Plug-in electric vehicles(PEVs) show enormous potential in reducing the consumption of fossil fuels and the emission of greenhouse gases. However, its relatively high price, which mainly comes from the battery system, impedes its popularization in market. Some researchers put forward that if the secondary use of EV batteries is achieved, it may offset part of the cost of electric vehicles. Researchers from US NREL play an important role in the identification of "the secondary use of EV battery". As PEVs energy storage device, Lithium ion battery is usually the most expensive part of electric vehicles, which still has some environmental pollution problems in the processing of used batteries. The secondary use of EV batteries could not only expand the application of electricity, but also promote the extensive application of PEVs. What’s more, their application in energy storage power gird could also supplement the electricity demand of the grid at peak times and help to create a cleaner and more flexible grid. NREL has confirmed that a capacity of 70% initial capacity is kept in the used lithium-ion batteries, which enables us to use their electrode materials again(valve regulated gel battery).