Soluble Polyimide Binder for Silicon Anodes
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Solution Overview
Problem
Current binder resins for lithium secondary batteries, particularly those using silicon as a negative electrode active material, face issues with adhesive strength, volume change compatibility, and heat treatment-induced oxidation, leading to poor charge/discharge efficiency and cycle characteristics.
Innovation Solution
A solvent-soluble polyimide binder resin with a repeating unit structure incorporating a carboxyl group, aromatic ether bond, or phenylindan structure is introduced, enhancing adhesion between active materials and current collectors, and allowing for improved volume change accommodation without the need for high-temperature heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binder resins such as PVDF are used with silicon-based active materials, then the electrode can be manufactured, but the active material is pulverized during charging and discharging due to large volume change, leading to deteriorated charge and discharge cycle characteristics
Solution Approach 1:
The invention changes the chemical composition parameters of the binder resin by incorporating specific functional groups (carboxyl groups, aromatic ether bonds, phenylindan structures) into the polyimide backbone. These parameter changes enable the binder to accommodate silicon's volume expansion (up to 300%) during lithiation while maintaining strong adhesion to both the active material and current collector, preventing pulverization and delamination that occur with conventional PVDF binders.
Solution Approach 2:
The invention creates a composite binder system by combining polyimide backbone structures with specific functional moieties (carboxyl groups for coordination bonding, aromatic ether bonds for flexibility, phenylindan structures for mechanical strength). This composite molecular structure provides both the adhesion strength needed to hold silicon particles together and the mechanical compliance to accommodate volume changes during cycling.
2Strength
If polyimide resin is used to improve adhesive strength and heat resistance, then the binder provides excellent adhesion, but high-temperature heat treatment is required to convert polyamic acid to polyimide, which may cause oxidation deterioration
Solution Approach 1:
The invention performs the imidization reaction in advance during the polymer synthesis stage, producing pre-formed polyimide resin that is then dissolved in NMP to create the binder solution. This preliminary conversion eliminates the need for subsequent high-temperature heat treatment of the electrode, thereby preventing oxidation deterioration of the silicon-based active material while still achieving the desired strong adhesion through the polyimide's molecular structure.
Solution Approach 2:
The invention replaces the thermal conversion process (heat treatment at high temperature to convert polyamic acid to polyimide) with a chemical synthesis approach where polyimide is directly formed and dissolved in solvent. This substitution eliminates the harmful thermal step that causes oxidation while maintaining the polyimide's excellent adhesive properties.
3Quantity of substance
If silicon-based active materials are used to increase energy density, then the battery capacity increases, but the volume change during lithium insertion and extraction causes active material separation from current collector
Solution Approach 1:
The invention changes the mechanical and chemical parameters of the binder resin by incorporating flexible aromatic ether bonds and phenylindan structures into the polyimide backbone. These parameter changes provide the binder with both strong adhesion capability and sufficient mechanical compliance to accommodate silicon's large volume expansion (up to 300%) during lithiation, maintaining structural stability and preventing active material separation from the current collector while enabling high energy density.
Data Source
AI summary
Provided are a binder resin for an electrode of a lithium secondary battery containing a solvent-soluble polyimide having a repeating unit represented by the following Formula [I], and a method of producing the binder resin for an electrode.(In the formula, Z represents an aromatic or alicyclic tetracarboxylic dianhydride residue, and Ar is an aromatic diamine residue having a carboxyl group and an aromatic diamine residue having an aromatic ether bond, or an aromatic diamine residue having a phenylindan structure).