Guosheng Li

Highly reversible Mg insertion in nanostructured Bi for Mg ion batteries

Rechargeable magnesium batteries have attracted wide attention for energy storage. Currently, most studies focus on Mg metal as the anode, but this approach is still limited by the properties of the electrolyte and poor control of the Mg plating/stripping processes. This paper reports the synthesis and application of Bi nanotubes as a high-performance anode material for rechargeable Mg ion batteries. The nanostructured Bi anode delivers a high reversible specific capacity (350 mAh/gBi or 3430 mAh/cm(3)Bi), excellent stability, and high Coulombic efficiency (95% initial and very close to 100% afterward). The good performance is attributed to the unique properties of in situ formed, interconnected nanoporous bismuth. Such nanostructures can effectively accommodate the large volume change without losing electric contact and significantly reduce diffusion length for Mg(2+). Significantly, the nanostructured Bi anode can be used with conventional electrolytes which will open new opportunities to study Mg ion battery chemistry and further improve its properties.

Ambipolar zinc-polyiodide electrolyte for a high-energy density aqueous redox flow battery

Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (~25 Wh l−1). Here we report a high-energy density aqueous zinc-polyiodide flow battery. Using the highly soluble iodide/triiodide redox couple, a discharge energy density of 167 Wh l−1 is demonstrated with a near-neutral 5.0 M ZnI2 electrolyte. Nuclear magnetic resonance study and density functional theory-based simulation along with flow test data indicate that the addition of an alcohol (ethanol) induces ligand formation between oxygen on the hydroxyl group and the zinc ions, which expands the stable electrolyte temperature window to from −20 to 50 °C, while ameliorating the zinc dendrite. With the high-energy density and its benign nature free from strong acids and corrosive components, zinc-polyiodide flow battery is a promising candidate for various energy storage applications.

Nanosheet-structured LiV3O8 with high capacity and excellent stability for high energy lithium batteries

Highly stable LiV3O8 with a nanosheet-structure was successfully prepared using polyethylene glycol (PEG) polymer in the precursor solution as the structure modifying agent, followed by calcination in air at 400 °C, 450 °C, 500 °C, and 550 °C. These materials provide the best electrochemical performance ever reported for LiV3O8 crystalline electrodes, with a specific discharge capacity of 260 mAh g−1 and no capacity fading over 100 cycles at 100 mA g−1. The excellent cyclic stability and high specific discharge capacity of the material are attributed to the novel nanosheets structure formed in LiV3O8. These LiV3O8 nanosheets are good candidates for cathode materials for high-energy lithium battery applications.

Coordination Chemistry in magnesium battery electrolytes: how ligands affect their performance

Magnesium battery is potentially a safe, cost-effective, and high energy density technology for large scale energy storage. However, the development of magnesium battery has been hindered by the limited performance and the lack of fundamental understandings of electrolytes. Here, we present a study in understanding coordination chemistry of Mg(BH4)2 in ethereal solvents. The O donor denticity, i.e. ligand strength of the ethereal solvents which act as ligands to form solvated Mg complexes, plays a significant role in enhancing coulombic efficiency of the corresponding solvated Mg complex electrolytes. A new electrolyte is developed based on Mg(BH4)2, diglyme and LiBH4. The preliminary electrochemical test results show that the new electrolyte demonstrates a close to 100% coulombic efficiency, no dendrite formation, and stable cycling performance for Mg plating/stripping and Mg insertion/de-insertion in a model cathode material Mo6S8 Chevrel phase.

A facile approach using MgCl2 to formulate high performance Mg2+ electrolytes for rechargeable Mg batteries

Rechargeable Mg batteries have been regarded as a viable battery technology for grid scale energy storage and transportation applications. However, the limited performance of Mg2+ electrolytes has been a primary technical hurdle to develop high energy density rechargeable Mg batteries. In this study, MgCl2 is demonstrated as a non-nucleophilic and cheap Mg2+ source in combination with Al Lewis acids (AlCl3, AlPh3 and AlEtCl2) to formulate a series of Mg2+ electrolytes, representing the simplest method to prepare Mg2+ conductive electrolytes (no precursor synthesis, free of recrystallization and giving quantitative yield). These electrolytes are characterized by high oxidation stability (up to 3.4 V vs. Mg), improved electrophile compatibility and electrochemical reversibility (up to 100% coulombic efficiency). Three electrolyte systems (MgCl2–AlCl3, MgCl2–AlPh3, and MgCl2–AlEtCl2) were fully characterized by multinuclear NMR (1H, 27Al{1H} and 25Mg{1H}) spectroscopies and electrochemical analysis. Single crystal X-ray diffraction and NMR studies consistently established molecular structures of the three electrolytes sharing a common Mg2+-dimer mono-cation, [(μ-Cl)3Mg2(THF)6]+, along with an anion (AlCl4−, AlPh3Cl− and AlEtCl3− respectively). Clean and dendrite free Mg bulk plating and viable battery performance were validated through representative studies using the MgCl2–AlEtCl2 electrolyte. The reaction mechanism of MgCl2 and the Al Lewis acids in THF is discussed to highlight the formation of the electrochemically active [(μ-Cl)3Mg2(THF)6]+ dimer mono-cation in these electrolytes and their improved performance compared to reported electrolytes using nucleophilic Mg2+ sources.

Liquid-metal electrode to enable ultra-low temperature sodium–beta alumina batteries for renewable energy storage

Commercial sodium-sulphur or sodium-metal halide batteries typically need an operating temperature of 300-350 °C, and one of the reasons is poor wettability of liquid sodium on the surface of beta alumina. Here we report an alloying strategy that can markedly improve the wetting, which allows the batteries to be operated at much lower temperatures. Our combined experimental and computational studies suggest that addition of caesium to sodium can markedly enhance the wettability. Single cells with Na-Cs alloy anodes exhibit great improvement in cycling life over those with pure sodium anodes at 175 and 150 °C. The cells show good performance even at as low as 95 °C. These results demonstrate that sodium-beta alumina batteries can be operated at much lower temperatures with successfully solving the wetting issue. This work also suggests a strategy to use liquid metals in advanced batteries that can avoid the intrinsic safety issues associated with dendrite formation.

Electrochemically stable cathode current collectors for rechargeable magnesium batteries

Rechargeable magnesium (Mg) batteries are attractive energy storage systems that could yield cost-effective energy solutions. Currently, however, no practical cathode current collector that can withstand more than 2.0 V in Mg2+ electrolytes has been identified; this greatly hinders cathode research. Here we identified that molybdenum (Mo) and tungsten (W) are electrochemically stable (>2.8 V) through formation of passive surface layers. The presented results could have a significant impact on the development of high voltage Mg batteries.

Cell degradation of a Na–NiCl2 (ZEBRA) battery

In this work, the parameters influencing the degradation of a Na–NiCl2 (ZEBRA) battery were investigated. Planar Na–NiCl2 cells using the β′′-alumina solid electrolyte (BASE) were tested with different C-rates, Ni/NaCl ratios, and capacity windows, in order to identify the key parameters for the degradation of the Na–NiCl2 battery. The morphology of NaCl and Ni particles was extensively investigated after 60 cycles under various test conditions using a scanning electron microscope. A strong correlation between the particle size (NaCl and Ni) and battery degradation was observed in this work. Even though the growth of both Ni and NaCl can influence the cell degradation, our results indicate that the growth of NaCl is a dominant factor in cell degradation. The use of excess Ni seems to play a role in tolerating the negative effects of particle growth on degradation since the available active surface area of Ni particles can still be sufficient even after particle growth. For NaCl, a large cycling window was the most significant factor, of which effects were amplified with decrease in the Ni/NaCl ratio.

Advanced intermediate temperature sodium–nickel chloride batteries with ultra-high energy density

Sodium-metal halide batteries have been considered as one of the more attractive technologies for stationary electrical energy storage, however, they are not used for broader applications despite their relatively well-known redox system. One of the roadblocks hindering market penetration is the high-operating temperature. Here we demonstrate that planar sodium–nickel chloride batteries can be operated at an intermediate temperature of 190 °C with ultra-high energy density. A specific energy density of 350 Wh kg−1, higher than that of conventional tubular sodium–nickel chloride batteries (280 °C), is obtained for planar sodium–nickel chloride batteries operated at 190 °C over a long-term cell test (1,000 cycles), and it attributed to the slower particle growth of the cathode materials at the lower operating temperature. Results reported here demonstrate that planar sodium–nickel chloride batteries operated at an intermediate temperature could greatly benefit this traditional energy storage technology by improving battery energy density, cycle life and reducing material costs.

Highly Reversible Zinc-Ion Intercalation into Chevrel Phase Mo6S8 Nanocubes and Applications for Advanced Zinc-Ion Batteries

This work describes the synthesis of Chevrel phase Mo6S8 nanocubes and its application as the anode material for rechargeable Zn-ion batteries. Mo6S8 can host Zn(2+) ions reversibly in both aqueous and nonaqueous electrolytes with specific capacities around 90 mAh/g, and exhibited remarkable intercalation kinetics and cyclic stability. In addition, we assembled full cells by integrating Mo6S8 anodes with zinc-polyiodide (I(-)/I3(-))-based catholytes, and demonstrated that such full cells were also able to deliver outstanding rate performance and cyclic stability. This first demonstration of a zinc-intercalating anode could inspire the design of advanced Zn-ion batteries.