High‐Temperature Formation of a Functional Film at the Cathode/Electrolyte Interface in Lithium–Sulfur Batteries: An In Situ AFM Study

Lithium–sulfur (Li–S) batteries have been attracting wide attention for their promising high specific capacity. A deep understanding of Li–S interfacial mechanism including the temperature (T) effect is required to meet the demands for battery modification and systematic study. Herein, the interfacial behavior during discharge/charge is investigated at high temperature (HT) of 60 °C in an electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI). By in situ atomic force microscopy (AFM), dynamic evolution of insoluble Li₂S₂ and Li₂S is studied at the nanoscale. An in situ formed functional film can be directly monitored at 60 °C after Li₂S nucleation. It retards side reactions and facilitates interfacial redox. The insight into the interfacial processes at HT provides direct evidence of the existence of the film and reveals its dynamic behavior, providing a new avenue for electrolyte design and performance enhancement.     

N- and S-doped ordered mesoporous carbon tubes with efficient S confinement for high-performance Li–S batteries

The insulating properties of S/Li₂S₂/Li₂S and the soluble Li₂S₄/Li₂S₆/Li₂S₈ obstruct the practical application of Li–S batteries. In this work, highly ordered N and S co-doped mesoporous carbon tubes (NSMCTBs) with high specific surface areas and large pore volume are employed to confine and improve the utilization efficiency of S species in Li–S batteries. The strong S_nLi₂?N interaction and S–S chemical bond between thiophenic S and Li₂S_n guarantee the exceptional electrochemical performance of as-prepared NSMCTBs/S cathode. A relatively high discharge capacity of 1315.2 mAh g^?1 is achieved for the first cycle at 0.5 C and maintained at 644.1 mAh g^?1 after 500 cycles. The NSMCTBs/S with high S content of up to 80%, it also delivers a discharge capacity of 1092.1 mAh g^?1 and considerable cycling performance. More importantly, the NSMCTBs/S can effectively suppress the self-discharge behavior of Li–S 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.     

A New Perspective on Li–SO2 Batteries for Rechargeable Systems

Primary Li–SO₂ batteries offer a high energy density in a wide operating temperature range with exceptionally long shelf life and have thus been frequently used in military and aerospace applications. Although these batteries have never been demonstrated as a rechargeable system, herein, we show that the reversible formation of Li₂S₂O₄, the major discharge product of Li–SO₂ battery, is possible with a remarkably smaller charging polarization than that of a Li–O₂ battery without the use of catalysts. The rechargeable Li–SO₂ battery can deliver approximately 5400 mAh g^?1 at 3.1 V, which is slightly higher than the performance of a Li–O₂ battery. In addition, the Li–SO₂ battery can be operated with the aid of a redox mediator, exhibiting an overall polarization of less than 0.3 V, which results in one of the highest energy efficiencies achieved for Li–gas battery systems.     

High-Energy Aqueous/Organic Hybrid Batteries Enabled by Cu2+ Redox Charge Carriers

Lithium||sulfur (Li||S) batteries are considered as one of the promising next-generation batteries due to the high theoretical capacity and low cost of S cathodes, as well as the low redox potential of Li metal anodes (−3.04 V vs. standard hydrogen electrode). However, the S reduction reaction from S to Li₂S leads to limited discharge voltage and capacity, largely hindering the energy density of Li||S batteries. Herein, high-energy Li||S hybrid batteries were designed via an electrolyte decoupling strategy. In cathodes, S electrodes undergo the solid-solid conversion reaction from S to Cu₂S with four-electron transfer in a Cu²⁺-based aqueous electrolyte. Such an energy storage mechanism contributes to enhanced electrochemical performance of S electrodes, including high discharge potential and capacity, superior rate performance and stable cycling behavior. As a result, the assembled Li||S hybrid batteries exhibit a high discharge voltage of 3.4 V and satisfactory capacity of 2.3 Ah g⁻¹, contributing to incredible energy density. This work provides an opportunity for the construction of high-energy Li||S batteries.     

Cation Additive Enabled Rechargeable LiOH-Based Lithium–Oxygen Batteries

Lithium–oxygen (Li–O₂) batteries have attracted extensive research interest due to their high energy density. Other than Li₂O₂ (a typical discharge product in Li–O₂ batteries), LiOH has proved to be electrochemically active as an alternative product. Here we report a simple strategy to achieve a reversible LiOH-based Li–O₂ battery by using a cation additive, sodium ions, to the lithium electrolyte. Without redox mediators in the cell, LiOH is detected as the sole discharge product and it charges at a low charge potential of 3.4 V. A solution-based reaction route is proposed, showing that the competing solvation environment of the catalyst and Li⁺ leads to LiOH precipitation at the cathode. It is critical to tune the cell chemistry of Li–O₂ batteries by designing a simple system to promote LiOH formation/decomposition.     

Mechanism of Lithium Storage in MoS2 and the Feasibility of Using Li2S/Mo Nanocomposites as Cathode Materials for Lithium–Sulfur Batteries

The most-popular strategy to improve the cycling stability and rate performance of the sulfur electrode in lithium–sulfur (Li–S) batteries is to astrict the sulfur in a conducting medium by using complicated chemical/physical processing. Lithium sulfide (Li₂S) has been proposed as an alternative electrode material to sulfur. However, for its application, it must meet challenges such as high instability in air together with all of the drawbacks of a sulfur–containing electrode. Herein, we report the feasibility of using Li₂S, which was obtained by electrochemical conversion of commercial molybdenum disulfide (MoS₂) into Li₂S and metallic molybdenium (Mo) at low voltages, as a high-performance active material in Li–S batteries. Metallic Mo prevented the dissolution of lithium polysulfides into the electrolyte and enhanced the conductivity of the sulfide electrode. Therefore, the in situ electrochemically prepared Li₂S/Mo composite exhibited both high cycling stability and high sulfur utilization.     

Amorphous Li2O2: Chemical Synthesis and Electrochemical Properties

When aprotic Li–O₂ batteries discharge, the product phase formed in the cathode often contains two different morphologies, that is, crystalline and amorphous Li₂O₂. The morphology of Li₂O₂ impacts strongly on the electrochemical performance of Li–O₂ cells in terms of energy efficiency and rate capability. Crystalline Li₂O₂ is readily available and its properties have been studied in depth for Li–O₂ batteries. However, little is known about the amorphous Li₂O₂ because of its rarity in high purity. Herein, amorphous Li₂O₂ has been synthesized by a rapid reaction of tetramethylammonium superoxide and LiClO₄ in solution, and its amorphous nature has been confirmed by a range of techniques. Compared with its crystalline siblings, amorphous Li₂O₂ demonstrates enhanced charge‐transport properties and increased electro‐oxidation kinetics, manifesting itself a desirable discharge phase for high‐performance Li–O₂ batteries.     

Intrinsic Stress-strain in Barium Titanate Piezocatalysts Enabling Lithium−Oxygen Batteries with Low Overpotential and Long Life

Rechargeable lithium−oxygen (Li−O₂) batteries with high theoretical energy density are considered as promising candidates for portable electronic devices and electric vehicles, whereas their commercial application is hindered due to poor cyclic stability caused by the sluggish kinetics and cathode passivation. Herein, the intrinsic stress originated from the growth and decomposition of the discharge product (lithium peroxide, Li₂O₂) is employed as a microscopic pressure resource to induce the built-in electric field, further improving the reaction kinetics and interfacial Lithium ion (Li⁺) transport during cycling. Piezopotential caused by the intrinsic stress-strain of solid Li₂O₂ is capable of providing the driving force for the separation and transport of carriers, enhancing the Li⁺ transfer, and thus improving the redox reaction kinetics of Li−O₂ batteries. Combined with a variety of in situ characterizations, the catalytic mechanism of barium titanate (BTO), a typical piezoelectric material, was systematically investigated, and the effect of stress-strain transformation on the electrochemical reaction kinetics and Li⁺ interface transport for the Li−O₂ batteries is clearly established. The findings provide deep insight into the surface coupling strategy between intrinsic stress and electric fields to regulate the electrochemical reaction kinetics behavior and enhance the interfacial Li⁺ transport for battery system.     

All-solid-state Li/S batteries with highly conductive glass–ceramic electrolytes

All-solid-state cells using sulfur-based cathode materials and Li₂S–P₂S₅ glass–ceramic electrolytes were successfully prepared and exhibited excellent cycling performance at room temperature. The cathode materials consisting of sulfur and CuS were synthesized by mechanical milling using sulfur and copper crystals as starting materials. The cell performance was influenced by the milling time for the cathode materials and the cell with cathode materials obtained by milling for 15 min retained large capacities over 650 mA h g⁻¹ for 20 cycles. Sulfur as well as CuS in cathode materials proved to be utilized as active materials on charge–discharge processes in the all-solid-state Li/S cells.     

Vanadium(III) Acetylacetonate as an Efficient Soluble Catalyst for Lithium–Oxygen Batteries

High donor number (DN) solvents in Li—O₂ batteries that dissolve superoxide intermediates in lithium peroxide (Li₂O₂) formation facilitate high capacities at high rates and avoid early cell death. However, their beneficial characteristics also result in an instability towards highly reactive superoxide intermediates. Furthermore, Li—O₂ batteries would deliver a superior energy density, but the multiphase electrochemical reactions are difficult to achieve when operating with only solid catalysts. Herein we demonstrate that vanadium(III) acetylacetonate (V(acac)₃) is an efficient soluble catalyst that can address these problems. During discharge, V(acac)₃ integrates with the superoxide intermediate, accelerating O₂ reduction kinetics and reducing side reactions. During charge, V(acac)₃ acts as a redox mediator that permits efficient oxidation of Li₂O₂. The cells with V(acac)₃ exhibit low overpotential, high rate performance, and considerable cycle stability.     

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.     

Chemistry Design Towards a Stable Sulfide‐Based Superionic Conductor Li4Cu8Ge3S12

Sulfide‐based superionic conductors with high ionic conductivity have been explored as candidates for solid‐state Li batteries. However, moisture hypersensitivity has made their manufacture complicated and costly and also impeded applications in batteries. Now, a sulfide‐based superionic conductor Li₄Cu₈Ge₃S₁₂ with superior stability was developed based on the hard/soft acid–base theory. The compound is stable in both moist air and aqueous LiOH aqueous solution. The electrochemical stability window was up to 1.5 V. An ionic conductivity of 0.9×10^?4 S cm with low activation energy of 0.33 eV was achieved without any optimization. The material features a rigid Cu‐Ge‐S open framework that increases its stability. Meanwhile, the weak bonding between Li⁺ and the framework promotes ionic conductivity. This work provides a structural configuration in which weak Li bonding in the rigid framework promotes an environment for highly conductive and stable solid‐state electrolytes.     

Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic Framework-based Catalysts

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li−S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li−S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal–organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S₈→Li₂S₄, while the missing cluster defects can catalyze the reaction of Li₂S₄→Li₂S, so as to effectively inhibit the shuttle effect. Hence, the Li−S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g⁻¹ delivers a capacity of 1087 mAh g⁻¹ at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm⁻² and E/S=3.9 mL g⁻¹, an areal capacity of 10.4 mAh cm⁻² for 45 cycles can still be obtained.     

Electrochemical Reactivation of Dead Li2S for Li−S Batteries in Non-Solvating Electrolytes

The use of non-solvating, or as-called sparingly-solvating, electrolytes (NSEs), is regarded as one of the most promising solutions to the obstacles to the practical applications of Li−S batteries. However, it remains a puzzle that long-life Li−S batteries have rarely, if not never, been reported with NSEs, despite their good compatibility with Li anode. Here, we find the capacity decay of Li−S batteries in NSEs is mainly due to the accumulation of the dead Li₂S at the cathode side, rather than the degradation of the anodes or electrolytes. Based on this understanding, we propose an electrochemical strategy to reactivate the accumulated Li₂S and revive the dead Li−S batteries in NSEs. With such a facile approach, Li−S batteries with significantly improved cycling stability and accelerated dynamics are achieved with diglyme-, acetonitrile- and 1,2-dimethoxyethane-based NSEs. Our finding may rebuild the confidence in exploiting non-solvating Li−S batteries with practical competitiveness.     

Polymer/colloid dual-phase electrolyte membrane for rechargeable lithium batteries

In this work, a polymer/ceramic phase-separation porous membrane is first prepared from polyvinyl alcohol–polyacrylonitrile water emulsion mixed with fumed nano-SiO₂ particles by the phase inversion method. This porous membrane is then wetted by a non-aqueous Li–salt liquid electrolyte to form the polymer/colloid dual-phase electrolyte membrane. Compared to the liquid electrolyte in conventional polyolefin separator, the obtained electrolyte membrane has superior properties in high ionic conductivity (1.9 mS?cm^?1 at 30 °C), high Li⁺ transference number (0.41), high electrochemical stability (extended up to 5.0 V versus Li⁺/Li on stainless steel electrode), and good interfacial stability with lithium metal. The test cell of Li/LiCoO₂ with the electrolyte membrane as separator also shows high-rate capability and excellent cycle performance. The polymer/colloid dual-phase electrolyte membrane shows promise for application in rechargeable lithium batteries.     

Lithium‐Rich Layered Oxide Li1.18Ni0.15Co0.15Mn0.52O2 as the Cathode Material for Hybrid Sodium‐Ion Batteries

Li‐rich layered oxide Li_1.18Ni_0.15Co_0.15Mn_0.52O₂ (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium‐ion battery and its Na⁺ storage properties are comprehensively studied in terms of galvanostatic charge–discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium‐ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g^?1 at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g^?1 for 200 cycles at 5 C rate. Moreover, ex situ ICP‐OES suggests interesting mixed‐ions migration processes: In the initial two cycles, only Li⁺ can intercalate into the LNCM cathode, whereas both Li⁺ and Na⁺ work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge–discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium‐ion batteries.     

Development of a new in situ cell for the X–ray Absorption Fine Structure analysis of the electrochemical reaction in a rechargeable battery and its application to the Lithium Battery Material,Li1+yMn2−yO4

An electrochemical cell was developed for the in situ transmission X–ray Absorption Fine Structure measurements of the charge/discharge process of the cathode materials of lithium secondary batteries, from which Li can be electrochemically deintercalated or intercalated. The dynamical structural behavior of Mn in Li(Mn_1.93Li_0.07)O₄, and Li(Mn_1.85Li_0.15)O₄ as a function of both excess Li content and the Li deintercalation was revealed using the in situ cell. The analysis disclosed the coexistence of two MnO₆–coordination polyhedra with different Mn–O distances for the Mn³⁺ and Mn⁴⁺ ions at the 16d site of the spinel structure. Because the charge–discharge process accompanies the oxidation–reduction of the Mn ions, this size difference causes an unfavorable lattice distortion for the electrode materials which can cause a loss of cell capacity after cyclic use of the cell. A partial substitution of Li for Mn will diminish this effect and will be favorable for the battery material.     

Formation of Nanostructured MnO/Co/Solid–Electrolyte Interphase Ternary Composites as a Durable Anode Material for Lithium‐Ion Batteries

Nanoporous MnO frameworks with highly dispersed Co nanoparticles were produced from MnCO₃ precursors prepared in a gel matrix. The MnO frameworks that contain 20 mol % Co exhibited excellent cycle performance as an anode material for Li‐ion batteries. The solid–electrolyte interphase (SEI) formed in the frameworks through the electrochemical reaction mediates the active materials, such as MnO, Mn, and Li₂O, during the conversion reaction in the charge–discharge cycle. The Co nanoparticles and SEI provide the electron and Li‐ion conductive networks, respectively. The ternary nanocomposites of the MnO framework, metallic Co nanoparticles, and embedded SEI are categorized as durable anode materials for Li‐ion batteries.     

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.