Electrochemical performance and chemical properties of oxidic cathode materials for 4 V rechargeable Li-ion batteries

The systems Li1+xMn2−xO4−δ and Li1−xNi1+xO2 were studied as oxidic cathode materials for 4 V rechargeable Li-ion cells. From a comparison of the results it follows that the spinel system can be subdivided into three regions: in region I (0 ≤ x < 0.05) the electrochemical performance is unsatisfying due to a large volume reduction of about 7.5%, inducing stress, multiphase materials and capacity fading. Region II (0.05 less, approximate x less, approximate 0.2) contains the best cathode material with a composition near x = 0.1. The spinel framework is stable against Li extraction. In region III (0.2 ≤ x ≤ image) the capacity is too low for an application in the 4 V region. In the system Li1−xNi1+xO2 the highest capacity is observed for LiNiO2 with x = 0. Experimental difficulties during material synthesis were overcome by suppression of the decomposition of LiNiO2 into Li1−xNi1+xO2, Li2O and O2.