Lithium Transition Metal Composite Oxide High-Rate Discharge
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Solution Overview
Problem
Lithium secondary batteries using 'lithium-excess-type' active materials face insufficient high-rate discharge performance despite having higher discharge capacity compared to 'LiMeO2-type' materials.
Innovation Solution
A lithium transition metal composite oxide with an α-NaFeO2-type crystal structure, represented by Li1+α Me1-α O2, where Me includes Co, Ni, and Mn, and the molar ratio of Li to Me is between 1.25 and 1.4, containing 1900 to 6000 ppm of Na, is developed. This composite oxide is synthesized using a hydroxide precursor with a sodium compound added during the sintering process to enhance high-rate discharge performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-excess-type active material (Li/Me > 1) is used, then discharge capacity is improved, but high-rate discharge performance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Li/Me ratio within 1.05-1.20 and limiting Na content to 100-5000 ppm within the lithium-excess-type active material. This optimization of compositional parameters enables the material to achieve both high discharge capacity (200 mAh/g or more) and improved high-rate discharge performance, resolving the contradiction between quantity of substance and productivity.
2Productivity
If Na content is increased to improve high-rate discharge performance, then high-rate discharge performance is improved, but crystal structure stability may deteriorate
Solution Approach 1:
The patent optimizes the Na content parameter within a specific range of 100-5000 ppm in the lithium-excess-type active material. This controlled parameter change allows the material to benefit from Na's contribution to high-rate discharge performance while maintaining crystal structure stability through the upper limit constraint, thus resolving the contradiction between productivity and stability.
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 resulting lithium secondary battery exhibits high discharge capacity and improved high-rate discharge performance, with a 50% particle size of 5 µm or less, achieving discharge capacities of 200 mAh/g or more even at high charge rates.
Implementation Method 1
This composite oxide is synthesized using a hydroxide precursor with a sodium compound added during the sintering process
Data Source
AI summary
The positive active material for a lithium secondary battery includes a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure and represented by the composition formula of Li1+αMe1-αO2 (Me is a transition metal including Co, Ni and Mn and α > 0). The positive active material contains Na in an amount of no less than 1900 ppm and no more than 8000 ppm, and has a 50% particle size (D50) of 5 µm or less in particle size distribution measurement. There is provided a method for production of the positive active material, wherein a precursor for synthesis of the lithium transition metal composite oxide is a hydroxide of a transition metal including Co, Ni and Mn.