Hierarchical porous Li4Ti5O12–TiO2 composite anode materials with pseudocapacitive effect for high-rate and low-temperature applications

Abstract

Dual-phase hierarchical porous Li₄Ti₅O₁₂–TiO₂ (HP LTO–TO) microspheres were synthesized using a topochemical conversion method and used as an anode material in high power lithium ion batteries, particularly for use in low temperature applications. The HP LTO–TO microspheres are composed of ultra-thin nanosheets with a large specific surface area for interface intercalation reactions and also to provide a much reduced diffusion path for both electrons and lithium ions. The HP LTO–TO electrode was found to exhibit excellent low-temperature cycling capability and rate performance. The discharge capacities of HP LTO–TO under a current rate of 0.2C reached 167 mA h g⁻¹ at 25 °C, 143 mA h g⁻¹ at 0 °C, 130 mA h g⁻¹ at −10 °C, and 94 mA h g⁻¹ at −40 °C. A discharge capacity of 77 mA h g⁻¹ is readily attainable at −20 °C at a high current rate of 5C. The aforementioned high capacity and rate performance at low temperature can be partially attributed to the novel hierarchical porous dual phase microsphere structure made up of thin nanosheets. It is also hypothesized that the co-existence of dual LTO and TO phases may create cation vacancies and/or result in a favorable interface between LTO and TO that permit fast charge and ion transport, even at very low temperatures. This can be attributed to the fact that HP LTO–TO has a relatively low activation energy for Li⁺ diffusion and a fast surface faradaic reaction, which benefits from the abundant dual-phase interfaces and grain boundaries, as well as the large specific surface area.