Graphene-Mediated Cathode Interfaces for Lithium-Ion Batteries

Luu, Norman Sean

doi:https://doi.org/10.21985/n2-jb87-r009

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Graphene-Mediated Cathode Interfaces for Lithium-Ion Batteries

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Lithium-ion battery technology is a critically important component of the emerging renewable energy infrastructure. Since battery technology was first commercialized in the 1990s, significant progress has been made in materials development, motivated by the prospect of higher energy and power densities, increased cycling longevity, and faster charging and discharging rates. However, new strategies to enhance the performance of battery materials can be realized by drawing inspiration from other scientific fields that have simultaneously experienced exponential growth. Nanomaterials present exciting value propositions for energy storage technologies due to the ability to control and engineer unique optoelectronic properties that emerge at the atomically thin limit. Therefore, integrating materials and knowledge from both fields provides a unique opportunity to significantly improve lithium-ion battery technology. This thesis centers around the combination of graphene and lithium-ion battery cathode materials. Through microstructural control of battery electrodes, material and cell testing, and extensive materials characterization, this thesis explores the impact of graphene coatings on the performance of Ni-rich layered oxides across wide operational conditions. Controlling the sensitive surface chemistry of LiNi0.8Al0.15Co0.05O2 (NCA) nanoparticles enables subsequent graphene coating procedures, which improve cycle life and rate capability performance at low temperatures. Similarly, graphene coatings are found to mitigate the high-voltage chemomechanical degradation of LiNi0.5Mn0.3Co0.2O2 (NMC532), suggesting a relationship between particle surface conductivity and the severity of such degradation. Finally, the extreme ambient sensitivity of LiNiO2 (LNO) can be easily addressed by a hydrophobic surface coating composed of graphene and ethyl cellulose, which itself is conducive to excellent electrochemical behavior. Together, these results demonstrate that graphene coatings are a facile and effective method to enhance the electrochemical performance of Ni-rich layered oxide cathodes for lithium-ion batteries. This work has an immediate impact for improving the library of commercially relevant cathode materials used for consumer electronics and electric vehicles. Although demonstrated here for Ni-rich layered oxides, this thesis establishes the prospect of utilizing graphene to control degradation and enhance reaction kinetics in other emerging energy storage systems. Overall, this work highlights the importance of understanding and controlling degradation for next-generation electrochemical energy storage technologies.

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