Gradient-Coated LiFePO4 Particles for Battery Water Resistance
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Solution Overview
Problem
Lithium iron phosphate-based non-aqueous electrolyte secondary batteries face issues with water reactivity and lithium diffusion due to moisture, leading to capacity deterioration and poor current release characteristics.
Innovation Solution
A non-aqueous electrolyte secondary battery design featuring a positive electrode with a core section of olivine type LiFePO4, an intermediate section of LiFexPyOz, and a surface section of LiFeaPbOc, where the molar concentration ratio of Fe to P increases continuously or intermittently from the surface to the core, enhancing lithium diffusion while maintaining water resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium iron phosphate is used as positive electrode active material, then electrochemical stability and thermal safety are improved, but water reactivity increases causing iron elution and capacity deterioration
Solution Approach 1:
The patent uses a composite coating structure consisting of Li3PO4 layer and carbon layer on lithium iron phosphate particles. This composite material approach combines the water resistance of Li3PO4 with the conductivity and additional protection of carbon, effectively reducing water reactivity while maintaining electrochemical stability.
Solution Approach 2:
The Li3PO4 coating acts as an intermediary layer between the lithium iron phosphate and the electrolyte, preventing direct contact and reaction with water. This intermediary layer blocks iron elution while allowing lithium ion diffusion, thus resolving the water reactivity issue.
2Object-affected harmful factors
If coating with Li3PO4 or carbon is applied to suppress water reaction, then water resistance is improved, but lithium diffusion is inhibited reducing charge-discharge capacity
Solution Approach 1:
The patent creates a dual-layer coating with different local properties: the inner Li3PO4 layer provides water resistance, while the outer carbon layer provides both protection and conductivity. Each layer performs its specific function locally, ensuring water resistance without significantly blocking lithium diffusion pathways.
Solution Approach 2:
The patent optimizes the thickness and composition parameters of the coating layers. By controlling the coating thickness to be thin enough and adjusting the Li3PO4 to carbon ratio, lithium ion diffusion is maintained while water resistance is achieved. The specific parameters are tuned to balance protection and ion transport.
3Quantity of substance
If very fine particle size lithium titanium composite oxide is used in negative electrode, then energy density is improved, but water of crystallization increases causing dissolution of lithium iron phosphate
Solution Approach 1:
The patent converts the harmful effect of water of crystallization from the negative electrode by using it to form a protective Li3PO4 layer on the positive electrode through controlled reaction. The water that would cause dissolution is instead utilized to create a protective coating, turning the harmful factor into a beneficial protective mechanism.
Solution Approach 2:
The patent applies preliminary protective coating to the lithium iron phosphate before assembly, creating a water-resistant barrier in advance. This preliminary anti-action prevents the water from the negative electrode from attacking the positive electrode material during battery operation.
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 design improves lithium ion diffusion and water resistance, maintaining charge-discharge capacity and rate characteristics, even under high temperature conditions, by allowing lithium ions to diffuse smoothly while preventing erosion.
Implementation Method 1
the diffusion of lithium in Li3PO4 or carbon almost does not occur inside the solid. Therefore, since such coating serves as an inhibitory factor against the diffusion into lithium iron phosphate
Implementation Method 2
lithium iron phosphate has a problem that the compound easily reacts with moisture, and iron is likely to be eluted from the positive electrode active material
Data Source
AI summary
A non-aqueous electrolyte secondary battery includes a positive electrode containing active material particles composed of a core section formed of olivine type LiFePO4; an intermediate section that lies on the outer side of the core section and has LiFexPyOz; and a surface section that lies on the outer side of the intermediate section and has LiFeaPbOc; and a negative electrode containing lithium titanate, in which battery the molar concentration ratio of Fe relative to P at the core section is greater than the average of x/y of LiFexPyOz, the average value of a/b of LiFeaPbOc at the surface section of the positive electrode active material particles is smaller than the average of x/y of LiFexPyOz, and the positive electrode active material particles include a region in which x/y of LiFexPyOz at the intermediate section increases continuously or intermittently in the direction from the surface section toward the core section.