Electrochemical Energy Storage Device for Electric Vehicles

Abstract

Because of an improved mass transfer process, chemical energy in a liquid phase, which has been absorbed into the micro-pores of porous electrodes, may be electrochemically converted into electrical energy at a high rate and with a long cycle life. Based on this principle, we demonstrated methods for a new electrochemical storage device, which had higher specific power, a much longer cycle life than existing storage batteries and a greater specific energy than existing supercapacitors. Even at the high current rate of 80 C for deep charge/discharge, a long cycle life (30,000) and good utilization efficiency have been achieved. This new device may be developed into a new family of energy storage systems with a variety of applications. The first important practical application could be on-board, rechargeable electric energy storage devices for electric vehicles. With the growing crises concerning natural resources and environmental pollutants, it has been an urgent need to utilize energy efficiently and cleanly. Specifically, the gradual depletion of petroleum resources has led to an immediate need for the development of battery-powered electric vehicle (EV) and hybrid electric vehicle (HEV). The power source has been the most critical problem in the development of EVs. One of the key challenges in the development of such a power source has been identifying a means to deliver/ accept high input/output power.Batteries have satisfactorily met many end-user demands when charged and discharged at a moderate rate. However, traditional batteries have been unable to meet the demands of very rapid and deep charging/discharging with a very long cycle life.1-5 For example, the energy and power of an "energy-type" Li ion battery were 160 Wh and 710 W, while those of a "power-type" Li ion battery were 107 Wh and 1250 W with the same weight, both manufactured by Johnson Controls-Saft Advanced Power Solutions (Joint venture between JCI and Saft). 6 These numbers illustrated that, upon increasing the power density by 76%, one third of the energy density was sacrificed by the battery.Supercapacitors have been developed as power-type energy storage devices for EV for acceleration, hill climbing and the recovery of braking energy. However, the main disadvantages of supercapacitors have been the low energy density and high cost. [7][8][9][10][11][12][13][14] A storage device for EVs/HEVs is expected to deliver highpower energy output pulses as well as having the capacity for rapid recharge. Thus, the device should possess the combined advantages of high specific power, a long life cycle, high specific energy, safety, and low cost.Here, we introduce a new device for energy storage that was based on the electrode reaction of porous electrodes soaked in the electrochemically active material in liquid solution. This paper illustrates our pursuits for high rate, deep charge-discharge and long cycle life performances that fulfill the requirements of electric vehicles and other portable devices. The performance of this device is discussed ...

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