High-Performance LiNi0.2Mn1.8O4 Spinel Cathode Material for Lithium Ion Batteries Obtained By Microwave-Assisted Synthesis

High energy density rechargeable lithium ion batteries are considered as more efficient energy storage devices for use from portable consumer electronics to large-scale applications. Apparently, the high voltage spinel and olivine lithium iron phosphate cathode materials are being considered as the target materials to achieve sustainable development, particularly for large-scale utility with energetic (energy and power density) and economic aspects. Obviously, the spinel materials are abruptly beginning to attract owing to its high electrochemical performance at room temperature. Unfortunately, the above material remains inferior due to its large capacity loss observed when operating at higher temperature. Obviously, the spinel, LiNi_0.5Mn_1.5O₄ with a potential plateau of~4.7V is abruptly beginning to attract owing to its high electrochemical performance at room temperature. Unfortunately, the specific composition of above material remains inferior due to its high operation potential which cause the electrolyte oxidation, especially a large capacity loss observed when operating at higher temperature [1, 2].

Considering the above aspects, the commercial lithium manganese oxide spinel, LiMn₂O₄ (LMO) cathode can become preferable candidate particularly with regard to costs, environmental and efficiency perspectives. However, the LMO also suffer from the rapid capacity fading with cycling due to the manganese dissolution at an elevated temperature which limits the practical use of this material for large-scale applications. Numerous efforts have been proposed to overcome this issue. Recently, researchers demonstrated the excellent performance of octahedral LMO and attributed it to their surface facets, especially {111} which allow for thinner SEI formation than {110} facets [3, 4].

LMO chemistry can be improved by doping with very small amount of the nickel, e.g., LiNi_0.2Mn_1.8O₄ [5]. As part our continuing investigations on the impact of microwave chemistry on the electrochemical performance of battery materials [6], we report the preparation of nickel-doped LMO (i.e., LiNi_0.2Mn_1.8O₄) with microwave irradiation as an essential step to achieve enhanced electrochemistry. As-prepared active Mn₃O₄ with well-shaped octahedral {011} facets morphology was doped with lithium and very low amount of Ni to give LiNi_0.2Mn_1.8O₄ spinel with exposed {111} facets (Fig.1a) that allowed for structural and cycle stability. In addition, the ^6,7Li MAS NMR shows the two isotropic Li resonance of nearly 528.4 - 604.7 ppm and 528-596.3 ppm for LMNO and LMNO-mic results the multiple Li environments by the distribution of Mn and Ni atoms.  Interestingly, the microwave irradiated spinel delivered a better cycle stability, rate capability, low impedance, and improved lithium diffusivity at different temperatures compared to the untreated one.

 In this presentation, we will discuss in detail our findings on the impact of microwave irradiation on the electrochemical performance of the LiNi_0.2Mn_1.8O₄ spinel at ambient and high temperature (60^oC). 

Fig.1: (a) SEM image of LMNO-mic with {111} facets, and (b) Cycle stability of LMNO and LMNO-mic at 60^oC

References

1)       O. K. Park, Y. Cho, S. Lee, H. C. Yoo, H. K. Song, J. Cho, Energy Environ. Sci. 2011, 4, 1621-1633.

2)       S. T. Myung, K. S. Lee, D. W. Kim, B. Scrosati, Y. K. Sun, Energy Environ. Sci. 2011, 4, 935-939.

3)       K. R. Chemelewski, E. S. Lee, W. Li, A. Manthiram, Chem. Mater. 2013, 25, 2890-2897.

4)       B. Hai, A. K. Shukla, H. Duncan, G. Chen, J. Mater. Chem. A, 2013, 1, 759-769

5)       M.A. Kebede, N. Kunjuzwa, C.J. Jafta, M.K. Mathe, K.I. Ozoemena, Electrochim. Acta 2014, 128, 172 - 177

6)       C.J. Jafta , M. K. Mathe , N. Manyala , W.D. Roos, K.I. Ozoemena, ACS Appl. Mater. Interfaces, 2013, 5, 7592−7598