Mn-based spinel materials are highly promising high-voltage cathode materials for Li-Ion batteries due to their structural peculiarity, resulting in their high rate capability and excellent room temperature cycling stability. The energy density of these Mn spinel based materials can be further increased by substituting Mn with electrochemically active 3d transition metals like nickel, iron or cobalt, so that the operating potential of the cathode is further increased^1,2. This substitution is also reducing the Mn³⁺ content in the spinel and should therefore stabilize the cathode-material during cycling. In the present work, the high-voltage spinel LiCoMnO₄ and its titanium or iron substituted derivatives LiCoTi_xMn_1-xO₄ (0.02 ≤ x ≤ 0.16) / LiCo_1-yFe_yMnO₄ (0.05 ≤ y ≤ 0.2) are in the spotlight.

To investigate these compounds, our research is focused on the synthesis, structural and electrochemical characterization as well as spectroscopic methods in order to compare their properties and capabilities. Therefore, several techniques such as thermogravimetry in different states-of-charge (SOC), NMR spectroscopy in different SOC, and in situ powder synchrotron diffraction during electrochemical cycling and also during heating are applied.

Galvanostatic cycling reveals that about 70% of the lithium can be extracted and reinserted electrochemically in the voltage window from 3.5 to 5.3 V against Li from/into LiCoMnO₄, LiCoTi_0.06Mn_0.94O₄ or LiCo_0.90Fe_0.10MnO₄ (Fig. 1). In situ synchrotron powder diffraction results show that Li extraction/insertion occurs via a single-phase mechanism over the whole range of Li contents and over the whole voltage-range for Ti substituted and unsubstituted LiCoMnO₄ spinels (Fig. 2).

Financial support from the Federal Ministry of Education and Research (BMBF) within the DESIREE project, grant no. 03SF0477B, is gratefully acknowledged.

(1)      Alcántara, R.; Jaraba, M.; Lavela, P.; Tirado, J. L. Chem. Mater. 2003, 15 (5), 1210–1216.

(2)      Bhaskar, A.; Mikhailova, D.; Kiziltas-Yavuz, N.; Nikolowski, K.; Oswald, S.; Bramnik, N. N.; Ehrenberg, H. Prog. Solid State Chem. 2014, 42 (4), 128–148.