Lithium Battery SEI Film Stability via Additive Composition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Rechargeable lithium batteries face degradation in cycle-life and performance due to the thermal instability of the SEI film, which can be damaged by increased electrochemical and thermal energy, leading to reduced capacity and output characteristics, especially at high temperatures.
Innovation Solution
Incorporating a positive active material represented by Chemical Formula LiaNixCoyMnzO2 and LiMnO2 in the positive electrode, along with lithium difluorophosphate (LiPO2F2) and vinylene carbonate as additives in the electrolyte, to enhance the battery's thermal stability and maintain high capacity and power characteristics at room and high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the battery operates at high temperature or stores electrochemical energy, then the SEI film is damaged or destroyed, but cycle-life characteristics and performance deteriorate
Solution Approach 1:
The patent applies preliminary action by forming a stable SEI film during initial charging cycles at controlled conditions before the battery enters normal operation. This pre-formed protective layer prevents subsequent damage during high-temperature operation or high-energy discharge cycles, thereby maintaining cycle-life characteristics even when the battery operates under stressful conditions
Solution Approach 2:
The invention implements beforehand cushioning by optimizing the electrolyte composition and initial charging protocol to create a robust SEI film that acts as a cushioning protective layer. This pre-established barrier absorbs and mitigates the harmful effects of thermal stress and electrochemical energy during subsequent high-power operations, preventing direct damage to the negative electrode structure
2Speed
If the SEI film is destroyed, then ion transport may improve, but the negative electrode structure becomes vulnerable to co-intercalation damage
Solution Approach 1:
The patent applies parameter changes by carefully controlling the composition ratios of lithium salt, organic solvent, and additive in the electrolyte, as well as controlling the voltage and current parameters during initial charging cycles. These parameter optimizations enable the formation of an SEI film with balanced properties: sufficiently dense to protect the electrode structure but with adequate lithium ion conductivity to maintain performance
3Quantity of substance
If the battery achieves high capacity, then energy density increases, but thermal stability of the SEI film decreases at high temperatures
Solution Approach 1:
The invention implements composite materials by creating a composite electrolyte system combining lithium salt, organic solvent, and specific additives in optimized ratios. This composite formulation enables the formation of a composite SEI film structure that incorporates both high-capacity lithium ion storage components and thermally stable protective components, achieving simultaneous high capacity and thermal 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 proposed configuration results in rechargeable lithium batteries with improved cycle-life and power characteristics, maintaining performance even when exposed to high temperatures by preventing resistance increases and ensuring stable operation.
Implementation Method 1
lithium ions are released from a positive active material, such as, for example, a lithium-transition metal oxide, and are transferred to a negative active material such as, for example, graphite, where the ions are intercalated into the negative active material
Implementation Method 2
the SEI film may act as an ion tunnel, allowing for the passage of lithium ions
Implementation Method 3
the SEI film prevents (or reduces) contact between the electrolyte and the negative active material, thereby preventing (or reducing) decomposition of the electrolyte
Data Source
AI summary
A rechargeable lithium battery includes a positive electrode including a positive active material, a negative electrode and an electrolyte including a lithium salt, an organic solvent and an additive. The positive active material includes a compound represented by Chemical Formula 1, and the additive includes about 0.5 to about 2 parts by weight of lithium difluorophosphate (LiPO2F2) and about 0.5 to about 3 parts by weight of vinylene carbonate, based on 100 parts by weight of the organic solvent.LiaNixCoyMnzO2 Chemical Formula 1.