Nanoscale phase separation, cation ordering, and surface chemistry in pristine Li_1.2Ni_0.2Mn_0.6O₂ for Li-ion batteries

Li-rich layered material Li_1.2Ni_0.2Mn _0.6O₂ possesses high voltage and high specific capacity, which makes it an attractive candidate for the transportation industry and sustainable energy storage systems. The rechargeable capacity of the Li-ion battery is linked largely to the structural stability of the cathode materials during the charge-discharge cycles. However, the structure and cation distribution in pristine Li_1.2Ni_0.2Mn_0.6O ₂ have not yet been fully characterized. Using a combination of aberration-corrected scanning transmission electron microscopy, X-ray energy-dispersive spectroscopy (XEDS), electron energy loss spectroscopy (EELS), and complementary multislice image simulation, we have probed the crystal structure, cation/anion distribution, and electronic structure of the Li _1.2Ni_0.2Mn_0.6O₂ nanoparticle. The electronic structure and valence state of transition-metal ions show significant variations, which have been identified to be attributed to the oxygen deficiency near certain particle surfaces. Characterization of the nanoscale phase separation and cation ordering in the pristine material are critical for understanding the capacity and voltage fading of this material for battery application.