Na-ion Capacitors Research Articles

CuS modified graphite from spent Li-ion batteries towards building high energy Na-ion capacitors via solvent-co-intercalation process

Sodium-ion capacitors (NICs) are one of the most modern hybrid energy storage devices, and they involve two different energy storage mechanisms (faradaic and non-faradaic). The NICs are bridging the gap between the Na-ion batteries and the capacitors with enhanced power and energy densities. This work explores a new combination electrode material, i.e., recovered graphite (RG) decorated with copper sulphide (CuS, CS) as the anode for the NIC application, in which graphite undergoes the solvent-co-intercalation process, and CuS adopts the conversion reaction. We also report the possibility of efficient direct recovery of the anode of dead/spent Li-ion batteries and upcycling as a battery-type component for NIC with commercially available activated carbon (AC) as the capacitor-type cathode. First, the Na-storage property is analyzed in the half-cell configuration, where the Na/RG-CS half-cell displayed excellent cyclic stability with a stable specific capacity of 113 mAh g−1 after 500 cycles with >96% coulombic efficiency in ether solutions. With a pre-sodiated form of RG-CS as anode and mass-balanced AC as a cathode, the NIC is fabricated. The NIC displayed a superior energy density of 64.6 Wh kg−1 with ultra-long cyclability for more than 10,000 cycles with >85% capacity retention. The compatibility of the NIC in different environmental conditions is also studied, and the cell renders better performance in all temperature conditions.

Elucidating High Initial Coulombic Efficiency, Pseudocapacitive Kinetics and Charge Storage Mechanism of Antiperovskite Carbide Ni3ZnC0.7@rGO Anode for Fast Sodium Storage in Ether Electrolyte.

To explore novel electrode materials with in-depth elucidation of initial coulombic efficiency (ICE), kinetics, and charge storage mechanisms is of great challenge for Na-ion storage. Herein, a novel 3D antiperovskite carbide Ni3ZnC0.7@rGO anode coupled with ether-based electrolyte is reported for fast Na-ion storage, exhibiting superior performance than ester-based electrolyte. Electrochemical tests and density functional theory (DFT) calculations show that Ni3ZnC0.7@rGO anode with ether-based electrolyte can promote charge/ion transport and lower Na+ diffusion energy barrier, thereby improving ICE, reversible capacity, rate, and cycling performance. Cross-sectional-morphology and depth profiling surface chemistry demonstrate that not only a thinner and more homogeneous reaction interface layer with less side effects but also a superior solid electrolyte interface (SEI) film with a high proportion of inorganic components are formed in the ether-based electrolyte, which accelerates Na+ transport and is the significant reason for the improvement of ICE and other electrochemical properties. Meanwhile, electrochemical and ex situ measurements have revealed conversion, alloying, and co-intercalation hybrid mechanisms of the Ni3ZnC0.7@rGO anode based on ether electrolyte. Interestingly, the Na-ion capacitors (SICs) designed by pairing with activated carbon (AC) cathode exhibit favorable electrochemical performance. Overall, this work provides deep insights on developing advanced materials for fast Na-ion storage.

Decoupling electrolyte strategy for a high-voltage Na-ion hybrid capacitor based on NaFeO2 and activated carbon

Sodium iron dioxide (NaFeO2) with high specific capacity, has been widely used as a kind of electrode materials for Na-ion batteries. When NaFeO2 is used as the battery-type electrode for aqueous Na-ion hybrid capacitors, there are a lot of technical challenges to meet, especially the narrow voltage window limited by the thermodynamic decomposition of water. We propose a novel decoupling electrolyte strategy to suppress the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on the NaFeO2 anode and the activated carbon (AC) cathode respectively, in order to expand the voltage window of the aqueous AC//NaFeO2 Na-ion hybrid capacitor. The alkaline anolyte (2 M NaOH) and the neutral catholyte (1 M Na2SO4) can be decoupled by the cation exchange membrane, which selectively allows the Na+ ions through the membrane to carry the electric currents in the charge/discharge process. The NaFeO2 sample with the stable crystal structure and oxygen vacancy defects, can provide a gravimetric specific capacitance of 101.1 F g−1 at 1 A g−1. Electrochemical kinetic analysis indicates that the capacitor-type behaviour is predominant in the electrochemical energy storage process of the AC//NaFeO2 Na-ion capacitor at the scan rates higher than 40 mV s−1. The AC//NaFeO2 Na-ion capacitor with the stable voltage window of 2 V, can provide an energy density of 12.6 Wh kg−1 at 1 kW kg−1. Due to its inhibiting effects on HER and OER, this decoupling electrolyte strategy holds great potential for constructing high-voltage aqueous energy storage devices.

Defect engineering on BiFeO3 through Na and V codoping for aqueous Na-ion capacitors

Sodium with low cost and high abundance is considered as a substitute element of lithium for batteries and supercapacitors, which need the appropriate host materials to accommodate the relatively large Na+ ions. Compared to Li+ storage, Na+ storage makes higher demands on the structural optimization of perovskite bismuth ferrite (BiFeO3). We propose a novel strategy of defect engineering on BiFeO3 through Na and V codoping for high-efficiency Na+ storage, to reveal the roles of oxygen vacancies and V ions played in the enhanced electrochemical energy storage performances of Na-ion capacitors. The formation of the oxygen vacancies in the Na and V codoped BiFeO3 (denoted as NV-BFO), is promoted by Na doping and suppressed by V doping, which can be demonstrated by XPS and EPR spectra. By the first-principles calculations, the oxygen vacancies and V ions in NV-BFO are confirmed to substantially lower the Na+ migration energy barriers through the space and electric field effects, to effectively promote the Na+ transport in the crystals. Electrochemical kinetic analysis of the NV-BFO//NV-BFO capacitors indicates the dominant capacitive-controlled capacity, which depends on fast Na+ deintercalation-intercalation process in the NV-BFO electrode. The NV-BFO//NV-BFO capacitors open up a new avenue for developing high-performance Na-ion capacitors.

Morphology Variations in Copper Sulfide Nanostructures as Anode Materials for Na-Ion Capacitors

Morphology Variations in Copper Sulfide Nanostructures as Anode Materials for Na-Ion Capacitors

Self-supported, additive-, and binder-free CuS nanowire array for high performing Na-ion capacitor

Na-ion capacitors are considered to be one of the most promising energy storage devices due to its low cost, safe, highly abundance in nature and comparable performance to lithium-ion capacitor. NICs provide high power density as well as good energy density in a single device. However, the lack of host materials to store Na-ions has challenged its commercialization. It is very important to investigate a suitable host material for the Na-ion capacitors. Metal chalcogenides shows significant electrochemical performance towards the NICs. The low capacitance value, stability in the electrolyte is the main drawbacks of the metal chalcogenides. The tailoring in the nanostructures and the component of the electrode can improve the electrochemical performance of Na-ion capacitors. Herein, a liquid-solid chemical method is developed to fabricate self-supported, binder, and additive-free CuS nanowires on porous copper foam electrode, and investigated for the first time as an anode for Na-ion capacitor. Using Cu-foam instead of Cu-foil as a substrate and current collector enhances the 5-fold capacitance (380 F g−1 at 1 A g−1) for Na-ion capacitors, which suggest the replacement of the Cu-foil as current collector. The involved conversion reaction in CuS NWs/Cu-foam is confirmed by in-situ XRD measurement. Since it is observed that the CuS NWs/Cu-foam exhibited good electrochemical and redox features with superior specific capacitance in three-electrode system, a symmetric device is assembled. The symmetric device shows 400 F g−1 of specific capacitance at 1 A g−1 with 28 Wh kg−1 of energy density and 1440 W kg−1 of power density. It is favourable that CuS nanowires are still preserving to the same morphology after 1000 charge-discharge cycles, which is confirmed by the SEM imaging.

Cork-Derived Carbon Sheets for High-Performance Na-Ion Capacitors.

S-doped carbon sheets have been easily prepared by deconstructing the 3D cellular structure of a fully sustainable and renewable biomass material such as cork through a mild ball-milling process. S-doping of the material (>14 wt % S) has been achieved by using sulfur as an earth-abundant, cost-effective, and environmentally benign S-dopant. Such synthesized materials provide large Na storage capacities in the range of 300-550 mAh g-1 at 0.1 A g-1 and can handle large current densities of 10 A g-1, providing 55-140 mAh g-1. Their increased packing density compared to the 3D pristine structure allows them to also provide good volumetric capacities in the range of 285-522 mAh cm-3 at 0.1 A g-1 and 53-133 mAh cm-3 at 10 A g-1. In addition, highly porous carbon sheets (SBET > 2700 m2 g-1) have been produced from the same carbon precursor by rationally designing the chemical activation approach. These materials are able to provide good anion storage capacities/capacitances of up to 100-114 mAh g-1/163-196 F g-1. A sodium-ion capacitor assembled with the optimized S-doped carbon sheets and the highly porous carbon sheets with mass matching ratios provided the best energy/power characteristics (90 Wh kg-1 at 29 kW kg-1) in combination with robust cycling stability over 10,000 cycles, with a capacity fade of only 0.0018% per cycle.

Biomass-derived carbon sponges for use as sodium-ion capacitor electrodes

A high performance Na-ion capacitor has been assembled by using S-doped carbon sponges and highly porous carbon sponges produced from biomass-derived products by using sustainable salt-templating approaches.

A dual carbon Na-ion capacitor based on polypyrrole-derived carbon nanoparticles

N/S-co-coped carbon nanoparticles (mean size ∼ 80–90 nm) have been synthesized by a simple strategy based on the preparation of polypyrrole nanospheres by a room temperature oxidative polymerization process followed by their S doping using elemental sulfur. The developed materials combine a highly disordered microstructure with a high level of N- and S-doping and short solid-state diffusion distances. These characteristics endow the materials with a large number of readily accessible adsorption/insertion sites for sodium storage, yielding thus high reversible capacities (of up to 726 mAh g−1 at 0.1 A g−1) that are well retained at high current rates (up to 188 mAh g−1 at 10 A g−1). The material with optimized Na storage performance was tested as the negative electrode in a sodium-ion capacitor, using as the positive electrode highly porous nanoparticles prepared by KHCO3 activation of the same polypyrrole nanospheres (SBET ∼ 2970 m2 g−1). The sodium-ion capacitor with an optimized positive-to-negative electrode mass ratio of 2 delivers as much as 69 Wh kg−1 at a high-power density of 25 kW kg−1, and can be successfully charged and discharged for 10000 cycles experiencing a capacity loss of only 0.0024% per cycle at 2 A g−1.

Developing potential aqueous Na-ion capacitors of Al2O3 with carbon composites as electrode material: Recycling medical waste to sustainable energy

Energy has become an unavoidable part of our day-to-day life; it can be generated from renewable sources of energy, avoiding the depletion of fossil fuels. Electrochemical energy stored is the most efficient and clean form of energy. The choice of electrode material plays a crucial role in the performance of batteries and supercapacitors. The energy storage devices can be made more sustainable and cost-effective if derived from waste. Rising demand of vaccines in this pandemic eon has accumulated the wastes, which need to be recycled promptly to avoid environmental pollution. In this study, the dumped vaccine-bottle caps which are made up of aluminum have been recovered successfully by leaching method, also in order to enhance the performance of the generated residue, it was supported by carbon to improve the conductivity of the derived metal oxides. The physical and electrochemical properties of the synthesized materials were analyzed by various advanced technologies. The re-synthesized Al2O3/C particles have been applied as electrode in Na2SO4 electrolyte for supercapacitor application. The Al2O3/C electrode delivered a specific capacity of 147 C g−1 in Na2SO4 at a current density of 1 A g−1. The Na-ion capacitor was fabricated with Al2O3/C and vulcan carbon (VC) electrodes then the device performance was optimized. A wide potential window of 2 V with good long-term stability was achieved for the aqueous Na-ion capacitor in 1 M Na2SO4 electrolyte. The device was found to deliver an energy density of 21 W h kg−1 at a power density of 8064 W kg−1. Thus, recycling and reuse of Al2O3/C electrode in Na-ion capacitor application can be incalculable step towards ecofriendly, cost-effective energy storage systems, additionally it also pave way to recycling other waste like used mask or covers.

Eco-Friendly Synthesis of 3D Disordered Carbon Materials for High-Performance Dual Carbon Na-Ion Capacitors.

An eco-friendly and sustainable salt-templating approach was proposed for the production of anode materials with a 3D sponge-like structure for sodium-ion capacitors using gluconic acid as carbon precursor and sodium carbonate as water-removable template. The optimized carbon material combined porous thin walls that provided short diffusional paths, a highly disordered microstructure with dilated interlayer spacing, and a large oxygen content, all of which facilitated Na ion transport and provided plenty of active sites for Na adsorption. This material provided a capacity of 314 mAh g-1 at 0.1 A g-1 and 130 mAh g-1 at 10 A g-1 . When combined with a 3D highly porous carbon cathode (SBET ≈2300 m2 g-1 ) synthesized from the same precursor, the Na-ion capacitor showed high specific energy/power, that is 110 Wh kg-1 at low power and still 71 Wh kg-1 at approximately 26 kW kg-1 , and a good capacity retention of 70 % over 10000 cycles.

Mn3O4 nanoparticles in situ embedded in TiO2 for High-Performance Na-ion capacitor: Balance between 3D ordered hierarchically porous structure and heterostructured interfaces

Sodium-ion hybrid capacitors (SICs) are recognized as a promising new energy storage devices. The design of anodes with high rates to balance the fast desorption/adsorption process in cathode is a key way to construct desirable SICs. Herein, Mn3O4 nanoparticles are in situ embedded in TiO2 to form Mn3O4@TiO2 nanocomposite as anode for SICs. The prepared Mn3O4@TiO2 nanocomposite shows hierarchically porous structure with macropores and mesopores. The Mn3O4 content in the composites can be adjusted to achieve the balance between the hierarchically porous structure and heterostructured Mn3O4/TiO2 interfaces. The optimized Mn3O4@TiO2 with ∼30 wt% Mn3O4 achieves this balance, delivering a large discharge capacity of 247.8 mAh g−1 at 1 A g−1 after 1000 cycles in SIBs. The assembled SICs by using Mn3O4@TiO2-2 as anode and commercial activated carbon as cathode can achieve a high energy and power densities of 106.5 Wh kg−1 and 10140.5 W kg−1, respectively, and an extended cycle life of 92.8 % retention after 5000 cycles. The good Na-ion storage performance mainly arises from the macropores that can provide rapid mass transfer channels, the mesopores that can offer high specific surface areas and highly dispersed Mn3O4 nanoparticles and abundant Mn3O4/TiO2 interfaces that can afford a lot of active sites.

Potassium oxysalt-assistant strategy towards heteroatom-doped porous carbon electrodes for high-performance Na-ion capacitors

Heteroatom-doped porous carbons are regarded as one of the most promising electrode materials for Na-ion capacitors (NICs). However, it is still necessary to further explore low-cost and high-efficiency strategy for their preparation. Herein, two gelatin-derived carbons (GCs) are directly prepared by a potassium oxysalt-assistant strategy. K2SO4 and K3PO4 are employed as multifunctional auxiliaries (template, activator, and dopant) for the preparation of seaweed-like N,S-doped porous carbon (NSGC) and honeycomb-like N,P-doped porous carbon (NPGC), respectively. The NSGC and NPGC are employed as electrodes for NICs and their energy-storage behaviours are detailly investigated. Electrochemical tests combined with in-situ Raman and X-ray diffraction (XRD) measurements reveal that the rich heteroatoms/defects, rational carbon interlayer distance, and hierarchical porous structures of the GCs result in their superior electrode performance in half cells. A pouch NIC constructed with the NSGC anode and the NPGC cathode exhibits high energy density (143 Wh kg−1), high power density (9 kW kg−1), and long lifetime (80% capacity retention after 8000 cycles), showing the good prospect of the carbon electrodes for use in NICs.

MoSe2 nanosheets confined in N-doped carbon fibers as robust and capacitive anode of high performance Na-ion capacitors

Enhancing the rate and cycle performance of anode materials is the key in developing high performance Li/Na/K-ion capacitors. Molybdenum selenide (MoSe2) has been well studied as a potential high rate anode material for Na-ion capacitors based on its lamellar structure and large interlayer space. However, the MoSe2 anode usually suffers from inferior cycling stability especially when directly exposing to electrolyte. Herein, a composite anode material with MoSe2 nanosheets confined in N-doped carbon fibers is prepared by electrospinning and post-selenization process, which exhibits highly capacitive Na ion storage behavior and stable cycle performance in Na-metal half cells. When it is coupled with a pomelo peel-derived porous carbon cathode that is pre-mixed with sodium oxalate as the pre-sodiation additive, the assembled Na-ion capacitors display outstanding energy-power performance, including ultrahigh energy densities of 116 and 79 Wh kg−1 achieved at 197 and 8318 W kg−1, respectively, and a quite good stability in a long term cycle test. These results convincingly demonstrate that the composite with MoSe2 nanosheets confined in N-doped carbon fibers can be promising high capacitive and stable anode material for high performance Na-ion capacitors.

Interlayer-Expanded Titanate Hierarchical Hollow Spheres Embedded in Carbon Nanofibers for Enhanced Na Storage.

Layered titanates are of great potential for hybrid Na-ion capacitors (NICs). However, the poor conductivity and sluggish reaction kinetics are the critical issues for the practical applications of titanates. Herein, an approach to synthesize magnesium titanate hierarchical hollow spheres embedded in carbon nanofibers (denoted as MTO@C) by electrospinning coupled with interlayer engineering processes is reported. 3D conductive carbon framework helps to enhance the electronic conductivity for binder-free electrode, while the expanded interlayer spacing of titanate hierarchical hollow spheres via the incorporation of Mg2+ ions help to reduce the charge transfer resistance and expose more active sites for Na storage. The interconnected hollow spheres can effectively accommodate the volume expansion during the repeated cycles. The results have shown that the MTO@C electrode can deliver a high capacity of 136mAhg-1 at 1Ag-1 with long lifespan. The assembled NIC device with MTO@C as anode and active carbon as cathode produces a high energy density of 110.3Whkg-1 at 112Wkg-1 and a high power density of 5380Wkg-1 at 41.9Whkg-1 , together with a high capacity retention of 80% after 5000 cycles.

Designing Na2Zn2TeO6-Embedded 3D-Nanofibrous Poly(vinylidenefluoride)-co-hexafluoropropylene-Based Nanohybrid Electrolyte via Electrospinning for Durable Sodium-Ion Capacitors

A novel solid-state electrospun nanohybrid polymer membrane electrolyte (esHPME) for sodium-ion capacitors to improve the ionic conductivity and energy density is demonstrated. A Na2Zn2TeO6 (NZTO)-embedded 3D-nanofibrous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanohybrid electrolyte has been reported as a high-sodium-ion conducting electrolyte for sodium-ion capacitor applications. PVDF-HFP based esHPMEs with different loadings (0, 5, 10, and 15 wt %) of NZTO nanoparticles are prepared by electrospinning and further activated by soaking them in a liquid electrolyte (1M of NaPF6 in EC/DMC, 1:1 v/v) to employ as the electrolyte-separator. Among the prepared esHPMEs, the 10 wt % NZTO-embedded esHPME exhibits the maximum ionic conductivity and electrochemical window of 2.5 V. The influence of hybridization between inorganic nanoparticles (NZTO) and the organic polymer (PVDF-HFP) is investigated by physical characterization and their electrochemical performance. A coin cell-type Na-ion supercapacitor is fabricated using battery-type Na0.67Co0.7Al0.3O2 as the anode and activated carbon as the cathode. The fabricated Na-ion supercapacitor [Na0.67Co0.7Al0.3O2/esHPME (10 wt % NZTO)/AC] delivered an energy density of 99.375 F g–1 at 1 A g–1 current density and exhibits 84% of capacity retention up to 1000 cycles of charge discharging. The Na-ion capacitor showed a maximum energy density and power density of 35.33 W h kg–1 and 1.6 kW kg–1, respectively. Thus, the present work demonstrates the great potential of the electrospun PVDF-HFP/NZTO-based nanohybrid membrane electrolyte for durable Na-ion capacitors.

High energy Na-Ion capacitor employing graphitic carbon fibers from waste rubber with diglyme-based electrolyte

Co–intercalation process using glyme-based solvents has brought new prospects for the reversible Na-intercalation into the graphitic materials. We report a high-energy Na-ion capacitor (SIC) with graphitic carbon nanofibers (GCNF) as a battery-type component obtained from the depolymerization of waste rubber. The kinetic study reveals that ~ 51% contribution is originated from the diffusion-controlled Faradaic mechanism for GCNF compared to the ~ 61% for commercial graphite powder. The synthesis procedure and less crystalline nature of the GCNF lead to the lowered intercalation potential, and extended Na-ion storage capacity in the lower potential region (vs. Na+/Na) which is significant compared to the graphite powder. Further, the half-cell delivered a discharge capacity of ~ 118 mAh g−1 irrespective of the applied current rate, which signifies the importance of this concept. In a SIC configuration with activated carbon, the SIC renders an energy density of 55.58 Wh kg−1 at 25 °C. In addition, exceptional low-temperature performance (<10 °C) is noted with a maximum energy density of 54.69 Wh kg−1 and > 97% capacity retention after 5000 cycles. This low-temperature performance, high energy density, and exceptional cyclability certainly offer a unique hybrid charge storage system that eventually explores the possibility of using graphitic carbon fibers towards balanced energy and power capabilities. On a lighter note, this study also provides the opportunity to handle the waste materials effectively for sustained charge storage applications.

Vacant Manganese-Based Perovskite Fluorides@Reduced Graphene Oxides for Na-Ion Storage with Pseudocapacitive Conversion/Insertion Dual Mechanisms.

Na-ion capacitors (NICs) and Na-based dual-ion batteries (Na-DIBs) have been considered to be promising alternatives to traditional lithium-ion batteries (LIBs) because of the abundance and low cost of the Na-ion, but their energy density, power density and life cycle are limited. Herein, dual-vacancy (including K+ and F- vacancies) perovskite fluoride K0.86 MnF2.69 @reduced graphene oxide (rGO; recorded as Mn-G) as anode for NICs and Na-DIBs has been developed. The special conversion/intercalation dual Na-ion energy storage mechanism and pseudocapacitive dynamics are analyzed in detail. The Mn-G//AC NICs and Mn-G//KS6 Na-DIBs delivered a maximum energy density of 92.7 and 187.6 W h kg-1 , a maximum power density of 20.2 and 21.12 kW kg-1 , and long cycle performance of 61.3 and 68.4 % after 1000 cycles at 5 A g-1 , respectively. Moreover, Mn-G//AC NICs and Mn-G//KS6 Na-DIBs can work well over a wide range of temperatures (-20 to 40 °C). These results make it competitive in Na-ion storage applications with high energy/power density over a wide temperature range.

Dual-carbon Na-ion capacitors: progress and future prospects

Dual-carbon-based sodium-ion capacitors (DC-NIC) engage carbonaceous electrodes as anode and cathode. High power and energy densities make it a suitable candidate for EV applications with capability to provide clean, green, and cost-effective energy.

Aqueous Na-ion capacitor with CuS graphene composite in symmetric and asymmetric configurations

The symmetric device shows a maximum specific energy density of 30 W h kg−1at a specific power density of 380 W kg−1, which was reduced to 4 W h kg−1at a highest specific power density of 4224 W kg−1.