Charge-discharge Stability Research Articles

Simple and cost-effective synthesis of activated carbon@few layers of graphene composite electrode for supercapacitor applications

We report a simple and low-cost technique to prepare a composite comprising of activated carbon and few layers of graphene sheets and fabricated as electrode material for supercapacitor (SC) applications. The composite is characterised by using Raman spectroscopy, powder X-ray diffraction (XRD), scanning electron microscope (SEM) and current-voltage (I-V) measurements. The synthesized composite is investigated by using galvanostatic chargedischarge (GCD) and cyclic voltammetry (CV) measurements in 3M KOH aqueous electrolyte to evaluate its electrochemical performance. The composite results high specific capacitance from 173 to 564 F/g at different scan rates (100-5 mV/s), analysed by CV and the capacitances resulted in GCD measurement were 196 to 587 F/g at various current densities (5-1 A/g). The cycle stability of the as-prepared AC/graphene composite is also tested and observed that 89% of capacitance is retained even after 5000 cycles which reveals the excellent long term chargedischarge stability of the prepared composite. Therefore, the composite performs very well in storage as well as life cycling. The obtained results suggest that AC/graphene composite can be a suitable electrode material for high-performance SC.

Effective Chemical Vapor Deposition and Characterization of N-Doped Graphene for High Electrochemical Performance.

Here we reports an effective synthetic method for the preparation of N-graphene upon thermal annealing of prepared graphene oxide in the existence of ammonia. N-doped graphene oxide was analysed using different characterization techniques like X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The nitrogen atom showed good binding with the graphene sheets, that are analysed by the X-ray photoelectron spectroscopy. The synthesized N-graphene have shown higher thermal stability compared with GO and graphene. The elcerochemnical performance like Cyclic voltammetry as well chronopotentiometry charge-discharge calculations revealed that the N-doped graphene exhibits remarkable behaviour favors a specific capacitance value about 209 F g-1 at 5 mV s-1 and 270 F g-1 for 1 A g-1 applied current density including outsanding charge-discharge stability about 98% of the initial capacitance subsequent 1000 cycles at 5 A g-1. The N-content in the graphene material with the optimized reaction parameters potentially improved electrode active material for energy storage applications.

Bifunctional MnO2/CNTs-Based Oxygen Catalysts with Tailored Catalytic Activity for Rechargeable Zn-Air Batteries

Metal-air batteries, as highly effective clean energy devices, play an important role in current sustainability development. Zn-air batteries are of great interest in future power devices due to eco-friendliness, superior safety, low-cost and high theoretical energy density. Yet, it remains challenging to identify inexpensive, high-efficient and durable bifunctional catalysts to boost various reactions for Zn-air batteries. a-MnO2 exhibits 2×2 tunnels with a unique orthorhombic structure shows a higher oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity than other-phase MnO2. In this work, metal oxide anchored MnO2/CNTs hybrid catalysts (M-MnO2/CNTs) are developed via a facile hydrothermal process. Indeed, M-MnO2/CNTs display better catalytic activity and stability than MnO2/CNTs. The improved performance and stability are originated from (i) the novel hierarchal structure improving the mass transport, (ii) the redistribution of electrons from metal ion to MnO2 activating the Mn catalytic sites, (iii) the coupling effect from the metal oxide and MnO2/CNTs. Particularly, the overpotential (ΔE) of Co-MnO2/CNTs is low to 0.803 V, which highly approaches the referenced Pt/C+IrO2 (ΔE: 0.801 V). Accordingly, the peak power density of the Co-MnO2/CNTs-based Zn-air battery reaches 342.7 mW cm-2. The recharge Zn-air battery also exhibits good charge-discharge stability with a low voltage gap of 0.72 V for 128 hours. This work provides an effective mothed to achieve MnO2/CNTs materials with tailored catalytic activity by anchoring different metal oxides, and reveals great potential in the field of high specific energy batteries for portable electronics, electrical vehicles, and wearable devices.

An overlooked issue for high-voltage Li-ion batteries: Suppressing the intercalation of anions into conductive carbon

Summary High-voltage Li-ion batteries have been extensively studied to increase energy density of batteries. However, their cycling stability has remained poor, despite various strategies being proposed to overcome the issues of high-potential cathodes, such as electrolyte oxidation and transition metal dissolution. Herein, we report anion intercalation into the cathode conductive carbon as an overlooked yet critical issue. We propose a concentrated sulfolane (SL)-based electrolyte that prevents anion intercalation via two mechanisms: (1) by offering a high activation barrier to intercalation via its strong anion-Li+ interaction and (2) by forming a sulfur-containing, anion-blocking SL-derived interphase. This electrolyte, used with graphitized acetylene black, which is oxidatively stable but usually susceptible to anion intercalation, enables the stable operation of a Li2CoPO4F/graphite full cell (cut-off voltage = 5.2 V), with 93% capacity retention after 1,000 cycles and an average Coulombic efficiency of ≥99.9%. This is a pivotal strategy to enhance the reversibility of >5 V Li-ion batteries on a commercial level.

Highly active electrocatalyst for rechargeable Zn-air battery: 3D Fe/N-based honeycomb-like carbon

Remarkable bifunctional electrocatalysts for oxygen reaction reduction (ORR) and oxygen evolution reaction (OER) are the key for rechargeable metal-air batteries. In this work, a novel 3D Fe/N-based honeycomb-like carbon with uniformly-distributed active centers were synthesized by agarose and FeCl3 as the precursor, which display excellent ORR performance with large diffusion-limited current density (≈7.5 mA cm−2) and Tafel slope (≈88 mV/dev), significantly superior to the commercial Pt/C electrode. In addition, Fe-NPC-1000 as cathode catalyst in Zn-air battery owns higher power density and charge-discharge stability in comparison with commercial Pt/C catalyst, which shows excellent potential in the realistic application of energy devices.

Simple and Cost-Effective Synthesis of Activated Carbon Anchored by Functionalized Multiwalled Carbon Nanotubes for High-Performance Supercapacitor Electrodes with High Energy Density and Power Density

We prepared a composite using activated carbon and functionalised multiwalled carbon nanotubes by a simple and cost-effective process and investigated its use for supercapacitor application. The electrochemical performance of the prepared composite has been investigated by galvanostatic charge-discharge (GCD) and cyclic voltammetry (CV) measurements in a three-electrode set-up. The composite resulted in maximum specific capacitance of 395 F/g at 5 mV/s as measured by CV, and of 372 F/g at 60 A/g by GCD measurement in 3M KOH aqueous electrolyte. High power and energy density of 75.27 kW/kg and 25.31 W·h/kg at 60 A/g have been respectively obtained for composite using GCD measurement. The long-term charge-discharge stability has been performed for the composite electrodes, and it is observed that 89% of capacitance is retained even after 5000 cycles. The achieved results suggest that the prepared activated carbon/multiwalled carbon nanotube composite can be a potential electrode material in high-performance supercapacitors for energy storage applications.

High Capacity and Energy Density Organic Lithium‐Ion Battery Based on Buckypaper with Stable π‐Radical

Owing to an increasing demand on high performance and rare-metal free energy storage systems, organic rechargeable battery has attracted much attention. To increase the capacity of the whole battery, we have fabricated coin-type buckypaper cells composed of a trioxotriangulene neutral radical derivative (H3 TOT) and single-walled carbon nanotubes as a cathode and lithium metal plate as an anode without current collector. The cells exhibited a stable charge-discharge behavior even at a 90 wt % H3 TOT content with a high-rate performance of 10 C originating from high electrical conductivity of H3 TOT. Furthermore, based on the four-stage redox ability of H3 TOT, the H3 TOT 90 wt % cathode showed a high capacity of approximately 260 mAh g-1 and a high energy density of 546 Wh g-1 . In view of the simple fabrication of the cathode and excellent performance, TOT-based buckypaper will open a new strategy for the flexible cells for next-generation energy storages.

Mono‐Doped Carbon Nanofiber Aerogel as a High‐Performance Electrode Material for Rechargeable Zinc‐Air Batteries

AbstractNitrogen‐doped porous carbon (NPC) materials have attracted increased attention for zinc‐air battery (ZAB) applications because of their comparable electrocatalytic activity to precious metals. However, few metal‐free NPC catalysts exhibit an oxygen reduction reaction performance better than Pt catalysts, together with high oxygen evolution reaction catalytic activity. Herein, an efficient oxygen electrocatalyst based on highly integrated carbon nanofiber (CNF) and NPC aerogels, with CNF as the core and NPC as the shell, is demonstrated. The NPC@CNF aerogels are prepared through a large‐scale, direct pyrolysis of metal‐organic frameworks and bacterial cellulose hybrids. This mono‐doped carbon material with nitrogen heteroatoms displays outstanding bifunctional performance compared to the individual counterparts, which demonstrates the effectiveness of morphological and structural engineering. Density functional theory calculations reveal that the active sites with the participation of multi‐electrons weaken the O−O bond and facilitate the four‐electron oxygen reduction in the dissociation pathway. The ZAB based on the NPC@CNF air electrode exhibits a peak density of 96 mW cm−2 and a stable charge–discharge durability of over 420 cycles with an overpotential increase of only 0.10 V, indicating that the mono‐doped NPC@CNF performs as one of the best bifunctional catalysts among those recently reported metal‐based and metal‐free catalysts.

Tuning the solution structure of electrolyte for optimal solid-electrolyte-interphase formation in high-voltage lithium metal batteries

The solvation structure of Li + plays a significant role in anode stability. The optimized electrolyte of 2.0 M LiDFOB/PC, allows stable charge–discharge of LNMO|Li cells by generating a dense layer of solid-electrolyte-interphase. The continuous reduction of electrolytes by Li metal leads to a poor lifespan of lithium metal batteries (LMBs). Low Coulombic efficiency (CE) and safety concern due to dendrite growth are the challenging issues for LMB electrolyte design. Novel electrolytes such as highly concentrated electrolytes (HCEs) have been proposed for improving interphase stability. However, this strategy is currently limited for high cost due to the use of a large amount of lithium salts as well as their high viscosity, reduced ion mobility, and poor wettability. In this work, we propose a new type of electrolyte having a moderate concentration. The electrolyte has the advantage of HCEs as the anion is preferentially reduced to form inorganic solid-electrolyte-interphase (SEI). Such optimization has been confirmed through combined spectroscopic and electrochemical characterizations and supported with the first-principle molecular dynamics simulation. We have shown the intrinsic connections between solution structure and their electrochemical stability. The 2.0 M LiDFOB/PC electrolyte, as predicted by our characterizations and simulations, allows stable charge–discharge of LNMO|Li cells at 5C for more than 1500 cycles. The 2.0 M electrolyte generates a dense layer of SEI containing fluoro-oxoborates, Li 3 BO 3 , LiF, Li 2 CO 3 , and some organic species effectively passivating the lithium metal, as confirmed by electron microscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance.

The Development of High-Power LIBs Separators

Separators present the crucial functions of separating the positive and negative electrodes due to the free flow of lithium ions through the liquid electrolyte that fills in their open pore. Separators for liquid electrolyte Lithium-ion batteries can be classified into porous polymeric membranes, nonwoven mats, and cellulose separators. When a lithium-ion battery is being overcharged, it releases the heat and results in the inner-short. The polyethylene (PE) separators used here had shut down at around 135°C to cool the exothermal batteries. To enhance the meltdown temperature of the separator, a PE separator was coated with polymers synthesized from various ethylene glycol dimethacrylate monomers. At the same time, nonwoven mats have the potential to be low cost and thermally stable separators. Furthermore, the lithium-ion phosphate/lithium half cell using cellulose separator exhibited stable charge-discharge capability even at 120 °C. This paper presents an overview of the PE and PP membranes of lithium-ion battery separators, discusses how to solve their disadvantages, and reviews the cellulose-based materials developed for potential application in the lithium-ion battery.

Constructing Co@WC1-x heterostructure on N-doped carbon nanotubes as an efficient bifunctional electrocatalyst for zinc-air batteries

Designing a bifunctional catalyst with efficient and consistent stability is important for development and application of zinc–air batteries. Herein, a Co@WC1-x/NCNTs composite that contains a heterostructure consisting of cobalt and tungsten carbide (WC1-x) and loaded on self-assembled N-doped carbon nanotubes (NCNTs), is synthesized from simple compounds using facile hydrothermal and calcination. Co@WC1-x/NCNTs composite demonstrates outstanding electrocatalytic performance for oxygen reduction reaction (ORR) with higher half-wave potential (0.81 V) and the current density of 5.75 mA cm−2, as well as for oxygen evolution reaction (OER) having a lower overpotential (330 mV). Furthermore, it possess an ultra-high power density of 290 mW cm−2, a specific capacity of 754.9 mAh g−1 and charge-discharge stability in zinc-air batteries. The superior electrocatalytic performance of the composite may be ascribed to the synergistic effect between Co@WC1-x heterostructure, and N-doped carbon nanotubes. The formation of a heterojunction interface between Co and WC1-x may make possible the enrichment of electrons from carbon to Co (NCNTs→WC1-x→Highly active sites Co) during the catalytic process. This in turn facilitates the electrocatalytic process. This research offers a meaningful strategy for exploring efficient bifunctional catalyst used in zinc-air batteries.

Lithium Polysulfide Sparingly Solvating Electrolyte for Practical High Energy Density Lithium Sulfur Battery

Safe and cheap rechargeable batteries with high energy density and long cycle performance are urgently required for the increasing market of portable electronic devices, electric vehicles (EV), and large-scale grid. Conventional lithium ion batteries (LIBs) based on Li-ion intercalation, which have been widely applied, could not satisfy the demand for higher energy density and greater driving range of EVs. Elemental sulfur, an inexpensive, abundantly available, and environmental-friendly material, has become one of the most promising positive electrode active materials because of its high theoretical specific capacity (1675 mAh g-1). Nevertheless, the commercialization of the rechargeable Li-S battery is still hindered by several main issues: the electronically insulating nature of sulfur and its discharge products (Li2S/Li2S2), the large volumetric expansion of 80% upon its full lithiation, the dissolution and shuttle effect of lithium polysulfide (LiPS).[1-4] To achieve the practical application of Li-S battery, high energy density and stable cycling performance both need to be focused on. However, for the traditional ether-based electrolyte of 1,3–dioxolane (DOL), and dimethoxyethane (DME) as solvent that is commonly utilized for Li-S battery, severe dissolution of sulfur species from cathode and shuttle effect of LiPS causes a loss of active material and poor cycling stability. To realize the high energy density of Li-S battery, the amounts of electrolyte in the whole battery system need to be controlled. Unfortunately, it is difficult to reduce the electrolyte/sulfur ratio (E/S [mL electrolyte/mg sulfur]) when using the conventional DOL/DME electrolyte because the electrodeposition of the LiPS was found to be significantly slower at high LiPS concentration for a given deposition substrate.[5] Therefore, development of novel electrolytes is of great importance to establishing high energy density Li-S batteries. Here, we report electrochemical performance of Li-S battery using the LiPS sparingly solvating electrolytes.[6-8] Based on these electrolytes, several advantages have been revealed. Firstly, the solubility of LiPS was greatly suppressed, and thus stable charge-discharge with high Coulombic efficiency was achieved in the Li-S batteries. Second, by utilizing pouch cell, we have achieved a high energy density (> 300 Wh kg-1) for Li-S battery under an extremely low E/S ratio of 3.0 μL mg-1. Third, gassing behavior of the Li-S battery using the DOL/DME electrolyte, which indicates high safety risk, could also be obviously depressed.To further improve the electrochemical performance of Li-S batteries based on LiPS sparingly solvating electrolytes with extremely low E/S ratios, we also explored sulfur electrode additives to improve the electrolyte wettability, various electrolyte additives to protect the lithium anode, and optimized making process for pouch cell. The detailed progress will be presented in the presentation. Acknowledgements This work was financially supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) of the Japan Science and Technology Agency (JST).

Cooperative Catalysis toward Oxygen Reduction Reaction under Dual Coordination Environments on Intrinsic AMnO3 -Type Perovskites via Regulating Stacking Configurations of Coordination Units.

It remains challenging for pure-phase catalysts to achieve high performance during the electrochemical oxygen reduction reaction to overcome the sluggish kinetics without the assistance of extrinsic conditions. Herein, a series of pristine perovskites, i.e., AMnO3 (A = Ca, Sr, and Ba), are proposed with various octahedron stacking configurations to demonstrate the cooperative catalysis over SrMnO3 jointly explored by experiments and first-principles calculations. Comparing with the unitary stacking of coordination units in CaMnO3 or BaMnO3 , the intrinsic SrMnO3 with a mixture of corner-sharing and face-sharing octahedron stacking configurations demonstrates superior activity (Ehalf-wave = 0.81 V), and charge-discharge stability over 400 h without the voltage gap (≈0.8 V) increasing in zinc-air batteries. The theoretical study reveals that, on the SrMnO3 (110) surface, the active sites switch from coordinatively unsaturated atop Mn (*OO, *OOH) to Mn-Mn bridge (*O, *OH). Therefore, the intrinsic dual coordination environments of Mn-Ocorner and Mn-Oface enable cooperative modulation of the interaction strength of the oxygen intermediates with the surface, inducing the decrease of the *OH desorption energy (rate-limiting step) unrestricted by scaling relationships with the overpotential of ≈0.28 V. This finding provides insights into catalyst design through screening intrinsic structures with multiple coordination unit stacking configurations.

(Oxalato)borate: The key ingredient for polyethylene oxide based composite electrolyte to achieve ultra-stable performance of high voltage solid-state LiNi0.8Co0.1Mn0.1O2/lithium metal battery

Searching novel polyethylene oxide (PEO) based composite electrolyte that can be compatible with high voltage cathodes (> 4 V) at room temperature is a long-standing challenge, but essential to achieve high-energy-density for solid-state lithium (Li) metal batteries. Herein, we develop an advanced dual-salts reinforced PEO/garnet solid-state composite electrolyte (SCE) with high ionic conductivity of 9 × 10 −4 S cm −1 and an electrochemical stability window up to ~ 4.7 V, where the lithium bis(oxalate)borate (LiBOB) is used as additive with LiClO 4 . The dual-salts reinforced SCE can achieve excellent room temperature cycling performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)/Li metal batteries. The multiplied polymer-ion interactions and formation of Li‒B‒O/C‒O species originated from the (oxalato)borate group of LiBOB effectively promotes the electrochemical stability of the PEO based composite electrolyte and its wetting properties with electrodes. Unwanted non-conductive decomposition products, such as Li 2 O and Li 2 CO 3 , and NCM particles cracking during cycling are successfully suppressed. The NCM811 solid-state cells using the optimized dual-salts composite electrolyte delivers high specific capacity of 190 mA h g −1 and exhibit stable cycling performance for more than 200 cycles at 25 °C. Stable charge–discharge performance of 4 V NCM solid-state battery are realized via addition of LiBOB salts to conventional single salt plasticized PEO solid-state composite electrolyte. Polymer electrolyte decomposition and active materials cracking at high voltage are suppressed by multiplied polymer-ion interactions and formation of stable C‒O/Li‒B‒O containing solid electrolyte interphase, leading to strikingly improvement in capacity retention. • A fast ion conducting dual-salts polyethylene oxide (PEO) based solid-state composite electrolyte (SCE) is developed. • Electrochemical stability of the SCE is greatly enhanced via addition of lithium bis(oxalate)borate (LiBOB) salt. • Adding LiBOB salt to the PEO-based SCE enables stable cycling of high voltage solid-state LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)/Li battery.

Moderate-Concentration Fluorinated Electrolyte for High-Energy-Density Si//LiNi0.8Co0.1Mn0.1O2 Batteries

Highly concentrated electrolytes, although promising, are of high cost and show high viscosity and unsatisfactory wettability toward electrodes and separators, making them unfavorable for practical applications. A more rational electrolyte design is thus needed. Here, we investigate moderately concentrated electrolytes and find that the lithium bis(fluorosulfonyl)imide (LiFSI) concentration effects on the capacity, rate capability, and cycling stability of Si anodes in an ethylene carbonate (EC)/diethyl carbonate (DEC) mixed electrolyte are opposite to those in a fluoroethylene carbonate (FEC) electrolyte. The reasons for these results are systematically examined using Raman spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique. A detailed X-ray photoelectron spectroscopy analysis is performed to study the solid electrolyte interphase chemistry. Al corrosion that occurs with the EC/DEC-based electrolyte can be effectively suppressed with the FEC-based electrolyte if an adequate LiFSI concentration is used. In the proposed 2 mLiFSI/FEC electrolyte, the Si anode has reversible capacities of 2630 and 855 mA h g–¹ at 0.2 and 5 A g–¹, respectively, and ∼75% capacity retention after 200 cycles (remarkably higher than that obtained with the EC/DEC-based electrolyte). This electrolyte also shows great compatibility with the high-energy-density LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NMC-811) cathode, allowing a stable charge–discharge of a Si//NMC-811 full cell.

Prussian blue analog Co3[Co(CN)6]2 as a cathode material for lithium–sulfur batteries

In this work, the authors proposed a unique strategy to prepare a high performance Lithium–Sulfur (Li–S) battery cathode by an N-rich nano-graphene hollow sphere from the Prussian blue analog Co3[Co(CN)6]2. The one-pot solution method with low cost materials was designed to synthesize the cathode by annealing with different temperatures and consistent HCl etching steps for the precursor. The Li–S batteries made by this precursor showed remarkable charge–discharge stability (570.4 mA h g−1 after 500 cycles at a 1 C current density) and outstanding rate performance (1145.5, 717.9, and 672.5 mA hg−1 at 0.1, 1.0, and 2.0 Ag−1 current densities) at 800 °C. The results indicated that the stable three-dimensional multi-layer hollow sphere structure relieved the volume expansion of sulfur, which had a significant impact on the polysulfide adsorption, inhibiting the “shuttle effect.” Also, the rich doping of nitrogen in this structure produced many defects and active sites that improved the interfacial adsorption of polysulfides. While Co3[Co(CN)6]2 shows its potential as a cathode material, the material design method used in this paper provides a unique approach to realizing a high performance sulfur cathode for Li–S batteries.

In-situ self-assembly host-guest carbon aerogels for robust electrochemical capacitors

As a type of promising candidates for electric double-layer capacitors (EDLCs) electrodes, carbon aerogels should possess large surface area, hierarchical porous structures and abundant surface groups. However, ordinary carbon aerogels derived from their aerogel precursors with a single component will not have the possibility to fit some key requirements for energy storage as expected, one of which is mainly generated by the damage of the original structures of the aerogel precursors during preparation processes (like drying, calcining, etc). In this work, polyacrylamide and polyaniline as the two component precursors of host-guest structure carbon aerogels, and such in-suit combination strategy let as-prepared hybrid gels have continuously interconnected porous structures and cross-linked mutual-supported networks so as to form more stable skeleton for resisting the damage of their precursor original structures during preparation processes. After the carbonization and activation treatment, the resulted host-guest carbon areogel exhibits high BET surface area of 2805.07 m2 g−1 and huge pore volume of 1.46 cm3 g−1, which is almost the sum of the host-carbon aerogel with the single component of polyacrylamide and the guest-carbon aerogel with the single component of polyaniline. When they are assembled as electrodes in a symmetric capacitor device, the host-guest carbon aerogels present high specific capacitance of 523 F g−1 (1 A g−1) and long term charge-discharge stability over 10,000 cycles.

Hierarchical bifunctional catalysts with tailored catalytic activity for high-energy rechargeable Zn-air batteries

For Zn-air batteries, much research is still needed to obtain low-cost, high-efficient, and strong durability bifunctional catalysts to promote various electrochemical reactions. In this article, MnO2/carbon-nanotubes (CNTs) hybrid catalysts anchored with a metal oxide (M−MnO2/CNTs) are developed via a facile hydrothermal process toward an efficient oxygen catalytic (evolution and reduction) reactions. M−MnO2/CNTs displays better catalytic activity than MnO2/CNTs. The overpotential of Co-MnO2/CNTs is lowered to 0.803 V, very close to that of Pt/C + IrO2 (0.801 V). Moreover, Co-MnO2/CNTs exhibits faster kinetics for oxygen evolution reaction with low Tafel slope (62 mV dec−1) than Pt/C + IrO2. The improved performance and stability originated from (i) the novel hierarchal structure improving the mass transport, (ii) the redistribution of electrons activating the Mn catalytic sites, (iii) the coupling effect between the metal oxide and MnO2/CNTs, and (iv) an excellent conductivity building a fast electron transfer high-way. The density functional theory results reveal that the anchored metal oxide cluster directly activates neighbor Mn sites on the surface of the hybrid catalyst, and enhances the oxygen catalytic activity by decreasing the bonding with OH and OOH. Accordingly, the maximum power density of the Co-MnO2/CNTs-based Zn-air battery reaches 342.7 mW cm−2. The Zn-air battery also exhibits good charge–discharge stability with a low voltage gap of 0.72 V for 128 h. This work provides an effective method to achieve MnO2/CNTs materials with tailored catalytic activity by anchoring different metal oxides and demonstrates great potential in the field of high specific energy batteries for electrical vehicles, portable electronics, and wearable devices.

Utilization of waste coir fibre architecture to synthesize porous graphene oxide and their derivatives: An efficient energy storage material

Now-a-day’s lot of researcher interest is directed towards the conversion of bioresources (waste) to carbon-based materials for meeting the demand of sustainable energy. In the present study, we have utilized waste coir fibres for the synthesis of graphene oxide and its derivatives. Microscopic investigation of coir fibre indicates that silica microspheres assembled in a regular pattern inside the cellulose matrix of coir fibre. Here, we have attempted to make water-soluble silica-based compound via reaction of coir with alkali metal hydroxide. Further, heating of water-soluble silicates-cellulose mixture leads to the formation of porous graphene oxide having high specific surface area (1114 m2/g). Doping of sulphur and nitrogen has been done via the chemical route, which leads to enhancement in electronic conductivity. The electrochemical study of bare and doped graphene oxide have been carried out using electrochemical work station. The electrochemical study confirms that nitrogen-doped graphene oxide has highest specific capacitance (278.6 F/g) as compared to bare graphene oxide (166.1 F/g) and sulphur doped graphene oxide (199.2 F/g) at 1 A/g discharge current because of high charge carrier density in nitrogen-doped graphene oxide (9.7 × 1014 cm−3). The galvanic charge-discharge (GCD) stability shows ∼82% capacitance retention after 2000 GCD cycle at 3 A/g of nitrogen-doped graphene. The above approach for conversion of low-value coir fibre to high-value energy storage material (graphene oxide) would certainly be interest of the researchers working in the field of energy storage, environmental pollution control, waste management, materials science, sustainable chemistry and engineering for achieving the goal of cleaner production technologies for better environmental sustainability.

Preparation and Properties of an Alginate-Based Fiber Separator for Lithium-Ion Batteries

The membrane is one of the key inner parts of lithium-ion batteries, which determines the interfacial structure and internal resistance, ultimately affecting the capacity, cycling, and safety performance of the cell. In this article, an alginate-based fiber composite membrane was successfully fabricated from cellulose and calcium alginate with flame-retardant properties via a traditional papermaking process. In the membrane, the calcium alginate plays a bridging role and the cellulose acts as a filler. After 100 cycles, lithium-ion batteries by the alginate-based fiber separator exhibited better capacity retention ratios (approximately 90%) compared with those of commercial PP separators. Furthermore, the alginate-based fiber separator demonstrated fine thermal stability and electrochemical properties, showing a stable charge-discharge capability and no hot melt shrinkage at higher temperatures, which is a breakthrough in improving the safety of the cell. This research affords a new way for the large-scale fabrication of safe lithium-ion battery separators.