MnO2 Cathode Research Articles

Modulating MnO2 Interface with Flexible and Self-Adhering Alkylphosphonic Layers for High-Performance Zn-MnO2 Batteries.

Metal oxides are essential electrode materials for high-energy-density batteries, but it remains highly challenging to modulate their interfacial charge-transfer process and improve their cycling stability. Here, using MnO2 nanofibers as an example, we describe the application of self-assembled alkylphosphonic modification layers for significantly improved cycling stability and high-rate performance of Zn-MnO2 batteries. Two modifier organic molecules with the same phosphonic functional group but different alkyl tail lengths were employed and systematically compared, including butylphosphonic acid (BPA) and decylphosphonic acid (DPA). The phosphonic groups form strong interfacial covalent bonding and assist the generation of conformal and flexible coatings with few nanometers thickness on a MnO2 surface. The intertwined alkylphosphonic molecules in the modulation layers have interconnected phosphonic groups, which improve interfacial charge transfer of H+ ions for fast conversion of MnO2 to MnOOH without compromising electrolyte wetting. Importantly, the coating layers effectively reduce dissolutive loss of Mn2+ from MnO2 during battery cycling since diffusion of both water molecules and divalent Mn2+ cations was inhibited across the modification layers. The flexible coatings could readily adapt to the morphological changes of MnO2 during battery cycling and provide long-lasting protection. Overall, we identified that BPA has the optimal balance of hydrophobic-hydrophilic components and enabled modified MnO2 cathodes with >30% improved discharge capacity compared with unmodified MnO2 cathodes, together with substantially improved long-term cycling stability with >60% capacity retention for 400 cycles in aqueous ZnSO4 electrolytes without any Mn2+ additive. This work provides new insights into tuning electrochemical pathways that move away from the prevailing rigid, ceramic coating-based surface modifications.

The Role of Al3+‐Based Aqueous Electrolytes in the Charge Storage Mechanism of MnOx Cathodes

AbstractRechargeable aqueous aluminium batteries are the subject of growing interest, however, the charge storage mechanisms at manganese oxide‐based cathodes remain poorly understood. In essense, every study proposes a different mechanism. Here, an in situ spectroelectrochemical methodology is used to unambiguously demonstrate that reversible proton‐coupled MnO2‐to‐Mn2+ conversion is the main charge storage mechanism occurring at MnO2 cathodes for a range of slightly acidic Al3+‐based aqueous electrolytes, with the Al3+ hexaaquo complex playing the key role of proton donor. In Zn/MnO2 assemblies, this mechanism is associated with high gravimetric capacities and discharge potentials, up to 560 mAh g‐1 and 1.65 V respectively, attractive efficiencies (CE > 99.5% and EE > 82%) and excellent cyclability (almost 100% capacity retention over 1 400 cycles at 2 A g‐1). Finally, a critical analysis of the data previously published on MnOx cathodes in Al3+‐based aqueous electrolytes is conducted to conclude on a universal charge storage mechanism, i.e., the reversible electrodissolution/electrodeposition of MnO2.

MnO2 cathode materials with the improved stability via nitrogen doping for aqueous zinc-ion batteries

The research and exploration of manganese-based aqueous zinc-ion batteries have been controversial of cycle stability and mechanism investigation, thus improving the stability and exploring storage mechanism are still the most main issue. Defect engineering has become an effective method to improve cycle stability. Herein, a nitrogen-doped ε-MnO2 (MnO2@N) has been prepared using electrochemical deposition and heat treatment under nitrogen atmosphere. As the cathode for zinc-ion batteries, the capacity retention rate of MnO2@N cathode is close to 100% after 500 cycles at 0.5 A g−1, while the capacity retention rate for the initial MnO2 cathode is 62%. At 5 A g−1, the capacity retention rate of MnO2@N cathode is 83% after 1000 cycles, which is much higher than the 27% capacity retention rate for the original MnO2 cathode. And it can be found that the oxygen vacancies increase after nitrogen doping, which can improve the conductivity of the MnO2@N cathode. Also, there is Mn-N bond in MnO2@N, which can enhance the electrochemical stability of MnO2@N cathode. In addition, the electrochemical mechanism of MnO2@N cathode has been explored by the CV, GCD and GITT tests. It is found that nitrogen doping promotes the intercalation of H+ and the corresponding capacity contribution. Compared with the original MnO2 cathode, the diffusion coefficient of H+ and Zn2+in MnO2@N cathode increases. Also, the reactions during the charging and discharging process are explored through the ex-situ XRD test. And this work may provide some new ideas for improving the stability of manganese-based zinc-ion batteries.

Comprehensive Electrochemical, Calorimetric Heat Generation and Safety Analysis of Na0.53MnO2 Cathode Material in Coin Cells

The sodium ion cells were assembled by using Na0.53MnO2 as cathode material, pure sodium metal as anode in case of half coin cells and coconut shell-derived hard carbon in case of full coin cells. Cyclic voltammetry, galvanostatic charge-discharge, and self-discharge analysis were conducted. A good rate capability, capacity retention, coulombic efficiency (99.5%), reproducibility and reversible Na-ion intercalation revealed a satisfactory performance of this cathode material. The safety related parameters including the heat generation during charging-discharging and thermal abuse tests have been executed by the means of sophisticated calorimetry instruments. It was observed that during the charging process less heat was generated than during discharging process. The exothermic reactions during thermal runaway were identified by using an accelerating rate calorimeter and pressure measurements during this thermal abuse test were performed as well. The thermal runaway of full coin cells occurred beyond 190 °C with a temperature rate (dT/dt) of 2.5 °C min−1. Such detailed analysis of heat generation and thermal abuse helps finding new and quantitative correlations between different critical thermal and safety related issues in future post Li batteries that are a prerequisite for the design of safer batteries, the safe upscaling and for the adaptation of the thermal management system.

Breakdown and Self-healing in Tantalum Capacitors

In this work, different types of polymer and MnO2 cathode capacitors are tested for scintillation breakdown using a constant current stress (CCS) technique modified to allow detection of amplitudes and duration of current spikes. Monitoring of leakage currents with time under bias is used to assess the effect of scintillations. The appearance and composition of damaged sites are examined after deprocessing and cross-sectioning. Thermal processes during scintillations are analyzed, a mechanism of breakdown based on growth of conductive filaments in the dielectric is suggested, and self-healing processes in polymer and MnO2 cathode capacitors is discussed.

Ultrafast Zinc–Ion–Conductor Interface toward High‐Rate and Stable Zinc Metal Batteries

AbstractThe corrosion, passivation, and dendritic growth of Zn anodes and the dissolution of cathodes hinder rechargeable aqueous zinc ion battery (AZIB) rejuvenation. In this work, a versatile Zn‐based montmorillonite (MMT) interlayer is constructed to achieve a stable rechargeable AZIB. The Zn‐based MMT coating Zn foil (MMT‐Zn) is designed to enable a high transference number for Zn2+ (t+ ≈ 0.82) and a freeway for Zn2+ migration to alleviate corrosion and passivation and suppress Zn dendrites. The results show the MMT‐Zn symmetrical batteries render dendrite‐free plating/stripping with an ultra‐stable and small overpotential (50 mV) and a long‐life span (1000 cycles) at 1 mA cm−2/0.25 mAh cm−2 and with 100 mV overpotential at ultrahigh current and capacity of 10 mA cm−2/45 mAh cm−2 (over 1000 h, 77% depth of discharge). The MMT interlayer is applied to the MnO2 cathode to inhibit the discharge product dissolving and diffusing into the electrolyte, so that the stability of the capacity is maintained. Thus, MMT‐Zn||MMT‐MnO2 delivers an ultra‐long cycle life and ultra‐high capacity (1100 cycles with 191.5 mAh g−1 at 2 C). Hopefully, Zn‐based MMT interlayer can be considered to improve the electrochemical performance of the metal anodes and soluble cathodes.

Carbon fiber reinforced Zn–MnO2 structural composite batteries

Structural composite batteries, which can simultaneously carry mechanical loads and store electric energy, have the potential to significantly reduce the system weight of electric-powered systems including electric cars, unmanned air systems, and mobile robots. Recent research in this area has primarily focused on carbon-fiber based lithium-ion batteries, which require stringent protection against factors such as toxicity, moisture, and overheating, making it particularly challenging to realize the potential of structural batteries. Herein, we propose a novel carbon fiber reinforced Zn–MnO2 structural composite battery featuring a MnO2 cathode and a zinc ion anode; carbon fibers conduct current and provide stiffness and strength. The resulting structural Zn–MnO2 composite battery, which can be manufactured using a simple vacuum consolidation process, without the need for inert gloveboxes, demonstrates an excellent tensile strength of 293 MPa and a high specific capacity of 145.9 mAh g−1. Moreover, the structural composite battery achieves an excellent energy density of 181.5 Wh kg−1 and retains 88.3% capacity after 100 cycles. The new carbon fiber Zn–MnO2 structural composite battery offers huge potential for next-generation energy-storing structures that are safe, eco-efficient, and provide multifunctional performance.

Thermophysical Characterization of a Layered P2 Type Structure Na0.53MnO2 Cathode Material for Sodium Ion Batteries

Over the last decade, the demand for safer batteries with excellent performance and lower costs has been intensively increasing. The abundantly available precursors and environmental friendliness are generating more and more interest in sodium ion batteries (SIBs), especially because of the lower material costs compared to Li-ion batteries. Therefore, significant efforts are being dedicated to investigating new cathode materials for SIBs. Since the thermal characterization of cathode materials is one of the key factors for designing safe batteries, the thermophysical properties of a commercial layered P2 type structure Na0.53MnO2 cathode material in powder form were measured in the temperature range between −20 and 1200 °C by differential scanning calorimetry (DSC), laser flash analysis (LFA), and thermogravimetry (TG). The thermogravimetry (TG) was combined with mass spectrometry (MS) to study the thermal decomposition of the cathode material with respect to the evolved gas analysis (EGA) and was performed from room temperature up to 1200 °C. The specific heat (Cp) and the thermal diffusivity (α) were measured up to 400 °C because beyond this temperature, the cathode material starts to decompose. The thermal conductivity (λ) as a function of temperature was calculated from the thermal diffusivity, the specific heat capacity, and the density. Such thermophysical data are highly relevant and important for thermal simulation studies, thermal management, and the mitigation of thermal runaway.

Direct Proof of the Reversible Dissolution/Deposition of Mn2+/Mn4+ for Mild-Acid Zn-MnO2 Batteries with Porous Carbon Interlayers.

Mild‐acid Zn‐MnO2 batteries have been considered a promising alternative to Li‐ion batteries for large scale energy storage systems because of their high safety. There have been remarkable improvements in the electrochemical performance of Zn‐MnO2 batteries, although the reaction mechanism of the MnO2 cathode is not fully understood and still remains controversial. Herein, the reversible dissolution/deposition (Mn2+/Mn4+) mechanism of the MnO2 cathode through a 2e− reaction is directly evidenced using solution‐based analyses, including electron spin resonance spectroscopy and the designed electrochemical experiments. Solid MnO2 (Mn4+) is reduced into Mn2+ (aq) dissolved in the electrolyte during discharge. Mn2+ ions are then deposited on the cathode surface in the form of the mixture of the poorly crystalline Zn‐containing MnO2 compounds through two‐step reactions during charge. Moreover, the failure mechanism of mild‐acid Zn‐MnO2 batteries is elucidated in terms of the loss of electrochemically active Mn2+. In this regard, a porous carbon interlayer is introduced to entrap the dissolved Mn2+ ions. The carbon interlayer suppresses the loss of Mn2+ during cycling, resulting in the excellent electrochemical performance of pouch‐type Zn‐MnO2 cells, such as negligible capacity fading over 100 cycles. These findings provide fundamental insights into strategies to improve the electrochemical performance of aqueous Zn‐MnO2 batteries.

Achieving long-cycle-life Zn-ion batteries through interfacial engineering of MnO2-polyaniline hybrid networks

Aqueous zinc ion batteries (ZIBs) are promising in large-scale energy storage application, due to their low cost, and high safety. However, the dissolution of MnO2 cathode and corresponding unintelligible Zn-storage mechanism hinder the development of high-performance aqueous ZIBs. In this work, we report an interfacial engineering strategy toward long-cycling performance of MnO2-polyaniline hybrid cathode. The three-dimensional networks of MnO2-polyaniline hybrid are in-situ deposited on a current collector of carbon cloth (PANI-MnO2/CC) via a hydrothermal reaction followed by a self-initiated polymerization. Due to the formed tight 3D network-like interfaces among carbon cloth, MnO2 and PANI, the prepared hybrid cathode possesses rapid charge transport ability, fast ion diffusion ability and stable structure. The Zn//PANI-MnO2/CC battery displays a high capacity of 286 mAh g−1 at 0.5 A g−1, excellent energy density of 349 Wh kg−1, and an outstanding long-term cycling performance (96.9 % capacity retention after 9000 cycles at 4.0 A g−1). This work provides a new pathway to fabricate aqueous ZIBs with high energy density and ultra-long durability.

Na0.44MnO2/Polyimide Aqueous Na-ion Batteries for Large Energy Storage Applications

Aqueous salt batteries with high concentrations of salt or water in salt aqueous systems have received considerable attention with focus on improving working voltage range and energy density. Here, the effect of NaClO4 salt concentration on the electrochemical performance and stability of tunnel-type Na0.44MnO2 (NMO) cathodes and organic polyimide (PI) derivative anodes was studied. High capacity retention and 100% coulombic efficiency were shown for NMO/PI full cell in saturated NaClO4 electrolyte. A high, stable capacity of 115 mAh/g was achieved for the PI anode material, and the full cell showed a stable capacity of 41 mAh/g at 2C rate for 430 cycles (calculated for the weight of NMO cathode). Even at a fast 5C rate, a discharge capacity of 33 mAh/g was maintained for 2,400 prolonged cycles with nearly 100% efficiency. The full cell device can achieve an average voltage of 1 V with energy density of 24 Wh/kg. This study highlights concentrated sodium perchlorate as a promising electrolyte solution for stabilization of electrodes and enhancement of electrochemical performance in aqueous media.

Successive electrochemical conversion reaction to understand the performance of aqueous Zn/MnO2 batteries with Mn2+ additive

Rechargeable aqueous zinc-manganese oxide (Zn/MnO2) batteries using Mn2+ as the electrolyte additive have recently attracted remarkable attention owing to their largely improved cycling stability. Herein, we find that the Zn/MnO2 batteries with Mn2+ additive still exhibit rapid capacity fading when cycling between 0.8 and 1.6 V vs. Zn/Zn2+, its improved performance is only observed when charged to a higher slope region (>1.6 V), which suggests that the improved performance of Mn2+ added Zn/MnO2 is not caused by suppressing the dissolution of MnO2 cathode. Inspired by this discovery, successive electrochemcial conversion reactions are scrutinized and proved for evaluating the performance of the Zn/MnO2 batteries after using Mn2+ as the electrolyte additive. By adding a certain amount of Mn2+ into the electrolyte, the battery can improve the capacity and cycling abilitily through converted electrodepostion of Mn2+. Specifically, the zinc sulfate hydroxide hydrate (Zn4SO4·(OH)6·4H2O) large-flake can initiate the generation of zinc vernadite nanosheets (ZnxMnO(OH)y) during the charge process (around 1.5 V vs. Zn/Zn2+), and then the zinc vernadite nanosheets can reversibly re-back to Zn4SO4·(OH)6·4H2O during the discharge process. Importantly, part of zinc vernadite nanosheets irreversibly transform into tunnel-like MnO2 nanocrystalline material when charging higher than 1.6 V vs. Zn/Zn2+, which can improve the specific capacity of Zn/MnO2 batteries in subsequent cycles and then make the Zn/MnO2 batteries exhibit excellent cycles stability. Finally, through a special zinc/carbon nanotube (Zn/CNT) battery, this successive electrochemcial conversion reactions are further verified.

Naphthalene dianhydride organic anode for a 'rocking-chair' zinc-proton hybrid ionbattery.

Rechargeable batteries consisting of a Zn metal anode and a suitable cathode coupled with a Zn2+ ion-conducting electrolyte are recently emerging as promising energy storage devices for stationary applications. However, the formation of high surface area Zn (HSAZ) architectures on the metallic Zn anode deteriorates their performance upon prolonged cycling. In this work, we demonstrate the application of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), an organic compound, as a replacement for the Zn-metal anode enabling the design of a 'rocking-chair'zinc-proton hybrid ion battery. The NTCDA electrode material displays a multi-plateau redox behaviour, delivering a specific discharge capacity of 143 mA h g-1 in the potential window of 1.4 V to 0.3 V vs. Zn|Zn2+. The detailed electrochemical characterization of NTCDA in various electrolytes (an aqueous solution of 1 M ZnOTF, an aqueous solution of 0.01 M H2SO4, and an organic electrolyte of 0.5 M ZnOTF/acetonitrile) reveals that the redox processes leading to charge storage involve a contribution from both H+ and Zn2+. The performance of NTCDA as an anode is further demonstrated by pairing it with a MnO2 cathode, and the resulting MnO2||NTCDA full-cell (zinc-proton hybrid ionbattery) delivers a specific discharge capacity of 41 mA h gtotal-1 (normalized with the total mass-loading of both anode and cathode active materials) with an average operating voltage of 0.80 V.

A comparison study of MnO2 and Mn2O3 as zinc-ion battery cathodes: an experimental and computational investigation.

The high specific capacity, low cost and environmental friendliness make manganese dioxide materials promising cathode materials for zinc-ion batteries (ZIBs). In order to understand the difference between the electrochemical behavior of manganese dioxide materials with different valence states, i.e., Mn(iii) and Mn(iv), we investigated and compared the electrochemical properties of pure MnO2 and Mn2O3 as ZIB cathodes via a combined experimental and computational approach. The MnO2 electrode showed a higher discharging capacity (270.4 mA h g−1 at 0.1 A g−1) and a superior rate performance (125.7 mA h g−1 at 3 A g−1) than the Mn2O3 electrode (188.2 mA h g−1 at 0.1 A g−1 and 87 mA h g−1 at 3 A g−1, respectively). The superior performance of the MnO2 electrode was ascribed to its higher specific surface area, higher electronic conductivity and lower diffusion barrier of Zn2+ compared to the Mn2O3 electrode. This study provides a detailed picture of the diversity of manganese dioxide electrodes as ZIB cathodes.

Research progress of tunnel-structural Na0.44MnO2 cathode for sodium-ion batteries: A mini review

Sodium-ion battery has been widely studied because of its abundant sodium resources and expectable electrochemical performance. The unique tunnel Na0.44MnO2 has attracted wide attention as one of the available cathode materials because of its low cost, as well as long cycle stability and rate capability in the non-aqueous and aqueous batteries. During the past decades, much efforts have been made to improve the electrochemical performance of the Na0.44MnO2. This review concisely describes the research progress of Na0.44MnO2 cathode for both non-aqueous and aqueous sodium-ion batteries, mainly focuses on the crystal structure, morphology, charge–discharge mechanism and influence of different synthesis and modification methods on the morphology and electrochemical performance. In addition, the main opportunities and challenges in this field are briefly commented and discussed.

Photoenhanced performance of Cobalt-intercalated 2-D manganese oxide sheets for rechargeable zinc–air batteries

Conversion and storage of renewable energy is an important step towards the sustainable future. In this work, we have combined photoconversion of solar energy and Zn–air batteries in a single device which could be an effective strategy for augmenting energy conversion and storage. We report the synthesis of inexpensive cobalt-doped 2D δ-MnO2 nanosheets by one-pot hydrothermal method. Spectroscopic and microscopic characterizations prove both in-plane and interplanar doping of cobalt in δ-MnO2 structure. The as-prepared catalyst shows the bifunctional catalytic activity toward oxygen reduction reaction as well as oxygen evolution reaction in presence and absence of visible light. Under light conditions, δ-MnO2 shows 11.56% increment in bifunctional activity. Moreover, the doped MnO2 sample exhibits 19.23% increment in bifunctional activity as compared with pristine δ-MnO2. Upon light irradiation, the doped MnO2 cathode electrode can execute four times enhancement in power density, 2.38% improvement in voltage difference between charging and discharging and 16.26% increment in round-trip efficiency. This work provides a simple and easy method to prepare stable and durable photoactive bifunctional catalysts for energy storage applications.

Effect of KOH Concentration on Mn(III) Dissolution in Rechargeable γ- MnO2 Cathodes

The low cost, high theoretical specific capacity (617 mAh g-1) and environmentally benign nature of MnO2 makes it a very attractive material for a host of electrical energy storage applications such as aqueous based Zn/MnO2 batteries or non-aqueous Li/MnO2 batteries and even supercapacitors. Realizing higher energy and power densities in γ- MnO2 cathodes is of crucial interest for both primary as well as secondary battery applications. But achieving a long lasting high energy density rechargeable MnO2 battery suffers from many setbacks. Prime among these setbacks is the inability of γ- MnO2 polymorph to retain its structural integrity when cycled to deeper depths of discharge (DOD). The most widely used model for γ- MnO2 discharge consists of a solid state proton-electron intercalation process upto the 1st electron forming MnOOH and a dissolution-precipitation process during the 2nd electron discharge forming Mn(OH)2. In this paper, we investigate the cycle life degradation mechanism of the γ- MnO2 polymorph in alkaline environment in the 1st electron region of discharge. We conduct three-electrode experiments on 80 wt. % loading γ- MnO2 cathodes to determine the failure mechanism in various KOH concentrations and at various depths of discharge. At 50 % DOD of the 1st electron, we find a significant effect of KOH concentration with upto 70 % retention of discharge capacity over 100 charge-discharge cycles in 10 wt. % KOH compared to only 20 cycles in 37 wt. % KOH. At 40 % DOD of the 1st electron of MnO2, we observe an astounding 177 % improvement in cycle life in 10 wt. % KOH in comparison to poor recyclability observed in 37 % KOH. Post mortem X-ray diffraction analysis revealed the presence of birnessite, δ- MnO2, in the cathode with nanoflower, nanosheet and nanowire morphologies of birnessite observed in 37 wt. %, 25 wt. % and 10 wt. % KOH respectively. To probe into the failure mechanism we conducted four-electrode Pt- wire experiments to detect Mn (III) soluble species during discharge, in-situ. The experiments indicate significant influence of KOH concentration with Mn(III) dissolution, as determined by the presence of δ-MnO2 deposited on the Pt wire, being detected in 37 wt. % KOH at just ~34 % DOD during the 1st electron discharge. We propose, in this paper, that the capacity fade of γ- MnO2 at high DOD of 1st electron is critically related to the amount of birnessite, which is formed during the charging of Mn (III) ions. Since birnessite discharges at a much lower potential than cycled to in our experiments, its contribution to discharge capacity in the 1st electron region of γ- MnO2 is negligible and hence, builds up as an inactive phase, ultimately resulting in capacity fade. Figure 1

Electrodeposited Zinc-Based Films As Anodes for Aqueous Zinc Batteries

In the past thirty years, there has been significant development in the search for alternative energy sources such as secondary battery systems. Zinc (fourth-most mined material) has attracted much attention due to its abundance, low-cost, and recyclability. More-over, as Zinc-based batteries can be manufactured with aqueous-based electrolytes, this allows for competition with Lithium-ion batteries, but with the advantage of enhanced safety. Zinc-based batteries (MnO2/Zinc) have been previously commercialized and are one of the dominant technologies in the battery market. However, the alkaline MnO2/Zinc battery is not currently considered re-chargeable due to the formation of zinc-dendrites, passivation of Zn metal, and cathode poisoning. In contrast to the alkaline system, the mild acidic system does not suffer from zinc passivation as there is negligible generation of zinc oxide/zinc hydroxide.In this work, we report a proof-of concept work where electrodeposited zinc-based anodes (zinc and copper-zinc) are used in mild aqueous zinc batteries. The study provides a comparison of commercial zinc foil, and electrodeposited zinc/copper-zinc in a mild aqueous zinc battery. Prior to this comparison, electrodeposition conditions are determined by cyclic voltammetry. The three anodes are further compared structurally through X-ray diffraction and scanning electron microscopy. Further electrochemical characterization was carried out in coin cells as symmetric/asymmetric and full cells to evaluate the feasibility of each anode. The electrodeposited zinc-based anodes exhibit low electrode polarization (~0.025V), and stable cycling performance from 0.25-10 mA cm-2 compared to commercial zinc foil. Coulombic efficiencies at 1 mA cm-2 were over 98% for the electrodeposited zinc-based materials and were maintained for over 100 cycles. Furthermore, full cells with an electrodeposited zinc and brass anode, EMD MnO2 cathode, in 1M ZnSO4 + 0.1M MnSO4 delivered capacities of 96.3, and 163 mAh g-1, respectively, at a 100 mA g− 1 compared to 92.1 mAh g-1 for commercial zinc. Lastly, the zinc-based anodes also show better rate capability at a current density of up to 3 A g-1.

Development of Alkaline Zn-Based Batteries for Grid Storage

For energy storage to become ubiquitous in the electric grid, safe, reliable low-cost electrochemical storage technologies manufactured at high volumes with low capital expenditures are needed. Alkaline batteries based on high capacity multi-electron conversion electrodes from low cost, abundant and safe materials, such as a Zn/MnO2 are a promising technology. These batteries have a theoretical specific energy rivaling that of Li-ion systems (Zn @820 mAh/g and MnO2 @617 mAh/g, with ~400 Wh/L) and costs reducible to <$50/kWh, when produced at scale (S. Banerjee et al.). While recent advances by Yadav et al. have demonstrated highly reversible Bi- and Cu-stabilized MnO2 electrodes that can achieve the full 2e- capacity of MnO2 in alkaline electrolyte, the ability to pair this electrode with Zn over 5000+ cycles, which equates to ~10-15 years of battery life, remains a difficult challenge. Zn anodes suffer from irreversible shape change, the redistribution of active material, and passivation over repeated charge and discharge, limiting their achievable capacity and lifetime. Pre-saturating the electrolyte with zincate [Zn(OH)4 2-], which minimizes dissolution of Zn from the anode and reduces the rate of hydrogen evolution, has recently been shown to enhance cycle life for ~10-35% depth-of-discharge (DOD) Zn anodes by ~100-200% (M. Lim et al.); however, Zn(OH)4 2- saturated electrolyte is incompatible with high DOD MnO2, and exacerbates the formation of electrochemically inactive phases, such as ZnMn2O4 at the cathode. Hence, using zincate-blocking separators, able to entrap the zincate within the anode and effectively isolate the MnO2 cathode from Zn(OH)4 2- crossover, while maintaining hydroxide/cation conductivity, is one approach to improve the reversible cycling of a Zn/MnO2 cell at high DOD of both MnO2 and Zn. More recently we have developed a series of permselective polymeric separators (Kolesnichenko et al.) and screened them using our newly-developed anodic stripping voltammetry crossover assay (Duay et al.) to identify those with Zn(OH)4 2- blocking ability. A primary discharge of MnO2 was used to demonstrate that a sustained 2nd e- discharge plateau, indicative of the absence of zinc species at the cathode, was observed only for Zn/MnO2 batteries that utilized our selective polymeric separators. Finally, application of these polymeric separators in rechargeable Zn/MnO2 batteries increased cycle life with higher coulombic efficiencies. Various aspects involved in improving the cycle life of Zn anodes at increased DOD, and of the application of polymeric separators in isolating the MnO2 cathode from soluble zincate and their ability to enable higher DOD cycling in Zn, will be discussed. This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Carbon-coated ultrathin metallic V5Se8 nanosheet for high-energy-density and robust potassium storage

Earth-abundant potassium is a promising alternative to lithium in energy-storage systems, but a pivotal limitation of potassium-ion batteries (KIBs) is their relatively low capacity and inferior cycle stability. Here we report the first synthesis of ultrathin metallic V5Se8 nanosheets embedded in porous carbon (graphene-like V5Se8@C) as a superior anode for KIBs, which achieves a high reversible depotassiation capacity along with unprecedented rate performance and outstanding cycling stability (a reversible depotassiation capacity of 145 mAh g–1 after 800 cycles at 4 A g–1 with 82.9% capacity retention). The impressive performances achieved are attributed to the synergistic contributions of the NiAs-type superstructure, ultrathin nanosheet architecture, sufficient accessible active sites, multi-dimensional electronic/ionic transport pathways and significant pseudocapacitive behaviors. Combined experimental analysis and first-principles calculations reveal fast reaction kinetics, high ionic/electronic conductivity and low diffusion barriers of K-ion in graphene-like V5Se8@C hybrid. Ex-situ characterizations confirm that V5Se8@C electrode undergo a reversible phase-evolution by the sequential intercalation and conversion reactions with synergistic K+-storage mechanisms. Furthermore, by coupling with pre-treated K0.5MnO2 cathode, the full-cell is demonstrated to exhibit large energy density of 160.2 Wh kg–1 with average discharge voltage of 2.2 V and capacity retention of 86% over 200 cycles. These desirable findings demonstrate graphene-like V5Se8@C nanosheets hold great practical application in future grid-scale energy storage.