Study on functional additives to improve electrochemical properties of spinel lithium manganese oxide cathode for lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) have been developed as useful and power source for electronic devices (e.g. cellular phones, laptop computer, portable devices, etc.). Furthermore, LIBs are one of the most promising energy storage devices for electric vehicles (EV), hybrid electric vehicles (HEV) and plug-in hybrid electric vehicle (PHEV) by reason of their high energy, high capacity retention and long cycle life. To be high energy density of batteries should be achieved by increasing discharge capacity of the cathode and/or by increasing the working potential of cathode materials. Among all candidate cathode materials, spinel lithium manganese oxide (LiMn2O4) has been considered as alternative cathode materials beyond layered lithium cobalt oxide (LiCoO2) because of low cost, eco-friendly, cyclability and it has a high specific capacity. However, the LiMn2O4 cathode suffers from manganese dissolution resulting in fast capacity fading. Therefore, it is strictly required that the manganese dissolution be restrained for attaining highly reliable batteries. In order to overcome capacity fading by manganese dissolution of the spinel LiMn2O4 cathode, functional additives are considered to alleviate the manganese dissolution on the cathode. Tris(trimethylsilyl) phosphite (TMSPi) is used as an oxidative additive for build-up of a protective layer on the cathode. To understand the effect of functional additives on the manganese dissolution based on result, the open circuit voltage (OCV) variation of full cells with the LiMn2O4 cathode during storing at 60 °C and capacity retention are investigated. The effect of sacrifical additive on the manganese dissolution is confirmed by the observation of surface morphology and the analysis of surface chemistry of cycled cathodes were carried out. Additionally, the impact of TMSPi additive on the cycling properties of LiMn2O4/graphite full cells at 60 °C is investigated. It is found that the addition of TMSPi can achieve noticeable improvement of the discharge capacity of half and full cells, and capacity retention of full cells during storing at 60 °C. In summary, it is suggested that TMSPi is a promising additive to make organic-inorganic based SEI on the cathode and improve cycling performance of half cells and full cells with the LiMn2O4 cathode.