Lithium Transition Metal Composite Oxide for Suppressing Particle Cracking
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining charge-discharge cycle performance due to cracks in positive active material particles caused by lithium ion expansion and shrinkage, particularly in materials like LiNi1/3Co1/3Mn1/3O2, which experience crystal anisotropy and structural changes during charging and discharging.
Innovation Solution
A lithium transition metal composite oxide with an α-NaFeO2 structure is developed, incorporating a specific ratio of FWHM(003)/FWHM(104) and containing fluorine or phosphorus on its surface, along with a sintering aid like lithium fluoride or phosphate, to enhance structural stability and reduce crystal anisotropy, thereby suppressing particle cracking and improving cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiNi1/3Co1/3Mn1/3O2 is used as positive active material to achieve higher discharge capacity (150 to 180 mAh/g), then capacity is improved, but particle cracking occurs due to crystal anisotropy and structural changes during charge-discharge cycles, deteriorating cycle performance
Solution Approach 1:
The patent controls the ratio of full width at half maximum FWHM(003)/FWHM(104) within 1.05 to 1.25 and the c/a ratio within 0.285 to 0.310 to optimize crystal structure parameters. This reduces crystal anisotropy and suppresses particle cracking during charge-discharge cycles, improving cycle performance while maintaining high discharge capacity
Solution Approach 2:
The patent uses composite lithium transition metal oxides containing multiple transition metals (Ni, Co, Mn) in specific ratios, combined with controlled crystal structure parameters. This composite approach achieves high discharge capacity while the optimized structure reduces cracking and improves cycle stability
2Adaptability or versatility
If Mn content in transition metal is increased to utilize abundant earth resources, then material availability is improved, but structure changes to spinel type when molar ratio (Mn/Me) exceeds 0.5, causing poor cycle performance
Solution Approach 1:
The patent optimizes the Mn content parameter by controlling the molar ratio (Mn/Me) to be 0.3 to 0.5, preventing spinel structure formation while utilizing abundant Mn resources. The controlled composition parameters maintain layered structure stability and prevent degradation during cycling
3Use of energy by moving object
If positive active material particles undergo lithium ion expansion and shrinkage during charge-discharge, then electrochemical function is achieved, but particle cracking occurs due to repeated structural changes, reducing cycle life
Solution Approach 1:
The patent controls crystal structure parameters (FWHM ratio and c/a ratio) to reduce anisotropic expansion and shrinkage during lithium ion insertion/extraction. This minimizes mechanical stress and particle cracking, extending cycle life while maintaining electrochemical functionality
Solution Approach 2:
The optimized crystal structure with controlled FWHM ratio and c/a ratio acts as a preemptive measure to cushion against mechanical stress during charge-discharge cycles, preventing crack formation before it occurs and extending battery lifespan
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 significantly improves charge-discharge cycle performance by maintaining structural integrity and reducing particle cracking, leading to higher capacity retention and extended battery life.
Implementation Method 1
caused by lithium ion expansion and shrinkage
Implementation Method 2
in a ratio FWHM (003)/FWHM (104) of a full width at half maximum FWHM (003) for a diffraction peak at 2θ＝18.6°±1° to a full width at half maximum FWHM (104) for a diffraction peak at 2θ＝44°±1°
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Provided is a positive active material for a lithium secondary battery which is excellent in charge-discharge cycle performance and in which cracks of active material particles with charge-discharge cycles are suppressed, a method for producing the positive active material, and a lithium secondary battery obtained using the positive active material. The positive active material for a lithium secondary battery includes a lithium transition metal composite oxide having an α-NaFeO2 structure, and having a diffraction peak at 2θ = 44 ± 1° and a diffraction peak at 2θ = 18.6 ± 1° in a powder X-ray diffraction diagram using a CuKα ray. In a ratio FWHM (003)/FWHM (104) of a full width at half maximum FWHM (003) for the diffraction peak at 2θ = 18.6 ± 1° to a full width at half maximum FWHM (104) for the diffraction peak at 2θ = 44 ± 1°, a ratio of FWHM (003)/FWHM (104) in a charge state immediately after a discharge state to FWHM (003)/FWHM (104) in the discharge state is 0.72 or more.