The growing demand for reliable, durable electrical energy systems to power electric and hybrid vehicles motivates worldwide efforts aimed at developing high-energy, high-power density batteries. One of the obstacles to widespread industry adoption is the lack of profound understanding and the ability to monitor and control the long-term degradation and capacity fading observed in these systems. Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) serial sectioning is used to reconstruct the evolution of the three-dimensional structure of Li-ion battery electrodes during extended cycling. High resolution imaging reveals microstructural information at the level of the composite framework consisting of the spheroidal micro-particles of the active material held together by the polymer matrix. The evolution of damage within the micro-particles of the active material can be seen in the form of voiding, cracking and ultimate fragmentation. In particular, when spherical micro-particles of Li-rich layered oxides are used as the cathode, it is found that the extent of fragmentation varied in the direction of Li⁺ diffusion current from the particle surface inwards. We use a simple model of the strain and strain gradient effects of Li⁺ transient diffusion within the electrode to identify the driving force for particle fragmentation, and discuss the implication of these results.

Quantification of residual stress gradients can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity. Highly focused local probe non-destructive techniques such as X-ray diffraction, electron diffraction or Raman spectroscopy have an established track record in determining spatial variations in the relative changes in residual stress with respect to a reference state for many structural materials. However, the interpretation of these measurements in terms of absolute stress values requires a strain-free sample often difficult to obtain due to the influence of chemistry, microstructure or processing route. With the increasing availability of focused ion beam instruments, a new approach has been developed which is known as the micro-scale ring-core focused ion beam-digital image correlation technique. This technique is becoming the principal tool for quantifying absolute in-plane residual stresses. It can be applied to a broad range of materials: crystalline and amorphous metallic alloys and ceramics, polymers, composites and biomaterials. The precise nano-scale positioning and well-defined gauge volume of this experimental technique make it eminently suitable for spatially resolved analysis, that is, residual stress profiling and mapping. Following a summary of micro-stress evaluation approaches, we focus our attention on focused ion beam-digital image correlation methods and assess the application of micro-scale ring-core methods for spatially resolved residual stress profiling. The sequential ring-core milling focused ion beam-digital image correlation method allows micro- to macro-scale mapping at the step of 10–1000 μm, while the parallel focused ion beam-digital image correlation approach exploits simultaneous milling operation to quantify stress profiles at the micron scale (1–10 μm). Cross-validation against X-ray diffraction results confirms that these approaches represent accurate, reliable and effective residual stress mapping methods.