Effects of Photochemical Oxidation of the Carbonaceous Additives on Li-S Cell Performance.

We introduce a simple and easy way to functionalize the surface of various carbonaceous materials through the ultraviolet light/ozone (UV/O) plasma where we utilize the zero-, one-, and two-dimensional carbon frameworks. In a general manner, the lamps of a UV/O generator create two different wavelengths (λ = 185 and 254 nm); the shorter wavelength (λ = 185 nm) dissociates the oxygen (O) in air and the longer wavelength (λ = 254 nm) dissociates the O and creates the reactive and monoatomic oxygen radical, which tends to incorporate onto the defects of the carbons. By tailoring the association and dissociation of the oxygen with various forms, carbon black, carbon nanofibers, and graphite flakes, chosen as representative models for the zero-, one-, and two-dimensional carbon frameworks, their structure can be oxidized, respectively, which is known as photochemical oxidation.

Direct Visualization of Lithium Polysulfides and Their Suppression in Liquid Electrolyte.

Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene liquid cell electron microscopy, we have visualized formation and diffusion of Li-PS simultaneous with morphological and phase evolutions of sulfur nanoparticles during lithiation.

Three-Dimensionally Aligned Sulfur Electrodes by Directional Freeze Tape Casting.

Rational design of sulfur electrodes is exceptionally important in enabling a high-performance lithium/sulfur cell. Constructing a continuous pore structure of the sulfur electrode that enables facile lithium ion transport into the electrode and mitigates the reconstruction of sulfur is a key factor for enhancing the electrochemical performance. Here, we report a three-dimensionally (3D) aligned sulfur electrode cast onto conventional aluminum foil by directional freeze tape casting.

Tracking the Chemical and Structural Evolution of the TiS Electrode in the Lithium-Ion Cell Using Operando X-ray Absorption Spectroscopy.

As the lightest and cheapest transition metal dichalcogenide, TiS possesses great potential as an electrode material for lithium batteries due to the advantages of high energy density storage capability, fast ion diffusion rate, and low volume expansion. Despite the extensive investigation of its electrochemical properties, the fundamental discharge-charge reaction mechanism of the TiS electrode is still elusive. Here, by a combination of ex situ and operando X-ray absorption spectroscopy with density functional theory calculations, we have clearly elucidated the evolution of the structural and chemical properties of TiS during the discharge-charge processes.

Electrochemical Reaction Mechanism of the MoS Electrode in a Lithium-Ion Cell Revealed by in Situ and Operando X-ray Absorption Spectroscopy.

As a typical transition metal dichalcogenide, MoS offers numerous advantages for nanoelectronics and electrochemical energy storage due to its unique layered structure and tunable electronic properties. When used as the anode in lithium-ion cells, MoS undergoes intercalation and conversion reactions in sequence upon lithiation, and the reversibility of the conversion reaction is an important but still controversial topic. Here, we clarify unambiguously that the conversion reaction of MoS is not reversible, and the formed LiS is converted to sulfur in the first charge process.

Freeze-Dried Sulfur-Graphene Oxide-Carbon Nanotube Nanocomposite for High Sulfur-Loading Lithium/Sulfur Cells.

The ambient-temperature rechargeable lithium/sulfur (Li/S) cell is a strong candidate for the beyond lithium ion cell since significant progress on developing advanced sulfur electrodes with high sulfur loading has been made. Here we report on a new sulfur electrode active material consisting of a cetyltrimethylammonium bromide-modified sulfur-graphene oxide-carbon nanotube (S-GO-CTA-CNT) nanocomposite prepared by freeze-drying. We show the real-time formation of nanocrystalline lithium sulfide (LiS) at the interface between the S-GO-CTA-CNT nanocomposite and the liquid electrolyte by in situ TEM observation of the reaction.

Revealing the Electrochemical Charging Mechanism of Nanosized LiS by in Situ and Operando X-ray Absorption Spectroscopy.

Lithium sulfide (LiS) is a promising cathode material for lithium-sulfur (Li/S) cells due to its high theoretical specific capacity (1166 mAh g) and ability to pair with nonmetallic lithium anodes to avoid potential safety issues. However, when used as the cathode, a high charging voltage (∼4 V versus Li/Li) is always necessary to activate LiS in the first charge process, and the voltage profile becomes similar to that of a common sulfur electrode in the following charge processes. In this report, we have prepared an electrode of nanosphere LiS particles and investigated its charging mechanism of the initial two charge processes by in situ and operando X-ray absorption spectroscopy.

X-ray Absorption Spectroscopy Characterization of a Li/S Cell.

The X-ray absorption spectroscopy technique has been applied to study different stages of the lithium/sulfur (Li/S) cell life cycle. We have investigated how speciation of S in Li/S cathodes changes upon the introduction of CTAB (cetyltrimethylammonium bromide, CH₃(CH₂)N⁺(CH₃)₃Br) and with charge/discharge cycling. The introduction of CTAB changes the synthesis reaction pathway dramatically due to the interaction of CTAB with the terminal S atoms of the polysulfide ions in the Na₂S solution.

A Conversation with Adam Heller.

Adam Heller, Ernest Cockrell Sr. Chair in Engineering Emeritus of the John J. McKetta Department of Chemical Engineering at The University of Texas at Austin, recalls his childhood in the Holocaust and his contributions to science and technology that earned him the US National Medal of Technology and Innovation in a conversation with Elton J.

Lithium Sulfide (Li2S)/Graphene Oxide Nanospheres with Conformal Carbon Coating as a High-Rate, Long-Life Cathode for Li/S Cells.

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W·h kg(-1), which is much higher than that of Li ion cells (400-600 W·h kg(-1)). However, problems of the S cathode such as highly soluble intermediate species (polysulfides Li2Sn, n = 4-8) and the insulating nature of S cause poor cycle life and low utilization of S, which prevents the practical use of Li/S cells. Here, a high-rate and long-life Li/S cell is proposed, which has a cathode material with a core-shell nanostructure comprising Li2S nanospheres with an embedded graphene oxide (GO) sheet as a core material and a conformal carbon layer as a shell.

Understanding the degradation mechanism of rechargeable lithium/sulfur cells: a comprehensive study of the sulfur-graphene oxide cathode after discharge-charge cycling.

Lithium/sulfur (Li/S) cells have attracted much attention due to their higher theoretical specific capacity and energy compared to those of current lithium-ion cells. However, the application of Li/S cells is still hampered by short cycle life. Sulfur-graphene oxide (S-GO) nanocomposites have shown promise as cathode materials for long-life Li/S cells because oxygen-containing functional groups on the surface of graphene oxide were successfully used as sulfur immobilizers by forming weak bonds with sulfur and polysulfides.

Durable carbon-coated Li2(S) core-shell spheres for high performance lithium/sulfur cells.

Lithium sulfide (Li2S) is an attractive cathode material with a high theoretical specific capacity (1166 mAh g(-1)). However, the poor cycle life and rate capability have remained significant challenges, preventing its practical application. Here, Li2S spheres with size control have been synthesized for the first time, and a CVD method for converting them into stable carbon-coated Li2S core-shell (Li2S@C) particles has been successfully employed.

A long-life, high-rate lithium/sulfur cell: a multifaceted approach to enhancing cell performance.

Lithium/sulfur (Li/S) cells are receiving significant attention as an alternative power source for zero-emission vehicles and advanced electronic devices due to the very high theoretical specific capacity (1675 mA·h/g) of the sulfur cathode. However, the poor cycle life and rate capability have remained a grand challenge, preventing the practical application of this attractive technology. Here, we report that a Li/S cell employing a cetyltrimethyl ammonium bromide (CTAB)-modified sulfur-graphene oxide (S-GO) nanocomposite cathode can be discharged at rates as high as 6C (1C = 1.

Lithium/sulfur batteries with high specific energy: old challenges and new opportunities.

In this review, we begin with a brief discussion of the operating principles and scientific/technical challenges faced by the development of lithium/sulfur cells. We then introduce some recent progress in exploring cathodes, anodes, and electrolytes for lithium/sulfur cells. In particular, several effective strategies used to enhance energy/power density, obtain good efficiencies, and prolong cycle life will be highlighted.

Nanostructured Li₂S-C composites as cathode material for high-energy lithium/sulfur batteries.

With a theoretical capacity of 1166 mA·h·g(-1), lithium sulfide (Li(2)S) has received much attention as a promising cathode material for high specific energy lithium/sulfur cells. However, the insulating nature of Li(2)S prevents the achievement of high utilization (or high capacity) and good rate capability. Various efforts have been made to ameliorate this problem by improving the contact between Li(2)S and electronic conductors.

SnS2 nanoparticle loaded graphene nanocomposites for superior energy storage.

SnS2 nanoparticle-loaded graphene nanocomposites were synthesized via one-step hydrothermal reaction. Their electrochemical performance was evaluated as the anode for rechargeable lithium-ion batteries after thermal treatment in an Ar environment. The electrochemical testing results show a high reversible capacity of more than 800 mA h g(-1) at 0.

Graphene oxide as a sulfur immobilizer in high performance lithium/sulfur cells.

The loss of sulfur cathode material as a result of polysulfide dissolution causes significant capacity fading in rechargeable lithium/sulfur cells. Here, we use a chemical approach to immobilize sulfur and lithium polysulfides via the reactive functional groups on graphene oxide. This approach enabled us to obtain a uniform and thin (around tens of nanometers) sulfur coating on graphene oxide sheets by a simple chemical reaction-deposition strategy and a subsequent low-temperature thermal treatment process.

Batteries for electric and hybrid-electric vehicles.

Batteries have powered vehicles for more than a century, but recent advances, especially in lithium-ion (Li-ion) batteries, are bringing a new generation of electric-powered vehicles to the market. Key barriers to progress include system cost and lifetime, and derive from the difficulty of making a high-energy, high-power, and reversible electrochemical system. Indeed, although humans produce many mechanical and electrical systems, the number of reversible electrochemical systems is very limited.

An effective stochastic excitation strategy for finding elusive NMR signals from solids.

The versatility of using a stochastic pulse sequence to elucidate peaks with a wide range of shifts, peak widths, and T(1) relaxation times is demonstrated. A stochastic sequence is combined with high speed magic angle spinning (MAS) to obtain the broad and largely shifted peak associated with (31)P in LiNiPO(4). A stochastic sequence is also used to obtain a spectrum of 85% H(3)PO(4), which has a much longer T(1) value.

X-ray absorption spectroscopy study of the LixFePO4 cathode during cycling using a novel electrochemical in situ reaction cell.

The extraction and insertion of lithium in LiFePO4 has been investigated in practical Li-ion intercalation electrodes for Li-ion batteries using Fe K-edge X-ray absorption spectroscopy (XAS). A versatile electrochemical in situ reaction cell was utilized, specifically designed for long-term X-ray experiments on battery electrodes during the lithium-extraction/insertion process in electrode materials for Li-ion batteries. The electrode contained about 7.

Hyperfine fields at the Li site in LiFePO(4)-type olivine materials for lithium rechargeable batteries: a (7)Li MAS NMR and SQUID study.

The (7)Li NMR isotropic shift for olivine LiMPO(4) (M = Fe, Mn, Co, Ni) is assigned to hyperfine coupling between the (7)Li nucleus and the transition metal unpaired electrons on the basis of the Curie-Weiss temperature dependence of the shift. The hyperfine shift arises from a linear combination of Li-O-M through-bond interactions wherein the unpaired A' electrons contribute a negative shift and the unpaired A' ' electrons contribute a positive shift. The hyperfine coupling constant is determined for each composition.