Improving Performance of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials for Lithium-Ion Batteries by Doping with Molybdenum-Ions: Theoretical and Experimental Studies

The work reported herein is an important continuation of our recent experimental and computational studies on Li[Ni_xCo_yMn_z]O₂ (x + y + z = 1) cathode materials for Li-ion batteries, containing minor amounts of multivalent cationic dopants like Al³⁺, Zr⁴⁺, W⁶⁺, Mo⁶⁺. On the basis of DFT calculations for LiNi_0.8Co_0.1Mn_0.1O₂, it was concluded that Mo⁶⁺ cations preferably substitute Ni cations in the layered structure due to the lowest substitution energy compared to Li, Co, and Mn. It was established that the electrochemical behavior of LiNi_0.8Co_0.1Mn_0.1O₂ as a positive electrode material for Li-ion batteries can be substantially improved by doping with 1-3 mol % of Mo⁶⁺, in terms of lowering the irreversible capacity loss during the first cycle, increasing discharge capacity and rate capability, decreasing capacity fade upon prolonged cycling, and lowering the voltage hysteresis and charge-transfer resistance. The latter is attributed to the presence of additional conduction bands near the Fermi level of the doped materials, which facilitate Li-ions and electron transfer within the doped material. This is expressed by a lower charge-transfer resistance of Mo-doped electrodes as shown by impedance spectroscopy studies. We also discovered unique segregation phenomena, in which the surface concentration of the transition metals and dopant differs from that of the bulk. This near surface segregation of the Mo-dopant seems to have a stabilization effect on these cathode materials.