We fabricated prismatic lithium-ion cells with a LiFePO4-based cathode material and examined the long-term cyclability and high thermal stability of the LiFePO4 in the cells to support the application of this material in large cells. The cells exhibited excellent long-term cyclability. In a high rate charge-discharge test, more than 6000 cycles were completed without any serious reduction in capacity. A cathode electrode sheet incorporating LiFePO4-based material taken from the cell after a test consisting of more than 8000 cycles exhibited little deterioration compared with an electrode sheet obtained from an unused cell. The thermal stability of the LiFePO4 in the cells was examined with a heating test at 180 degrees C, a nail penetration test, and a crush test. Although the cell case swelled slightly in the heating test, the cells did not smoke or catch fire in any of the safety tests. The cathode electrode taken from the prismatic cell used in the 180 degrees C heating test had a similar capacity and discharge profile to a cathode taken from an untested cell. (c) 2005 The Electrochemical Society.