Co-Doped LiMnFePO4 Cathode With Carbon Shell for Better Cycling
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Solution Overview
Problem
Lithium manganese iron phosphate cathode materials suffer from poor cycle performance, rate performance, and processing performance compared to lithium iron phosphate cathode materials, limiting their potential in battery applications.
Innovation Solution
A multi-site co-doped lithium manganese iron phosphate composite material with a core-shell structure, where the core is doped with Mg, V, Al, Ba, Ti, Ca, or Zn at the iron site, B and/or Si at the phosphorus site, and F, Cl, or Br at the oxygen site, and a carbon shell layer is coated on the surface, enhancing structural stability, ionic conductivity, and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium manganese iron phosphate cathode materials are used to achieve higher voltage platform and theoretical energy density, then the voltage platform reaches 3.8V to 4.1V and theoretical energy density increases by 10% to 20% compared to lithium iron phosphate, but the cycle performance becomes shorter, rate performance deteriorates, and processing performance worsens
Solution Approach 1:
The patent applies multi-site co-doping with different elements at specific crystallographic sites (A-site: Mg, V, Al, Ba, Ti, Ca, Zn; B-site: B, Si; C-site: F, Cl, Br) to locally optimize the lattice structure. This targeted local modification stabilizes the crystal structure during cycling while maintaining the high voltage platform, resolving the contradiction between energy density and cycle performance
Solution Approach 2:
The patent creates a composite doped structure combining multiple dopant elements at different sites within the LiMn0.6Fe0.4-xAyP1-yDyO4-zEz framework. This composite approach synergistically improves structural stability, electrical conductivity, and ion diffusion, thereby enhancing cycle performance while preserving the high energy density characteristics
2Use of energy by moving object
If lithium manganese iron phosphate cathode materials are used to achieve higher voltage platform and theoretical energy density, then the voltage platform reaches 3.8V to 4.1V and theoretical energy density increases by 10% to 20% compared to lithium iron phosphate, but the rate performance becomes poorer
Solution Approach 1:
The patent introduces dopant elements (particularly B and Si at phosphorus sites, and F/Cl/Br at oxygen sites) that locally enhance the electronic conductivity and facilitate lithium ion diffusion pathways. This local optimization enables faster charge-discharge rates while maintaining the high voltage platform and energy density
Solution Approach 2:
The patent modifies the crystal lattice parameters through multi-site doping, changing the unit cell dimensions and bonding characteristics. These parameter changes improve the electrical conductivity and ion transport properties, enabling better rate performance while preserving the high energy density advantage
3Use of energy by moving object
If lithium manganese iron phosphate cathode materials are used to achieve higher voltage platform and theoretical energy density, then the voltage platform reaches 3.8V to 4.1V and theoretical energy density increases by 10% to 20% compared to lithium iron phosphate, but the processing performance becomes poorer
Solution Approach 1:
The patent incorporates dopant elements into the precursor mixture before sintering, performing preliminary doping action during the preparation stage. This approach simplifies the manufacturing process by combining multiple doping steps into a single synthesis operation, improving processing performance while achieving the desired high energy density material
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 composite material improves specific capacity, cycle performance, and rate capability of secondary batteries by stabilizing the lattice structure, reducing polarization, and facilitating Li+ diffusion, while the carbon shell layer ensures small particle size and high compacted density, enhancing energy density and cycle stability.
Implementation Method 1
adding a first organic carbon source and mixing for reaction, drying a resulting mixture and crushing, whereby obtaining a precursor powder
Implementation Method 2
a carbon shell layer, which is coated on an outer surface of the core
Data Source
Figure 1
AI summary
The present application discloses a multi-site co-doped lithium manganese iron phosphate composite material and a preparation method thereof, and a secondary battery. The multi-site co-doped lithium manganese iron phosphate composite material includes: a core, and a carbon shell coated on an outer surface of the core. The core includes an active material having a general chemical formula represented by LiMn0.6Fe0.4-xAxP1-yDyO4-zEz, A includes at least one of Mg, V, Al, Ba, Ti, Ca, and Zn; D includes B and/or Si; E includes at least one of F, Cl, and Br; 0 < x≤0.2, 0<y<1, 0<z<4. By co-doping the iron, phosphorus, and oxygen sites of the lithium manganese iron phosphate material, the specific capacity, structural stability, and ionic conductivity of the material are improved, and the polarization is reduced. The carbon shell improves the electrical conductivity of the material, limits the particle size of the composite material, and the particle size is small, thereby improving the compacted density of the composite material.