Fabricating a thin gradient surface layer to enhance the cycle stability of Ni-rich cathode materials

• Published in: Journal of alloys and compounds 2022-02, Vol.893, p.162162, Article 162162
• Main Authors: Feng, Zhijie, Liu, Yali, Qian, Ruicheng, Song, Hui, Liu, Meng, Li, Panpan, Lyu, Yingchun, Xiao, Dongdong, Guo, Bingkun
• Format: Article
• Language: English
• Subjects: Cathodes; Cycles; Electric vehicles; Electrochemical performance; Electrode materials; Flux density; Gradient structure; Lithium; Lithium-ion batteries; Mechanical properties; Mechanical strain; Ni-rich cathode; Nickel; Rechargeable batteries; Structural stability; Surface layers; Surface stability; Surface structure; Surface structure stability; Tensile stress; Transition metals
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.162162

•A thin gradient surface layer is fabricated on LiNi0.90Co0.05Mn0.05O2.•The mechanical fusion and co-lithiation method is easy up-scaled.•The gradient structure results from the element interdiffusion during annealing.•The outer layer with smaller lattice parameters reduces the surface tensile stress.•The gradient structure material shows a capacity retention of 84% after 200 cycles. [Display omitted] Although Ni-rich cathode materials have made a great success in the field of electric vehicles due to their high capacity and low cost, many efforts are still focused on further increasing their capacity through increasing the Ni content. However, the increased Ni content usually leads to a more serious surface structure reconstruction and hence higher resistance during electrochemical cycling, which has become a major issue for Ni-rich cathodes. In order to explore a balance between surface structure stability and high energy density, a model Ni-rich material with transition metal ion gradient is prepared using a mechanical fusion and co-lithiation method, which is easy for large-scale fabrication. The gradient structure sample contains an inter bulk of LiNi0.90Co0.05Mn0.05O2 and a thin gradient outer layer with lower nickel content. The gradient sample shows a superior cycling property, rate retention, and improved safety performance. Systematic study suggests that the possible reasons for the improved electrochemical and mechanical performance of the gradient nickel-rich materials are the high stability of lower-Ni surface and the decreased surface tensile stress. This work provides an easy up-scaled method to build a gradient structure and a further in-depth understanding on its structure stabilization mechanisms, which are essential for developing high energy-density lithium-ion batteries.