Constructing a robust Li-rich Mn-based oxide cathode with oxygen vacancies and strong B-O bonds by BN treatment

Abstract

Li-rich Mn-based oxide cathodes are one of the most promising cathode candidates for high energy density over 400 Wh kg−1, deriving from oxygen redox of Li-O-Li configuration. However, the deep oxygen oxidation would lead to the formation of peroxides and superoxides (O2n−, 0 < n ≤ 2) and even oxygen (O2), accompanied by crystal phase transformation and structure collapse. Herein, an integrative strategy of simultaneously regulating the right amount of oxygen vacancies (OVs) and B-atom doping is proposed to achieve differentially modification of both R-3 m and C2/m phases. Firstly, Rietveld refinement, HRTEM and in situ XRD results reveal that the linear increase of OVs content is achieved by regulating the amount of BN and the selective introduction of OVs inside the C2/m phase makes the oxygen partial pressure lower in the weak O-Li-O bonds of TM-layer and inhibits oxygen release at over 4.5 V. Meanwhile, kinetics test shows oxygen defects would accelerate the Li+ diffusion and reduce the electronic impedance driven by uneven local charge distribution. Secondly, lattice analysis shows the strong covalent B-O bonds located at the tetrahedral site not only prevent the overoxidation of the oxygen atoms at high voltage, but also hinder the migration of Mn atoms through tetrahedral sites, which effectively avoids the damage of the crystal structure. As a result, the modified cathode exhibits the excellent discharge specific capacity of 272 mA h g−1 at 0.1C, higher rate performance of 145 mA h g−1 at 5C, an outstanding capacity retention rate of 93% at 1C and lower voltage decay value of 0.43 V after 200 cycles. This promising strategy could simultaneously achieve both high energy density and superior cycling stability and help to advance industrial application of Li-rich Mn-based Cathodes.