Si Negative Electrode Carbon Coating for Battery Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries using Si materials in the negative electrode face significant capacity degradation due to the expansion and contraction of Si materials during charge and discharge cycles, leading to poor cycle characteristics despite the use of additives like vinylene carbonate or fluoroethylene carbonate in the electrolyte solution.
Innovation Solution
A lithium ion secondary battery design featuring a negative electrode with a Si material and a specific carbon coating, where the C1s XPS spectrum ratio of peak intensity at 290 eV to 285 eV is 0.7 or more, forming a protective coating film that suppresses electrolyte decomposition, and using a fluorinated acid anhydride in the electrolyte solution to enhance cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si material is used in the negative electrode to increase energy density, then the capability of absorbing and releasing lithium ions per unit volume is improved, but the capacity retention rate deteriorates due to expansion and contraction decomposing the electrolyte solution
Solution Approach 1:
A carbon coating layer with specific structure (indicated by C1s XPS spectrum ratio Ia/Ib ≥ 0.7) is applied to the Si material surface, forming a flexible protective film that accommodates expansion and contraction while preventing electrolyte decomposition
Solution Approach 2:
The negative electrode uses a composite structure combining Si material with carbon coating, leveraging the high lithium ion absorption of Si and the protective properties of carbon to achieve both high capacity and good cycle stability
2Object-affected harmful factors
If additives like vinylene carbonate or fluoroethylene carbonate are added to the electrolyte solution to form protective coating films, then the decomposition of electrolyte solution is suppressed, but the cycle characteristics still deteriorate with large capacity drop
Solution Approach 1:
The invention changes the chemical composition parameters of the electrolyte by introducing fluorinated acid anhydride (at 0.01-5 wt% based on total electrolyte mass), which fundamentally alters the coating formation mechanism to produce more stable protective films
Solution Approach 2:
Fluorinated acid anhydride acts as an intermediary substance that mediates between the Si material and electrolyte, forming a stable interface layer that prevents direct harmful interactions and improves cycle stability
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 exhibits improved cycle characteristics and capacity retention with the Si material, as the carbon coating and fluorinated acid anhydride form a protective film that reduces electrolyte decomposition, leading to enhanced stability and performance.
Implementation Method 1
a ratio (Ia/Ib) of a peak intensity (Ia) at 290 eV to a peak intensity (Ib) at 285 eV is 0.7 or more in a C1s spectrum obtained by surface analysis of the negative electrode by X-ray photoelectron spectroscopy
Implementation Method 2
the capacity retention rate of a battery using the Si material in the negative electrode can be improved by using fluoroethylene carbonate and vinylene carbonate as additives
Data Source
AI summary
A purpose of one embodiment of the present invention is to provide a lithium ion secondary battery which has improved cycle characteristics and comprises a Si material in the negative electrode. The lithium ion secondary battery according to the present invention comprises a negative electrode comprising a negative electrode active material, a positive electrode comprising a positive electrode active material and an electrolyte solution, wherein the negative electrode active material comprises a Si material, and a ratio (Ia/Ib) of a peak intensity (Ia) at 290 eV to a peak intensity (Ib) at 285 eV is 0.7 or more in a C1s spectrum obtained by surface analysis of the negative electrode by X-ray photoelectron spectroscopy.