Synergetic effects of Na⁺-Mo⁶⁺ co-doping on layered Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode for high performance lithium-ion batteries

The Li-rich Mn-based material, with high energy density, less toxicity and low cost, is regarded as one of the potential cathode candidates for the next generation lithium-ion batteries (LIBs). However, some issues need to be addressed before large-scale commercialized application, such as capacity attenuation, low initial coulomb efficiency and poor rate performance, caused by the structure defects and oxygen escape from the crystal lattice at high voltage. Here, the Na⁺ and Mo⁶⁺ dopants are introduced to Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ by sol-gel method, with slight Li⁺ displaced by Na⁺ and tiny Mo⁶⁺ substituting transition metal ions, respectively. The doping effects on the Li layer spacing, Li/Ni mixing and oxygen vacancy defects have been examined. Regarding the doped samples, the valence states of transition metal elements and electrochemical performance are systematically studied. The Na⁺ and Mo⁶⁺ co-doping not only expands the lithium layer spacing and reduces cationic disorder to promote the Li⁺ diffusion and enhance the rate capability, but also stabilizes the oxygen skeleton, inhibits oxygen loss, and suppresses the migration of transition metal ions to improve the cyclic performance. As a result, Li_1.18Na_0.02(Mn_0.54Ni_0.13Co_0.13)_0.98Mo_0.02O₂ delivers 122.8 mAh.g⁻¹ at 5 C and 262.9 mAh.g⁻¹ at 0.2 C, retaining 90% capacity after 150 cycles.