Double-Layer Cathode Structure for Lithium Battery Overcharge Cutoff
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Solution Overview
Problem
Lithium secondary batteries face instability issues during overcharge, leading to potential ignition or explosion due to the generation of gas, which conventional venting methods inadequately address, especially in high-capacity batteries used in electric vehicles.
Innovation Solution
A positive electrode with a double-layer structure, comprising a first layer with an olivine-structured active material, a conductive agent, and a volume expansion resin that melts and expands at high temperatures to interrupt the charge current, and a second layer with a layer-structured active material, enhancing stability and preventing overcharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional venting methods are used to release gas during overcharge, then gas pressure is reduced, but battery stability and safety are not sufficiently secured
Solution Approach 1:
The patent applies preliminary anti-action by incorporating a volume expansion resin in the first positive electrode active material layer that proactively interrupts charge current before dangerous gas accumulation occurs. During overcharge, the resin undergoes volume expansion to physically block the conductive path, preventing the harmful effects of overcharge before they can develop into safety issues.
Solution Approach 2:
The patent converts the harmful effect of volume expansion during overcharge into a beneficial safety mechanism. The volume expansion resin utilizes the thermal and volumetric changes that normally indicate problematic overcharge conditions to trigger a protective response, where the expansion itself becomes the mechanism for interrupting the harmful charge current.
2Device complexity
If a single-layer positive electrode active material layer is used, then device complexity is low, but overcharge protection capability is insufficient
Solution Approach 1:
The patent applies segmentation by dividing the positive electrode active material layer into two distinct layers: a first layer containing the volume expansion resin and a second layer without it. This segmentation allows each layer to perform its specific function - the first layer provides overcharge protection through resin expansion, while the second layer maintains electrochemical performance, achieving both protection and performance without excessive complexity.
Solution Approach 2:
The patent applies local quality by concentrating the volume expansion resin specifically in the first positive electrode active material layer adjacent to the current collector, while the second layer remains free of resin. This localized placement ensures that the protection mechanism is positioned where it is most effective for interrupting charge current, while maintaining optimal electrochemical properties in the second layer.
3Quantity of substance
If high-capacity positive electrode active materials are used to increase energy density, then battery capacity increases, but stability during overcharge deteriorates
Solution Approach 1:
The patent applies composite materials by combining high-capacity positive electrode active materials with a volume expansion resin in the first layer. This composite structure allows the battery to achieve high capacity from the active materials while the resin provides overcharge protection, resolving the contradiction between capacity and stability during overcharge conditions.
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 double-layer structured positive electrode effectively terminates overcharge by blocking the conductive path, improving battery stability while maintaining higher energy density compared to single-layer designs.
Implementation Method 1
a volume expansion resin, in which volume expansion occurs at a high temperature during overcharge, is included in the first positive electrode active material layer
Implementation Method 2
the first positive electrode active material layer acts as an insulating layer due to melting and expansion of the volume expansion resin at a high temperature during overcharge
Data Source
Figure 1
AI summary
The present invention relates to a secondary battery cathode for improving stability upon overcharging and a lithium secondary battery comprising the same and, specifically, to a secondary battery cathode and a lithium secondary battery comprising the same, the secondary battery cathode being a cathode comprising a cathode active material formed on a cathode current collector, wherein the cathode active material has a two-layer structure including a first cathode active material layer formed on the cathode current collector and a second cathode active material layer formed on the first cathode active material layer, the first cathode active material layer includes a first cathode active material, a conductive material, and a volume expansion resin allowing volume expansion to occur at high temperature upon overcharging, and the second cathode active material layer includes a second cathode active material.