Polyacrylate Binder Cross-Linking for Silicon Anode Crease Prevention
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Solution Overview
Problem
Lithium ion secondary batteries using silicon or silicon oxide as negative electrode active materials face issues with expansion and contraction during charging and discharging, leading to stress on the negative electrode current collector, which can result in creases and falloff of the active material layer, reducing cycle characteristics.
Innovation Solution
A negative electrode with a polyacrylate binder where 1% or more of carboxylic groups at the terminals of polyacrylic acid are cross-linked with magnesium or alkaline earth metals, providing a cross-linking degree of 1 to 90% and an average polymerization degree of 3,000 to 30,000, to adjust adhesion and mechanical strength, thereby reducing stress and creases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyacrylic resin is used as negative electrode binder to improve adhesion between negative electrode active material layer and negative electrode current collector, then adhesion is improved, but stress from expansion and contraction is applied to negative electrode current collector causing creases
Solution Approach 1:
The patent changes the chemical parameters of the binder by cross-linking carboxylic groups with magnesium or alkaline earth metals to create polyacrylate. This chemical modification adjusts the adhesion strength to an optimal level that prevents both falloff and crease formation during charging/discharging cycles
Solution Approach 2:
The patent creates a composite binder system by combining polyacrylic acid with magnesium or alkaline earth metals to form polyacrylate. This composite material provides balanced mechanical properties and adhesion characteristics that resolve the contradiction between strong bonding and stress accommodation
2Reliability
If high adhesion between binder and negative electrode current collector is used to suppress falloff of negative electrode active material layer, then falloff is suppressed, but irreversible form change (crease) occurs in quick charging/discharging
Solution Approach 1:
The patent modifies the binder parameters through controlled cross-linking of carboxylic groups (1% or more) with magnesium or alkaline earth metals. This parameter adjustment creates optimal adhesion strength that suppresses falloff while accommodating expansion/contraction stress without causing creases
Solution Approach 2:
The patent uses polyacrylic acid as a base binder material and creates modified versions through chemical cross-linking. This approach allows optimization of adhesion properties while maintaining the fundamental binder function of holding active material particles together
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 creases and falloff of the negative electrode active material layer, improving the mechanical strength and cycle stability of the battery by managing the adhesion between the active material and current collector.
Implementation Method 1
1% or more of carboxylic groups at terminals of side chains of polyacrylic acid are cross-linked with magnesium or alkaline earth metal
Implementation Method 2
Silicon can electrochemically intercalate and deintercalate lithium ions
Implementation Method 3
improve the adhesion between the negative electrode active material layer and the negative electrode current collector
Data Source
AI summary
A negative electrode for a lithium ion secondary battery, which has high energy density and which can suppress a crease (form change) of a negative electrode active material layer and a negative electrode current collector caused by the expansion and contraction occurring along with the quick charging and discharging and also suppress the falloff of the negative electrode active material layer after the quick charging and discharging cycle, and a lithium ion secondary battery using the negative electrode. The negative electrode for a lithium ion secondary battery and the lithium ion secondary battery include: a negative electrode active material including 5% or more of silicon or silicon oxide; a binder that is polyacrylate whose carboxylic groups at terminals of side chains of polyacrylic acid are cross-linked with magnesium or alkaline earth metal; and a negative electrode current collector.