Optimization of LiB electrode with bi-diameter active particles using a microstructure-resolved model

The microstructure of electrodes significantly affects the performance of lithium-ion batteries (LiBs), and using bi-diameter active particles is a simple but effective way to regulate the microstructure of commercial LiB electrodes. Herein, to optimize the LiB cathode of bi-diameter active particles, a microstructure-resolved model is developed and validated. The results indicate that randomly packing of bi-diameter active particles is optimal when the electrolyte diffusion limitation is mild, as it provides the highest volume fraction of active materials. Under strong electrolyte diffusion limitations, layered packing with small particles near the separator is preferred. This is because particles near the current collector have a low lithiation state. Besides, optimizing the random packing can further improve the energy density. For energy-oriented LiBs, a low volume fraction of small particles (0.2) is preferred due to the higher volume fraction of active materials. For power-oriented LiBs, a high volume fraction of small particles (0.8) is better because it reduces diffusion limitations. This work should serve to guide the optimal design of electrode microstructure for achieving high-performance LiBs.

电极的微观结构对锂离子电池（LiBs）的性能具有显著影响，而采用双粒径活性颗粒（bi-diameter active particles）是调控商用锂离子电池电极微观结构的一种简便却高效的手段。在此，为优化采用双粒径活性颗粒的锂离子电池正极，本研究构建并验证了一款微观结构解析模型（microstructure-resolved model）。研究结果表明，当电解液扩散限制（electrolyte diffusion limitation）较为温和时，双粒径活性颗粒的随机堆砌为最优排布方式，因其可实现最高的活性物质体积分数。在电解液扩散限制较强的工况下，优先采用小颗粒靠近隔膜（separator）的分层堆砌结构，这是因为集流体（current collector）附近的颗粒锂化状态（lithiation state）较低。此外，对随机堆砌结构进行优化可进一步提升能量密度。面向能量型锂离子电池，优选体积分数为0.2的低占比小颗粒，以此获得更高的活性物质体积分数；而面向功率型锂离子电池，优选体积分数为0.8的高占比小颗粒，因其可有效降低扩散限制。本研究可为实现高性能锂离子电池的电极微观结构优化设计提供指导。