Combined Electron Paramagnetic Resonance and Atomic Absorption Spectroscopy/Inductively Coupled Plasma Analysis As Diagnostics for Soluble Manganese Species from Mn-Based Positive Electrode Materials in Li-ion Cells

Abstract

Manganese dissolution from positive electrodes significantly reduces the durability of lithium-ion batteries. Knowledge of dissolution rates and oxidation states of manganese ions is essential for designing effective mitigation measures for this problem. We show that electron paramagnetic resonance (EPR) combined with atomic absorption spectroscopy (AAS) or inductively coupled plasma (ICP) can determine both manganese dissolution rates and relative Mn(3+) amounts, by comparing the correlation between EPR and AAS/ICP data for Mn(2+) standards with that for samples containing manganese cations dissolved from active materials (LiMn2O4 (LMO) and LiNi(0.5)Mn(1.5)O4 (LNMO)) into the same electrolyte solution. We show that Mn(3+), and not Mn(2+), is the dominant species dissolved from LMO, while Mn(2+) is predominant for LNMO. Although the dissolution rate of LMO varies significantly for the two investigated materials, due to particle morphology and the presence of Cr in one of them, the Mn speciation appears independent of such details. Thus, the relative abundance of dissolved manganese ions in various oxidation states depends mainly on the overall chemical identity of the active material (LMO vs LNMO). We demonstrate the relevance of our methodology for practical batteries with data for graphite-LMO cells after high-temperature cycling or stand at 4.2 V.

Mn2+ or Mn3+? Investigating transition metal dissolution of manganese species in lithium ion battery electrolytes by capillary electrophoresis

“…Furthermore, the dissolution of Mn 2+ was accelerated at elevated temperatures due to the decomposition of the electrolyte. The absence of Mn 3+ is contrary to those studies, which reported dissolution of Mn 2+ and Mn 3+ from LMO or LNMO cathode materials into LIB electrolytes [38, 39].…”

“…Nevertheless, several studies report on dissolved Mn 3+ being the main manganese species in common electrolyte in case of the LMO cathode, with abundances of 67–78% after storage and 60–80% after electrochemically treatment in LMO||Graphite cells. For LNMO, the Mn 3+ amount in the electrolyte after storage was reported to be 12–44% of total dissolved manganese [38, 39].…”

“…investigated separators from LMO‐based cells after cycling at 50°C, containing polymeric aza‐15‐crown‐5 ethers as Mn ion scavenging agent with XANES, revealing an average oxidation state close to +3 [25]. Other studies showed the dissolution of both manganese species for LNMO and LMO cathode materials in standard carbonate‐based electrolytes after storage and battery operation, with a high fraction of Mn 3+ [38, 39].…”

Electrochemical reduction of bicarbonate on carbon nanotube-supported silver oxide: An electrochemical impedance spectroscopy study

“…Inductive loops have been ascribed to electrochemical asymmetries, which are observed within the studied range of potentials. Some hypotheses have been proposed in the literature to explain this phenomenon, including the heterogeneity of the ions distribution inside the electrode to generate concentration cells between different particles of electrode or the phase change of the active material during the EIS measurement[34]. The charge transfer resistance is further decreased by reducing the potential to -1.4 V.…”

A Comprehensive Study of Manganese Deposition and Side Reactions in Li-Ion Battery Electrodes

“…However, Shilina et al recently argued that Mn 3+ not Mn 2+ is the dominant species dissolved from the LiMn 2 O 4 material while Mn 2+ is predominant for the LiNi 0.5 Mn 1.5 O 4 material. 19 This result is contradicting to the previous knowledge that Mn 2+ ions are the only soluble species that dissolve from the LiMn 2 O 4 cathode material. While this aspect needs to be investigated further, it was quite clear that additional manganese was observed with decomposed electrolyte products in the SEI layers of the graphite surface under various experimental conditions.…”