Interfacial thermodynamics-inspired electrolyte strategy to regulate output voltage and energy density of battery chemistry

In situ synthetic C encapsulated δ-MnO2 with O vacancies: a versatile programming in bio-engineering

In this study, we successfully synthesized a δ-MnO2 cathode with O vacancies, encapsulated by C derived from pyromellitic acid, using a facile hydrothermal method followed by annealing in an Ar atmosphere. The cathode's structural stability and charge transfer kinetics are enhanced by inhibiting the formation of the by-product Zn4SO4(OH)6·4H2O, regulating the Mn valence state, and suppressing the Jahn-Teller effect through the synergy of C encapsulation and O vacancies. This results in remarkable electrochemical performance, including a large capacity of 421.2 mAh g-1 at 0.1 A g-1, a high specific energy density of 595.53 Wh kg-1, and exceptional long-cycle life stability with 90.88% over 4000 cycles at 10 A g-1, together with superior coulombic efficiency (∼100%) in pure ZnSO4 electrolyte. Moreover, the cathode materials demonstrate specific antitumor efficacy. In brief, this work introduces an in situ synthetic C encapsulated δ-MnO2 with O vacancies expected to be applied in both large-scale energy storage and biomedicine.

Effective Proton Conduction in Quasi-Solid Zinc-Manganese Batteries via Constructing Highly Connected Transfer Pathways

Elusive ion behaviors in aqueous electrolyte remain a challenge to break through the practicality of aqueous zinc-manganese batteries (AZMBs), a promising candidate for safe grid-scale energy storage systems. The proposed electrolyte strategies for this issue most ignore the prominent role of proton conduction, which greatly affects the operation stability of AZMBs. Here we report a water-poor quasi-solid electrolyte with efficient proton transfer pathways based on the large-space interlayer of montmorillonite and strong-hydration Pr3+ additive in AZMBs. Proton conduction is deeply understood in this quasi-solid electrolyte. Pr3+ additive not only dominates the proton conduction kinetics, but also regulates the reversible manganese interfacial deposition. As a result, the Cu@Zn||α-MnO2 cell could achieve a high specific capacity of 433 mAh g-1 at 0.4 mA cm-2 and an excellent stability up to 800 cycles with a capacity retention of 92.2 % at 0.8 mA cm-2 in such water-poor quasi-solid electrolyte for the first time. Ah-scale pouch cell with mass loading of 15.19 mg cm-2 sustains 100 cycles after initial activation, which is much better than its counterparts. Our work provides a new path for the development of zinc metal batteries with good sustainability and practicality.

Dual Ion Co-Insertion Induced Spontaneous and Reversible Phase Conversion Chemistry for Unprecedented Zn2+ Storage

Prussian blue analogues are highly promising electrode materials due to their versatile electrochemical activity and low cost. However, they often suffer from severe structural damage caused by the Jahn-Teller distortion and dissolution of high-spin outer metal ions, resulting in poor cycle life. Material modification and electrolyte regulation have been the common approaches to address this issue, albeit with very limited success. We report here a novel and efficient strategy to preserve structural stability by co-inserting Co2+ and Zn2+ ions in KCo[Fe(CN)6]. This co-insertion induced a spontaneous and reversible phase conversion by the replacement of low-spin inner ion (Fe3+), which efficiently relieves structural damage caused by Jahn-Teller distortion and metal-ion dissolution, leading to an outstanding Zn2+ storage capacity and an exceptional improvement of cycle life with a capacity retention of 97.7 % over 4400 cycles at 40 C. We also demonstrated the enhancement of co-intercalation on ion migration using a combined approach of experimental and density functional theory (DFT) calculations. This work provides an important progress to solve the cycle stability of Prussian blue analogues towards their practical application as electrode materials for aqueous batteries.

Advancements in Manganese-Based Cathode for Sustainable Energy Utilization

Manganese-based compounds, especially manganese oxides, are one of the most exceptional electrode materials. Specifically, manganese oxides have gained significant interest owing to their unique crystal structures, high theoretical capacity, abundant natural availability and eco-friendly nature. However, as transition metal semiconductors, manganese oxide possess low electrical conductivity, limited rate capacity, and suboptical cycle stability. Thus, combining manganese oxides with carbon or other metallic materials can significantly improve their electrochemical performance. These composites increase active sites and conductivity, thereby improving electrode reaction kinetics, cycle stability, and lifespan of supercapacitors (SCs) and batteries. This paper reviews the latest applications of Mn-based cathodes in SCs and advanced batteries. Moreover, the energy storage mechanisms were also proposed. In this review, the development prospects and challenges for advanced energy storage applications of Mn-based cathodes are summarized.

Zinc Chemistries of Hybrid Electrolytes in Zinc Metal Batteries: From Solvent Structure to Interfaces

Along with the booming research on zinc metal batteries (ZMBs) in recent years, operational issues originated from inferior interfacial reversibility have become inevitable. Presently, single-component electrolytes represented by aqueous solution, "water-in-salt," solid, eutectic, ionic liquids, hydrogel, or organic solvent system are hard to undertake independently the task of guiding the practical application of ZMBs due to their specific limitations. The hybrid electrolytes modulate microscopic interaction mode between Zn2+ and other ions/molecules, integrating vantage of respective electrolyte systems. They even demonstrate original Zn2+ mobility pattern or interfacial chemistries mechanism distinct from single-component electrolytes, providing considerable opportunities for solving electromigration and interfacial problems in ZMBs. Therefore, it is urgent to comprehensively summarize the zinc chemistries principles, characteristics, and applications of various hybrid electrolytes employed in ZMBs. This review begins with elucidating the chemical bonding mode of Zn2+ and interfacial physicochemical theory, and then systematically elaborates the microscopic solvent structure, Zn2+ migration forms, physicochemical properties, and the zinc chemistries mechanisms at the anode/cathode interfaces in each type of hybrid electrolytes. Among of which, the scotoma and amelioration strategies for the current hybrid electrolytes are actively exposited, expecting to provide referenceable insights for further progress of future high-quality ZMBs.

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.

Solid State Zinc and Aluminum ion batteries: Challenges and Opportunities

Solid-state zinc ion batteries (ZIBs) and aluminum-ion batteries (AIBs) are deemed as promising candidates for supplying power in wearable devices due to merits of low cost, high safety, and tunable flexibility. However, their wide-scale practical application is limited by various challenges, down to the material level. This Review begins with elaboration of the root causes and their detrimental effect for four main limitations: electrode-electrolyte interface contact, electrolyte ionic conductivity, mechanical strength, and electrochemical stability window of the electrolyte. Thereafter, various strategies to mitigate each of the described limitation are discussed along with future research direction perspectives. Finally, to estimate the viability of these technologies for wearable applications, economic-performance metrics are compared against Li-ion batteries.

Bromine Assisted MnO2 Dissolution Chemistry: Toward a Hybrid Flow Battery with Energy Density of over 300 Wh L-1

Mn²⁺ /Mn³⁺ redox pair has been considered as a promising cathode for high energy density batteries, due to its attractive features of high redox potential, solubility and outstanding kinetics. However, the disproportionation side reaction of Mn³⁺ , which results in accumulation of "dead" MnO₂ limits its reversibility and further energy density. Herein, a novel catholyte based on mixture of Mn²⁺ and Br^- was proposed for flow batteries with high energy density and long cycle life. In the design, the "dead" MnO₂ can be fully discharged via Br^- by a chemical-electrochemical reaction. Coupled with Cd/Cd²⁺ as anode, the assembled Bromine-Manganese flow battery (BMFB) demonstrates a high energy efficiency of 76 % at 80 mA cm^-2 with energy density of 360 Wh L^-1 . The battery assembled with silicotungstic acid as anode could continuously run for over 2000 cycles at 80 mA cm^-2 . With high power density, energy density and durability, the BMFB shows great potential for large-scale energy storage.