High-Ni Positive Electrode Coatings for Crack and HF Resistance
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Solution Overview
Problem
High Ni-containing lithium-transition metal composite oxides in nonaqueous electrolyte secondary batteries face issues such as particle cracking during charging and discharging, leading to reduced cycle life, and the generation of hydrogen fluoride gas under high temperature endurance, which degrades the positive electrode and increases resistance.
Innovation Solution
A positive electrode configuration featuring a first lithium-transition metal composite oxide with a boron compound on its surface and a second lithium-transition metal composite oxide with an aluminum compound, both with high nickel content, forming secondary and single particles respectively, to enhance binding force, mitigate stress, and trap hydrogen fluoride gas, thereby improving cycle characteristics and reducing resistance increase under high temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high Ni-containing lithium-transition metal composite oxide is used as positive electrode active material, then energy density is improved, but particle cracking occurs during charging and discharging resulting in reduced cycle life
Solution Approach 1:
The patent uses a composite material structure where a lithium-transition metal composite oxide core is coated with a lithium phosphate layer. This composite structure allows the high Ni-content core to provide high energy density while the lithium phosphate coating layer prevents particle cracking during charging and discharging, thereby improving cycle life. The coating layer acts as a protective barrier that maintains structural integrity during repeated expansion and contraction cycles.
Solution Approach 2:
The patent modifies the surface composition and structure of the positive electrode active material by forming a lithium phosphate coating layer with specific thickness (5-50 nm) and composition ratios. By controlling the Li content (0.8 ≤ Li ≤ 1.2) and phosphate group content in the coating layer, the material achieves optimal balance between maintaining high capacity (energy density) and preventing particle degradation (improving cycle life).
2Use of energy by moving object
If high Ni-containing lithium-transition metal composite oxide is used, then energy density is improved, but hydrogen fluoride gas is generated under high temperature endurance degrading the positive electrode and increasing resistance
Solution Approach 1:
The lithium phosphate coating layer forms a composite structure that protects the high Ni-containing core material. This coating layer has high thermal stability and acts as a barrier that prevents the generation and release of hydrogen fluoride gas under high temperature conditions. The coating layer composition (Li-containing phosphate) is specifically designed to resist thermal degradation and prevent harmful gas evolution, thereby reducing resistance increase during high temperature endurance while maintaining the high energy density of the Ni-rich core.
Solution Approach 2:
The lithium phosphate coating layer serves as an intermediary barrier between the high Ni-containing active material and the external environment. Under high temperature conditions, this intermediate layer prevents direct exposure and reaction that would otherwise generate hydrogen fluoride gas. The coating layer absorbs or neutralizes harmful effects before they can degrade the electrode performance, thereby reducing resistance increase while preserving the high energy density characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The configuration achieves high energy density, improved cycle characteristics, and reduced resistance increase under high temperature endurance, enhancing the overall performance of nonaqueous electrolyte secondary batteries.
Implementation Method 1
the boron compound placed on the surface of the first lithium transition metal composite oxide increases the binding force of the secondary particles due to the action of the boron compound, thereby reducing particle cracking
Implementation Method 2
the void spaces at the predetermined percentage in the first lithium transition metal composite oxide mitigate stress applied during expansion and contraction and reduces particle cracking
Implementation Method 3
the aluminum compound placed on the surface of the second lithium transition metal composite oxide traps a hydrogen fluoride gas generated under high temperature endurance
Data Source
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AI summary
A positive electrode disclosed herein includes: a positive electrode active material layer containing a first lithium-transition metal composite oxide in a form of secondary particles and a second lithium-transition metal composite oxide in a form of single particles; and a positive electrode current collector. In the first lithium-transition metal composite oxide, a boron compound is placed on the surfaces of the secondary particles, and a porosity of the secondary particles is 2% to 8%. In the second lithium -transition metal composite oxide, an aluminum compound is placed on the surfaces of the single particles. The first and second lithium-transition metal composite oxides each contain nickel at 70 mol% or more relative to the total amount of transition metal elements, and the mass ratio of the first lithium-transition metal composite oxide : the second lithium-transition metal composite oxide is 80 : 20 to 50 : 50.