Positive Electrode Porosity Control for Battery Cycle Life
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries for electric vehicles face challenges in maintaining high capacity, high output, and durability due to increased porosity in the positive electrode active material layer, leading to uneven lithium ion exchange and particle cracking, which deteriorates cycle characteristics.
Innovation Solution
A non-aqueous electrolyte secondary battery with a variation in porosity of the positive electrode active material layer set to 6.0% or less, ensuring a high capacity, high density, and large area, which improves durability by alleviating electro-current constriction and suppressing side reactions caused by overvoltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the positive electrode active material layer is increased to achieve high capacity, then the battery capacity increases, but the porosity of the active material layer decreases, inhibiting permeation of the non-aqueous electrolyte and making lithium ion exchange difficult
Solution Approach 1:
The patent applies local quality by creating different porosity zones within the positive electrode active material layer. The layer includes a first region with higher porosity (30-70%) for efficient lithium ion exchange and a second region with lower porosity (10-50%) for high capacity density. This spatial differentiation allows each region to optimize its function, resolving the contradiction between capacity and ion exchange efficiency.
Solution Approach 2:
The positive electrode active material layer is segmented into multiple regions with distinct porosity characteristics. This segmentation allows the battery to simultaneously achieve high capacity (through dense material packing in the second region) and good cycle characteristics (through adequate electrolyte permeation in the first region), thereby resolving the technical contradiction.
2Quantity of substance
If the porosity of the positive electrode active material layer is decreased to increase capacity density, then the battery capacity increases, but the exchange of lithium ions becomes partially difficult and reaction becomes non-uniform
Solution Approach 1:
The patent implements local quality by assigning different porosity values to different regions of the positive electrode. The first region maintains higher porosity (30-70%) to ensure uniform lithium ion exchange and reaction distribution, while the second region uses lower porosity (10-50%) to maximize capacity density. This resolves the contradiction between capacity density and reaction uniformity.
3Quantity of substance
If the positive electrode active material layer is made denser to improve capacity, then the battery capacity increases, but positive electrode active material particles are easily cracked due to overcharge or overdischarge states
Solution Approach 1:
The patent applies local quality by creating a porosity gradient within the positive electrode active material layer. The first region with higher porosity (30-70%) acts as a buffer zone that facilitates uniform lithium ion distribution, preventing localized overcharge or overdischarge conditions that would cause particle cracking. The second region with lower porosity (10-50%) provides high capacity density while the overall structure maintains particle integrity through this protective gradient.
Solution Approach 2:
The high-porosity first region serves as a cushioning zone that prevents harmful stress concentration in the low-porosity second region. By providing this protective structure in advance, the patent prevents particle cracking before it occurs during charge-discharge cycles, thereby maintaining strength while achieving high capacity.
4Quantity of substance
If the battery is designed for high capacity and high density application to electric vehicles, then the cruising distance increases, but the cycle characteristics deteriorate due to uneven lithium ion exchange
Solution Approach 1:
The patent resolves the contradiction between high capacity and long cycle life by implementing local quality with differentiated porosity regions. The first region with higher porosity (30-70%) ensures uniform lithium ion exchange and prevents localized degradation, extending cycle life. The second region with lower porosity (10-50%) maximizes capacity density for extended cruising distance. Together, they achieve both high capacity and durable cycle characteristics.
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
This configuration significantly enhances the battery's cycle characteristics, maintaining a high capacity retention rate even after repeated charging and discharging, particularly in electric vehicles, where high current usage is common.
Implementation Method 1
permeation of the non-aqueous electrolyte into the active material layer is inhibited by the porosity of the active material layer decreasing
Implementation Method 2
the porosity of the active material layer decreasing
Implementation Method 3
charge and discharge reactions of a battery occur as ions such as lithium ions are absorbed into and desorbed from an electrode active material
Data Source
Figure 1
Figure 2~3
AI summary
Provided is a non-aqueous electrolyte secondary battery which has improved battery durability in the battery having a high capacity, a high density, and a large area. A non-aqueous electrolyte secondary battery including a power generating element including a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a surface of a positive electrode current collector, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a surface of a negative electrode current collector, and a separator, a ratio of a rated capacity to a pore volume of the positive electrode active material layer being 1.40 Ah/cc or more, a ratio of a battery area to a rated capacity being 4.0 cm2/Ah or more, and a rated capacity being 30 Ah or more, wherein a variation in porosity in the positive electrode active material layer is 6.0% or less.