Positive Electrode Undercoat Layer for Thermal Runaway Resistance
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Solution Overview
Problem
Lithium-ion batteries face safety risks due to internal short circuits caused by mechanical abuse, leading to thermal runaway, fire, and explosion.
Innovation Solution
A positive electrode sheet with an undercoat layer made of a first carbon material with high resistivity, which increases the short-circuit point resistance and prevents violent reactions during mechanical abuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the positive electrode current collector directly contacts the positive electrode active layer, then the battery structure is simple and manufacturing is easy, but mechanical abuse causes isolation film destruction and internal short circuit leading to thermal runaway
Solution Approach 1:
The patent segments the interface between the positive electrode current collector and the positive electrode active layer by introducing an undercoat layer. This undercoat layer is divided into a first undercoat layer directly on the current collector and a second undercoat layer adjacent to the active layer, creating distinct functional zones that prevent direct contact and isolate potential short circuit paths.
Solution Approach 2:
The undercoat layer acts as an intermediary component between the positive electrode current collector and the positive electrode active layer. This intermediate layer with controlled resistivity (10^-3 to 10^3 Ω·cm) mediates the interface, preventing direct electrical contact while maintaining structural integrity, thereby blocking the path for internal short circuits during mechanical abuse.
2Reliability
If the undercoat layer has high resistivity to increase short-circuit point resistance, then safety is improved, but electrical conductivity for normal operation may be compromised
Solution Approach 1:
The patent applies local quality by creating undercoat layers with different resistivity characteristics in different locations. The first undercoat layer has different properties than the second undercoat layer, allowing the interface to have high resistivity where needed for safety (near the current collector) while maintaining adequate conductivity where needed for normal operation (near the active layer).
Solution Approach 2:
The undercoat layer is constructed as a composite structure with multiple layers having different material compositions and resistivity ranges. This composite approach allows the overall structure to exhibit both high resistivity for safety (blocking short circuits) and sufficient conductivity for normal battery operation, as each layer contributes different electrical properties.
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 implementation of the positive electrode sheet with a high-impedance undercoat layer effectively enhances the safety performance of lithium-ion batteries by reducing the likelihood of thermal runaway and improving cycle performance.
Implementation Method 1
the undercoat layer includes a first carbon material; a powder resistivity of the first carbon material is not lower than 0.26 Ω·cm
Data Source
AI summary
A positive electrode sheet and application thereof, where the positive electrode sheet includes a positive electrode current collector, an undercoat layer and a positive electrode active layer, the undercoat layer being located on at least one surface of the positive electrode current collector, and the positive electrode active layer being located on a surface of the undercoat layer far away from the positive electrode current collector; where, the undercoat layer includes a first carbon material, and a powder resistivity of the first carbon material is not lower than 0.2 Ω·cm. The undercoat layer included in the positive electrode sheet of the present application has high impedance, and when mechanical abuse occurs, the lithium-ion battery is not prone to thermal runaway, effectively improving the safety of battery.