Fluorinated Electrolyte Additive for SEI Film Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving improved lifetime characteristics due to uneven solid electrolyte interface (SEI) film formation and excessive degradation at high temperatures or high voltages, especially when using conventional electrolytes or additives that react with the cathode and electrolyte, leading to irreversible capacity loss and reduced battery performance.
Innovation Solution
Incorporating a non-aqueous electrolyte additive with a salt of an anion represented by Chemical Formula 1, featuring Cs+ or Rb+, which forms stable coating films on the cathode and anode surfaces, reducing side-reactivity and maintaining lithium ion elution control, thereby enhancing the battery's high temperature and low temperature lifetime characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrolyte additives are used, then the SEI film formation is improved, but degradation occurs at high temperature or high voltage leading to irreversible capacity loss
Solution Approach 1:
The patent introduces a novel electrolyte additive with a specific molecular structure containing fluorinated cyclic carbonate groups and carboxylate groups. By changing the chemical parameters of the additive (introducing F atoms and specific functional groups), the SEI film becomes more stable at high temperatures and voltages, preventing degradation and irreversible capacity loss while maintaining battery lifetime.
Solution Approach 2:
The patent employs a composite electrolyte additive that combines multiple functional groups (fluorinated cyclic carbonate, carboxylate, and other oxygen-containing groups) within a single molecular structure. This composite approach allows the additive to perform multiple functions simultaneously: forming stable SEI film, suppressing degradation reactions, and maintaining ion conductivity, thereby resolving the contradiction between SEI stability and battery lifetime.
2Manufacturing precision
If electrolyte additive amount is increased to improve SEI film uniformity, then SEI film quality improves, but cathode surface degradation and electrolyte oxidation increase
Solution Approach 1:
The patent optimizes the concentration of the novel electrolyte additive to a specific range (0.01-5 wt%, preferably 0.1-2 wt%). At this optimized concentration, the additive forms uniform SEI film without causing excessive cathode degradation or electrolyte oxidation. The specific molecular structure of the additive allows it to be effective at low concentrations, avoiding the harmful effects of excessive additive amounts.
Solution Approach 2:
The electrolyte additive acts as an intermediary substance that mediates between the electrode surfaces and the bulk electrolyte. It forms a protective SEI film that prevents direct contact between the electrolyte and electrode surfaces, thereby preventing degradation and oxidation reactions while maintaining uniform film formation. The additive's specific structure allows it to fulfill this mediating role effectively at optimal concentrations.
3Power
If high driving voltage is achieved through electrolyte composition, then discharge voltage increases, but electrochemical stability at charge-discharge voltage range becomes challenging
Solution Approach 1:
The patent modifies the electrochemical parameters of the electrolyte by introducing a novel additive with fluorinated cyclic carbonate and carboxylate groups. These structural modifications increase the electrochemical stability window of the electrolyte, enabling it to remain stable at high discharge voltages (3.6-3.7V) while preventing decomposition and degradation reactions that would otherwise occur at such high potentials.
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 additive improves the stability and performance of lithium secondary batteries by maintaining a stable SEI film, reducing degradation, and ensuring consistent lithium ion flow, resulting in improved high temperature and low temperature storage characteristics and extended battery life.
Implementation Method 1
lithium reacts with an electrolyte and carbon the composing the anode active material on the surface of the anode active material (such as a graphite-based material), thereby resulting in the production of a compound such as Li2CO3, Li2O, or LiOH. These compounds form a solid electrolyte interface (SEI) film on the surface of the anode active material.
Implementation Method 2
lithium ions generated from a cathode active material such as a lithium metal oxide, or the like, migrate to an anode active material such as a graphite-based material, or the like, and are intercalated between layers of the anode active material.
Implementation Method 3
Electrical energy is generated by oxidation and reduction reactions when lithium ions are intercalated and de-intercalated in the cathode and anode.
Data Source
AI summary
Provided is an electrolyte additive including a salt of an anion represented by Chemical Formula 1 below, with Cs+ or Rb+:wherein A is O or S, and R1 and R2 are each independently a C1-C10 alkyl group in which all or some of the hydrogen atoms are substituted with halogen atoms.