Nanostructured Manganese Dioxide for Hybrid Supercapacitor Electrodes

Hybrid supercapacitors, as emerging energy storage devices, have gained much attention in recent years due to their high energy density, fast charge/discharge and long cyclabilities. Among the wide range of systems covered by this topic, low cost, environmental friendliness and high power provide MnO2 with great characteristics to be a competitive candidate. The present work reports a hybrid aqueous supercapacitor system using a commercial activated carbon as the negative electrode and a synthesized manganese dioxide as the positive electrode. Two manganese dioxide polymorphs (α-MnO2 and δ-MnO2) were tested in different neutral and basic aqueous electrolytes. In this way, full cell systems that reached an energy density of 15.6 Wh kg−1 at a power density of 1 kW kg−1 were achieved. The electrode–electrolyte combination explored in this study exhibits excellent performance without losing capacity after 5000 charge/discharge cycles, leading to a promising approach towards more sustainable, high-performance energy storage systems.This research was funded by the Ministerio de Ciencia, Innovación y Universidades (PID2019-107468RB-C21 and TED2021-131517B-C21) and Gobierno Vasco/Eusko Jaurlaritza (IT1546-22)

Fabrication of high-performance dual carbon Li-ion hybrid capacitor: mass balancing approach to improve the energy-power density and cycle life

Most lithium-ion capacitor (LIC) devices include graphite or non-porous hard carbon as negative electrode often failing when demanding high energy at high power densities. Herein, we introduce a new LIC formed by the assembly of polymer derived hollow carbon spheres (HCS) and a superactivated carbon (AC), as negative and positive electrodes, respectively. The hollow microstructure of HCS and the ultra large specific surface area of AC maximize lithium insertion/diffusion and ions adsorption in each of the electrodes, leading to individual remarkable capacity values and rate performances. To optimize the performance of the LIC not only in terms of energy and power densities but also from a stability point of view, a rigorous mass balance study is also performed. Optimized LIC, using a 2:1 negative to positive electrode mass ratio, shows very good reversibility within the operative voltage region of 1.5-4.2V and it is able to deliver a specific cell capacity of 28mAh(-1) even at a high current density of 10Ag(-1). This leads to an energy density of 68Wh kg(-1) at an extreme power density of 30kWkg(-1). Moreover, this LIC device shows an outstanding cyclability, retaining more than 92% of the initial capacity after 35,000 charge-discharge cycles.Spanish Ministry of Economy and Competiveness (MINECO/FEDER) (RTI2018-096199-B-I00) and the Basque Government (Elkartek 2018) are acknowledge for the financial support of this work. We also thank Maria Echeverria and Maria Jauregui for the acquisition of the TEM images and the XRD patterns, respectively

Graphene as Vehicle for Ultrafast Lithium Ion Capacitor Development Based on Recycled Olive Pit Derived Carbons

Herein we report a series of lithium ion capacitors (LICs) with extraordinary energy-to-power ratios based on olive pit recycled carbons and supported on graphene as a conducting matrix. LICs typically present limited energy densities at high power densities due to the sluggish kinetics of the battery-type electrode. To circumvent this limitation, the hard carbon (HC) was embedded in a reduced graphene oxide (rGO) matrix. The addition of rGO into the negative electrode not only forms a 3D interpenetrating carbon network but also wraps HC particles, facilitating ion diffusion and enhancing the electronic conductivity notably at high power densities. Electrochemical impedance spectroscopy (EIS) analysis reveals that charge-transfer resistance at electrode-electrolyte interphase and the charge-transport resistance within the electrode are considerably lower in the presence of rGO. In addition, charge-transport resistance remains constant upon cycling even at increasing current densities. Capacity gain at high current densities, owing to the reduction of the electrode resistance, triggers the overall LIC performance, allowing for the assembly of an ultrafast LIC delivering up to 200 Wh kg(AM)(-1) at low power rates and 100 Wh kg(AM)(-1). (C) The Author(s) 2019. Published by ECS.We thank the European Union (Graphene Flagship, Core 2, grant number 785219), the Spanish Ministry of Science and Innovation (MICINN/FEDER) (RTI2018-096199-B-I00) and the Basque Government (Elkartek 2018) for the financial support of this work. M. Arnaiz thanks the Spanish Ministry of Science, Innovation and Universities for her FPU pre-doctoral fellowship (FPU15/04876)