Core-shell anode delivers 4x efficiency boost to sodium-ion batteries

Researchers at the Federal Institute for Materials Research and Testing (BAM) in Germany have developed a low-cost, environmentally friendly core-shell anode for sodium-ion batteries (SIBs) that significantly improves their initial charge efficiency to 82 percent—four times higher than uncoated hard carbon anodes. The anode features a porous hard carbon core for high sodium storage capacity, coated with an ultra-thin protective shell that acts as a molecular filter. This shell allows sodium ions to pass while blocking larger electrolyte molecules that cause unwanted side reactions, thus controlling the formation of a protective film on the shell rather than inside the core. This design reduces the irreversible loss of storage capacity during the first charge cycle, a major limitation in current sodium-ion batteries. Sodium-ion batteries are considered a promising alternative to lithium-ion batteries due to sodium’s abundance, lower cost, and environmental benefits. However, they have historically suffered from low initial efficiency because electrolyte molecules penetrate the porous anode during the first charge, consuming