Study on Li_xNi_0.5Mn_1.5O₄ (x = 0.8, 0.9, 1, 1.1, and 1.2) high-voltage cathode for lithium-ion batteries

Samples Li_xNi_0.5Mn_1.5O₄ (x = 0.8, 0.9, 1.0, 1.1, and 1.2) are synthesized to study the effects of Li contents. When Li contents are not enough, part of the nickel-manganese oxides cannot transfer to LiNi_0.5Mn_1.5O₄ and remain in the product. When Li contents are too much, small amount of lithium-rich oxide is formed. In voltage window of 3.5~4.95 V, Li_1.0Ni_0.5Mn_1.5O₄ has the best rate performance due to that the spinel provide a three-dimensional pathway for lithium-ion diffusion. Li_0.8Ni_0.5Mn_1.5O₄ and Li_0.9Ni_0.5Mn_1.5O₄ show low specific capacities and poor rate performance due to the remained nickel-manganese oxides. Li_1.1Ni_0.5Mn_1.5O₄ and Li_1.2Ni_0.5Mn_1.5O₄ have lower initial coulombic efficiencies due to the existence of lithium-rich oxide. In voltage window of 1.95~4.95 V, the samples can deliver high specific energy above 800 Wh Kg⁻¹. With the existence of lithium-rich oxide, Li_1.2Ni_0.5Mn_1.5O₄ shows good cycling stability with a high specific energy of 645 Wh Kg⁻¹ after 50 cycles.