Pseudocapacitive Characteristics of Low-Carbon Silicon Oxycarbide for Lithium-Ion Capacitors

Developments in conducting polymer-, metal oxide-, and carbon nanotube-based composite electrode materials for supercapacitors: a review

Supercapacitors are the latest development in the field of energy storage devices (ESDs). A lot of research has been done in the last few decades to increase the performance of supercapacitors. The electrodes of supercapacitors are modified by composite materials based on conducting polymers, metal oxide nanoparticles, metal-organic frameworks, covalent organic frameworks, MXenes, chalcogenides, carbon nanotubes (CNTs), etc. In comparison to rechargeable batteries, supercapacitors have advantages such as quick charging and high power density. This review is focused on the progress in the development of electrode materials for supercapacitors using composite materials based on conducting polymers, graphene, metal oxide nanoparticles/nanofibres, and CNTs. Moreover, we investigated different types of ESDs as well as their electrochemical energy storage mechanisms and kinetic aspects. We have also discussed the classification of different types of SCs; advantages and drawbacks of SCs and other ESDs; and the use of nanofibres, carbon, CNTs, graphene, metal oxide-nanofibres, and conducting polymers as electrode materials for SCs. Furthermore, modifications in the development of different types of SCs such as pseudo-capacitors, hybrid capacitors, and electrical double-layer capacitors are discussed in detail; both electrolyte-based and electrolyte-free supercapacitors are taken into consideration. This review will help in designing and fabricating high-performance supercapacitors with high energy density and power output, which will act as an alternative to Li-ion batteries in the future.

Hydrothermal synthesis and electrochemical properties of Sn-based peanut shell biochar electrode materials

Using activated-carbon-based electrodes derived from waste biomass in super-capacitor energy technologies is an essential future strategy to achieve sustainable energy and environmental protection. Biomass feed-stocks such as bamboo and straw have been used to prepare activated carbon-based electrodes. This experiment used peanut shells (waste biomass) as carbon precursors. Peanut shell-activated biochar materials were prepared using KOH activation and heat treatment, and SnO2@KBC-CNTs, a composite electrode material of biochar loaded with tin oxide. It was produced through hydrothermal synthesis, utilizing SnCl4-5H2O as the tin precursor. The application of KOH activators during pyrolysis markedly enhanced the porosity and specific surface area of the resultant activated biochar, due to effective dispersion and degradation of pyrolytic products. Characterized by a micro-mesoporous structure, the composite's pores boasted a specific surface area of 158.69 m2 g-1. When tested at a density of current of 0.5 A g-1, the specific capacitance of SnO2@KBC-CNTs reached 198.62 F g-1, nearly doubling the performance of the KBC electrode material alone. Moreover, the composite demonstrated a low ion transfer resistance of 0.71 Ω during charge-discharge cycles.

Stable Zn Metal Anodes with Limited Zn-Doping in MgF2 Interphase for Fast and Uniformly Ionic Flux

The practical applications of aqueous Zn metal batteries are currently restricted by the inherent drawbacks of Zn such as the hydrogen evolution reaction, sluggish kinetics, and dendrite formation. To address these problems, herein, a limitedly Zn-doped MgF₂ interphase comprising an upper region of pure, porous MgF₂ and a lower region of gradient Zn-doped MgF₂ is achieved via radio frequency sputtering technique. The porous MgF₂ region is a polar insulator whose high corrosion resistance facilitates the de-solvation of the solvated Zn ions and suppression of hydrogen evolution, resulting in Zn metal electrodes with a low interfacial resistance. The Zn-doped MgF₂ region facilitates fast transfer kinetics and homogeneous deposition of Zn ions owing to the interfacial polarization between the Zn dopant and MgF₂ matrix, and the high concentration of the Zn dopant on the surface of the metal substrate as fine nuclei. Consequently, a symmetric cell incorporating the proposed Zn metal exhibits low overpotentials of ~ 27.2 and ~ 99.7 mV without Zn dendrites over 250 to 8000 cycles at current densities of 1.0 and 10.0 mA cm^-2, respectively. The developed Zn/MnO₂ full cell exhibits superior capacity retentions of 97.5% and 84.0% with average Coulombic efficiencies of 99.96% after 1000 and 3000 cycles, respectively.

Advanced and Emerging Negative Electrodes for Li-Ion Capacitors: Pragmatism vs. Performance

Li-ion capacitors (LICs) are designed to achieve high power and energy densities using a carbon-based material as a positive electrode coupled with a negative electrode often adopted from Li-ion batteries. However, such adoption cannot be direct and requires additional materials optimization. Furthermore, for the desired device’s performance, a proper design of the electrodes is necessary to balance the different charge storage mechanisms. The negative electrode with an intercalation or alloying active material must provide the high rate performance and long-term cycling ability necessary for LIC functionality—a primary challenge for the design of these energy-storage devices. In addition, the search for new active materials must also consider the need for environmentally friendly chemistry and the sustainable availability of key elements. With these factors in mind, this review evaluates advanced and emerging materials used as high-rate anodes in LICs from the perspective of their practical implementation.

Hierarchically Designed Nitrogen-Doped MoS2/Silicon Oxycarbide Nanoscale Heterostructure as High-Performance Sodium-Ion Battery Anode

Molybedenum disulfide (MoS₂) is regarded as a promising anode material for next-generation sodium-ion batteries (SIBs) owing to its high theoretical capacity. However, its low conductivity, large volume changes, and undesirable phase transformation hinder its practical applications. In this study, we synthesize a hierarchically designed core-shell heterostructure based on nitrogen-doped MoS₂/C and silicon oxycarbide (SiOC) (N-MoS₂/C@SiOC) via the facile pyrolysis of a suspension of an N-MoS₂/polyfurfural precursor in silicone oil. The in situ nitrogen doping in a two-dimensional MoS₂ structure with carbon incorporation leads to the enlargement of the interlayer spacing and enhancement of the electronic conductivity and mechanical stability, which allows the facile, highly reversible insertion and extraction of sodium ions upon cycling. Further, the nanoscale SiOC shell with surface capacitive reactivity provides a conductive pathway, preventing unfavorable side reactions at the electrode/electrolyte interface and acting as a structure-reinforcing buffer against severe volume expansion issues. As a result, the N-MoS₂/C@SiOC composite exhibits high reversible capacity (540.7 mAh g^-1), high-capacity retention (>100% after 200 cycles), and excellent rate capability up to 10 A g^-1. The simple hierarchical core-shell design strategy developed in this study allows for the fabrication of high-performance metal sulfide anodes as well as other high-capacity anode materials for energy storage applications.

Silicon Oxycarbide-Graphite Electrodes for High-Power Energy Storage Devices

Herein we present a study on polymer-derived silicon oxycarbide (SiOC)/graphite composites for a potential application as an electrode in high power energy storage devices, such as Lithium-Ion Capacitor (LIC). The composites were processed using high power ultrasound-assisted sol-gel synthesis followed by pyrolysis. The intensive sonication enhances gelation and drying process, improving the homogenous distribution of the graphitic flakes in the preceramic blends. The physicochemical investigation of SiOC/graphite composites using X-ray diffraction, ²⁹Si solid state NMR and Raman spectroscopy indicated no reaction occurring between the components. The electrochemical measurements revealed enhanced capacity (by up to 63%) at high current rates (1.86 A g⁻¹) recorded for SiOC/graphite composite compared to the pure components. Moreover, the addition of graphite to the SiOC matrix decreased the value of delithiation potential, which is a desirable feature for anodes in LIC.

Synthesis of Hierarchical Porous Ni1.5Co1.5S4/g-C3N4 Composite for Supercapacitor with Excellent Cycle Stability

In this work, the hierarchical porous Ni1.5Co1.5S4/g-C3N4 composite was prepared by growing Ni1.5Co1.5S4 nanoparticles on graphitic carbon nitride (g-C3N4) nanosheets via a hydrothermal route. Due to the self-assembly of larger size g-C3N4 nanosheets as a skeleton, the prepared nanocomposite possesses a unique hierarchical porous structure that can provide short ions diffusion and fast electron transport. As a result, the Ni1.5Co1.5S4/g-C3N4 composite exhibits a high specific capacitance of 1827 F g-1 at a current density of 1 A g-1, which is 1.53 times that of pure Ni1.5Co1.5S4 (1191 F g-1). In particular, the Ni1.5Co1.5S4/g-C3N4//activated carbon (AC) asymmetric supercapacitor delivers a high energy density of 49.0 Wh kg-1 at a power density of 799.0 W kg-1. Moreover, the assembled device shows outstanding cycle stability with 95.5% capacitance retention after 8000 cycles at a high current density of 10 A g-1. The attractive performance indicates that the easily synthesized and low-cost Ni1.5Co1.5S4/g-C3N4 composite would be a promising electrode material for supercapacitor application.

Plasma-Assisted Surface Modification on the Electrode Interface for Flexible Fiber-Shaped Zn-Polyaniline Batteries

A novel flexible fiber-shaped zinc-polyaniline battery (FZPB) is proposed to enhance the electrochemical performance, mass loading, and stability of polyaniline cathodes. To this end, electron-cyclotron-resonance oxygen plasma-modified carbon fibers are employed. During plasma treatment, on the carbon-fiber surface, O₂⁺ plasma breaks the C-C, C-H, and C-N bonds to form C radicals, while the O₂ molecules are broken down to reactive oxygen species (O⁺, O²⁺, O₂⁺, and O₂²⁺). The C radicals and the reactive oxygen species are combined to homogeneously form oxygen functional groups, such as -OH, -COOH, and -C═O. The surface area and total pore volume of the treated carbon fibers increase as the plasma attacks. During electrodeposition, aniline interacts with the oxygen functional groups to form N-O and N-H bonds and π-π stacking, resulting in a homogeneous and high-loading polyaniline structure and improved adhesion between polyaniline and carbon fibers. In an FZPB, the cathode with plasma-treated carbon fibers and a polyaniline loading of 0.158 mg mg_CF^-1 (i.e., 2.36 mg cm_CF^-1) exhibits a capacity retention of 95.39% after 200 cycles at 100 mA g^-1 and a discharge capacity of 83.96 mA h g^-1 at such a high current density of 2000 mA g^-1, which are ∼1.67 and 1.24 times those of the pristine carbon-fiber-based one, respectively. Furthermore, the FZPB exhibits high flexibility with a capacity retention of 86.4% after bending to a radius of 2.5 mm for 100 cycles as a wearable energy device.

Cable-like heterogeneous porous carbon fibers with ultrahigh-rate capability and long cycle life for fast charging lithium-ion storage devices

In this paper, we propose a space-confined foaming approach to fabricate cable-like heterogeneous porous carbon fibers (Si-CPCFs) containing an inner graphitized carbon "conductor" and an outer Si-doping amorphous carbon "shield". Benefiting from the fast Li⁺ intercalation and high conductivity of the "inner conductor", and the rich pseudocapacitance of the "outer shield", the Si-CPCFs exhibit an ultrahigh-rate capability and cycling performance, leading to a high capacity of 132 mA h g^-1 even at an ultra-high current density of 100 A g^-1 after 10 000 cycles. The assembled lithium ion hybrid supercapacitors (LIHCs) also deliver a superior energy density of 50 W h kg^-1 at an ultra-high power density of 113 kW kg^-1, really achieving both a high energy density and power density of LIHCs. The success of the cable-like heterogeneous porous carbon architecture proposes a new direction to circumvent the discrepancy in kinetics and capacity mismatch, and also attracts more attention to heterogeneous nanostructures with multiple functions.

Building Next-Generation Li-ion Capacitors with High Energy: An Approach beyond Intercalation

Hybridization of two prominent electrochemical energy storage systems, such as high-energy Li-ion batteries and high-power supercapacitors into a single system, tends to deliver high-energy and high-power capabilities; such systems are often called Li-ion capacitors (LICs). The utilization of battery-type electrodes, which undergo a traditional intercalation process, in LICs provides the necessary energy; however, their limited reversible capacities and higher redox potentials (except graphite and hard carbon) hinder achieving high values. Using materials that can undergo either alloying or conversion or both together with Li, rather than intercalation, is an attractive approach to achieve high energy without compromising both power capability and cyclability. This Perspective discusses the possibility of using high-capacity, exhibiting relatively lower redox potential than transition metal-based intercalation hosts, low-cost materials in conversion and alloying reactions with Li, along with prelithiation strategies (Aravindan, V.; Lee, Y.-S.; Madhavi, S. Best Practices for Mitigating Irreversible Capacity Loss of Negative Electrodes in Li-Ion Batteries. Adv. Energy Mater. 2017, 7, 1602607). Future prospects on working with alloying and conversion-type materials are discussed in detail.