Lithium Compound Coated Oxide Active Material for All-Solid Batteries
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Solution Overview
Problem
Interfacial reactions between sulfide solid electrolytes and oxide active materials in all-solid-state lithium secondary batteries lead to increased interfacial resistance, deteriorating cycle characteristics and high-rate performance, due to the formation of resistive layers and lithium depletion layers.
Innovation Solution
A cathode active material with a lithium compound coating layer, composed of lithium salts like lithium hydroxide and lithium carbonate, is applied to the surface of oxide particles, either simultaneously during synthesis or as a secondary process, to suppress these reactions and enhance lithium ion diffusion paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a sulfide solid electrolyte is used in an all-solid-state lithium secondary battery, then superior lithium ion conductivity is achieved, but interfacial reactions occur between the electrolyte and oxide active material leading to increased interfacial resistance
Solution Approach 1:
A lithium compound coating layer is introduced as an intermediary substance between the sulfide solid electrolyte and the oxide active material. This coating layer mediates the interface by preventing direct contact and reaction between the electrolyte and active material, thereby suppressing the formation of resistive layers and lithium depletion layers while maintaining lithium ion conductivity.
Solution Approach 2:
The invention creates a composite structure consisting of the oxide active material core and the lithium compound coating shell. This composite material approach allows combining the high lithium ion conductivity of sulfide electrolytes with the stability provided by the lithium compound coating, resolving the contradiction between conductivity and interfacial stability.
2Reliability
If a coating layer is applied to suppress interfacial reactions, then cycle characteristics and high-rate characteristics are improved, but additional coating processes and complex process conditions are required
Solution Approach 1:
The coating process is merged with the existing sintering process by adding lithium compounds as precursors before sintering. The lithium compound coating layer is formed in-situ during the sintering process through decomposition and reaction of the precursors, eliminating the need for separate coating steps and reducing process complexity.
Solution Approach 2:
Lithium compound precursors are pre-added to the mixture before sintering. This preliminary action ensures that the lithium compound coating layer forms automatically during the subsequent sintering process, preventing the need for complex post-synthesis coating operations.
3Reliability
If transition metal oxide coating materials are used to suppress side reactions, then interfacial resistance is reduced, but the choice of coating materials is limited and costs increase
Solution Approach 1:
The invention changes the chemical composition parameter of the coating layer by using lithium compounds instead of transition metal oxides. This parameter change expands the range of suitable coating materials to include various lithium compounds (carbonate, hydroxide, nitrate, acetate, citrate, sulfate) that can form effective coating layers, increasing material versatility while maintaining performance.
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 lithium compound coating layer effectively reduces resistive layer formation and lithium depletion, improving the contact area between the active material and electrolyte, resulting in enhanced cycle characteristics and high-rate performance of all-solid-state lithium secondary batteries.
Implementation Method 1
a coating layer composed of a lithium compound surrounding the surface of oxide particles... can suppress side reactions, such as the formation of a resistive layer by diffusion of the metal elements
Implementation Method 2
enhance lithium ion diffusion paths... improving the contact area between the active material and electrolyte
Data Source
AI summary
The present invention relates to an oxide active material surface-treated with a lithium compound, a method for preparing the same, and an all-solid lithium secondary battery capable of effectively suppressing an interface reaction in a solid electrolyte by adopting the same. In the all-solid lithium secondary battery comprising an electrode containing a positive electrode active material and a sulfide-based solid electrolyte, the positive electrode active material according to the present invention can significantly improve battery characteristics since a coating layer formed of a lithium compound is formed while surrounding a particle surface to act as a functional coating layer which suppresses the interface reaction of the sulfide-based solid electrolyte and the electrode. In addition, in cases where the active material is synthesized and coated with a lithium compound at the same time, a lithium salt and a transition metal salt are dissolved in a solvent through stirring, to prepare a solution, followed by drying and heat treatment, and here, the prepared active material has a form in which a mixture generated from an excessive amount of lithium salt which is synthesized and then remains on the particle surface having a structure capable of absorbing and releasing lithium is coated on the particle surface to form a coating layer. In addition, in cases where the previously synthesized active material is coated with a lithium compound, the active material and a lithium salt are dissolved in a solvent through stirring, followed by drying and heat-treatment, and here, the prepared active material has a form in which a mixture generated from an excessive amount of lithium salt which is synthesized and then remains on the particle surface having a structure capable of absorbing and releasing lithium is coated on the particle surface to form a coating layer.