Positive Electrode Plate Composition for Capacity-Thermal Stability Tradeoff
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries face challenges in achieving enhanced charged capacity while maintaining excellent thermal stability, as increased charged capacity often degrades thermal stability.
Innovation Solution
A positive electrode plate comprising a first lithium-(transition metal) composite oxide and a second lithium-(transition metal) composite oxide with specific particle size and lithium-to-metal ratios, where the second active material has a smaller average particle size and a crystallite size of 800 nm or more, and the lithium-to-metal ratios in both materials are optimized to enhance capacity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the charged capacity is increased, then the battery capacity is enhanced, but the thermal stability is degraded
Solution Approach 1:
The positive electrode active material is segmented into two distinct types: large-particle first active material (D50: 12-20 μm) and small-particle second active material (D50: 2-8 μm). This segmentation allows each particle size to fulfill different functional roles - the large particles provide thermal stability while the small particles enhance charged capacity, resolving the contradiction between capacity and stability.
Solution Approach 2:
Different regions of the particle size distribution are assigned different chemical compositions and functions. The first active material has Li/M ratio of 1.05-1.12 optimized for thermal stability, while the second active material has Li/M ratio of 0.98-1.04 optimized for charged capacity. This local quality differentiation enables simultaneous achievement of both thermal stability and high capacity.
2Quantity of substance
If small particle size active material is used, then the charged capacity is enhanced, but the thermal stability is reduced
Solution Approach 1:
The active material is divided into two particle size segments with distinct thermal properties. The second active material with small particle size (D50: 2-8 μm) and crystallite size of 800 nm or more provides high charged capacity, while the first active material with large particle size (D50: 12-20 μm) provides thermal stability. This segmentation resolves the contradiction by distributing functions across different size segments.
Solution Approach 2:
The patent creates a composite active material system combining two lithium-(transition metal) composite oxides with different particle sizes and compositions. The composite structure allows the small-particle second active material to contribute to capacity while the large-particle first active material contributes to thermal stability, achieving both objectives simultaneously.
3Quantity of substance
If the lithium-to-metal ratio is increased, then the charged capacity is enhanced, but the structural stability is compromised
Solution Approach 1:
The lithium-to-metal ratio is locally optimized for each active material type: the first active material has Li/M ratio of 1.05-1.12 for structural stability, while the second active material has Li/M ratio of 0.98-1.04 for charged capacity. This local quality optimization resolves the contradiction between capacity enhancement and structural stability.
Solution Approach 2:
The patent changes the lithium-to-metal ratio parameter differently for the two active materials. By setting Li/M ≥ 1.05 for the first active material and Li/M ≤ 1.04 for the second active material, the patent optimizes each material's properties for its intended function, resolving the contradiction between capacity and stability through parameter differentiation.
Data Source
AI summary
A positive electrode plate includes a first active material that is a lithium-(transition metal) composite oxide, and a second active material that is a lithium-(transition metal) composite oxide having a smaller average particle size (D50) than the first active material. A crystallite size of the second active material is 800 nm or more. A ratio (Li/M) between a number of moles of lithium (Li) and a total number of moles of transition metal (M) in the first active material is 1.05 or more. A ratio (Li/M) between a number of moles of lithium (Li) and a total number of moles of transition metal (M) in the second active material is 1.04 or less.