Micro-mesoporous cobalt phosphosulfide (Co3S4/CoP/NC) nanowires for ultrahigh rate capacity and ultrastable sodium ion battery

The construction of heterostructure materials has been demonstrated as the promising approach to design high-performance anode materials for sodium ion batteries (SIBs). Herein, micro-mesoporous cobalt phosphosulfide nanowires (Co3S4/CoP/NC) with Co3S4/CoP hetero-nanocrystals encapsulating into N-doped carbon frameworks were successfully synthesized via hydrothermal reaction and subsequent phosphosulfidation process. The obtained micro-mesoporous nanowires greatly improve the charge transport kinetics from the facilitation of the charge transport into the inner part of nanowire. When evaluated as SIBs anode material, the Co3S4/CoP/NC presents outstanding electrochemical performance and battery properties owing to the synergistic effect between Co3S4 and CoP nanocrystals and the conductive carbon frameworks. The electrode material delivers outstanding reversible rate capacity (722.33 mAh/g at 0.1 A/g) and excellent cycle stability with 522.22 mAh/g after 570 cycles at 5.0 A/g. Besides, the Ex-situ characterizations including XRD, XPS, and EIS further revealed and demonstrated the outstanding sodium ion storage mechanism of Co3S4/CoP/NC electrode. These findings pave a promising way for the development of novel metal phosphosulfide anodes with unexpected performance for SIBs and other alkali ion batteries.

Inducing Mn defects within MnTiO3 cathode for aqueous zinc-ion batteries

Layered manganese-based cathode materials are considered as one of the promising cathodes benefit from inherent low manufacturing cost, non-toxic and high safety in aqueous zinc-ion batteries (AZIBs). However, the sluggish reaction kinetics within layered cathodes is inevitable due to the poor electrical/ionic conductivity. Herein, MnTiO3 is reported as a new cathode material for AZIBs and in-situ induced Mn-defect within MnTiO3 during the first charging is desirable to improve the reaction kinetics to a great extent. Additionally, DFT calculations further demonstrate that MnTiO3 with manganese defects exhibits a uniform charge distribution at the defect sites, enhancing the attraction towards H+ and Zn2+ ions. Furthermore, it performs good cycling stability which can obtain 115 mA h g-1 even at 400 mA g-1 after 450 cycles and the discharge capacity reaches up to 233.8 mAh/g at 100 mA g-1 when Mn-defect MnTiO3 was employed as the cathode. This research could provide a new method for the development and mechanism research of cathode materials for AZIBs.

Highly stable and reversible Zn anodes enabled by an electrolyte additive of sucrose

Aqueous zinc-ion batteries (ZIBs) are one of the most promising candidates for electric energy storage devices due to their merits of low cost and high safety. However, the notorious side reactions and dendrite formation on zinc anodes impede the commercialization of ZIBs. In this work, a cheap and edible electrolyte additive sucrose is applied to address the above issues. Sucrose with hydroxyl groups can react as zincophilic sites to adsorb Zn2+. As verified by Raman and FT-IR spectroscopy, the solvation structure of Zn2+ and the hydrogen bonds can be regulated by the sucrose molecule. The weakened solvated structure of Zn2+ and lowered coupling degree between Zn2+ and SO42- can inhibit the hydrogen evolution reaction (HER) and the generation of the sulfate by-product. Furthermore, a solid electrolyte interphase (SEI)-like ion buffer layer is formed because of the preferentially adsorbed sucrose, which can increase the nucleation overpotential and equalize the ion distribution. The enriched Zn nucleation sites and inhibited 2D diffusion of Zn2+ resulting from the sucrose additive enable uniform Zn deposition. Thus, improved performances of symmetric Zn||Zn, asymmetric Zn||Cu and Zn||VO2 cells are realized. The Zn||Zn cell exhibits a highly reversible cycling performance for 1200 h and 400 h at 5 mA cm-2/1 mA h cm-2 and 10 mA cm-2/5 mA h cm-2, respectively. This work provides a readily available and edible additive to improve the performance of ZIBs.

Advances of Zn Metal-Free "Rocking-Chair"-Type Zinc Ion Batteries: Recent Developments and Future Perspectives

Aqueous zinc ion battery (AZIBs) has attracted the attention of many researchers because of its safety, economy, environmental protection, and high ionic conductivity of electrolytes. However, the battery greatly suffers from zinc dendrite produced by zinc metal anode leading to poor cycle life and even unsafe problems, which limit its further development for various important applications. It is known that the success of the commercialization of lithium-ion batteries (LIBs) is mainly due to replacement of lithium metal anode with graphite, which avoids the formation of Li dendrite. Therefore, it is an important step to develop aqueous zinc ion anode to replace conventional zinc metal one with zinc-metal free anode material. In this review, the working principle and development prospect of "rocking-chair" AZIBs are introduced. The research progress of different types of zinc metal-free anode materials and cathode materials in "rocking-chair" AZIBs is reviewed. Finally, the limitations and challenges of the Zn metal-free "rocking-chair" AZIBs as well as solutions are deeply discussed, aiming to provide new strategies for the development of advanced zinc-ion batteries.

Multi-Ion Engineering Strategies toward High Performance Aqueous Zinc-Based Batteries

As alternatives to batteries with organic electrolytes, aqueous zinc-based batteries (AZBs) have been intensively studied. However, the sluggish kinetics, side reactions, structural collapse, and dissolution of the cathode severely compromise the commercialization of AZBs. Among various strategies to accelerate their practical applications, multi-ion engineering shows great feasibility to maintain the original structure of the cathode and provide sufficient energy density for high-performance AZBs. Though multi-ion engineering strategies could solve most of the problems encountered by AZBs and show great potential in achieving practical AZBs, the comprehensive summaries of the batteries undergo electrochemical reactions involving more than one charge carrier is still in deficiency. The ambiguous nomenclature and classification are becoming the fountainhead of confusion and chaos. In this circumstance, this review overviews all the battery configurations and the corresponding reaction mechanisms are investigated in the multi-ion engineering of aqueous zinc-based batteries. By combing through all the reported works, this is the first to nomenclate the different configurations according to the reaction mechanisms of the additional ions, laying the foundation for future unified discussions. The performance enhancement, fundamental challenges, and future developing direction of multi-ion strategies are accordingly proposed, aiming to further accelerate the pace to achieve the commercialization of AZBs with high performance.

Wide-Potential-Window Bimetallic Hydrated Eutectic Electrolytes with High-Temperature Resistance for Zinc-Ion Hybrid Capacitors

Aqueous zinc-ion hybrid capacitors (ZHCs) are considered ideal energy-storage devices. However, the common aqueous Zn2+ -containing electrolytes used in ZHCs often cause parasitic reactions during charging-discharging owing to free water molecules. Hydrated eutectic electrolytes (HEEs) that bind water molecules through solvation shells and hydrogen bonds can be applied at high temperatures and within a wide potential window. This study reports a novel bimetallic HEE (ZnK-HEE), consisting of zinc chloride, potassium chloride, ethylene glycol, and water, which enhances the capacity and electrochemical reaction kinetics of ZHCs. The bimetallic solvation shell in ZnK-HEE is studied by molecular dynamics and density functional theory, confirming its low step-by-step desolvation energy. A Zn//activated carbon ZHC in ZnK-HEE shows a high operating voltage of 2.1 V, along with an ultrahigh capacity of 326.9 mAh g-1 , power density of 2099.7 W kg-1 , and energy density of 343.2 Wh kg-1 at 100 °C. The reaction mechanisms of charging-discharging process are investigated by ex situ X-ray diffraction. This study reports a promising electrolyte for high-performance ZHCs, which exhibits high-temperature resistance and is operable within a wide potential window.

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.