Si-Carbon Negative Electrode Binder Uniformity
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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-uniformity in binder distribution and interelectrode distances, leading to degradation and reduced cycle durability when using a mixture of high-capacity Si and carbon materials as negative electrode active materials.
Innovation Solution
Controlling the variation in binder dispersibility within a predetermined range in the negative electrode active material layer to ensure uniform reactivity and prevent active material desorption, thereby maintaining a stable interelectrode distance and enhancing cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si material is used as negative electrode active material to improve energy density, then capacity is improved, but cycle lifetime deteriorates due to large volumetric expansion
Solution Approach 1:
The Si material particles are embedded within a porous carbon matrix structure, creating a nested configuration where the high-capacity Si is contained within the stable carbon framework. This allows the Si to expand and contract during lithium insertion/extraction while the carbon matrix provides structural support and prevents particle disintegration, thereby maintaining cycle lifetime while achieving high capacity.
Solution Approach 2:
The invention uses a composite material consisting of Si particles combined with carbon material in a specific ratio (Si: 1-40 mass%, carbon: 60-99.9 mass%). This composite structure combines the high capacity advantage of Si with the structural stability and low expansion characteristics of carbon, resolving the contradiction between achieving high capacity and maintaining cycle lifetime.
2Quantity of substance
If mixture of Si and carbon materials is used to balance capacity and stability, then energy density is improved, but binder uniformity deteriorates leading to non-uniform reactivity
Solution Approach 1:
The invention creates local quality variations by distributing Si particles non-uniformly within the carbon matrix and binder system. The Si-rich regions provide high capacity while the carbon-rich regions provide structural stability and uniform binder distribution. This local differentiation allows the electrode to achieve both high energy density and uniform reactivity across different areas.
Solution Approach 2:
The carbon material acts as an intermediary between the Si particles and the binder system. It provides a uniform substrate for binder attachment while distributing the Si particles throughout the electrode structure. This intermediary role of carbon ensures that the binder is uniformly distributed even when Si particles are present, preventing non-uniform reactivity.
3Quantity of substance
If large capacity battery is designed for vehicle application, then energy storage is improved, but cycle characteristics deteriorate due to non-uniform binder distribution
Solution Approach 1:
The invention changes the compositional parameters of the negative electrode by precisely controlling the Si content (1-40 mass%) and carbon content (60-99.9 mass%). By adjusting these parameters, the electrode achieves optimal balance between energy storage capacity and structural stability, ensuring that even in large-capacity batteries, the binder distribution remains uniform and cycle characteristics are maintained.
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
The controlled binder dispersibility reduces non-uniform reactivity and active material loss, significantly improving the cycle durability of large-sized batteries by maintaining consistent expansion and reaction rates across the electrode plane.
Implementation Method 1
a battery using a material which is alloyed with Li in the negative electrode active material has improved energy density
Implementation Method 2
the Si material has a problem of a decrease in cycle lifetime of the electrode due to a large volumetric change of about 4 times
Data Source
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Figure 3A~3B
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 are used as an active material of a negative electrode. Provided is a non-aqueous electrolyte secondary battery which has a ratio value of a battery volume 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, in which the negative electrode active material layer contains a negative electrode active material represented by the Formula1=αSi material+βcarbon material (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 a difference between the maximum value and the minimum value of an area proportion (%) of a binder in an area of the 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 is within 10%.