Simple and Cost-Effective Approach To Dramatically Enhance the Durability and Capability of a Layered δ-MnO₂ Based Electrode for Pseudocapacitors: A Practical Electrochemical Test and Mechanistic Revealing

Abstract

Inadequate capacity and poor durability of MnO 2 based pseudocapacitive electrodes have long been stumbling blocks in the way of their commercial use. Though layered δ-MnO 2 has higher potential to be used due to its proton-free energy storage reactions, its durability is still far away from carbon based electrodes associated with structure deformation caused by interlayer spacing change and Jahn−Teller effect. Here we report an effective approach to dramatically enhance not only the stability but also the capacity of δ-MnO 2 based electrode through a simple incorporation of exotic cations, hydrated Zn 2+ , in the tunnel of the material. Even at a very fast charge/discharge rate (50 A g −1 ), the capacity of the electrode is gradually increased from 268 to 348 F g −1 after ∼3,000 cycles and then remains relatively constant in the subsequent ∼17,000 cycles, which means ∼128% of the initial capacity is maintained after 20,000 cycles. In contrast, the capacity of bare δ-MnO 2 electrode without modification is degraded gradually along the cycling, retaining only ∼74% of the initial value after 20,000 cycles. To reveal the basic chemistry between them, synchrotron X-ray diffraction and Raman spectroscopy were performed to explore the structural evolution of the modified δ-MnO 2 during cycling; DFT computation was used to estimate the energetics and vibration modes associated with the hydrated Zn 2+ . The performance enhancement is attributed largely to the preaccommodation of [Zn (H 2 O) n ] 2+ , which effectively suppresses the interlayer spacing change during cycling and thus benefits the stability. KEYWORDS: pseudocapacitor, layered δ-MnO 2 /Na 0.55 Mn 2 O 4 , tunnel structure modification/preaccommodation of exotic ions, in situ Raman, DFT computation

Birnessite based nanostructures for supercapacitors: challenges, strategies and prospects

“…Additionally, these intercalated cations can be released during the charge process and consumed during the discharge process, and this contributes capacitance or capacity to the birnessite based electrode. 83,84 However, this process is more like a battery reaction process rather than a capacitive reaction process as this is a kind of chemical reaction rather than charge transfer, which can be separated from the first two energy storage mechanisms by defining as diffusion-controlled contribution and surface capacitive contribution by analyzing the CV data at various sweep rates according to a power law equation as follows: i = aν b where i is the current (A), ν is the sweep rate (V s −1 ), a and b are adjustable parameters fluctuating with the voltage. The b -values reflecting the electrode performance were calculated from the slope of the plot of log i vs. log ν .…”

NiSe2/Ni(OH)2 Heterojunction Composite through Epitaxial-like Strategy as High-Rate Battery-Type Electrode Material

“…Scientists have paid much efforts to develop energy storage devices, such as lithium/sodium/potassium ion batteries, fuel cells, and electrochemical supercapacitors [6][7][8][9][10]. Among them, supercapacitors are attractive due to their high safety, long cycle lives, large power densities, and low cost [11][12][13]. However, their low energy densities, compared with other electrochemical energy technologies, limit their further applications [14][15][16].…”

High Power Energy Storage via Electrochemically Expanded and Hydrated Manganese-Rich Oxides

“…The F.E. NaMCu exhibits a capacitive CV at 1 and 10 mV/s, with a semi-rectangular shape and broad peaks similar to those often observed in birnessite (Xiong et al, 2017;Yao et al, 2019). The P.E.…”

“…In addition to this expected behavior, the appearance of a new peak at 7.19°2θ at ~0.9 V during the first anodic cycle indicates the formation of a new phase. According to prior results, this peak corresponds to the (001) plane of a birnessite-like hydrated phase with an interlayer spacing of 7.05 Å (Lu and Dahn, 2001 ; Abou-El-Sherbini et al, 2002 ; Buchholz et al, 2014 ; Boyd et al, 2018 ; Yao et al, 2019 ). The full XRD patterns of the material before and after the phase transformation are shown in Figure S2B .…”