Ultra-Uniform and Functionalized Nano-Ion Divider for Regulating Ion Distribution toward Dendrite-Free Lithium-Metal Batteries.

Ionic dividers with uniform pores and functionalized surfaces display significant potential for solving Li-dendrite issues in Li-metal batteries. In this study, single metal and nitrogen co-doped carbon-sandwiched MXene (M-NC@MXene) nanosheets are designed and fabricated, which possess highly ordered nanochannels with a diameter of ≈10 nm. The experiments and computational calculations verified that the M-NC@MXene nanosheets eliminate Li dendrites in several ways: (1) redistributing the Li-ion flux via the highly ordered ion channels, (2) selectively conducting Li ions and anchoring anions by heteroatom doping to extend the nucleation time for Li dendrites, and (3) tightly staggering on a routine polypropylene (PP) separator to obstruct the growth path of Li dendrites. With a Zn-NC@MXene-coated PP divider, the assembled Li||Li symmetric battery shows an ultralow overpotential of ≈25 mV and a cycle life of 1500 h at a high current density of 3 mA cm-2 and high capacity of 3 mAh cm-2 . Remarkably, the life of a Li||Ni83 pouch cell with an energy density of 305 Wh kg-1 is improved by fivefold. Moreover, the remarkable performance of Li||Li, Li||LiFePO4 , and Li||sulfur batteries reveal the significant potential of the well-designed multifunctional ion divider for further practical applications.

Solvent-Free Synthesis of Polymer Spheres and the Activation to Porous Carbon Spheres for Advanced Aluminum-Ion Hybrid Capacitors.

Porous carbon spheres (PCSs) characteristic of perfect symmetry and ideal rheological property have great potential in electrochemical energy storage (EES). However, conventional synthesis of PCSs heavily relies on solution-based methods that may lead to environmental issues. Herein, an environment-friendly solvent-free method toward the facile and mass production of m-phenylenediamine-formaldehyde (MPF) resin spheres, which can be converted into PCSs after carbonization and activation is reported. An ultrahigh productivity of 25.89 g in a 100-mL container and an impressive percent yield of 98.89% can be achieved for the MPF resin spheres, which are further converted into carbon spheres with a reasonable yield of 14.5% after carbonization. When employed as the cathode material for aluminum-ion hybrid capacitors, the obtained PCSs afford a double-layer capacity of ≈200 mAh g-1 , the highest value among reported porous carbon materials for Al-based EES devices. It is anticipated that the solvent-free synthesis method for PCSs developed here may play a significant role in other EES devices, such as magnesium-ion and calcium-ion hybrid capacitors.

Deciphering Structural Origins of Highly Reversible Lithium Storage in High Entropy Oxides with In Situ Transmission Electron Microscopy.

Configurational entropy-stabilized single-phase high-entropy oxides (HEOs) have been considered revolutionary electrode materials with both reversible lithium storage and high specific capacity that are difficult to fulfill simultaneously by conventional electrodes. However, precise understanding of lithium storage mechanisms in such HEOs remains controversial due to complex multi-cationic oxide systems. Here, distinct reaction dynamics and structural evolutions in rocksalt-type HEOs upon cycling are carefully studied by in situ transmission electron microscopy (TEM) including imaging, electron diffraction, and electron energy loss spectroscopy at atomic scale. The mechanisms of composition-dependent conversion/alloying reaction kinetics along with spatiotemporal variations of valence states upon lithiation are revealed, characterized by disappearance of the original rocksalt phase. Unexpectedly, it is found from the first visualization evidence that the post-lithiation polyphase state can be recovered to the original rocksalt-structured HEOs via reversible and symmetrical delithiation reactions, which is unavailable for monometallic oxide systems. Rigorous electrochemical tests coupled with postmortem ex situ TEM and bulk-level phase analyses further validate the crucial role of structural recovery capability in ensuring the reversible high-capacity Li-storage in HEOs. These findings can provide valuable guidelines to design compositionally engineer HEOs for almighty electrodes of next-generation long-life energy storage devices.

Ni Single Atoms on MoS2 Nanosheets Enabling Enhanced Kinetics of Li-S Batteries.

The practical application of Li-S batteries is seriously hindered due to its shuttle effect and sluggish redox reaction, which requires a better functional separator to solve the problems. Herein, polypropylene separators modified by MoS2 nanosheets with atomically dispersed nickel (Ni-MoS2 ) are prepared to prevent the shuttle effect and facilitate the redox kinetics for Li-S batteries. Compared with pristine MoS2 nanosheets, Ni-MoS2 nanosheets exhibit both excellent adsorption and catalysis performance for overcoming the shuttle effect. Assembled with this novel separator, the Li-S batteries exhibit an admirable cycling stability at 2 C over 400 cycles with 0.01% per cycle decaying. In addition, even with a high sulfur loading of 7.5 mg cm-2 , the battery still provides an initial capacity of 6.9 mAh cm-2 and remains 5.9 mAh cm-2 after 50 cycles because of the fast convention of polysulfides catalyzed by Ni-MoS2 nanosheets, which is further confirmed by the density functional theory (DFT) calculations. Therefore, the proposed strategy is expected to offer a new thought for single atom catalyst applying in Li-S batteries.

Ultrathin Cobalt Phthalocyanine@Graphene Oxide Layer-Modified Separator for Stable Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur (Li-S) batteries have aroused great attention due to their high energy density and low cost. However, Li-S batteries suffer from rapid capacity decay owing to the shuttle effect of the intermediate polysulfides. To tackle this issue, functional separators with the ability to absorb polysulfides play a vital role to block them from passing through the separator. Herein, an ultrathin and lightweight layer of graphene oxide (GO) loaded with Co phthalocyanine (CoPc) is fabricated on a polypropylene (PP) separator. The thickness of CoPc@GO is about 200 nm with a low areal mass of 22 µg cm-2. CoPc is uniformly dispersed on GO sheets through π-π interactions, which inhibits the shuttle effect and facilitates the conversion of the intermediate polysulfides. In consequence, the battery with a CoPc@GO-PP separator exhibits good cycling stability with a low-capacity decay rate of 0.076% per cycle at 1 C over 400 cycles and a high specific capacity of 919 mA h g-1 after 250 cycles at 0.5 C.

A Durable Ni-Zn Microbattery with Ultrahigh-Rate Capability Enabled by In Situ Reconstructed Nanoporous Nickel with Epitaxial Phase.

Powering device for miniaturized electronics is highly desired with well-maintained capacity and high-rate performance. Though Ni-Zn microbattery can meet the demand to some extent with intrinsic fast kinetic, it still suffers irreversible structure degradation due to the repeated lattice strain. Herein, a stable Ni-Zn microbattery with ultrahigh-rate performance is rationally constructed through in situ electrochemical approaches, including the reconstruction of nanoporous nickel and the introduction of epitaxial Zn(OH)2 nanophase. With the enhanced ionic adsorption effect, the superior reactivity of the superficial nickel-based nanostructure is well stabilized. Based on facile miniaturization and electrochemical techniques, the fabricated nickel microelectrode exhibits 63.8% capacity retention when the current density is 500 times folded, and the modified hydroxides contribute to the great stability of the porous structure (92% capacity retention after 10 000 cycles). Furthermore, when the constructed Ni-Zn microbattery is measured in a practical metric, excellent power density (320.17 mW cm-2 ) and stable fast-charging performance (over 90% capacity retention in 3500 cycles) are obtained. This surface reconstruction strategy for nanostructure provides a new direction for the optimization of electrode structure and enriches high-performance output units for integrated microelectronics.

Three-dimensional graphene-supported nickel disulfide nanoparticles promise stable and fast potassium storage.

Nickel sulfide (NiS2) is generally regarded as an appropriate anode for manufacturing new-type potassium-ion batteries (PIBs), while the development and application of NiS2 are hampered by poor intrinsic electrical conductivity and huge volumetric change during potassiation/de-potassiation. Herein, we construct self-adaptive NiS2 nanoparticles confined to a three-dimensional graphene oxide (NiS2/3DGO) electrode via in situ sulfurization and self-assembly processes. The as-obtained NiS2/3DGO exhibits high reversible capacity (391 mA h g-1) and outstanding rate behavior (stable cycling at 1000 mA g-1) for PIBs. Furthermore, in situ X-ray diffractometry and ex situ Raman test results elucidate partially reversible transformation from the cubic NiS2 phase to the KxNiS2 intermediate, followed by generating a Ni0 and K2S4 product. This phenomenon is caused by the conversion reaction mechanism of NiS2 nanocrystals along with an amorphous phase transition during the initial cycle. Such understandings may shed new light on the application of metal sulfides and give directions to design novel electrodes with desirable structural stability and lifespan.

3D Nitrogen-Doped Graphene Encapsulated Metallic Nickel-Iron Alloy Nanoparticles for Efficient Bifunctional Oxygen Electrocatalysis.

Invited for the cover of this issue is Liqiang Mai and co-workers at Wuhan University of Technology. The image depicts Ni3 Fe alloy nanoparticles encapsulated in N-doped graphene as an efficient bifunctional oxygen electrocatalyst toward rechargeable Zn-air batteries, which is expected to drive the electric vehicle. Read the full text of the article at 10.1002/chem.201904722.

3D Nitrogen-Doped Graphene Encapsulated Metallic Nickel-Iron Alloy Nanoparticles for Efficient Bifunctional Oxygen Electrocatalysis.

It is extremely desirable to explore high-efficient, affordable and robust oxygen electrocatalysts toward rechargeable Zn-air batteries (ZABs). A 3D porous nitrogen-doped graphene encapsulated metallic Ni3 Fe alloy nanoparticles aerogel (Ni3 Fe-GA1 ) was constructed through a facile hydrothermal assembly and calcination process. Benefiting from 3D porous configuration with great accessibility, high electrical conductivity, abundant active sites, optimal nitrogen content and strong electronic interactions at the Ni3 Fe/N-doped graphene heterointerface, the obtained aerogel showed outstanding catalytic performance toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Specifically, it exhibited an overpotential of 239 mV to attain 10 mA cm-2 for OER, simultaneously providing a positive onset potential of 0.93 V within a half-wave potential of 0.8 V for ORR. Accordingly, when employed in the aqueous ZABs, Ni3 Fe-GA1 achieved higher power density and superior reversibility than Pt/C-IrO2 catalyst, making it a potential candidate for rechargeable ZABs.

Engineering Oxygen Vacancies in a Polysulfide-Blocking Layer with Enhanced Catalytic Ability.

The practical application of the lithium-sulfur (Li-S) battery is seriously restricted by its shuttle effect, low conductivity, and low sulfur loading. Herein, first-principles calculations are conducted to verify that the introduction of oxygen vacancies in TiO2 not only enhances polysulfide adsorption but also greatly improves the catalytic ability and both the ion and electron conductivities. A commercial polypropylene (PP) separator decorated with TiO2 nanosheets with oxygen vacancies (OVs-TiO2 @PP) is fabricated as a strong polysulfide barrier for the Li-S battery. The thickness of the OVs-TiO2 modification layer is only 500 nm with a low areal mass of around 0.12 mg cm-2 , which enhances the fast lithium-ion penetration and the high energy density of the whole cell. As a result, the cell with the OVs-TiO2 @PP separator exhibits a stable electrochemical behavior at 2.0 C over 500 cycles, even under a high sulfur loading of 7.1 mg cm-2 , and an areal capacity of 5.83 mAh cm-2 remains after 100 cycles. The proposed strategy of engineering oxygen vacancies is expected to have wide applications in Li-S batteries.

Bilayered microelectrodes based on electrochemically deposited MnO2/polypyrrole towards fast charge transport kinetics for micro-supercapacitors.

Micro-supercapacitors (MSCs) are promising power solution facilities for miniaturized portable electronic devices. Microfabrication of on-chip MSC with high specific capacitance and high energy density is still a great challenge. Herein, we report a high-performance MnO2/polypyrrole (PPy) microelectrode based MSC (MnO2/PPy-MSC) by modern micromachining technology. Interdigital Au micro current collectors were obtained by photolithography, physical vapor deposition and lift off. A layer of PPy was electrochemically deposited on Au current collectors followed by deposition of urchin-like MnO2 micro/nanostructures. The electrochemical performance of MnO2/PPy-MSC was explored employing LiClO4/PVA gel electrolyte. The assembled MSC demonstrated a high areal capacitance of 13 mF cm-2, an energy density of 1.07 × 10-3 mW h cm-2 and a power density of 0.53 mW cm-2. In addition, the MnO2/PPy-MSC showed an improved cycling stability, retaining 84% of the initial capacitance after 5000 CV cycles at a scan rate of 500 mV s-1. Our proposed strategy provides a versatile and promising method for the fabrication of high-performance MSCs with large-scale applications.

A rechargeable aluminum-ion battery based on a VS2 nanosheet cathode.

As a typical member of transition-metal dichalcogenides (TMDs), VS2 has been evaluated as the aluminum-ion battery cathode for the first time. To further improve their stability and conductivity, the as-prepared VS2 nanosheets are modified with graphene (denoted as G-VS2). And the G-VS2 electrode delivers a high initial discharge capacity of 186 mA h g-1 at 100 mA g-1 with almost 100% coulombic efficiency after 50 cycles. Furthermore, an explicit intercalation mechanism of Al into G-VS2 has been investigated by in/ex situ XRD, ex situ Raman and TEM spectroscopy. And the G-VS2 composite proves to be an impressive cathode material for aluminum-ion batteries (AIBs). This work might put forward the application of TMDs in AIBs.

A porous nickel cyclotetraphosphate nanosheet as a new acid-stable electrocatalyst for efficient hydrogen evolution.

The stability of non-precious metal-based electrocatalysts for the acidic hydrogen evolution reaction (HER) is of great importance. Here, we have used nickel cyclotetraphosphate (Ni2P4O12) nanosheet arrays as a HER electrocatalyst for the first time. The Ni2P4O12 arrays were obtained through a facile low-temperature phosphorylation process and possess superior HER catalytic activities and stability in acid. The Ni2P4O12 delivers a small overpotential of 131.8 mV at -10 mA cm-2 and a low Tafel slope of 47.8 mV dec-1 in 0.5 M H2SO4, comparable to most of the non-precious metal-based catalysts. Importantly, the Ni2P4O12 shows a negligible potential change (6.5 mV) over 80 000 s continuous testing in acid. The remarkable catalytic performances of Ni2P4O12 are mainly attributed to the inductive effect of P4O124- and its polymer-like structure, promoting it as a potential acid-stable HER electrocatalyst.

Novel layered iron vanadate cathode for high-capacity aqueous rechargeable zinc batteries.

A layered iron vanadate Fe5V15O39(OH)9·9H2O nanosheet is first introduced to an aqueous zinc battery system as a cathode material, which delivers a high capacity of 385 mA h g-1 at 0.1 A g-1 and remarkable cycling performance at high current density (over 80% capacity retention after 300 cycles at 5 A g-1).

Low-crystalline iron oxide hydroxide nanoparticle anode for high-performance supercapacitors.

Carbon materials are generally preferred as anodes in supercapacitors; however, their low capacitance limits the attained energy density of supercapacitor devices with aqueous electrolytes. Here, we report a low-crystalline iron oxide hydroxide nanoparticle anode with comprehensive electrochemical performance at a wide potential window. The iron oxide hydroxide nanoparticles present capacitances of 1,066 and 716 F g-1 at mass loadings of 1.6 and 9.1 mg cm-2, respectively, a rate capability with 74.6% of capacitance retention at 30 A g-1, and cycling stability retaining 91% of capacitance after 10,000 cycles. The performance is attributed to a dominant capacitive charge-storage mechanism. An aqueous hybrid supercapacitor based on the iron oxide hydroxide anode shows stability during float voltage test for 450 h and an energy density of 104 Wh kg-1 at a power density of 1.27 kW kg-1. A packaged device delivers gravimetric and volumetric energy densities of 33.14 Wh kg-1 and 17.24 Wh l-1, respectively.

Porous Nickel-Iron Selenide Nanosheets as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction.

Exploring non-noble and high-efficiency electrocatalysts is critical to large-scale industrial applications of electrochemical water splitting. Currently, nickel-based selenide materials are promising candidates for oxygen evolution reaction due to their low cost and excellent performance. In this work, we report the porous nickel-iron bimetallic selenide nanosheets ((Ni0.75Fe0.25)Se2) on carbon fiber cloth (CFC) by selenization of the ultrathin NiFe-based nanosheet precursor. The as-prepared three-dimensional oxygen evolution electrode exhibits a small overpotential of 255 mV at 35 mA cm(-2) and a low Tafel slope of 47.2 mV dec(-1) and keeps high stability during a 28 h measurement in alkaline solution. The outstanding catalytic performance and strong durability, in comparison to the advanced non-noble metal catalysts, are derived from the porous nanostructure fabrication, Fe incorporation, and selenization, which result in fast charge transportation and large electrochemically active surface area and enhance the release of oxygen bubbles from the electrode surface.

Integrated SnO2 nanorod array with polypyrrole coverage for high-rate and long-life lithium batteries.

Conversion/alloying reactions, in which more lithium ions are involved, are severely handicapped by the dramatic volume changes. A facile and versatile strategy has been developed for integrating the SnO2 nanorod array in the PPy nanofilm for providing a flexible confinement for anchoring each nanorod and maintaining the entire structural integrity and providing sustainable contact; therefore, exhibiting much more stable cycling stability (701 mA h g(-1) after 300 cycles) and better high-rate capability (512 mA h g(-1) at 3 A g(-1)) when compared with the core-shell SnO2-PPy NA.