Comparison Study of a Thermal-Driven Microstructure in a High-Ni Cathode for Lithium-Ion Batteries: Critical Calcination Temperature for Polycrystalline and Single-Crystalline Design.

High-Ni layered oxide cathodes are promising candidates for lithium-ion batteries due to their high energy density. However, their cycle stability is compromised by the poor mechanical durability of the particle microstructure. In this study, we investigate the impact of the calcination temperature on microstructural changes, including primary particle growth and pore evolution, using LiNi0.88Mn0.08Co0.04O2 (N884), with an emphasis on the critical calcination temperature for polycrystalline and single-crystal designs in high-Ni cathodes. As the calcination temperature increases, the primary particles undergo a rectangular growth pattern while the pore population decreases. Beyond a certain critical temperature (in this case, 850 °C), a sudden increase in primary particle size and a simultaneous rapid reduction in the pore population are observed. This sudden microstructure evolution leads to poor cycle retention in N884. In contrast, single-crystal particles, free of grain boundaries, synthesized at this critical temperature exhibit superior cycle retention, underscoring the significance of microstructural design over crystalline quality for achieving long-term cyclability. Our study sheds light on the interplay between calcination temperature and microstructural evolution, proposing the critical temperature as a key criterion for single-crystal synthesis.

Development of microstrain in aged lithium transition metal oxides.

Cathode materials with high energy density for lithium-ion batteries are highly desired in emerging applications in automobiles and stationary energy storage for the grid. Lithium transition metal oxide with concentration gradient of metal elements inside single particles was investigated as a promising high-energy-density cathode material. Electrochemical characterization demonstrated that a full cell with this cathode can be continuously operated for 2500 cycles with a capacity retention of 83.3%. Electron microscopy and high-resolution X-ray diffraction were employed to investigate the structural change of the cathode material after this extensive electrochemical testing. It was found that microstrain developed during the continuous charge/discharge cycling, resulting in cracking of nanoplates. This finding suggests that the performance of the cathode material can be further improved by optimizing the concentration gradient to minimize the microstrain and to reduce the lattice mismatch during cycling.