Positive Electrode Active Material Balancing Energy Density and Cycle Life
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Solution Overview
Problem
Existing positive electrode materials in non-aqueous electrolyte secondary batteries face challenges in achieving good cycling performance and input-output properties due to oxidative degradation and structural changes caused by lithium-rich and high nickel content materials, leading to degradation of capacity and cycling performance.
Innovation Solution
A positive electrode active material comprising a first lithium-rich composite oxide with larger secondary particles and a second high nickel content composite oxide with smaller secondary particles, balanced in a specific ratio and content, along with the inclusion of carbon nanotubes and carbon black to enhance electronic conductivity and reduce structural changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-rich and high nickel content composite oxide is used to increase capacity, then volumetric energy density is improved, but oxidative degradation and structural changes occur leading to poor cycling performance
Solution Approach 1:
The positive electrode active material is segmented into two distinct types: Type A with lithium-rich composition (0.13≤a1≤0.33, 0≤x1≤0.3, 0.47≤y1≤0.67, 0≤z1≤0.3) and Type B with high nickel content (0.6≤x2≤1, 0≤y2≤0.3, 0≤z2≤0.3). This segmentation allows each type to contribute its strengths while mitigating individual weaknesses, resolving the contradiction between high capacity and cycling stability
Solution Approach 2:
The invention creates a composite positive electrode active material by combining Type A lithium-rich composite oxide and Type B high nickel content composite oxide in a specific ratio (20-70 mass% Type A, 30-80 mass% Type B). This composite structure enables the material to achieve both high volumetric energy density and good cycling performance by leveraging the complementary properties of the two components
2Quantity of substance
If high nickel content composite oxide is used to increase capacity, then volumetric energy density is improved, but input-output properties deteriorate due to structural changes
Solution Approach 1:
The invention optimizes the compositional parameters of Type B high nickel content composite oxide by controlling the nickel content (0.6≤x2≤1) and adding metallic elements M2 (0≤y2≤0.3, 0≤z2≤0.3) to modify the crystal structure. This parameter optimization maintains high capacity while improving structural stability and electronic conductivity, thereby enhancing input-output properties
3Quantity of substance
If lithium-rich composite oxide is used to increase capacity, then volumetric energy density is improved, but oxidative degradation occurs leading to capacity loss
Solution Approach 1:
The Type B high nickel content composite oxide acts as an intermediary component that stabilizes the overall structure of the positive electrode active material. By combining Type A and Type B in a specific ratio, the Type B component mitigates the oxidative degradation tendency of Type A, reducing harmful effects while preserving high capacity
Data Source
AI summary
A positive electrode active material comprises a first active material represented by a formula (I) that is secondary particles each consisting of 50 or more primary particles aggregated together, as well as a second active material represented by a formula (II) that is at least one of single particles and secondary particles each consisting of 2 to 10 primary particles aggregated together. The formula (I) and the formula (II) are as specified in the claims. A content of the first active material in the positive electrode active material is from 20 to 70 mass%. A ratio (D150/D250) of an average particle size (D150) of the first active material to an average particle size (D250) of the second active material is from 2.45 to 5.95.