Critical currents across grain boundaries in YBCO : The role of grain boundary structure

Miller Dean J.,Gray Kenneth E.,Field Michael B.,Kim, Dong-Ho The Korean Superconductivity Society 1999 Progress in superconductivity Vol.1 No.1

Measurements across single grain boundaries in YBCO thin films and bulk bicrystals have been used to demonstrate the influence of grain boundary structure on the critical current carried across the grain boundary. In particular, we show that one role of grain boundary structure is to change the degree of pinning along the boundary, thereby influencing the critical current. This effect can be used to explain the large difference in critical current density across grain boundaries in thin films compared to that for bulk bicrystal. These differences illustrate the distinction between the intrinsic mechanism of coupling across the grain boundary that determines the maximum possible critical current across a boundary and the measured critical current which is limited by dissipation due to the motion of vortices.

<i>In Situ</i> Formed Ir₃Li Nanoparticles as Active Cathode Material in Li-Oxygen Batteries

Halder, Avik,Ngo, Anh T.,Luo, Xiangyi,Wang, Hsien-Hau,Wen, J. G.,Abbasi, Pedram,Asadi, Mohammad,Zhang, Chengji,Miller, Dean,Zhang, Dongzhou,Lu, Jun,Redfern, Paul C.,Lau, Kah Chun,Amine, Rachid,Assary, American Chemical Society [etc.] 2019 The Journal of physical chemistry A Vol. No.

<P>Lithium-oxygen (Li-O<SUB>2</SUB>) batteries are a promising class of rechargeable Li batteries with a potentially very high achievable energy density. One of the major challenges for Li-O<SUB>2</SUB> batteries is the high charge overpotential, which results in a low energy efficiency. In this work size-selected subnanometer Ir clusters are used to investigate cathode materials that can help control lithium superoxide formation during discharge, which has good electronic conductivity needed for low charge potentials. It is found that Ir particles can lead to lithium superoxide formation as the discharge product with Ir particle sizes of ∼1.5 nm giving the lowest charge potentials. During discharge these 1.5 nm Ir nanoparticles surprisingly evolve to larger ones while incorporating Li to form core-shell structures with Ir<SUB>3</SUB>Li shells, which probably act as templates for growth of lithium superoxide during discharge. Various characterization techniques including DEMS, Raman, titration, and HRTEM are used to characterize the LiO<SUB>2</SUB> discharge product and the evolution of the Ir nanoparticles. Density functional calculations are used to provide insight into the mechanism for formation of the core-shell Ir<SUB>3</SUB>Li particles. The <I>in situ</I> formed Ir<SUB>3</SUB>Li core-shell nanoparticles discovered here provide a new direction for active cathode materials that can reduce charge overpotentials in Li-O<SUB>2</SUB> batteries.</P> [FIG OMISSION]</BR>

Synthesis of full concentration gradient cathode studied by high energy X-ray diffraction

Li, Yan,Xu, Rui,Ren, Yang,Lu, Jun,Wu, Huiming,Wang, Lifen,Miller, Dean J.,Sun, Yang-Kook,Amine, Khalil,Chen, Zonghai Elsevier 2016 Nano energy Vol.19 No.-

<P><B>Abstract</B></P> <P>Nickel-rich metal oxides have been widely pursued as promising cathode materials for high energy-density lithium-ion batteries. Nickel-rich lithium transition metal oxides can deliver a high specific capacity during cycling, but can react with non-aqueous electrolytes. In this work, we have employed a full concentration gradient (FCG) design to provide a nickel-rich core to deliver high capacity and a manganese-rich outer layer to provide enhanced stability and cycle life. <I>In situ</I> high-energy X-ray diffraction was utilized to study the structural evolution of oxides during the solid-state synthesis of FCG lithium transition metal oxide with a nominal composition of LiNi<SUB>0.6</SUB>Mn<SUB>0.2</SUB>Co<SUB>0.2</SUB>O<SUB>2</SUB>. We found that both the pre-heating step and the sintering temperature were critical in controlling phase separation of the transition metal oxides and minimizing the content of Li<SUB>2</SUB>CO<SUB>3</SUB> and NiO, both of which deteriorate the electrochemical performance of the final material. The insights revealed in this work can also be utilized for the design of other nickel-rich high energy-density cathode materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Solid-state synthesis of FCG cathode is investigated by <I>in situ</I> XRD. </LI> <LI> Covariance analysis and Rietveld refinement are used to analyze the HEXRD data. </LI> <LI> Synthetic optimization of FCG cathode with excellent electrochemical performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Benefit from the covariance analysis and Rietveld refinement of <I>in situ</I> HEXRD data during the solid state synthesis, we can optimized the solid state synthesis conditions in a short time. And the full concentration gradient cathode composites (nickel-rich core and manganese-rich outer layer) with excellent electrochemical performance are obtained.</P> <P>[DISPLAY OMISSION]</P>

Synthesis of Porous Carbon Supported Palladium Nanoparticle Catalysts by Atomic Layer Deposition: Application for Rechargeable Lithium–O₂ Battery

Lei, Yu,Lu, Jun,Luo, Xiangyi,Wu, Tianpin,Du, Peng,Zhang, Xiaoyi,Ren, Yang,Wen, Jianguo,Miller, Dean J.,Miller, Jeffrey T.,Sun, Yang-Kook,Elam, Jeffrey W.,Amine, Khalil American Chemical Society 2013 Nano letters Vol.13 No.9

<P>In this study, atomic layer deposition (ALD) was used to deposit nanostructured palladium on porous carbon as the cathode material for Li–O<SUB>2</SUB> cells. Scanning transmission electron microscopy showed discrete crystalline nanoparticles decorating the surface of the porous carbon support, where the size could be controlled in the range of 2–8 nm and depended on the number of Pd ALD cycles performed. X-ray absorption spectroscopy at the Pd K-edge revealed that the carbon supported Pd existed in a mixed phase of metallic palladium and palladium oxide. The conformality of ALD allowed us to uniformly disperse the Pd catalyst onto the carbon support while preserving the initial porous structure. As a result, the charging and discharging performance of the oxygen cathode in a Li–O<SUB>2</SUB> cell was improved. Our results suggest that ALD is a promising technique for tailoring the surface composition and structure of nanoporous supports in energy storage devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-9/nl401833p/production/images/medium/nl-2013-01833p_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl401833p'>ACS Electronic Supporting Info</A></P>

A lithium–oxygen battery based on lithium superoxide

Lu, Jun,Jung Lee, Yun,Luo, Xiangyi,Chun Lau, Kah,Asadi, Mohammad,Wang, Hsien-Hau,Brombosz, Scott,Wen, Jianguo,Zhai, Dengyun,Chen, Zonghai,Miller, Dean J.,Sub Jeong, Yo,Park, Jin-Bum,Zak Fang, Zhigang Nature Publishing Group, a division of Macmillan P 2016 Nature Vol.529 No.7586

<P>Batteries based on sodium superoxide and on potassium superoxide have recently been reported(1-3). However, there have been no reports of a battery based on lithium superoxide (LiO2), despite much research(4-8) into the lithium-oxygen (Li-O-2) battery because of its potential high energy density. Several studies(9-16) of Li-O-2 batteries have found evidence of LiO2 being formed as one component of the discharge product along with lithium peroxide (Li2O2). In addition, theoretical calculations have indicated that some forms of LiO2 may have a long lifetime(17). These studies also suggest that it might be possible to form LiO2 alone for use in a battery. However, solid LiO2 has been difficult to synthesize in pure form(18) because it is thermodynamically unstable with respect to disproportionation, giving Li2O2 (refs 19, 20). Here we show that crystalline LiO2 can be stabilized in a Li-O-2 battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of Li2O2. A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline LiO2. Our results demonstrate that the LiO2 formed in the Li-O-2 battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). We anticipate that this discovery will lead to methods of synthesizing and stabilizing LiO2, which could open the way to high-energy-density batteries based on LiO2 as well as to other possible uses of this compound, such as oxygen storage.</P>