Li/Mn-Rich Layered Transition-Metal Oxides As High-Energy Cathode Materials for Lithium Ion Batteries

Abstract

The class of Li-Mn-rich layered transition metal oxides (LMR-NCM) is one of the most promising candidates for cathode materials in advanced lithium ion batteries (LIBs) due to their high specific discharge capacity of up to 300 mAh/g and specific energy up to 1000 Wh/kg at material level.[1-4] Furthermore, those materials contain a high content of low-cost manganese due to the addition of a Li2MnO3 component compared to standard layered transition metal oxides, which at the same time enables the access of additional capacity. Nevertheless, a strong capacity and voltage fade as well as a poor rate capability plagues the class of LMR-NCM materials. The pronounced reversible oxygen redox activity (causing the voltage hysteresis), the transition metal migration and a phase transition to a spinel-like phase (causing the voltage fade) add to an even stronger fade of the specific energy and inhibit the commercialisation of these cathode materials so far.To closely study the underlying phenomena, LMR-NCM oxides with different morphologies are synthesized. Therefore, the syntheses via coprecipitation in a Couette-Taylor flow reactor and in a conventional flask are compared. The constant monitoring of critical parameters during the synthesis by means of the reactor leads to dense spherical particles with a narrow particle size distribution. These characteristics offer a spherical cathode material with enhanced capacity retention due to a more compact structure with a lower surface area. Also, taking the voltage fade into consideration allows a more objective evaluation of LMR-NCM oxides materials especially in direct comparison with state-of-the-art NCM-based cathodes.[1] E. M. Erickson, F. Schipper, T. R. Penki, J.-Y. Shin, C. Erk, F.-F. Chesneau, B. Markovsky, D. Aurbach J. Electrochem. Soc. 2017, 164, A6341 – A6348.[2] B. Qiu, M. Zhang, L. Wu, J. Wang, Y. Xia, D. Qian, H. Liu, S. Hy, Y. Chen, K. An, Y. Zhu, Z. Liu, Y. S. Meng Nat. Commun. 2016, 7, 12108.[3] D. Andre, S.-J. Kim, P. Lamp, S. F. Lux, F. Maglia, O. Paschos, B. Stiaszny J. Mater. Chem. A 2015, 3, 6709 – 6732.[4] T. Placke, R. Kloepsch, S. Dühnen, M. Winter J. Solid State Electrochem. 2017, 21, 1939 – 1964.