Polyimide Binder Structure for Silicon Anode Volume Change
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Solution Overview
Problem
Conventional power storage devices with polyimide binders face challenges in achieving high capacity and cycle characteristics suitable for industrial applications like electric/hybrid automobiles and all-solid-state batteries, as they fail to withstand volume changes of electrode active materials like silicon, leading to deterioration in cycle characteristics and mechanical properties.
Innovation Solution
A polyimide-based binder with a repeated breaking energy retention ratio of 70% or more and a melting point above 300°C, formed by imidizing a polyamic acid solution with specific repeating units, is developed to enhance the mechanical and cycle characteristics of power storage devices, particularly for negative electrodes with large volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If general-purpose binders such as polyvinylidene fluoride or rubber-based resin are used to form negative electrode active material layer, then the electrode can be formed, but disintegration of the negative electrode active material layer or interfacial peeling occurs due to volume change, leading to deterioration of cycle characteristics
Solution Approach 1:
The patent changes the chemical and physical parameters of the binder by using polyimide with specific repeating units containing aromatic rings and imide groups, which provides superior mechanical strength and thermal stability compared to conventional binders, enabling the electrode to withstand volume changes during cycling
Solution Approach 2:
The patent creates a composite structure where silicon-based particles are bound within a polyimide matrix, forming a robust composite material that maintains structural integrity while accommodating volume expansion and contraction during charge-discharge cycles
2Reliability
If polyimide is used as binder to improve cycle characteristics, then capacity retention improves, but cracks occur in the negative electrode active material layer and island-like structure forms, which is insufficient for industrial applications requiring high capacity and high cycle characteristics
Solution Approach 1:
The patent optimizes the chemical structure parameters of polyimide by specifying repeating units with aromatic rings and imide groups, achieving a balance between flexibility for volume change accommodation and strength for crack prevention, thereby simultaneously improving capacity retention and mechanical strength
Solution Approach 2:
The polyimide binder forms a flexible matrix that can deform with volume changes of the electrode material, preventing crack formation while maintaining structural integrity, thus achieving both high capacity retention and mechanical strength required for industrial applications
3Reliability
If conventional polyimides are used for all-solid-state batteries, then some mechanical characteristics are achieved, but they do not sufficiently exhibit the functions required for all-solid-state batteries due to absence of liquid buffer layer
Solution Approach 1:
The patent modifies the physical and chemical parameters of polyimide to achieve appropriate flexibility and adhesion properties for all-solid-state batteries, where the binder must compensate for the absence of liquid buffer by providing both mechanical strength and adaptability to solid-state interface changes
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 polyimide-based binder significantly improves the cycle and mechanical characteristics of power storage devices, maintaining high capacity retention and mechanical properties even under large volume changes, making it suitable for industrial applications and all-solid-state batteries.
Implementation Method 1
which is obtained by imidizing a polyamic acid solution comprising a repeating unit represented by the following general formula (I)
Implementation Method 2
binding silicon-based particles having an average particle size of 1 to 10 microns using polyimide which has excellent mechanical properties
Implementation Method 3
an island-like structure having a space capable of absorbing volume expansion during charging/discharging is formed
Data Source
AI summary
A polyimide-based binder for power storage device having a repeated breaking energy retention ratio of 70% or more. The use of the binder enables improvement of a power storage device having a high capacity.