Stable Interfaces in a Sodium Metal-Free, Solid-State Sodium-Ion Battery with Gradient Composite Electrolyte.

Composite electrolytes (CE) combining a ceramic filler and a polymer matrix is an effective way to enhance battery safety. But the increased ceramic filler mass fraction decreases the flexibility, which increases the interfacial resistance. To alleviate interfacial resistance further, a gradient composite electrolyte (GCE) using a Sc, Ge-doped Na3Zr2Si2PO12 (NZSP) as the ceramic filler and poly(ethylene oxide) (PEO) as the polymer matrix is proposed. The outer layer contains a low concentration of ceramic filler to improve interfacial contact, and the central layer contains a high concentration of ceramic filler to inhibit dendrite penetration. This GCE possesses an enhanced conductivity (4.0 × 10-5 S cm-1 at 30 °C) and a reduced interfacial resistance. Furthermore, the safety was boosted using Sn4P3@CNT/C as the high-capacity anode active material and Na3V2(PO4)3 (NVP) as the cathode active material. This ultrasafe sodium metal-free, solid-state sodium-ion battery (SSSIB) displays an impressive cycling performance.

ZIF-8 derived hollow carbon to trap polysulfides for high performance lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) have a high theoretical energy density and are low cost. However, the undesirable shuttle effect with the solid discharge product, Li2S, greatly impedes their market penetration. Conductive carbon materials with functional elements are beneficial in controlling the shuttle effect and can reactivate the Li2S, leading to improved long term cycling performance of LSBs. Herein, we report zinc (Zn) and nitrogen (N) co-doped ZIF-8 derived hollow carbon (ZHC) as a promising separator coating for LSBs to control the shuttle effect. The hollow area in the ZHC is identified to be around 250 nm with a carbonized outer surface thickness of approximately 50 nm. The presence of Zn and N in the nanohollow carbon structure helps to mitigate polysulfide (PS) diffusion in LSBs. Furthermore, the hollow interior of the carbon acts as a PS pocket to physically capture the PS and in addition Zn and N chemically attract the PS through polar-polar and metal sulfide interactions. The ZHC with its unique architecture and functional groups shows a promising performance with an initial specific capacity (S.cap) of 842 mA h g-1 at 4.80 mg cm-2 and cycling stability until 400 cycles, which is considerably higher in comparison with the cycling performance of parent ZIF-8.

Zn Electrodeposition by an In Situ Electrochemical Liquid Phase Transmission Electron Microscope.

Alternative battery technologies are required to meet growing energy demands and to solve the limitations of the present energy technologies. As such, it is necessary to look beyond lithium-ion batteries. Zinc batteries enable high power density while being sourced from abundant and cost-effective materials. In this paper, the effect of the applied current and electrolyte flow rate on the early stage of Zn dendrite formation was characterized by in situ electrochemical liquid phase transmission electron microscopy (EC-LPTEM). For the first time, the square root relation is revealed between time and Zn dendrite growth on the lateral direction, indicating a diffusion-limited growth. It is intriguing that a higher applied current leads to longer incubation time. In situ EC-LPTEM can provide a useful strategy for understanding characteristics of unstable dendritic growth. The finding can help rationalize the electrode engineering design and parameters selection to avoid dendrite formation.

Biomimetic Sn4P3 Anchored on Carbon Nanotubes as an Anode for High-Performance Sodium-Ion Batteries.

Recently, Sn4P3 has emerged as a promising anode for sodium-ion batteries (SIBs) due to the high specific capacity. However, the use of Sn4P3 has been impeded by capacity fade and an inferior rate performance. Herein, a biomimetic heterostructure is reported by using a simple hydrothermal reaction followed by thermal treatment. This bottlebrush-like structure consists of a stem-like carbon nanotube (CNT) as the electron expressway and mechanical support; fructus-like Sn4P3 nanoparticles as the active material; and the permeable stoma-like thin carbon coating as the buffer layer. Having benefited from the biomimetic structure, a superior electrochemical performance is obtained in the SIBs. It exhibits a high capacity of 742 mA h g-1 after 150 cycles at 0.2C, and superior rate performance with 449 mA h g-1 at 2C after 500 cycles. Moreover, the sodium storage mechanism is confirmed by cyclic voltammetry and ex situ X-ray diffraction and transmission electron microscopy. In situ electrochemical impedance spectroscopy was adopted to analyze the reaction dynamics. This research represents a further step toward figuring out the inferior electrochemical performance of other metal phosphide materials.

Multifunctional Effects of Sulfonyl-Anchored, Dual-Doped Multilayered Graphene for High Areal Capacity Lithium Sulfur Batteries.

Li-S batteries (LSBs) require a minimum 6 mAh cm-2 areal capacity to compete with the state-of-the-art lithium ion batteries (LIBs). However, this areal capacity is difficult to achieve due to a major technical issue-the shuttle effect. Nonpolar carbon materials limit the shuttle effect through physical confinement. However, the polar polysulfides (PSs) only provide weak intermolecular interactions (0.1-0.7 eV) with these nonpolar carbon materials. The physically encapsulated PSs inside the nonpolar carbon scaffold eventually diffuses out and starts shuttling. Chemically interactive hosts are more effective at interacting with the PSs due to high binding energies. Herein, a multifunctional separator coating of nitrogen-doped multilayer graphene (NGN) and -SO3 - containing Nafion (N-NGN) is used to mitigate PS shuttling and to produce a high areal capacity LSB. The Nafion is used as a binder instead of PVDF to provide an additional advantage of -SO3 - to chemically bind the PS. The motive of this research is to investigate the effect of highly electronegative N and -SO3 - (N-NGN) in comparison with the -OH, -COOH, and -SO3 - groups from a hydroxyl graphene and Nafion composite (N-OHGN) to mitigate PS shuttling in LSBs. The highly conductive doped graphene architecture (N-NGN) provides efficient pathways for both electrons and ions, which accelerates the electrochemical conversion at high sulfur loading. Moreover, the electron-rich pyridine N and -SO3 - show strong chemical affinity with the PS through polar-polar interactions, which is proven by the superior electrochemical performance and density functional theory calculations. Further, the N-NGN (5 h) produces a maximum areal capacity of 12.0 and 11.0 mAh cm-2, respectively, at 15 and 12 mg cm-2 sulfur loading. This areal capacity limit is significantly higher than the required areal capacity of LSBs for commercial application, which shows the significant strength of N-NGN as an excellent separator coating for LSBs.