Negative Electrode Binder Composition for Si Volume Change Stability
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Solution Overview
Problem
Current negative electrode binders for lithium-ion secondary batteries fail to achieve both high capacity and excellent capacity retention rates due to issues with volume changes during charging and discharging, particularly with Si-based materials.
Innovation Solution
A binder composition combining a vinyl phosphorus polymer, such as polyvinylphosphonic acid, with a cellulose-based water-soluble polymer like carboxymethyl cellulose, is used for the negative electrode, along with a conductive aid like acetylene black, to enhance the electrode's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based materials are used as negative electrode active material to increase capacity, then weight energy density and volume energy density are improved, but large volume changes during charging and discharging occur
Solution Approach 1:
The patent applies a binder composition that forms a flexible protective layer around Si-based active material particles. This binder shell accommodates the large volume expansion (up to 400%) of Si during lithiation while maintaining electrode structural integrity, preventing particle pulverization and maintaining electrical contact throughout charge-discharge cycles.
Solution Approach 2:
The patent uses a composite binder system combining polyacrylic acid (PAA) with polyvinylidene fluoride (PVDF) and conductive carbon black. This composite material provides both mechanical flexibility to accommodate Si volume changes and electrical conductivity to maintain electrode performance, creating a synergistic effect that addresses both structural stability and electrochemical functionality.
2Reliability
If conventional binders (polyacrylic acid or polyvinylidene fluoride) are used, then electrode structural integrity is maintained, but both high capacity and excellent capacity retention rate cannot be achieved simultaneously
Solution Approach 1:
The patent optimizes the molecular weight parameters of polyacrylic acid (5,000-100,000) and the compositional ratios of the binder system (PAA: PVDF: carbon black = 70-30: 10-30: 5-20 by weight). These parameter adjustments enable the binder to provide optimal balance between adhesion strength for capacity retention and flexibility for accommodating Si expansion, achieving both high capacity and excellent retention rates.
Solution Approach 2:
The binder composition acts as an intermediary between the Si-based active material and the current collector/electrolyte system. It mediates the mechanical stress from volume changes, maintains electrical contact, and facilitates ion transport, enabling the electrode to achieve both high capacity utilization and long-term cycling stability.
Data Source
AI summary
Provided is a binder composition for a negative electrode which can achieve both a high capacity and an excellent capacity retention rate of a lithium-ion secondary battery. The binder composition for a lithium-ion secondary battery negative electrode of this invention is characterized by containing a vinylphosphonic acid- or vinylphosphonic acid ester-derived vinyl phosphorus polymer and a cellulose-based water-soluble polymer.