Green Synthesis of Manganese-Rich Carbonate Precursor with High Sphericity for Cobalt-Free Lithium-Rich Cathode Materials through Two-Stage Continuous Coprecipitation Method

Cobalt-free Li-rich Mn-based cathode materials with the formula xLi2MnO3·(1 – x) LiMO2 (M = Ni, Mn, Fe...) are regarded as the most promising cathode materials for industrialization. However, the Li-rich Mn-based precursors prepared by the conventional continuous coprecipitation method using ammonia–water as a complexing agent suffer from several drawbacks, including environmental concerns, uneven particle size distribution, and poor sphericity. To address these issues, we developed a novel approach to reduce environmental pollution, lower raw material consumption, and prepare cobalt-free lithium-rich manganese cathode precursors with uniform particle size distribution and good sphericity. Specifically, sodium carbonate and sulfate were used as raw materials to prepare Ni0.25Mn0.75CO3 precursors via a two-stage continuous coprecipitation method. The resulting Ni0.25Mn0.75CO3 precursors exhibited a homogeneous elemental distribution, a uniform primary particle size, and a narrow size distribution of secondary particles. Compared to the carbonate precursor prepared by the traditional continuous coprecipitation with ammonia–water as the complexing agent, the precursor prepared in this study had better particle size distribution and sphericity, compact internal structure, and no internal voids. Moreover, this preparation method is both environmentally friendly and cost-effective. To further evaluate the performance of the carbonate precursor, Ni0.25Mn0.75CO3 was prepared into Li1.2Mn0.6Ni0.2O2 cathode material by optimizing the sintering conditions. The resulting Li1.2Mn0.6Ni0.2O2 cathode material featured a loose and porous internal structure with a uniform distribution of nickel, manganese, and oxygen elements within its particles. The discharge capacity of the cathode material was 217.8 mAh/g at 2–4.6 V and 0.1 C rate. The capacity retention rate was 95.9% after 200 cycles. Additionally, it exhibited a high-rate discharge capacity of 154.6 mAh/g at 5 C. Notably, compared with the Li1.2Mn0.6Ni0.2O2 cathode material prepared by the traditional continuous coprecipitation method, the material synthesized in this study demonstrated superior discharge capacity, cycling performance, and thermal stability. This study provides valuable insights into the green preparation of Ni0.25Mn0.75CO3 precursors and Li1.2Mn0.6Ni0.2O2 cathode materials, offering a sustainable and efficient pathway for their industrial application.