Lithium Transition Metal Composite Oxide Porous Structure
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Solution Overview
Problem
Lithium secondary batteries require a positive active material with high initial efficiency and excellent high rate discharge performance, particularly for applications in electric and hybrid automobiles, where existing materials like LiCoO2 and lithium-excess-type materials fall short in terms of initial efficiency and high rate discharge performance.
Innovation Solution
A lithium transition metal composite oxide with an α-NaFeO2 structure, comprising Co, Ni, and Mn, with a molar ratio of Li/Me between 1.2 and 1.6, and a pore volume of 0.055 to 0.08 cc/g, exhibiting a single phase belonging to the R3-m space group at 1000°C, is used, along with an acid treatment process to enhance porosity and crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-excess-type active material (Li/Me > 1) is used to increase discharge capacity, then discharge capacity is improved, but initial efficiency deteriorates
Solution Approach 1:
The patent introduces a porous structure with controlled pore volume (0.03-0.08 mL/g) and pore size (3-60 nm) into the lithium-excess-type active material. This porous structure increases the contact area between the active material and electrolyte, facilitating better lithium ion insertion/extraction kinetics and improving initial efficiency while maintaining high discharge capacity.
Solution Approach 2:
The patent optimizes specific parameters including pore volume (0.03-0.08 mL/g), pore size (3-60 nm), and specific surface area (0.5-5.0 m²/g) to achieve the balance between discharge capacity and initial efficiency. By controlling these physical parameters, the material structure is optimized to improve lithium ion diffusion while maintaining the lithium-excess composition.
2Quantity of substance
If charge is performed to high potential (>4.3V) to achieve large discharge capacity, then discharge capacity is improved, but cycle performance deteriorates
Solution Approach 1:
The porous structure with optimized pore volume and pore size provides缓冲 space for volume expansion during charging to high potential, reducing mechanical stress and structural degradation. This enables the material to maintain structural integrity during repeated charge-discharge cycles, improving cycle performance while allowing charge to high potential for high discharge capacity.
Solution Approach 2:
The patent creates a composite structure combining the lithium-excess-type active material with a porous matrix or coating layer. This composite structure protects the active material from direct exposure to harsh conditions during high-potential charging, reducing side reactions and structural collapse, thereby improving cycle performance while maintaining high discharge capacity.
3Stability of the object's composition
If LiCoO2 is used as positive active material, then material stability is improved, but discharge capacity deteriorates
Solution Approach 1:
The patent develops a composite material that combines the stability of LiCoO2 with the high capacity characteristics of lithium-excess-type materials. The composite structure allows the stable LiCoO2 phase to provide structural framework and stability, while the lithium-excess phase contributes to high discharge capacity, achieving both material stability and high discharge capacity simultaneously.
Solution Approach 2:
The patent creates a heterostructure where different regions of the material have different compositions and properties. The core or certain regions maintain the stable LiCoO2 structure, while surface or other regions have the lithium-excess composition with porous structure. This local quality differentiation allows the material to exhibit both stability from LiCoO2 regions and high capacity from lithium-excess regions.
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 provides a lithium secondary battery with high initial efficiency and excellent high rate discharge performance, maintaining a stable crystal structure and improving lithium ion insertion/extraction and electrolyte diffusion.
Implementation Method 1
along with an acid treatment process to enhance porosity and crystallinity
Implementation Method 2
improving lithium ion insertion/extraction and electrolyte diffusion
Data Source
AI summary
Provided is a positive active material for a lithium secondary battery containing a lithium transition metal composite oxide. The lithium transition metal composite oxide has an α-NaFeO2 structure. A transition metal (Me) includes Co, Ni and Mn and a molar ratio Li/Me of lithium (Li) to the transition metal is larger than 1.2 and smaller than 1.6. The lithium transition metal composite oxide has a pore volume of 0.055 to 0.08 cc/g in a pore region in which a pore size, at which a differential pore volume determined by a BJH method from an adsorption isotherm using a nitrogen gas adsorption method exhibits a maximum value, is within a range up to 60 nm, and exhibits a single phase belonging to a space group R3-m at 1000° C.