Areal Capacitance Research Articles

Achievement of advanced alkaline Ni-Zn batteries with good durability at a high areal capacity of 10 mAh cm−2 via the synergistic regulation of dual electrolyte additives

Though obvious advantages in terms of safety, cost, environmental compatibility and electrochemical performance (e.g, power and energy density), the commercial application of alkaline Ni-Zn batteries, a number of traditional aqueous batteries, is still under great restrictions owing to the poor durability (commonly less than 100 cycles). In this work, an effective electrolyte modification process using dual additives of hydroxy-rich carboxymethyl cellulose (CMC) that can inhibit hydrogen evolution reaction (HER) and suppress Zn dendrites, and benzyltrimethylammonium bromide (BTMAB) that can mitigate passivation and oxygen evolution reaction (OER) is developed. Meanwhile, our home made C coated ZnO (ZnO@C) microspheres were used as initial anode materials without the using of any other expensive composites. With a fixed areal charge capacity of 10 mAh cm−2, the flat type full cell matched with commercial Ni(OH)2 cathode can deliver a high average discharge capacity of ∼9.6 mAh cm−2 (corresponding to an average CE of 96 %) for a long lifespan of over 390 cycles, which drops to 8.2 mAh cm−2 at 400th cycle accompanied by the appearance of a peak in the charge curve. The cumulative discharge capacity of a full cell can reach ∼4,000 mAh cm−2 in 420 cycles’ cycling, much larger than that using commercial Zn/ZnO anode and the ZnO@C anode in unmodified or single additive modified electrolyte (less than 1,500 mAh cm−2).

Effect of processing parameters on the properties of carbon paper as a free-standing supercapacitor electrode

As newly emerging energy storage devices, supercapacitors are being investigated thoroughly by researchers. Free-standing electrode is one of the major research focuses in this area, which not only avoids the use of resistive binders but also simplifies device assembly. The study describes the synthesis and study of carbon fiber-based carbon carbon composite paper (heat treated to different temperatures) as a free-standing supercapacitor electrode. Due to the inert nature of carbon paper, it was activated to create defect sites and to increase the specific surface area. Electrochemical studies suggested that activated carbon paper heat treated to 750°C (ACP-750) exhibited the highest areal capacitance of 11.4 F/cm2 (422.2 F/g) at the current density 2.5 mA/cm2 (0.09 A/g), probably due to the generation of larger number of defect sites (as depicted by XRD and RAMAN studies). ACP-750 electrode was used to fabricate the solid-state symmetric supercapacitor device that exhibited an energy density 0.77 Wh/cm2 at a power density of 2.34 W/cm2. The electrode was allowed to age (ACPA-750), after which it exhibited enhanced specific capacitance of 16.8 F/cm2 (622.2 F/g) at a current density 2.5 mA/cm2. ACPA-750//ACPA-750 device delivered maximum energy density of 1.66Wh/cm2 at a power density of 3 W/cm2. The device exhibited a coulombic efficiency of 96.1% and capacitance retention of 89% after 10,000 cycles.

Pseudocapacitive Na ion storage in binder-less, carbon additive-free Nb2O5-x electrode synthesised via solvothermal-assisted electro-coating with enhanced areal capacitance and lowered impedance parameters

Negatrodes with wide negative operating voltage, high electrochemical storage capacity, and intrinsic metal ion intercalation abilities are vital to the continuous development of storage devices with simultaneous energy and power density improvement. Herein, we report binder-less coating of non-stoichiometric vacancy-implanted Nb2O5-x as carbon additive-free negatrode on FTO substrate for asymmetric supercapacitor and sodium ion capacitor applications. The negatrode was fabricated through vacuum-less and low-temperature solvothermal-assisted electro-coating technique and yielded several orders of enhancement in its areal capacitance and retained ca. 90 % of its capacity after 5000 cycles of charge-discharge in aqueous Na+ electrolyte. The solvothermal treated electro-coated electrode (STT_Nb2O5-x) achieved an areal capacitance of 22.58 mF/cm2, which was far higher than those of hydrothermal-treated electro-coated HTT_Nb2O5 and Nb2O5 electrodes. The solvothermal treatment simultaneously enhanced the electro-coated samples' impedance properties and mass load through oxygen vacancy implantation and re-crystallization of the electro-coated Nb2O5 layer, respectively. This study presented a facile and energy-efficient technique of direct coating of defect-enhanced pseudocapacitive nanomaterials for the fabrication of electrochemical storage devices.

High cycling stability polyaniline/carbon sphere/graphene ternary nanocomposite cathode material for asymmetric supercapacitors

Here, an asymmetric supercapacitor of the ternary nanocomposite polyaniline/carbon sphere/graphene (PANI/CS/G) is developed through a green strategy via the in-situ polymerization of aniline in carbon sphere/graphene (CS/G) dispersion prepared in a ball-mill method coupled with hydrothermal treatment. A strong interaction and thus the coverage of CS/G with PANI is revealed from the material characterization using XRD, FTIR and Raman spectroscopic techniques, and also from FESEM and HRTEM images. Uniform distribution of PANI over the CS/G provided an effective conducting network and enhanced diffusion of the electrolyte ions. PANI/CS/G showed a specific capacitance of 145.02 mF/cm2 at a current density of 1 mA/cm2 in 1 M H2SO4 originating from the electrostatic double layer capacitance behavior of the CS/G and pseudocapacitance of PANI. The fabricated asymmetric coin cell device with PANI/CS/G cathode and CS/G anode showed the highest areal capacitance of 320.78 mF/cm2 (@ 1 mA/cm2), a maximum energy density of 18.99 Wh/kg (@ 0.21 A/g), and a highest power density of 6088.48 W/kg (@ 8.68 A/g). The device displayed 101.6 % capacitance retention after 10000 cycles, indicating the effect of CS/G in diminishing the volume changes of PANI during the charge-discharge process, which usually affects the cyclic stability. By lighting a green LED, the real sense energy storage application of the supercapacitor is evaluated.

Promoting Preferential Zn (002) Deposition with a Low-Concentration Electrolyte Additive for Highly Reversible Zn-Ion Batteries.

Aqueous zinc-ion batteries have promising potential as energy storage devices due to their low cost and environmental friendliness. However, their development has been hindered by zinc dendrite formation and parasitic side reactions. Herein, we introduce a low-concentration sodium benzoate (NaBZ) electrolyte additive to stabilize the electrode-electrolyte interface and promote deposition on the Zn (002) crystal plane. From experimental characterization and computational analyses, NaBZ was found to adsorb on the Zn surface and inhibit side reactions while guiding homogeneous Zn deposition on the (002) plane. Consequently, Zn|Zn symmetric cells with the NaBZ additive cycled stably for over 1000 h at a current density of 0.5 mA cm-2 and an areal capacity of 0.5 mAh cm-2, while Zn|Cu cells showed excellent reversibility with a Coulombic efficiency of 99.05%. Moreover, Zn|Na0.33V2O5 full cells achieve a high specific capacity of 124 mAh g-1 while cycling for 600 h at 2 A g-1. These findings present a low-cost electrolyte modification strategy for reversible zinc-ion batteries.

Flexible zinc-ion hybrid supercapacitor based on Co2+-doped polyaniline/V2O5 electrode

With the rapid advancement of renewable energy sources and portable electronic devices, the demand for high-performance energy storage systems is growing, driving continuous progress in supercapacitor technology. Zinc-ion hybrid supercapacitors (ZIHS), known for their higher safety, cost-effectiveness, and environmental friendliness, have become a hot research topic. Vanadium pentoxide (V2O5) possesses flexible multivalence, low cost, low toxicity, wide voltage window, high capacitance, and high energy density. However, its poor electrical conductivity and low cycling stability hinder its electrochemical performance, thus limiting its application in ZIHS. Here, we propose a novel strategy of incorporating Co2+ ions and conductive polyaniline (PANI) with V2O5 (CoVO-PANI) as cathode materials for ZIHS. The synergistic effect between cobalt ions and polyaniline have led to an expansion of the interlayer spacing in CoVO-PANI, which reduce the binding energy of Zn2+ ion insertion, decrease the diffusion barrier of Zn2+ ion insertion, and enhanced the electronic conductivity of the material for electron transport. In result, the CoVO-PANI@CC//2 M ZnSO4//AC@CC can reach the areal capacitance of 847.3 mF cm−2 at 1 mA cm−2. Following 2000 times at 50 mA cm−2, the CoVO-PANI@CC//2 M ZnSO4//AC@CC maintains a retention rate of 81.37 %, and can achieve a Coulombic efficiency of 100 %. The assembled flexible ZIHS device exhibits excellent flexibility and stability, with an areal capacitance of 775.6 mF cm−2 at 1 mA cm−2. This work demonstrates the tremendous potential of CoVO-PANI@CC as a cathode material for ZIHS.

Advanced MXene/Graphene Oxide/Lignosulfonate Inks for 3D Printing Thick Electrodes with Vertically Aligned Pores to Dually Boost Mass Loading and Areal Capacitance

AbstractDirect ink writing 3D printing, using ink extrusion, promises to transform conventional 2D thin electrodes into 3D thick architectures for high‐performance supercapacitors. However, formulating 3D printing inks and designing 3D architectures for electrodes remain challenges. In this work, a novel MXene/graphene oxide/lignosulfonate (MGL) ink with excellent rheological properties is developed for 3D printing MGL thick electrodes with vertically aligned architectures. The MGL ink exhibited excellent shear‐thinning properties for smooth 3D printing and shape retention after printing. The 3D‐printed MGL thick electrode, with a thickness of up to 4 mm, achieved a breakthrough mass loading of 72.1 mg cm−2, resulting in an extremely high areal capacitance of 8.6 F cm−2 that is 9.6 times greater than the value observed for the bulk MGL electrode (0.9 F cm−2). Additionally, supercapacitors using the 3D MGL electrode achieved an energy density of 505.3 µWh cm−2, significantly surpassing the value for bulk MGL electrode (52.8 µWh cm−2). This enhancement is attributed to the efficient design of the electrodes, where vertically aligned pores in the 3D MGL electrode enhanced ion transfer and reaction kinetics. This study demonstrates an innovative approach for formulating inks and provides guidance for designing 3D thick electrodes with rapid ion transport and excellent electrochemical performance.

Inkjet‐Printed 2D Heterostructures for Smart Textile Micro‐Supercapacitors

AbstractWearable electronic textiles (e‐textiles) have emerged as promising healthcare solutions, offering point‐of‐care diagnostics while maintaining breathability, comfort, durability, and environmental stability with strong mechanical performance. However, the lack of thin and flexible power supplies hinders their practical adoption. In this regard, textile‐based micro‐energy storage devices present an appealing solution. Inkjet printing offers the capability to produce high‐quality prints with sharp details and versatile substrate compatibility, making it an ideal choice for a wide array of printing applications. Here, the preparation of a range of inkjet‐printable 2D material inks is reported for the fabrication of ultra‐flexible and machine‐washable textile micro‐supercapacitors. Then 2D material heterostructures are proposed to enhance the performance of textile supercapacitors. This study reveals that a unique combination of highly conductive graphene with an insulator hexagonal boron nitride (h‐BN) can enhance the areal capacitance of graphene‐based textile supercapacitors by ≈82.48%. The heterostructure‐based supercapacitors also demonstrate higher energy (≈18.06 µWh cm−2) and power densities (≈4333.33 µW cm−2) with excellent capacitance retention (≈95% after 1000 cycles). These findings on inkjet‐printed heterostructure‐based supercapacitors may herald a new era for the future application of high‐performance micro‐supercapacitors within textile‐based wearable technology.

Seeding Co Atoms on Size Effect‐Enabled V2C MXene for Kinetically Boosted Lithium–Sulfur Batteries

AbstractLithium‐sulfur (Li–S) batteries are facing a multitude of challenges, mainly pertaining to the sluggish sulfur redox kinetics and rampant lithium dendrite growth on the cathode and anode side, respectively. In this sense, MXene has shown conspicuous advantages in serving as a dual‐functional promotor for Li–S batteries throughout the morphologic engineering, but still suffers from poor electrocatalytic activity and insufficient lithophilic sites. Herein, atomically dispersed Co sites are seeded onto the size effect‐enabled V2C MXene spheres (Co‐VC), leading to the generation of unique coordination configurations and rich active sites. Electrochemical tests combined with synchrotron radiation X‐ray 3D nano‐computed tomography and theoretical calculations unravel that Co‐VC with optimal coordination environments simultaneously boost sulfur reaction kinetics and lithium nucleation. As a consequence, Li–S batteries with Co‐VC modified separator can sustain a stable operation over 700 cycles with negligible capacity decay at 1.0 C, and delivers an areal capacity of 9.0 mAh cm−2 and desired cyclic performance at a high sulfur loading of 7.6 mg cm−2 with a lean electrolyte dosage of 4.0 µL mgS−1 at 0.1 C. The work opens a new avenue for boosting atomic‐scale site design with the aid of 2D substrates toward pragmatic Li–S batteries.

Cation Adsorption Engineering Enables Dual Stabilizations for Fast‐Charging Zn─I2 Batteries

AbstractAqueous zinc‐iodine (Zn─I2) battery is a promising energy storage system due to its inherent safety, high theoretical capacity, sustainability, and cost‐effectiveness. However, the shuttle effect of polyiodide severely affects the stable loading of active iodine and even accelerates the corrosion of the Zn anode, thus impeding its further advancement. Herein, a unique trimethylsulfonium cation (TMS+) with strong adsorption is proposed to stabilize both the iodine cathode and Zn anode. Benefiting from the robust interaction between TMS+ and polyiodide, the electrolyte can effectively immobilize large‐capacity iodine in the form of oily precipitate, thus avoiding the shuttle effect of polyiodide and the Zn corrosion. Additionally, TMS+ can be preferentially adsorbed on various Zn facets, inducing an electrostatic shielding effect to inhibit Zn dendrite growth. Consequently, Zn anode can be stably cycled over 3400 h at 5 mA cm−2/5 mAh cm−2, and a large areal capacity of 2.71 mAh cm−2 as well as long‐life stability over 6400 cycles is achieved for Zn─I2 battery. Furthermore, cation adsorption engineering is practically utilized in pouch cells, realizing superior fast‐charging stability over 790 cycles. This electrolyte modification with dual stabilizations is anticipated to be applied to other metal‐iodine batteries as a cost‐effective, facile, and safe strategy.

Advanced 3D Micro‐Electrodes for On‐Chip Zinc‐Ion Micro‐Batteries

AbstractThe development of high‐performance planar micro‐batteries featuring safer, cost‐effective systems is crucial for powering smart devices such as medical implants, micro‐robots, micro‐sensors, and the Internet of Things (IoT). However, current on‐chip micro‐batteries suffer from limited energy density within constrained device footprints due to challenges in effectively loading high‐capacity active materials onto micro‐electrodes. Innovative designs for advanced micro‐electrodes are needed for on‐chip micro‐batteries. This work introduces advanced, highly porous 3D gold (Au) scaffold‐based interdigitated electrodes (IDEs) as current collectors, which enable effective loading of active materials (Zn and polyaniline) without compromising overall conductivity and significantly increase active mass loading. These 3D Au scaffold‐based micro‐batteries (3D P‐ZIMB) offer substantially higher energy storage performance (≈135% enhancement) compared to conventional micro‐batteries (C‐ZIMB) when materials loaded onto flat Au IDEs. Furthermore, the 3D P‐ZIMB demonstrates higher areal capacities (≈35 µAh cm−2) and areal energy (≈31.05 µWh cm−2) than most high‐performance on‐chip micro‐batteries, and it delivers a much higher areal power (≈3584.35 µW cm−2) than high‐performance on‐chip micro‐supercapacitors. In‐depth postmortem investigations reveal that the 3D P‐ZIMB avoids issues like material peeling, sluggish electrolyte ion diffusion, and dendrite formation on the anode, while maintaining identical material morphologies and structural characteristics. Therefore, this study presents a smart strategy to enhance the electrochemical performance of planar micro‐batteries and advance the field of on‐chip micro‐battery research.

Ballistic-aggregated Carbon Nanofoam in Target-side of Pulsed Laser Deposition for Energy Storage Applications.

In pulsed laser deposition, along the traditionally exploited deposition on the front-side of the plasma-plume, a coating forms on the surface of the target as well. For reproducibility, this residue is usually cleaned and discarded. Here we instead investigate the target-side coated materials and employ them as a binder-free supercapacitor electrode. The ballistic-aggregated, target-side nanofoam is compact and features a larger fraction of sp2-carbon, higher nitrogen content with higher graphitic-N and lower oxygen content with fewer COOH groups than that of diffusive-aggregated conventional nanofoams. They are highly hydrogenated graphite-like amorphous carbon and superhydrophilic. The resulting symmetric micro-supercapacitor delivers higher volumetric capacitance of 522 mF/cm3 at 100 mV/s and 104% retention after 10000 charge-discharge cycles over conventional nanofoam (215 mF/cm3 and 85% retention) with an areal capacitance of 134 μF/cm2 at 120 Hz and ultrafast frequency response. Utilizing the normally discarded target-side material can therefore enable high performing devices while reducing waste, cost and energy input per usable product. leading towards a greater sustainability on nanomaterials synthesis and deposition techniques.

Synergistic design of processable Nb2O5-TiO2 bilayer nanoarchitectonics: enabling high coloration efficiency and superior stability in dual-band electrochromic energy storage

This paper introduces a proof of concept for a dual-band electrochromic (EC) device to modulate solar light transmission across visible and near-infrared regions selectively. EC materials based on ion insertion/extraction mechanisms also present the possibility for energy storage, widening its functionality to the supercapacitor platform. The bi-functional performance of dual-band radiation control and energy storage was achieved by exploiting two earth-abundant metal oxides that could absorb two different spectral regions when electrochemically charged. The bilayer structure was prepared using a one-step hydrothermal method, which produced Nb2O5-TiO2 bilayer on fluorine-doped tin oxide (FTO) conducting glass substrates. The nano-dimensions of the active materials endorse the development of high-transparency thin film under open circuit conditions. The variations in the TiO2 annealing temperature influence the crystallinity and surface morphology of the thin films, which influence the performance of dual-band EC energy storage. The well-optimized NT-500 sample facilitated exclusive electron-charge transport, producing excellent electrochemical performance in dual-band EC and energy storage. A large optical modulation of 80.4 % and 89.8 % at 600 nm and 800 nm (near-infrared) was achieved with an enhanced areal capacitance of 88.1 mF/cm2 and excellent cycling stability after continuous coloring/bleaching cycles for 18,000 s. This paper presents a prototype bi-functional device based on NT-500, which showed independent control and modulation of visible and near-infrared transmittance. Notably, the device retained excellent energy storage performance alongside its advanced optical functionalities. This bilayer nanostructure capitalizes on the inherent electrochemical properties of both materials and introduces novel features that can potentially revolutionize the platform of EC-energy storage.

Integration of vanadium diphosphide with 2D cobalt phosphide architected as an extensible redox active positrode for alkaline supercapacitor

Metal phosphides in the form of rationally constructed two-dimensional (2D) nanosheets hold significant promise as versatile materials for energy storage applications. This study introduces a novel hybrid supercapacitor electrode, composed of a binder-free vanadium phosphide integrated cobalt phosphide (VP@CP) on a nickel foam substrate. The fabrication process involves the hydrothermal growth of Co2(OH)2BDC (BDC- 1,4-benzenedicarboxylate) nanosheets on a Ni-foam substrate (CMF-Ni), followed by the deposition of VO2 on CMF nanosheets (VO@CMF-Ni) using chronoamperometry and phosphorization of the VO@CMF-Ni to yield VP@CP-Ni nanosheets. Particularly, the density functional theory (DFT) results show that the VP2 integrated Co2P sample provides metallic behavior and low adsorption energy of OH− ions, resulting in improved electrochemical redox process. These bimetallic phosphides exhibit outstanding properties, including enhanced pathways for rapid ion transport and storage, increased electronic conductivity, and expanded electroactive regions facilitating the faradaic charge storage process. Due to the presence of vanadium and cobalt coupled sites, the fabricated VP@CP-Ni electrode was able to attain a maximum areal capacity (CAR) of 971 mA h cm−2 at 6 mA cm−2. Additionally, the fabricated hybrid device (HDC) exhibits an impressive specific energy (SE) of 30.9 Wh kg−1 at a specific power (SP) of 1344 W kg−1, and excellent cyclic durability. These remarkable results stimulate the exploration of such possible 2D VP@CP-Ni nanosheets with promising charge storage electrode capabilities to develop a future era of energy storage devices.

Superhydrophobic metal-organic framework layers as multifunctional ion-conducting interfaces for ultra-stable Zn anodes

Aqueous zinc batteries (AZBs) show great promise for cost-effective, high-safety, and large-scale energy storage. Yet, corrosion and dendrite formation at the Zn anode interface undermine its stability, shortening the cycle life. In this work, a fluorosilane-modified metal-organic framework layer (F-MOF) is successfully prepared as a multifunctional ion-conductive interface to stabilize the Zn anode. The designed MOF-based artificial layer provides a uniform pathway for Zn deposition, while its hydrophobic nature prevents negative effects such as hydrogen evolution and corrosion. According to density functional theory (DFT) calculations, the hydration energy of Zn2+ in F-MOF@Zn(002) is reduced while the adsorption energy for Zn2+ is increased. This facilitates the desolvation process on the Zn anode surface, promoting uniform Zn deposition. Consequently, the lifespan of the F-MOF-coated Zn anode extends beyond 2000 h at a current density of 1 mA cm−2 (areal capacity: 0.5 mAh cm−2), significantly outlasting both bare Zn (225 h) and MOF-coated Zn (751 h) anodes. Additionally, the assembled coin cells and pouch-type full cells prove the practical availability of F-MOF@Zn anodes for AZBs. The F-MOF@Zn//MnO2 full cell maintains a high-capacity retention exceeding 91.9 % even after 1000 cycles. This work highlights the practical application potential of hydrophobic MOF coatings for AZBs.

Laser‐Induced Formation of Fine Porous Graphitic Carbon for Eco‐Friendly Supercapacitors

An electric double‐layer capacitor (EDLC), which is one of the pivotal energy storage devices, provides rapid charge–discharge capabilities and an extended cycle life. Areal capacitance, a key indicator of EDLC performance, increases with the specific surface area of its electrodes. This study demonstrates a method for significantly increasing the specific surface area in the laser‐induced graphitization of biodegradable polymers by incorporating NaHCO3 into the composite sheet, generating not only microscale pores but also a large number of nanoscale fine pores. Furthermore, it shows that using these structures as EDLC electrodes leads to a substantial increase in areal capacitance. An increase in the number of fine pores formed in the structure and a corresponding rise in the areal capacitance of the fabricated EDLC are observed with the increase in the NaHCO3 weight ratio. Notably, the composite sheets are composed of natural‐derived, biodegradable materials, while NaHCO3 is known for its low corrosivity and biotoxicity. The proposed method thus offers a pathway for fabricating energy storage devices with minimal environmental impact, ensuring their eco‐friendly disposal post‐use.

Vertical-channel hierarchically porous 3D printed electrodes with ultrahigh mass loading and areal energy density for Li-ion batteries

Lithium-ion batteries (LIBs) are renowned for their high energy density, long lifespan, and minimal self-discharge, making them a prominent power supply system. However, the persistent demand for improved energy density coupled with mechanical stability remains a significant challenge, as efforts to enhance electrode thickness or achieve geometric complexity through conventional ink-casting methods have yielded limited results. To tackle this challenge, we applied a three-dimensional (3D) printing technique to swiftly construct 3D thick electrodes with ultrahigh mass loading. Combined with unidirectional ice-templating process, high mass loading electrodes with hierarchically porous structures were successfully fabricated. The mass loading of the 3D electrodes can reach up to 73.83 mg cm−2, significantly enhancing the areal capacity. The low tortuosity and good mechanical resilience of these structures enable fast ion and charge transport, leading to significant improvements in areal energy density without sacrificing the power density. The assembled full cell exhibits an impressive areal capacity of 10.34 mAh cm⁻2 at 0.2 C and an excellent energy density of 18.41 mWh cm−2, surpassing other 3D printed lithium-ion batteries. This approach marks a significant advancement in electrode structural design towards higher areal capacity and energy density, showcasing the intriguing potential of 3D printed batteries for practical applications. Additionally, it also highlights the scalability and design versatility provided by 3D printing technique.

Enhanced performance of Lithium–Sulfur cells via novel nano-sized iron-plated sulfur composites

Lithium–sulfur cells are promising energy-storage systems because of their high energy density and the desirable electrochemical utilization rates of cost-effective sulfur cathodes. However, the commercialization of high-performance lithium–sulfur cells, which are characterized by a high discharge capacity and cyclic stability, necessitates simultaneous optimization of both the cell-fabrication parameters and cell-performance values. Here, we introduce a novel iron-plated sulfur composite featuring nano-sized conductive iron plating applied to micro-sized insulating sulfur particles through an innovative electroless-iron plating method. The iron-plated sulfur composite facilitates the realization of a lean-electrolyte lithium–sulfur cell at a low electrolyte-to-sulfur ratio of 5 μL mg−1, enabling high-loading sulfur cathodes (sulfur loadings of 10–14 mg cm−2) to attain a reversible discharge capacity (945–1033 mAh g−1) and a cycle life of 400 cycles. These well-controlled cell-fabrication parameters, coupled with the high cell performance, result in improved performance metrics, such as high areal capacity (10–13 mAh cm−2), improved energy density (22–28 mWh cm−2), and a low electrolyte-to-capacity ratio (4.8 μL mAh−1). These advancements are attributable to the incorporation of plated nano-sized iron, which endows the cathode with rapid electron/ion transfer, robust polysulfide retention, and heightened electrocatalysis capabilities for conversion-type battery chemistry.

Crystalline/Amorphous Co2P2O7 cathode with outstanding areal capacity for High-Performance Zinc-Cobalt battery

It is still a challenge to develop aqueous rechargeable Zn-based alkaline batteries with high energy density, power density and excellent stability. Herein, a crystalline/amorphous Co2P2O7 self-supporting on the Ni foam is fabricated as a cathode material of aqueous Zn-based alkaline batteries. The unique crystalline/amorphous structure endows the electrode material with more exposed active sites, higher redox species coverage, larger electrochemical surface area (ECSA), smaller charge-transfer resistance, lower reaction energy barriers and faster electrochemical reaction kinetics process, which clarifies an explicit structure–property relationship simultaneously. As a result, the crystalline/amorphous Co2P2O7 (CP-P-450) electrode assembled as CP-P-450//Zn battery achieves an extraordinary areal capacity of 2.49 mAh cm−2 at 5 mA cm−2, satisfactory rate performance, excellent cyclic durability (96.6 % retention after 4000 cycles) and impressive energy density (4.16 mAh cm−2) and peak power density (115.94 mW cm−2). The quasi-solid CP-P-450//Zn battery can drive a variety of electrical appliances working well even under abuse tests, demonstrating excellent safety and application potential. This study provides an effective strategy towards excellent comprehensive energy storage performance of aqueous Zn-based alkaline batteries through structuring the crystalline/amorphous phase in cathodes.

Light-weight flexible symmetric supercapacitors based on magnesium-zinc codoped MnO2 nanostructures on carbon cloth as enhanced-performance binder-free electrodes

Developing advanced flexible supercapacitors with high energy and power density is a critical research goal. One promising approach involves combining manganese dioxide (MnO2) with a three-dimensional carbon substrate. This strategy leads to the creation of supercapacitor electrode materials that exhibit high specific capacitance, stability, and environmental friendliness. However, the challenge lies in addressing the low electrical conductivity of MnO2, which limits the rate of electron transfer. The incorporation of metal ions enhances the conductivity of manganese oxide, resulting in a significant increase in lattice defects. These defects create abundant active sites for energy storage. In this study, we developed flexible electrodes based on magnesium-doped MnO2, zinc-doped MnO2, and magnesium-zinc codoped MnO2 nanostructures deposited on carbon cloth (CC) via a one-step hydrothermal method. The supercapacitive behavior of these electrodes was investigated using CV and GCD measurements. The as-prepared electrodes exhibit good electrical conductivity, and their interconnected network structure, composed of sponge-shaped nanostructure layers, results in a large specific surface area. This network also facilitates efficient pathways for effective electron transport. The optimized Mg-Zn codoped MnO2@CC sample exhibits a high capacitance of 79.9 mF/cm² at 0.7 mA/cm² and good rate performance, reaching around 46.59 mF/cm² up to 1.5 mA/cm² in the three-electrode system. Notably, the areal capacitance values calculated from the CV curves for all Mg-Zn codoped MnO2@CC electrodes surpass those of Mg-doped MnO2@CC and Zn-doped MnO2@CC. A flexible symmetric supercapacitor assembled using the best Mg-Zn codoped MnO2@CC as both positive and negative electrodes and PVA-Na2SO4 gel electrolyte delivers a desirable energy density of 0.196 mWh/cm2 at 2.38 mW/cm2. Furthermore, this fabricated supercapacitor demonstrates a broad voltage window of 2.25 V and remarkable cycling stability, retaining 83 % of its initial performance after 4000 charge-discharge cycles.