Carbon Material Surface Functional Groups for Battery SEI Stability
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving high capacity and stable high-temperature storage characteristics due to excessive reactions at the initial charge and gas generation, which are not adequately addressed by existing surface modification techniques for carbon materials.
Innovation Solution
A carbon material with a specific surface functional group composition, including oxygen-containing and halogen groups, is used to suppress excessive reactions with the electrolytic solution, stabilize the SEI film, and enhance the battery's capacity and high-temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface modification is performed to form a good SEI film, then high-temperature storage characteristics are improved, but irreversible capacity increases due to excessive reaction of acidic functional groups with electrolytic solution
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content of acidic functional groups (carboxyl and carbonyl groups) to be 5 m-equivalent/kg or less, and adjusting the oxygen-containing functional group content to specific ranges. This optimization balances the SEI film formation capability for high-temperature stability while minimizing excessive reactions that cause irreversible capacity loss.
Solution Approach 2:
The patent creates a composite surface structure on the carbon material by combining controlled amounts of acidic functional groups with specific oxygen-containing functional groups. This composite functional group configuration enables the carbon material to form a stable SEI film that provides both high-temperature storage characteristics and reduced irreversible capacity.
2Stability of the object's composition
If surface modification is performed to form a good SEI film, then stability is improved, but gas generation increases due to side reactions
Solution Approach 1:
The patent reduces gas generation by optimizing the content of acidic functional groups to 5 m-equivalent/kg or less and controlling oxygen-containing functional group content within specific ranges. This parameter optimization minimizes side reactions between the carbon material surface and electrolytic solution while maintaining sufficient SEI film stability.
3Quantity of substance
If electrode density is increased to raise battery capacity, then energy density is improved, but battery swelling increases due to gas generation
Solution Approach 1:
The patent enables higher electrode density packing by reducing gas generation through controlled surface functional group content. With acidic functional groups at 5 m-equivalent/kg or less and oxygen-containing functional groups optimized, the carbon material produces minimal gas during SEI film formation, allowing the battery to be designed with reduced gas accommodation volume and thus achieving higher effective capacity.
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 carbon material effectively reduces irreversible capacity and gas generation, enabling a lithium ion secondary battery with high capacity and excellent high-temperature storage characteristics.
Implementation Method 1
A protective film called SEI (Solid Electrolyte Interface) is usually formed on the surface of the carbon material negative electrode by a reaction with an electrolytic solution, whereby chemical stability of the negative electrode is maintained.
Implementation Method 2
the film is highly subject to effects of the amount of an oxygen-containing functional group such as carboxyl group and carbonyl group on the carbon particle surface or the surface structure of a carbon material
Data Source
AI summary
To provide a negative electrode material capable of giving a lithium ion secondary battery that is sufficiently small in the charge/discharge irreversible capacity observed at the initial cycle stage, has excellent high-temperature storage characteristics, and reduced in the gas generation at the initial cycle stage as well as during high-temperature storage. A carbon material for lithium ion secondary battery, wherein the surface functional group amount O/C value represented by the following formula 1 is from 1 to 4% and the sum (Cl/C+S165/C) of the surface functional group amount Cl/C value represented by the following formula 2 and the surface functional group amount S165/C value represented by the following formula 3 is from 0.05 to 0.5%: O/C value%=O atom concentration determined based on the peak area of the spectrum of O1s in X-ray photoelectron spectroscopyXPSanalysis/C atom concentration determined based on the peak spectrum of C1s in XPS analysis×100 Cl/C value%=Cl atom concentration determined based on the peak area of the spectrum of C12p in XPS analysis/C atom concentration determined based on the peak area ofthe spectrum of C1s in XPS analysis×100 S165/C value%=S165atom concentrationbased onthe peak area of the peak near165eVin the spectrum corresponding to S2p in XPS analysis/C atom concentration determined based on thepeak of spectrum of C1s in XPS analysis×100.