Layered Cathode Structure for High-Temperature Lithium Battery Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining stability and lifespan under harsh environmental conditions, particularly at high temperatures, due to the deterioration of cell stability and life-span properties when designed for high capacity.
Innovation Solution
A cathode for lithium secondary batteries is designed with a multi-layered structure comprising a first cathode active material layer with secondary particle particles and a second layer with single particle shape particles, where the ratio of their SPAN values and metal compositions are optimized to enhance thermal and penetration stability, while the first layer provides high power and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the lithium secondary battery is designed for high capacity using lithium metal oxide as cathode active material, then the power and energy density are improved, but the cell stability at high temperature and life-span properties are deteriorated
Solution Approach 1:
The cathode active material layer is divided into two distinct layers: a first layer containing secondary particle cathode active material particles and a second layer containing single particle cathode active material particles. This segmentation allows each layer to contribute different properties - the first layer provides high capacity while the second layer improves thermal stability and prevents particle cracking, thus resolving the contradiction between high capacity and cell stability.
Solution Approach 2:
Different regions of the cathode active material layer are assigned different particle types with specific properties. The first layer uses secondary particles optimized for capacity, while the second layer uses single particles optimized for stability. This local differentiation of material properties enables the cathode to simultaneously achieve high capacity in the first layer and high stability in the second layer, resolving the technical contradiction.
2Quantity of substance
If the cathode active material layer is designed for high capacity, then the energy density is improved, but the life-span properties are deteriorated
Solution Approach 1:
The cathode active material layer is segmented into two layers with different particle characteristics. The first layer with secondary particles provides high energy density, while the second layer with single particles extends the battery life-span by preventing particle cracking during charging/discharging cycles. This segmentation resolves the contradiction between energy density and life-span.
Solution Approach 2:
The cathode employs a composite structure combining two types of cathode active material particles - secondary particles in the first layer and single particles in the second layer. This composite material approach allows the battery to achieve both high energy density from the first layer and extended life-span from the second layer, resolving the contradiction between these two parameters.
3Power
If the cathode active material particles are designed for high power, then the charging rate is improved, but the thermal stability is deteriorated
Solution Approach 1:
The cathode is segmented into two layers where the first layer contains secondary particle cathode active material optimized for high power and fast charging rate, while the second layer contains single particle cathode active material optimized for thermal stability. This segmentation allows the battery to achieve both high power performance and thermal stability simultaneously.
Solution Approach 2:
Different regions of the cathode are assigned different particle types with localized quality optimization. The first layer uses secondary particles for high power applications, while the second layer uses single particles for thermal stability. This local quality differentiation resolves the contradiction between power and thermal stability.
Data Source
AI summary
A cathode for a lithium secondary battery includes a cathode current collector, and a cathode active material layer including a first cathode active material layer and a second cathode active material layer sequentially stacked on the cathode current collector. The first cathode active material layer includes first cathode active material particles having a secondary particle structure, and the second cathode active material layer includes second cathode active material particles having a single particle shape. A ratio of a SPAN value of the second cathode active material particles relative to a SPAN value of the first cathode active material particles is in a range from 2 to 4.5.