Remarkable Capacity Retention Research Articles

Electrochemical performance of mixed-phase 1T/2H MoS2 synthesized by conventional hydrothermal v/s microwave-assisted hydrothermal method for supercapacitor applications

Mixed-phase 1T/2H MoS2 has been receiving immense attention as an electrode material for supercapacitors due to the synergistic effects of both the phases. Herein, we synthesized mixed-phase 1T/2H MoS2 via two different techniques: conventional hydrothermal (HT) and microwave-assisted hydrothermal (MHT) technique. The formation of MoS2 is confirmed through X-ray diffraction pattern, scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman-spectra, and X-ray photoelectron spectra. The electrochemical performance of the two samples is investigated using cyclic voltammetry (CV), Gravimetric charging-discharging (GCD) and electrochemical impedance spectroscopy (EIS). MoS2 synthesized via MHT method (MS-MW) and HT method (MS-HT) deliver capacitances of 421 F g−1 and 742 F g−1 at 5 mV s−1, respectively. The energy density of MS-HT (57 Wh kg−1) is almost double than that of MS-MW (30 Wh kg−1). MS-HT also exhibited remarkable capacitance retention of 91% over 1200 cycles, compared with MS-MW. The results demonstrate that MoS2 synthesized by the hydrothermal method delivers superior electrochemical performance.

Electrochemical performance of the Li-rich layered Li1.2Mn0.54Ni0.13Co0.13O2 cathode material influenced by Fe3+ doping

The extensive application of the layered Li-rich Mn-based cathode material is limited due to the inferior cycling stability, rate capability and voltage decay. The electrochemical performance of Fe 3+ doping Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 cathode material synthesized by sol-gel method was investigated in this paper. It is indicated that Fe 3+ doping Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 cathode material shows excellent electrochemical performance at high current intensity rates, especially the cycling stability and capacity retention. The cathode Li 1.2 Mn 0.54 Ni 0.13 Co 0.12 Fe 0.01 O 2 exhibits excellent initial discharge capacities of 193.5 mAh g −1 at 1 C, 179.8 mAh g −1 at 2 C and 119.6 mAh g −1 at 5 C, and expresses remarkable capacity retention of 87.1% at 1 C and 84.0% at 2 C after 100 charge/discharge cycles, respectively. It is attributed to the beneficial effects of the Fe 3+ doping in the cathode material, which enlarges the lithium layer spacing, decreases charge-transfer resistance and accelerates the Li + diffusion, significantly slows down the decomposition of Li 2 MnO 3 , and efficiently alleviates the irreversible loss of lattice oxygen and the Mn dissolution during cycling. ● Fe 3+ doping maintains well layered structure and phase stability. ● Fe 3+ doping enhances cycling stability and rate capability. ● Fe 3+ doping inhibits the decomposition of Li 2 MnO 3 and loss of lattice oxygen. ● Fe 3+ doping enlarges layer spacing and improves the Li + diffusion coefficient.

An All‐Solid‐State Battery Based on Sulfide and PEO Composite Electrolyte

Replacing liquid electrolytes with solid polymer electrolytes (SPEs) is considered as a vital approach to developing sulfur (S)-based cathodes. However, the polysulfides shuttle and the growth of lithium (Li) dendrites are still the major challenges in polyethylene oxide (PEO)-based electrolyte. Here, an all-solid-state Li metal battery with flexible PEO-Li10 Si0.3 PS6.7 Cl1.8 (LSPSCl)-C-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) composite cathode (FCC) and PEO-LSPSCl-LiTFSI composite electrolyte (S-CPE) is designed. The initial capacity of the Li|S-CPE|FCC battery is 414 mAh g-1 with 97.8% capacity retention after 100 cycles at 0.1 A g-1 . Moreover, the battery displays remarkable capacity retention of 80% after 500 cycles at 0.4 A g-1 . Cryo-transmission electron microscopy (Cryo-TEM) reveals rich large-sized Li2 CO3 particles at the Li/PEO interface blocking the Li+ transport, but the layer with rich Li2 O nanocrystals, amorphous LiF and Li2 S at the Li/S-CPE interface suppresses the growth of lithium dendrite and stabilizes the interface. In situ optical microscopy demonstrates that the excellent cyclic stability of FCC is ascribed to the reversible shuttle of P-S-P species, resulting from the movement of ether backbone in PEO. This study provides strategies to mitigate the polysulfide shuttle effect and Li dendrite formation in designing high energy density solid-state Li-S-based batteries.

PEDOTS:PSS@KNF Wire‐Shaped Electrodes for Textile Symmetrical Capacitor

AbstractThe emerging wearable electronics and e‐textiles have motivated tremendous interests in textile energy storage microdevices. Among them, fiber‐shaped capacitors (FSCs) offer unique properties because of their 1D configuration and reliable energy storage. In recent years, many works focused on the development of 1D fibrous‐shaped electrodes usually involving complex material synthesis and techniques. Herein, an easy procedure for the preparation of composite fibers made by PEDOT:PSS infiltration in gel‐state Kevlar nanofiber (KNF) wires is proposed. The PEDOT:PSS@KNF 1D electrodes are mechanically robust, conductive, and flexible. The symmetric FSCs integrated in textile show remarkable capacitance retention under deformation, average capacitance of 1.1 mF, volumetric energy density of 71 mWh cm−3, and ability to power on a blue light‐emitting diode.

Constructing ultrafine Cu nanoparticles encapsulated by N-doped carbon nanosheets with fast kinetics for high-performance lithium/sodium storage

Carbon-based materials are extensively applied in Li/Na-ion batteries (LIBs/SIBs) anode material. Nevertheless, the poor rate performance, sluggish reaction kinetics, and fast capacity fading during cycling process seriously impedes large-scale commercial application. Herein, ultrafine Cu nanoparticles encapsulated within N-doped carbon nanosheets (labeled Cu/NC) with enlarged interlayer distances, increased intrinsic defects, abundant metallic Cu sites, and hierarchical porous structure were facilely and efficiently fabricated by a room-temperature grinding followed by high temperature pyrolysis. The Cu/NC as electrodes show a high capacity of 788 mAh g−1 in LIBs, and 434 mA h g−1 in SIBs at 0.2 A g−1, as well as good cycling stability with 123 mAh g−1 for LIBs and 177 mAh g−1 for SIBs at 10 A g−1 after 2000 cycles. The as-assembled sodium-ion hybrid capacitors (SIHCs) deliver a high energy/power density of 97 Wh kg−1 at 181 W kg−1, remarkable capacity retention of 95.8% after 10,000 cycles and practical applications (69 LEDs can be easily lighted). The experimental results couple with theoretical calculation indicate that the incorporating of Cu and N species can provide abundant active sites and structural defects, resulting in fast reaction kinetics for Li/Na-ion storage.

In-situ formation of Li0.5Mn0.5O coating layer through defect controlling for high performance Li-rich manganese-based cathode material

Li-rich layered oxide of Li1.2Mn0.6Ni0.2O2 (LMNO) with a considerable specific capacity and higher voltage is regarded as a kind of promising cathode material. However, it suffers from transition metal ion dissolution and oxygen escape that leads to rapid capacity decay. In addition, the poor lithium-ion diffusion kinetics gives rise to unsatisfied rate performance. Herein, a stable layer of Li0.5Mn0.5O (LMO) out of LMNO is in-situ constructed through acetic passivation and following calcination process. The generated defect structure in the composite material exhibits fast ion diffusion kinetics and the produced LMO layer can stabilize the substructure, resulting in elevated cycling stability and rate performance. In specific, the LMNO@LMO material exhibits a high initial coulombic efficiency of 80.3% and remarkable capacity retention of 80.7% after 200 cycles at 1 C. Besides, the composite material reveals prominent rate performance that delivers discharge capacities of 158 and 131 mAh g−1 at 5 and 10 C, respectively. At last, this study presents a new approach to optimizing the Li-rich cathode materials.

Engineering Bamboo Leaves Into 3D Macroporous Si@C Composites for Stable Lithium-Ion Battery Anodes.

Silicon is considered as the most promising candidate for anodes of next generation lithium-ion batteries owing to its natural abundance and low Li-uptake potential. Building a macroporous structure would alleviate the volume variation and particle fracture of silicon anodes during cycling. However, the common approaches to fabricate macroporous silicon are complex, costly, and high energy-consuming. Herein, bamboo leaves are used as a sustainable and abundant resource to produce macroporous silicon via a scalable magnesiothermic reduction method. The obtained silicon inherits the natural interconnected network from the BLs and the mesopores from the BL-derived silica are engineered into macropores by selective etching after magnesiothermic reduction. These unique structural advantages lead to superior electrochemical performance with efficient electron/ion transport and cycling stability. The macroporous Si@C composite anodes deliver a high capacity of 1,247.7 mAh g−1 after 500 cycles at a current density of 1.0 A g−1 with a remarkable capacity retention of 98.8% and average Coulombic efficiency as high as 99.52% for the same cycle period. Furthermore, the rate capabilities of the Si@C composites are enhanced by conformal carbon coating, which enables the anode to deliver a capacity of 538.2 mAh g−1 at a high current density of 4.0 A g−1 after 1,000 deep cycles. Morphology characterization verifies the structural integrity of the macroporous Si@C composite anodes. This work demonstrated herein provides a simple, economical, and scalable route for the industrial production of macroporous Si anode materials utilizing BLs as a sustainable source for high-performance LIBs.

Highly Deformable, Conductive Double-Network Hydrogel Electrolytes for Durable and Flexible Supercapacitors.

Developing flexible energy storage devices with the ability to retain capacitance under extreme deformation is promising but remains challenging. Here, we report the development of a durable supercapacitor with remarkable capacitance retention under mechanical deformation by utilizing a physical double-network (DN) hydrogel as an electrolyte. The first network is hydrophobically associating polyacrylamide cross-linked by nanoparticles, and the second network is Zn2+ cross-linked alginate. Through soaking such a DN hydrogel into a high concentration of ZnSO4 solution, a highly deformable electrolyte with good conductivity is fabricated, which also shows adhesion to diverse surfaces. Directly attaching the hydrogel electrolyte to two pieces of an active carbon cloth facilely produces a flexible supercapacitor with a high specific capacitance and theoretical energy density. Remarkable capacitance retention under tension, compression, and bending is observed for the supercapacitor, which can also maintain above 87% of the initial capacitance after 4000 charge-discharge cycles. This study provides a simple way to fabricate hydrogel electrolytes for deformable yet durable supercapacitors, which is expected to inspire the development of next-generation flexible energy storage devices.

Understanding the anchoring effect on Li plating with Indium Tin oxide layer functionalized hosts for Li metal anodes

Li dendrites caused by nonuniform Li plating and locally concentrated ion/electron flux would give rise to poor cycling performance and safety issues of short-circuit and so on. Herein, a functional nanolayer consisting of Indium Tin oxide (ITO) nanoparticles on 3D Cu foam was fabricated as case study to understand the mechanism of metal oxides on anchoring Li metal spots and how initial Li nucleation influences the following dendrites growth. Based on the experimental and theoretical results, it is demonstrated that not only the pristine metal oxides have higher binding energy with Li atom, but also in situ formed alloy phase during alloying process performs a great importance on homogeneous nucleation, thus leading to ordered ion/electron distribution and fast kinetics. Therefore, excellent wettability and even self-propagation behavior between ITO-Cu foam and molten Li are achieved, meanwhile the half cells with ITO-Cu foam electrodes exhibit an ultralow nucleation overpotential of 2 mV under 0.5 mA cm−2. When the designed ITO-Cu foam@Li anodes is matched with LFP (LiFePO4) cathodes, the constructed full cells can empower superior cycling stability for over 1000 cycles at 5C (3.4 mA cm−2), and remarkable specific capacity (149 mAh g−1) and capacity retention (80% for 250 cycles) even with ultrahigh mass loading (15.3 mg cm−2), which provides an avenue to regulate Li deposition/dissolution for high energy Li metal batteries.

Strengthened the structural stability of in-situ F− doping Ni-rich LiNi0.8Co0.15Al0.05O2 cathode materials for lithium-ion batteries

Layered Ni-rich oxides have always been considered as highly promising cathode materials for high-energy–density lithium-ion batteries, whereas they have been confronted with technical bottlenecks sprung from short cycle life and thermal instability. In this work, F− doping as one feasible approach has been introduced into LiNi0.8Co0.15Al0.05O2 for alleviating the limitations by stabilizing the layered structure. The stoichiometric LiNi0.8Co0.15Al0.05O2-xFx (0 ≤ x ≤ 0.1) composite powders doped with different amounts of NH4F powders are precisely synthesized by in-situ modified method, which are strictly identified by physicochemical methods. The characterization results demonstrate that F ions successfully enter into the lattice of LiNi0.8Co0.15Al0.05O2-xFx (0 ≤ x ≤ 0.1) and that the targeted LiNi0.8Co0.15Al0.05O1.96F0.04 composite powders possess the most ordered layered structure with compact surface morphology when the doping amount of F− is up to 4 % based on the weight of the precursor Ni0.8Co0.15Al0.05(OH)2 composite powders. Moreover, the half-cell assembled with the LiNi0.8Co0.15Al0.05O1.96F0.04 composite electrode presents a reversible discharge specific capacity of 157.8 mAh g−1 with remarkable capacity retention of 98.3 % after 100cycles at 2.0C at 25 °C. Even at an elevated temperature of 60 °C and a high current density of 5.0C, it still delivers an improved discharge specific capacity of 142.6 mAh g−1 with excellent capacity retention of 89.1 %. The outstanding improvements in the terms of the lithium storage performance are principally attributed to the stronger metal-F bonds substituting the metal-O bonds with introducing F ions into the lattice, which can not only effectively stabilize the host structure to preserve the structural integrity, but also prevent the erosion of HF and suppress the increment of the polarization degree during continuous cycling processes. Therefore, the F− doping strategy may provide a novel horizon to construct layered Ni-rich cathode materials with improved structural stability and durable electrochemical performance for lithium-ion batteries.

Improved supercapacitor performance based on sustainable synthesis using chemically activated porous carbon

Porous carbon-based materials are among the most promising materials for future electrochemical energy storage and conversion and are sustainable and environmentally acceptable. The development of highly porous carbon compounds from biomass has become a popular topic of study. Herein, we report interconnected porous-structured carbon obtained from a biowaste precursor. Pine tree (Casuarina) seeds were carbonized by using 9 M concentrated sulfuric acid (H2SO4), and the obtained pine tree seed carbon (PTC) was activated by mixing various ratios with potassium hydroxide (1:1, 1:3, 1:5 ratio) and performing simple microwave pyrolysis. The pore size and surface area of the generated carbon could be fine-tuned. The surface area increased considerably as the KOH concentration increased, with an excellent specific surface area of 929.9 m2 g−1 (1:3 mass ratio). The synthesized porous carbon showed a high charge storage capacitance of 210 F g− 1 at 1 A/g, as well as remarkable capacitance retention after 10,000 charge/discharge cycles, even at a high current density. The remarkable electrochemical storage behaviour of hierarchically porous structured carbon networks is related to the optimal combination of micro- and mesoporous morphology with increased defect sites at the edges, which results in a higher surface area and enhanced conductivity.

Fabricating advanced asymmetric supercapacitors by flame growing carbon nanofibers on surface engineered stainless steel electrode and modulating the redox active electrolyte

A straightforward approach for preparing a hierarchical carbon nanofiber (CNF) electrode through surface-engineering of a stainless steel microwire mesh (SS) current collector is developed. Surface-engineering is achieved via controlled chemical etching SS and subsequent flame depsotion of a CNF coating. In contrast to pristine SS, the surface-engineered SS do not only comprise a unique surface texture but also a higher catalytic activity facilitating the direct growth of CNFs in an ethanol flame. Therefore, the as-fabricated electrode exhibits a high specific capacitance of 2988 F/g at 25 mA/cm 2 in a redox active electrolyte containing Fe 2+/3+ optimized for this electrode/electrolyte system. To maximize their capacitive performance, supercapacitors in a newly designed dual-asymmetric electrode/electrolyte (DASCs) configuration are assembled. Both the CNF positive electrode and the alpha‑molybdenum oxide (MoO 3 ) nanobelt negative electrode are capable to operate in their most suitable electrolyte. Consequently, the DASCs deliver an ultrahigh energy density of 96 Wh/kg at 114 W/Kg and a remarkable capacitance retention. Our results demonstrate the effectiveness of this surface engineering approach for fabricating electrodes, the redox activity modulation of the electrolyte, and the newly designed configuration of the capacitors, on enhancing their performance. • A facile 2-step method for flame catalytic deposition of CNFs on stainless steel mesh was developed. • Surface-engineering provided the resurfaced catalytically active sites for CNF deposition. • Surface-engineering of the mesh provided CNF electrodes with enhanced charge transfer ability. • Supercapacitors with new configuration of dual-asymmetric electrode/electrolyte were assembled. • The flexible solid state device exhibited remarkable energy density of 96 Wh/kg at 114 W/kg.

Nitrogen, sulfur Co-doped carbon nanosheets embedded with CoS/Co9S8 composite for high-stability lithium storage

Metal sulfides have emerged as eminent candidates for anodes in lithium-ion batteries because of their low cost and high theoretical capacity. Nevertheless, their Li storage performance is hindered by their inherent low conductivity and dramatic volume changes. To exceed this limitation, in this study, we synthesized a composite material comprising heterostructured CoS/Co 9 S 8 grains incorporated into N, S co-doped carbon (labeled as CSCS-C-800) through a solid-state pyrolysis reaction. The N, S co-doped carbon matrix could boost electrical conductivity and protect cobalt sulfides from volume changes. Furthermore, the heterostructured CoS/Co 9 S 8 possesses abundant electrochemical active sites owing to its ubiquitous crystal boundary between the CoS and Co 9 S 8 grains. Benefiting from the synergy of the two components, CSCS-C-800 displayed a satisfactory cycling lifespan, achieving remarkable capacity retention of 90% and low capacity fading per cycle of 0.025% during 400 successive cycles at 0.5 A g −1 . We believe that these outcomes obtained herein will be helpful in obtaining advanced metal sulfide-based materials for applications in electrochemical charge storage systems.

Enhancing the Performance of a Metal-Free Self-Supported Carbon Felt-Based Supercapacitor with Facile Two-Step Electrochemical Activation.

Carbon felt (CF) is an inexpensive carbon-based material that is highly conductive and features extraordinary inherent surface area. Using such a metal-free, low-cost material for energy storage applications can benefit their practical implementation; however, only limited success has been achieved using metal-free CF for supercapacitor electrodes. This work thoroughly studies a cost-effective and simple method for activating metal-free self-supported carbon felt. As-received CF samples were first chemically modified with an acidic mixture, then put through a time optimization two-step electrochemical treatment in inorganic salts. The initial oxidative exfoliation process enhances the fiber’s surface area and ultimately introduced oxygen functional groups to the surface, whereas the subsequent reduction process substantially improved the conductivity. We achieved a 205-fold enhancement of capacitance over the as-received CF, with a maximum specific capacitance of 205 Fg−1, while using a charging current density of 23 mAg−1. Additionally, we obtained a remarkable capacitance retention of 78% upon increasing the charging current from 0.4 to 1 Ag−1. Finally, the cyclic stability reached 87% capacitance retention after 2500 cycles. These results demonstrate the potential utility of electrochemically activated CF electrodes in supercapacitor devices.

Long Cycle Life and High‐Rate Sodium Metal Batteries Enabled by Regulating 3D Frameworks with Artificial Solid‐State Interphases

AbstractThe major challenge for sodium metal anodes is Na dendrite growth owing to the unstable and fragile solid–electrolyte interphase (SEI), leading to terrible cycle life and safety hazards. Constructing a robust SEI around a 3D porous host is considered to be a facile and efficient approach to stabilize Na metal anodes. Here, a durable 3D porous SnCl4@Na–rGO metal anode is fabricated by the in situ chemical reaction of SnCl4‐containing carbonate electrolyte with Na–rGO. Attributed to the robust SEI and the stereoscopic structure, the symmetric cells achieve a prolonged cycle life of 500 h without voltage fluctuation at 2 mA cm−2 and 2 mAh cm−2. Moreover, the Na3V2(PO4)3||SnCl4@Na–rGO full cell exhibits long‐term cycle stability (>600 cycles) and remarkable capacity retention (>92%). The novel approach provides an efficacious strategy for the practical implementation of Na metal batteries.

Significantly fastened redox kinetics in single crystal layered oxide cathode by gradient doping

Nickel-rich layered cathode is a forefront candidate for lithium-ion batteries; however, structural degradation such as intragranular cracking and phase transition in polycrystals focus researchers’ attention towards single-crystals. Nevertheless, the sluggish ionic transport and redox kinetics in single-crystals hinder their rate capability and electrochemical performance in harsh conditions. Herein, a synergy of gradient Nb doping on single-crystal LiNi0.8Co0.1Mn0.1O2 stabilizes the core by strong Nb-O bond and induces Li/Ni antisite migration forming a disordered buffer layer on the surface. The disordered structure maintains the structural integrity by suppressing the phase transition and triggering the Li+ transport. Thus, the modified single-crystal (SNCM@Nb-2) delivers remarkable capacity retention of 92.54% after 100 cycles at 1 C between 2.7 and 4.3 V@ 25 °C (84.26% for SNCM, respectively) and 86.7% at an elevated temperature of 55 °C (SNCM 76.69%). The fast redox kinetics results in remarkably enhanced rate capability and ultra-stable high voltage performance at 4.5 V with SNCM@Nb-2 delivers an initial discharge capacity of 285.2 mAh g−1 with retention of 79.8% (SNCM with 192.1 mAh g−1, 64.1%). The findings of this study provide advancement for the inadequate kinetic properties of single-crystal Ni-rich cathodes under harsh operational conditions.

Hierarchical Cobalt‐Nickel Double Hydroxide Arrays Assembled on Naturally Sedimented Ti3C2Tx for High‐Performance Flexible Supercapacitors

AbstractFlexible electrodes with excellent energy storage and conversion properties that can be produced by a simple process are highly desirable for supercapacitors. Herein, Cobalt‐Nickel double hydroxide (CoNi‐DH) micro‐nanosheet arrays are prepared uniformly on naturally sedimented Ti3C2Tx films by an etching‐deposition‐growth process to form a CoNi‐DH@Ti3C2Tx heterostructure. The naturally sedimented Ti3C2Tx film serves as the substrate to minimize aggregation of the CoNi‐DH nanoarrays to enhance the electrical conductivity. Furthermore, the hierarchical structure comprised of the CoNi‐DH interconnected nanoarrays promotes electrolyte access. By taking advantage of the excellent electrical conduction and high theoretical specific capacitance, the flexible CoNi‐DH@Ti3C2Tx electrode in the supercapacitor delivers a superior specific capacitance of 919.5 F g−1 at 1 A g−1, and remarkable capacitance retention of 89.6% after 5000 cycles at 20 A g−1. Density‐functional theory calculations are performed to investigate the charge density difference and partial density of states of CoNi‐DH@Ti3C2Tx and the theoretical assessment suggests that the chemical bonds between Ti3C2Tx and CoNi‐DH are critical to the charge transport, electrical conductivity, and structural stability.

In-Situ growing tungsten Sulfide/Carbon nanosheets on sodium titanate nanorods to stabilize Surface-Structure for enhanced Sodium-ion storage

Sodium-ions hybrid capacitors (SIHCs) have been recognized as one of the most potential energy storage devices, which can deliver high power and energy densities simultaneously. However, the sluggish kinetics of electrode materials severely restricts the performance of SIHCs. Herein, N, P-codoped carbon and WS2 nanosheets coating on sodium titanate nanorods (NTO@WS2/N, PC) were first designed by in-situ growing process and sulfuration treatment for boosting sodium-ion storage. Specifically, NTO@WS2/N, PC electrodes displayed a satisfactory specific capacity of 274.7 mAh g−1 at 3.0 A g−1 after 1200 cycles. Furthermore, as-assembled SIHCs delivered high-energy density of 112.1 Wh kg−1 and high-power density of 4334.4 W kg−1. Besides, long-term cycling test revealed that a remarkable capacity retention rate of 89.7% was obtained at 8.0 A g−1 after 2000 cycles. The excellent cycling stability and rate property could be ascribed to following aspects. On the one hand, N, P-codoped carbon could enhance the electrical conductivity and strengthen the structural integrality of the composites. On the other hand, ultrathin WS2 nanosheets and one-dimensional (1D) NTO nanorods structure were conducive to the rapid diffusion of Na+. This work provides a convenient technique to stabilize the structure of electrode materials, which can promote the practical application of SIHCs.

Oxygen Vacancies Enhanced NiCo2O4 Nanoarrays on Carbon Cloth as Cathode for Flexible Supercapacitors with Excellent Cycling Stability

AbstractDefect engineering such as oxygen vacancy in heterostructured electrode materials has emerged as a promising strategy to improve material performance in energy storage and conversion fields. The most common methods to introduce oxygen vacancies in energy materials usually involve high temperature treatment or strong reducing agents. In this work, we adopted a mild solvothermal treatment method to introduce oxygen vacancies into NiCo2O4 (Vo‐NiCo2O4) nanoarrays. Owing to the increased oxygen vacancies and the improved surface area, the as‐prepared Vo‐NiCo2O4 on carbon cloth (Vo‐NiCo2O4@CC) shows a high specific capacitance of 1389 mF cm−2 under the current density of 0.5 mA cm−2, and a remarkable capacitance retention of 93.8 % after 10000 cycles when used as cathode for supercapacitor. Moreover, an aqueous asymmetric supercapacitor was assembled using Vo‐NiCo2O4@CC as cathode and AC@CC as anode and this device delivers a high energy density of 43.6 Wh kg−1 at a power density of 281 W kg−1. In addition, the as‐assembled quasi‐solid state asymmetric supercapacitor exhibits excellent mechanical flexibility and functions well while being bent at large angles or being twisted. This work offers a facile, cost‐effective and practical available approach to finely tune the surface property of electrode materials towards flexible energy storage devices for wearable applications.

Positive Role of Fluorine Impurity in Recovered LiNi0.6Co0.2Mn0.2O2 Cathode Materials.

Lithium-ion battery (LIB) recycling is considered as an important component to enable industry sustainability. A massive number of LIBs in portable electronics, electric vehicles, and grid storage will eventually end up as wastes, leading to serious economic and environmental problems. Hence, tremendous efforts have been made to improve the hydrometallurgical recycling process because it is the most promising option for handling end-of-life LIBs owing to its wide applicability, low cost, and high productivity. Despite these advantages, some extra elements (Al, Fe, C, F, and so forth) remain as impurities in the removal process and are retained in the solution, which is a great challenge to obtain high-quality cathode materials. In this work, the impacts caused by fluorine impurity on the LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode are intensively investigated via hydrometallurgical coprecipitation for the first time. Our results show that up to 1 at. % fluorine impurity brings a positive influence on the recovered material due to a higher Ni2+ ratio on the surface of cathode particles. In addition, the presence of fluoride ions during coprecipitation could lead to the formation of holes in cathode particles, which improves the rate capability and cyclability dramatically. Compared to the virgin material, the capacity of the NCM622 material with 0.2 at. % fluorine impurity is boosted by ∼8% (167.7 mA h/g) with a remarkable capacity retention of 98.0% after 100 cycles at 0.33 C. Besides, the cathode with 0.2 at. % fluorine impurity shows a far better rate performance, especially at high rates (∼7% increased at 5 C) than that of virgin. These results convince that a low concentration of fluorine impurity is desirable in the hydrometallurgical recycling process. More importantly, this study offers implications in the design of high-performance NCM622 cathode materials via coprecipitation production with ion doping in the near future.