Galactomannan binding agents for silicon anodes in Li-ion batteries

The challenge to incorporate Si into Li-ion battery anodes has attracted much attention. Binding agents are a critical component in a battery that may also be used to enhance electrode performance. Herein, we report the use of galactomannans-a low-cost, environmentally friendly, biorenewable polymer-as a novel binding agent for Si-containing electrodes. Silicon-containing electrodes with as low as 5 wt% binder show large reversible capacities with >90% charge retention after 100 cycles without the use of electrolyte additives. Large capacities and low binder content when compared to carboxymethyl cellulose allows for greater energy densities and fast Li-extraction for high-power applications. The performance enhancement may be attributed to polymer-particle interactions between the hydroxyl groups of galactomannans and the native-oxide layer of Si. These interactions, coupled with the inherent mechanical integrity of galactomannan thin films, allow for minimal cracking and delamination of the electrode upon lithiation. An undamaged electrode microstructure during large volume expansions allows for coulombic efficiencies >99%. Galactomannans also experience ample polymer swelling in common electrolyte solvents, which leads to rapid Li transport and higher ionic conductivities than other biopolymer-bound electrodes. Galactomannan binders may thus provide a critical step forward in next-generation lithium-ion batteries.