Rocking‐chair based lithium‐ion batteries (LIBs) have extensively applied to consumer electronics and electric vehicles (EVs) for solving the present worldwide issues of fossil fuel exhaustion and ...environmental pollution. However, due to the growing unprecedented demand of LIBs for commercialization in EVs and grid‐scale energy storage stations, and a shortage of lithium and cobalt, the increasing cost gives impetus to exploit low‐cost rechargeable battery systems. Dual‐ion batteries (DIBs), in which both cations and anions are involved in the electrochemical redox reaction, are one of the most promising candidates to meet the low‐cost requirements of commercial applications, because of their high working voltage, excellent safety, and environmental friendliness compared to conventional rocking‐chair based LIBs. However, DIB technologies are only at the stage of fundamental research and considerable effort is required to improve the energy density and cycle life further. We review the development history and current situation, and discuss the reaction kinetics involved in DIBs, including various anionic intercalation mechanism of cathodes, and the reactions at the anodes including intercalation and alloying to explore promising strategies towards low‐cost DIBs with high performance.
Beyond conventional batteries: This Review presents the development history and state of the art of DIBs and presents the reaction kinetics and corresponding critical issues including the various anionic intercalation mechanisms of cathodes, and the reactions at the anodes, including intercalation and alloying, to explore promising strategies towards low‐cost DIBs with high performance.
Calcium-ion batteries (CIBs) are attractive candidates for energy storage because Ca
has low polarization and a reduction potential (-2.87 V versus standard hydrogen electrode, SHE) close to that of ...Li
(-3.04 V versus SHE), promising a wide voltage window for a full battery. However, their development is limited by difficulties such as the lack of proper cathode/anode materials for reversible Ca
intercalation/de-intercalation, low working voltages (<2 V), low cycling stability, and especially poor room-temperature performance. Here, we report a CIB that can work stably at room temperature in a new cell configuration using graphite as the cathode and tin foils as the anode as well as the current collector. This CIB operates on a highly reversible electrochemical reaction that combines hexafluorophosphate intercalation/de-intercalation at the cathode and a Ca-involved alloying/de-alloying reaction at the anode. An optimized CIB exhibits a working voltage of up to 4.45 V with capacity retention of 95% after 350 cycles.
Large-scale implementation of electrochemical hydrogen production requires several fundamental issues to be solved, including understanding the mechanism and developing inexpensive electrocatalysts ...that work well at high current densities. Here we address these challenges by exploring the roles of morphology and surface chemistry, and develop inexpensive and efficient electrocatalysts for hydrogen evolution. Three model electrocatalysts are flat platinum foil, molybdenum disulfide microspheres, and molybdenum disulfide microspheres modified by molybdenum carbide nanoparticles. The last catalyst is highly active for hydrogen evolution independent of pH, with low overpotentials of 227 mV in acidic medium and 220 mV in alkaline medium at a high current density of 1000 mA cm
, because of enhanced transfer of mass (reactants and hydrogen bubbles) and fast reaction kinetics due to surface oxygen groups formed on molybdenum carbide during hydrogen evolution. Our work may guide rational design of electrocatalysts that work well at high current densities.
Electroactive organic materials with tailored functional groups are of great importance for aqueous Zn–organic batteries due to their green and renewable nature. Herein, a completely new ...N‐heteroaromatic material, hexaazatrinaphthalene‐phenazine (HATN‐PNZ) is designed and synthesized, by an acid‐catalyzed condensation reaction, and its use as an ultrahigh performance cathode for Zn‐ion batteries demonstrated. Compared with phenazine monomer, it is revealed that the π‐conjugated structure of N‐heteroaromatics can effectively increase electron delocalization, thereby improving its electrical conductivity. Furthermore, the enlarged aromatic structure noticeably suppresses its dissolution in aqueous electrolytes, thus enabling high structural stability. As expected, the HATN‐PNZ cathode delivers a large reversible capacity of 257 mAh g−1 at 5 A g−1, ultrahigh rate capability of 144 mAh g−1 at 100 A g−1, and an extremely long cycle life of 45 000 cycles at 50 A g−1. Investigation of the charge‐storage mechanism demonstrates the synergistic coordination of both Zn2+ and H+ cations with the phenanthroline groups, with Zn2+ first followed by H+, accompanying the reversible formation of zinc hydroxide sulfate hydrate. This work provides a molecular‐engineering strategy for superior organic materials and adds new insights to understand the charge‐storage behavior of aqueous Zn–organic batteries.
The synthesis of a novel π‐conjugated N‐heteroaromatic hexaazatrinaphthalene‐phenazine (HATN‐PNZ) material is reported, and its use as an ultrahigh performance cathode for Zn‐ion batteries is demonstrated. The enlarged aromatic structure noticeably suppresses its dissolution in aqueous electrolytes, thus enabling high structural stability and long cycling life.
Potassium-ion batteries are a compelling technology for large scale energy storage due to their low-cost and good rate performance. However, the development of potassium-ion batteries remains in its ...infancy, mainly hindered by the lack of suitable cathode materials. Here we show that a previously known frustrated magnet, KFeC
O
F, could serve as a stable cathode for potassium ion storage, delivering a discharge capacity of ~112 mAh g
at 0.2 A g
and 94% capacity retention after 2000 cycles. The unprecedented cycling stability is attributed to the rigid framework and the presence of three channels that allow for minimized volume fluctuation when Fe
/Fe
redox reaction occurs. Further, pairing this KFeC
O
F cathode with a soft carbon anode yields a potassium-ion full cell with an energy density of ~235 Wh kg
, impressive rate performance and negligible capacity decay within 200 cycles. This work sheds light on the development of low-cost and high-performance K-based energy storage devices.
An N‐superdoped 3D graphene network structure with an N‐doping level up to 15.8 at% for high‐performance supercapacitor is designed and synthesized, in which the graphene foam with high conductivity ...acts as skeleton and nested with N‐superdoped reduced graphene oxide arogels. This material shows a highly conductive interconnected 3D porous structure (3.33 S cm−1), large surface area (583 m2 g−1), low internal resistance (0.4 Ω), good wettability, and a great number of active sites. Because of the multiple synergistic effects of these features, the supercapacitors based on this material show a remarkably excellent electrochemical behavior with a high specific capacitance (of up to 380, 332, and 245 F g−1 in alkaline, acidic, and neutral electrolytes measured in three‐electrode configuration, respectively, 297 F g−1 in alkaline electrolytes measured in two‐electrode configuration), good rate capability, excellent cycling stability (93.5% retention after 4600 cycles), and low internal resistance (0.4 Ω), resulting in high power density with proper high energy density.
A N‐superdoped 3D graphene network structure is synthesized to achieve a highly conductive interconnected 3D porous structure and high N‐doping level simultaneously. The supercapacitors based on this material show a remarkably high capacity, good rate capability, and excellent cycling stability.
Atomically thin 2D materials have received intense interest both scientifically and technologically. Bismuth oxyselenide (Bi2O2Se) is a semiconducting 2D material with high electron mobility and good ...stability, making it promising for high‐performance electronics and optoelectronics. Here, an ambient‐pressure vapor–solid (VS) deposition approach for the growth of millimeter‐size 2D Bi2O2Se single crystal domains with thicknesses down to one monolayer is reported. The VS‐grown 2D Bi2O2Se has good crystalline quality, chemical uniformity, and stoichiometry. Field‐effect transistors (FETs) are fabricated using this material and they show a small contact resistivity of 55.2 Ω cm measured by a transfer line method. Upon light irradiation, a phototransistor based on the Bi2O2Se FETs exhibits a maximum responsivity of 22 100 AW−1, which is a record among currently reported 2D semiconductors and approximately two orders of magnitude higher than monolayer MoS2. The Bi2O2Se phototransistor shows a gate tunable photodetectivity up to 3.4 × 1015 Jones and an on/off ratio up to ≈109, both of which are much higher than phototransistors based on other 2D materials reported so far. The results of this study indicate a method to grow large 2D Bi2O2Se single crystals that have great potential for use in optoelectronic applications.
Because of the high quality of vapor–solid grown material and its excellent contact resistance, Bi2O2Se phototransistors show an ultrahigh photoresponse (22 100 AW−1), record specific detectivity (3.4 × 1015 Jones), and a high on/off ratio (≈109). All these values are much higher than those of phototransistors based on other 2D materials including MoS2 and commercial photodetectors using Si and III–V materials.
A flexible, large-area three-dimensional porous N-doped carbon microtube (NCMT) sponge was prepared via a simple and low-cost process of pyrolyzing facial cotton. Due to its unique structure with a ...micron-scale hollow core and well-graphitized and interconnected porous walls, the NCMT sponge exhibits incomparable electrocatalytic activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) with a small potential difference of 0.63 V between the OER current density at 10 mA cm-2 and the ORR current density at -3 mA cm-2, which is the best to date.
Advanced beyond-silicon electronic technology requires both channel materials and also ultralow-resistance contacts to be discovered
. Atomically thin two-dimensional semiconductors have great ...potential for realizing high-performance electronic devices
. However, owing to metal-induced gap states (MIGS)
, energy barriers at the metal-semiconductor interface-which fundamentally lead to high contact resistance and poor current-delivery capability-have constrained the improvement of two-dimensional semiconductor transistors so far
. Here we report ohmic contact between semimetallic bismuth and semiconducting monolayer transition metal dichalcogenides (TMDs) where the MIGS are sufficiently suppressed and degenerate states in the TMD are spontaneously formed in contact with bismuth. Through this approach, we achieve zero Schottky barrier height, a contact resistance of 123 ohm micrometres and an on-state current density of 1,135 microamps per micrometre on monolayer MoS
; these two values are, to the best of our knowledge, the lowest and highest yet recorded, respectively. We also demonstrate that excellent ohmic contacts can be formed on various monolayer semiconductors, including MoS
, WS
and WSe
. Our reported contact resistances are a substantial improvement for two-dimensional semiconductors, and approach the quantum limit. This technology unveils the potential of high-performance monolayer transistors that are on par with state-of-the-art three-dimensional semiconductors, enabling further device downscaling and extending Moore's law.
Modulating electronic structure of monolayer transition metal dichalcogenides (TMDCs) is important for many applications, and doping is an effective way toward this goal, yet is challenging to ...control. Here, the in situ substitutional doping of niobium (Nb) into TMDCs with tunable concentrations during chemical vapor deposition is reported. Taking monolayer WS2 as an example, doping Nb into its lattice leads to bandgap changes in the range of 1.98–1.65 eV. Noteworthy, electrical transport measurements and density functional theory calculations show that the 4d electron orbitals of the Nb dopants contribute to the density of states of Nb‐doped WS2 around the Fermi level, resulting in an n‐ to p‐type conversion. Nb‐doping also reduces the energy barrier of hydrogen absorption in WS2, leading to an improved electrocatalytic hydrogen evolution performance. These results highlight the effectiveness of controlled doping in modulating the electronic structure of TMDCs and their use in electronic related applications.
Substitutional doping is an important approach to modulate the electronic structure of 2D transition metal dichalcogenides (TMDCs). Using in situ substitutional doping during the chemical vapor deposition process, Nb‐doped TMDCs are grown with variable doping concentrations. The doping modulates the electronic structure of TMDCs and results in the realization of p‐type transport behavior and improved hydrogen evolution reaction performance.
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