LiMnFePO4 Secondary Particle Gradient for Stable High-Energy Cathodes
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Solution Overview
Problem
Lithium manganese phosphate batteries face challenges with low energy density and high manganese dissolution during charging and discharging, leading to energy loss and poor cycle stability due to manganese precipitation and polarization issues.
Innovation Solution
A positive electrode active material with a secondary particle structure featuring a manganese-rich inner lithium manganese iron phosphate primary particle and a manganese-poor outer lithium manganese iron phosphate primary particle, with a controlled area ratio and carbon coating, to reduce manganese dissolution and enhance interface stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium manganese phosphate is used as positive electrode material, then higher plateau voltage and energy density are achieved, but manganese dissolution and polarization increase during charging and discharging
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core contains lithium manganese phosphate (high Mn content) for energy density, while the outer shell contains lithium iron phosphate (low Mn content) for stability. This spatial differentiation of material composition allows each region to perform its specific function: the core provides high voltage and energy density, while the shell prevents manganese dissolution and reduces polarization during cycling.
Solution Approach 2:
The patent uses composite materials by combining lithium manganese phosphate and lithium iron phosphate in a core-shell configuration. The composite structure integrates the advantages of both materials: LiMnPO4 contributes high plateau voltage and energy density, while LiFePO4 provides structural stability and resistance to manganese dissolution. The controlled composition gradient at the interface further optimizes the composite performance.
2Reliability
If lithium iron phosphate is used as positive electrode material, then structural stability and cycle life are improved, but plateau voltage and energy density are limited
Solution Approach 1:
The patent applies segmentation by dividing the positive electrode material into distinct inner core and outer shell regions. The inner core is composed primarily of lithium manganese phosphate to maximize energy density, while the outer shell is composed primarily of lithium iron phosphate to ensure structural stability and long cycle life. This segmentation allows the electrode to simultaneously achieve high energy density and excellent cycle stability.
3Use of energy by moving object
If manganese content is increased in lithium manganese phosphate, then energy density is improved, but manganese dissolution and precipitation during cycling worsen
Solution Approach 1:
The patent uses the outer shell of lithium iron phosphate as an intermediary protective layer that prevents direct contact between the high-manganese core and the electrolyte. This intermediary shell blocks manganese dissolution into the electrolyte while allowing lithium ion transport. The shell acts as a barrier that mediates between the high-manganese core (which needs to dissolve some Mn for capacity) and the electrolyte (which causes harmful Mn precipitation on the negative electrode).
Data Source
Figure 1
AI summary
A positive electrode active material, an electrochemical device, and an electronic apparatus are provided. The positive electrode active material includes a secondary particle. An inner side of the secondary particle includes first lithium manganese iron phosphate in a form of a primary particle, and an outer side of the secondary particle includes second lithium manganese iron phosphate in the form of the primary particle. A general chemical formula of the first lithium manganese iron phosphate is LixMnaFe1-a-a'M1a'PO4, 0.9≤x≤1.10, 0.4≤a≤0.9, and 0.001≤a'≤0.02, and a general chemical formula of the second lithium manganese iron phosphate in the form of the primary particle is LiyMnbFe1-b-b'M2b'PO4, 0.9≤y≤1.10, 0<b≤0.6, and 0.001≤b'≤0.02, where a > b, M1 and M2 are each one or more of Mg, Ti, V, Ni, Co, and Al. An area ratio (S) of the first lithium manganese iron phosphate to the second lithium manganese iron phosphate satisfies S≥(0.4-b)/(a-0.4).