Two-Layer Graphite Negative Electrode for Li-Ion Cycle Stability

Solution Overview

Problem

The reduction of charge/discharge cycle characteristic is problematic in lithium ion secondary batteries.

Innovation Solution

A negative electrode for lithium ion secondary batteries is designed with a two-layer structure, where the second layer consists of graphite particles with a particle internal porosity of 10% or lower and a water contact angle of 50° or lower, and the first layer consists of graphite particles with a porosity greater than 10%, enhancing adhesiveness and facilitating electrolyte infiltration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If graphite particles with high porosity (>10%) are used in the negative electrode, then adhesiveness to the electricity collector is improved, but charge/discharge cycle characteristic deteriorates due to particle detachment

Engineering Contradiction:

ImproveadhesivenessVSAvoidcharge/discharge cycle characteristic

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The negative electrode mixture layer is divided into two distinct layers: a first layer containing high-porosity graphite particles (>10%) for strong adhesiveness to the electricity collector, and a second layer containing low-porosity graphite particles (≤10%) for superior charge/discharge cycle characteristic. This segmentation allows each layer to optimize its function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the negative electrode are assigned different graphite particle properties: the first layer (near the electricity collector) uses high-porosity particles for adhesion, while the second layer (outer region) uses low-porosity particles for cycle stability. This local differentiation of material properties resolves the contradiction between adhesion and cycle performance.

Inventive Principle:

Principle #3Local quality

2Reliability

If graphite particles with low porosity (≤10%) are used in the negative electrode, then charge/discharge cycle characteristic is improved, but adhesiveness to the electricity collector deteriorates

Engineering Contradiction:

Improvecharge/discharge cycle characteristicVSAvoidadhesiveness

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The negative electrode mixture layer is divided into two distinct layers: a first layer containing high-porosity graphite particles (>10%) for strong adhesiveness to the electricity collector, and a second layer containing low-porosity graphite particles (≤10%) for superior charge/discharge cycle characteristic. This segmentation allows each layer to optimize its function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the negative electrode are assigned different graphite particle properties: the first layer (near the electricity collector) uses high-porosity particles for adhesion, while the second layer (outer region) uses low-porosity particles for cycle stability. This local differentiation of material properties resolves the contradiction between adhesion and cycle performance.

Inventive Principle:

Principle #3Local quality

3Reliability

If a single-layer negative electrode structure is used, then device complexity is reduced, but charge/discharge cycle characteristic deteriorates due to inability to simultaneously achieve adhesion and low resistance

Engineering Contradiction:

Improvecharge/discharge cycle characteristicVSAvoidnegative electrode structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The negative electrode mixture layer is divided into two distinct layers: a first layer containing high-porosity graphite particles (>10%) for strong adhesiveness to the electricity collector, and a second layer containing low-porosity graphite particles (≤10%) for superior charge/discharge cycle characteristic. This segmentation allows each layer to optimize its function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the negative electrode are assigned different graphite particle properties: the first layer (near the electricity collector) uses high-porosity particles for adhesion, while the second layer (outer region) uses low-porosity particles for cycle stability. This local differentiation of material properties resolves the contradiction between adhesion and cycle performance.

Inventive Principle:

Principle #3Local quality

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 design improves the charge/discharge cycle characteristic by reducing lithium ion resistance and suppressing particle detachment, resulting in higher capacity maintenance over multiple cycles.

Implementation Method 1

lithium ions are caused to move between the positive electrode and the negative electrode to charge or discharge the battery

Methodology Applied

Scientific EffectLithium ion transport: Ion Repulsion/Attraction

Implementation Method 2

a water contact angle of the second layer is 50° or lower

Methodology Applied

Scientific EffectWetting: Wetting

Data Source

PatentEP4037015B1Negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Publication Date: 2025.07.02 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

Figure 1~2
Figure 3

AI summary

This negative electrode is provided with a negative electrode current collector, and a negative electrode mixture layer formed on the negative electrode current collector, wherein: the negative electrode mixture layer comprises a first layer arranged on the negative electrode current collector, and a second layer arranged on the first layer; the second layer includes graphite particles A having a particle internal porosity of at most 10%: the first layer includes graphite particles B having a particle internal porosity of more than 10%; and the second layer has a water contact angle of at most 50°.