Polymer Additive Island Regions in Battery Positive Electrodes
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Solution Overview
Problem
Existing positive electrode active materials in secondary batteries, while improving thermal stability, result in high resistance and degrade battery performance when conductivity is controlled to suppress Joule heat generation during internal short circuits.
Innovation Solution
Incorporating a polymer material with a melting point or thermal decomposition temperature between 200°C and 500°C as an additive in the positive electrode active material layer, dispersed as island-shaped regions, and using a separator with a heat-resistant layer to manage internal short circuits by blocking conductive paths and increasing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conductivity of the positive electrode active material is controlled to suppress Joule heat generation during internal short circuits, then thermal stability and safety are improved, but the battery has high resistance as a whole, leading to degradation of battery performance
Solution Approach 1:
The patent applies local quality by dispersing polymer material as island-shaped regions within the positive electrode active material layer. These localized polymer regions provide thermal stability and Joule heat suppression exactly where needed (at short circuit sites) without requiring the entire electrode to have reduced conductivity, thus maintaining overall battery performance while achieving safety improvements at specific critical locations.
2Object-affected harmful factors
If the polymer material melts and diffuses to block conductive paths during internal short circuits, then the short-circuit current is reduced and safety is improved, but the resistance increases at high temperatures
Solution Approach 1:
The patent utilizes phase transitions by selecting a polymer material with a melting point between 200°C and 500°C. During normal operation at room temperature, the polymer remains solid and does not affect conductivity. When an internal short circuit causes temperature to rise above the polymer's melting point, the polymer melts and diffuses to block conductive paths, reducing short-circuit current. This temperature-dependent phase transition enables automatic safety activation only when needed, without permanently increasing resistance during normal operation.
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
Achieves both high safety and good battery performance by reducing short-circuit current and preventing excessive temperature rise through the polymer material's melting and diffusion, maintaining resistance at room temperature and increasing it at high temperatures.
Implementation Method 1
the polymer material forms and is dispersed as a plurality of island-shaped regions... the polymer material's melting and diffusion
Implementation Method 2
the polymer material's melting and diffusion, maintaining resistance at room temperature and increasing it at high temperatures
Implementation Method 3
Joule heat generated by the short-circuited current... Joule heat generation by a short-circuit current is suppressed
Data Source
Figure 1
AI summary
A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator provided between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer carried on the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material, a binder, and an additive. The additive is a polymer material having a melting point or thermal decomposition temperature of 200°C or higher and 500°C or lower. In a cross section of the positive electrode active material layer, the polymer material forms and is dispersed as a plurality of island-shaped regions. The separator includes a base layer and a heat-resistant layer layered on the base layer. The melting point or thermal decomposition temperature of the polymer material is equal to or higher than a melting point of the base layer.