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New concepts in ceramic conducting oxides for improved energy storage devices

Final Report Summary - CONFIES (New concepts in ceramic conducting oxides for improved energy storage devices)

Abstract: The main objectives proposed in this project have been achieved and the results published and disseminated in the most appropriate platforms. The main results for each task are summarised as:

Objective 1: Synthesis of new ceramic oxides via soft chemistry procedures
Task 1: Synthesis of new materials
The synthesis of different families of Li-conductors has been performed via the nitrate-citrate route. Specifically, the following families have been prepared after several trials: Perovskite type Li3xLa2/3-xTiO3-d (x=0.11 LLTO), Perovskites of composition Li3xLa2/3-xTi1-yMgyO3-d (x= 0.11 and y=0.05 and 0.1) Garnets Li7-3xGax□2xLa3Zr2O12 (where □ represents a vacancy and x= 0.15 0.2 and 0.3) Garnets Li7-2xZnx□xLa3Zr2O12 (where □ represents a vacancy and x= 0.15 0.2 and 0.3). Garnets Li7-4xGex□3xLa3Zr2O12 (where □ represents a vacancy and x= 0.05 and 0.1) and Pyrochlore based materials of composition ASbTeO6 (A= K, Li and H3O).

Objective 2: Study of the factors governing the transport properties
Task 2: Structural, Chemical and Thermal analysis
The purity of all the phases under study was assessed by X-ray diffraction (XRD) measurements. In all the cases, the synthesis conditions were optimised to obtain single high purity phases with the desired crystal structure. Rietveld refinement of the data was performed with the Fullprof program to evaluate crystal structure features. We have also analysed the chemical composition of the samples by inductively-coupled plasma optical emission spectrometry (ICP-OES). The theoretical stoichiometry of the samples was confirmed within the limits of the technique. Furthermore, 1H, 7Li and 71Ga magic angle spinning nuclear magnetic resonance (MAS-NMR) was used evaluate the different cation populations, chemical environments and mobility. Neutron powder diffraction (Fig. 1 in attached file) was used to analyse the crystal structure features of the materials and to analyse the Li location and mobility.

Task 3. Electrical characterization
Impedance spectroscopy measurements have been performed using a Solartron 1260A impedance/gain-phase analyser. The impedance data were collected using the Z-plot software from 10 MHz to 1 Hz at open circuit voltage using the two electrode configuration and with a signal amplitude of 50 mV (Fig 2 in attached file.)

Task 4: Electron microscopy measurements and trace diffusion experiments
Scanning Electron Microscopy (SEM – SEM Quanta 200 FEG) operated in low vacuum mode at a voltage of 20 kV was used to analyse the microstructure of the samples. The grain shape and boundaries were revealed by thermal etching. The grain size distribution was calculated with the software Estereologia from a 2500m2 surface area (Fig. 2c in attached).

Task 5: Tracer ionic diffusion measurements
In order to investigate the surface composition, the LLTO sample was analysed by low energy ion scattering (LEIS). Fig. 3 shows the LLTO surface spectrum obtained by 3 keV He+ scattering. The presence of the C peak after the oxygen plasma exposure suggests the formation of a carbonate layer on the surface, as this would not be removed during the cleaning procedure. A surface peak corresponding to La cations located on the A-site of the LLTO perovskite appears at 2213 eV, although most of the surface would be covered by the carbonate layer and other contaminants (e.g. Na), as indicated by the small surface peak. The Ti atoms are then located underneath the AO plane termination of the LLTO perovskite implying that both Li cation and cation vacancies might be exposed in the surface facilitating the ion-exchange.

Overall summary
The research directed towards the initial goals proposed in this project has given important results in the field of conducting ceramic oxides.
- We have been able to analyse and control the effect of moisture in ceramics with high Li-conductivity which has huge implications for their integration in commercial batteries.
- We have secured the money to buy a glove box for the synthesis, processing and integration of ceramic electrolytes into secondary batteries through a Capital for Great Technologies grant “Advanced Materials, Robotics and Autonomous Systems and Grid-scale Energy Storage” EPSRC (Total secured at Imperial College: £14,283k)
- This project has led to two undergraduate research projects (Wheatcroft and Russo) and a PhD student (Brugge) and so the continuation of the project is ensured.
- During the period of this fellowship Dr Aguadero was able to secure a Lectureship position in the Department of Materials at Imperial College to continue the research initiated by this fellowship.
- The results of this project have produced 6 papers, attendance at up to 20 conferences and 5 invited seminars and workshops. Further papers and conferences will secure the further dissemination of all the results of this research.