Researchers at Stanford University have proposed enhancing solid electrolyte interphase stability in lithium metal batteries to improve cycling performance.
Lithium metal batteries employ metallic lithium as an anode, eliminating the need for electrode materials that store lithium ions found in conventional lithium-ion batteries (LiBs). This single layer of lithium near the anode reduces its size and weight significantly. Despite their potential advantages, these batteries require a durable and stable layer, called the solid electrolyte interphase (SEI), between the Li metal anode and electrolyte to ensure reliable performance. However, stabilizing the SEI remains difficult.
Researchers at Stanford University have proposed a novel approach to enhance the stability of the SEI in lithium metal batteries, potentially enhancing their cycling performance. Lithium metal battery capacity loss is attributed to Li’s reaction with the electrolyte. A stable SEI layer derived from Li’s reaction with salt, rather than solvents, has been found to correlate with extended cell cycle life.
The team coated the electrodes with a specially designed polymer to promote salt-derived SEI formation in lithium metal batteries. The polymer comprises a polysiloxane backbone with PyTFSI and perfluorinated side chains. The researchers aimed to enhance salt-derived SEI formation using a polymer that promotes salt presence and reduces solvent presence at the interface. The siloxane-based polymer with SP2 side chains selectively transports salt over solvent in H-Cell experiments, increasing salt-derived SEI content across various electrolyte types. After evaluating various side chain chemistries, the team identified the optimal polymer coating formulation. During initial analyses, it demonstrated excellent electrochemical performance and favorable interactions with salt and solvent.
The researchers conducted experiments to assess the impact of their approach on SEI regulation in lithium metal battery cells, resulting in extended cycle life. They tested their polymer-coating technique with various electrolytes, including ether, carbonate, and fluorinated 1,4-dimethoxylbutane electrolyte (FDMB). The researchers demonstrated the compatibility of their polymer coating with three key electrolyte types in lithium metal batteries. As new electrolytes are discovered, the range of compatible electrolytes may expand. The team plan to conduct further studies to evaluate the benefits and applicability of their method.
Further exploration of the materials design space will be conducted to identify additional compositions with salt-phobic and solvent-philic properties. The potential of combining this design with new electrolyte formulations will also be investigated.
Reference : Zhuojun Huang et al, A salt-philic, solvent-phobic interfacial coating design for lithium metal electrodes, Nature Energy (2023). DOI: 10.1038/s41560-023-01252-5