Unveiling the critical role of polymeric binders for silicon negative electrodes in lithium-ion full cells

Because of its natural abundance and high theoretical specific capacity (3579 mAh g^-1, based on Li₁₅Si₄), silicon and its composites have been extensively studied as the negative electrode for future high energy density lithium-ion batteries. While rapid failure due to the significant volumetric strain of lithium-silicon reactions makes bulk silicon unsuitable for practical applications, silicon nanoparticles can sustain the large volume changes without fracturing. However, polymeric binders are usually required to maintain the structural integrity of electrodes made of particles. Recent lithium-ion half-cell tests have shown that lithium ionexchanged Nafion (designated as Li-Nafion) and sodium alginate are highly promising binders for nanoparticle silicon electrodes. Nevertheless, there is scant information on the performance and durability of these electrodes in full cell tests which are likely to reveal the role of binders under more realistic conditions. This work focuses on understanding the role of various binders in lithium-ion full cells consisting of Si negative electrode and LiNi_1/3Mn_1/3Co_1/3O₂ positive electrode. This study demonstrates, possibly for the first time, that silicon nanoparticles with either Li-Nafion or sodium alginate as binder can maintain a constant capacity of 1200 mAh g^-1 for more than 100 cycles. In addition, during deep charge/discharge cycling, silicon electrodes containing Li-Nafion, Nafion, and sodium alginate can exhibit better capacity retention and higher specific capacity than that of silicon electrodes using polyvinylidene fluoride (PVDF) as a binder.