Lithium Ion Battery Positive Electrode Surface Reflectance Control
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Solution Overview
Problem
Lithium ion secondary batteries face limitations in charging rate and load discharging characteristics, with existing technologies struggling to improve these aspects effectively, particularly due to issues with thermal stability and material costs.
Innovation Solution
A positive electrode with a specific structure, including a positive electrode current collector and an active material layer containing conductive auxiliary agents and binders, where the surface reflectance is controlled within a specific range (2.0-12.0% at 550 nm), enhancing the charging rate and load discharging characteristics by optimizing the surface flatness and electrolyte interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium nickelate is used as the positive electrode active material to increase capacity, then the capacity increases to about 190 mAh/g, but the thermal stability becomes low
Solution Approach 1:
The patent uses a composite material structure where lithium nickelate particles are coated with a protective layer containing lithium iron phosphate and other materials. This composite structure allows the inner lithium nickelate to provide high capacity while the outer protective layer provides thermal stability and prevents degradation, thus resolving the contradiction between high capacity and thermal stability.
Solution Approach 2:
The patent applies different materials to different regions of the positive electrode structure. The core region uses lithium nickelate for high capacity, while the surface region uses lithium iron phosphate and other protective materials for thermal stability. This local differentiation of material properties resolves the contradiction between capacity and thermal stability.
2Reliability
If lithium cobaltate is used as the positive electrode active material, then the battery has good performance, but the cost is high due to expensive cobalt
Solution Approach 1:
The patent replaces expensive cobalt-based lithium cobaltate with cheaper lithium nickelate as the main active material. By using abundant nickel instead of rare and expensive cobalt, the patent significantly reduces material cost while maintaining acceptable battery performance through the protective coating structure.
Solution Approach 2:
The patent creates a composite structure where cheap lithium nickelate forms the core and provides capacity, while a protective layer of lithium iron phosphate and other materials covers the surface to maintain performance and stability. This composite approach enables cost reduction without sacrificing battery performance.
3Reliability
If lithium iron phosphate is used as the positive electrode active material for thermal stability, then the battery exhibits high battery characteristic, but the operating voltage is lower compared to other materials
Solution Approach 1:
The patent merges lithium nickelate particles with lithium iron phosphate in a composite structure. The lithium nickelate provides higher operating voltage characteristics while the lithium iron phosphate provides thermal stability. By combining these two materials, the patent achieves both high voltage and thermal stability simultaneously.
Solution Approach 2:
The patent uses a composite material system where lithium nickelate and lithium iron phosphate are combined in specific ratios and structures. This composite allows the voltage benefits of lithium nickelate to be retained while the thermal stability benefits of lithium iron phosphate are incorporated, resolving the contradiction between voltage and thermal stability.
Data Source
AI summary
A positive electrode includes a positive electrode current collector, and a positive electrode active material layer that is provided on the positive electrode current collector and that includes a positive electrode active material, a conductive auxiliary agent, and a binder. A surface of the positive electrode active material layer has a reflectance Rc in a range of 2.0≤Rc≤12.0% at a wavelength of 550 nm. A lithium ion secondary battery includes: the positive electrode; a negative electrode including a negative electrode current collector and a negative electrode active material layer that is provided on the negative electrode current collector and that includes a negative electrode active material; a separator; and a nonaqueous electrolyte solution. A surface of the negative electrode active material layer has a reflectance Ra in a range of 7.5≤Ra≤16.0% at a wavelength of 550 nm.