Cesium Salt Electrolyte Additive for Stable SEI Film Formation
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving improved lifetime characteristics due to uneven or poorly formed solid electrolyte interface (SEI) films, leading to degradation and irreversible capacity loss, especially under high temperature and high voltage conditions.
Innovation Solution
Incorporating a non-aqueous electrolyte additive comprising a salt of an anion with Cs+ or Rb+, derived from a nitrogen atom-containing compound, such as cesium bis(trifluoromethanesulfonyl)imide, and lithium difluoro bis(oxalato) phosphate, which forms a stable and uniform SEI coating film on the anode and cathode surfaces, reducing side-reactivity and maintaining lithium ion flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrolyte additives are used, then the SEI film formation is improved, but the cathode surface degradation and electrolyte oxidation occur during high temperature or high voltage reactions
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte additive by introducing a specific compound with fluorinated cyclic carbonate structure. This parameter change enables the additive to form a stable SEI film that prevents cathode degradation and electrolyte oxidation during high temperature or high voltage reactions, resolving the contradiction between improving SEI film formation and preventing harmful side reactions
Solution Approach 2:
The fluorinated cyclic carbonate compound acts as an intermediary substance that mediates between the electrolyte and the cathode surface. It forms a protective interface layer that allows lithium ion transport while preventing direct contact between the electrolyte and cathode, thereby preventing cathode surface degradation and electrolyte oxidation without compromising SEI film formation
2Reliability
If the amount of electrolyte additive is increased to improve SEI film uniformity, then the lifetime characteristics improve, but the irreversible capacity loss increases due to degradation and oxidation reactions
Solution Approach 1:
The patent optimizes the concentration parameter of the electrolyte additive to a specific range (0.01-5 wt%). Within this optimized parameter range, the additive achieves uniform SEI film formation that improves lifetime characteristics while minimizing degradation and oxidation reactions, thereby reducing irreversible capacity loss. This parameter optimization resolves the contradiction between improving lifetime and reducing energy loss
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 enhances the battery's high temperature and low temperature storage characteristics, improves lifetime and resistance, and maintains stable performance by preventing cathode degradation and ensuring effective lithium ion movement, resulting in improved output and stability.
Implementation Method 1
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 the layers of the anode active material. Herein, since lithium is highly reactive, it reacts at the surface of the anode active material (such as a graphite-based material) with the electrolyte and the carbon composing the anode active material, thereby resulting in the production of compounds 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
Implementation Method 3
The SEI film acts as an ion tunnel and allows only lithium ions to pass through. Since the SEI film has the effect of an ion tunnel, it blocks organic solvent molecules with a high molecular weight moving together with the lithium ions in the electrolyte from being inserted between the layers of the anode active material
Implementation Method 4
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
The present invention provides an electrolyte additive comprising a salt of an anion, derived from a nitrogen-atom-containing compound, with Cs+ or Rb+.Further, the present invention provides an electrolyte additive further comprising lithium difluoro bis(oxalato) phosphate.The present invention provides a non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, and the electrolyte additive, and may provide a lithium secondary battery comprising: a cathode employing a cathode active material; an anode employing an anode active material; a separator interposed between the cathode and the anode; and the non-aqueous electrolyte.