The electric vehicle market has been experiencing explosive growth, with global sales surpassing $1 trillion in 2022. But limited driving range is presenting a big constraint on adoption. High-capacity anode materials such as silicon can offer at least 10 times the capacity of graphite or other anode materials now available. However, the problem is that volume expansion of high-capacity anode materials during the reaction with lithium poses a threat to battery performance and stability.
To mitigate this issue, researchers have been investigating polymer binders that can effectively control volumetric expansion. However, previous research has focused solely on chemical crosslinking and hydrogen bonding. Chemical crosslinking involves covalent bonding between binder molecules, making them solid. But this approach has a fatal flaw; once broken, the covalent bonds cannot be restored. On the other hand, hydrogen bonding is a reversible secondary bonding between molecules based on electronegativity differences; but the bonds are relatively weak.
Fortunately, a Korean research team recently demonstrated a high-capacity silicon anode created by layering charged polymers. Their research results were published in the journal Advanced Functional Materials. The new polymer developed by the research team not only utilizes hydrogen bonding but also takes advantage of attraction between positive and negative charges. These forces have 250 times the strength of hydrogen bonding, yet they are also reversible; this makes it easy to control volumetric expansion.
The surface of the high-capacity anode material is mostly negatively charged, and the layers of charged polymers are arrayed alternately with positive and negative charges to effectively bind with the anode. Furthermore, the team introduced polyethylene glycol to regulate the physical properties and facilitate lithium-ion diffusion, enabling the high-capacity electrodes and maximum energy density typically associated with lithium-ion batteries.
This research holds the potential to significantly increase the energy density of lithium-ion batteries through the incorporation of high-capacity anode materials, thereby dramatically extending the driving range of electric vehicles. This silicon-based anode material could potentially increase driving range at least tenfold.