A low-cost and Li-rich organic coating on a Li4Ti5O12 anode material enabling Li-ion battery cycling at subzero temperatures

Abstract

In this paper, we report the surface modification of the Li₄Ti₅O₁₂ (LTO) anode material with a freshly prepared Li-rich PTCLi₄ organic molecule using a spray-dryer technique. In addition, burning the resulting powder yielded an electrode material with a few-nanometer-thick carbon coating. For comparison, carbon-coated LTO powder was prepared with graphene oxide (GO) using the same protocol. Organic molecules were first characterized using FTIR, XPS, TGA, XRD, and SEM methods. PTCLi₄-coated LTO powders were observed via SEM and the corresponding EDX mapping as well as micro-Raman and XPS spectroscopic analyses confirmed the efficient surface coverage of the anode material. After the burning, a graphitic-like carbon coating with an I_D/I_G of approximately 0.76 and a thickness of a few nanometers was confirmed by TEM observations. Thermogravimetric analyses revealed that the content of carbon varied from 0.3 to 1.5 wt%, depending on the reaction conditions and material used (i.e., PTCLi₄ or GO). Interestingly, electrochemical cycling at 25 °C of PTCLi₄-coated LTO electrodes gave rise to superior performance compared to that of the pristine electrode, especially at high C-rates, and carbon-coated electrodes showed intermediate performance. Most importantly, the good cyclability of PTCLi₄-coated LTO electrodes was observed with a specific capacity of 145 mA h g⁻¹ after 100 cycles at a C/2 rate with an average coulombic efficiency of 100%. XPS analyses performed on aged electrodes revealed a low degradation of the electrolyte with a lower concentration of LiF on the surface of the PTCLi₄-coated LTO electrodes. Finally, the cycling of LTO electrodes demonstrated the potential of using the PTCLi₄ coating to increase the Li-ion transfer at the electrode–electrolyte interface at subzero temperatures. In fact, the PTCLi₄-coated LTO electrode delivered almost the same specific capacity at a C/2 rate when cycled at –20 °C as the pristine electrode cycled at 25 °C.