Silicon Negative Electrode Pillar Structure for Battery Cycle Life

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Solution Overview

Problem

The adhesion between the active material and the current collector in silicon-containing negative electrodes for lithium secondary batteries is insufficient, leading to reduced current collection properties and charge/discharge cycle characteristics due to expansion and contraction.

Innovation Solution

A negative electrode configuration with a first mix layer and a second mix layer, where the second mix layer has a higher expansion coefficient and includes pillar portions to absorb expansion stress, and the first mix layer with higher electrical conductivity is placed between the second mix layer and the current collector to reduce stress and improve adhesion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a silicon-containing material is used as an active material, then the battery capacity is improved, but the adhesion between the active material and current collector deteriorates due to volume expansion and contraction

Engineering Contradiction:

Improvebattery capacityVSAvoidadhesion between active material and current collector

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The negative electrode mix layer is divided into multiple layers with different compositions and functions. The first mix layer contains silicon-containing active material particles and forms a buffer structure, while the second mix layer contains different active material particles. This segmentation allows each layer to handle specific stresses, improving overall adhesion while maintaining high capacity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A binder is introduced as an intermediary substance between the active material particles and the current collector. The binder creates a flexible adhesive layer that accommodates volume changes of the silicon-containing active material during charge-discharge cycles, preventing direct detachment from the current collector while maintaining electrical contact.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the binder percentage is increased to improve adhesion, then the adhesion between mix layer and current collector is improved, but the electrical conductivity of the mix layer deteriorates

Engineering Contradiction:

Improveadhesion between mix layer and current collectorVSAvoidelectrical conductivity reduction

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

Different regions of the negative electrode are designed with different binder contents. The first mix layer, which is in direct contact with the current collector, has a higher binder content to ensure strong adhesion. The second mix layer has a lower binder content to maintain better electrical conductivity. This local differentiation resolves the contradiction between adhesion and conductivity requirements.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The negative electrode uses a composite structure with multiple mix layers containing different active material particles and binder combinations. This composite approach allows optimization of each layer's properties - the first layer prioritizes adhesion with higher binder content, while the second layer prioritizes conductivity with lower binder content, achieving overall system performance.

Inventive Principle:

Principle #40Composite materials

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

This configuration enhances the initial charge/discharge efficiency and cycle characteristics of lithium secondary batteries by reducing stress on the current collector and improving adhesion, resulting in improved battery performance.

Implementation Method 1

The expansion coefficient of the second mix layer during charge is higher than the expansion coefficient of the first mix layer during charge

Methodology Applied

Scientific EffectExpansion: Thermal Expansion

Data Source

PatentUS10109856B2Negative electrode for nonaqueous electrolyte secondary batteries

Publication Date: 2018.10.23 PANASONIC ENERGY CO LTD

AI summary

A negative electrode including a current collector, a first mix layer containing first active material particles and a binder, and a second mix layer containing second active material particles and a binder. The first mix layer is placed on the current collector. The second mix layer overlies the first mix layer. The first active material particles and the second active material particles contain Si. The second mix layer includes a plurality of pillar portions. The expansion coefficient of the second mix layer during charge is higher than the expansion coefficient of the first mix layer during charge. The electrical conductivity of the first mix layer is higher than the electrical conductivity of the second mix layer.