A carbon-coated platelike LiFePO4 particle (space group: Pnma) was prepared by employing a hydrothermal method at 190 degrees C. The obtained particle had a preferred crystal orientation with a (020) texture, which was revealed by transmission electron microscopy and electron diffraction. After the hydrothermal treatment, further heat-treatments at high temperatures (400-800 degrees C) were carried out to increase the electrical conductivity of the carbon layer, and the conductivity was considerably improved by heat-treatment at temperatures higher than 700 degrees C. The obtained LiFePO4/C particle exhibited a high-rate charge-discharge capability in a liquid electrolyte of 1.0 mol dm(-3) LiPF6/ethylene carbonate+diethyl carbonate (1:1 volume ratio). The discharge capacity of the particle was more than 100 mAh g(-1) at a discharge rate of 10 C. Furthermore, an all-solid-state cell comprising Li/polymer electrolyte/LiFePO4 was fabricated using a block copolymer electrolyte consisting of polyethylene oxide and polystyrene, and the charge-discharge performance of the cell was examined at 30 degrees C. The all-solid-state cell exhibited a discharge capacity of 122 mAh g(-1) at a rate of 0.5 C (147 mu A cm(-2)) even at around room temperature. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2988048] All rights reserved.