In recent years, Li-rich, Mn-based Li[Li_1-x-yMe_xMn_y]O₂ (Me=Co, Fe, Cr, Ni, etc.) cathode materials have received world-wide attention for their high capacity (>250 mAhg^-1) when operating at high voltage [1]. However, the cathode materials still suffer from poor rate capability and gradual capacity degradation during cycling, accompanied with hysteresis and voltage fade [2]. In order to overcome those issues, extensive studies have been performed to improve the electrochemical performance of Li[Li_1-x-yMe_xMn_y]O₂ cathode materials. Among all the factors investigated, it was found that Mn/Ni content of Li[Li_1-x-yMe_xMn_y]O₂ could be an important factor that limits the rate capability and influences the capacity/voltage fade [3]. As such, in this paper, we study the effects of Mn/Ni content of Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂on structure, morphology, rate capability, capacity degradation and voltage fade during cycling.

Fig.1. The cycle performance of Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂in the voltage range of 2.5-4.6 V at 1.0 C after three formation cycles in the voltage of 2.0-4.8 V at 0.1 C, (a) discharge capacity and (b) median voltage of discharge

Results and Discussion

Fig. 1 shows the capacity cycling performance (Fig. 1 (a)) and median voltage of discharge (Fig. 1 (b) of Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂ (x=0, 0.02, 0.04, 0.06) in the voltage range of 2.5-4.6 V at 1.0 C after three formation cycles in the voltage of 2.0-4.8 V at 0.1 C. As shown in Fig. 1(a), it can be seen that initial discharge capacities decrease with x value increasing in the voltage of 2.0-4.8 V at 0.1 C ,during the formation cycles. Meanwhile, Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂ (x=0, 0.02, 0.04, 0.06) delivers the initial discharge capacity of 181.0, 178.4, 157.6, 142.7 mAhg^-1 in the voltage of 2.5-4.6 V at 1.0 C and capacity retention are 75.0, 87.2, 90.0 and 88.9% of an initial discharge capacity after 200 cycles, respectively. Fig. 1(b) shows the variation of median voltage of discharge of Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂ (x=0, 0.02, 0.04, 0.06) over 200 cycles. It is noted that Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂ shows much smaller voltage fade with x value increasing. Our results indicate that the Li_1.13Mn_0.54-xNi_0.27+xCo_0.06O₂ with lower Mn content and higher Ni content demonstrates much better electrochemical performance with high capacity retention and small voltage fade comparing to Li_1.13Mn_0.54Ni_0.27Co_0.06O₂.

References

[1]  M. M. Thackeray, S.-Ho Kang, C. S. Johnson, J. T. Vaughey, R. Benedek and S. A. Hackney, J. Mater. Chem., 17, 3112 (2007).

[2]  J.R. Croy, K. G. Gallagher, M. Balasubramanian, B. R. Long, and M. M. Thackeray, J. Electrochem. Soc., 161(3), A318 (2014).

[3]  E.-S. Lee, A. Manthiram, J. Mater. Chem. A, 2, 3932 (2014).