Lithium ion batteries have the advantages of light weight, large capacity, and no memory effect, making them widely used – many digital devices use lithium ion batteries as power sources, although their prices are relatively expensive. Lithium ion battery has a high energy density, its capacity is 1.5~2 times of that of Nickel–metal hydride battery with the same weight, and it has a very low self discharge rate. In addition, lithium-ion batteries have the advantages of almost no “memory effect” and no toxic substances, which are also important reasons for their widespread application.