Hydrophobic Two-Dimensional Layered Superstructure of a Polyoxometalate Cluster as the Cathode Material for Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries hold promise for sustainable energy storage, yet challenges in finding high-performance cathode materials persist. Polyoxovanadates (POVs) are emerging as potential candidates due to their structural diversity and robust redox activity. Despite their potential, issues like dissolution in electrolytes, structural degradation, and byproduct accumulation persist. This work introduces a POV-based hydrophobic two-dimensional (2D) layered superstructure that addresses these challenges. The hydrophobic nature minimizes POV dissolution, enhancing structural stability and inhibiting phase transitions during cycling. The 2D arrangement ensures a larger surface area and improved electronic conductivity, resulting in faster kinetics and higher specific capacity. The superstructure demonstrates improved cycle life and an increased operating voltage, marking a significant advancement in POV-based cathode materials for aqueous zinc-ion batteries.

Trade-Off between Rough and Smooth Electrode Surfaces toward Stable Zn Stripping/Plating in Aqueous Electrolytes.

The effects of surface roughness on the performance of the Zn metal anode in aqueous electrolytes are investigated by experiments and computational simulations. Smooth surfaces can homogenize the nucleation and growth of Zn, which helps to form a flat Zn anode under high current density. In spite of these advantages, the whole surface of the smooth electrode serves as the reactive contact area for parasitic reactions, generating severe hydrogen evolution, corrosion, and byproduct formation, which seriously hinder the long-term cycle stability of the Zn anode. To trade off this double-sided effect, we identify a medium degree of surface roughness that could stabilize the Zn anode for 1000 h cycling at 1.0 mAh cm-2. The electrode also enabled stable cycling for 800 h at a high current density of 5.0 mAh cm-2. This naked Zn metal anode with optimized surface roughness holds great promise for direct use in aqueous zinc ion batteries.

Chiral Transfer and Evolution in Cysteine Induced Cobalt Superstructures.

Chiral organic additives have unveiled the extraordinary capacity to form chiral inorganic superstructures, however, complex hierarchical structures have hindered the understanding of chiral transfer and growth mechanisms. This study introduces a simple hydrothermal synthesis method for constructing chiral cobalt superstructures with cysteine, demonstrating specific recognition of chiral molecules and outstanding electrocatalytic activity. The mild preparation conditions allow in situ tracking of chirality evolution in the chiral cobalt superstructure, offering unprecedented insights into the chiral transfer and amplification mechanism. The resulting superstructures exhibit a universal formation process applicable to other metal oxides, extending the understanding of chiral superstructure evolution. This work contributes not only to the fundamental understanding of chirality in self-assembled structures but also provides a versatile method for designing chiral inorganic nanomaterials with remarkable molecular recognition and electrocatalytic capabilities.

Zwitterion Intercalated Manganese Dioxide Nanosheets as High-Performance Cathode Materials for Aqueous Zinc Ion Batteries.

In this study, a novel approach is introduced to address the challenges associated with structural instability and sluggish reaction kinetics of δ-MnO2 in aqueous zinc ion batteries. By leveraging zwitterionic betaine (Bet) for intercalation, a departure from traditional cation intercalation methods, Bet-intercalated MnO2 (MnO2-Bet) is synthesized. The positively charged quaternary ammonium groups in Bet form strong electrostatic interactions with the negatively charged oxygen atoms in the δ-MnO2 layers, enhancing structural stability and preventing layer collapse. Concurrently, the negatively charged carboxylate groups in Bet facilitate the rapid diffusion of H+/Zn2+ ions through their interactions, thus improving reaction kinetics. The resulting MnO2-Bet cathode demonstrates high specific capacity, excellent rate capability, fast reaction kinetics, and extended cycle life. This dual-function intercalation strategy significantly optimizes the electrochemical performance of δ-MnO2, establishing it as a promising cathode material for advanced aqueous zinc ion batteries.

Electrochemical Failure Mechanism of δ-MnO2 in Zinc Ion Batteries Induced by Irreversible Layered to Spinel Phase Transition.

Phase transitions of Mn-based cathode materials associated with the charge and discharge process play a crucial role on the rate capability and cycle life of zinc ion batteries. Herein, a microscopic electrochemical failure mechanism of Zn-MnO2 batteries during the phase transitions from δ-MnO2 to λ-ZnMn2O4 is presented via systematic first-principle investigation. The initial insertion of Zn2+ intensifies the rearrangement of Mn. This is completed by the electrostatic repulsion and co-migration between guest and host ions, leading to the formation of λ-ZnMn2O4. The Mn relocation barrier for the λ-ZnMn2O4 formation path with 1.09 eV is significantly lower than the δ-MnO2 re-formation path with 2.14 eV, indicating the irreversibility of the layered-to-spinel transition. Together with the phase transition, the rearrangement of Mn elevates the Zn2+ migration barrier from 0.31 to 2.28 eV, resulting in poor rate performance. With the increase of charge-discharge cycles, irreversible and inactive λ-ZnMn2O4 products accumulate on the electrode, causing continuous capacity decay of the Zn-MnO2 battery.

Polyoxometalate Supported Single Transition Metal Atom as a Redox Mediator for Li-O2 Batteries.

Keggin-type polyoxometalate (POM) supported single transition metal (TM) atom (TM1/POM) as an efficient soluble redox mediator for Li-O2 batteries is comprehensively investigated by first-principles calculations. Among the pristine POM and four kinds of TM1/POM (TM = Fe, Co, Ni, and Pt), Co1/POM not only maintains good structural and thermodynamic stability in oxidized and reduced states but also exhibits promising electro(chemical) catalytic performance for both oxygen reduction reaction and oxygen evolution reaction (OER) in Li-O2 batteries with the lowest Gibbs free energy barriers. Further investigations demonstrate that the moderate binding strength of Li2-xO2 (x = 0, 1, and 2) intermediates on Co1/POM guarantees favorable Li2O2 formation and decomposition. Electronic structure analyses indicate that the introduced Co single atom as an electron transfer bridge can not only efficiently improve the electronic conductivity of POM but also regulate the bonding/antibonding states around the Fermi level of [Co1/POM-Li2O2]ox. The solvent effect on the OER catalytic performance and the electronic properties of [Co1/POM-Li2O2]ox with and without dimethyl sulfoxide solvent are also investigated.

Physicochemical Synergistic Separator Coating Induces Uniform and Rapid Deposition of Li and Zn Ions.

Li and Zn metal batteries are the most promising candidates to replace conventional Li-ion batteries. However, a series of issues, especially dendrites caused by uneven deposition of cations during charge-discharge cycles, hinder their practical application. Here, we proposed a facile separator modification method which combines physical and chemical forces to regulate uniform and rapid deposition of both Li+ and Zn2+. Physically, the electronegativity of modified separators drives rapid transport of metal ions via a surface diffusion mode. Chemically, the polar surface functional groups on coated separators induce uniform deposition of metal ions so that the dendrite growth is effectively inhibited. As a result, the Li and Zn metal anodes employing modified separators can cycle stably for over 1000 h under a large current density of 10 mA cm-2.

Ionic Layer Epitaxy Growth of Organic/Inorganic Composite Protective Layers for Large-Area Li and Zn Metal Anodes.

Li and Zn metal batteries using organic and aqueous electrolytes, respectively, are desirable next-generation energy storage systems to replace the traditional Li-ion batteries. However, their cycle life and safety performance are severely constrained by a series of issues that are attributed to dendrite growth. To solve these issues, a nanothick ZnO-oleic acid (ZnO-OA) composite protective layer is developed by a facile ionic layer epitaxy method. The ZnO-OA layer provides strong lithophilic and zincophilic properties, which can effectively induce uniform ion deposition. As a result, the ZnO-OA protected Li and Zn metal anodes can cycle stably for over 600 and 1000 h under a large current density of 10 mA cm-2. Employing the ZnO-OA protected anodes, the Li||LiFePO4 cell can maintain a capacity retention of 99.5% after 600 cycles at a 1 C rate and the Zn||MnO2 cell can operate stably for 1000 cycles at 1 A g-1 current density.

Defect-Engineered VS2 Electrocatalysts for Lithium-Sulfur Batteries.

Defective two-dimensional transition metal dichalcogenides can be effective electrocatalysts for Li-S batteries, but the relationship between defect types and battery performance is unclear. In this work, we designed S vacancy-type SV-VS2 and V self-intercalated-type VI-VS2 and measured their catalytic activities in Li-S batteries. Compared with self-intercalating V atoms, S vacancies accelerated Li+ diffusion and SV-VS2 as a Li+ "reservoir" promoted the sulfur conversion kinetics significantly. In addition, the presence of sulfur vacancies promoted the lithiation behavior of SV-VS2 during discharge, leading to an enhancement of the catalytic ability of SV-VS2. However, this lithiation phenomenon weakened the catalytic activity of VI-VS2. Overall, SV-VS2 had better adsorption and catalytic activity. Li-S batteries with SV-VS2-coated separators delivered high rate performance and excellent cycling stability, with a capacity decay rate of 0.043% over 880 cycles at 1.0 C. This work provides an effective strategy for designing efficient Li-S battery electrocatalysts using defect engineering.

Two-Dimensional Organic-Inorganic Heterostructure as a Multifunctional Protective Layer for High Performance Zinc Metal Anode.

Dendrite growth and side reactions of Zn metal anodes remain unresolved obstacles for practical application of aqueous Zn ion batteries. Herein, a two-dimensional (2D) organic-inorganic heterostructure with controlled thickness was constructed as a protective layer for a Zn metal anode. The reduction of uniformly distributed polyoxometalate in the layer causes a negative charge density gradient, which can accelerate zinc ion transfer, homogenize zinc deposition, and shield sulfates at the electrode interface, while the exposed hydrophobic alkyl chain of the layer can isolate the direct contact of water with the Zn anode. As a result of the synergetic effect, this 2D organic-inorganic heterostructure enables high Zn plating/stripping reversibility, with high average Coulombic efficiencies of 99.97% for 3700 cycles at 2 mA cm-2. Under high Zn utilization conditions, a high areal-capacity full cell with hundreds of cycles was demonstrated.

Uniform Zinc Deposition Regulated by a Nitrogen-Doped MXene Artificial Solid Electrolyte Interlayer.

The dendrite growth and side reactions of zinc metal anode in mildly acidic electrolytes seriously hinder the practical application of aqueous zinc-ion battery. To address these issues, an artificial protective layer of nitrogen-doped MXene (NMX) is used to protect the zinc anode. The NMX protective layer has high conductivity and uniformly distributed zincophilic sites, which can not only homogenize the local electric field on the electrode interface but also accelerate the kinetics for Zn deposition. As a result, the NMX protective layer induces uniform zinc deposition and reduces the overpotential of the electrode. Encouragingly, this NMX-protected Zn anode can cycle stably for 1900 h at 1 mA cm-2 and 1 mAh cm-2 . In asymmetric cells, it achieves high cycle reversibility with an average Coulomb efficiency of 99.79% for 4800 cycles at 5 mA cm-2 .

A Multifunctional Organic Electrolyte Additive for Aqueous Zinc Ion Batteries Based on Polyaniline Cathode.

The practical applications of aqueous zinc ion batteries are hindered by the formation of dendrites on the anode, the narrow electrochemical window of electrolyte, and the instability of the cathode. To address all these challenges simultaneously, a multi-functional electrolyte additive of 1-phenylethylamine hydrochloride (PEA) is developed for aqueous zinc ion batteries based on polyaniline (PANI) cathode. Experiments and theoretical calculations confirm that the PEA additive can regulate the solvation sheath of Zn2+ and form a protective layer on the surface of the Zn metal anode. This broadens the electrochemical stability window of the aqueous electrolyte and enables uniform deposition of Zn. On the cathode side, the Cl- anions from PEA enter the PANI chain during charge and release fewer water molecules surrounding the oxidized PANI, thus suppressing harmful side reactions. When used in a Zn||PANI battery, this cathode/anode compatible electrolyte exhibits excellent rate performance and long cycle life, making it highly attractive for practical applications.

Temperature-Dependent Nucleation and Electrochemical Performance of Zn Metal Anodes.

A fundamental understanding of the nucleation and growth behaviors of Zn metal anodes over a wide range of temperatures is of great value for suppressing Zn dendrite growth. However, work focused on the early nucleation and growth behavior of Zn metal at various temperatures is still absent. Here, we study the effect of cycling temperature on Zn nuclei size and areal density and find that low temperature induces a smaller and dense nucleus, which prevents the formation of dendrites. Based on this finding, a cooling-treatment-based self-healing strategy is developed to in situ eliminate dendrites, which effectively prolongs the lifespan of the Zn anode by 520%. This novel self-healing strategy could be employed as a reliable strategy for restoring batteries in situ to reach a longer lifespan.

Stabilizing Interface pH by Mixing Electrolytes for High-Performance Aqueous Zn Metal Batteries.

Aqueous zinc metal batteries with mild acidic electrolytes are considered promising candidates for large-scale energy storage. However, the Zn anode suffers from severe Zn dendrite growth and side reactions due to the unstable interfacial pH and the absence of a solid electrolyte interphase (SEI) protective layer. Herein, a novel and simple mixed electrolyte strategy is proposed to address these problems. The mixed electrolytes of 2 M ZnSO4 and 2 M Zn (CF3 SO3 )2 can efficiently buffer the interfacial pH and induce the in situ formation of the organic-inorganic SEI layer, which eliminates dendrite growth and prevents side reactions. As a result, Zn anodes in mixed electrolyte exhibit a lifespan enhancement over 400 times, endure stable cycling over 270 h at a high DOD of 62% and achieve high Zn plating/stripping reversibility with an average CE of 99.5% for 1000 cycles at 1 mA cm-2 . The findings pave the way for developing practical electrolyte systems for Zn batteries.

A Rigid-Flexible Protecting Film with Surface Pits Structure for Dendrite-Free and High-Performance Lithium Metal Anode.

An artificial organic/inorganic composite protecting film for lithium metal anode with one-side surface pits structure was prepared by poly(vinylidene fluoride-co-hexafluoropropylene) and Al2O3+LiNO3 inorganic additives. Due to the unique surface structure, the composite film can not only serve as an artificial protective film, but also act as an additional lithium plating host, which synergistically enabled the lithium metal anode to adapt to high current densities meanwhile maintain dendrite-free during long-term cycling. As a result, the protected lithium metal anode can operate stably for 1000 h at a high current density of 10.0 mA cm-2. When paired with a LiFePO4 or sulfur cathode, the full cells with unflooded electrolyte showed significantly improved cycling performance, demonstrating great potential of this artificial protecting film in lithium metal batteries.

An Amorphous/Crystalline Incorporated Si/SiOx Anode Material Derived from Biomass Corn Leaves for Lithium-Ion Batteries.

The fabrication of silicon (Si) anode materials derived from high silica-containing plants enables effective utilization of subsidiary agricultural products. However, the electrochemical performances of synthesized Si materials still require improvement and thus need further structural design and morphology modifications, which inevitably increase preparation time and economic cost. Here, the conversion of corn leaves into Si anode materials is reported via a simple aluminothermic reduction reaction without other modifications. The obtained Si material inherits the structural characteristics of the natural corn leaf template and has many inherent advantages, such as high porosity, amorphous/crystalline mixture structure, and high-valence SiOx residuals, which significantly enhance the material's structural stability and electrode adhesive strength, resulting in superior electrochemical performances. Rate capability tests show that the material delivers a high capacity of 1200 mA h g-1 at 8 A g-1 current density. After 300 cycles at 0.5 A g-1 , the material maintains a high specific capacity of 2100 mA h g-1 , with nearly 100% capacity retention during long-term cycling. This study provides an economical route for the industrial production of Si anode materials for Lithium-Ion batteries.

Structure, charge transfer, and kinetic properties of NaVPO4F with Na+ extraction: a comprehensive first-principles study.

First-principles calculations combined with density functional theory were performed to illuminate the electrochemical properties of NaVPO4F. During desodiation to VPO4F, a ∼11% volume change was observed, which was ∼2% greater than that from LiVPO4F to VPO4F. An intermediate phase was observed while examining the structural stability during Na+ extraction from NaVPO4F. The voltage profile showed a distinct charging plateau positioned at ∼4.0 V. Bader charge analysis elucidated the reduction of charge-oriented V cations during Na+ extraction. The achieved electron density profiles were examined to analyze the influence of Na+ extraction on V-F and V-O bonds during the desodiation process. The most facile diffusion pathway for Na+ was discerned, with a minimum energy barrier of 0.85 eV. On the basis of these results, NaVPO4F was suggested as a promising cathode material for Na-ion batteries.

Charge transfer dynamics in chlorophyll-based biosolar cells.

We fabricated a chlorophyll (Chl)-based biosolar cell with H2Chl-sensitized TiO2 as an acceptor and (ZnChl)n as a donor. This solar cell gives a relatively high quantum yield from the absorption spectral contribution from both the donor and acceptor species. We employed subpicosecond time-resolved absorption spectroscopy (TAS) to study the excited state dynamics at the Chl interface. A charge transfer (CT) state between TiO2-H2Chl and (ZnChl)n was observed at 640 nm after excitation at the Qy peaks, 680 nm and 720 nm. This CT state is entirely different from the CT states observed for either TiO2-H2Chl (TiO2-H2Chl/spiro-OMeTAD) or TiO2-(ZnChl)n systems. Due to the slower charge transfer process from H2Chl+ to TiO2 as compared to that from (ZnChl)n+ to H2Chl, the CT lifetimes of H2Chl--(ZnChl)n+ (τ1 = 0.1 ps, τ2 = 1.4 ps) excited at 720 nm are slightly shorter than that excited at 680 nm (τ1 = 0.2 ps, τ2 = 5.6 ps). The TAS results suggest that the interface of TiO2-H2Chl and (ZnChl)n not only transfers holes as spiro-OMeTAD does, but also provides a built-in field for charge dissociation between the two Chl species.

Flexible MnS-Carbon Fiber Hybrids for Lithium-Ion and Sodium-Ion Energy Storage.

Nanostructures can improve battery capacity and cycle life, especially with sulfide electrodes. In this work, a freestanding flexible electrode, consisting of MnS nanoparticles embedded onto carbon nanofibers, was prepared by electrospinning. The produced hybrid was used as an electrode for lithium-ion and sodium-ion batteries. MnS nanoparticles have a size of about 5 nm and the particles are evenly distributed in the carbon nanofibers. Carbon nanofibers act as electronic conductors and buffer the volume change, while MnS nanoparticles react through rapid electrochemical reaction. As a Li-ion battery anode, this hybrid electrode exhibits specific capacities from 240 mAh g-1 at a high current density of 5 A g-1 , up to 600 mAh g-1 at 200 mA g-1 .

Self-Assembled CoS Nanoflowers Wrapped in Reduced Graphene Oxides as the High-Performance Anode Materials for Sodium-Ion Batteries.

It remains a big challenge to identify high-performance anode materials to promote practical applications of sodium-ion batteries. Herein, the facile synthesis of CoS nanoflowers wrapped in reduced graphene oxides (RGO) is reported, and their sodium storage properties are systematically studied in comparison with bare CoS. The CoS@RGO nanoflowers deliver a high reversible capacity of 620 mAh g-1 at a current density of 100 mA g-1 and superior rate capability with discharge capacity of 329 mAh g-1 at 4 A g-1 , much higher than those of the bare CoS. Evidenced by electrochemical impedance spectra and ex-situ SEM images, the improvement in the sodium storage performance is found to be due to the introduction of RGO which serves as a conducting matrix, to not only increase the kinetic properties of CoS, but also buffer the volume change and maintain the integrity of working electrodes during (de)sodiation processes. More importantly, the pseudocapacitive contribution of more than 89 % is only observed in the CoS@RGO nanocomposites, owing to the enhanced specific area and surface redox behavior.