Effect of positive electrode microstructure in all-solid-state lithium-ion battery on high-rate discharge capability

Abstract

The transport of lithium (Li) in the composite electrode structure composed of an active material and a solid electrolyte in an all-solid-state lithium-ion battery (LIB) affects the power density of the battery. Thus, intercalation in the active material and Li-ion transport in the electrolyte material are key processes to determine the performance of the battery. Therefore, it is necessary to understand the correlation between electrode microstructure and LIB performance. In this regard, simulation models that allow for practical consideration of various electrode structures provide valuable information as to how well the design of the electrode structure can improve battery performance.The present study describes two unique numerical simulation techniques developed to investigate essential constitutive correlations between the power density and the microstructural descriptors for the positive electrode, such as the volume fraction of LiCoO2 (VLCO), the particle size of LiCoO2 (dLCO) and solid electrolyte (dSE). First, a phase-field method is used to construct a wide range of composite particle distribution 3D microstructures, where structural changes leading to a decrease in the free energy of the target system are simulated. Conventional calculations for the electrochemical reaction, Li diffusion in the active material, and the potential distribution in the electrode are combined with the structural properties to investigate the influence of the electrode microstructure on the high rate discharge capacity. Second, a regression model, such as a neural network, is used to obtain a comprehensive relationship between the high-rate capacity and microstructural parameters extracted from the 3D microstructure.The simulations demonstrated that the size ratio of dLCO to dSE influences the characteristics of the high-rate discharge process by adjusting the degree of tortuosity of the Li conduction path. The transition from high to low capacity at 10 mA/cm2 occurs with the VLCO of 70–80 vol% for dLCO:dSE = 0.8 μm: 0.8 μm, and 75–85 vol% for dLCO:dSE = 2.3 μm: 0.8 μm by maintaining a low tortuous Li-ion path even at low SE volume fractions. This relative particle size effect is more prominent when the intrinsic ionic conductivity of lithium exceeds 5.0 × 10−4 S/cm.