Cartilage-inspired coating helps battery cathodes resist cracks in lab

Every time lithium ions enter or leave a battery cathode, the particle changes shape. At the boundaries between its tiny crystals, that repeated motion can concentrate stress until cracks appear. Researchers in Hong Kong have now tested an extremely thin polymer coating designed to spread that stress and protect the cathode during repeated cycling.

The idea came from cartilage. Qiang Liu of Hong Kong Polytechnic University, working with researchers including Ph.D. student Yutong Liu and professor Guohua Chen, studied how cartilage distributes force under repetitive loading. Their coating is soft and flexible at the grain boundaries — the interfaces where crystals meet — and acts as a mechanical buffer rather than simply trying to strengthen the brittle material.

That distinction matters for nickel-rich layered oxides, cathode materials used for high-capacity electrodes. Traditional approaches have focused on raising the threshold at which cracks form. Liu’s team instead deposited a shape-memory polymer layer that deforms under mechanical stress and then recovers, helping to delocalize and dissipate the energy produced as lithium moves in and out. In experiments and simulated battery cycling, coated particles maintained their structural integrity better than uncoated ones.

The researchers tested the strategy on several widely used cathode materials, including layered oxides with different nickel and lithium contents and lithium iron phosphate. They reported improvements in cycling stability and rate capability, alongside fewer cracks. The study builds on a 2019 Nature Energy paper from Liu’s team, which found that a polymer coating applied to electrode grain boundaries could suppress cracking but had not yet resolved why.

So what changes in practice? If the coating can be integrated into battery manufacturing, it could help preserve cathode performance over repeated use and support longer-lasting, potentially higher-energy batteries. That benefit remains prospective: the reported evidence comes from laboratory characterization and simulated cycling.