Advanced Asymmetric Supercapacitors Based on Ni(OH)2/Graphene and Porous Graphene Electrodes with High Energy Density

Our modern and technological society requests enhanced energy storage devices to tackle the current necessities. In addition, wearable electronic devices are being demanding because they offer many facilities to the person wearing it. In this manuscript, a historical review is made about the available energy storage devices focusing on super-capacitors and lithium-ion batteries, since they currently are the most present in the industry, and the possible polymeric materials suitable on wearable energy storage devices. Polymers are a suitable option because they not only possess remarkable mechanical resistance, flexibility, long life-times, easy manufacturing techniques and low cost in addition to they can be environmentally friendly, nontoxic, and even biodegradable too. Moreover, the electrical and electrochemical polymer properties can be tunning with suitable fillers giving to versatile conducting polymer composites with a good cost and properties' ratio. Although the advances are promising, there are still many drawbacks that need to be overcome. Future research should focus on improving both the performance of materials and their processability on an industrial scale, where additive manufacturing offers many possibilities. The sustainability of new energy storage devices should not

In order to achieve high energy and power densities, a high-voltage asymmetric electrochemical supercapacitor has been developed, with activated carbon (AC) as the negative electrode and a silicon carbide-MnO2 nanoneedle (SiC-N-MnO2) composite as the positive electrode. A neutral aqueous Na2SO4 solution was used as the electrolyte. SiC-N-MnO2 was prepared by packing growing MnO2 nanoneedle crystal species in only one direction on the silicon carbide surface. AC was oxidized by thermal treatment in order to introduce oxygen-containing functional groups. Owing to the high capacitance and excellent rate performance of SiC-N-MnO2 and AC, as well as the synergistic effects of the two electrodes, a constructed asymmetric supercapacitor exhibited superior electrochemical performance. The optimized asymmetric supercapacitor could be cycled reversibly in the voltage range from 0 to 1.9 V, and it exhibited a specific capacitance of 59.9 F g(-1) at a scan rate of 2 mV s(-1) and excellent energy density and power density (30.06 W h kg(-1) and 113.92 W kg(-1), respectively) with a specific capacitance loss of less than 3.1% after 1000 charge-discharge cycles, indicating excellent electrochemical stability. These encouraging results show great potential in terms of developing energy storage devices with high energy and power densities for practical applications.

Asymmetric supercapacitors with metal-like ternary selenides and porous graphene electrodes

Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO2 composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na2SO4 electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO2 and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0–1.8 V, and exhibits maximum energy density of 51.1 Wh kg−1, which is much higher than that of MnO2//DWNT cell (29.1 Wh kg−1). Additionally, graphene/MnO2//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.

Fe(CN)63− ion-modified MnO2/graphene ribbons can provide extra pseudocapacitance from the Fe(CN)63−/Fe(CN)64− redox reaction for high energy density supercapacitors.

Asymmetric supercapacitors based on 3D graphene-wrapped V2O5 nanospheres and Fe3O4@3D graphene electrodes with high power and energy densities

The crucial request for alternative clean energy technologies to replace conventional fossil fuels and drive technological advancement in consumer and wearable electronics, electric vehicles etc. has led to great advancement in electrochemical energy storage systems research. The lithium-ion battery possesses high energy density while the supercapacitor can guarantee high power density. However, modern technologies such as integrated solar and wind energy solutions require a blend of high energy and power density devices, which is a great challenge. Presently, there is increased research interest in aqueous hybrid supercapacitors, a device capable of combining the high energy density of rechargeable batteries and the high-power density of electric-double layer capacitors.The current hotspot of the hybrid supercapacitor research is the zinc-ion hybrid supercapacitor owing to its several advantages such as the abundance of Zinc resource over lithium, high theoretical capacity of Zn, double charge transfer compared to univalent Lithium, environmental safety and high energy/power density. Wang et al first reported the carbon zinc-ion hybrid supercapacitor in 2018 by directly using zinc foil as anode and bio-carbon as cathode to realize long stability up to 20000 cycles. Next, Dong et al also developed an activated carbon-based zinc-ion hybrid supercapacitor which achieved a high energy density of ~84 Wh kg-1 and power density of 14.9 kW kg-1 in a potential window of 0.2 – 1.8 V. Despite the rapid advances over a short period in this class of energy storage devices, some problems still exist. The coulombic efficiency of Zinc-ion hybrid supercapacitors is inferior in low-cost ZnSO4 electrolytes owing to side reactions between the electrolyte and the Zn anode, while the mass loading of commonly used carbon cathode is extremely low (less than 2 mg cm-2). Importantly, the charge storage mechanism in zinc-ion hybrid supercapacitors is unclear.In this work, we developed high performance zinc-ion hybrid supercapacitors with superior charge storage, improved rate capability, and high power and energy density using a high mass density carbon anode with superior capacitive/pseudocapacitive storage. We successfully reveal that the charge storage of zinc-ion hybrid supercapacitors is extensively limited in zinc sulfate electrolytes and successfully address the coulombic efficiency problem using by modifying the electrolyte. Finally, using techniques such as in-situ Raman spectroscopy and X-ray diffraction analysis, we probe the charge storage mechanism and unravel a double cation charge storage mechanism, resulting in high energy density and extended potential window. Finally, our work provides crucial insights into understanding the charge storage process of zinc-ion hybrid supercapacitors and designing hybrid supercapacitors with new material chemistries.

All-functionalized-graphene ribbon films for flexible asymmetric supercapacitors with ultrahigh energy and power densities

Asymmetric supercapacitors with high energy density are fabricated using a self‐assembled reduced graphene oxide (RGO)/MnO2 (GrMnO2) composite as a positive electrode and a RGO/MoO3 (GrMoO3) composite as a negative electrode in safe aqueous Na2SO4 electrolyte. The operation voltage is maximized by choosing two metal oxides with the largest work function difference. Because of the synergistic effects of highly conductive graphene and highly pseudocapacitive metal oxides, the hybrid nanostructure electrodes exhibit better charge transport and cycling stability. The operation voltage is expanded to 2.0 V in spite of the use of aqueous electrolyte, revealing a high energy density of 42.6 Wh kg−1 at a power density of 276 W kg−1 and a maximum specific capacitance of 307 F g−1, consequently giving rise to an excellent Ragone plot. In addition, the GrMnO2//GrMoO3 supercapacitor exhibits improved capacitance with cycling up to 1000 cycles, which is explained by the development of micropore structures during the repetition of ion transfer. This strategy for the choice of metal oxides provides a promising route for next‐generation supercapacitors with high energy and high power densities.

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

We develop zirconium-templated NiO/NiOOH nanosheets on nickel foam and polypyrrole-embedded in exfoliated carbon fiber cloth as complementary electrodes for an asymmetric battery-type supercapacitor device. We achieve high volumetric energy and power density by the modification of commercially available current collectors (CCs). The modified CCs provide the source of active material, actively participate in the charge storage process, provide a larger surface area for active material loading, need no additional binders or conductive additives, and retain the ability to act as the CC. Nickel foam (NF) CCs are modified by use of a soft-templating/solvothermal treatment to generate NiO/NiOOH nanosheets, where the NF is the source of Ni for the synthesis. Carbon-fiber cloth (CFC) CCs are modified by an electrochemical oxidation/reduction process to generate exfoliated core-shell structures (ECFC). Electropolymerization of pyrrole into the shell structure produces polypyrrole embedded in exfoliated core-shell material (PPy@rECFC). Battery-type supercapacitor devices are produced with NiO/NiOOH@NF and PPy@rECFC as positive and negative electrodes, respectively, to demonstrate the utility of this approach. Volumetric energy densities for the full-cell device are in the range of 2.60-4.12 mWh cm-3 with corresponding power densities in the range of 9.17-425.58 mW cm-3. This is comparable to thin-film lithium-ion batteries (0.3-10 mWh cm-3) and better than some commercial supercapacitors (<1 mWh cm-3).1 The energy and power density is impressive considering that it was calculated using the entire cell volume (active materials, separator, and both CCs). The full-cell device is highly stable, retaining 96% and 88% of capacity after 2000 and 5000 cycles, respectively. These results demonstrate the utility of directly modifying the CCs and suggest a new method to produce high volumetric energy density and power density storage devices.

Capacitive contribution matters in facilitating high power battery materials toward fast-charging alkali metal ion batteries

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

Construction of high electrical conductive nickel phosphide alloys with controllable crystalline phase for advanced energy storage

Novel Na0.5Bi0.5TiO3 based, lead-free energy storage ceramics with high power and energy density and excellent high-temperature stability