Density impact on performance of composite Si/graphite electrodes

The ability of alkali-substituted binders for composite Si and graphite negative electrodes to minimize capacity fade for lithium ion batteries is investigated. Polymer films and electrodes are described and characterized by FTIR following immersion in electrolyte (1:2 EC:DMC) for 24 h. FTIR analysis following electrode formation displayed similar alkali-ion-dependent shifts in peak location suggesting that changes in the vibrational structure of the binder are maintained after electrode formation. The Si and graphite composite electrodes prepared using the alkali-substituted polyacrylates were also exposed to electrochemical cycling and it has been found that the performance of the Na-substituted binder is superior to a comparable density K-substituted system. However, in comparing performance across many different electrode densities, attention needs to be placed on making comparisons at similar densities, as low-density electrodes tend to exhibit lower capacity fade over cycling. This is highlighted by a 6 % difference between a low-density K-substituted electrode and a high-density Na-substituted sample. This low variance between the two systems makes it difficult to quickly make a direct evaluation of binder performance unless electrode density is tightly controlled. Graphical Abstract