Effect of Short-Chain Polymer Binders on Mechanical and Electrochemical Performance of Silicon Anodes

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Polymer binders are crucial components in providing both mechanical support and chemical stability to the structure of porous Li-ion electrodes. Particularly in silicon anodes, active material undergoes substantial volume expansion of up to 280%. As is shown in Figure 1, due to the restriction of the current collector, these silicon materials tend to expand vertically and so this requires substantial rearrangement of particles and plastic deformation.However, conventional binders such as polyacrylic acid (PAA) and polyimide (PI), while providing satisfactory initial capacity, suffer from mechanical rigidity due to their long polymer chains, leading to diminished long-term performance.Our research attempts to address this limitation by exploring the use of short-chain polymer binders, which may offer improved flexibility to accommodate the substantial volume changes of silicon particles. Although our previous work indicated that shorter polymer chains might compromise the adhesion to the copper current collector, we have developed a multilayer anode (MLA) structure featuring an adhesion layer to mitigate this issue. As is shown in Figure 2, this adhesion layer, placed between the silicon-containing bulk layer and the copper current collector, is designed to enhance the interface stability without sacrificing the mechanical compliance provided by short-chain polymers.Our experiments demonstrate that cells combining both long and short-chain PAA binders outperformed those with conventional PAA alone, delivering initial capacity of 2200 mAh/g at a 0.1C rate, compared to 1700 mAh/g for pristine PAA cells. At the early stages of development of the MLA-style anode with an adhesion layer, there was not an observed increase in performance, though experiments are ongoing, and we will report on latest results.We believe that the introduction of a strategic blend of different molecular weight binders can offer a promising solution to some of the challenges faced by silicon-based anodes. Figure 1