Abstract: A dual‐coating process was developed to prepare a unique yolk–shell silicon–reduced graphene oxide/amorphous carbon (YS‐Si@rGO/a‐C) anode material. The nanostructured Si composite anode material consists of Si cores, evenly wrapped with a first coating of graphene oxide constructed through electrostatic self‐assembly, and a shell of a second reinforced coating of graphene oxide/amorphous carbon, integrated by using an economic hydrothermal carbonization process. Thermal reduction and HF etching were then applied to reduce graphene oxide into graphene and to create the required void space to endow the hybrid material with sufficient mechanical strength and to buffer against stresses induced by volume changes of the Si nanoparticles. The obtained YS‐Si@rGO/a‐C composite anode material has structural integrity together with conductive 3D‐network beneficial to its electrochemical performance, attributed to the synergy of electrostatic self‐assembly and hydrothermal carbonization. As a result, the composite anode has a superior initial coulombic efficiency of 76 %, surpassing other published Si/G composite anodes, as well as an initial cycle reversible capacity of 1668 mAh g −1 at 0.4 A g −1 and a capacity retention of 75 % after over 100 cycles, when compared with the yolk–shell structured Si@a‐C anode.

Abstract: In situ diffuse reflectance infrared Fourier‐transformed spectroscopy (DRIFTS) investigations have been made to examine solid‐electrolyte interphase (SEI) formation on lithium‐rich Li 1.2 Ni 0.2 Mn 0.6 O 2 (LLNMO) and LiCoO 2 cathodes during first‐ and second‐cycle charging and discharging. This DRIFTS technique allows us to clarify SEI formation with different charging voltages. Both cathodes revealed the formation of the same surface species during first‐cycle charging, initially including ethylene carbonate (EC) adsorption, and SEI species, for example, ROCOF, RCOOR, Li 2 CO 3 , ROCO 2 Li, and PF x , are formed above the onset potential, namely 4.0 and 4.5 V for LiCoO 2 and LLNMO, respectively. The onset potentials correspond to the upper limit of the reversible redox potential range for transition‐metal couples (e.g. Co 3+ /Co 4+ in LiCoO 2 and Ni 2+ /Ni 4+ in LLNMO), which account for the intrinsic instability of these cathode materials. Such results suggest the participation of intermediate reactive oxygen species in SEI formation. SEI species continue to form during the discharge process when the potential is scanned cathodically below 3.6 and 4.0 V for LiCoO 2 and LLNMO, respectively. Similar SEI species are also observed during the second cycle charge–discharge over LLNMO, where additional oxidized species such as carboxylate (−COO−) and CO 2 are also found during charging. With the exception of PF x , all of the observed SEI species can be attributed to the oxidative decomposition of the organic solvent, EC. Finally, possible reaction mechanisms related to the oxidative decomposition of EC are discussed.

Abstract: The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One possible cathode material are the Li-rich layered oxide compounds xLi 2 MnO 3 .(1-x)LiMO 2 (M= Ni, Mn, Co) (0.5= 〈 x= 〈 1.0) that exhibit capacities over 280 mAh g -1 . In this class of compounds, lithium ions reside in both lithium layer and transition metal layer of close packed oxygen framework, typical from O3 type layered oxides like LiCoO 2 . 1 , 2 Large irreversible capacities are often observed in these materials due to irreversible oxygen loss or side reactions stemming for the electrolyte. It has been also observed using ex-situ NMR that lithium reinsertion back into the transition metal layer is little to none. However, these studies have not revealed the dynamic process of lithium migration for the Li-rich material under operando electrochemical cycling conditions. Neutron scattering has several distinct advantages for battery studies: 1) The sensitivity of neutron to light elements such as lithium and oxygen are significant in order to determine their position in the crystal structure; 2) Compares to the X-ray, the neutron shows larger scattering contrast between neighboring elements in the periodic table specifically the scattering lengths; and 3) The deep penetration capability of neutron allows simultaneous observation of the cathode and anode. 3 However, challenges exist in broadening the application of operando neutron diffraction for Li-ion batteries research. First, limited by the generation reactions of neutrons, the neutron flux is usually several orders of magntitude lower than X-rays. In another words, longer acquisition times as well as larger amounts of samples are required for neutron diffraction experiments. In addition, the existence of hydrogen, which has a large incoherent neutron-scattering cross-section, is detrimental to the signal-to-noise ratio of neutron diffraction pattern. Separators (polyethylene based porous membrane) and poly carbonate based electrolyte solutions contain a considerate amount of hydrogen. These two major reasons pose significant challenges to operando neutron diffraction for lithium ion battery research although it is such a powerful technique for light elements like lithium. In order to gain more in-depth insights about the lithium (de-)intercalation mechanisms in Li-rich layered oxides, track particularly the lithium ions in transition metal layer, operando neutron diffraction experiments were designed to quantitatively observe lithium migration in this type of oxides during the electrochemical process.   In this study, we use amorphous silicon as an anode for the neutron diffraction battery design in order to avoid any overlap of signal that may be associated with the anode material. We perform operando neutron diffraction to probe lithium and oxygen for a high Li-rich (HLR), Li[Li x/3 Ni (3/8-3x/8) Co (1/4-x/4) Mn (3/8+7x/24) O 2 (x = 0.6) material, and low Li-rich (LLR), Li[Li x/3 Ni (1/3-x/3) Co (1/3-x/3) Mn (1/3+x/3) O 2 (x = 0.24) material with varying degrees of the high voltage plateau. In conjunction with the operando neutron diffraction, density functional theory (DFT) calculations were used to explore the incorporation of dilute oxygen vacancy, its affect on the lattice mechanics and oxygen positions. We also observe site-dependent lithium migration taking place during different stage of charging/discharge processes. Furthermore, this work demonstrates the potential of investigating dynamic changes of light elements in large format (10-100 times larger format than the typical operando cells for synchrotron X-ray diffraction) prismatic and cylindrical batteries under realistic cycling condition via operando neutron diffraction method.  Acknowledgements UCSD’s efforts are supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, Subcontract No. 7073923, under the Advanced Battery Materials Research (BMR) Program. The neutron experiments benefited from the SNS user facility, sponsored by the office of Basic Energy Sciences (BES), the Office of Science of the DOE. H.L. acknowledges the financial support from the China Scholarship Council under Award No. 2011631005. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575.   Reference 1.             H. Liu, D. Qian, M. G. Verde, M. Zhang, L. Baggetto, K. An, Y. Chen, K. J. Carroll, D. Lau, M. Chi, G. M. Veith and Y. S. Meng, Acs Appl Mater Inter , 2015, 7 , 19189-19200. 2.             M. G. Verde, H. D. Liu, K. J. Carroll, L. Baggetto, G. M. Veith and Y. S. Meng, Acs Appl Mater Inter , 2014, 6 , 18868-18877. 3.             H. D. Liu, C. R. Fell, K. An, L. Cai and Y. S. Meng, J Power Sources , 2013, 240 , 772-778. Figure 1

Abstract: Interest in non-flammable solid-state battery electrolytes continues to grow as they hold promise for batteries with increased safety, reliability, and energy density. They are nonflammable, stable over a wide temperature range, have a large electrochemical window, and potentially allow for the use of metallic Li anodes [1]. One particular solid-state electrolyte is the Lithium-rich anti-perovskite (LiRAP) with the formula Li 3 OX where X is a halogen or a mixture of halogens. Conductivities of 〉 1 mS/cm were previously reported [2]. Interest in the material grew as the conductivity varied with different processing conditions thus opening the door to improvement with structura tweaking and optimization [3] . Whenever new a lithium compound is discovered in the battery field, interest in a sodium analog also arises. Na-ion batteries are considered a possible lower-cost alternative to lithium ion batteries due to the abundance of sodium. The conductivity of various Na-rich anti-perovskite (NaRAP) compounds with varying halogens were also previously reported [4].  Here we compare different synthesis methods for the Na 3 OBr compound, namely conventional cold-pressed sintering and spark plasma sintering. Spark plasma sintering enables a shorter processing time and more tightly-packed, dense pellets [5]. We report that the Na ionic conductivity for Na 3 OBr remained at similar values regardless of the synthesis method. Acknowledgements This work was supported by the National Science Foundation under grant number ACI-1053575. References [1] Thangadurai, V., Pinzaru, D., Narayanan, S., Baral, A. “Fast Solid State Li Ion Conducting Garnet-Type Structure Metal Oxides for Energy Storage”. J. Phys. Chem. Lett. ,  2015 ,  6  (2), pp 292–299. doi :  10.1021/jz501828v [2] Wang, Y, Richards, W. D., Ong, S. P., Miara, L. J., Kim, J. C., Mo, Y., and Ceder, G. “Design principles for solid-state lithium superionic conductors”. Nature Materials , 2015 , 14, pp 1026-1031. doi: 10.1038/nmat4369 [3] Deng, Z., Radhakrishnan, B., Ong, S. P. “Rational Composition Optimization of the Lithium-Rich Li3Ocl1-xBrx Anti-Perovskite Superionic Conductors”. Chem. Mater. 2015 , 27 (10), pp 3749-3755. doi: 10.1021/acs.chemmater.5b00988 [4] Wang, Y., Wang, Q., Liu, Z., Zhou, Z., Li, S., Zhu, J., Zou, R., Wang, Y., Lin, J., Zhao, Y.  “Structural manipulation approaches towards enhanced sodium ionic conductivity in Na-rich antiperovskites.” J. Power Sources 2015 , 293 , pp 735–740. doi: 10.1016/j.jpowsour.2015.06.002 [5] Sairam, K., Sonber, J. K., Murthy, T.S.R.Ch., Subramanian, C., Fotedar, R. K., Nanekar, P., Hubli, R.C. “Influence of spark plasma sintering parameters on densification and mechanical properties of boron carbide”. Int. Journal of Refractory Metals and Hard Materials , 2013 , 42, pp 185-192. doi: 10.1016/j.ijrmhm.2013.09.004

Abstract: The need to increase energy density in the layered oxide positive electrode materials has lead to a push to higher voltages. 1 However, as a consequence of these higher voltages, the cycle stability drops considerably due to lattice contraction, electrode surface reactions with the electrolyte, and related strain.  The lithium-excess layered oxides, a subset of layered oxide materials, exhibit one of the highest capacities in positive electrode materials due to the addition of anion redox pairs to compensate the charge mechanism 2 . While promising, this material also suffers from thermodynamic instabilities and surface transformations when charged to higher voltages, necessary to utilize its full capacity 3 . Operando coherent X-ray diffraction is an eloquent technique that has provided information in the nonequilibrium structural dynamics at the single particle level in lithium battery spinel positive electrode materials 4 . In addition, through phase retrieval algorithms, three-dimensional defect dynamics can also be determined to understand the nanoscale mechanisms during high voltage cycling 5,6 .   In this study, we apply the same principles to the lithium excess layered oxide, Li 1.2 Ni 0.133 Mn 0.533 Co 0.133 O 2 where a plateau can be observed for the Li-rich material at 4.5 V that correspond to a simultaneous extraction of lithium and oxygen. Figure (Left) illustrates powder diffraction at the (003) bragg peak during electrochemical cycling illuminating ~ 20 individual particles where they can be found at relatively high and low angles during the plateau region. Figure 2(right) is the corresponding single particle diffractive imaging for two different primary particles of the same material. Interestingly, an inhomogeneous structural evolution during the first charge occurs where some particles shows a delay before moving to lower angles.  Acknowledgements This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-SC0001805. Y.S.M., S.H. and H.L. acknowledge the support by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, Subcontract No. 7073923, under the Advanced Battery Materials Research (BMR) Program. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.             (1)        Liu, W.; Oh, P.; Liu, X.; Lee, M.-J.; Cho, W.; Chae, S.; Kim, Y.; Cho, J. Angew. Chem. Int. Ed. 2015 , n/a.             (2)        Yu, H.; Zhou, H. J. Phys. Chem. Lett. 2013 , 4 , 1268.             (3)        Xu, B.; Fell, C. R.; Chi, M.; Meng, Y. S. Energy & Environmental Science 2011 , 4 , 2223.             (4)        Singer, A.; Ulvestad, A.; Cho, H. M.; Kim, J. W.; Maser, J.; Harder, R.; Meng, Y. S.; Shpyrko, O. G. Nano Lett. 2014 , 14 , 5295.             (5)        Ulvestad, A.; Singer, A.; Cho, H. M.; Clark, J. N.; Harder, R.; Maser, J.; Meng, Y. S.; Shpyrko, O. G. Nano Lett. 2014 , 14 , 5123.             (6)        Ulvestad, A.; Singer, A.; Clark, J. N.; Cho, H. M.; Kim, J. W.; Harder, R.; Maser, J.; Meng, Y. S.; Shpyrko, O. G. Science 2015 , 348 , 1344. Figure 1

Abstract: The demand for high-energy dense materials that are also capable of extended charging and discharging cycling has brought the lithium-rich layered oxide compounds as leading contenders for the next generation of lithium ion battery cathode materials for consumer use. 1 While promising, these materials suffer from thermodynamic instabilities and surface transformations when charged to higher voltages, which are unique and deviate from the degradation mechanisms of the classical layered oxides 2 . One considerable difference between the classical and lithium rich layered oxides is the oxygen activity or oxygen loss and the impact it has on the surrounding environment. Figure 1 is the electrochemical charging and discharging profile for the stoichiometric LiNi 0.4 Mn 0.4 Co 0.2 O 2 (442) and the lithium rich Li 1.2 Ni 0.133 Mn 0.533 Co 0.133 O 2 (Li-rich) where a plateau can be observed for the Li-rich material at 4.5 V that corresponds to a simultaneous extraction of lithium and oxygen.  To obtain a better understanding of differences in the oxygen activity, x-ray absorption spectroscopy (XAS) was used to probe the O K-edge and the different transition metal L-edges on the surface and sub-surface using three penetrations depths (Auger, Electron-Yield, and Fluorescence) at different states of charge for 442 and Li-rich. Scanning transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were also employed in an attempt to elucidate key differences within the surfaces between the classical and lithium rich layered oxide materials when subjected to similar high voltage cycling. Differences in the d-p hybridization can be observed between 442 and Li-rich materials, where 442 shows a more dramatic decrease within the d-p hybridization compared to the Li-rich after charging to 4.8 V and discharged to 2.0 V. This is evident from  the drop of intensity of the low energy band within the O K-edge XAS spectra (Figure 2). Within the Co-free analogous material, the drop in hybridization showed higher dependence on Ni (Figure 3). 3 With the involvement of Co within the charge compensation mechanism, the oxygen activity is more complex where, unlike the Co-free materials, the increase of the spectral weight of the pre-edge of the lower energy band is more pronounced. In addition, this change is highly dependent on the current rate that is applied where slower rates give rise to larger changes within the oxygen environment while high current rates after extended cycling show minimal decrease of the hybridization. Acknowledgements The authors acknowledge the financial support from the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. DOE under Contract No. DE-AC02- 05CH11231, under the Batteries for Advanced Transportation Technologies (BATT) Program. The synchrotron X-ray portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the US Department of Energy Office of Science by Stanford University. S/TEM and EELS experiments were performed at the Center for Functional Nanomaterials, Brookhaven National Laboratory.             (1)        Yu, H.; Zhou, H. The Journal of Physical Chemistry Letters 2013 , 4 , 1268.             (2)        Xu, B.; Fell, C. R.; Chi, M.; Meng, Y. S. Energy & Environmental Science 2011 , 4 , 2223.             (3)        Hy, S.; Cheng, J.-H.; Liu, J.-Y.; Pan, C.-J.; Rick, J.; Lee, J.-F.; Chen, J.-M.; Hwang, B. J. Chemistry of Materials 2014 , 26 , 6919. Figure 1

Abstract: Solid-state electrolytes (SSE’s) are crucial in realizing the potential of novel rechargeable batteries. All-solid-state batteries with inorganic solid electrolytes offer a number of advantages by improving safety, reliability, and cost [1]. Sulfide glasses are promising as a solid electrolyte due to their superionic ionic conductivity [3] . Na 3 PS 4 is a glass-ceramic that is precipitated from the sulfide glass matrix, exhibiting ionic conductivities of 10 -6 and 10 -4 S/cm for the tetragonal and cubic phases, respectively [4]. Here we provide a simple synthesis process for stabilizing the cubic phase, which also reduces the activation energy to 330 meV. We also investigate anion doping, which can further improve upon this result by increasing Na vacancies, via a composition curve of Cl-doping to determine optimal concentration of (1-x)Na 3 PS 4 -xNaCl, for 0 〉 x 〉 0.0625. Acknowledgements This work was supported by National Science Foundation under grant number ACI-1053575. References [1]      Kamaya, Noriaki et al. “A Lithium Superionic Conductor.” Nature Materials 10.9 (2011): 682–686. Web. [2]      Hayashi, Akitoshi et al. “Superionic Glass-Ceramic Electrolytes for Room-Temperature Rechargeable Sodium Batteries.” Nature Communications 3.May (2012): 856. Web.Tatsumisago, Masahiro, and Akitoshi Hayashi. “Sulfide Glass-Ceramic Electrolytes for All-Solid-State Lithium and Sodium Batteries.” International Journal of Applied Glass Science 10 (2014): 226–235. Web. [3]      Ribes, M., B. Barrau, and J.L Souquet. “Sulfide Glasses: Glass Forming Region, Structure and Ionic Conduction of Glasses in Na2S-XS2 (X=Si, Ge), Na2S-P2S5, and Li2SGeS2 Systems.” Journal of Non-Crystalline Solids 39 (1980): 271–276. Print. [4]      Hayashi, Akitoshi et al. “Superionic Glass-Ceramic Electrolytes for Room-Temperature Rechargeable Sodium Batteries.” Nature Communications 3.May (2012): 856. Web. Figure 1

Abstract: Rechargeable all-solid-state lithium-ion batteries utilizing a fast lithium superionic conductor electrolyte (SCE) has the potential to revolutionize energy storage by providing an inherently safer, less flammable alternative to traditional organic electrolyte-based batteries.  Synthesized from 70Li 2 S:30P 2 S 5 glass-ceramic, the Li 7 P 3 S 11  metastable crystal is a promising SCE that exhibits very high ionic conductivity of 17 mS/cm, comparable to those of liquid electrolytes. In this work, we present a combined computational and experimental study on this compound. We find that though Li 7 P 3 S 11 is predicted unstable at zero temperature, it becomes stable at 630 K when vibrational entropy contributions are accounted for, in excellent agreement with experimental measurements. We will also report on the calculated surface energies and Wulff shape of the Li 7 P 3 S 11  crystal. Finally, we demonstrate that ab initio molecular dynamics (AIMD) simulations predict Li 7 P 3 S 11 to have a significantly higher room-temperature ionic conductivity than previously reported, suggesting that there is significant scope for the further optimization of this material.

Abstract: The Simons Observatory (SO) is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. We describe the scientific goals of the experiment, motivate the design, and forecast its performance. SO will measure the temperature and polarization anisotropy of the cosmic microwave background in six frequency bands centered at: 27, 39, 93, 145, 225 and 280 GHz. The initial configuration of SO will have three small-aperture 0.5-m telescopes and one large-aperture 6-m telescope, with a total of 60,000 cryogenic bolometers. Our key science goals are to characterize the primordial perturbations, measure the number of relativistic species and the mass of neutrinos, test for deviations from a cosmological constant, improve our understanding of galaxy evolution, and constrain the duration of reionization. The small aperture telescopes will target the largest angular scales observable from Chile, mapping ≈ 10% of the sky to a white noise level of 2 μK-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, r , at a target level of σ( r )=0.003. The large aperture telescope will map ≈ 40% of the sky at arcminute angular resolution to an expected white noise level of 6 μK-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the Large Synoptic Survey Telescope sky region and partially with the Dark Energy Spectroscopic Instrument. With up to an order of magnitude lower polarization noise than maps from the Planck satellite, the high-resolution sky maps will constrain cosmological parameters derived from the damping tail, gravitational lensing of the microwave background, the primordial bispectrum, and the thermal and kinematic Sunyaev-Zel'dovich effects, and will aid in delensing the large-angle polarization signal to measure the tensor-to-scalar ratio. The survey will also provide a legacy catalog of 16,000 galaxy clusters and more than 20,000 extragalactic sources.