High-capacity Silicon (Si) anodes in Li-ion batteries have suffered from the problem of poor cycling performance caused by the extreme volume and stress fluctuations that deteriorate the active Si material rapidly and result in catastrophic battery failure. Polymeric binders have proven to be highly effective in improving the extent of cycling of Si-anodes. There are few crucial properties that these binders should possess in order to improve Si-anode performance, such as strong interfacial adhesion, high mechanical flexibility, rapid Li ion and electronic conduction, and chemical stability. In this work, we examine the interplay of these properties for three widely used binders for Si anodes: pyrolyzed polyacrylonitrile (PPAN), polyacrylonitrile (PAN), and polyaniline (PANI). To understand the behavior of each binder, we apply our developed Si/C/H/N/Li ReaxFF reactive force field to examine the interfacial, mechanical, and conduction properties of each binder, which is then compared to experimental measurements. We determine that PPAN is the most suitable binder, as it has the strongest interfacial adhesion to Si, is highly flexible and deformable, and also has high affinity and conduction for Li-ions. Our results agree well with the experimental results demonstrating the excellent cyclic performance of Si/PPAN anodes. This investigation not only provides details to better evaluate essential binder properties, but also reveals the structural features that are responsible for determining these properties. Such knowledge is highly beneficial in optimizing binder properties and engineering high performance Si/binder composite anode materials for high-capacity Li-ion batteries.

Investigating binder materials for Si anode in Li-ion battery using reactive force fields

ACS Spring Meeting 2021

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