Formation is where a freshly assembled cell gets its first charge and discharge, building the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers that govern the cell’s rate capability, safety and cycle life for the rest of its service life. It is also one of the slowest and most capital-intensive steps on the line: a conventional constant-current formation protocol can run for days, and every cell has to sit in a dedicated cycling channel for the whole of that time. One recent review of gigafactory process equipment put formation and its associated aging step at up to 30% of a plant’s production capital expense and around a quarter of its floor space, which is why shortening formation time without degrading the interphase it is meant to build has become a significant area of manufacturing process research.1 The Formation & Aging overview covers the process more broadly, including its cost and cycle-time context; this page focuses specifically on protocols aimed at cutting that time down.
Pulsed and Elevated-Rate Current Protocols
The most direct lever on formation time is the current profile itself. Instead of a single low, continuous current sustained for many hours, a pulsed protocol alternates higher-current charge pulses with short rest periods. The rest period matters as much as the pulse: it gives lithium ions time to redistribute at the anode surface before the next pulse arrives, which is what keeps a faster protocol from simply building a rougher, less uniform SEI than a slow one would.
Researchers at Oak Ridge National Laboratory compared a fast, pulsed formation protocol against ORNL’s own slower baseline protocol on graphite/NMC 532 cells with a standard EC:DEC electrolyte. Electrochemical impedance spectroscopy showed the faster protocol actually produced a lower surface film (interphase) resistance than the baseline, and the two protocols were then tracked through 1,300 aging cycles, with the fast-formed cells showing better capacity retention over that run rather than worse.2 That result is the reason pulsed-current formation gets taken seriously as more than just a time-saving shortcut: on this data, a well-tuned fast protocol did not trade cycle life for speed, it improved on both.
Temperature: the Other Acceleration Lever
Current profile is only one of the two main levers process engineers pull to shorten formation. The other is temperature: reaction kinetics during SEI and CEI formation follow Arrhenius behaviour, so running formation warmer speeds up interphase growth and lowers over-potentials, at the cost of tending toward a less compact, more organic SEI structure than a cooler, slower formation would build. That trade-off, and the specific temperature-dependent effects reported in the literature, are covered in depth on the Formation Temperature page. In practice, current profile and temperature are tuned together rather than in isolation, since both act on the same underlying SEI-forming reactions.
A Related but Separate Bottleneck: Electrolyte Wetting
Fast formation is often mentioned in the same breath as fast electrolyte wetting, and it’s worth being clear that they are two different process steps with two different sets of countermeasures. Wetting has to finish, electrolyte fully penetrating the porous electrode and separator stack, before formation cycling can meaningfully begin, and it has historically been just as slow: tens of hours of passive soak time under vacuum is a normal baseline. That bottleneck is covered on the Electrolyte Filling page, including the vacuum-assisted filling process itself. A 2025 study from the University of Texas at Austin took a different approach to accelerating wetting specifically: rather than relying on passive soak time, it applied pulsed mechanical pressure to the cell, mechanically pumping electrolyte into the pore structure, and cut impregnation time to under an hour without a measurable performance penalty.3 That work is written up in full, first-hand, on Sponge-Inspired Electrolyte Wetting.
A production line chasing overall cycle-time reduction generally has to attack both bottlenecks: faster wetting gets cells into formation sooner, and faster formation gets them out of the cycling channel sooner, but neither one on its own solves the other.
References
- Advanced lithium-ion battery process manufacturing equipment for gigafactories: Past, present, and future perspectives, on formation and aging’s share of plant capital cost and floor space
- Seong Jin An, Jianlin Li, Zhijia Du, Claus Daniel, David L. Wood III, Fast Formation Cycling for Lithium Ion Batteries, Journal of Power Sources, Volume 342, 2017, pp. 846-852, Oak Ridge National Laboratory
- Wenlong Li, Zishuo Zhao, Ayrton Yanyachi, Saravana Kuppan, Zhao Liu, Jigang Zhou, Ofodike Ezekoye, Hadi Khani and Yijin Liu, Sponge-Inspired Pressing Approach to Facilitate Electrolyte Wetting in Li-Ion Pouch Cells, Journal of The Electrochemical Society, Volume 172, Number 9, 2025
See also: Formation & Aging, Formation Temperature, Electrolyte Filling, Sponge-Inspired Electrolyte Wetting, Smart Battery Development