Carbonate- Versus Hydroxide-Based Precursors for Synthesis of Lithium/Manganese-Rich Cathodes

Cathodes made of lithium-manganese-rich layered oxide (LMR) have the potential to increase the energy density of lithium ion batteries while reducing their costs. However, the material is less stable than the currently used lithium-nickel-manganese-cobalt oxide (NMC) and suffers from oxygen, voltage, and capacity loss. A team from MEET Battery Research Center at the University of Münster, Helmholtz Institute Münster of Forschungszentrum Jülich, and the South Korean company LG Energy Solution has now investigated the influence of synthesis and calcination parameters on the discharge capacity and cycle stability of LMR cathodes.

Higher Discharge Capacity Not Necessarily Beneficial

The scientists compared the cyclic performance of two differently synthesized LMR compounds: The LMR-typical carbonate precursor (LMR-CO₃) and a hydroxide precursor (LMR-(OH)₂) were used. They discovered that LMR-CO₃ contains numerous voids in its structure due to CO₂ escape during calcination, a heat treatment used to achieve the final composition. This results in a particularly large surface area, which can lead to oxygen loss and, consequently, to undesirable manganese redox reactions (specifically, the conversion of Mn⁴⁺ to problematic Mn³⁺). These reactions subsequently destabilize the material’s physical structure. In contrast, the surface area of LMR-(OH)₂ is comparable to that of NMC after calcination.

Although both materials have similar initial charging capacities, LMR-CO₃ undergoes more extensive lithiation during discharge. “The resulting additional capacity stems from the Mn³⁺/Mn⁴⁺ redox reaction during discharge. However, this reaction promotes structural degradation of the material and, in the long term, leads to a faster capacity loss of the battery cells,” explains MEET researcher Pranti Sutar. “We therefore conclude that a higher discharge capacity is not necessarily beneficial for LMR cathodes.”

Instead, the results highlight that the material structure is largely determined by the method of synthesis and calcination. Controlled limitation of lithiation can suppress detrimental Mn3+ redox reactions and thus improve cycle stability. Dr Johannes Kasnatscheew, head of the MEET research division Materials, sums up: “Elucidating these mechanistic relationships provides a route toward designing LMR cathodes with a better balance between energy density and long-term stability.”

Entire Study Available

The detailed results have been published in the journal “Small Science” by Pranti Sutar, Laurin Profanter, Tim Messink, Dr Uta Rodehorst, Dr Dominik Voigt and Dr Johannes Kasnatscheew, MEET Battery Research Center, Johannes Helmut Thienenkamp, Annalena Krude and PD Dr Gunther Brunklaus, Helmholtz Institute Münster, Dr Hyuck Hur, LG Energy Solution, as well as Prof. Dr Martin Winter, MEET Battery Research Center and Helmholtz Institute Münster.