Ternary Rotational Polyanion Coupling Enables Fast Li Ion Dynamics in Tetrafluoroborate Ion Doped Antiperovskite Li2OHCl Solid Electrolyte.

Li-rich antiperovskite (LiRAP) hydroxyhalides are emerging as attractive solid electrolyte (SEs) for all-solid-state Li metal batteries (ASSLMBs) due to their low melting point, low cost, and ease of scaling-up. The incorporation of rotational polyanions can reduce the activation energy and thus improve the Li ion conductivity of SEs. Herein, we propose a ternary rotational polyanion coupling strategy to fasten the Li ion conduction in tetrafluoroborate (BF4 -) ion doped LiRAP Li2OHCl. Assisted by first-principles calculation, powder X-ray diffraction, solid-state magnetic resonance and electrochemical impedance spectra, it is confirmed that Li ion transport in BF4 - ion doped Li2OHCl is strongly associated with the rotational coupling among OH-, BF4 - and Li2-O-H octahedrons, which enhances the Li ion conductivity for more than 1.8 times with the activation energy lowering 0.03 eV. This work provides a new perspective to design high-performance superionic conductors with multi-polyanions.

Metal-organic framework (MOF)-incorporated polymeric electrolyte realizing fast lithium-ion transportation with high Li+ transference number for solid-state batteries.

Composite polymer electrolytes (CPEs) show significant advantages in developing solid-state batteries due to their high flexibility and easy processability. In CPEs, solid fillers play a considerable effect on electrochemical performances. Recently, metal-organic frameworks (MOFs) are emerging as new solid fillers and show great promise to regulate ion migration. Herein, by using a Co-based MOF, a high-performance CPE is initially prepared and studied. Benefiting from the sufficient interactions and pore confinement from MOF, the obtained CPE shows both high ionic conductivity and a high Li+ transference number (0.41). The MOF-incorporated CPE then enables a uniform Li deposition and stable interfacial condition. Accordingly, the as-assembled solid batteries demonstrate a high reversible capacity and good cycling performance. This work verifies the practicability of MOFs as solid fillers to produce advanced CPEs, presenting their promising prospect for practical application.

Li-Rich Antiperovskite/Nitrile Butadiene Rubber Composite Electrolyte for Sheet-Type Solid-State Lithium Metal Battery.

Lithium-rich antiperovskites (LiRAPs) hold great promise to be the choice of solid-state electrolytes (SSEs) owing to their high ionic conductivity, low activation energy, and low cost. However, processing sheet-type solid-state Li metal batteries (SSLiB) with LiRAPs remains challenging due to the lack of robust techniques for battery processing. Herein, we propose a scalable slurry-based procedure to prepare a flexible composite electrolyte (CPE), in which LiRAP (e.g., Li2OHCl0.5Br0.5, LOCB) and nitrile butadiene rubber (NBR) serve as an active filler and as a polymer scaffold, respectively. The low-polar solvent helps to stabilize the LiRAP phase during slurry processing. It is found that the addition of LOCB into the NBR polymer enhances the Li ion conductivity for 2.3 times at 60°C and reduces the activation energy (max. 0.07 eV). The as-prepared LOCB/NBR CPE film exhibits an improved critical current of 0.4 mA cm-2 and can stably cycle for over 1000 h at 0.04 mA cm-2 under 60°C. In the SSLiB with the sheet-type configuration of LiFePO4(LFP)||LOCB/NBR CPE||Li, LFP exhibits a capacity of 137 mAh/g under 60 at 0.1°C. This work delivers an effective strategy for fabrication of LiRAP-based CPE film, advancing the LiRAP-family SSEs toward practical applications.

Configuring solid-state batteries to power electric vehicles: a deliberation on technology, chemistry and energy.

Solid-state batteries (SSBs) have been widely regarded as a promising electrochemical energy storage technology to power electric vehicles (EVs) that raise battery safety and energy/power densities as kernel metrics to achieve high-safety, long-range and fast-charge operations. Governments around the world have set ambitious yet imperative goals on battery energy density; however, sluggish charge transport and challenging processing routes of SSBs raise doubts of whether they have the possibility to meet such targets. In this contribution, the battery development roadmap of China is set as the guideline to direct how material chemistries and processing parameters of SSBs need to be optimized to fulfill the requirements of battery energy density. Starting with the identification of bipolar cell configurations in SSBs, the blade cell dimension is then selected as an emerging cell format to clarify weight breakdown of a solid NCM523||Li cell. Quantifying energy densities of SSBs by varying key cell parameters reveals the importance of active material content, cathode layer thickness and solid-electrolyte-separator thickness, whereas the thicknesses of the lithium metal anode and bipolar current collector have mild impacts. Even in the pushing conditions (200 µm for the cathode layer and 20 µm for the solid electrolyte separator), high-nickel ternary (NCM) cathodes hardly meet the expectation of the battery development roadmap in terms of gravimetric energy density at a cell level, while lithium- and manganese-rich ternary (LM-NCM) and sulfur cathodes are feasible. In particular, solid lithium-sulfur batteries, which exhibit exciting gravimetric energy density yet inferior volumetric energy density, need to be well-positioned to adapt diverse application scenarios. This analysis unambiguously defines promising battery chemistries and establishes how key parameters of SSBs can be tailored to cooperatively follow the stringent targets of future battery development.

Lithium-Rich Anti-perovskite Li2OHBr-Based Polymer Electrolytes Enabling an Improved Interfacial Stability with a Three-Dimensional-Structured Lithium Metal Anode in All-Solid-State Batteries.

All-solid-state lithium-metal batteries, with their high energy density and high-level safety, are promising next-generation energy storage devices. Their current performance is however compromised by lithium dendrite formation. Although using 3D-structured metal-based electrode materials as hosts to store lithium metal has the potential to suppress the lithium dendrite growth by providing a high surface area with lithiophilic sites, their rigid and ragged interface with solid-state electrolytes is detrimental to the battery performance. Herein, we show that Li2OHBr-containing poly(ethylene oxide) (PEO) polymer electrolytes can be used as a flexible solid-state electrolyte to mitigate the interfacial issues of 3D-structured metal-based electrodes and suppress the lithium dendrite formation. The presence of Li2OHBr in a PEO matrix can simultaneously improve the mechanical strength and lithium ion conductivity of the polymer electrolyte. It is confirmed that Li2OHBr does not only induce the PEO transformation of a crystalline phase to an amorphous phase but also serves as an anti-perovskite superionic conductor providing additional lithium ion transport pathways and hence improves the lithium ion conductivity. The good interfacial contact and high lithium ion conductivity provide sufficient lithium deposition sites and uniform lithium ion flux to regulate the lithium deposition without the formation of lithium dendrites. Consequently, the Li2OHBr-containing PEO polymer electrolyte in a lithium-metal battery with a 3D-structured lithium/copper mesh composite anode is able to improve the cycle stability and rate performance. The results of this study provide the experimental proof of the beneficial effects of the Li2OHBr-containing PEO polymer electrolyte on the 3D-structured lithium metal anode.

C=C π Bond Modified Graphitic Carbon Nitride Films for Enhanced Photoelectrochemical Cell Performance.

Applications of graphitic carbon nitride (g-CN) in photoelectrochemical and optoelectronic devices are still hindered due to the difficulties in synthesis of g-CN films with tunable chemical, physical and catalytic properties. Herein we present a general method to alter the electronic and photoelectrochemical properties of g-CN films by annealing. We found that N atoms can be removed from the g-CN networks after annealing treatment. Assisted by theoretical calculations, we confirm that upon appropriate N removal, the adjacent C atoms will form new C=C π bonds. Detailed calculations demonstrate that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are located at the structure unit with C=C π bonds and the electrons are more delocalized. Valence band X-ray photoelectron spectroscopy spectra together with optical absorption spectra unveil that the structure changes result in the alteration of the g-CN energy levels and position of band edges. Our results show that the photocurrent density of the annealed g-CN film is doubled compared with the pristine one, thanks to the better charge separation and transport within the film induced by the new C=C π bonds. An ultrathin TiO2 film (2.2 nm) is further deposited on the g-CN film as stabilizer and the photocurrent density is kept at 0.05 mA cm-2 at 1.23 V versus reversible hydrogen electrode after two-cycle stability assessment. This work enables the applications of g-CN films in many electronic and optoelectronic devices.

Graphitic Carbon Nitride Film: An Emerging Star for Catalytic and Optoelectronic Applications.

Graphitic carbon nitride (g-CN) is a unique organic semiconductor that has been widely applied as a visible-light-driven photocatalyst. However, these applications are primarily based on g-CN powders. Applications of g-CN in devices are hindered because of difficulties associated with the synthesis of high-quality g-CN films. This work reviews the latest advances in g-CN films. The deposition methods are summarized and the structural, optical, and electronic properties of g-CN films and their applications in catalysis, solar cells, and light-emitting diodes are outlined. Moreover, the challenges remaining in this field are also discussed.

A durable surface-enhanced Raman scattering substrate: ultrathin carbon layer encapsulated Ag nanoparticle arrays on indium-tin-oxide glass.

The application of Ag nanostructures to surface-enhanced Raman scattering (SERS) is hindered by their chemical instability. Fabrication of durable Ag-based SERS substrates is therefore of great significance in practical applications. In this work, ultrathin C-layer-encapsulated Ag nanoparticle arrays (UCL-Ag-NAs) are successfully fabricated on the surface of indium-tin-oxide (ITO) glass, using a hydrothermal method, for use as durable SERS substrates. The problem of Ag nanoparticles dissolving during the hydrothermal process is solved by using ZnO powder as a pH-buffering reagent. The SERS signal intensity of UCL-Ag-NAs decreases, accompanied by an improvement in Raman signal stability, as the C-layer thickness increases. Raman spectra show that the SERS signal intensities obtained from UCL-Ag-NAs with C-layers of 4.5 nm and 7.3 nm stored for 180 days are 64.9% and 77.8% of those obtained from as-prepared counterparts. The SERS intensity of the UCL-Ag-NA (C-layer of 4.5 nm) is 152.7% that of the bare Ag NA after 180 days of storage. XPS spectra confirm that the C-layer effectively suppresses the oxidation of the Ag NA. This methodology can be generalized to improve the durability of other dimensional Ag nanostructures for SERS applications.

Efficient emission facilitated by multiple energy level transitions in uniform graphitic carbon nitride films deposited by thermal vapor condensation.

Graphitic carbon nitride (g-CN) films are important components of optoelectronic devices, but current techniques for their production, such as drop casting and spin coating, fail to deliver uniform and pinhole-free g-CN films on solid substrates. Here, versatile, cost-effective, and large-area growth of uniform and pinhole-free g-CN films is achieved by using a thermal vapor condensation method under atmospheric pressure. A comparison of the X-ray diffraction and Fourier transform infrared data with the calculated infrared spectrum confirmed the graphitic build-up of films composed of tri-s-triazine units. These g-CN films possess multiple active energy states including π*, π, and lone-pair states, which facilitate their efficient (6% quantum yield in the solid state) photoluminescence, as confirmed by both experimental measurements and theoretical calculations.

Carbon dot loading and TiO2 nanorod length dependence of photoelectrochemical properties in carbon dot/TiO2 nanorod array nanocomposites.

Photoelectrochemcial (PEC) properties of TiO2 nanorod arrays (TNRA) have been extensively investigated as they are photostable and cost-effective. However, due to the wide band gap, only the UV part of solar light can be employed by TiO2. To enhance the photoresponse of TNRA in the visible range, carbon dots (C dots) were applied as green sensitizer in this work by investigating the effects of C dot loading and length of TiO2 nanorod on the PEC properties of TNRA/C dot nanocomposites. As the C dot loading increases, the photocurrent density of the nanocomposites was enhanced and reached a maximum when the concentration of the C dots was 0.4 mg/mL. A further increase in the C dot concentration decreased the photocurrent, which might be caused by the surface aggregation of C dots. A compromise existed between charge transport and charge collection as the length of TiO2 nanorod increased. The incident photon to current conversion efficiency (IPCE) of the TNRA/C dot nanocomposites in the visible range was up to 1.2-3.4%. This work can serve as guidance for fabrication of highly efficient photoanode for PEC cells based on C dots.

Synthesis of Carbon Materials-TiO2 Hybrid Nanostructures and Their Visible-Light Photo-catalytic Activity.

Activated carbon, graphene, carbon nanotubes and fullerene were incorporated into TiO2 by a solvothermal approach and thermal annealing to produce carbon materials-TiO2 hybrid nanostructures. The carbon materials-TiO2 products were characterised by using SEM, TEM, XRD, Raman spectroscopy, X-ray photo-electron spectroscopy, UV-visible spectroscopy and photo-luminescence. The aim was to study the interactions between the main TiO2 phase and the carbon components, and the relationships between morphology, structure and photo-degradation of the rhodamine B (RhB) dye. An enhanced photo-catalytic degradation of RhB was achieved when using these nanocomposites over that for only using pure TiO2 . The superiority in photo-catalytic activities on the RhB molecules resulted from contributions from the excellent adsorption property, favourable chemical bond formation (TiOC), narrower band gap, smaller particle size and effective charge-carrier separation of the nanocomposites. Compared with the graphene-, carbon nanotube- and fullerene-TiO2 products, activated carbon-TiO2 exhibited weaker interactions between carbon and titania, lower adsorption for RhB and a larger band gap, which led to lower photo-catalytic activity of RhB.