State-of-Charge Distribution of Single-Crystalline NMC532 Cathodes in Lithium-Ion Batteries: A Critical Look at the Mesoscale

Kröger, Till-Niklas; Wölke, Jan Mathis; Harte, Patrick; Beuse, Thomas; Winter, Martin; Nowak, Sascha; Wiemers-Meyer, Simon

Abstract

The electrochemical response of layered lithium transition metal oxides LiMO2 [M=Ni, Mn, Co; e. g., Li(Ni0.5Mn0.3Co0.2)O2 (NMC532)] with single-crystalline architecture to slow and fast charging protocols and the implication of incomplete and heterogeneous redox reactions on the active material utilization during cycling were the subject of this work. The role of the active material size and the influence of the local microstructural and chemical ramifications in the composite electrode on the evolution of heterogeneous state of charge (SOC) distribution were deciphered. For this, classification-single-particle inductively coupled plasma optical emission spectroscopy (CL-SP-ICP-OES) was comprehensively supplemented by various post mortem analytical techniques. The presented results question the impact of surface-dependent failure mechanisms of single crystals for the evolution of SOC heterogeneity and identify the deficient structural flexibility of the composite electrode framework as the main driver for the observed non-uniform active material utilization.