Highly Improved Cycling Stability of Anion De-/Intercalation in the Graphite Cathode for Dual-Ion Batteries

Constructing a 5.2 V High-Voltage Electrolyte via TMSB Additive Enables Ultrahigh Rate Performance Graphite-Based Dual-Ion Batteries

The development of carbon-based dual-ion batteries (DIBs) is essentially limited by the oxidation decomposition of the electrolyte at high voltage and the unsatisfactory stability of the cathode-electrolyte interface (CEI). Herein, to address these notorious issues, we successfully achieved a high-performance DIB by introducing the Tris(trimethylsiloxy)boron (TMSB) additive. It effectively regulated the solvation structure of the original 2 M LiPF6-solved EMC electrolyte. As a result, it not only weakens the coordination between the PF6- anion and EMC solvent but also suppresses EMC decomposition at the cathode interface. Such regulation facilitates the formation of a stable CEI layer enriched with highly ion-conductive inorganic components. Benefitting from the optimized interfacial kinetics, the graphite cathode delivers exceptional stability and rate capability, achieving 87.86% capacity retention after 2000 cycles at 5.2 V and 84.21% capacity retention at 50 C.

Anion Redistribution in Solvation Structure Enables a Stable Graphite Cathode in Dual-Ion Batteries

The electrochemical properties of anions as carriers in graphite-based dual-ion batteries (GDIBs) play an important role in achieving long cycling stability and high-rate performance. However, anion behavior in the electrolyte was neglected in previous studies. To balance high voltage and fast conduction, the anion behavior after introducing diluent in a highly concentrated electrolyte|high concentrated electrolyte (HCE) to form locally highly concentrated electrolyte|locally high concentrated electrolyte (LHCE) in GDIBs was deeply investigated. In contrast to the highly aggregated coordinated ion pairs in the HCE, more free anions can be attained in the LHCE without significant reunion. These free anions can rapidly migrate to the electrode surface under the electric field drive and then intercalate between graphite layers with a lower energy barrier. Meanwhile, an inorganic-rich interfacial layer with rapid ion conduction and a thinner thickness can be formed to prevent further decomposition of anions and stabilize the structure of the cathode. As a consequence, the dual-graphite DIBs achieved a superior capacity of 98.3% after 1000 cycles at a high rate of 200 mA g-1 in LHCE, and the corresponding pouch cells exhibited a stable cycling process. This work advances the understanding of anion chemistry, enabling the regulation of the anion status to enhance the electrochemical performance of GDIBs.

Transition metal phosphide/ molybdenum disulfide heterostructures towards advanced electrochemical energy storage: recent progress and challenges

Transition metal phosphide @ molybdenum disulfide (TMP@MoS2) heterostructures, consisting of TMP as the core main catalytic body and MoS2 as the outer shell, can solve the three major problems in the field of renewable energy storage and catalysis, such as lack of resources, cost factors, and low cycling stability. The heterostructures synergistically combine the excellent conductivity and electrochemical performance of transition metal phosphides with the structural robustness and catalytic activity of molybdenum disulfide, which holds great promise for clean energy. This review addresses the advantages of TMP@MoS2 materials and their synthesis methods-e.g., hydrothermal routes and chemical vapor deposition regarding scalability and cost. Their electrochemical energy storage and catalytic functions e.g., hydrogen and oxygen evolution reactions (HER and OER) are also extensively explored. Their potential within battery and supercapacitor technologies is also assessed against leading performance metrics. Challenges toward industry-scale scalability, longevity, and environmental sustainability are also addressed, as are optimization and large-scale deployment strategies.

Magnetically-Controlled Graphite Alignment for Fast and Stable Anion Intercalation

Dual-ion batteries (DIBs) are emerging as promising candidates for fast-charging electric vehicles owing to their ability to intercalate both cations and anions. However, increasing the energy density of DIBs, especially with thick graphite cathodes, remains a challenge due to structural instability during anion intercalation. In this study, a magnetically controlled method is introduced to vertically align graphite particles in thick electrodes, significantly improving the performance of DIBs. This novel architecture creates dense, low-tortuosity paths for fast anion transport and structural stability, allowing for high mass loadings exceeding 20 mg cm-2. The vertically aligned graphite cathodes demonstrate a discharge capacity of 1.02 mAh cm-2 at 5 C, retaining 85.6% capacity after 1000 cycles at 1 C, outperforming randomly and horizontally aligned graphite electrodes. Optimized electrodes also exhibit superior structural integrity and reduced formation of cathode electrolyte interphase compared to conventional designs. This study highlights the effectiveness of electrode architectural optimization in enhancing both energy density and fast-charging capabilities, providing a straightforward approach to developing next-generation DIBs with high performance and stability for practical applications in electric vehicles.

PF6 - and Na+ Co-Intercalation in Graphite Cathode of Sodium Dual-Ion Batteries by Enhanced Surface Concentration Effect

Dual-ion batteries are attracting much attention due to the joint participation of anions and cations in the energy storage process. However, this unique battery configuration imposes high demands on the cathode, which typically presents an inferior rate performance. Herein, we employ graphite in different microcrystalline sizes as cathodes, associated with high concentration electrolyte to construct sodium dual-ion batteries. The results of in-situ XRD and Raman evidence that the surface effect is enhanced by suitably small graphite microcrystals, where a greater surface involvement affords more electro-activated regions for the ions. Furthermore, the analysis of sputtering XPS confirms that the PF6 - is accompanied by the co-intercalation of Na+ into cathodes by constructing the model of concentration effect, thus accelerating the kinetic process. In conclusion, the co-intercalation of PF6 - together with Na+ is demonstrated under the influence of enhanced surface concentration effect in cathodes, and thus the cathodes exhibit a superior rate performance with a capacity of 103.6 mAh g-1 at a rate of 2 C and a rate retention of 94.8 % even at 50 C. This work provides new insights to explain the mechanism of ion intercalation in dual-ion batteries and offers a perspective for the construction of high energy storage systems.

Helmholtz Plane Regulation Empowers PF6 - Permselectivity Towards High Coulombic Efficiency Dual Ion Battery of 5.5 V

High-voltage dual ion battery (DIB) is promising for stationary energy storage applications owing to its cost-effectiveness, which has been a hot topic of research in rechargeable battery fields. However, it still suffers from rapid battery failure caused by the severe solvent co-intercalation and electrolyte oxidation. To address these bottlenecks, herein a functional electrolyte additive hexafluoroglutaric anhydride (HFGA) is presented based on a Helmholtz plane regulation strategy. It is demonstrated that the HFGA can precisely enter into the Helmholtz plane and positively regulate anion solvation behaviors near the graphite electrode surface owing to its considerable H-F affinity with ethyl methyl carbonate (EMC), thus alleviating EMC-related co-intercalation and oxidation decomposition during DIB charging. Meanwhile, HFGA can copolymerize with the presence of PF5 at the Helmholtz plane to participate in forming a CF2-rich CEI layer with excellent PF6 - permselectivity, conducive to achieving PF6 - de-solvation and simultaneously suppressing electrolyte oxidation decomposition. By virtue of such beneficial effects, the graphite cathode enables a 5.5 V DIB with a prominent capacity retention of 92 % and a high average Coulombic efficiency exceeding 99 % within 2000 cycles at 5 C, demonstrating significantly enhanced electrochemical reversibility. The Helmholtz plane regulation strategy marks a milestone in advancing DIB technologies.

Molecular Synergistic Effects Mediate Efficient Interfacial Chemistry: Enabling Dendrite-Free Zinc Anode for Aqueous Zinc-Ion Batteries

The primary cause of the accelerated battery failure in aqueous zinc-ion batteries (AZIBs) is the uncontrollable evolution of the zinc metal-electrolyte interface. In the present research on the development of multiadditives to ameliorate interfaces, it is challenging to elucidate the mechanisms of the various components. Additionally, the synergy among additive molecules is frequently disregarded, resulting in the combined efficacy of multiadditives that is unlikely to surpass the sum of each component. In this study, the "molecular synergistic effect" is employed, which is generated by two nonhomologous acid ester (NAE) additives in the double electrical layer microspace. Specifically, ethyl methyl carbonate (EMC) is more inclined to induce the oriented deposition of zinc metal by means of targeted adsorption with the zinc (002) crystal plane. Methyl acetate (MA) is more likely to enter the solvated shell of Zn2+ and will be profoundly reduced to produce SEI that is dominated by organic components under the "molecular synergistic effect" of EMC. Furthermore, MA persists in a spontaneous hydrolysis reaction, which serves to mitigate the pH increase caused by the hydrogen evolution reaction (HER) and further prevents the formation of byproducts. Consequently, the 1E1M electrolyte not only extends the cycle life of the zinc anode to 3140 cycles (1 mA h cm-2 and 1 mA cm-2) but also extends the life of the Zn//MnO2 full battery, with the capacity retention rate still at 89.9% after 700 cycles.

New-Concept Metal-Based Artificial SEI Film of Polyimide Anode Material in Dual-Ion Batteries

Organic material polyimides (PI) are widely used in secondary batteries due to green safety, renewables, and structural designability. However, problems such as low conductivity and structural damage of polyimide electrode materials seriously limit its practical application. Herein, an innovative in situ modification method with CaCl2 is used to construct pure Al metal-based artificial SEI film on the surface of PI to improve the electrochemical performance of organic dual-ion batteries. Compared with the pure PI material, it has a noticeable improvement in cycle performance. Importantly, characterization results of the physicochemical analysis show that the pure Al metal-based artificial SEI film formed in situ on the surface of the PI material plays a key role in isolating and improving the electrochemical performance of PI anode materials. The innovative approach offers an efficacious strategy to construct pure metal-based artificial SEI films for the practical implementation of organic batteries.

Strategies for improving cathode electrolyte interphase in high-performance dual-ion batteries

Dual-ion batteries (DIBs) offer high energy density due to the ability to intercalate both anions and cations, thereby increasing the cutoff voltage and battery capacity. Graphite, with its ordered layered structure and cost-effectiveness, is commonly employed as the cathode material for DIBs. However, the discharge capacity of graphite cathodes is relatively low, and their cycling stability is poor, limiting the practical applications of DIBs. The formation of cathode electrolyte interphase (CEI) on the graphite cathode surface is closely related to anion behavior. Constructing a stable cathode electrolyte interface is crucial for improving the stability of anion storage. Therefore, we introduce a series of strategies to enhance the quality of the CEI layer, including additives, binders, main salts or solvents, high-concentration electrolytes, doping elements, artificial CEI, and graphite surface modifications. These strategies improve the CEI by enhancing anion transport rates, increasing anion solvation capabilities, and improving the structural stability of graphite cathodes, which is of profound significance for increasing the capacity and stability of DIBs. This review provides inspiration for future CEI research, encouraging further exploration of resources of CEI components and improvement strategies to further promote the development of DIBs technology.

Realized Record Capacity and Rate Performance of Dual-Carbon Batteries Constructed by Introducing Superhard Nanodiamonds

Dual-ion batteries (DIBs) are becoming an important technology for energy storage. To overcome the disadvantages of traditional electrodes and electrolytes, here we assemble a dual-carbon DIB with nanodiamond (ND)-modified crimped graphene (DCG) and electrolyte. The DCG anode and cathode realize high capacities of 1121 mA h g-1 and 149 mA h g-1, respectively, at 0.1 A g-1. The corresponding DCG//DCG full cells present a high capacity of 143 mA h g-1 at 1 A g-1 after 3300 cycles, which is superior to most reported results. Achieving these record performances is strongly dependent on the formed DCG electrodes with expanded interlayer spacing and abundant active sites, and NDs dispersed in DCG and electrolytes are very helpful for enhancing the storage of both cations and anions, effectively suppressing the irreversible decomposition of electrolytes. This work breaks through the bottleneck of graphitic-based DIBs, paving the way for realizing high-performance DIBs applied in industry.

2D Exfoliation Chemistry Towards Covalent Pseudo-Layered Phosphate Framework Derived by Radical/Strain-Synergistical Process

2D compounds exfoliated from weakly bonded bulk materials with van der Waals (vdW) interaction are easily accessible. However, the strong internal ionic/covalent bonding of most inorganic crystal frameworks greatly hinders 2D material exfoliation. Herein, we first proposed a radical/strain-synergistic strategy to exfoliate non-vdW interacting pseudo-layered phosphate framework. Specifically, hydroxyl radicals (⋅OH) distort the covalent bond irreversibly, meanwhile, H2O molecules as solvents, further accelerating interlayered ionic bond breakage but mechanical expansion. The innovative 2D laminar NASICON-type Na3V2(PO4)2O2F crystal, exfoliated by ⋅OH/H2O synergistic strategy, exhibits enhanced sodium-ion storage capacity, high-rate performance (85.7 mAh g-1 at 20 C), cyclic life (2300 cycles), and ion migration rates, compared with the bulk framework. Importantly, this chemical/physical dual driving technique realized the effective exfoliation for strongly coupled pseudo-layered frameworks, which accelerates 2D functional material development.

Defect engineering unveiled: Enhancing potassium storage in expanded graphite anode

Expanded graphite (EG) stands out as a promising material for the negative electrode in potassium-ion batteries. However, its full potential is hindered by the limited diffusion pathway and storage sites for potassium ions, restricting the improvement of its electrochemical performance. To overcome this challenge, defect engineering emerges as a highly effective strategy to enhance the adsorption and reaction kinetics of potassium ions on electrode materials. This study delves into the specific effectiveness of defects in facilitating potassium storage, exploring the impact of defect-rich structures on dynamic processes. Employing ball milling, we introduce surface defects in EG, uncovering unique effects on its electrochemical behavior. These defects exhibit a remarkable ability to adsorb a significant quantity of potassium ions, facilitating the subsequent intercalation of potassium ions into the graphite structure. Consequently, this process leads to a higher potassium voltage. Furthermore, the generation of a diluted stage compound is more pronounced under high voltage conditions, promoting the progression of multiple stage reactions. Consequently, the EG sample post-ball milling demonstrates a notable capacity of 286.2 mAh g-1 at a current density of 25 mA g-1, showcasing an outstanding rate capability that surpasses that of pristine EG. This research not only highlights the efficacy of defect engineering in carbon materials but also provides unique insights into the specific manifestations of defects on dynamic processes, contributing to the advancement of potassium-ion battery technology.

Crucial Roles of Ethyl Methyl Carbonate in Lithium-Ion and Dual-Ion Batteries: A Review

The essential role of electrolyte solutions in traditional electrochemical energy storage devices is crucial to enhancing their performance. Consequently, a wide array of electrolyte mixtures along with diverse electrodes have been extensively explored across different models of secondary batteries. Fascinatingly, the role of ethyl methyl carbonate (EMC) as a key cosolvent in the electrolyte mixture of commercial lithium-ion batteries with a graphite anode is garnering growing attention in alternative rechargeable dual-ion batteries utilizing graphite cathodes. In this context, the advancement and function of EMC as a solvent in electrolyte mixtures for lithium-ion and dual-ion batteries were extensively and thoroughly examined in this analysis, encompassing the genesis, synthesis process, and diverse characteristics for the practical uses of these batteries. Here, the review aims to guide readers in understanding EMC's function and impact as a cosolvent in electrolyte mixtures for both major secondary lithium-ion and dual-ion batteries, considering their distinct physicochemical characteristics.

A comprehensive review of various carbonaceous materials for anodes in lithium-ion batteries

With the advent of lithium-ion batteries (LIBs), the selection and application of electrode materials have been the subject of much discussion and study. Among them, graphite has been widely investigated for use as electrode materials in LIBs due to its abundant resources, low cost, safety and electrochemical diversity. While it is commonly recognized that conventional graphite materials utilized for commercial purposes have a limited theoretical capacity, there has been a steady emergence of new and improved carbonaceous materials for use as anodes in light of the progressive development of LIBs. In this paper, the latest research progress of various carbon materials in LIBs is systematically and comprehensively reviewed. Firstly, the rocking chair charging and discharging mechanism of LIBs is briefly introduced in this paper, using graphite anodes as an example. After that, the general categories of carbonaceous materials are highlighted, and the recent research on the recent progress of various carbonaceous materials (graphite-based, amorphous carbon-based, and nanocarbon-based) used in LIB anodes is presented separately based on the classification of the structural morphology, emphasizing the influence of the morphology and structure of carbon-based materials on the electrochemical performance of the batteries. Finally, the current challenges of carbonaceous materials in LIB applications and the future development of other novel carbonaceous materials are envisioned.

Surface Decoration of TiC Nanocrystals onto the Graphite Anode Enables Fast-Charging Lithium-Ion Batteries

To significantly reduce the charging time of commercial lithium-ion batteries (LIBs), it is essential to control the surface properties of graphite anodes because the charging process involves sluggish interfacial kinetics between graphite and the electrolyte. For the effective surface modification of graphite, herein we demonstrate the surface decoration with titanium carbide (TiC) nanocrystals onto graphite particles via a simple wet-coating process. The high electrical conductivity, low Li+ adsorption energy, and small surface diffusion barrier of the TiC nanocrystals facilitate fast Li+ adsorption and migration in the graphite surface by reducing the overpotential upon the charging process. The feasibility of the TiC nanocrystal-decorated graphite (TiC@AG) anode is thoroughly examined with an in-depth understanding of the interfacial reaction mechanism. Furthermore, the full-cell with a commercial cathode (LiNi0.8Co0.1Mn0.1O2) and TiC@AG anode demonstrates an impressive capacity retention (94.5%) after 300 cycles under fast-charging condition (3 C-charging and 1 C-discharging) without any sign of Li plating. The charging time of the TiC@AG full-cell was estimated at 16.2 min (80% of state of charge), which is substantially shorter than that of the artificial graphite full-cell. Our findings offer practical insights into the design principles of advanced graphite anodes, contributing to the realization of fast-charging LIBs.

Non-aqueous Liquid Electrolyte Additives for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have been recognized as one of the most promising new energy storage devices for their rich sodium resources, low cost and high safety. The electrolyte, as a bridge connecting the cathode and anode electrodes, plays a vital role in determining the performance of SIBs, such as coulombic efficiency, energy density and cycle life. Therefore, the overall performance of SIBs could be significantly improved by adjusting the electrolyte composition or adding a small number of functional additives. In this review, the fundamentals of SIB electrolytes including electrode-electrolyte interface and solvation structure are introduced. Then, the mechanisms of electrolyte additive action on SIBs are discussed, with a focus on film-forming additives, flame-retardant additives and overcharge protection additives. Finally, the future research of electrolytes is prospected from the perspective of scientific concepts and practical applications.

Porous organic polymers-based fluorescent chemosensors for Fe(III) ions-a functional mimic of siderophores

Extended organic polymers such as amorphous Covalent Organic Polymers (COPs) and crystalline Covalent Organic Frameworks (COFs) are emerging functional polymeric materials that have recently been shown promises as luminescent materials for chemosensing applications. A wide variety of luminescence COPs and COFs have been synthesized and successfully used as fluorescence-sensing materials for hazardous environmental pollutants and toxic contaminants. This review exemplifies various COPs and COFs-based fluorescence sensors for selective sensing of Fe(III) ions. The fluorescence sensors are sorted according to their structural features and each section provides a detailed discussion on the synthesis and fluorescence sensing ability of different COPs and COFs towards Fe(III) ions. Also, this review highlights the limitations of the existing organic polymer-based chemosensors and future perspectives on translating COPs and COFs-based fluorescence sensors for the practical detection of Fe(III) ions.

Azacyclic Anchor-Enabled Cohesive Graphite Electrodes for Sustainable Anion Storage

Advanced energy-storage devices are indispensable for expanding electric mobility applications. While anion intercalation-type redox chemistry in graphite cathodes has opened the path to high-energy-density batteries, surpassing the limited energy density of conventional lithium-ion batteries , a significant challenge remains: the large volume expansion of graphite upon anion intercalation. In this study, a novel polymeric binder and cohesive graphite cathode design for dual-ion batteries (DIBs) is presented, which exhibits remarkable stability even under high voltage conditions (>5 V). The innovative binder incorporates an acrylate moiety ensuring superior oxidative stability and self-healing features, along with an azide moiety, which allows for azacyclic covalent bonding with graphite and interchain crosslinking. A simple 1-h ultraviolet treatment is sufficient for binder fixation within the electrode, leading to the covalent bond formation with graphite and the creation of a robust three-dimensional network. This modification facilitates deeper and more reversible anion intercalation, leading to improved capacity, extended lifespan, and sustainable anion storage. The binder design, exhibiting exceptional adhesive properties and effective stress mitigation, enables the construction of ultrathick graphite cathodes. These findings provide valuable insights for the development of advanced binders, paving the way for high-performance DIBs.

Significant Strain Dissipation via Stiff-Tough Solid Electrolyte Interphase Design for Highly Stable Alloying Anodes

The pulverization of alloying anodes significantly restricts their use in lithium-ion batteries (LIBs). This study presents a dual-phase solid electrolyte interphase (SEI) design that incorporates finely dispersed Al nanoparticles within the LiPON matrix. This distinctive dual-phase structure imparts high stiffness and toughness to the integrated SEI film. In comparison to single-phase LiPON film, the optimized Al/LiPON dual-phase SEI film demonstrates a remarkable increase in fracture toughness by 317.8 %, while maintaining stiffness, achieved through the substantial dissipation of strain energy. Application of the dual-phase SEI film on an Al anode leads to a 450 % enhancement in cycling stability for lithium storage in dual-ion batteries. A similar enhancement in cycling stability for silicon anodes, which face severe volume expansion issues, is also observed, demonstrating the broad applicability of the dual-phase SEI design. Specifically, homogeneous Li-Al alloying has been observed in conventional LIBs, even when paired with a high mass loading LiNi0.5 Co0.3 Mn0.2 O2 cathode (7 mg cm-2 ). The dual-phase SEI film design can also accelerate the diffusion kinetics of Li-ions through interface electronic structure regulation. This dual-phase design can integrate stiffness and toughness into a single SEI film, providing a pathway to enhance both the structural stability and rate capability of alloying anodes.

Cycling-Induced Capacity Increase of Bulk and Artificially Layered LiTaO3 Anodes in Lithium-Ion Batteries

Tantalum-based oxide electrodes have recently drawn much attention as promising anode materials owing to their hybrid Li+ storage mechanism. However, the utilization of LiTaO3 electrode materials that can deliver a high theoretical capacity of 568 mAh g-1 has been neglected. Herein, we prepare a layered LiTaO3 electrode formed artificially by restacking LiTaO3 nanosheets using a facile synthesis method and investigate the Li+ storage performance of this electrode compared with its bulk counterpart. The designed artificially layered anode reaches specific capacities of 474, 290, and 201 mAh g-1, respectively, at 56 (>500 cycles), 280 (>1000 cycles), and 1120 mAg-1 (>2000 cycles) current densities. We also determine that the Li+ storage capacity of the layered LiTaO3 demonstrates a cycling-induced capacity increase after a certain number of cycles. Adopting various characterization techniques on LiTaO3 electrodes before and after electrochemical cycling, we attribute the origin of the cycling-induced improvement of the Li+ storage capacity in these electrodes to the amorphization of the electrode after cycling, formation of metallic tantalum during the partially irreversible conversion mechanism, lower activation overpotential of electrodes due to the formation of Li-rich species by the lithium insertion mechanism, and finally the intrinsic piezoelectric behavior of LiTaO3 that can regulate Li+ diffusion kinetics.

High-performance expanded graphite regenerated from spent lithium-ion batteries by integrated oxidation and purification method

Currently, the recycling of spent lithium-ion batteries (LIBs) has mainly been focused on the extraction of precious metals, such as lithium, cobalt and nickel from cathodes, while the waste graphite anode has been overlooked due to its low-cost production and abundant resources reserve. However, there are enormous potential value and pollution risk in the view of graphite recycling. Thus, we propose an original method to prepare expanded graphite (EG) as new anode material generated from waste graphite in LIBs which integrates the oxidation and purification in one-step. By regulating the oxidizability of potassium hypermanganate in the sulfur-phosphorus mixed acid system, the expansion of graphite and removal of impurities are realized simultaneously and thoroughly. As anticipated, the shortening of preparation process and purification procedure can also reduce the generation of polluting substances and production cost. It displays excellent electrochemical performance (reversible capacity of 435.8 mAh·g-1 at 0.1C and long-term cycling property of 370 mAh·g-1 at 1C after 1000 cycles), which is even higher than that of pristine commercial graphite. This delicate strategy of high-performance expanded graphite recycling achieves the integration of purification and value-added processes, providing the instructive guide to regenerate industrial-grade anode materials for the increasing LIBs demand in the future.

Soft Carbon as Cathode with High Rate Performance for Dual-Ion Batteries via Fast PF6 - Intercalation Improved by Surface Effect

Dual-ion battery is a new type of battery in which both anions and cations participate in the energy storage process. However, this unique battery configuration imposes high requirements on the cathode, which typically presents a poor rate performance due to the sluggish diffusion dynamics and intercalation reaction kinetics of anions. Herein, we report petroleum coke-based soft carbon as the cathode for dual-ion batteries, exhibiting a superior rate performance with a specific capacity of 96 mAh g-1 at a rate of 2 C and 72 mAh g-1 remained even at 50 C. In situ XRD and Raman demonstrate that the anions can directly form lower-stage graphite intercalation compounds during the charge process owing to the surface effect, skipping the long evolutionary process from higher to lower stage, thus significantly improving the rate performance. This study highlights the impact of the surface effect and provides a promising perspective for dual-ion batteries.

Hybridizing Tetraglyme to Aqueous Electrolyte with Concentrated Salts Promote Intercalation of Anions on Graphite Cathode in Dual-Ion Battery

The amount of support salt in electrolytes determines the capacity of a dual-ion battery (DIB), and highly concentrated electrolytes are required for developing the high energy density DIB. In this study, hybrid aqueous tetraglyme (G4) electrolyte is investigated to develop high energy density aqueous DIB that is composed of carbon and Mo6 S8 for cathode and anode, respectively. Impedance measurement reveals that introduced G4 increases the activation energy of the anode; however, decreases the activation energy for anion intercalation into the carbon cathode. This decreases the activation energy resulted from the G4 molecule strongly solvated to Li+ resulting in weakening anion trapped in "contact ion pair" in concentrated aqueous electrolyte. So, hybrid G4-aqueous electrolyte is useful for better electrochemical intercalation of anion. In addition, this hybrid electrolyte is highly stable by formation of stable solid electrode-electrolyte interphase on Mo6 S8 anode and discharge capacity of 37 mAh g-1 , and 72% retained capacity after 500 cycles with a high average coulombic efficiency of 93% is achieved.

Titanium Doping Induced the Suppression of Irreversible Phase Transformation at High Voltage for V-based Phosphate Cathodes of Na-Ion Batteries

Polyanionic material, specifically the NASICON-type material, is considered a promising cathode material for Na-ion batteries (SIBs) because of its stable structure and high operating voltage. Further, it improves the energy density correlated with the well utilization of all Na in the compound. For Na3 V2 (PO4 )2 F3 (NVPF), the extraction of the third Na, reported as the electrochemical inactivated, can be realized at a high voltage region while forming an irreversible tetragonal phase. In this study, we introduce Ti doping to the Na2 VTi(PO4 )2 F3 (NVTPF) material; we reveal that the Ti-doped NVTPF could effectively suppress the irreversible phase transformation, thus successfully harnessing Na in a wide voltage range. Experimental study discloses that the Ti-substituted Na2 VTi(PO4 )2 F3 could take up the Na+ from Amam phase to Cmc21 phase between 1.0 V and 4.8 V reversibly accounting for the 2 Na+ transportation that shows favorable Na+ kinetics and structural stability. Our research provides the strategy to stabilize the polyanion structure upon charging at a high voltage range and inspires the utilization of full sodium in the polyanionic materials, which could be considered as a material design for future conventional applications.

Solvation Structure Modulation of High-Voltage Electrolyte for High-Performance K-Based Dual-Graphite Battery

Due to the advantages of dual-ion batteries (DIBs) and abundant resources, potassium-based dual-carbon batteries (K-DCBs) have wide application prospects. However, conventional carbonate ester-based electrolyte systems have obvious drawbacks such as poor oxidation resistance and difficulty in sustaining the anion intercalation process at high voltages, which seriously affect the capacity and cycle performance of K-DCBs. Therefore, a rational design of more efficient novel electrolyte systems is urgently required to realize high-performance K-DCBs. Herein, a solvation structure modulation strategy for the K-DCB electrolyte systems is reported. Consequently, substantial K⁺ ion storage improvement at the graphite anode and enhanced bis(fluorosulfonyl)imide anion (FSI^- ) intercalation capacity at the graphite cathode are successfully realized simultaneously. As a proof-of-concept, the assembled K-DCB exhibited a discharge capacity of 103.4 mAh g^-1 , and after 400 cycles, ≈90% capacity retention is observed. Moreover, the energy density of the K-DCB full cell reached 157.6 Wh kg^-1 , which is the best performance in reported K-DCBs till date. This study demonstrates the effectiveness of solvation modulation in improving the performance of K-DCBs.

Fundamental Understanding and Optimization Strategies for Dual-Ion Batteries: A Review

There has been increasing demand for high-energy density and long-cycle life rechargeable batteries to satisfy the ever-growing requirements for next-generation energy storage systems. Among all available candidates, dual-ion batteries (DIBs) have drawn tremendous attention in the past few years from both academic and industrial battery communities because of their fascinating advantages of high working voltage, excellent safety, and environmental friendliness. However, the dynamic imbalance between the electrodes and the mismatch of traditional electrolyte systems remain elusive. To fully employ the advantages of DIBs, the overall optimization of anode materials, cathode materials, and compatible electrolyte systems is urgently needed. Here, we review the development history and the reaction mechanisms involved in DIBs. Afterward, the optimization strategies toward DIB materials and electrolytes are highlighted. In addition, their energy-related applications are also provided. Lastly, the research challenges and possible development directions of DIBs are outlined.

Electrochemistry-Driven Interphase Doubly Protects Graphite Cathodes for Ultralong Life and Fast Charge of Dual-Ion Batteries

Dual-ion batteries (DIBs) with graphite as cathode material, show superiority in terms of sustainability, affordability, and environmental impact over Li-ion batteries that rely on transition-metal based cathodes. However, graphite cathodes severely suffer from poor structural stability during anion storage at high potentials because of the co-intercalation and oxidative decomposition of electrolytes. This work presents an in situ electrochemistry-driven route to create a bifunctional interphase through implantation of diethylenetriaminepenta(methylene-phosphonic acid) (DTPMP) on the surface of graphite particles. The reaction mechanisms and functions of DTPMP are investigated both experimentally and theoretically. The DTPMP-derived interphase not only improves the antioxidative stability of electrolytes but also benefits the desolvation of PF₆ ^- anions, which doubly protect the graphitic structure and give rise to fast-charge and ultralong cycling performance of graphite cathodes in DIBs.

Ultrafast Charge and Long Life of High-Voltage Cathodes for Dual-Ion Batteries via a Bifunctional Interphase Nanolayer on Graphite Particles

Dual-ion batteries (DIBs) with Co/Ni-free cathodes especially graphite cathodes are very attractive energy storage systems in the long run because of the cost effectiveness and sustainability. However, graphite cathodes severely suffer from poor structural stability during anions storage at high potentials owing to the oxidative decomposition of electrolytes and volume expansion. This work proposes an artificial cathode/electrolyte interphase (CEI) strategy by implanting polyphosphoric acid (PPA) nanofilms tightly on natural graphite (NG) particles via interfacial hydrogen bonding. The electrochemical results show that the PPA-modified graphite cathodes possess enhanced charge-discharge reversibility, accelerated electrode reaction kinetic, decreased resistance, decelerated self-discharge, and prolonged cycling life. Through post-analyses on the cycled graphite cathodes, the improved performance is mainly attributed to the PPA-based CEI, which effectively mitigates the electrolyte decomposition and protects the graphitic structure. More interestingly, the hydrogen bonding interactions between poly(vinyldifluoride) (PVDF) binder and PPA as validated through density functional theory calculations and practical experiments can increase the contact sites of PVDF chains on NG@PPA particles. Meanwhile, the cross-linking effect of PPA can enhance the mechanical strength of PVDF, thus the long life of NG@PPA cathode is also correlated with the improved mechanical stability of the entire electrode.

Spreading the Landscape of Dual Ion Batteries: from Electrode to Electrolyte

The working mechanism of a dual-ion battery (DIB) differs from that of a lithium-ion battery (LIB) in that the anions in the electrolyte of the former can be intercalated as well. Researchers have been paying close attention to this device because of its high voltage, low price, and environmental friendliness. However, DIBs are still in their early research stages, and numerous issues need to be addressed and investigated further. Initially, this Review explains how DIBs work in principle and discusses the progress of electrode materials for cathode and anode. Furthermore, since the electrolytes used as the active material, as well as anion, solvent, and additives, have a significant impact on the DIB's capacity and voltage, the current status is also presented in terms of electrolytes, followed by an outlook on confronting the challenges. A comprehensive summary from electrode to electrolyte will guide the development of next-generation DIBs.

An Integrated Design of Electrodes for Flexible Dual-Ion Batteries

Due to the widespread employment of carbon materials in novel dual-ion batteries (DIBs) with high energy density, they possess the potential for large-scale energy storage and are inexpensive and environmentally friendly. However, drawbacks such as Al current collector corrosion and significant self-weight, as well as lithium metal abuse and poor deposition reversibility, impair the energy density and cycle performance of lithium-graphite DIBs (Li-G DIBs), severely limiting their application potential. Therefore, an integrated electrode structure design was proposed. That is, the flexible graphite and single-walled carbon nanotubes (SWCNTs) composite cathode (GSC), which is light-weight and self-supporting, and the self-supporting lithium metal anode, which is loaded on the flexible carbon cloth (CC) derived from waste mask (Li@CC), were prepared. Not only were the impacts of current collector corrosion and active material exfoliation avoided on the electrochemical performance, but the areal loading of Li metal was also regulated and its reversibility of deposition enhanced. At a current density of 200 mA g^-1 , the constructed Li@CC//GSC full cell could release a specific capacity of 100.5 mAh g^-1 , and the capacity retention rate after 300 cycles was greater than 80 %. Moreover, the fabricated flexible Li@CC//GSC full cell is not only recyclable and produces less environmental pollution but also has potential applications in wearable devices.

Ultrathin positively charged electrode skin for durable anion-intercalation battery chemistries

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF₆^--intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries.

Multiscale Polymeric Materials for Advanced Lithium Battery Applications

Riding on the rapid growth in electric vehicles and the stationary energy storage market, high-energy-density lithium-ion batteries and next-generation rechargeable batteries (i.e., advanced batteries) have been long-accepted as essential building blocks for future technology reaching the specific energy density of 400 Wh kg^-1 at the cell-level. Such progress, mainly driven by the emerging electrode materials or electrolytes, necessitates the development of polymeric materials with advanced functionalities in the battery to address new challenges. Therefore, it is urgently required to understand the basic chemistry and essential research directions in polymeric materials and establish a library for the polymeric materials that enables the development of advanced batteries. Herein, based on indispensable polymeric materials in advanced high-energy-density lithium-ion, lithium-sulfur, lithium-metal, and dual-ion battery chemistry, the key research directions of polymeric materials for achieving high-energy-density and safety are summarized and design strategies for further improving performance are examined. Furthermore, the challenges of polymeric materials for advanced battery technologies are discussed.

Room Temperature Halide-Eutectic Solid Electrolytes with Viscous Feature and Ultrahigh Ionic Conductivity

A viscous feature is beneficial for a solid electrolyte with respect to assembling solid-state batteries, which can change the solid-solid contacts from point to face. Here, novel halide-based deep eutectic solid electrolytes (DESEs) prepared by a facile ball milling method is reported. The mixture of halides triggers the deep eutectic phenomena by intermolecular interactions, leading to diverse morphologies and viscous statuses in terms of composition. Chemical- and micro-structure analyses via the cryogenic technique reveal that the LiCl and LiF nanoparticles are dispersed in an amorphous halide matrix, which endow freely mobile ions for fast ion transport. The optimized DESE thus achieves low activation energy and high ionic conductivity of 16 mS cm^-1 at room temperature, one of the highest values among various electrolytes so far. By integrating with the active materials to form a composite cathode, the viscous DESE yields a super-dense composite pellet which possesses intensively enhanced ionic conductivity in contrast to those formed by the sulfide-based electrolyte additives, demonstrating an attractive application prospect.

A montmorillonite-modification strategy enabling long cycling stability of dual-ion batteries

Lithium‖graphite dual-ion batteries (DIBs) have received widespread attention due to their low cost and high operating voltage (nearly 5 V). However, DIBs face several challenges such as decomposition of the electrolyte under high voltage and structural deterioration of graphite. Herein, montmorillonite (MMT) is employed to generate a favorable and robust cathode electrolyte interface (CEI) layer on the graphite surface. As a result, the DIBs exhibit a 100% capacity retention for 500 cycles at 2C. Even after 1000 cycles at 5C, the capacity retention is still as high as 99%.

Flat-Zigzag Interface Design of Chalcogenide Heterostructure toward Ultralow Volume Expansion for High-Performance Potassium Storage

Heterostructure construction of layered metal chalcogenides can boost their alkali-metal storage performance, where the charge transfer kinetics can be promoted by the built-in electric fields. However, these heterostructures usually undergo interface separation due to severe layer expansion, especially for large-size potassium accommodation, resulting in the deconstruction of heterostructures and battery performance fading. Herein, first a stable interface design strategy where two metal chalcogenides with totally different layer-morphologies are stacked to form large K⁺ transport channels, rendering ultralow interlayer expansion, is presented. As a proof of concept, the flat-zigzag MoS₂ /Bi₂ S₃ heterostructures stacked with zigzag-morphology Bi₂ S₃ and flat-morphology MoS₂ present an ultralow expansion ratio (1.98%) versus MoS₂ (9.66%) and Bi₂ S₃ (9.61%), which deliver an ultrahigh potassium storage capacity of above 600 mAh g^-1 and capacity retention of 76% after 500 cycles, together with the built-in electric field of heterostructures. Once the heterostructures are used as an anode for potassium-based dual-ion batteries (K-DIBs), it achieves a superior full-cell capacity of ≈166 mAh g^-1 with a capacity retention of 71% after 400 cycles, which is an outstanding performance among the reported K-DIBs. This proposed interface stacking strategy may offer a new way toward stable heterostructure design for metal ions storage and transport applications.

Mesocarbon Microbeads Boost the Electrochemical Performances of LiFePO4 ||Li4 Ti5 O12 through Anion Intercalation

Li-ion batteries with LiFePO₄ cathode and Li₄ Ti₅ O₁₂ anode show promise for storing renewable energy. However, their low output voltage results in a low energy density. In contrast, dual-ion batteries with graphite cathode and Li₄ Ti₅ O₁₂ anode can achieve a high output voltage of >3.0 V. In this study, mesocarbon microbeads (MCMB)@LiFePO₄ ||Li₄ Ti₅ O₁₂ dual-ion batteries are developed to address these issues. In the cathode, MCMB improves the conductivity of LiFePO₄ and increases the output voltage by the intercalation of anions in the cell voltage range of 2.1-3.5 V. Moreover, the LiFePO₄ shell sustains the structural integrity of MCMB and generates in situ a cathode-electrolyte interphase (CEI) with rich LiF. Owing to these unique compositional and structural features, MCMB@LiFePO₄ ||Li₄ Ti₅ O₁₂ manifests much better electrochemical performance than LiFePO₄ ||Li₄ Ti₅ O₁₂ and MCMB||Li₄ Ti₅ O₁₂ . It sustains 89.6 % of the initial capacity after 1200 cycles at 0.2 A g^-1 and achieves a specific energy up to 128 Wh kg^-1 at 179 W kg^-1 .

An Advanced High-Entropy Fluorophosphate Cathode for Sodium-Ion Batteries with Increased Working Voltage and Energy Density

Impossible voltage plateau regulation for the cathode materials with fixed active elemental center is a pressing issue hindering the development of Na-superionic-conductor (NASICON)-type Na₃ V₂ (PO₄ )₂ F₃ (NVPF) cathodes in sodium-ion batteries (SIBs). Herein, a high-entropy substitution strategy, to alter the detailed crystal structure of NVPF without changing the central active V atom, is pioneeringly utilized, achieving simultaneous electronic conductivity enhancement and diffusion barrier reduction for Na⁺ , according to theoretical calculations. The as-prepared carbon-free high-entropy Na₃ V_1.9 (Ca,Mg,Al,Cr,Mn)_0.1 (PO₄ )₂ F₃ (HE-NVPF) cathode can deliver higher mean voltage of 3.81 V and more advantageous energy density up to 445.5 Wh kg^-1 , which is attributed by the diverse transition-metal elemental substitution in high-entropy crystalline. More importantly, high-entropy introduction can help realize disordered rearrangement of Na⁺ at Na(2) active sites, thereby to refrain from unfavorable discharging behaviors at low-voltage region, further lifting up the mean working voltage to realize a full Na-ion storage at the high voltage plateau. Coupling with a hard carbon (HC) anode, HE-NVPF//HC SIB full cells can deliver high specific energy density of 326.8 Wh kg^-1 at 5 C with the power density of 2178.9 W kg^-1 . This route means the unlikely potential regulation in NASICON-type crystal with unchangeable active center becomes possible, inspiring new ideas on elevating the mean working voltage for SIB cathodes.

Concentrated Electrolyte for High-Performance Ca-Ion Battery Based on Organic Anode and Graphite Cathode

Due to the large abundance, low redox potential, and multivalent properties of calcium (Ca), Ca-ion batteries (CIBs) show promising prospects for energy storage applications. However, current research on CIBs faces the challenges of unsatisfactory cycling stability and capacity, mainly restricted by the lack of suitable electrolytes and electrode materials. Herein, we firstly developed a 3.5 m concentrated electrolyte with a calcium bis(fluorosulfonyl)imide (Ca(FSI)₂ ) salt dissolved in carbonate solvents. This electrolyte significantly improved the intercalation capacity for anions in the graphite cathode and contributed to the reversible insertion of Ca²⁺ in the organic anode. By combining this concentrated electrolyte with the low-cost and environmentally friendly graphite cathode and organic anode, the assembled Ca-based dual-ion battery (Ca-DIB) exhibits 75.4 mAh g^-1 specific discharge capacity at 100 mA g^-1 and 84.7 % capacity retention over 350 cycles, among the best results known for CIBs.

High-Performance Dual-Ion Battery Based on a Layered Tin Disulfide Anode

Energy issues have attracted great concern worldwide. Developing new energy has been the main choice, and the exploitation of the electrochemical energy storage devices plays an important role. Herein, a high-performance dual-ion battery system is proposed, which consists of a graphite cathode and SnS₂ anode, with a high-concentration lithium salt electrolyte (4 M LiTFSI). The benefits from the typical sandwich-like layer structure of SnS₂ are as follows: the highest discharge specific capacity of the battery could reach 130.0 mA h g^-1 at a current density of 100 mA g^-1, and even under an ultra-high current density of 2000 mA g^-1, the highest capacity of 66.3 mA h g^-1 is still achieved, with an outstanding capacity retention over 100% after 1000 cycles. Inspiringly, this system delivers an excellent low self-discharge of 1.19%/h, surpassing most of the reported dual-ion batteries. In addition, the working mechanism and structural stability are also investigated by X-ray diffraction and Raman spectra, indicating a good reversibility. These results reveal that this graphite/SnS₂ dual-ion battery system could provide a promising alternative for a future high-performance energy storage device.

A PF6 - -Permselective Polymer Electrolyte with Anion Solvation Regulation Enabling Long-Cycle Dual-Ion Battery

Graphitic carbon that allows reversible anion (de)intercalation is a promising cathode material for cost-efficient and high-voltage dual-ion batteries (DIBs). However, one notorious but overlooked issue is the incomplete interfacial anion desolvation, which not only reduces the oxidative stability of electrolytes, but also results in solvent co-intercalation into graphite layers. Here, an "anion-permselective" polymer electrolyte with abundant cationic quaternary ammonium motif is developed to weaken the PF₆ ^- -solvent interaction and thus facilitates PF₆ ^- desolvation. This strategy significantly inhibits solvent co-intercalation as well as enhances the oxidation resistance of electrolyte, ensuring the structural integrity of graphite. As a result, the as-assembled graphite||Li cell achieves a superior cyclability with an average Coulombic efficiency of 99.0% (vs 95.7% for baseline electrolyte) and 87.1% capacity retention after 2000 cycles even at a high cutoff potential of 5.4 V versus Li⁺ /Li. Besides, this polymer also forms a robust cathode electrolyte interface, working together to enable a long-life DIB. This strategy of tuning anion coordination environment provides a promising solution to regulate solvent co-intercalation chemistry for DIBs.

A dual conducting network corbelled hydrated vanadium pentoxide cathode for high-rate aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) are widely recognized for their excellent safety and high theoretical capacity but are hindered by the scarcity of cathode materials with high-rate performance and stability. Herein, a dual conducting network corbelled hydrated vanadium pentoxide that involves structural water as a pillar to enlarge the layer spacing of vanadium pentoxide and ensure cycling stability was reported. Along with the proton co-insertion, the hydrated vanadium pentoxide delivers nearly theoretical specific capacities of 524.6 mA h g^-1 at 0.3 A g^-1 and 258.7 mA h g^-1 at 10 A g^-1, which was largely due to non-faradaic contribution, and retains 196.8 mA h g^-1 at 4.8 A g^-1 after 1100 cycles. Notably, a high energy density of 409.3 W h kg^-1 at 0.3 A g^-1 and a power density of 6666.4 W kg^-1 at 10 A g^-1 have also been achieved. The design strategy offers a potential path to develop high-rate ZIBs.

A synergistic exploitation to produce high-voltage quasi-solid-state lithium metal batteries

The current Li-based battery technology is limited in terms of energy contents. Therefore, several approaches are considered to improve the energy density of these energy storage devices. Here, we report the combination of a heteroatom-based gel polymer electrolyte with a hybrid cathode comprising of a Li-rich oxide active material and graphite conductive agent to produce a high-energy "shuttle-relay" Li metal battery, where additional capacity is generated from the electrolyte's anion shuttling at high voltages. The gel polymer electrolyte, prepared via in situ polymerization in an all-fluorinated electrolyte, shows adequate ionic conductivity (around 2 mS cm^-1 at 25 °C), oxidation stability (up to 5.5 V vs Li/Li⁺), compatibility with Li metal and safety aspects (i.e., non-flammability). The polymeric electrolyte allows for a reversible insertion of hexafluorophosphate anions into the conductive graphite (i.e., dual-ion mechanism) after the removal of Li ions from Li-rich oxide (i.e., rocking-chair mechanism).