Lithium Transition Metal Phosphate Cathode Particles with Carbon Coating
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Solution Overview
Problem
Lithium transition metal phosphate cathode active materials, such as LiFePO4, face limitations in adhesion to cathode collectors, high output characteristics, and energy density due to low electrical conductivity and unstable olivine crystal structures, which hinder the commercialization of lithium secondary batteries.
Innovation Solution
The development of lithium transition metal phosphate particles with a specific structure, comprising first and second secondary particles formed by agglomeration of primary particles with different average diameters, and a porous structure to improve adhesion and processability, along with a carbon coating layer to enhance electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiFePO4 is used as cathode active material, then high-temperature stability and low cost are improved, but electrical conductivity is poor and internal resistance increases
Solution Approach 1:
The patent uses LiFePO4 as the base material and coats it with carbon material to create a composite structure. The carbon coating layer provides electrical conductivity while maintaining the high-temperature stability of LiFePO4, thus resolving the contradiction between reliability and energy loss.
Solution Approach 2:
The patent creates a porous structure within the LiFePO4 particles by controlling the sintering process. This porous structure increases the surface area and provides pathways for lithium ion diffusion, reducing internal resistance while maintaining the structural stability of LiFePO4.
2Quantity of substance
If olivine crystal structure is used, then theoretical capacity is achieved, but adhesion to cathode collector is poor due to spring back phenomenon
Solution Approach 1:
The patent divides the cathode structure into multiple layers: the LiFePO4 active material layer, the carbon coating layer, and the binder layer. This segmentation allows each layer to perform its specific function - the binder layer provides adhesion to the cathode collector while the LiFePO4 layer maintains theoretical capacity.
Solution Approach 2:
The patent introduces a binder as an intermediary substance between the LiFePO4 particles and the cathode collector. This binder mediates the adhesion problem by providing mechanical bonding while allowing the LiFePO4 particles to maintain their olivine crystal structure and theoretical capacity.
3Productivity
If particle size is reduced to nanoscale, then lithium ion movement path is shortened and discharge capacity increases, but exfoliation from cathode collector increases and more binder is required
Solution Approach 1:
The patent creates a composite structure where nanoscale LiFePO4 particles are embedded in a carbon matrix. This composite structure provides mechanical strength and reduces exfoliation, allowing the use of smaller particles for higher discharge capacity without requiring excessive binder.
Solution Approach 2:
The carbon coating layer acts as a flexible shell around the nanoscale LiFePO4 particles. This thin film provides mechanical protection and reduces exfoliation from the cathode collector, enabling the use of smaller particles for enhanced discharge capacity while minimizing binder requirements.
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 approach minimizes exfoliation from the cathode collector, increases battery capacity and output, and improves process efficiency by reducing the spring back phenomenon and internal resistance, thereby enhancing the performance and commercial viability of lithium secondary batteries.
Implementation Method 1
along with a carbon coating layer to enhance electrical conductivity
Implementation Method 2
a porous structure to improve adhesion and processability, along with a carbon coating layer
Data Source
AI summary
Provided are a cathode active material including lithium transition metal phosphate particles, including a first secondary particle formed by agglomeration of two or more first primary particles, and a second secondary particle formed by agglomeration of two or more second primary particles in the first secondary particle, and a method of preparing the same.Since the cathode active material may include first and second primary particles having different average particle diameters, the exfoliation of the cathode active material from a cathode collector may be minimized and performance characteristics, such as high output characteristics and an increase in available capacity, of a secondary battery may be further improved.