Improving the Electrochemical Performance of Li4Ti5O12 Anode By Phosphorus Reduction at a Relatively Low Temperature

Abstract

The current commercial Li ion battery composed of a transitional-metal oxide cathode and graphite anode cannot meet the demands of these vehicles due to the poor rate capability and safety issues (dendritic lithium) of the graphite anode. Li4Ti5O12(LTO) is used to replace graphite because it is lithium dendrite free and shows a long cycle life as a result of its minimal lattice expansion (less than 1%) during the charge/discharge process. However, its intrinsically poor electronic conductivity has restricted LTO from showing high rate performance. Reducing Ti4+ in LTO to more conductive Ti3+ can help increase the conductivity. There are two main ways to reduce Ti4+ in LTO to Ti3+, one method is done by using a transition metal, such as Cr, Mo, Cu, Co, or Ta, to partially replace Li or Ti in the lattice, and another approach is to use reducing reagents. Almost all the reported methods require high temperature (higher than 600 oC), which limits the application of these approaches. In this work, A novel and efficient method is demonstrated to improve the electrochemical performance of LTO. In contrast to other methods, inexpensive red phosphorus powder is used as a reducing reagent, and the reduction is conducted at a relatively low temperature of 400 oC. Charging/discharging test results show that the phosphorus treated LTO (LTO/P) can deliver a capacity of 75mAh g-1 at 16 C (1 C=170 mAh g-1), while the LTO electrode can only deliver less than 50 mAh g-1. After 160 cycles at 1C, LTO/P electrode can maintain a capacity retention of 96%, while the LTO only maintain 90% capacity, demonstrating a much-improved electrochemical performance. Cyclic voltammetry at different scan rates and EIS results disclose that both Li+ diffusion and electronic diffusion are enhanced for the LTO/P electrode. In addition, this simple, inexpensive, and efficient method can also be expanded to improve the electrochemical performance of other metal-oxide anode materials such as MoO3, offering a low cost and effective way for Li4Ti5O12 and metal-oxide anode applications.