The effect of volume change and stack pressure on solid‐state battery cathodes

Solid-state lithium batteries may provide increased energy density and improved safety compared with Li-ion technology. However, in a solid-state composite cathode, mechanical degradation due to repeated cathode volume changes during cycling may occur, which may be partially mitigated by applying a significant, but often impractical, uniaxial stack pressure. Herein, we compare the behavior of composite electrodes based on Li4Ti5O12 (LTO) (negligible volume change) and Nb2O5 (+4% expansion) cycled at different stack pressures. The initial LTO capacity and retention are not affected by pressure but for Nb2O5, they are significantly lower when a stack pressure of <2 MPa is applied, due to inter-particle cracking and solid-solid contact loss because of cyclic volume changes. This work confirms the importance of cathode mechanical stability and the stack pressures for long-term cyclability for solid-state batteries. This suggests that low volume-change cathode materials or a proper buffer layer are required for solid-state batteries, especially at low stack pressures

2020 roadmap on solid-state batteries

Li-ion batteries have revolutionized the portable electronics industry and empowered the electric vehicle (EV) revolution. Unfortunately, traditional Li-ion chemistry is approaching its physicochemical limit. The demand for higher density (longer range), high power (fast charging), and safer EVs has recently created a resurgence of interest in solid state batteries (SSB). Historically, research has focused on improving the ionic conductivity of solid electrolytes, yet ceramic solids now deliver sufficient ionic conductivity. The barriers lie within the interfaces between the electrolyte and the two electrodes, in the mechanical properties throughout the device, and in processing scalability. In 2017 the Faraday Institution, the UK's independent institute for electrochemical energy storage research, launched the SOLBAT (solid-state lithium metal anode battery) project, aimed at understanding the fundamental science underpinning the problems of SSBs, and recognising that the paucity of such understanding is the major barrier to progress. The purpose of this Roadmap is to present an overview of the fundamental challenges impeding the development of SSBs, the advances in science and technology necessary to understand the underlying science, and the multidisciplinary approach being taken by SOLBAT researchers in facing these challenges. It is our hope that this Roadmap will guide academia, industry, and funding agencies towards the further development of these batteries in the future

Processing of Bi-2212 high temperature superconducting wires

Bi-2212 high temperature superconductors can be used for producing very high magnetic fields. They are studied at CERN for potential use in accelerator magnets. The powder-in-tube wires are produced by inserting Bi 2212 particles into a Ag matrix. In order to transport high supercurrents the Bi 2212 needs to be melted during a processing heat treatment in a process gas containing oxygen. For the processing of Bi-2212 wires a 100 bar overpressure furnace has been designed at CERN. The first part of this thesis describes the setting up of a high pressure gas supply system and its installation. To ensure the safe operation of the overpressure furnace the high pressure reaction cell has been pressure tested up to 250 bar. A LabVIEW program was developed in order to control the pressure during the heat treatment and to record the furnace temperature. The oxygen partial pressure in the process gas influences the phase sequence and the Bi-2212 melting temperature. The phase changes during the processing of Bi-2212 wires at different oxygen partial pressures have been studied by means of in situ synchrotron X-ray diffraction experiments, performed at the high energy scattering beamline ID15B at the European Synchrotron

High Energy Density Single Crystal NMC/Li6PS5Cl Cathodes for All-Solid-State Lithium Metal Batteries

To match the high capacity of metallic anodes, all-solid-state batteries (ASSBs) re- quire high energy density, long-lasting composite cathodes such as Ni-Mn-Co (NMC)- based lithium oxides mixed with a solid-state electrolyte (SSE). However in practice, cathode capacity typically fades due to NMC cracking and increasing NMC/SSE in- terface debonding because of NMC pulverization, which is only partially mitigated by the application of a high cell pressure during cycling. Using smart processing proto- cols we report a single crystal particulate LiNi0.83Mn0.06Co0.11O2 and Li6PS5Cl SSE composite cathode with outstanding discharge capacity of 210 mAh g−1 at 30 °C. A first cycle coulombic efficiency of >85%, and >99% thereafter, was achieved despite a 5.5% volume change during cycling. A near-practical discharge capacity at a high areal capacity of 8.7 mAh cm−2 was obtained using a novel asymmetric anode/cathode cycling pressure of only 2.5 MPa/0.2 MPa.</div

Structural changes in the silver-carbon composite anode interlayer of solid-state batteries

Ag-carbon composite interlayers have been reported to enable Li-free (anodeless) cycling of solid-state batteries. Here, we report structural changes in the Ag-graphite interlayer, showing that on charge, Li intercalates electrochemically into graphite, subsequently reacting chemically with Ag to form Li-Ag alloys. Discharge is not the reverse of charge but rather passes through Li-deficient Li-Ag phases. At higher charging rates, Li intercalation into graphite outpaces the chemical reactions with Ag, delaying the formation of the Li-Ag phases and resulting in more Li metal deposition at the current collector. At and above 2.5 mA·cm−2, Li dendrites are not suppressed. Ag nanoparticles do not suppress dendrites more effectively than does an interlayer of graphite alone. Instead, Ag in the carbon interlayer results in more homogeneous Li and Li-Ag formation on the current collector during charge

Thiocyanate-Ligated Heterobimetallic {PtM} Lantern Complexes Including a Ferromagnetically Coupled 1D Coordination Polymer

A series of heterobimetallic lantern complexes with the central unit {PtM­(SAc)₄(NCS)} have been prepared and thoroughly characterized. The {Na­(15C5)}­[PtM­(SAc)₄(NCS)] series, <b>1</b> (Co), <b>2</b> (Ni), <b>3</b> (Zn), are discrete compounds in the solid state, whereas the {Na­(12C4)₂)}­[PtM­(SAc)₄(NCS)] series, <b>4</b> (Co), <b>5</b> (Ni), <b>6</b> (Zn), and <b>7</b> (Mn), are ion-separated species. Compound <b>7</b> is the first {PtMn} lantern of any bridging ligand (carboxylate, amide, etc.). Monomeric <b>1</b>–<b>7</b> have M²⁺, necessitating counter cations that have been prepared as {(15C5)­Na}⁺ and {(12C4)₂Na}⁺ variants, none of which form extended structures. In contrast, neutral [PtCr­(tba)₄(NCS)]_∞ <b>8</b> forms a coordination polymer of {PtCr}⁺ units linked by (NCS)⁻ in a zigzag chain. All eight compounds have been thoroughly characterized and analyzed in comparison to a previously reported family of compounds. Crystal structures are presented for compounds <b>1</b>–<b>6</b> and <b>8</b>, and solution magnetic susceptibility measurements are presented for compounds <b>1</b>, <b>2</b>, <b>4</b>, <b>5</b>, and <b>7</b>. Further structural analysis of dimerized {PtM} units reinforces the empirical observation that greater charge density along the Pt-M vector leads to more Pt···Pt interactions in the solid state. Four structural classes, one new, of {MPt}···{PtM} units are presented. Solid state magnetic characterization of <b>8</b> reveals a ferromagnetic interaction in the {PtCr­(NCS)} chain between the Cr centers of <i>J</i>/<i>k</i>_B = 1.7(4) K

Aqueous Superparamagnetic Magnetite Dispersions with Ultrahigh Initial Magnetic Susceptibilities

Superparamagnetic nanoparticles with a high initial magnetic susceptibility χ_o are of great interest in a wide variety of chemical, biomedical, electronic, and subsurface energy applications. In order to achieve the theoretically predicted increase in χ_o with the cube of the magnetic diameter, new synthetic techniques are needed to control the crystal structure, particularly for magnetite nanoparticles larger than 10 nm. Aqueous magnetite dispersions (Fe₃O₄) with a χ_o of 3.3 (dimensionless SI units) at 1.9 vol %, over 3- to 5-fold greater than those reported previously, were produced in a one-pot synthesis at 210 °C and ambient pressure via thermal decomposition of Fe­(II) acetate in triethylene glycol (TEG). The rapid nucleation and focused growth with an unusually high precursor-to-solvent molar ratio of 1:12 led to primary particles with a volume average diameter of 16 nm and low polydispersity according to TEM. The morphology was a mixture of stoichiometric and substoichiometric magnetite according to X-ray diffraction (XRD) and Mössbauer spectroscopy. The increase in χ_o with the cube of magnetic diameter as well as a saturation magnetization approaching the theoretical limit may be attributed to the highly crystalline structure and very small nonmagnetic layer (∼1 nm) with disordered spin orientation on the surface

Uranium–Nitrogen Multiple Bonding: The Case of a Four-Coordinate Uranium(VI) Nitridoborate Complex

While uranium imido complexes are well established in the literature, complexes featuring a uranium nitride functionality are rare. Data pertaining to terminal uranium nitrides are limited to the spectroscopic observation of the binary uranium nitrides UN and NUN and the ternary nitride NUF[subscript 3] under matrix conditions. We are interested in the uranium nitride functional group as it incorporates metal-ligand multiple bonding, valence f orbitals, and redox activity