Carbon Nanofiber Electrolyte Additive for Battery Cycle Life
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Solution Overview
Problem
Negative electrode active materials with high volume expansion rates, such as silicon, experience reduced cycle characteristics due to the formation of a coating membrane from non-aqueous electrolytes on carbon nanofibers, which impairs their stress-relieving function and current-collecting ability.
Innovation Solution
Incorporating a first lithium salt like LiBF4 or LiB(C2O4)2 in the non-aqueous electrolyte at a specific concentration and ratio relative to carbon nanofibers, forming a protective membrane on the nanofibers that inhibits the formation of a coating membrane from the solvent, maintaining the stress-relieving function and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon nanofibers are used as conductive agent in negative electrode, then current-collecting ability is improved, but side reaction with non-aqueous electrolyte is facilitated forming coating membrane that reduces charge-discharge efficiency
Solution Approach 1:
The patent introduces LiBF4 as an intermediary substance in the non-aqueous electrolyte that mediates between the carbon nanofibers and the solvent. LiBF4 preferentially reacts with carbon nanofibers to form a protective LiF coating layer, preventing the solvent from directly contacting and reacting with the carbon nanofibers. This intermediary mechanism resolves the contradiction by allowing carbon nanofibers to maintain their current-collecting function while eliminating harmful side reactions with the solvent.
Solution Approach 2:
The patent changes the chemical composition parameters of the non-aqueous electrolyte by adding LiBF4 at specific concentrations (0.01-1.0 mol/L). This parameter change transforms the electrolyte's interaction characteristics with carbon nanofibers, shifting from harmful solvent-based coating formation to beneficial LiBF4-based protective layer formation, thereby resolving the contradiction between current-collecting ability and side reaction prevention.
2Reliability
If carbon nanofibers are used to relieve stress during expansion, then current-collecting ability is maintained, but coating membrane formation fills the space between nanofibers and deprives them of stress absorption function
Solution Approach 1:
LiBF4 acts as an intermediary that forms a controlled protective layer on carbon nanofibers, preventing uncontrolled solvent-based coating formation. This intermediary action preserves the inter-fiber spaces necessary for stress absorption while maintaining current-collecting pathways, resolving the contradiction between these two functions.
Solution Approach 2:
The patent converts the potentially harmful side reaction between LiBF4 and carbon nanofibers into a beneficial protective mechanism. The LiF coating formed from LiBF4 decomposition serves as a protective layer that prevents further harmful reactions while preserving the physical structure needed for stress absorption, transforming a harmful process into a beneficial one.
3Object-generated harmful factors
If LiBF4 is added to non-aqueous electrolyte to inhibit side reaction, then coating membrane formation is reduced, but charge-discharge efficiency is reduced due to formation of coating membrane from non-aqueous solvent
Solution Approach 1:
The patent optimizes the concentration parameter of LiBF4 in the non-aqueous electrolyte (0.01-1.0 mol/L) to achieve the right balance. At these specific concentrations, LiBF4 provides sufficient protection against side reactions without forming excessive coating membranes that would impede charge-discharge efficiency, resolving the contradiction between side reaction inhibition and energy efficiency.
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 maintains the current-collecting ability and cycle characteristics of non-aqueous electrolyte secondary batteries with high-capacity negative electrode active materials by preventing the solvent-derived coating membrane formation, thus improving battery performance.
Implementation Method 1
the first lithium salt included in the non-aqueous electrolyte has a concentration of 0.05 mol/dm3 or less
Data Source
AI summary
A non-aqueous electrolyte secondary battery of the present invention includes a positive electrode including a positive electrode material mixture, a negative electrode including a negative electrode material mixture, and a non-aqueous electrolyte including a non-aqueous solvent and a first lithium salt and a second lithium salt dissolved in the non-aqueous solvent. The negative electrode material mixture includes a material capable of absorbing and desorbing lithium ions, and carbon nanofibers. The material capable of absorbing and desorbing lithium ions has a ratio A/B of a volume A in a charged state to a volume B in a discharged state of 1.2 or more. The first lithium salt is at least one selected from the group consisting of LiBF4 and LiB(C2O4)2. The second lithium salt is a salt other than the first lithium salt. The first lithium salt is included in the non-aqueous electrolyte at a weight ratio of 10−4 or more relative to the carbon nanofibers. The first lithium salt included in the non-aqueous electrolyte has a concentration of 0.05 mol/dm3 or less.