Silicon has been regarded as the next generation anode material for the lithium-ion batteries due to its high theoretical specific capacity and low costs. However, Si particle experiences repeated volume changes in size up to 300 % during cycling, which leads to a series of problems and thus fast fading of capacities. Recently people have been working on some polymer binders that show improved cycling performance, such as CMC, alginate, poly(acrylic acid) (PAA), and some synthetic conductive polymers. Among these polymer binders, PAA offers tunable properties and improved anode stability due to the interaction with the surface of the Si particles. However, the performance of PAA based binders is still far from ideal and much work is needed for further engineering their mechanical properties. In this paper, we introduced a novel polymeric binder, poly(4-vinylbenzoic acid) (P4VBA), which also has a carboxylic acid group and an additional benzene. This novel binder has been synthesized with different molecular weights using RAFT polymerization. The introduced benzene moiety is believed not only to enhance the stiffness of this novel binder but also lead to the syndiotactic conformations, possibly due to the enhanced steric hindrance of the repeating unit. Therefore, the carboxylic acid groups of P4VBA binders are more evenly allocated around the backbones, thus leading to better adhesions to the Si particles. This speculation was supported by the half-cell cycling tests. As shown in <b>Figure 1</b>, when used in the NMP based lamination, the electrodes containing P4VBA binders have shown much improved cycling performance compared to the cells of PAA binders. It is also observed that the high molecular weight of P4VBA binders can afford better cycling performance. The dramatic improvements of this novel binder has confirmed that this P4VBA binder could be a good candidate as binders for the Si anode of lithium-ion batteries.

Novel polymeric binder for the silicon anode of lithium-ion batteries

256th National Meeting (2018)

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