Agglomerated Lithium Iron Phosphate Cathode for Calendering Stability
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Solution Overview
Problem
Lithium iron phosphate cathode materials for lithium-ion secondary batteries suffer from low Li ion diffusivity and electron conductivity, leading to poor charge and discharge characteristics, especially at lower temperatures, and are prone to deformation and conductive carbon film peeling during the calendering process, resulting in uneven electrode structures and decreased conductivity.
Innovation Solution
A cathode material composed of agglomerated particles coated with a carbonaceous film, formed by agglomeration of primary particles represented by General Formula LixAyDzPO4, with specific particle size and surface area characteristics, and a manufacturing method involving slurry preparation, granulation, and calcination in a non-oxidative atmosphere to enhance Li ion and electron conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lithium iron phosphate primary particles are miniaturized to improve charge and discharge characteristics, then Li ion diffusivity and electron conductivity improve, but specific surface area increases causing slurry viscosity increase and requiring more binder
Solution Approach 1:
Multiple primary particles are aggregated to form secondary particles with controlled size distribution (D50: 3-10 μm, D90: 15 μm or less). This merging approach reduces the total specific surface area compared to using only miniaturized primary particles, thereby reducing slurry viscosity and binder requirements while maintaining improved charge/discharge characteristics from the fine primary particle structure
Solution Approach 2:
The invention creates a hierarchical structure where the surface of secondary particles is coated with conductive carbon film and/or metal elements (Li, Na, K). This local quality enhancement at the particle surface improves electron conductivity and charge transfer without requiring excessive binder, addressing the conductivity issue locally rather than throughout the entire slurry matrix
2Ease of manufacture
If secondary particles are formed by granulation to improve electrode mixture slurry properties, then handling improves, but pores among particles cause uneven electrode structure and decreased conductivity
Solution Approach 1:
The invention严格控制 the particle size parameters of secondary particles (D50: 3-10 μm, D90: 15 μm or less) and specific surface area (0.01-1.0 m²/g). By optimizing these parameters, the particles achieve good flowability and packing density, enabling uniform electrode structure formation without excessive pores, thus maintaining both ease of manufacture and structural reliability
Solution Approach 2:
Secondary particles are formed by aggregating multiple primary particles with different sizes and shapes. This composite structure creates interlocking arrangements that reduce void spaces between particles, improving electrode mixture slurry properties and ensuring uniform electrode structure while maintaining good conductivity
3Productivity
If pores are present in secondary particles to improve electrolyte penetration, then ion transport may improve, but secondary particles deform or break and carbon films peel during calendering
Solution Approach 1:
The invention allows for controlled porosity within secondary particles while maintaining overall particle integrity. The porous structure enables electrolyte penetration and ion transport, while the aggregated nature of secondary particles from multiple primary particles provides mechanical strength to prevent deformation and breaking during calendering
Solution Approach 2:
Conductive carbon film and/or metal element coatings are applied to the surface of secondary particles. These thin films provide structural reinforcement to the particle surface, preventing carbon film peeling during calendering while maintaining electrical conductivity. The films act as flexible protective shells that accommodate particle deformation without peeling
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 improves Li ion and electron conductivity, leading to enhanced charge and discharge characteristics, reduced internal resistance, and increased discharge capacity, while preventing deformation and carbon film peeling, thus stabilizing battery performance across various temperatures.
Implementation Method 1
coated with a carbonaceous film
Implementation Method 2
calcination in a non-oxidative atmosphere
Data Source
AI summary
A cathode material for a lithium-ion secondary battery made of agglomerated particles formed by agglomeration of a plurality of primary particles of a cathode active material represented by General Formula (1) below which are coated with a carbonaceous film, in which, in a case in which a cathode mixture layer including the cathode material, a conductive auxiliary agent, and a binding agent in a weight ratio (the cathode material/the conductive auxiliary agent/the binding agent) of 90:5:5 is calendered on a 30 μm-thick aluminum current collector at a total applied pressure of 5 t/250 mm, a film thickness change percentage of the cathode mixture layer before and after the calendering is 30% or less,LixAyDzPO4 (1).