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Gao, Tao

Publications and source records attributed to Gao, Tao.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Spatial dynamics of lithiation and lithium plating during high-rate operation of graphite electrodes

The principal inhibitor of fast charging lithium ion cells is the graphite negative electrode, where favorable conditions for lithium plating occur at high charge rates, causing accelerated degradation and safety concerns. The local response of graphite, both at the electrode and particle level, when exposed to fast charging conditions of around 6C is not well understood. Consequently, the conditions that lead to the onset of lithium plating, as well as the local dynamics of lithium plating and stripping, have also remained elusive. Here, we use high-speed (100 Hz) pencil-beam X-ray diffraction to repeatedly raster along the depth of a 101 μm thick graphite electrode in 3 μm steps during fast (up to 6C) charge and discharge conditions. Consecutive depth profiles from separator to current collector were each captured in 0.5 seconds, giving an unprecedented spatial and temporal description of the state of the electrode and graphite's staging dynamics during high rate conditions. The electrode is preferentially activated near the separator, and the non-uniformity increases with rate and is influenced by free-energy barriers between graphite's lithiation stages. The onset of lithium plating and stripping was quantified, occurring only within the first 15 μm from the separator. The presence of lithium plating changed the behavior of the underlying graphite, such as causing co-existence of LiC 6 and graphite in the fully discharged state. Finally, the staging behavior of graphite at different rates was quantified, revealing a high dependency on rate and drastic hysteresis between lithiation and delithiation.

25 ENERGY STORAGE↗
DOE OSTI2020

A chemically stabilized sulfur cathode for lean electrolyte lithium sulfur batteries

Lithium sulfur batteries (LSBs) are promising next-generation rechargeable batteries due to the high gravimetric energy, low cost, abundance, nontoxicity, and high sustainability of sulfur. However, the dissolution of high-order polysulfide in electrolytes and low Coulombic efficiency of Li anode require excess electrolytes and Li metal, which significantly reduce the energy density of LSBs. Quasi-solid-state LSBs, where sulfur is encapsulated in the micropores of carbon matrix and sealed by solid electrolyte interphase, can operate under lean electrolyte conditions, but a low sulfur loading in carbon matrix (<40 wt %) and low sulfur unitization (<70%) still limit the energy density in a cell level. Here, we significantly increase the sulfur loading in carbon to 60 wt % and sulfur utilization to ∼87% by dispersing sulfur in an oxygen-rich dense carbon host at a molecular level through strong chemical interactions of C–S and O–S. In an all-fluorinated organic lean electrolyte, the C/S cathode experiences a solid-state lithiation/delithiation reaction after the formation of solid electrolyte interphase in the first deep lithiation, completely avoiding the shuttle reaction. The chemically stabilized C/S composite retains a high reversible capacity of 541 mAh⋅g −1 (based on the total weight of the C/S composite) for 200 cycles under lean electrolyte conditions, corresponding to a high energy density of 974 Wh⋅kg −1 . The superior electrochemical performance of the chemical bonding-stabilized C/S composite renders it a promising cathode material for high-energy and long-cycle-life LSBs.

25 ENERGY STORAGE↗
DOE OSTI2019

A Pyrazine-Based Polymer for Fast-Charge Batteries

The lack of high-power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries. Here, poly(hexaazatrinaphthalene) (PHATN), an environmentally benign, abundant and sustainable polymer, is employed as a universal cathode material for these batteries. In Na-ion batteries (NIBs), PHATN delivers a reversible capacity of 220 mAh g -1 at 50 mA g -1 , corresponding to the energy density of 440 Wh kg -1 , and still retains 100 mAh g -1 at 10 Ag -1 after 50 000 cycles, which is among the best performances in NIBs. Such an exceptional performance is also observed in more challenging Mg and Al batteries. PHATN retains reversible capacities of 110 mAh g -1 after 200 cycles in Mg batteries and 92 mAh g -1 after 100 cycles in Al batteries. DFT calculations, X-ray photoelectron spectroscopy, Raman, and FTIR show that the electron-deficient pyrazine sites in PHATN are the redox centers to reversibly react with metal ions.

25 ENERGY STORAGE↗
DOE OSTI2019

Tuning Anionic Chemistry To Improve Kinetics of Mg Intercalation

Rechargeable Mg batteries (RMBs) hold great promise for high energy density in consumer electronics because of the high theoretical volumetric capacity and dendrite-free stripping/plating of Mg. Their development, however, is severely limited by the sluggish diffusion of Mg 2+ in inorganic cathodes, mainly induced by strong interaction between Mg 2+ and host anions. In this paper, for the first time, we systematically investigate how anionic chemistry (O, S, and Se) affects Mg 2+ migration in layered MX 2 (M = Ti and V; X = O, S, and Se), by combining theoretical density functional theory (DFT) calculations with electrochemical characterizations. At room temperature, TiSe 2 and VSe 2 achieve much better electrochemical performance than TiS 2 and VS 2 , due to the faster migration of Mg 2+ in selenide than in sulfide and oxide, as demonstrated by electrochemical kinetic characterizations and DFT calculations. The improved kinetics of selenide can be attributed to three criteria: (i) larger diffusion channel, (ii) weaker interaction between Mg 2+ and anion lattice, and (iii) higher electronic conductivity. Finally, the three criteria might not only be applicable to layered materials but also be generalizable to materials with other structures, like Chevrel phase, spinel, olivine, etc., which paves the way for the future design and modification of intercalation materials for RMBs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Very High Cycle Fatigue of a Cast Aluminum Alloy: Size Effect and Crack Initiation

Fatigue properties of an Al-Si-Cu cast alloy were investigated with life up to very high cycle fatigue regime. Particular attention was given to specimen size effect and fatigue crack initiation mechanism. Uniaxial fatigue tests with constant amplitudes were carried out by using ultrasonic fatigue testing machine operating at 20 kHz, compared to the results obtained by using conventional hydraulic fatigue machine at 35 Hz. In order to evaluate the size effect, two sets of specimens with different dimensions were used. The results show that the fatigue strength of the studied alloy decreases with the increase in specimen size. Scanning electron microscopy observation of fracture surfaces revealed that most fatigue cracks initiated from microstructural defects such as porosity located on specimen surface or in subsurface. Weibull statistical analysis of fatigue data accounting for size effect was performed to predict the fatigue life of the Al-Si-Cu alloy in the very high cycle regime. Good agreement was found between the fatigue life prediction and the experimental data.

36 MATERIALS SCIENCE↗
DOE OSTI2018

How Water Accelerates Bivalent Ion Diffusion at the Electrolyte/Electrode Interface

The effect of H 2 O in electrolytes and in electrode lattices on the thermodynamics and kinetics of reversible multivalent-ion intercalation chemistry based on a model platform of layered VOPO 4 has been investigated. The presence of H 2 O at the electrolyte/electrode interface plays a key role in assisting Zn 2+ diffusion from electrolyte to the surface, while H 2 O in the lattice structure alters the working potential. More importantly, a dynamic equilibrium between bulk electrode and electrolyte is eventually reached for H 2 O transport during the charge/discharge cycles, with the water activity serving as the key parameter determining the direction of water movement and the cycling stability.

25 ENERGY STORAGE↗
DOE OSTI2018

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 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. Furthermore, the co-substitution strategy to tune the thermodynamic features of the reactions could be extended to other high energy conversion materials for improved performance.

25 ENERGY STORAGE↗
DOE OSTI2018

A Universal Organic Cathode for Ultrafast Lithium and Multivalent Metal Batteries

Abstract Low‐cost multivalent battery chemistries (Mg 2+ , Al 3+ ) have been extensively investigated for large‐scale energy storage applications. However, their commercialization is plagued by the poor power density and cycle life of cathodes. A universal polyimides@CNT (PI@CNT) cathode is now presented that can reversibly store various cations with different valences (Li + , Mg 2+ , Al 3+ ) at an extremely fast rate. The ion‐coordination charge storage mechanism of PI@CNT is systemically investigated. Full cells using PI@CNT cathodes and corresponding metal anodes exhibit long cycle life (>10000 cycles), fast kinetics (>20 C), and wide operating temperature range (−40 to 50 °C), making the low‐cost industrial polyimides universal cathodes for different multivalent metal batteries. The stable ion‐coordinated mechanism opens a new foundation for the development of high‐energy and high‐power multivalent batteries.

Fan, Xiulin↗
DOE OSTI2018

An artificial interphase enables reversible magnesium chemistry in carbonate electrolytes

Magnesium-based batteries possess potential advantages over their lithium counterparts. However, reversible Mg chemistry requires a thermodynamically stable electrolyte at low potential, which is usually achieved with corrosive components and at the expense of stability against oxidation. In lithium-ion batteries the conflict between the cathodic and anodic stabilities of the electrolytes is resolved by forming an anode interphase that shields the electrolyte from being reduced. This strategy cannot be applied to Mg batteries because divalent Mg 2+ cannot penetrate such interphases. Here, we engineer an artificial Mg 2+ -conductive interphase on the Mg anode surface, which successfully decouples the anodic and cathodic requirements for electrolytes and demonstrate highly reversible Mg chemistry in oxidation-resistant electrolytes. The artificial interphase enables the reversible cycling of a Mg/V 2 O 5 full-cell in the water-containing, carbonate-based electrolyte. This approach provides a new avenue not only for Mg but also for other multivalent-cation batteries facing the same problems, taking a step towards their use in energy-storage applications.

25 ENERGY STORAGE↗