Highly Concentrated Electrolyte towards Enhanced Energy Density and Cycling Life of Dual-Ion Battery

Dual-ion batteries (DIBs) have attracted much attention owing to their low cost, high voltage, and environmental friendliness. As the source of active ions during the charging/discharging process, the electrolyte plays a critical role in the performance of DIBs, including capacity, energy density, and cycling life. However, most used electrolyte systems based on the LiPF₆ salt demonstrate unsatisfactory performance in DIBs. We have successfully developed a 7.5 mol kg⁻¹ lithium bis(fluorosulfonyl)imide (LiFSI) in a carbonate electrolyte system. Compared with diluted electrolytes, this highly concentrated electrolyte exhibits several advantages: 1) enhanced intercalation capacity and cycling stability of the graphite cathode, 2) optimized structural stability of the Al anode, and 3) significantly increased battery energy density. A proof-of-concept DIB based on this concentrated electrolyte exhibits a discharge capacity of 94.0 mAh g⁻¹ at 200 mA g⁻¹ and 96.8 % capacity retention after 500 cycles. By counting both the electrode materials and electrolyte, the energy density of this DIB reaches up to ≈180 Wh kg⁻¹, which is among the best performances of DIBs reported to date.     

A Bipolar and Self‐Polymerized Phthalocyanine Complex for Fast and Tunable Energy Storage in Dual‐Ion Batteries

Bipolar redox organics have attracted interest as electrode materials for energy storage owing to their flexibility, sustainability and environmental friendliness. However, an understanding of their application in all‐organic batteries, let alone dual‐ion batteries (DIBs), is in its infancy. Herein, we propose a strategy to screen a variety of phthalocyanine‐based bipolar organics. The self‐polymerizable bipolar Cu tetraaminephthalocyanine (CuTAPc) shows multifunctional applications in various energy storage systems, including lithium‐based DIBs using CuTAPc as the cathode material, graphite‐based DIBs using CuTAPc as the anode material and symmetric DIBs using CuTAPc as both the cathode and anode materials. Notably, in lithium‐based DIBs, the use of CuTAPc as the cathode material results in a high discharge capacity of 236 mAh g^?1 at 50 mA g^?1 and a high reversible capacity of 74.3 mAh g^?1 after 4000 cycles at 4 A g^?1. Most importantly, a high energy density of 239 Wh kg^?1 and power density of 11.5 kW kg^?1 can be obtained in all‐organic symmetric DIBs.     

Construction of CoO/Co‐Cu‐S Hierarchical Tubular Heterostructures for Hybrid Supercapacitors

Hierarchical hollow structures for electrode materials of supercapacitors could enlarge the surface area, accelerate the transport of ions and electrons, and accommodate volume expansion during cycling. Besides, construction of heterostructures would enhance the internal electric fields to regulate the electronic structures. All these features of hierarchical hollow heterostructures are beneficial for promoting the electrochemical properties and stability of electrode materials for high‐performance supercapacitors. Herein, CoO/Co‐Cu‐S hierarchical tubular heterostructures (HTHSs) composed of nanoneedles are prepared by an efficient multi‐step approach. The optimized sample exhibits a high specific capacity of 320 mAh g^?1 (2300 F g^?1) at 2.0 A g^?1 and outstanding cycling stability with 96.5 % of the initial capacity retained after 5000 cycles at 10 A g^?1. Moreover, an all‐solid‐state hybrid supercapacitor (HSC) constructed with the CoO/Co‐Cu‐S and actived carbon shows a stable and high energy density of 90.7 Wh kg^?1 at a power density of 800 W kg^?1.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

MnO2 Nanosheets Grown on Nitrogen‐Doped Hollow Carbon Shells as a High‐Performance Electrode for Asymmetric Supercapacitors

A hierarchical hollow hybrid composite, namely, MnO₂ nanosheets grown on nitrogen‐doped hollow carbon shells (NHCSs@MnO₂), was synthesized by a facile in situ growth process followed by calcination. The composite has a high surface area (251 m²g^?1) and mesopores (4.5 nm in diameter), which can efficiently facilitate transport during electrochemical cycling. Owing to the synergistic effect of NHCSs and MnO₂, the composite shows a high specific capacitance of 306 F g^?1, good rate capability, and an excellent cycling stability of 95.2 % after 5000 cycles at a high current density of 8 A g^?1. More importantly, an asymmetric supercapacitor (ASC) assembled by using NHCSs@MnO₂ and activated carbon as the positive and negative electrodes exhibits high specific capacitance (105.5 F g^?1 at 0.5 A g^?1 and 78.5 F g^?1 at 10 A g^?1) with excellent rate capability, achieves a maximum energy density of 43.9 Wh kg^?1 at a power density of 408 W kg^?1, and has high stability, whereby the ASC retains 81.4 % of its initial capacitance at a current density of 5 A g^?1 after 4000 cycles. Therefore, the NHCSs@MnO₂ electrode material is a promising candidate for future energy‐storage systems.     

Design of Advanced MnO/N‐Gr 3D Walls through Polymer Cross‐Linking for High‐Performance Supercapacitor

Three‐dimensional, vertically aligned MnO/nitrogen‐doped graphene (3D MnO/N‐Gr) walls were prepared through facile solution‐phase synthesis followed by thermal treatment. Polyvinylpyrrolidone (PVP) was strategically added to generate cross‐links to simultaneously form 3D wall structures and to incorporate nitrogen atoms into the graphene network. The unique wall features of the as‐prepared 3D MnO/N‐Gr hybirdes provide a large surface area (91.516 m² g^?1) and allow for rapid diffusion of the ion electrolyte, resulting in a high specific capacitance of 378 F g^?1 at 0.25 A g^?1 and an excellent charge/discharge stability (93.7 % capacity retention after 8000 cycles) in aqueous 1 m Na₂SO₄ solution as electrolyte. Moreover, the symmetric supercapacitors that were rationally designed by using 3D MnO/N‐Gr hybrids exhibit outstanding electrochemical performance in an organic electrolyte with an energy density of 90.6 Wh kg^?1 and a power density of 437.5 W kg^?1.     

Cyclohexanehexone with Ultrahigh Capacity as Cathode Materials for Lithium‐Ion Batteries

Organic carbonyl compounds show potential as cathode materials for lithium‐ion batteries (LIBs) but the limited capacities (<600 mA h g^?1) and high solubility in electrolyte restrict their further applications. Herein we report the synthesis and application of cyclohexanehexone (C₆O₆), which exhibits an ultrahigh capacity of 902 mA h g^?1 with an average voltage of 1.7 V at 20 mA g^?1 in LIBs (corresponding to a high energy density of 1533 Wh kg^?1 ). A preliminary cycling test shows that C₆O₆ displays a capacity retention of 82 % after 100 cycles at 50 mA g^?1 because of the limited solubility in high‐polarity ionic liquid electrolyte. Furthermore, the combination of DFT calculations and experimental techniques, such as Raman and IR spectroscopy, demonstrates the electrochemical active C=O groups during discharge and charge processes.     

Excellent Capacitive Performance of a Three‐Dimensional Hierarchical Porous Graphene/Carbon Composite with a Superhigh Surface Area

Three‐dimensional hierarchical porous graphene/carbon composite was successfully synthesized from a solution of graphene oxide and a phenolic resin by using a facile and efficient method. The morphology, structure, and surface property of the composite were investigated intensively by a variety of means such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). It is found that graphene serves as a scaffold to form a hierarchical pore texture in the composite, resulting in its superhigh surface area of 2034 m²g^?1, thin macropore wall, and high conductivity (152 S m^?1). As evidenced by electrochemical measurements in both EMImBF₄ ionic liquid and KOH electrolyte, the composite exhibits ideal capacitive behavior, high capacitance, and excellent rate performance due to its unique structure. In EMImBF₄, the composite has a high energy density of up to 50.1 Wh kg^?1 and also possesses quite stable cycling stability at 100 °C, suggesting its promising application in high‐temperature supercapacitors. In KOH electrolyte, the specific capacitance of this composite can reach up to an unprecedented value of 186.5 F g^?1, even at a very high current density of 50 A g^?1, suggesting its prosperous application in high‐power applications.     

Perovskite SrCo0.9Nb0.1O3−δ as an Anion‐Intercalated Electrode Material for Supercapacitors with Ultrahigh Volumetric Energy Density

We have synthesized and characterized perovskite‐type SrCo_0.9Nb_0.1O_3−δ (SCN) as a novel anion‐intercalated electrode material for supercapacitors in an aqueous KOH electrolyte, demonstrating a very high volumetric capacitance of about 2034.6 F cm⁻³ (and gravimetric capacitance of ca. 773.6 F g⁻¹) at a current density of 0.5 A g⁻¹ while maintaining excellent cycling stability with a capacity retention of 95.7 % after 3000 cycles. When coupled with an activated carbon (AC) electrode, the SCN/AC asymmetric supercapacitor delivered a specific energy density as high as 37.6 Wh kg⁻¹ with robust long‐term stability.     

Highly Stable Aqueous Zinc‐Ion Storage Using a Layered Calcium Vanadium Oxide Bronze Cathode

Cost‐effective aqueous rechargeable batteries are attractive alternatives to non‐aqueous cells for stationary grid energy storage. Among different aqueous cells, zinc‐ion batteries (ZIBs), based on Zn²⁺ intercalation chemistry, stand out as they can employ high‐capacity Zn metal as the anode material. Herein, we report a layered calcium vanadium oxide bronze as the cathode material for aqueous Zn batteries. For the storage of the Zn²⁺ ions in the aqueous electrolyte, we demonstrate that the calcium‐based bronze structure can deliver a high capacity of 340 mA h g^?1 at 0.2 C, good rate capability, and very long cycling life (96 % retention after 3000 cycles at 80 C). Further, we investigate the Zn²⁺ storage mechanism, and the corresponding electrochemical kinetics in this bronze cathode. Finally, we show that our Zn cell delivers an energy density of 267 W h kg^?1 at a power density of 53.4 W kg^?1.     

Stabilizing Lithium into Cross‐Stacked Nanotube Sheets with an Ultra‐High Specific Capacity for Lithium Oxygen Batteries

Although lithium–oxygen batteries possess a high theoretical energy density and are considered as promising candidates for next‐generation power systems, the enhancement of safety and cycling efficiency of the lithium anodes while maintaining the high energy storage capability remains difficult. Here, we overcome this challenge by cross‐stacking aligned carbon nanotubes into porous networks for ultrahigh‐capacity lithium anodes to achieve high‐performance lithium–oxygen batteries. The novel anode shows a reversible specific capacity of 3656 mAh g^?1, approaching the theoretical capacity of 3861 mAh g^?1 of pure lithium. When this anode is employed in lithium–oxygen full batteries, the cycling stability is significantly enhanced, owing to the dendrite‐free morphology and stabilized solid–electrolyte interface. This work presents a new pathway to high performance lithium–oxygen batteries towards practical applications by designing cross‐stacked and aligned structures for one‐dimensional conducting nanomaterials.     

KOH direct treatment of kombucha and in situ activation to prepare hierarchical porous carbon for high-performance supercapacitor electrodes

Kombucha, a renewable biomass, has been successfully utilized as an accessible carbon source to fabricate kombucha-derived hierarchical porous carbon (KHPC) by KOH direct treatment and in situ activation. The prepared KHPC shows an interconnected hierarchical porous structure, a pore volume of 0.41 cm³ g^?1, and a specific surface area of 917 m² g^?1. Due to the multiple synergistic effects of these advantages, the KHPC-3 exhibits a high specific capacitance of 326 F g^?1 at a current density of 1 A g^?1 in 6 M KOH, good rate capability of 82% retention from 1 to 20 A g^?1, and cycling performance with 91.3% retention over 5000 cycles. Moreover, the KHPC-3 symmetric supercapacitor reveals a good energy density of 20.97 Wh kg^?1 at a power density of 871.2 W kg^?1 and retains 8.08 Wh kg^?1 at 6330 W kg^?1 in 1 M Na₂SO₄ electrolyte. Therefore, the KHPC obtained via the simple synthesis process shows great promise as an electrode material in energy storage devices.     

Facile Synthesis of A 3D Flower‐Like Mesoporous Ni@C Composite Material for High‐Energy Aqueous Asymmetric Supercapacitors

A 3D flower‐like mesoporous Ni@C composite material has been synthesized by using a facile and economical one‐pot hydrothermal method. This unique 3D flower‐like Ni@C composite, which exhibited a high surface area (522.4 m² g^?1), consisted of highly dispersed Ni nanoparticles on mesoporous carbon flakes. The effect of calcination temperature on the electrochemical performance of the Ni@C composite was systematically investigated. The optimized material (Ni@C 700) displayed high specific capacity (1306 F g^?1 at 2 A g^?1) and excellent cycling performance (96.7 % retention after 5000 cycles). Furthermore, an asymmetric supercapacitor (ASC) that contained Ni@C 700 as cathode and mesoporous carbon (MC) as anode demonstrated high energy density (60.4 W h kg^?1 at a power density of 750 W kg^?1).     

Facile preparation of nitrogen-doped porous carbon for high performance symmetric supercapacitor

In this work, the micromolecule l-glutamic acid (Glu) is employed as nitrogen-rich precursor to prepare a novel porous carbon, and ZnCl₂ is used as activating agent to improve the surface area and electrochemical performance of the carbon. The nitrogen content of the carbon (Glu-2.5) prepared by Glu and ZnCl₂ with a mass ratio of 1:2.5 retains as high as 7.1 % at an activation temperature of 700 °C. The surface area and pore volume of Glu-2.5 are 1007.4 m² g^?1 and 0.57 cm³ g^?1, respectively. Glu-2.5 exhibits a high specific capacitance of 330.6 F g^?1 in 2 M KOH electrolyte at the current density of 1 A g^?1and good cycling stability (89 % retention of capacitance after 5000 charge/discharge cycles). More importantly, the assembled symmetric supercapacitor using Glu-2.5 as electrodes reveals a high energy density (16.7 Wh kg^?1) under the power density of 404.7 W kg^?1. Owing to its inherent advantages, Glu-2.5 could be a promising and scalable alternative applied to energy storage/conversion.     

Synthesis of Phosphorus‐Doped Graphene and its Wide Potential Window in Aqueous Supercapacitors

Phosphorus‐doped (P‐doped) graphene with the P doping level of 1.30 at % was synthesized by annealing the mixture of graphene and phosphoric acid. The presence of P was confirmed by elemental mapping and X‐ray photoelectron spectroscopy, while the morphology of P‐doped graphene was revealed by using scanning electron microscopy and transmission electron microscopy. To investigate the effect of P doping, the electrochemical properties of P‐doped graphene were tested as a supercapacitor electrode in an aqueous electrolyte of 1 M H₂SO₄. The results showed that doping of P in graphene exhibited significant improvement in terms of specific capacitance and cycling stability, compared with undoped graphene electrode. More interestingly, the P‐doped graphene electrode can survive at a wide voltage window of 1.7 V with only 3 % performance degradation after 5000 cycles at a current density of 5 A g^?1, providing a high energy density of 11.64 Wh kg^?1 and a high power density of 831 W kg^?1.     

Pumpkin‐Derived Porous Carbon for Supercapacitors with High Performance

Pumpkin has been employed for the first time as a renewable, low‐cost precursor for the preparation of porous carbon materials with excellent performance. Unlike most other precursors, pumpkin is rich in sugars and starch, and it has advantageous properties for large‐scale production. The as‐prepared materials adopted a unique morphology that consisted of numerous fused sphere‐like carbon grains with a high specific surface area (2968 m² g^?1), abundant micro and mesopores, and excellent electrochemical properties. The pumpkin‐derived activated carbon (PAC) material not only exhibited a high specific capacitance of 419 F g^?1, but also showed considerable cycling stability, with 93.6 % retention after 10 000 cycles. Moreover, a symmetrical supercapacitor that was based on PAC showed a high energy density of 22.1 W h kg^?1 in aqueous electrolyte. These superior properties demonstrate that PAC holds great promise for applications in electrochemical energy‐storage devices.     

An Environmentally Friendly and Flexible Aqueous Zinc Battery Using an Organic Cathode

Rechargeable batteries have been used to power various electric devices and store energy from renewables, but their toxic components (namely, electrode materials, electrolyte, and separator) generally cause serious environment issues when disused. Such toxicity characteristic makes them difficult to power future wearable electronic devices. Now an environmentally friendly and highly safe rechargeable battery, based on a pyrene‐4,5,9,10‐tetraone (PTO) cathode and zinc anode in mild aqueous electrolyte is presented. The PTO‐cathode shows a high specific capacity (336 mAh g^?1) for Zn²⁺ storage with fast kinetics and high reversibility. Thus, the PTO//Zn full cell exhibits a high energy density (186.7 Wh kg^?1), supercapacitor‐like power behavior and long‐term lifespan (over 1000 cycles). Moreover, a belt‐shaped PTO//Zn battery with robust mechanical durability and remarkable flexibility is first fabricated to clarify its potential application in wearable electronic devices.     

Solvent-derived Fluorinated Secondary Interphase for Reversible Zn-graphite Dual-ion Batteries

The irreversibility of anion intercalation-deintercalation is a fundamental issue in determining the cycling stability of a dual-ion battery (DIB). In this work, we demonstrate that using a partially fluorinated carbonate solvent can drive a beneficial fluorinated secondary interphase layer formation. Such layer facilitates reversible anion (de−)intercalation processes by impeding solvent molecule co-intercalation and the associated graphite exfoliation. The enhanced reversibility of anion transport contributes to the overall cycling stability for a Zn-graphite DIB—a high Coulombic efficiency of 98.5 % after 800 cycles, with an attractive discharge capacity of 156 mAh g⁻¹ and a mid-point discharge voltage of ≈1.7 V (at 0.1 A g⁻¹). In addition, the formed fluorinated secondary interphase suppresses the self-discharge behavior, preserving 29 times of the capacity retention rate compared to the battery with a commonly used carbonate solvent, after standing for 24 hours. This work provides a simple and effective strategy for addressing the critical challenges in graphite-based DIBs and contributes to fundamental understanding to help accelerate their practical application.     

Poly(2,5‐dimercapto‐1,3,4‐thiadiazole) as a Cathode for Rechargeable Lithium Batteries with Dramatically Improved Performance

Organosulfur compounds with multiple thiol groups are promising for high gravimetric energy density electrochemical energy storage. We have synthesized a poly(2,5‐dimercapto‐1,3,4‐thiadiazole) (PDMcT)/poly(3,4‐ethylenedioxythiophene) (PEDOT) composite cathode for lithium‐ion batteries with a new method and investigated its electrochemical behavior by charge/discharge cycles and cyclic voltammetry (CV) in an ether‐based electrolyte. Based on a comparison of the electrochemical performance with a carbonate‐based electrolyte, we found a much higher discharge capacity, but also a very attractive cycling performance of PDMcT by using a tetra(ethylene glycol) dimethyl ether (TEGDME)‐based electrolyte. The first discharge capacity of the as‐synthesized PDMcT/PEDOT composite approached 210 mAh g^?1 in the TEGDME‐based electrolyte. CV results clearly show that the redox reactions of PDMcT are highly reversible in this TEGDME‐based electrolyte. The reversible capacity remained around 120 mAh g^?1 after 20 charge/discharge cycles. With improved cycling performance and very low cost, PDMcT could become a very promising cathode material when combined with a TEGDME‐based electrolyte. The poor capacity in the carbonate‐based electrolyte is a consequence of the irreversible reaction of the DMcT monomer and dimer with the solvent, emphasizing the importance of electrolyte chemistry when studying molecular‐based battery materials.     

Advanced High‐Voltage Aqueous Lithium‐Ion Battery Enabled by “Water‐in‐Bisalt” Electrolyte

A new super‐concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra‐high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO₂ as the anode material, and a 2.5 V aqueous Li‐ion cell based on LiMn₂O₄ and carbon‐coated TiO₂ delivered the unprecedented energy density of 100 Wh kg^?1 for rechargeable aqueous Li‐ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the “water‐in‐salt” electrolyte further pushed the energy densities of aqueous Li‐ion cells closer to those of the state‐of‐the‐art Li‐ion batteries.