Enhancing the Electrochemical Performances by Wet Ball Milling to Introduce Structural Water into an Electrolytic MnO₂/Graphite Nanocomposite Cathode for Zinc-Ion Batteries

Abstract

The introduction of structural water in cathode materials of zinc-ion batteries can reduce electrostatic interactions to promote zinc-ion diffusion. However, it is difficult to introduce structural water in MnO 2 cathodes due to annealing for crystallinity. For the first time, we introduce structural water into MnO 2 /graphite nanocomposites by simple wet ball milling of a mixture of electrolytic MnO 2 and natural graphite. The composites of nanorod MnO 2 /graphite exhibit a high discharge capacity (312 mA h g −1 at 0.1 A g −1 ), which is more than twice that of electrolytic MnO 2 (130 mA h g −1 at 0.1 A g −1 ). It also shows an outstanding rate capacity and cyclic stability that retains 80.1% of the incipient capacity after 1000 cycles at 1 A g −1 . MnO 2 /graphite composites with certain structural water and oxygen vacancies exhibit excellent electrochemical properties, mainly because the presence of structural water and oxygen vacancies can promote Zn 2+ ion diffusion of the materials. Through the results of density functional theory calculations and experiments, we verify the adsorption between structural water and crystal planes and identify the positions of structural water, mainly on the (102) and ( 110) planes of ε-MnO 2 , which make an impact on ion diffusion. This feasible wet ball milling can not only obtain the composite electrode materials with excellent electrochemical performances but also provide an approach for future synthesis of composite materials with structural water and oxygen vacancies.

Single-Atom Platinum Implanted on Manganese Dioxide Boosted the High-Rate Performance of Cathodes for Zinc-Ion Batteries

“…Low stirring speed and suitable heating temperature made single-atom Pt uniformly anchored on MnO 2 loaded on carbon cloth during the process of electrochemical deposition. Wet ball milling could achieve the nanocrystallization of Pt-MnO 2 and made its particles finer and more uniform, which could improve the electrochemical performance of electrode materials. , XRD patterns in Figure b illustrate that the peaks at 12.5°, 25.2°, 37.3°, and 65.6° are indexed to the (0 0 1), (0 0 2), (−1 1 1), and (0 2 0) planes of δ-MnO 2 , respectively, with a space group of C 2/ m (JCPDS no. 80-1098).…”

Effect of MnO2 Polymorphs’ Structure on Low-Temperature Catalytic Oxidation: Crystalline Controlled Oxygen Vacancy Formation

“…The pyrolusite-type β-MnO 2 ( P 42/ mnm ) has a rutile-type structure with infinite [MnO 6 ] octahedral chains that share opposing edges. Each chain is connected with four similar chain corners, leading to the formation of (1 × 1) tunnels in this structure. − The structural feature of γ-MnO 2 is the random intergrowth of ramsdellite-type (1 × 2 tunnels) and pyrolusite (1 × 1 tunnels) matrices, where the basic building blocks of [MnO 6 ] octahedra share the corners and edges. , The structure of birnessite-type δ-MnO 2 consists of [MnO 6 ] octahedral sheets that share edges, forming a two-dimensional (2D) layer structure with the interlayers filled with K + OH – or H 2 O. , The structure of akhtenskite-type ε-MnO 2 is a polymorph of MnO 2 with a hexagonal symmetry, first discovered by De Wolff et al It exhibits a NiAs-type structure with half cationʼs vacancies and Mn 4+ randomly distributed. , However, the ordered structure of ε-MnO 2 and the DFT calculations have also been proposed and performed in recent years, respectively. − Hong and co-authors revealed a ε-MnO 2 material by acid leaching of LiMnO x . The formation energies of oxygen vacancies were calculated based on both bulk and surface ε-MnO 2 by DFT calculations .…”

“…They revealed that doping Fe could greatly increase the oxygen vacancy concentration of ε-MnO 2 , thereby improving the toluene oxidation activity. Zhang and co-authors also calculated the adsorption energies of H 2 O for the ε-MnO 2 planes (102) and (110) . In this paper, we established a reliable unit cell model according to the space group ( P 63/ mmc , #194) of ε-MnO 2 and the unit cell parameters ( a = b = 0.2786 nm, c = 0.4412 nm, α = β = 90°, γ = 120°).…”

“…Zhang and co-authors also calculated the adsorption energies of H 2 O for the ε-MnO 2 planes (102) and (110). 22 In this paper, we established a reliable unit cell model according to the space group (P63/ mmc, #194) of ε-MnO on the catalytic activity during formaldehyde oxidation. They reported that δ-MnO 2 exhibited the best catalytic activity for formaldehyde oxidation, which was attributed to the tunnel structure and to active lattice oxygen species.…”

A two-dimensional conductive polymer/V2O5 composite with rapid zinc-ion storage kinetics for high-power aqueous zinc-ion batteries

“…Meanwhile, the higher ionic conductivity (∼1 S cm −1 ) in aqueous electrolytes enables a superior power density compared to non-aqueous systems. 7 To date, various materials suitable for reversible Zn 2+ insertion/extraction have been investigated as cathodes for ZIBs, mainly including manganese-based composites, vanadium-based composites, and Prussian blue analogues, [8][9][10][11][12][13][14][15][16][17][18][19] among which vanadium pentoxide (V 2 O 5 ) has attracted widespread attention owing to its multiple valence states and thus remarkable theoretical capacity of 589 mA h g −1 for Zn 2+ storage (based on a two-electron transfer process). [20][21][22][23][24][25][26][27][28][29] Nevertheless, the poor intrinsic conductivity and the sluggish ion diffusion kinetics caused by the narrow layer spacing in the V 2 O 5 framework result in inferior rate capability and unsatisfactory cycling performances.…”