Rational Design of a Cross-Linked Composite Solid Electrolyte for Li-Metal Batteries.

The interfacial problem caused by solid-solid contact is an important issue faced by a solid-state electrolyte (SSE). Herein, a cross-linked composite solid electrolyte (CSE) poly(vinylene carbonate) (PVCA)─ethoxylated trimethylolpropane triacrylate (ETPTA)─Li1.5Al0.5Ge1.5(PO4)3 (LAGP) (PEL) is prepared by in situ thermal polymerization. The ionic conductivity and Li+ transference number (tLi+) of PEL increase significantly due to the addition of LAGP, which can reach 1.011 × 10-4 S cm-1 and 0.451 respectively. The electrochemical stable window is also widened to 4.68 V. Benefiting from the integrated interfacial structure, the assembled coin cell shows low interfacial resistance. The all-solid-state NCM622|PEL|Li coin cell exhibits an initial discharge capacity of 169.7 mA h g-1 and 70% capacity retention over 100 cycles at 0.2 C, demonstrating excellent cycling stability.

Double-Protected Layers with Solid-Liquid Hybrid Electrolytes for Long-Cycle-Life Lithium Batteries.

Lithium-ion batteries (LIBs) with liquid electrolytes (LEs) have problems such as electrolyte leakage, low safety profiles, and low energy density, which limit their further development. However, LIBs with solid electrolytes are safer with better energy and high-temperature performance. Thus, solid electrolyte system batteries have attracted widespread attention. However, due to the inherent rigidity of the LATP solid electrolyte, there is a high interface impedance at the LATP/electrode. In addition, the Ti element in LATP easily reacts with the Li metal. Here, we dripped an LE at the LATP/electrode interface (solid-liquid hybrid electrolytes) to reduce its interface impedance. A composite polymer electrolyte (CPE) protective film (containing PVDF, SN, and LiTFSI) was then cured in situ at the LATP/Li interface to avoid side reactions of LATP. The discharge specific capacity of the LiFePO4/LATP-12% LE-CPE/Li system is up to 150 mAh g-1, and the capacity retention rate is still 96% after 250 cycles. In addition, the NCM622/PVDF-LATP-12% LE/Li system has an initial reversible capacity of 170 mAh g-1. This study reports an approach that can protect solid electrolytes from lithium metal instability.

Effect of Organic Electrolyte on the Performance of Solid Electrolyte for Solid-Liquid Hybrid Lithium Batteries.

The interface problem caused by the contact between the electrodes and the solid electrolyte was the main factor hindering the development of solid-state batteries. To enhance the electrode|solid electrolyte interface property, we designed a hybrid electrolyte, the combination of x vol % Li1.3Al0.3Ti1.7(PO4)3 (LATP) inorganic solid electrolyte and 1 - x vol % liquid organic electrolyte (LE). In this work, the 1 - x vol % LE was dropped between the electrode and the solid electrolyte, and it is found that the electrochemical performance of the LiFePO4|Li solid-liquid hybrid battery is significantly improved. At the current density of 0.1 and 0.5 C, the LATP with 15% liquid organic electrolyte could deliver a specific capacity of 160.5 and 124.3 mAh g-1, respectively; moreover, the specific discharge capacity remained as high as 111 mAh g-1 at 0.5 C after 100 cycles, indicating that the larger interface impedance was eliminated. The LE may have three functions: (1) forming a solid-liquid electrolyte interphase on the surface of the LATP particles to prevent further reduction of LATP, (2) wetting the electrode and solid electrolyte to reduce the interface resistance, and (3) improving interfacial Li-ion transport.

Zirconium-Redox-Shuttled Cross-Electrophile Coupling of Aromatic and Heteroaromatic Halides.

Transition metal-catalyzed cross-electrophile coupling (XEC) is a powerful tool for forging C(sp2)-C(sp2) bonds in biaryl molecules from abundant aromatic halides. While syntheses of unsymmetrical biaryl compounds through multimetallic XEC is of high synthetic value, selective XEC of two heteroaromatic halides remains elusive and challenging. Herein we report a homogeneous XEC method which relies on a zirconaaziridine complex as a shuttle for dual palladium catalyzed processes. The zirconaaziridine-mediated palladium (ZAPd) catalyzed reaction shows excellent compatibility with various functional groups and diverse heteroaromatic scaffolds. In accord with density functional theory (DFT) calculations, a redox-transmetallation between the oxidative addition product and the zirconaaziridine is proposed as the crucial elementary step. Thus, cross-coupling selectivity using a single transition metal catalyst is controlled by the relative rate of oxidative addition of Pd(0) into the aromatic halide. Overall, the concept of a combined reducing and transmetallating agent offers opportunities for development of transition-metal reductive coupling catalysis.

LiFePO4-coated LiNi0.6Co0.2Mn0.2O2 for lithium-ion batteries with enhanced cycling performance at elevated temperatures and high voltages.

LiNi0.6Co0.2Mn0.2O2 (NCM622) is a highly promising cathode material owing to its high capacity; however, it is characterized by inferior cycling performance and safety problems. We report a novel strategy to improve electrochemical characteristics and safety issues of NCM622 by coating it with LiFePO4 (LFP). Although having a lower capacity, LFP is a safe and long-cycle cathode material; it is more chemically and thermally stable than NCM622 when exposed to common electrolytes. The LFP-coated NCM622 (NCM@LFP) showed similar rate performance and cycling performance at room temperature compared with the pristine NCM622 under the same conditions. However, significant differences between the NCM622 and NCM@LFP began to emerge at high temperatures. During cycling at 1C for 100 cycles at 55 °C, NCM@LFP showed much improved specific discharge capacity retentions of 92.4%, 90.9%, and 88.2% in the voltage ranges of 3-4.3 V, 3-4.4 V and 3-4.5 V, respectively. The NCM622 suffered significant discharge specific capacity decay under the same condition. In addition, as demonstrated by the delayed exothermic peak in the differential scanning calorimetry (DSC) test, NCM@LFP exhibited excellent thermal stability compared with NCM622, which is critical to battery safety.

CeO2-modified P2-Na-Co-Mn-O cathode with enhanced sodium storage characteristics.

To improve the cycling stability and dynamic properties of layered oxide cathodes for sodium-ion batteries, surface modified P2-Na0.67Co0.25Mn0.75O2 with different levels of CeO2 was successfully synthesized by the solid-state method. X-ray photoelectron spectra, X-ray diffraction and Raman spectra show that the P2-structure and the oxidation state of cobalt and manganese of the pristine oxide are not affected by CeO2 surface modification, and a small amount of Ce4+ ions have been reduced to Ce3+ ions, and a few Ce ions have entered the crystal lattice of the P2-oxide surface during modification with CeO2. In a voltage range of 2.0-4.0 V at a current density of 20 mA g-1, 2.00 wt% CeO2-modified Na0.67Co0.25Mn0.75O2 delivers a maximum discharge capacity of 135.93 mA h g-1, and the capacity retentions are 91.96% and 83.38% after 50 and 100 cycles, respectively. However, the pristine oxide presents a low discharge capacity of 116.14 mA h g-1, and very low retentions of 39.83% and 25.96% after 50 and 100 cycles, respectively. It is suggested that the CeO2 modification enhances not only the maximum discharge capacity, but also the electric conductivity and the sodium ion diffusivity, resulting in a significant enhancement of the cycling stability and the kinetic characteristics of the P2-type oxide cathode.

Hydrophobicity-guided self-assembled particles of silver nanoclusters with aggregation-induced emission and their use in sensing and bioimaging.

Distinctive aggregation-induced emission (AIE) phenomenon of thiolate-protected silver nanoclusters (AgNCs) has been revealed; these AgNCs have shown great potential for exploitation and utilization, but their applications as a bright luminogen in the chemosensing and bioimaging areas are greatly limited by their ultralow brightness in an aqueous solution. Herein, we report facile fabrication of hydrophobicity-guided self-assembled particles of silver nanoclusters with aggregation-induced emission. A hydrophobic ligand, thiosalicylic acid, was adopted to prepare AgNCs via a one-step way, and thiosalicylic acid-capped AgNCs showed significant AIE behavior. This AIE property of AgNCs enables them to selectively respond to multiple external stimuli such as solvent polarity, pH and environmental temperature. The hydrophobic nature of thiosalicylic acid as capping ligands of AgNCs drives a self-assembly process of AgNCs in an aqueous solution that results in the formation of self-assembled particles of AgNCs with bright luminescence. Sensitive detection of mercuric ion based on the highly luminescent AgNC AIE particles was achieved in terms of a strong quenching effect of mercuric ion. Cellular viability and luminescence imaging performance of the AgNC AIE particles on living cells were also evaluated for the first time. This study demonstrates the fabrication of AIE particles of silver nanoclusters with bright luminescence guided by hydrophobic interaction and reveals excellent bioimaging performance of AIE particles in living cells.