All-Solid-State Battery Binder Composition for High-Voltage Cycle Life
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Solution Overview
Problem
Existing binders for all-solid-state secondary batteries inhibit ionic conduction and fail to provide adequate cycle life characteristics, especially under high voltage conditions.
Innovation Solution
A binder composition comprising a polymer (A) with specific repeating units derived from unsaturated carboxylic acid esters and compounds with tertiary amino groups, having a weight-average molecular weight between 250,000 and 3,000,000, and exhibiting an endothermic peak at −10° C. or lower.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a binder component is added to the mixture to improve moldability, then workability is improved, but ionic conduction between solid electrolytes is inhibited
Solution Approach 1:
The invention changes the chemical parameters of the binder by specifying a polymer containing repeating units from unsaturated carboxylic acid esters and compounds with tertiary amino groups, with controlled molecular weight (250,000-3,000,000) and glass transition temperature (≤-10°C). These parameter changes enable the binder to provide adequate moldability while maintaining ionic conduction properties.
Solution Approach 2:
The invention uses a composite polymer structure combining different repeating units: unsaturated carboxylic acid ester units (for binding and flexibility), tertiary amino group units (for ionic conduction enhancement), and optionally hydroxyl group units (for additional bonding). This composite material approach allows simultaneous achievement of moldability and ionic conduction.
2Strength
If a polymer compound is used as binder under conventional voltage, then binding properties are favorable, but cycle life characteristics under high voltage are insufficient
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by incorporating tertiary amino groups which provide oxidation resistance, and controls the molecular weight and glass transition temperature parameters. These changes enable the binder to maintain binding properties while achieving adequate cycle life characteristics under high voltage conditions.
Solution Approach 2:
The invention converts the potential harm of polymer coverage on solid electrolyte surface (which would normally inhibit ionic conduction) into a benefit by selecting specific polymer chemistry that maintains or enhances ionic conduction through the tertiary amino groups, while the polymer provides necessary binding and oxidation resistance.
3Strength
If the polymer molecular weight is increased to improve binding properties, then binding strength is enhanced, but ionic conductivity may be reduced
Solution Approach 1:
The invention optimizes the molecular weight parameter to a specific range (250,000-3,000,000) and controls the glass transition temperature (≤-10°C). This parameter optimization ensures that the polymer has sufficient molecular weight for binding properties while maintaining chain mobility and flexibility that facilitate ionic conduction.
Data Source
AI summary
A binder for an all-solid-state secondary battery that can control a decrease in ionic conductivity, is excellent in binding properties and oxidation resistance, and can realize favorable cycle life characteristics even under a high voltage; and a binder composition for an all-solid-state secondary battery containing the binder. A binder for an all-solid-state secondary battery includes a polymer (A) which includes a repeating unit (a1) derived from an unsaturated carboxylic acid ester (excluding an unsaturated carboxylic acid ester having a hydroxyl group) and a repeating unit (a2) derived from a compound having a tertiary amino group, a weight-average molecular weight (Mw) of the polymer (A) being from 250000 to 3000000, and an endothermic peak being observed at −10° C. or lower when differential scanning calorimetry (DSC) is performed on the polymer (A) in accordance with JIS K 7121.