Li-rich Mn-based cathode materials have become an important candidate for next generation lithium-ion battery cathodes due to their high discharge specific capacity and wide voltage window. The Li-rich Mn-based oxide xLi₂MnO₃·(1-x)LiTMO₂ (TM=Mn、Ni、Co、Fe, etc.) exhibits advantages such as high energy density (~1000 W·h·kg^-1), and low cost. The layered Li-rich material consists of two components: LiTMO₂ and Li₂MnO₃. The Li₂MnO₃ component can be activated during the first charge above 4.5 V, and the oxygen redox reaction provides unique high capacity. However, severe side reactions and irreversible lattice oxygen release can trigger particle cracking, microcracks, and gas generation, leading to significant electrochemical performance degradation. Single-crystallization of particles, by eliminating grain boundaries, helps improve the structural stability of cathode materials and represents an effective strategy for enhancing battery cycling performance.

This study developed a simple and effective synthesis method to obtain micron-sized single-crystal Li-rich Mn-based cathode materials. Specifically, Mn_0.54Co_0.13Ni_0.13(CO₃)_0.8 precursor was synthesized using a carbonate co-precipitation method. The synthesized precursor was then mixed with 5% excess of Li₂CO₃ in a mortar. The mixture was loaded into a cylindrical pellet die with a diameter of 14 mm, and 300 MPa pressure was applied to the powder mixture in the cylindrical die and maintained for 1 min before removal. A two-step calcination process (with a heating rate of 3 ℃·min^-1) was employed, with the sample calcined in air at 500 ℃ for 3 h, and at 950 ℃ for 15 h. Finally, the sample was cooled to room temperature and ground to obtain the lithium-rich single-crystal material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LR-SC).

By employing a precursor densification strategy to reduce interfacial fusion resistance between particles and enhance mass transfer at particle interfaces, it facilitated grain fusion growth and enabled the formation of micron-sized single-crystal particles of LR-SC with particle sizes ranging from 1 μm to 3 μm. The results indicate that the coin cell assembled with the single crystal material delivers an initial discharge capacity of 243.3 mA·h·g^-1 at 0.2 C. Compared with polycrystals, the capacity retention rate after 200 cycles at 0.5 C is increased from 44.9% to 73.1%. The assembled pouch cell (10 mA·h) keeps 78.8% capacity retention rate after 250 cycles at 1 C, displaying remarkable rate capability and cycling stability.

The synthesized single-crystal Li-rich Mn-based cathode material exhibits uniform particle size, superior interfacial stability and cycling stability. By comparing the failure processes of single-crystal particles and polycrystalline secondary spherical particles, its stabilization mechanism was revealed. Compared with typical polycrystalline cathodes, the single-crystal material mitigates the transformation of the layered structure of layer into spinel and rock-salt phases, releasing only minimal gas during the first cycle, significantly enhancing the safety and practicality of material applications. This method provides a simple and feasible way for synthesizing micron-sized single-crystal Li-rich Mn-based cathode materials.