Thick Cathode Particle Design for Low-Resistance Li-Ion Batteries
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries face challenges in maintaining capacity and uniform reaction occurrence within the electrode thickness, leading to increased ionic resistance and impaired input-output properties when the electrode is thickened.
Innovation Solution
Incorporating a positive electrode active material with a layered structure, featuring secondary particles with an average size of 8.0 µm or more and a DBP oil absorption ratio of 0.3 or more to the BET specific surface area, which enhances electrolyte retention and ion diffusion, along with a thickness of 80 µm or more for the positive electrode active material layer, and a content rate of secondary particles at 50 mass% or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the electrode is made thicker to increase capacity, then the battery capacity increases, but the input-output properties and cycling performance are impaired due to increased ionic resistance
Solution Approach 1:
The patent applies local quality by controlling the particle size distribution of the positive electrode active material. Specifically, it uses a mixture of fine particles (3 µm or less) and coarse particles (8 µm or more) in specific ratios. The fine particles ensure good contact and reaction uniformity in local regions, while the coarse particles provide sufficient capacity. This local optimization of particle characteristics resolves the contradiction between increasing capacity (thicker electrode) and maintaining performance (low ionic resistance).
Solution Approach 2:
The patent changes the particle size parameter of the positive electrode active material to resolve the contradiction. By specifying that coarse particles have a diameter of 8 µm or more and fine particles have a diameter of 3 µm or less, and by controlling their mixing ratio, the patent optimizes the balance between capacity (benefiting from larger total volume) and ionic resistance (benefiting from appropriate particle size distribution). This parameter control enables thicker electrodes to maintain both high capacity and good input-output properties.
2Quantity of substance
If the electrode is made thicker, then the battery capacity increases, but the reactions become less uniform in the thickness direction due to increased ionic resistance
Solution Approach 1:
The patent applies local quality by using a bimodal particle size distribution in the positive electrode active material. The fine particles (≤3 µm) fill gaps and ensure uniform reaction distribution in local regions, while the coarse particles (≥8 µm) contribute to overall capacity. This local optimization ensures that even in thicker electrodes, reactions remain uniform throughout the thickness direction, resolving the contradiction between capacity increase and reaction uniformity.
Solution Approach 2:
The patent effectively creates a porous-like structure through the particle size distribution. The mixture of fine and coarse particles creates void spaces and pathways that facilitate electrolyte penetration and ion diffusion throughout the electrode thickness. This pseudo-porous structure, achieved through careful particle size selection and mixing ratio control, maintains reaction uniformity even in thicker electrodes by ensuring adequate electrolyte access throughout the electrode volume.
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 inhibits the increase of ionic resistance, ensuring more uniform reactions and improved capacity retention, particularly when the positive electrode active material layer is thickened, thereby enhancing the battery's performance.
Implementation Method 1
a higher ratio of the DBP oil absorption number of secondary particles to the BET specific surface area of the secondary particles means that the oil absorption number per area of the secondary particles is high, namely, the positive electrode active material is highly capable of retaining the electrolyte solution
Implementation Method 2
Ionic resistance refers to diffusability of ions inside the electrode. The lower the ionic resistance value is, the easier the ions can diffuse inside the electrode
Data Source
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AI summary
A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material having a layered structure, the positive electrode active material is in the form of secondary particles, the secondary particles have an average particle size of 8.0 µm or more, and a ratio of a DBP oil absorption number of the secondary particles to a BET specific surface area of the secondary particles is 0.3 or more.