Advanced Characterisation Techniques Applied to Battery Materials

Porous electrodes support a wide range of electrochemical and physical processes and are fundamental to the operation of a variety of battery types. While 1-dimensional models have been accurate in predicting cell performances at low cycling rates, they fail to account for degradation and ageing. These effects are directly relatable to the complex 3-dimensional nature of porous electrodes. Advances in X-ray computed tomography (CT) have allowed for the non-destructive imaging of a broad range of battery materials, with studies ranging from microstructural analysis to in-situ and in-operando characterisation. The availability of a variety of micro- and nano-CT instruments at the Electrochemical Innovations Lab at University College London, offers an unparalleled opportunity to characterize a variety of electrode materials across a range of length-scales, from 10s nm to 10s μm. The focus of this project is subdivided in analysing commercially available battery materials and materials used in next-generation batteries. Because of the stable electrochemical performance of most commercially available electrodes, the analysis of these materials focuses on understanding how different calendering and manufacturing methods affect the electrode on the micro- and nano- length scales. Metrics such as the particles size and porosity distributions, or transport parameters such as the tortuosity factor are studied. Furthermore these material are used as a model to develop novel sample preparation methods as well novel miniature in-situ cells for X-ray imaging. A novel laser micro-machining sample preparation method has also been developed. This can produce electrode pillars with diameters below 100 μm whilst maintaining the structure and directionality of the electrode, allowing for a clear identification of microstructural features and changes caused by the calendering process on the electrode. Figure 1 a) shows a virtual slice of a graphite anode micro-machined into a pillar and characterised with combined absorption and phase contrast imaging. Fig 1 b) presents a volume rendering of the graphite pillar along with the copper current collector. For next-generation battery systems, there is a lack of in-depth microstructural studies that not only analyse and compare different types of electrode structures but also relate how these affect and are affected by battery performance and cycling. To increase the repeatability of the experiments and the representativeness of th