Improving Electrochemical Properties by Sodium Doping for Lithium-Rich Layered Oxides

Li-rich manganese base oxides with a high specific capacity of nearly 300 mA h g-1 are acting as the most superior cathode material for high-energy density lithium-ion batteries. However, voltage decaying and poor rate capability critically restrict their applications. In order to solve this problem, the Na ion was used to dope into the lattice of the Li-rich manganese base oxides through solid-state reactions. All prepared samples are highly crystalline, and Na+ is uniformly distributed. The doping of Na+ does not adversely affect the parallel crystal plane structure. The charge-discharge capacities can be effectively increased by doping of Na ions. The rate performance of Li1.2Na0.03[Ni0.2464Mn0.462Co0.0616]O2 (LNa0.03NMC) is improved significantly, and the discharge capacities are 248, 234, 209, 190, 172, and 138 mA h·g-1 at 0.1, 0.2, 0.5, 1, 2, and 5 C, respectively. After 110 cycles of Li1.2Na0.03[Ni0.2464Mn0.462Co0.0616]O2 at 1 C, the reversible capacity only reduced from the initial 194.4-188.9 mA h·g-1 and only attenuates from 3.710 to 3.622 V of average discharge voltage. This work demonstrates that doping of Na ions not only stabilizes lattice layers of lithium-rich layered cathode but also facilitates the diffusion of Li ions in the crystal lattice.