Dual‐Salt Mg‐Based Batteries with Conversion Cathodes

Mg batteries as the most typical multivalent batteries are attracting increasing attention because of resource abundance, high volumetric energy density, and smooth plating/stripping of Mg anodes. However, current limitations for the progress of Mg batteries come from the lack of high voltage electrolytes and fast Mg‐insertable structure prototypes. In order to improve their energy or power density, hybrid systems combining Li‐driven cathode reaction with Mg anode process appear to be a potential solution by bypassing the aforementioned limitations. Here, FeS _x (x = 1 or 2) is employed as conversion cathode with 2–4 electron transfers to achieve a maximum energy density close to 400 Wh kg^?1, which is comparable with that of Li‐ion batteries but without serious dendrite growth and polysulphide dissolution. In situ formation of solid electrolyte interfaces on both sulfide and Mg electrodes is likely responsible for long‐life cycling and suppression of S‐species passivation at Mg anodes. Without any decoration on the cathode, electrolyte additive, or anode protection, a reversible capacity of more than 200 mAh g^?1 is still preserved for Mg/FeS₂ after 200 cycles.     

Toward a Magnesium‐Iodine Battery

The quest for new electrolyte and cathode materials is a crucial point for beyond‐lithium‐ion energy storage systems. Following this, an electrolyte for secondary magnesium batteries based on a new iodoaluminate ionic liquid and δ‐MgI₂ is reported. Promising electrochemical performance in terms of Mg plating‐stripping, coulombic efficiency, and conductivity, demonstrates the potential of this iodine‐based system for future Mg secondary batteries.     

A Rechargeable Battery with an Iron Metal Anode

To date, tremendous efforts of the battery community are devoted to batteries that employ Li⁺, Na⁺, and K⁺ as charge carriers and nonaqueous electrolytes. However, aqueous batteries hold great promise for stationary energy storage due to their inherent low cost and high safety. Among metal batteries that use aqueous electrolytes, zinc metal batteries are the focus of attention. In this study, iron as an anode candidate in aqueous batteries is investigated because iron is undoubtedly the most earth‐abundant and cost‐effective metal anode. Reversible iron plating/stripping in a FeSO₄ electrolyte is demonstrated on the anode side and reversible topotactic (de)insertion of Fe²⁺ in a Prussian blue analogue cathode is showcased. Furthermore, it is revealed that LiFePO₄ can pair up with the iron metal anode in a hybrid cell, delivering stable performance as well.     

A Low-Cost and Recyclable Mg/SOCl2 Primary Battery Via Synergistic Solvation and Kinetics Regulation

Lithium/thionyl chloride (Li/SOCl₂) primary batteries are appealing power solutions because of their remarkable electrochemical performances. However, their mass applications are hindered by the challenges in sustainability, cost and safety concerns owing to the employed Li chemistry. Here, magnesium (Mg) chemistry is shown as a promising alternative through synergistic optimization of electrolyte solvation and electrode reaction kinetics. The first Mg/SOCl₂ primary battery yields surprisingly high specific capacities up to ≈14 000 mAh g⁻¹ at a decent discharge voltage of ≈1.67 V, which outperforms the state-of-the-art Mg-based primary batteries. In addition, it retains almost 100% of the original capacity after 20-day reservation. The impressive battery performances are originated from the stabilized MgCl₂ formation on high-surface-area carbon cathode and suppressed Mg anode corrosion via the Mg-induced solvation effect. Mg/SOCl₂ primary batteries are promising candidates for low-cost and recyclable power supplies, and they thus open new avenues for the development of sustainable battery chemistries.     

Designing Dendrite‐Free Zinc Anodes for Advanced Aqueous Zinc Batteries

Zn metal has been regarded as the most promising anode for aqueous batteries due to its high capacity, low cost, and environmental benignity. Zn anode still suffers, however, from low Coulombic efficiency due to the side reactions and dendrite growth in slightly acidic electrolytes. Here, the Zn plating/stripping mechanism is thoroughly investigated in 1 m ZnSO₄ electrolyte, demonstrating that the poor performance of Zn metal in mild electrolyte should be ascribed to the formation of a porous by‐product (Zn₄SO₄(OH)₆·xH₂O) layer and serious dendrite growth. To suppress the side reactions and dendrite growth, a highly viscoelastic polyvinyl butyral film, functioning as an artificial solid/electrolyte interphase (SEI), is homogeneously deposited on the Zn surface via a simple spin‐coating strategy. This dense artificial SEI film not only effectively blocks water from the Zn surface but also guides the uniform stripping/plating of Zn ions underneath the film due to its good adhesion, hydrophilicity, ionic conductivity, and mechanical strength. Consequently, this side‐reaction‐free and dendrite‐free Zn electrode exhibits high cycling stability and enhanced Coulombic efficiency, which also contributes to enhancement of the full‐cell performance when it is coupled with MnO₂ and LiFePO₄ cathodes.     

Template-Sacrificed Hot Fusion Construction and Nanoseed Modification of 3D Porous Copper Nanoscaffold Host for Stable-Cycling Lithium Metal Anodes

Lithium (Li) metal anodes have been proposed as a promising candidate for high-energy-density electrode materials in secondary batteries. However, the dendrite growth and unstable electrode–electrolyte interfaces during Li plating/stripping are fatal to their practical applications. Herein, the construction of 3D porous Au/Cu nanoscaffold prepared via a convenient template-sacrificed hot fusion construction method and a nanoseed modification process as an effective Li metal hosting material are proposed. The Au/Cu nanoscaffold can spatially guide uniform deposition of Li metal free from the growth of Li dendrites due to the homogenous Li⁺ ion flux and negligible nucleation overpotential. Moreover, the Cu skeleton can relieve volume change and stabilize local current density during cycling processes. Benefiting from these advantages, the symmetric cells based on self-supported Li-filled Au/Cu (Li-Au/Cu) nanoscaffold electrodes present highly stable Li plating/stripping for more than 1000 h with a low voltage hysteresis less than 90 mV and a long lifespan over 1300 h at 1.0 mA cm^–2 in carbonate-based electrolytes. Impressively, the Li-Au/Cu nanoscaffold||LiFePO₄ full cells also exhibit exceptional cycling stability and rate performance. This work provides a promising strategy to construct dendrite-free lithium metal anodes toward high-performance lithium metal batteries.     

Nip the Sodium Dendrites in the Bud on Planar Doped Graphene in Liquid/Gel Electrolytes

Sodium (Na) metal is the most promising alternative anode to metallic lithium for high‐energy batteries due to the low cost and high abundance of Na resources, but it suffers from severe dendritic/mossy growth at high current densities. Understanding Na nucleation/growth mechanism in different electrolyte systems is the key to tackling this issue but is complicated by the structural complexities of existing substrates for Na plating/stripping. Herein, well‐defined planar doped graphene substrates are synthesized as model plating platforms to unravel a binding energy dominant Na nucleation‐growth mode. The dopants (e.g., boron) in doped graphene and the regions close to the dopants possess high binding energies with Na atoms, providing abundant preferential nucleation sites and contributing to uniform Na plating/stripping. Accordingly, the boron‐doped graphene regulated Na anode exhibits long‐term stability at high current densities in both liquid and polymer electrolytes. The results enhance the understanding of Na nucleation/growth for stabilizing Na metal batteries.     

Separation Effect of Graphene Sheets with N,O Codoping and Molybdenum Clusters for Reversible Lithium–Iodine Batteries

Lithium–iodine (Li–I₂) batteries with ideal discharge potential plateau and abundant iodine resources have attracted considerable attention. However, the poor electrical conductivity of iodine with high solubility in organic electrolytes, and the Li dendrite issue have severely limited the practical application of Li–I₂ batteries. Herein, this work demonstrates that the bifunctionalization of polypropylene (PP) separator with molybdenum clusters on N, O codoped graphene nanosheets (Mo-rGO@PP) is efficient to promote the reversible redox reactions of polyiodides to suppress the shuttle effect, and enhance the Li affinity for the uniform Li plating/stripping. Typically, the Li symmetric battery assembled with Mo-rGO@PP separator exhibits an ultralong lifespan of >2000 h with a low overpotential of <25 mV at 10 mA cm⁻². With such a separation effect to effectively suppress the polyiodide shuttle and dendrite growth, the Li–I₂ battery delivers a long cycle life of over 6000 cycles with a reversible capacity of 170 mAh g⁻¹ at 10 C. With deep insights into the ion flux and redox regulation, this work demonstrates the promising advances via the separation effect for developing high-performance redox batteries.     

Local Strong Solvation Electrolyte Trade-Off between Capacity and Cycle Life of Li-O2 Batteries

Li-O₂ batteries are promising energy storage devices with ultra-high theoretical energy density. However, in practice they show severe capacity fading and limited cycle life, meaning that more suitable electrolytes are urgently needed. Here, solvents are combined with high donor number and low donor number, and a Li salt to produce a new local strong solvation effect electrolyte. High discharge capacity and good cycling performance are achieved when the optimized electrolyte is used in a Li-O₂ battery. The optimized electrolyte inhibits side reactions within the battery and facilitates stable solid electrolyte interphase film formation on the surfaces of Li anode. This work opens a new route for the design of high-performance electrolytes to increase both capacity and cycle life of Li-O₂ batteries.     

Armoring LiNi1/3Co1/3Mn1/3O2 Cathode with Reliable Fluorinated Organic–Inorganic Hybrid Interphase Layer toward Durable High Rate Battery

Ternary layered oxide materials have attracted extensive attention as a promising cathode candidate for high‐energy‐density lithium‐ion batteries. However, the undesirable electrochemical degradation at the electrode–electrolyte interface definitively shortens the battery service life. An effective and viable approach is proposed for improving the cycling stability of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode using lithium difluorophosphate (LiPO₂F₂) paired with fuoroethylene carbonate (FEC) as co‐additives into conventional electrolytes. It is found that the co‐additives can greatly reduce the interface charge transfer impedance and significantly extend the life span of LiNi_1/3Co_1/3Mn_1/3O₂//Li (NMC//Li) batteries. The developed cathode demonstrates exceptional capacity retention of 88.7% and remains structural integrity at a high current of 5C after 500 cycles. Fundamental mechanism study indicates a dense, stable fluorinated organic–inorganic hybrid cathode‐electrolyte interphase (CEI) film derived from LiPO₂F₂ in conjunction with FEC additives on the surface of NMC cathode material, which significantly suppresses the decomposition of electrolyte and mitigates the dissolution of transition metal ions. The interfacial engineering of the electrode materials stabilized by the additives manipulation provides valuable guidance for the development of advanced cathode materials.     

A Mixed Lithium‐Ion Conductive Li2S/Li2Se Protection Layer for Stable Lithium Metal Anode

Constructing artificial solid‐electrolyte interphase (SEI) on the surface of Li metal is an effective approach to improve ionic conductivity of surface SEI and buffer Li dendrite growth of Li metal anode. However, constructing of homogenous ideal artificial SEI is still a great challenge. Here, a mixed lithium‐ion conductive Li₂S/Li₂Se (denoted as LSSe) protection layer, fabricated by a facile and inexpensive gas–solid reaction, is employed to construct stable surface SEI with high ionic conductivity. The Li₂S/Li₂Se‐protected Li metal (denoted as LSSe@Li) exhibits a stable dendrite‐free cycling behavior over 900 h with a high lithium stripping/plating capacity of 3 mAh cm^?2 at 1.5 mA cm^?2 in the symmetrical cell. Compared to bare Li anode, full batteries paired with LiFePO₄, sulfur/carbon, and LiNi_0.6Co_0.2Mn_0.2O₂ cathodes all present better battery cycling and rate performance when LSSe@Li anode is used. Moreover, Li₂Se exhibits a lower lithium‐ion migration energy barrier in comparison with Li₂S which is proved by density functional theory calculation.     

Effect of the Anion Activity on the Stability of Li Metal Anodes in Lithium‐Sulfur Batteries

With the significant progress made in the development of cathodes in lithium‐sulfur (Li‐S) batteries, the stability of Li metal anodes becomes a more urgent challenge in these batteries. Here the systematic investigation of the stability of the anode/electrolyte interface in Li‐S batteries with concentrated electrolytes containing various lithium salts is reported. It is found that Li‐S batteries using LiTFSI‐based electrolytes are more stable than those using LiFSI‐based electrolytes. The decreased stability is because the N–S bond in the FSI^? anion is fairly weak and the scission of this bond leads to the formation of lithium sulfate (LiSO_x) in the presence of polysulfide species. In contrast, in the LiTFSI‐based electrolyte, the lithium metal anode tends to react with polysulfide to form lithium sulfide (LiS_x), which is more reversible than LiSO_x formed in the LiFSI‐based electrolyte. This fundamental difference in the bond strength of the salt anions in the presence of polysulfide species leads to a large difference in the stability of the anode‐electrolyte interface and performance of the Li‐S batteries with electrolytes composed of these salts. Therefore, anion selection is one of the key parameters in the search for new electrolytes for stable operation of Li‐S batteries.     

Toward High‐Performance Hybrid Zn‐Based Batteries via Deeply Understanding Their Mechanism and Using Electrolyte Additive

Aqueous hybrid Zn‐based batteries (ZIBs), as a highly promising alternative to lithium‐ion batteries for grid application, have made considerable progress recently. However, few studies have been reported that investigate their working mechanism in detail. Here, the operando synchrotron X‐ray diffraction is employed to thoroughly investigate the operational mechanism of a hybrid LiFePO₄(LFP)/Zn battery, which indicates only Li⁺ extraction/insertion from/into cathode during cycling. Based on this system, a cheap electrolyte additive, sodium dodecyl benzene sulfonate, is proposed to effectively enhance its electrochemical properties. The influence of the additive on the Zn anode and LFP cathode is comprehensively studied, respectively. The results show that the additive modifies the intrinsic deposit pattern of Zn²⁺ ions, rendering Zn plating/stripping highly reversible in an aqueous medium. On the other hand, the wettability of the LFP electrode is visibly a meliorated by introducing the surfactant additive, accelerating the Li‐ion diffusion at the LFP electrode/electrolyte interface, as indicated by the overpotential measurements. Benefiting from these effects, the Zn/LFP batteries deliver high rate capability and cycling stability in both coin cells and pouch cells.     

Confined Sulfur in Microporous Carbon Renders Superior Cycling Stability in Li/S Batteries

The use of sulfur in the next generation Li‐ion batteries is currently precluded by its poor cycling stability caused by irreversible Li₂S formation and the dissolution of soluble polysulfides in organic electrolytes that leads to parasitic cell reactions. Here, a new C/S cathode material comprising short‐chain sulfur species (predominately S₂) confined in carbonaceous subnanometer and the unique charge mechanism for the subnano‐entrapped S₂ cathodes are reported. The first charge–discharge cycle of the C/S cathode in the carbonate electrolyte forms a new type of thiocarbonate‐like solid electrolyte interphase (SEI). The SEI coated C/S cathode stably delivers ≈600 mAh g^?1 capacity over 4020 cycles (0.0014% loss cycle^?1) at ≈100% Coulombic efficiency. Extensive X‐ray photoelectron spectroscopy analysis of the discharged cathodes shows a new type of S₂ species and a new carbide‐like species simultaneously, and both peaks disappear upon charging. These data suggest a new sulfur redox mechanism involving a separated Li⁺/S^2? ion couple that precludes Li₂S compound formation and prevents the dissolution of soluble sulfur anions. This new charge/discharge process leads to remarkable cycling stability and reversibility.     

Regulating the Water Molecular in the Solvation Structure for Stable Zinc Metal Batteries

Rechargeable aqueous zinc batteries are promising energy storage devices because of their low cost, high safety, and high energy density. However, their performance is plagued by the unsatisfied cyclability due to the dendrite growth and hydrogen evolution reaction (HER) at the Zn anode. Herein, it is demonstrated that the concentrated hybrid aqueous/non-aqueous ZnCl₂ electrolytes constitute a peculiar chemical environment for not only the Zn-ions but also water molecules. The high concentration of chloride ions substitutes the H₂O molecular in the solvation structure of Zn²⁺, while the acetonitrile further interacts with H₂O to decrease its activity. The hybrid electrolytes both inhibit the dendrite formation and HER, enabling an ultrahigh average Coulombic efficiency of 99.9% in the Zn||Cu half-cell and a highly reversible Zn plating/stripping with a low overpotential of 21 mV. Using this hybrid electrolyte, the Zn||polytriphenylamine (PTPAn) full cell deliveres a high discharge capacity of 110 mAh g⁻¹, a high power density of 9200 W kg⁻¹ at 100 °C and maintains 85% of the capacity for over 6000 cycles at 10 °C. This study provides a deep understanding between the solvation structure and columbic efficiency of Zn anode, thus inspiring the development for stable Zn batteries.     

Ionic Liquid Analogs of AlCl3 with Urea Derivatives as Electrolytes for Aluminum Batteries

The ionic liquid analog, formed through the mixture of urea and AlCl₃, has previously shown to serve as a low‐cost electrolyte for an aluminum‐graphite battery, while maintaining good performance and achieving high Coulombic efficiency. Undesirable are the relatively high viscosity and low conductivity of this electrolyte, when compared to chloroaluminate ionic liquids with organic cations. In this work, the fundamental changes to the electrolyte resulting from using derivatives of urea (N‐methyl urea and N‐ethyl urea), again mixed with AlCl₃, are examined. These electrolytes are shown to have significantly lower viscosities (η = 45, 67, and 133 cP when using N‐ethyl urea, N‐methyl urea, and urea, respectively, at 25 °C). The associated batteries exhibit higher intrinsic discharge voltages (2.04 and 2.08 V for N‐methyl urea and N‐ethyl urea electrolytes, respectively, vs 1.95 V for urea system@100 mA g^?1 specific current for ≈5 mg cm^?2 loading), due to changes in concentrations of ionic species. Aluminum deposition is directly observed to primarily occur through reduction of Al₂Cl₇^? when AlCl₃ is present in excess, in contrast to previously suggested cationic Al‐containing species, via operando Raman spectroscopy performed during cyclic voltammetry.     

Mechanistic Investigation of Polymer-Based All-Solid-State Lithium/Sulfur Battery

Although employing solid polymer electrolyte (SPE) in all-solid-state lithium/sulfur (ASSLS) batteries is a promising approach to obtain a power source with both high energy density and safety, the actual performance of SPE-ASSLS batteries still lag behind conventional lithium/sulfur batteries with liquid ether electrolyte. In this work, combining characterization methods of X-ray photoelectron spectroscopy, in situ optical microscopy, and three-electrode measurement, a direct comparison between these two battery systems is made to reveal the mechanism behind their performance differences. In addition to polysulfides, it is found that the initial elemental sulfur can also dissolve into and diffuse through the SPE to reach the anode. Different from the shuttle effect that causes uniform corrosion on the anode in a liquid electrolyte, dissolved sulfur species in SPE unevenly passivate the anode surface and lead to the inhomogeneous Li⁺ plating/stripping at the anode/SPE solid-solid interface. Such inhomogeneity eventually causes void formation at the interface, which leads to the failure of SPE-ASSLS batteries. Based on this understanding, a protection interlayer is designed to inhibit the shuttling of sulfur species, and the modified SPE-ASSLS batteries show much-improved performance in cycle life.     

MXene-Based Anode-Free Magnesium Metal Battery

Rechargeable magnesium batteries (RMBs) are promising next-generation low-cost and high-energy devices. Among all RMBs, anode-free magnesium metal batteries that use in situ magnesium-plated current collectors as negative electrodes can afford optimal energy densities. However, anode-free magnesium metal batteries have remained elusive so far, as their practical application is plagued by low Mg plating/stripping efficiency due to nonuniform Mg deposition on conventional anode current collectors. Herein, for the first time, an anode-free Mg-metal battery is developed by employing a 3D MXene (Ti₃C₂T_x) film with horizontal Mg electrodeposition. The magnesiophilic oxygen and reactive fluorine terminations in MXene enable an enriched local magnesium-ion concentration and a durable magnesium fluoride-rich solid electrolyte interphase on the Ti₃C₂T_x film surface. Meanwhile, Ti₃C₂T_x MXene exhibits a high lattice geometrical fit with Mg (≈96%) to guide the horizontal electrodeposition of Mg. Consequently, the developed Ti₃C₂T_x film achieves reversible Mg plating/stripping with high Coulombic efficiencies (>99.4%) at high-current-density (5.0 mA cm⁻²) and high-Mg-utilization (50%) conditions. When this Ti₃C₂T_x film is coupled with a pre-magnesized Mo₆S₈ cathode, the anode-free Mg-metal full-cell prototype exhibits a volumetric energy density five times higher than its standard Mg-metal counterpart. This work provides insights into the rational design of anode current collectors to guide horizontal Mg electrodeposition for anode-free Mg metal batteries.     

Sol Electrolyte: Pathway to Long-Term Stable Lithium Metal Anode

Lithium (Li) metal batteries are the subject of intense study due to their high energy densities. However, uncontrolled dendrite growth and the resulting pulverization of Li foil during the repeated plating/stripping process seriously diminish their cycling life. Herein, a facile approach using octaphenyl polyoxyethylene (OP-10)-based sol electrolyte is proposed to alleviate Li anode pulverization. This sol electrolyte possesses better ionic conductivity compared to gel and solid-state electrolytes and also homogenizes Li ion diffusion throughout the entire electrolyte efficiently. As a result, Li/Li symmetric cells using this sol electrolyte demonstrate long-term cycling stability for up to 1800 h, with a plating capacity of 3.0 mAh cm⁻² without deteriorating the integrity of the thin Li foil. Using a conventional liquid electrolyte, electrode pulverization and battery failure can be observed after just three cycles. More importantly, a parameter of “throwing power” is introduced in a metal Li battery system to characterize the homogenizing ability of Li deposition in different electrolyte systems, which can serve as a guide to the efficient selection of electrolytes for Li metal batteries.     

Highly Reversible Zn Anode Enabled by Controllable Formation of Nucleation Sites for Zn‐Based Batteries

Aqueous Zn batteries have drawn tremendous attention for their several advantages. However, the challenges of Zn anodes such as the corrosion and ZnO densification have compromised their application in rechargeable Zn‐based batteries. In this paper, a straightforward strategy is employed to facilitate the uniform Zn stripping/plating of the Zn anode through using a ZrO₂ coating layer, which contributes to the controllable nucleation sites for Zn²⁺ and fast Zn²⁺ transportation through the favorable Maxwell–Wagner polarization. As a result, the low polarization (24 mV at 0.25 mA cm^?2), high Coulombic efficiency (99.36% at 20 mA cm^?2), and long cycle life (over 3800 h at 0.25 mA cm^?2) can be obtained for the ZrO₂‐coated Zn anode. It is believed that the ZrO₂ coating layer can also act as an inert physical barrier to decrease the contact of the anode and electrolyte, thus reducing both the Zn corrosion and formation of ZnO densification, and then improve the reversibility of Zn anode. The results demonstrated in this work provide an appealing strategy for the future development of rechargeable Zn‐based batteries.