Silicon-Graphite Core-Shell Anode for Battery Volume Expansion
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Solution Overview
Problem
Silicon-based negative electrode active materials in secondary batteries face limitations due to excessive volume change during charge and discharge, and side reactions with electrolyte solutions, which reduce battery lifetime and efficiency.
Innovation Solution
A negative electrode active material comprising a carbonaceous matrix with a silicon core coated by an oxide layer containing SiOx (0<x≤2) and a lithium silicate layer, further covered by a LiF coating layer, combined with flaky graphite particles, to control volume expansion and side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based particles are used as negative electrode active material, then discharge capacity is improved, but volume expansion during charge and discharge increases excessively
Solution Approach 1:
The patent applies nested structure by placing silicon-based particles inside hollow graphite particles, forming a core-shell configuration where the silicon core is nested within the graphite shell. This nested structure allows the silicon to expand during lithiation while the hollow graphite shell accommodates the volume change, preventing excessive overall volume expansion and maintaining electrode integrity.
Solution Approach 2:
The patent creates a composite material system combining silicon-based particles with graphite particles. The composite structure leverages the high capacity of silicon while using graphite's stable structure to constrain volume expansion. The composite hollow graphite particle acts as both a structural framework and a buffer for silicon expansion.
2Quantity of substance
If silicon-based particles are used as negative electrode active material, then discharge capacity is improved, but side reaction with electrolyte solution increases
Solution Approach 1:
The patent introduces a coating layer on the silicon-based particles that acts as an intermediary between the silicon and the electrolyte solution. This coating layer prevents direct contact and harmful side reactions between silicon and electrolyte, while still allowing lithium ion transport. The coating serves as a protective mediator that maintains electrical functionality while blocking detrimental chemical reactions.
3Object-generated harmful factors
If carbon coating layer is formed on silicon-based particle surface, then side reaction with electrolyte solution is controlled, but volume expansion control becomes insufficient
Solution Approach 1:
The patent moves from a simple surface coating to a nested hollow structure where silicon particles are positioned inside hollow graphite particles. This nested configuration provides three-dimensional space for silicon expansion during lithiation, offering superior volume control compared to two-dimensional surface coatings alone.
Solution Approach 2:
The patent creates a composite hollow graphite particle structure that combines the protective coating function with the volume accommodation function. The composite structure integrates both the coating layer for chemical stability and the hollow graphite matrix for mechanical volume management.
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 initial efficiency, discharge capacity, and capacity retention while reducing electrode thickness change rates, improving the overall performance and stability of secondary batteries.
Implementation Method 1
the oxide layer which is disposed on the silicon core and includes SiO x (0<x≤2), and a lithium silicate layer which is disposed on the oxide layer
Implementation Method 2
a LiF coating layer which is disposed on the lithium silicate layer... effectively control the changes in volume during charge and discharge of the secondary battery and the side reaction with the electrolyte solution
Implementation Method 3
The negative electrode includes a negative electrode active material in which lithium ions from the positive electrode are intercalated and deintercalated
Data Source
Figure 1~2
Figure 3
AI summary
The present invention relates to a negative electrode active material which includes a carbonaceous matrix including a first particle and a second particle, wherein the first particle includes a silicon core, an oxide layer which is disposed on the silicon core and includes SiOx (0<x≤2), and a coating layer which covers at least a portion of a surface of the oxide layer and includes LiF, and the second particle is flaky graphite.