Jiagang Xu

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 ion-exchanged 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 LiNi1/3Mn1/3Co1/3O2 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.

Binder-free lithium ion battery electrodes made of silicon and pyrolized lignin

The synthesis, characterization, and performance of a binder-free negative electrode for a lithium-ion battery, consisting of renewable biopolymer lignin and silicon nanoparticles, are reported. By mixing, coating, and subsequent pyrolization, we fabricated uniformly interconnected core–shell composite films of Si/C directly on the current collector, allowing for the assembly of coin-cells without the need of binder and conductive carbon. An excellent electrochemical performance was observed with a high specific capacity of 1557 mA h g−1 and a stable rate performance from 0.18 A g−1 to 1.44 A g−1. Moreover, the Si–pLig electrode can be reversibly cycled at 0.54 A g−1 with 89.3% capacity retention over 100 cycles. We also unveil a beneficial effect of 0.5% polyethylene oxide (PEO) on the morphology and electrochemical behavior of the Si/C composite electrodes.

Systematic Investigation of the Alucone-Coating Enhancement on Silicon Anodes

Polyvinylidene fluoride (PVDF) is the most popular binder in commercial lithium-ion batteries but is incompatible with a silicon (Si) anode because it fails to maintain the mechanical integrity of the Si electrode upon cycling. Herein, an alucone coating synthesized by molecular layer deposition has been applied on the laminated electrode fabricated with PVDF to systematically study the sole impact of the surface modification on the electrochemical and mechanical properties of the Si electrode, without the interference of other functional polymer binders. The enhanced mechanical properties of the coated electrodes, confirmed by mechanical characterization, can help accommodate the repeated volume fluctuations, preserve the electrode structure during electrochemical reactions, and thereby, leading to a remarkable improvement of the electrochemical performance. Owing to the alucone coating, the Si electrodes achieve highly reversible cycling performance with a specific capacity of 1490 mA h g-1 (0.90 mA h cm-2) as compared to 550 mA h g-1 (0.19 mA h cm-2) observed in the uncoated Si electrode. This research elucidates the important role of surface modification in stabilizing the cycling performance and enabling a high level of material utilization at high mass loading. It also provides insights for the future development of Si anodes.