Tao Zhanga, b, Jing Maoa, b, *, Kehua Daid, c, Yuchun Zhaid, Guosheng Shaoa, b, Ruimin Qiaoe, Wanli Yange, Gao Liuc,*
aSchool of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450002, China
bInternational Joint Research Laboratory for Low-Carbon & Environmental Materials of Henan Province, Zhengzhou University, Zhengzhou 450002, China
cEnergy Storage and Distributed Resource Division, Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
dSchool of Materials and Metallurgy, Northeastern University, Shenyang 110004, China
eAdvanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
* Corresponding author. Email: Maojing@zzu.edu.cn
The LiMn1.5Ni0.5O4 (LNMO) with spinel structure is a promising cathode material candidate for next generation lithium-ion batteries for EV, HEV, energy storage, etc., for its high working voltage of ~4.7 V and capacity of ~130 mAh g−1 1-7.
A PVP (polyvinylpyrrolidone)-assisted gel combustion method developed by our group is used to synthesize LiNi0.5Mn1.5O4 materials with high rate and cycling performance. The as-prepared LiNi0.5Mn1.5O4 delivered 132.9 mAh g−1, 130.2 mAh g−1, 128.1 mAh g−1 and 124.5 mAh g−1 at rates of 1 C, 5 C, 10 C and 15 C, respectively, and demonstrated excellent capacity retentions of 97.3% after 200 cycles with 1 C rate at room temperature.
To further improve the performance, Cr-doped, Nb-doped and Co-doped LNMO are synthesized with same method. Cr-doping and light Nb-doping (LiNb0.02Ni0.49Mn1.49O4) improve the rate performance of LNMO. The Li+ chemical diffusion coefficient at different SOC suggests both Cr and light Nb doping fasten Li+ diffusion in LNMO particles. The impedance spectras show both RSEI and Rct are reduced by Cr and light Nb doping. The cycling performance is improved by Cr or Nb doping, and Cr-doping increases both coulombic efficiency and energy efficiency of LNMO at 1C cycling. The LiCr0.1Ni0.45Mn1.45O4 remains 94.1% capacity after 500 cycles at 1C, during the cycling the coulombic efficiency and energy efficiency keeps over 99.7% and 97.5%, respectively.
The LiCo0.1Ni0.45Mn1.45O4 has much better rate capability while its specific capacity at C/5 is 10% lower than that of LNMO. At 15C rate, their specific capacities are closed, and the LiCo0.1Ni0.45Mn1.45O4 delivers 86.2% capacity relative to C/5, and this value for LNMO is only 77.0%. The DLi+ values of LiCo0.1Ni0.45Mn1.45O4 are 1~2 times higher than that of LNMO in most SOC region. The LiCo0.1Ni0.45Mn1.45O4 shows very excellent cycling performance, which is the best value compared with literatures. After 1000 cycles, the LiCo0.1Ni0.45Mn1.45O4 still delivers 94.1% capacity. Moreover, its coulombic efficiency and energy efficiency keep at 99.84% and over 97.3% during 1C cycling, respectively.
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