Reversible Deposition/Dissolution of Double Hydroxides to Modulate Electrolyte pH Enabling High-Performance Aqueous Zinc-Ion Batteries.

Vanadium oxide has been extensively studied as a host of zinc ion intercalation but still suffers from low conductivity, dissolution, and byproduct accumulation during cycling. Here, we hydrothermally synthesize the VO2@MXene Ti3C2 (MV) composite and find that in the MV//3 M Zn(CF3SO3)2//Zn system, the double hydroxide Zn12(CF3SO3)9(OH)15·nH2O (ZCOH) uniformly covers VO2 during the charging process and dissolves reversibly during the discharge process. In situ X-ray diffraction of the MV combined with in situ pH measurements reveals that ZCOH acts as a pH buffer during cycling, which is beneficial to the cycling stability of batteries. And the theoretical calculation indicates that the decomposition energy required by ZCOH on the MV surface is lower than that on pure VO2, which is more conducive to ZCOH dissolution. The coin battery exhibits high-rate performance of 65.1% capacity retention at a current density of 15 A g-1 (compared to 0.6 A g-1) and a long cycling life of 20,000 cycles with a capacity retention of 80.7%. For a 22.4 mA h soft-packaged battery, its capacity remains at 72.1% after 2000 cycles. This work demonstrates the active role of ZCOH in the electrochemical process of VO2 and provides a new perspective for exploiting this mechanism to develop high-performance aqueous zinc-ion battery vanadium oxide cathode materials.

Solvation Modulation Enhances Anion-Derived Solid Electrolyte Interphase for Deep Cycling of Aqueous Zinc Metal Batteries.

Stable Zn anodes with a high utilization efficiency pose a challenge due to notorious dendrite growth and severe side reactions. Therefore, electrolyte additives are developed to address these issues. However, the additives are always consumed by the electrochemical reactions over cycling, affecting the cycling stability. Here, hexamethylphosphoric triamide (HMPA) is reported as an electrolyte additive for achieving stable cycling of Zn anodes. HMPA reshapes the solvation structures and promotes anion decomposition, leading to the in situ formation of inorganic-rich solid-electrolyte-interphase. More interestingly, this anion decomposition does not involve HMPA, preserving its long-term impact on the electrolyte. Thus, the symmetric cells with HMPA in the electrolyte survive ≈500 h at 10 mA cm-2 for 10 mAh cm-2 or ≈200 h at 40 mA cm-2 for 10 mAh cm-2 with a Zn utilization rate of 85.6 %. The full cells of Zn||V2 O5 exhibit a record-high cumulative capacity even under a lean electrolyte condition (E/C ratio=12 µL mAh-1 ), a limited Zn supply (N/P ratio=1.8) and a high areal capacity (6.6 mAh cm-2 ).

Lattice oxygen-mediated electron tuning promotes electrochemical hydrogenation of acetonitrile on copper catalysts.

Copper is well-known to be selective to primary amines via electrocatalytic nitriles hydrogenation. However, the correlation between the local fine structure and catalytic selectivity is still illusive. Herein, we find that residual lattice oxygen in oxide-derived Cu nanowires (OD-Cu NWs) plays vital roles in boosting the acetonitrile electroreduction efficiency. Especially at high current densities of more than 1.0 A cm-2, OD-Cu NWs exhibit relatively high Faradic efficiency. Meanwhile, a series of advanced in situ characterizations and theoretical calculations uncover that oxygen residues, in the form of Cu4-O configuration, act as electron acceptors to confine the free electron flow on the Cu surface, consequently improving the kinetics of nitriles hydrogenation catalysis. This work could provide new opportunities to further improve the hydrogenation performance of nitriles and beyond, by employing lattice oxygen-mediated electron tuning engineering.

Novel Bilayer-Shelled N, O-Doped Hollow Porous Carbon Microspheres as High Performance Anode for Potassium-Ion Hybrid Capacitors.

With the advantages of high energy/power density, long cycling life and low cost, dual-carbon potassium ion hybrid capacitors (PIHCs) have great potential in the field of energy storage. Here, a novel bilayer-shelled N, O-doped hollow porous carbon microspheres (NOHPC) anode has been prepared by a self-template method, which is consisted of a dense thin shell and a hollow porous spherical core. Excitingly, the NOHPC anode possesses a high K-storage capacity of 325.9 mA h g-1 at 0.1 A g-1 and a capacity of 201.1 mAh g-1 at 5 A g-1 after 6000 cycles. In combination with ex situ characterizations and density functional theory calculations, the high reversible capacity has been demonstrated to be attributed to the co-doping of N/O heteroatoms and porous structure improved K+ adsorption and intercalation capabilities, and the stable long-cycling performance originating from the bilayer-shelled hollow porous carbon sphere structure. Meanwhile, the hollow porous activated carbon microspheres (HPAC) cathode with a high specific surface area (1472.65 m2 g-1) deriving from etching NOHPC with KOH, contributing to a high electrochemical adsorption capacity of 71.2 mAh g-1 at 1 A g-1. Notably, the NOHPC//HPAC PIHC delivers a high energy density of 90.1 Wh kg-1 at a power density of 939.6 W kg-1 after 6000 consecutive charge-discharge cycles.

Plastic-derived sandwich-like porous carbon nanosheet-supported hexagonal carbon micro-flakes for K-ion storage.

Novel sandwich-like porous carbon nanosheet-supported hexagonal carbon micro-flakes (WPWMC) are fabricated via a one-step hydrothermal route at 700 °C with polyethylene as the precursor and magnesium as the inducer. Through various characterizations, it is confirmed that the hexagonal carbon micro-flakes exhibit (002) orientation, which exposes abundant edge active sites and shortens the K+ transmission path. Moreover, the inside cross-linked carbon nanosheets with abundant pores can accelerate ion diffusion and increase the capacitive contribution. The WPWMC anode displays a high reversible capacity (528.7 mA h g-1 at 0.2 A g-1), good rate capability (152.7 mA h g-1 at 10 A g-1) and long-term cycle stability (112.1 mA h g-1 at 5 A g-1 after 10 000 cycles). Furthermore, the WPWMC//CMK-3 hybrid capacitor exhibits an energy density of 222.7 W h kg-1 at 446.2 W kg-1. This work provides an idea for transforming waste plastic into value-added materials.

Fluoride-Based Stable Quasi-Solid-State Zinc Metal Battery with Superior Rate Capability.

Aqueous zinc metal batteries are limited in practical applications due to their short lifespans. Herein, a LaF3-coated Zn anode (LF@Zn) is investigated to induce the uniform Zn deposition and successfully build a separator-free quasi-solid-state zinc metal battery. The LF@Zn enables smooth and dendrite-free Zn deposition, owing to the homogeneous Zn2+ flux regulated by the LaF3-based quasi-solid-state electrolyte. It can also suppress the corrosion side reactions by modulating the [Zn(H2O)6]2+ solvation sheath. The polarization of plating and stripping is relatively modest due to the reduced diffuse energy of desolvated Zn2+ in the quasi-solid-state electrolyte. In a separator-free symmetric cell, the LF@Zn anode shows a significantly prolonged lifespan of over 1300 h at 2 mA cm-2 and a superior rate performance with only 156 mV at an ultrahigh current density of 50 mA cm-2. A LF@Zn//VO2 quasi-solid-state full cell exhibits outperforming rate capability and a long cyclic performance for up to 3000 cycles at 6.0 A g-1. A stable Zn anode is established in this work with a fluoride-based quasi-solid-state electrolyte, opening up a new avenue for protecting metal anodes.

Integrating Chemical Pre-Potassiation with Pre-Modulated KF-Rich Electrolyte Interfaces for Dual-Carbon Potassium Ion Hybrid Capacitor.

Herein, a chemical pre-potassiation strategy via simultaneously treating both glucose derived carbon (GDC) anode and commercial activated carbon (CAC) cathode in potassium-naphthalene-tetrahydrofuran solution is developed for potassium ion hybrid capacitor (PIHC). Combined with in situ and ex situ characterizations, a radical reaction between pre-potassiation reagent and carbon electrodes is confirmed, which not only deactivates electrochemical irreversible sites, but also promotes to pre-form a uniform and dense KF-rich electrolyte film on the electrodes. As a result, the pre-potassiation treatment presents multiple advantages: (I) the initial Coulombic efficiency (CE) of the GDC anode increases from 45.4 % to 84.0 % with higher rate capability; (II) the CAC cathode exhibits the improved cycling CEs and stability due to the enhanced resistance to electrolyte oxidation at 4.2 V; (III) the assembled PIHC achieves a high energy density of 172.5 Wh kg-1 with cycling life over 10000 cycles.

Rational Screening of Artificial Solid Electrolyte Interphases on Zn for Ultrahigh-Rate and Long-Life Aqueous Batteries.

Solid electrolyte interphase (SEI) on Zn anodes plays a pivotal role for high-rate and long-life aqueous batteries, because it effectively inhibits side reactions and dendritic growth. Many materials are explored as SEIs by a trial-and-error approach. Herein, an exercisable way is proposed to screen the potential SEIs on Zn anodes in view of dendrite-suppressing ability and charge-transfer property theoretically. As an output of this screening, Zn3 (BO3 )2 (ZBO) is checked experimentally. In symmetrical cells, Zn@ZBO runs over 250 h at an ultrahigh current density of 50 mA cm-2 for a large areal capacity 10 mAh cm-2 . In full cells, Zn@ZBO||MnO2 shows an impressive cumulative capacity (≈406 mAh cm-2 ) under harsh conditions, i.e., a lean electrolyte condition (10 µL mAh-1 ), limited Zn supply (negative/positive electrode capacity ratio, N/P ratio = 2.3), and high areal capacity (5.0 mAh cm-2 ). The significance of this work lies in not only the first report of ZBO on Zn showing excellent electrochemical performance, but also a feasible way to screen the promising SEI materials for other metal anodes.

Revealing the interface-rectifying functions of a Li-cyanonaphthalene prelithiation system for SiO electrode.

Chemical prelithiation is regarded as a crucial method for improving the initial Coulombic efficiency (ICE) of Li-storage anodes. Herein, a substituent-engineered Li-cyanonaphthalene chemical prelithiation system is designed to simultaneously enhance the ICE and construct a multifunctional interfacial film for SiO electrodes. X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS), nuclear magnetic resonance (NMR) spectroscopy and atomic force microscopy (AFM) prove that the Li-cyanonaphthalene prelithiation reagent facilitates the formation of a rectified solid electrolyte interface (SEI) film in two ways: (1) generation of a gradient SEI film with an organic outer layer (dense N-containing organics, ROCO2Li) and an inorganic LiF-enriched inner layer; (2) homogenization of the horizontal distribution of the composition, mechanical properties and surface potential. As a result, the prelithiated SiO electrode exhibits an ICE above 100%, enhanced CEs during cycling, better cycle stability and inhibition of lithium dendrite formation in the overcharged state. Notably, the prelithiated hard carbon/SiO (9:1)‖LiCoO2 cell displays an enhancement in the energy density of 62.3%.

In Situ Formation of Nitrogen-Rich Solid Electrolyte Interphase and Simultaneous Regulating Solvation Structures for Advanced Zn Metal Batteries.

Zn metal as one of promising anode materials for aqueous batteries suffers from notorious dendrite growth, serious Zn corrosion and hydrogen evolution. Here, a bifunctional electrolyte additive, N-methyl pyrrolidone (NMP), is developed to improve the electrochemical performance of Zn anode. NMP not only alters the solvation structure of Zn2+ , but also in situ produces a dense N-rich solid-electrolyte-interphase layer on Zn foils. This layer protects Zn foils from corrosive electrolytes and benefits the uniform plating/stripping of Zn. Hence, the asymmetrical cells with NMP in the electrolyte retain a high coulombic efficiency of 99.8 % over 1000 cycles. The symmetric cells survive ≈200 h for 10 mAh cm-2 at a high Zn utilization of 85.6 %. The full cells of Zn||MnO2 show an impressive cumulative capacity even with lean electrolyte (E/C ratio=10 µL mAh-1 ), limited Zn supply (N/P ratio=2.3) and high areal capacity (5.0 mAh cm-2 ).

Zinc-Assisted Cobalt Ditelluride Polyhedra Inducing Lattice Strain to Endow Efficient Adsorption-Catalysis for High-Energy Lithium-Sulfur Batteries.

Developing a conductive catalyst with high catalytic activity is considered to be an effective strategy for improving cathode kinetics of lithium-sulfur batteries, especially at large current density and with lean electrolytes. Lattice-strain engineering has been a strategy to tune the local structure of catalysts and to help understand the structure-activity relationship between strain and catalyst performance. Here, Co0.9 Zn0.1 Te2 @NC is constructed after zinc atoms are uniformly doped into the CoTe2 lattice. The experimental/theoretical results indicate that a change of the coordination environment for the cobalt atom by the lattice strain modulates the d-band center with more electrons occupied in antibonding orbitals, thus balancing the adsorption of polysulfides and the intrinsic catalytic effect, thereby activating the intrinsic activity of the catalyst. Benefiting from the merits, with only 4 wt% dosages of catalyst in the cathode, an initial discharge capacity of 1030 mAh g-1 can be achieved at 1 C and stable cycling performances are achieved for 1500/2500 cycles at 1 C/2 C. Upon sulfur loading of 7.7 mg cm-2 , the areal capacity can reach 12.8 mAh cm-2 . This work provides a guiding methodology for the design of catalytic materials and refinement of adsorption-catalysis strategies for the rational design of cathode in lithium-sulfur batteries.

A solid-to-solid metallic conversion electrochemistry toward 91% zinc utilization for sustainable aqueous batteries.

The diffusion-limited aggregation (DLA) of metal ion (Mn+) during the repeated solid-to-liquid (StoL) plating and liquid-to-solid (LtoS) stripping processes intensifies fatal dendrite growth of the metallic anodes. Here, we report a new solid-to-solid (StoS) conversion electrochemistry to inhibit dendrites and improve the utilization ratio of metals. In this StoS strategy, reversible conversion reactions between sparingly soluble carbonates (Zn or Cu) and their corresponding metals have been identified at the electrode/electrolyte interface. Molecular dynamics simulations confirm the superiority of the StoS process with accelerated anion transport, which eliminates the DLA and dendrites in the conventional LtoS/StoL processes. As proof of concept, 2ZnCO3·3Zn(OH)2 exhibits a high zinc utilization of ca. 95.7% in the asymmetry cell and 91.3% in a 2ZnCO3·3Zn(OH)2 || Ni-based full cell with 80% capacity retention over 2000 cycles. Furthermore, the designed 1-Ah pouch cell device can operate stably with 500 cycles, delivering a satisfactory total energy density of 135 Wh kg-1.

Microsized Gray Tin as a High-Rate and Long-Life Anode Material for Advanced Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are developed to address the serious concern about the limited resources of lithium. To achieve high energy density, anode materials with a large specific capacity and a low operation voltage are highly desirable. Herein, microsized particles of gray Sn (α-Sn) are explored as an anode material of SIBs for the first time. The distinct structure of α-Sn endows it the reduced volume change, the improved interaction with polymer binders and the in situ formation of amorphous Sn, as supported by in situ XRD, TEM and DFT calculations. Therefore, α-Sn exhibits an excellent electrochemical performance, much better than ß-Sn widely used before. Even microsized particles of α-Sn without any treatments deliver a capacity of ∼451 mAh g-1 after 3500 cycles at 2 A g-1 or ∼464 mAh g-1 at 4 A g-1 in a rate test. The results indicate the promising potential of α-Sn in SIBs.

Synergistic Chaotropic Effect and Cathode Interface Thermal Release Effect Enabling Ultralow Temperature Aqueous Zinc Battery.

Although rechargeable zinc-ion batteries are promising candidates for next-generation energy storage devices, their inferior performance at subzero temperatures limits their practical application. Here, a strategy to destroy the H-bond network by adding synergistic chaotropic regents is reported, thus reducing the freezing point of the aqueous electrolyte below -90 °C. Owing to the synergistic chaotropic effect between urea and Zn(ClO4 )2 and the thermal release effect on the cathode interface during charging, Zn//VO2 batteries feature a specific capacity of 111.4 mAh g-1 and stability after ≈1000 cycles with 81.9% capacity retention at -40 °C. This work demonstrates that the synergistic chaotropic effect and the thermal effect on the interface can effectively widen the operation range of temperature of aqueous electrolytes and maintain fast kinetics, which provides a new design strategy for all-weather aqueous zinc batteries.

Regulating Surface Reaction Kinetics through Ligand Field Effects for Fast and Reversible Aqueous Zinc Batteries.

Designing water-deficient solvation sheath of Zn2+ by ligand substitution is a widely used strategy to protect Zn metal anode, yet the intrinsic tradeoff between Zn nucleation/dissolution kinetics and the side hydrogen evolution reaction (HER) remains a huge challenge. Herein, we find boric acid (BA) with moderate ligand field interaction can partially replace H2 O molecules in the solvation sheath of Zn2+ , forming a stable water-deficient solvation sheath. It enables fast Zn nucleation/dissolution kinetics and substantially suppressed HER. Crucially, by systematically comparing the ligand field strength and solvation energies between BA and the ever-reported electrolyte additives, we also find that the solvation energy has a strong correlation with Zn nucleation/dissolution kinetics and HER inhibition ability, displaying a classic volcano behavior. The modulation map could provide valuable insights for solvation sheath design of zinc batteries and beyond.

Monodispersed flower-like MXene@VO2 clusters for aqueous zinc ion batteries with superior rate performance.

Monoclinic B phase VO2 with a distinctive tunnel structure is regarded as a viable cathode material for use in aqueous zinc ion batteries (AZIBs). However, the low electron conductivity and poor rate performance prevent it from being used further. Herein, we report 3D flower-like MXene nanosheets loaded with the VO2 cluster (MXene@VO2) synthesized via a one-step hydrothermal process, where MXene nanosheets were spontaneously stacked as a skeleton for the growth of VO2 nanobelts. The synergistic effect between MXene nanosheets with high electronic conductivity and VO2 nanobelts with a unique tunnel structure benefitted the electron and Zn2+ transport; the 3D hybrid structure with a high specific surface area provided an increased contact area with the electrolyte and a shortened distance of the Zn2+ transfer path. As a result, this material exhibits a promising Zn2+ storage behavior with a superior rate capability (363.2 mA h g-1 at 0.2C and 169.1 mA h g-1 at 50C) and outstanding long-cycling performance (206.6 mA h g-1 and 76% capacity retention over 5000 cycles at 20C). In addition, a self-charging battery could be prepared by using oxygen in air to oxidize vanadium oxide with lower valence states. Our prepared MXene@VO2 composite with a synergistic effect has been proved to be a promising cathode for AZIBs, offering a progressive paradigm for the development of AZIBs.

Constructing Reactive Micro-Environment in Basal Plane of MoS2 for pH-Universal Hydrogen Evolution Catalysis.

MoS2 represents a promising catalyst for the hydrogen evolution reaction (HER) in water splitting, but the inefficient catalytic activity in a pH-universal environment is an obstacle to developing practical applications. Boosting and balancing the water dissociation and hydrogen desorption kinetics is crucial in designing high-performance catalysts for the overall pH range. Herein, it is experimentally demonstrated that cobalt single-atom doping can effectively construct a reactive CoMoS micro-environment on the basal plane of MoS2 and thus alter the uniformity of surface electron density, which is further confirmed by the theoretical results. The reactive micro-environment consisting of single-atom Co with the surrounding Mo and S atoms possesses excellent water dissociation and hydrogen desorption kinetics, exhibiting a superior performance of 36 mV at 10 mA cm-2 with a Tafel slope of 33 mV dec-1 in the alkaline condition. Meanwhile, it also shows worthy activity in the acidic (97 mV) and neutral (117 mV) environments. This work provides a facile strategy to improve the HER catalysis of MoS2 in pH-universal environments.

Bimetallic Bi-Sn microspheres as high initial coulombic efficiency and long lifespan anodes for sodium-ion batteries.

Anode materials with a high initial coulombic efficiency and a long lifespan are highly desirable for sodium-ion batteries. Here, bimetallic µ-BiSn microspheres well combine the high capacity of Sn and the good stability of Bi together, exhibiting superior electrochemical performance, such as a high initial Coulombic efficiency (90.6%), a good cycling stability (541 mA h g-1 after 3000 cycles at 2 A g-1) and an excellent rate capability (393 mA h g-1 at 10 A g-1).

Niobium Diboride Nanoparticles Accelerating Polysulfide Conversion and Directing Li2S Nucleation Enabled High Areal Capacity Lithium-Sulfur Batteries.

The shuttle effect of polysulfides and Li2S sluggish nucleation are the major problems hampering the further development of lithium-sulfur batteries. The reasonable design for sulfur host materials with catalytic function has been an effective strategy for promoting polysulfide conversion. Compared with other types of transition metal compounds, transition metal borides with high conductivity and catalytic capability are more suitable as sulfur host materials. Herein, a niobium diboride (NbB2) nanoparticle with abundant and high-efficiency catalytic sites has been synthesized by facile solid-phase reaction. The NbB2 with both high conductivity and catalytic nature could regulate 3D-nucleation and growth of Li2S, decrease the reaction energy barrier, and accelerate the transformation of polysulfides. Thus, the NbB2 cathode could retain a high capacity of 1014 mAh g-1 after 100 cycles. In addition, the high initial specific capacities of 703/609 mAh g-1 are also achieved at 5 C/10 C and could run for 1000/1300 cycles within a low decay rate of 0.057%/0.051%. Even with a high sulfur loading up to 16.5 mg cm-2, an initial areal capacity of 17 mAh cm-2 could be achieved at 0.1 C. This work demonstrates a successful method for enhancing the kinetics of polysulfide conversion and directing Li2S nucleation.

Highly Reversible Zn Metal Anodes Enabled by Freestanding, Lightweight, and Zincophilic MXene/Nanoporous Oxide Heterostructure Engineered Separator for Flexible Zn-MnO2 Batteries.

Aqueous zinc (Zn)-ion batteries are regarded as promising candidates for large-scale energy storage systems because of their high safety, low cost, and environmental benignity. However, the dendrite issue of Zn anode hinders their practical application. Herein, a freestanding, lightweight, and zincophilic MXene/nanoporous oxide heterostructure engineered separator is designed to stabilize a Zn metal anode. The nanoporous oxides prepared by a one-step vacuum distillation technique afford the advantages of large surface area, high porosity, and homogeneous porous structure. The zincophilic MXene@oxides layer can homogenize the electric field distribution, facilitate ion diffusion kinetics, reduce local current density, and promote even Zn ionic flux, which will regulate uniform Zn deposition and suppress side reactions. Accordingly, dendrite-free Zn anodes with stable cyclability are achieved for over 500 h at an ultrahigh area capacity of 10 mAh cm-2. Besides, flexible, long-lifespan, and high-rate N/S-doped three-dimensional MXene@MnO2||Zn full cells are constructed with the engineered separator. Moreover, this strategy can be successfully extended to lithium, sodium, potassium, and magnesium metal batteries, indicating that separator regulation is a universal approach to overcome the challenges of metal batteries.