Novel Strontium Titanate (STO)- Li1.2Ni0.2Mn0.6O2 (LNMO) Composite Cathode Materials with Improved Electrochemical Performance for Lithium-Ion Batteries

摘要

The rapid development of hybrid electric vehicles (HEVs) and electric vehicles (EVs) during the last decade requires lithium- ion batteries (LIBs) with better safety design, long cycle life and higher capacity. However, current design of LIBs has several intrinsic drawbacks that greatly hinder further applications of LIBs in terms of automobile and stationary energy storage. Layered Li- rich oxide cathodes xLi2MnO3?(1 - x)LiMO2 (0 < x < 1, M = Ni, Mn, Co) have been extensively investigated because of their high specific capacity (250 mAh g-1), reduced cost and improved safety and stability. Such high specific capacity results from the Li2MnO3 component offering excess lithium source and stabilizing electrode structure over 4.5 V. Nevertheless, LNMO cathodes suffer from several flaws including high irreversible capacity during initial charge& discharge process, poor cycle performance and gradual voltage drop. Some of the predominant causes for these flaws are the direct contact between electrolyte and LMNO, phase conversion of layered LNMO and side reactions during charge and discharge process. In order to improve the electrochemical performances of LNMO regarding energy density and stability, we apply a small amount (5% weight fraction) of STO nanoparticles as coating agent. STO nanoparticles were synthesized from a solvothermal method and the morphology as well as crystallinity of which was examined, showing that the STO nanoparticles were highly crystallized with an averaged diameter of 20 nm. The results of electrochemical tests indicated that the specific capacity and stability of STO- LNMO composites were improved, exhibiting that the electrochemically inert coating agent can protect matrix cathode materials from the corrosion of electrolytes, improve structural stability and prevent side reactions.