Fast-charging graphite-based anode enabled by gradient silicon: from mechanism revelation to electrode design

Abstract

Fast-charging performance is one of the most important indicators for advanced lithium-ion batteries (LIBs). Herein, the fast-charging performance of routine graphite (Gr) and silicon (Si) anodes has been systematically studied, which shows that the Si anode has better performance than the Gr anode at fast-charging rate due to more reversible lithium (Li) plating/stripping and unique self-dissolve property of Li deposits. It is revealed for the first time that the good fast-charging performance of the Si anode essentially depends on the easy Li⁺ desolvation in electrolyte and fast Li⁺ diffusion in solid electrolyte interface and lithiated Si. Based on this finding, a Si/Gr composite anode with gradient Si content (denoted Si/Gr-Grad) is prepared by an industrially feasible spraying method. The tailored design simultaneously improves the capacity and reversibility of Gr-based anode under fast-charging condition. The full cell using the Si/Gr-Grad anode and the LiFePO₄ cathode with limited N/P ratio delivers a high capacity retention of 84.3% after 500 cycles at 4C. Even paired with the LiNi_0.6Co_0.2Mn_0.2O₂ cathode in Ah-level pouch cell, the Si/Gr-Grad anode enables the full cell to show good safety and cycling performance at 4C. Our work highlights the important roles of Si component and gradient structure in electrode design for fast-charging LIBs.