Enhanced performance in mixture DMSO/ionic liquid electrolytes: Toward rechargeable Li –O2 batteries

A mixture electrolyte based on dimethyl sulfoxide (DMSO) and 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP][NTf₂], with excellent reversibility of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been reported for Li–O₂ batteries. The effect of the mixture electrolyte on current density, oxygen solubility, diffusion coefficient and oxygen reduction reaction (ORR) mechanism was investigated. The presence of [BMP][NTf₂] increases the solubility of oxygen and while DMSO improves the reversibility of ORR and OER by facilitating the solubility of Li₂O_x. Cyclic voltammetric studies showed that mixed electrolyte showed significantly enhanced current density and reversibility for ORR and OER compared to pure DMSO or [BMP][NTf₂].     

Magnetohydrodynamic Interface-Rearranged Lithium Ions Distribution for Uniform Lithium Deposition and Stable Lithium Metal Anode

Uneven lithium (Li) electrodeposition hinders the wide application of high-energy-density Li metal batteries (LMBs). Current efforts mainly focus on the side-reaction suppression between Li and electrolyte, neglecting the determinant factor of mass transport in affecting Li deposition. Herein, guided Li⁺ mass transport under the action of a local electric field near magnetic nanoparticles or structures at the Li metal interface, known as the magnetohydrodynamic (MHD) effect, are proposed to promote uniform Li deposition. The modified Li⁺ trajectories are revealed by COMSOL Multiphysics simulations, and verified by the compact and disc-like Li depositions on a model Fe₃O₄ substrate. Furthermore, a patterned mesh with the magnetic Fe−Cr₂O₃ core-shell skeleton is used as a facile and efficient protective structure for Li metal anodes, enabling Li metal batteries to achieve a Coulombic efficiency of 99.5 % over 300 cycles at a high cathode loading of 5.0 mAh cm⁻². The Li protection strategy based on the MHD interface design might open a new opportunity to develop high-energy-density LMBs.     

Olefin-Linked Covalent Organic Frameworks with Electronegative Channels as Cationic Highways for Sustainable Lithium Metal Battery Anodes

Despite the enormous interest in Li metal as an ideal anode material, the uncontrollable Li dendrite growth and unstable solid electrolyte interphase have plagued its practical application. These limitations can be attributed to the sluggish and uneven Li⁺ migration towards Li metal surface. Here, we report olefin-linked covalent organic frameworks (COFs) with electronegative channels for facilitating selective Li⁺ transport. The triazine rings and fluorinated groups of the COFs are introduced as electron-rich sites capable of enhancing salt dissociation and guiding uniform Li⁺ flux within the channels, resulting in a high Li⁺ transference number (0.85) and high ionic conductivity (1.78 mS cm⁻¹). The COFs are mixed with a polymeric binder to form mixed matrix membranes. These membranes enable reliable Li plating/stripping cyclability over 700 h in Li/Li symmetric cells and stable capacity retention in Li/LiFePO₄ cells, demonstrating its potential as a viable cationic highway for accelerating Li⁺ conduction.     

Unveiling the Critical Role of Ion Coordination Configuration of Ether Electrolytes for High Voltage Lithium Metal Batteries

Albeit ethers are favorable electrolyte solvents for lithium (Li) metal anode, their inferior oxidation stability (<4.0 V vs. Li/Li⁺) is problematic for high-voltage cathodes. Studies of ether electrolytes have been focusing on the archetype glyme structure with ethylene oxide moieties. Herein, we unveil the crucial effect of ion coordination configuration on oxidation stability by varying the ether backbone structure. The designed 1,3-dimethoxypropane (DMP, C3) forms a unique six-membered chelating complex with Li⁺, whose stronger solvating ability suppresses oxidation side reactions. In addition, the favored hydrogen transfer reaction between C3 and anion induces a dramatic enrichment of LiF (a total atomic ratio of 76.7 %) on the cathode surface. As a result, the C3-based electrolyte enables greatly improved cycling of nickel-rich cathodes under 4.7 V. This study offers fundamental insights into rational electrolyte design for developing high-energy-density batteries.     

Fast,Reversible Lithium Storage with a Sulfur/Long‐Chain‐Polysulfide Redox Couple

The cathodic reactions in Li–S batteries can be divided into two steps. Firstly, elemental sulfur is transformed into long‐chain polysulfides (S₈?Li₂S₄), which are highly soluble in the electrolyte. Next, long‐chain polysulfides undergo nucleation reaction and convert into solid‐state Li₂S₂ and Li₂S (Li₂S₄?Li₂S) by slow processes. As a result, the second‐step of the electrochemical reaction hinders the high‐rate application of Li–S batteries. In this report, the kinetics of the sulfur/long‐chain‐polysulfide redox couple (theoretical capacity=419 mA h g^?1) are experimentally demonstrated to be very fast in the Li–S system. A Li–S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates. The meso‐/micropores in the interlayer are responsible for accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. Therefore, utilizing the sulfur/long‐chain polysulfide redox couple with an efficient interlayer configuration in Li–S batteries may be a promising choice for high‐power applications.     

In-Situ Constructing A Heterogeneous Layer on Lithium Metal Anodes for Dendrite-Free Lithium Deposition and High Li-ion Flux

Constructing efficient artificial solid electrolyte interface (SEI) film is extremely vital for the practical application of lithium metal batteries. Herein, a dense artificial SEI film, in which lithiophilic Zn/Li_xZn_y are uniformly but nonconsecutively dispersed in the consecutive Li⁺-conductors of Li_xSiO_y, Li₂O and LiOH, is constructed via the in situ reaction of layered zinc silicate nanosheets and Li. The consecutive Li⁺-conductors can promote the desolvation process of solvated-Li⁺ and regulate the transfer of lithium ions. The nonconsecutive lithiophilic metals are polarized by the internal electric field to boost the transfer of lithium ions, and lower the nucleation barrier. Therefore, a low polarization of ≈50 mV for 750 h at 2.0 mA cm⁻² in symmetric cells, and a high capacity retention of 99.2 % in full cells with a high lithium iron phosphate areal loading of ≈13 mg cm⁻² are achieved. This work offers new sights to develop advanced alkali metal anodes for efficient energy storage.     

Supramolecular Polymer Ion Conductor with Weakened Li Ion Solvation Enables Room Temperature All-Solid-State Lithium Metal Batteries

Improved durability, enhanced interfacial stability, and room temperature applicability are desirable properties for all-solid-state lithium metal batteries (ASSLMBs), yet these desired properties are rarely achieved simultaneously. Here, in this work, it is noticed that the huge resistance at Li metal/electrolyte interface dominantly impeded the normal cycling of ASSLMBs especially at around room temperature (<30 °C). Accordingly, a supramolecular polymer ion conductor (SPC) with “weak solvation” of Li⁺ was prepared. Benefiting from the halogen-bonding interaction between the electron-deficient iodine atom (on 1,4-diiodotetrafluorobenzene) and electron-rich oxygen atoms (on ethylene oxide), the O-Li⁺ coordination was significantly weakened. Therefore, the SPC achieves rapid Li⁺ transport with high Li⁺ transference number, and importantly, derives a unique Li₂O-rich SEI with low interfacial resistance on lithium metal surface, therefore enabling stable cycling of ASSLMBs even down to 10 °C. This work is a new exploration of halogen-bonding chemistry in solid polymer electrolyte and highlights the importance of “weak solvation” of Li⁺ in the solid-state electrolyte for room temperature ASSLMBs.     

Eutectic-Based Polymer Electrolyte with the Enhanced Lithium Salt Dissociation for High-Performance Lithium Metal Batteries

The deployment of lithium metal anode in solid-state batteries with polymer electrolytes has been recognized as a promising approach to achieving high-energy-density technologies. However, the practical application of the polymer electrolytes is currently constrained by various challenges, including low ionic conductivity, inadequate electrochemical window, and poor interface stability. To address these issues, a novel eutectic-based polymer electrolyte consisting of succinonitrile (SN) and poly (ethylene glycol) methyl ether acrylate (PEGMEA) is developed. The research results demonstrate that the interactions between SN and PEGMEA promote the dissociation of the lithium difluoro(oxalato) borate (LiDFOB) salt and increase the concentration of free Li⁺. The well-designed eutectic-based PAN_1.2-SPE (PEGMEA: SN=1: 1.2 mass ratio) exhibits high ionic conductivity of 1.30 mS cm⁻¹ at 30 °C and superior interface stability with Li anode. The Li/Li symmetric cell based on PAN_1.2-SPE enables long-term plating/stripping at 0.3 and 0.5 mA cm⁻², and the Li/LiFePO₄ cell achieves superior long-term cycling stability (capacity retention of 80.3 % after 1500 cycles). Moreover, Li/LiFePO₄ and Li/LiNi_0.6Co_0.2Mn_0.2O₂ pouch cells employing PAN_1.2-SPE demonstrate excellent cycling and safety characteristics. This study presents a new pathway for designing high-performance polymer electrolytes and promotes the practical application of high-stable lithium metal batteries.     

A Stable Lithium–Oxygen Battery Electrolyte Based on Fully Methylated Cyclic Ether

Ether‐based electrolytes are commonly used in Li–O₂ batteries (LOBs) because of their relatively high stability. But they are still prone to be attacked by superoxides or singlet oxygen via hydrogen abstract reactions, which leads to performance decaying during long‐term operation. Herein we propose a methylated cyclic ether, 2,2,4,4,5,5‐hexamethyl‐1,3‐dioxolane (HMD), as a stable electrolyte solvent for LOBs. Such a compound does not contain any hydrogen atoms on the alpha‐carbon of the ether, and thus avoids hydrogen abstraction reactions. As the result, this solvent exhibits excellent stability with the presence of superoxide or singlet oxygen. In addition the CO₂ evolution during charge process is prohibited. The LOB with HMD‐based electrolyte was able to run up to 157 cycles, 4 times more than with 1,3‐dioxolane (DOL) or 1,2‐dimethoxyethane (DME) based electrolytes.     

Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen

Solid alkali metal carbonates are universal passivation layer components of intercalation battery materials and common side products in metal‐O₂ batteries, and are believed to form and decompose reversibly in metal‐O₂/CO₂ cells. In these cathodes, Li₂CO₃ decomposes to CO₂ when exposed to potentials above 3.8 V vs. Li/Li⁺. However, O₂ evolution, as would be expected according to the decomposition reaction 2 Li₂CO₃→4 Li⁺+4 e^?+2 CO₂+O₂, is not detected. O atoms are thus unaccounted for, which was previously ascribed to unidentified parasitic reactions. Here, we show that highly reactive singlet oxygen (¹O₂) forms upon oxidizing Li₂CO₃ in an aprotic electrolyte and therefore does not evolve as O₂. These results have substantial implications for the long‐term cyclability of batteries: they underpin the importance of avoiding ¹O₂ in metal‐O₂ batteries, question the possibility of a reversible metal‐O₂/CO₂ battery based on a carbonate discharge product, and help explain the interfacial reactivity of transition‐metal cathodes with residual Li₂CO₃.     

Synergistic Engineering of Defects and Heterostructures Enhance Lithium/Sodium Storage Properties of F-SnO2-x-SnS2-x Nanocrystals Supported on N,S-Graphene

Phase engineering of the electrode materials in terms of designing heterostructures, introducing heteroatom and defects, improves great prospects in accelerating the charge storage kinetics during the repeated Li⁺/Na⁺ insertion/deintercalation. Herein, a new design of Li/Na-ion battery anodes through phase regulating is reported consisting of F-doped SnO₂-SnS₂ heterostructure nanocrystals with oxygen/sulfur vacancies (V_O/V_S) anchored on a 2D sulfur/nitrogen-doped reduced graphene oxide matrix (F-SnO_2-x-SnS_2-x@N/S-RGO). Consequently, the F-SnO_2-x-SnS_2-x@N/S-RGO anode demonstrates superb high reversible capacity and long-term cycling stability. Moreover, it exhibits excellent great rate capability with 589 mAh g⁻¹ for Li⁺ and 296 mAh g⁻¹ at 5 A g⁻¹ for Na⁺. The enhanced Li/Na storage properties of the nanocomposites are not only attributed to the increase in conductivity caused by V_O/V_S and F doping (confirmed by DFT calculations) to accelerate their charge-transfer kinetics but also the increased interaction between F-SnO_2-x-SnS_2-x and Li/Na through heterostructure. Meanwhile, the hierarchical F-SnO_2-x-SnS_2-x@N/S-RGO network structure enables fast infiltration of electrolyte and improves electron/ion transportation in the electrode, and the corrosion resistance of F doping contributes to prolonged cycle stability.     

In-situ deposition of Pd/Pd_4S heterostructure on hollow carbon spheres as efficient electrocatalysts for rechargeable Li-O_2 batteries

The sluggish kinetics of oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) have always restricted the development of lithium oxygen batteries(LOBs).Herein,hollow carbon spheres loaded with Pd/Pd_4S heterostructure(Pd/Pd_4S@HCS) were successfully prepared via the in-situ deposition to improve the electrocatalytic activities for both ORR and OER in LOBs.With the welldispersed Pd/Pd_4S nanoparticles,the hierarchical composite with large specific surface area offers favorable transport channels for ions,electron and oxygen.Especially,the Pd/Pd_4S nanoparticles could exhibit excellent electrochemical performance for ORR and OER due to their intrinsic catalytic property and interfacial effect from the heterostructure.Therefore,the LOBs with Pd/Pd_4S@HCS as cathode catalyst show improved specific capacities,good rate ability and stable cycling performance.     

Electron Redistribution Enables Redox-Resistible Li6PS5Cl towards High-Performance All-Solid-State Lithium Batteries

Sulfide electrolytes with high ionic conductivity hold great promise for all-solid-state lithium batteries. However, the parasitic redox reactions between sulfide electrolyte and Li metal result in interfacial instability and rapid decline of the battery performance. Herein, a redox-resistible Li₆PS₅Cl (LPSC) electrolyte is created by regulating the electron distribution in LPSC with Mg and F incorporation. The introduction of Mg triggers the electron agglomeration around S atom, inhibiting the electron acceptance from Li, and F generates the self-limiting interface, which hinders the redox reactions between LPSC and Li metal. This redox-resistible Li₆PS₅Cl-MgF₂ electrolyte therefore presents a high critical current density (2.3 times that of pristine electrolyte). The LiCoO₂/Li₆PS₅Cl-MgF₂/Li cell shows an outstanding cycling stability (93.3 %@100 cycles at 0.2 C). This study highlights the electronic structure modulation to address redox issues on sulfide-based lithium batteries.     

A Highly Efficient All-Solid-State Lithium/Electrolyte Interface Induced by an Energetic Reaction

The energetic chemical reaction between Zn(NO₃)₂ and Li is used to create a solid-state interface between Li metal and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) electrolyte. This interlayer, composed of Zn, ZnLi_x alloy, Li₃N, Li₂O, and other species, possesses strong affinities with both Li metal and LLZTO and affords highly efficient conductive pathways for Li⁺ transport through the interface. The unique structure and properties of the interlayer lead to Li metal anodes with longer cycle life, higher efficiency, and better safety compared to the current best Li metal electrodes operating in liquid electrolytes while retaining comparable capacity, rate, and overpotential. All-solid-state Li||Li cells can operate at very demanding current–capacity conditions of 4 mA cm⁻²–8 mAh cm⁻². Thousands of hours of continuous cycling are achieved at Coulombic efficiency >99.5 % without dendrite formation or side reactions with the electrolyte.     

Recycling Application of Li–MnO2 Batteries as Rechargeable Lithium–Air Batteries

The ever‐increasing consumption of a huge quantity of lithium batteries, for example, Li–MnO₂ cells, raises critical concern about their recycling. We demonstrate herein that decayed Li–MnO₂ cells can be further utilized as rechargeable lithium–air cells with admitted oxygen. We further investigated the effects of lithiated manganese dioxide on the electrocatalytic properties of oxygen‐reduction and oxygen‐evolution reactions (ORR/OER). The catalytic activity was found to be correlated with the composition of Li_xMnO₂ electrodes (0<x<1) generated in situ in aprotic Li–MnO₂ cells owing to tuning of the Mn valence and electronic structure. In particular, modestly lithiated Li_0.50MnO₂ exhibited superior performance with enhanced round‐trip efficiency (ca. 76 %), high cycling ability (190 cycles), and high discharge capacity (10 823 mA h g_carbon^?1). The results indicate that the use of depleted Li–MnO₂ batteries can be prolonged by their application as rechargeable lithium–air batteries.     

Identifying Reactive Sites and Transport Limitations of Oxygen Reactions in Aprotic Lithium‐O2 Batteries at the Stage of Sudden Death

Discharging of the aprotic Li‐O₂ battery relies on the O₂ reduction reaction (ORR) forming solid Li₂O₂ in the positive electrode, which is often characterized by a sharp voltage drop (that is, sudden death) at the end of discharge, delivering a capacity far below its theoretical promise. Toward unlocking the energy capabilities of Li‐O₂ batteries, it is crucial to have a fundamental understanding of the origin of sudden death in terms of reactive sites and transport limitations. Herein, a mechanistic study is presented on a model system of Au|Li₂O₂|Li⁺ electrolyte, in which the Au electrode was passivated with a thin Li₂O₂ film by discharging to the state of sudden death. Direct conductivity measurement of the Li₂O₂ film and in situ spectroscopic study of ORR using ¹⁸O₂ for passivation and ¹⁶O₂ for further discharging provide compelling evidence that ORR (and O₂ evolution reaction as well) occurs at the buried interface of Au|Li₂O₂ and is limited by electron instead of Li⁺ and O₂ transport.     

A Highly Efficient All‐Solid‐State Lithium/Electrolyte Interface Induced by an Energetic Reaction

The energetic chemical reaction between Zn(NO₃)₂ and Li is used to create a solid‐state interface between Li metal and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) electrolyte. This interlayer, composed of Zn, ZnLi_x alloy, Li₃N, Li₂O, and other species, possesses strong affinities with both Li metal and LLZTO and affords highly efficient conductive pathways for Li⁺ transport through the interface. The unique structure and properties of the interlayer lead to Li metal anodes with longer cycle life, higher efficiency, and better safety compared to the current best Li metal electrodes operating in liquid electrolytes while retaining comparable capacity, rate, and overpotential. All‐solid‐state Li||Li cells can operate at very demanding current–capacity conditions of 4 mA cm^?2–8 mAh cm^?2. Thousands of hours of continuous cycling are achieved at Coulombic efficiency >99.5 % without dendrite formation or side reactions with the electrolyte.     

Directing (110) Oriented Lithium Deposition through High-flux Solid Electrolyte Interphase for Dendrite-free Lithium Metal Batteries

Controlling lithium (Li) electrocrystallization with preferred orientation is a promising strategy to realize highly reversible Li metal batteries (LMBs) but lack of facile regulation methods. Herein, we report a high-flux solid electrolyte interphase (SEI) strategy to direct (110) preferred Li deposition even on (200)-orientated Li substrate. Bravais rule and Curie-Wulff principle are expanded in Li electrocrystallization process to decouple the relationship between SEI engineering and preferred crystal orientation. Multi-spectroscopic techniques combined with dynamics analysis reveal that the high-flux CF₃Si(CH₃)₃ (F₃) induced SEI (F₃-SEI) with high LiF and −Si(CH₃)₃ contents can ingeniously accelerate Li⁺ transport dynamics and ensure the sufficient Li⁺ concentration below SEI to direct Li (110) orientation. The induced Li (110) can in turn further promote the surface migration of Li atoms to avoid tip aggregation, resulting in a planar, dendrite-free morphology of Li. As a result, our F₃-SEI enables ultra-long stability of Li||Li symmetrical cells for more than 336 days. Furthermore, F₃-SEI modified Li can significantly enhance the cycle life of Li||LiFePO₄ and Li||NCM811 coin and pouch full cells in practical conditions. Our crystallographic strategy for Li dendrite suppression paves a path to achieve reliable LMBs and may provide guidance for the preferred orientation of other metal crystals.     

The sum is more than its parts: stability of MnFe oxide nanoparticles supported on oxygen-functionalized multi-walled carbon nanotubes at alternating oxygen reduction reaction and oxygen evolution reaction conditions

Successful design of reversible oxygen electrocatalysts does not only require to consider their activity towards the oxygen reduction (ORR) and the oxygen evolution reactions (OER), but also their electrochemical stability at alternating ORR and OER operating conditions, which is important for potential applications in reversible electrolyzers/fuel cells or metal/air batteries. We show that the combination of catalyst materials containing stable ORR active sites with those containing stable OER active sites may result in a stable ORR/OER catalyst if each of the active components can satisfy the current demand of their respective reaction. We compare the ORR/OER performances of oxides of Mn (stable ORR active sites), Fe (stable OER active sites), and bimetallic Mn_0.5Fe_0.5 (reversible ORR/OER catalyst) supported on oxidized multi-walled carbon nanotubes. Despite the instability of Mn and Fe oxide for the OER and the ORR, respectively, Mn_0.5Fe_0.5 exhibits high stability for both reactions.

     

Ni3FeN‐Supported Fe3Pt Intermetallic Nanoalloy as a High‐Performance Bifunctional Catalyst for Metal–Air Batteries

Electrocatalysts for both the oxygen reduction and evolution reactions (ORR and OER) are vital for the performances of rechargeable metal–air batteries. Herein, we report an advanced bifunctional oxygen electrocatalyst consisting of porous metallic nickel‐iron nitride (Ni₃FeN) supporting ordered Fe₃Pt intermetallic nanoalloy. In this hybrid catalyst, the bimetallic nitride Ni₃FeN mainly contributes to the high activity for the OER while the ordered Fe₃Pt nanoalloy contributes to the excellent activity for the ORR. Robust Ni₃FeN‐supported Fe₃Pt catalysts show superior catalytic performance to the state‐of‐the‐art ORR catalyst (Pt/C) and OER catalyst (Ir/C). The Fe₃Pt/Ni₃FeN bifunctional catalyst enables Zn–air batteries to achieve a long‐term cycling performance of over 480 h at 10 mA cm⁻² with high efficiency. The extraordinarily high performance of the Fe₃Pt/Ni₃FeN bifunctional catalyst makes it a very promising air cathode in alkaline electrolyte.