Cobalt-free concentration-gradient Li[Ni0.9Mn0.1]O2 cathode material for lithium-ion batteries

Abstract The cathodes of LiNiO2 (LNO), Li[Ni0.9Mn0.1]O2 (LNM91) and the concentration gradient material Li[Ni0.9Mn0.1]O2 (G-LNM91) were synthesized by co-precipitation method, and SEM, XRD, TEM and electrochemical tests were performed. SEM images show that the primary needle-like particles on spherical surface of the gradient G-LNM91 are the densest. The results of EDX linear scan show that for gradient precursor G-NM91, the relative atomic content of Ni element gradually decreases from 98.21% at the center of the particle to 80.66% at the cross surface of the particle (the content of Mn from 1.79% gradually increases to 19.34%). For the final product G-LNM91, the relative atomic content of Ni element in the center decreases to 94.07%, and at the edge increases to 85.17%. XRD tests indicate that the samples doped with Mn have good layered structure. TEM images show that the lattice fringes of the samples doped with Mn are more obvious. The results of Electrochemical performance tests show that manganese substitution has a significant effect on improving the cycle performance of LiNiO2, and G-LNM91 has the best cycle performance. Under a voltage range of 2.75–4.3 V, the initial discharge capacity of G-LNM91 cathode material at 0.1 C is 200 mA h/g. After 200 cycles at 1 C, the capacity retention rate remains around 87.5%. The initial discharge capacity of LNM91 is 180 mA h/g and the retention rate is 78.5%; the capacity retention rate of LiNiO2 is only 55.2%, even though the initial specific discharge capacity is 207 mA h/g.