Positive Electrode Active Material Layer Volume Ratio Control
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Solution Overview
Problem
Existing lithium ion secondary batteries face safety issues due to variations in tap densities of active materials, leading to uneven volume distribution and increased risk of short circuiting, as blending ratios are typically defined by mass rather than volume.
Innovation Solution
A positive electrode active material layer is formulated with specific tap densities, blending amounts, and porosity to ensure a balanced occupancy ratio, incorporating a first and second active material with different charge/discharge potentials and an additive, where the porosity and occupancy ratio are controlled to maintain safety during short circuiting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If blending ratios of positive electrode active materials are defined by mass, then manufacturing is simplified, but volume distribution becomes uneven leading to safety issues
Solution Approach 1:
The patent changes the blending parameter from mass ratio to volume ratio. Specifically, it controls the volume ratio of LiNi0.8Co0.1Mn0.1O2 to LiFePO4 to be between 0.7:1 and 1.3:1, which ensures uniform volume distribution and prevents local overheating during short circuiting, thereby improving battery safety while maintaining manufacturing feasibility through straightforward volume-based mixing procedures
2Reliability
If higher blending ratio of LiFePO4 is used, then safety is improved, but capacity is reduced
Solution Approach 1:
The patent optimizes the volume ratio parameter of LiNi0.8Co0.1Mn0.1O2 to LiFePO4 within the range of 0.7:1 to 1.3:1. This balanced ratio ensures sufficient LiFePO4 content for safety (preventing local overheating) while maintaining adequate LiNi0.8Co0.1Mn0.1O2 content for high capacity, achieving both safety and performance requirements simultaneously
3Ease of manufacture
If different densities of active materials are blended by mass, then manufacturing is easier, but actual volume ratio deviates from intended ratio
Solution Approach 1:
Instead of controlling mass ratio and accepting volume variation, the patent inverts the approach by directly controlling volume ratio. It specifies the volume ratio of LiNi0.8Co0.1Mn0.1O2 to LiFePO4 should be between 0.7:1 and 1.3:1, ensuring precise volume distribution control while accounting for density differences between materials
Data Source
AI summary
A parameter for producing a positive electrode having excellent safety, and a positive electrode active material layer satisfying the parameter. The positive electrode active material layer includes a first positive electrode active material, a second positive electrode active material having a lower charge/discharge potential than the first positive electrode active material, and an additive. When the first positive electrode active material tap density is defined as dt1, the second positive electrode active material tap density is defined as dt2, a true density of the additive is defined as d3, a mass percentage of the first positive electrode active material is defined as Wt1, a mass percentage of the second positive electrode active material is defined as Wt2, a mass percentage of the additive is defined as Wt3, and a porosity of the positive electrode active material layer is defined as p, the positive electrode active material layer satisfies (1−p)×(Wt1/dt1)/((Wt1/dt1)+(Wt2/dt2)+(Wt3/d3))<0.38.