![Lithium-ion batteries, the most widely used form of rechargeable battery today, conventionally run on graphite-based anodes. Scientists have been looking into replacing these graphite anodes […]](/wp-content/uploads/2013/02/NEWSICON2-620x300.png "A Battery That Heals Its Own Cracks")
Lithium-ion batteries, the most widely used form of rechargeable battery today, conventionally run on graphite-based anodes. Scientists have been looking into replacing these graphite anodes with silicon-based ones given the much higher charge-holding capacity of silicon. However, silicon anodes degrade more rapidly because holding more charge also means taking in more lithium ions during the charging process – silicon anodes expand much more drastically (up to 300%) due to extensive lithiation after being charged, leading to their fracturing and loss of conductivity.
To overcome this problem, a team of researchers at Stanford University laminated SiMP anodes with a coating of self-healing polymer (SHP). Two properties of the SHP allows it to self heal – its randomly-branched, amorphous (irregularly packed), extensively hydrogen-bonded structure, and its low glass-transition temperature (Tg). When a stretching force is applied on the SHP, the weak, reversible hydrogen bonds break preferentially to the strong covalent bonds of the SHP’s backbone. The low Tg gives the SHP a rubber-like malleability at ambient temperature and allows it to randomly rearrange its molecular functional groups such that new hydrogen bonds can be formed, effectively achieving autonomous self-healing.
When the anode fractures due to the expansion of the SiMP anodes, the SHP changes conformation in response and its hydrogen bonds dynamically reassociate to “heal” the fracture and hold the anodic structure intact such that electrical contact can be maintained. This design allows the anodes to retain 80% of their capacity after 90 charge/discharge cycles, whereas SiMP anodes laminated with non-self-healing polymers could only retain up to 47% capacity after 20 cycles.
Although the design appears promising, further optimization of the anode is still needed before it can be used in consumer electronics – a cell phone battery typically needs to survive several hundred cycles.
Source: C Wang et al, Nat. Chem., 2013, DOI: 10.1038/nchem.1802
