Insight into the improved cycling stability of sphere-nanorod-like micro-nanostructured high voltage spinel cathode for lithium-ion batteries

Currently, developing cathode material with high energy density and good cycling performance is one of the key challenges for lithium-ion batteries. LiNi0.5-xMn1.5+xO4 (LNMO) spinel cathode has attracted great attention as the most promising cathode candidate due to its extraordinarily high operating voltage, but its inferior long-term cycling stability has limited its further development. In this work, we successfully designed LNMOs with specific facets and different morphologies, among which the hybrid sphere-nanorod-like micro-nanostructured LNMO possesses excellent cycling performance, with capacity of over 107.8 mAh g−1 after 1000 cycles at 10 C and superior rate capability up to 10 C. Its superior rate capability is found to originate from the large Li-O bond length by Rietveld refinement, which contributes to decreased charge transfer resistance and ease of Li insertion/extraction at tetrahedral sites. On the other hand, the excellent cycling stability comes from its having the least structural deformation from mechanistic reactions, which involve the longest solid-solution reaction, the highest spinel structural tolerance/stability up to Δ = ~0.69 Li, and a highly reversible two-phase reaction during charge and discharge in the hybrid LNMO, as revealed by the in operando synchrotron X-ray powder diffraction results. Moreover, the hybrid LNMO exhibits surface planes (210) with the highest Mn defect formation energy, prohibiting Mn3+ disproportionation and further stabilizing its cycling stability. This work not only demonstrates the importance of crystallographic and morphological controls on the high-voltage spinel performance, but also opens a window for battery engineers and researchers to develop battery technology for high-power applications.