High energy density at high power density is still a challenge for the current Li‐ion capacitors (LICs) due to the mismatch of charge‐storage capacity and electrode kinetics between capacitor‐type cathode and battery‐type anode. In this work, B and N dual‐doped 3D porous carbon nanofibers are prepared through a facile method as both capacitor‐type cathode and battery‐type anode for LICs. The B and N dual doping has profound effect in tuning the porosity, functional groups, and electrical conductivity for the porous carbon nanofibers. With rational design, the developed B and N dual‐doped carbon nanofibers (BNC) exhibit greatly improved electrochemical performance as both cathode and anode for LICs, which greatly alleviates the mismatch between the two electrodes. For the first time, a 4.5 V “dual carbon” BNC//BNC LIC device is constructed and demonstrated, exhibiting outstanding energy density and power capability compared to previously reported LICs with other configurations. In specific, the present BNC//BNC LIC device can deliver a large energy density of 220 W h kg−1 and a high power density of 22.5 kW kg−1 (at 104 W h kg−1) with reasonably good cycling stability (≈81% retention after 5000 cycles).

Metal sulfides are promising anode materials for sodium-ion batteries due to their large specific capacities. The practical applications of metal sulfides in sodium-ion batteries, however, are still limited due to their large volume expansion, poor cycling stability, and sluggish electrode kinetics. In this work, a two-dimensional heterostructure of CoS (CoS and CoS) quantum dots embedded N/S-doped carbon nanosheets (CoS@NSC) is prepared by a sol-gel method. The CoS quantum dots are in situ formed within ultrafine carbon nanosheets without further sulfidation, thus resulting in ultrafine CoS particle size and embedded heterostructure. Meanwhile, enriched N and S codoping in the carbon nanosheets greatly enhances the electrical conductivity for the conductive matrix and creates more active sites for sodium storage. As a result, the hybrid CoS@NSC electrode shows excellent rate capability (600 mAh g at 0.2 A g and 500 mAh g at 10 A g) and outstanding cycling stability (87% capacity retention after 200 cycles at 1 A g), making it promising as an anode material for high-performance sodium-ion batteries. A CoS@NSC//NaMnO full cell is demonstrated, and it can deliver a specific capacity of 414 mAh g (based on the mass of CoS@NSC) at a current density of 0.2 A g.

Zn batteries potentially offer the highest energy density among aqueous batteries that are inherently safe, inexpensive, and sustainable. However, most cathode materials in Zn batteries suffer from capacity fading, particularly at a low current rate. Herein, it is shown that the ZnCl 2 "water-in-salt" electrolyte (WiSE) addresses this capacity fading problem to a large extent by facilitating unprecedented performance of a Zn battery cathode of Ca 0.20 V 2 O 5 •0.80H 2 O. Upon increasing the concentration of aqueous ZnCl 2 electrolytes from 1 m to 30 m, the capacity of Ca 0.20 V 2 O 5 •0.80H 2 O rises from 296 mAh g −1 to 496 mAh g −1 ; its absolute working potential increases by 0.4 V, and most importantly, at a low current rate of 50 mA g −1 , that is, C/10; its capacity retention increases from 8.4% to 51.1% over 100 cycles. Ex situ characterization results point to the formation of a new ready-to-dissolve phase on the electrode in the dilute electrolyte. The results demonstrate that the Zn-based WiSE may provide the underpinning platform for the applications of Zn batteries for stationary grid-level storage.

The sluggish ion diffusion and electrolyte freezing with volumetric changes limit the low-T performance of rechargeable batteries. Herein, we report a high-rate aqueous proton battery (APB) operated at and below -78 o C via a 62 wt% (9.5 m) H 3 PO 4 electrolyte. The APB is a rocking-chair battery that operates with protons commuting between a Prussian blue cathode and a MoO 3 anode. At -78 o C, the APB full cells exhibit stable cycle life for 450 cycles, high round-trip efficiency of 85%, and appreciable power performance. The APB delivers 30% of its room-temperature capacity even at -88 o C. The proton storage mechanism is investigated by ex situ synchrotron XRD, XAS, and XPS. The APB pouch cells demonstrate nil capacity fading at -78 o C, which offers a safe and reliable candidate for high-latitude applications.

Potassium‐ion batteries (PIBs) are one of the emerging energy‐storage technologies due to the low cost of potassium and theoretically high energy density. However, the development of PIBs is hindered by the poor K+ transport kinetics and the structural instability of the cathode materials during K+ intercalation/deintercalation. In this work, birnessite nanosheet arrays with high K content (K0.77MnO2⋅0.23H2O) are prepared by “hydrothermal potassiation” as a potential cathode for PIBs, demonstrating ultrahigh reversible specific capacity of about 134 mAh g−1 at a current density of 100 mA g−1, as well as great rate capability (77 mAh g−1 at 1000 mA g−1) and superior cycling stability (80.5% capacity retention after 1000 cycles at 1000 mA g−1). With the introduction of adequate K+ ions in the interlayer, the K‐birnessite exhibits highly stabilized layered structure with highly reversible structure variation upon K+ intercalation/deintercalation. The practical feasibility of the K‐birnessite cathode in PIBs is further demonstrated by constructing full cells with a hard–soft composite carbon anode. This study highlights effective K+‐intercalation for birnessite to achieve superior K‐storage performance for PIBs, making it a general strategy for developing high‐performance cathodes in rechargeable batteries beyond lithium‐ion batteries.