Wettability refers to the ability of the electrolyte to spread and penetrate the porous electrode materials, crucial for battery performance and safety. Poor wettability can lead to issues like reduced capacity, increased resistance and safety problems.
It is useful to consider the Washburn equation as this describes capillary flow. Hence it describes the absorption of liquid into a porous medium and is expressed as h² = (r * σ * t * cos θ) / (2 * μ) where h is imbibition distance, r is capillary radius, σ is surface tension, t is time, θ is contact angle, and μ is liquid viscosity.
How long this takes depends on [2]:
- chemical composition of the materials
- layer thickness
- layer density
- wetting properties of the electrolyte
Davoodabadi et al [3] propose a measurement method to establish the electrolyte imbibition rate and go to show:
- Increasing salt concentration adversely influences electrolyte wetting rate.
- Switching from EC-DEC system to EC-EMC system improves electrolyte wetting rate.
- Imbibition into the graphite anode is much faster than that into the NMC532 cathode.
Sponge-Inspired Electrolyte Wetting
When we wash dishes, we never wait for water to slowly creep into a sponge. We just give it a squeeze, and it wets almost instantly.
References
- Washburn’s equation, Wikipedia
- Wetting of battery electrodes, Kruss Scientific
- Ali Davoodabadi, Jianlin Li, Yongfeng Liang, David L. Wood, Timothy J. Singler, Congrui Jin, Analysis of electrolyte imbibition through lithium-ion battery electrodes, Journal of Power Sources, Volume 424, 2019
Related Reading
- Electrolyte Motion Induced Salt Inhomogeneity – another electrolyte-transport effect that interacts with how well electrodes wet.
See also: High-Concentration Electrolytes