Effect of Bottlebrush Particle Architecture on Their Efficiency as Protective Layers in Li-Metal Batteries

Due to their impressive energy density, lithium-metal batteries have great potential to replace the widely used lithium-ion batteries. However, some challenges, like dendrite growth and the formation of "dead" lithium, still hamper their industrial application to this day. Artificial solid electrolyte interfaces (aSEIs) provide a protective coating on lithium electrodes to enforce uniform lithium stripping/plating. Especially, poly-(ethylene glycol)-based polymers are promising due to their high ionic conductivity, but a challenge remains in their lack of mechanical strength. By grafting these polymers from inorganic nanoparticles, such as silica, the high ionic conductivity can be combined with the mechanical strength of the nanoparticles. The physicochemical properties of these bottlebrush particles (BBPs) are determined by the grafting density (GD), inorganic fraction, and molecular mass of the grafted polymer chains. Each of these parameters has a significant influence on the materials' mechanical and conducting properties. In this work, each of these parameters and their effect on performance as aSEIs for lithium-metal anodes were studied. While high-molecular mass and grafting densities with low inorganic fractions can increase ion conductivity, as well as the mechanical strength of the material, unwanted elevated polarization was observed. Conversely, low GD samples provided significant enhancement of mechanical strength but reduced ionic conductivity. Overall, intermediate GD of 0.23 chains nm^-2, high inorganic fraction of ca. 10 wt %, and intermediate molecular mass of ca. 100,000 g mol^-1 provided the optimal balance for the tested BBPs of ionic conductivity, mechanical properties to prevent dendrite formation, as well as reduced polarization.