Pre-Activated Cascade Redox Enables High-Voltage Multi-Electron Anion Storage in Graphite.

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.

A sustainable LiFePO4/graphite hybrid cathode capable of stepwise cation and anion storage

Boosting the kinetics of PF6− into graphitic layers for the optimal cathode of dual-ion batteries: The rehearsal of pre-intercalating Li+

Dual‐ion batteries (DIBs) represent a transformative platform in energy storage applications, owing to their exceptional capability to operate at elevated voltages (above 5.0 V) while maintaining a low production cost. However, their actual capacity is severely limited by the anion‐only intercalation in conventional graphite cathodes. Here, we present a graphite cathode featuring multiscale disordered architectures (SDG‐800), achieved via a one‐step yet multifunctional pyrolysis strategy to simultaneously realize the low‐temperature catalytic graphitization with controlled vacancy defects, the formation of micropores, and the doping of heteroatoms. The unique architectures of SDG‐800 serve as a platform for synergistic ion reservoirs, effectively activating multi‐mode ion co‐storage mechanisms within a single electrode. When integrated into a DIB, the SDG‐800 cathode exhibits a record‐breaking capacity of 264 mAh g −1 (representing a 2.4‐fold enhancement over conventional graphite), coupled with an impressive energy density of 648 Wh kg − 1 and a long cycling durability exceeding 1400 cycles. This work provides an innovative design strategy for graphite‐based cathodes in high‐performance DIB systems.

LiPF6 dissolved in dimethyl carbonate (DMC) is one of the cheapest groups of electrolyte solutions in dual-ion batteries. Generally, the discharge capacity of anion storage delivered by the graphite cathode grows with increasing LiPF6 concentration. This fact is consistent with the irreversible storage of DMC-solvated PF6-, and then, the underlying mechanism is clarified by the electrochemical tests and ex situ X-ray diffraction (XRD) measurements of graphite cathodes as well as infrared (IR) and Raman spectroscopy characterizations of solutions. Moreover, quaternary ammonium salts have facile dissociation, which can effectively regulate the solvation state of the anion and the interaction between ion pairs in the electrolyte. A small amount of tetrabutylammonium hexafluorophosphate (TBAPF6) is introduced into the highly concentrated LiPF6-DMC solution to improve the performance of the graphite cathode. The discharge capacity of the Li/graphite cell has increased by approximately 50%. This effect is also correlated with the solvation state of the anion. This study provides an insightful clue for the choice of electrolyte solution in dual-ion batteries.

In-situ implanted carbon nanofilms into lithium titanate with 3D porous structure as fast kinetics anode for high-performance dual-ion battery

Dual ion batteries (DIBs) have recently gained significant attention due to their potential to directly address several shortcomings of current battery technologies. They demonstrate high operating potential (beyond 4.5 V vs Li/Li+) and excellent performance without the use of transition metal oxides.1,2 Specifically, both the cathode and anode of graphite-based DIBs are made of graphite, making them environmentally friendly and cost-effective.However, the high operating voltage leads to continuous electrolyte decomposition, resulting in faster capacity fading and low coulombic efficiency. In addition, repeated solvent co-intercalation causes graphite exfoliation and structural instability. Therefore, constructing a stable cathode–electrolyte interphase (CEI) that minimizes unnecessary electrolyte consumption and side reactions—similar to the solid electrolyte interphase (SEI) on lithium-ion battery (LIB) anodes—is a viable strategy for improving DIB performance. Meanwhile, the solvation behavior of anions as a function of salt concentration, and its effect on interphase formation at a graphite cathode has not been fully elucidatedHere, we utilized scanning electrochemical microscopy (SECM) for in situ investigation of the CEI on multi-layer graphene (MLG) as a model cathode for graphite DIBs. SECM feedback images and probe scan curves reveal clear differences in CEI formations at different electrolyte concentrations. These CEIs exhibited a distinct passivating interphase behavior, suggesting accelerated and continuous electrolyte decomposition in some electrolyte conditions but not in others. To further correlate resulting CEIs with structural stability, we performed Raman spectroscopy, while in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) provided insight into intermediate species and products formed during anion intercalation. Together, our study reveal how electrolyte concentration governs interfacial chemistry and structural integrity, offering key insights for improving the long-term stability and performance of DIBs.

Dual-ion batteries (DIBs) are a new kind of energy storage device that store energy involving the intercalation of both anions and cations on the cathode and anode simultaneously. They feature high output voltage, low cost, and good safety. Graphite was usually used as the cathode electrode because it could accommodate the intercalation of anions (i.e., PF6-, BF4-, ClO4-) at high cut-off voltages (up to 5.2 V vs. Li+/Li). The alloying-type anode of Si can react with cations and boost an extreme theoretic storage capacity of 4200 mAh g-1. Therefore, it is an efficient method to improve the energy density of DIBs by combining graphite cathodes with high-capacity silicon anodes. However, the huge volume expansion and poor electrical conductivity of Si hinders its practical application. Up to now, there have been only a few reports about exploring Si as an anode in DIBs. Herein, we prepared a strongly coupled silicon and graphene composite (Si@G) anode through in-situ electrostatic self-assembly and a post-annealing reduction process and investigated it as an anode in full DIBs together with home-made expanded graphite (EG) as a fast kinetic cathode. Half-cell tests showed that the as-prepared Si@G anode could retain a maximum specific capacity of 1182.4 mAh g-1 after 100 cycles, whereas the bare Si anode only maintained 435.8 mAh g-1. Moreover, the full Si@G//EG DIBs achieved a high energy density of 367.84 Wh kg-1 at a power density of 855.43 W kg-1. The impressed electrochemical performances could be ascribed to the controlled volume expansion and improved conductivity as well as matched kinetics between the anode and cathode. Thus, this work offers a promising exploration for high energy DIBs.

The state-of-the-art energy storage technology at the grid-scale is currently the lithium-ion battery (LIB). However, LIB cathodes often contain costly and resource-constrained transition metals such as cobalt, which has prompted interest in alternative battery chemistries. Dual-ion batteries (DIBs) – which pair typical LIB anodes with a graphite cathode – exploiting simultaneous anion intercalation and cation deposition/alloying/intercalation at their respective electrodes – have been recently proposed as such an alternative. In DIBs, the electrolyte is both the source and sink of all active ions; therefore, the presence of extraneous chemical species such as solvents constrains practical cell-level energy densities. Therefore, solventless, low-melting molten salts, free of organic solvents and bulky, ionic liquid cations, are an attractive alternative to conventional DIB electrolytes. Herein, we investigate a lithium-based molten salt as a DIB electrolyte that can enable operation at intermediate temperatures (<120°C). We explore the physicochemical properties of this molten salt system and investigate the structural and compositional evolution of anion-graphite intercalation compounds during anion intercalation into graphite cathodes. Finally, we probe the performance of the molten salt electrolyte in half-cells and full-cells to understand capacity fading and other potential cell failure mechanisms. We show that this molten salt has great promise as an electrolyte that can enable energy-dense, next-generation DIBs.

Sodium-based dual-ion batteries via coupling high-capacity selenium/graphene anode with high-voltage graphite cathode

Anion‐intercalation in graphite cathodes enables high‐power, high‐voltage, and low‐cost dual‐ion batteries (DIBs). However, irreversible graphite exfoliation during cycling progressively degrades electrical contacts, a phenomenon that prevailing failure models attribute to substantial volume variations during anion (de)intercalation. Here, we reveal that the irreversible decomposition of co‐intercalated solvents constitutes the critical, yet overlooked driver of exfoliation and the subsequent loss of electrical connectivity. Potential‐dependent operando tracking unveils that co‐intercalated solvents such as ethyl methyl carbonate (EMC) decompose above 4.9 V vs. Li/Li + in the confined gallery space. This process generates gaseous products that induce localized stress heterogeneity, directly triggering exfoliation. In light of this revised mechanism, we revisit the role of fluoroethylene carbonate (FEC) in improving graphite cathode reversibility, and demonstrate that it functions by inhibiting solvent co‐intercalation, contrary to the previously held belief of protective interphase formation. Thus, by clarifying the failure pathway, our work identifies solvent exclusion as a key design principle for high‐voltage graphite cathodes in DIBs.

Electrochemical anion storage plays a critical role in the development of hybrid ion capacitors and dual-ion batteries. However, the mechanism of the interaction between electrolytes and anion storage remains unknown. Herein, we systematically investigate the electrochemical anion-storage properties of polypyrrole (PPy) cathodes in different chain-length ether-based electrolytes. In dimethyl ether (DME)-based electrolytes, the PPy cathode delivers a specific capacity of 91 mAh g–1 at 100 mA g–1 after 200 cycles and maintained 60 mAh g–1 at 5 A g–1. The shorter-chain DME exhibits weaker anion-solvent interactions, enabling rapid anion desolvation behavior, thus enhancing ion storage kinetics. Further experimental analysis and theoretical computation verify that the shorter-chain solvents exhibit reduced solvation energy barriers and optimized interfacial charge transfer. This work highlights the critical role of solvent molecular structure in regulating anion storage kinetics, providing a strategic electrolyte design for approaching high-performance sodium-ion hybrid capacitors and dual-ion batteries.

Rechargeable batteries based on anion intercalation graphite cathodes

Anion intercalation in the graphite cathode of a dual-ion battery (DIB) occurs at unusually high voltage (>4.5 V K + /K). This exacerbates electrolyte degradation and corrosion of Al current collectors, leading to poor coulombic efficiency (CE), typically <90%, and short cell life as a result. These limitations can be mitigated if a stable cathode-electrolyte interface layer (CEI) can form on the graphite electrode. In this study, we demonstrate that the performance of a potassium-based DIB can be improved with a triallyl phosphate (TAP) monomer added in 6 m KN(SO 2 CF 3 ) 2 (KTFSI)-dimethyl carbonate (DMC) electrolyte. The TAP additive forms a stable polymeric CEI on the graphite particles and thus increases the CE of the cell to 97%–99%. Together with MoS 2 -negative electrodes with a pre-formed solid electrolyte interphase (SEI) layer, the DIB concept has been shown to offer specific capacities from ∼40 to 80 mAh g −1 with an average discharge voltage of 3.7 V. • Design principle for high-performance MoS 2 -graphite dual-ion battery is proposed • Impact of electrolyte additives on the negative and positive electrodes is investigated • Triallyl phosphate is used to generate a polymeric CEI on graphite cathode • MoS 2 with pre-formed SEI layer ensures stable cycling and high coulombic efficiency A dual-ion battery operates at unusually high voltage, which is needed to intercalate anions in a graphite cathode. Asfaw et al. explore strategies to create more stable electrode-electrolyte interfaces in an effort to design potassium-based MoS 2 -natural-graphite dual-ion battery with high coulombic efficiency and long cycle life.

Compared with conventional lithium‐ion battery systems, anion‐intercalation in graphite cathodes opens avenues for the development of batteries with groundbreaking power density. This study explores the enhancement of dual‐ion batteries (DIBs) by gel polymer electrolyte (GPE) enhanced with surface‐charged nanoclays, focusing on overcoming traditional challenges such as electrolyte decomposition, anion‐solvent co‐intercalation, and interfacial instability at the graphite cathode. Three nanoclays including montmorillonite, kaolinite, and halloysite are compared by incorporating them into GPE and evaluating their effect on the electrochemical properties, ion conduction, and mechanical integrity of DIBs. Particular attention is paid to the halloysite because of its differential internal and external surface charges, which generate charge separation, facilitate optimal lithium‐ion transport, and mitigate undesirable anion‐solvent interactions. These results indicate that halloysite‐incorporated GPE (HS‐G) significantly improves DIB performance, as demonstrated by extended cycle life, robust capacity retention at fast charge/discharge rates of 20 C, and operational stability over a wide temperature range (0–60 °C). These improvements are attributed to the unique structural advantages of HS‐G, including effective charge separation, enhanced anion diffusion, and reduced solvent co‐intercalation, which provide an environmentally friendly and cost‐effective approach to advanced DIB applications.