Lithium-Ion Cathode Material with Lithium Phosphate Surface Stabilization
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Solution Overview
Problem
Positive electrode active materials for lithium ion secondary batteries, such as LiNi1-x-yCoxAlO2, experience significant capacity degradation due to structural changes during repeated charging and discharging, limiting their performance.
Innovation Solution
A manufacturing process involving the mixing of lithium-transition metal composite oxides with lithium phosphate, followed by mechanical stress application and heat treatment, results in a layered rock-salt type crystal structure where finely crystallized lithium phosphate covers and disperses within the lithium-transition metal composite oxide particles, stabilizing the structure and maintaining capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiNi1-x-yCoxAlyO2 (NCA) is used as positive electrode active material, then high capacity is achieved, but structural change occurs during charge and discharge leading to capacity degradation
Solution Approach 1:
Lithium phosphate is introduced as an intermediary substance that forms a coating layer on the surface of the NCA particles. This intermediary layer acts as a buffer between the NCA and the electrolyte, suppressing structural changes during charge-discharge cycles while maintaining high capacity. The lithium phosphate coating prevents direct contact and harmful interactions, thereby resolving the contradiction between high capacity and structural stability.
Solution Approach 2:
The invention creates a composite material structure where lithium phosphate is combined with LiNi1-x-yCoxAlyO2 to form a core-shell type composite. The NCA core provides high capacity while the lithium phosphate shell provides structural stability and protects against degradation. This composite approach allows both high capacity and structural stability to coexist.
2Quantity of substance
If LiNiO2 is used as positive electrode active material, then high capacity is achieved, but large structural change occurs during charging and discharging
Solution Approach 1:
Lithium phosphate serves as an intermediary layer that constrains and buffers the large structural changes occurring in LiNiO2 during charge-discharge cycles. This intermediary coating prevents excessive expansion and contraction of the crystal structure, thereby reducing capacity degradation while maintaining high capacity.
Solution Approach 2:
The invention changes the physical and chemical parameters of the LiNiO2 surface by coating it with lithium phosphate. This modification alters the surface properties, reducing the magnitude of structural changes during electrochemical cycling while preserving the high capacity characteristics of LiNiO2.
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 process enhances the battery's capacity retention and suppresses capacity decrease during repeated charge-discharge cycles, addressing the structural change-related degradation issues of existing materials.
Implementation Method 1
a milling process of applying a mechanical stress to a mixture obtained in the mixing process to form the lithium-transition metal composite oxide having the crystal structure of a layered structure and the lithium phosphate into an amorphous or low-crystalline NiO-like rock-salt type crystal structure
Implementation Method 2
a heat treatment process of subjecting the mixture having the amorphous or low-crystalline NiO-like rock-salt type crystal structure obtained in the milling process to a heat treatment to obtain a lithium-transition metal composite oxide having a layered rock-salt type crystal structure in which lithium phosphate is finely crystallized and dispersed
Implementation Method 3
lithium phosphate is finely crystallized and dispersed
Data Source
AI summary
A mixing process of mixing a lithium-transition metal composite oxide with lithium phosphate; a milling process of applying mechanical stress to a mixture obtained in the mixing process to form the lithium-transition metal composite oxide having a layered crystal structure and the lithium phosphate into an amorphous or low-crystalline NiO-like rock-salt type crystal structure; and a heat treatment process of subjecting the mixture to a heat treatment to obtain a lithium-transition metal composite oxide having a layered rock-salt type crystal structure in which lithium phosphate is finely crystallized and dispersed, wherein the lithium-transition metal composite oxide is represented by a general formula: LisNi1-x-y-zCoxMnyMzO2+α, and the crystallized lithium phosphate covers a surface of a primary particle of the lithium-transition metal composite oxide, and is dispersed inside or on a surface of a secondary particle of the lithium-transition metal composite oxide having the layered rock-salt type crystal structure.