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The entropic heat coefficient (i.e., dU/dT) of Li[Ni x Co y Mn z ]O 2 /graphite before and after cycle was determined using the electrochemical thermodynamics measurements (ETMs) tool. DU/dT could be attributed to the individual electrodes for this notable battery and associates with the Li-intercalated state. Lithium intercalation number in negative and positive electrode was calculated and compared for the battery before and after cycle, respectively. Results show that the trend of dU/dT with Li-intercalated state before and after cycle is basically consistent except for the initial and maximum state. DU/dT has the typical characteristics of stage structures of graphite. In particular, these changes is independent of the battery aging. Negative electrode has greater Li-intercalated depth loss than that of positive electrode after cycle, thus negative electrode is the dominant degradation factor of the battery.

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A 288V/8Ah manganese type Li-ion battery system for hybrid electric vehicle was developed. The performances of single-cell and battery system were tested. For the single-cell, the discharge power and regen power are more than 312.5W and 250W at 45-85% DOD, respectively, and the cycle life is more than 2000 cycles. For the battery system, the continuous discharge power is 41kW at 20C rate, and an 80% charge capacity can be achieved in 10 minutes. The values of voltage difference of 80 single-cells are stable with 0.05V, 0.1V and 0.2V at 1C, 10C and 20C rate in the range of 15%-75% DOD in the battery system, respectively. The discharge power and regen power of battery system are more than 25kW and 20kW at 45-85% DOD, respectively, and its available energy is about 1000Wh. The 288V/8Ah battery system with a good discharge rate performance and a fast charging capability could be used in HEV.