Li2MnO3 Cathode Material Fluoro Doping for Crystallinity
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Solution Overview
Problem
Current lithium secondary battery cathode active materials with a layered structure, particularly those containing Li2MnO3, face challenges in achieving high capacity and simultaneously maintaining a lifespan characteristic of 90% or more and a rate capability of 80% or more due to structural instability and low electrical conductivity, especially when fired at low temperatures.
Innovation Solution
A lithium-excess lithium metal composite compound with a layered structure doped with a fluoro compound, where the FWHM value is within 0.164 to 0.185 degrees and the c-axis length is between 14.241 Å to 14.2429 Å, is used, allowing for enhanced crystallinity and lithium ion mobility, thereby improving lifespan and rate capability when fired at 800°C or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If Li2MnO3 is used to increase capacity and lifespan at high voltage, then capacity and lifespan characteristics are improved, but rate capability deteriorates due to low electrical conductivity
Solution Approach 1:
The patent uses a composite material system consisting of Li2MnO3 combined with LiMO2 (where M is Ni, Co, or Mn) in a layered structure. This composite approach allows Li2MnO3 to provide high capacity and lifespan at high voltage, while LiMO2 contributes better electrical conductivity to maintain rate capability. The synergistic combination resolves the contradiction between lifespan improvement and rate capability deterioration.
Solution Approach 2:
The patent creates a mixed structure where Li2MnO3 and LiMO2 are distributed in specific proportions and configurations within the cathode material. By optimizing the local composition and structure, the material achieves regions with high capacity characteristics (Li2MnO3-rich areas) and regions with high conductivity (LiMO2-rich areas), thereby simultaneously achieving long lifespan and good rate capability.
2Quantity of substance
If firing is performed at low temperature (700°C) to increase capacity, then capacity is increased to 240 mAh/g or more, but lifespan characteristic and rate capability are significantly reduced by approximately 70% due to reduced crystallinity
Solution Approach 1:
The patent optimizes the firing temperature parameter to a specific range (600-800°C, preferably 650-750°C) to achieve the desired balance. By precisely controlling this thermal parameter, the material develops sufficient crystallinity for structural stability and long lifespan, while avoiding excessive temperature that would reduce capacity. This parameter optimization resolves the contradiction between high capacity and long lifespan.
Solution Approach 2:
The composite structure of Li2MnO3 and LiMO2 enables the material to achieve high capacity at lower firing temperatures while maintaining structural stability. The LiMO2 component provides structural support that compensates for the reduced crystallinity at low temperatures, allowing the material to simultaneously achieve high capacity (240 mAh/g or more) and long lifespan without the severe performance degradation seen in single-phase materials.
3Quantity of substance
If Li2MnO3 content is increased to improve high voltage performance, then capacity and lifespan at high voltage are improved, but structural stability deteriorates after lithium deintercalation
Solution Approach 1:
The patent creates a composite where Li2MnO3 (providing high capacity) is combined with LiMO2 (providing structural stability). The LiMO2 component acts as a structural framework that maintains stability during lithium deintercalation, while Li2MnO3 contributes high capacity. This composite strategy resolves the contradiction between high capacity and structural stability.
Solution Approach 2:
The patent performs preliminary doping of the cathode material with elements (such as Al, Ti, or Zr) before the final firing process. This preliminary action modifies the crystal structure in advance to enhance stability, allowing the material to withstand lithium deintercalation without structural collapse, even when Li2MnO3 content is high for achieving high capacity.
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 approach enables the production of a cathode active material that exhibits high capacity, a lifespan characteristic of 90% or more, and a rate capability of 80% or more, making it suitable for high-capacity lithium secondary batteries, while maintaining structural stability and conductivity.
Implementation Method 1
doping a lithium metal composite oxide including Li2MnO3 having a layered structure containing lithium in excess with a fluoro compound and firing the oxide at low temperature
Implementation Method 2
firing the oxide at low temperature
Data Source
AI summary
The present invention relates to a cathode active material for a lithium secondary battery, a method for preparing the same, and a lithium secondary battery including the same. Provided is a cathode active material composed of a lithium-excess lithium metal composite compound including Li2MnO3 having a layered structure, and doped with a fluoro compound, wherein an FWHM (half value width) value is within a range from 0.164 degree to 0.185 degree.