Design Strategy for Optimal Mixing Ratio Based on Structure–Performance Correlation of SC–PC NCM811 Cathodes

Abstract

This study proposes an optimized mixing ratio of single-crystal (SC) and polycrystalline (PC) NCM811 particles as a cathode material design strategy to enhance the performance and lifespan of high-energy- density lithium-ion batteries. SC particles offer superior mechanical stability, which is advantageous for long-term cycling durability. However, their low specific surface area can increase interfacial resistance with conductive agents and result in discontinuous electronic pathways, limiting electrolyte penetration and rate capability. In contrast, PC particles have a porous structure and high surface area, which promote ion diffusion and electronic conductivity, but are structurally vulnerable to particle fracture and degradation during repeated charge–discharge cycles.

In this work, five SC:PC mixing ratios (SP10, SP73, SP55, SP37, SP01) were systematically investigated to evaluate the effects on electrode structural properties (porosity, tortuosity, and electrolyte uptake), transport characteristics (composite conductivity, charge transfer resistance (Rct), and lithium- ion diffusion coefficient (DLi⁺)), and electrochemical performance (rate capability and cycle stability). Among them, the SC:PC = 3:7 composition (SP37) demonstrated a densely packed yet uniformly porous structure that enabled continuous and efficient transport pathways for both ions and electrons. As a result, the SP37 electrode achieved a capacity retention of 66.77% at 3C under 2.5 mAh cm⁻² and 78.5% after 200 cycles at 0.5C. Under high-loading conditions (5.0 mAh cm⁻²), the same composition maintained 46.5% capacity at 3C and 73.5% retention after 100 cycles at 0.5C, validating its structural scalability and practical applicability.

These improvements are not merely due to compositional averaging from particle mixing, but are attributed to the optimized transport mechanism arising from the structural and functional complementarity between SC and PC particles. This study quantitatively establishes the causal correlations among structure, mechanism, and performance in SC–PC composite electrodes and presents a practical framework for composition optimization in high-energy-density cell design.