Andrew Lushington

As a competitive anode material for sodium-ion batteries, a commercially available red phosphorus, featured with a high theoretical capacity (2596 mAh g-1) and a suitable operative voltage plateau (0.1~0.6 V), has confronted with a severe structural instability and a rapid capacity degradation upon the large volumetric change. In particular, the fundamental determining factors for phosphorus anode materials are yet poorly understood, and their interfacial stability against the ambient air has not been explored and clarified. Herein, a high-performance phosphorus/carbon anode material has simply been fabricated through ball-milling the carbon black and red phosphorus, delivering a high reversible capacity of 1070 mAh g-1 at 400 mA g-1 after 200 cycles and a superior rate capability of 479 mAh g-1 at 3200 mA g-1. More importantly, we firstly reveal the significance of inhibiting phosphorus/carbon electrode materials from exposing to air, even for a short period, on achieving a good electrochemical performance, which would sharply decrease the reversible capacities. With the assistance of synchrotron-based X-ray techniques, the formation and accumulation of insulating phosphate compounds can be spectroscopically identified, leading to the decay of electrochemical performance. At the same time, these passivation layers on the surface of electrode were found to occur via a self-oxidation process in ambient air. To maintain the electrochemical advantages of phosphorus anodes, it is necessary to inhibit their contact to air through a rational coating or an optimal storage condition. Additionally, the employment of a FEC (fluorinated ethylene carbonate) additive facilitates the decomposition of electrolyte and favors the formation of a robust solid electrolyte interphase layer, which may suppress the side reactions between the active Na-P compounds and electrolyte. These findings could enlighten the surface protection and interfacial stability of phosphorus anodes for high-performance sodium-ion batteries.

Carbonate-based electrolytes demonstrate safe and stable electrochemical performance in lithium-sulfur batteries. However, only a few types of sulfur cathodes with low loadings can be employed and the underlying electrochemical mechanism of lithium-sulfur batteries with carbonate-based electrolytes is not well understood. Here, we employ in operando X-ray absorption near edge spectroscopy to shed light on a solid-phase lithium-sulfur reaction mechanism in carbonate electrolyte systems in which sulfur directly transfers to Li₂S without the formation of linear polysulfides. Based on this, we demonstrate the cyclability of conventional cyclo-S₈ based sulfur cathodes in carbonate-based electrolyte across a wide temperature range, from −20 °C to 55 °C. Remarkably, the developed sulfur cathode architecture has high sulfur content (>65 wt%) with an areal loading of 4.0 mg cm⁻². This research demonstrates promising performance of lithium-sulfur pouch cells in a carbonate-based electrolyte, indicating potential application in the future.

Na metal anode attracts increasing attention as a promising candidate for Na metal batteries (NMBs) due to the high specific capacity and low potential. However, similar to issues faced with the use of Li metal anode, crucial problems for metallic Na anode remain, including serious moss‐like and dendritic Na growth, unstable solid electrolyte interphase formation, and large infinite volume changes. Here, the rational design of carbon paper (CP) with N‐doped carbon nanotubes (NCNTs) as a 3D host to obtain Na@CP‐NCNTs composites electrodes for NMBs is demonstrated. In this design, 3D carbon paper plays a role as a skeleton for Na metal anode while vertical N‐doped carbon nanotubes can effectively decrease the contact angle between CP and liquid metal Na, which is termed as being “Na‐philic.” In addition, the cross‐conductive network characteristic of CP and NCNTs can decrease the effective local current density, resulting in uniform Na nucleation. Therefore, the as‐prepared Na@CP‐NCNT exhibits stable electrochemical plating/stripping performance in symmetrical cells even when using a high capacity of 3 mAh cm⁻² at high current density. Furthermore, the 3D skeleton structure is observed to be intact following electrochemical cycling with minimum volume change and is dendrite‐free in nature.

Carbon coating is a commonly employed technique for improving the conductivity of active materials in lithium ion batteries. The carbon coating process involves pyrolysis of organic substance on lithium iron phosphate particles at elevated temperature to create a highly reducing atmosphere. This may trigger the formation of secondary phases in the active materials. Here, we observe a conductive phase during the carbon coating process of lithium iron phosphate and the phase content is size, temperature, and annealing atmosphere dependent. The formation of this phase is related to the reducing capability of the carbon coating process. This finding can guide us to control the phase composition of carbon-coated lithium iron phosphate and to tune its quality during the manufacturing process.

Metallic Na anode is considered as a promising alternative candidate for Na ion batteries (NIBs) and Na metal batteries (NMBs) due to its high specific capacity, and low potential. However, the unstable solid electrolyte interphase layer caused by serious corrosion and reaction in electrolyte will lead to big challenges, including dendrite growth, low Coulombic efficiency and even safety issues. In this paper, we first demonstrate the inorganic–organic coating via advanced molecular layer deposition (alucone) as a protective layer for metallic Na anode. By protecting Na anode with controllable alucone layer, the dendrites and mossy Na formation have been effectively suppressed and the lifetime has been significantly improved. Moreover, the molecular layer deposition alucone coating shows better performances than the atomic layer deposition Al₂O₃ coating. The novel design of molecular layer deposition protected Na metal anode may bring in new opportunities to the realization of the next-generation high energy-density NIBs and NMBs.

Sodium‐ion batteries are widely considered as promising energy storage systems for large‐scale applications, but their relatively low energy density hinders further practical applications. Developing high‐voltage cathode materials is an effective approach to increase the overall energy density of sodium‐ion batteries. When cut‐off voltage is elevated over 4.3 V, however, the cathode becomes extremely unstable due to structural transformations as well as metal dissolution into the electrolytes. In this work, the cyclic stability of P2‐Na_0.66(Mn_0.54Co_0.13Ni_0.13)O₂ (MCN) electrode at a cut‐off voltage of 4.5 V is successfully improved by using ultrathin metal oxide surface coatings (Al₂O₃, ZrO₂, and TiO₂) deposited by an atomic layer deposition technique. The MCN electrode coated with the Al₂O₃ layer exhibits higher capacity retention among the MCN electrodes. Moreover, the rate performance of the MCN electrode is greatly improved by the metal oxide coatings in the order of TiO₂ < Al₂O₃ < ZrO₂, due to increased fracture toughness and electrical conductivity of the metal oxide coating layers. A ZrO₂‐coated MCN electrode shows a discharge capacity of 83 mAh g⁻¹ at 2.4 A g⁻¹, in comparison to 61 mAh g⁻¹ for a pristine MCN electrode. Cyclic voltammetry and electrochemical impedance analysis disclose the reduced charge transfer resistance from 1421 to 760.2 Ω after cycles, suggesting that the metal oxide coating layer can effectively minimize the undesirable phase transition, buffer inherent stress and strain between the binder, cathode, and current collector, and avoid volumetric changes, thus increasing the cyclic stability of the MCN electrode.

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.