Japanese researchers have developed an innovative one-step process to regenerate lithium-ion batteries that have lost capacity due to carrier ion depletion. This regeneration method, published in Joule magazine, could significantly reduce the time, energy and cost associated with traditional battery recycling processes.
The growing demand for lithium-ion batteries in consumer electronics and electric vehicles has led to concerns about the sustainability of battery production and disposal. Current recycling methods involve dismantling spent batteries, recovering materials through hydro- or pyrometallurgical refining, and resynthesizing electrode materials. While direct recycling aims to return recovered electrode materials to their active state without raw material synthesis, these processes still require significant resources.
Lithium-ion batteries can lose capacity over time due to two main factors: damage to the active material and loss of carrier ions. The latter is particularly common in temperature-controlled systems used for batteries in large-scale applications. The new regeneration process developed by the Japanese researchers targets batteries that have experienced capacity degradation primarily due to carrier ion loss.
During the charging process, Li+ carrier ions move from the cathode to the anode while electrons flow in the same direction. Some of these Li+ ions are consumed by irreversible reductive decomposition at the graphite anode/electrolyte interface, forming a solid-electrolyte interface (SEI) film. Although the SEI film prevents further decomposition, long-term cycling gradually depletes the carrier Li+ ions, resulting in reduced capacity.
The researchers’ approach is to use alkali metal arenide reduction reagents, such as lithium naphthalenide (Li-Naph), to restore capacity by providing both electrons and Li+ ions to the cathode. By controlling the reduction potential of the arenides above 1.5 V through the dielectric constant effect of solvation, the team successfully demonstrated capacity recovery without degrading the internal components of the battery, particularly the graphite anode.
In preliminary studies using simulated capacity degraded laminated cells with LiNi1/3Co1/3Mn1/3O2 (NCM) cathodes and graphite anodes, the researchers tested various solutions containing Li-Naph and electrolyte mixtures. The most promising results were obtained using a mixture of Li-Naph in dimethoxyethane (DME) and a standard battery electrolyte. This combination resulted in capacity recovery without a drop in cell open circuit voltage or deterioration of cycling characteristics.
The researchers emphasized that the addition of a substance with both electrons and carrier Li+ ions is critical to providing the reaction driving force necessary for capacity recovery. Even in simulated capacity depleted batteries containing only new carrier Li+ ions, repeated cycling without the recovery reagent did not result in increased capacity.
This breakthrough one-step regeneration process has the potential to revolutionize the battery recycling industry by significantly reducing the complexity and resource intensity of current methods. By extending the life of lithium-ion batteries and minimizing the need for raw material extraction, this innovation could contribute to a more sustainable and circular energy storage economy.
As the demand for lithium-ion batteries continues to grow, the development of efficient and cost-effective regeneration methods will be essential to ensure the long-term viability of this critical technology. The one-step process developed by the Japanese researchers represents a significant step forward in this regard and offers a promising solution for restoring the capacity of degraded batteries while minimizing environmental impact and resource consumption.