Rechargeable Zn-MnO2 Batteries Research Articles

Proton Self‐Limiting Effect of Solid Acids Boosts Electrochemical Performance of Zinc‐ion Batteries

AbstractAt present, aqueous rechargeable Zn–MnO2 batteries have attracted widespread attention as green potential application for renewable energy storage devices. MnO2 cathode has great potential for application, but its proton reaction results in side reactions of cathode, electrolyte consumption, and dramatic pH value changes, suffering from capacity degradation. To address the issues caused by proton deficit, a proton–limited domain strategy is proposed by integrating solid acids (Sulfonic acid type polystyrene–divinylbenzene, SATP) with proton exchange reactions into MnO2. SATP can act as a new proton source increasing the amount of H+ and reducing the generation of zinc hydroxide sulfate, by–product of proton at the cathode interface, via proton exchange reactions of ‐HSO3– group. As a result, Zn–MnO2/SATP battery delivered with excellent rate performance (218.4 mAh g–1 at 2 A g–1) and high cycling stability (the retained capacity of 115.8 mAh g–1 after 500 cycles at a current density of 1 A g–1. This work provides an innovative strategy for high performance aqueous Zn–MnO2 batteries.

Phase-Modified Strongly Coupled δ/ε-MnO2 Homojunction Cathode for Kinetics-Enhanced Zinc-Ion Batteries.

Rechargeable Zn-MnO2 batteries using mild water electrolytes have garnered significant interest owing to their impressive theoretical energy density and eco-friendly characteristics. However, MnO2 suffers from huge structural changes during the cycles, resulting in very poor stability at high charge-discharge depths. Briefly, the above problems are caused by slow kinetic processes and the dissolution of Mn atoms in the cycles. In this paper, a 2D homojunction electrode material (δ/ε-MnO2) based on δ-MnO2 and ε-MnO2 has been prepared by a two-step electrochemical deposition method. According to the DFT calculations, the charge transfer and bonding between interfaces result in the generation of electronic states near the Fermi surface, giving δ/ε-MnO2 a more continuous distribution of electron states and better conductivity, which is conducive to the rapid insertion/extraction of Zn2+ and H+. Moreover, the strongly coupled Mn-O-Mn interfacial bond can effectively impede dissolution of Mn atoms and thus maintain the structural integrity of δ/ε-MnO2 during the cycles. Accordingly, the δ/ε-MnO2 cathode exhibits high capacity (383 mAh g-1 at 0.1 A g-1), superior rate performance (150 mAh g-1 at 5 A g-1), and excellent cycling stability over 2000 cycles (91.3% at 3 A g-1). Profoundly, this unique homojunction provides a novel paradigm for reasonable selection of different components.

MnO2/Mn2+ chemistry: Charging protocol and electrolyte regulation

Aqueous rechargeable Zn-MnO2 batteries based on the dissolution/deposition mechanism of MnO2/Mn2+are gaining increasing attention due to their high capacity and structural simplicity. One of the major concerns is the Mn2+/Mn3+side reaction, which hampers the coulombic efficiency (CE) due to Mn3+(aq) disproportionation. However, factors affecting Mn3+ formation have not been systematically investigated. In this study, we utilized in situ optical microscopy and Scanning Electron Microscopy (SEM) to evaluate the formation of Mn3+ by observing its disproportionation product: the randomly deposited MnO2. We found that an excessively high charging voltage and a low electrolyte pH (pH<4.2) were shown to adversely accelerate Mn3+ formation. Most reports on the Mn2+/MnO2 cathode indicate a coulombic efficiency of only 80 % on carbon felt (thickness: 2.5 mm) at 2 mAh/cm2 due to the inherently low electrical conductivity of MnO2. Here with the optimized charging protocol and the utilization of the anode-friendly, methanesulfonic acid (MSA)-containing electrolyte, we achieved a CE of nearly 100 % for up to 200 cycles at 2 mAh/cm2. This work gives guidelines on the electrolyte design and charging protocol optimization towards high-performance MnO2/Mn2+cathodes.

Post-Lithium Batteries with Zinc for the Energy Transition

The energy transition is only feasible by using household or large photovoltaic powerplants. However, efficient use of photovoltaic power independently of other energy sources can only be accomplished employing batteries. The ever-growing demand for the stationary storage of volatile renewable energy poses new challenges in terms of cost, resource availability and safety. The development of Lithium-Ion Batteries (LIB) has been tremendously pushed by the mobile phone industry and the current need for high-voltage traction batteries. This path of global success is primarily based on its high energy density. Due to changing requirements, other aspects come to the fore that require a rebalancing of different technologies in the “Battery Ecosystem”. In this paper we discuss the evolution of zinc and manganese dioxide-based aqueous battery technologies and identify why recent findings in the field of the reaction mechanism and the electrolyte make rechargeable Zn-MnO2 batteries (ZMB), commonly known as so-called Zinc-Ion batteries (ZIB), competitive for stationary applications. Finally, a perspective on current challenges for practical application and concepts for future research is provided. This work is intended to classify the current state of research on ZMB and to highlight the further potential on its way to the market within the “Battery Ecosystem”, discussing key parameters such as safety, cost, cycle life, energy and power density, material abundancy, sustainability, modelling and cell/module development.

(Invited) Recycling and Upcycling Electrode Materials from Spent Lithium-Ion and Alkaline Batteries

Lithium-ion batteries (LIBs) and alkaline batteries have been widely used in electric vehicles and portable electronics, dominating the energy storage market for decades,[1] but their recycling/upcycling has lagged far behind. Re/up-cycling batteries is urgently needed because it can not only preserve raw materials such as Li, Co, Ni, Mn, Al, and Cu for LIBs as well as Zn, Mn, Fe for alkaline batteries but also reduce hazardous wastes towards the environment.[2] Despite previous efforts made on re/up-cycling LIBs and alkaline batteries, there remains an urgent demand for simple, economic, environmentally benign, and energy-saving approaches.For LIB recycling, the dominated recycling methods including pyrometallurgy and hydrometallurgy are destructive and criticized of high energy consumption, undesirable economic outputs, and water contamination. By contrast, non-destructive methods such as solid-state sintering[3] and hydrothermal treatment coupled with short annealing (HT-SA) [4-5]are more promising. However, these emerged direct recycling approaches are deficient at regenerating outdated cathode materials to meet current market need. As such, upcycling (i.e., upgraded regeneration of cathodes) through surface engineering (coating[6] and doping[7-9]) or bulk reconstruction[10] has been developed. In our work, we demonstrate one upcycling approach to regenerate LiCoO2 cathode through an improved HT-SA approach in which a coating layer is prepared accompanied with the regeneration process. The upcycled cathode material shows improved electrochemical performance surpassing the pristine electrode materials.For alkaline battery recycling, the major recycling still focuses on hydrometallurgy and pyrometallurgy. Hydrometallurgical processes generally follow different steps of pre-treatment and subsequent leaching and separation of different metals by electrolysis, extraction or precipitation.[11] Another approach for treating spent alkaline battery materials is upcycling towards other applications such as supercapacitors,[12] catalysis[13], micronutrient fertilizer,[14] Mn alloy fabrication.[14] In our work, for the first time, we directly upcycle both zinc anode and Mn-based cathode for their use in rechargeable Zn-MnO2 batteries by a simple yet efficient annealing procedure. Zn was regenerated in a reductive atmosphere and the regenerated Zn shows high Coulombic efficiency and long life in symmetric cells while the regenerated Mn-based cathode shows superior performance than fresh MnO2 with regards to capacity, rate, and life. Under optimized N/P ratio, the regenerated Zn and MnO2 was paired to make rechargeable Zn-MnO2 batteries delivering excellent performance, comparable or even superior to state-of-the-art Zn-MnO2 batteries. Reference [1] Li, M.; Lu, J.; Chen, Z.; Amine, K.Advanced Materials 2018, 30, 1800561.[2] Rarotra, S.; Sahu, S.; Kumar, P.; Kim, K.-H.; Tsang, Y. F.; Kumar, V.; Kumar, P.; Srinivasan, M.; Veksha, A.; Lisak, G. ChemistrySelect 2020, 5, 6182.[3] Fan, M.; Chang, X.; Guo, Y.-J.; Chen, W.-P.; Yin, Y.-X.; Yang, X.; Meng, Q.; Wan, L.-J.; Guo, Y.-G., Energy Environ. Sci. 2021, 14 (3), 1461-1468.[4] Xu, P.; Dai, Q.; Gao, H.; Liu, H.; Zhang, M.; Li, M.; Chen, Y.; An, K.; Meng, Y. S.; Liu, P.; Li, Y.; Spangenberger, J. S.; Gaines, L.; Lu, J.; Chen, Z., Joule 2020, 4 (12), 2609-2626.[5] Shi, Y.; Chen, G.; Liu, F.; Yue, X.; Chen, Z., ACS Energy Lett. 2018, 3 (7), 1683-1692.[6] Meng, X.; Cao, H.; Hao, J.; Ning, P.; Xu, G.; Sun, Z., ACS Sustain. Chem. Eng. 2018, 6 (5), 5797-5805.[7] Wu, J.; Lin, J.; Fan, E.; Chen, R.; Wu, F.; Li, L., ACS Appl. Energy Mater. 2021, 4 (3), 2607-2615.[8] Fan, X.; Tan, C.; Li, Y.; Chen, Z.; Li, Y.; Huang, Y.; Pan, Q.; Zheng, F.; Wang, H.; Li, Q. J. Hazard. Mater. 2021, 410, 124610.[9] Xu, B.; Dong, P.; Duan, J.; Wang, D.; Huang, X.; Zhang, Y., Ceram. Int. 2019, 45 (9), 11792-11801.[10] Gaines, L.; Dai, Q.; Vaughey, J. T.; Gillard, S. Recycling 2021, 6 (2).[11] Ferella, F.; De Michelis, I.; Vegliò, F. Journal of Power Sources 2008, 183, 805.[12] Farzana, R.; Hassan, K.; Sahajwalla, V.Scientific Reports 2019, 9, 8982.[13] Gallegos, M. V.; Falco, L. R.; Peluso, M. A.; Sambeth, J. E.; Thomas, H. J.Waste Management 2013, 33, 1483.[14] Hu, X.; Robles, A.; Vikström, T.; Väänänen, P.; Zackrisson, M.; Ye, G., Journal of Hazardous Materials 2021, 411, 124928.

Float-charging protocol in rechargeable Zn–MnO2 batteries: Unraveling the key role of Mn2+ additives in preventing spontaneous pH changes

Aqueous rechargeable Zn–MnO2 batteries have been attracting increasing interest in recent years due to their relatively high energy density, non-toxicity, non-flammability, and low-cost. However, the battery chemistry still faces several challenges limiting the performance of some key performance indicators and preventing its commercial deployment. Among these, cycle stability and lifespan are important, especially for stationary energy applications, and require improvement. In this work, a spontaneous reaction between Zn metal and electrolytes evolving hydrogen and Zn ions is shown to drive the electrolyte pH towards alkaline conditions, which in turn hinders the reversible electrochemical reactions at both positive and negative electrodes. Proton release during the oxidation of a Mn2+ additive and promotion of the oxygen evolution reaction (OER) at the positive electrode by implementing a float-charging protocol (constant voltage at the end of the charging process) is proposed as a simple strategy to restore the initial pH. Using a pH indicator dissolved in the electrolyte and assembling the electrochemical cell in a spectrophotometer cuvette, the effect of floating voltage is evaluated in operando, allowing optimization of the floating voltage to enable the electrolyte pH to remain stable.

Hydroxyl Conducting Hydrogels Enable Low-Maintenance Commercially Sized Rechargeable Zn-MnO2 Batteries for Use in Solar Microgrids.

Zinc (Zn)–manganese dioxide (MnO2) rechargeable batteries have attracted research interest because of high specific theoretical capacity as well as being environmentally friendly, intrinsically safe and low-cost. Liquid electrolytes, such as potassium hydroxide, are historically used in these batteries; however, many failure mechanisms of the Zn–MnO2 battery chemistry result from the use of liquid electrolytes, including the formation of electrochemically inert phases such as hetaerolite (ZnMn2O4) and the promotion of shape change of the Zn electrode. This manuscript reports on the fundamental and commercial results of gel electrolytes for use in rechargeable Zn–MnO2 batteries as an alternative to liquid electrolytes. The manuscript also reports on novel properties of the gelled electrolyte such as limiting the overdischarge of Zn anodes, which is a problem in liquid electrolyte, and finally its use in solar microgrid applications, which is a first in academic literature. Potentiostatic and galvanostatic tests with the optimized gel electrolyte showed higher capacity retention compared to the tests with the liquid electrolyte, suggesting that gel electrolyte helps reduce Mn3+ dissolution and zincate ion migration from the Zn anode, improving reversibility. Cycling tests for commercially sized prismatic cells showed the gel electrolyte had exceptional cycle life, showing 100% capacity retention for >700 cycles at 9.5 Ah and for >300 cycles at 19 Ah, while the 19 Ah prismatic cell with a liquid electrolyte showed discharge capacity degradation at 100th cycle. We also performed overdischarge protection tests, in which a commercialized prismatic cell with the gel electrolyte was discharged to 0 V and achieved stable discharge capacities, while the liquid electrolyte cell showed discharge capacity fade in the first few cycles. Finally, the gel electrolyte batteries were tested under IEC solar off-grid protocol. It was noted that the gelled Zn–MnO2 batteries outperformed the Pb–acid batteries. Additionally, a designed system nameplated at 2 kWh with a 12 V system with 72 prismatic cells was tested with the same protocol, and it has entered its third year of cycling. This suggests that Zn–MnO2 rechargeable batteries with the gel electrolyte will be an ideal candidate for solar microgrid systems and grid storage in general.

From spent Zn–MnO2 primary batteries to rechargeable Zn–MnO2 batteries: A novel directly recycling route with high battery performance

For the first time, spent Zn–MnO2 primary batteries are recycled to directly build rechargeable Zn–MnO2 batteries with a mixed solution of sulfuric acid and hydrogen peroxide as the leachate, which aimed to the efficient recovery of spent Zn–MnO2 primary batteries and the realization of high-powered rechargeable Zn–MnO2 batteries. After simple purification, the leached liquid is directly used as the working solution to prepare an electrolytic rechargeable Zn–MnO2 battery. The experimental results show that the performance of the recycling solution of the neutral Zn–MnO2 primary battery was better than that of the alkaline Zn–MnO2 primary battery, and both performed better than the solution prepared with chemically pure reagents. After optimizing the pH of the working solution and charging current, the obtained rechargeable Zn–MnO2 battery can provide an energy efficiency of 72.33 % ± 0.55, a coulombic efficiency of 90.17 % ± 0.71, and excellent cycle stability. These experimental results show that spent Zn–MnO2 primary batteries can be successfully recycled to prepare rechargeable Zn–MnO2 batteries, demonstrating very good application potential.

Parasitic electrodeposition in Zn-MnO2 batteries and its suppression for prolonged cyclability

The utilization of mildly acidic electrolyte and corresponding Mn salt pairing unlocked a path toward highly rechargeable Zn-MnO2 batteries, but long-term feasibility of these cathode-preserving strategy under practical conditions is never verified. In this study, in-situ MnO2 electrodeposition occurring in the battery recharging process is discovered to be a side reaction that substantially nullifies the practicality of the strategy. Particularly, it is identified to be responsible for irreversibly converting the electrolyte Mn ions to electrochemically passive species and triggering battery performance deterioration. These newfound recognitions lead to the formulation of a kinetic inhibition strategy, which is executed through an unconventional cathode electrode design. Specifically, graphite nanosheets with limited surface defects are incorporated into MnO2 electrodes to hinder the rate determining Mn adsorption process and thus effectively suppress the electrodeposition reaction. The resulting thin film binder-free MnO2 electrodes achieve near-full one-electron capacity reversibly for over 600 cycles, with an average columbic efficiency of ~99.8%. Overall, this study reveals the importance of suppressing MnO2 electrodeposition in Zn-MnO2 batteries and provides a contrasting view on key factors that dictate the stability of the system.

Hybridizing δ-Type MnO2 With Lignin-Derived Porous Carbon as a Stable Cathode Material for Aqueous Zn–MnO2 Batteries

With the advantages of intrinsic safety, low price, high output potential, and acceptable energy density, aqueous rechargeable Zn-MnO2 batteries are gradually emerging as promising energy storage devices in recent years. Unfortunately, the structural instability and poor electrical conductivity of manganese dioxides still hinder their further applications. To tackle these issues, we demonstrate a high-performance cathode material for Zn-MnO2 batteries by hybridizing lignin-derived porous carbon with δ-MnO2 (denoted as LPC/δ-MnO2). Benefiting from the high electrical conductivity of porous carbon, the LPC/δ-MnO2 cathode material can offer high discharge capacity of 332.3 mAh g–1 at 0.2 A g–1 and excellent high-rate capability (196.1 mAh g–1 at 5 A g–1). Meanwhile, the assembled Zn-MnO2 battery displays good long-term cycling stability (82% capacity retention after 1000 cycles). Such superior performances are attributed to the synergetic effect of nanostructured δ-MnO2 and porous carbon scaffold, which is in favor of rapid Zn2+ ion diffusion and large contribution ratio of pseudocapacitive Zn2+ ion intercalation. The results of this study show great prospects of hybridizing biomass-derived carbon framework with electrochemically active materials towards advanced energy storage materials.

Anchoring MnO2 on nitrogen-doped porous carbon nanosheets as flexible arrays cathodes for advanced rechargeable Zn–MnO2 batteries

Controllable construction of advanced Mn-based cathodes is of great importance for the development of flexible rechargeable Zn-MnO2 batteries. Herein we report an effective flexible composite strategy to construct integrated arrays cathodes by rationally anchoring active MnO2 on novel N-doped porous carbon nanosheets (N-CNSs) arrays grown on carbon cloth. Typically, hydrothermal-synthesized MnO2 nanoflakes are strongly anchored on the conductive N-CNSs skeleton forming flexible N-CNSs@MnO2 core/shell arrays. Interestingly, active Zn anode is also compatible with N-CNSs skeleton forming flexible integrated anode. Positive effects are demonstrated in the above N-CNSs@MnO2 core/shell arrays including good flexibility, high electrical conductivity, large porosity & specific surface area, and strong mechanical stability. Accordingly, the Zn ion storage kinetics is optimized in the obtained N-CNSs@MnO2 cathodes, which can deliver a high capacity of 303.7 ​mAh g−1 ​at 0.2 ​A ​g−1 and superior long-term lifespan (91.6% retention after 1800 cycles at 2 ​A ​g−1) in aqueous electrolyte. More importantly, the as-assembled flexible quasi-solid-state N-CNSs@MnO2//N-CNSs@Zn battery can exhibit a high energy density of 150.6 ​Wh kg−1 with a power density of 7.9 ​kW ​kg−1. Our work shows a novel carbon-based flexible design for construction of high-performance Zn-MnO2 devices.

Introducing Oxygen Defects into Phosphate Ions Intercalated Manganese Dioxide/Vertical Multilayer Graphene Arrays to Boost Flexible Zinc Ion Storage

AbstractDesigned and fabricated flexible high‐performance MnO2 cathode materials are highly desirable for developing advanced rechargeable Zn–MnO2 batteries. In this work, a facile phosphorization process is reported for introducing oxygen defects into phosphate ions intercalated manganese dioxide/vertical multilayer graphene (VMG) arrays, forming an integrated P‐MnO2‐x@VMG cathode. The oxygen defects and phosphate ions intercalation are achieved simultaneously via phosphorization. The former can increase the electrical conductivity of MnO2, while the latter is able to expand its interlayer spacing accelerating ion transfer. Furthermore, flexible VMG conductive networks provide excellent peripheral charge transfer and endow the cathode with favorable mechanical strength. Benefiting from these virtues, the obtained P‐MnO2‐x@VMG cathode demonstrates high capacity (302.8 mAh g−1 at 0.5 A g−1) and long‐term cycling stability (&gt;90% capacity retention after 1000 cycles at 2.0 A g−1) in aqueous electrolytes. More impressively, the P‐MnO2‐x@VMG cathode exhibits a high energy density of 369.5 Wh kg−1 in quasi‐solid‐state flexible devices (P‐MnO2‐x@VMG//Zn@VMG), and thereby shows great prospects for applications in wearable electronics. This work demonstrates a new synergistic way to construct high‐performance electrodes for energy storage toward divalent metal ions.

Electrolyte Effect on the Electrochemical Performance of Mild Aqueous Zinc-Electrolytic Manganese Dioxide Batteries.

Recently, mild aqueous rechargeable Zn-MnO2 batteries have attracted increasing interest for energy storage due to the low cost of Zn and Mn resources, high safety, and environmental benignity. Extensive types of MnO2 have been proposed as the cathodes in the literature, but the different reported performance and lack of a thorough understanding of reactions in MnO2 cathodes greatly hinder the practical applications of mild aqueous Zn-MnO2 batteries. Here, we revealed the correlation between the reaction mechanisms and the used electrolytes for the mild aqueous zinc-electrolytic manganese dioxide (EMD) batteries. In optimal Zn(TFSI)2-based electrolyte, the EMD cathode exhibits a mixed diffusion-controlled conversion reaction between EMD and H+ and diffusion-free "pseudocapacitance"-like reactions. This mechanism enables excellent cycling stability of an EMD cathode over 5000 cycles with a capacity retention of 94.6%. This study provides a useful insight into developing reversible MnO2 cathodes through rational control of reaction mechanisms for high performance mild aqueous Zn-MnO2 batteries.

A Hollow-Structured Manganese Oxide Cathode for Stable Zn-MnO₂ Batteries.

Aqueous rechargeable zinc-manganese dioxide (Zn-MnO2) batteries are considered as one of the most promising energy storage devices for large scale-energy storage systems due to their low cost, high safety, and environmental friendliness. However, only a few cathode materials have been demonstrated to achieve stable cycling for aqueous rechargeable Zn-MnO2 batteries. Here, we report a new material consisting of hollow MnO2 nanospheres, which can be used for aqueous Zn-MnO2 batteries. The hollow MnO2 nanospheres can achieve high specific capacity up to ~405 mAh g−1 at 0.5 C. More importantly, the hollow structure of birnessite-type MnO2 enables long-term cycling stability for the aqueous Zn-MnO2 batteries. The excellent performance of the hollow MnO2 nanospheres should be due to their unique structural properties that enable the easy intercalation of zinc ions.

Rechargeability and economic aspects of alkaline zinc–manganese dioxide cells for electrical storage and load leveling

Batteries based on manganese dioxide (MnO2) cathodes are good candidates for grid-scale electrical energy storage, as MnO2 is low-cost, relatively energy dense, safe, water-compatible, and non-toxic. Alkaline Zn–MnO2 cells, if cycled at reduced depth of discharge (DOD), have been found to achieve substantial cycle life with battery costs projected to be in the range of $100 to 150 per kWh (delivered). Commercialization of rechargeable Zn–MnO2 batteries has in the past been hampered due to poor cycle life. In view of this, the work reported here focuses on the long-term rechargeability of prismatic MnO2 cathodes at reduced DOD when exposed to the effects of Zn anodes and with no additives or specialty materials. Over 3000 cycles is shown to be obtainable at 10% DOD with energy efficiency >80%. The causes of capacity fade during long-term cycling are also investigated and appear to be mainly due to the formation of irreversible manganese oxides in the cathode. Analysis of the data indicates that capacity loss is rapid in the first 250 cycles, followed by a regime of stability that can last for thousands of cycles. A model has been developed that captures the behavior of the cells investigated using measured state of charge (SOC) data as input. An approximate economic analysis is also presented to evaluate the economic viability of Zn–MnO2 batteries based on the experiments reported here.