Application of LiCoO₂Particles Coated with Lithium Ortho-Oxosalt Thin Films to Sulfide-Type All-Solid-State Lithium Batteries

Abstract

Amorphous oxide thin films in the pseudobinary system Li 4 SiO 4 -Li 3 PO 4 and Li 4 GeO 4 -Li 3 PO 4 were fabricated using pulsed laser deposition (PLD) with a KrF excimer laser. The ionic conductivities of obtained thin films were 10 −8 to 10 −6 S cm −1 at room temperature. Bulk-type all-solid-state batteries using LiCoO 2 particles surface-modified with ortho-oxosalt thin films were constructed to assess the influence of oxide coatings on cell performances. Higher ion-conductive oxide thin films studied here are useful for decreasing the interfacial resistance of all-solid-state cells. The interfacial resistance was lowest in the cell using Li 3.5 Si 0.5 P 0.5 O 4 coatings as a buffer layer with estimated thickness of ca. 45 nm. We investigated the dependence of interfacial resistance on film thickness for the oxide systems fabricated in this study. Among them, much lower interfacial resistance was achieved in the cells using Li 3 PO 4 coatings with film thickness of less than 45 nm. All-solid-state cells using Li 3 PO 4 -coated LiCoO 2 charged and discharged without marked capacity-fading during 30 cycles. Larger discharge capacity after cycling tests was achieved in a cell with a smaller interfacial resistance. The cell using Li 3 PO 4 -coated LiCoO 2 operated at a high current density of 6.4 mA cm −2 with a capacity of 54 mAh g −1 .

Effect of excess Li2S on electrochemical properties of amorphous li3ps4 films synthesized by pulsed laser deposition

“…Figure A illustrates two thin‐film batteries using Li/Li 3 PO 4 /LiCoO 2 and Li/Li 3 PS 4 /Li 3 PO 4 /LiCoO 2 , fabricated on MgO substrates. The Li 3 PO 4 layer was also introduced in the battery with the Li 3 PS 4 film electrolyte to suppress the resistive layer that generally forms at the LiCoO 2 /Li 3 PS 4 interface . The LiCoO 2 cathode (200 nm) and Li anode layers (1.5 μm) were separated by a larger square Li 3 PO 4 (~1 μm)/Li 3 PS 4 (~0.75 μm) integrated electrolyte layer or a Li 3 PO 4 (~2 μm) single electrolyte layer.…”

On the Functionality of Coatings for Cathode Active Materials in Thiophosphate‐Based All‐Solid‐State Batteries

“…Finally, PLD can also be used to produce coatings for cathode active materials. [93] Copyright 2015, The Electrochemical Society. a,b) Adapted with permission.…”

“…[95,99] Additionally, Ito et al recently generated a series of ≈45 nm oxide coatings on LCO. [93] Therein, the SSB containing Li 3 PO 4 -coated LCO exhibited smaller interfacial resistances, enhanced cycle life over 30 cycles, and improved capacities at higher current densities. One drawback of PLD is that it is a line-of-sight technique, which makes achieving homogeneous coatings rather challenging.…”

“…Up to now, very few studies have tested the efficacy of phosphatebased coatings; however, the results have indicated that such materials can effectively decrease the interfacial resistance, mitigate SE degradation, and enhance the battery performance. [93,95]…”

Design Strategies, Practical Considerations, and New Solution Processes of Sulfide Solid Electrolytes for All‐Solid‐State Batteries

“…Consistently, the phosphates (PO 4 3− ) and sulfites (SO 3 2− ) were directly detected by time‐of‐flight secondary ion mass spectrometry measurements of the cycled LiNi 0.8 Co 0.15 Al 0.05 O 2 –75Li 2 S·25P 2 S 5 electrode . To solve this cathode interface incompatibility issue, the application of protective oxide coating layers, such as LiNbO 3 , LiNb 0.5 Ta 0.5 O 3 , Li 4 Ti 5 O 12 , Ta 2 O 5 , Al 2 O 3 , and Li 3 PO 4 between sulfide SEs and LiCoO 2 was demonstrated in previous experiments. Computational studies confirmed the improved interface stability and compatibility from the thermodynamic perspective …”