Reversible Crosslinked Polymer Binder for Recyclable Lithium Sulfur Batteries with High Performance

Owing to the negative impact of the extensive utilization of batteries on the environment, sustainability of the cells needs to be included in the systemic research of batteries. Herein, a dissolvable ionic crosslinked polymer (DICP) is exploited as a binder for lithium–sulfur batteries by crosslinking the polyacrylic acid and polyethyleneimine through carboxy‐amino ionic interaction. This interaction is pH‐controlled, and therefore, the crosslinked binder network can be readily dissociated under basic conditions, providing a facile strategy enabling valuable components recycled through a convenient washing method. The sulfur cathode prepared using the recycled carbon–sulfur composite can deliver comparable capacity as that of fresh electrode. In addition, evidence from cell performance and characterizations, such as in situ X‐ray absorption spectroscopy, in situ UV–visible spectroscopy, X‐ray photoelectron spectroscopy, and density functional theory calculation, confirms that DICP is a more effective binder than its commercial counterpart on suppressing polysulfide dissolution in the electrolyte. Exploiting reversible crosslinked polymer binder for recyclable Li–S batteries with ameliorated electrochemical performance, this study illuminates sustainable development for large‐scale energy storage systems.     

Rational Designs for Lithium-Sulfur Batteries with Low Electrolyte/Sulfur Ratio

Lithium-sulfur batteries (LSBs) are considered a promising next-generation energy storage device owing to their high theoretical energy density. However, their overall performance is limited by several critical issues such as lithium polysulfide (PS) shuttles, low sulfur utilization, and unstable Li metal anodes. Despite recent huge progress, the electrolyte/sulfur ratio (E/S) used is usually very high (≥20 µL mg⁻¹), which greatly reduces the practical energy density of devices. To push forward LSBs from the lab to the industry, considerable attention is devoted to reducing E/S while ensuring the electrochemical performance. To date, however, few reviews have comprehensively elucidated the possible strategies to achieve that purpose. In this review, recent advances in low E/S cathodes and anodes based on the issues resulting from low E/S and the corresponding solutions are summarized. These will be beneficial for a systematic understanding of the rational design ideas and research trends of low E/S LSBs. In particular, three strategies are proposed for cathodes: preventing PS formation/aggregation to avoid inadequate dissolution, designing multifunctional macroporous networks to address incomplete infiltration, and utilizing an imprison strategy to relieve the adsorption dependence on specific surface area. Finally, the challenges and future prospects for low E/S LSBs are discussed.     

Hollow Molybdate Microspheres as Catalytic Hosts for Enhancing the Electrochemical Performance of Sulfur Cathode under High Sulfur Loading and Lean Electrolyte

Lithium–sulfur battery possesses a high energy density; however, its application is severely blocked by several bottlenecks, including the serious shuttling behavior and sluggish redox kinetics of sulfur cathode, especially under the condition of high sulfur loading and lean electrolyte. Herein, hollow molybdate (CoMoO₄, NiMoO₄, and MnMoO₄) microspheres are introduced as catalytic hosts to address these issues. The molybdates present a high intrinsic electrocatalytic activity for the conversion of soluble lithium polysulfides, and the unique hollow spherical structure could provide abundant sites and spatial confinement for electrocatalysis and inhibiting shuttling, respectively. Meanwhile, it is demonstrated that the unique adsorption of molybdates toward polysulfides exhibits a “volcano-type” feature with the catalytic performance following the Sabatier principle. The NiMoO₄ hollow microspheres with moderate adsorption show the highest electrocatalytic activity, which is favorable for enhancing the electrochemical performance of sulfur cathode. Especially, the S/NiMoO₄ composite could achieve a high areal capacity of 7.41 mAh cm⁻² (906.2 mAh g⁻¹) under high sulfur loading (8.18 mg cm⁻²) and low electrolyte/sulfur ratio (E/S, 4 µL mg⁻¹). This work offers a new perspective on searching accurate rules for selecting and designing effective host materials in the lithium–sulfur battery.     

Carbonized Polyacrylonitrile‐Stabilized SeSx Cathodes for Long Cycle Life and High Power Density Lithium Ion Batteries

A facile synthesis of selenium sulfide (SeS_x)/carbonized polyacrylonitrile (CPAN) composites is achieved by annealing the mixture of SeS₂ and polyacrylonitrile (PAN) at 600 °C under vacuum. The SeS_x molecules are confined by N‐containing carbon (ring) structures in the carbonized PAN to mitigate the dissolution of polysulfide and polyselenide intermediates in carbonate‐based electrolyte. In addition, formation of solid electrolyte interphase (SEI) on the surface of SeS_x/CPAN electrode in the first cycle further prevents polysulfide and polyselenide intermediates from dissolution. The synergic restriction of SeS_x by both CPAN matrix and SEI layer allows SeS_x/CPAN composites to be charged and discharged in a low‐cost carbonate‐based electrolyte (LiPF₆ in EC/DEC) with long cycling stability and high rate capability. At a current density of 600 mA g^?1, it maintains a reversible capacity of 780 mAh g^?1 for 1200 cycles. Moreover, it retains 50% of the capacity at 60 mA g^?1 even when the current density increases to 6 A g^?1. The superior electrochemical performance of SeS_x/CPAN composite demonstrates that it is a promising cathode material for long cycle life and high power density lithium ion batteries. This is the first report on long cycling stability and high rate capability of selenium sulfide‐based cathode material.     

Electrode Design for Lithium–Sulfur Batteries: Problems and Solutions

Pursuit of advanced batteries with high‐energy density is one of the eternal goals for electrochemists. Over the past decades, lithium–sulfur batteries (LSBs) have gained world‐wide popularity due to their high theoretical energy density and cost effectiveness. However, their road to the market is still full of thorns. Apart from the poor electronic conductivity of sulfur‐based cathodes, LSBs involve special multielectron reaction mechanisms associated with active soluble lithium polysulfides intermediates. Accordingly, the electrode design and fabrication protocols of LSBs are different from those of traditional lithium ion batteries. This review is aimed at discussing the electrode design/fabrication protocols of LSBs, especially the current problems on various sulfur‐based cathodes (such as S, Li₂S, Li₂S_x catholyte, organopolysulfides) and corresponding solutions. Different fabrication methods of sulfur‐based cathodes are introduced and their corresponding bullet points to achieve high‐quality cathodes are highlighted. In addition, the challenges and solutions of sulfur‐based cathodes including active material content, mass loading, conductive agent/binder, compaction density, electrolyte/sulfur ratio, and current collector are summarized and rational strategies are refined to address these issues. Finally, the future prospects on sulfur‐based cathodes and LSBs are proposed.     

Reconciling Mass Loading and Gravimetric Performance of MnO2 Cathodes by 3D-Printed Carbon Structures for Zinc-Ion Batteries

To promote the real application of zinc-ion batteries (ZIBs), reconciling the high mass loading and gravimetric performance of MnO₂ electrodes is of paramount importance. Herein, the rational regulation of 3D-printed carbon microlattices (3DP CMs) enabling an ultrathick MnO₂ electrode with well-maintained gravimetric capacities is demonstrated. The 3DP CMs made of graphene and carbon nanotubes (CNTs) are fabricated by direct ink 3D printing and subsequent high-temperature annealing. 3D printing enables a periodic structure of 3DP CMs, while the thermal annealing contributes to high conductivity and defective surfaces. Due to these structural merits, uniform electrical field distribution and facilitated MnO₂ deposition over the 3DP CMs are permitted. The optimal electrode with MnO₂ loaded on the 3DP CMs can achieve a record-high specific capacity of 282.8 mAh g⁻¹ even at a high mass loading of 28.4 mg cm⁻² and high ion transfer dynamics, which reconciles the loading mass and gravimetric performance. As a result, the aqueous ZIBs based on the 3DP CMs loaded MnO₂ afford an outstanding performance superior to most of the previous reports. This study reveals the essential role of interaction between active materials and current collectors, providing an alternative strategy for designing high-performance energy storage devices.     

Stabilizing the Interphase in Cobalt-Free,Ultrahigh-Nickel Cathodes for Lithium-Ion Batteries

High-nickel layered oxide cathodes, such as LiNi_1-x-yMn_xCo_yO₂ (NMC) and LiNi_1-x-yCo_xAl_yO₂ (NCA), are at the forefront for implementation in high-energy-density lithium-ion batteries. The presence of cobalt in both cathode chemistries, however, largely deters their application due to fiscal and humanitarian issues affiliated with cobalt sourcing. Increasing the Ni content drives down the Co content, but introduces additional structural and electrochemical problems attributed to high-Ni cathodes. Herein a dually modified cobalt-free ultrahigh-nickel cathode 0.02B-LiNi_0.99Mg_0.01O₂ (NBM) is presented with 1 mol% Mg and 2 mol% B that exhibits a high initial 1C discharge capacity of 210 mA h g⁻¹ with a 20% capacity retention improvement over 500 cycles when benchmarked against LiNiO₂ (LNO) in pouch full cell configurations with graphite anode. Postmortem analyses reveal the enhanced performance stems from reduced active lithium inventory loss and localized surface reactivity in the NBM cathode. The stabilized cathode-electrolyte interphase subsequently reduces transition-metal dissolution and ensuing chemical crossover to the graphite anode, which prevents further catalyzed parasitic reactions that harmfully passivate the anode surface. Altogether, this study aims to highlight the importance of electrode characterization and analysis from an interphasial viewpoint and to push the ongoing research to stabilize cobalt-free ultrahigh-Ni cathodes for industrial feasibility.     

Decoding Li+/Na+ Exchange Route Toward High-Performance Mn-Based Layered Cathodes for Li-Ion Batteries

Li⁺/Na⁺ exchange has been extensively explored as an effective method to prepare high-performance Mn-based layered cathodes for Li-ion batteries, since the first report in 1996 by P. G. Bruce (Nature, 1996. 381, 499–500). Understanding the detailed structural changes during the ion-exchange process is crucial to implement the synthetic control of high-performance layered Mn-based cathodes, but less studied. Herein, in situ synchrotron X-ray diffraction, density functional theory calculations, and electrochemical tests are combined to conduct the systemic studies into the structural changes during the ion-exchange process of an Mn-only layered cathode O3-type Li_0.67[Li_0.22Mn_0.78]O₂ (LLMO) from the corresponding counterpart P3-type Na_0.67[Li_0.22Mn_0.78]O₂ (NLMO). The temperature-resolved observations combined with theoretical calculations reveal that the Li⁺/Na⁺ exchange is favorable thermodynamically and composited with two tandem topotactic phase transitions: 1) from NLMO to a layered intermediate through ≈60% of Li⁺/Na⁺ exchange. 2) then to the final layered product LLMO through further Li insertion. Moreover, the intermediate-dominate composite is obtained by slowing down the exchange kinetics below room temperature, showing better electrochemical performance than LLMO obtained by the traditional molten-salt method. The findings provide guides for the synthetic control of high-performance Mn-based cathodes under mild conditions.     

Gas Pickering Emulsion Templated Hollow Carbon for High Rate Performance Lithium Sulfur Batteries

A CO₂ in water nanoparticle stabilized Pickering emulsion is used to template micrometer sized hollow porous nitrogen doped carbon particles for high rate performance lithium sulfur battery. For the first time, nanoparticles serve the dual role of an emulsion stabilizer and a pore template for the shell, directly utilizing in situ generated CO₂ bubbles as template for the core. The minimalistic nature of this method does not require expensive surfactants or additional core templates. Upon polymerization of melamine formaldehyde onto CO₂, a robust polymer/silica composite shell is formed and transformed into a porous shell upon washing. The micrometer‐sized hollow morphology in combination with its nitrogen rich porous shell demonstrates impressive rate capabilities of 670 and 500 mAh g^?1 even at a high rate of 7C and 9C, respectively. This material also possesses excellent cycle durability, exhibiting a low capacity decay of 0.088%/cycle over 300 cycles. Measurement of the shuttle current and impedance provides interesting insight into the polysulfide mass transfer mechanism of hollow structured sulfur hosts.     

Iron Fluoride–Carbon Nanocomposite Nanofibers as Free‐Standing Cathodes for High‐Energy Lithium Batteries

The development of low‐cost, high‐energy cathodes from nontoxic, broadly available resources is a big challenge for the next‐generation rechargeable lithium or lithium‐ion batteries. As a promising alternative to traditional intercalation‐type chemistries, conversion‐type metal fluorides offer much higher theoretical capacity and energy density than conventional cathodes. Unfortunately, these still suffer from irreversible structural degradation and rapid capacity fading upon cycling. To address these challenges, here a versatile and effective strategy is harnessed for the development of metal fluoride–carbon (C) nanocomposite nanofibers as flexible, free‐standing cathodes. By taking iron trifluoride (FeF₃) as a successful example, assembled FeF₃–C/Li cells with a high reversible FeF₃ capacity of 550 mAh g^?1 at 100 mA g^?1 (three times that of traditional cathodes, such as lithium cobalt oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide) and excellent stability (400+ cycles with little‐to‐no degradation) are demonstrated. The promising characteristics can be attributed to the nanoconfinement of FeF₃ nanoparticles, which minimizes the segregation of Fe and LiF upon cycling, the robustness of the electrically conductive C network and the prevention of undesirable reactions between the active material and the liquid electrolyte using the composite design and electrolyte selection.     

Thermal Reductive Perforation of Graphene Cathode for High-Performance Aluminum-Ion Batteries

Controlling the structure of graphene-based materials with improved ion intercalation and diffusivity is crucial for their applications, such as in aluminum-ion batteries (AIBs). Due to the large size of AlCl₄⁻ ions, graphene-based cathodes have specific capacities of ≈60 to 148 mAh g⁻¹, limiting the development of AIBs. A thermal reductive perforation (TRP) strategy is presented, which converts three-layer graphene nanosheets to surface-perforated graphene materials under mild temperature (400 °C). The thermal decomposition of block copolymers used in the TRP process generates active radicals to deplete oxygen and create graphene fragments. The resultant material has a three-layer feature, in-plane nanopores, >50% expanded interlayer spacing, and a low oxygen content comparable to graphene annealed at a high temperature of ≈3000 °C. When applied as an AIB cathode, it delivers a reversible capacity of 197 mAh g⁻¹ at a current density of 2 A g⁻¹ and reaches 92.5% of the theoretical capacity predicted by density-functional theory simulations.     

Progress of Phosphate-based Polyanion Cathodes for Aqueous Rechargeable Zinc Batteries

Aqueous rechargeable zinc batteries (ARZBs) are recently prevailing devices that utilize the abundant Zn resources and the merits of aqueous electrolytes to become a competitive alternative for large-scale energy storage. Benefiting from the unique inductive effect and flexible structure, the past five years have experienced a diversiform of phosphate-based polyanion materials that are used as cathodes in ARZBs. In this review, the most recent advances in the Zn²⁺ storage mechanisms and electrolyte optimization of the phosphate-based cathodes of ARZBs, which mainly focus on vanadium/iron-based phosphates and their derivatives are presented. Furthermore, in addition to significant progress on polyanion phosphate-based cathode materials, the design strategies both for electrode materials and compatible electrolytes are also elaborated to improve the energy density and extend the cycling life of aqueous Zn/polyanion batteries.     

Tuning Electrochemical Properties of Nitroaromatic Cathodes by Function-Oriented Design for Rechargeable Lithium-Ion Batteries

Rechargeable lithium-ion batteries (LIBs) based on organic cathodes are an attractive alternative energy storage technology owing to the low cost and sustainability. Recently, nitro functionality in dinitrobenzenes is successfully demonstrated as an electrochemically reversible high-capacity redox group. In this study, a function-oriented design is employed to further disclose the effects of substituting functional groups and molecular conjugate structures on electrochemical properties of a range of nitroaromatic derivatives as organic cathodes for rechargeable LIBs. In specific, it is revealed that the redox potential of nitroaromatic cathodes can be effectively adjusted by introducing distinct electronically inducible functional groups, while the cyclic life can be significantly prolonged with the introduction of the hydrophilic groups. When constructed with extended π-conjugated structures, the electronic conductivity and electrochemical kinetics of nitroaromatics are increased significantly owing to their various long-range π–π stacking. Moreover, density-functional theory calculations further provide theoretical insights into the distinct electrochemical behaviors of the various nitroaromatics in the molecular level. This is the first study that reveals the influences of substituting groups and conjugated structures on the electrochemical performance of nitroaromatic cathode materials, which enables a function-oriented molecular design of such organic materials and sheds light on their future development.     

Layered Oxide Cathodes Promoted by Structure Modulation Technology for Sodium‐Ion Batteries

Considering the ever‐growing climatic degeneration, sustainable and renewable energy sources are needed to be effectively integrated into the grid through large‐scale electrochemical energy storage and conversion (EESC) technologies. With regard to their competent benefit in cost and sustainable supply of resource, room‐temperature sodium‐ion batteries (SIBs) have shown great promise in EESC, triumphing over other battery systems on the market. As one of the most fascinating cathode materials due to the simple synthesis process, large specific capacity, and high ionic conductivity, Na‐based layered transition metal oxide cathodes commonly suffer from the sluggish kinetics, multiphase evolution, poor air stability, and insufficient comprehensive performance, restricting their commercialization application. Here, this review summarizes the recent advances in layered oxide cathode materials for SIBs through different optimal structure modulation technologies, with an emphasis placed on strategies to boost Na⁺ kinetics and reduce the irreversible phase transition as well as enhance the store stability. Meanwhile, a thorough and in‐depth systematical investigation of the structure–function–property relationship is also discussed, and the challenges as well as opportunities for practical application electrode materials are sketched. The insights brought forward in this review can be considered as a guide for SIBs in next‐generation EESC.     

Carbonyl‐β‐Cyclodextrin as a Novel Binder for Sulfur Composite Cathodes in Rechargeable Lithium Batteries

As one of the essential components in electrodes, the binder affects the performance of a rechargeable battery. By modifying β‐cyclodextrin (β‐CD), an appropriate binder for sulfur composite cathodes is identified. Through a partial oxidation reaction in H₂O₂ solution, β‐CD is successfully modified to carbonyl‐β‐cyclodextrin (C‐β‐CD), which exhibits a water solubility ca. 100 times that of β‐CD at room temperature. C‐β‐CD possesses the typical properties of an aqueous binder: strong bonding strength, high solubility in water, moderate viscosity, and wide electrochemical windows. Sulfur composite cathodes with C‐β‐CD as the binder demonstrate a high reversible capacity of 694.2 mA h g_(composite)^?1 and 1542.7 mA h g_(sulfur)^?1, with a sulfur utilization approaching 92.2%. The discharge capacity remains at 1456 mA h g_(sulfur)^?1 after 50 cycles, which is much higher than that of the cathode with unmodified β‐CD as binder. Combined with its low cost and environmental benignity, C‐β‐CD is a promising binder for sulfur cathodes in rechargeable lithium batteries with high electrochemical performance.     

Organoboron-Containing Polymer Electrolytes for High-Performance Lithium Batteries

Polymer electrolytes (PEs) have been deemed as a sought-after candidate for next-generation lithium batteries. Substantial effort has been dedicated to exploiting PEs with improved comprehensive performance. Organoboron compounds have aroused great interest in PEs due to their distinct characteristics such as high design diversity, excellent thermal stability, promoting lithium-ion transportation, and raising Li⁺ transference number. Organoboron compounds also have unique functions that facilitate the development of a stable solid electrolyte interface on the electrode surface. Their diversified structures and multiple functions are fundamentally associated with boron's hybridization form that determines the electronic structure of boron as a central atom. Here, recent advancement in organoboron-containing PEs is reviewed in the aspect of polymer matrixes with boron moieties and organoboron additives for PEs. This review aims to highlight the diverse roles and high application potentials of organoboron compounds utilized in PEs. It is anticipated to provide a clear perspective of organoboron-containing PEs and to spur more research interests for the exploration of safe and efficient lithium batteries.     

Progress on the Critical Parameters for Lithium–Sulfur Batteries to be Practically Viable

Lithium–sulfur batteries have great potential to satisfy the increasing demand of energy storage systems for portable devices, electric vehicles, and grid storage because of their extremely high specific capacity, cost‐effectiveness, and environmental friendliness. In spite of all these merits, the practical utilization of lithium–sulfur batteries is impeded by commonly known challenges, such as low sulfur utilization (<80%), short life (<200 cycles), fast capacity fade, and severe self‐discharge effect, which mainly result from the i) low conductivity of the active material, ii) serious polysulfide shuttling, iii) large volume changes, and iv) lithium–metal anode contamination/corrosion. Numerous approaches are reported to effectively mitigate these issues. Indeed, such approaches have shown enhanced lithium–sulfur battery performances. However, many reports overlook the critical parameters, including sulfur loading (<13 mg cm^?2), sulfur content (<70 wt%), and electrolyte/sulfur ratio (>11 µL mg^?1), that significantly affect the analyzed electrochemical characteristics, energy density, and practicality of lithium–sulfur batteries. This review highlights the trends and progress in making cells fulfilling these fabrication parameters and discuss the challenges of the amount of sulfur and electrolyte in fabricating cells with practically necessary parameters and with high electrochemical utilization and efficiency.     

Unveiling the Anionic Redox Chemistry in Phosphate Cathodes for Sodium-Ion Batteries

Anionic redox chemistry has aroused increasing attention in sodium-ion batteries (SIBs) by virtue of the appealing additional capacity. However, up to now, anionic redox reaction has not been reported in the mainstream phosphate cathodes for SIBs. Herein, the ultrathin VOPO₄ nanosheets are fabricated as promising cathodes for SIBs, where the oxygen redox reaction is first activated accompanied by reversible ClO₄⁻ (from the electrolyte) insertion/extraction. As a result, the VOPO₄ cathode harvests a record-high capacity (168 mAh g⁻¹ at 0.1 C) among its counterparts ever reported. Moreover, the ClO₄⁻ insertion efficiently expands the interlayer spacing of VOPO₄ and accelerates the ion diffusion, enabling an unprecedentedly high rate performance (69 mAh g⁻¹ at 30 C). Via systematic ex situ characterizations and theoretical computations, the anionic redox chemistry and charge storage mechanism upon cycling are thoroughly elucidated. This study opens up a new avenue toward high-energy phosphate cathodes for SIBs by triggering anionic redox reactions.     

Novel Insoluble Organic Cathodes for Advanced Organic K‐Ion Batteries

Organic redox‐active molecules are inborn electrodes to store large‐radius potassium (K) ion. High‐performance organic cathodes are important for practical usage of organic potassium‐ion batteries (OPIBs). However, small‐molecule organic cathodes face serious dissolution problems against liquid electrolytes. A novel insoluble small‐molecule organic cathode [N,N′‐bis(2‐anthraquinone)]‐perylene‐3,4,9,10‐tetracarboxydiimide (PTCDI‐DAQ, 200 mAh g^?1) is initially designed for OPIBs. In half cells (1–3.8 V vs K⁺/K) using 1 m KPF₆ in dimethoxyethane (DME), PTCDI‐DAQ delivers a highly stable specific capacity of 216 mAh g^?1 and still holds the value of 133 mAh g^?1 at an ultrahigh current density of 20 A g^?1 (100 C). Using reduced potassium terephthalate (K₄TP) as the organic anode, the resulting K₄TP||PTCDI‐DAQ OPIBs with the electrolyte 1 m KPF₆ in DME realize a high energy density of maximum 295 Wh kg^?1_cathode (213 mAh g^?1_cathode × 1.38 V) and power density of 13 800 W Kg^?1_cathode (94 mAh g^?1 × 1.38 V @ 10 A g^?1) during the working voltage of 0.2–3.2 V. Meanwhile, K₄TP||PTCDI‐DAQ OPIBs fulfill the superlong lifespan with a stable discharge capacity of 62 mAh g^?1_cathode after 10 000 cycles and 40 mAh g^?1_cathode after 30 000 cycles (3 A g^?1). The integrated performance of PTCDI‐DAQ can currently defeat any cathode reported in K‐ion half/full cells.