High-Voltage LiNi1/2Mn3/2O₄ Spinel: Cationic Order and Particle Size Distribution

Lithium–nickel manganese spinel, LiNi 1/2 Mn 3/2 O 4, is capable to intercalate lithium reversible at a high voltage delivering a high specific energy when used as cathode material for lithium ion batteries. In this study, the effects of cationic order and particle size distribution on the lithium intercalation in high-voltage LiNi 1/2 Mn 3/2 O 4 spinel are examined by the application of diffraction and spectroscopic techniques. At 400 °C, nonstoichiometric LiNi 1/2 Mn 3/2 O 4-δ with a disordered spinel structure and particle size distribution between between 10 and 20 nm is obtained. 7 Li NMR with ultrafast spinning rates and electron paramagnetic resonance spectroscopy show that Ni 2+, Mn 3+, and Mn 4+ ions are nonuniformly distributed forming nanoscale domains with (Ni 2+,Mn 4+ )-, (Ni 2+,Mn 4+,Mn 3+ )-, and (Mn 3+,Mn 4+ ) compositions, respectively, the entirely cubic spinel structure being preserved. By increasing the annealing temperature, the amount of Mn 3+ decreases, and Ni 2+ and Mn 4+ tend to set up a long-range order. The particles start to grow above 600 °C, reaching submicrometer dimensions at 800 °C. Acid treatment of ordered submicrometer LiNi 1/2 Mn 3/2 O 4 modifies the particle size distribution without change of the cationic distribution. Cationic Ni,Mn distribution affects the Li + extraction/insertion from/into LiNi 1/2 Mn 3/2 O 4, while the particle size distribution has an impact on the rate capability and on the interaction with the electrolyte. After storing of the spinels in electrolyte solutions, the nanosized particles are covered with LiF/Li x PF y O z /P 2 O 5, while Ni,MnF 2 /Li x PF y compounds are deposited on the surface of the submicrometer particles. Ordered LiNi 1/2 Mn 3/2 O 4 with a three-modal particle size distribution displays the best rate capability.