Li-Ion Battery Negative Electrode Surface Chemistry for SEI Stability
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Solution Overview
Problem
Conventional lithium ion secondary batteries experience capacity retention issues due to solvent decomposition and lithium consumption at the negative electrode's surface, leading to reduced durability.
Innovation Solution
A negative electrode with an organic molecule having a dielectric constant higher than the electrolyte solvent is chemically bonded to the active material, modifying the SEI coating film to enhance polarity and stability, reducing solvent interaction and lithium consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional graphite is used as negative electrode active material, then battery capacity is achieved, but solvent decomposition occurs at the outermost surface leading to SEI coating film growth and lithium consumption
Solution Approach 1:
An organic molecule with high dielectric constant is introduced as an intermediary substance between the graphite negative electrode and the electrolyte solvent. This intermediary layer prevents direct contact between the solvent and graphite surface, suppressing solvent decomposition and SEI coating film growth while allowing lithium ion insertion/extraction to proceed normally.
Solution Approach 2:
The dielectric constant parameter of the substance at the electrode surface is changed by introducing an organic molecule with dielectric constant of 90 or more. This parameter change modifies the electrical properties at the interface, reducing solvent decomposition and stabilizing the electrolyte solution, thereby reducing lithium consumption.
2Reliability
If SEI coating film grows on negative electrode surface, then initial capacity is formed, but durability deteriorates due to lithium consumption
Solution Approach 1:
The organic molecule acts as a mediator that forms a stable interface layer between the electrolyte and graphite. This layer prevents excessive SEI coating film growth and lithium consumption during cycling, thereby improving both initial capacity formation and long-term durability with higher capacity retention rates.
Solution Approach 2:
By changing the dielectric constant parameter at the electrode interface through the organic molecule, the stability of the electrolyte solution is improved and solvent decomposition is suppressed. This leads to reduced lithium consumption and improved battery durability with better capacity retention over time.
3Loss of substance
If organic molecule with high dielectric constant is chemically bonded to negative electrode active material, then solvent decomposition is suppressed and lithium consumption is reduced, but device complexity increases
Solution Approach 1:
The organic molecule is chemically bonded only at the outermost surface (edge surface) of the graphite crystal, not throughout the entire electrode structure. This localized modification suppresses solvent decomposition at the critical interface where it occurs, reducing lithium consumption without requiring complex changes to the overall electrode structure.
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 approach improves the capacity retention rate and durability of lithium ion secondary batteries by suppressing solvent decomposition and lithium consumption, resulting in higher performance and longer battery life.
Implementation Method 1
an organic molecule having a dielectric constant larger than that of an electrolyte solvent is chemically bonded to the negative electrode active material
Implementation Method 2
the organic molecule may have a molecular structure that undergoes polarization in a single molecule or between molecules
Implementation Method 3
a negative electrode for a lithium ion secondary battery, including a negative electrode active material to which an organic molecule having a dielectric constant larger than that of an electrolyte solvent is chemically bonded
Implementation Method 4
desolvation of lithium salt in the electrolyte solution is promoted, and the electrolyte solution is stabilized, and accordingly, the decomposition of the electrolyte solution is suppressed
Data Source
AI summary
To provide a negative electrode for a lithium ion secondary battery having more improved durability than conventionally, and a lithium ion secondary battery including the same.A negative electrode for a lithium ion secondary battery including a negative electrode active material in which an organic molecule having a dielectric constant larger than that of an electrolyte solvent is chemically bonded, and a lithium ion secondary battery including the same.Preferable examples of the organic molecule include a molecule having a relative dielectric constant of 90 or more at a frequency of 10 kHz, a molecule having a molecular structure that undergoes polarization in a single molecule or between molecules, a zwitter ion compound having a positive electric charge and a negative electric charge in one molecule, hydroxy acid, and a molecule having a molecular weight of 39 to 616.