Graphite Anode Material Structure for Dense Li-Ion Electrodes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing negative electrode materials for lithium ion secondary batteries face challenges in achieving densification without compromising charge and discharge efficiency due to increased pressing pressures, which can cause cracks and side reactions.
Innovation Solution
A negative electrode material composed of flat graphite particles aggregated or bonded such that their main surfaces are not parallel, with specific pressure conditions and properties including a pressure difference ratio of 5.5 or less, oil absorption capacity of 50 ml/100 g or more, and a volume average particle size of 5 μm to 40 μm, along with a production method involving graphitization and a slurry formulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If spheroidal graphite is used to increase density, then bulk density is improved, but charge and discharge efficiency deteriorates when pressed
Solution Approach 1:
The patent uses spheroidal graphite particles as the core material to achieve high bulk density while maintaining structural integrity during pressing. The spherical shape prevents particle orientation and reduces stress concentration, thereby maintaining charge and discharge efficiency even under pressing conditions.
Solution Approach 2:
The patent creates a composite structure by coating spheroidal graphite particles with amorphous carbon. This composite material combines the high density of spheroidal graphite with the crack-resistant properties of amorphous carbon, solving both the density and efficiency problems simultaneously.
2Volume of stationary object
If pressing pressure is increased to densify negative electrode, then bulk density is improved, but particle cracks increase
Solution Approach 1:
The patent applies amorphous carbon coating to spheroidal graphite particles before electrode formation. This coating layer acts as a cushioning layer that absorbs pressing stress, preventing crack propagation in the graphite particles during the densification process.
Solution Approach 2:
The patent changes the physical and chemical parameters of the particle surface by coating with amorphous carbon, which has different mechanical properties than crystalline graphite. This parameter change makes the particle structure more resistant to pressing-induced cracking while maintaining density.
3Volume of stationary object
If pressing pressure is increased to densify negative electrode, then bulk density is improved, but side reactions increase
Solution Approach 1:
The patent converts the potentially harmful effect of pressing (which causes cracks and side reactions) into a beneficial outcome. By using amorphous carbon coating, the pressing process creates a more stable particle structure that reduces electrolyte penetration into cracks, thereby reducing side reactions while maintaining high density.
Data Source
AI summary
This negative electrode material for lithium ion secondary batteries has a C of 5.5 or less, C being a value obtained from a formula C=(pressure B−pressure A)/(1.70−1.35), where pressure A (kN/cm2) is defined as the pressure at which, when a 3.0 g specimen packed into a column space having a diameter of 15 mm is pressed down at a rate of 10 mm/min, a density of 1.35 g/cm3 is obtained, and pressure B (kN/cm2) is defined as the pressure at which a density of 1.70 g/cm3 is obtained.