Layered Lithium Cathode Structure for High-Temperature Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining stability and life-span, particularly at extreme temperatures, due to the deterioration of cell stability and performance 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 particles and a second layer with single particles, where the ratio of their SPAN values and metal compositions are optimized to enhance thermal and mechanical stability, and a concentration gradient in the first layer improves conductivity 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 cathode active material, then the capacity and power are improved, but the cell stability at high temperature deteriorates 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 particles with high nickel content for high capacity, and a second layer containing single particles with lower nickel content for thermal stability. This segmentation allows each layer to perform its specialized function, resolving the contradiction between high capacity and high temperature stability.
Solution Approach 2:
Different regions of the cathode are assigned different compositions and structures optimized for their specific functions. The first layer (secondary particles, high Ni) is positioned where high capacity is needed, while the second layer (single particles, lower Ni) is positioned to provide thermal stability. This local differentiation of properties allows simultaneous optimization of capacity and stability.
2Power
If the cathode active material layer is designed for high capacity, then the power is improved, but the life-span properties of the battery are deteriorated
Solution Approach 1:
The cathode is segmented into two layers with different particle structures and compositions. The first layer with secondary particles provides high power and capacity, while the second layer with single particles provides long-term stability and extended life-span, resolving the contradiction between power and duration.
Solution Approach 2:
The cathode uses a composite structure combining two types of cathode active material particles with different characteristics. The secondary particles (high Ni) and single particles (lower Ni) work together in a composite arrangement, allowing the system to achieve both high power output and extended operational life-span.
3Quantity of substance
If high nickel content is used in cathode active material particles, then the capacity is improved, but the thermal stability deteriorates
Solution Approach 1:
The cathode structure implements local quality differentiation by creating two layers with different nickel contents. The first layer has high nickel content (0.65-0.95) for high capacity, while the second layer has lower nickel content (0.30-0.70) for thermal stability. This spatial differentiation of composition allows simultaneous achievement of high capacity and thermal stability.
Solution Approach 2:
The cathode active material is segmented into two distinct layers based on nickel content and particle structure. The high-nickel first layer is separated from the lower-nickel second layer, allowing each segment to perform its specialized function without compromising the other, thus resolving the capacity-thermal stability contradiction.
4Quantity of substance
If secondary particle structure is used in cathode active material, then the capacity is improved, but the particle cracking during charging/discharging increases
Solution Approach 1:
The cathode uses two types of particles with different structures: secondary particles in the first layer for high capacity and single particles in the second layer for structural integrity. This segmentation of particle types allows the system to benefit from both high capacity and resistance to particle cracking.
Solution Approach 2:
Different particle structures are assigned to different layers based on functional requirements. The secondary particles (aggregated structure) are placed in the first layer where capacity is prioritized, while single particles (intact structure) are placed in the second layer where structural stability is prioritized, preventing particle cracking.
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.