Si-Graphite Negative Electrode Composition for Swelling Control
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Solution Overview
Problem
Si-containing particles in negative electrodes for nonaqueous electrolyte secondary batteries swell significantly during charge and discharge cycles, leading to potential malfunctions and reduced capacity maintenance due to increased stress and risk of cracking.
Innovation Solution
A negative electrode with a high spring constant and easy elongation properties is developed, incorporating a current collector with a negative electrode active material layer containing graphite and Si-containing particles, along with carboxymethyl cellulose, poly acrylic acid, and styrene butadiene rubber as binders, to suppress swelling and maintain capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the rigidity of the negative electrode is enhanced to decrease the swell, then the swell of the negative electrode is reduced, but the swell stress of the negative electrode active material becomes high causing cracks and reduced capacity maintenance rate
Solution Approach 1:
The patent optimizes the spring constant parameter of the negative electrode to a specific range (70-400 kN/mm) to achieve the right balance between rigidity and elasticity. This parameter change allows the electrode to resist swelling while maintaining sufficient elasticity to prevent cracks in the active material during charge-discharge cycles.
Solution Approach 2:
The negative electrode uses a composite structure combining graphite particles (0.5-5 μm) with silicon oxide particles (0.1-1 μm), where the harder graphite provides structural support and the softer silicon oxide absorbs swelling stress, creating a synergistic effect that balances rigidity and stress mitigation.
2Quantity of substance
If Si-containing particles are used as negative electrode active material to increase capacity, then the specific capacity is improved, but the swell rate during charging increases leading to electrode malfunction
Solution Approach 1:
The patent uses particles of different sizes and properties in specific proportions: graphite particles (0.5-5 μm) provide structural stability while silicon oxide particles (0.1-1 μm) provide high capacity. The size differentiation and specific ratio (graphite 70-95 wt%, silicon oxide 5-30 wt%) create local quality variations that balance capacity and swelling resistance.
Solution Approach 2:
The graphite particles act as a counterweight to the swelling tendency of silicon oxide particles. The harder, more rigid graphite structure compensates for the swelling stress generated by silicon oxide during lithium insertion, preventing electrode deformation while maintaining high capacity.
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 solution effectively reduces swelling and stress on the negative electrode active material, preventing cracks and maintaining a high capacity maintenance rate by balancing rigidity and elongation, thus enhancing the battery's performance and longevity.
Implementation Method 1
the Si-containing particle has a specific capacity larger than the graphite, but has a higher swell rate at an electrically charging time
Implementation Method 2
As the binder, a carboxymethyl cellulose (CMC), a poly acrylic acid (PAA), and a styrene butadiene rubber (SBR) are included
Implementation Method 3
by making the negative electrode be easily elongated, it is possible to mitigate the swell stress of the negative electrode active material caused by charge and discharge
Data Source
AI summary
The herein disclosed negative electrode is a negative electrode for a nonaqueous electrolyte secondary battery that includes a current collector, and a negative electrode active material layer disposed on a single surface or both surfaces of the current collector. The negative electrode active material layer includes a negative electrode active material and a binder. A graphite particle and a Si-containing particle are included as the negative electrode active material. A carboxymethyl cellulose (CMC), a poly acrylic acid (PAA), and a styrene butadiene rubber (SBR) are included as the binder. A spring constant in a thickness direction of the negative electrode is equal to or more than 70 kN/mm and not more than 400 kN/mm, and a yield loop height on a stiffness test is equal to or less than 13 mm.