The effect of Na doping on layered LiNi1/3Co1/3Mn1/3O2 single-crystal structure as a cathode for lithium-ion batteries

A cathode with single-crystal structure for Li-ion batteries is shown to provide stable cycle performance because of its integrated crystal structure and smaller internal stress. Here, Na+ ions with larger radius are doped into LiNi1/3Co1/3Mn1/3O2 (LNCMO) single-crystal nanoparticles through a simple sol-gel method to further improve the rate capability. Different amounts of Na doping are considered to illustrate the cooperative effect of single-crystal structure and Na doping. The results indicate that a Li0.9Na0.1Ni1/3Co1/3Mn1/3O2 cathode has a discharge capacity of 193.7 mAh g(-1) at 0.2 C, much higher than the 174.8 mAh g(-1) of its undoped counterpart. After 50 cycles, the capacity retention is enhanced from 71.3% for undoped LNCMO to 89.2% for Li0.9Na0.1Ni1/3Co1/3Mn1/3O2. At the same time, Li0.9Na0.1Ni1/3Co1/3Mn1/3O2 delivers a discharge capacity of 137.9 mAh g(-1) at 10 C, about twice the capacity of LNCMO. Na ions doped into the lattice can magnify the distances between lithium layers and act as pins for more stable structure and faster kinetics of Li+-ion diffusion.