Lithium Composite Oxide Particle Strength Tuning for Cycle Retention
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Solution Overview
Problem
Lithium metal composite oxides used in lithium secondary batteries are prone to particle cracking during the electrode pressing step, leading to voids and contact failures, which decrease the cycle characteristics of the battery.
Innovation Solution
A lithium metal composite oxide with specific particle size and strength distributions, where first particles have a diameter less than or equal to 50% cumulative volume D50 and second particles exceed D50, with controlled average and standard deviations of particle strength, is used to prevent cracking and enhance contact between particles and conductive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If particles having a small particle diameter are used, then the specific surface area increases and lithium ion reaction characteristics improve, but the particles crack in the electrode pressing step to generate voids
Solution Approach 1:
The invention changes the particle strength parameter by controlling the standard deviation of particle strength (σ) to be 5 MPa or less. This parameter control ensures that particles with small diameters (high specific surface area) maintain sufficient strength during electrode pressing, preventing cracking and void formation while preserving the benefits of high surface area for lithium ion reaction.
2Strength
If the average particle strength is increased to prevent cracking, then the particle durability improves, but the distribution of particle strength becomes wider making control difficult
Solution Approach 1:
The invention identifies and controls the standard deviation of particle strength (σ) as the key parameter. By maintaining σ at 5 MPa or less, the invention achieves a narrow particle strength distribution where particles exhibit uniform strength characteristics. This allows for reliable crack prevention during electrode pressing while maintaining precise manufacturing control.
3Reliability
If particles are pressed to improve contact between positive electrode and active material, then the contact characteristics improve, but particles crack and voids are generated
Solution Approach 1:
The invention changes the particle strength uniformity parameter (standard deviation σ ≤ 5 MPa) to enable particles to withstand electrode pressing without cracking. This parameter control ensures that particles maintain their integrity during the pressing process, achieving good contact between the positive electrode and active material while preventing void formation.
Data Source
AI summary
An object of the present invention is to provide a lithium metal composite oxide, when used as a positive electrode active material for a lithium secondary battery, capable of obtaining a lithium secondary battery having a high cycle retention rate, and a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery in which the lithium metal composite oxide is used. This lithium metal composite oxide is a particulate lithium metal composite oxide, comprising first particles having a particle diameter equal to or less than a 50% cumulative volume particle size D50 of the lithium metal composite oxide and second particles having a particle diameter exceeding the D50, in which the D50 is 2 to 20 μm, an average particle strength PS of the first particles is larger than an average particle strength PB of the second particles, and a standard deviation σS of the particle strength of the first particles is larger than a standard deviation σB of the particle strength of the second particles.