LiFePO4 Cathode Material Synthesis via Polymer Carbonization
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Solution Overview
Problem
Lithium-ion secondary batteries using LiFePO4 as a positive electrode active material face challenges in achieving sufficient electronic and ionic conductivities, resulting in limited discharge capacity at high discharge current densities.
Innovation Solution
A method involving the polymerization of a mixture containing Fe, Li, PO4 ions, hydroxy acid, and polyol, with a specific molar ratio of polyol to hydroxy acid, followed by heating to produce LiFePO4 active material particles with a crystallite size of 30 to 99 nm and carbon support, enhancing ionic and electronic conductivities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiFePO4 is used as positive electrode active material, then safety is improved, but electronic and ionic conductivities deteriorate
Solution Approach 1:
The patent changes the crystallite size parameter of LiFePO4 to 30-99 nm range, which fundamentally alters the electronic and ionic conductivity characteristics. This parameter change enables sufficient discharge capacity at high discharge current densities while maintaining the safety advantages of LiFePO4
Solution Approach 2:
The patent creates a composite structure where LiFePO4 crystallites are embedded in a carbon matrix. This composite material combines the safety and electrochemical activity of LiFePO4 with the high conductivity of carbon, resolving the contradiction between safety and conductivity
2Reliability
If LiFePO4 is used as positive electrode active material, then safety is improved, but discharge capacity at high discharge current density deteriorates
Solution Approach 1:
The patent changes the crystallite size parameter to 30-99 nm, which dramatically improves the discharge capacity at high discharge current densities. The reduced crystallite size shortens ion diffusion paths and increases surface area, enabling high productivity while maintaining safety
Solution Approach 2:
The carbon-coated LiFePO4 composite structure enables high discharge capacity at high current densities by providing efficient electron transport pathways through the carbon matrix while maintaining the safe electrochemical behavior of LiFePO4
3Loss of energy
If crystallite size is reduced to 30-99 nm, then ionic conductivity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses polyol and hydroxy acid as intermediary agents that control crystallite growth during synthesis. These intermediaries regulate the formation process to achieve the target crystallite size range of 30-99 nm, making precise size control achievable
Solution Approach 2:
The patent employs specific molar ratios of polyol to hydroxy acid (1.3:1 to 16:1) as controllable parameters that directly influence crystallite size. By adjusting these chemical parameters, precise control over the 30-99 nm crystallite size range is achieved
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 method yields active material particles with improved ionic and electronic conductivities, enabling a lithium-ion secondary battery to achieve a sufficient discharge capacity at high discharge current densities.
Implementation Method 1
the hydroxy acid is coordinated to the Fe, Li, or PO4 ion, so as to form their complex, thereby allowing the Fe, Li, and PO4 ions to disperse into the polyol
Implementation Method 2
polymerizing the polyhydric alcohol and polycarboxylic acid by dehydration condensation
Implementation Method 3
polymerizing the polyhydric alcohol and polycarboxylic acid by dehydration condensation
Implementation Method 4
heating thus obtained polymer
Implementation Method 5
heating the polymer, so as to yield an active material containing an active material particle and carbon
Implementation Method 6
Li ion diffusion paths in the crystal structure of LiFePO4 exist along the b axis alone, Li ions in an electrolytic solution can easily diffuse into crystal structures of active material particles
Data Source
AI summary
A method of manufacturing an active material having a sufficient discharge capacity at a high discharge current density, an active material obtained thereby, an electrode using the same, and a lithium-ion secondary battery equipped therewith are provided. The method of manufacturing an active material comprises a step of polymerizing a mixture containing an Fe ion, an Li ion, a PO4 ion, a hydroxy acid, and a polyol, the mixture containing the polyol by a molar ratio 1.3 to 16 times that of the hydroxy acid, so as to yield a polymer; and a step of heating the polymer, so as to yield an active material containing an active material particle and carbon. The active material particle is mainly composed of LiFePO4.