Li-rich layered materials are the promising high capacity cathode with superior energy density for the next-generation Li-ion batteries. The existence of excess lithium in these cathodes resulted in the high discharge capacity (>250 mAh g^-1) with excellent structural and electrochemical stability. However, several challenges that hinder their application are poor rate capability and electrochemical Li irreversibility due to O₂ loss in the first charging cycle and undesired phase transformation during cycling.[1]

Extensive efforts has been made to improve the Li reversibility, employing aliovalent metal doping in the Li₂MO₃ component due to an enhanced structural stability and improved electronic conductivity.[2, 3] In a step further, an intentional inclusion of excess lithium as a charge compensation in the aliovalent doped Li₂MO₃ cathodes were least investigated.

Herein, we report Li_2+xRu_1-xCo_xO₃ (x = 0, 0.1, 0.2, and 0.5) cathode with an enhanced electrochemical Li reversibility at high C rate. The structural and electrochemical properties were investigated by X-ray diffraction, solid-state NMR, X-ray photoelectron spectroscopy, galvanostatic cycling, and cyclic voltammetry to understand the enhancement in the Li reversibility and rate capability of the cathode. High-performance Li_2.1Ru_0.9Co_0.1O₃ cathode delivered an initial capacity of 250 mAh g⁻¹ and enhanced Li⁺ extraction of 1.00 mol (78 % capacity retention) after 50 cycles at 1C compared to 0.48 mol of Li⁺ extraction in the pristine Li₂RuO₃. Low Co³⁺ content could realize an enhanced reversible Li⁺ extraction originating from the cation ordering, facile charge transfer, and improved reversible anion-redox chemistry. The origin of the enhanced Li reversibility on the structural and electrochemical properties of cathodes were investigated.

References

1. M.M. Thackeray, C.S. Johnson, J.T. Vaughey, N. Li, S.A. Hackney, J. Mater. Chem., 15 (2005) 2257-2267.
2. M. Sathiya, K. Ramesha, G. Rousse, D. Foix, D. Gonbeau, A.S. Prakash, M.L. Doublet, K. Hemalatha, J.M. Tarascon, Chem. Mater., 25 (2013) 1121-1131.
3. M. Sathiya, G. Rousse, K. Ramesha, C.P. Laisa, H. Vezin, M.T. Sougrati, M.L. Doublet, D. Foix, D. Gonbeau, W. Walker, A.S. Prakash, M. Ben Hassine, L. Dupont, J.M. Tarascon, Nat. Mater., 12 (2013) 827-835.