Cathode For Zn-ion Batteries Research Articles

Exploring the Enhanced Zinc Storage Performance of α-MnSe Polyhedral Microspheres and H+/Zn2+ Co-Insertion Mechanism.

The newly emerged Mn-based selenides as cathodes for aqueous Zn-ion batteries (ZIBs) have drawn researchers' interest because of their lower electronegativity and better electronic conductivity compared with the corresponding Mn-based oxides. Nevertheless, the energy storage mechanism of Mn-based selenides still needs to be further clarified. Herein, the MnSe/Se and MnSe polyhedral microspheres are reported as cathodes for ZIBs, and the MnSe cathode achieves significantly enhanced specific capacity, rate performance, and cycling stability. In-depth kinetic analysis confirms that the MnSe cathode presents better kinetic behavior and density functional theory (DFT) calculations verify the fast diffusion kinetics of the MnSe cathode. More importantly, systematic ex situ characterizations reveal that the microstructured MnSe can exist stably during the charge-discharge process and store energy with H+/Zn2+ co-insertion mechanism, which is greatly different from the phase transformation of the nanostructured α-MnSe reported in the literature. Additionally, it is verified that the different types of separators exhibit remarkably different zinc storage performance of the MnSe cathode. This study not only offers a good guidance for developing high-performance ZIBs Mn-based cathode materials and explores the effect of separators on the zinc storage performance, but also provides new insights into the energy storage mechanism of the MnSe cathode.

A stable ZnMn2O4 cathode for aqueous Zn-ion batteries via Ni doping to suppress Mn dissolution

ZnMn2O4 (ZMO) emerges as a promising cathode for aqueous Zn-ion batteries due to its high theoretical capacity of 224 mAh g−1 and operating voltage of ∼1.9 V (vs. Zn2+/Zn). However, it suffers from capacity degradation over cycling, attributed to the dissolution of redox-active Mn through Mn3+ disproportionation. In this study, we propose a strategy to stabilize ZMO cathodes by transforming Mn3+ into Mn4+ via Ni doping, aiming for charge balance. The ZnMn2−xNixO4 (x = 0, 0.5, 1.0, and 1.5) with different Ni amounts was prepared by straightforward precipitation and calcination. The mitigation of redox-active Mn dissolution enhanced the specific capacity of all Ni-doped ZMO compared to 201 mAh g−1 of ZMO. ZnMn1.5Ni0.5O4 and ZnMnNiO4 exhibit 277 and 278 mAh g−1, respectively, surpassing ZMO’s theoretical capacity (224 mAh g−1) of ZMO. This additional capacity was attributed to MnOx deposition on the cathode and the charge storage reaction with Zn-ion within the MnOx deposit. Furthermore, Ni doping induces a structural transition of the tetragonal into a cubic spinel, expanding the unit cell volume. This structural modification combined with suppressed Mn dissolution contributes to improved cycling stability. ZnMnNiO4 exhibits 80 % retention of initial capacity after 1000 cycles, outperforming ZMO (57 % retention). The expanded unit cell reduces repulsion between inserted Zn ions, enabling a higher rate performance than pure ZMO. The change in Mn valence states induced by Ni doping enhanced the lifespan and rate capability of ZMO cathodes, underscoring their potential as cathodes for Zn-ion batteries.

Effect of pre-inserted monovalent cations on vanadium-based cathode materials for rechargeable aqueous zinc-ion batteries

Understanding the effect of pre-inserted cations in vanadium-based from a comprehensive perspective plays a vital role in exploring novel cathode materials for Zn-ion storage. In this work, we provide a study of monovalent cations (i.e., Na+, K+, and NH4+) on the Zn2+ storage behaviors of proton-substituted vanadates (i.e., NaVO, KVO, and NH4VO), revealing the intrinsic property (e.g., hydration capacity, bonding strength) of monovalent ions has a significant impact on the amount of pre-inserted cations and crystal water in stacked V–O layers, as well as the morphology of the obtained products, and the structural evolution during the activated process. Due to the enhancement of the ion-diffusion kinetics and stronger capacitance properties from the synergistic effect by pre-inserted Na+ ions and crystal water, the NaVO cathode exhibits superior rate performance and better energy efficiency (60.87 % at 10 A g−1), delivers a high specific capacity of 427.0 mAh g−1 at 0.2 A g−1 and retains 74.3 % of capacity after 1900 cycles at 2 A g−1. Moreover, the correlation between the pre-inserted cations in the cathode and the issues (e.g., side-products and dendrites) of the Zn anode has been revealed, providing new insight into designing high-performance cathodes for Zn ion batteries.

High-Performance Aqueous Zinc-Organic Battery with a Photo-Responsive Covalent Organic Framework Cathode.

Covalent organic framework (COF) materials, known for their robust porous character, sustainability, and abundance, have great potential as cathodes for aqueous Zn-ion batteries (ZIBs). However, their application is hindered by low reversible capacity and discharge voltage. Herein, a donor-acceptor configuration COF (NT-COF) is utilized as the cathode for ZIBs. The cell exhibits a high discharge voltage plateau of ≈1.4V and a discharge capacity of 214 mAh g-1 at 0.2 A g-1 when utilizing the Mn2+ electrolyte additive in the ZnSO4 electrolyte. A synergistic combination mechanism is proposed, involving the deposition/dissolution reactions of Zn4SO4(OH)6·4H2O and the co-(de)insertion reactions of H+ and SO4 2- in NT-COF. Meanwhile, the NT-COF with a donor-acceptor configuration facilitates efficient generation and separation of electron-hole pairs upon light exposure, thereby enhancing electrochemical reactions within the battery. This leads to a reduction in charging voltage and internal overvoltage, ultimately minimizing electricity consumption. Under ambient weather conditions, the cell exhibits an average discharge capacity of 430 mAh g-1 on sunny days and maintains consistent cycling stability for a duration of 200 cycles (≈19 days) at 0.2 A g-1. This research inspires the advancement of Zn-organic batteries for high-energy-density aqueous electrochemical energy storage systems or photo-electrochemical batteries.

Construction of amorphous V2O5@Ti3C2Tx synergistic heterostructure on 3D carbon cloth substrate by a self-assembled strategy towards high-performance aqueous Zn-ion batteries

The emerging aqueous Zn-ion batteries (ZIBs) with their low price and inherent safety are showing strong competitiveness in the energy storage field. In this work, layer-by-layer stacked amorphous V2O5@Ti3C2Tx heterostructures anchored on three-dimensional carbon cloth (3D CC), synthesized by annealing process and subsequent in-situ electrochemical induction, are reported as high capacity and stable cathode for ZIBs. In this composite cathode, amorphous V2O5@Ti3C2Tx synergistic heterostructure provides isotropic Zn2+ migration channels and rapid electron transfer kinetics, while the 3D CC substrate can ensure that the bulk phase in the electrode material is also utilized to maximize the synergistic effect. As a result, the CC/a-V2O5@Ti3C2Tix cathode achieves a high specific capacity of 567 mAh/g at 0.1 A/g, a satisfactory rate performance of 213 mAh/g at 10 A/g, together with a long cycle life of 96.2 % capacity retention after 2000 cycles. Ex-situ characterizations show that the CC/a-V2O5@Ti3C2Tx cathode undergoes a highly reversible Zn2+/H+ co-intercalation/deintercalation mechanism during the discharge/charging process. In addition, based on the CC/a-V2O5@Ti3C2Tx cathode, the assembled flexible ZIB can operate properly under different bending degrees, showing its practicality in flexible devices. This work provides insight into the rational design of cathode materials with high Zn-storage performance.

Made to Measure Squaramide COF Cathode for Zinc Dual‐Ion Battery with Enriched Storage via Redox Electrolyte

AbstractAqueous rechargeable batteries are promising grid‐scale energy storage devices because of their affordability, operational safety, and environmental benignity. Among these, Zn‐ion batteries (ZIBs) have unfolded new horizons. Designing superior cathodes for ZIBs is crucial. Covalent organic frameworks (COFs) can be made redox active with a high storage surface. Here, for the first time, a chelating COF with redox‐active ZnI2 in a ZnSO4(aq) electrolyte is combined. Including iodide harvests an approximately threefold enhancement in capacity from 208 to 690 mAh g−1 at 1.5 A g−1, the highest among all the COF‐derived ZIBs. Remarkably, a charge–discharge curve at 1.3 V exhibits very limited dropout voltage and super‐flat platform, with a remarkable capacity of 600 mAh g−1 at 5 A g−1 stable up to 6000 cycles, confirming that the polyiodide generation and storage are sustainable. The COF's dual‐ion storage (Zn2+ and polyidode) delivers a ZIB with the highest energy density. Spectro‐electrochemical measurements coupled with X‐ray photoelectron spectroscopy unambiguously unveil the existence of multiple polyiodide species, with I3− and IO3− ions as the prominent species. The latter gets reduced at the COF electrode under an applied potential, leaving I3− as the major species stored on the COF. The prospect of COF‐polyiodide(aq) is a windfall for metal‐ion batteries.

Coupling Zn2+ doping and rich oxygen vacancies in MnO2 nanowire toward advanced aqueous zinc-ion batteries

Easy collapse of structure and sluggish reaction kinetics restrict the practical application of MnO2 in the field of aqueous Zn-ion batteries (ZIBs). To circumvent these obstacles, Zn2+ doping MnO2 nanowire electrode material with rich oxygen vacancies is prepared by one-step hydrothermal method combined with plasma technology. The experimental results indicate that Zn2+ doping MnO2 nanowire not only stabilizes the interlayer structure of MnO2, but also provide additional specific capacity as electrolyte ions. Meanwhile, plasma treatment technology induces the oxygen-deficient Zn-MnO2 electrode optimizing the electronic structure to improve the electrochemical behavior of the cathode materials. Especially, the optimized Zn/Zn-MnO2 batteries obtain outstanding specific capacity (546 mAh g−1 at 1 A g−1) and superior cycling durability (94% over 1000 continuous discharge/charge tests at 3 A g−1). Greatly, the H+ and Zn2+ reversible co-insertion/extraction energy storage system of Zn//Zn-MnO2-4 battery is further revealed by the various characterization analyses during the cycling test process. Further, from the perspective of reaction kinetics, plasma treatment also optimizes the diffusion control behavior of electrode materials. This research proposes a synergistic strategy of element doping and plasma technology, which has enhanced the electrochemical behaviors of MnO2 cathode and shed light on the design of the high-performance manganese oxide-based cathodes for ZIBs.

Enhanced cycling stability achieved by the nitrogen doped carbon coating layer for electrodeposited Mn3O4 in aqueous zinc ion batteries

Aqueous rechargeable Zn-ion batteries (ZIBs) are promising candidates for large scale energy storage. Unfortunately, their application is hindered by the quick capacity fading. Herein, the Mn3O4@N-doped carbon coated carbon cloth electrodes (Mn3O4@NC/CC) are prepared by electrodeposition and calcination and are used as the cathode for ZIBs. The thickness of the electrodeposited Mn3O4 is ∼ 200 nm, and the NC layer is ∼ 10 nm. The ZIB with Mn3O4@NC/CC displays the capacity of 265.8 mAh g−1 at 0.2 A g−1, and has a high reversible capacity of 165.6 mAh g−1 after 2000 charged − discharged cycles at 3 A g−1. The capacitive-controlled processes contribute mainly to the charge storage mechanism. The introduction of NC layer can effectively prevent the disintegration of active material during charge-discharge cycling. The NC layer can also hinder the diffusion of Zn2+ and enhance Rct, that leads to suppressed Zn ion insertion/extraction and possibly milder change in crystal structure. Ex-situ characterization shows that the Mn3O4 is irreversibly converted to R-MnO2 after multiple charge − discharge cycles, and both H+ and Zn2+ participate in the charge storage processes.

Mo-Pre-Intercalated MnO2 Cathode with Highly Stable Layered Structure and Expanded Interlayer Spacing for Aqueous Zn-Ion Batteries

Although manganese-based oxides possess high voltage and low cost, the sluggish reaction kinetics and poor structural stability hinder their applications in aqueous rechargeable Zn-ion batteries (ZIBs). Herein, a molybdenum (Mo) pre-intercalation strategy is proposed to solve the above issues of δ-MnO2. The pre-intercalated Mo dopants, acting as the interlayer pillars, can not only expand the interlayer spacing but also reinforce the layered structure of δ-MnO2, finally achieving enhanced reaction kinetics and superb cycling stability during carrier (de)intercalation. Moreover, oxygen defects, introduced due to Mo-pre-intercalation, play a critical role in the fast reaction kinetics and capacity improvement of the Mo-pre-intercalated δ-MnO2 (Mo-MnO2) cathode. Therefore, the Mo-MnO2 cathode displays a high energy density of 451 Wh kg-1 (based on cathode mass), excellent rate capability, and admirable long-term cycling performance with a high capacity of 159 mAhg-1 at 1.0 A g-1 after 1000 cycles. In addition, the energy storage mechanism of Zn2+/H+ stepwise reversible (de)intercalation is also revealed by ex situ experiments. This work provides an insightful guide for boosting the electrochemical performance of Mn-based oxide cathodes for ZIBs.

High-performance 3D biphasic NH4V3O8/Zn3(OH)2V2O7·2H2O synthesized by rapid chemical precipitation as cathodes for Zn-ion batteries

Vanadate with layered structures and large open frameworks has been extensively explored as cathodes materials for aqueous Zn-ion batteries (ZIBs), and superior Zn-ion storage performance have been achieved. The biphasic vanadate materials are investigated to be conducive for further performance improvement. However, the lack of rapid and scalable synthesis strategies poses stiff challenges for the wider industrial economy of vanadate. Herein, the 3D biphasic NH4V3O8/Zn3(OH)2V2O7·2H2O (NVO/ZVO) were obtained via rapid microwave irradiation assisted chemical precipitation. The prepared electrode by NVO/ZVO with multiple nanoflower-structures presents a high specific capacity (332 mAh g−1 at 0.1 A g−1), together with exceedingly good energy density (281 Wh kg−1) and power density (94 W kg−1). Moreover, it can maintain a specific capacity of 92 % (132 mAh g−1) after 1000 cycles at a high current density of 10 A g−1. The high electrochemical performance of the cathode can be ascribed to the energy storage mechanism of dual-ion intercalation. This work provides key insights into the rapid synthesis of high-performance biphasic vanadate cathode materials for advanced ZIBs.

A new Li2Mn3O7 cathode for aqueous Zn-Ion battery with high specific capacity and long cycle life based on the realization of the reversible Li+ and H+ co-extraction/insertion

• Li 2 Mn 3 O 7 is firstly reported as the new cathode for aqueous Zn-ion battery. • Complex storage mechanism is discussed by In-situ XRD and ex-situ XPS. • Excellent performance is related to reversible Li + /H + co-extraction/insertion. • Dynamic mechanism of electrode and reason of capacity variation were pointed. Aqueous Zn-ion batteries (ZIBs) are expected to be used for practical energy storage and grid-scale applications because of their low-cost, high-safety and environmental friendliness. However, it is still a major challenge to achieve a suitable cathode for ZIBs with a high energy density and long cycle life. Herein, we reported a new cathode Li 2 Mn 3 O 7 for aqueous ZIBs and have studied in detail the role of Li + as electrolyte additives in further improving electrochemical performance. The Li + in the additive-contained electrolyte itself not only facilitates the reversible extraction/insertion of Li + in Li 2 Mn 3 O 7 but also effectively reduce the decomposition effect of Li 2 Mn 3 O 7 caused by the charge process through the re-insertion of Li + in subsequent discharge process and thus realizes the reversible deintercalation/intercalation of H + . Owing to the realization of the reversible Li + and H + co-extraction/insertion caused by the use of Li + additive, the Li 2 Mn 3 O 7 electrode exhibits a high reversible specific capacity of 242 mAh g −1 with nearly 100% coulombic efficiency at 200 mA g −1 current density. In particular, due to the enhanced capacitive contribution, Li 2 Mn 3 O 7 electrode presented an impressive life span at high current density 2 A g −1 , and after 1000 cycles, a stable specific capacity greater than 100 mAh g −1 can be maintained, which is significantly better than that of manganese oxide-based cathode materials in ZIBs. Furthermore, by In-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS), we discuss in detail the complex energy storage mechanism of Li 2 Mn 3 O 7 as cathode material for ZIBs with electrolyte containing Li + additive for the first time. Based on the high specific capacity and big current life span, aqueous ZIBs with Li 2 Mn 3 O 7 exbibit a great potential for large scale electrical energy storage.

K-Ion intercalated V6O13 with advanced high-rate long-cycle performance as cathode for Zn-ion batteries

Aqueous Zn-ion batteries (AZIBs) are regarded as potential candidates for large-scale energy storage devices due to their low cost, high safety, and abundant Zn resources.

Ni-doped δ-MnO2 as a cathode for Zn-ion batteries

Among the cathode materials for zinc-ion batteries, manganese oxides have been extensively studied. Thermal decomposition method was adopted to synthesize the Ni-doped δ-MnO2 material, called as NixMn1-xO2. The electrochemical performance and energy storage mechanism of NixMn1-xO2 were studied in 2M ZnSO4 + 0.2M MnSO4 electrolyte. Nickel doping can significantly improve the electrochemical activity of δ-MnO2. Therefore, Ni-doped δ-MnO2 shows better electrochemical cycling performance than δ-MnO2. At 100 mA g−1, NixMn1-xO2 (x=0.2) the specific capacity of 280mAh g−1 in the second circle, and the corresponding voltage platform is 1.36V and 1.23 two discharge voltage platforms. After 100 cycles, the specific capacity of NixMn1-xO2 (x=0.2) still maintain 167 mAh g−1 at a current density of 100 mA g−1. In addition, we also proved that Zn2+ and H+ are co-intercalated into NixMn1-xO2 during the process of charge and discharge and the electrochemical reaction is highly reversible. This research broadens the thinking of exploring ZIBs cathode materials with good specific capacity and cycle performance.

Reversible Molecular and Ionic Storage Mechanisms in High-Performance Zn0.1V2O5·nH2O Xerogel Cathode for Aqueous Zn-Ion Batteries.

The cathode is a critical component for aqueous Zn-ion batteries (ZIBs) to achieve high capacity and long stability. In this work, we demonstrate a dissolution-free, low-Zn-preinserted bilayer-structured V2O5 xerogel cathode, Zn0.1V2O5·nH2O (ZnVO), with excellent capacity and stability using a low-cost ZnSO4 electrolyte. Its discharge capacity reaches 463 mAh g-1 at 0.2 A g-1 and 240 mAh g-1 at 10 A g-1, while 93% and 88% of its capacity are retained at 0.2 A g-1 for 200 cycles and at 10 A g-1 for 20 000 cycles, respectively. We then show that the outstanding performance of ZnVO is derived from the enlarged gallery spacing by the solvent water intercalation and the water stable V2O5 bilayer structure. We further unveil via ab initio molecular dynamics that H+ is largely originated from the dissociation of the gallery water, while OH- moves out of the gallery to form Zn4(SO4)(OH)6·5H2O with ZnSO4 electrolyte on the surface of ZnVO; the intercalated Zn2+ forms aquo complex [Zn(H2O)6]2+ with the gallery water. Our theoretical analysis also suggests that the gallery water and solvent water in the electrolyte are statistically the same and functionally equivalent. Overall, this study shows the promise of ZnVO as a practical cathode for ZIBs and offers fundamental insights into the roles of gallery water, solvent water, bilayer V2O5 structure, and dual Zn2+/H+ intercalation mechanisms in achieving high capacity and long stability.

Defect modulation of ZnMn2O4 nanotube arrays as high-rate and durable cathode for flexible quasi-solid-state zinc ion battery

• A novel N-ZMO NTAs is developed as advanced cathode for ZIBs. • The N-ZMO NTAs have high electrical conductivity and stable architecture. • The flexible quasi-solid-state ZIBs show decent energy/power density with long-term stability. The exploration of a stable and high-rate cathode is very important for rechargeable Zn ion batteries (ZIBs). With unique merits of rich abundance, low price, and environmental friendliness, spinel ZnMn 2 O 4 (ZMO) hold great promise as a cathode material for ZIBs. However, its inherent low electronic conductivity and large volume variation in the process of charge/discharge severely restrict the rate capability and durability. Herein, the novel N-doping coupled oxygen vacancies modulated ZMO nanotube arrays (NTAs) (N-ZMO NTAs) are fabricated as high-performance cathode for rechargeable ZIBs. Taking advantages of high electrical conductivity, fast ion diffusion, high surface area, sufficient active sites, and stable hollow nanotubular architecture, the N-ZMO NTAs show an admirable capacity (223 mA h g −1 at 0.1 A g −1 ), decent rate capability (133.3 mA h g −1 at 4 A g −1 ) and distinguished long-term durability (92.1% after 1500 cycles). Furthermore, a flexible quasi-solid-state ZIBs is fabricated with N-ZMO NTAs cathode, which achieves favorable energy density (214.6 W h kg −1 ), superb power density (4 kW kg −1 ), and impressive long-term stability (88.6% after 1500 cycles), outperforming most state-of-the-art ZIBs. This study may shed light on designing advanced cathodes for advanced ZIBs.

Cu-MOF-derived and porous Cu0.26V2O5@C composite cathode for aqueous zinc-ion batteries

One fundamental issue for developing high-performance Zn-ion batteries (ZIBs) is the exploration of stable and efficient cathode materials that can reversibly intercalate zinc ions at a high capacity and potential. Layered vanadium oxides have been regarded as a suitable candidate for this purpose due to their high zinc-ion storage capacity. However, the sluggish kinetics of zinc-ion intercalation/deintercalation and the poor conductivity of vanadium oxides are still the bottle bottlenecks that impede the further enhancement of their performance for ZIBs. Addressing this issue, we herein demonstrate a direct impregnation and conversion strategy to prepare a Cu-doped V2O5 and hierarchical porous carbon (Cu0.26V2O5@C) composite as the cathode for ZIBs. In this protocol, the Cu doping can promote the zinc-ion migration by broadening and stabilizing the layered structure of V2O5, the hierarchical porosity can enlarge the contact between the active material and the electrolyte to achieve efficient infiltration of the electrolyte into the material, while the carbon host can improve the electronic conductivity. The combination of these merits thus delivers a high specific capacity (328.8 mAh g−1 at 0.2 A g−1), high rate performance (163.8 mAh g−1 at 2 A g−1), and excellent long-term cyclic stability with 93.5% capacity retention after 500 cycles.

Highly stable H2V3O8/Mxene cathode for Zn-ion batteries with superior rate performance and long lifespan

Low electrical conductivity of the cathode for rechargeable aqueous Zn-ion batteries (RAZIBs) significantly limits the rate capability and shortens the cycling life. Herein, a highly stable composite is developed as a promising cathode by directly growing non-oriented H2V3O8 nanowires on 2D Mxene sheets. This composite architecture shows enhanced electrical conductivity and faster diffusion for charge transportation, resulting in improved rate performance and prolonged cycling life. Compared with the pristine H2V3O8 (306 mAh·g−1 at 0.2 A·g−1 and 900 cycles at 5 A·g−1), the resultant H2V3O8/Mxene composite exhibits larger specific capacities (365 mAh·g−1 at 0.2 A·g−1) and longer cycling life (≈84% capacity retention over 5600 cycles at 5 A·g−1). Even at 10 and 20 A·g−1, this composite cathode also delivers capacities of 164 and 73 mAh·g−1 for over 1900 and 500 cycles, respectively. Such superior electrochemical performance of RAZIB is ascribed to the enhanced electrical conductivity and improved charge transport kinetics. Furthermore, the reversible co-intercalation electrochemical reaction mechanism of Zn2+ and water was systemically demonstrated through various ex-situ characterizations. Additionally, highly safe and flexible solid-state ZIBs with polyacrylamide/cellulose nanofiber (CNF) hydrogel electrolyte deliver high capacities (317.4 mAh·g−1 at 0.2 A·g−1) and long cycle life (over 6600 cycles at 10 A·g−1). The solid-state batteries are still workable even at different harsh environments, such as freezing at −18 ℃ (152.5 mAh·g−1 at 0.5 A·g−1) and heating at 40 ℃ (307.3 mAh·g−1 at 0.5 A·g−1).

Electrochemically activated MnO cathodes for high performance aqueous zinc-ion battery

Aqueous Zn-ion batteries (ZIBs) attract ever-growing attention due to low cost, high safety, and environmental friendliness. Among the limited cathode candidates, manganese-based oxides stand out owing to large ion channels and multiple valence of Mn. Notably, MnO, thought to be inactive before, actually exhibits high energy densities in AZIBs, thus arousing wide interests. Herein, the electrochemical behavior of MnO electrode is extensively investigated in ZnSO4 electrolytes with different concentration of MnSO4. It is confirmed that the inactive MnO is electrochemically activated during the initial charge process. Greatly, the initial capacity and the following cycling stability of MnO electrode strongly depends on the concentration of MnSO4, indicating that the activation of MnO could be attributed to Mn dissolution, leading to the higher valence of Mn as evidenced by ex-situ XPS analysis. Greatly, a H+/Zn2+ co-insertion mechanism is suggested for the as-activated Mn1-xO electrode according to the ex-situ XRD results. In addition, by constructing a core-sheath MnO@N-doped graphene scrolls (MnO@NGS) configuration through a modified hydrothermal process, the reversible capacity of MnO has been successfully improved to 288 mAh g−1 (0.1 A g−1), leading to high energy density of 367 mWh g−1. More importantly, benefiting from the graphene wrapping and sufficient internal voids, 98% of the initial capacity can be retained after 300 cycles (0.5 A g−1), much better than the unmodified MnO and MnO2 electrodes. This work is expected to deepen the understanding of the charge-storage mechanism of MnO and help to design durable manganese-based cathodes for ZIBs.

Uncovering the Potential of M1-Site-Activated NASICON Cathodes for Zn-Ion Batteries.

There is a long-standing consciousness that the rhombohedral NASICON-type compounds as promising cathodes for Li+ /Na+ batteries should have inactive M1(6b) sites with ion (de)intercalation occurring only in the M2 (18e) sites. Of particular significance is that M1 sites active for charge/discharge are commonly considered undesirable because the ion diffusion tends to be disrupted by the irregular occupation of channels, which accelerates the deterioration of battery. However, it is found that the structural stability can be substantially improved by the mixed occupation of Na+ /Zn2+ at both M1 and M2 when using NaV2 (PO4 )3 (NVP) as a cathode for Zn-ion batteries. The results of atomic-scale scanning transmission electron microscopy, analysis of ab initio molecular dynamics simulations, and an accurate bond-valence-based structural model reveal that the improvement is due to the facile migration of Zn2+ in NVP, which is enabled by a concerted Na+ /Zn2+ transfer mechanism. In addition, significant improvement of the electronic conductivity and mechanical properties is achieved in Zn2+ -intercalated ZnNaV2 (PO4 )3 in comparison with those of Na3 V2 (PO4 )3 . This work not only provides in-depth insight into Zn2+ intercalation and dynamics in NVP unlocked by activating the M1 sites, but also opens a new route toward design of improved NASICON cathodes.

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-MoO3- 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.