Electrode balancing as a key factor in lithium-ion batteries: From fundamentals to ultrafast charging

The negative-to-positive (N/P) capacity ratio is a critical yet often overlooked parameter in lithium-ion battery (LIB) design. It strongly influences performance, safety, and long-term aging. This review highlights how the N/P ratio affects key factors such as solid electrolyte interphase (SEI) growth, lithium plating, dendrite formation, and irreversible capacity loss in liquid-electrolyte LIBs. We focus on systems using LiCo O 2 (LCO) and LiFe PO 4 (LFP) cathodes paired with graphite, as well as Li Mn 2 O 4 (LMO) and LFP cathodes paired with Li 4 Ti 5 O 12 (LTO). Studies and modeling approaches for determining the optimal N/P ratio are summarized, including its influence on electrode potential and electrochemical performance. For graphite-based cells, an N/P ratio above 1.0 is essential to minimize lithium plating and extend cycle life, whereas LTO-based cells can operate at an N/P ratio of 1.0 or lower without plating concerns. We also review simulations demonstrating how the N/P ratio impacts internal potential distribution, thermal behavior, and lithium transport. Overall, this review presents a practical framework for the engineering of next-generation lithium-ion batteries (LIBs) that facilitate ultra-fast charging capabilities, while ensuring safety and long-term durability are not compromised.