A team of researchers from Hanyang University in South Korea has demonstrated that surface modification of graphite using amorphous Al₂O₃ is an efficient way to improve the fast charging capability of graphite anode materials for lithium ion batteries.

Schematic illustration of the proposed synthetic route for Al₂O₃ coated on a graphite surface. Kim et al.

In a paper in the Journal of Power Sources, the researchers report that surface-engineered graphite with 1 wt% Al₂O₃ exhibits a reversible capacity of about 337.1 mAh g⁻¹, even at a high rate of 4000 mA g⁻¹, corresponding to 97.2% of the capacity obtained at a current density of 100 mA g⁻¹.

Along with rapid expansion of electric vehicle (EV) markets have come greater demands on lithium ion batteries (LIBs). These face various technical challenges for EV applications in terms of energy density, power density, reliability and safety. In particular, fast charging capability is a highly valued feature because it shortens the charging time of LIBs. Unfortunately, current lithium ion battery technology cannot fully meet the desired charging rates for EVs. To resolve this LIB technical drawback, it is of utmost importance to find suitable battery materials that can be operated at extremely fast charging rates without sacrificing the electrochemical performance and safety of the battery. To attain this goal, various strategies have been implemented to improve the charging capability of LIBs with varying levels of success.

… It is well recognized that wettability between the electrolyte and the electrode plays a crucial role in determining the electrochemical performance of LIBs.

… In this work, amorphous Al₂O₃ was introduced to improve the fast charging capability of graphite anode material. It is well known that amorphous Al₂O₃ coatings can significantly improve wettability of the battery materials, such as graphite, and separators. We anticipated that an amorphous Al₂O₃ coating would promote electrolyte penetration over the entire surface area of the graphite electrode, thereby enhancing the fast charging capability of the graphite anode material.

—Kim et al.

Full cell tests adopting LiCoO₂ cathodes and Al₂O₃-coated graphite anodes confirmed that the introduction of amorphous Al₂O₃ can improve the fast charging capability of graphite anode materials.

Wettability tests and electrochemical impedance spectroscopy analysis revealed that this fast charging improvement results from the increased electrolyte wettability on the graphite that is induced by the Al₂O₃ layer on its surface.

Our proposed material concept, i.e., introduction of a shell layer to improve the electrolyte wettability of a graphite electrode, may be a practical way of improving the fast charging capability of graphite as an anode material for use in high-power LIBs.

—Kim et al.

Resources

• Dae Sik Kim, Yeong Eun Kim, Hansu Kim (2019) “Improved fast charging capability of graphite anodes via amorphous Al₂O₃ coating for high power lithium ion batteries,” Journal of Power Sources, Volume 422, Pages 18-24 doi: 10.1016/j.jpowsour.2019.03.027