On the Manganese Dissolution Process from LiMn<sub>2</sub>O<sub>4</sub> Cathode Materials
Yonas Tesfamhret, Haidong Liu, Zhigang Chai, Erik J. Berg, Reza Younesi
Abstract
Abstract Transition metal (TM) dissolution is a process experienced by most cathode materials based on lithium transition metal oxides. Spinel LiMn 2 O 4 (LMO) is the best‐known cathode material that suffers from TM dissolution. Therefore, LMO is selected here to understand the dissolution process and derive an inductively coupled plasma optical emission spectroscopy (ICP‐OES) method for quantifying dissolved metal ions. Furthermore, the LMO powder is coated with thin Al 2 O 3 films of different thicknesses using atomic layer deposition (ALD) in an attempt to suppress the dissolution of Mn. Two different types of counter electrodes, lithium iron phosphate (LFP) and Li‐metal, were used to investigate the role of the counter electrode on Mn dissolution. HF is identified as the lead cause of Mn dissolution, through comparisons of cells containing LiPF 6 or LiClO 4 based electrolytes. The results show that Li‐metal counter electrode effectively minimizes the dissolution process via likely consuming HF and H 2 O impurity. In contradiction to the purpose of the protective Al 2 O 3 thin film coating, surface coated LMO showed higher dissolution of Mn compared to pristine LMO, both in LFP||LMO and Li||LMO configurations. Al 2 O 3 is proposed to generate H 2 O when reacts with HF. H 2 O could have the possibility to migrate back in the electrolyte and participate in the hydrolysis of LiPF 6 , resulting in more HF and thereby more Mn dissolution.