Non-Aqueous Electrolyte Salt Ratios for Stable Li-Ion Battery Interfaces
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Solution Overview
Problem
Current non-aqueous electrolytes in secondary batteries face challenges in achieving high thermal stability, ionic conductivity, and electrochemical window while preventing aluminum foil corrosion and dendrite growth, which affects cycle, storage, and kinetic performance.
Innovation Solution
A non-aqueous electrolyte composition comprising specific lithium salts and solvents, where the first lithium salt, second lithium salt, and third lithium salt are used in controlled proportions to form a dense, stable interfacial film on electrodes, enhancing ion conductivity and thermal stability, and the addition of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide improves ionic conductivity and reduces hydrolysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional non-aqueous electrolytes are used, then ionic conductivity can be maintained, but thermal stability and electrochemical window are insufficient, and aluminum foil corrosion and dendrite growth occur
Solution Approach 1:
The patent employs a composite electrolyte system combining multiple lithium salts (lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium trifluoromethanesulfonate) with specific mass ratios. This composite approach creates synergistic effects where each salt contributes different properties: LiFSO2N provides thermal stability and SEI formation, LiPF6 enhances ionic conductivity, and LiCF3SO3 suppresses aluminum foil corrosion. The combination resolves the contradiction by achieving both high reliability and protection against harmful factors simultaneously.
Solution Approach 2:
The patent optimizes the mass ratios of different lithium salts as key parameters to balance competing requirements. Specifically, LiFSO2N is maintained at 5-20 mass% for thermal stability and SEI quality, LiPF6 at 75-90 mass% for ionic conductivity, and LiCF3SO3 at 0.1-5 mass% for aluminum foil protection. By precisely controlling these parameter ranges, the electrolyte achieves both improved cycle/storage performance and resistance to aluminum foil corrosion and dendrite growth.
2Speed
If electrolyte composition is optimized for high ionic conductivity, then kinetic performance improves, but thermal stability and interfacial film stability deteriorate
Solution Approach 1:
The patent fine-tunes the concentration parameters of lithium salts to achieve optimal balance. LiPF6 is kept high (75-90 mass%) to ensure fast lithium ion transport and good kinetic performance. Meanwhile, LiFSO2N (5-20 mass%) and LiCF3SO3 (0.1-5 mass%) are maintained at specific levels to ensure thermal stability and form stable interfacial films. This parameter optimization resolves the contradiction by allowing high ionic conductivity while maintaining composition stability.
Solution Approach 2:
LiFSO2N acts as an intermediary substance that mediates between the conflicting requirements of ionic conductivity and interfacial stability. It forms a stable SEI layer that protects the electrode interface while allowing lithium ion transport. This intermediary layer enables the system to achieve both fast kinetics (from LiPF6) and stable interfacial composition (from LiFSO2N-derived SEI), resolving the contradiction between speed and 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 electrolyte achieves simultaneous good cycle, storage, and kinetic performance by forming a dense, low-impedance interfacial film, reducing irreversible lithium consumption, and improving lithium ion transport, thereby stabilizing the battery's performance and safety.
Implementation Method 1
Non-aqueous electrolyte plays a role of conducting ions between the positive and negative electrodes
Implementation Method 2
the non-aqueous electrolyte can also passivate the aluminum foil collector and form a dense, stable and low-impedance interfacial film on the surface of the positive active material and the negative active material
Implementation Method 3
the addition of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide improves ionic conductivity and reduces hydrolysis
Data Source
AI summary
A non-aqueous electrolyte includes an electrolyte salt and a non-aqueous solvent. The electrolyte salt includes a first lithium salt, a second lithium salt, and a third lithium salt, and the content A1 of the first lithium salt, the content A2 of the second lithium salt, and the content A3 of the third lithium salt, based on a total mass of the non-aqueous electrolyte, satisfy that: A1+A2+A3 is below 1%, A1/A2 is from 0.016 to 40, and A1/(A2+A3) is from 0.006 to 13.5.