Layered Positive Electrode Layout for Nail Penetration Safety
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Solution Overview
Problem
Lithium secondary batteries face safety concerns due to nail penetration, which can cause short-circuits and increase the risk of ignition and explosion, and existing designs compromise energy density with additional conductive material layers that do not contribute to capacity.
Innovation Solution
A positive electrode design with a layered structure, where the lower layer portion has a higher content of conductive material compared to the upper layer portion, enhancing resistance and safety without increasing the overall content of conductive material, thereby improving nail penetration stability and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive material layer is added between the current collector and active material layer to improve nail penetration stability, then safety is improved, but energy density is reduced due to increased thickness without capacity contribution
Solution Approach 1:
The patent applies local quality by creating a lower layer portion of the active material layer with higher conductive material content (10-59 parts by weight based on 100 parts by weight of conductive material in the upper layer) specifically at the interface with the current collector. This localized enhancement provides the necessary resistance improvement for nail penetration stability only where needed, while the upper layer portion maintains higher active material content for capacity, thus resolving the contradiction between safety and energy density.
2Reliability
If the content of conductive material in the lower layer portion is increased to enhance resistance during nail penetration, then nail penetration stability is improved, but the overall content of conductive material increases causing loss of energy density
Solution Approach 1:
The invention concentrates conductive material in the lower layer portion adjacent to the current collector, where it is most needed for resistance during nail penetration. The upper layer portion contains less conductive material, maximizing active material content and capacity. This spatial differentiation resolves the contradiction by providing high resistance only where structurally necessary.
Solution Approach 2:
The active material layer is segmented into two distinct portions with different conductive material contents: a lower layer portion (10-59 parts by weight ratio) with high conductive material for safety, and an upper layer portion with lower conductive material for capacity. This segmentation allows each region to optimize its function without compromising the other.
3Reliability
If the positive electrode active material has low electroconductivity (0.0001-0.0004 S/cm) to increase resistance during short-circuit, then nail penetration stability is improved, but initial output and long-term cycle characteristics may be affected
Solution Approach 1:
The patent applies local quality by confining the low electroconductivity active material (0.0001-0.0004 S/cm) to the lower layer portion where it provides resistance for nail penetration stability. The upper layer portion uses active material with higher electroconductivity (0.008-0.015 S/cm) to ensure good initial output and cycle characteristics. This spatial differentiation resolves the contradiction between safety and performance.
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 effectively enhances safety and cycle performance by maximizing active material loading while maintaining initial output and long-term characteristics, as demonstrated by passing nail penetration tests and maintaining capacity over multiple cycles.
Implementation Method 1
nail penetration stability can be improved by increasing the resistance of an active material layer adjacent to a current collector when a short-circuit occurs so that the short circuit current may be reduced
Implementation Method 2
each of the upper layer portion and the lower layer portion of the positive electrode active material layer includes a positive electrode active material, binder polymer and a conductive material
Data Source
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AI summary
Disclosed is a positive electrode for a lithium secondary battery, which includes: a positive electrode current collector; and a positive electrode active material layer including an upper layer portion and a lower layer portion, wherein each of the upper layer portion and the lower layer portion of the positive electrode active material layer includes a positive electrode active material, binder polymer and a conductive material, and the positive electrode active material has an electroconductivity of 0.0001-0.0004 S/cm, and the content of the conductive material contained in the lower layer portion is 10-59 parts by weight based on 100 parts by weight of the content of the conductive material contained in the upper layer portion, or the positive electrode active material has an electroconductivity of 0.008-0.015 S/cm, and the content of the conductive material contained in the lower layer portion is 10-30 parts by weight based on 100 parts by weight of the content of the conductive material contained in the upper layer portion.