Influence of Manganese Dissolution on the Degradation of Surface Films on Edge Plane Graphite Negative-Electrodes in Lithium-Ion Batteries

Abstract

The influence of Mn-ion dissolved in electrolyte solution on the electrochemical properties of graphite negative-electrodes was investigated using edge plane highly oriented pyrolytic graphite (HOPG) by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ atomic force microscopy (AFM). Redox currents due to intercalation and de-intercalation reactions of Li-ion at an edge plane HOPG electrode significantly decreased with an increase in the cycle number. Both the surface film and interfacial Li-ion transfer resistances remarkably increased in the presence of Mn-ion, and particularly at potentials below 0.6 V, indicating that some irreversible reactions should occur. X-ray photoelectron spectra indicate that Mn metal was deposited on the edge plane HOPG, and then oxidized into divalent (or higher) Mn under open-circuit conditions. These results suggest that the deposited Mn metal should be oxidized to decompose the electrolyte itself and/or the original surface film reductively. Electrochemical AFM observation showed that very fine particles smaller than 0.1 μm were formed on edge plane HOPG in the initial potential cycle in electrolyte containing Mn-ion, and then larger particles were observed after further potential cycles. The effects of film-forming additives on the deposition of Mn on the edge plane HOPG electrode were also investigated.Various kinds of lithium 3d-transition metal oxides have been used as active materials in positive electrodes in commercially available lithium-ion batteries. The working potentials depend largely on reduction reactions of the 3d-transition metals within oxides, which involve the intercalation (insertion) of Li-ion from the electrolyte and the injection of electrons from the external circuit. Hence, lithium 3d-transition metal compounds containing Mn, Fe, Co and Ni have been widely explored to develop active materials with high working potentials and large discharge capacities. As a result, a variety of promising active materials have been created, but some of them are known to dissolve in electrolyte solution, particularly at elevated temperatures. 1,2 The dissolution of active materials results in a decrease in the reversible capacities of positive electrodes. In addition, dissolved 3d-transition metal-ion, and particularly Mn-ion, is known to cause a deterioration in the performance of graphite negative-electrodes. 3,4 The Mn-ion should deposit on a negative electrode because the working potentials, e.g., ca. 0.25 V vs. Li/Li + for graphite, are usually very low compared to the deposition potentials. 5,6 These technical issues must be solved because Mn-based active materials including spinel LiMn 2 O 4 are promising active materials for the positive electrode in lithium-ion batteries for large-sized and/or high-power applications. Many studies have been conducted to suppress the dissolution of LiMn 2 O 4 positive-electrodes, and several effective methods have been reported, such as surface coating of LiMn 2 O 4 , 7,8 lithium excess Li 1+x Mn 2 O 4 9 and el...

Review—Multifunctional Materials for Enhanced Li-Ion Batteries Durability: A Brief Review of Practical Options

“…For example, the Mn dissolution rate from LMO is greater at high potentials (above 4 V vs. Li/Li + ) than at lower potentials (below 4 V vs. Li/Li + ), a fact which is inconsistent with the disproportionation concept, since the fraction of Mn 4+ cations in the LMO lattice increases with increasing potential. 13,17 While a very large number of studies in the literature report a variety of results on the oxidation state of Mn species in the negative or positive electrodes of cycled LMO-graphite cells, 11,[18][19][20][21] Mitigation measures for Mn dissolution.-Several mitigation measures for the dissolution of Mn ions and its consequences were proposed in the literature over the past two decades: electrolyte optimization by a judicious choice of additives; [26][27][28][29][30][31][32][33] elemental substitutions in the LMO lattice, 7,13,17,34,35 in order to increase the average oxidation state of the Mn ions; surface coatings on the active material powder or electrodes, in order to avoid direct contacts between electrode and electrolyte solution, and thus prevent HF and other acid attack on the active material; [36][37][38][39][40][41][42] chemically active binders; [43][44][45][46][47][48][49][50] an inorganic Mn ions scavenging barrier layer such as lithium titanate 51 or a solid Li-ion conducting and Mn ions blocking membrane 52 placed in the inter-electrode space; and the utilization of chemically activ...…”

Transition Metal Dissolution, Ion Migration, Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells

“…[20][21][22][23] This last source, especially the dissolution of Mn and its deposition in the negative electrode SEI, has been shown to be particularly detrimental to cell performance. [24][25][26] All steps of the dissolution, migration, and incorporation process involving the TM ions are insufficiently understood, and even the state of TMs in the SEI continues to be the subject of controversy (see Refs. 27-29 for a review).…”

An azamacrocyclic electrolyte additive to suppress metal deposition in lithium-ion batteries

“…Reductive electrolyte decomposition and concomitant film deposition are reported to be succeeded by metal deposition on graphite electrodes [4,7,8,14]. In such a case, a significant increase in film resistance is expected.…”

“…The detrimental effect of Mn dissolution on LMO positive electrode is minor as the reversible capacity of LMO only decreases by a marginal amount [5]. However, the harmful effect on negative electrodes is more critical [6][7][8], particularly on graphite electrodes on which the dissolved Mn ions are readily electroplated [1,3]. In such cases, several undesirable features ensue.…”