NaClO4 Electrolyte Research Articles

Optimizing O3-type cathode materials with modified collector for sodium-ion batteries: Insights of interfacial reaction between collector and electrolyte

In order to obtain a sodium-ion battery with high energy density and good kinetic properties, high specific capacity of O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM111) cathode material and high ion migration rate of NaClO4 electrolyte are selected. The cycling performance of NaNi1/3Fe1/3Mn1/3O2 is tested at 0.5 C after pre-activation at 0.1 C. During the electrochemical testing, a kind of side reaction products are found on the surface of the electrode piece. Through Scanning emission microscopy (SEM), X-ray photoelectron spectroscopy analysis (XPS) and Raman tests, side reaction products are found on the current collector with NaClO4 and Fluoroethylene carbonate (FEC). The protective layers are constructed on the surface of Al foil to effectively avoid the occurrence of side reactions. The prepared half cells have excellent stability and rate performance by the modified current collector. After 100 cycles at 0.5 C, the specific discharge capacity is 106 mA h g−1. The specific discharge capacity at 5 C is 107.2 mA h g−1. This measure provides a new idea to the NFM111 cathode materials electrochemical test and offers research basis for the design of sodium ion battery with excellent dynamic performance. Meanwhile, it also eliminates industry doubts about the performance of sodium-ion batteries.

Benchmarking the Performance of Lithium and Sodium‐Ion Batteries With Different Electrode and Electrolyte Materials

ABSTRACTSodium‐ion (Na‐ion) batteries are considered a promising alternative to lithium‐ion (Li‐ion) batteries due to the abundant availability of sodium, which helps mitigate supply chain risks associated with Li‐ion batteries. Many studies have focused on the design of Li‐ion batteries, exploring their energy, power, and cost aspects. However, there is still a lack of similar research conducted on Na‐ion batteries. A comparison of the cell voltage characteristics and rate capability of sodium and lithium‐ion batteries using different types of electrodes and electrolytes. For sodium‐ion batteries electrolytes used are NaPF6 and NaClO4 and electrodes used are NaCoO2, NaNiO2, NaFePO4, (Na3V2(PO4)3), graphite, hard carbon, sodium metal, and sodium titanate. For lithium‐ion batteries with LiPF6 and KOH electrolytes and electrodes as LiCoO2, NMC, LVP, Li2MnSiO4, graphite, silicon, lithium titanate (LTO), lithium metal. A thorough analysis of six important performance metrics is part of the investigation: Ragone plots, Electrolyte salt concentration versus spatial coordinate, electrolyte potential versus spatial coordinate, Cell voltage versus battery cell state of charge, Cell voltage versus time, and state variable versus time. Comparing operating voltage and rated capacity NMC and graphite is selected for lithium‐ion batteries as this combination provides operating voltage up to 4.2 V and a rated capacity of 275 Wh/kg, for sodium‐ion for NaCoO2 and hard carbon which has an operating voltage of 2.5–3.8 V and rated capacity around 200 Wh/kg and another combination of electrode as NaFePO4 and sodium metal with NaClO4 electrolyte has a maximum operating voltage of 2.8–3.8 V and rated capacity around 200 Wh/kg. This paper shows significant influence of electrolyte selection on battery performance. The Ragone plots demonstrate that LiPF6 electrolytes in lithium‐ion batteries and NaPF6 electrolytes in sodium‐ion batteries both exhibit superior specific energy densities compared to their KOH and NaClO4 counterparts, respectively. The work presented in this paper encourages researchers to select alternate electrolytes and electrodes for lithium‐ion and sodium‐ion batteries in order to obtain optimal device performance.

Sequential growth controlled copper vanadate nanopebbles embedded thin films: Electrode to asymmetric supercapacitive device assembly

Supercapacitor performance critically relies on the design of electrodes with both superior electrochemical and mechanical properties. In this study, we present a cost-effective and scalable approach for the synthesis of copper vanadate (Cu3V2O8) nanopebbles integrated into a thin film, tailored for supercapacitor applications. The synthesis was accomplished using the successive ionic layer adsorption and reaction (SILAR) method, which enabled precise control over the deposition of Cu3V2O8 on a stainless steel (SS) substrate. Detailed structural, morphological, and elemental characterizations confirm the successful formation and reveal critical insights into the chemical bonding and oxidation state at material. The supercapacitive performance of Cu3V2O8 electrode has been evaluated in an aqueous NaClO4 electrolyte to assess pseudocapacitive behavior. The Cu3V2O8 electrode exhibited a specific capacitance of 443 F g−1 at 5 mV s−1 scan rate. Additionally, liquid configured an asymmetric device was designed using Multiwalled carbon nanotubes (MWCNT) combined with Cu3V2O8, yielding a specific capacitance of 116 F g−1 at 5 mV s−1 with an energy density of 8.43 Wh kg−1 and a power density of 345.4 W kg−1, while maintaining capacitance retention of 76 % even after 4000 cycles as stability test. This work highlights the potential of Cu3V2O8 based materials for excellent performance of new avenues for energy storage.

Molecular Dynamics Simulation Investigation of Freezing Point Depression in NaClO4 Electrolyte Solution by CaCl2.

The development of inorganic antifreeze electrolytes is of paramount importance for the application of sodium-ion batteries under low-temperature conditions. However, there is little reported about their molecular mechanism for lowering the freezing point of electrolytes. Therefore, this study explores the mechanism by which CaCl2 lowers the freezing point of the NaClO4 electrolyte. Hexagonal ice (ice Ih) was used as the ice seed, and CaCl2 was selected as the antifreeze agent. The coexistence system of ice and solution was constructed to simulate the freezing process. It was found that there is ion rejection at the ice layer, with ions predominantly distributed in the solution. Over time, ions form an ion adsorption layer at the ice-solution interface. The radial distribution function (RDF) and spatial distribution function (SDF) of Na+, ClO4-, Ca2+, and Cl- revealed that ions form the first solvation shells with water molecules. The interaction energy between ions and water molecules is greater than that between ice nuclei and water. Therefore, ions are better able to maintain the stability of their solvation shells and inhibit the growth of ice Ih through a mechanism of competition for water molecules. Furthermore, the dissolution free energy of Na+ and Ca2+ in the aqueous phase was studied. The results indicated that Ca2+ has a stronger affinity for water molecules than Na+, making it more competitive in competing for water with ice Ih. Therefore, CaCl2 in NaClO4 solution can reduce the freezing point. This work provides a molecular-level understanding of how CaCl2 reduces the freezing point of NaClO4 solution, which is beneficial for designing strategies for low-temperature electrolytes.

Highly matched electrode for all-solid-state sodium-ion fiber hybrid supercapacitor with wide temperature and high energy density

In order to solve the kinetic mismatch problem of hybrid supercapacitors, a simple and effective assembly technology for wide temperature all-solid-state sodium-ion fiber hybrid supercapacitor is proposed based on anode and cathode with optimal volume capacity ratio and complementary potential windows. Ti3C2Tx fiber anode is produced by wet spinning in acetic acid bath. It reveals an excellent volume capacity of 406 F cm−3, good cycle stability of 90 % retention in 1 M NaClO4 electrolyte, high conductivity of 3303 S cm−1, and tensile strength of 80 MPa. NaV3O8/rGO (NVO/rGO) fiber cathode is obtained by wet spinning and hydrothermal treating, exhibiting high matched volumetric capacitance and improved rate performance. Moreover, a wide temperature all-solid-state sodium-ion fiber hybrid supercapacitor (PVA EGHG NVO/rGO//Ti3C2Tx AFSIC) is assembled using polyvinyl alcohol ethylene glycol hydrogel (PVA EGHG) as separator and electrolyte. The AFSIC shows an outstanding volumetric specific capacitance of 76 F cm−3 at 0.1 A cm−3, and a maximum volumetric energy density of 30.6 mWh cm−3 at a power density of 83.2 mW cm−3. In addition, it can be bend to diverse degrees without significant change in its electrochemical performance. In addition, the AFSIC exhibites exceptional capacitance and outstanding flexibility in a wide temperature range of −40 to 60 °C, showing that the PVA EGHG NVO/rGO//Ti3C2Tx AFSIC has wide prospect in the area of wearable electronic components.

Solvothermally Synthesized Nickel-Doped Marigold-Like SnS2 Microflowers for High-Performance Supercapacitor Electrode Materials.

Two-dimensional transition-metal dichalcogenides (TMDs) have emerged as promising capacitive materials for supercapacitors owing to their layered structure, high specific capacity, and large surface area. Herein, Ni-doped SnS2 microflowers were successfully synthesized via a facile one-step solvothermal approach. The obtained Ni-doped SnS2 microflowers exhibited a high specific capacitances of 459.5 and 77.22 F g-1 at current densities of 2 and 10 A g-1, respectively, in NaClO4 electrolyte, which was found to be higher than that of SnS2-based electrodes in various electrolytes such as KOH, KCl, Na2SO4, NaOH, and NaNO3. Additionally, these microflowers demonstrate a good specific energy density of up to 51.69 Wh kg-1, at a power density of 3204 Wkg-1. Moreover, Ni-doped SnS2 microflowers exhibit a capacity retention of 78.4% even after 5000 cycles. Better electrochemical performance of the prepared electrode may be attributed to some important factors, including the utilization of a highly ionic conductive and less viscous NaClO4 electrolyte, incorporation of Ni as a dopant, and the marigold flower-like morphology of the Ni-doped SnS2. Thus, Ni-doped SnS2 is a promising electrode material in unconventional high-energy storage technologies.

CO2-regulated, ultrahigh-concentration aqueous electrolytes for high energy and power of supercapacitors

Aqueous supercapacitors are recognized for their high power density, ultralong cycle life, and reliable safety. However, their widespread applications are impeded by low energy density arising from the narrow electrochemical stability windows of aqueous electrolytes. Although the use of high-concentration aqueous electrolytes can mitigate this issue, sluggish ion diffusion within these electrolytes results in decreased capacitance and power performance of supercapacitors. Herein, we propose the simultaneous achievement of high energy and power density of supercapacitors using carbon dioxide (CO2)-regulated high-concentration aqueous electrolytes. The introduction of CO2 enables greater capacitance in sodium perchlorate (NaClO4)-containing electrolyte than sodium nitrate (NaNO3)- and sodium bis (fluorosulfonyl)imide (NaFSI)-containing electrolytes. This is attributed to the increased H+ concentration and the unique interaction between CO2 and ClO4−, leading to a denser counter-ion arrangement on the electrode surface. Notably, the CO2-regulation strategy is effective in a nearly-saturated 17 mol kg−1 NaClO4 electrolyte, showing an increase in energy density of up to 27.8 %, while maintaining a high 2.2 V operating voltage and a long >20 000 cycle life of supercapacitors. This study offers a distinct insight into the regulation of high-concentration aqueous electrolytes for comprehensive enhancement of supercapacitor performance.

Heteroatom(S) (N, S, P) Co‐Doped Reduced Graphene Oxide‐Based Binder‐Free Novel Energy Storage Electrode Material for High Energy Density Supercapacitor

AbstractThis manuscript reports a one‐pot synthesis of ternary heteroatoms (N/S/P) co‐doped reduced graphene oxide as an electrode material by simultaneous reduction/doping of/into graphene oxide employing eco‐friendly natural molecule(s) (thiamine monophosphate (TM) and thiamine pyrophosphate (TP)) under mild heating (≤60 °C) and near‐neutral pH (≤8) conditions. It produces N, S, P co‐doped rGO‐TM and N, S, P co‐doped rGO‐TP nanohybrids displaying a well‐connected porous microstructure with significantly doped atomic(%) ‐N (10.0%), S (4.1%), P (0.1%) and N (6.7%), S (2.0%), and P (0.5%), respectively. The symmetric supercapacitor designed using N, S, P‐rGO‐TM‐10 in water‐in‐salt 17 m NaClO4 electrolyte exhibits stable cell voltage of 3.0 V, superb gravimetric energy density (areal energy density) of 47.9 Wh kg−1@522.8 W g−1 (0.2363 Wh cm−2@ 2.5 W cm−2); the excellent cyclic stability (88.8 %) and Coulombic efficiency (99.2%) even after 20 000 cycles. Their energy storage capability is corroborated by the illumination of 109 white LEDs upon lighting a single SSC for 50 s each, driving a motor to run a fan, and forming the tandem device by joining three such cells in series.

Hydrogen bond-induced configuration and electron transfer on layered double hydroxide for high-performance sodium-iodine batteries

Sodium-iodine (Na-I2) batteries are appealing electrochemical energy storage devices owing to the low cost and high energy density. However, they are constrained by shuttle effect due to the high solubility of iodine/iodide in electrolyte and the sluggish reaction kinetics of I2 ↔ 2I−. Accordingly, Na-I2 batteries with superficial redox mechanism and superior rate capability almost seem impossible. Herein, a layered double hydroxide (LDH) formulated as Ni2Al(OH)4.2(CO3)1.4·2H2O (NiAl-LDH) and an iodine-decorated LDH (NiAl-LDH-I2) were synthesized. When used as the Na-I2 battery cathode in the NaClO4 electrolyte, NiAl-LDH-I2 exhibits an increasing capacity, accompanied with a transformation from the (de)intercalation to the surface-controlled (pseudo)capacitive behavior. This is ascribed to irreversible reduction reaction of ClO4− → Cl− and the formation of I+-Cl− on the LDH surface over an overcharge process. Density functional theory (DFT) calculations reveal that the adsorbed I2 and I-Cl both exhibit zigzag chain-like configurations, which are not easily intercalated into the interlayer space of NiAl-LDH, but can be anchored on the NiAl-LDH surface via multiple hydrogen bonds. These hydrogen bonds can stabilize I+ to boost the multi-electron redox reaction of 2I− ↔ I2 ↔ 2I+. The adsorbed I2 is activated by the electron transfer and the elongation of I-I bond, then fasten the reaction kinetics of I2 ↔ 2I−. Therefore, NiAl-LDH-I2 shows outstanding rate capability and cycling performance with a large capacity of 310/ 210 mAh/g at 0.3/ 1.5 A/g and excellent capacity retention over 2700 cycles.

Dual–ion symmetric hybrid supercapacitor built by vanadium oxide with expanded interlayers: The intercalation of cation–anion pair and reversible redox of anion excited by Al3+

The development of aluminum ion batteries (AIBs) is retarded by the low capacity of intercalation cathode and ineffective aluminum dissolution/deposition at Al anode. To solve the issues, benzoquinone(BQ)–preinserted hydrated vanadium oxide formulated as (BQ)0.04V2O5·0.87H2O (BQ-VO) with a large interlayer spacing of 13.3 Å was synthesized, which was used as both cathode and anode with Al(ClO4)3 acetonitrile (AN) electrolyte to fabricate a symmetric aluminum–ion supercapacitor. BQ-VO delivers a large capacity of ~152 mAh g−1 at 0.2 A g−1 in the range of 0–1.5 V, which is associated with the intercalation of ion (such as ClO4−, Al3+ or Al3+ − ClO4− pair) into BQ-VO and the reversible redox reaction of ClO4− ↔ Cl−, giving rise to a novel symmetric dual–ion hybrid supercapacitor. The reversible conversion of ClO4− ↔ Cl− is not observed in NaClO4 AN electrolyte, which is only excited by Al3+, leading to a continuous increasing capacity in the early stage of the cycling test. On the contrary, in the NaClO4 AN electrolyte, BQ-VO illustrates a surface-controlled capacitive performance with excellent cycling stability. Molecular dynamic (MD) simulations reveal that Al3+ and Na+ possess different solvation/anion sheaths, leading to different electrochemical performances of BQ-VO in the Al(ClO4)3 and NaClO4 electrolytes. The present work provides a routine to utilize the redox reaction of halide for energy storage.

Fully-Printed Flexible Aqueous Rechargeable Sodium-Ion Batteries.

The flexible aqueous rechargeable sodium-ion batteries (ARSIBs) are a promising portable energy storage system that can meet the flexibility and safety requirements of wearable electronic devices. However, it faces huge challenges in mechanical stability and facile manufacturing processes. Herein, the first fully-printed flexible ARSIBs with appealing mechanical performance by screen-printing technique is prepared, which utilizes Na3V2(PO4)2F3/C (NVPF/C) as the cathode and 2% nitrogenous carbon-loaded Na3MnTi(PO4)3/C (NMTP/C/NC) as the anode. In particular, the organic co-solvent ethylene glycol (EG) is cleverly added to 17m (molkg-1) NaClO4 electrolyte to prepare a 17 m NaClO4-EG mixed electrolyte. This mixed electrolyte can withstand low temperatures of -20°C in practical applications. Encouragingly, the fully-printed flexible ARSIBs (NMTP/C/NC//NVPF/C) exhibit a discharge capacity of 40.1mAhg-1, an energy density of 40.1Whkg-1, and outstanding cycle performance. Moreover, these batteries with various shapes can be used as an energy wristband for an electronic watch in the bending states. The fully-printed flexible ARSIBs in this work are expected to shed light on the development of energy for wearable electronics.

In-situ synthesis of N, S co-doped electrode material by an environmentally benign method towards designing of high voltage (3.0 V) binder-free sustainable aqueous symmetric supercapacitor

In aqueous electrolyte based symmetric supercapacitor, the decomposition of water to evolve hydrogen and oxygen occurs in relatively lower potential window, thereby, limits its cell voltage and needs to be modified so as to achieve high energy density. This manuscript reports a novel greener approach for an in-situ synthesis of N, S co-doped reduced graphene oxide (N, S co-doped rGO-10/20) nanohybrids as porous electrode material for designing a binder-free and up-scaled mass-loaded (5.0 mg cm−2) high voltage (3.0 V) aqueous symmetric supercapacitor in water-in-salt (WIS), 17 m NaClO4 electrolyte. A fairly rich co-doping/integration of heteroatoms (N (7.2 %) and S (1.5 %)) into the rGO matrix takes place through the formation of C-N, C-S and C-SOx-C bonds. The N, S co-doped rGO-20 nanohybrids in three-electrode system shows the pseudocapacitive behavior with the electrochemical stability of potential window (ESPW) of 3.0 V. In two electrodes set-up, the optimized aqueous symmetric supercapacitor cell (SSC) in WIS shows the superb cell voltage at 3.0 V (highest reported to-date), a fairly high areal energy density@areal power density (0.256 (mWh cm−2)@5.239 (mW cm−2)) at 0.7 A/g with excellent capacitance retention (93.7 %) and Coulombic efficiency (99.3 %) after 20 k cycles. Its energy storage capability is further validated by illumination of 125 white LEDs and 91 green LEDs upon lighting a single SSC for 50 s each and forming the tandem device with high cyclic stability (102 %). Under open circuit, SSC exhibits self-discharge to 2.4 V without any further appreciable discharge till 24 h.

Development of a New Type of Electrochemical Reactor for Low Temperature Lime and Cement Production

The cement industry is responsible for more than 8% of the global CO2 emissions, making it one of the largest contributors to global warming. Two-thirds of these emissions are coming from unavoidable process gases caused by the calcination reaction of limestone (CaCO3). The remaining emissions are mainly coming from the combustion of fossil fuels. Due to the high temperature requirement (≈1500°C), direct electrification is difficult to consider. For these two reasons, the cement industry is therefore known as a challenging sector to decarbonize.A new electrochemical pathway for cement production has gained prominence in the scientific literature in recent years [1]. This technology has the potential to electrify the cement and lime production while producing at the same time valuable gases (O2, CO2, H2). It is based on a new type of hybrid electrolyser capable of working with solid, liquid and gaseous phases. Thanks to the acidity generated by water oxidation at the anode, the solid limestone feed, precursor of cement, is being dissolved. This dissolution produces pure CO2 which is mixed with pure O2 generated by electrolysis and which is easily captured for later use. The calcium ions are then migrating towards the cathode under the effect of the electric field. The OH- hydroxyl ions, produced at the cathode by water reduction, meet the calcium ions to form the final solid product, hydrated lime (Ca(OH)2). This lime can be used as such or converted into cement by additional steps.In this research, a laboratory-scale setup has been developed to study the feasibility of such a process. Different geometries have been tested and the main operational parameters affecting the different steps of the process have been investigated. Our results show first of all the formation and stabilization of a pH gradient within the electrolyser, which allows at the same time for the complete dissolution of CaCO3 in the acidic anodic environment while producing a white precipitate of Ca(OH)2 at the cathode. The setup also presents ideal faradaic efficiencies when using an IrO2 coated titanium anode and a nickel cathode in a 1M NaClO4 electrolyte. Alternative electrode materials, including a 316L stainless steel anode and an Inconel 718 cathode, have been considered as well. Finally, it was shown that the energetic efficiency can be further improved by pushing the kinetics of the dissolution and precipitation reactions through increasing the mobility of calcium ions, using Ca-based electrolytes, like Ca(ClO4)2. Based on our results, all the elementary concepts behind the hybrid electrolyser have been established, and a first blueprint of a continuous industrial process will be proposed.[1] - L. D. Ellis, et al. (2019). Toward electrochemical synthesis of cement—An electrolyzer-based process for decarbonating CaCO3 while producing useful gas streams. PNAS , 117, 12584-12591. Figure 1

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors with high energy density and wide temperature range

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors (PVA EGHG Ti3C2Tx FSCs) with high energy density and wide temperature range are constructed by using polyvinyl alcohol (PVA)-ethylene glycol hydrogel (EGHG)-sodium perchlorate (NaClO4) as electrolyte and separator, and Ti3C2Tx fiber as electrodes. Ti3C2Tx fiber is prepared using 130 mg mL−1 Ti3C2Tx nanosheet ink as an assembly unit in a coagulation bath of isopropyl alcohol (IPA) and distilled water with 5 wt% CaCl2 by a wet spinning method. The prepared Ti3C2Tx fiber exhibits a specific capacity of 385 F cm−3 and a capacitance retention of 94 % after 10,000 cycles in 1 M NaClO4 electrolyte. The assembled PVA EGHG Ti3C2Tx FSCs deliver a specific capacitance of 41 F cm−3, a volumetric energy density of 5 mWh cm−3, and a capacitance retention of 92 % after 500 times continuous bending. Furthermore, it shows good flexibility and excellent capacitance over a wide temperature range of −40 to 40 °C and maintains its electrochemical performance under varying degrees of bending. This study provides a viable strategy for designing and assembling all-solid-state neutral symmetric fiber supercapacitors with high energy density and wide temperature range.

Ozone- and Hydroxyl Radical-Mediated Oxidation of Pharmaceutical Compounds Using Ni-Doped Sb-SnO2 Anodes: Degradation Kinetics and Transformation Products.

Electrochemical oxidation provides a versatile technique for treating wastewater streams onsite. We previously reported that a two-layer heterojunction Ni-Sb-SnO2 anode (NAT/AT) can produce both ozone (O3) and hydroxyl radical (•OH). In this study, we explore further the applicability of NAT/AT anodes for oxidizing pharmaceutical compounds using carbamazepine (CBZ) and fluconazole (FCZ) as model probe compounds. Details of the oxidation reaction kinetics and subsequent reaction products are investigated in the absence and presence of chloride (Cl-) and sulfate (SO4 2-). In all cases, faster or comparable degradation kinetics of CBZ and FCZ are achieved using the double-layered NAT/AT anode coupled with a stainless steel (SS) cathode in direct comparison to an identical setup using a boron-doped diamond anode. Production of O3 on NAT/AT enhances the elimination of both parent compounds and their transformation products (TPs). Very fast CBZ degradation is observed during NAT/AT-SS electrolysis in both NaClO4 and NaCl electrolytes. However, more reaction products are identified in the presence of Cl- than ClO4 - (23 TPs vs 6). Rapid removal of FCZ is observed in NaClO4, while the degradation rate is retarded in NaCl depending on the [Cl-]. In SO4 2--containing electrolytes, altered reaction pathways and transformation product distributions are observed due to sulfate radical generation. SO4 ·- oxidation produces fewer hydroxylated products and promotes the oxidation of aldehydes to carboxylic acids. Similar trend in treatment performance is observed in mixtures of CBZ and FCZ with other pharmaceutical compounds in latrine wastewater and secondary WWTP effluent.

Ion dynamics into different pore size distributions in supercapacitors under compression

Compressing supercapacitor (SCs) electrode is essential for improving the energy storage characteristics and minimizing ions’ distance travel, faradaic reactions, and overall ohmic resistance. Studies comprising the ion dynamics in SC electrodes under compression are still rare. So, the ionic dynamics of five aqueous electrolytes in electrodes under compression were studied in this work for tracking electrochemical and structural changes under mechanical stress. A superionic state is formed when the electrode is compressed until the micropores match the dimensions with the electrolyte’s hydrated ion sizes, which increases the capacitance. If excessive compression is applied, the accessible pore regions decrease, and the capacitance drops. Hence, as the studied hydrated ions have different dimensions, the match between ion/pore sizes differs. To the LiOH and NaClO4 electrolytes, increasing the pressure from 60 to 120 and 100 PSI raised the capacitance from 13.5 to 35.2 F g−1 and 30.9 to 39.0 F g−1, respectively. So, the KOH electrolyte with the lowest and LiCl with the biggest combination of hydrated ion size have their point of maximum capacitance (39.5 and 36.7F g−1) achieved at 140 and 80 PSI, respectively. To LiCl and KCl electrolytes, overcompression causes a drop in capacitance higher than 23%.

Flexible Solid-State Aqueous Sodium-Ion Capacitor Using Mesoporous Self-Heteroatom-Doped Carbon Electrodes

Supercapacitors find numerous applications such as in consumer electronics, peak power demands, capturing surge power, etc. Various types of carbon materials are explored as electrode material. In this work, disordered mesoporous carbon was synthesized from expired medicinal capsule covers by sulfonation and subsequent chemical activation was carried out with KOH. Powder X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller studies, and X-ray photoelectron spectroscopy were utilized to characterize the generated carbon which confirmed the disordered carbon had a large surface area with stratified pores. The testing for electrochemical charge storage was conducted on a three-electrode setup comprising an aqueous 1 M NaClO4 electrolyte that exhibited a high 324 F g–1 specific capacitance at 0.4 A g–1, revealing suitability for sodium-ion ultracapacitor. Consequently, CR2032 coin-type sodium-ion capacitors were fabricated using both aqueous and nonaqueous electrolytes. The laboratory prototype capacitor with the aqueous electrolyte delivered 42 Wh kg–1 specific energy at 179 W kg–1 specific power. Besides, the capacitor with the nonaqueous electrolyte showed a remarkable 54.3 Wh kg–1 specific energy at 540 W kg–1 specific power. The Coulombic efficiency exhibited by both devices was about 99% even at the 10000th charge–discharge cycle. The amplified charge storage performance of the disordered carbon was ascribed to the presence of homogeneous mesopores that led to enhanced accessibility of the electrode/electrolyte contact area. According to the results of the power law and Dunn’s approach, the mesoporous carbon electrode was found to have a considerable diffusive charge storing mode involving Na+ intercalation in the sodium-ion nonaqueous ultracapacitor. A green-light-emitting diode could run continuously for 16 min on a single charge using the laboratory prototype CR-2032 coin-type nonaqueous ultracapacitor. Interestingly, a homemade solid-state flexible sodium-ion ultracapacitor was also fabricated that impressively manifested 13.7 Wh kg–1 specific energy at 180 W kg–1 specific power in 180° bent angle.

Effect of electrolyte and carbon material on the electrochemical performance of high-voltage aqueous symmetric supercapacitors

The energy storage capability of the aqueous supercapacitors is mainly attributed to the relatively low operating voltage of the device, as the thermodynamic decomposition voltage of water is 1.23 V. Therefore, the extension of the working voltage of the aqueous capacitor beyond the electrolyte decomposition limit is an important subject for the development of environmentally friendly energy storage devices. In this study, a commercial activated carbon (AC) and synthesized phosphorus-doped reduced graphene oxide (P-rGO) were used to gain insight into the influence of both textural properties and the surface chemistry on the electrochemical performance of high-voltage aqueous supercapacitors. Materials on the opposite end of the spectrum (highly porous, undoped AC and heteroatom-rich phosphorus-doped reduced graphene oxide with low porosity) were compared in a symmetric cell, operating in a wide voltage window of 2.0 V in 2 M NaClO4 electrolyte. Additionally, AC-based cell was tested in 1 M Na2SO4 solution to assess the differences in its performance in different sodium-based electrolytes. The obtained results demonstrate that both a porous structure and high contribution of heteroatoms, which improve the hydrophilicity of the electrode, are required to achieve high specific energy density values. However, with increasing current and higher power densities, a developed porous structure is required to maintain good energy storage characteristics. Achieving high operating voltage in the aqueous symmetric full-carbon supercapacitors is a promising energy storage solution. The assembled devices show a good specific energy density of up to 13 Wh kg−1 at a power density of 30 W kg−1.Graphical abstract

Influence of concentration and temperature dependent dielectric constants on the thermodynamics of electrolytes

The symmetric Poisson–Boltzmann theory, the modified Poisson–Boltzmann theory, and the mean spherical approximation are utilized to calculate the osmotic coefficient, and the individual and mean activity coefficients of model KCl, LiCl, NaCl, and NaClO4 electrolytes all dissociated in water where the dielectric constant depends on concentration. The theories are also employed to compute the same thermodynamic quantities for HCl and NaCl solutions where the dielectric constant is now temperature dependent. In each situation the theoretical predictions are compared with the corresponding exact benchmark Monte Carlo simulation results. The mean spherical approximation and the modified Poisson–Boltzmann theory reproduce the simulation data for osmotic coefficient quantitatively and that for the mean activity almost quantitatively. The individual activities are accurately represented by the modified Poisson–Boltzmann theory but only qualitatively by the symmetric Poisson–Boltzmann and the mean spherical approximation. In general, the symmetric Poisson–Boltzmann theory shows good agreement with the simulations at low concentrations but deviates at higher concentrations.

Tailoring Pure Inorganic Electrolyte for Aqueous Sodium‐Ion Batteries Operating at −60 °C

AbstractAqueous sodium‐ion batteries (ASIBs) have attracted increasing attention for next‐generation energy storage technologies due to their abundant resources and environmentally‐safe, while their application scenarios are severely limited by the high freezing point of conventional aqueous electrolytes. To overcome the aforementioned issues of ASIBs, a novel hybrid 3.5 m Mg(ClO4)2+0.5 m NaClO4 electrolyte (m: mol kg−1) with an ultra‐low freezing point (<−80 °C) is proposed. The exceptional anti‐freezing feature is mainly attributed to the higher ionic potential of Mg2+, greatly affecting the chemical environment of water molecules and inhibiting ice formation under subzero conditions. Benefiting from the superiority of ionic conductivity (4.86 mS cm−1) for the hybrid electrolyte at −60 °C, the full cell of active carbon||NaTi2(PO4)3@C delivers an ultra‐long lifespan of 10000 cycles under 8 C (1 C=133 mA g−1) at −60 °C. More importantly, some representative devices in daily life including smartphone and motor can be powered by ASIBs at −60 °C. Therefore, this work provides a rational and effective strategy for design and application of ASIBs with excellent electrochemical performance that can work in extremely cold environments.