Fast Lithium Ion Conduction in Lithium Phosphidoaluminates

Abstract

Solid electrolyte materials are crucial for the development of high‐energy‐density all‐solid‐state batteries (ASSB) using a nonflammable electrolyte. In order to retain a low lithium‐ion transfer resistance, fast lithium ion conducting solid electrolytes are required. We report on the novel superionic conductor Li9AlP4 which is easily synthesised from the elements via ball‐milling and subsequent annealing at moderate temperatures and which is characterized by single‐crystal and powder X‐ray diffraction. This representative of the novel compound class of lithium phosphidoaluminates has, as an undoped material, a remarkable fast ionic conductivity of 3 mS cm−1 and a low activation energy of 29 kJ mol−1 as determined by impedance spectroscopy. Temperature‐dependent 7Li NMR spectroscopy supports the fast lithium motion. In addition, Li9AlP4 combines a very high lithium content with a very low theoretical density of 1.703 g cm−3. The distribution of the Li atoms over the diverse crystallographic positions between the [AlP4]9− tetrahedra is analyzed by means of DFT calculations.

Na2Ge3P3 and Na5Ge7P5 Comprising Heteroatomic Polyanions Mimicking the Structure of Fibrous Red Phosphorus

“…The occupation of Ge4 and P2 on the mixed position is 0.43(2) and 0.57(2), respectively. Partial defects were tested for all Na positions, which led to lower occupation factors of 0.89(5) for the Na2 site, suggesting a correlation between the Na content and the mixed Ge/P position, resulting in the refined composition Na 4.76(10) Ge 6.88(6) P 5.12 (6) , which is very close to the charge balanced composition Na 4+x Ge 6+x P 6-x . Therefore, in the final refinement these correlated occupancies have been restrained.…”

“…[ 4,5 ] The highest value for phosphide‐based materials of 3 mS · cm –1 was recently reported for Li 9 AlP 4 . [ 6 ]…”

“…[4,5] The highest value for phosphide-based materials of 3 mS•cm -1 was recently reported for Li 9 AlP 4 . [6] In the system Na/Tt/P a broader variety of connection patterns has been reported for the heavier homologues of Si (Tt = Ge, Sn) enabling the formation of Tt-Tt bonds and for-P atoms, respectively. These cages contain Ge-Ge bonds and form one-dimensional tubes by sharing three atoms.…”

Rechargeable Battery Electrolytes Capable of Operating over Wide Temperature Windows and Delivering High Safety

“…Fässler and co‐workers designed the solid electrolyte Li 9 AlP 4 by substituting the Si 4+ in Li 8 SiP 4 with Al 3+ to increase the concentration of Li ions. [ 254 ] This new electrolyte demonstrated a remarkable improvement in ionic conductivity (σ = 3 mS cm −1 vs 4.5 × 10 −2 mS cm −1 for Li 8 SiP 4 ).…”

Aliovalent substitution in phosphide‐based materials – Crystal structures of Na10AlTaP6 and Na3GaP2 featuring edge‐sharing EP4 tetrahedra (E=Al/Ta and Ga)

“…Illustrative examples of this manifold structural variety are Li 10 Si 2 P 6 , which features edgesharing SiP 4 double tetrahedra, [6] Li 2 SiP 2 /Li 2 GeP 2 and LiSi 2 P 3 , [7][8][9] where SiP 4 and GeP 4 tetrahedra are condensed to a network of super-tetrahedra, Li 3 Si 3 P 7 with double layers formed by vertexsharing SiP 4 tetrahedra, [6] and LiGe 3 P 3 with a two-dimensional polyanion comprising GeP 4 and Ge(P 3 Ge) tetrahedra. [8] A formally aliovalent substitution of the tetrel by a triel element leads to the lithium phosphidotrielates Li 3 AlP 2 and Li 3 GaP 2 which contain two-dimensional layers of corner-and edge-sharing tetrahedra, [4,10] whereas the corresponding Li 3 InP 2 shows a polyanionic framework of corner-sharing InP 4 supertetrahedra. [11] While lithium-based phosphides have already been studied intensively, much less is reported about the corresponding sodium species.…”