A Graphite∥PTCDI Aqueous Dual-Ion Battery

Polyimide-Based Aqueous Potassium Energy Storage Systems Using Concentrated WiSE Electrolyte

Aqueous batteries are considered as promising alternative power sources due to their eco-friendly, cost-effective, and nonflammable attributes. Employing organic-based electrode materials offers further advantages toward building greener and sustainable systems, owing to their tunability and environmental friendliness. In order to enhance the energy and power densities, superconcentrated aqueous electrolytes, such as water-in-salt electrolytes (WiSE), have renewed the interest in aqueous batteries due to their enhanced stability and much wider electrochemical stability window (>1.23 V) compared with the traditional aqueous electrolytes. Here, we present a perylene diimide-based electrode material (PDI-Urea) as an appealing anode for aqueous potassium energy storage systems and investigate their electrochemical performance in three WiSE electrolytes, namely, 30 M potassium acetate, 40 M potassium formate and 30 M potassium bis(fluorosulfonyl)imide (KFSI). To explore the potential of PDI-Urea for potassium-based electrochemical energy systems, we fabricated full cell devices such as aqueous potassium dual-ion battery (APDIB) and aqueous K-ion battery (AKIB) and studied their electrochemical properties with 30 M KFSI electrolyte. The full cell K-ion battery, using a PBA cathode, exhibited excellent electrochemical performance with good rate capability and impressive capacity retention of 91% upon 1000 cycles. Further, the reaction mechanism of the electrodes is systematically analyzed using ex-situ studies.

A Review of Anode Materials for Dual-Ion Batteries

Distinct from "rocking-chair" lithium-ion batteries (LIBs), the unique anionic intercalation chemistry on the cathode side of dual-ion batteries (DIBs) endows them with intrinsic advantages of low cost, high voltage, and eco-friendly, which is attracting widespread attention, and is expected to achieve the next generation of large-scale energy storage applications. Although the electrochemical reactions on the anode side of DIBs are similar to that of LIBs, in fact, to match the rapid insertion kinetics of anions on the cathode side and consider the compatibility with electrolyte system which also serves as an active material, the anode materials play a very important role, and there is an urgent demand for rational structural design and performance optimization. A review and summarization of previous studies will facilitate the exploration and optimization of DIBs in the future. Here, we summarize the development process and working mechanism of DIBs and exhaustively categorize the latest research of DIBs anode materials and their applications in different battery systems. Moreover, the structural design, reaction mechanism and electrochemical performance of anode materials are briefly discussed. Finally, the fundamental challenges, potential strategies and perspectives are also put forward. It is hoped that this review could shed some light for researchers to explore more superior anode materials and advanced systems to further promote the development of DIBs.

Reversible Insertion of [AlCl4 ]- Superhalides in Graphite

Graphite-based dual-ion batteries are with potential higher energy density, making them a unique candidate in energy storage systems. However, anion insertion into graphite in aqueous environment remains a significant challenge. Herein, we report that the reversible insertion of Al-Cl superhalide into expanded graphite (EG) delivers an ultrahigh specific capacity of ~171 mAh g-1 from an aqueous deep eutectic solvent (DES) gel electrolyte of 50 m ChCl+5 m AlCl3 . High-resolution transmission electron microscopy (HRTEM), Raman spectra and X-ray diffraction (XRD) show that the EG generates turbostratic structure during Al-Cl superhalide (de)insertion instead of presenting typical graphite intercalation compounds (GIC), thus attributing to the high capacity during Al-Cl superhalide insertion.

Sustainable Dual-Ion Batteries beyond Li

The limitations of resources used in current Li-ion batteries may hinder their widespread use in grid-scale energy storage systems, prompting the search for low-cost and resource-abundant alternatives. "Beyond-Li cation" batteries have emerged as promising contenders; however, they confront noteworthy challenges due to the scarcity of suitable host materials for these cations. In contrast, anions, the other crucial component in electrolytes, demonstrate reversible intercalation capacity in specific materials like graphite. The convergence of anion and cation storage has given rise to a new battery technology known as dual-ion batteries (DIBs). This comprehensive review presents the current status, advancements, and future prospects of sustainable DIBs beyond Li. Notably, most DIBs exhibit similar cathode reaction mechanisms involving anion intercalation, while the distinguishing factor lies in the cation types functioning at the anode. Accordingly, the review is organized into sections by various cation types, including Na-, K-, Mg-, Zn-, Ca-, Al-, NH4 + -, and proton-based DIBs. Moreover, a perspective on these novel DIBs is presented, along with proposed protocols for investigating DIBs and promising future research directions. It is envisioned that this review will inspire fresh concepts, ideas, and research directions, while raising important questions to further tailor and understand sustainable DIBs, ultimately facilitating their practical realization.

An Ultrahigh-Capacity Dual-Ion Battery Based on a Free-Standing Graphite Paper Cathode and Flower-Like Heterojunction Anode of Tin Disulfide and Molybdenum Disulfide

Dual-ion batteries have been considered as a competitive energy-storage device. However, owing to the lack of suitable high-capacity density and rapid-charging electrode materials, designing a cost-effective and high-performance dual-ion battery is still a great challenge. Herein, an ultrahigh-capacity dual-ion battery is constructed based on a carbon-nanotubes (CNTs) containing SnS2 -MoS2 @CNTs heterojunction anode and highly crystalline free-standing graphite paper serves as cathode. The SnS2 -MoS2 @CNTs heterojunction consisting of ultrathin nanosheets was prepared via a facile two-step hydrothermal method and shows flower-like morphology and high crystallinity. Benefiting from the unique design concept, the graphite paper/SnS2 -MoS2 @CNTs dual-ion battery delivers a high capacity of 274.2 mAh g-1 at 100 mA g-1 and has an outstanding capacity retention of 95 % after 300 cycles under 400 mA g-1 . Even at a high current density of 2 A g-1 the battery still retains a considerable capacity of 112.3 mAh g-1 . More importantly, the battery shows an extremely low self-discharge of 0.006 % h-1 after resting for 24 h. Characterization using SEM and XRD further demonstrate the excellent cycling stability and good reversibility. Consequently, this constructed dual-ion battery could be a promising energy storage device and provide new insights for the design of high-performance dual-ion batteries.

Next-generation magnesium-ion batteries: The quasi-solid-state approach to multivalent metal ion storage

Mg-ion batteries offer a safe, low-cost, and high-energy density alternative to current Li-ion batteries. However, nonaqueous Mg-ion batteries struggle with poor ionic conductivity, while aqueous batteries face a narrow electrochemical window. Our group previously developed a water-in-salt battery with an operating voltage above 2 V yet still lower than its nonaqueous counterpart because of the dominance of proton over Mg-ion insertion in the cathode. We designed a quasi-solid-state magnesium-ion battery (QSMB) that confines the hydrogen bond network for true multivalent metal ion storage. The QSMB demonstrates an energy density of 264 W·hour kg-1, nearly five times higher than aqueous Mg-ion batteries and a voltage plateau (2.6 to 2.0 V), outperforming other Mg-ion batteries. In addition, it retains 90% of its capacity after 900 cycles at subzero temperatures (-22°C). The QSMB leverages the advantages of aqueous and nonaqueous systems, offering an innovative approach to designing high-performing Mg-ion batteries and other multivalent metal ion batteries.

Application-Based Prospects for Dual-Ion Batteries

Dual-ion batteries (DIBs) exhibit a distinct set of performance advantages and disadvantages due to their unique storage mechanism. However, the current cyclability/energy density tradeoffs of anion storage paired with the intrinsic required electrolyte loadings of conventional DIBs preclude their widespread adoption as an alternative to lithium-ion batteries (LIBs). Despite this, their reduced desolvation penalty and low-cost electrode materials may warrant their employment for low-temperature and/or grid storage applications. To expand beyond these applications, this Perspective reviews the prospects of solid salt storage and halogen intercalation-conversion as viable methods to increase DIB energy densities to a level on-par with LIBs. Fundamental limitations of conventional DIBs are examined, technology spaces are proposed where they can make meaningful impact over LIBs, and potential strategies are outlined to improve cell-level energy densities necessary for the widespread adoption of DIBs.

Aqueous OH- /H+ Dual-Ion Zn-Based Batteries

Aqueous Zn-based batteries hold multiple advantages of eco-friendliness, easy accessibility, high safety, easy fabrication, and fast kinetics, while their widespread applications have been greatly limited by the relatively narrow thermodynamically stable potential windows (i. e., 1.23 V) of water and the mismatched pH conditions between cathode and anode, which presents challenges regarding how to maximize the output voltage and the energy density. Recently, aqueous OH^- /H⁺ dual-ion Zn-based batteries (OH^- /H⁺ -DIZBs), where the Zn anode reacts with hydroxide ions (OH^- ) in alkaline electrolyte while hydrogen ions (H⁺ ) are involved in the cathode reaction in the acidic electrolyte, have been reported to be capable of broadening the working voltage and improving the energy density, which offers practical feasibility toward overcoming the above limitations. This Review thus takes this chance to investigate the recent progress on aqueous OH^- /H⁺ -DIZBs. First, the concept and the history of such OH^- /H⁺ -DIZBs are introduced, and then special emphasis is put on the working mechanisms, the progress of the development of new batteries, and how the electrolytes improve their performance. Finally, the challenges and opportunities in this field are discussed.

Difluoro(oxalato)borate's Role in the Intercalation Behavior of Mixed Anions from Sulfolane

Some previous studies have found the synergistic effect of mixed anions in dual-ion batteries (DIBs). In this work, both lithium tetrafluoroborate (LiBF₄ ) and lithium difluoro(oxalato)borate (LiDFOB) were dissolved in sulfolane (SL) solvent, and the resultant solutions were applied for DIBs. The storage behavior of mixed anions in natural graphite positive electrodes was investigated. In-situ X-ray diffraction measurements revealed both anions could participate in the formation of graphite intercalation compounds. Their evolution followed with the decreasing tendency of discharge capacities as the content of LiDFOB increased in solutions. The exchange of anions was discussed.

Charge Carriers for Aqueous Dual-Ion Batteries

Environmental and safety concerns of energy storage systems call for application of aqueous battery systems which have advantages of low cost, environmental benignity, safety, and easy assembling. Among the aqueous battery systems, aqueous dual-ion batteries (ADIBs) provide high possibility for achieving excellent battery performance. Compared with the "rocking chair" batteries with only one type of carrier involved in the charging and discharging, ADIBs with both cations and anions as charge carriers possess diverse selections of electrodes and electrolytes. Charge carriers are the basis of the configuration of ADIBs. In this Review, cations and anions that could be applied in ADIBs are demonstrated with corresponding electrode materials and favorable electrolytes. Some insertion mechanisms are emphasized to provide insights for the possibilities to enhance the practical performances of ADIBs.

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.

A 2.75 V ammonium-based dual-ion battery

The popular metal-ion batteries (MIBs) suffer from environmental and economic issues because of their heavy dependency on nonrenewable metals. Here, we propose a metal-free ammonium (NH₄ ⁺ )-based dual-ion battery with a record-breaking operation voltage of 2.75 V. The working mechanism of this sustainable battery involves the reversible anion (PF₆ ^- ) intercalation chemistry in graphite cathode and NH₄ ⁺ intercalation behavior in PTCDI (3,4,9,10-perylenetetracarboxylic diimide) anode. This new battery configuration successfully circumvented the reduction susceptibility of NH₄ ⁺ and the lack of mature NH₄ ⁺ -rich cathodes for NH₄ ⁺ ion batteries (AIBs). The customized organic NH₄ ⁺ electrolyte endows the graphite||PTCDI full battery with durable longevity (over 1000 cycles) and a high energy density (200 Wh kg^-1 ). We show that the development of AIBs should be high-voltage-oriented while circumventing low operation potential to avoid NH₄ ⁺ reduction.