PTC Layer Nonconductive Fillers Battery Safety
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Solution Overview
Problem
Lithium ion secondary batteries face safety issues due to temperature-induced recovery of the conductive network in PTC layers, reducing their current blocking function and overall safety at high temperatures.
Innovation Solution
Incorporating a PTC layer with nonconductive filler particles and a highly crystalline polyethylene emulsion resin, where the filler particles function as spacers and protrude to fit into pores, maintaining the insulating properties and preventing recovery of the conductive network, even at high temperatures, with specific diameter and height relationships to ensure effective contact and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the PTC layer thickness is reduced to improve battery energy density, then productivity is improved, but the insulating function may be compromised
Solution Approach 1:
The nonconductive filler particles are distributed throughout the PTC layer with a specific size ratio (0.7t ≤ D50_f) that creates localized insulating zones. These particles act as spacers that maintain the insulating structure even when the overall layer thickness is reduced. This allows the PTC layer to be made thinner to improve energy density while the filler particles ensure the insulating function is maintained through their localized presence and spacing effect.
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 solution ensures high safety and improved cycle characteristics of lithium ion secondary batteries by maintaining the insulating function of the PTC layer at high temperatures, suppressing the recovery of the conductive network and preventing contact failure, thus enhancing thermal safety and capacity retention.
Implementation Method 1
a PTC layer which is provided at least either between the positive electrode mixture layer and the positive electrode current collector or between the negative electrode mixture layer and the negative electrode current collector, the PTC layer having a positive temperature coefficient of resistance
Implementation Method 2
when the temperature rises, the crystallinity of a crystalline polymer in the PTC layer decreases, the volume expands, and the conductive network is thereby cut
Data Source
AI summary
A lithium ion secondary battery that includes a positive electrode, a negative electrode, a separator, a nonaqueous electrolytic solution, and a PTC layer between a positive electrode mixture layer and a positive electrode current collector and/or between a negative electrode mixture layer and a negative electrode current collector, the PTC layer having a positive temperature coefficient of resistance. The PTC layer contains nonconductive filler particles, and the electronic resistance at 120° C. is equal to or more than 100 times the electronic resistance at room temperature.