1. Introduction
With the rapid development of smart grid, electric vehicle technology and unmanned aerial vehicles (UAVs), energy storage devices have received great attention in recent years [1], [2]. As compared with the traditional lead-acid batteries, nickel cadmium batteries and nickel hydrogen batteries, Lithium-ion (Li-ion) batteries have many advantages of high energy density, low self discharge rate, no memory effect, etc. Thus, it is likely to be the most potential energy storage device.