Defect Promoted Capacity and Durability of N-MnO2- x Branch Arrays via Low-Temperature NH3 Treatment for Advanced Aqueous Zinc Ion Batteries

Electrochemical Generation of Hydrated Zinc Vanadium Oxide with Boosted Intercalation Pseudocapacitive Storage for a High-Rate Flexible Zinc-Ion Battery

With the surging development of flexible wearable and stretchable electronic devices, flexible energy-storage devices with excellent electrochemical properties are in great demand. Herein, a flexible Zn-ion battery comprised by hydrated zinc vanadium oxide/carbon cloth (ZnVOH/CC) as the cathode is developed, and it shows a high energy density, superior lifespan, and good safety. ZnVOH/CC is obtained by the in situ transformation of hydrated vanadium oxide/carbon cloth (VOH/CC) by an electrochemical method, and the intercalation pseudocapacitive reaction mechanism is discovered for ZnVOH/CC. The co-insertion/deinsertion of H⁺/Zn²⁺ is observed; the H⁺ insertion dominates in the initial discharge stage and the high-rate electrochemical process, while Zn²⁺ insertion dominates the following discharge stage and the low-rate electrochemical procedure. An ultrastable reversible capacity of 135 mAh g^-1 at 20 A g^-1 is obtained after 5000 cycles without capacity fading. Moreover, the as-assembled flexible zinc-ion battery can operate normally under rolled, folded, and punched conditions with superior safety. It is capable to deliver a high discharge capacity of 184 mAh g^-1 at 10 A g^-1 after 170 cycles. This work paves a new way for designing low-cost, safe, and quick-charging energy-storage devices for flexible electronics.

Recent Development of Mn-based Oxides as Zinc-Ion Battery Cathode

Manganese-based oxide is arguably one of the most well-studied cathode materials for zinc-ion battery (ZIB) due to its wide oxidation states, cost-effectiveness, and matured synthesis process. As a result, there are numerous reports that show significant strides in the progress of Mn-based oxides as ZIB cathode. However, ironically, due to the sheer number of Mn-based oxides that have been published in recent years, there remain certain contemplations with regards to the electrochemical performance of each type of Mn-based oxides and their performance comparison among various Mn polymorphs and oxidation states. Thus, to provide a clearer indication of the development of Mn-based oxides, the recent progress in Mn-based oxides as ZIB cathode was summarized systematically in this Review. More specifically, (1) the classification of Mn-based oxides based on the oxidation states (i. e., MnO₂ , Mn₃ O₄ , Mn₂ O₃ , and MnO), (2) their respective polymorphs (i. e., α-MnO₂ and δ-MnO₂ ) as ZIB cathode, (3) the modification strategies commonly employed to enhance the performance, and (4) the effects of these modification strategies on the performance enhancement were reviewed. Lastly, perspectives and outlook of Mn-based oxides as ZIB cathode were discussed at the end of this Review.

Polymorphic Effects on Electrochemical Performance of Conversion-Based MnO2 Anode Materials for Next-Generation Li Batteries

In this study, four different MnO₂ polymorphs are synthesized with a controlled morphology of hollow porous structures to systematically investigate the influences of polymorphs in conversion-based material. As the structure of these materials transforms into nanosized metal and maintains an extremely low-crystalline phase during cell operation, the effects of polymorphs are overlooked as compared to the case of insertion-based materials. Thus, differences in the ion storage behaviors among various MnO₂ polymorphs are not well identified. Herein, the structural changes, charge storage reaction, and electrochemical performance of the different MnO₂ polymorphs are investigated in detail. The experimental results demonstrate that the charge storage reactions, as part of which spinel-phased MnO₂ formation is observed after lithiation and delithiation instead of recovery of the original phases, are similar for all the samples. However, the electrochemical performance varies depending on the initial crystal structure. Among the four polymorphs, the spinel-type λ-MnO₂ delivers the highest reversible capacity of ≈1270 mAh g^-1 . The structural similarity between the cycled and pristine states of λ-MnO₂ induces faster kinetics, resulting in the better electrochemical performance. These findings suggest that polymorphs are another important factor to consider when designing high-performance materials for next-generation rechargeable batteries.

Boosting zinc ion energy storage capability of inert MnO cathode by defect engineering

Aqueous zinc ion battery constitutes a safe, stable and promising next-generation energy storage device, but suffers the lack of suitable host compounds for zinc ion storage. Development of a facile way to emerging cathode materials is strongly requested toward superior electrochemical activities and practical applications. Herein, defect engineering, i.e., simultaneous introduction of nitrogen dopant and oxygen vacancy into commercial and low-cost MnO, is proposed as a positive strategy to activate the originally inert phase for kinetically propelling its zinc ion storage capability. Both experimental characterization and theoretical calculations demonstrate that the nitrogen dopant significantly improves the electric conductivity of electrochemical inert MnO. Simultaneously, the oxygen vacancy creates sufficient large inserted channels and available activated adsorption sites for zinc ions storage. These synergistic structural advantages obviously ameliorate the electrochemical performance of inert MnO. Therefore, even without any conductive agent additive, the as-prepared material shows high specific capacity, superb rate capability, prolonged cycling stability and attractive energy density, which are dramatically superior to those of the pristine MnO as well as many other host cathode materials. This work presents fresh insights on the role of defect engineering in the enhancement of the intrinsic electrochemical reactivity of inert cathode, and an effective strategy for scalable fabrication of high-performance cathode for zinc ion battery.

Neatly arranged mesoporous MnO2 nanotubes with oxygen vacancies for electrochemical energy storage

Intrinsically poor conductivity, sluggish ion transfer kinetics, and limited specific area are the three main obstacles that confine the electrochemical performance of manganese dioxide in supercapacitors. Herein, one-dimensional mesoporous MnO2 nanotubes were prepared using a polycarbonate film as a template and a large number of oxygen vacancies were introduced by calcination under a N2 atmosphere. The effects of calcination temperature on the crystal structure, micro-morphology and electrochemical performance of MnO2 nanotubes were studied. The presence of oxygen vacancies increases the redox capacity of ov-MnO2-300 nanotubes, and the unique one-dimensional mesoporous structure also provides an effective channel for ion transport. Therefore, the ov-MnO2-300 nanotube has an excellent specific capacitance of 459.0 F g-1 at a current density of 1 A g-1 and also has outstanding rate performance and cycle performance. An asymmetric supercapacitor assembled with ov-MnO2-300 nanotubes as the positive electrode and graphene@MoS2 as the negative electrode delivered an energy density of 40.2 W h kg-1 at a power density of 1024 W kg-1. The excellent capacitance performance is mostly attributed to the introduction of oxygen vacancies to increase the intrinsic conductivity of MnO2, and the unique one-dimensional mesoporous nanotube structure increases the active sites of redox reactions.

N, O co-doped chlorella-based biomass carbon modified separator for lithium-sulfur battery with high capacity and long cycle performance

As a lithium-ion secondary battery with high energy density, lithium-sulfur batteries have very bright development prospects. But the shuttle effect is still a thorny issue in the development process. The N, O co-doped chlorella-based biomass carbon (CBBC) synthesized by chemical activation method possesses a microporous and mesoporous composite structure, large specific surface area, and good electrical conductivity. The CBBC interlayer can improve the wettability between the separator and the electrolyte, and accelerate the transmission of Li⁺. N, O heteroatoms have a strong chemical adsorption operation for LiPs. The modified separator restrains lithium polysulfide through physical barriers and chemical adsorption, and improves the capacity and cycle performance of lithium-sulfur batteries. The batteries with CBBC exhibit excellent cycling stability (0.067% per cycle at 0.5C) and better rate performance (918 mAh g^-1 at 2C). The first discharge capacity at 0.05C was 1540 mAh g^-1. Even after 600 cycles the discharge capacity retains 656 mAh g^-1 at 0.5C. The low price and simple preparation of CBBC interlayer is an attractive choice for improving lithium-sulfur batteries.

Anchoring SnS2 on TiC/C Backbone to Promote Sodium Ion Storage by Phosphate Ion Doping

Tin disulfide (SnS₂ ) shows promising properties toward sodium ion storage with high capacity, but its cycle life and high rate capability are still undermined as a result of poor reaction kinetics and unstable structure. In this work, phosphate ion (PO₄ ^3- )-doped SnS₂ (P-SnS₂ ) nanoflake arrays on conductive TiC/C backbone are reported to form high-quality P-SnS₂ @TiC/C arrays via a hydrothermal-chemical vapor deposition method. By virtue of the synergistic effect between PO₄ ^3- doping and conductive network of TiC/C arrays, enhanced electronic conductivity and enlarged interlayer spacing are realized in the designed P-SnS₂ @TiC/C arrays. Moreover, the introduced PO₄ ^3- can result in favorable intercalation/deintercalation of Na⁺ and accelerate electrochemical reaction kinetics. Notably, lower bandgap and enhanced electronic conductivity owing to the introduction of PO₄ ^3- are demonstrated by density function theory calculations and UV-visible absorption spectra. In view of these positive factors above, the P-SnS₂ @TiC/C electrode delivers a high capacity of 1293.5 mAh g^-1 at 0.1 A g^-1 and exhibits good rate capability (476.7 mAh g^-1 at 5 A g^-1 ), much better than the SnS₂ @TiC/C counterpart. This work may trigger new enthusiasm on construction of advanced metal sulfide electrodes for application in rechargeable alkali ion batteries.

Nitrogen-Incorporated Cobalt Sulfide/Graphene Hybrid Catalysts for Overall Water Splitting

Water electrolysis is an advanced and sustainable energy conversion technology used to generate H₂ . However, the low efficiency of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) hampers the overall water-splitting catalytic performance. Here, a hybrid catalyst was constructed from N-doped CoS₂ nanoparticles on N,S-co-doped graphene nanosheets (N-CoS₂ /G) using a facile method, and the catalyst exhibited excellent bifunctional activity. Introduction of N atoms not only promoted the adsorption of reaction intermediates, but also bridged the CoS₂ nanoparticles and graphene to improve electron transfer. Moreover, using thiourea as both N- and S-source ensured synthesis of much smaller-sized nanoparticles with more surface active sites. Surprisingly, the N-CoS₂ /G exhibited superior catalytic activity with a low overpotential of 260 mV for the OER and 109 mV for the HER at a current density of 10 mA cm^-2 . The assembled N-CoS₂ /G : N-CoS₂ /G electrolyzer substantially expedited overall water splitting with a voltage requirement of 1.58 V to reach 10 mA cm^-2 , which is superior to most reported Co-based bifunctional catalysts and other non-precious-metal catalysts. This work provides a new strategy towards advanced bifunctional catalysts for water electrolysis.

Unravelling the Mechanism of Rechargeable Aqueous Zn-MnO2 Batteries: Implementation of Charging Process by Electrodeposition of MnO2

Poor cycling stability and mechanistic controversies have hindered the wider application of rechargeable aqueous Zn-MnO2 batteries. Herein, direct evidence was provided of the importance of Mn2+ in this type of battery by using a bespoke cell. Without pre-addition of Mn2+ , the cell exhibited an abnormal discharge-charge profile, meaning it functioned as a primary battery. By adjusting the Mn2+ content in the electrolyte, the cell recovered its charging ability through electrodeposition of MnO2 . Additionally, a dynamic pH variation was observed during the discharge-charge process, with a precipitation of Zn4 (OH)6 (SO4 )⋅5H2 O buffering the pH of the electrolyte. Contrary to the conventional Zn2+ intercalation mechanism, MnO2 was first converted into MnOOH, which reverted to MnO2 through disproportionation, resulting in the dissolution of Mn2+ . The charging process occurred by the electrodeposition of MnO2 , thus improving the reversibility through the availability of Mn2+ ions in the solution.

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.

Constructing the Efficient Ion Diffusion Pathway by Introducing Oxygen Defects in Mn2O3 for High-Performance Aqueous Zinc-Ion Batteries

Mn-based cathodes are admittedly the most promising candidate to achieve the practical applications of aqueous zinc-ion batteries because of the high operating voltage and economic benefit. However, the design of Mn-based cathodes still remains challenging because of the vulnerable chemical architecture and strong electrostatic interaction that lead to the inferior reaction kinetics and rapid capacity decay. These intrinsic drawbacks need to be fundamentally addressed by rationally decorating the crystal structure. Herein, an oxygen-defective Mn-based cathode (Oc_u-Mn₂O₃) is designed via a doping low-valence Cu-ion strategy. The oxygen defect can modify the internal electric field of the material and enhance the substantial electrostatic stability by compensating for the nonzero dipole moment. With the merits of oxygen deficiency, the Oc_u-Mn₂O₃ electrode exhibits the significant diffusion coefficient in the range from 1 × 10^-6 to 1 × 10^-8, and good rate performance. In addition, the Oc_u-Mn₂O₃ maintains the highly reversible cyclic stability with the capacity retention of 88% over 600 cycles. The charge storage mechanism is explored as well, illustrating that the oxygen defects can improve the electrochemical active sites of H⁺ insertion, achieving a better charge-storage capacity than Mn₂O₃.

Atomic Engineering Catalyzed MnO2 Electrolysis Kinetics for a Hybrid Aqueous Battery with High Power and Energy Density

Research interest and achievements in zinc aqueous batteries, such as alkaline Zn//Mn, Zn//Ni/Co, Zn-air batteries, and near-neutral Zn-ion and hybrid ion batteries, have surged throughout the world due to their features of low-cost and high-safety. However, practical application of Zn-based secondary batteries is plagued by restrictive energy and power densities in which an inadequate output plateau voltage and sluggish kinetics are mutually accountable. Here, a novel paradigm high-rate and high-voltage Zn-Mn hybrid aqueous battery (HAB) is constructed with an expanded electrochemical stability window over 3.4 V that is affordable. As a proof of concept, catalyzed MnO₂ /Mn²⁺ electrolysis kinetics is demonstrated in the HAB via facile introduction of Ni²⁺ into the electrolyte. Various techniques are employed, including in situ synchrotron X-ray powder diffraction, ex situ X-ray absorption fine structure, and electron energy loss spectroscopy, to reveal the reversible charge-storage mechanism and the origin of the boosted rate-capability. Density functional theory (DFT) calculations reveal enhanced active electron states and charge delocalization after introducing strongly electronegative Ni. Simulations of the reaction pathways confirm the enhanced catalyzed electrolysis kinetics by the facilitated charge transfer at the active O sites around Ni dopants. These findings significantly advance aqueous batteries a step closer toward practical low-cost application.

Binding Zinc Ions by Carboxyl Groups from Adjacent Molecules toward Long-Life Aqueous Zinc-Organic Batteries

The newly emerged aqueous Zn-organic batteries are attracting extensive attention as a promising candidate for energy storage. However, most of them suffer from the unstable and/or soluble nature of organic molecules, showing limited cycle life (≤3000 cycles) that is far away from the requirement (10 000 cycles) for grid-scale energy storage. Here, a new aqueous zinc battery is proposed by using sulfur heterocyclic quinone dibenzo[b,i]thianthrene-5,7,12,14-tetraone (DTT) as the cathode. The cell shows a high reversible capacity of 210.9 mAh g_DTT ^-1 at 50 mA g_DTT ^-1 with a high mass loading of 5 mg_DTT cm^-2 , along with a fast kinetics for charge storage. Electrochemical measurements, ex situ analyses, and density functional theory calculation successfully demonstrate that the DTT electrode can simultaneously store both protons (H⁺ ) and Zn²⁺ to form DTT₂ (H⁺ )₄ (Zn²⁺ ), where Zn²⁺ is bound to the carboxyl groups from the adjacent DTT molecules with improved stability. Benefitting from the improved molecular stability and the inherent low solubility of DTT and related discharge products, the DTT//Zn full cell exhibits a superlong life of 23 000 cycles with a capacity retention of 83.8%, which is much superior to previous reports.

Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High-Capacity and High-Rate Fiber-Shaped Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α-MoO₃ holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO₃ cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al₂ O₃ coating and phosphating process, the constructed Zn//P-MoO_{3- x} @Al₂ O₃ battery delivers impressive capacity of 257.7 mAh g^-1 at 1 A g^-1 and superior rate capability (57% capacity retention at 20 A g^-1 ), dramatically surpassing the pristine Zn//MoO₃ battery (115.8 mAh g^-1 ; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm^-3 ) as well as favorable energy density (14.4 mWh cm^-3 ; 240 Wh kg^-1 ) are both achieved by the fiber-shaped quasi-solid-state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high-performance ZIBs.