(Invited) A Multifunctional Polynorbonene Binder System Enabling Next-Generation Lithium-Ion Batteries

Abstract

Polynobornene (PNBE), a material commonly used in your shoes or for the tires of supercars, can also be highly influential to the development of next-generation batteries (Kim et al., 2022). When designing the batteries of tomorrow, we are interested in polymeric materials with precisely defined dynamic mechanical properties, increased ionic or conductivity, specific chemical interactions and moonshots like stable and healable interfaces (Lopez et al., 2019). PNBE provides high chemical and thermal stability, low shrinkage, and strong adhesion properties that lead to enhanced electrode stability and electrical conductivity(Le et al., 2020). Possessing a highly flexible nature allows PNBE to conform to the shape of an electrode – making PNBE an ideal multifunctional binder. Consider some persisting problems associated with batteries, for example Si electrodes typically fail due to cracks in the Si particles creating new surfaces for electrolyte decomposition/solid electrolyte interphase formation, and due to the Si becoming electrically disconnected from the rest of the electrode and ultimately terminating cycling (Ryu et al., 2004) . PNBE can address both aforementioned pain points, low shrinkage and flexibility can help mitigate the impact of cracking that occurs within an electrode over time by maintaining the structural integrity, and strong adhesion properties promote effective binding of the active material and the rest of the electrode. With increasing concerns about cobalt, there has been a move to replace oxides with phosphates. Substituting a substantial fraction of Mn, for Fe in LiFePO 4 leads to a material with an energy density approaching that of the oxides, while substantially lessening environmental concerns. Unfortunately, Mn dissolution causes a poor cycle lifetime. In an effort to reduce Mn dissolution, a mixture of PNBE and PVDF was used as a binder system. The PNBE was designed to have ether-type comb-branch functionalities that aid in Mn trapping, while the PVDF had suitable viscosity and mechanical properties. Figure 1 shows cycle lifetime results conducted at 45°C on a 2Ah LMFP-Graphite cell containing a 4%PVDF/1%PNBE binder system. The results show very good lifetime, with the capacity retention nearly 90% after 1,000 cycles. Given the difficulty with cycling of LMFP due to Mn dissolution, these results show good promise for this approach. This talk will highlight the opportunities and challenges of custom and enabling PNBE binder systems for LMFP, and other battery systems. References Kim, N.-Y., Moon, J., Ryou, M.-H., Kim, S.-H., Kim, J.-H., Kim, J.-M., Bang, J., & Lee, S.-Y. (2022). Amphiphilic Bottlebrush Polymeric Binders for High-Mass-Loading Cathodes in Lithium-Ion Batteries. Advanced Energy Materials , 12 (1), 2102109. https://doi.org/https://doi.org/10.1002/aenm.202102109 Le, D., Samart, C., Lee, J.-T., Nomura, K., Kongparakul, S., & Kiatkamjornwong, S. (2020). Norbornene-Functionalized Plant Oils for Biobased Thermoset Films and Binders of Silicon-Graphite Composite Electrodes. ACS Omega , 5 (46), 29678–29687. https://doi.org/10.1021/acsomega.0c02645 Lopez, J., Mackanic, D. G., Cui, Y., & Bao, Z. (2019). Designing polymers for advanced battery chemistries. Nature Reviews Materials , 4 (5), 312–330. https://doi.org/10.1038/s41578-019-0103-6 Ryu, J. H., Kim, J. W., Sung, Y.-E., & Oh, S. M. (2004). Failure Modes of Silicon Powder Negative Electrode in Lithium Secondary Batteries. Electrochemical and Solid-State Letters , 7 (10), A306. https://doi.org/10.1149/1.1792242 Figure 1