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Enhancing Fast Lithium Ion Conduction in Li4GeO4–Li3PO4 Solid Electrolytes

“…This enhancement in lithium ionic conductivity upon V 5+ codoping is consistent with the results of molecular dynamics (MD) simulations, which suggests that the introduction of additional types of cations into the LISICON system should further improve ionic conductivity . Indeed, we found that the ionic conductivity of Li 3.53 (Ge 0.75 P 0.25 ) 0.7 V 0.3 O 4 is comparable to those of Li 3.6 Ge 0.6 V 0.4 O 4 and Li 3.70 Ge 0.85 W 0.15 O 4 , which are the highest values reported to date for lithium ionic conduction in LISICON systems. The activation energy of Li 3.53 (Ge 0.75 P 0.25 ) 0.7 V 0.3 O 4 was comparable to that of Li 3.6 Ge 0.6 V 0.4 O 4 (Table S2), and hence, the corresponding ionic diffusion barriers were concluded to be nearly the same.…”

“…In the LISICON system, compositions with larger lattice volumes typically afford higher ionic conductivity. However, a comparison with the reported binary cationic Li–Ge–V–O system ( a = 10.896(1) Å, b = 6.2516(8) Å, and c = 5.1571(6) Å) with a larger lattice volume and a relatively high ionic conductivity (∼4.0 × 10 –5 S cm –1 ) indicated that the ternary cationic Li 3.53 (Ge 0.75 P 0.25 ) 0.7 V 0.3 O 4 system produced upon V 5+ codoping shows a smaller lattice volume (−9.12 (2)%) but a higher ionic conductivity (5.1 × 10 –5 S cm –1 ). This implies that the lattice volume is no longer the main influencing factor for realizing high ionic conductivity in the codoped system containing five identical elements.…”

“…The general ion diffusion mechanism for achieving significant enhancement of the solid solution ionic conductivity in LISICON systems was thought to be caused by the increased concentration of defects, which act as charge carriers. The initial exploration of suitable materials for LISICON focused on single cation systems (Li–X–O: X = P 5+ , Si 4+ , or Ge 4+ ), which had relatively low room-temperature ionic conductivity (<10 –10 S cm –1 ). − The cation doping of these single-cation materials (Li-X–Y–O: X with Y = Zn 2+ with Ge 4+ , V 5+ with Ge 4+ , Al 3+ with Ge 4+ , or Al 3+ with Si 4+ ) enhanced their ion-conducting properties (10 –7 –10 –5 S cm –1 ) due to the introduction of defects (lithium interstitial and/or lithium vacancy) in the structures. ,− The highest conductivity obtained using such an approach was ∼4.0 × 10 –5 S cm –1 for Li 3.6 Ge 0.6 V 0.4 O 4 and Li 3.7 Ge 0.85 W 0.15 O 4 . , While these strategies were successful, they were limited to the use of a single type of cations for doping the original composition. It has been recently reported that the cation codoping could further enhance the ionic conductivity of the LISICON materials, by lowering the Li + ion conduction barrier.…”

Thio‐/LISICON and LGPS‐Type Solid Electrolytes for All‐Solid‐State Lithium‐Ion Batteries

“…[63] A great deal of research indicates that cation doping can effectively improve the ionic conductivity of single-cation materials (Li-X-O: X = P 5+ , Si 4+ , and Ge 4+ ). [42,[65][66][67][68][69] The highest conductivity by means of cation doping is about 4.0 × 10 −5 S cm −1 for Li 3.6 Ge 0.6 V 0.4 O 4 and Li 3.7 G e 0.85 W 0.15 O 4 . [44,67] The conductivity of LISICON-type electrolyte is able to be raised to a new level by cation codoping.…”

Alkali Metal Cation and Proton Conductors: Relationships between Composition, Crystal Structure, and Properties

“…Striped tetrahedra ¼ GeO 4 ; gray tetrahedra ¼ (Li,Zn)O 4 ; the white polyhedra are partially occupied by lithium. The structures of Li 3.75 Ge 0.75 V 0.25 O 4 and Li 3.70 Ge 0.85 W 0.15 O 4[235] differ only in minor details.…”