Positive Electrode Safety Layer for Overcharge Current Cutoff
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Solution Overview
Problem
Lithium-ion secondary batteries face safety issues such as fires and explosions due to thermal runaway during overcharge or abuse, which existing technologies fail to adequately prevent.
Innovation Solution
A positive electrode plate with a safety layer containing a binding material, a conductive material, and an overcharge-sensitive material that includes a monosaccharide structural unit and a carbonate or phosphate group, designed to react and disrupt the conductive network upon overcharge, increasing internal resistance and preventing thermal runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PTC materials are used for safety protection, then volume expansion occurs under high temperature, but the reliability is insufficient because the material may not actuate in time during rapid thermal runaway
Solution Approach 1:
The patent changes the fundamental parameter of the safety material from PTC (positive temperature coefficient) to overcharge-sensitive material that undergoes chemical degradation at specific overcharge voltages. This material transforms from relying on temperature-based physical changes to voltage-triggered chemical changes, enabling faster and more reliable activation during overcharge events before thermal runaway occurs.
Solution Approach 2:
The patent replaces the mechanical/physical mechanism of PTC materials (volume expansion due to crystallinity changes) with a chemical mechanism (oxidation degradation of overcharge-sensitive material). This substitution allows the safety layer to respond more reliably and quickly to overcharge conditions without depending on temperature rise and physical expansion.
2Reliability
If PTC materials are used, then resistance changes occur due to temperature rise, but the preparation process factors affect crystallinity uncontrollably
Solution Approach 1:
The patent changes the controlling parameter from temperature-dependent crystallinity to voltage-dependent chemical degradation. The overcharge-sensitive material's oxidation potential is inherently determined by its chemical structure rather than being affected by preparation process variables like temperature and coating speed, eliminating the uncontrollability issue.
Solution Approach 2:
The patent extracts the safety function from the temperature-dependent PTC mechanism and transfers it to a voltage-sensitive chemical degradation mechanism. This separates the safety activation trigger from the preparation process parameters, making the safety performance independent of manufacturing variations.
3Reliability
If a safety layer is added to prevent thermal runaway, then overcharge protection is improved, but the device complexity increases
Solution Approach 1:
The patent merges the safety function directly into the electrode plate structure by integrating the overcharge-sensitive material into the safety layer that is already part of the electrode assembly. This combines the active material layer, conductive material, and safety function into a single integrated structure, avoiding the need for separate safety devices.
Solution Approach 2:
The safety layer serves multiple functions: it provides overcharge protection through chemical degradation, maintains electrical conductivity during normal operation through the conductive material network, and prevents thermal runaway. This multi-functionality reduces the need for additional separate safety components.
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 layer effectively cuts off charge current during overcharge, preventing fires and explosions, and enhances the overcharge safety performance of the battery by ensuring reliable activation even under low temperature conditions.
Implementation Method 1
the overcharge-sensitive material can react chemically and degrade even under a relatively low temperature, thereby changing a physical structure of the material
Implementation Method 2
detaching conductive material particles in the safety layer, and disrupting a conductive network in the safety layer
Implementation Method 3
This sharply increases an internal resistance of the electrochemical energy storage apparatus, and blocks conduction of electrons
Data Source
AI summary
This application provides a positive electrode plate, including a positive current collector, a positive active material layer on at least one side of the positive current collector, and a safety layer between the positive active material layer and the positive current collector. The positive active material layer includes a positive active material. The safety layer includes a binding material, a conductive material, and an overcharge-sensitive material. The overcharge-sensitive material is a polymer that includes a monosaccharide structural unit and that includes at least one of a carbonate group and a phosphate group. An average diameter x of the conductive material and a weight-average molecular weight y of the overcharge-sensitive material satisfy Formula 1.