LiCoO2 Core-Amorphous Layer Composite for Battery Cycle Stability
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Solution Overview
Problem
Existing positive electrode active materials face challenges in maintaining high capacity and cycle characteristics, especially when subjected to high charging voltages, due to unstable Li insertion and separation reactions and metal elution issues.
Innovation Solution
A positive electrode active material is developed with secondary particles formed by aggregating primary particles, where the core particles have high crystallinity and a low crystallinity covering layer with the same composition, mitigating lattice distortion and enhancing phase transition reversibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high charging voltage is used to increase chargeable and dischargeable capacity, then capacity is improved, but Li insertion and separation reactions become unstable causing capacity deterioration
Solution Approach 1:
The patent uses a composite particle structure consisting of a crystalline core particle and an amorphous surface layer. The core particle provides high capacity through stable Li insertion and separation reactions, while the amorphous surface layer suppresses metal elution and stabilizes the electrode material at high charging voltages. This composite structure resolves the contradiction by combining the advantages of both crystalline and amorphous phases.
Solution Approach 2:
The patent applies different crystallinity characteristics to different parts of the particle: the core region maintains high crystallinity for efficient Li ion insertion and separation, while the surface layer has low crystallinity (amorphous phase) to suppress side reactions and metal elution. This local differentiation of material properties allows simultaneous achievement of high capacity and good cycle characteristics.
2Reliability
If amorphous LiCoO2 is used as positive electrode active material to improve cycle characteristic, then cycle characteristic is improved, but capacity significantly decreases
Solution Approach 1:
The patent creates a composite particle with an amorphous surface layer on a crystalline core, where the core provides high capacity through efficient Li ion insertion and separation reactions enabled by its crystalline structure, while the amorphous surface layer provides stability and suppresses degradation reactions. This composite approach overcomes the limitation of using purely amorphous material.
Solution Approach 2:
The patent differentiates the crystallinity of different regions: the core particle maintains high crystallinity for high capacity, while only the surface layer has low crystallinity for stability. This localized application of amorphous phase avoids the capacity loss associated with fully amorphous structures while retaining the stabilizing effects at the surface.
3Ease of operation
If surface is covered with amorphous lithium transition metal oxide to reduce movement resistance of lithium ions, then movement resistance is reduced, but capacity decreases due to inability to ensure reversibility of crystalline phase transition
Solution Approach 1:
The patent uses a composite structure where the crystalline core particle maintains the ability to undergo reversible crystalline phase transitions for high capacity, while the amorphous surface layer provides low resistance to Li ion movement. The core's crystalline structure ensures phase transition reversibility, overcoming the limitation of fully amorphous coatings.
Solution Approach 2:
The patent confines the amorphous phase to the surface layer to minimize its impact on overall capacity, while the core particle retains high crystallinity for reversible phase transitions. This localized amorphous coating provides the desired low movement resistance without sacrificing the capacity benefits of crystalline phase transition reversibility in the bulk material.
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 configuration improves the cycle characteristic and reduces metal elution, resulting in a battery with high capacity and stability under high charging conditions.
Implementation Method 1
Li insertion and separation that are necessary for crystalline phase transition are used
Data Source
AI summary
A positive electrode active material includes secondary particles obtained by aggregation of a plurality of primary particles. The primary particles include, core particles including a lithium composite oxide, and a layer that is provided on surfaces of the core particles and includes a lithium composite oxide. The lithium composite oxide included in the core particles and the lithium composite oxide included in the layer have the same composition or almost the same composition, and crystallinity of the lithium composite oxide included in the layer is lower than crystallinity of the lithium composite oxide included in the core particles.