Electrochemical Behavior of Electrolytic Manganese Dioxide in Aqueous KOH and LiOH Solutions: A Comparative Study

Abstract

As an inexpensive and high capacity oxidant, electrolytic manganese dioxide (γ-MnO 2 ) is of interest as a cathode for secondary aqueous batteries. Electrochemical behavior of γ-MnO 2 was characterized in aqueous 5.0 M KOH and LiOH solutions, and found to depend strongly upon cation identity. In LiOH and mixed LiOH / KOH solutions, Li-ion intercalation appeared to operate in competition with proton intercalation, being favored at higher [Li + ] and, for mixed electrolytes, lower sweep rates. Electrochemical and in situ X-ray diffraction data indicated that γ-MnO 2 underwent a chemically irreversible transformation upon the first reduction in LiOH solution, while in KOH solution, structure was largely unchanged after the first cycle. These experiments with γ-MnO 2 as well as with a closely-related, ramsdellite-like sample, suggest that depending on sample morphology/rate capability, the irreversible process proceeds either through a solid-solution reaction or a two-phase reaction followed by a solid-solution reaction. While discharge capacity and capacity retention during galvanostatic cycling of γ-MnO 2 were worse in LiOH than in KOH solution, some improvement was noted in a mixed LiOH/KOH solution. Electrolytic manganese dioxide (EMD or ε/γ-MnO 2 ) is the material most commonly employed as the cathode in primary alkaline batteries and primary non-aqueous lithium cells owing to its relatively low cost, low toxicity, high reduction potential, and high gravimetric capacity. Unfortunately, MnO 2 -based secondary cells tend to have limited cycle life, due to the conversion of active material into electrochemically inactive or electronically resistive phases, such as hausmannite (Mn 3 O 4 ) or hetaerolyte (ZnMn 2 O 4 ) in aqueous cells, 1,2 and to pulverization associated with large changes in volume with state of charge.3 Under certain conditions, however, γ-MnO 2 can be cycled with relatively good capacity retention. Major criteria for reversible cycling are to limit the depth of discharge to minimize the solubility of manganese in lower oxidation states, and to avoid the formation of soluble high oxidation state species during charging (i.e. MnO 4 2− ). 4,5,6,7 It has also been reported that the use of LiOH instead of KOH as the electrolyte can improve the cycle life of γ-MnO 2 . 8 The structure of γ-MnO 2 is highly defective both in terms of type and concentration of defects. According to the De Wolff model, the structure is thought to be an intergrowth of ramsdellite and pyrolusite layers (Fig. 1).9,10 Both phases have tunnel-structures, as is apparent from the viewpoint in Fig. 1. γ-MnO 2 also contains microtwinning defects, which introduce kinks to the tunnel structure.10 Manganese vacancies can also be present and necessitate the incorporation of protons (Ruetschi protons) in the structure to maintain charge balance. 12In aqueous KOH or NH 4 Cl media (in the case of a Leclanché cell), the reduction of the Mn 4+ to Mn 3+ is accompanied by the incorporation of protons into the tunnels in the structure (along th...

Regenerable Cu-intercalated MnO2 layered cathode for highly cyclable energy dense batteries

“…( c ) Comparison of the best MnO 2 cathodes reported in literature for aqueous Zn-MnO 2 batteries. ( d ) Comparison of the areal capacities and cycle life obtained gathered from reported results in literature 60 61 62 63 . CAES, compressed air energy storage; PHS, pumped hydro storage; SMES, superconducting magnetic energy storage.…”

3D LiMn2O4 thin-film electrodes for high rate all solid-state lithium and Li-ion microbatteries

“…(0<x<1) with x the level of lithiation. [23][24] As illustrated in equations 4 and 5, there is a 0.05 V potential difference between the formal potential of the Li-ion intercalation reaction for LiMn2O4 and that for MnO2. The formal potential can be obtained from the difference in peak potential, the provided diffusion coefficients are the same for oxidation and reduction.…”

Effect of Sub-nanoparticle Architecture on Cycling Performance of MnO2 Battery Cathodes through Thermal Tuning of Polymorph Composition

“…The better electrochemical performance of these highly disordered polymorphs compared to the ordered phases, α-MnO 2 , β-MnO 2 , and R-MnO 2 , is attributed to the combination of the Mn 4+ vacancies and defects facilitating ion intercalation. − The structures of γ-MnO 2 and ε-MnO 2 are commonly described as random intergrowths of 1 × 1 (pyrolusite) and 1 × 2 (ramsdellite) channels; however, ε-MnO 2 possesses a much higher concentration of microtwinning defects (twinning planes in both pyrolusite and ramsdellite domains) and much smaller ordered crystalline domains. γ-MnO 2 mostly has De Wolff faults (single channels in the ramsdellite matrix) that create a rather ordered structure of alternating 1 × 2 and 1 × 1 channels. ,,− EMD, typically prepared by electrodeposition, usually shows poor crystallinity with broad diffraction peaks, and mainly contains short-range γ-MnO 2 segments with random occurrence of ε-MnO 2 and β-MnO 2 polymorphs…”

“…The generally accepted mechanism for discharge of MnO 2 in alkaline electrolyte (KOH) involves intercalation of H + ions with formation of reduced oxyhydroxide (MnOOH). Deeper discharge results in irreversible formation of electrochemically inactive phases (Mn­(OH) 2 , Mn 2 O 3 , Mn 3 O 4 , and Zn­Mn 2 O 4 ) accompanied by a significant increase in the lattice parameters, and some dissolution of Mn 2+ species. , It is accepted that K + ions are too large for reversible intercalation and their insertion into the structure retards the protonation mechanism and rechargeability . In nonaqueous Li-ion batteries, Li + ions intercalate into MnO 2 instead of protons, forming Li x ­MnO 2 on discharge. ,, Therefore, the use of LiOH electrolyte instead of KOH is suggested to be beneficial for performance of MnO 2 cathodes in alkaline electrolytes.…”

“…Deeper discharge results in irreversible formation of electrochemically inactive phases (Mn­(OH) 2 , Mn 2 O 3 , Mn 3 O 4 , and Zn­Mn 2 O 4 ) accompanied by a significant increase in the lattice parameters, and some dissolution of Mn 2+ species. , It is accepted that K + ions are too large for reversible intercalation and their insertion into the structure retards the protonation mechanism and rechargeability . In nonaqueous Li-ion batteries, Li + ions intercalate into MnO 2 instead of protons, forming Li x ­MnO 2 on discharge. ,, Therefore, the use of LiOH electrolyte instead of KOH is suggested to be beneficial for performance of MnO 2 cathodes in alkaline electrolytes.…”