Sulfurized Cathode Coating for Stable Sulfide Electrolyte Interfaces
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Solution Overview
Problem
Sulfide-based solid electrolytes in all-solid-state secondary batteries face issues with undesired reactions at the interface with cathode active materials, leading to increased resistance and deterioration of electrochemical properties due to the limited compatibility of conventional oxide coatings and the reduction in lithium ion conductivity when forming a liquid coating layer.
Innovation Solution
A cathode active material with a sulfurized coating layer comprising a lithium transition metal oxide core and a sulfur component, formed through a vapor deposition process, which includes a first alkali metal oxide layer and a second sulfur component layer, enhancing compatibility and conductivity with sulfide-based solid electrolytes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sulfide-based solid electrolyte is dissolved in an organic solvent to form a liquid coating layer, then the coating can be applied onto the coating material, but the lithium ion conductivity is significantly reduced causing the additional coating layer to act as a new resistance layer
Solution Approach 1:
The patent changes the physical state parameter of the sulfide-based solid electrolyte from liquid (dissolved in organic solvent) to solid form. This is achieved by removing the organic solvent and directly forming a solid coating layer, thereby maintaining high lithium ion conductivity while still providing effective protection against side reactions.
2Ease of manufacture
If a sulfide-based solid electrolyte is dissolved in an organic solvent to form a liquid, then the liquid can be applied onto the coating material, but forming the sulfide-based solid electrolyte into a liquid and applying it evenly is challenging
Solution Approach 1:
The patent extracts and removes the organic solvent from the system, eliminating the need to handle and apply liquid solutions. This leaves only the sulfide-based solid electrolyte in solid form, which can be directly applied as a coating without the complexities of solvent evaporation, uniform distribution, and potential residue issues.
3Object-affected harmful factors
If a coating material is applied to reduce side reaction between cathode active material and sulfide-based solid electrolyte, then side reaction is reduced, but the coating material has limited compatibility with sulfide-based solid electrolyte making long-term stable contact challenging
Solution Approach 1:
The patent creates a composite coating layer structure consisting of multiple components: a first coating layer containing lithium phosphate and a second coating layer containing lithium sulfide. This composite structure combines the protective properties against side reactions with the compatibility and stable contact properties of sulfide-based materials, achieving both reduced side reactions and long-term stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The sulfurized coating layer effectively prevents side reactions, maintains high lithium ion conductivity, and improves long-term stability and high-rate charging and discharging capabilities by controlling lithium ion concentration, resulting in enhanced Coulombic efficiency and extended battery lifespan.
Implementation Method 1
a method involves coating the surface of the cathode active material with a material that is stable in the sulfide-based solid electrolyte
Implementation Method 2
formed through a vapor deposition process
Implementation Method 3
sulfide-based solid electrolytes, which exhibit high lithium-ion conductivity
Data Source
AI summary
A cathode active material for a lithium secondary battery includes a core component comprising a lithium transition metal oxide and a sulfurized coating layer to enhance lithium-ion conductivity and cycle life. The coating layer may include a sulfur component and may be structured with a dual-layer configuration, where a first layer of alkali metal oxide is applied on the core component and a second sulfurized layer is disposed on the first layer. Methods for manufacturing the cathode active material involve forming a coating layer using vapor deposition or heat-treating a mixture of the core component and sulfur precursors, creating a uniform, thin sulfurized layer. This structure mitigates side reactions with sulfide-based solid electrolytes, resulting in improved coulombic efficiency, rate performance, and stability.