Suppressing Unfavorable Interfacial Reactions Using Polyanionic Oxides as Efficient Buffer Layers: Low-Cost Li₃PO₄ Coatings for Sulfide-Electrolyte-Based All-Solid-State Batteries

Abstract

The poor electrochemical performance of all solidstate batteries (ASSBs) that use sulfide electrolytes can be attributed to undesirable side reactions at the cathode/sulfideelectrolyte interface; this issue can be addressed via surface coating. Ternary oxides such as LiNbO 3 and Li 2 ZrO 3 are generally used as coating materials because of their high chemical stabilities and ionic conductivities. However, their relative high cost discourages their use in mass production. In this study, Li 3 PO 4 was introduced as a coating material for ASSBs, because phosphates possess good chemical stabilities and ionic conductivities. Phosphates also prevent the exchange of S 2− and O 2− in the electrolyte and cathode and, thus, inhibit interfacial side reactions caused by ionic exchange, because they contain the same anion (O 2− ) and cation (P 5+ ) species as those present in the cathode and sulfide electrolyte, respectively. Furthermore, the Li 3 PO 4 coatings can be prepared using low-cost source materials such as polyphosphoric acid and lithium acetate. We investigated the electrochemical performance of the Li 3 PO 4 -coated cathodes and found that the Li 3 PO 4 coating significantly improved the discharge capacities, rate capabilities, and cyclic performances of the all-solid-state cell. While the discharge capacity of the pristine cathode was ∼181 mAh• g −1 , that of 0.15 wt % Li 3 PO 4 -coated cathode was ∼194−195 mAh•g −1 . And the capacity retention of the Li 3 PO 4 -coated cathode over 50 cycles was much superior (∼84−85%) to that of the pristine sample (∼72%). Simultaneously, the Li 3 PO 4 coating reduced the side reactions and interdiffusion at the cathode/sulfide-electrolyte interfaces. The results of this study demonstrate the potential of low-cost polyanionic oxides, such as Li 3 PO 4 , as commercial coating materials for ASSBs.

A Perspective on the Requirements of Ni‐rich Cathode Surface Modifications for Application in Lithium‐ion Batteries and All‐Solid‐State Lithium‐ion Batteries

“…The presence of phosphorus in the coating led to extended cyclability by further suppressing side reactions associated with oxygen exchange between the cathode and electrolyte (Figure 5b). [81] Negi et al conducted a study where they implemented a surface modification technique using a composite Al 2 O 3 /LiAlO 2 on Ni 0.70 Co 0.15 Mn 0.15 . [29] One sample was subjected to further annealing, while another sample received only the coating treatment.…”

“…Figure 5. a) Schematic and b) corresponding cycle data for lithium phosphate coatings prepared by different precursors to modify the coated morphology. [Reproduced from Ref [81]. Copyright (2023), with permission from American Chemical Society], c) Schematic showing the influence of coating morphology on the contact between the cathode material and the solid electrolyte with d) scanning electron microscopy (SEM) images of the Alu-coated NCM powder before and after additional annealing, highlighting the increased contact.…”

Improving Interfacial Stability for All-Solid-State Secondary Batteries with Precursor-Based Gradient Doping

“…Notably, several widely used oxide coatings with low electronic conductivity alleviate the decomposition of sulfide electrolytes by limiting the electron exchange. 25−29 Although various ternary oxides 30−37 and polyanionic oxides 38,39 have been extensively investigated as cathode coatings, the effective control of interfacial reactions in ASSBs requires further investigation. This study introduces a novel approach, precursor-based gradient doping using low-cost oxide-based materials followed by cathode fabrication, to synthesize cathodes that ensure minimal electrode−electrolyte reactions and facilitate interface stabilization.…”

“…Consequently, sulfide electrolytes of the Li 6 PS 5 Cl (argyrodite) series, which exhibit a slightly lower ionic conductivity and higher interfacial cathode-compatibility than those of the Li 10 GeP 2 S 12 series (which exhibit an ionic conductivity comparable to that of liquid electrolytes), have been predominantly used in ASSBs. − Additionally, cathode coatings (with low sulfide-electrolyte reactivity and high ionic conductivity) that minimize the electrolyte–electrode interfacial reactions in the system have been used to construct practicable ASSBs. Notably, several widely used oxide coatings with low electronic conductivity alleviate the decomposition of sulfide electrolytes by limiting the electron exchange. − Although various ternary oxides − and polyanionic oxides , have been extensively investigated as cathode coatings, the effective control of interfacial reactions in ASSBs requires further investigation.…”

“…Notably, several widely used oxide coatings with low electronic conductivity alleviate the decomposition of sulfide electrolytes by limiting the electron exchange. 25 − 29 Although various ternary oxides 30 − 37 and polyanionic oxides 38 , 39 have been extensively investigated as cathode coatings, the effective control of interfacial reactions in ASSBs requires further investigation.…”