Monitoring local redox processes in LiNi0.5Mn1.5O4 battery cathode material by in operando EPR spectroscopy

Abstract

Despite the multitude of analytical methods available to characterize battery cathode materials, identifying the factors responsible for material aging is still challenging. We present the first investigation of transient redox processes in a spinel cathode during electrochemical cycling of a lithium ion battery by in operando electron paramagnetic resonance (EPR). The battery contains a LiNiMnO (LNMO) spinel cathode, which is a material whose magnetic interactions are well understood. The evolution of the EPR signal in combination with electrochemical measurements shows the impact of Mn on the Li motion inside the spinel. Moreover, state of charge dependent linewidth variations confirm the formation of a solid solution for slow cycling, which is taken over by mixed models of solid solution and two-phase formation for fast cycling due to kinetic restrictions and overpotentials. Long-term measurements for 480 h showed the stability of the investigated LNMO, but also small amounts of cathode degradation products became visible. The results point out how local, exchange mediated magnetic interactions in cathode materials are linked with battery performance and can be used for material characterization.

Resolving chemical and spatial heterogeneities at complex electrochemical interfaces in Li ion batteries

“…In contrast, lithiation (discharge) of NMC811 is expected to increase paramagnetic interactions between the substrate and the CEI, leading to signal dephasing in SSNMR. Accordingly, both EPR in the active material, 61,[64][65][66][67][68] which is supported by control experiments comparing NMC811 with NMC532, NMC111, and LNMO (LiNi0.5Mn1.5O4) (Figures S1-S2).…”

Rechargeable Batteries from the Perspective of the Electron Spin

“…More recently, researchers have claimed to detect oxidized oxygen species at high voltages in alkali rich cathodes, whose anomalous capacity is often attributed to anionic redox. 30,31 Significant progress in operando EPR data processing and analysis has been made by Niemöller et al 32 The introduction of a ruby reference into the operando EPR-electrochemical cell enabled them to correct for signal phase changes due to the cell's evolving impedance during electrochemical cycling, and a methodology was devised to monitor battery processes through a combined analysis of the evolution of the signal intensity and linewidth as a function of charge. Within this scheme, changes in TM oxidation states are monitored through the degree of exchange narrowing, which not only depends on the concentration of paramagnetic centers, as previously seen, but also on the nature vacancies) in the as-prepared LiNi0.…”

EPR Imaging of Metallic Lithium and its Application to Dendrite Localisation in Battery Separators

“…Currents of 10 mA were applied for 10 min in each direction for 200 cycles until a short circuit was detected. Afterwards, the separator was extracted without any further cleaning procedure and fixed in a sample holder described elsewhere 45 under argon atmosphere for EPR imaging.…”