Dual-Size Single-Crystal Cathode Material for Higher Packed Density
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Solution Overview
Problem
The packed density of single-crystalline Li—Ni—Mn—Co or Li—Ni—Co—Al oxide positive electrode active materials in lithium-ion rechargeable batteries is relatively low due to porosity between particles, leading to a larger volume occupation.
Innovation Solution
A positive electrode active material comprising a mixture of two single-crystalline lithium transition metal oxide powders with different median particle sizes, where one powder constitutes 3 μm to 15 μm and the other 0.5 μm to 3 μm, and their weight fraction ratio is between 5 wt.% and 40 wt.%, enhancing the pressed density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-crystalline Li-Ni-Mn-Co or Li-Ni-Co-Al oxide particles are used as positive electrode active material, then mechanical strength and cycle stability are improved, but packed density decreases due to porosity between particles
Solution Approach 1:
The patent applies the nesting principle by forming a core-shell structure where single-crystalline particles (core) are coated with amorphous material (shell). The amorphous coating fills the porosity between crystalline particles, nesting the beneficial mechanical strength of single crystals with the density-enhancing properties of amorphous material. This resolves the contradiction by maintaining cycle stability from the single-crystalline core while improving packed density through the amorphous shell that reduces inter-particle porosity.
Solution Approach 2:
The patent employs composite materials by combining single-crystalline lithium transition metal oxide with amorphous coating material to create a hybrid positive electrode active material. The composite structure integrates the high mechanical strength and electrochemical stability of single crystals with the density-enhancing and porosity-reducing properties of amorphous material, thereby simultaneously achieving both improved cycle stability and higher packed density.
2Strength
If single-crystalline particles with larger size are used, then mechanical strength increases, but volume occupation increases due to porosity
Solution Approach 1:
The amorphous material is nested around the single-crystalline particles, forming a compact core-shell structure. The amorphous shell fills the void spaces between larger crystalline particles, effectively reducing the overall volume occupation while preserving the mechanical strength benefits of the single-crystalline core structure.
Solution Approach 2:
The patent changes the physical and chemical parameters of the particle structure by creating a dual-phase composite with distinct crystalline and amorphous regions. The amorphous phase has different packing characteristics that reduce porosity, while the crystalline phase maintains mechanical strength. This parameter change in structural organization resolves the volume occupation issue without sacrificing strength.
Data Source
AI summary
The present invention provides a positive electrode active material for lithium-ion secondary batteries, comprising: (i) a first lithium transition metal oxide, comprising single-crystalline particles having a median particle size D50A of between 3 μm and 15 μm, as determined by laser particle size analysis, and (ii) a second lithium transition metal oxide, comprising single-crystalline particles having a median particle size D50B of between 0.5 μm and 3 μm, as determined by laser particle size analysis, wherein a weight fraction φB of said second lithium transition metal oxide with respect to the total weight of said positive electrode active material is between 5 wt. % and 40 wt. %.