Optimization of Process Parameters during Solid State Synthesis of LiMn2O4 as Cathode Material for Lithium-Ion Batteries

One focus of the present research of Lithium-Ion Batteries is the development of higher energy and higher power density materials. Spinels like LiMn₂O₄ exhibit a potential of 4.1 V v.s. Li/Li⁺ that can be further increased by substitution of Mn by transition metals like Ni. Those substituted spinels like LiMn_1.5Ni_0.5O₄ are highly interesting cathode-materials for the high-energy range up to 5 V. The synthesis of spinels via a solid state route enables the production of high amounts up to 100 g with inexpensive starting materials and a combined step for milling and homogeni­zation of the raw materials. However, the solid state synthesis is a challenging approach regarding an adequate homogenization and a potential eva­po­ra­tion of Li during calcination^[1].

The present work aims the characterization of calcined cathode-materials to control the processing parameters in order to prepare single-phase spinel materials. Therefore, different compositions of Li_xMn₂O₄ have been synthesized from Li₂CO₃ and MnO₂ as starting materials, applying different milling parameters and calcination conditions. The calcined powders were then characterized by powder diffraction (XRD) and electron-paramagnetic-resonance spectroscopy (EPR). It is known that Li₂MnO₃ might be formed during the calcination process as an undesirable lithium-rich secondary phase^[2]. Thus, particular attention has been paid on this phase. The formation of Li₂MnO₃ may occur by non-homogeneous mixing or remaining coarse particles of Li₂CO₃ in the powder mixture. The EPR is a highly sensitive method to obtain even small amounts of Li₂MnO₃ besides LiMn₂O₄in the calcined product and is therefore highly interesting for this application.

[1] Y. Lee, The Effects of Lithium and Oxygen Contents Inducing Capacity Loss of the LiMn₂O₄    Obtained at High Synthetic Temperature, Journal of Electroceramics, 9, 209 – 214, 2002.

[2] V. Massarotti et al., Stoichiometry of Li₂MnO₃ and LiMn₂O₄ Coexisting Phases: XRD and EPR Characterization, Journal of Solid State Chemistry, 128, 80 – 86, 1997.