Layered High-Ni Cathode Structure for Short-Circuit Thermal Stability
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Solution Overview
Problem
Secondary batteries with high-content nickel (High-Ni) NCM positive electrode active materials face poor thermal stability and are vulnerable to exothermic reactions due to internal short circuits, compromising their safety and performance.
Innovation Solution
A positive electrode for lithium secondary batteries with a two-layer structure, where the upper layer has a controlled low content of conductive material to suppress electrical conductivity and the lower layer maintains typical or slightly higher conductive material content, enhancing thermal stability and preventing exothermic reactions during internal short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-content nickel (High-Ni) NCM positive electrode active material is used to increase energy density, then output characteristics and energy density are improved, but thermal stability deteriorates and the battery becomes vulnerable to exothermic reactions
Solution Approach 1:
The positive electrode active material layer is divided into two distinct layers: a lower layer in contact with the current collector and an upper layer. The lower layer has higher conductive material content (0.5 wt% or more) to ensure electrical conductivity, while the upper layer has lower conductive material content (0.15 wt% or less) to suppress electrical conductivity and prevent exothermic reactions. This segmentation allows each layer to perform its specific function optimally.
Solution Approach 2:
Different regions of the positive electrode active material layer are assigned different properties. The lower layer near the current collector has higher conductivity to facilitate electron transport, while the upper layer has lower conductivity to reduce the risk of exothermic reactions. This local differentiation of properties resolves the contradiction between needing conductivity for power output and needing low conductivity for thermal stability.
2Power
If conductive material content is increased to maintain electrical conductivity, then output characteristics are improved, but thermal stability and resistance to exothermic reactions deteriorate
Solution Approach 1:
The electrode structure is segmented into two layers with different conductive material contents. The lower layer contains 0.5 wt% or more conductive material to ensure adequate electrical conductivity for power output, while the upper layer contains 0.15 wt% or less conductive material to suppress electrical conductivity and prevent exothermic reactions. This segmentation allows the system to achieve both high power output and resistance to harmful exothermic reactions.
Solution Approach 2:
The conductive material content is locally optimized in different regions: higher content (0.5 wt% or more) in the lower layer where electrical conductivity is critical for power output, and lower content (0.15 wt% or less) in the upper layer where suppressing conductivity prevents exothermic reactions. This local quality differentiation resolves the technical contradiction.
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 two-layer structure improves thermal stability and prevents explosions, maintaining high output characteristics by reducing electrical conductivity in the upper layer while ensuring adequate conductivity in the lower layer, thus enhancing safety and performance.
Implementation Method 1
the upper positive electrode active material layer has a conductive material content of 0.15 wt% or less with respect to the upper positive electrode active material layer
Implementation Method 2
thermal stability can be increased in case of an internal short circuit of the battery
Data Source
Figure 1~2
AI summary
The present invention relates to a cathode for a lithium secondary battery, a manufacturing method therefor, and a lithium secondary battery comprising the cathode. The cathode for a lithium secondary battery comprises a cathode active material layer formed to contain a very low content of conductive material at the outermost side thereof, whereby the cathode can have high thermal stability when an internal short-circuit of a battery occurs, and can achieve high-power properties when applied to a secondary battery.