Composite Positive Electrode Active Material for High Voltage Battery Stability
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Solution Overview
Problem
Existing positive electrode active materials for lithium-ion batteries face challenges in maintaining high capacity and cycle stability, particularly at high charging voltages due to unintended Li insertion and separation reactions, leading to capacity deterioration and metal elution issues.
Innovation Solution
A 2-layer-covered composite particle positive electrode active material is developed, comprising a high crystallinity lithium composite oxide core particle with a low crystallinity lithium composite oxide first layer and an oxide or fluoride second layer, which mitigates lattice distortion and enhances phase transition reversibility, reducing metal elution and improving cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a high charging voltage is used to increase chargeable and dischargeable capacity, then capacity is improved, but unintended Li insertion and separation reactions occur causing capacity deterioration
Solution Approach 1:
The invention uses a composite structure consisting of a crystalline lithium composite oxide core particle and an amorphous lithium composite oxide coating layer. The core particle provides high capacity through crystalline phase transition, while the amorphous coating layer suppresses unintended Li insertion and separation reactions at the surface, thereby maintaining cycle stability at high charging voltages
Solution Approach 2:
The invention applies different crystallinity characteristics to different parts of the positive electrode active material: the core particle has high crystallinity to enable phase transition and high capacity, while the surface coating layer has low crystallinity (amorphous) to prevent harmful reactions. This local differentiation of material properties resolves the contradiction between capacity and cycle stability
2Reliability
If amorphous LiCoO2 is used as positive electrode active material to improve cycle characteristic, then cycle stability is improved, but capacity significantly decreases
Solution Approach 1:
The invention creates a composite structure where the crystalline core particle (providing high capacity through phase transition) and amorphous coating layer (providing cycle stability) work together. This composite approach allows the material to simultaneously achieve high capacity and excellent cycle characteristics, overcoming the limitation of using purely amorphous material
3Reliability
If surface of powder body is covered with amorphous lithium transition metal oxide to reduce movement resistance of lithium ions, then cycle characteristic is improved, but capacity decreases at high potential
Solution Approach 1:
The invention optimizes the coating layer composition to have low crystallinity (amorphous) structure with controlled thickness. This local modification at the surface reduces Li ion movement resistance and suppresses harmful reactions, while the bulk core particle maintains high crystallinity for capacity, achieving both cycle stability and high capacity at high potentials
4Quantity of substance
If high potential charging is performed to increase capacity, then chargeable capacity is improved, but metal elution occurs frequently
Solution Approach 1:
The amorphous coating layer acts as a protective barrier between the crystalline core particle and the electrolyte at high potentials. This composite structure prevents metal elution from the core particle while allowing the system to operate at high charging voltages for increased capacity
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 solution achieves a high capacity and excellent cycle stability by mitigating lattice distortion and reducing metal elution, thereby enhancing the battery's performance and longevity.
Implementation Method 1
an unintentional Li insertion and separation reaction of the positive electrode active material occurs due to a locally higher potential state
Implementation Method 2
Li insertion and separation that are necessary for crystalline phase transition are used
Data Source
AI summary
A positive electrode active material includes: a particle including a lithium composite oxide; a first layer that is provided on a surface of the particle and includes a lithium composite oxide; and a second layer that is provided on a surface of the first layer. The lithium composite oxide included in the particle and the lithium composite oxide included in the first layer have the same composition or almost the same composition, the second layer includes an oxide or a fluoride, and the lithium composite oxide included in the first layer has lower crystallinity than the lithium composite oxide included in the particle.