Preparation And Properties Studies Of Si-Based Anode Materials For Lithium-ion Battery

As the electric cars and a variety of portable electric devices develop rapidly, new anodematerials （The theory capacity of graphite anode which is commercial is very low）forlithium-ion battery with high capacity and stability needs further study. Si-based anode ispaied more attentionbecause it has high capacity（4200mAh/g）. In order to solve problem ofSi anode material（large volume expansion and bad cycling stability）, silicon powder whichwas made as the main active substance to prepare the Si/C composite and Si/Al/C compositeby using the methods of ball milling、doping other substance and coating glucose. Thecomposites avoid large irreversible capacity and improved cycling stability.The first discharge/charge capacity of pure Si anode is1439.9/253.5mAh/g, however,and the initial columbic efficiency was only17.6%. There is a large irreversible capacity.After40cycles, the discharge/charge capacity is only9-20mAh/g, so it is useless of value.The Si/C composite is prepared to develop the performance of pure silicon. Thedischarge/charge capacity（1283.4/956.1mAh/g） and initial columbic efficiency（74.5％） arethe best when the ratio of graphite is80wt％. The large irreversible capacity is obviouslyimproved. After50cycles, the discharge/charge capacity reduce to294.7/292mAh/g, butinitial columbic efficiency reach to99.1％. Then that material is coated by glucose and bepyrolyzed at600℃, so the Si/C composite is prepared. Initial columbic efficiency and cyclingstability are improved when glucose is at the ratio of50％. The first columbic efficiency reachto75.8％; after50cycles the discharge/charge capacity maintain at369.8/358.8mAh/g, andinitial columbic efficiency increase to97％.Silicon powder and aluminum powder were mixed by ball milling, and the best millingtime is15h with the particle size169nm. XRD revealed that some of the micrometer crystalsilicon transformed into amorphous, with the appearance of new substances, suchasAl_3.21Si_0.47and Al₄Si. When the amount of aluminates reached to30wt%, the materials hadan initial discharge capacity of1801.7mAh/g, while the irreversible capacity was still large.Secondly, the materials were modified by doping graphite when the amount of graphitereached to50wt%, the materials had an initial discharge/charge capacity of1716.8/970.3mAh/g. The composite had an initial columbic efficiency of98.8%, and adischarge capacity of200mAh/g after50cycles. On this basis glucose was coated andpyrolyzed at600℃to get Si/Al/C composite. The composites showed an initial dischargecapacity of1312mAh/g, with an initial columbic efficiency of72.9%, and the capacityretained at445.1mAh/g after50cycles with the columbic efficiency of above96.9%.