Lithium Secondary Battery Positive Electrode Active Material Crystallite Ratio
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Solution Overview
Problem
Conventional lithium secondary batteries using lithium-containing composite metal oxides as positive electrode active materials struggle to achieve high initial coulombic efficiency, which is crucial for maintaining capacity and performance over cycles.
Innovation Solution
A positive electrode active material with a specific crystallite size ratio (α/β) of 1 to 1.75, a composition of Li[Li x (Ni a Co b Mn c M d ) 1-x ]O 2, and a hexagonal or monoclinic crystal structure, where x, a, b, c, and d are within defined ranges, enhancing the isotropic morphology and reducing volume change during charge/discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lithium-containing composite metal oxide is used as positive electrode active material, then the battery can be manufactured with standard materials, but the initial coulombic efficiency is insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the crystallite size ratio (α/β) to be 1 to 1.75, where α is the crystallite size within 2θ = 18.7 ± 1° and β is the crystallite size within 2θ = 44.6 ± 1°. This specific parameter control of the crystal morphology significantly improves initial coulombic efficiency while maintaining manufacturability through established synthesis methods
Solution Approach 2:
The patent uses composite materials by combining multiple transition metals (Ni, Co, Mn, and optionally Fe, Cr, Ti, Mg, Al, or Zr) in a lithium-containing composite oxide structure. This composite approach optimizes both the initial coulombic efficiency and structural stability, resolving the contradiction between performance and ease of manufacture
2Reliability
If the crystallite size ratio (α/β) is controlled to 1 to 1.75, then the initial coulombic efficiency is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent transforms the manufacturing challenge by identifying the crystallite size ratio (α/β) as the critical parameter to control within 1 to 1.75. By focusing on this ratio rather than absolute crystallite sizes, the patent improves initial coulombic efficiency while providing a clear, measurable target for quality control in manufacturing
Solution Approach 2:
The patent replaces direct mechanical control of crystallite growth with chemical composition control. By adjusting the metal ratios (Ni:Co:Mn:Fe/Cr/Ti/Mg/Al/Zr) in the composite oxide, the crystallite size ratio is indirectly controlled, reducing the need for precise mechanical or physical processing parameters
3Use of energy by moving object
If high nickel content is used to increase capacity, then the energy density is improved, but the thermal stability deteriorates
Solution Approach 1:
The patent uses composite materials by combining Ni (for high capacity) with Co, Mn, and stabilizing metals (Fe, Cr, Ti, Mg, Al, or Zr) in specific ratios. This composite structure maintains high energy density from the nickel content while the other metals provide thermal stability, resolving the contradiction between energy density and thermal stability
Solution Approach 2:
The patent applies local quality by distributing different metal elements in specific positions within the layered oxide structure. The stabilizing metals are incorporated into the transition metal layer to provide local thermal stability while the nickel content maintains high capacity, achieving both high energy density and thermal stability simultaneously
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
This configuration results in a lithium secondary battery with improved initial coulombic efficiency, cycle performance, and thermal stability, making it suitable for automotive applications.
Implementation Method 1
crystallite size α is within a peak region of 2θ = 18.7 ± 1° and the crystallite size β is within a peak region of 2θ = 44.6 ± 1°, each determined by a powder X-ray diffraction measurement using Cu-Ka ray
Data Source
Figure 1A~1B
Figure 2A~2B
AI summary
A positive electrode active material, which has a crystallite size α/crystallite size β ratio (α/β) of 1 to 1.75 or less, wherein the crystallite size α is within a peak region of 2θ = 18.7 ± 1° and the crystallite size β is within a peak region of 2θ = 44.6 ± 1°, each determined by a powder X-ray diffraction measurement using Cu-Kα ray, and has a composition represented by formula (I) below: Li[Lix(NiaCobMncMd)1-x]O2 (I) wherein 0 ≦ x ≦ 0.2, 0.3 < a < 0.7, 0 < b < 0.4, 0 < c < 0.4, 0 ≦ d < 0. 1, a + b + c + d = 1, and M is at least one metal selected from the group consisting of Fe, Cr, Ti, Mg, Al and Zr.