High Formability and Fast Lithium Diffusivity in Metastable Spinel Chloride for Rechargeable All‐Solid‐State Lithium‐Ion Batteries

Abstract

Materials with high formability and Li‐ion diffusivity are desired to realize safe bulk‐type all‐solid‐state Li‐ion batteries with high energy density. Spinel‐type Li2FeCl4, which is expected as a Li‐ion‐conductive electrode, adopts the high‐temperature cubic phase (space group: Fd‐3m) by a mechanochemical synthesis method. The powder‐compressed pellet shows a high relative density of 92% and large neck formation between the particles. An analysis of the distribution of relaxation times from the AC impedance results indicates that the contribution of the grain boundary impedance is almost negligible (≈3%) in the powder‐compressed pellet. Even the Li diffusion coefficient, which is underestimated by the Nernst–Einstein equation, is several orders of magnitude higher than those of conventional oxide and sulfide electrode materials. Analyzing the diffusion pathways using a classical force field calculation suggests that stabilizing the high‐temperature phase at room temperature delocalizes Li ions in the diffusion pathway, thus realizing high Li‐ion diffusivity. The Li2FeCl4 green compact containing 10 wt% carbon as an electron‐conductive additive shows a one‐electron charge reaction with a capacity of 126 mAh g−1, with no large overpotential at a high operating voltage of 3.6 V versus Li/Li+ at 30 °C.

Screening chloride Li‐ion conductors using high‐throughput force‐field molecular dynamics

“…However, we revisited LMC as a prospective solid electrolyte, as our calculations indicated it should have high Li-ion conductivity. The high-energy mechanochemical method used for LMC synthesis promotes ionic conduction by introducing lattice defects 64,65 and yielded a white powder (Figure 4A), in agreement with the large predicted bandgap (Figure 1C). The absence of the raw material peak and the appearance of the target compound peak in the experimental XRD pattern (Figure 4B) indicated that LMC was obtained as the only phase.…”

Applying the HSAB design principle to the 3.5 V-class all-solid-state Li-ion batteries with a chloride electrolyte

“…Li 2 FeCl 4 has a high working potential (3.65 V vs. Li + /Li) because of the high electronegativity of chlorine, similar to the induced effect of the PO 4 unit in LiFePO 4 with the same Fe 2+ ion. 33,34 The above acid-base reactions are expected to be suppressed if the electrode/electrolyte materials are both chlorides. In fact, the 27 Al MAS-NMR spectrum (Fig.…”

Materials informatics for discovery of ion conductive ceramics for batteries

“…We also evaluated the experimental ionic conductivities for promising samples from exhaustive search results. Samples of Li 2 FeCl 4 , 16) LiAlCl 4 , 17) Na 2 V 3 O 7 , 18) and Mg 0.6 Al 1.2 Si 1.8 O 6 19) were selected as fast ion conductors and showed relatively good ionic conductivity in the experiment. However, discrepancies between the BVFF calculation and the experimental measurement (incl.…”