LMFP Cathode Blend Balancing Rate Performance and Energy Density
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Solution Overview
Problem
Existing lithium manganese iron phosphate batteries face a challenge in achieving both high rate performance and energy density due to the reduction in compaction density caused by reducing particle size, which affects ionic conductivity and ion migration path.
Innovation Solution
A positive electrode active material comprising a blend of first and second lithium iron manganese phosphate particles with different particle sizes and manganese molar ratios, where the first particle with a smaller size and higher manganese content enhances rate performance, and the second particle with a larger size and lower manganese content improves compaction density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the particle size of lithium manganese iron phosphate is reduced to shorten ion migration path, then the rate performance is improved, but the compaction density decreases
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the particle composition varies spatially. The core region has a different Mn/(Mn+Fe) molar ratio than the shell region, allowing different parts of the same particle to serve different functions: the core provides high capacity while the shell maintains stability and density, thus resolving the contradiction between rate performance and compaction density
Solution Approach 2:
The patent uses composite materials by combining lithium manganese iron phosphate with different Mn/(Mn+Fe) molar ratios within the same particle structure. This creates a composite active material where regions with different chemical compositions work together to simultaneously achieve high ion migration speed and high compaction density
2Productivity
If the particle size is reduced to improve rate performance, then the capacity per gram increases, but the energy density decreases
Solution Approach 1:
The patent applies parameter changes by systematically varying the Mn/(Mn+Fe) molar ratio as a key parameter within different regions of the particle. By optimizing this compositional parameter spatially, the material achieves both high specific capacity (from smaller effective diffusion paths in the shell) and high energy density (from efficient packing enabled by the core structure)
3Power
If the Mn content is increased to improve voltage plateau, then the energy density is improved, but the ionic conductivity decreases
Solution Approach 1:
The patent applies local quality by creating spatial variation in Mn content within the particle structure. Regions with higher Mn content provide high voltage plateau and energy density, while regions with lower Mn content (or different composition) maintain good ionic conductivity. This local differentiation resolves the contradiction between power and reliability
Solution Approach 2:
The patent uses composite materials by integrating phases or regions with different Mn/(Mn+Fe) molar ratios. The high-Mn regions contribute to high voltage and energy density, while the low-Mn regions contribute to ionic conductivity, creating a composite active material that achieves both high power and high reliability
Data Source
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AI summary
The present disclosure provides a positive electrode active material, a positive electrode, a battery, and a device. The positive electrode active material comprises a first lithium iron manganese phosphate particle and a second lithium iron manganese phosphate particle. The particle size D50 of the first lithium iron manganese phosphate particle is less than the particle size D50 of the second lithium iron manganese phosphate particle. The Mn/(Mn+Fe) molar ratio in the first lithium iron manganese phosphate particle is x, the Mn/(Mn+Fe) molar ratio in the second lithium iron manganese phosphate particle is y, and x>y. The positive electrode active material of the present disclosure comprises two kinds of lithium iron manganese phosphate particles having different particle size ranges and different manganese contents in combination. The first lithium iron manganese phosphate particle of small particle size particle having a high manganese content supports the instantaneous high-power output of the battery in the process of high-rate discharge, to improve the rate performance of the battery. The second lithium iron manganese phosphate particle of large particle size having a low manganese content improves the capacity per gram of the active material, enhances the compaction density, and increases the energy density of the battery.