Efficient Pulse Formation to Stabilize SEI Film and Improve Performance of Commercial Lithium-ion Batteries

Pulse formation can shorten the production time of lithium-ion batteries, but the optimal current density remains unclear. This work systematically investigates the effects of five pulse formation rates (0.5 C, 0.8 C, 1.0 C, 1.15 C, and 1.25 C) on the structure and performance of the solid-electrolyte interphase (SEI) in commercial lithium iron phosphate (LFP)/graphite cylindrical batteries. The reinforcement learning algorithm is introduced to optimize the forming process parameters globally. We found that thick, chemically heterogeneous SEI layers appeared under a lower formation current density, and the high formation rates provoked vigorous side reactions and drastic SEI surface roughening, seriously deteriorating the electrochemical robustness of batteries. The optimal activation current density is close to 1 C, that is an ultra-thin (∼9 nm), dense and compositionally homogeneous SEI film formed, which reduced correspondingly the Li⁺ transport energy barrier, interfacial impedance, and side reactions. Consequently, the batteries exhibit a capacity retention rate as high as 92.45% after 1000 cycles at 0.33 C, with only 0.17 Ah of lithium loss over the first 300 cycles. This work establishes a constructive guideline for the efficient formation and long-term operation of high-energy-density commercial batteries.