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

Recent development of manganese dioxide-based materials as zinc-ion battery cathode

The development of advanced cathode materials for zinc-ion batteries (ZIBs) is a critical step in building large-scale green energy conversion and storage systems in the future. Manganese dioxide is one of the most well-studied cathode materials for zinc-ion batteries due to its wide range of crystal forms, cost-effectiveness, and well-established synthesis processes. This review describes the recent research progress of manganese dioxide-based ZIBs, and the reaction mechanism, electrochemical performance, and challenges of manganese dioxide-based ZIBs materials are systematically introduced. Optimization strategies for high-performance manganese dioxide-based materials for ZIBs with different crystal forms, nanostructures, morphologies, and compositions are discussed. Finally, the current challenges and future research directions of manganese dioxide-based cathodes in ZIBs are envisaged.

Converting commercial Bi2O3 particles into Bi2O2Se@Bi4O8Se nanosheets for "rocking chair" zinc-ion batteries

The development of a low-cost, high-capacity, and insertion-type anode is key for promoting "rocking chair" zinc-ion batteries. Herein, commercial Bi2O3 (BiO) particles are transformed into Bi2O2Se@Bi4O8Se (BiOSe) nanosheets through a simple selenylation process. The change in morphology from commercial BiO particle to BiOSe nanosheet leads to an increased specific surface area of the material. The enhanced electronic/ionic conductivity results in its excellent electrochemical kinetics. Ex situ XRD and XPS tests prove the intercalation-type mechanism of BiO and BiOSe as well as the superior electrochemical reversibility of BiOSe compared to BiO. Furthermore, the H+/Zn2+ co-insertion mechanism of BiOSe is revealed. This makes BiOSe to have low discharge plateaus of 0.38/0.68 V, a high reversible capacity of 182 mA h g-1 at 0.1 A g-1, and a long cyclic life of 500 cycles at 1 A g-1. Besides, the BiOSe//MnO2 "rocking chair" zinc-ion battery offers a high capacity of ≈90 mA h g-1 at 0.2 A g-1. This work provides a reference for turning commercial material into high-performance anode for "rocking chair" zinc-ion batteries.

Ni-doped Bi2O2CO3 nanosheet with H+/Zn2+ co-insertion for "rocking chair" zinc-ion battery

Developing insertion-type anode is key to advancing "rocking chair" zinc-ion batteries, though there are few reported insertion-type anodes. Herein, the Bi₂O₂CO₃ is a high-potential anode, with a special layered structure. A one-step hydrothermal method was used to prepare Ni-doped Bi₂O₂CO₃ nanosheet, and also a free-standing electrode consisting of Ni-Bi₂O₂CO₃ and CNTs was designed. Both cross-linked CNTs conductive networks and Ni doping improve charge transfer. Ex situ tests (XRD, XPS, TEM, etc.) reveal the H⁺/Zn²⁺ co-insertion mechanism of Bi₂O₂CO₃ and that Ni doping improves its electrochemical reversibility and structural stability. Therefore, this optimized electrode offers a high specific capacity of 159 mAh g^-1 at 100 mA g^-1, a suitable average discharge voltage of ≈0.400 V, and a long-term cycling stability of 2200 cycles at 700 mA g^-1. Besides, the Ni-Bi₂O₂CO₃//MnO₂ "rocking chair" zinc-ion battery (based on the total mass of cathode and anode) delivers a high capacity of ≈100 mAh g^-1 at 50.0 mA g^-1. This work provides a reference for designing high-performance anode in zinc-ion batteries.

Vanadium Oxide-Based Cathode Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Design Strategy

Aqueous zinc ion batteries (AZIBs) are an ideal choice for a new generation of large energy storage devices because of their high safety and low cost. Vanadium oxide-based materials have attracted great attention in the field of AZIB cathode materials due to their high theoretical capacity resulting from their rich oxidation states. However, the serious structural collapse and low intrinsic conductivity of vanadium oxide-based materials cause rapid capacity fading, which hinders their further applications in AZIB cathode materials. Here, the structural characteristics and energy storage mechanisms of vanadium oxide-based materials are reviewed, and the optimization strategies of vanadium oxide-based cathode materials are summarized, including substitutional doping, vacancy engineering, interlayer engineering, and structural composite. Finally, the future research and development direction of vanadium oxide-based AZIBs are prospected in terms of cathode, anode, electrolyte, non-electrode components, and recovery technology.

Amorphous Heterostructure Derived from Divalent Manganese Borate for Ultrastable and Ultrafast Aqueous Zinc Ion Storage

Aqueous zinc-manganese (Zn-Mn) batteries have promising potential in large-scale energy storage applications since they are highly safe, environment-friendly, and low-cost. However, the practicality of Mn-based materials is plagued by their structural collapse and uncertain energy storage mechanism upon cycling. Herein, this work designs an amorphous manganese borate (a-MnBO_x ) material via disordered coordination to alleviate the above issues and improve the electrochemical performance of Zn-Mn batteries. The unique physicochemical characteristic of a-MnBO_x enables the inner a-MnBO_x to serve as a robust framework in the initial energy storage process. Additionally, the amorphous manganese dioxide, amorphous Zn_x MnO(OH)₂ , and Zn₄ SO₄ (OH)₆ ·4H₂ O active components form on the surface of a-MnBO_x during the charge/discharge process. The detailed in situ/ex situ characterization demonstrates that the heterostructure of the inner a-MnBO_x and surface multicomponent phases endows two energy storage modes (Zn²⁺ /H⁺ intercalation/deintercalation process and reversible conversion mechanism between the Zn_x MnO(OH)₂ and Zn₄ SO₄ (OH)₆ ·4H₂ O) phases). Therefore, the obtained Zn//a-MnBO_x battery exhibits a high specific capacity of 360.4 mAh g^-1 , a high energy density of 484.2 Wh kg^-1 , and impressive cycling stability (97.0% capacity retention after 10 000 cycles). This finding on a-MnBO_x with a dual-energy storage mechanism provides new opportunities for developing high-performance aqueous Zn-Mn batteries.

Hierarchical manganese valence gradient MnO2via phosphorus doping for cathode materials with improved stability

The search for a method for enhancing the electrochemical performance of manganese dioxide is still a challenge. Herein, we report a rod-like P-MnO_x cathode material with a hierarchical manganese gradient valence through the phosphatization process. For the incorporation of P, Mn₃O₄ was formed on the surface of MnO₂ and exhibited a gradient valence structure, while the oxygen defect concentration in P-MnO_x increased. The unique structure was verified via XRD, TEM and XPS. As the cathode material for a supercapacitor, the specific capacitance of P-MnO_x was 126.3 F g^-1, which was four times that of MnO₂. The assembling of the coin cells of aqueous ZIBs with P-MnO_x also showed good rate performance. The electrochemical performance of the synthesised P-MnO_x cathode was enhanced for the synergistic effect of improved conductivity and structural stability.

Recycling of Zinc-Carbon Batteries into MnO/ZnO/C to Fabricate Sustainable Cathodes for Rechargeable Zinc-Ion Batteries

Acidic zinc-carbon dry batteries have been widely used in life because of their low cost. However, a great quantity of used batteries is discarded as refuse, which not only wastes resources but also leads to environmental contamination. To reuse spent batteries on a large scale, this study concerns a simple, effective, and sustainable strategy to turn them into MnO/ZnO/C composites. After a conventional leaching treatment followed by pyrolysis, the rust cathode materials can be reduced to MnO/ZnO/C. When serving as a rechargeable zinc-ion battery cathode, this electrode provides a maximum reversible capacity of around 362 mAh g^-1 _MnO ) and a rate capability of 191 mAh g^-1 _MnO at a high current rate of 1.20 A g^-1 . Furthermore, ZnO gradually dissolves in the electrolyte with the increase of discharge cycles, replenishing the Zn²⁺ content in the electrolyte and further enhancing cycling stability (98.02 % after 500 cycles). The device also exhibits a remarkable energy density of 336.37 Wh kg^-1 , low self-discharge rate, and can efficiently power a LED panel. This strategy offers an economical and facile route to convert zinc-carbon battery waste into useful materials for aqueous rechargeable zinc ion batteries.

Insight on Cathodes Chemistry for Aqueous Zinc-Ion Batteries: From Reaction Mechanisms, Structural Engineering, and Modification Strategies

By virtue of low cost, eco-friendliness, competitive gravimetric energy density, and intrinsic safety, more and more attention has increasingly focused on aqueous zinc ion batteries (AZIBs) as a promising alternative for scalable energy storage. However, plagued by a complex interfacial process, sluggish dynamics, lability of electrodes and electrolytes, insufficient energy density, and poor cycle life heavily restrict practical applications of AZIBs, indicating that profound understandings on cathode storage chemistry are necessarily needed. Hence, this paper comprehensively summarizes recent advance in cathodes with critical insight on the energy storage mechanism. Furthermore, the issues and challenges for high-performance cathodes are meticulously explored, presenting inspiring structural engineering and modification strategies. Finally, rational evaluations on representative cathodes are rendered, suggesting the potential development direction of AZIBs.

Conductive copper glue constructs a reversible and stable zinc metal anode interface for advanced aqueous zinc ion battery

Aqueous zinc (Zn) ion battery (AZIB) has become one of the research hotspot in the field of energy storage due to its low cost, green environmental protection, high theoretical capacity, and high safety. However, the unrestrained growth of the dendrites leads to the occurrence of side reactions, such as corrosion of the electrodes and generation of hydrogen, which reduces the coulombic efficiency and performance of the battery. Herein, a simple method reports pasting a conductive copper glue (CCG) coating on the surface of Zn anode to improve the serious dendrite growth. The coating has strong intermolecular interaction and high conductivity, which not only avoids the occurrence of side reactions but also facilitates the uniform deposition of Zn²⁺ ions, preventing dendrite formation. The symmetrical battery assembled with Zn anode modified by CCG coating delivers longer cycle life (167 h) and lower voltage hysteresis (≈26 mV), which is much better than that of bare Zn symmetrical battery (30 h, ≈67 mV). Furthermore, the full battery assembly with modified Zn anode and stainless steel (SS) supported V₂O₅ nanospheres (VO-SS) cathode exhibit high capacity and long cycle life (113.5 mAh g^-1 after 4000 cycles at 4.8 A g^-1).

Tremella-like Hydrated Vanadium Oxide Cathode with an Architectural Design Strategy toward Ultralong Lifespan Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising systems for energy storage due to their operational safety, low cost, and environmental friendliness. However, the development of suitable cathode materials is plagued by the sluggish dynamics of Zn²⁺ with strong electrostatic interaction. Herein, an Al³⁺-doped tremella-like layered Al_0.15V₂O₅·1.01H₂O (A-VOH) cathode material with a large pore diameter and high specific surface area is demonstrated to greatly boost electrochemical performance as ZIB cathodes. Resultant ZIBs with a 3 M Zn(CF₃SO₃)₂ electrolyte deliver a high specific discharge capacity of 510.5 mAh g^-1 (0.05 A g^-1), and an excellent energy storage performance is well maintained with a specific capacity of 144 mAh g^-1 (10 A g^-1) even after ultralong 10,000 cycles. The decent electrochemical performance roots in the novel tremella-like structure and the interlayer of Al³⁺ ions and water molecules, which could improve the electrochemical reaction kinetics and structural long cycle stability. Furthermore, the assembled coin-type cells could power a light-emitting diode (LED) lamp for 2 days. We believed that the design philosophy of unique morphology with abundant active sites for Zn²⁺ storage will boost the development of competitive cathodes for high-performance aqueous batteries.

Boosting the zinc ion storage capacity and cycling stability of interlayer-expanded vanadium disulfide through in-situ electrochemical oxidation strategy

Metallic vanadium dichalcogenides with high conductivity and large layer spacing are fantastically potential to be cathode candidates for aqueous zinc ion batteries. However, simply reliance on the reversible Zn²⁺ intercalation/deintercalation process in the layer structure of vanadium dichalcogenides makes it suffer from low specific capacity and limited cycling number. Here we report a facile in-situ electrochemical oxidation strategy to boost the zinc ion storage capacity of interlayer-expanded vanadium disulfide (VS₂·NH₃) hollow spheres with satisfying cyclic stability. The hydrated vanadium oxide (V₂O₅·nH₂O) generated from oxidized VS₂·NH₃, are endowed with reduced nanosheet size and subordinated porous structure, which provides abundant accessible sites and accelerates the zinc ion diffusion process. As a result, the VS₂·NH₃ derived cathode after the electrochemical oxidation process delivers a high reversible capacity of 392 mA h g^-1 at 0.1 A g^-1 and long cyclic stability (110% capacity retention at 3 A g^-1 after 2000 cycles). The efficient oxidation process of VS₂·NH₃ cathode and the storage mechanism in the subsequent cycles are schematically investigated. This work not only reveals the zinc ion storage mechanism of the oxidized VS₂·NH₃ but also sheds light on advanced design for high-performance Zn ion cathode materials.

Cathode materials for aqueous zinc-ion batteries: A mini review

Although lithium-ion batteries (LIBs) have many advantages, they cannot satisfy the demands of numerous large energy storage industries owing to their high cost, low security, and low resource richness. Aqueous zinc-ion batteries (ZIBs) with low cost, high safety, and high synergistic efficiency have attracted an increasing amount of attention and are considered a promising choice to replace LIBs. However, the existing cathode materials for ZIBs have many shortcomings, such as poor electron and zinc ion conductivity and complex energy storage mechanisms. Thus, it is crucial to identify a cathode material with a stable structure, substantial limit, and suitability for ZIBs. In this review, several typical cathode materials for ZIBs employed in recent years and their detailed energy storage mechanisms are summarized, and various methods to enhance the electrochemical properties of ZIBs are briefly introduced. Finally, the existing problems and expected development directions of ZIBs are discussed.