Cathode Active Material Coating for CEI-Stable Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries face drawbacks such as high oxidation activity and slow solid-state lithium ion transport due to continuous oxidative decomposition of the electrolyte on the positive electrode, leading to reduced power performance and cycle life.
Innovation Solution
A positive electrode active material is developed with a substrate of lithium salts like Li[NiaCobMnc]O2 and a coating layer containing fluorine and phosphorus, such as lithium difluorophosphate, which blocks corrosive decomposition and forms a cathode electrolyte interface film, improving film structure and lithium ion transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional positive electrode active material is used, then the battery can operate, but the oxidation activity is high and electrolyte decomposition occurs continuously, reducing power performance and cycle life
Solution Approach 1:
A coating layer containing fluorine and phosphorus (e.g., lithium difluorophosphate) is introduced as an intermediary between the positive electrode active material substrate and the electrolyte. This coating layer acts as a mediator that reduces the direct harmful interaction between the high oxidation activity substrate and the electrolyte, thereby suppressing electrolyte decomposition while maintaining battery operation.
Solution Approach 2:
The coating layer converts the harmful high oxidation activity of the substrate into a beneficial effect by forming a stable cathode electrolyte interface film. The fluorine and phosphorus elements in the coating layer suppress electrolyte decomposition and promote the formation of a protective film, turning the potentially harmful oxidation activity into a mechanism that enhances cycle life and power performance.
2Power
If the electrolyte decomposes continuously on the positive electrode, then the battery can function, but power performance and cycle life are reduced
Solution Approach 1:
The coating layer serves as an intermediary that prevents direct contact between the electrolyte and the positive electrode active material substrate. This intermediary layer suppresses the continuous decomposition of the electrolyte, reducing energy loss and improving power performance by maintaining electrolyte integrity.
Solution Approach 2:
The coating layer changes the chemical composition parameters at the electrode-electrolyte interface by introducing fluorine and phosphorus elements. This parameter change suppresses electrolyte decomposition reactions and promotes the formation of a stable interface film, thereby reducing electrolyte consumption and improving power performance.
3Reliability
If a coating layer with fluorine and phosphorus is applied, then electrolyte decomposition is blocked and cycle life improves, but the device structure becomes more complex
Solution Approach 1:
The coating layer is applied locally only on the surface of the positive electrode active material substrate, where it is needed to suppress electrolyte decomposition. This local application approach improves cycle life without requiring complex modifications to the entire battery structure, maintaining relative simplicity while achieving enhanced reliability.
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
This solution significantly enhances the power performance and cycle life of lithium-ion batteries by reducing electrolyte consumption and decomposition, while maintaining effective lithium utilization and stability.
Implementation Method 1
the second lithium salt to form CEI (cathode electrolyte interface) films in situ on surfaces of the first lithium salt particles
Implementation Method 2
surface of the first lithium salt is coated with a coating layer containing the second lithium salt, which not only blocks the corrosive decomposition of the first lithium salt by the electrolyte
Implementation Method 3
improving the film structure and the transport speed of lithium ions in the positive electrode active material
Data Source
AI summary
This application provides a positive electrode active material. Surface of a first lithium salt is coated with a coating layer containing a second lithium salt, which not only blocks the corrosive decomposition of the first lithium salt by the electrolyte but also allows the second lithium salt to form CEI films in situ on surfaces of the first lithium salt particles, thereby improving the film structure and avoiding the decomposition of active components in the electrolyte. Additionally, the second lithium salt contains both elements fluorine and phosphorus, which makes the composition of the film formed as consistent as possible with the composition of the film formed by lithium hexafluorophosphate in the electrolyte, thereby reducing the consumption of active lithium in the electrolyte. The positive electrode active material of this application can significantly improve the power performance and cycle life of batteries.