Study on high-voltage cathode material LiNi_0.5Co_0.2Mn_0.3O₂

Soft package lithium-ion batteries were fabricated by using LiNi_0.5Co_0.2Mn_0.3O₂ as cathode material, and electrochemical tests were performed at different upper voltage limits (4.2 V, 4.25 V, 4.3 V, 4.35 V). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the pole pieces after 100 cycles. The XRD pattern showed that the batteries after 100 cycles still had a α-NaFeO₂ type structure and a layered structure. But the batteries′ I₀₀₃/I₁₀₄ ratio was less than 1.2 and cation disorder increased when the upper limit of voltage was 4.35 V. When the upper voltage limits was 4.2 V, 4.25 V, 4.3 V, and 4.35 V, the first discharge capacity of the batteries was 161.5 mAh/g, 162.9 mAh/g, 169.2 mAh/g, and 176.6 mAh/g, respectively. When the upper voltage limit was 4.25 V, 4.3 V and 4.35 V, the capacity was 0.87%, 4.77% and 9.35% higher than that at the upper voltage limit of 4.2 V, respectively. After 200 cycles (0.2 C), the batteries′ capability retention rate was 95.09%, 94.41%, 95.52%, and 95.56%, respectively, at the upper voltage limits of 4.2 V, 4.25 V, 4.3 V and 4.35 V. At the upper voltage limit of 4.35 V, although the batteries had cation disorder, their electrochemical performance was the best. It may be due to excessive charge injection of high valence Co ions into the Li layer. Thus, high electron conductivity was obtained when Co ions passed through the grain boundary network inside the large secondary particles.