The rechargeable Li–liquid battery was developed using waste Li ion battery materials immersed in water and used as the liquid cathode. Either the Li metal or Li ions (by the formation LixC6 or Li4+xTi5O12) was harvested from waste Li ion source materials such as a waste anode (LixC6), cathode (LixFePO4), and electrolyte (LiPF6 in EC:DEC) by charging the cell, which then discharged with the waste products in the liquid cathode solution to produce electric energy. When the Li4Ti5O12 was used as the anode with the waste products as the cathode in the proposed battery system, a good cycle-life with high coulombic efficiency was observed.