Fabrication of Vertically Aligned Nanocomposite thin-films to probe lithium diffusion through the electrode/electrolyte interface

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Since the pioneering work of John Goodenough and co-workers in 1980, Li-ion batteries have become the number one choice to power electronic devices such as mobile phones and laptops. However, they pose significant safety issues due to containing flammable Li electrolytes, and Li dendrite growth between electrodes causing short circuiting and eventual battery death. Solid state electrolytes, an alternative to the conventual liquid electrolytes, can overcome these issues as they are non-flammable and supress dendrite growth. Also, with the right structuring, they have potential for higher energy storage capabilities. However, solid state materials generally suffer from lower conductivities, which limits battery performance. This can be attributed to 1) high interfacial impedances between electrode/electrolyte materials and 2) low conductivities limited by structure. Materials discovery focusing on the latter point currently dominates research in the field. A better understanding of the interface between solid state battery materials could contribute significantly to enhancing the performance of solid state batteries. However, there are limited experimental techniques to directly probe the interface (which are often difficult to perform) owing to it being buried and very small (few nm thick). Vertically Aligned Nanocomposite (VAN) thin-films could address this issue, as they have a significantly larger interface surface area. This might enhance signals in experiments such as solid state NMR, and allow direct probing of the interface. Also, due to the self-assembling nature of VANs, these films offer an easy method to form high interface surface areas. The initial aims of this project will be to synthesise and probe carefully chosen VAN films containing Li materials relevant to solid state batteries. At the time of writing, there are no reported Li VAN films in literature, so these studies will form some of the preliminary work in this area. Solid state NMR studies on these materials (in collaboration with the Grey Group, Cambridge) will be performed to probe the interface and, if signal enhancement is present and allows, Li ion migration across it. Beyond this, these studies will explore potential applications within the solid state thin film battery field by synthesis of 3D interdigitated cathode/electrolyte/anode materials.