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A supercritical carbon dioxide (SCCO2) fluid, characterized by gas‐like diffusivity, near‐zero surface tension, and excellent mass transfer properties, is used as a precursor to produce silicon oxycarbide (SiOC) coating. SCCO2 disperses and reacts with Si particles to form an interfacial layer consisting of Si, O, and C. After an 850 °C annealing process, a conformal SiOC coating layer forms, resulting in core‐shell Si@SiOC particles. High‐resolution transmission electron microscopy and its X‐ray line‐scan spectroscopy, X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy, are used to examine the SiOC formation mechanism. Effects of SCCO2 interaction time on the SiOC properties are investigated. The SiOC layer connects the Si@SiOC particles, improving electron and Li+ transport. Cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy are employed to examine the role of SiOC during charging/discharging. Operando X‐ray diffraction data reveal that the SiOC coating reduces crystal size of the formed Li15Si4 and increases its formation/elimination reversibility during cycling. The Si@SiOC electrode shows a capacitiy of 2250 mAh g−1 at 0.2 A g−1. After 500 cycles, the capacity retention is 72% with Coulombic efficiency above 99.8%. A full cell consisting of Si@SiOC anode and LiNi0.8Co0.1Mn0.1O2 cathode is constructed, and its performance is evaluated. [ABSTRACT FROM AUTHOR]

A cost‐effective chemical prelithiation solution, which consists of Li+, polyaromatic hydrocarbon (PAH), and solvent, is developed for a model hard carbon (HC) electrode. Naphthalene and methyl‐substituted naphthalene PAHs, namely 2‐methylnaphthalene and 1‐methylnaphthalene, are first compared. Grafting an electron‐donating methyl group onto the benzene ring can decrease electron affinity and thus reduce the redox potential, which is validated by density functional theory calculations. Ethylene glycol dimethyl ether (G1), diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether solvents are then compared. The G1 solution has the highest conductivity and least steric hindrance, and thus the 1‐methylnaphthalene/G1 solution shows superior prelithiation capability. In addition, the effects of the interaction time between Li+ and 1‐methylnaphthalene in G1 solvent on the electrochemical properties of a prelithiated HC electrode are investigated. Nuclear magnetic resonance data confirm that 10‐h aging is needed to achieve a stable solution coordination state and thus optimal prelithiation efficacy. It is also found that appropriate prelithiation creates a more Li+‐conducing and robust solid‐electrolyte interphase, improving the rate capability and cycling stability of the HC electrode. [ABSTRACT FROM AUTHOR]

To enhance Li storage properties, nitrogenation methods are developed for Si anodes. First, melamine, urea, and nitric oxide (NO) precursors are used to nitrogenize carbon‐coated Si particles. The properties of the obtained particles are compared. It is found that the NO process can maximize the graphitic nitrogen (N) content and electronic conductivity of a sample. In addition, optimized N functional groups and O─C species on the electrode surface increase electrolyte wettability. However, with a carbon barrier layer, NO hardly nitrogenizes the Si cores. Therefore, bare Si particles are reacted with NO. Core‐shell Si@amorphous SiNx particles are produced using a facile and scalable NO treatment route. The effects of the NO reaction time on the physicochemical properties and charge–discharge performance of the obtained materials are systematically examined. Finally, the Si@SiNx particles are coated with N‐doped carbon. Superior capacities of 2435 and 1280 mAh g−1 are achieved at 0.2 and 5 A g−1, respectively. After 300 cycles, 90% of the initial capacity is retained. In addition, differential scanning calorimetry data indicate that the multiple nitrogenation layers formed by NO significantly suppress electrode exothermic reactions during thermal runaway. [ABSTRACT FROM AUTHOR]

This study reports five types of metal-doped (Co, Cu, Sn, V, and Zr) NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP)/polymer composite solid electrolytes (CSEs) enabling Li4Ti5O12 (LTO) anodes to have high rate capability and excellent cycling performance. The high Li+-conductivity LATP samples are successfully synthesized through a modified sol–gel method followed by thermal calcination. We find that the cation dopants clearly influence the substitution of Al for Ti, with the type of dopant serving as a crucial factor in determining the ionic conductivity and interfacial resistance of the solid electrolyte. The CSE containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and Sn-LATP shows an ionic conductivity of 1.88 × 10−4 S cm−1 at ambient temperature. The optimum conductivity can be attributed to alterations in the lattice parameters and Li+ transport pathways owing to Sn doping. The solid-state cell equipped with the LTO-supported CSE containing Sn-LATP fillers demonstrates both excellent high rate capability at 5 C (with a capacity retention of 86% compared to the value measured at 0.2 C) and superior cycling stability, maintaining high Coulombic efficiency (>99.0%) over 510 cycles. These findings indicate that the proposed CSE is highly promising for use in solid-state lithium batteries with desirable charge–discharge properties and high durability. [ABSTRACT FROM AUTHOR]

Self‐discharge, which is associated with energy efficiency loss, is a critical issue that hinders practical applications of rechargeable aluminum batteries (RABs). The self‐discharge properties of two commonly‐used RAB positive electrode materials, namely natural graphite (NG) and expanded graphite (EG), are investigated in this work. EG, which has a wider spacing between graphitic layers and a larger surface area, has a higher self‐discharge rate than that of NG. After 12 h of rest, NG and EG electrodes retain 74% and 63% of their initial capacities, respectively, after charging up to 2.4 V at 0.3 A g−1. Operando X‐ray diffraction, X‐ray photoelectron spectroscopy, and energy‐dispersive X‐ray spectroscopy are employed to study the self‐discharge mechanism. The self‐discharge loss is related to the spontaneous deintercalation of AlCl4− anions from the graphite lattice charge‐compensated by Cl2 gas evolution at the same electrode and can be restored (i.e., no permanent damage is caused to the electrodes) in the next charge‐discharge cycle. It is found that the charging rate and depth of charge also affect the self‐discharge properties. In addition, the self‐discharge rates of NG in 1‐ethyl‐3‐methylimidazolium chloride–AlCl3 and urea–AlCl3 electrolytes are compared. [ABSTRACT FROM AUTHOR]

High entropy oxide (HEO) has emerged as a new class of anode material for Li‐ion batteries (LIBs) by offering infinite possibilities to tailor the charge–discharge properties. While the advantages of single‐phase HEO anodes are realized, the effects of a secondary phase are overlooked. In this study, two kinds of Co‐free HEOs are prepared, containing Cr, Mn, Fe, Ni, and Zn, for use as LIB anodes. One is a plain cubic‐structure high entropy spinel oxide HESO (C) prepared using a solvothermal method. The other HESO (C+T) contains an extra secondary phase of tetragonal spinel oxide and is prepared using a hydrothermal method. It is demonstrated that the secondary tetragonal spinel phase introduces phase boundaries and defects/oxygen vacancies within HESO (C+T), which improve the redox kinetics and reversibility during electrode lithiation/delithiation. Density functional theory calculation is performed to assess the phase stability of cubic spinel, tetragonal spinel, and rock‐salt structures, and validate the cycling stability of the electrodes upon charging–discharging. The secondary‐phase‐induced rate capability and cyclability enhancement of HEO electrodes are for the first time demonstrated. A HESO (C+T)||LiNi0.8Co0.1Mn0.1O2 full cell is assembled and evaluated, showing a promising gravimetric energy density of ≈610 Wh kg−1 based on electrode‐active materials. [ABSTRACT FROM AUTHOR]

Transition metal high‐entropy oxides (HEOs) are an attractive class of anode materials for high‐performance lithium‐ion batteries (LIBs). However, owing to the multiple electroactive centers of HEOs, the Li+ storage mechanism is complex and debated in the literature. In this work, operando quick‐scanning X‐ray absorption spectroscopy (XAS) is used to study the lithiation/delithiation mechanism of the Cobalt‐free spinel (CrMnFeNiCu)3O4 HEO. A monochromator oscillation frequency of 2 Hz is used and 240 spectra are integrated to achieve a 2 min time resolution. High‐photon‐flux synchrotron radiation is employed to increase the XAS sensitivity. The results indicate that the Cu2+ and Ni2+ cations are reduced to their metallic states during lithiation but their oxidation reactions are less favorable compared to the other elements upon delithiation. The Mn2+/3+ and Fe2+/3+ cations undergo two‐step conversion reactions to form metallic phases, with MnO and FeO as the intermediate species, respectively. During delithiation, the oxidation of Mn occurs prior to that of Fe. The Cr3+ cations are reduced to CrO and then Cr0 during lithiation. A relatively large overpotential is required to activate the Cr reoxidation reaction. The Cr3+ cations are found after delithiation. These results can guide the material design of HEOs for improving LIB performance. [ABSTRACT FROM AUTHOR]

A facile method for preparing hierarchical carbon composites that contain activated carbon (AC), carbon nanospheres (CNSs), and carbon nanotubes (CNTs) for use as the electrode material in supercapacitors (SCs) was developed. The CNS/CNT network enabled the formation of three‐dimensional conducting pathways within the highly porous AC matrix, effectively reducing the internal resistance of an SC electrode. The specific capacitance, cyclability, voltage window, temperature profile during charging/discharging, leakage current, gas evolution, and self‐discharge of the fabricated SCs were systematically investigated and the optimal CNS/CNT ratio was determined. A 2.5 V floating aging test at 70 °C was performed on SCs made with various hierarchical carbon electrodes. Electrochemical impedance spectroscopy, postmortem electron microscopy, Raman spectroscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy analyses were conducted to examine the electrode aging behavior. A hierarchical carbon architecture with an appropriate AC/CNS/CNT constituent ratio could significantly improve charge‐discharge performance, increase cell reliability, and decrease the aging‐related degradation rate. [ABSTRACT FROM AUTHOR]

High entropy oxide (HEO) is a new class of lithium‐ion battery anode with high specific capacity and excellent cyclability. The beauty of HEO lies in the unique tailorable properties with respect to tunable chemical composition, which enables the use of infinite element combinations to develop new electrode materials. This study synthesizes a series of Co‐free spinel‐type HEOs via a facile hydrothermal method. Based on quaternary medium‐entropy (CrNiMnFe)3O4, the fifth elements of V, Mg, and Cu are added, and their ability to form single‐phase HEOs is investigated. It is demonstrated that the chemical composition of HEOs is critical to the phase purity and corresponding charge–discharge performance. The oxygen vacancy concentration seems to be decisive for the rate capability and reversibility of the HEO electrodes. An inactive spectator element is not necessary for achieving high cyclability, given that the phase purity of the HEO is wisely controlled. The single‐phase (CrNiMnFeCu)3O4 shows a great high‐rate capacity of 480 mAh g−1 at 2000 mA g−1 and almost no capacity decay after 400 cycles. Its phase transition behavior during the lithiation/delithiation process is characterized with operando X‐ray diffraction. A (CrNiMnFeCu)3O4||LiNi0.8Co0.1Mn0.1O2 cell is constructed with 590 Wh kg−1 (based on electrode materials) gravimetric energy density. [ABSTRACT FROM AUTHOR]

Supercritical CO2 (SCCO2), characterized by gas‐like diffusivity, low surface tension, and excellent mass transfer properties, is applied to create a SiOx/carbon multi‐layer coating on Si particles. Interaction of SCCO2 with Si produces a continuous SiOx layer, which can buffer Si volume change during lithiation/delithiation. In addition, a conformal carbon film is deposited around the Si@SiOx core. Compared to the carbon film produced via a conventional wet‐chemical method, the SCCO2‐deposited carbon has significantly fewer oxygen‐containing functional groups and thus higher electronic conductivity. Three types of carbon precursors, namely, glucose, sucrose, and citric acid, in the SCCO2 syntheses are compared. An eco‐friendly, cost‐effective, and scalable SCCO2 process is thus developed for the single‐step production of a unique Si@SiOx@C anode for Li‐ion batteries. The sample prepared using the glucose precursor shows the highest tap density, the lowest charge transfer resistance, and the best Li+ transport kinetics among the electrodes, resulting in a high specific capacity of 918 mAh g−1 at 5 A g−1. After 300 charge–discharge cycles, the electrode retains its integrity and the accumulation of the solid electrolyte interphase is low. The great potential of the proposed SCCO2 synthesis and composite anode for Li‐ion battery applications is demonstrated. [ABSTRACT FROM AUTHOR]

High entropy spinel oxide (HESO) nanoparticles were synthesized via a surfactant-assisted hydrothermal method and used as a novel anode material in a lithium-ion battery. The HESO consists of non-equimolar cations of Cr, Mn, Fe, Co, and Ni dispersed in two Wyckoff sites with various valence states. Due to a strong entropy-induced phase stabilization effect of the HESO, no inactive MgO structural pillars, which are exclusively present in the reported rock salt type high entropy oxides, are required to achieve high electrode cycling stability. A superior charge–discharge capacity of 1235 mA h g−1, the highest among all known HEOs, is obtained with 90% capacity retention after 200 cycles. The unique HESO is also characterized by plenty of oxygen vacancies and three-dimensional Li+ transport pathways. Also, great high-rate performance, i.e., 500 mA h g−1 @ 2000 mA g−1, of the HESO electrode is demonstrated. [ABSTRACT FROM AUTHOR]

Rechargeable aluminum batteries (RABs) are extensively developed due to their cost‐effectiveness, eco‐friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture‐sensitive and corrosive. To address these problems, a 4‐ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4‐ethylpyridine molar ratio on the electrode charge–discharge properties are systematically examined. A maximum graphite capacity of 95 mAh g−1 is obtained at 25 mA g−1. After 1000 charge–discharge cycles, ≈85% of the initial capacity can be retained. In situ synchrotron X‐ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon‐fiber paper electrodes are confirmed in the 4‐ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N2‐filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications. [ABSTRACT FROM AUTHOR]

Bis(trifluoromethylsulfonyl)imide (TFSI)-based ionic liquid (IL) has high thermal and electrochemical stability, but it is not an ideal battery electrolyte due to the poor rate capability of cells that use it, problematic anode compatibility, and high cost. The incorporation of a carbonate solvent could mitigate these problems, but it would also lead to serious Al current collector corrosion at high potential. This long-existing problem is overcome in this study by modulating the LiTFSI concentration and IL/carbonate ratio in the hybrid electrolyte. The Al corrosion and electrolyte decomposition side reactions at 5 V (vs. Li+/Li) can be suppressed in 3 M LiTFSI 25%-IL electrolyte, in which good performance of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode is achieved. Capacities of 140 and 88 mA h g−1 were measured at 0.1 and 2C, respectively (vs. 25 mA h g−1 at 2C for a plain LiTFSI/PMP–TFSI IL electrolyte). After 300 charge–discharge cycles, 90% of the initial LNMO capacity was retained. This electrolyte also shows low flammability and great wettability toward a polyethylene separator. Moreover, this electrolyte allows elevated-temperature storage and operation of LNMO cells at 55 °C, which is not possible with the conventional carbonate electrolyte. Good compatibility of the electrolyte with a graphite anode is also demonstrated. The proposed electrolyte design concept has great potential for next-generation 5 V Li-ion batteries. [ABSTRACT FROM AUTHOR]

To realize the sustainability of Na‐ion batteries (NIBs) for large‐scale energy storage applications, a resource‐abundant and cost‐effective anode material is required. In this study, sugarcane bagasse (SB), one of the most abundant types of biowaste, is chosen as the carbon precursor to produce a hard carbon (HC) anode for NIBs. SB has a great balance of cellulose, hemicellulose, and lignin, which prevents full graphitization of the pyrolyzed carbon but ensures a sufficiently ordered carbon structure for Na+ transport. Compared with HC derived from waste apples, which are pectin‐rich and have less cellulose than SB, SB‐derived HC (SB‐HC) has fewer defects and a lower oxygen content. SB‐HC thus has a higher first‐cycle sodiation/desodiation coulombic efficiency and better cycling stability. In addition, SB‐HC has a unique flake‐like morphology, which can shorten the Na+ diffusion length, and higher electronic conductivity (owing to more sp2‐hybridized carbon), resulting in superior high‐rate charge–discharge performance to apple‐derived HC. The effects of pyrolysis temperature on the material characteristics and electrochemical properties, evaluated by using chronopotentiometry, cyclic voltammetry, and electrochemical impedance spectroscopy, are systematically investigated for both kinds of HC. [ABSTRACT FROM AUTHOR]

Ionic‐liquid (IL) electrolytes, characterized by large potential windows, intrinsic ionic conductivity, low environmental hazard, and high safety, are used for micropore‐ and mesopore‐rich activated‐carbon (ACmicro and ACmeso) supercapacitors. IL electrolytes consisting of various cations [1‐ethyl‐3‐methylimidazolium (EMI+), N‐propyl‐N‐methylpyrrolidinium (PMP+), and N‐butyl‐N‐methylpyrrolidinium (BMP+)] and various anions [bis(trifluoromethylsulfonyl)imide (TFSI−), BF4−, and bis(fluorosulfonyl)imide (FSI−)] are investigated. The electrolyte conductivity, viscosity, and ion transport properties at the ACmicro and ACmeso electrodes are studied. In addition, the capacitance, rate capability, and cycling stability of the two types of AC electrodes are systematically examined and post‐mortem material analyses are conducted. The effects of IL composition on the charge–discharge capacitances of the ACmicro electrodes are more pronounced than those for the ACmeso electrodes. The FSI‐based IL electrolytes, for which electrochemical properties are cation dependent, are found to be promising. Incorporating EMI+ with FSI− results in a low electrolyte viscosity and a fast ion transport, giving rise to optimized electrode capacitance and rate capability. Replacing EMI+ with PMP+ increases the cell voltage (to 3.5 V) and maximum energy density (to 42 Wh kg−1) of the ACmicro cell at the cost of cycling stability. A puzzle of pores and ions: A suitable combination of activated carbon pore size and ionic‐liquid (IL) composition can achieve desirable electric double‐layer capacitor performance. A bis(fluorosulfonyl)imide (FSI)‐based IL is more promising than the bis(trifluoromethylsulfonyl)imide (TFSI)‐ and BF4‐based IL counterparts. Replacing 1‐ethyl‐3‐methylimidazolium with N‐propyl‐N‐methylpyrrolidinium increases the cell voltage to 3.5 V, improving the energy density of the supercapacitor. [ABSTRACT FROM AUTHOR]

SnO2@CMK‐8 composite, a highly promising anode for Na‐ion batteries (NIBs), was incorporated with polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and NaCMC/NaPAA mixed binders to optimize the electrode sodiation/desodiation properties. Synergistic effects between NaCMC and NaPAA led to the formation of an effective protective film on the electrode. This coating layer not only increased the charge–discharge Coulombic efficiency, suppressing the accumulation of solid–electrolyte interphases, but also kept the SnO2 nanoparticles in the CMK‐8 matrix, preventing the agglomeration and removal of oxide upon cycling. The adhesion strength and stability towards the electrolyte of the binders were evaluated. In addition, the charge–transfer resistance and apparent Na+ diffusion of the SnO2@CMK‐8 electrodes with various binders were examined and post‐mortem analyses were conducted. With NaCMC/NaPAA binder, exceptional electrode capacities of 850 and 425 mAh g−1 were obtained at charge–discharge rates of 20 and 2000 mA g−1, respectively. After 300 cycles, 90 % capacity retention was achieved. The thermal reactivity of the sodiated electrodes was studied by using differential scanning calorimetry. The binder effects on NIB safety, in terms of thermal runaway, are discussed. Binders, keepers: Binder selection is crucial for the sodiation/desodiation kinetics, cycling stability, SEI growth, and thermochemical stability of composite anodes in Na‐ion batteries. A sodium carboxymethylcellulose/sodium polyacrylate mixed binder was used to obtain exceptional electrode capacities of 850 and 425 mAh g−1 at charge–discharge rates of 20 and 2000 mA g−1, respectively, and 90 % capacity retention was achieved after 300 cycles. [ABSTRACT FROM AUTHOR]

Electrolyte formulations are vital for the proper functioning of Na-ion batteries. A systematic study is conducted to optimize the electrolyte for a SnO2/graphene anode, which is prepared via a supercritical-CO2-assisted synthesis method. The effects of a propylene carbonate (PC) and ethylene carbonate (EC) solvent combination and a fluoroethylene carbonate (FEC) additive on the electrode charge–discharge properties are examined. Incorporations of EC and FEC promote the formation of a more robust solid electrolyte interphase layer, improving the cyclic stability of the electrode compared to that found for an electrode in a PC-only electrolyte containing 1 M NaClO4 salt. Nevertheless, at 60 °C, an N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid electrolyte clearly outperforms the PC/EC/FEC carbonate-based electrolyte in terms of electrode capacity, rate capability, and cyclic stability. This work indicates that the electrode sodiation/desodiation performance remarkably depends on the electrolyte composition, which should be optimized for various application demands and operation temperatures of batteries. [ABSTRACT FROM AUTHOR]

In this article, we investigate the electrochemical performance of the amorphous sodium iron carbonophosphate upon transitioning from organic electrolytes (lithium hexafluorophosphate (LiPF 6) –ethylene carbonate (EC): diethyl carbonate (DEC) based) to ionic-liquid (N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide; PMP-FSI) based electrolytes. The amorphous sodium iron carbonophosphate is synthesized using microwave-assisted hydrothermal process to obtain the desired phase and microstructure. The nanoparticle morphology, along with the amorphous structure, results in excellent electrochemical properties when tested as cathode for lithium-ion and sodium-ion batteries with organic and ionic-liquid based electrolytes. It is observed that the room-temperature and high-temperature (∼60 °C) cycling performance is superior when ionic-liquids are used instead of organic electrolytes, resulting in nearly fade-free electrochemical cells. Specific capacity retention of ∼97% is reported after 500 cycles with 3 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/PMP-FSI ionic-liquid at a specific current density of 400 mAg−1 (room temperature), in comparison to ∼70% after 500 cycles for 1 M LiPF 6 in EC: DEC = 1:1. At high temperatures (∼60 °C), ionic-liquids outperform the conventional organic electrolytes in terms of capacity retention and rate capability. Post-mortem analysis of the electrodes indicates that a dense and ionically conductive protective film, composed of anion-reduced moieties, is responsible for the superior high-temperature performance of amorphous sodium iron carbonophosphate with the ionic-liquids. [Display omitted] • Electrochemical evaluation of amorphous Na 2 FePO 4 CO 3 with ionic-liquid electrolytes. • Thermodynamic model based on polarization work proposed for mechanism of operation. • Measurements of electrochemical properties at room temperature and 60 °C. • Nearly fade-free cycling characteristics established at room temperature and 60 °C. • Excellent rate-capability upto charge-discharge rate of ∼20C established. [ABSTRACT FROM AUTHOR]

Ultrafine CuO nanoparticles are successfully encapsulated into two ordered mesoporous carbons (OMCs) with different pore architectures, namely CMK-8 with a 3D cubic mesostructure and CMK-3 with a 2D hexagonal mesostructure, and used as anodes in sodium-ion batteries. The electrochemical test results demonstrate that the CuO@CMK-8 nanocomposite with ultra-small CuO nanoparticles (around 4 nm in diameter) and a high content of CuO (78%) exhibits superior electrochemical performance as compared to that of the CuO@CMK-3 nanocomposite and the pristine CuO electrodes. The CuO@CMK-8 anode delivers an initial discharge capacity of 1405 mA h g−1 with a reversible capacity of 768 mA h g−1 at a current density of 20 mA g−1. At a current density of 100 mA g−1, it provides a reversible capacity of 477 mA h g−1 after 200 cycles with coulombic efficiency over 99%. The remarkable enhancement of the electrochemical performance of the CuO@CMK-8 nanocomposite can be attributed to the electrically conductive network of CMK-8 in the CuO@CMK-8 nanocomposite wherein the ultra-small CuO nanoparticles supported on CMK-8 act as a synergistic elastic buffer. Furthermore, cyclic voltammetry, ex situ XRD, SEM and TEM measurements provide deeper insights to the reversible conversion reaction in the CuO@CMK-8 nanocomposite system during the sodiation/desodiation process. [ABSTRACT FROM AUTHOR]

High-energy-density 0.5Li 2 MnO 3 –0.5Li(Mn 0.375 Ni 0.375 Co 0.25 )O 2 composite cathodes for lithium rechargeable batteries are synthesized using an auto-combustion method. The electrode charge–discharge properties are studied at 25 and 50 °C in Li + -containing N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP–TFSI) and N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PMP–TFSI) ionic liquid (IL) electrolytes. The IL electrolytes have a high decomposition temperature (∼400 °C) and thus are ideal for high-safety applications. Compared to Li + /BMP–TFSI IL, Li + /PMP–TFSI IL exhibits higher ionic conductivity and lower viscosity. As a result, the composite cathode shows superior electrochemical performance in Li + /PMP–TFSI IL electrolyte. With the increase in cell temperature from 25 to 50 °C, the maximum capacities and rate capabilities of both IL cells improve significantly. Thus at 50 °C, discharge capacities of 304 mAh g −1 (@10 mA g −1 ) and 223 mAh g −1 (@100 mA g −1 ) are obtained for the Li + /PMP–TFSI cell. These capacities are superior to those for a control cell made with the same composite cathode and a conventional organic electrolyte. At elevated temperature, the cyclability of the composite cathode in the IL electrolytes is markedly higher than that obtained in a conventional organic electrolyte. [ABSTRACT FROM AUTHOR]

• Single-step, scalable, and residual-free method is developed to produce NHGNSs. • GNS, HGNS, and NHGNS additives in AC electrodes are systematically compared. • GNSs shield the AC surface from ion accessibility, decreasing electrode performance. • NHGNSs improve electrode wettability, ion diffusion, interfacial conductivity. • Effects of electrode additives on reliability of AC cells are first investigated. A facile and cost-effective method is developed to produce nitrogen (N)-doped holey graphene nanosheets (NHGNSs) using rapid heating under an NO atmosphere. This is a single-step and residual-free process wherein the holey structure and N doping are simultaneously created. In this study, we employ three kinds of additives, namely graphene (GNSs), holey graphene (HGNSs), and NHGNSs, in activated carbon (AC) electrodes. The conventional GNS additive though improves electronic conductivity of the AC electrode greatly hinders the ionic conductivity, decreasing supercapacitive performance in propylene carbonate electrolyte. HGNSs with large accessible surface area and efficient ion transport pathways outperform the GNS electrode additive. The NHGNSs, owing to the dual benefits of the holey structure and high electronic conductivity, is the best additive for the AC electrode. The NHGNSs improve electrode wettability toward electrolyte, enhance ion diffusion, and reduce interfacial contact resistance, thereby promoting rate capability of the AC cell. In addition, the effects of electrode additives on reliability of AC cells are investigated for the first time. The NHGNSs effectively suppress the leakage current and electrode gassing under operation. An effective strategy to improve charge-discharge performance, cyclability, and reliability of electric double-layer supercapacitors is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]