Research On Film-Forming Electrolyte Additive In Lithium-Ion Batteries

The increasing concerns on energy, environment and the rapid development of modern science and technology have more demands on batteries. The interface of electrode/electrolyte exists solid electrolyte interphase(SEI film) in the lithium-ion batteries. The film has important influence on the safety, self-discharge, capability, low temperature performance, Coulombic Efficiency and the irreversible capacity of the lithium-ion batteries. So it is important to chose the apt electrolyte and it's additive. Excellent electrolyte and it's additive will conduce to form the SEI film which has steady structure and good performance.On the base of review the development of lithium-ion battery and its additive in detail, carbon bisulfide(CS₂) was chosen as the film-forming electrolyte additive by theory calculation. Scanning Electron Microscope(SEM) and X-ray Photoelectron Spectroscopy(XPS) studies indicated that the additive of CS₂ took part in the SEI film-forming in the process of battery cycles. The elements of carbon, oxygen and fluorin are the main members in the compounds of SEI film. Sulfur is also one of the main elements of the SEI film when the electrolyte included additive of CS₂. The dominate compounds of SEI film are ROLi(R denotes alkyl), lithium carbonate, Li2CO3, sulphate, polyolefines and LiF. Cyclic Voltammetry(CV) and charge-discharge analysis also indicated that the full SEI film formed on the surface of the mesocarbon microbead(MCMB) anode material in the first cycle.To EC-based electrolyte, the presence of CS₂ has a very positive impact on the cyclic performance of the MCMB electrodes used. After 50 cycles, the specific capacity of the Li/MCMB battery increased by 5% compared with the capacity of the first discharge. The specific capacity of Li/MCMB battery decreased by 3% in the electrolyte without CS₂. The presence of CS₂ improved the rate capability properties of the Li/MCMB batteries. The additive of CS₂ has the active influence on the Coulombic Efficiency of the Li/LiCoO₂ battery, and the Coulombic Efficiency is enhanced by 2.5%. The presence of CS₂ in solution decreased the impedance of SEI film by 10%. The CV study indicated that CS₂ decompounded at about the potential of 1.7².0V(vs. Li/Li+). The reductive...