Li1.5La1.5MO6 (M = W6+, Te6+) as a new series of lithium-rich double perovskites for all-solid-state lithium-ion batteries

Solid-state batteries are a proposed route to safely achieving high energy densities, yet this architecture faces challenges arising from interfacial issues between the electrode and solid electrolyte. Here we develop a novel family of double perovskites, Li1.5La1.5MO6 (M = W6+, Te6+), where an uncommon lithium-ion distribution enables macroscopic ion diffusion and tailored design of the composition allows us to switch functionality to either a negative electrode or a solid electrolyte. Introduction of tungsten allows reversible lithium-ion intercalation below 1 V, enabling application as an anode (initial specific capacity >200 mAh g-1 with remarkably low volume change of ∼0.2%). By contrast, substitution of tungsten with tellurium induces redox stability, directing the functionality of the perovskite towards a solid-state electrolyte with electrochemical stability up to 5 V and a low activation energy barrier (<0.2 eV) for microscopic lithium-ion diffusion. Characterisation across multiple length- and time-scales allows interrogation of the structure-property relationships in these materials and preliminary examination of a solid-state cell employing both compositions suggests lattice-matching avenues show promise for all-solid-state batteries

Preparation, characterization and conductivity studies of NaAlSb(PO₄)₃ and HAlSb(PO₄)₃

347-354NaAlSb(PO4)3 and HAlSb(PO4)3 are prepared by solid-state and metathesis reactions respectively. They are characterized by powder XRD, IR and solid-state 31P-MAS NMR spectroscopy. These two compounds crystallize in the hexagonal NASICON structure with the space group of RC. Their infrared spectra exhibit characteristic vibrational bands of PO4 tetrahedra. The 31P-MAS NMR spectra of NaAlSb(PO4)3 and HAlSb(PO4)3 are characterized by a symmetric single peak around 9 ppm suggesting only one type of phosphorous in the hexagonal lattice. The activation energies for conduction and relaxation are more for NaAlSb(PO4)3 compared to the values of HAlSb(PO4)3. The isothermal conductivity of NaAlSb(PO4)3 i s higher than the conductivity of HAlSb(PO4)3. The imaginary parts of the impedance, (Z'') and electric modulus (M'') against log frequency show single peaks in both Z''  and M'' spectra