Positive Electrode Safety Coating for PTC Short-Circuit Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium-ion batteries face safety hazards due to internal short circuits, which can lead to fires and explosions under abnormal conditions. Existing solutions, such as using Positive Temperature Coefficient (PTC) materials, either compromise electrochemical performance or fail to provide adequate safety enhancements.
Innovation Solution
A positive electrode plate design featuring a metal current collector, a positive active material layer, and a safety coating with a fluorinated polyolefin and/or chlorinated polyolefin polymer matrix, conductive material, and inorganic filler. The safety coating is strategically placed between the metal current collector and the positive active material layer, with specific weight percentages for each component to enhance safety and electrical performance.
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 material to provide safety functions without directly interfering with the electrochemical reactions in the active material layer, thus resolving the contradiction between safety improvement and electrochemical performance maintenance.
Solution Approach 2:
The patent introduces an intermediate PTC coating layer between the current collector and the active material layer. This intermediary layer provides the safety function through its PTC effect while allowing ionic and electronic transport to proceed through it, thereby mediating between safety requirements and electrochemical performance without direct conflict.
2Reliability
If a separate PTC material layer is placed between the current collector and active material layer, then safety performance is improved, but the PTC material layer is dissolved by solvent during coating, destroying the PTC effect
Solution Approach 1:
The patent modifies the chemical composition parameters of the PTC coating by selecting polymer materials with specific resistance to NMP solvent, such as polyvinylidene fluoride (PVDF) and its derivatives. By changing the material parameters to be solvent-resistant, the PTC layer maintains its structural integrity and PTC effect during the coating process, preventing dissolution and maintaining safety performance.
3Reliability
If a PTC material layer is used, then safety performance is improved, but the PTC layer is squeezed to the edge during compaction, allowing direct contact between active material layer and current collector
Solution Approach 1:
The patent creates a composite PTC coating layer by combining PTC materials with binder materials and potentially other functional materials. This composite structure provides mechanical strength and adhesion to the current collector, preventing the PTC layer from being squeezed to the edges during compaction. The composite nature ensures both safety function and positional stability under mechanical stress.
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 proposed design significantly improves the safety and electrical performance of lithium-ion batteries, including cycle performance and safety during nail penetration, while maintaining effective PTC effects and reducing the risk of internal short circuits.
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
when the active material slurry is coated on the surface of the PTC material layer, the solvent (such as N-methyl-2-pyrrolidone NMP) in the slurry would dissolve the PTC material of the PTC layer
Data Source
AI summary
The present application relates to a positive electrode plate and an electrochemical device. The positive electrode plate comprises a metal current collector, a positive active material layer and a safety coating disposed between the metal 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 a fluorinated polyolefin and/or chlorinated polyolefin polymer matrix, wherein based on the total weight of the safety coating, the polymer matrix is present in a weight percentage of 35-75% by weight, the conductive material is present in a weight percentage of 5-25% by weight and the inorganic filler is present in a weight percentage of 10-60% by weight, and wherein the metal current collector has an elongation at break δ fulfilling 0.8%≤δ≤4%.