SiOx Negative Electrode Binder Composition for Cycle-Stable Batteries
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving improved energy density and extended life due to volume changes in silicon-based negative electrode active substances during charging and discharging, which affect the durability of the binder and contact between active substance particles.
Innovation Solution
A negative electrode active substance layer comprising a silicon-based active substance (SiOx) and a carbon-based active substance, with a binder that includes poly(meth)acrylic acid or its derivatives, and optionally carbon nanotubes, is used, with specific mass ratios to enhance energy density and cycle life by stabilizing the electrode structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active substance (SiOx) is used to increase capacity, then energy density is improved, but volume changes during charge-discharge cycles cause binder deterioration and loss of electrical contact
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by incorporating polyacrylic acid and its derivatives with specific functional groups (carboxyl, hydroxyl, amino) that can chemically interact with silicon oxide surfaces. This chemical interaction creates a more stable binder-active substance interface that accommodates volume changes during lithiation and delithiation cycles, preventing binder deterioration while maintaining electrical contact.
Solution Approach 2:
The patent creates a composite binder system combining polyacrylic acid derivatives with additional functional components that have affinity for both silicon-based active substance and conductive materials. This composite structure provides multiple functions: mechanical binding, chemical stabilization of SiOx surface, and maintenance of electrical conductivity network throughout charge-discharge cycles despite volume expansion/contraction.
2Quantity of substance
If silicon-based active substance (SiOx) is used to increase capacity, then energy density is improved, but electrical contact between active substance particles is lost during cycling
Solution Approach 1:
The polyacrylic acid-based binder acts as an intermediary material between silicon-based active substance particles and conductive additives. Its molecular structure with flexible chains and functional groups allows it to maintain continuous electrical pathways through the active substance aggregate even when individual particles undergo significant volume changes during lithium insertion and extraction, preventing loss of electrical contact.
Solution Approach 2:
The patent modifies the electrical and mechanical parameters of the binder matrix by using polyacrylic acid derivatives with controlled molecular weight, functional group density, and crosslinking degree. These parameter adjustments enable the binder to maintain optimal electrical conductivity and mechanical flexibility throughout charge-discharge cycles, ensuring stable electrical contact between active substance particles despite volume fluctuations.
Data Source
AI summary
Provided is a negative electrode for nonaqueous electrolyte secondary batteries including: a negative electrode active substance layer that includes a negative electrode active substance; and a binder, in which the negative electrode active substance includes a silicon-based active substance that contains SiOx (where x is a number satisfying 0.5≤x≤1.6), and a carbon-based active substance, the binder contains a poly(meth)acrylic acid, a metal salt of poly(meth)acrylic acid, an alkyl ester of poly(meth)acrylic acid, or a mixture of multiple compounds selected from these compounds, a content of the silicon-based active substance relative to a total solid content of the negative electrode active substance layer is more than 10% by mass to less than 80% by mass, and a content of the binder relative to a total solid content of the negative electrode active substance layer is 2% by mass or more to less than 10% by mass.