Si-Graphite Negative Electrode Uniformity for Battery Cycle Life
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with large capacity and area face challenges in achieving sufficient charge and discharge cycle characteristics due to non-uniform distribution and reaction rates of Si and carbon materials in the negative electrode active material layer, leading to degradation and reduced cycle durability.
Innovation Solution
Controlling the ratio of battery volume to rated capacity and varying the dispersibility and coating amount of Si and carbon materials within specific ranges in the negative electrode active material layer to ensure uniform expansion and reaction across the battery plane, thereby maintaining excellent cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si material is used to increase capacity, then energy density is improved, but cycle lifetime deteriorates due to large volumetric expansion
Solution Approach 1:
The patent applies local quality by creating a composite negative electrode structure where Si material particles are distributed within a graphite matrix. The graphite provides structural stability while Si provides high capacity, with each material performing its optimal function in its specific location. This resolves the contradiction by allowing Si to contribute to capacity without suffering from its own volumetric expansion issues alone.
Solution Approach 2:
The patent uses composite materials by combining Si material with graphite to form a negative electrode active material layer. The composite structure allows Si to provide high theoretical capacity (3600 mAh/g) while graphite provides structural stability and small expansion (1.2 times), thereby achieving both high capacity and good cycle lifetime simultaneously.
2Quantity of substance
If multiple negative electrode active materials are mixed to achieve high capacity, then energy density is improved, but manufacturing precision deteriorates due to non-uniform distribution
Solution Approach 1:
The patent applies preliminary action by pre-mixing the Si material and graphite in specific proportions (0.1-40 mass% Si, 58-97.9 mass% graphite) before electrode fabrication. This predetermined uniform distribution ensures that when the electrode is manufactured, the materials are already evenly dispersed, preventing local concentration variations that would lead to non-uniform expansion and reaction rates.
Solution Approach 2:
The patent achieves homogeneity by carefully controlling the mixing ratio and distribution of Si material and graphite in the negative electrode active material layer. The patent specifies that the content of Si material should be 0.1-40 mass% and graphite 58-97.9 mass%, ensuring a homogeneous composite structure that prevents local non-uniformity and maintains consistent electrochemical performance across the entire electrode.
3Quantity of substance
If battery size is increased for vehicle application, then capacity is improved, but cycle characteristics deteriorate due to amplified non-uniformity
Solution Approach 1:
The patent applies local quality by ensuring that the composite structure of Si particles within graphite matrix is maintained uniformly throughout the entire large-area negative electrode. This local composite structure prevents local non-uniform expansion even in large batteries, as each local region has the same stable Si-graphite configuration, thereby maintaining good cycle characteristics despite the large battery size.
Solution Approach 2:
The patent achieves homogeneity across the entire battery by controlling the uniform distribution of Si and graphite materials throughout the negative electrode active material layer. This homogeneous composition ensures that expansion and reaction rates are uniform across the entire battery plane, preventing local non-uniformity from amplifying as battery size increases, thus maintaining excellent cycle characteristics in large-capacity batteries.
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 ensures uniform reaction and reduced non-uniformity in the negative electrode active material layer, enhancing the cycle durability and capacity retention of large-sized batteries by minimizing variations in expansion and reactivity across the battery plane.
Implementation Method 1
a material which is alloyed with Li in the negative electrode active material has improved energy density
Implementation Method 2
a Si material absorbs and desorbs 3.75 mol of lithium ion per mol in charging and discharging
Implementation Method 3
the battery is charged and discharged by absorbing lithium ions into graphite crystals and desorbing the lithium ions therefrom
Implementation Method 4
volumetric expansion of a graphite material in the case of absorbing Li ions is about 1.2 times
Data Source
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Figure 3(a)~3(b)
AI summary
Provided is a means for achieving sufficient charge and discharge cycle characteristics in a non-aqueous electrolyte secondary battery having a large capacity and a large area even when a mixture of a high-capacity Si material and a carbon material having small expansion is used as a negative electrode active material. A non-aqueous electrolyte secondary battery which has a ratio value of a battery volume (a product of a projected area of the battery including a battery outer casing body and a thickness of the battery) to a rated capacity of 10 cm3/Ah or less and a rated capacity of 3 Ah or more, the battery including: a power generating element including a positive electrode comprising a positive electrode active material layer containing a positive electrode active material formed on a surface of a positive electrode current collector, a negative electrode comprising a negative electrode active material layer containing a negative electrode active material formed on a surface of a negative electrode current collector, and a separator, wherein the negative electrode active material layer contains a negative electrode active material represented by the following Formula (1): α (Si material) + β (carbon material) (1) (in the formula, the Si material is one or two or more kinds selected from the group consisting of SiOx that is a mixture of amorphous SiO2 particles and Si particles (x represents the number of oxygen atoms satisfying an atomic valence of Si) and a Si-containing alloy; the carbon material is one or two or more kinds selected from the group consisting of graphite, non-graphitizable carbon, and amorphous carbon; α and β represent % by mass of each component in the negative electrode active material layer; and 80 ≤ α + β ≤ 98, 0.1 ≤ α ≤ 40, and 58 ≤ β ≤ 97.9 are satisfied), and when area proportions (%) of the Si material and the carbon material in an area of a field of view of each image of cross-sections of the negative electrode active material layer in a case where a plurality of arbitrary places is selected in a plane of the negative electrode active material layer are designated as S (%) and (100 - S) (%), respectively, a difference between a maximum value and a minimum value of S is within 5%.