Electrode Kinetic Modeling And Structure Optimization For High-rate Lithium-Ion Batteries

With the explosive growth of the global power battery industry,high-rate lithium-ion batteries have become the focus of technological development.The lithium-ion battery electrodes are ion-intercalation electrodes with a composite porous structure,in which there is charge/mass transport in multiple phases and interfacial electrochemical reaction.Under high-rate charging/discharging,these kinetic processes form an obvious coupling relationship,resulting in complex rate-limiting mechanisms of the battery and great challenges in precise electrode design.Therefore,this work lauches a systematic study on the electrode kinetic modeling and structure optimization for high-rate lithium-ion batteries.A single-layer particle electrode structure and its decoupling measurement method are designed to achieve the separation of single-process overpotentials and solve the problem of inaccurate kinetic measurement caused by electrode multi-process coupling.This method is applied to the precise measurement of the interfacial reaction rate constant and the solid-phase Li⁺diffusion coefficient of electrode active particles.The study shows that there is a deviation of about 1 order of magnitude in the reaction rate constant measured by conventional electrode measurements.The solid-phase Li⁺diffusion coefficient measured by traditional electrochemical methods based on small current testing is lower,while the actual value tends to increase with the increasing rate.Meanwhile,the curved Tafel plot in the charge transfer kinetics of the electrode/electrolyte interface and the limitations of the classic Butler-Volmer model at high lithiation state and high current density are revealed.An interfacial-ion intercalation reaction model is proposed to accurately reveal the limiting process of electrode kinetics at high rates,which is a problem that is not well described by the Butler-Volmer model.By considering the electrostatic interaction between intercalated ions and the host material crystal,the model accurately predicts the ultra-high rate behavior for different active particles.This model is applied to establish a multi-process coupled porous electrode kinetic model,and a rate-limiting process identification method based on overpotential decomposition is proposed to reveal the limiting process and its evolution under different electrode structure designs and material systems.As a verification,the liquid-phase Li⁺transport kinetics that restrict the rate performance of high-capacity（>4 m Ah/cm²）Li Ni_0.5Mn_0.3Co_0.2O₂||Li batteries are experimentally regulated.The proposed decoupling measurement method and electrode kinetic model are applied to investigate the triggering mechanism of Li plating under fast charging conditions,revealing that the Li plating overpotential≤0 V is the triggering condition for Li plating on graphite.Based on this overpotential-triggering mechanism,a Li-plating kinetics model for porous graphite electrodes is established,accurately predicting the Li deposition/stripping behavior on the graphite electrode surface during 1-4C rate charging processes.The phenomena of Li plating caused by different rate-limiting processes are successfully explained by the model,and it is verified by the experimental result that Li plating can be controlled via regulating liquid-phase ion transport and interfacial charge transfer kinetics.Finally,a systematic optimization strategy for designing fast-charging graphite electrodes is proposed.A chemical foaming manufacturing process and optimized design method for oriented-pore structured electrodes are developed and significantly enhance the rate performance of the thick electrodes with Li Ni_0.5Mn_0.3Co_0.2O₂ material,which is limited by liquid-phase Li⁺transport.The principle of chemical foaming formation and control methods for structural parameters of the oriented pores are studied,and the stability of the chemical foaming process is verified.Using 3D electrochemical simulation of the porous electrode kinetics model,a unique transport mode with two ion pathways in the oriented pore electrodes is revealed,and the optimal oriented porosity is designed.Rate testing shows that the oriented-pore electrodes display a discharge capacity of about 8 times that of the conventional electrodes at 5C rate.