Although the crack volume now contributes to the overall particle volume (particle volume post charging is defined as NMC + cracked voxels within the particle boundary (see figure ), we may have expected a more modest increase. Some increase in the volume can be attributed to the volume expansion of lattice grains in the c-lattice direction (up to 5%), and then during collapse the reduction in size manifests as intergranular cracking. However, this expansion is approximately 2% in this direction with the a-lattice parameter up to 210 mAh.g 1 . 2 it is con- ceivable that during expansion of the c-lattice to 4.1 V, the crystal grains (which are orientated randomly) experience a variety of complex stress/strain interactions, maximised at the grain boundaries. We propose that the overall volume expansion of the secondary agglomerate is due to the release of thermally induced residual stresses when grain boundary cracking occurs. The residual stresses may have been introduced during the high-temperature sintering process while the primary particles were fused. When the stresses are released during the delithiation process, the particles will expand and impinge upon one another, resulting in a net volume expansion. Substantiating this hypothesis is a matter for future work.