Lithium Titanate Oxide Anode Impedance Mitigation
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Solution Overview
Problem
Lithium-ion rechargeable cells with lithium titanate oxide (LTO) as a negative electrode active material face limited operating and storage temperatures due to impedance growth on the positive electrode, which restricts their application and requires environmental control, especially at elevated temperatures above 35 °C.
Innovation Solution
Incorporating an impedance growth reducing additive, such as fluoroethylene carbonate, in the electrolyte to form a stable LiF interface layer on the negative electrode during the first formation cycle, which mitigates impedance growth on the cathode and enhances cycle life and power capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If lithium titanate oxide (LTO) is used as negative electrode active material, then mechanical stability and volume constancy are improved, but operating temperature range is limited due to impedance growth on positive electrode
Solution Approach 1:
A passivation layer is formed on the LTO negative electrode surface during the first formation cycle before the cell enters service. This preliminary action creates a protective barrier that prevents subsequent impedance growth on the positive electrode, enabling elevated temperature operation. The passivation layer is formed by holding the negative electrode potential below the reduction potential of the electrolyte additive during initial charging.
Solution Approach 2:
The invention changes the chemical composition parameters of the electrolyte by adding specific additives (fluoroethylene carbonate, vinyl carbonate, or vinyl ethylene carbonate) that alter the electrochemical behavior during formation. This parameter change enables the formation of a stable passivation layer containing LiF and organic components, which fundamentally changes the long-term stability characteristics of the cell at elevated temperatures.
2Reliability
If environmental control is implemented to prevent impedance growth, then positive electrode impedance stability is improved, but system complexity increases
Solution Approach 1:
The cell performs self-protection against impedance growth through automatic formation of a passivation layer during the first charge cycle. The electrolyte additive automatically reduces at the LTO surface when potential conditions are met, creating a protective layer without external intervention. This self-service mechanism eliminates the need for active environmental control systems, cooling apparatus, or complex monitoring equipment.
3Strength
If passivation layer is formed on carbon-based negative electrode, then exfoliation is prevented, but this approach is unnecessary for LTO-based cells
Solution Approach 1:
Instead of forming a passivation layer to prevent exfoliation of the negative electrode (the conventional approach for graphite), the invention forms a passivation layer on the LTO negative electrode to prevent impedance growth on the positive electrode - essentially reversing the purpose and location of protection. The LTO's inherent mechanical stability eliminates exfoliation concerns, but the passivation layer serves the opposite function of protecting the cathode.
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 solution allows lithium-ion batteries with LTO-based chemistry to operate at elevated temperatures with reduced impedance growth, maintaining high cycle life and power capability without the need for cooling systems, thus expanding their application range.
Implementation Method 1
during the first charge of the cell (also known as the first formation cycle), a compound added to the electrolyte reduces at a potential which is higher than the intercalation potential of the solvated lithium ions. On reducing, it forms a passivation layer on the carbon-containing material
Implementation Method 2
it forms a passivation layer on the carbon-containing material before any intercalation of the lithium. The lithium ion thus penetrates into the carbon by itself
Data Source
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AI summary
A lithium-ion battery including a negative electrode (anode) containing lithium titanate oxide (Li4Ti5O12) (LTO) as an active material and a stable interface layer disposed on a surface of the electrode; a positive electrode (cathode); an electrolyte containing a solvent and an impedance growth reducing additive; and a separator disposed between the electrodes. The LTO-based cell with the stable interface layer on the negative electrode is formed by holding the potential of the negative electrode below the reduction potential of the impedance growth reducing additive for a sufficient length of time during a first formation cycle. The stable interface layer on the negative electrode mitigates impedance growth on the positive electrode over cycle life. When the impedance growth reducing additive is fluoroethylene carbonate (C3H3FO3), the stable interface layer includes a LiF deposit.