Positive Electrode Safety Coating for High-Temperature Current Cutoff
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Solution Overview
Problem
Lithium ion batteries are prone to fire and explosion due to internal short circuits, and existing safety measures using PTC materials in the electrode active material layer or as a separate layer face issues such as dissolution, deformation, and adverse effects on electrochemical performance.
Innovation Solution
A positive electrode plate with a safety coating comprising a fluorinated polyolefin or chlorinated polyolefin polymer matrix, conductive material, and inorganic filler, stabilized by crosslinking and incorporating inorganic fillers like metal oxides, is used between the current collector and the electrode active material layer to enhance safety and 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 separates the safety function from the electrochemical function by placing PTC material in a dedicated safety coating layer rather than mixing it with the electrode active material layer. This segmentation allows each layer to perform its specific function without interfering with the other, resolving the contradiction between safety performance and electrochemical performance.
Solution Approach 2:
The patent introduces a binder as an intermediary substance between the PTC material and the electrode active material. The binder prevents direct contact between PTC particles and the active material, thereby preventing the PTC material from interfering with electrochemical reactions while still maintaining the safety function.
2Reliability
If a separate PTC material layer is placed between the current collector and electrode active material layer, then safety effect is achieved, but the PTC material layer is dissolved by solvent during coating
Solution Approach 1:
The patent uses a binder that is soluble in the coating solvent, allowing the binder to dissolve and release the PTC material onto the current collector surface. The binder serves its purpose during the coating process and then disappears, leaving a stable PTC material layer that is not affected by subsequent solvents.
Solution Approach 2:
The patent changes the solubility parameters of the binder to match the coating solvent, enabling the binder to dissolve during the coating process. This parameter change allows the PTC material to be properly deposited while the binder disappears, preventing dissolution issues in subsequent steps.
3Reliability
If PTC material layer is used, then safety performance is improved, but the PTC material layer is squeezed to the edge during compacting
Solution Approach 1:
The patent applies the PTC material layer to the current collector surface before the electrode active material layer is coated. This preliminary action ensures that the PTC material layer is already in position and protected by the subsequent electrode layer, preventing it from being squeezed to the edge during compacting.
Solution Approach 2:
The patent uses a thin film structure where the electrode active material layer acts as a protective shell over the PTC material layer. This thin film structure prevents the PTC material layer from being displaced during compacting while still allowing the safety function to operate.
4Speed
If PTC material is added to improve safety, then response speed needs improvement, but current blocking effect needs enhancement
Solution Approach 1:
The patent optimizes the particle size, composition, and thickness parameters of the PTC material layer to achieve both fast response speed and strong current blocking effect. By carefully controlling these parameters, the PTC layer can rapidly increase in resistance when heated while maintaining effective current blocking capability.
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 safety coating effectively blocks current at high temperatures, improving safety by preventing electrochemical reactions and maintaining electrochemical performance, with faster response times and reduced internal resistance growth.
Implementation Method 1
the polymer matrix is fluorinated polyolefin and/or chlorinated polyolefin having a crosslinked structure
Implementation Method 2
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, the resistivity of the PTC material increases rapidly stepwise.
Data Source
AI summary
This application relates to a positive electrode plate and an electrochemical device. The positive electrode plate includes a current collector, a positive electrode active material layer and a safety coating disposed between the current collector and the positive electrode active material layer, wherein the safety coating includes a polymer matrix, a conductive material and an inorganic filler; and wherein the polymer matrix is fluorinated polyolefin and/or chlorinated polyolefin having a crosslinked structure. When the electrochemical device (such as a capacitor, a primary battery, or a secondary battery) is in a high temperature condition or an internal short circuit occurs, the positive electrode plate can quickly disconnect the circuit, thereby improving the high temperature safety of the electrochemical device.