Negative Thermal Expansion Behavior Enabling Good Electrochemical‐Energy‐Storage Performance at Low Temperatures

Abstract

Metal‐ion batteries (such as lithium‐ion batteries) are very popular energy‐storage devices nowadays. However, low temperatures cause their poor electrochemical kinetics and performance, significantly limiting their wide applications in cold environments. Here, we propose that electrochemical energy‐storage materials with negative‐thermal‐expansion (NTE) behavior can enable good low‐temperature electrochemical performance, which becomes a new strategy to tackle the low‐temperature issues of metal‐ion batteries. LiTi2(PO4)3 (LTP) with an a‐direction thermal expansion coefficient of −1.1 × 10−7 K−1 is used as a model material. As the temperature decreases, the transverse vibration of O atoms not only increases the transverse distances among O atoms connected to Li/Ti atoms, but also widens the Li+‐transport channels and enlarges Li+‐insertion sites along the [12 ‐1] direction, which are mainly controlled by the lattice parameter a. Consequently, carbon‐coated LTP (C‐LTP) retains good electrochemical performance at −10 °C, including fast Li+ diffusivity (84% of that at 25 °C), large capacity (96% of the theoretical capacity), and superior rate capability (83% capacity retention at 5C vs. 0.5C). Moreover, the more open crystal structure of LTP at the lower temperature allows smaller maximum unit‐cell‐volume expansion, resulting in better cycling stability of C‐LTP at −10 °C (96.8% capacity retention over 1000 cycles at 2C).