Positive Electrode Safety Coating for Nail Penetration Protection
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Solution Overview
Problem
Lithium-ion batteries face safety hazards due to internal short circuits, which are not adequately addressed by existing PTC materials in the electrode active material layer or separate safety coatings, leading to compromised electrochemical performance and safety issues during abnormal conditions.
Innovation Solution
A positive electrode plate design featuring a safety coating between the current collector and the active material layer, composed of a polymer matrix of fluorinated polyolefin and/or chlorinated polyolefin, an inorganic filler, and a conductive material, with specific weight ratios and crosslinking treatment to enhance stability and response speed.
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 applied to the current collector, and an active material layer. This segmentation allows the PTC materials to be concentrated in the safety coating where they provide thermal protection without interfering with the electrochemical reactions in the active material layer, thus resolving the contradiction between safety performance and electrochemical performance.
2Reliability
If a separate PTC material layer is placed between the current collector and the active material layer, then safety effect is achieved, but the PTC layer is dissolved by solvent and enters the active material layer destroying the PTC effect
Solution Approach 1:
The patent employs composite material construction for the PTC safety coating layer, combining PTC materials with binder materials and other additives to form a stable, solvent-resistant coating. This composite structure prevents the PTC materials from dissolving into the active material layer during solvent evaporation, maintaining the integrity and effectiveness of the PTC layer while achieving the desired safety effect.
3Reliability
If a PTC material layer is used, then safety performance is improved, but during compacting the PTC material layer is squeezed to the edge causing direct contact between active material layer and current collector
Solution Approach 1:
The patent utilizes a thin film PTC safety coating applied directly to the current collector surface. This thin film structure is flexible yet stable, conforming to the current collector and maintaining continuous coverage during the compacting process. The thin film design prevents the PTC material from being squeezed to the edges, ensuring that the active material layer remains separated from the current collector throughout the battery assembly process, thereby maintaining both safety performance and structural stability.
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 design improves safety performance, particularly during nail penetration, while maintaining electrical performance and cycle life, by stabilizing the safety coating and enhancing the PTC effect, thus preventing internal short circuits and improving overcharge safety.
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 polymer matrix is fluorinated polyolefin and/or chlorinated polyolefin... the solvent (such as NMP) in the slurry would dissolve the PTC material of the PTC layer... which not only destroys the PCT effect of the PTC layer
Implementation Method 3
the safety coating includes a polymer matrix, a conductive material and an inorganic filler... the weight ratio of the polymer matrix and the conductive material is 2 or more
Data Source
AI summary
The present application relates to a positive electrode plate and an electrochemical device. The positive electrode plate comprises a current collector, a positive active material layer and a safety coating disposed between the current collector and the positive active material layer, the safety coating comprising a polymer matrix, a conductive material and an inorganic filler, wherein the polymer matrix is fluorinated polyolefin and/or chlorinated polyolefin and the weight ratio of the polymer matrix to the conductive material is 2 or more. The positive electrode plate may improve the safety performance during nail penetration of the electrochemical device such as a capacitor, a primary battery or a secondary battery.