Galactomannan-Bound Battery Electrodes for High-Performance Applications

Lithium-ion batteries are ubiquitous energy storage devices, yet expanding market needs require higher energy and power densities than presently available. Inexpensive materials with low-processing costs stimulate the exploration of novel battery materials. One possible solution to meet charge capacity demands is through the incorporation of silicon in anode materials. However, volume expansions during lithiation leads to fractured electrodes and binders, which leads to electronic isolation. Binding agents are a critical component in a battery and may also be used to enhance electrode performance. Herein, we report the use of galactomannans—an inexpensive, environmentally friendly, biorenewable polymer—as a novel binder for Si electrodes. Silicon-containing electrodes with as low as 5 wt.% binder exhibit large reversible capacities with > 90% charge retention after 100 cycles without use of electrolyte additives. Increased capacities allow for greater energy densities while lower binder content allows for fast Li-extraction for high-power applications (Figures 1a, b). The observed performance enhancement may be attributed to polymer-particle interactions between the hydroxyl groups of galactomannans and native-oxide layer of Si. The interactions, coupled with the inherent mechanical integrity of galactomannan thin films, allow for minimal electrode cracking and delamination upon lithiation. The undamaged electrode microstructure during large volume expansions (Figure 1c) allows for columbic efficiencies > 99% to be observed. Galactomannans also experience ample polymer swelling in common electrolyte solvents, which leads to rapid Li transport and lower resistivities than other biopolymer-bound electrodes. Galactomannan binders may thus provide a critical step forward in next-generation lithium-ion batteries.

Figure 1. (a) Charge/discharge profiles of guar gum-bound Si electrodes and (b) Li-extraction capacities using guar gum and locust bean gum as binders. Electrodes were lithiated at 0.05-C and delithiated at the specified C-rate. (c) The scanning electron microscope image shows the undamaged porous electrode structure of galactomannan-bound Si nanoparticles after 50 charge/discharge cycles of deep lithiation at 1-C.