Suppressed capacity/voltage fading of high-capacity lithium-rich layered materials via the design of heterogeneous distribution in the composition

Abstract

Lithium-rich layered materials, Li_1+xM_1−xO₂ (M = Mn, Ni, Co), have been under intense investigation as high-performance cathode materials for lithium ion batteries due to their high discharge capacity, low cost and environmental benignity. Unfortunately, the practical uses of these oxides have so far been hindered by their severe capacity and voltage fading during high voltage cycling (>4.5 V vs. Li/Li⁺). In an attempt to overcome these problems, herein, a novel lithium-rich Li_1.14[Mn_0.60Ni_0.25Co_0.15]_0.86O₂ microsphere with heterogeneous distribution in the composition has been reasonably designed and successfully synthesized via a co-precipitation method. The chemical composition in the spherical particle is gradually altered by increasing the Mn concentration while reducing the Co content from the particle center to the outer layer. At the same time, the Ni content remains almost constant throughout the particle. The coin cell with the heterogeneous cathode material delivers a high discharge capacity of over 230 mA h g⁻¹ between 2.0 V and 4.6 V, and shows excellent cyclic stability due to the continuous increase of the stable tetravalent Mn towards the outer surface of the spherical particles, corresponding to 93.8% capacity retention after 200 cycles at 0.5 C. More importantly, the as-prepared material exhibits a significantly lower discharge voltage decay compared with conventional materials, which may mainly be ascribed to the suppression of the layered-to-spinel transformation in the Co-rich/Mn-depleted regions of the spherical particle. The capacity and voltage fading of the lithium-rich layered material are simultaneously suppressed by the special architecturual design, and the results here will shed light on developing cathode materials with special structures and superior electrochemical properties for high-performance lithium ion batteries.