Graphite Anode Micropore Control for Long-Cycle Li-Ion Batteries
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Solution Overview
Problem
Existing non-aqueous electrolyte secondary batteries with graphite particles as negative electrode active materials face deterioration in long-term charge-discharge cycle performance due to side reactions with the non-aqueous electrolyte, particularly at micropores smaller than 2 nm, which are not effectively addressed by current technologies that only test up to 50 cycles.
Innovation Solution
The use of graphite particles with a volume of micropores 2 nm or less, and a mass of 0.3 mm3/g or less, as determined by a nitrogen adsorption isotherm using the DFT method, as the negative electrode active material, helps suppress side reactions and improve long-term charge-discharge cycle characteristics by minimizing exposure of the basal portions of graphite crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If graphite particles with larger micropore volume are used to enhance high-rate characteristics, then high-rate performance is improved, but long-term cycle characteristics deteriorate due to increased side reactions with non-aqueous electrolyte
Solution Approach 1:
The patent applies parameter changes by precisely controlling the micropore volume of graphite particles to be 0.003 cm³/g or less, as determined by nitrogen adsorption isotherm measurement according to the HK method. This parameter optimization resolves the contradiction by finding the optimal balance point where high-rate characteristics are maintained while side reactions with non-aqueous electrolyte are suppressed, thereby improving long-term cycle characteristics.
2Speed
If micropores with size of 1 nm or less are increased to improve high-rate discharge characteristics, then discharge rate is enhanced, but capacity retention after long-term cycles decreases
Solution Approach 1:
The patent applies parameter changes by controlling the volume of micropores with size of 1 nm or less to be within a specific range (0.0010 to 0.0020 cm³/g according to HK method). This optimized parameter range allows sufficient high-rate discharge performance while minimizing harmful side reactions that would otherwise reduce capacity retention after long-term cycling.
3Productivity
If graphite particles are subjected to covering treatment for practical use, then high-rate characteristics are enhanced, but long-term stability deteriorates due to exposure of basal portions
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different regions of graphite particles. The covering treatment is selectively applied to edge portions while controlling micropore formation in basal portions. This localized approach enhances high-rate characteristics through edge portion modification while maintaining long-term stability by preventing harmful side reactions at basal portions.
Solution Approach 2:
The patent applies parameter changes by controlling the volume ratio of edge portions to total particle volume to be within a specific range. This parameter optimization ensures that covering treatment of edge portions provides sufficient high-rate performance while limiting the overall micropore volume to prevent long-term stability deterioration.
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 approach significantly enhances the long-term cycle characteristics of non-aqueous electrolyte secondary batteries by reducing side reactions, as evidenced by higher capacity retention rates after 500 charge-discharge cycles compared to batteries with graphite particles having larger volumes of micropores.
Implementation Method 1
a volume per mass of micropores having a micropore size of 2 nm or less, of 0.3 mm3/g or less, as determined from a nitrogen adsorption isotherm
Data Source
AI summary
A nonaqueous electrolyte secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode contains, as a negative electrode active material, graphite particles having a volume per mass, of pores having a diameter of 2 nm or less determined by the DFT method from nitrogen adsorption isotherm, of 0.3 mm3/g or less.