Polyimide Binder for Silicon Anode Lithium Ion Battery

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Solution Overview

Problem

Lithium ion secondary batteries using silicon or silicon-based materials face challenges with short charge and discharge cycle life due to pulverization from lithium ion occlusion and release, leading to insufficient energy density and cycle characteristics.

Innovation Solution

A lithium ion secondary battery design incorporating a negative electrode with a silicon compound and a polyimide binder, where lithium is occluded in both the active material and binder during discharge, maintaining energy density and cycle life through controlled volume changes and improved binding properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon or silicon-based materials are used as negative electrode active material, then energy density is improved, but charge and discharge cycle life deteriorates due to pulverization

Engineering Contradiction:

Improveenergy densityVSAvoidcharge and discharge cycle life

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies this principle by using a polyimide binder that forms a flexible matrix around silicon particles. The polyimide binder accommodates volume changes of silicon during lithium ion occlusion and release, preventing pulverization while maintaining structural integrity. This flexible binding mechanism allows the electrode to withstand repeated expansion and contraction cycles.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent applies this principle by creating a composite negative electrode structure where silicon particles are embedded in a polyimide binder matrix. This composite structure combines the high capacity of silicon with the mechanical stability and binding properties of polyimide, achieving both high energy density and improved cycle life.

Inventive Principle:

Principle #40Composite materials

2Strength

If polyimide binder is used in negative electrode, then binding performance is improved, but imide ring opening occurs leading to binder degradation

Engineering Contradiction:

Improvebinding performanceVSAvoidbinder structural stability

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The patent applies this principle by controlling the electrochemical potential window and operating conditions to prevent imide ring opening. By maintaining the electrode potential within specific ranges and controlling the charge-discharge conditions, the polyimide binder remains stable and retains its binding functionality without undergoing irreversible chemical changes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies this principle by designing the polyimide binder structure and electrode composition to preemptively prevent imide ring opening. The binder is formulated with appropriate cross-linking and structural features that resist electrochemical degradation before it can occur, ensuring long-term stability during battery operation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 battery achieves enhanced cycle characteristics and high energy density by suppressing imide ring opening and maintaining binding performance over time, extending the battery's life and capacity retention.

Implementation Method 1

lithium is occluded in both the negative electrode active material and the negative electrode binder even during discharge

Methodology Applied

Scientific EffectLithium ion occlusion: Absorption (physical)

Implementation Method 2

pulverization due to the fact that the electrode active material itself expands and shrinks when lithium ions are occluded and released

Methodology Applied

Scientific EffectVolume expansion: Thermal Expansion

Data Source

PatentUS9160004B2Lithium ion secondary battery

Publication Date: 2015.10.13 NEC CORP

AI summary

In a lithium ion secondary battery including a positive electrode, a separator, and a negative electrode opposed to the positive electrode with an intervention of the separator, the negative electrode includes a negative electrode active material including a silicon compound, and a negative electrode binder including a particular polyimide, and lithium is occluded in both the negative electrode active material and the negative electrode binder even during discharge.