Lithium Phosphate Coated Cathode for Battery Stability
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Solution Overview
Problem
Lithium secondary batteries face degradation due to reactions between lithium compounds on the cathode active material surface and the electrolyte, leading to increased surface resistance and reduced battery performance.
Innovation Solution
A lithium phosphate layer is formed on the surface of lithium-transition metal oxide cathode active materials using phosphoric acid, which consumes residual lithium compounds and prevents degradation without hindering lithium ion movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a composite metal oxide is used as cathode active material, then battery capacity and power are improved, but surface degradation occurs due to reaction with electrolyte
Solution Approach 1:
A lithium phosphate layer is introduced as an intermediary coating on the cathode active material surface. This layer acts as a protective barrier between the composite metal oxide and the electrolyte, preventing direct harmful reactions while allowing lithium ion transport, thus resolving the contradiction between maintaining high power performance and ensuring surface stability.
Solution Approach 2:
The invention creates a composite structure consisting of the cathode active material core and the lithium phosphate coating layer. This composite material approach combines the high capacity benefits of composite metal oxides with the protective and ion-conductive properties of lithium phosphate, simultaneously achieving improved power and reliability.
2Ease of manufacture
If lithium compound remains on cathode active material surface, then manufacturing simplicity is maintained, but surface resistance increases due to reaction with electrolyte
Solution Approach 1:
The lithium phosphate layer is formed as a preliminary treatment step before battery assembly. This preliminary action converts the problematic residual lithium compounds into a beneficial protective coating, preventing future surface resistance issues while maintaining manufacturing efficiency through a straightforward coating process.
Solution Approach 2:
The invention converts the harmful residual lithium compounds on the surface into beneficial lithium phosphate through reaction with phosphoric acid. This transformation turns the source of surface resistance and degradation into a protective layer that enhances surface stability and ion conductivity.
3Reliability
If heterometal oxide coating is applied to cathode active material, then surface degradation is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The invention uses phosphoric acid, a cheap and readily available material, to form the protective lithium phosphate layer. This approach replaces complex heterometal oxide coatings with a simpler, more cost-effective solution that achieves the same protective function without requiring sophisticated coating equipment or rare materials.
Solution Approach 2:
The invention changes the chemical composition parameters of the surface layer from complex heterometal oxides to simple lithium phosphate. This parameter change simplifies the coating composition while maintaining protective functionality, reducing manufacturing complexity and cost.
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 phosphate layer effectively reduces surface resistance, enhances battery performance by maintaining discharge capacity over cycles, and improves the cathode's thermal stability and reversibility.
Implementation Method 1
the at least one lithium compound reacts with the phosphoric acid to obtain a cathode active material coated with a lithium phosphate layer
Implementation Method 2
a lithium phosphate layer formed on a surface of the cathode active material and consisting essentially of Li3PO4, LiOH, and Li2CO3
Data Source
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AI summary
Provided are a cathode material for a lithium secondary battery, and a lithium secondary battery containing the same. The cathode material for a lithium secondary battery comprises: a cathode active material, which is a lithium-transition metal oxide, and a lithium phosphate layer coated on a surface of the cathode active material.