Lithium Battery Cathode Concentration Gradient for High-Temperature Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges with high-temperature storage and life-span properties, particularly due to thermal instability of lithium transition metal oxides used as cathode active materials, which lead to reduced capacity and lifespan when used in severe environments.
Innovation Solution
A lithium secondary battery design incorporating a cathode active material with a concentration gradient of metals between the core and surface parts, combined with an anode made of graphite with a specific lattice distance, to enhance high-temperature storage and life-span properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-capacity cathode active material is used to increase battery capacity, then energy density is improved, but life-span and high-temperature storage properties deteriorate
Solution Approach 1:
The cathode active material employs a concentration gradient structure where the metal component concentration varies between the core and surface parts. Specifically, the surface part has a lower metal component concentration compared to the core, creating a gradient distribution. This local variation in composition allows different regions to perform different functions: the core provides high capacity while the surface maintains stability, thereby resolving the contradiction between capacity and reliability.
2Quantity of substance
If lithium transition metal oxide is used as cathode active material, then battery capacity is achieved, but thermal instability occurs during high-temperature storage causing metal component desorption
Solution Approach 1:
The concentration gradient structure creates a surface region with reduced metal component concentration, which forms a more thermally stable layer. This surface layer acts as a protective barrier that prevents metal component desorption during high-temperature storage, while the core maintains high capacity. The gradient transition zone between core and surface further enhances structural stability by reducing stress concentration.
3Reliability
If artificial graphite is used with cathode active material to prevent metal desorption, then some protection is achieved, but improvement in life-span and high-temperature storage properties is insufficient
Solution Approach 1:
The invention extracts the protective function from the anode side and relocates it to the cathode side by creating a concentration gradient structure within the cathode active material itself. The surface part of the cathode material inherently provides protection against metal desorption and thermal instability, eliminating the need for complex anode modifications or additional protective layers, thus simplifying the overall device structure while achieving the desired reliability improvement.
Data Source
AI summary
A lithium secondary battery including a cathode, an anode and a non-aqueous electrolyte. The cathode includes a cathode active material containing lithium-metal oxide of which at least one of metals has a concentration gradient region between a core part and a surface part thereof. The lithium-metal oxide includes elements M1, M2, and M3. M3 has a concentration gradient region with increased concentration between the core part and the surface part, M1 has a concentration gradient region with decreased concentration between the core part and the surface part, and M2 has a constant concentration from the core part and the surface part. The anode includes graphite having an average lattice distance d002 of 3.356 to 3.365 Å.