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Na3V2(PO4)2F3 with a NASICON (Na-superionic conductor) structure is a promising cathode material for sodium-ion batteries (NIBs) due to its high-energy density and great cycling stability. However,...

In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2–Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 °C preserves a large fraction of hydrous RuO2·xH2O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2–Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg−1 at a power density of 8,720 W kg−1 (or 8.3 Wh L−1 at 15,000 W L−1). In addition, an excellent durability of 97.6% capacitance retention after 3,000 charge-discharge cycles is found for this electrode. The proposed RuO2–Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.

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.

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.

The reliability of electric double-layer capacitors (EDLCs), long overlooked, is important for practical applications. For instance, issues like leakage current (leading to energy loss and heat generation), gassing (increasing internal pressure), and aging (causing capacity fading and cell resistance to rise) greatly affect the applicability of EDLCs. A hierarchical electrode design is developed in the present work to deal with these problems. The hierarchical carbon composites that consist of activated carbon (AC), zero-dimensional carbon nanospheres (CNSs) and one-dimensional CNTs are fabricated using a facile and cost-effective method, which can be easily scaled up for mass production. The charge-discharge properties, operation voltage, temperature profile during charging/discharging, leakage current, gas evolution, and self-discharge of the EDLCs are systematically investigated. The electronic conductivity of the electrodes is found to crucially influence the EDLC overall performance. A hierarchical carbon architecture with an appropriate AC/CNS/CNT constituent ratio can significantly improve charge-discharge capacitances, increase cell reliability, and decrease the aging-related degradation rate.

Recently, high entropy oxide (HEO) materials received compelling research consideration for lithium-ion batteries (LIBs) owing to their exceptional cycling stability, high specific capacity, and exclusive tailorable properties. This unique tailorable aspect of HEO enables the use of infinite metal cation combinations to develop new electrode materials with exciting and unexplored properties. In this study, we developed a series of Co-free spinel-type HEO (HESO) anodes via a facile hydrothermal method. The effects of various elemental combination on phase purity, morphology, crystallinity, microstructures, valence states, and electrochemical charge-discharge properties of the HESO electrodes are systematically studied. For the first time, we demonstrate that the chemical composition of HESOs is crucial to the phase purity, morphology, and oxygen vacancy concentration. The oxygen vacancy concentration seems to have a substantial impact on the rate capability and reversibility of the HEO electrodes. This study demonstrates that an electrochemically 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 capability and no capacity fading after 400 cycles. In addition, the charge/discharge behavior was examined using operando X-ray diffraction. According to the operando XRD analysis, a spinel-to-rock salt phase transition is observed for (CrNiMnFeCu)3O4 before the formation of short-range ordered nano-crystals during the first lithiation. The nano-crystalline nature is preserved upon cycling. The the practical feasibility of HEO anode is evaluated by constructing a 4MCu||LiNi0.8Co0.1Mn0.1O2 full cell.

Defect engineering, such as manipulating oxygen vacancies (OVs), which can alter the local structure and electronic properties of metal oxides, has attracted increasing attention for improving the charge-storage performance of electrode materials. In this work, a high-pressure hydrogenation method was developed to fabricate oxygen-deficient TiO2. Two TiO2 phases, namely rutile (TiO2-R) and anatase (TiO2-A), and their hydrogenated phases (denoted with the prefix “H”) are investigated as sodium-ion battery (SIB) anodes. The charge-discharge properties of both phases can be significantly enhanced via the hydrogenation treatment. The introduction of OVs increases the electronic and ionic conductivity of TiO2, and the disordered TiO2 provides more electro-active sites for sodiation/desodiation reactions. For the first time, electrochemcial properties of the H-TiO2-R and H-TiO2-A electrodes are systematically compared. The H-TiO2-A electrode exhibits an excellent high-rate capacity of 100 mAh g–1 at 10000 mA g–1 and great cycling stability of 80% capacity retention after 4500 cycles. The superior performance is well supported by a generalized gradient approximation Perdew-Burke-Ernzerhof density functional calculation. The proposed anode and material modification strategy have great potential for high-power and high-durability SIB applications.

Electrolyte is a key component in high-voltage lithium-ion batteries (LIBs). Bis(trifluoromethanesulfonyl)imide-based ionic liquid (IL)/organic carbonate hybrid electrolytes have been a research focus owing to their excellent balance of safety and ionic conductivity. Nevertheless, corrosion of Al current collectors at high potentials usually happens for this kind of electrolyte. In this study, this long-standing problem is solved via the modulation of the IL/carbonate ratio and LiPF6 concentration in the hybrid electrolyte. The proposed electrolyte suppresses Al dissolution and electrolyte oxidation at 5 V (vs Li+/Li) and thus allows for ideal lithiation/delithiation performance of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode even at 55 °C. The underlying mechanism is examined in this work. Excellent cycling stability (97% capacity retention) for an LNMO cathode after 300 cycles is achieved. This electrolyte shows good wettability toward a polyethylene separator and low flammability. In addition, satisfactory compatibility with both graphite and Si-based anodes is confirmed. The proposed electrolyte design strategies have great potential for applications in high-voltage LIBs.

This study adopts high-concentration ether electrolytes to improve high-rate capability, cycling stability, and Coulombic efficiency (CE) for lithium ion batteries with lithium anode. A series of ether-based electrolytes including lithium bis(fluorosulfonyl)imide (LiFSI)-glyme/ethylene carbonate (EC), LiFSI-glyme/EC, LiFSI-diglyme/EC, LiFSI-triglyme/EC, LiFSI-tetraglyme (G4)/EC, and LiFSI-1,3-dioxolane (DOL)/EC, along with commonly used LiPF6-DEC/EC were prepared to delineate the influences of concentration, chain length, molecular structure (linear or ring ether), and EC additive on the electrochemical performance of Li anodes. An optimum composition for ether-based electrolyte was determined resulting in significant improvement in anti-flammability as well as CE at both low and high rates. At ultra-high current density operation (e.g. 6 mA cm−2), the CE was 95.5 and 97.1% with 3 M LiFSI-G4/EC and 3 M LiFSI-DOL/EC, respectively. Using 1 M LiPF6 carbonate-based electrolyte tend to grow a needle-like dendritic structure when depositing lithium metal on Cu foils, whereas high-concentration ether electrolyte promotes a knot-like and rounded Li metal microstructure. High concentration EC-based electrolytes, are capable of facilitating Li+ almost in tandem with solvent molecules, thereby reducing the number of free molecules, reducing the chance of side reaction with Li metal, and subsequently inhibiting the formation of dendritic Li structures.

Palladium (Pd) nanoparticles, ionic liquids (ILs), or both are integrated with graphene sheets to serve as an electrochemical sensor for detecting various bio-species. Ascorbic acid (AA), uric acid...

In this work, we have compared the electrochemical characteristics of auto combustion synthesized 0.3Li2MnO3–0.7LiMn1.5Ni0.5O4 composite cathode using conventional organic electrolyte and Li+/PMP-TFSI (N-propyl-N-methyl pyrrolidinium-bis(trifluoromethanesulfonyl) imide) ionic liquid (IL) at 25 °C and 60 °C. At 60 °C, IL electrolyte yields superior specific discharge capacity, cycleability, rate performance and voltage fading characteristics of the composite cathode. We have argued that the superiority of IL electrolyte is related to its relatively higher decomposition temperature. The effect of ILs on the cycle induced layered to nickel free spinel phase transformation in the composite cathode is also investigated by post cycling XRD.

Hard carbon (HC) is a promising anode for sodium-ion batteries. The current hurdles for the HC electrodes are insufficient coulombic efficiency (CE), rate capability, and cyclic stability. This study reveals that an intelligent electrolyte design can effectively overcome these limitations. The sodium salt, concentration, and solvent of the electrolytes are systematically investigated. Incorporation of ethylene carbonate (EC) in propylene carbonate (PC) electrolyte can promote the formation of contact ion pairs and ion aggregates between Na+ and FSI–. At a moderate concentration, the 3 mol dm−3 NaFSI in PC:EC electrolyte with reasonable conductivity and viscosity can lead to the formation of a robust organic–inorganic balanced solid–electrolyte interphase, which is thoroughly examined by electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. With this, the first-cycle and steady-state CE of the HC electrode is increased to 85% and>99.9%, respectively, and the reversible sodiation/desodiation capacities at high rates are markedly improved. In addition, 95% of the initial capacity can be retained after 500 charge–discharge cycles. The proposed electrolyte represents a huge step towards HC electrodes with high effectiveness and durability for electrochemical Na+ storage.

In this study, various nitrogen-containing functional groups, namely, pyridine (N-6), pyrrole (N-5), oxidized N (N-O), and quaternary N (N-Q), are created on activated carbon (AC) surface via melamine, ammonia, and nitric oxide doping methods. N-5 and N-6 groups markedly alter the specific surface area and pore size of AC. N-O is found to affect electrolyte wettability, and the N-Q content is closely associated with AC electronic conductivity. The nitrogen-containing groups do not contribute to pseudocapacitance in propylene carbonate and acetonitrile electrolytes. However, the nitric-oxide-treated carbon (AC-NO) exhibits the best high-rate charge-discharge performance among the investigated materials. The N-Q-enriched and N-5/N-6-depleted AC-NO most effectively suppresses the leakage current and gas evolution of supercapacitors. Online gas chromatography is used to analyze the gaseous species produced from AC electrodes. With an appropriate surface functionality on carbon, the cell voltage can be increased to ∼3 V, increasing the energy and power densities. The aging behavior of the carbon electrodes with and without nitrogen modification after being floated at 2.5 V and 70 °C for 3 days is investigated. An effective strategy for enhancing supercapacitor performance and reliability is proposed.

We demonstrate a facile and effective method, which is low-cost and easy to scale up, to fabricate holey graphene nanosheets (HGNSs) via ultrafast heating during synthesis. Various heating temperatures are used to modify the material properties of HGNSs. First, we use HGNSs as the electrode active materials for electric double-layer capacitors (EDLCs). A synthesis temperature of 900 &deg, C seems to be optimal, i.e., the conductivity and adhesion of HGNSs reach a compromise. The gravimetric capacitance of this HGNS sample (namely HGNS-900) is 56 F&middot, g&minus, 1. However, the volumetric capacitance is low, which hinders its practical application. Secondly, we incorporate activated carbon (AC) into HGNS-900 to make a composite EDLC material. The effect of the AC:HGNS-900 ratio on the capacitance, high-rate performance, and cycling stability are systematically investigated. With a proper amount of HGNS-900, both the electrode gravimetric and volumetric capacitances at high rate charging/discharging are clearly higher than those of plain AC electrodes. The AC/HGNS-900 composite is a promising electrode material for nonaqueous EDLC applications.

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 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.

Co-free high entropy spinel oxide (HESO) with all metals being active for use as anode in Li-ion battery (LIB) is demonstrated for the first time. The HESO, (CrMnFeNiCu)3O4, was synthesized via a simple and scalable hydrothermal method followed by post annealing at temperatures ranging from 800 to 1000 °C. The post annealing provides a simple way to control the particle size and crystallinity. As a result, the missing link between the anode performance and the critical factors of particle size and crystallinity/phase is reported for Co-free high entropy oxide. The HESO anode with balanced crystallinity and particle size displays optimized electrochemical performance. It shows excellent cycling stability (∼99%) after 250 cycles and the excellent rate capability. The structure evolution during cycling was examined using in operando XRD, indicating the existence of nano-crystalline structure after the lithiation/delithiation reactions. This feature is favorable for enhancing electrode cyclability. This study thus opens a new window of opportunity for the development of next-generation LIB electrode materials.

In this study, Si nanoparticles with interweaving carbon nanotubes are wrapped by graphitic sheets to achieve high conductivity and high dimensional stability of a composite anode (denoted as Si/CNT/G) for Li-ion batteries. In addition, an ionic liquid (IL) electrolyte that consists of ether-side-chain pyrrolidinium, asymmetric imide, and a high Li+ fraction is prepared. This electrolyte is for the first time employed for Si-based Li-ion batteries. Decomposition of the ether groups creates organic components in the solid electrolyte interphase (SEI). The high Li+ concentration promotes decomposition of the (fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTFSI−) anions, leading to a LiF- and Li3N-rich SEI. The organic-inorganic balanced SEI is responsible for the excellent charge-discharge properties of the Si/CNT/G anode. The FTFSI− anions exhibit low corrosivity toward the Al current collector and high compatibility with the LiNi0.8Co0.1Mn0.1O2 (NCM-811) cathode. With a charging voltage of 4.5 V, remarkable reversible capacities and cycling stability of NCM-811 in the high-Li+-fraction N-methoxyethyl-N-methylpyrrolidinium/FTFSI IL electrolyte are observed. Differential scanning calorimetry is used to examine the interfacial exothermic reactions between the delithiated NCM-811 and various electrolytes. After 300 charge-discharge cycles, the capacity retention of a Si/CNT/G||NCM-811 full cell with the proposed IL electrolyte is 80% with a Coulombic efficiency of ∼99.9%. These values are significantly higher than those of the conventional carbonate electrolyte cell.

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.

In this work, CuO samples with three different nanostructures, i.e., nanoflakes, nanoellipsoids, and nanorods, are successfully synthesized by a facile and environmentally friendly hydrothermal app...

Transition-metal high-entropy oxides (HEOs) are promising electrode materials for lithium-ion batteries (LIBs) due to their superior electrochemical properties and excellent long-term cycling stability. The performance of HEOs for LIBs is highly correlated with their microstructures, especially their evolution during charging/discharging. However, there is limited information regarding this topic in the literature. In this study, the unique transition behavior of a spinel HEO, (CrMnFeCoNi)3O4, at various states of charge and cycle numbers is examined in detail for the first time. Although the elemental segregation of lithiated HEO particles is observed, the crystal structure remains spinel, leading to great cyclability. Mn nanocrystals form at 0.5 V lithiation and metallic Cr, Fe, Ni, and Co particles form at 0.01 V lithiation. The spinel CrxFe3-xO4 and LiNixCo1-xO2 phases act as seeds that grow by devouring surrounding metal nanoparticles during delithiation. The Mn can reversibly move at least dozens of nanometers across the oxide during lithiation/delithiation. The detailed cycling mechanism is examined using electron energy-loss spectroscopy. The reversible valence state variations of the constituent elements are observed. The results provide an in-depth understanding of the fundamental lithiation/delithiation mechanism of HEO, which will facilitate the development of better multi-element HEOs for Li+ storage applications.

The chloroaluminate ion storage properties of various carbonaceous electrodes, namely soft carbon (SC), hard carbon (HC), activated carbon (AC), and ordered mesoporous carbon CMK-8, are investigated. The effects of carbon crystallinity, surface area, and pore size are systematically examined. Due to their non-ideal graphitic structures, the charge–discharge capacities of SC and HC electrodes are unfavorable for practical applications, although SC, with its relatively high crystallinity, outperforms HC. The high-surface-area AC and CMK-8 exhibit reversible capacities of 59.0 and 100.5 mAh g−1, respectively, at 300 mA g−1. Pore size and geometry play important roles in determining the electrochemical properties. The CMK-8 framework not only serves as an electronic conduction pathway but also provides interpenetrating three-dimensional open channels for electrolyte accessibility and complex AlCl4− anion transport. The charge storage mechanism of the CMK-8 electrode, confirmed by electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry, has a capacitive contribution and a diffusion-controlled intercalation/deintercalation contribution. Based on this unique mechanism, great rate capability, and excellent cyclability of the CMK-8 electrode are demonstrated.

Ionic liquids (ILs), with wide electrochemical stability window, high thermal stability, and nonvolatility, are promising electrolytes for lithium-ion batteries. Among ILs with various types of anion, bis(fluorosulfonyl)imide (FSI−)-based ILs are particularly appealing owing to their high ionic conductivity, low viscosity, and great anode compatibility. However, strong corrosivity of FSI− toward the Al current collector at high potential restricts their practical utilization. In this study, three strategies are implemented to overcome this limitation. Li+ fraction modulation, FSI−/bis(trifluoromethyl)sulfonylimide (TFSI−) molar ratio optimization, and their synergistic combination are used to achieve optimal charge–discharge of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode with an Al substrate. The effects of the IL composition on the electrochemical properties of a graphite anode are also investigated. The proposed IL electrolyte, which lacks any organic solvents, has an optimal Li+/FSI−/TFSI− molar ratio and thus can effectively suppress the Al corrosion, allowing a 5-V graphite//LNMO full cell to be realized. A reversible capacity of ~ 135 mAh g−1 (based on LNMO) and a capacity retention of ~ 85% after 200 cycles are found for the full cell. This study opens a new route for FSI−-based IL electrolytes in the field of high-voltage and high-safety lithium-ion battery applications.

The electrolyte is a key component in determining the performance of sodium-ion batteries. A systematic study is conducted to optimize the electrolyte formulation for a Sb2S3/graphene anode, which is synthesized via a facile solvothermal method. The effects of solvent composition and fluoroethylene carbonate (FEC) additive on the electrochemical properties of the anode are examined. The propylene carbonate (PC)-based electrolyte with FEC can ensure the formation of a reliable solid-electrolyte interphase layer, resulting in superior charge–discharge performance, compared to that found in the ethylene carbonate (EC)/diethyl carbonate (DEC)-based electrolyte. At 60 °C, the carbonate-based electrolyte cannot function properly. At such an elevated temperature, however, the use of an N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid electrolyte is highly promising, enabling the Sb2S3/graphene electrode to deliver a high reversible capacity of 760 mAh g–1 and retain 95% of its initial perform...

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.

Nanosized SnO2 particles (∼2 nm in diameter) are embedded in ordered mesoporous CMK-8 carbon with unique three-dimensional interconnected pore channels and used as a sodium-ion battery (NIB) anode. Due to the CMK-8 confinement effects, the growth of SnO2 is suppressed during synthesis, leading to high material electroactivity. The CMK-8 not only serves as an electronic conducting pathway, but also creates interpenetrating tunnels, which guarantee electrolyte accessibility and thus Na+ transport throughout the electrode. Moreover, the change in the SnO2 volume during sodiation/desodiation can be accommodated by the CMK-8 framework. With a high tap density of ∼1000 mg cm-3 (vs. ∼800 mg cm-3 for the conventional NIB anode, hard carbon), the SnO2/CMK-8 anode shows a high reversible capacity of 800 mA h g-1 and excellent rate capability, delivering 330 mA h g-1 in ∼10 min. The electrode charge storage mechanism is examined using synchrotron X-ray diffraction. We confirm that CMK-8 incorporation can effectively promote the SnO2-Sn conversion reaction and Sn-Na alloying reaction, which are known to be thermodynamically/kinetically difficult, increasing the electrode charge-discharge performance.

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.

© 2019 The Royal Society of Chemistry. 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 elevatederature 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.

Robust Ru-based thin films are successfully fabricated by single- (SA) and multiple-annealing (MA) thermal decomposition methods and are utilized as high-performance electrodes for the supercapacitors. Two critical parameters, the annealing temperature and treatment duration, are engineered for synthesizing stable thin-film electrodes. It is found that the SA thermal decomposition technique at 250 °C for 6 h results in stable RuO2 electrodes with remarkable electrochemical performance. The MA approach consists of 2- and 3-stage thermal treatment steps. The maximal capacitance of MA-treated capacitor reaches as high as 308.8 F g−1. The MA-treated electrodes deliver exceptional rate capability as well as superior cycling stability (93% capacitance retention upon 2000 cycles). The enhanced performance is attributed to the multistep thermal stages along with the layer-by-layer deposition, enabling enhanced heat transfer to individual thin layers. An optimal thermal treatment procedure is assessed empowering enhanced capacitive performance due to high hydrous RuO2·xH2O ratio, reduced crystalline structure, facile electrolyte wetting, and stable adhesion between the deposits and the Ti substrate. The robust design of MA-treated thin film deposits paves the way for synthesizing high-performance electrodes for the supercapacitors.

Supercritical CO2 (SCCO2) fluid, which has gas-like diffusivity, extremely low viscosity, and near-zero surface tension, is used to synthesize SnO2 nanoparticles (a 1-nm diameter is achievable), which are uniformly dispersed and tightly anchored on graphene nanosheets (GNSs) and carbon nanotubes (CNTs). The discharge capacity, rate capability, and cyclic stability of the synthesized SnO2/GNS and SnO2/CNT nanocomposites are compared. This study also tunes the SCCO2 temperature (and thus its fluid density) and finds that this factor crucially affects the SnO2 size and distribution, determining the resulting electrochemical properties. The sodiation/desodiation mechanism of the SnO2/GNS electrode is examined using synchrotron ex situ X-ray absorption and X-ray diffraction techniques, together with transmission electron microscopy. We confirm that while the oxide conversion reaction is reversible, the sluggish Sn–Na alloying/dealloying reaction is responsible for the lower measured capacity as compared to the theoretical value. The first-cycle efficiency loss is mainly attributed to the trapping of Na in the electrode surface solid electrolyte interphase layer.

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.

This work adopts a thermal decomposition (TD) method for fabricating electrochemically exfoliated graphene (ECG)-modified ruthenium oxide thin film as the electrode material for high-performance supercapacitors. The TD technique consists of three consecutive thermal annealing steps for layer-by-layer coating of RuO2/ECG on the Ti substrate. We have demonstrated that the ECG content is the key factor influencing the electrochemical performance of the composite electrodes. The introduction of an appropriate amount of ECG within the composites facilitates the utilization of RuO2 and enables high capacitance, low charge transfer resistance, high rate capability, and superior durability. An optimal ECG content (5 wt.%) mixed with deposited RuO2 forms a three-dimensional conductive framework, capable of offering a synergistic effect for enhanced charge transfer as well as fast ionic diffusion. The specific capacitance of the RuO2/ECG electrode reaches as high as 407 F g−1 while maintaining the high capacitance (> 97%) during prolonged cycling (2000 cycles). The Ragone plot confirms that the RuO2/ECG capacitor enables a high energy density of 10.2 Wh kg−1 while delivering a remarkable power density of 9.2 kW kg−1. The RuO2/ECG composite developed in this work paves the way for designing robust electrode materials for high-performance supercapacitors.

Cubic-phase Li7La3Zr2O12 (LLZO) garnet is a promising solid electrolyte candidate for next-generation Li batteries. As a viable approach, the desired cubic-phase formation of LLZO relies on elemental doping. In this regard, various dopants such as Al and Ga are doped into the LLZO samples, which are synthesized using a solid-state reaction method. The Al- and Ga-doped LLZO can transform to a cubic-phase garnet at 900 °C. After 1200 °C sintering, a Li2ZrO3 impurity phase is found for the Al-doped LLZO pellet, which still shows many voids and inhomogeneous particles on the surface. The Ga doping seems to be attractive since it can effectively stabilize the cubic phase and desired microstructure within 900–1200 °C. Based on the optimized Ga-doped LLZO (LGLZO), various electrolyte architecture designs are developed that include LGLZO pellet electrolytes with and without poly(ethylene oxide) (PEO)-lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)-LGLZO coating, and hybrid electrolyte layers of PEO-LiTFSI, PEO-LGLZO, and PEO-LiTFSI-LGLZO composites. Li//LiFePO4 (LFP) cells with various types of electrolytes are assembled, and their charge-discharge properties are investigated. The all-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell exhibits satisfactory charge storage performance, which has revealed potential for practical applications.

Highly concentrated lithium bis(fluorosulfonyl)imide (LiFSI) salt dissolved in carbonate solvent is employed as a high-performance and robust organic electrolyte for Li-ion batteries. The influences of Li salt type, concentration, and solvent type (such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylene carbonate (EC)) on the electrochemical properties of Li metal and graphite anodes are systematically assessed. A superior electrolyte composition of 5.5 M LiFSI-DMC/EC is achieved, enhancing the anti-flammability, coulombic efficiency, and high rate capability. The optimal efficiency values of Li electrodeposition/stripping utilizing 5.5 M LiFSI-DMC/EC are 97.0% and 94.5% at 0.4 and 6 mA cm−2, respectively. Such an enhanced performance is due to the formation of a three-dimensional ion network, composed of contact ion pairs (CIPs) and ion aggregates (AGGs) in the highly concentrated LiFSI electrolyte, which effectively decreases the number of free solvent molecules and inhibits the formation of undesired dendritic Li structures. Raman spectroscopy is employed to confirm the formation of CIP and AGG compounds within the electrolyte. The electrochemical data of the 5.5 M LiFSI-DMC/EC electrolyte cell demonstrates a remarkable improvement in the specific capacity and rate capability of a graphite anode.

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.

SnO

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.

Mixtures of N-butyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL) and conventional organic carbonate electrolyte are used for high-capacity LiNi0.8Co0.15Al0.05O2 (LNCA) electrodes in Li-ion batteries. Increasing the IL content ratio in the mixtures can increase the electrolyte's thermal stability and retard its flammability. However, the optimal electrolyte composition depends on the operating temperature. At 25 °C, the plain organic electrolyte is preferred due to its highest ionic conductivity among the tested electrolytes. This electrolyte is volatile at 50 °C, and thus the incorporation of 25 wt% IL can improve the cyclic stability of the LNCA electrode. The LNCA dissolution and electrolyte decomposition at 75 °C are clearly suppressed with a high IL ratio in the mixed electrolyte. At such a high temperature, with 75 wt% of IL incorporation a high electrode capacity of 195 mA h g−1 is obtained at 30 mA g−1; 50% of this capacity can be retained when the charge–discharge rate increases to 700 mA g−1. Moreover, less than 20% capacity decay is found after 100 cycles.

Nanosized SnO

Hard carbon (HC), probably the most potential anode for sodium-ion batteries, currently encounters three major obstacles, which are low first-cycle coulombic efficiency, unsatisfactory charge–discharge kinetics, and insufficient cyclic stability. Our developed electrolyte can effectively improve these properties. The concept of using moderately concentrated electrolyte is proposed to deal with the limitations of high cost, low conductivity, and poor viscosity (or wettability) of superconcentrated electrolytes. The crucial roles of ethylene carbonate in the moderately concentrated electrolyte are explored in this study. With the formation of well-balanced robust inorganic–organic solid–electrolyte interphase, the first-cycle as well as steady-state coulombic efficiency of the HC electrode significantly improved to 85% and >99.9%, respectively. This electrolyte significantly improved the charge−discharge capacities at high current rates. Furthermore, after 500 sodiation−desodiation cycles, 95% of the initial capacity can be maintained. The proposed electrolyte design strategies are expected to be applicable to other battery electrodes to boost their energy-storage performance.