Optimizing the Hydrothermal Synthesis of Micro-Sized Olivine LiFePO<sub>4</sub>

The low tap density of LiFePO4 is hindering the energy and power density of lithium-ion batteries in portable electronics, electric vehicles, and stationary electricity storage applications. As part of our work to investigate the pathological mechanism of performance degradation in large particle LiFePO4, micro-sized pristine LiFePO4 without modifications, such as surface coating or bulk doping, was first prepared hydrothermally by optimizing the synthesis parameters in this work. The influences of precursor concentration, solution pH, hydrothermal temperature, and heating time on the phase structure, particle size, and morphology of the products were systematically investigated. It was found that the particle size of LiFePO4 increases with decreasing pH value, increasing precursor concentration, increasing hydrothermal temperature, and increasing heating time during hydrothermal synthesis. The performance degradation of large particle LiFePO4 was demonstrated by these intrinsic samples. The specific discharge capacity decreased from 152 to 80 mAh·g-1 at 0.1C rate when the particle size was increased from 0.7 to 16.5 μm. Moreover, less capacities were retained after 100 cycles at 1C rate for larger particle materials. Finally, the optimized LiFePO4 with a distorted diamond shape was prepared for later investigation of the plausible mechanism of performance degradation in large particle LiFePO4. Its electrochemical performance was preliminarily discussed, and will need to be improved in future to obtain practical high energy/power density LiFePO4 cathodes for lithium-ion batteries. [Article] doi: 10.3866/PKU.WHXB201209271 www.whxb.pku.edu.cn 物理化学学报(Wuli Huaxue Xuebao) Acta Phys. -Chim. Sin. 2012, 28 (12), 2885-2892 December Received: July 3, 2012; Revised: September 7, 2012; Published on Web: September 27, 2012. ∗Corresponding author. Email: ylxu@mail.xjtu.edu.cn; Tel: +86-29-82665161 C Editorial office of Acta Physico-Chimica Sinica 2885 Acta Phys. -Chim. Sin. 2012 Vol.28