LiMnFePO4 Gradient Electrode for Battery Energy Density
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in energy density, cycle life, and high-temperature endurance, particularly in applications requiring high output and safety, due to limitations in the positive electrode material LiFePO4, which results in decreased electromotive force and reduced performance at elevated temperatures.
Innovation Solution
The development of a positive electrode active material with an olivine structure represented by LiMn1−x−yFexMyPO4, where 0<x≤0.5 and 0≤y≤0.2, with a specific Fe ratio gradient (β<α) and the addition of a carbon-containing material on the surface, enhancing electron conductivity and suppressing interface resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiFePO4 is used as positive electrode material, then chemical stability and safety are improved, but energy density and electromotive force decrease
Solution Approach 1:
The patent applies local quality by creating a Fe concentration gradient within the LiMn1-x-yFexMyPO4 particles, where the surface region has higher Fe content (α) than the central portion (β). This gradient structure allows the surface to provide enhanced stability while the interior maintains higher voltage characteristics, thus resolving the contradiction between chemical stability and energy density.
Solution Approach 2:
The patent uses composite materials by combining LiMn1-x-yFexMyPO4 with carbon-containing materials on the surface. This composite structure provides both the chemical stability of the olivine structure and the electrical conductivity needed for high energy density performance, while the Fe gradient optimizes the balance between stability and voltage.
2Reliability
If LiFePO4 is used as positive electrode material, then safety is improved, but cycle life and float charge resistance decrease
Solution Approach 1:
The Fe concentration gradient (α>β) creates a protective surface layer with higher Fe content that enhances float charge resistance and cycle life, while maintaining the overall safety benefits of the LiFePO4-based olivine structure. The surface enrichment acts as a protective barrier during long-term storage and cycling.
Solution Approach 2:
The patent changes the Fe concentration parameter spatially within the particle structure, creating a gradient from the center to the surface. This parameter variation optimizes both cycle life and float charge resistance by having higher Fe content at the surface where electrochemical reactions occur most frequently.
3Reliability
If Fe ratio is increased in LiMn1-x-yFexMyPO4, then stability is improved, but electromotive force and energy density decrease
Solution Approach 1:
The patent resolves this contradiction by making the Fe distribution non-uniform, with higher Fe content (α) at the surface and lower Fe content (β) in the central portion. This local quality variation allows the surface to provide stability while the interior contributes more to electromotive force, achieving both goals simultaneously.
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 solution improves the lithium absorbing-releasing performance, reduces capacity degradation, and enhances cycle life, float charge resistance, and discharge rate performance, even at high charging states, thereby increasing the energy density and stability of nonaqueous electrolyte batteries.
Implementation Method 1
the addition of a carbon-containing material on the surface, enhancing electron conductivity and suppressing interface resistance
Implementation Method 2
improves the lithium absorbing-releasing performance
Data Source
AI summary
According to one embodiment, there is provided a positive electrode active material containing positive electrode active material particles. The positive electrode active material particles have an olivine structure. The positive electrode active material particles are represented by LiMn1−x−yFexMyPO4 (0<x≤0.5, 0≤y≤0.2, and M is at least one element selected from the group consisting of Mg, Ni, Co, Sn, and Nb) and satisfy, Formula (1) below.β<α (1),wherein α is a ratio of Fe in LiMn1−α−yFeαMyPO4, and β is a ratio of Fe in LiMn1−β−yFeβMyPO4.