Li<bold>3</bold>PO<bold>4</bold> Coated Li[Ni<bold>0.75</bold>Co<bold>0.1</bold>Mn<bold>0.15</bold>]O<bold>2</bold> Cathode for All-Solid-State Batteries Based on Sulfide Electrolyte

Abstract

Surface coating of cathodes is an essential process for all-solid-state batteries (ASSBs) based on sulfide electrolytes as it efficiently suppresses interfacial reactions between oxide cathodes and sulfide electrolytes. Based on computational calculations, Li 3 PO 4 has been suggested as a promising coating material because of its higher stability with sulfides and its optimal ionic conductivity. However, it has hardly been applied to the coating of ASSBs due to the absence of a suitable coating process, including the selection of source material that is compatible with ASSBs. In this study, polyphosphoric acid (PPA) and (NH 4 ) 2 HPO 4 were used as source materials for preparing a Li 3 PO 4 coating for ASSBs, and the properties of the coating layer and coated cathodes were compared. The Li 3 PO 4 layer fabricated using the (NH 4 ) 2 HPO 4 source was rough and inhomogeneous, which is not suitable for the protection of the cathodes. Moreover, the water-based coating solution with the (NH 4 ) 2 HPO 4 source can deteriorate the electrochemical performance of high-Ni cathodes that are vulnerable to water. In contrast, when an alcohol-based solvent was used, the PPA source enabled the formation of a thin and homogeneous coating layer on the cathode surface. As a consequence, the ASSBs containing the Li 3 PO 4 -coated cathode prepared by the PPA source exhibited significantly enhanced discharge and rate capabilities compared to ASSBs containing a pristine cathode or Li 3 PO 4 -coated cathode prepared by the (NH 4 ) 2 HPO source.

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.…”

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

“…In particular, we investigated the possibility of using low-cost sources to replace the expensive alkoxide-based sources (such as ethoxide) commonly used for ASSB coatings. In this study, polyphosphoric acid (PPA) was used as the P source for the Li 3 PO 4 coating because of its ability to form a thin and uniform layer and its relatively low cost. , Replacing lithium ethoxide, which is generally used as a Li source for homogeneous coatings, ,,,,, with other inexpensive source materials such as lithium acetate or nitrate, may also be advantageous for commercialization and mass production. The properties of the coatings prepared using various lithium sources were compared.…”

Rational Design of Multifunctional Surface Modification for Ni-Rich Layered Cathodes of Lithium-Ion Batteries

“…Although numerous factors could influence the energy density of LIBs, it is broadly known that the energy density of the cell is closely related to the specific capacity and voltage, which can be realized by electrode materials. − In this regard, the exploration of electrode materials, which can offer greater specific capacity with a higher voltage than that of conventional electrode materials, has increased exponentially over the past years. In terms of cathode materials, there has been a marked increase in intensive research focusing on advanced cathode materials that can achieve higher specific capacity than that of the conventional layered LiCoO 2 (LCO) material, especially focusing on LiNi x Co y Mn z O 2 (LNCM) cathode materials with a high Ni content. − The Ni-rich LNCM cathode material is considered to be an advanced cathode material, in which part of the Co component in the LCO cathode material is replaced with Ni and Mn due to its desirable electrochemical behaviors.…”