In a 2014 paper exploring prospects for reducing the processing cost of Li-ion batteries, a team from Oak Ridge National Laboratory (ORNL) explained that formation cycling refers to the electrochemical side reactions involved with creating the solid electrolyte interface (SEI) layer. The SEI forms during the first several charge/discharge cycles; an ideal SEI layer should be thin, minimally porous, electrochemically inert, electronically resistive, and ionically conductive.

To form stable SEI layers that cover all of the electrode surface area and ensure good lithium ion conductivity and rate capability, there must be complete wetting of the electrode and separator pores.

In practice, however, there are substantial barriers to wetting—the separator pores (polyethylene surface energy is 35-36 mN m^-1 and polypropylene surface energy is only 30.1 mN m^-1), the electrode binder, and the conductive carbon black additive. A period of ~12-24 h under vacuum is required to achieve adequate wetting during the cumbersome electrolyte filling process of cell assembly, and it still leaves a substantial fraction of the smallest pore volume unwetted.

Formation cycling is performed after a lithium ion cell has been constructed, tap charged, and rested for ~24 h, and it has a significant economic impact on lithium ion battery manufacturing. The formation process requires that battery producers install many thousands of cycling stations to complete the process, which results in a heavy capital equipment investment, a much larger plant size, and a considerable manufacturing bottleneck.

—Wood et al.

The aim of Effiform is to optimize the material, process and systems technologies used in the initial charging (formation) of lithium-ion cells for industrial applications.

The “EffiForm” project is being funded by the German Federal Ministry of Education and Research (BMBF) as part of its program “Battery 2020 – battery materials for future electro-mobile and stationary applications”.

Over the three-year project period, thyssenkrupp, as a supplier of formation systems, will focus on creating the basis for efficient and innovative industrial-scale formation.

This will be a key step in translating the project findings into leading formation systems for the mass production of lithium-ion cells, leading in turn to reduced production costs of Li-ion battery systems.

Resources

• David L. Wood III, Jianlin Li, Claus Daniel (2014) “Prospects for reducing the processing cost of lithium ion batteries,” Journal of Power Sources, Volume 275, Pages 234-242 doi: 10.1016/j.jpowsour.2014.11.019