Mixed phase sodium manganese oxide as cathode for enhanced aqueous zinc-ion storage

Synergistic Effect of Dual Phases to Improve Lithium Storage Properties of Nb2O5

Niobium pentoxides (Nb2O5) present great potential as next-generation anode candidates due to exceptional lithium-ion intercalation kinetics, considerably high capacity, and reasonable redox potential. Although four phases of Nb2O5 including hexagonal, orthorhombic, tetragonal, and monoclinic polymorphs show diverse characteristics in electrochemical performance, stable lifetime, high specific capacity, and fast intercalation properties cannot be delivered simultaneously with a single phase. Herein, this issue is addressed by generating a homogeneous mixture of orthorhombic and monoclinic crystals at the nanoscale. Reversible lithium-ion intercalation/deintercalation of the monoclinic phase is achieved, and exceptional lithium storage sites are created at the interface of the two phases. As a result, electrochemical features of stable lifetime from the orthorhombic phase and high specific performance from the monoclinic phase are harmoniously combined. This dual-phase Nb2O5/C nanohybrids deliver as high as 380 mA h g-1 (0.01-3.0 V) and 184 mA h g-1 (1.0-3.0 V) after 200 cycles. The essential principle of property enhancement is further confirmed through in situ XRD measurements and DFT calculations. The dual-phase concept can be further applied on electrodes with multiphases to achieve high electrochemical performance.

Vanadium Pentoxide Nanofibers/Carbon Nanotubes Hybrid Film for High-Performance Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) with the characteristics of low production costs and good safety have been regarded as ideal candidates for large-scale energy storage applications. However, the nonconductive and non-redox active polymer used as the binder in the traditional preparation of electrodes hinders the exposure of active sites and limits the diffusion of ions, compromising the energy density of the electrode in ZIBs. Herein, we fabricated vanadium pentoxide nanofibers/carbon nanotubes (V₂O₅/CNTs) hybrid films as binder-free cathodes for ZIBs. High ionic conductivity and electronic conductivity were enabled in the V₂O₅/CNTs film due to the porous structure of the film and the introduction of carbon nanotubes with high electronic conductivity. As a result, the batteries based on the V₂O₅/CNTs film exhibited a higher capacity of 390 mAh g^-1 at 1 A g^-1, as compared to batteries based on V₂O₅ (263 mAh g^-1). Even at 5 A g^-1, the battery based on the V₂O₅/CNTs film maintained a capacity of 250 mAh g^-1 after 2000 cycles with a capacity retention of 94%. In addition, the V₂O₅/CNTs film electrode also showed a high energy/power density (e.g., 67 kW kg^-1/267 Wh kg^-1). The capacitance response and rapid diffusion coefficient of Zn²⁺ (~10^-8 cm^-2 s^-1) can explain the excellent rate capability of V₂O₅/CNTs. The vanadium pentoxide nanofibers/carbon nanotubes hybrid film as binder-free cathodes showed a high capability and a stable cyclability, demonstrating that it is highly promising for large-scale energy storage applications.

Uniform Zn Deposition Achieved by Ag Coating for Improved Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) are considered as a promising energy storage system due to their low cost and high safety merits. However, they suffer from the challenge of uncontrollable dendrite growth due to a non-uniform zinc deposition, which increases internal resistance and causes battery failure. Herein, Ag coating fabricated by a facile surface chemistry route on zinc metal was developed to guide uniform zinc deposition. Ag-coated Zn shows improved electrolyte wettability, a small zinc deposition overpotential, and fast kinetics for zinc deposition/dissolution. Direct optical visualization and scanning electron microscopy images show uniform zinc deposition due to the introduction of Ag coating. As a result, the Ag-coated Zn anode can sustain up to 1450 h of repeated plating/stripping with a low overpotential in symmetric cells at a current density of 0.2 mA cm^-2, while an improved performance is realized for full cells paired with a V₂O₅-based cathode. This work provides a facile and effective approach to improve the electrochemical performance of ZIBs.

A Facile Chemical Method Enabling Uniform Zn Deposition for Improved Aqueous Zn-Ion Batteries

Rechargeable aqueous Zn-ion batteries (ZIBs) have gained great attention due to their high safety and the natural abundance of Zn. Unfortunately, the Zn metal anode suffers from dendrite growth due to nonuniform deposition during the plating/stripping process, leading to a sudden failure of the batteries. Herein, Cu coated Zn (Cu-Zn) was prepared by a facile pretreatment method using CuSO₄ aqueous solution. The Cu coating transformed into an alloy interfacial layer with a high affinity for Zn, which acted as a nucleation site to guide the uniform Zn nucleation and plating. As a result, Cu-Zn demonstrated a cycling life of up to 1600 h in the symmetric cells and endowed a stable cycling performance with a capacity of 207 mAh g^-1 even after 1000 cycles in the full cells coupled with a V₂O₅-based cathode. This work provides a simple and effective strategy to enable uniform Zn deposition for improved ZIBs.