Inorganic solid Li ion conductors: An overview

The solid lithium-ion electrolyte “Li7La3Zr2O12” (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, 6Li and 7Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24dLi site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy Ea characterizing long-range ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 × 10−4 Scm−1 to 4 × 10−4 Scm−1 depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 × 10−6 Scm−1, Ea = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb–Wagner polarization technique. The electronic transference number te− is of the order of 10−7. Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.

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Structure and dynamics of the fast lithium ion conductor “Li7La3Zr2O12”

Developing reversible lithium metal anodes with high rate capability is one of the central aims of current battery research. Lithium metal anodes are not only required for the development of innova...

Physicochemical Concepts of the Lithium Metal Anode in Solid-State Batteries.

Nickel ferrite (NiFe2O4) nanoparticles with an average crystallite size of about 8.6 nm were prepared by mechanochemical synthesis (mechanosynthesis). In-field Mossbauer spectroscopy and high-resolution TEM studies revealed a nonuniform structure of mechanosynthesized NiFe2O4 nanoparticles consisting of an ordered core surrounded by a disordered grain boundary (surface) region. The inner core of a NiFe2O4 nanoparticle is considered to possess a fully inverse spinel structure with a Neel-type collinear spin alignment, whereas the surface shell is found to be structurally and magnetically disordered due to the nearly random distribution of cations and the canted spin arrangement. As a consequence of frustrated superexchange interactions in the surface shell, the mechanosynthesized NiFe2O4 exhibits a reduced nonsaturating magnetization, an enhanced coercivity, and a shifted hysteresis loop. The study also demonstrates that one can tailor the magnetic properties of mechanosynthesized NiFe2O4 particles by suit...

Nanocrystalline Nickel Ferrite, NiFe2O4: Mechanosynthesis, Nonequilibrium Cation Distribution, Canted Spin Arrangement, and Magnetic Behavior

Solid-State Li NMR with Applications to the Translational Dynamics in Ion Conductors

Lithium niobate has been chosen as a model system for spectroscopic studies of the influence of different structural forms and preparation routes of an ionic conductor on its ion transport properties. The Li diffusivity in nanocrystalline LiNbO3, prepared either mechanically by high energy ball milling or chemically by a sol-gel route, was studied by means of impedance and solid state 7Li NMR spectroscopy. The Li diffusivity turned out to be strongly correlated with the different grain boundary microstructures of the two nanocrystalline samples and with the degree of disorder introduced during preparation, as seen especially by HRTEM and EXAFS. Although in both samples nanostructuring yields an enhancement of the Li diffusivity compared to that in coarse grained LiNbO3, the Li diffusivity in ball milled LiNbO3 is much higher than in chemically prepared nanocrystalline LiNbO3. The former LiNbO3 sample has a large volume fraction of highly disordered interfacial regions which seem to be responsible for fast Li diffusion and to have a structure very similar to that of the amorphous form. This is in contrast to the chemically prepared sample where these regions have a smaller volume fraction.

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NMR and impedance studies of nanocrystalline and amorphous ion conductors: lithium niobate as a model system.

Electrochemical dopamine-sensing surfaces were fabricated by deposition of graphene sheets modified with cobalt tetrasulfonated phthalocyanine on glassy carbon electrodes (CoTSPc/Gr-GC) using differential pulse amperometry. Differential pulse stripping voltammetry was used to detect dopamine (DA) and the influence of pH value, scan rate, accumulation potential and time as well as dopamine concentration on the performance of CoTSPc/Gr-GC electrodes was investigated. The modified electrodes were successfully used as sensors for the selective and high sensitive determination of DA in presence of high concentrations of ascorbic acid (AA) and uric acid (UA) with a detection limit of 0.87 nM over the dynamic linear range of 20 nM to 220 nM.

A sensitive and selective graphene/cobalt tetrasulfonated phthalocyanine sensor for detection of dopamine

Impedance Spectroscopy Study of Li Ion Dynamics in Single Crystal, Microcrystalline, Nanocrystalline and Amorphous LiNbO3

Oxygen-18 surface exchange and diffusion in Li2O-deficient single crystalline lithium niobate

Long-range Li diffusion parameters of amorphous LiNbO3 are probed by 7 Li two-time spin-alignment echo NMR spectroscopy which is sensitive to slow Li dy- namics. The jump rates which were extracted from the spin-alignment echo decay curves exhibit Arrhenius behaviour between 293 K and 413 K. The activation energy (0.41(1) eV) is in good agreement with that of the high-temperature flank of the 7 Li NMR spin- lattice relaxation rate peak. The latter was predicted to be about 0.4 eV when taking into account the frequency dependence of the corresponding spin-lattice relaxation rates on the low-T flank (see Wilkening et al., Phys. Chem. Chem. Phys. 4 (2002) 3246). Previous measurements of the spin-lattice relaxation rate had to be restricted to temperatures below 450 K in order to avoid crystallization of the material. Thus, only the low-temperature flank of the diffusion induced spin-lattice relaxation rate peak had been accessible yield- ing information about short-range Li diffusion.

Muayad Masoud

Papers

NMR and impedance studies of nanocrystalline and amorphous ion conductors: lithium niobate as a model system.

A sensitive and selective graphene/cobalt tetrasulfonated phthalocyanine sensor for detection of dopamine

Impedance Spectroscopy Study of Li Ion Dynamics in Single Crystal, Microcrystalline, Nanocrystalline and Amorphous LiNbO3

Oxygen-18 surface exchange and diffusion in Li2O-deficient single crystalline lithium niobate

Li dynamics in amorphous LiNbO 3 as probed by solid state NMR on different length scales