Remarkable Capacity Retention Research Articles

Capacitive deionization with MoS2/g-C3N4 electrodes

The issue of insufficient freshwater resources has become a worldwide problem, restricting social and economic development. As a promising technology, capacitive deionization (CDI) has been developed to address this problem. In this work, MoS2/g-C3N4 composite with a high supercapacitor performance was successfully synthesized and assembled as the CDI electrode material with its electrochemical properties deeply evaluated. The results demonstrated that the MoS2/g-C3N4-based electrode demonstrated a large specific capacitance of 118.3 F/g (at 1 A/g) and a remarkable rate capacitance retention of 52.16% (61.7 F/g) (at 10 A/g). Moreover, the MoS2/g-C3N4-based electrode exhibited obvious improvement in desalination performance with the maximum electrosorption capacity of 24.5 mg/g. The hierarchical architecture, enhanced conductivity, large surface area, and negative zeta potential of MoS2/g-C3N4 composite facilitated the fast diffusion of ions. The enhanced ions adsorption performance of the MoS2/g-C3N4-based electrode was evaluated based on a capacitive contribution of 85.26% and a diffusion-controlled contribution of 14.74%.

Extremely stretchable, sticky and conductive double-network ionic hydrogel for ultra-stretchable and compressible supercapacitors

Stretchable and wearable electronic devices have attracted increasing attention for the realization of stretchable and compressible energy storage devices. To adapt to human body motion under rigorous and extreme working conditions, it is highly desirable to develop supercapacitors with remarkable capacitance retention during substantial stretching and compressing. Here, an intrinsically ultra-stretchable and compressible supercapacitor with remarkable capacitance retention is successfully constructed based on a new extremely stretchable, sticky and conductive double-network (DN) ionic hydrogel electrolyte. The hydrogel electrolyte with extreme stretchability (>18,000%), high toughness, good compression recovery performance, and conductivity (2.0 S/m) is achieved by introducing a chemically and physically crosslinked polyacrylamide-polyvinylpyrrolidone (PAAM-PVP) DN and LiCl electrolyte. In particular, the adhesive force of the hydrogel electrolyte surface is enhanced 13 times due to “salting-out effect”. A supercapacitor fabricated based on this DN hydrogel electrolyte exhibits superior intrinsic ultra-stretchability (2500% strain), the ability to withstand compressibility (up to 7100-times the weight of the supercapacitor), and a high specific capacity (308.9 F/g at a current density of 0.21 A/g). More importantly, the supercapacitor shows remarkable capacitance retention (87% at 2500% tensile strain, 90% at 7100-fold compressive weight). In addition, the wrinkled-structured all-solid supercapacitor maintained over 97% capacitance after being stretched to 200% for 6000 cycles, and maintained 104% capacitance after being compressed to 7100-times its own weight for 1000 cycles. This work provides new insights into the synthesis of ionic electrolyte and promotes the development of next-generation all-solid-state energy storage devices with high stretchability and compressibility.

Synthesis of Stacked Graphene-Sn Composite as a High-Performance Anode for Lithium-Ion Capacitors

A Lithium-ion capacitor (LIC) is composed of an electrochemical capacitor-like cathode and battery-like anode which store charge based on non-faradaic and faradaic processes, respectively. As an anode material for LIC, graphite is widely used because of its physical and electrochemical advantages. In the LIC system, stable cyclability at the high rate conditions is essential for bridging the gap between lithium-ion batteries and supercapacitors. However, there have been reported that the low working potential of graphite (close to 0.05 V vs Li/Li+) causes Li plating on the graphite surface and non-unity coulombic efficiency at high current charge/discharge results in degradation of cycle performance. To overcome this issue, stacked reduced graphene oxide-tin (SrGO-Sn) composite by co-reduction of graphene oxide and Sn2+ are studied in this work. The LIC consisting of SrGO-Sn anode shows good long-term cyclability with a remarkable capacity retention of 85, 77, and 60% at 10,000, 50,000, and 100,000th cycle and coulombic efficiency of 98% after 120,000 cycles. We believe that this study presents a new approach to the design of the high-performance LIC using an alternative to conventional graphite-based anode materials.

Dual-Functional Template-Directed Synthesis of MoSe2/Carbon Hybrid Nanotubes with Highly Disordered Layer Structures as Efficient Alkali-Ion Storage Anodes beyond Lithium.

Sodium/Potassium-ion batteries (SIBs/PIBs) have recently received tremendous attention because of their particular features of cost-effectiveness and promising energy density, which hold great potential for large-scale applications. Nevertheless, it still has a common bottleneck issue that is the sluggish kinetics of Na+/K+ intercalation, which raises more rigorous requirement on the electrode candidates regarding the morphology, dimension, and architecture. Herein, we have constructed unique MoSe2-based hybrid nanotubes with wall structures composed of highly disordered MoSe2 layers embedded in phosphorus and nitrogen co-doped carbon matrix (denoted MoSe2⊂PNC-HNTs), by a facile two-step strategy using Se nanorods as the dual-functional template, i.e., shape-directed agent and in situ selenization resources. Benefitting from the combined features of the one-dimensional (1D) hollow interior, hybrid wall structure with high disorder, and the phosphorus and nitrogen co-doping-induced abundant defect sites in the carbon matrix, the MoSe2⊂PNC-HNT anode exhibits high specific capacities of 280 and 262 mA h g-1 over 200 cycles at the current density of 0.1 A g-1 for Na+ and K+ storage, respectively, and achieves remarkable capacity retention rates of 87.0% at 2 A g-1 over 3500 cycles for Na-ion storage and 80.1% at 1 A g-1 after 500 cycles for K-ion storage.

High performance flexible supercapacitors including redox active molybdate incorporated Poly(vinylphosphonic acid) hydrogels

Novel gel polymer electrolyte (hydrogel) was prepared by incorporation of poly (vinylphosphonic acid) (PVPA) as a host matrix and redox active ammonium molybdate, Mo. Supercapacitors including active carbon electrodes were fabricated using hydrogels, PVPA/MoX where X represents the percent fraction of Mo in PVPA. All the electrolytes were in gel form and show excellent bending and stretching properties in a device. The electrochemical performance of the devices was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) experiments. Surprisingly, the specific capacitance (Cs) of the device increased to 1276 F g−1 which is at least 50 times enhancement by introducing Mo as mediator compared to the PVPA based system. The supercapacitor with PVPA/Mo10 has the highest energy density of 180.2 Wh kg−1 at a power density of 500 W kg−1. The device with the same hydrogel structure exhibited higher performance after 2300 charge-discharge cycles and the maintained 85% of its initial capacitance performance. A supercapacitor was fabricated using PVPA/Mo10 and tested under bent and twisted conditions confirming remarkable capacitance retention.

Ultrasensitive Fe3+ luminescence sensing and supercapacitor performances of a triphenylamine-based TbIII-MOF

The reasonable selection of functional ligands and active metal centers is a priority to fabricate multifunctional metal-organic framework (MOF) materials. Herein, a 3D bifunctional TbIII-MOF, [Tb(TCBPA)∙DMF]n (1) (H3TCBPA ​= ​tris(4′-carboxybiphenyl)amine), is constructed by photoelectricity active triarylamine chromophore and Tb(III) to show excellent photochemical sensing and supercapacitor performances. In 1, the TCBPA3− linkers bridge Tb(III) nodes in a highly torsional fashion to form a non-interpenetrating structure containing 1D rhombic channels with an effective window size of 10.6 ​× ​11.4 ​Å2. The strong green emission and multiple nitrogen/oxygen active sites make 1 work as a reusable heterogeneous fluorescent sensor for ultrasensitive detection of Fe3+ ion with a low detection limit of 3.56 ​ppb. Electrochemical experiments show that the TbIII-MOF exhibits a high specific capacitance of 346 ​F ​g−1 ​at 1 ​A ​g−1 and a remarkable capacitance retention of 93% after 2000 cycles, suggesting outstanding long-term cycling stability and reversibility. Additionally, the possible Fe3+ sensing mechanism was also investigated systematically.

Bioinspired Binders Actively Controlling Ion Migration and Accommodating Volume Change in High Sulfur Loading Lithium–Sulfur Batteries

AbstractHigh‐loading lithium–sulfur batteries have gained considerable fame for possessing high area capacity, but face a stern challenge from capacity fading because of serious issues, including “polysulfides shuttling,” insulating S/Li2S, large volume changes, and the shedding of S/C particles during drying or the cell encapsulation process. Herein, a bioinspired water‐soluble binder framework is constructed via intermolecular physical cross‐linking of functional side chains hanging on the terpolymer binder. Experimental results and density‐functional theory (DFT) calculations reveal that this network binder featuring superior volume change accommodation can also capture lithium polysulfides (LiPSs) through strong anchoring of O, N+ actives to LiPSs by forming Li···O and N+···Sx2− bonds. In addition, the abundant negative charged sulfonate coordination sites and good electrolyte uptake of the designed binder endow the assembled cells with high lithium ion conductivity and fast lithium ion diffusion. Consequently, a remarkable capacity retention of 98% after 350 cycles at 1 C and a high areal capacity of 12.8 mA h cm−2 with high sulfur loading of 12.0 mg cm−2 are achieved by applying the environmentally friendly binder.

Electrospun Core-Shell Nanofibrous Membranes with Nanocellulose-Stabilized Carbon Nanotubes for Use as High-Performance Flexible Supercapacitor Electrodes with Enhanced Water Resistance, Thermal Stability, and Mechanical Toughness.

A high-performance flexible supercapacitor electrode with a core-shell structure is successfully developed from cellulose nanocrystal (CNC)-stabilized carbon nanotubes (CNTs). By incorporating poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA), a cross-linked nanofibrous membrane (CNT-CNC/PVA-PAA) is prepared as the core material via directional electrospinning, followed by a thermal treatment. The flexible supercapacitor electrodes are eventually fabricated via the in situ polymerization of polyaniline (PANI), which was used as the coating shell material, on the aligned electrospun nanofibers. By taking advantage of the thermally induced esterification cross-linking that occurs among PVA, PAA, and the CNT-CNC nanohybrids, the membranes present with enhanced water resistance, mechanical strength, and thermal stability. After the surface coating of the PANI shell, the optimized PANI@CNT-CNC/PVA-PAA nanofibrous membranes exhibit a large porosity, an enhanced specific surface area, a superior tensile strength of ∼54.8 MPa, and a favorable electroconductivity of ∼0.44 S m-1. As expected, the nanofibrous electrodes with a specific capacitance of 164.6 F g-1 can maintain 91% of the original capacitance after 2000 cycles. The symmetrical solid-state supercapacitor assembled by the nanofibrous electrodes shows an excellent capacitance of 155.5 F g-1 and a remarkable capacitance retention of 92, 90, and 89% after 2000 cycles under flat, bending, and twisting deformations, respectively.

Universal construction of ultrafine metal oxides coupled in N-enriched 3D carbon nanofibers for high-performance lithium/sodium storage

To develop high-performance lithium/sodium-ion batteries, new method for the mass production of distinctive nanomaterials with ultrafine transition metal oxides intimately coupled in 3D carbon matrix still remains challenging. Herein, a universal strategy for synthesizing ultrafine metal oxide quantum dots (3–6 nm) tightly embedded in nitrogen-enriched 3D carbon nanofiber networks {MO@NCFs (MO = Co3O4, Mn3O4, Fe3O4)} is reported in a scalable manner. The MO@NCFs are constructed by coordinating nanofibrous carboxymethyl chitosan (CMCh) hydrogels and metal ions to form a stable metal-polysaccharide framework, and then by pyrolyzing process to generate hierarchically porous structure. The in situ and confined coordination in the CMCh framework can not only generate the metal oxides quantum dots with ultrafine size, but also endow the quantum dots to be robustly embedded in N-enriched 3D carbon nanofiber networks, leading to fast electron and ion transport, and excellent structural stability. As expected, the Co3O4@ NCFs exhibit a high Li+ storage capacity of 1199 mAh g−1 at 200 mA g−1, and a good cycling lifespan with capacity retention of 721 mAh g−1 at 1000 mA g−1 after 400 discharge/charge cycles. For sodium storage, the Co3O4@NCFs display superior capacities of 645 mAh g−1 at 100 mA g−1, good rate capability (191 mAh g−1 at 4000 mA g−1), and remarkable capacity retention of 301 mAh g−1 at 1000 mA g−1 after 400 cycles. This work provides a facile pathway to construct firmly coupled carbon hybrids by utilizing sustainable polymers derived from seafood waste for enhancing energy storage.

In situ fusion of MoO3/Na2Ti3O7 nanotube nanocomposite for improved electrochemical performance

There has been an increased interest in developing efficient and low-cost electrodes for supercapacitor applications using simplified synthesis procedures. Herein, a simple, easy, in situ synthesis of molybdenum trioxide (MoO3) nanosheets supported with sodium titanate nanotubes (Na2Ti3O7 NTs) and their application as electrodes for a supercapacitor has been reported. The electrochemical properties of Na2Ti3O7 NTs and MoO3/Na2Ti3O7 nanocomposite were studied using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The MoO3/Na2Ti3O7 NTs demonstrated a specific capacitance of 104.22 F g−1 at a current density of 1 A g−1, with remarkable capacitance retention. The MoO3/Na2Ti3O7 NT nanocomposite provided significantly improved electrochemical performance compared to that of pure Na2Ti3O7 NTs. These results have shown that incorporating MoO3 nanosheets into Na2Ti3O7 NTs led to improved capacitance.

Superior electrochemical performance of O3-type NaNi0.5-xMn0.3Ti0.2ZrxO2 cathode material for sodium-ion batteries from Ti and Zr substitution of the transition metals

Due to the low cost and abundance of sodium, sodium-ion batteries (SIBs) show great potential as energy storage devices. As far as the current research is concerned, cathode materials are still the bottleneck for boosting the performance of SIBs. O3-type layered NaNi0.5Mn0.5O2 is considered as an important cathode material of SIBs, but its irreversible phase transition, poor stability in air, and sluggish kinetics usually lead to reduced capacity, poor rate performance and high cost for material storage, which largely limit the large-scale application. Herein, a remarkable O3-type layered material NaNi0.5-xMn0.3Ti0.2ZrxO2 (NaNMTZ, x = 0.02, 0.05), with stable phase structure has been synthesized by the solid-phase method. The partial substitution of electrochemical inactive Ti/Zr brings about higher electronic delocalization and entropy of mixing leading to enhanced structural stability. In addition, the enlarged interlayer spacing and good conductivity contribute to better rate capability. The micro-nano structure leads to faster Na+ diffusion rates and shorter diffusion paths for both ions and electrons. Therefore, NaNi0.45Mn0.3Ti0.2Zr0.05O2 exhibits an initial reversible capacity of 141.4 mAh g−1 with a coulombic efficiency of 98.8% and remarkable capacity retention of 70% after 200 cycles at 0.05C, presenting better electrochemistry performance than the conventional NaNi0.5Mn0.5O2. This study provides a new angle to design high capacity cathode materials with high rate capability and cycling stability through crystal lattice modulation.

Sodium cholate as efficient green reducing agent for graphene oxide via flow reaction for flexible supercapacitor electrodes

In this work, sodium cholate (NaC) was used as novel green reducing agent for graphene oxide (GO) reduction at 90 °C and short synthesis time using a continuous segmented flow reaction system. As a comparison, we had used the common reducing agent which is glucose to study its chemical and electrochemical properties. The morphologies of GO and reduced-graphene oxide (rGO) were characterized with X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), Fourier transformed infrared (FTIR), Raman and Ultraviolet–Visible (UV–Vis) spectroscopy analysis demonstrated that reduction of GO occurred. For electrochemical measurements, the rGO was cast on carbon cloth to investigate the electrochemical performance with cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements. NaC assisted rGO (rGO–NaC) was able to achieve a specific capacitance up to 94 F g−1 at 0.1 A g−1 and remarkable capacitance retention of 103% after 10,000 cycles. A flexible test shows that rGO–NaC bendable at 0°–60°. These results demonstrate that rGO–NaC is promising as flexible supercapacitors electrodes.

A 3D Lithiophilic Mo2 N-Modified Carbon Nanofiber Architecture for Dendrite-Free Lithium-Metal Anodes in a Full Cell.

The pursuit for high-energy-density batteries has inspired the resurgence of metallic lithium (Li) as a promising anode, yet its practical viability is restricted by the uncontrollable Li dendrite growth and huge volume changes during repeated cycling. Herein, a new 3D framework configured with Mo2 N-mofidied carbon nanofiber (CNF) architecture is established as a Li host via a facile fabrication method. The lithiophilic Mo2 N acts as a homogeneously pre-planted seed with ultralow Li nucleation overpotential, thus spatially guiding a uniform Li nucleation and deposition in the matrix. The conductive CNF skeleton effectively homogenizes the current distribution and Li-ion flux, further suppressing Li-dendrite formation. As a result, the 3D hybrid Mo2 N@CNF structure facilitates a dendrite-free morphology with greatly alleviated volume expansion, delivering a significantly improved Coulombic efficiency of ≈99.2% over 150 cycles at 4 mA cm-2 . Symmetric cells with Mo2 N@CNF substrates stably operate over 1500 h at 6 mA cm-2 for 6 mA h cm-2 . Furthermore, full cells paired with LiNi0.8 Co0.1 Mn0.1 O2 (NMC811) cathodes in conventional carbonate electrolytes achieve a remarkable capacity retention of 90% over 150 cycles. This work sheds new light on the facile design of 3D lithiophilic hosts for dendrite-free lithium-metal anodes.

NiMoO4 nanorods@hydrous NiMoO4 nanosheets core-shell structured arrays for pseudocapacitor application

In this work, homogeneous NiMoO4 nanorods@hydrous NiMoO4 nanosheets core/shell nanostructure were assembled on nickel foam by a two-step hydrothermal method and incorporate with an anneal process. Benefiting from their core/shell nanostructure and homogeneous nanocomposites, the arrays present high areal capacitance up to 6.34 F/cm2 at 4 mA/cm2 and display a remarkable specific capacitance retention of 89% after 5000 cycles. When the current density increases to 70 mA/cm2, the capacitance is 3.13 F/cm2 displayed good rate capability. The excellent electrochemical properties allow them to be used as a promising electrode material for pseudocapacitors, which has a wide application prospect in the field of electrochemical capacitor.

Lasagna-Inspired Zn Anode Design for High-Energy Rechargeable Aqueous Batteries

A key aspect of any future battery technology development is safety. Although lithium-based batteries are ubiquitous, there are still challenges related to their energy density, cycle life, cost and safety. In regard to safety, compared with organic electrolyte, aqueous rechargeable batteries may provide a safer alternative for reliable, low-cost and large-scale energy storage systems. As seen from the penetration test in Fig. 1a-1b, the battery with organic electrolyte catches fire, yet the battery with aqueous electrolyte is relatively safe. Moreover, aqueous batteries have high ion conductivity and cost effectiveness. Generally, the cell voltage and energy density of aqueous batteries are lower than those of organic-based batteries (e.g. Li-ion) because of the relatively smaller electrochemical stability window of water. Among all the metals that are stable in water, zinc is the most active and has the lowest possible operating potential. This means using Zn anode can increase overall cell voltage of aqueous batteries. Moreover, zinc is globally available, inexpensive (3.19 USD kg-1), and has high capacity (820 Ah kg-1 and 5854 Ah L-1). Zinc-based aqueous batteries also possess the stability to be operated in ambient air. Accordingly, Zn aqueous rechargeable batteries are promising to become a safer energy storage system. Among zinc-based aqueous batteries, Zn-air batteries have high theoretical volumetric energy density, which is around three times that of conventional Li-ion batteries (LIB). Zn anodes have been investigated in neutral/mild acidic aqueous electrolytes. Yet in order to pair them with oxygen cathode to reach the highest energy density, alkaline aqueous electrolyte is ideal, in which the oxygen electrode has low polarization. In alkaline aqueous electrolyte, Zn anode undergoes a Zn (s) ↔ Zn(OH)4 2- (aq) ↔ ZnO (s) conversion. This solid-solute-solid transformation and insulating discharge product ZnO lead to three vital challenges: 1) ZnO passivates Zn surface and prevents further discharging, leading to low Zn utilization; 2) ZnO is insulating and can hardly be charged back to Zn; 3) diffusion of Zn(OH)4 2- causes the loss of active material and change of electrode morphology. Thus, anode modification and protection are needed to alleviate the passivation and dissolution. We firstly designed a Zn mesh@GO anode (Fig 1c). Graphene oxide (GO) layers on the Zn mesh surface deliver electrons across insulating ZnO and can slow down the Zn dissolution. However, the utilization of zinc is still low because passivation problem is not completely solved. Through SEM investigation, critical passivation size was found to be ~ 2 µm. Thus, we further designed a lasagna-inspired ZnO@GO anode (Fig 1d). ZnO nanoparticles are encapsulated by GO. ZnO lasagna structure has three features: 1) the size of ZnO nanoparticles is smaller than the critical size of passivation; 2) the fabrication of ZnO lasagna anode starts with commercially available ZnO nanoparticles (~100 nm), and is compatible with the roll-to-roll process, which is ideal for large-scale manufacturing; 3) GO allows permeation of OH- and water, and prevents loss of Zn active material through blocking bigger Zn(OH)4 2-. As a result, such lasagna anode achieves a high volumetric capacity of 2308 Ah/L and a remarkable capacity retention of 86% after 150 cycles. In contrast, the open-structured ZnO nanoparticle anode, without the protection of GO, completely died after 90 cycles. Figure 1

Mo-Modified P2-type Manganese Oxide Nanoplates with an Oriented Stacking Structure and Exposed {010} Active Facets as a Long-Life Sodium-Ion Battery Cathode.

Layered manganese-based cathode materials are of great interest because of their high specific capacities for sodium-ion batteries. However, the Jahn-Teller effect and the inevitable phase transition are detrimental for achieving considerable cycling stability and rate capability. Herein, a P2-type manganese oxide nanoplate cathode material modified by Mo-substitution with an oriented stacking structure and exposed {010} active facets is reported. The manganese oxide nanoplate cathode yields remarkable capacity retention of 86% after 1200 cycles at 10 C (2000 mA g-1). The specific power density is estimated to be as high as 530 W kg-1 with a specific discharge capacity 143.9 mA h g-1 at 1 C and 89.6% capacity retention up to 100 cycles. The superior electrochemical performances can be attributed to the efficient chemical modification and the unique structural features of the present manganese oxide nanoplate. Mo-modification can endow the manganese oxide cathode with enlarged lattice space and average oxidation state and thus favorable Na+ diffusion to inhibit the Jahn-Teller effect and improve the structure stability, thereby achieving an extremely long cycling life. A multilayer oriented stacking nanoplate structure with exposed {010} active facets is also beneficial for providing more surface active sites and shortening the Na+ diffusion path, leading to better rate capability.

Polycrystalline 1-D TiN-based free-standing composite electrode for high performance of Li-polysulfide cells

Li‑sulfur batteries are expected to transform electrochemical energy storage technology by taking it to the next level, as it holds the possibility to obtain a higher energy density levels than state-of-the-art Li-ion batteries. The poor electrical conductivity of sulfur and the high diffusivity of the intermediate lithium polysulfides create various problems, which limit the utilization of the full potential of these batteries. Polar conductive sulfur hosts such as titanium nitride (TiN) make it possible to realize remarkable improvements in active material utilization and capacity retention outcomes over long-term cycling. It has not been possible to use these polar, conductive, ceramic materials for higher active material loading (>2 mg cm−2) due to their low flexibility compared to carbonaceous materials. Here, we demonstrate the possibility of designing a three-dimensional free-standing electrode using polycrystalline 1-D TiN for a relatively high sulfur loading of 2.5 mg cm−2. The electrochemical performance of this 1-D TiN-based electrode is compared to that of an electrode based on 1-D TiO2 (the starting material for TiN synthesis). The results demonstrate the catalytic effect of TiN by virtue of its endowed conductivity, leading to remarkable capacity retention and better active material utilization at high C-rates compared to a TiO2-based electrode.

In Situ FTIR-Assisted Synthesis of Nickel Hexacyanoferrate Cathodes for Long-Life Sodium-Ion Batteries.

Prussian blue analogs (PBAs) with stable framework structures are ideal cathodes for rechargeable sodium-ion batteries. The chelating agent-assisted coprecipitate method is an effective way to obtain low-defect PBAs that can limit the appearance of too many vacancies and water molecules and achieve an optimized Na-storage performance. However, for this method, the mechanism of chelating agent-assisted synthesis is still unclear. Herein, the synthesis process of nickel hexacyanoferrate (NiHCF) has been investigated by in situ infrared spectroscopy detection. The results show that the chelating agent oxalate slows down the nucleation process and effectively inhibits the formation of the Fe-C≡N-Ni frame in the aging process, producing highly crystallized and low-defect NiHCF samples. High-quality NiHCF presents a high specific capacity of 86.3 mAh g-1 (a theoretical value of ∼85 mAh g-1), an ultrastable cyclic retention of 90% over 800 cycles, and a remarkable high capacity retention of 74.6% at a current density of 4250 mA g-1 (50C). Particularly, the NiHCF//hard carbon full cell presents a high specific energy density of over 210 Wh kg-1 and an outstanding cyclic stability without obvious capacity attenuation over 1000 cycles.

Effects of Li3PO4 additive on the electrochemical properties of Li2FeSiO4 as cathode material for lithium-ion batteries

Li2FeSiO4/C is successfully modified by Li3PO4 additive to achieve excellent electrochemical properties. In comparison with bare Li2FeSiO4/C, the samples with Li3PO4 show no changes in the morphology and structure, which are verified by X-ray powder diffraction and scanning electron microscopy results. High resolution transmission electron microscopy image confirms that Li2FeSiO4/C and Li3PO4 exist in the form of nanocomposites. When used as LIB cathodes, the Li2FeSiO4/Li3PO4/C composites show notably improved electrochemical performance with outstanding high rate performance and superior cyclability than those of Li2FeSiO4/C. The sample with 6 mmol% (LFS-6) exhibits a large discharge capacity of 114.1 mAh g−1 with a remarkable capacity retention of 104.2% over 100 cycles at 10 C, which are much better than those of Li2FeSiO4/C (89.0 mAh g−1 and capacity retention of 75.9%). The enhancement in the electrochemical properties of Li2FeSiO4/C may be attributed to the existence of Li3PO4 additive with high ionic conductivity, which can accelerate the lithium ions diffusion capability and facilitate the charge transfer process.

Intermixed Cation–Anion Aqueous Battery Based on an Extremely Fast and Long‐Cycling Di‐Block Bipyridinium–Naphthalene Diimide Oligomer

AbstractAqueous batteries, particularly those integrating organic active materials functioning in a neutral pH environment, stand out as highly promising contenders in the stationary electrochemical storage domain, owing to their unparalleled safety, sustainability, and low‐cost materials. Herein, a novel di‐block oligomer, serving as the negative electrode of an all‐organic aqueous battery, is shown to offer exceptional output capabilities. The battery's performance is further enhanced by a unique intermixed p/n‐type storage mechanism, which is able to simultaneously exchange light and naturally abundant Na+, Mg2+, and Cl−. Reaching up to 105 mAh g−1, this system shows remarkable capacity retention for several thousand cycles (6500 cycles, ≈40 days) in various neutral electrolytes, including raw ocean water (≈3000 cycles, ≈75 days). The surprisingly fast kinetics of this di‐block oligomer allow to attain an unmatched specific capacity of near to 60 mAh g−1electrode while entirely devoid of conducting additives, and more than 80 mAh g−1electrode with 10% carbon additive, as well as displaying an areal capacity as high as 3.4 mAh cm−2 at C rate. Full cell validation was demonstrated over 1600 cycles by virtue of a commercial 2,2,6,6‐tétraméthylpipéridin‐1‐yl)oxyl (TEMPO) molecule, which permitted an energy density of close to 40 Wh kg−1materials at C rate in a self‐pH‐buffered and inexpensive aqueous electrolyte.