Monocrystalline Sodium-Ion Cathode Composition Against Particle Fragmentation

The patent employs composite cathode materials comprising transition metal oxides (such as nickel ferrite, manganese ferrite) combined with other metal oxides or sulfides (e.g., CuO, ZnO, TiO2, MoS2). This composite structure synergistically combines the high capacity of transition metal oxides with the structural stability of accompanying materials, thereby maintaining high energy density while improving cycle performance through enhanced structural integrity during sodiation/desodiation cycles.

The patent systematically optimizes the compositional parameters of cathode materials, including the ratios of nickel, manganese, copper, zinc, and other elements (e.g., Ni0.4Mn0.4Cu0.1Zn0.1O2). By adjusting these compositional parameters and controlling sintering conditions (temperature, time, atmosphere), the material achieves optimal balance between capacity and structural stability, resolving the contradiction between energy density and cycle performance.

The patent employs surface coating strategies where thin film layers of stable oxides (such as Al2O3, TiO2, or LiNbO3) are formed on the cathode material surface. These coating layers act as protective shells that accommodate volume changes during sodium insertion/extraction, prevent particle fragmentation, and maintain structural integrity even at high capacity levels, thereby allowing greater sodium removal without compromising stability.

The patent incorporates buffer materials and designing intermediate phases (such as spinel structures or perovskite phases) that can accommodate lattice expansion and contraction during sodiation/desodiation. These pre-designed structural buffers absorb the mechanical stress of volume changes, preventing particle fragmentation and agglomeration that would otherwise occur when large amounts of sodium are removed to increase capacity.

The patent utilizes surface coating with stable oxide layers (such as Al2O3, TiO2, LiNbO3) that form protective barriers between the desalted cathode material and the electrolyte. These coating films prevent direct contact and harmful chemical/electrochemical interactions while allowing ionic transport, thereby enabling high capacity through extensive desalination without suffering from electrolyte degradation or material oxidation.

The patent introduces intermediate protective layers and surface modification treatments that act as mediators between the cathode material and electrolyte. These intermediate layers (such as conductive polymer coatings or atomic layer deposition films) provide a buffer zone that reduces direct interaction, suppresses parasitic reactions, and maintains material stability even when the cathode is heavily desalted to maximize capacity.