Regulating Parameters Manipulating Lattice Change and Isotropy in Intergrown Li-Rich Zero-Strain Cathode

One of the representative degradation mechanisms of Li-ion batteries are predominantly reported as the degradation at cathode and electrolyte interfaces. Anisotropic volume changes of conventional layered type cathode materials cause intergranular cracks in secondary particles, leading to new interface exposure that initiates side reactions with the electrolyte, oxygen evolution, transition metal (TM) dissolution, and irreversible phase transitions. Furthermore, volume changes of cathode also result in mechanical contact loss at the electrolyte interface in solid-state battery systems, which leads to the formation of isolated particles from ionic or electronic percolating network. Although single crystalline cathodes have been suggested as an alternative to address these issues, strain accumulation on intrinsic defects or nanopores initially present in the particles during charge and discharge finally leads to the degradation accompanying the formation of high dimensional defects. Designing the advanced cathode materials having zero-strain or zero-volume character has been proved to address the issues, however, study on systematic control of lattice parameter and revealing the regulating parameters for modulating it including the isotropy/anisotropy is still lacking. In this work, we aim to reveal the factors affecting to the behavior of lattice changes in layered-rocksalt intergrown cathode [1]. The mechanism determining the lattice parameter change and isotropy/anisotropy has been elucidated that it is affected by not only each phase distribution within the particle but also lattice mismatch between layered and rocksalt phases at the boundary level during charge and discharge. Both phase distribution and lattice mismatch are governed by kinetics of nucleation and growth of each phase and intermixing of transition metals between two phases during synthesis process. It is revealed that higher lattice coherency at interface is proved to be more effective suppress the lattice and volume changes. Unlike conventional strategies that tune the composition of transition metals for designing the zero-strain cathode such as high-entropy[2], disordered rocks salt cathode [3], these results suggest that composition-independent parameters can achieve the zero-strain behavior. Ultimately, our work introduces new degrees of freedom in designing advanced cathode materials for future Li-ion batteries and solid-state batteries.<br/>[1] N. Li et al, Nature Communications <b>12, </b>2348 (2021)<br/>[2] R. Zhang et al, Nature, <b>610</b>, 67-73 (2022)<br/>[3] Zhao et al, Joule <b>6</b>, 1654-1671 (2022)