LiF-Coated LTO Negative Electrode for Moisture-Resistant Lithium Batteries
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Solution Overview
Problem
Lithium secondary batteries face issues with battery performance degradation due to side reactions caused by moisture in the active material and loss of the solid electrolyte interface (SEI) layer, which affects the stability and lifespan of the battery.
Innovation Solution
A negative electrode active material is developed by reacting lithium titanium oxide with a fluorine-containing polymer at 300°C - 500°C to form a stable lithium fluoride (LiF) coating layer, reducing moisture content and preventing adsorption of outside moisture, thereby enhancing battery performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Li 4 Ti 5 O 12 is coated with fluorine-containing polymer such as PVDF by mixing the material with the polymer and heating, then moisture content in the active material is decreased and adsorption of outside moisture is prevented, but the coating layer does not form a stable LiF film, leading to SEI layer loss and side reactions
Solution Approach 1:
The patent changes the chemical composition parameters of the coating layer by incorporating lithium fluoride (LiF) in addition to fluorine-containing polymer. This compositional modification transforms the coating from merely moisture-resistant to chemically stable, preventing SEI layer loss and side reactions with organic electrolyte that occur with PVDF-only coatings.
Solution Approach 2:
The patent creates a composite coating layer combining lithium fluoride (LiF) and fluorine-containing polymer (PVDF). This composite structure synergistically provides both the chemical stability of LiF to prevent SEI layer degradation and the moisture resistance of PVDF, resolving the harmful side reactions that occur with single-material coatings.
2Use of energy by moving object
If graphite is used as negative electrode active material, then high discharge voltage of 3.6 V and excellent reversibility are achieved, but low capacity with respect to energy density per unit volume occurs due to low graphite density
Solution Approach 1:
The patent uses composite materials (Li 4 Ti 5 O 12 core with LiF-PVDF coating) that combine the advantages of different materials: the high voltage stability and reversibility of lithium titanium oxide with the protective moisture-resistant coating, achieving both high energy density and high capacity per unit volume without the swelling problems of pure graphite.
Solution Approach 2:
The patent applies local quality modification by coating only the surface of the Li 4 Ti 5 O 12 particles with LiF-PVDF composite. This localized treatment provides moisture resistance and chemical stability at the particle surface while maintaining the high capacity properties of the bulk material, optimizing both energy density and capacity per unit volume.
3Quantity of substance
If Si-based negative electrode active materials are used, then high capacity is achieved, but extreme volume change during charge/discharge causes particle splitting and poor lifespan characteristics
Solution Approach 1:
The patent applies beforehand cushioning by creating a robust LiF-PVDF coating layer on Li 4 Ti 5 O 12 particles before they undergo charge/discharge cycles. This pre-formed protective coating prevents particle splitting and structural degradation during volume changes, ensuring long lifespan characteristics while maintaining high capacity.
Solution Approach 2:
The patent changes the material parameters by selecting Li 4 Ti 5 O 12 with specific stoichiometry (x=4, y=5) and coating it with LiF-PVDF composite. This material selection and surface modification provide both high capacity and structural stability during cycling, resolving the lifespan problem of Si-based materials while maintaining high capacity.
4Duration of action of stationary object
If oxide negative electrodes such as LTO are used, then high electricity capacity maintenance ratio and stable lifespan characteristics are achieved, but battery degradation occurs due to high moisture content in the active material itself
Solution Approach 1:
The patent extracts moisture from the Li 4 Ti 5 O 12 active material through high-temperature heating (400-500°C) under vacuum or inert atmosphere before coating. This extraction of harmful moisture prevents subsequent battery degradation while preserving the stable lifespan characteristics of the oxide material.
Solution Approach 2:
The patent uses inert atmosphere (vacuum or nitrogen) during the heating and coating processes to prevent moisture absorption by the Li 4 Ti 5 O 12 particles. This inert environment protection, combined with the hydrophobic PVDF coating, eliminates battery degradation from moisture while maintaining the excellent lifespan characteristics of the oxide electrode.
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 LiF coating layer effectively inhibits SEI layer loss and side reactions, leading to improved battery performance and stable expression of battery characteristics, including enhanced discharge capacity and cycle lifespan.
Implementation Method 1
reacting the core comprising the lithium titanium oxide represented by Formula (1) with a fluorine-containing polymer at 300°C - 500°C
Implementation Method 2
preventing loss of a solid electrolyte interface (SEI) layer through formation of a stable lithium fluoride (LiF) film
Data Source
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AI summary
Disclosed are a negative electrode active material for lithium secondary batteries, a method of preparing the same and a lithium secondary battery including the same. More particularly, the negative electrode active material includes a core that includes a lithium titanium oxide represented by Formula 1 below and a coating layer that is located in a surface of the core and includes fluorine, and thus, a moisture content in the active material is decreased and adsorption of outside moisture is inhibited, thereby removing concern for side reaction occurrence due to moisture. In addition, loss of an SEI layer may be prevented due to a stable fluorine-containing coating layer formed on a surface of the active material. As a result, battery performance may be enhanced and stable expression thereof is possible: [Formula 1] LixTiyO4 , wherein x and y are the same as defined in the present specification.