Ion Transport Kinetics Research Articles

Preparation of hierarchical porous carbon by pyrolyzing sargassum under microwave: The internal connection between structure−oriented regulation and performance optimization of supercapacitors

To find an effective correlation between the preparation process and the application performance of symmetric supercapacitors, the relationship between the structural characteristics of biomass porous carbon and the electrochemical performances of supercapacitors was studied. Based on a response surface experimental design, the pore structure of biochar produced by the microwave pyrolysis of sargassum was adjusted through the collaborative optimization of key parameters, and graded sargassum porous carbon (SPC) with different pore characteristics was successfully prepared. Three representative samples, SPC−1, SPC−2, and SPC−3, were selected by systematically exploring the effects of the specific surface area (SSA), pore volume (Vtotal), and pore size distribution on the electrochemical performances. The SSA and Vtotal values of SPC−1 were 1500.50 m2 g−1 and 1.0513 cm3 g−1, respectively. The large number of micropores provided space for electronic storage, allowing it to have an excellent electronic storage capacity. The SSA of SPC−2 was 2019.90 m2 g−1, and Vtotal was 1.2241 cm3 g−1. The rich micropores resulted in a good charge–discharge rate. The SSA of SPC−3 was as high as 2103.20 m2 g−1, and Vtotal was 1.4756 cm3 g−1. The micron−level mesopores between the SPC−3 carbon skeletons acted as ion buffer reservoirs to shorten the ion diffusion distance and produce excellent rate performances. Subsequently, the morphology and surface properties of porous carbon samples were characterized. The study revealed that hierarchical porous carbon materials with excellent properties must achieve a balance of the microstructure and surface properties and their influence on the electrochemistry. A higher degree of graphitization could bring about a high pore regularity, thereby optimizing the ion transport kinetics. Heteroatoms could increase redox active surface sites and provide additional pseudocapacitance, but the resulting defect structure formed a large number of pores with high edge roughness in the carbon material, which had a certain negative impact on the capacity properties of the materials. The above findings can provide technical support and a theoretical basis for controlling the pore networks and directionally optimizing the performances of supercapacitors by adjusting the pore structure of biochar.

Ultra-thin graphene cube framework@TiO2 heterojunction as high-performance anode materials for lithium ion batteries

Here, we proposed a new strategy to build the integrated graphene cube (Gr) framework@TiO2 composite to improve the ion transport kinetics and electrical conductivity of TiO2 as a long-life and high-capacity anode for lithium ion batteries. Combined with the salt template method for ultra-thin framework, the distinct structure of Gr@TiO2 shows an excellent electrochemical performance, e.g., initial coulombic efficiency (ICE), rate performance and specific capacity, due to the increased kinetics of lithium ions. Through this method, the integrity is dramatically improved and the pulverization and agglomeration of the anode after long-term cycles are restrained. The optimized Gr@TiO2 displays a high stable reversible capacity of 179.5 mAh g−1 after 4000 cycles at 1 A g−1, excellent rate performance (125.5 mAh g−1 at 5 A g−1). Kinetic studies through Electrochemical Impedance Spectra, Galvanostatic Intermittent Titration Technique and Linear Sweep Voltammetry confirm that the electrical conductivity and ion transport kinetics are dramatically improved through the ultra-thin graphene cube framework as a heterojunction structure of Gr@TiO2.

Stable silicon anodes realized by multifunctional dynamic cross-linking structure with self-healing chemistry and enhanced ionic conductivity for lithium-ion batteries

Silicon anodes have attracted enormous attention with the merits of outstanding theoretical capacity for high-energy-density lithium-ion batteries. However, the drastic volume variation will destroy the structural integrity of the electrode system during the alloying/dealloying process. Herein, based on the supramolecular self-assembly, a multifunctional dynamic cross-linking strategy with self-healing chemistry and enhanced ionic conductivity for silicon electrode network structure is rationally designed by amino-functionalized silicon (Si-NH2) and dopamine-modified poly(acrylic acid) (PAA-DA). Dynamic reversible hydrogen bonds and ionic bonds are formed by random cross-linking of the primitives carried by the material, which endow the electrode with rapid self-healing ability and strong adhesion, and provide a continuous internal pathway for the electrode system. Moreover, the presence of polar groups can beneficially heighten the transport kinetics of lithium ions. The prepared Si-NH2@PAA-DA electrode displays excellent high-rate capability with a reversible capacity of 2671.6 mAh g−1 at 1 C (1 C = 4000 mA g−1) and superior cycle stability (2160.1 mAh g−1 after 100 cycles at 400 mA g−1). Therefore, this design idea with dynamic reversible and multi-crosslink network structure provides in-depth insights for the advancement of the next-generation high-energy-density batteries.

Surface optimized P2-Na2/3Ni1/3Mn2/3O2 cathode material via conductive Al-doped ZnO for boosting sodium storage

Layered transition-metal oxides have been potential as high-performance cathode materials for sodium-ion batteries (SIBs), however, suffer from the undesirable side reactions between cathode/electrolyte interface during cycling. One improvement strategy by surface coatings is typically used, but at the compromise of lowering ion transport kinetics and poor rate capability. Herein, we report a surface optimized high-rate P2-Na2/3Ni1/3Mn2/3O2 cathode material for SIBs via a highly conductive Al-doped ZnO (AZO). By tuning the calcination temperatures, the optimized cathode material coated with 1 wt% AZO at 500 °C exhibits decent cycling and rate performances (66.2 mAh g−1 with a capacity retention of 82.6% at 5C after 500 cycles). Electrochemical kinetics analysis demonstrates that the NM@AZO-500 exhibits a high Na+ diffusion coefficient and a low charge-transfer resistance, and in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) reveal that the AZO coating effectively relieves the lattice stress during cycles and inhibits undesirable side reaction; all of which give rise to the observed enhancement. The result promises an effective surface optimized route for high-performance cathode materials for SIBs by coating highly conductive oxide.

Highly Reversible Zinc Anode Enabled by a Cation-Exchange Coating with Zn-Ion Selective Channels.

Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted extensive attention due to their low cost and high safety. However, the critical issues of dendrite growth and side reactions on the Zn metal anode hinder the commercialization of ZIBs. Herein, we demonstrated that the formation of Zn4SO4(OH)6·5H2O byproducts is closely relevant to the direct contact between the Zn electrode and SO42-/H2O. On the basis of this finding, we developed a cation-exchange membrane of perfluorosulfonic acid (PFSA) coated on the Zn surface to regulate the Zn plating/stripping behavior. Importantly, the PFSA film with abundant sulfonic acid groups could simultaneously block the access of SO42- and H2O, accelerate the Zn2+ ion transport kinetics, and uniformize the electrical and Zn2+ ion concentration field on the Zn surface, thus achieving a highly reversible Zn plating/stripping process with corrosion-free and dendrite-free behavior. Consequently, the PFSA-modified Zn anode exhibits high reversibility with 99.5% Coulombic efficiency and excellent plating/stripping stability (over 1500 h), subsequently enabling a highly rechargeable Zn-MnO2 full cell. The strategy of the cation-exchange membrane proposed in this work provides a simple but efficient method for suppression of side reactions.

Regulated lithium deposition behavior by chlorinated hybrid solid-electrolyte-interphase for stable lithium metal anode

Lithium (Li) metal is the ultimate anode material for use in next-generation batteries in the pursuit of higher energy densities. However, the traditional solid electrolyte interphase (SEI) owns the disadvantages of large interfacial impedance, low Li ions migration rate and easy fragility. Herein, this is the first report that reveals in detail the rationality of Li deposition beneath the chlorinated hybrid layer and fast ion transport kinetics at LiCl/Li interface through density functional theory (DFT) estimation. Based on this, an artificial SEI layer enriched with LiCl, LiZn alloy and in-situ ring-opening polymerization of poly(tetrahydrofuran) (PTMG) is constructed on lithium metal surface. The glow-discharge optical emission spectroscopy (GD-OES) results revealed that LiCl is mainly enriched on the surface of the artificial SEI, its excellent electron-blocking ability could inhibit the electron flow tunneling from the Li metal to SEI, which prevents the generation of Li0. As expected, the Li metal anode with an artificial chlorinated hybrid SEI layer exhibits excellent cycle performance over 2000 h with lower overpotential of 11 mV at 1 mA cm−2. Moreover, full-cell delivers higher capacity retention and coulombic efficiency after long cycles under high LiFePO4 loading (at 17.4 mg cm−2, 3.0 mAh cm−2).

Novel Polymer/Barium Intercalated Vanadium Pentoxide with Expanded Interlayer Spacing as High-Rate and Durable Cathode for Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (AZIBs) exhibit great potential in large-scale energy storage systems. However, limited reaction kinetics and poor long-cycle stability restrict the application of vanadium oxide cathode materials. Herein, we designed and successfully synthesized a novel composite material with polyethylene glycol (PEG) and barium cation (Ba2+) preintercalated between the layers of vanadium pentoxide, denoted as PEG-Ba0.38V2O5·nH2O (PEG-BVO), as a cathode material of AZIBs. The optimized PEG-BVO material shows a uniform nanobelt-like structure with the expanded interlayer spacing of 1.07 nm, significantly promoting the transport kinetics of zinc ions. The theoretical calculation results unravel that an interlayer spacing of 1.07 nm may be at the most stable state for this layered composite structure, ensuring a robust architecture for rapid reversible (de)intercalation of zinc ions. As a result, the PEG-BVO electrode (with a large mass loading of 4 mg cm-2) exhibits an outstanding electrochemical performance including a high specific capacity (345 mAh g-1 at 0.1 A g-1), decent rate capability (up to 175 mAh g-1 at 10 A g-1), and long-term cycling stability (98.8% capacity retention upon 4000 cycles at 6 A g-1). Our discovery provides a new guest preinsertion strategy to construct a robust layered vanadium-based electrode with the expanded interlayer spacing, and the as-prepared PEG-Ba0.38V2O5·nH2O shows great potential as a high-rate positive electrode for AZIBs.

Nanoconfined SnS2 in robust SnO2 nanocrystals building heterostructures for stable sodium ion storage

Transition-metal dichalcogenides are emerging as a class of attractive host materials for Na+ insertion, owing to its high theoretical specific capacity, whereas the intrinsic low conductivity and huge volume fluctuations during deep cycles severely restrict their practical applications. Heterostructure engineering can not only optimize ion transport kinetics to boost rate property but confine mechanical degradation by participation of the second phases. In order to cushion the internal stress and dramatic volume variations induced by the large radius of Na+, herein we introduced a more robust material (SnO2) to construct CC@SnS2/SnO2 heterostructure for sodium-ion batteries (SIBs). The experimental and density functional theory calculations indicate that compressive stress at the heterogeneous interface can effectively buffer the sodiation-induced internal strain by 10%, further maintain the structural stability and improve the cycling performances. Meanwhile, the involvement of inert SnO2 phase, which effectively alleviate the serious volume expansion caused by the active SnS2 upon an extensive sodiation/desodiation process. As expected, the CC@SnS2/SnO2 composite exhibits high reversible capacity (694.7 mAh g−1 at 0.2 A g−1) and long-term cycling retention (78.3% after 100 cycles). Our work inspire a pathway of the selection of heterogeneous materials toward a highly stable SIBs anode.

Optimizing porous structure of carbon electrodes for temperature-independent capacitance at sub-zero temperatures

Fundamental understanding of ion transport in porous carbon materials with different pore size is of great importance for carbon electrode-based supercapacitors to realize the ability of rapid charge/discharge process and high energy density at broad operating temperatures. Herein, hierarchically porous carbon frameworks are synthesized as model electrodes by using a tunable one-pot strategy in the presence of salt template and pore-forming agent. Density functional theory calculation reveals that the size of micropores can significantly influence the solvation energy and desolvation time of electrolyte, thereby affecting the ion transport kinetics and the specific capacitance of porous carbon electrode, particularly at low temperatures. The accordingly optimized carbon electrode material with rational micropore size and interconnected hierarchical pores exhibits the specific capacitance of 200 and 245F·g−1 at −40 and 60 °C, respectively. The as-fabricated symmetric supercapacitor can deliver an exceptional energy density of 63.4 Wh·kg−1 under power density of 1.5 kW·kg−1 at −40 °C. In addition, the device has the ability for fast charge/discharge process at low temperature, as evidenced by the energy density of 34.3 Wh·kg−1 under an ultrahigh power density of 37.5 kW·kg−1 at − 40 °C.

Pr6O11 interfacial engineering toward high-performance NCM523

Developing an efficient method to achieve fast discharge/charge ability and long-cycle life for LiNixCoyMn1-x-yO2 (NCM) cathodes remains an urgent and challenging problem to effectively improve the overall performance of Lithium-ion batteries (LIBs). In this study, NCM523 uniformly modified by Pr6O11 nanoparticles (NCM-Pr6O11) were prepared using simple liquid-phase mixing and annealing methods. Pr6O11 interface engineering for NCM-Pr6O11 composites can significantly enhance the electronic conductivity, boost the ion transport kinetics, improve the interface compatibility with electrolyte, and inhibit the structural destruction of secondary particles of NCM, making the composite with obviously enhanced LIB performance including cycle stability, energy density and thermal safety. The capacity retention of NCM-b samples tested at 25 °C and 60 °C can deliver 77.4% and 78.5%, respectively, higher than those of pure NCM electrodes. Furthermore, the assembled NCM-b//graphite full cells show improved thermal safety and excellent LIB performance even with a capacity retention of 86.1% after 1000 cycles. Thus, such a simple modification strategy for NCM cathodes provides promising enlightenment for the production of LIBs with high-energy density.

Design of a fast ion-transport interlayer on cathode-electrolyte interface for solid-state lithium metal batteries

For the safety and high-energy-density, solid-state lithium metal batteries (SSLMBs) have aroused researchers’ interest, especially utilizing high-nickel layered cathode of LiNi0.8Co0.15Al0.05O2 (NCA) that coupling with solid polymer-based electrolyte (SPE). However, the applications of SPE-based SSLMBs with NCA cathode were still trucked by the deficient physical contact between NCA cathode and solid electrolyte, which contributes to the high contact resistance at cathode-electrolyte interface and thus the non-uniform delithiation/lithiation kinetics of NCA particles. Here, we designed a fast ion-transport interlayer on NCA cathode particles by chelating effect between functional group on polymer electrolyte and metal ions in NCA (PGII-NCA), aiming to build an unobstructed channel for enhanced ion-transport kinetics on NCA surface. The SSLMBs with PGII-NCA cathode deliver high capacity of 156.4 mAh g−1 and maintain 91.3% capacity after 100 cycles at room temperature. Thus, we suggest that this design strategy of modifying the NCA surface by chelating copolymer gel layer is an effective approach to tackle the sluggish kinetics on cathode-electrolyte interface, boosting the practical application of SSLMBs.

Overcoming Ion Transport Barrier by Plasma Heterointerface Engineering: Epitaxial Titanium Carbonitride on Nitrogen-Doped TiO2 for High-Performance Sodium-Ion Batteries.

Anatase TiO2 is a promising anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) due to its high specific capacity, low cost, and excellent cycle stability. However, low electrical conductivity and poor Na+ ion transport in TiO2 limit its practical applications. Here, substantially boosted Na+ ion transport and charge transfer kinetics are demonstrated by constructing a near-ideal non-rectifying titanium carbonitride/nitrogen-doped TiO2 (TiCx N1- x /N-TiO2 ) heterostructure. Owing to the fast plasma effects and metastable hybrid phases, the TiCx N1- x is epitaxially grown on TiO2 . Energy band engineering at the interface induces high electron densities and a strong built-in electric field, which lowers the Na+ diffusion barrier by a factor of 1.7. As a result, the TiCx N1- x /N-TiO2 electrode exhibits excellent electrochemical performance. The reversible specific capacities at rates of 0.1 and 10 C reach 312.3 and 173.7 mAh g-1 , respectively. After 600 cycles of charge and discharge at 10 C, the capacity retention rate is 98.7%. This work discovers an effective non-equilibrium plasma-enabled process to construct heterointerfaces that can enhance Na+ ion transport and provides generic guidelines for the design of heterostructures for a broader range of energy storage, separation, and other devices that rely on controlled ionic transport.

Vertically Oriented MXene Bridging the Frequency Response and Capacity Density Gap for AC‐Filtering Pseudocapacitors

AbstractElectrochemical capacitors (ECs) with high‐rate characteristics demonstrate great promise for replacing bulky aluminum electrolytic capacitors with alternate current (AC)‐filtering functions. Currently, the performance of AC‐line filtering ECs is limited by the vast gap between the ionic transport kinetics and capacity density of electrode materials. Herein, vertically oriented MXene and reduced graphene oxide composite (VMG) electrodes are prepared by electrochemical co‐deposition to bridge the performance gap for AC‐line filtering ECs. Benefiting from the unique pseudocapacitive characteristic and vertically interconnected microstructure, the VMG‐based EC exhibits an outstanding areal capacitance of 1.14 mF cm−2 with a phase angle of −80° at 120 Hz. Moreover, by utilizing the advantages of MXene at negative potential, an asymmetric pseudocapacitor is constructed with an energy density up to 805 µF V2 cm−2 at 120 Hz, which can be further incorporated in portable and wearable devices with excellent environmental ripple filtering capability in diverse scenarios.

Critical Role of Structural Water for Enhanced Li+ Insertion Kinetics in Crystalline Tungsten Oxides

Electrochemical ion insertion into transition metal oxides forms the foundation of several energy technologies. Transition metal oxides can exhibit sluggish ion transport and/or phase-transformation kinetics during ion insertion that can limit their performance at high rates (<10 min). In this study, we investigate the role of structural water in transition metal oxides during Li+ insertion using staircase potentiostatic electrochemical impedance spectroscopy (SPEIS) and electrochemical quartz crystal microbalance (EQCM) analysis of WO3·H2O and WO3 thin-film electrodes. Overall, the presence of structural water in WO3·H2O improves Li+ insertion kinetics compared to WO3 and leads to a less potential-dependent insertion process. Operando electrogravimetry and 3D Bode impedance analyses of nanostructured films reveal that the presence of structural water promotes charge accommodation without significant co-insertion of solvent, leading to our hypothesis that the electrochemically induced structural transitions of WO3 hinder the electrode response at faster timescales (<10 min). Designing layered materials with confined fluids that exhibit less structural transitions may lead to more versatile ion-insertion hosts for next-generation electrochemical technologies.

Carbon-coated hydrated vanadium dioxide for high-performance aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) show enormous potential in large-scale energy supply and storage attribute to safety and economy. However, the slow transport dynamics and unstable structural stability of the conventional cathodes hinder the further development of AZIBs. In this work, carbon-coated hydrated vanadium dioxide (HVO@C) was prepared by a one-step hydrothermal method. The introduction of water molecules provides suitable ambient spacing for rapidly accommodating and transporting cations, the coating of carbon further stabilizes the structure of the material and improves the conductivity of the material. The synergistic merits of pre-intercalated water molecules and carbon encapsulation are beneficial for both electron and ion transport kinetics. And the content of water molecules is controlled by regulating V/C ratio. Electrochemical results revealed that the H1.99VO@C/Zn batteries yield a good reversible specific capacity (329.0 mA h g−1 at 1 A g−1) with superior cycling stability (174.2 mA h g−1 at 5 A g−1 after 1000 cycles). This work provides a strategy for developing safe and high-performance energy storage equipment by pre-intercalated defect and carbon encapsulation.

Biomass‐Derived Hierarchically Porous (Nitrogen, Phosphorus) Co‐Doped SiOx/C Composite Nanosheet Architectures for Superior Lithium Storage and Ultra‐Long Cycle Performance

AbstractBiomasses receive much attention as carbon sources for anodes of high‐energy lithium‐ion batteries and cathodes of lithium‐sulfur batteries due to their low costs, easy availability and potentially high capacities which unfortunately deliver unsatisfactory performances normally. However, biomasses used as silicon instead of carbon‐dominated sources have never been touched before. Here, we report a facile preparation of nitrogen and phosphorus heteroatoms co‐doped hierarchically porous and cross‐linked SiOx/C composite nanosheet architectures from catkins without the introduction of alien Si (N/P‐SiOx/C‐NSs) using chemical exfoliation and treatments. This unique structure composed of novel multiple‐phase composites is revealed to show superior fast kinetics and ultra‐long cycle life with about 340 mAh g−1 and almost no capacity decay after 10000 cycles at 10 A g−1, far beyond those of conventional carbon and SiOx‐based anode materials. The superior performance is closely related to excellent electronic conduction arising from the cross‐linkage architecture, well‐graphitized carbon and uniform co‐doping of nitrogen and phosphorus, rapid ionic transport kinetics from rich hierarchical pores, and outstanding stability from the rigid nanosheet networks. This study sets a precedent of catkins as silicon instead of conventional carbon‐only sources for anode materials, which can largely enhance the role of biomasses in energy storage.

Operando monitoring of ion activities in aqueous batteries with plasmonic fiber-optic sensors

Understanding ion transport kinetics and electrolyte-electrode interactions at electrode surfaces of batteries in operation is essential to determine their performance and state of health. However, it remains a challenging task to capture in real time the details of surface-localized and rapid ion transport at the microscale. To address this, a promising approach based on an optical fiber plasmonic sensor capable of being inserted near the electrode surface of a working battery to monitor its electrochemical kinetics without disturbing its operation is demonstrated using aqueous Zn-ion batteries as an example. The miniature and chemically inert sensor detects perturbations of surface plasmon waves propagating on its surface to rapidly screen localized electrochemical events on a sub-μm-scale thickness adjacent to the electrode interface. A stable and reproducible correlation between the real-time ion insertions over charge-discharge cycles and the optical plasmon response has been observed and quantified. This new operando measurement tool will provide crucial additional capabilities to battery monitoring methods and help guide the design of better batteries with improved electro-chemistries.

Rational Design of 1D Porous Carbon Microtubes Supporting Multi‐size Bi2O3 Nanoparticles for Ultra‐long Cycle Life Lithium‐Ion Battery Anodes

AbstractMulti‐size Bi2O3 nanoparticles supported by 1‐dimensional (1D) porous carbon microtubes (ms‐Bi2O3/CMTs) were favorably constructed through surface‐ion release and in‐ situ oxidation strategy. The prominent 1D porous microtube materials with multi‐size nanoparticles structure can furnish more plentiful electrochemical active sites and shorten lithium storage paths for high‐speed redox reactions, which was conducive to ion transport kinetics. The CV tests with various scan rates verified lithium storage mechanism of ms‐Bi2O3/CMTs with diffusion/capacitance control coexistence. The complexes illustrated an ultra‐long cycle life and extraordinary reversible capacity: it still had a specific capacity of 392.6 mAh g−1 after 3000 cycles at 1 A g−1; and it manifested 546.3 mAh g−1 when it returned to 0.05 A g−1 and continued to 100 cycles after experiencing different current densities of 0.05–5 A g−1, which indicated that ms‐Bi2O3/CMTs is a prospective anode for lithium‐ion batteries (LIBs).

Synthesis, Characterizations, and Electrochemical Performances of Highly Porous, Anhydrous Co0.5Ni0.5C2O4 for Pseudocapacitive Energy Storage Applications.

Electrochemical energy storage relies essentially on the development of innovative electrode materials with enhanced kinetics of ion transport. Pseudocapacitors are excellent candidates to bridge the performance gap between supercapacitors and batteries. Highly porous, anhydrous Ni0.5Co0.5C2O4 is envisaged here as a potential electrode for pseudocapacitor applications, mainly because of its open pore framework structure, which poses inherent structural stability due to the presence of planar oxalate anions (C2O42–), and active participation of Ni2+/3+ and Co2+/3+ results in high intercalative charge storage capacity in the aqueous KOH electrolyte. The Ni0.5Co0.5C2O4 electrode shows specific capacitance equivalent to 2396 F/g at 1 A/g in the potential window of 0.6 V in the aqueous 2 M KOH electrolyte by galvanostatic charge/discharge experiments. Predominant pseudocapacitive mechanism seems to operative behind high charge storage due to active participation of Ni2+/3+ and Co2+/3+ redox couple as intercalative (inner) and surface (outer) charges stored by porous anhydrous Co0.5Ni0.5C2O4 were close to high 38 and 62% respectively. Further, in full cell asymmetric supercapacitors (ASCs) in which porous anhydrous Co0.5Ni0.5C2O4 was used as the positive electrode and activated carbon (AC) was utilized as the negative electrode, in the operating potential window 1.6 V, the highest specific energy of 283 W h/kg and specific power of ∼817 W/kg were achieved at 1 A/g current rates. Even at a very high power density of 7981 W/kg, the hybrid supercapacitor still attains an energy density of ∼75 W h/kg with high cyclic stability at a 10 A/g current rate. The detailed electrochemical studies confirm higher cyclic stability and a superior electrochemical energy storage property of porous anhydrous Co0.5Ni0.5C2O4, making it a potential pseudocapacitive electrode for large energy storage applications.

Crystal Facet and Architecture Engineering of Metal Oxide Nanonetwork Anodes for High-Performance Potassium Ion Batteries and Hybrid Capacitors.

Metal oxides are considered as prospective dual-functional anode candidates for potassium ion batteries (PIBs) and hybrid capacitors (PIHCs) because of their abundance and high theoretic gravimetric capacity; however, due to the inherent insulating property of wide band gaps and deficient ion-transport kinetics, metal oxide anodes exhibit poor K+ electrochemical performance. In this work, we report crystal facet and architecture engineering of metal oxides to achieve significantly enhanced K+ storage performance. A bismuth antimonate (BiSbO4) nanonetwork with an architecture of perpendicularly crossed single crystal nanorods of majorly exposed (001) planes are synthesized via CTAB-mediated growth. (001) is found to be the preferential surface diffusion path for superior adsorption and K+ transport, and in addition, the interconnected nanorods gives rise to a robust matrix to enhance electrical conductivity and ion transport, as well as buffering dramatic volume change during insertion/extraction of K+. Thanks to the synergistic effect of facet and structural engineering of BiSbO4 electrodes, a stable dual conversion-alloying mechanism based on reversible six-electron transfer per formula unit of ternary metal oxides is realized, proceeding by reversible coexistence of potassium peroxide conversion reactions (KO2↔K2O) and BixSby alloying reactions (BiSb ↔ KBiSb ↔ K3BiSb). As a result, BiSbO4 nanonetwork anodes show outstanding potassium ion storage in terms of capacity, cycling life, and rate capability. Finally, the implementation of a BiSbO4 nanonetwork anode in the state-of-the-art full cell configuration of both PIBs and PIHCs shows satisfactory performance in a Ragone plot that sheds light on their practical applications for a wide range of K+-based energy storage devices. We believe this study will propose a promising avenue to design advanced hierarchical nanostructures of ternary or binary conversion-type materials for PIBs, PIHCs, or even for extensive energy storage.