Si-C Negative Electrode Binder for Expansion-Stable Lithium Batteries
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving suitable energy density and managing expansion characteristics, particularly with silicon-based negative active materials that experience significant volume changes during charging and discharging, leading to potential detachment from the current collector.
Innovation Solution
A negative electrode comprising a current collector with a Si-C composite and crystalline carbon active materials, coated with a copolymer binder derived from (meth)acrylic acid and (meth)acrylonitrile monomers, which enhances adhesion and orientation, reducing expansion and maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative active material is used to achieve high discharge specific capacity, then energy density is improved, but volume expansion occurs during charging and discharging causing detachment from current collector
Solution Approach 1:
The silicon particles are embedded within a carbon matrix structure, where the carbon material acts as a container or host that accommodates the silicon particles. This nested configuration allows the silicon to expand and contract within the carbon framework without detaching from the current collector, effectively resolving the volume expansion issue while maintaining high capacity
Solution Approach 2:
The invention uses a composite structure combining silicon-based active material with carbon material. The composite Si-C negative active material leverages the high capacity of silicon while the carbon component provides structural stability and prevents volume expansion, thereby simultaneously achieving high energy density and structural integrity
2Strength
If copolymer binder is used to improve adhesion and suppress expansion, then structural integrity is improved, but manufacturing complexity increases
Solution Approach 1:
The invention specifies a copolymer binder composed of two repeating units with particular compositional parameters: the first repeating unit derived from (meth)acrylic acid-based monomer and the second from (meth)acrylonitrile monomer. By controlling the compositional parameters and ratios of these repeating units, the binder achieves optimal adhesion and expansion suppression properties while maintaining manageable manufacturing complexity through defined compositional ranges
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 suppresses volume expansion, improves energy density, and ensures the negative active material remains firmly adhered to the current collector, even after charge and discharge cycles, thereby enhancing the battery's cycle-life characteristics and preventing detachment.
Implementation Method 1
a copolymer binder includes a first repeating unit derived from a (meth)acrylic acid-based monomer and a second repeating unit derived from a (meth)acrylonitrile monomer
Implementation Method 2
a crystalline carbon second negative active material (e.g., in a form of particles), wherein a DD (Degree of Divergence) value
Data Source
Figure 1
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AI summary
A negative electrode for a rechargeable lithium battery includes a current collector, and a negative active material layer on the current collector and including a copolymer binder, a Si-C composite negative active material, and a crystalline carbon negative active material, wherein the copolymer binder includes a (meth)acrylic acid-based repeating unit and a (meth)acrylonitrile-based repeating unit, and a DD (Degree of Divergence) value defined by Equation 1 is about 30 or more. DDDegreeofDivergence=Ia/Itotal*100 wherein, Ia is a sum of peak intensities at 2θ = 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 77.5±0.2° measured by XRD utilizing a Cu Kα ray, and Itotal is a sum of peak intensities at 2θ = 26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, 77.5±0.2° measured by XRD utilizing a Cu Kα ray.