High voltage cathode materials for rechargeable lithium-ion batteries that can be produced from cheap raw materials through a facile synthetic route are desired for emerging energy applications such as portable electronic devices and electric vehicles. Incorporating the monoclinic C2/m Li₂MnO₃ to form a “layered-layered” integrated structure cathode with the hexagonal R-3m LiMO₂ (M = Ni, Mn, and Co) has been first proposed by Thackeray and co-workers.¹ This layered-layered cathode structure has been proven to be a viable option to achieve higher capacity of >200 mAh g^-1 and to operate at a higher voltage above 4.5 V vs. Li/Li⁺.¹ Typically, the layered-layered cathode materials need to be prepared using a co-precipitation process by adding excess Li source to transition metal precursors because this process allows to access a high degree of homogeneous structural integration of layered-layered character at the atomic scale leading to improved electrochemical performances. Recently, an alternate synthetic process route was developed, where Li₂MnO₃ and LiMO₂ are prepared separately and mechanochemically-alloyed with a high-energy ball‑milling method.^2-5 This synthetic route achieve the same crystallographic features and very similar electrochemical performance with the powders produced with co-precipitation.^2-5

Adding a third spinel component, for example, LiNi_0.5Mn_1.5O₄, to this layered-layered composite cathode has been proposed to allow a fast Li⁺ diffusion and to operate even at a higher voltage (>4.7 V vs. Li/Li⁺).^6-9 Here, we have precisely controlled the mole ratio of C2/m Li₂MnO₃, R-3m LiNi_0.5Mn_0.3Ni_0.2O₂, and Fd-3m LiNi_0.5Mn_1.5O₄ to form a closely-connected “layered-layered-spinel” composite cathode materials using a robust and efficient solid state high-energy ball-milling process.¹⁰ We have carried out both ex situ and synchrotron-based in situ x-ray diffraction (XRD) analysis and observe that there are less structural distortions during charge/discharge cycling.¹⁰ Furthermore, we carry out density functional theory (DFT) calculations with van der Waals (vdW) correction to explain reduced phase transformation and enhanced stabilization in the integrated cathode system that lead to a large and stable capacity of ~200 mAh g^-1 operating at high voltages up to 4.9 V vs. Li/Li⁺.¹⁰

References:

[1] M. M. Thackeray, S. -H. Kang, C. S. Johnson, J. T. Vaughey, R. Benedek, and S. A. Hackney. J. Mater. Chem. 2007, 17, 3112-3125.

[2] W. C. West, J. Soler, and B. V. Ratnakumar. J. Power Sources 2012, 204, 200-204.

[3] S. Kim, C. Kim, J. -K. Noh, S. Yu, S. -J. Kim, W. Chang, W. C. Choi, K. Y. Chung, and B. -W. Cho. J. Power Sources 2012, 220, 422-429.

[4] S. Kim, C. Kim, Y. -I. Jhon, J. -K. Noh, S. H. Vemuri, R. Smith, K. Y. Chung, M. S. Jhon, and B. -W. Cho. J. Mater. Chem. 2012, 22, 25418-25426.

[5] J. -K. Noh, S. Kim, H. Kim, W. Choi, W.Chang, D. Byun, B. -W. Cho, and K. Y. Chung. Sci. Rep. 2014, 4, 4847.

[6] S. -H. Park, S. -H. Kang, C. S. Johnson, K. Amine, and M. M. Thackeray. Electrochem. Commun. 2007, 9, 262-268.

[7] E. -S. Lee, A. Huq, H. -Y. Chang, and A. Manthiram. Chem. Mater. 2012, 24, 600.

[8] D. Kim, G. Sandi, J. R. Croy, K. G. Gallagher, S. -H. Kang, E. Lee, M. D. Slater, C. S. Johnson, and M. M. Thackeray. J. Electrochem. Soc. 2013, 160, A31-A38.

[9] B. R. Long, J. R. Croy, J. S. Park, J. Wen, D. J. Miller, and M. M. Thackeray. J. Electrochem. Soc. 2014, 161, A2160-A2167.

[10] S. Kim, J. -K. Noh, M. Aykol, Z. Lu, H. Kim, W. Choi,  C. Kim, K. Y. Chung, C. Wolverton, and B. -W. Cho. ACS Appl. Mater. Interfaces, 2015, DOI: 10.1021/acsami.5b08906.

Acknowledgement:

This work was supported by Northwestern-Argonne Institute of Science and Engineering (NAISE). This work was also supported by the National Research Foundation of Korea Grant funded by the Korean Government (MSIP)" (NRF-2011-C1AAA001-0030538) and by KIST Institutional Program (Project No. 2E25303).

Figure Caption:

The 1^st cycle charge/discharge profiles of layered-layered-spinel composite cathode materials consist of Li₂MnO₃, LiNi_0.5Mn_0.3Co_0.2O₂, and LiNi_0.5Mn_1.5O₄ prepared with solid state high-energy ball-milling method. The scanning electron microscopy (SEM) images of the raw Li₂MnO₃, LiNi_0.5Mn_0.3Co_0.2O₂, and LiNi_0.5Mn_1.5O₄ powders are provided. The chemical structures of the layered-layered composite cathode materials and the spinel Li_1+xNi_0.5Mn_1.5O₄ cathode compound are shown.