Performance degradation of Li_xFePO_4 (x = 0, 1) induced by postannealing

Authors: XIAOFEI SUN, YOULONG XU, XIAOYU ZHENG, XIANGFEI MENG, RUI ZHANG

Abstract: Olivine LiFePO_4 has been studied for more than a decade as a promising cathode material for rechargeable lithium batteries. However, the low electric conductivity and tap density still hinder its large-scale commercialization. Micro-sized LiFePO_4 is prepared by an optimized hydrothermal method in this paper. The influence of postannealing on the physicochemical properties of LiFePO_4 and FePO_4 is investigated to understand the plausible mechanism for performance degradation. It is found that postannealing even chemical delithiation greatly affects the particle size, morphology, pore distribution, surface area, and probably the lattice strain of Li_xFePO_4 (x = 0, 1). Consequently, the electrochemical performances of annealed materials are severely deteriorated because of the sluggish lithium diffusion, difficult electrolyte accessibility, and incomplete phase transition during charge/discharge. In addition, the ``self-healing'' process along with cycling is analyzed by in-situ synchrotron X-ray diffraction.

Keywords: Lithium iron phosphate, hydrothermal synthesis, postannealing, chemical delithiation, lithium ion battery, energy storage and conversion

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