Research Of The Compatibility Of Electrolyte Of Li₄Ti₅O₁₂ Soft-package Batteries

An electric vehicle ?EV? powered by a rechargeable lithium-ion battery or a electrochemical supercapacitor with both high power and high energy densities is an ideal solution to reduce environmental pollution. Li-ion intercalated compound Li4Ti5O12 has been demonstrated to be one of the most promising electrode materials for such applications,because it has a flat voltage range, high reversible capacity ?175mAh·g-1?, and especially the long cycling performance due to no structural change ?zero-strain? during charge-discharge cycling. However, the large scale application of Li4Ti5O12 has been limited due to its low electronic conductivity, which results in fading of capacity during cycling and severely polarization at high charge and discharge rate. However,Li₄Ti5O12 exhibits low electronic conductivity and low lithium-ion diffusion coefficient, which greatly limit its rate performance. The addition of additives in the electrolyte is one of the most economic and effective way to improve the performance of lithium ion batteries. Therefore, this dissertation will use LiBOB, LiODFB and LiTFSI as an electrolyte additive, trying to improve the compatibility of Li4Ti5O12 anode materials and electrolyte, so as to improve the electrochemical performance of lithium titanate battery.In this dissertation, the influence of electrolyte additive LiBOB, LiODFB and LiTFSI on the electrochemical performance of LiMn2O4 half-cell and Li4Ti5O12 half-cell is investigated. The results show that the LiMn2O4 half-cell with additive in the electrolyte exhibit higher rate capability and more stable cyclic performance, but there is no obvious difference between various additives; The Li4Ti5O12 half-cell with LiTFSI in the electrolyte exhibit higher coulombic efficiency and more stable cyclic performance. The discharge capacity of the Li4Ti5O12 half-cell reaches 173.53 mAh·g-1,its specific capacity decreased from 172.02 mAh·g-1 to 168.45 mAh·g-1 after 60 cycles, and its capacity retention keeps at 97.92%.The LiMn2O4/ Li4Ti5O12soft package batteries in different electrolyte additives are assembled, and the cyclic performance and constant current charge-discharge of the batteries are tested. The results show that the Li4Ti5O12 soft package batteries with LiTFSI in the electrolyte exhibit higher capacity, and its capacity retention keeps at 82.15% after 100 cycles,but The capacity retention of the Li4Ti5O12 soft package batteries without additives only 74.35%. The Li4Ti5O12 electrodes were characterized by XRD and SEM before and after the cycle, found that the positions of Li4Ti5O12 peak unchanged, but the peak intensity change obviously. The SEI film on the surface of Li4Ti5O12 with LiTFSI in the electrolyte is relatively continuous and smooth. This SEI film can improve the electrochemical performance of batteries, on the other hand can enhance the stability of electrolyte on the surface of electrode.With acetonitrile as the solvent, add LiBF4, LiPF6 and LiClO4 respectively as electrolyte,assembled into different Li4Ti5O 12 soft package batteries,and the cyclic performance and constant current charge-discharge of the batteries are tested. The capacity of Li4Ti5O12 soft package batteries with LiClO4/ acetonitrile as the electrolyte with the highest capacity, which reach to 2094.4mAh, and the cyclic performance of Li4Ti5O12 soft package batteries with LiPF6 as the electrolyte better than the Li4Ti5O12 soft package batteries with LiBF4 as the electrolyte; Through the SEM found that there is SEI film formationed on the surface of Li4Ti5O12 electrode, the SEI film more thicker and complete on the surface of Li4Ti5O12 electrodes with LiBF4 and LiClO4 as the electrolyte. There are a lot of sediment on the surface of LiMn2O4 electrode, this is due to LiBF4 and LiPF6 decomposition can produce HF to corrosion of the electrode of LiMn2O4.