Silicon Negative Electrode Composition for Swelling-Resistant Cycling
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high energy density and excellent cycle-life characteristics, particularly with silicon-based negative active materials that experience significant volume expansion during charge and discharge.
Innovation Solution
A negative electrode comprising a silicon-based active material, a room-temperature molten salt, and a volume expansion-reduced binder, where the binder is derived from poly(meth)acrylic acid-based monomers and copolymers, and the room-temperature molten salt includes specific cations and fluorine atom-included anions, optimizing the weight ratios and amounts to enhance flexibility and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based negative active material is used to achieve high energy density, then energy density is improved, but volume expansion occurs during charge and discharge
Solution Approach 1:
The patent employs a flexible binder comprising polyvinylidene fluoride and carboxymethyl cellulose that forms a compliant matrix around the silicon-based active material particles. This flexible binder system accommodates the volume expansion of silicon during lithiation while maintaining electrode structural integrity and preventing particle detachment from the current collector.
Solution Approach 2:
The patent creates a composite electrode structure combining silicon-based active material particles with a dual-component binder system (polyvinylidene fluoride and carboxymethyl cellulose). This composite approach leverages the high capacity of silicon while the composite binder matrix provides mechanical stability and ion transport pathways, resolving the contradiction between high energy density and volume expansion.
2Ease of manufacture
If conventional binders are used, then manufacturing is simple, but adhesion to current collector deteriorates due to volume expansion
Solution Approach 1:
The patent uses a composite binder system combining polyvinylidene fluoride and carboxymethyl cellulose in specific weight ratios. This composite binder provides both strong adhesion to the current collector and flexibility to accommodate silicon volume expansion, maintaining electrode integrity throughout charge-discharge cycles while remaining compatible with conventional manufacturing processes.
Solution Approach 2:
The patent optimizes the weight ratio components of the binder system and controls the amount of binder relative to active material to achieve optimal balance between adhesion strength and expansion accommodation. By adjusting these parameters, the binder maintains strong current collector adhesion while providing sufficient compliance to silicon volume changes.
3Strength
If binder amount is increased to improve adhesion, then adhesion is improved, but ionic conductivity deteriorates
Solution Approach 1:
The patent precisely controls the weight ratio between binder and active material, and the specific ratio between the two binder components, to achieve optimal performance. This parameter optimization ensures sufficient adhesion strength while maintaining adequate porosity and ion transport pathways, preventing excessive binder from blocking electrolyte access to active material particles.
Solution Approach 2:
The dual-component binder composite creates a hierarchical structure where one component provides adhesion function and the other maintains porosity and ion conductivity. This composite architecture allows the binder to fulfill multiple functions simultaneously, achieving strong adhesion without sacrificing ionic conductivity.
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 adhesion to the current collector, and enhances cycle-life characteristics while maintaining high energy density, preventing crack occurrence and ensuring sufficient ionic conductivity.
Implementation Method 1
a volume expansion-reduced binder
Implementation Method 2
improves adhesion to the current collector
Implementation Method 3
generates electrical energy due to an oxidation and reduction reaction when lithium ions are intercalated and deintercalated into the positive electrode and the negative electrode
Implementation Method 4
ensuring sufficient ionic conductivity
Data Source
AI summary
Provided are a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same, wherein the negative electrode includes a current collector and a negative active material layer positioned on the current collector, and the negative active material layer includes a silicon-based negative active material, a room-temperature molten salt, and a volume expansion-reduced binder.