PTC Safety Coating on Lithium-Ion Battery Electrodes
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Solution Overview
Problem
Lithium-ion batteries face safety hazards due to internal short circuits, which existing PTC material modifications fail to adequately address, affecting both safety and electrical performance.
Innovation Solution
A positive electrode plate design featuring a current collector, a positive active material layer, and a safety coating with a polymer matrix and conductive material, where fluorinated polyolefin or chlorinated polyolefin functions as both the PTC matrix and binder, and an inorganic filler is added to enhance stability and response speed, reducing internal resistance and improving safety during nail penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PTC materials are added to the electrode active material layer, then safety performance is improved, but electrochemical performance deteriorates
Solution Approach 1:
The patent divides the electrode structure into distinct functional layers: a current collector, a PTC safety coating layer, and an active material layer. This segmentation allows the PTC layer to provide safety functions without compromising the electrochemical performance of the active material, as the PTC layer is separated from the active material and does not interfere with its electrochemical reactions.
Solution Approach 2:
The PTC coating layer acts as an intermediary between the current collector and the active material layer. It provides safety protection through its positive temperature coefficient characteristics while allowing electrical current to pass through at normal operating temperatures, thus mediating between safety requirements and electrochemical performance.
2Reliability
If a separate PTC material layer is placed between the current collector and active material layer, then safety effect is achieved, but the PTC material is dissolved by solvent in slurry destroying the PTC effect
Solution Approach 1:
The patent uses composite materials in the PTC coating layer, combining PTC materials with binder materials and potentially other additives. This composite structure enhances the stability of the PTC material against solvent dissolution while maintaining the PTC effect. The binder material provides a matrix that protects the PTC material particles from direct contact and dissolution by the solvent in the active material slurry.
3Reliability
If PTC material layer is used, then safety performance is improved, but the layer is squeezed to the edge during compacting causing direct contact between active material and current collector
Solution Approach 1:
The PTC safety coating is applied as a thin film layer on the current collector. This thin film structure is more resistant to displacement during the compacting process compared to thicker layers. The coating forms a flexible yet stable layer that maintains its position between the current collector and active material even under compression, preventing edge migration.
4Reliability
If PTC material is added to improve safety, then resistance increases at high temperature, but internal resistance of the battery increases affecting electrical performance
Solution Approach 1:
The patent optimizes the parameters of the PTC coating layer, including its thickness, composition, and PTC characteristics. The coating is designed to maintain low resistance at normal operating temperatures while exhibiting high resistance only at elevated temperatures that indicate unsafe conditions. By carefully controlling the PTC transition temperature and the thickness of the coating, the patent minimizes internal resistance during normal operation while ensuring safety protection when needed.
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 significantly enhances the safety and electrical performance of lithium-ion batteries by improving the stability and response speed of the PTC safety coating, reducing internal resistance, and preventing short circuits during abnormal conditions like nail penetration.
Implementation Method 1
A PTC (Positive Temperature Coefficient) material is a positive temperature coefficient heat sensitive material, which has the characteristic that its resistivity increases with increasing temperature. When the temperature exceeds a certain temperature, its resistivity increases rapidly stepwise.
Implementation Method 2
the safety coating comprises a polymer matrix and a conductive material
Data Source
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AI summary
The present application relates to a positive electrode plate and an electrochemical device. The positive electrode plate includes a current collector (10), a positive active material layer (14) and a safety coating (12) disposed between the current collector (10) and the positive active material layer (14), the safety coating (12) including a polymer matrix and a conductive material, wherein the polymer matrix is fluorinated polyolefin and/or chlorinated polyolefin, and when the safety coating (12) and the positive active material layer (14) are collectively referred to as a positive film layer, the positive film layer includes Na ions and/or K ions at a content of 100 ppm or more, and has an absorption peak at 1646 cm-1 in infrared absorption spectrum. The positive electrode plate may improve safety performance at elevated temperature of the electrochemical device such as capacitor, primary battery or secondary battery by quickly disconnecting the circuit at high temperature conditions or when an internal short circuit occurs.