The development and industrial application of advanced lithium based energy-storage materials are directly related to the innovative production techniques and the usage of inexpensive precursor materials. Flame spray pyrolysis (FSP) is a promising technique that overcomes the challenges in the production processes such as scalability, process control, material versatility, and cost. In the present study, phase pure anode material LiTiO (LTO) was designed using FSP via extensive systematic screening of lithium and titanium precursors dissolved in five different organic solvents. The effect of precursor and solvent parameters such as chemical reactivity, boiling point, and combustion enthalpy on the particle formation either via gas-to-particle (evaporation/nucleation/growth) or via droplet-to-particle (precipitation/incomplete evaporation) is discussed. The presence of carboxylic acid in the precursor solution resulted in pure (>95 mass %) and homogeneous LTO nanoparticles of size 4-9 nm, attributed to two reasons: (1) stabilization of water sensitive metal alkoxides precursor and (2) formation of volatile carboxylates from lithium nitrate evidenced by attenuated total reflection Fourier transform infrared spectroscopy and single droplet combustion experiments. In contrast, the absence of carboxylic acids resulted in larger inhomogeneous crystalline titanium dioxide (TiO) particles with significant reduction of LTO content as low as ∼34 mass %. In-depth particle characterization was performed using X-ray diffraction with Rietveld refinement, thermogravimetric analysis coupled with differential scanning calorimetry and mass spectrometry, gas adsorption, and vibrational spectroscopy. High-resolution transmission electron microscopy of the LTO product revealed excellent quality of the particles obtained at high temperature. In addition, high rate capability and efficient charge reversibility of LTO nanoparticles demonstrate the vast potential of inexpensive gas-phase synthesis for energy-storage materials.

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Li7La3Zr2O12 (LLZO) and related compounds are considered as promising candidates for future all-solid-state Li-ion battery applications. Still, the processing of those materials into thin membranes with the right stoichiometry and crystal structure is difficult and laborious. The sensitivity of the Li-ion conductive garnets against moisture and the associated Li+/H+ cation exchange makes their processing even more difficult. Formulation of suitable polymer/ceramic hybrid solid state electrolytes could be a prosperous way to reach the future large scale production of solid state Li-ion batteries. In fact, solvent mediated and/or slurry based wet-processing of the LLZO, e.g., tape-casting, could result in irreversible Li-ion loss of the pristine material due to Li+/H+ cation exchange. The concomitant structural changes and loss in functionality in terms of Li-ion conductivity are the results of the above process. Therefore, in the present work a systematic study on the chemical stability and structural retention of Al-substituted LLZO in different solvents is reported. It was found that Li+/H+ exchange in LLZO occurs upon solvent immersion, and its magnitude is dependent on the availability of −OH functional groups of the solvent molecules. As a result, a larger degree of Li+/H+ exchange causes higher increase of the lattice parameter of the LLZO, determined by synchrotron diffraction analyses. The expansion of the cubic unit cell was ascertained, when Li+ was replaced by H+ in the host lattice, by ab initio computational studies. The application of the most common solvent as dispersion medium, i.e., high purity water, causes the most significant Li+/H+ exchange and, therefore, structural change, while acetonitrile was proven to be the best suitable solvent for wet postprocessing of LLZO. Finally, computational calculations suggested that the Li+/H+ exchange could result in diminished ionic, i.e., mixed Li+–H+, conductivity due to the insertion of protons with lower mobility than that of Li-ions.

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