Positive Electrode Particle Layout for Silicon-Anode Cycle Stability
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries using silicon as the negative electrode active material face significant capacity deterioration due to expansion and contraction during charge and discharge, leading to poor cycle characteristics, particularly because of uneven resistance distribution and deep discharge at the ends of the electrode.
Innovation Solution
A wound electrode assembly is designed with a positive electrode mixture layer containing a combination of non-aggregated and secondary lithium-containing transition metal composite oxide particles, where the ends have a higher concentration of secondary particles and the center has a higher concentration of non-aggregated particles, to balance deterioration rates and inhibit deep discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon material is used as negative electrode active material to increase battery capacity, then battery capacity increases, but expansion and contraction of silicon material becomes particularly large at ends of electrode assembly causing considerable deterioration of cycle characteristics
Solution Approach 1:
The positive electrode mixture layer is designed with non-uniform particle distribution: first regions at both ends contain a larger amount of second composite oxide particles (secondary particles formed by aggregation of primary particles), while the second region in the center contains a larger amount of first composite oxide particles (non-aggregated particles). This local variation in particle type and size distributes expansion and contraction more evenly across the electrode assembly, reducing stress concentration at the ends and improving cycle characteristics while maintaining high capacity
2Reliability
If non-uniform particle distribution is implemented in positive electrode mixture layer to improve cycle characteristics, then cycle characteristics improve, but device complexity increases due to regional differentiation requirements
Solution Approach 1:
The patent implements local quality by creating first regions at both ends with higher concentration of second composite oxide particles and a second region in the center with higher concentration of first composite oxide particles. This regional differentiation targets the specific problem of uneven expansion and contraction at electrode ends, improving cycle characteristics through localized material optimization rather than uniform composition throughout
Solution Approach 2:
The patent changes the particle size parameter and particle aggregation state parameter of the lithium-containing transition metal composite oxide in different regions of the positive electrode mixture layer. By controlling the distribution of particle sizes (first particles: 2-20 μm, second particles: formed by aggregation of 50 nm-5 μm primary particles) and aggregation states (non-aggregated vs. secondary particles), the patent achieves balanced expansion and contraction characteristics across the electrode assembly
Data Source
AI summary
With respect to a nonaqueous electrolyte secondary battery according to one embodiment of the present invention, a positive electrode comprises a mixture layer that contains first composite oxide particles, which are non-agglomerated particles having a volume-based median diameter of 2 μm to 20 μm, and second composite oxide particles, which are secondary particles each are composed of agglomerated primary particles having an average particle diameter of 50 nm to 5 μm. The mixture layer has: first regions which extend from both edges of the mixture layer in the width direction in a length that exceeds 10% of the total width of the mixture layer; and a second region that is sandwiched between the first regions. More second composite oxide particles are contained in the first regions than the first composite oxide particles. More first composite oxide particles are contained in the second region than the second composite oxide particles.