Porous Amorphous Carbon Coating for Silicon Anodes

Solution Overview

Problem

Conventional carbon coating methods for silicon-based negative electrode active materials in lithium secondary batteries hinder lithium ion diffusion due to the lack of pores, leading to reduced rate capability and life characteristics, and involve hazardous materials that are environmentally unfriendly.

Innovation Solution

A method is developed to form a porous amorphous carbon coating on silicon-based particles using a metal-phenolic network (MPN) formed from tannic acid and an iron salt, followed by heat treatment and acid treatment to remove iron ions, creating a nanoscale porous structure that enhances lithium ion diffusion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional pitch coating or CVD method is used to form carbon coating layer, then carbon coating is achieved, but pores are not formed in the coating layer which reduces lithium ion diffusion

Engineering Contradiction:

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention employs a porous carbon coating layer formed through a unique process: first forming a carbon-containing layer, then etching it with nitric acid to create a porous structure. This porous structure enables effective lithium ion diffusion while maintaining the protective function of the carbon coating, resolving the contradiction between achieving carbon coating and enabling ion diffusion.

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The invention extracts unnecessary dense carbon structure from the coating layer by using nitric acid etching. This removes the harmful dense structure that blocks ion diffusion while retaining the beneficial carbon coating framework, thereby improving lithium ion diffusion without compromising the coating's protective role.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If conventional carbon coating methods are used, then carbon coating is formed, but rate capability and life characteristics are degraded

Engineering Contradiction:

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention changes the chemical and structural parameters of the carbon coating layer by introducing a two-step process: carbon deposition followed by nitric acid etching. This transforms the coating from a dense, ion-blocking structure to a porous, ion-friendly structure, thereby improving rate capability and life characteristics while maintaining process feasibility.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional methods are used, then carbon coating is achieved, but the process is environmentally unfriendly and complex

Engineering Contradiction:

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention replaces complex physical vapor deposition methods (CVD) with a chemical solution-based approach using nitric acid etching. This substitution simplifies the manufacturing process, reduces equipment requirements, and improves environmental friendliness while achieving the desired porous carbon coating structure that enhances battery performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 method improves lithium ion diffusion, thereby enhancing the rate capability and life characteristics of lithium secondary batteries while being environmentally friendly and simpler than conventional methods.

Implementation Method 1

a second step of adding an iron salt and tannic acid to the silicon dispersion and stirring to form a reaction layer of the iron salt and the tannic acid on surfaces of the silicon-based particles

Methodology Applied

Scientific EffectChemical reaction: Chemical Bonding

Implementation Method 2

a third step of heat treating the reaction layer of the iron salt and the tannic acid to form an amorphous carbon coating layer

Methodology Applied

Scientific EffectCarbonization: Pyrolysis

Implementation Method 3

a fourth step of acid treating the amorphous carbon coating layer to form a porous amorphous carbon coating layer

Methodology Applied

Scientific EffectAcid dissolution: Hydrolysis

Implementation Method 4

a porous amorphous carbon coating layer formed on surfaces of the silicon-based particles... containing nanoscale pores, diffusion of lithium ions is easy

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentEP4606768A1Method for preparing negative electrode active material for lithium secondary battery, and negative electrode active material for lithium secondary battery prepared thereby

Publication Date: 2025.08.27

AI summary

The present invention relates to a method of preparing a negative electrode active material for a lithium secondary battery, which includes a first step of forming a silicon dispersion by dispersing silicon-based particles in a solvent; a second step of adding an iron salt and tannic acid to the silicon dispersion and stirring to form a reaction layer of the iron salt and the tannic acid on surfaces of the silicon-based particles; a third step of heat treating the reaction layer of the iron salt and the tannic acid to form an amorphous carbon coating layer; and a fourth step of acid treating the amorphous carbon coating layer to form a porous amorphous carbon coating layer, and a negative electrode active material prepared thereby.