Positive Electrode Active Material with Magnesium Doping for Cobalt Elution
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in achieving high capacity and excellent charge and discharge cycle performance, with issues such as capacity degradation and instability under high-voltage charging, particularly due to the elution of transition metals like cobalt.
Innovation Solution
A positive electrode active material composed of lithium, cobalt, magnesium, oxygen, and fluorine, with a pseudo-spinel crystal structure and specific diffraction peak positions, is developed, which inhibits cobalt elution and maintains stability during high-voltage charging, using a manufacturing method involving the mixing and heating of lithium, cobalt, and magnesium sources with fluorine, and subsequent heat treatment to distribute magnesium uniformly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high-voltage charging is used to increase battery capacity, then energy density is improved, but cobalt elution occurs causing capacity degradation and reduced reliability
Solution Approach 1:
A coating layer comprising lithium phosphate and/or lithium fluorophosphate is formed on the surface of the positive electrode active material particles. This coating layer acts as an intermediary barrier between the active material and the electrolyte, preventing cobalt elution during high-voltage charging while allowing lithium ion transport, thus maintaining both high energy density and capacity retention
Solution Approach 2:
The surface composition and structure of the positive electrode active material are modified by forming a coating layer with specific chemical composition (lithium phosphate and/or lithium fluorophosphate). This changes the surface properties to be more stable at high voltages, preventing cobalt dissolution into the electrolyte while maintaining electrochemical performance
2Use of energy by moving object
If high-voltage charging is used to increase battery capacity, then energy density is improved, but structural stability deteriorates
Solution Approach 1:
The coating layer of lithium phosphate and/or lithium fluorophosphate serves as a protective intermediary that stabilizes the crystal structure during high-voltage charging. It prevents structural degradation and phase transitions that would otherwise occur at high voltages, maintaining both structural stability and high energy density
Solution Approach 2:
A composite structure is created by combining the positive electrode active material core with a coating layer shell. This composite material approach allows the inner core to provide high capacity while the outer coating provides structural stability and chemical inertness during high-voltage operation
3Reliability
If conventional coating methods are used to prevent cobalt elution, then reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The coating layer is formed on the positive electrode active material particles before electrode fabrication. This preliminary action ensures that the protective coating is already in place during subsequent manufacturing steps, simplifying the overall process by combining coating and electrode making into a integrated sequence rather than requiring post-assembly treatments
Solution Approach 2:
The coating formation process utilizes controlled precipitation reactions by adjusting pH and adding chelating agents, which are standard chemical parameters in battery manufacturing. This approach maintains reliability improvement while using conventional manufacturing parameters rather than requiring complex new equipment or processes
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 solution provides a high-capacity lithium-ion battery with improved cycle performance and safety by preventing cobalt elution and maintaining structural stability during high-voltage charging, resulting in a reliable and efficient energy storage system.
Implementation Method 1
subsequent heat treatment to distribute magnesium uniformly
Implementation Method 2
a pseudo-spinel crystal structure and specific diffraction peak positions
Data Source
AI summary
A positive electrode active material, which has higher capacity and excellent charge and discharge cycle performance, for a lithium-ion secondary battery is provided. The positive electrode active material includes lithium, cobalt, magnesium, oxygen, and fluorine; when a pattern obtained by powder X ray diffraction using a CuKα1 ray is subjected to Rietveld analysis, the positive electrode active material has a crystal structure having a space group R-3m, a lattice constant of an a-axis is greater than 2.814×10(−10th power) m and less than 2.817×10(−10th power) m, and a lattice constant of a c-axis is greater than 14.05×10(−10th power) m and less than 14.07×10(−10th power) m; and in analysis by X-ray photoelectron spectroscopy, a relative value of a magnesium concentration is higher than or equal to 1.6 and lower than or equal to 6.0 with the cobalt concentration regarded as 1.