The lithium ion battery, which is mainly composed of cathode, anode, separator, and electrolyte, is one of the most popular energy storage devices. Among the components, the cathode is the key to the battery’s electrochemical performance, affecting power density and cycle life. Over the past two decades a great deal of attention has been directed to the representative cathode material, olivine-structured LiFePO₄ due to high energy density, excellent thermal stability, attractive cost, and environmental benign. In order to achieve a high-rate electrochemical performance, researchers have long been committed to shortening the diffusion distance of lithium ion, that is, to reducing the crystal size along the [010] direction. Recent thought-provoking research has pointed out that the electrode is composed of ensembles of particles, and the electrode’s electrochemical performance is ultimately determined by the fraction of actively intercalating particles. Therefore, how to obtain a high number of active particles is a core problem in the research of LiFePO₄ as a cathode material.

To solve this problem, the research group led by Prof. Wang Xiaohui from the Institute of Metal Research, Chinese Academy of Sciences (IMR, CAS) for the first time synthesized 12 nm-thick [100]-oriented LiFePO₄ nanoflakes by a simple one-pot solvothermal method though creating an acidic synthesis environment as waterless as possible, on the basis of their early studies (J. Phys. Chem. C 114: 16806 (2010); Phys. Chem. Chem. Phys. 14: 2669 (2012); CrystEngCommun 16: 10112 (2014)). As identified by voltage hysteresis experiments, the electrode was composed of the [100]-oriented LiFePO₄ nanoflakes. It is intriguing that the ultrathin [100]-oriented LiFePO₄ shows excellent rate performance and cycling stability. It delivers a discharge capacity of 122 mAh g−1 (72 percent of theoretical capacity) even at a current rate of 20 C (60 min/20 = 3 min) and retains a capacity of 90 percent after 1000 cycles at 10 C.

This work offers the new idea that decreasing the Li+ diffusion direction along the b axis is not the only way to design high-performance LiFePO₄ cathode materials; rather, it can also be achieved by reducing the distance along the a axis through increasing the active population.

The results are published in Nano Letters(16: 795-799). They exhibit the smallest voltage gap by far. In addition, potentiostatic intermittent titration technique experiments indicate that both the activation rate and conversion rate in the [100]-oriented LiFePO₄ nanoflake electrode are all significantly large. Such experimental results demonstrate a high percentage of active population for the [100]-oriented nanoflake electrode.

Contact: 

Prof. Wang Xiaohui

Email: wang@imr.ac.cn

Institute of Metal Research, Chinese Academy of Sciences 

72 Wenhua Road, Shenyang 110016, Liaoning, China