A Dual‐Carbon Battery Based on Potassium‐Ion Electrolyte

Although potassium‐ion batteries (KIBs) have been considered to be promising alternatives to conventional lithium‐ion batteries due to large abundance and low cost of potassium resources, their development still stays at the infancy stage due to the lack of appropriate cathode and anode materials with reversible potassium insertion/extraction as well as good rate and cycling performance. Herein, a novel dual‐carbon battery based on a potassium‐ion electrolyte (named as K‐DCB), utilizing expanded graphite as cathode material and mesocarbon microbead as anode material is developed. The working mechanism of the K‐DCB is investigated, which is further demonstrated to deliver a high reversible capacity of 61 mA h g^‐1 at a current density of 1C over a voltage window of 3.0–5.2 V, as well as good cycling performance with negligible capacity decay after 100 cycles. Moreover, the high working voltage with medium discharge voltage of 4.5 V also enables the K‐DCB to meet the requirement of some high‐voltage devices. With the merits of environmental friendliness, low cost and high energy density, the K‐DCB shows attractive potential for future energy storage application.     

Integrated Configuration Design for Ultrafast Rechargeable Dual‐Ion Battery

In this work, an integrated dual‐ion battery design is reported with active materials, current collectors, and separator, assembled in one flexible component. An aluminum film is deposited directly onto one side of the 3D porous glass fiber separator to form a porous anode. Cathode active materials are loaded on the other side of the separator with aluminum film deposited on the top as current collector. This design demonstrates ultrafast charge/discharge rate up to 120 C while maintaining high capacity of 116.1 mA h g^?1. Moreover, long‐term stability of over 1500 cycles at a high rate of 60 C is achieved. The estimated energy density remains as high as 232.6 W h kg^?1 at an ultrahigh power density of 22634.5 W kg^?1.     

A Review on the Features and Progress of Dual‐Ion Batteries

Despite the wide application of lithium‐ion batteries in portable electronic devices and electric vehicles, the demand for new battery systems with the merits of high voltage, environmental friendliness, safety, and cost efficiency is still quite urgent. This perspective focuses on dual‐ion batteries (DIBs), in which, both the cations and anions are involved in the battery reaction. An anion's intercalation/deintercalation process on the cathode side allows the DIBs to operate at high voltages, which is favorable for enhanced energy density. However, electrolytes with a wide electrochemical window and suitable anion‐intercalation materials with highly reversible capacities should be developed. The progress of research into stable organic electrolytes, ionic liquids, and their effects on the electrochemical performances of DIBs are first discussed. Thereafter, the anion‐host materials including graphitic materials, organic materials, and their working mechanisms are discussed in detail. In addition, recently emerging DIB systems with high‐capacity anodes, or sodium‐, potassium‐ion involved battery reactions are also reviewed. The authors' recent work, demonstrating a generalized DIB construction using metal foil as both current collector and alloying anode material, which is successfully extended into lithium‐, sodium‐, and potassium‐based DIBs, is also discussed.     

Rational Construction of Nitrogen‐Doped Hierarchical Dual‐Carbon for Advanced Potassium‐Ion Hybrid Capacitors

Potassium‐ion hybrid capacitors (PIHCs), elaborately integrate the advantages of high output power as well as long lifespan of supercapacitors and the high energy density of batteries, and exhibit great possibilities for the future generations of energy storage devices. The critical next step for future implementation lies in exploring a high‐rate battery‐type anode with an ultra‐stable structure to match the capacitor‐type cathode. Herein, a “dual‐carbon” is constructed, in which a three‐dimensional nitrogen‐doped microporous carbon polyhedron (NMCP) derived from metal‐organic frameworks is tightly wrapped by two‐dimensional reduced graphene oxide (NMCP@rGO). Benefiting from the synergistic effect of the inner NMCP and outer rGO, the NMCP@rGO exhibits a superior K‐ion storage capability with a high reversible capacity of 386 mAh g^?1 at 0.05 A g^?1 and ultra‐long cycle stability with a capacity of 151.4 mAh g^?1 after 6000 cycles at 5.0 A g^?1. As expected, the as‐assembled PIHCs with a working voltage as high as 4.2 V present a high energy/power density (63.6 Wh kg^?1 at 19 091 W kg^?1) and excellent capacity retention of 84.7% after 12 000 cycles. This rational construction of advanced PIHCs with excellent performance opens a new avenue for further application and development.     

An Ultrafast Rechargeable Hybrid Sodium‐Based Dual‐Ion Capacitor Based on Hard Carbon Cathodes

Hybrid sodium‐based dual‐ion capacitors (NDICs), which integrate the advantages of supercapacitors and sodium‐ion batteries, have attracted tremendous attention recently. In this work, hybrid sodium‐based dual‐ion capacitors are successfully developed with nitrogen‐doped microporous hard carbon as the cathode and soft carbon as the anode. N‐doping is beneficial to the functional groups, porous structure, and electric conductivity of hard carbon. Hybrid NDICs possess a wide voltage range (0.01–4.7 V), high‐energy density of 245.7 W h kg^?1 at a power density of 1626 W kg^?1, long cycle life (1000 cycles), and outstanding rate performance.     

A Dual‐Insertion Type Sodium‐Ion Full Cell Based on High‐Quality Ternary‐Metal Prussian Blue Analogs

Prussian blue analogs (PBAs) are especially investigated as superior cathodes for sodium‐ion batteries (SIBs) due to high theoretical capacity (≈170 mA h g^?1) with 2‐Na storage and low cost. However, PBAs suffer poor cyclability due to irreversible phase transition in deep charge/discharge states. PBAs also suffer low crystallinity, with considerable [Fe(CN)₆] vacancies, and coordinated water in crystal frameworks. Presently, a new chelating agent/surfactant coassisted crystallization method is developed to prepare high‐quality (HQ) ternary‐metal Ni_xCo_1?x[Fe(CN)₆] PBAs. By introducing inactive metal Ni to suppress capacity fading caused by excessive lattice distortion, these PBAs have tunable limits on depth of charge/discharge. HQ‐Ni_xCo_1?x[Fe(CN)₆] (x = 0.3) demonstrates the best reversible Na‐storage behavior with a specific capacity of ≈145 mA h g^?1 and a remarkably improved cycle performance, with ≈90% capacity retention over 600 cycles at 5 C. Furthermore, a dual‐insertion full cell on the cathode and NaTi₂(PO₄)₃ anode delivers reversible capacity of ≈110 mA h g^?1 at a current rate of 1.0 C without capacity fading over 300 cycles, showing promise as a high‐performance SIB for large‐scale energy‐storage systems. The ultrastable cyclability achieved in the lab and explained herein is far beyond that of any previously reported PBA‐based full cells.     

Hierarchically Porous N‐Doped Carbon Fibers as a Free‐Standing Anode for High‐Capacity Potassium‐Based Dual‐Ion Battery

Potassium‐based dual‐ion batteries (KDIBs) have emerged as a new generation of rechargeable batteries, due to their high cell voltage, low cost, and the natural abundance of potassium resources. However, the low capacity and poor cycling stability largely hinder the further development of KDIBs. Herein, the fabrication of hierarchically porous N‐doped carbon fibers (HPNCFs) as a free‐standing anode for high‐performance KDIBs is reported. With a free‐standing hierarchical structure (micro/meso/macropores and nanochannels) and high‐content of nitrogen doping, the HPNCFs not only provide intrinsic electron pathways and efficient ion transport channels, but also afford sufficient free space to tolerate the volume change during cycling. Consequently, the KDIBs made from a graphite cathode and an optimized HPNCFs anode deliver a high reversible capacity of 197 mAh g^?1 at a specific current of 50 mA g^?1, and excellent cycling stability (65 mAh g^?1 after 346 cycles at a specific current of 100 mA g^?1, the capacity calculation of the KDIBs is based on the mass of the anode). These results indicate that the properly designed HPNCFs can effectively improve the capacity and cycling stability of the KDIBs, indicating a great potential for applications in the field of high‐performance energy‐storage devices.     

An In Situ Interface Reinforcement Strategy Achieving Long Cycle Performance of Dual‐Ion Batteries

Dual‐ion batteries (DIBs) with high operation voltage offer promising candidates for low‐cost clean energy chemistries. However, there still exist tough issues, including structural collapse of the graphite cathode due to solvent co‐intercalation and electrolyte decomposition on the electrode/electrolyte interface, which results in unsatisfactory cyclability and fast battery failure. Herein, Li₄Ti₅O₁₂ (LTO) modified mesocarbon microbeads (MCMBs) are proposed as a cathode material. The LTO layer functions as a skeleton and offers electrocatalytic active sites for in situ generation of a favorable and compatible cathode electrolyte interface (CEI) layer. The synergetic LTO‐CEI network can change the thermodynamic behavior of the PF₆^? intercalation process and maintain the structural integrity of the graphite cathode, as a “Great Wall” to protect the cathode from structural collapse and electrolyte decomposition. Such LTO‐CEI reinforced cathode exhibits a prolonged cyclability with 85.1% capacity retention after 2000 cycles even at cut‐off potential of 5.4 V versus Li⁺/Li. Moreover, the LTO‐modified MCMB (+)//prelithiated MCMB (?) full cell exhibits a high energy density of ≈200 Wh kg^?1, remarkably enhanced cyclability with 93.5% capacity retention after 1000 cycles. Undoubtedly, this work offers in‐depth insight into interface chemistry, which can arouse new originality to boost the development of DIBs.     

Rechargeable Dual‐Ion Batteries with Graphite as a Cathode: Key Challenges and Opportunities

Rechargeable graphite dual‐ion batteries (GDIBs) have attracted the attention of electrochemists and material scientists in recent years due to their low cost and high‐performance metrics, such as high power density (≈3–175 kW kg^?1), energy efficiency (≈80–90%), long cycling life, and high energy density (up to 200 Wh kg^?1), suited for grid‐level stationary storage of electricity. The key feature of GDIBs is the exploitation of the reversible oxidation of the graphite network with concomitant and highly efficient intercalation/deintercalation of bulky anionic species between graphene layers. In this review, historical and current research aspects of GDIBs are discussed, along with key challenges in their development and practical deployment. Specific emphasis is given to the operational mechanism of GDIBs and to unbiased and correct reporting of theoretical cell‐level energy densities.     

Fast Diffusion of Multivalent Ions Facilitated by Concerted Interactions in Dual‐Ion Battery Systems

Sluggish solid‐phase diffusion has been an essential issue in developing intercalation electrode materials using multivalent ions. Compared to monovalent Li ions, the diffusion of multivalent ions is still not well understood. Here, combining first‐principles calculations with electrochemical experiments, it is shown that the diffusion of divalent Mg ions is significantly facilitated in Li–Mg dual‐ion systems, and the activation energy is remarkably reduced by the concerted interactions of the preceding Li ions and following Mg ions. Thus, making dual‐ion systems is a promising way to construct high‐energy‐density, rechargeable batteries with multivalent ions. This work will provide a new perspective on solid‐phase diffusion that is typically a rate‐controlling process in battery systems and fuel cell devices.     

Development of Safe and Sustainable Dual‐Ion Batteries Through Hybrid Aqueous/Nonaqueous Electrolytes

In this study, a new dual‐ion battery (DIB) concept based on an aqueous/non‐aqueous electrolyte is reported, combining high safety in the form of a nonflammable water‐in‐salt electrolyte, a high cathodic stability by forming a protective interphase on the negative electrode (non‐aqueous solvent), and improved sustainability by using a graphite‐based positive electrode material. Far beyond the anodic stability limit of water, the formation of a stage‐2 acceptor‐type graphite intercalation compound (GIC) of bis(trifluoromethanesulfonyl) imide (TFSI) anions from an aqueous‐based electrolyte is achieved for the first time, as confirmed by ex‐situ X‐ray diffraction. The choice of negative electrode material shows a huge impact on the performance of the DIB cell chemistry, i.e., discharge capacities up to 40 mAh g^?1 are achieved even at a high specific current of 200 mA g^?1. In particular, lithium titanium phosphate (LiTi₂(PO₄)₃; LTP) and lithium titanium oxide (Li₄Ti₅O₁₂; LTO) are evaluated as negative electrodes, exhibiting specific advantages for this DIB setup. In this work, a new DIB storage concept combining an environmentally friendly, transition‐metal‐free, abundant graphite positive electrode material, and a nonflammable water‐based electrolyte is established, thus paving the path toward a sustainable and safe alternative energy storage technology.     

Enhanced Kinetics Harvested in Heteroatom Dual‐Doped Graphitic Hollow Architectures toward High Rate Printable Potassium‐Ion Batteries

Carbonaceous materials have emerged as promising anode candidates for potassium‐ion batteries (PIBs) due to overwhelming advantages including cost‐effectiveness and wide availability of materials. However, further development in this realm is handicapped by the deficiency in their in‐target and large‐scale synthesis, as well as their low specific capacity and huge volume expansion. Herein the precise and scalable synthesis of N/S dual‐doped graphitic hollow architectures (NSG) via direct plasma enhanced chemical vapor deposition is reported. Thus‐fabricated NSG affording uniform nitrogen/sulfur co‐doping, possesses ample potassiophilic surface moieties, effective electron/ion‐transport pathways, and high structural stability, which bestow it with high rate capability (≈100 mAh g^?1 at 20 A g^?1) and a prolonged cycle life (a capacity retention rate of 90.2% at 5 A g^?1 after 5000 cycles), important steps toward high‐performance K‐ion storage. The enhanced kinetics of the NSG anode are systematically probed by theoretical simulations combined with operando Raman spectroscopy, ex situ X‐ray photoelectron spectroscopy, and galvanostatic intermittent titration technique measurements. In further contexts, printed NSG electrodes with tunable mass loading (1.84, 3.64, and 5.65 mg cm^?2) are realized to showcase high areal capacities. This study demonstrates the construction of a printable carbon‐based PIB anode, that holds great promise for next‐generation grid‐scale PIB applications.     

Core–Shell Aluminum@Carbon Nanospheres for Dual‐Ion Batteries with Excellent Cycling Performance under High Rates

Dual‐ion battery (DIB) has been proposed as a novel energy storage device with the merits of high safety, low cost and environmental friendliness. Herein, we have developed core/shell aluminum@carbon nanospheres (nAl@C) as anode material for DIB. The nanoscale framework is composed of an Al nanosphere and an amorphous carbon outer layer that is conductive and protective, facilitating the formation of a stable SEI film during cycling. Owing to the core‐shell structural design, the nAl@C nanospheres demonstrate significantly enhanced electrochemical performance in a nAl@C‐graphite DIB. The DIB exhibites high rate performance as well as superior cycling stability with a capacity of 88 mA h g^‐1 with 94.6% capacity retention and high Coulombic efficiency (> 99.5%) after 1000 cycles at a high current rate of 15 C. In addition, the nAl@C‐G DIB deliveres an ultrahigh specific energy of 148 W h kg^‐1 at a high power density of 3701 W kg^‐1, which is much better than most commercial lithium‐ion batteries.     

A Flexible Dual‐Ion Battery Based on PVDF‐HFP‐Modified Gel Polymer Electrolyte with Excellent Cycling Performance and Superior Rate Capability

Dual‐ion batteries (DIBs) have attracted increasing attention owing to their merits of high working voltage, low cost, and especially environmental friendliness. However, the cycling stability of most DIBs is still unsatisfying due to the decomposition of conventional liquid carbonate electrolytes under high working voltages. Exploration of gel polymer electrolytes (GPEs) with good electrochemical stability at high voltage is a possible strategy to optimize their cycling stability. A high‐performance flexible DIB based on a poly(vinylidene fluoride‐hexafluoro propylene) GPE codoped with poly(ethylene oxide) and graphene oxide via weak bond interactions is herein reported for the first time. The prepared polymer electrolyte shows a 3D porous network with significantly improved ionic conductivity up to 2.1 × 10^?3 S cm^?1, which is favorable for fast ionic transportation of both cations and anions. As a result, this DIB exhibits excellent cycling stability with a capacity retention of 92% after 2000 cycles at a high current rate of 5C (1C is corresponding to 100 mA g^?1), which is among the best performances of DIBs. Moreover, good flexibility and thermal stability (up to 90 °C) are also achieved for this battery, indicating its potential applications for high‐performance flexible energy storage devices.     

Ultra‐Lightweight 3D Carbon Current Collectors: Constructing All‐Carbon Electrodes for Stable and High Energy Density Dual‐Ion Batteries

Dual‐ion batteries (DIBs) attract great interest because they allow two types of ions for reversibly intercalating into electrodes, resulting in various advantages. However, there are three critical problems using graphite‐based cathodes, namely, low active material proportion in the electrodes, current collector corrosion, and massive cathode variation. For addressing these problems, an ultra‐lightweight 3D carbon current collector (CCC) is developed to fabricate all‐carbon electrodes as both cathodes and anodes. Compared with the conventional DIBs using Al and Cu foils as current collectors, the DIBs with 3D CCC of electrically conductive pathways and sufficient ionic diffusion channels deliver enhanced specific capacity stabilized around 140 and 120 mAh g^?1 at 0.5 and 1C, respectively. The electrochemically inert 3D CCC could essentially promote the energy density when calculating the entire electrode mass, along with long‐life cycle stability of 1000 cycles at 5C and no electrochemical corrosion on either anodes or cathodes. With an in situ optical microscope, the cathode expansion is found to massively reduce because the porous 3D CCC could effectively alleviate the huge volume. The results suggest a novel strategy for achieving low‐cost and high energy density DIBs with both mechanically and electrochemically stable features.