Rational design of N-doped CNTs@C3N4 network for dual-capture of biocatalysts in enzymatic glucose/O2 biofuel cells.

Carbonaceous materials are promising electrode materials for enzymatic biofuel cells (EBFCs) due to their excellent electrical conductivity, chemical and physical stability and biocompatibility. Design and preparation of carbon materials with a hollow structure and a rough surface are of great significance for immobilization of enzymes both inside and outside the carbon materials for EBFC applications. We report herein the synthesis of novel carbonaceous materials consisting of bamboo-shaped hollow N-doped carbon nanotubes (N-CNTs) and C3N4 nanosheets (denoted as N-CNTs@C3N4) as electrode materials for dual-capture of enzymes in glucose/O2 EBFCs. The combination of one-dimensional N-CNTs with an open structure and two-dimensional C3N4 nanosheets forms a three-dimensional crosslinking network that significantly enhances the immobilization of enzymes, electrode stability, and mass transfer of substrates, thus boosting the EBFC performance. As a result, EBFCs equipped with N-CNTs@C3N4 can generate a high open circuit potential of 0.93 V and output a maximum power density of 0.57 mW cm-2 at 0.47 V. Additionally, the as-fabricated glucose/O2 EBFCs are capable of directly harvesting energy from various soft drinks, which indicates the promising applications of the N-CNTs@C3N4 nanocomposite as an electrode material for EBFCs.

Confining Pyrrhotite Fe7 S8 in Carbon Nanotubes Covalently Bonded onto 3D Few-Layer Graphene Boosts Potassium-Ion Storage and Full-Cell Applications.

The pyrrhotite Fe7 S8 with mixed Fe-valence possesses high theoretical capacity, high conductivity, low discharge/charge voltage plateaus, and superior redox reversibility but suffers from structural degradation upon (de)potassiation process due to severe volume variations. Herein, to conquer this issue, a novel hierarchical architecture of confining nano-Fe7 S8 in carbon nanotubes covalently bonded onto 3D few-layer graphene (Fe7 S8 @CNT@3DFG) is designed for potassium storage. Notably, CNTs could successfully grow on the surface of 3DFG via a tip-growth model under the catalytic effect of Fe3 C. Such structure enables the hierarchical confinement of 0D nano-Fe7 S8 to 1D CNTs and further 1D CNTs to 3DFG, effectively buffering the volume variations, prohibiting the agglomeration of Fe7 S8 nanograins, and boosting the ionic/electronic transportation through the stable and conductive CNTs-grafted 3DFG framework. The as-prepared Fe7 S8 @CNT@3DFG electrode delivers an exceptional rate capability (502 mAh g-1 at 50 mA g-1 with 277 mAh g-1 at 1000 mA g-1 ) and an excellent long-term cyclic stability up to 1300 cycles. Besides, the in-situ XRD and ex-situ XPS/HRTEM results first elucidate the highly reversible potassium-storage mechanism of Fe7 S8 . Furthermore, the designed potassium full-cell employing Fe7 S8 @CNT@3DFG anode and potassium Prussian blue (KPB) cathode delivers a promising energy density of ≈120 Wh kg-1 , demonstrating great application prospects.

Iron Selenide Microcapsules as Universal Conversion-Typed Anodes for Alkali Metal-Ion Batteries.

Rechargeable alkali metal-ion batteries (AMIBs) are receiving significant attention owing to their high energy density and low weight. The performance of AMIBs is highly dependent on the electrode materials. It is, therefore, quite crucial to explore suitable electrode materials that can fulfil the future requirements of AMIBs. Herein, a hierarchical hybrid yolk-shell structure of carbon-coated iron selenide microcapsules (FeSe2 @C-3 MCs) is prepared via facile hydrothermal reaction, carbon-coating, HCl solution etching, and then selenization treatment. When used as the conversion-typed anode materials (CTAMs) for AMIBs, the yolk-shell FeSe2 @C-3 MCs show advantages. First, the interconnected external carbon shell improves the mechanical strength of electrodes and accelerates ionic migration and electron transmission. Second, the internal electroactive FeSe2 nanoparticles effectively decrease the extent of volume expansion and avoid pulverization when compared with micro-sized solid FeSe2 . Third, the yolk-shell structure provides sufficient inner void to ensure electrolyte infiltration and mobilize the surface and near-surface reactions of electroactive FeSe2 with alkali metal ions. Consequently, the designed yolk-shell FeSe2 @C-3 MCs demonstrate enhanced electrochemical performance in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries with high specific capacities, long cyclic stability, and outstanding rate capability, presenting potential application as universal anodes for AMIBs.

Blowing Iron Chalcogenides into Two-Dimensional Flaky Hybrids with Superior Cyclability and Rate Capability for Potassium-Ion Batteries.

Chalcogenide-based anodes are receiving increasing attention for rechargeable potassium-ion batteries (PIBs) due to their high theoretical capacities. However, they usually exhibit poor electrochemical performance due to poor structural stability, low conductivity, and severe electrolyte decomposition on the reactive surface. Herein, a method analogous to "blowing bubbles with gum" is used to confine FeS2 and FeSe2 in N-doped carbon for PIB anodes with ultrahigh cyclic stability and enhanced rate capability (over 5000 cycles at 2 A g-1). Several theoretical and experimental methods are employed to understand the electrodes' performance. The density functional theory calculations showed high affinity for potassium adsorption on the FeS2 and FeSe2. The in situ XRD and ex situ TEM analysis confirmed the formation of several intermediate phases of the general formula KxFeS2. These phases have high conductivity and large interlayer distance, which promote reversible potassium insertion and facilitate the charge transfer. Also, the calculated potassium diffusion coefficient during charge/discharge further proves the enhanced kinetics. Furthermore, The FeS2@NC anode in a full cell also exhibits high cyclic stability (88% capacity retention after 120 cycles with 99.9% Coulombic efficiency). Therefore, this work provides not only an approach to overcome several challenges in PIB anodes but also a comprehensive understanding of the mechanism and kinetics of the potassium interaction with chalcogenides.

CoSe2/N-doped carbon porous nanoframe as an anode material for potassium-ion storage.

Transition metal selenides (TMS), on account of their relatively high theoretical capacity, unique electrical properties, easy compositing and low cost, are considered to be a candidate anode material for potassium-ion batteries. However, the cycling stability of TMS is unsatisfactory owing to the large intercalation/deintercalation of K ions. Herein, a CoSe2/N-doped carbon porous frame (CoSe2@NC) is successfully synthesized through a simple mixing and sintering approach and displays excellent potassium storage performance. Plentiful C-N bonds in the precursor can induce the formation of homogeneous N-doped carbon matrix and C-N-Co bonds, thus endowing robust structure and high electronic conductivity for superior cycling stability. Therefore, the unique porous nanoframe suppresses volume expansion and provides more diffusion paths for K ions. After 1000 cycles at 50 mA g-1, a high capacity of 311.3 mA h g-1 is acquired. When the current density increases to 500 mA g-1, the CoSe2@NC can still maintain a capacity of 184.5 mA h g-1 after 1000 cycles. The high performance, easy compositing and low cost of the CoSe2@NC make it a favorable material for application in KIBs.

Amorphous carbon coated SnO2 nanohseets on hard carbon hollow spheres to boost potassium storage with high surface capacitive contributions.

Potassium-ion batteries (KIBs) have becoming a prospective energy storage technique, due to the abundant potassium resources in the earth crust, approximate redox potential and similar electrochemical behavior of potassium and lithium. However, the insufficient capacity, poor stability and volume expansion of electrode materials during charge and discharge are main factors restricting the further development of KIBs. This work reports an amorphous carbon coated SnO2 nanohseets on hard carbon hollow spheres (AC/SnO2@HCHS) anode with enhanced potassium storage performance. The HCHS acts as a carrier for SnO2 nanosheets, providing high electrical conductivity and stable skeleton. The self-assembled SnO2 nanosheets with high surface area ensures sufficient contact with the electrolyte. Amorphous carbon wrapping can not only relieve SnO2 volume expansion but also provide surface-induced capacitive capacity. As a consequence, the AC/SnO2@HCHS anode presents excellent potassium-ion storage performance with high discharge capacity of 346 mAh g-1 at 0.1 A g-1 over 200 cycles, ultra-long cycling lifetime and outstanding rate capability (236 mAh g-1 at 1 A g-1 over 1000 cycles).

Flexible N doped carbon/bubble-like MoS2 core/sheath framework: Buffering volume expansion for potassium ion batteries.

Suitable anode materials for potassium ion batteries (KIBs) with high capacity, good reversibility and stable cycling performances are still in large demand. Here, flexible N doped carbon/bubble-like MoS2 core/sheath framework (MoS2/NCS) is prepared as an anode material for potassium ion batteries. The N doped carbon sponge (NCS) skeleton with good conductivity and high surface area guarantees superior rate capability and high stability of MoS2/NCS anode. The chemical bonds (CMo) firmly bridge MoS2 and NCS together, which further ensures MoS2/NCS stable cycling performance. More importantly, volume expansion is greatly buffered during cycling by this unique structure: the voids between bubble-like MoS2 sheath and NCS core can effectively buffer volume expansion generated during potassium intercalation/deintercalation; the enlarged interlayer spacing contribute more space to buffer volume change; the ultrathin nanosheets can shorten the charge diffusion distance and buffer volume change. As a consequence, MoS2/NCS delivers a capacity of 374 mAh g-1 over 200 cycles at 50 mA g-1. Even at 1000 mA g-1, a capacity of 212 mAh g-1 can still be obtained over 1000 cycles. We believe this MoS2/NCS structure will highlight the potential of MoS2 in practical KIBs applications.

Collaborative Design of Hollow Nanocubes, In Situ Cross-Linked Binder, and Amorphous Void@SiOx @C as a Three-Pronged Strategy for Ultrastable Lithium Storage.

Although silicon-based materials are ideal candidate anodes for high energy density lithium-ion batteries, the large volumetric expansion seriously damages the integrity of the electrodes and impedes commercial processes. Reasonable electrode design based on adjustable structures of silicon and strong binders prepared by a facile method is still a great challenge. Herein, a three-pronged collaborative strategy via hollow nanocubes, amorphous Void@SiOx @C, and in situ cross-linked polyacrylic acid and d-sorbitol 3D network binder (c-PAA-DS) is adopted to maintain structural/electrode integrality and stability. The all-integrated c-PAA-DS/Void@SiOx @C electrode delivers excellent mechanical property, which is attributed to ductility of the c-PAA-DS binder and high adhesion energy between Void@SiOx @C and c-PAA-DS calculated by density functional theory. Benefiting from the synergistic effect of accommodation of the hollow structure, protection of outer carbon shell, amorphous Void@SiOx @C, and strong adhesive c-PAA-DS binder, c-PAA-DS/Void@SiOx @C shows excellent electrochemical performance. Long cycling stability with a reversible capacity of 696 mAh g-1 is obtained, as well as tiny capacity decay after 500 cycles at 0.5 A g-1 and high-rate performance. The prelithiated Void@SiOx @C||LiNi0.5 Co0.2 Mn0.3 O2 (NCM523) full cell is also assembled and shows a reversible capacity of 157 mAh g-1 at 0.5 C, delivering an excellent capacity retention of 94% after 160 cycles.

Hollow Multihole Carbon Bowls: A Stress-Release Structure Design for High-Stability and High-Volumetric-Capacity Potassium-Ion Batteries.

Potassium-ion batteries are potential alternatives to lithium-ion batteries for large-scale energy storage considering the low cost and high abundance of potassium. However, it is challenging to obtain stable electrode materials capable of undergoing long-term potassiation/depotassiation due to the high accumulated stress associated with the huge volume variation of the electrode. Here, we simulate the von Mises stress distributions of four different carbon three-dimensional models under an isotropic initial stress by the finite element method and reveal the critical role of the structure of a hollow multihole bowl on the strain-relaxation behavior. In this regard, nitrogen/oxygen codoped carbon hollow multihole bowls (CHMBs) are synthesized via hydrothermal carbonization coupled with an emulsion-templating strategy using biomass as the carbon source. Consistent with our simulation results, the CHMB anode remains stable for over 1000 cycles and delivers a high reversible capacity of 304 mAh g-1 at 0.1 A g-1. In addition to the reduced stress accumulation, the good electrochemical performances are also attributed to the surface capacitive mechanism and the shortened electron/ion transport distance in CHMBs. In particular, the CHMB composite electrode has a volumetric specific capacity 56% higher than that of hollow spheres due to the high tapped density of the bowl-shaped particles.

High-Throughput Production of Zr-Doped Li4 Ti5 O12 Modified by Mesoporous Libaf3 Nanoparticles for Superior Lithium and Potassium Storage.

Li4 Ti5 O12 is a promising anode for lithium-ion batteries due to its zero-strain properties. However, its low conductivity has greatly affected its rate performance. At the same time, the electrolyte decomposition during cycling also needs to be solved, especially at low cut-off voltage. Herein, using a high-throughput two-step method, we synthesized Zr-doped LTO modified by mesoporous LiBaF3 nanoparticles for alkali-ion storage. The doping of Zr can enhance the electronic conductivity and facilitate the rate performance. Meanwhile, the coating of mesoporous LiBaF3 nanoparticles can form a mesoporous surface with large pore size (ca. 3-10 nm), which can benefit the alkali ion diffusion and simultaneously restrain the formation of an excess solid electrolyte interface to a reasonable range. The optimized material is used as an advanced anode for both lithium-ion and potassium-ion batteries, and good battery behavior including high-rate performance and high stability is achieved.

Deeply Nesting Zinc Sulfide Dendrites in Tertiary Hierarchical Structure for Potassium Ion Batteries: Enhanced Conductivity from Interior to Exterior.

Transition metal sulfides are deemed as attractive anode materials for potassium-ion batteries (KIBs) due to their high theoretical capacities based on conversion and alloying reaction. However, the main challenges are the low electronic conductivity, huge volume expansion, and consequent formation of unstable solid electrolyte interphase (SEI) upon potassiation/depotassiation. Herein, zinc sulfide dendrites deeply nested in the tertiary hierarchical structure through a solvothermal-pyrolysis process are designed as an anode material for KIBs. The tertiary hierarchical structure is composed of the primary ultrafine ZnS nanorods, the secondary carbon nanosphere, and the tertiary carbon-encapsulated ZnS subunits nanosphere structure. The architectural design of this material provides a stable diffusion path and enhances effective conductivity from the interior to exterior for both K+ ions and electrons, buffers the volume expansion, and constructs a stable SEI during cycling. A stable specific capacity of 330 mAh g-1 is achieved after 100 cycles at the current density of 50 mA g-1 and 208 mAh g-1 at 500 mA g-1 over 300 cycles. Using density functional theory calculations, we discover the interactions between ZnS and carbon interface can effectively decrease the K+ ions diffusion barrier and therefore promote the reversibility of K+ ions storage.

A new dual-ion battery based on amorphous carbon.

The Na-based dual-ion batteries (NDIBs), combining the advantages of Na-ion batteries and dual-ion batteries, are attracting more attention due to their merits of abundant source, low cost and high energy density. However, the main challenges faced by NDIBs are their low capacity and poor cycling. Herein, we report a new ion storage mechanism for high-performance NDIBs using amorphous carbon (AOMC) as cathode. Unlike the graphite carbon that can only accommodate the PF6- anion (typical DIB system), the AOMC herein can both accommodate Na+ cation and PF6- anion due to its amorphous feature, which is conceptually new dual-ion system for achieving much higher capacity. Ex-situ X-ray photoelectron spectroscopy, X-ray diffraction and Raman studies reveal that the disordered carbon in the AOMC can be transformed to the partial graphitic stacking in short range, improving both capacity and cycling stability of NDIBs. As a consequence, the AOMC delivers a highly reversible storage capacity of 136 mAh g-1 for 800 cycles at a very high current density of 2.0 A g-1, much higher than all the reported NDIBs. Such concept can be generalized to develop high-performance dual-ion full cell using sodium ion pre-intercalated materials as anode and AOMC as cathode.

Metallic Octahedral CoSe2 Threaded by N-Doped Carbon Nanotubes: A Flexible Framework for High-Performance Potassium-Ion Batteries.

Due to the abundant and low-cost K resources, the exploration of suitable materials for potassium-ion batteries (KIBs) is advancing as a promising alternative to lithium-ion batteries. However, the large-sized and sluggish-kinetic K ions cause poor battery behavior. This work reports a metallic octahedral CoSe2 threaded by N-doped carbon nanotubes as a flexible framework for a high-performance KIBs anode. The metallic property of CoSe2 together with the highly conductive N-doped carbon nanotubes greatly accelerates the electron transfer and improves the rate performance. The carbon nanotube framework serves as a backbone to inhibit the agglomeration, anchor the active materials, and stabilize the integral structure. Every octahedral CoSe2 particle arranges along the carbon nanotubes in sequence, and the zigzag void space can accommodate the volume expansion during cycling, therefore boosting the cycling stability. Density functional theory is also employed to study the K-ion intercalation/deintercalation process. This unique structure delivers a high capacity (253 mAh g-1 at 0.2 A g-1 over 100 cycles) and enhanced rate performance (173 mAh g-1 at 2.0 A g-1 over 600 cycles) as an advanced anode material for KIBs.