Descriptor-Based Graded Electrode Microstructures Design Strategies of Lithium-Ion Batteries for Enhanced Rate Performance

Abstract

Microstructure engineering of electrodes is one of the efficient routes to improve rate performance of lithium-ion batteries (LIBs). Currently, there is a lack of descriptors to rationally guide the regional electrode design. Here, we propose two descriptors, the time differential of the average state of lithium (SoL) and the span of SoL in individual particles, to identify the rate performance constraints across the electrode depth. 3D microstructure-based electrochemical simulations are performed on a homogeneous electrode, and the predictability of the microstructure-based model is verified with the experimental measurement on a LiNi1/3Mn1/3Co1/3O2 electrode. At electrode level, the descriptors divide the electrode into four regions, namely, a solid-state transport (SST)-controlled region, two mixed SST and liquid-state transport (LST)-controlled regions (SST-dominant and LST-dominant, respectively), and an LST-controlled region. Based on these insights, dual-gradient electrodes are designed with smaller particles in the SST-controlled region and graded porosity increasing from current collector to the separator. Results show that the optimized dual-gradient electrode has significantly more excellent LST capability compared to the homogeneous electrode, thus improving the utilization of particles near the collector. As a result, the capacity performance of the optimized dual-gradient electrode increases by 39% at 5C without sacrificing the gravimetric energy density.

Keywords

• lithium-ion batteries
• microstructure-based 3D model
• electrode penetration depth
• regional electrode design
• graded particle size and porosity