1070 mAh/g after 15 cycles were get when the materials were treated under the current density of200 m A/g. In addition, the average Coulomb efficiency was about 80% except the one in first cycle that was 71.8%.(2) tetraethyl orthosilicate was hydrolyzed with the help of various soft templates to prepare silica nanospheres first, then magnesium was utilized to reduce these silica under 700 °C, finally silicon nanospheres with uniform particle sizes were generated.When ferrocene to be used as the template, the generated silicon nanospheres got a loose construction, while some spheres broke down. When treated under the currentdensity of 200 mA/g, first cycle’s discharge capacity reached 1400 mAh/g and it faded to 1124 mAh/g after 15 cycles. The Coulomb efficiency was 71.8% in the first cycle and about 80% in other circulations. In addition, each discharge capacity was far bigger than the charge capacity in the former cycle.(3) the HF/HNO3 hybrid acid which can etch silicon isotropically and the KOH that can etch anisotropically, both two were used successively to process micrometer-scaled bulk silicon. Finally silicon micro/nanochips with whose particles sizes ranging from 100 nm to 1 μm were prepared. Acid etches first or base etches first could lead to thoroughly different morphology. When acid etches first and then base etched, the generated silicon micro/nanochips had obvious edges and corners. This kind of materials had a discharge capacity of 2093 mAh/g in the first cycle while this capacity faded to 1019 mAh/g after 5 cycles. The Coulomb didn’t exceed 75%.