Biwei Xiao

In situ self-catalyzed formation of core–shell LiFePO4@CNT nanowires for high rate performance lithium-ion batteries

In situ self-catalyzed core–shell LiFePO4@CNT nanowires can be fabricated by a two-step synthesis, where one-dimensional LiFePO4 nanowires with a diameter of 20–30 nm were encapsulated into CNTs, and 3D conducting networks of CNTs were obtained from in situ carbonization of a polymer. LiFePO4@CNT nanowires deliver a capacity of 160 mA h g−1 at 17 mA g−1, and 65 mA h g−1 at 8500 mA g−1 (50 C, 1.2 minutes for charging and 1.2 minutes for discharging).

Unravelling the Role of Electrochemically Active FePO4 Coating by Atomic Layer Deposition for Increased High-Voltage Stability of LiNi0.5Mn1.5O4 Cathode Material

Ultrathin amorphous FePO4 coating derived by atomic layer deposition (ALD) is used to coat the 5 V LiNi0.5Mn1.5O4 cathode material powders, which dramatically increases the capacity retention of LiNi0.5Mn1.5O4. It is believed that the amorphous FePO4 layer could act as a lithium‐ions reservoir and electrochemically active buffer layer during the charge/discharge cycling, helping achieve high capacities in LiNi0.5Mn1.5O4, especially at high current densities.

Atomically precise growth of sodium titanates as anode materials for high-rate and ultralong cycle-life sodium-ion batteries

Sodium-ion batteries (SIBs) have received increasing attention for applications in large-scale energy storage systems due to their low cost, high energy density, and high abundance of the sodium element. Nanosizing electrode materials becomes a key strategy to overcome the problems resulting from the sluggish kinetics of large sodium ions, thereby achieving good performance in SIBs. Herein, we developed an atomic layer deposition (ALD) approach for atomically precise fabrication of sodium titanate anode materials. This ALD process shows excellent controllability over the growth rate, film thickness, composition of sodium titanates, and high flexibility of coating uniform sodium titanate films onto various dimensions of substrates. Moreover, the amorphous sodium titanate deposited on carbon nanotubes exhibits high specific capacity, excellent rate capability, and ultra-long cycling life (∼100 mA h g−1 after 3500 cycles). It is expected that the ALD approach developed herein can be extended to well-defined fabrication of other sodium-containing electrode materials for SIBs.

Nanoscale stabilization of Li–sulfur batteries by atomic layer deposited Al2O3

An atomic layer deposited (ALD) Al2O3 coating applied to sulfur cathodes has been studied in this paper. It is demonstrated that the Al2O3 coating improves the cycling stability of Li–sulfur batteries. The underlying mechanism by synchrotron-based X-ray photoelectron spectroscopy was investigated. The coating layer not only protects the polysulfide from dissolution, but also facilitates the utilization of sulfur, demonstrating improved electrochemical performances.

Atomic layer deposited aluminium phosphate thin films on N-doped CNTs

Uniform amorphous aluminium phosphate thin films with precisely controlled thickness and tunable composition were deposited on nitrogen-doped carbon nanotubes at 150 °C through a new atomic layer deposition approach.

Origin of the high oxygen reduction reaction of nitrogen and sulfur co-doped MOF-derived nanocarbon electrocatalysts

Developing an economical, highly active and durable material to replace the conventional, expensive noble metal electrocatalyst is an important milestone in the development of fuel cell technology. Nanocarbon materials are considered as promising catalysts toward the oxygen reduction reaction (ORR) in fuel cells, due to their reasonable balance between low-cost, long-life durability and high catalytic activity in alkaline media. In this work, we present the fabrication of N,S-co-doped nanocarbon derived from a metal-organic framework (MOF) precursor for use as an electrocatalyst towards ORR. High resolution transmission electron microscopy (HRTEM) mapping demonstrates the uniform distribution of N and S atoms into the nanocarbon skeleton. The nitrogen absorption–desorption isotherms indicate that the MOF-derived N,S-co-doped nanocarbon has a high specific surface area (2439.9 m2 g−1) and a porous structure. Importantly, the N,S-co-doped nanocarbon exhibits higher catalytic activity toward ORR, better long-term stability and methanol tolerance than commercial Pt/C catalyst. First-principles calculations demonstrate that the remarkable electrochemical properties of N,S-co-doped nanocarbon are mainly attributed to the synergistic effect from the N and S dopants. Moreover, for the first time, it is revealed that the N,S-coupled dopants in nanocarbon can create active sites with higher catalytic activity for ORR than the isolated N and S-dopants. This finding on the structure–performance relationship of the co-doped nanocarbon provides guidelines for the design of high performance electrocatalysts.

Nanoscale Manipulation of Spinel Lithium Nickel Manganese Oxide Surface by Multisite Ti Occupation as High-Performance Cathode

A novel two-step surface modification method that includes atomic layer deposition (ALD) of TiO2 followed by post-annealing treatment on spinel LiNi0.5 Mn1.5 O4 (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn2 O4 (TMO)-like spinel phase resulting from the reaction of TiO2 with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO-like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO2 growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic-scale surface structural modification using ALD and post-treatment, which is of great importance for the future design of cathode materials.

Utilizing the full capacity of carbon black as anode for Na-ion batteries via solvent co-intercalation

Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage solely relies on the disordered region of the carbon materials in a carbonate-based electrolyte. The solvent co-intercalation mechanism for Na ions has been recently reported in natural graphite anodes for Na-ion batteries with ether-based electrolytes, but their capacities are still unsatisfactory. We show here for the first time that by combining regular Na ion storage in the disordered carbon layer and solvent co-intercalation mechanism in the graphitized layer of a commercial N330 carbon black as an anode material for Na-ion batteries in ether-based electrolyte, the reversible capacity could be fully realized and doubled in magnitude. This unique sodium intercalation process resulted in a significantly improved electrochemical performance for the N330 electrode with an initial reversible capacity of 234 mAh·g–1 at 50 mA·g–1 and a superior rate capability of 105 mAh·g–1 at 3,200 mA·g–1. When cycled at 3,200 mA·g–1 over 2,000 cycles, the electrode still exhibited a highly reversible capacity of 72 mAh·g–1 with a negligible capacity loss per cycle (0.0167%). Additionally, surface-sensitive C K-edge X-ray absorption spectroscopy, with the assistance of electrochemical and physicochemical characterizations, helped in identifying the controlled formation and evolution of a thin and robust solid electrolyte interphase film. This film not only reduced the resistance for sodium ion diffusion, but also maintained the structural stability of the electrode for extended cycle reversibility. The superior electrochemical performance of N330 carbon black strongly demonstrated the potential of applying ether-based electrolytes for a wide range of carbon anodes apart from natural graphite.