Ampere-hour-scale soft-package potassium-ion hybrid capacitors enabling 6-minute fast-charging

Extreme fast charging of Ampere-hour (Ah)-scale electrochemical energy storage devices targeting charging times of less than 10 minutes are desired to increase widespread adoption. However, this metric is difficult to achieve in conventional Li-ion batteries due to their inherent reaction mechanism and safety hazards at high current densities. In this work, we report 1 Ah soft-package potassium-ion hybrid supercapacitors (PIHCs), which combine the merits of high-energy density of battery-type negative electrodes and high-power density of capacitor-type positive electrodes. The PIHC consists of a defect-rich, high specific surface area N-doped carbon nanotube-based positive electrode, MnO quantum dots inlaid spacing-expanded carbon nanotube-based negative electrode, carbonate-based non-aqueous electrolyte, and a binder- and current collector-free cell design. Through the optimization of the cell configuration, electrodes, and electrolyte, the full cells (1 Ah) exhibit a cell voltage up to 4.8 V, high full-cell level specific energy of 140 Wh kg-1 (based on the whole mass of device) with a full charge of 6 minutes. An 88% capacity retention after 200 cycles at 10 C (10 A) and a voltage retention of 99% at 25 ± 1 °C are also demonstrated

Thermogalvanic cells demonstrate inherent physiochemical limitations in redox-active electrolytes at water-in-salt concentrations

Summary: The majority of usable energy generated by humanity is lost as waste heat, but thermogalvanic systems (or thermocells) can address this problem by converting low-grade waste heat directly into electricity using redox chemistry. The concentration of the redox couple is a critical parameter; almost invariably, higher concentrations result in more power. This study exploits the simple synergy between Na+ and K+ counter ions to achieve—to the best of our knowledge—the most concentrated stable aqueous ferricyanide/ferrocyanide thermocell to date, at 1.6 m [Fe(CN)6]3−/4−. Despite increasing the concentration by 400% relative to the standard K3/K4[Fe(CN)6] electrolyte (0.4 m), electrical power production increased only 166%. Pushing the system from conventional salt-in-water electrolytes into the quasi-stable water-in-salt region (up to 2.4 m) resulted in a decrease in power. Detailed characterization highlighted the various physicochemical hurdles introduced by these extremely concentrated electrolytes; the identified issues have direct relevance to other energy systems also seeking to use the highest possible concentration

Preparation of porous manganese hydroxide film and its application in supercapacitors

736-741Preparation of a manganese hydroxide film by electrochemically induced deposition method is reported here. The morphology and crystal structure of the film have been investigated by scanning electron microscopy and X-ray diffraction, respectively. The possible deposition mechanism of the film is also discussed. Moreover, the capacitive properties of the film have been evaluated by cyclic voltammetry and galvanostatic charge-discharge method. The results indicate that the morphology of the deposits depends on the amount and size of evolved H₂ bubbles, which can be adjusted by changing the composition of electrolyte and deposition current density. The capacitive properties of film are affected by the deposition parameters. The film prepared under the optimum deposition conditions shows excellent capacitive properties: high specific capacitance (493 F g⁻¹ in 0.1 M Na₂SO₄ aqueous solution from 0 to 1 V at a current density of 1 mA cm⁻²), high electrochemical reversibility and excellent long-term charge-discharge cycle stability (2.2% loss of the specific capacitance observed at the 2000th cycle under the charge-discharge current density of 10 mA cm⁻²)