Core-Shell LiMnPO4 Cathode Material for Low Mn Dissolution
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Solution Overview
Problem
Lithium manganese phosphate positive electrode active materials in secondary batteries are prone to Li/Mn antisite defects and severe manganese dissolution during charge and discharge, leading to poor safety performance, cycling performance, and capacity retention.
Innovation Solution
A positive electrode active material with a core-shell structure is developed, where the core includes LiMnPO4 doped with specific elements and coated with a first layer of crystalline pyrophosphate and a second layer of carbon, reducing Li/Mn antisite defects and manganese dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium manganese phosphate is used as positive electrode active material, then the battery can achieve basic energy storage function, but Li/Mn antisite defects and severe manganese dissolution occur during charge and discharge, leading to poor safety performance and cycling performance
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core maintains the original lithium manganese phosphate composition while the shell provides protective functionality. The shell layer is specifically designed with controlled thickness (5-50 nm) and composition to locally address the manganese dissolution problem at the surface, while preserving the bulk material's electrochemical properties. This local modification approach resolves the contradiction by concentrating the protective function where it is most needed (at the electrode-electrolyte interface) without compromising the overall capacity.
Solution Approach 2:
The patent employs composite materials by combining lithium manganese phosphate with other materials to form a core-shell structure. The shell layer comprises composite composition including metal oxides, metal phosphates, or carbon materials coated on the lithium manganese phosphate core. This composite structure synergistically combines the high capacity of lithium manganese phosphate with the stability and protective properties of the shell material, effectively suppressing manganese dissolution and antisite defects while maintaining good electrochemical performance.
2Reliability
If doping elements are added to lithium manganese phosphate, then Li/Mn antisite defects are reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies preliminary action by incorporating doping elements during the initial synthesis of lithium manganese phosphate rather than attempting post-synthesis modification. The doping elements (such as Ni, Co, Mn, Zn, Cu, Li, or their combinations) are introduced in the precursor mixture before solid-state reaction or other synthesis methods. This preliminary incorporation ensures uniform distribution of doping elements throughout the crystal structure, effectively reducing Li/Mn antisite defects from the outset and simplifying the overall manufacturing process by avoiding complex post-processing steps.
3Reliability
If shell coating is applied to reduce manganese dissolution, then cycling performance is improved, but the impedance may increase and lithium ion transport may be hindered
Solution Approach 1:
The patent applies porous materials by designing the shell layer with controlled porosity and nanostructure that allows efficient lithium ion diffusion while providing protective functionality. The shell layer's porous structure or nanoscale morphology creates multiple diffusion pathways for lithium ions, reducing transport resistance despite the presence of the coating. This approach resolves the contradiction by maintaining ion transport efficiency while achieving the protective effect against manganese dissolution and improving cycling performance.
Solution Approach 2:
The patent employs parameter changes by carefully optimizing the shell layer thickness (5-50 nm), composition ratios, and crystalline structure to balance protection and ion transport. By adjusting these parameters, the shell layer provides sufficient protection against manganese dissolution while maintaining adequate lithium ion conductivity. The specific parameter ranges are optimized to ensure that the protective function does not come at the cost of excessive impedance, thus resolving the contradiction between cycling performance improvement and ion transport resistance.
Data Source
AI summary
Provided are a positive electrode active material with a core-shell structure, a preparation method of positive electrode active material, a positive electrode plate, a secondary battery, a battery module, a battery pack, and an electric apparatus. The positive electrode active material includes a core containing LimAxMn1-yByP1-zCzO4-nDn, a first coating layer covering the core and containing a crystalline pyrophosphate MaP2O7 and an oxide M′bOc, and a second coating layer covering the first coating layer. The positive electrode active material in this application can reduce the generation of Li/Mn antisite defects, reduce the dissolution of manganese, and decrease the lattice change rate, increasing the capacity of the secondary battery and improving the cycling performance, high-temperature storage performance, and safety performance of the secondary battery.