The reactivity of mixtures of high voltage spinel cathode materials LiNiMnO, LiFeMnO, and LiCoMnO cosintered with LiAlTi(PO) and LiLaZrTaO electrolytes is studied by thermal analysis using X-ray-diffraction and differential thermoanalysis and thermogravimetry coupled with mass spectrometry. The results are compared with predicted decomposition reactions from first-principles calculations. Decomposition of the mixtures begins at 600 °C, significantly lower than the decomposition temperature of any component, especially the electrolytes. For the cathode + LiLaZrTaO mixtures, lithium and oxygen from the electrolyte react with the cathodes to form highly stable LiMnO and then decompose to form stable and often insulating phases such as LaZrO, LaO, LaTaO, TiO, and LaMnO which are likely to increase the interfacial impedance of a cathode composite. The decomposition reactions are identified with high fidelity by first-principles calculations. For the cathode + LiAlTi(PO) mixtures, the Mn tends to oxidize to MnO or MnO, supplying lithium to the electrolyte for the formation of LiPO and metal phosphates such as AlPO and LiMPO (M = Mn, Ni). The results indicate that high temperature cosintering to form dense cathode composites between spinel cathodes and oxide electrolytes will produce high impedance interfacial products, complicating solid state battery manufacturing.

Bulk-type SSLB based on LLZ:Ta achieves high specific areal capacity and operational current densities.

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