Sz-Chian Liou

Red Phosphorus–Single-Walled Carbon Nanotube Composite as a Superior Anode for Sodium Ion Batteries

Sodium ion batteries (SIBs) have been considered as a top alternative to lithium ion batteries due to the earth abundance and low cost of sodium compared with lithium. Among all proposed anode materials for SIBs, red phosphorus (P) is a very promising candidate because it has the highest theoretical capacity (∼2600 mAh/g). In this study, a red P-single-walled carbon nanotube (denoted as red P-SWCNT) composite, in which red P is uniformly distributed between tangled SWCNTs bundles, is fabricated by a modified vaporization-condensation method. Benefiting from the nondestructive preparation process, the highly conductive and mechanically strong SWCNT network is preserved, which enhances the conductivity of the composite and stabilizes the solid electrolyte interphase. As a result, the red P-SWCNT composite presents a high overall sodium storage capacity (∼700 mAh/gcomposite at 50 mA/gcomposite), fast rate capability (∼300 mAh/gcomposite at 2000 mA/gcomposite), and stable long-term cycling performance with 80% capacity retention after 2000 sodiation-desodiation cycles. The red P-SWCNT composite fabricated by the vaporization-condensation method significantly extends the cycling stability of P/carbon composite from current ∼100 cycles to ∼2000 cycles.

Non-flammable electrolyte enables Li-metal batteries with aggressive cathode chemistries

Rechargeable Li-metal batteries using high-voltage cathodes can deliver the highest possible energy densities among all electrochemistries. However, the notorious reactivity of metallic lithium as well as the catalytic nature of high-voltage cathode materials largely prevents their practical application. Here, we report a non-flammable fluorinated electrolyte that supports the most aggressive and high-voltage cathodes in a Li-metal battery. Our battery shows high cycling stability, as evidenced by the efficiencies for Li-metal plating/stripping (99.2%) for a 5 V cathode LiCoPO4 (~99.81%) and a Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode (~99.93%). At a loading of 2.0 mAh cm−2, our full cells retain ~93% of their original capacities after 1,000 cycles. Surface analyses and quantum chemistry calculations show that stabilization of these aggressive chemistries at extreme potentials is due to the formation of a several-nanometre-thick fluorinated interphase.A fluorinated electrolyte forms a few-nanometre-thick interface both at the anode and the cathode that stabilizes lithium-metal battery operation with high-voltage cathodes.

Scalable fabrication of SnO2/eo-GO nanocomposites for the photoreduction of CO2 to CH4

Artificial photosynthesis uses a catalyst to convert CO2 into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO2) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO2 reduction compared to SnO2 and commercialized TiO2 (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.

Author Correction: Non-flammable electrolyte enables Li-metal batteries with aggressive cathode chemistries

In the version of this Article originally published, in the first paragraph of the Methods, HFE was incorrectly given as 2,2,2-Trifluoroethyl-3ʹ,3ʹ,3ʹ,2ʹ,2ʹ-pentafluoropropyl ether; it should have been 1,1,2,2-tetrafluoroethyl-2ʹ,2ʹ,2ʹ-trifluoroethyl ether. This has now been corrected in the online versions of the Article.

High energy-density and reversibility of iron fluoride cathode enabled via an intercalation-extrusion reaction

Iron fluoride, an intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh kg–1. However, poor electrochemical reversibility due to repeated breaking/reformation of metal fluoride bonds poses a grand challenge for its practical application. Here we report that both a high reversibility over 1000 cycles and a high capacity of 420 mAh g−1 can be realized by concerted doping of cobalt and oxygen into iron fluoride. In the doped nanorods, an energy density of ~1000 Wh kg−1 with a decay rate of 0.03% per cycle is achieved. The anion’s and cation’s co-substitutions thermodynamically reduce conversion reaction potential and shift the reaction from less-reversible intercalation-conversion reaction in iron fluoride to a highly reversible intercalation-extrusion reaction in doped material. The co-substitution strategy to tune the thermodynamic features of the reactions could be extended to other high energy conversion materials for improved performance.Poor electrochemical reversibility of the conversion-type cathode materials remains an important challenge for their practical applications. Here, the authors report a highly reversible fluoride cathode material with low hysteresis through concerted doping of cobalt and oxygen into iron fluoride.

Electron Microscopy Study of ALD Protective Coating on the FeOF Electrode

Rechargeable Li-ion batteries have become instrumental in powering portable electronics and battery electric vehicles due to their high energy density. The demand of developing next-generation higher energy density electrode materials has risen significantly in recent years. Iron fluoride (FeF3) and iron oxyfluoride (FeOF) have been widely investigated as a positive electrode material because of their high theoretical capacity in the range of 500 ~ 800 mAh/g [1]. However, the metallic Fe and insulting LiF, formed through the conversion reaction during the discharge process results in poor reversibility and capacity retention [1]. To mitigate the degradation of the electrode materials upon cycling, a thin protective layer of solid electrolyte lithium phosphor oxynitride (LiPON), via atomic layer deposition (ALD) was developed and applied on the FeOF particles [2, 3]. This study reports microstructure and chemical evolutions of FeOF with and without the protective thin films before and after discharge process using both electron microscopy and focused ion beam (FIB) technology.

A Novel Approach in Sample Preparation of Li Content Materials for TEM Research

Lithium (Li)-ion rechargeable batteries have attracted world-wide interest due to their high energy density, tiny memory effect, and low maintenance for powering portable electronics, hybrid electric vehicles, and aerospace applications. To improve battery efficiency and life time, understanding the microstructure evolution at electrode/electrolyte interface during charge/discharge (conversion reaction) processes is critical [1]. However, due to high reactivity of Li to moisture, TEM specimen preparation for Li content materials has been challenging. Focused ion beam (FIB) technology has thus become the most popular method to prepare TEM specimen for Li-ion materials. Furthermore, porous solid-state electrolyte, e.g. lithium phosphorous oxynitride (LiPON), is susceptible to damage by ion beam bombardment during milling [2]. To fully characterize the moisture and ion beam sensitive interface (LiPON/FeOF), a unique approach by combing FIB technique and ultra-microtome was performed and evaluated.