High Capacity Silicon-Containing Anode Materials For Lithium-ion Batteries

There is an intense interest in developing new nigh capacity electrode material for lithium ion batteries to catch up with the development of HEV and portable devices. Silicon is the most attractive active material of anode for its largest theoretical insertion capacity of all known host materials. The lithium insertion/desertion in silicon and silicides has been investigated in detail in this thesis. Hereby, new silicon/carbon composites and silicon-containing compounds were developed and investigated.It has been commonly accepted that the serious volume expansion/contraction caused by lithium insertion/desertion, which leads to a loss of electrical conductivity, is the key to the poor cyclability of silicon. This thesis firstly reports that the formation and growth of SEI layer occurring on the surface of silicon during lithium ion insertion is also very important. SEI layer could be formed below 0.1 V (Li+/Li), whereas a continuous SEI layer is only formed at a lower voltage. Although SEI la/ers are mainly composed of LiF and Li2CO3, some trace of silicon-containing compound s also found simultaneously.Comparing with the crystalline silicon, NiSi2 crystal presents relatively higher structure stability and thus better cyclability although both have face-centered cubic structure. This structure stability is closely related to the non-stoichiometric compounds of NiSix formed during lithium ion insertion.Considering the volume expansion and surface phenomena of silicon as anode material for lithium ion batteries, high capacity silicon/carbon composite was designed and prepared by solid-state reaction. Its cyclability and first coloumbic efficiency aremuch better than silicon. The composite structure with silicon dispersed in carbon matrix is beneficial to improving the electric contact. Furthermore, the silicon covered by carbon could be protected from the direct contact with electrolyte and reduces the corrosion. Si-Al/C composite material was prepared also. Si-Al/C composite as anode material has a capacity about 600mAh/g for its first Li+ insertion and the first coulombic efficiency up to 85%. Its capacity retention is about 90% after 25 cycles.Based on the investigation of structure stability, silicon-containing materials LixSiNy and LixSiChNy with low volume expansion were firstly prepared by ball milling. LixSiO2Ny material has pretty good cycleability and rate performance. The reversible capacity after 110 cycles keeps above 460mAh/g, about 89% of the second cycle capacity at the current density of 0.3mA/cm2. A further study on these materials needs to clarify the insertion-desertion mechanism of lithium and improve their electrochemical performances.