Rechargeable Na/Cl2 and Li/Cl2 batteries.

Lithium-ion batteries (LIBs) are widely used in applications ranging from electric vehicles to wearable devices. Before the invention of secondary LIBs, the primary lithium-thionyl chloride (Li-SOCl2) battery was developed in the 1970s using SOCl2 as the catholyte, lithium metal as the anode and amorphous carbon as the cathode1-7. This battery discharges by lithium oxidation and catholyte reduction to sulfur, sulfur dioxide and lithium chloride, is well known for its high energy density and is widely used in real-world applications; however, it has not been made rechargeable since its invention8-13. Here we show that with a highly microporous carbon positive electrode, a starting electrolyte composed of aluminium chloride in SOCl2 with fluoride-based additives, and either sodium or lithium as the negative electrode, we can produce a rechargeable Na/Cl2 or Li/Cl2 battery operating via redox between mainly Cl2/Cl- in the micropores of carbon and Na/Na+ or Li/Li+ redox on the sodium or lithium metal. The reversible Cl2/NaCl or Cl2/LiCl redox in the microporous carbon affords rechargeability at the positive electrode side and the thin alkali-fluoride-doped alkali-chloride solid electrolyte interface stabilizes the negative electrode, both are critical to secondary alkali-metal/Cl2 batteries.

Shedding light on rechargeable Na/Cl2 battery.

Advancing new ideas of rechargeable batteries represents an important path to meeting the ever-increasing energy storage needs. Recently, we showed rechargeable sodium/chlorine (Na/Cl2) (or lithium/chlorine Li/Cl2) batteries that used a Na (or Li) metal negative electrode, a microporous amorphous carbon nanosphere (aCNS) positive electrode, and an electrolyte containing dissolved aluminum chloride and fluoride additives in thionyl chloride [G. Zhu et al., Nature 596, 525-530 (2021) and G. Zhu et al., J. Am. Chem. Soc. 144, 22505-22513 (2022)]. The main battery redox reaction involved conversion between NaCl and Cl2 trapped in the carbon positive electrode, delivering a cyclable capacity of up to 1,200 mAh g-1 (based on positive electrode mass) at a ~3.5 V discharge voltage [G. Zhu et al., Nature 596, 525-530 (2021) and G. Zhu et al., J. Am. Chem. Soc. 144, 22505-22513 (2022)]. Here, we identified by X-ray photoelectron spectroscopy (XPS) that upon charging a Na/Cl2 battery, chlorination of carbon in the positive electrode occurred to form carbon-chlorine (C-Cl) accompanied by molecular Cl2 infiltrating the porous aCNS, consistent with Cl2 probed by mass spectrometry. Synchrotron X-ray diffraction observed the development of graphitic ordering in the initially amorphous aCNS under battery charging when the carbon matrix was oxidized/chlorinated and infiltrated with Cl2. The C-Cl, Cl2 species and graphitic ordering were reversible upon discharge, accompanied by NaCl formation. The results revealed redox conversion between NaCl and Cl2, reversible graphitic ordering/amorphourization of carbon through battery charge/discharge, and probed trapped Cl2 in porous carbon by XPS.

A high-performance potassium metal battery using safe ionic liquid electrolyte.

Potassium secondary batteries are contenders of next-generation energy storage devices owing to the much higher abundance of potassium than lithium. However, safety issues and poor cycle life of K metal battery have been key bottlenecks. Here we report an ionic liquid electrolyte comprising 1-ethyl-3-methylimidazolium chloride/AlCl3/KCl/potassium bis(fluorosulfonyl) imide for safe and high-performance batteries. The electrolyte is nonflammable and exhibits a high ionic conductivity of 13.1 mS cm-1 at room temperature. A 3.6-V battery with K anode and Prussian blue/reduced graphene oxide cathode delivers a high energy and power density of 381 and 1,350 W kg-1, respectively. The battery shows an excellent cycling stability over 820 cycles, retaining ∼89% of the original capacity with high Coulombic efficiencies of ∼99.9%. High cyclability is also achieved at elevated temperatures up to 60 °C. Uniquely, robust K, Al, F, and Cl-containing passivating interphases are afforded with this electrolyte, which is key to superior battery cycling performances.

High-Capacity Rechargeable Li/Cl2 Batteries with Graphite Positive Electrodes.

Developing new types of high-capacity and high-energy density rechargeable batteries is important to future generations of consumer electronics, electric vehicles, and mass energy storage applications. Recently, we reported ∼3.5 V sodium/chlorine (Na/Cl2) and lithium/chlorine (Li/Cl2) batteries with up to 1200 mAh g-1 reversible capacity, using either a Na or a Li metal as the negative electrode, an amorphous carbon nanosphere (aCNS) as the positive electrode, and aluminum chloride (AlCl3) dissolved in thionyl chloride (SOCl2) with fluoride-based additives as the electrolyte [Zhu et al., Nature, 2021, 596 (7873), 525-530]. The high surface area and large pore volume of aCNS in the positive electrode facilitated NaCl or LiCl deposition and trapping of Cl2 for reversible NaCl/Cl2 or LiCl/Cl2 redox reactions and battery discharge/charge cycling. Here, we report an initially low surface area/porosity graphite (DGr) material as the positive electrode in a Li/Cl2 battery, attaining high battery performance after activation in carbon dioxide (CO2) at 1000 °C (DGr_ac) with the first discharge capacity ∼1910 mAh g-1 and a cycling capacity up to 1200 mAh g-1. Ex situ Raman spectroscopy and X-ray diffraction (XRD) revealed the evolution of graphite over battery cycling, including intercalation/deintercalation and exfoliation that generated sufficient pores for hosting LiCl/Cl2 redox. This work opens up widely available, low-cost graphitic materials for high-capacity alkali metal/Cl2 batteries. Lastly, we employed mass spectrometry to probe the Cl2 trapped in the graphitic positive electrode, shedding light into the Li/Cl2 battery operation.

Selective and High Current CO2 Electro-Reduction to Multicarbon Products in Near-Neutral KCl Electrolytes.

Reducing CO2 to value-added multicarbon (C2+) fuels and chemicals using renewable energy is a viable way to circumvent CO2 buildup in the atmosphere and facilitate closing the carbon cycle. To date it remains a challenge to achieve high product selectivity and long-term stability of electrocatalytic carbon dioxide reduction reaction (CO2RR) especially at practically relevant high current levels >100 mA cm-2. Here, we report a simple electrodeposited Cu electrocatalyst on a hydrophobic porous gas-diffusion layer (GDL) electrode affording stable and selective CO2RR to C2+ products in near-neutral KCl electrolytes. By directing the CO2 stream to fully submerged hydrophobic GDLs in a H-cell, high C2+ partial current densities near 100 mA cm-2 were achieved. In a flow-cell setup, the Cu/GDL cathode in 2 M KCl afforded stable CO2RR superior to that in widely used KOH electrolytes. We found that Cu etching/corrosion associated with trace oxygen played a role in the catalyst instability in alkaline media under cathodic CO2RR conditions, a problem largely suppressed in near-neutral electrolyte. A two-electrode CO2 electrolyzer was constructed with a Cu/GDL cathode in KCl catholyte and an anode comprised of nickel-iron hydroxide on nickel foam (NiFe/NF) in a KOH anolyte separated by Nafion membrane. By periodically adding HCl to the KCl catholyte to compensate the increasing pH and remove accumulated (bi)carbonates, we observed little decay over ∼30 h in flow-cell CO2RR activity and selectivity at 150 mA cm-2 with a high Faradaic efficiency (FE) of ∼75% and energy efficiency of 40% for C2+ products.

Rechargeable Li/Cl2 Battery Down to -80 °C.

Low temperature rechargeable batteries are important to life in cold climates, polar/deep-sea expeditions, and space explorations. Here, this work reports 3.5-4 V rechargeable lithium/chlorine (Li/Cl2 ) batteries operating down to -80 °C, employing Li metal negative electrode, a novel carbon dioxide (CO2 ) activated porous carbon (KJCO2 ) as the positive electrode, and a high ionic conductivity (≈5-20 mS cm-1 from -80 °C to room-temperature) electrolyte comprised of aluminum chloride (AlCl3 ), lithium chloride (LiCl), and lithium bis(fluorosulfonyl)imide (LiFSI) in low-melting-point (-104.5 °C) thionyl chloride (SOCl2 ). Between room-temperature and -80 °C, the Li/Cl2 battery delivers up to ≈29 100-4500 mAh g-1 first discharge capacity (based on carbon mass) and a 1200-5000 mAh g-1 reversible capacity over up to 130 charge-discharge cycles. Mass spectrometry and X-ray photoelectron spectroscopy probe Cl2 trapped in the porous carbon upon LiCl electro-oxidation during charging. At -80 °C, Cl2 /SCl2 /S2 Cl2 generated by electro-oxidation in the charging step are trapped in porous KJCO2 carbon, allowing for reversible reduction to afford a high discharge voltage plateau near ≈4 V with up to ≈1000 mAh g-1 capacity for SCl2 /S2 Cl2 reduction and up to ≈4000 mAh g-1 capacity at ≈3.1 V plateau for Cl2 reduction.

Chlorine effect on the formation of carbon nanofibers.

Platelet graphite nanofibers (GNFs) and turbostratic carbon nanofibers (CNFs) are synthesized by the thermal evaporation and decomposition of a polymer-based mixture at 700 degrees C using Ni as a catalyst. The mixture consists of poly(ethylene glycol) (PEG), serving as the carbon source, and hydrochloric acid solution (HCl(aq)), serving as the promoter/additive for the growth of CNFs. High-purity zigzag-shaped platelet GNFs form with 10 wt% HCl(aq) as an additive in the PEG. The diameters of the platelet GNFs are in the range of 40-60 nm, with lengths of a few micrometers. High-resolution transmission electron microscopy images indicate a high degree of graphitization and well ordered graphene layers along the fiber axis. In contrast, high-purity turbostratic CNFs form with 20 wt% HCl(aq) in the PEG. The diameter and length of the turbostratic CNFs are 20-40 nm and a few micrometers, respectively. The participation of HCl in the thermal process leads to the formation of Ni-Cl compounds. The amount of chlorine affects the shape of the Ni catalyst, which determines the type of CNF formed.

A Nonflammable High-Voltage 4.7 V Anode-Free Lithium Battery.

Anode-free lithium-metal batteries employ in situ lithium-plated current collectors as negative electrodes to afford optimal mass and volumetric energy densities. The main challenges to such batteries include their poor cycling stability and the safety issues of the flammable organic electrolytes. Here, a high-voltage 4.7 V anode-free lithium-metal battery is reported, which uses a Cu foil coated with a layer (≈950 nm) of silicon-polyacrylonitrile (Si-PAN, 25.5 µg cm-2 ) as the negative electrode, a high-voltage cobalt-free LiNi0.5 Mn1.5 O4 (LNMO) as the positive electrode and a safe, nonflammable ionic liquid electrolyte composed of 4.5 m lithium bis(fluorosulfonyl)imide (LiFSI) salt in N-methyl-N-propyl pyrrolidiniumbis(fluorosulfonyl)imide (Py13 FSI) with 1 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as additive. The Si-PAN coating is found to seed the growth of lithium during charging, and reversibly expand/shrink during lithium plating/stripping over battery cycling. The wide-voltage-window electrolyte containing a high concentration of FSI- and TFSI- facilitates the formation of stable solid-electrolyte interphase, affording a 4.7 V anode-free Cu@Si-PAN/LiNi0.5 Mn1.5 O4 battery with a reversible specific capacity of ≈120 mAh g-1 and high cycling stability (80% capacity retention after 120 cycles). These results represent the first anode-free Li battery with a high 4.7 V discharge voltage and high safety.

A carbonyl iron/carbon fiber material for electromagnetic wave absorption.

A carbonyl iron/carbon fiber material consisting of carbon fibers grown on micrometer-sized carbonyl iron sphere, was synthesized by chemical vapor deposition using a mixture of C2H2 and H2. The hollow-core carbon fibers (outer diameter: 140 nm and inner diameter: 40 nm) were composed of well-ordered graphene layers which were almost parallel to the long axis of the fibers. A composite (2 mm thick) consisting of the carbonyl iron/carbon fibers and epoxy resin demonstrated excellent electromagnetic (EM) wave absorption. Minimum reflection losses of -36 dB (99.95% of EM wave absorption) at 7.6 GHz and -32 dB (99.92% of EM wave absorption) at 34.1 GHz were achieved. The well-dispersed and network-like carbon fibers in the resin matrix affected the dielectric loss of the EM wave while the carbonyl iron affected the magnetic loss.

Structural changes in fibrous carbon nanomaterials produced by adding sulfur during chemical vapor deposition.

Vapor-grown carbon fibers (VGCFs), platelet graphite nanofibers (PGNFs), turbostratic carbon nanofibers (CNFs), and carbon spheres were continuously produced by the thermal decomposition of ethanol in the presence of an Fe catalyst and a sulfur promoter at 1100 degrees C under a nitrogen/hydrogen atmosphere in a vertical chemical vapor deposition reactor. The sulfur concentration dramatically affected the morphology and microstructure of the carbon materials produced. A large amount of sulfur in the catalytic precursor led to the direct pyrolysis of hydrocarbons and the formation of carbon spheres (Fe:S = 1:10) while a lower amount of sulfur led to the formation of fibrous carbon materials, including VGCFs (Fe:S = 1:0.2), PGNFs (Fe:S = 1:2), and turbostratic CNFs (Fe:S = 1:5). The degree of poisoning of the catalysts determined the precipitation of the graphene layers, allowing the different types of carbon material to form.

High-Safety and High-Energy-Density Lithium Metal Batteries in a Novel Ionic-Liquid Electrolyte.

Rechargeable lithium metal batteries are next generation energy storage devices with high energy density, but face challenges in achieving high energy density, high safety, and long cycle life. Here, lithium metal batteries in a novel nonflammable ionic-liquid (IL) electrolyte composed of 1-ethyl-3-methylimidazolium (EMIm) cations and high-concentration bis(fluorosulfonyl)imide (FSI) anions, with sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) as a key additive are reported. The Na ion participates in the formation of hybrid passivation interphases and contributes to dendrite-free Li deposition and reversible cathode electrochemistry. The electrolyte of low viscosity allows practically useful cathode mass loading up to ≈16 mg cm-2 . Li anodes paired with lithium cobalt oxide (LiCoO2 ) and lithium nickel cobalt manganese oxide (LiNi0.8 Co0.1 Mn0.1 O2 , NCM 811) cathodes exhibit 99.6-99.9% Coulombic efficiencies, high discharge voltages up to 4.4 V, high specific capacity and energy density up to ≈199 mAh g-1 and ≈765 Wh kg-1 respectively, with impressive cycling performances over up to 1200 cycles. Highly stable passivation interphases formed on both electrodes in the novel IL electrolyte are the key to highly reversible lithium metal batteries, especially for Li-NMC 811 full batteries.

Synthesis of ZnO nanowires and their applications as an ultraviolet photodetector.

High purity ZnO nanowire arrays were synthesized uniformly on a 1.5 cm x 2 cm tin-doped indium oxide (ITO) glass substrate. The ZnO nanowire arrays were formed with a uniform diameter distribution of 30-50 nm and a length of about 5 microm, synthesized via thermal decomposition of zinc acetate at 300 degrees C in air. Analysis by X-ray diffraction and transmission electron microscopy showed that the ZnO nanowires are of single crystal structure with a preferred growth orientation of [001]. A study of the growth mechanism showed that it is a vapor-solid (VS) growth process. The synthesis of these nanowires begins with the processes of dehydration, vaporization, decomposition, and oxidation of the zinc acetate. Next, the ZnO clusters are deposited to form seeds that give rise to selective epitaxial growth of the ZnO nanowires. Optical analysis of ZnO nanowires was performed by UV-visible and fluorescence spectrophotometry, investigating both the photocurrent characteristics and UV photoresponse of the ZnO nanowire photodetectors. A study of optical properties showed that the as-produced ZnO nanowires have great potential as UV photodetectors/sensors.

A safe and non-flammable sodium metal battery based on an ionic liquid electrolyte.

Rechargeable sodium metal batteries with high energy density could be important to a wide range of energy applications in modern society. The pursuit of higher energy density should ideally come with high safety, a goal difficult for electrolytes based on organic solvents. Here we report a chloroaluminate ionic liquid electrolyte comprised of aluminium chloride/1-methyl-3-ethylimidazolium chloride/sodium chloride ionic liquid spiked with two important additives, ethylaluminum dichloride and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide. This leads to the first chloroaluminate based ionic liquid electrolyte for rechargeable sodium metal battery. The obtained batteries reached voltages up to ~ 4 V, high Coulombic efficiency up to 99.9%, and high energy and power density of ~ 420 Wh kg-1 and ~ 1766 W kg-1, respectively. The batteries retained over 90% of the original capacity after 700 cycles, suggesting an effective approach to sodium metal batteries with high energy/high power density, long cycle life and high safety.

In situ synthesis of platelet graphite nanofibers from thermal decomposition of poly(ethylene glycol).

Platelet graphite nanofibers (PGNFs) were synthesized by in situ thermal decomposition from a mixture containing poly(ethylene glycol) (PEG) serving as the carbon source and nickel chloride (NiCl(2)) serving as the catalytic precursor. The mixture was conducted by thermal treatment under a nitrogen atmosphere at 750 degrees C and results found PGNFs with high purity and a uniform diameter distribution formed without hydrocarbon gases in the process. Observations using field-emission scanning electron microscopy and high-resolution transmission electron microscopy revealed PGNFs with a high degree of graphitization, well-ordered graphene layers, and uniform diameters of 10-20 nm. Thermogravimetry-differential scanning calorimetry-mass spectrometry was employed to study the thermal decomposition phenomena of the mixture (PEG/NiCl(2)) before the thermal process. The analysis clarified the in situ synthesis growth mechanism of PGNFs from the mixture.

Formation of SnO2 Nanowires Using Thermal Evaporation of SnO.

SnO2 nanowires (NWs) were grown on a catalyst-coated silicon wafer via the thermal evaporation of SnO powder at 20-30 mTorr. Three types of catalyst, namely Fe, Pt, and Au, were used for the synthesis of the SnO2 NWs. The results show that Pt and Au can be used for the formation of SnO2 NWs. Depending on the experimental conditions, the diameter and length of the SnO2 NWs obtained with Au catalyst are in the ranges of 20-65 nm and a few hundred nanometers to a few micrometers, respectively. The size of the Au nanocatalyst greatly affects the diameter of the SnO2 NWs. With increasing particle size of the Au catalyst, the diameter of the SnO2 NWs increased. In addition, the results show that the synthesis of SnO2 NWs can be conducted at 500 degrees C, which is compatible with low-temperature processes.

Flat Panel Light Source with Lateral Gate Structure Based on SiC Nanowire Field Emitters.

A field-emission light source with high luminance, excellent luminance uniformity, and tunable luminance characteristics with a novel lateral-gate structure is demonstrated. The lateral-gate triode structure comprises SiC nanowire emitters on a Ag cathode electrode and a pair of Ag gate electrodes placed laterally on both sides of the cathode. The simple and cost-effective screen printing technique is employed to pattern the lateral-gates and cathode structure on soda lime glass. The area coverage of the screen-printed cathode and gates on the glass substrate (area: 6 × 8 cm(2)) is in the range of 2.04% - 4.74% depending on the set of cathode-gate electrodes on the substrate. The lateral-gate structure with its small area coverage exhibits a two-dimensional luminance pattern with high brightness and good luminance uniformity. A maximum luminance of 10,952 cd/cm(2) and a luminance uniformity of >90% can be achieved with a gate voltage of 500 V and an anode voltage of 4000 V, with an anode current of 1.44 mA and current leakage to the gate from the cathode of about 10%.

Complete corrosion inhibition through graphene defect passivation.

Graphene is expected to enable superior corrosion protection due to its impermeability and chemical inertness. Previous reports, however, demonstrate limited corrosion inhibition and even corrosion enhancement of graphene on metal surfaces. To enable the reliable and complete passivation, the origin of the low inhibition efficiency of graphene was investigated. Combining electrochemical and morphological characterization techniques, nanometer-sized structural defects in chemical vapor deposition grown graphene were found to be the cause for the limited passivation effect. Extremely fast mass transport on the order of meters per second both across and parallel to graphene layers results in an inhibition efficiency of only ∼50% for Cu covered with up to three graphene layers. Through selective passivation of the defects by atomic layer deposition (ALD) an enhanced corrosion protection of more than 99% was achieved, which compares favorably with commercial corrosion protection methods.

A 3D α-Fe2O3 nanoflake urchin-like structure for electromagnetic wave absorption.

An α-Fe(2)O(3) nanoflake urchin-like structure is formed via the thermal oxidation of micrometre-sized iron spheres in air at temperatures of 300-400 °C. The material consists of α-Fe(2)O(3) nanoflakes grown perpendicularly to the sphere surface, a layer of a mixture of α-Fe(2)O(3) and Fe(3)O(4) as the oxidation shell, and an iron core. The ranges of the tip diameters of the nanoflakes are 20-30 nm (300 °C), 30-50 nm (350 °C), and 60-100 nm (400 °C). A composite consisting of the α-Fe(2)O(3) nanoflake urchin-like structure and an epoxy resin exhibits an excellent electromagnetic (EM) wave absorption ability. A small tip diameter (20-30 nm) and a high density (3 × 10(13) nanoflakes m(-2)) lead to a good network structure and good EM wave absorption. A minimum reflection loss (RL) of -33.8 dB (99.93% of EM wave absorption) at 7.8 GHz can be achieved using a 70 wt% urchin-like material as the filler in the resin matrix. In addition, a composite containing 60 wt% unchin-like material exhibits dual-frequency EM wave absorption. The peaks of the minimum RL values are located at 9.7 GHz (-26.2 dB) and 25.2 GHz (-21.0 dB). The unique morphology of the α-Fe(2)O(3) nanoflake urchin-like material is believed to be a key factor in the enhancement of the EM wave absorption.

Formation of three-dimensional urchin-like α-Fe2O3 structure and its field-emission application.

A three-dimensional urchin-like α-Fe(2)O(3) microstructure is formed via a simple, template-free, and one-step thermal oxidation of Fe spheres in an air atmosphere at temperatures in the range of 300-450 °C. The urchin-like α-Fe(2)O(3) microstructure consists of crystalline α-Fe(2)O(3) nanoflakes grown perpendicularly on the surface of the sphere, a shell layer of α-Fe(2)O(3)/Fe(3)O(4), and an Fe core. During the oxidation process, the nanoflakes germinate and grow from cracks in the oxidation layer on the surface. The length of the nanoflakes increases with oxidation time. The tip diameters of the nanoflakes are in ranges of 10-20 nm at 300 °C, 20-30 nm at 350 °C, and 40-60 nm at 400 °C; the length can reach up to a few micrometers. The field-emission characteristics of the samples are experimentally studied and simulated. The results show that the urchin-like emitter has a low turn-on field of 2.8 V/µm, high field-enhancement factor of 4313, excellent emission uniformity of over 4 cm(2), and good emission stability during a 24 h test.

Synthesis of a CNT-grafted TiO(2) nanocatalyst and its activity triggered by a DC voltage.

Carbon nanotube (CNT)-grafted TiO(2) (CNT/TiO(2)) was synthesized as an electrically conductive catalyst that exhibits redox ability under electrical excitation besides ultraviolet (UV) irradiation. The CNT/TiO(2) material was synthesized by a two-step process. Ni nanoparticles were photodeposited onto TiO(2) first. The Ni nanoparticles then served as seeds for the growth of CNTs using the chemical vapor deposition (CVD) of C(2)H(2). The CNT/TiO(2) nanocomposite exhibits strong oxidation activity toward NO gas molecules via both photocatalysis under UV irradiation and electrocatalysis under a DC voltage of 500 V in dark conditions.