A long-lifespan, flexible zinc-ion secondary battery using a paper-like cathode from single-atomic layer MnO2 nanosheets

Seed-Assisted Reversible Dissolution/Deposition of MnO2 for Long-Cyclic and Green Aqueous Zinc-Ion Batteries

Manganese oxide (MnO2) based aqueous zinc-ion batteries (AZIBs) are considered to be a promising battery for grid-scale energy storage. However, they usually suffer from the great challenge of capacity attenuation due to Mn dissolution and irreversible structural transformation. Herein, full use of the shortcomings is made to design high-performance cathode-free AZIBs. Manganese-based Prussian blue analog (Mn-PBA) is selected as a seed layer to provide a stable MnO2 electrodeposition surface. Thanks to the large specific surface area and manganophilic nature of Mn-PBA, the deposition/dissolution kinetics between Mn2+ and MnO2 are significantly enhanced. Systematic studies revealed the mechanism of MnO2 deposition-dissolution related to the reversible transformation of manganese oxide hydroxide and zinc hydroxide sulfate hydrate. Based on this, the developed cathode-free AZIBs exhibit outstanding rate performance (with a specific capacity of 273.7 mAh g-1 at 1 A g-1) and extraordinary cycle stability (maintaining a specific capacity of 52.3 mAh g-1 after 50 000 cycles at 20 A g-1). Furthermore, the AZIBs with non-toxic, biocompatible materials can be directly discarded after use, without causing pollution to the environment, which is expected to help achieve the sustainable development goals.

Inside-out regulation of MnO toward fast reaction kinetics in aqueous zinc ion batteries

An "inside-out regulation" strategy is proposed to improve the Zn2+ storage of MnO by Ni doping into the lattice and graphene wrapping outside the nanoparticles. The as-prepared Ni-MnO@rGO exhibits 112 mA h g-1 at 2.0 A g-1 over 800 cycles, due to the improved transport of electrons and ions from the synergistical function of intrinsic doping and external graphene encapsulation.

Amorphous K-Buserite Microspheres for High-Performance Aqueous Zn-Ion Batteries and Hybrid Supercapacitors

Aqueous Zn-ion batteries (AZIBs) and Zn-ion hybrid supercapacitors (AZHSCs) are considered promising energy-storage alternatives to Li-ion batteries due to the attractive merits of low-price and high-safety. However, the lack of suitable cathode materials always hinders their large-scale application. Herein, amorphous K-buserite microspheres (denoted as K-MnO_x ) are reported as cathode materials for both AZIBs and AZHSCs, and the energy-storage mechanism is systematically revealed. It is found that K-MnO_x is composed of rich amorphous K-buserite units, which can irreversibly be transformed into amorphous Zn-buserite units in the first discharge cycle. Innovatively, the transformed Zn-buserite acts as active materials in the following cycles and is highly active/stable for fast Zn-diffusion and superhigh pseudocapacitance, enabling the achievement of high-efficiency energy storage. In the AZIBs, K-MnO_x delivers 306 mAh g^-1 after 100 cycles at 0.1 A g^-1 with 102% capacity retention, while in the AZHSCs, it shows 515.0/116.0 F g^-1 at 0.15/20.0 A g^-1 with 92.9% capacitance retention at 5.0 A g^-1 after 20 000 cycles. Besides, the power/energy density of AZHSCs device can reach up to 16.94 kW kg^-1 (at 20 A g^-1 )/206.7 Wh kg^-1 (at 0.15 A g^-1 ). This work may provide some references for designing next-generation aqueous energy-storage devices with high energy/power density.

Nanocrystal Conversion Chemistry within Slit-like 2D Nanogap for High-Rate Cyclic Stability of Lithium-Ion Battery Anodes

Nanoscale optimization of late transition-metal oxides for fixing the reversible lithiation/delithiation mechanism with an in-depth mechanistic understanding of nanocrystal (NC) conversion chemistry is important for furthering next-generation Li-ion battery (LIB) technologies. Herein, 1 nm-thin Ni₃CoO_x (1 nm-NCO) nanosheets synthesized through isomorphic transformation of NiCo layered double hydroxides within a two-dimensional (2D)-SiO₂ envelope are chosen. The interconversion of metal/metal-oxide NCs under redox-switching thermal treatment, while retaining reversibility, inspired the accomplishment of identical consequences under the harsh operational conditions of LIB redox cycles by application of the thin-NCO-defined 2D nanospace. During charge/discharge cycles, 1 nm-NCO covered with an in situ formed solid-electrolyte-interphase layer enables fully reversible interconversion between the reactive NC redox pairs, as evidenced by detailed morphological and electrochemical analyses, thus providing high-rate capability with a specific capacity of 61.2% at 5.0 C relative to 0.2 C, outstanding cycle stability delivering a reversible capacity of 1169 mAh g^-1, and 913 mAh g^-1 with high average Coulombic efficiency (>99.2%) at 3.0 and 5.0 C for 1000 cycles, respectively, which has not been achieved with other transition-metal oxides. Such a nanospace-confinement effect on sustainability of reactive NCs to follow-up a highly reversible conversion reaction at fast charging in LIBs is operative within a slit-like ultrathin 2D nanogap from 1 nm-NCO only, as a relatively thicker 7 nm-NCO anode, with accompanying larger space available, has evidenced poor reversibility of NCs and inadequate cyclic stability under potential high-power density LIB application.

Developing High-Performance In-Plane Flexible Aqueous Zinc-Ion Batteries with Laser-Scribed Carbon-Supported All Electrodeposited Electrodes

Developing high-performance, safer, and affordable flexible batteries is of urgent need to power the fast-growing flexible electronics market. In this respect, zinc-ion chemistry employing aqueous-based electrolytes represents a promising combination considering the safety, cost efficiency, and both high energy and high-power output. Herein, we represent a high-performance flexible in-plane aqueous zinc-ion miniaturized battery constructed with all electrodeposited electrodes, i.e., MnO2 cathode and zinc anode with polyimide-derived interdigital patterned laser-scribed carbon (LSC) as the current collector as well as the template for electrodeposition. The LSC possesses a cross-linked network of graphitic carbon sheet, which offers large surface area over low footprint and ensures active materials loading with a robust conductive network. The LSC with high zincophilic characteristic also offers dendrite-free zinc deposition with very low Zn2+ plating stripping overpotential. Benefitting from the Zn//MnO2-rich redox chemistry, the ability of the 3D LSC network to uniformly distribute reaction sites, and the architectural merits of in-plane interdigitated electrode configuration, we report very high capacity values of ∼549 mAh/g (or ∼523 μAh/cm2) and 148 mAh/g (or 140 μAh/cm2) at 0.1 A/g (0.095 mA/cm2) and 2 A/g (1.9 mA/cm2) currents, respectively. The device was also able to maintain a high capacity of 196 mAh/g (areal capacity of 76.19 μAh/cm2) at 1 A/g (0.95 mA/cm2) current after 1350 cycles. The flexibility of the device was demonstrated in polyacryl amide (PAM) gel polymer soaked with a 2 M ZnSO4 and 0.2 M MnSO4 electrolyte, which exhibited a comparable specific capacity of ∼102-110 mAh/g in flat condition and different bending (100° or 160° bending) conditions. The device does not use any conventional current collector, separator, and conductive or polymer additives. The overall process is highly scalable and can be completed in less than a couple of hours.

Proton Insertion Promoted a Polyfurfural/MnO2 Nanocomposite Cathode for a Rechargeable Aqueous Zn-MnO2 Battery

Rechargeable aqueous Zn-MnO₂ batteries using a mild electrolyte have attracted considerable interest because of their high output voltage, high safety, low cost, and environmental friendliness. However, poor cycling stability remains a significant issue for their applications. Equally, the energy storage mechanism involved is still controversial thus far. Herein, porous polyfurfural/MnO₂ (PFM) nanocomposites are prepared via a facile one-step method. When tested in a rechargeable aqueous Zn-MnO₂ cell, the PFM nanocomposites deliver high specific capacity, considerable rate performance, and excellent long-term cyclic stability. Based on the experimental results, the role of the hydrated basic zinc sulfate layer being linked to the cycling stability of the aqueous rechargeable zinc-ion batteries is revealed. The mechanistic details of the insertion reaction based on the H⁺ ion storage mechanism are proposed, which plays a crucial role in maintaining the cycling performance of the rechargeable aqueous Zn-MnO₂ cell. We expect that this work will provide an insight into the energy storage mechanism of MnO₂ in aqueous systems and pave the way for the design of long-term cycling stable electrode materials for rechargeable aqueous Zn-MnO₂ batteries.

Hydrogen-Bonding Interactions in Hybrid Aqueous/Nonaqueous Electrolytes Enable Low-Cost and Long-Lifespan Sodium-Ion Storage

Although "water-in-salt" electrolytes have opened a new pathway to expand the electrochemical stability window of aqueous electrolytes, the electrode instability and irreversible proton co-insertion caused by aqueous media still hinder the practical application, even when using exotic fluorinated salts. In this study, an accessible hybrid electrolyte class based on common sodium salts is proposed, and crucially an ethanol-rich media is introduced to achieve highly stable Na-ion electrochemistry. Here, ethanol exerts a strong hydrogen-bonding effect on water, simultaneously expanding the electrochemical stability window of the hybridized electrolyte to 2.5 V, restricting degradation activities, reducing transition metal dissolution from the cathode material, and improving electrolyte-electrode wettability. The binary ethanol-water solvent enables the impressive cycling of sodium-ion batteries based on perchlorate, chloride, and acetate electrolyte salts. Notably, a Na_0.44MnO₂ electrode exhibits both high capacity (81 mAh g^-1) and a remarkably long cycle life >1000 cycles at 100 mA g^-1 (a capacity decay rate per cycle of 0.024%) in a 1 M sodium acetate system. The Na_0.44MnO₂/Zn full cells also show excellent cycling stability and rate capability in a wide temperature range. The gained understanding of the hydrogen-bonding interactions in the hybridized electrolyte can provide new battery chemistry guidelines in designing promising candidates for developing low-cost and long-lifespan batteries based on other (Li⁺, K⁺, Zn^2+, Mg²⁺, and Al³⁺) systems.