Design Principles of Quinone Redox Systems for Advanced Sulfide Solid-State Organic Lithium Metal Batteries.

The emergence of solid-state battery technology presents a potential solution to the dissolution challenges of high-capacity small molecule quinone redox systems. Nonetheless, the successful integration of argyrodite-type Li6PS5Cl, the most promising solid-state electrolyte system, and quinone redox systems remains elusive due to their inherent reactivity. Here, a library of quinone derivatives is selected as model electrode materials to ascertain the critical descriptors governing the (electro)chemical compatibility and subsequently the performances of Li6PS5Cl-based solid-state organic lithium metal batteries (LMBs). Compatibility is attained if the lowest unoccupied molecular orbital level of the quinone derivative is sufficiently higher than the highest occupied molecular orbital level of Li6PS5Cl. The energy difference is demonstrated to be critical in ensuring chemical compatibility during composite electrode preparation and enable high-efficiency operation of solid-state organic LMBs. Considering these findings, a general principle is proposed for the selection of quinone derivatives to be integrated with Li6PS5Cl, and two solid-state organic LMBs, based on 2,5-diamino-1,4-benzoquinone and 2,3,5,6-tetraamino-1,4-benzoquinone, are successfully developed and tested for the first time. Validating critical factors for the design of organic battery electrode materials is expected to pave the way for advancing the development of high-efficiency and long cycle life solid-state organic batteries based on sulfides electrolytes.

Constructing an Interlaced Catalytic Surface via Fluorine-Doped Bimetallic Oxides for Oxygen Electrode Processes in Li-O2 Batteries.

Lithium-oxygen (Li-O2) batteries, renowned for their high theoretical energy density, have garnered significant interest as prime candidates for future electric device development. However, their actual capacity is often unsatisfactory due to the passivation of active sites by solid-phase discharge products. Optimizing the growth and storage of these products is a crucial step in advancing Li-O2 batteries. Here, a fluorine-doped bimetallic cobalt-nickel oxide (CoNiO2- xFx/CC) with an interlaced catalytic surface (ICS) and a corncob-like structure is proposed as an oxygen electrode. Unlike conventional oxide electrodes with a "single adsorption catalytic mechanism," the ICS of CoNiO2- xFx/CC offers a "competitive adsorption catalytic mechanism," where oxygen sites facilitate oxygen conversion while fluorine sites contribute to the growth of Li2O2. This results in a change in Li2O2 morphology from a surface film to toroidal particles, effectively preventing the burial of active sites. Additionally, the unique open architecture aids in the capture and release of oxygen and the formation of well-contacted Li2O2/electrode interfaces, which benefits the complete decomposition of Li2O2 products. Consequently, the Li-O2 battery with a CoNiO2- xFx/CC cathode demonstrates a high specific capacity of up to 30923 mAh g-1 and a lifespan exceeding 580 cycles, surpassing most reported metal oxide-based cathodes.

A Hybrid-Salt Strategy for Modulating the Li+ Solvation Sheathes and Constructing Robust SEI in Non-Flammable Electrolyte Lithium Metal Batteries.

The electrode interface determines the performance of an electrochemical energy storage system. Using traditional electrolyte organic additives and high-concentration electrolyte emerging recently are two generally strategies for improving the electrode interface. Here, a hybrid-salt electrolyte strategy is proposed for constructing the stable electrode interface. Through the solubilization effect of phosphate ester on LiNO3, a hybrid-salts-based non-flammable phosphate ester electrolyte system (HSPE) with LiPF6 and LiNO3 as Li salts has been developed. By the strong interaction between NO3 - and Li+, the Li+ solvation sheath and solvent behaviors have been modulated, thus the undesirable effects of phosphate ester are eliminated and a robust SEI is formed. Experimental results and theoretical calculations illustrate that NO3 - as a kind of strongly coordinating anion can reduce the number of TEP molecules and lower the reduction reactivity of TEP. The reconfigured Li+ solvation structure allows the formation of an inorganic-rich SEI on the electrode surface. As a result, in the designed HSPE, the average coulombic efficiency of lithium plating/stripping is increased to 99.12 %. This work explored a new approach to construct the electrode interface and addressing the poor interface performance issue of phosphate esters.

A dicarbonate solvent electrolyte for high performance 5 V-Class Lithium-based batteries.

Rechargeable lithium batteries using 5 V positive electrode materials can deliver considerably higher energy density as compared to state-of-the-art lithium-ion batteries. However, their development remains plagued by the lack of electrolytes with concurrent anodic stability and Li metal compatibility. Here we report a new electrolyte based on dimethyl 2,5-dioxahexanedioate solvent for 5 V-class batteries. Benefiting from the particular chemical structure, weak interaction with lithium cation and resultant peculiar solvation structure, the resulting electrolyte not only enables stable, dendrite-free lithium plating-stripping, but also displays anodic stability up to 5.2 V (vs. Li/Li+), in additive or co-solvent-free formulation, and at low salt concentration of 1 M. Consequently, the Li | |LiNi0.5Mn1.5O4 cells using the 1 M LiPF6 in 2,5-dioxahexanedioate based electrolyte retain >97% of the initial capacity after 250 cycles, outperforming the conventional carbonate-based electrolyte formulations, making this, and potentially other dicarbonate solvents promising for future Lithium-based battery practical explorations.

An intrinsic polymer electrolyte via in situ cross-linked for solid lithium-based batteries with high performance.

Since the introduction of poly(ethylene oxide) (PEO)-based polymer electrolytes more than 50 years, few other real polymer electrolytes with commercial application have emerged. Due to the low ion conductivity at room temperature, the PEO-based electrolytes cannot meet the application requirements. Most of the polymer electrolytes reported in recent years are in fact colloidal/composite electrolytes with plasticizers and fillers, not genuine electrolytes. Herein, we designed and synthesized a cross-linked polymer with a three-dimensional (3D) mesh structure which can dissolve the Li bis(trifluoromethylsulfonyl)imide (LiTFSI) salt better than PEO due to its unique 3D structure and rich oxygen-containing chain segments, thus forming an intrinsic polymer electrolyte (IPE) with ionic conductivity of 0.49 mS cm-1 at room temperature. And it can hinder the migration of large anions (e.g. TFSI-) in the electrolyte and increase the energy barrier to their migration, achieving Li+ migration numbers (tLi+) of up to 0.85. At the same time, IPE has good compatibility with lithium metal cathode and LiFePO4 (LFP) cathode, with stable cycles of more than 2,000 and 700 h in Li//Li symmetric batteries at 0.2 and 0.5 mAh cm-2 current densities, respectively. In addition, the Li/IPE/LFP batteries show the capacity retention >90% after 300 cycles at 0.5 C current density. This polymer electrolyte will be a pragmatic way to achieve commercializing all-solid-state, lithium-based batteries.

Single-atom site catalysis in Li-S batteries.

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

An Endogenous Prompting Mechanism for Sulfur Conversions Via Coupling with Polysulfides in Li-S Batteries.

The sluggish kinetics process and shuttling of soluble intermediates present in complex conversion between sulfur and lithium sulfide severely limit the practical application of lithium-sulfur batteries. Herein, by introducing a designated functional organic molecule to couple with polysulfide intermediators, an endogenous prompting mechanism of sulfur conversions has thus been created leading to an alternative sulfur-electrode process, in another words, to build a fast "internal cycle" of promotors that can promote the slow "external cycle" of sulfur conversions. The coupling-intermediators between the functional organic molecule and polysulfides, organophosphorus polysulfides, to be the "promotors" for sulfur conversions, are not only insoluble in the electrolyte but also with higher redox-activity. So the sulfur-electrode process kinetics is greatly improved and the shuttle effect is eliminated simultaneously by this strategy. Meanwhile, with the endogenous prompting mechanism, the morphology of the final discharge product can be modified into a uniform covering film, which is more conducive to its decomposition when charging. Benefiting from the effective mediation of reaction kinetics and control of intermediates solubility, the lithium-sulfur batteries can act out excellent rate performance and cycling stability.

A Novel Metal-Organic-Framework-Based Composite Solid Electrolyte for Lithium Metal Batteries.

Solid-state lithium metal batteries are hindered from practical applications by insufficient room-temperature ionic conductivity and poor electrode/electrolyte interfaces. Herein, we designed and synthesized a high ionic conductivity metal-organic-framework-based composite solid electrolyte (MCSE) with the synergy of high DN value ligands from Uio66-NH2 and succinonitrile (SN). XPS and FTIR reveal that the amino group (-NH2) of Uio66-NH2 and the cyano group (-C≡N) of SN have a stronger solvated coordination with Li+, which can promote the dissociation of crystalline LiTFSI, achieving an ionic conductivity of 9.23 × 10-5 S cm-1 at RT. Afterward, a flexible polymer electrolyte membrane (FPEM) with admirable ionic conductivity (1.56 × 10-4 S cm-1 at RT) and excellent electrode/electrolyte interfaces (86.2 Ω for the Li|20% FPEM|Li cell and 303.1 Ω for the LiFePO4|20% FPEM|Li cell) was successfully obtained after compounding the MCSE with polyethylene oxide (PEO). Moreover, a stable solid electrolyte layer (SEI) was formed in situ on the surface of the lithium metal, which enables the Li|20% FPEM|Li cell to exhibit remarkable cycling stability (1000 h at a current density of 0.05 mA cm-2). At the same time, the assembled LiFePO4|20% FPEM|Li cell offers a discharge-specific capacity of 155 mAh g-1 at 0.1 C and a columbic efficiency of 99.5% after 200 cycles. This flexible polymer electrolyte provides a possibility for operating long lifespan solid-state electrochemical energy storage systems at RT.

Regulating SEI Components of Sodium Anode via Capturing Organic-Molecule Intermediates in Ester-Based Electrolyte.

Highly reversible sodium metal anodes are still regarded as a stubborn hurdle in ester-based electrolytes due to the issue of uncontrollable dendrites and incredibly unstable interphase. Evidently, a strong protective film on sodium is decisive, while the quality of the protective film is mainly determined by its components. However, it is challenging to actively adjust the expected components. This work can regulate the solid electrolyte interphase (SEI) components by introducing a functional electrolyte additive (2-chloro-1,3-dimethylimidazoline hexafluorophosphate (CDIH, namely CDI+ +PF6 - )) into FEC/PC ester-based electrolyte. Specifically, the chloride element in the CDI+ can easily react to form a NaF/NaCl-rich SEI together with the decomposition products of FEC; then the CDI+ without chlorine as a gripper to capture the organic-molecule intermediates generated during FEC decomposition to greatly reduce the content of unstable organic components in SEI, which can be confirmed by molecular dynamic simulation and experiment. Eventually, a highly reversible Na deposition behavior can be delivered. As expected, under the action of CDIH additives, the Na||Na symmetrical cell performs an excellent long-term cycling (>800 h, 0.5 mA cm-2 -0.5 mAh cm-2 ) and rate performance (0.5-4 mA cm-2 ). Furthermore, the Na||PB full cell exhibits the outstanding electrochemical performance with small polarization.

Ultrafast and Ultralarge Lithium-Ion Storage Enabled by Fluorine-Nitrogen Co-Implanted Carbon Tubes.

As a holy grail in electrochemistry, both high-power and high-energy electrochemical energy storage system (EES) has always been a pursued dream. To simultaneously achieve the "both-high" EES, a rational design of structure and composition for storage materials with characteristics of battery-type and capacitor-type storage is crucial. Herein, fluorine-nitrogen co-implanted carbon tubes (FNCT) have been designed, in which plentiful active sites and expanded interlayer space have been created benefiting from the heteroatom engineering and the fluorine-nitrogen synergistic effect, thus the above two-type storage mechanism can get an optimal balance in the FNCT. The implanted fluorine heteroatoms can not only amplify interlayer spacing, but also induce the transformation of nitrogen configuration from pyrrole nitrogen to pyridine nitrogen, further promoting the activity of the carbon matrix. The extraordinary electrochemical performance as results can be witnessed for FNCT, which exhibit fast lithium-ion storage capability with a high energy density of 119.4 Wh kg-1 at an ultrahigh power density of 107.5 kW kg-1 .

Morphology-Dictated Mechanism of Efficient Reaction Sites for Li2O2 Decomposition.

In the pursuit of a highly reversible lithium-oxygen (Li-O2) battery, control of reaction sites to maintain stable conversion between O2 and Li2O2 at the cathode side is imperatively desirable. However, the mechanism involving the reaction site during charging remains elusive, which, in turn, imposes challenges in recognition of the origin of overpotential. Herein, via combined investigations by in situ atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS), we propose a universal morphology-dictated mechanism of efficient reaction sites for Li2O2 decomposition. It is found that Li2O2 deposits with different morphologies share similar localized conductivities, much higher than that reported for bulk Li2O2, enabling the reaction site not only at the electrode/Li2O2/electrolyte interface but also at the Li2O2/electrolyte interface. However, while the mass transport process is more enhanced at the former, the charge-transfer resistance at the latter is sensitively related to the surface structure and thus the reactivity of the Li2O2 deposit. Consequently, for compact disk-like deposits, the electrode/Li2O2/electrolyte interface serves as the dominant decomposition site, which causes premature departure of Li2O2 and loss of reversibility; on the contrary, for porous flower-like and film-like Li2O2 deposits bearing a larger surface area and richer surface-active structures, both the interfaces are efficient for decomposition without premature departure of the deposit so that the overpotential arises primarily from the sluggish oxidation kinetics and the decomposition is more reversible. The present work provides instructive insights into the understanding of the mechanism of reaction sites during the charge process, which offers guidance for the design of reversible Li-O2 batteries.

Superfast Mass Transport of Na/K Via Mesochannels for Dendrite-Free Metal Batteries.

Fast ion diffusion in anode hosts enabling uniform distribution of Li/Na/K is essential for achieving dendrite-free alkali-metal batteries. Common strategies, e.g. expanding the interlayer spacing of anode materials, can enhance bulk diffusion of Li but are less efficient for Na and K due to their larger ionic radius. Herein, a universal strategy to drastically improve the mass-transport efficiency of Na/K by introducing open mesochannels in carbon hosts is proposed. Such pore engineering can increase the accessible surface area by one order of magnitude, thus remarkably accelerating surface diffusion, as visualized by in situ transmission electron microscopy. In particular, once the mesochannels are filled by the Na/K metals, they become the superfast channels for mass transport via the mechanism of interfacial diffusion. Thus-modified carbon hosts enable Na/K filling in their inner cavities and uniform deposition across the whole electrodes with fast kinetics. The resulting Na-metal anodes can exhibit stable dendrite-free cycling with outstanding rate performance at a high current density of up to 30 mA cm-2 . This work presents an inspiring attempt to address the sluggish transport issue of Na/K, as well as valuable insights into the mass-transport mechanism in porous anodes for high-performance alkali-metal storage.

An Organic Redox Mediator with a Defense-Donor for Lithium Anode in Lithium-Oxygen Batteries.

Lithium-oxygen batteries (LOBs) suffer from large charge overpotential and unstable Li metal interface, which can be attributed to the inefficient charge transport at the insulating Li2 O2 /cathode interface and the severe oxygen corrosion issue on the Li anode surface. The use of soluble redox mediators (RMs) can effectively enhance the charge transport between Li2 O2 and cathode, thus greatly reducing the charge overpotential. However, oxidized RMs will also shuttle to the anode side and react with the Li metal, which not only results in the loss of both the RMs and the electrical energy efficiency but also exacerbates the Li anode corrosion. Herein, an organic compound-acetylthiocholine iodide (ATCI), in which a big cation group is contained, is proposed as a defense-donor RM for lithium anode in LOBs to simultaneously address the above issues. During charge, it can accelerate the oxidation kinetics of Li2 O2 via its iodide anion redox couple (I- /I3 - ). Meanwhile, its cation segment (ATC+ ) can move to the anode surface via electric attraction and in situ forms a protective interfacial layer, which prevents the Li anode from the attack of oxidized RM and oxygen species. Consequently, the ATCI-containing LOBs can achieve both a low charge potential (≈3.49 V) and a long cycle life (≈190 cycles).

In Situ Constructing a Catalytic Shell for Sulfur Cathode via Electrochemical Oxidative Polymerization.

Sluggish multiphase reaction kinetics and severe shuttle effect of lithium polysulfides (LiPSs) are two major challenges facing lithium-sulfur (Li-S) batteries, which largely prevent them from becoming a reality. Herein, a shell with catalytic function for sulfur cathode is in situ constructed through an ingenious electrochemical oxidative polymerization strategy by introducing hexafluorocyclotriphosphazene (HFPN) as additives, which suppresses the shuttle effect and promotes efficient sulfur conversion. The shell with abundant heteroatoms effectively confines polysulfides to the cathode matrix by chemically interacting with them to eliminate capacity degradation. Moreover, the shell exhibits high catalytic activities, which turns Li2S(2) into an activated state and facilitates its dissociation. The functionalized shell substantially advances the performance of Li-S batteries, thanks to efficient lithium-ion transportation and abundant adsorption-catalytic sites. As a result, Li-S batteries demonstrate superb resistance to self-discharge, ultrastable cycle performance, and greatly enhanced rate capability. Impressively, the batteries show an ultralow capacity decay rate of 0.034% throughout 700 cycles at 2C. They deliver a capacity of 517 mAh g-1 even at a 4C rate, exhibiting relieved electrochemical polarization and excellent sulfur utilization. This work provides an ingenious strategy to construct adsorption-catalytic nets for next-generation Li-S batteries with enhanced lifespan and electrochemical performance.

Regulating Lithium Plating/Stripping Behavior by a Composite Polymer Electrolyte Endowed with Designated Ion Channels.

The urgent demand for high energy and safety storage devices is pushing the development of lithium metal batteries. However, unstable solid electrolyte interface (SEI) formation and uncontrollable lithium dendrite growth are still huge challenges for the practical use of lithium metal batteries. Herein, a composite polymer electrolyte (CPE) endowed with designated ion channels is fabricated by constructing nanoscale Uio66-NH2 layer, which has uniformly distributed pore structure to regulate reversible Li plating/stripping in lithium metal batteries. The regular channels within the Uio66-NH2 layer work as an ion sieve to restrict larger TFSI- anions inside its channels and extract Li+ across selectively, which result in a high Li-ion transference number ( t Li + ${t_{{\rm{L}}{{\rm{i}}^{\bm{ + }}}}}$ ) of 0.6. Moreover, CPE provides high ion conductivity (0.245 mS cm-1 at room temperature) and expanded oxidation window (5.1 V) and forms a stable SEI layer. As a result, the assembled lithium metal batteries with CPE exhibit outstanding cyclic stability and capacity retention. The Li/CPE/Li symmetric cell continues plating/stripping over 500 h without short-circuiting. The Li/CPE/LFP cell delivers a reversible capacity of 149.3 mAh g-1 with a capacity retention of 99% after 100 cycles.

Thin Nano Cages with Limited Hollow Space for Ultrahigh Sulfur Loading Lithium-Sulfur Batteries.

Owning to its various advantages, the lithium-sulfur battery is one of the research hot spots for new energy storage systems. Diverse hollow structures with specific morphologies have been used as the sulfur host materials to adsorb or/and catalyze the polysulfides, and can in particular concurrently inhibit the volume expansion during electrochemical processes in lithium-sulfur batteries. However, hollow space with a large volume will restrict the performance of the cell under high sulfur area loading, which is a very important indicator for the practical applications of the lithium-sulfur battery. Here, we report a nano thin cage cobalt acid zinc (ZnCo2O4) with limited hollow space as the cathode catalyst for lithium-sulfur batteries, which greatly reduces the electrode volume occupied by the hollow structure. The hollow volume of these thin cages is much smaller than those of the normally reported hollow materials in the literatue. The electrochemical performance of lithium-sulfur batteries with ZnCo2O4 thin cages could greatly improve due to the unique structure and the synergistic adsorption/catalytic effect of Zn/Co sites, especially at an ultrahigh S area load. Under a high S loading of 8 mg cm-2, the cell could keep a reversible capacity of 600 mAh g-1 after 500 cycles. Even at a sulfur loading of 10 mg cm-2, the cell still releases a discharge capacity of 1000 mAh g-1 which is equivalent of an area capacity of 10 mAh cm-2. This work provides a feasible way to develop lithium sulfur batteries with a high area sulfur load. This idea provides a possible solution to develop a Li-S battery at high area S loading and move one step closer to the practical applications.

In situ Raman spectroscopy reveals the structure evolution and lattice oxygen reaction pathway induced by the crystalline-amorphous heterojunction for water oxidation.

One of the most successful approaches for balancing the high stability and activity of water oxidation in alkaline solutions is to use amorphous and crystalline heterostructures. However, due to the lack of direct evidence at the molecular level, the nano/micro processes of amorphous and crystalline heterostructure electrocatalysts, including self-reconstruction and reaction pathways, remain unknown. Herein, the Leidenfrost effect assisted electrospray approach combined with phase separation was used for the first time to create amorphous NiO x /crystalline α-Fe2O3 (a-NiO x /α-Fe2O3) nanowire arrays. The results of in situ Raman spectroscopy demonstrate that with the increase of the potential at the a-NiO x /α-Fe2O3 interface, a significant accumulation of OH can be observed. Combining with XAS spectra and DFT calculations, we believe that more OH adsorption on the Ni centers can facilitate Ni2+ deprotonation to achieve the high-valence oxidation of Ni4+ according to HSAB theory (Fe3+ serves as a strong Lewis acid). This result promotes the electrocatalysts to follow the lattice oxygen activation mechanism. This work, for the first time, offers direct spectroscopic evidence for deepening the fundamental understanding of the Lewis acid effect of Fe3+, and reveals the synergistic effect on water oxidation via the unique amorphous and crystalline heterostructures.

An Encapsulation-Based Sodium Storage via Zn-Single-Atom Implanted Carbon Nanotubes.

The properties of high theoretical capacity, low cost, and large potential of metallic sodium (Na) has strongly promoted the development of rechargeable sodium-based batteries. However, the issues of infinite volume variation, unstable solid electrolyte interphase (SEI), and dendritic sodium causes a rapid decline in performance and notorious safety hazards. Herein, a highly reversible encapsulation-based sodium storage by designing a functional hollow carbon nanotube with Zn single atom sites embedded in the carbon shell (ZnSA -HCNT) is achieved. The appropriate tube space can encapsulate bulk sodium inside; the inner enriched ZnSA sites provide abundant sodiophilic sites, which can evidently reduce the nucleation barrier of Na deposition. Moreover, the carbon shell derived from ZIF-8 provides geometric constraints and excellent ion/electron transport channels for the rapid transfer of Na+ due to its pore-rich shell, which can be revealed by in situ transmission electron microscopy (TEM). As expected, Na@ZnSA -HCNT anodes present steady long-term performance in symmetrical battery (>900 h at 10 mA cm-2 ). Moreover, superior electrochemical performance of Na@ZnSA -HCNT||PB full cells can be delivered. This work develops a new strategy based on carbon nanotube encapsulation of metallic sodium, which improves the safety and cycling performance of sodium metal anode.

High-Performance Lithium-Oxygen Batteries Using a Urea-Based Electrolyte with Kinetically Favorable One-Electron Li2 O2 Oxidation Pathways.

Glymes are the most widely used electrolyte solvents in lithium-oxygen batteries (LOBs) due to their relatively high stability. However, their associated LOBs have long been plagued by large charge overpotential, which is closely related to the sluggish two-electron Li2 O2 oxidation mechanism. Here, we report a new electrolyte solvent-1,1,3,3-tetramethylurea (TMU) for LOBs with high performance and an alternative mechanism, where a kinetically favorable one-electron Li2 O2 oxidation pathway can happen in the urea electrolyte system, thus leading to a much lower charge overpotential (≈0.51 V) compared to the tetraglyme-based LOBs (≈1.27 V). Besides, TMU also exhibits good stability since it does not contain any α-hydrogen atoms that are vulnerable to be attacked by superoxide species, thus suppressing the hydrogen abstraction side reactions. Consequently, the TMU-based LOBs can stably work for more than 135 cycles, which is four times that of the tetraglyme-based LOBs (≈28 cycles).

Single-dispersed polyoxometalate clusters embedded on multilayer graphene as a bifunctional electrocatalyst for efficient Li-S batteries.

The redox reactions occurring in the Li-S battery positive electrode conceal various and critical electrocatalytic processes, which strongly influence the performances of this electrochemical energy storage system. Here, we report the development of a single-dispersed molecular cluster catalyst composite comprising of a polyoxometalate framework ([Co4(PW9O34)2]10-) and multilayer reduced graphene oxide. Due to the interfacial charge transfer and exposure of unsaturated cobalt sites, the composite demonstrates efficient polysulfides adsorption and reduced activation energy for polysulfides conversion, thus serving as a bifunctional electrocatalyst. When tested in full Li-S coin cell configuration, the composite allows for a long-term Li-S battery cycling with a capacity fading of 0.015% per cycle after 1000 cycles at 2 C (i.e., 3.36 A g-1). An areal capacity of 4.55 mAh cm-2 is also achieved with a sulfur loading of 5.6 mg cm-2 and E/S ratio of 4.5 µL mg-1. Moreover, Li-S single-electrode pouch cells tested with the bifunctional electrocatalyst demonstrate a specific capacity of about 800 mAh g-1 at a sulfur loading of 3.6 mg cm-2 for 100 cycles at 0.2 C (i.e., 336 mA g-1) with E/S ratio of 5 µL mg-1.