Research On Silicon Based Anode For High Capacity Lithium Ion Batteries

Silicon-based anode is the hot topic for lithium ion battery due to the highest theoretical specific capacity and natural resource abundance. However, the huge volume expansion during the lithiation and delithiuation process, which results in the poor cycleability, greatly hinders the commercial application. The dissertation reviewed the research actuality of silicon based anode and introduced the high temperature pyrolysis and liquid-phase methods to synthesize silicon/graphite/carbon composite and nano-silicon/polyaniline composite, respectively, to promote the electrochemical performance of silicon based anode.Silicon/graphite/carbon composite was synthesized by high temperature pyrolysis method, and the cycle performance influenced by graphite species, particle division, electrode annealing and lithium salt additive was investigated. The result showed that the composite exhibited a good electrochemical performance by using flake-like graphite and proper particle division, which delivered a delithiation capacity of 774.2 mAh·g-1, a columbic efficiency of 81.8% and capacity retention of 98.2% after 50 cycles. The silicon/graphite/carbon composite was used as anode of prismatic cell (053648A) with the designed capacity of 800 mAh possessed a discharge capacity of 721 mAh.By using the XPS, SEM, EIS analysis means, the SEI film process of silicon was investigated. The result showed that the SEI film process of silicon was similar to that of graphite for both formation potential and ingredients. Because of the volume expansion during the lithiation and delithiation process, the SEI film experienced a formation, destruction, restoration, destruction, formation process companion with the volume change of silicon. Simply adding inorganic lithium salt couldn't promote the electrochemical performance of silicon/graphite/carbon composite. By adding sodium dodecyl sulfonate, the cycle performance of silicon/graphite/carbon composite was improved. The delithiation capacity was 781.2 mAh·g-1 and the capacity retention was 94.2% up to 50 cycles.The Si/PANi composite was synthesized by a simple polymerization process in a nano-silicon contained ethanol aquous solution or micro-emulsion methods. The result showed that the nSi/PANi-1 composite synthesized in an ethanol aquous solution exhibited an electrochemical performance with a delithiation capacity of 1940.3 mAh·g-1, initial efficiency of 64.3%, capacity retention of 91.5% after 25 cycles. For the micro-emulsion method, the nSi/PANi-2 composite exhibited a capacity of of 2320.2 mAh·g-1, initial efficiency of 60.6%, capacity retention of 92.3% after 30 cycles. By using the diazo-reaction of p-Phenylenediamine, grafting the aniline monomer on the nano-silicon and followed by a polymerization process to synthesized the nSi/PANi-3 composite, which exhibited a capacity of of 2408.7 mAh·g-1, initial efficiency of 64.0%, capacity retention of 74.0% after 40 cycles.