Non-Aqueous Battery Electrolyte and Graphite Mix for Low Self-Discharge
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Solution Overview
Problem
Existing non-aqueous electrolyte secondary batteries using sulfonylimide compounds exhibit significant self-discharge during storage, particularly when low-crystallinity graphite is used as the negative electrode material, and there is a need to improve storage characteristics.
Innovation Solution
A non-aqueous electrolyte secondary battery is designed with a non-aqueous electrolytic liquid containing a sulfonylimide compound and specific additives, combined with a negative electrode comprising a mixture of low- and high-crystallinity graphites, to suppress self-discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-crystallinity graphite is used as negative electrode material, then manufacturing cost is reduced, but self-discharge increases during storage
Solution Approach 1:
The patent applies parameter changes by precisely controlling the crystallinity of graphite through spheroidization treatment and classification processes. The invention specifies that the graphite should have a specific full-width at half-maximum (FWHM) value of 28-35 cm⁻¹ and spheroidization ratio of 0.85-0.95, transforming the graphite properties to achieve both low cost and suppressed self-discharge during storage
Solution Approach 2:
The patent uses composite materials by combining spheroidized low-crystallinity graphite with specific electrolyte additives (fluorinated cyclic carbonate compounds and phosphorus-containing compounds). This composite approach allows the use of cheaper low-crystallinity graphite while the electrolyte additives compensate for the increased self-discharge tendency, achieving both cost reduction and improved storage characteristics
2Reliability
If sulfonylimide compound is used as electrolyte salt, then battery performance is improved, but self-discharge increases during storage
Solution Approach 1:
The patent introduces intermediary substances (electrolyte additives) that mediate between the sulfonylimide compound and the graphite electrode. The fluorinated cyclic carbonate and phosphorus-containing compounds act as intermediaries that form protective films on the electrode surface, preventing direct harmful interactions that cause self-discharge while allowing the sulfonylimide compound to maintain its performance benefits
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte by adding specific fluorinated cyclic carbonate compounds (0.1-5 wt%) and phosphorus-containing compounds (0.01-1 wt%) to the sulfonylimide-based electrolyte. This parameter modification suppresses the self-discharge tendency of sulfonylimide compounds without compromising their performance-enhancing properties
Data Source
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AI summary
Provided is a non-aqueous electrolyte secondary battery provided with: a non-aqueous electrolytic liquid that contains a sulfonylimide compound and a chain carbonate-based solvent and/or a saturated cyclic carbonate-based solvent, and contains at least one selected from the group consisting of a carbonate species, an unsaturated cyclic carbonate-based compound, a compound represented by General Formula (4) of MPOcFd, and a phosphorus atom-containing compound represented by General Formula (5) of [-P(=O)(OR1)O-]n; a negative electrode containing a first graphite having a D/G ratio of greater than 0.7 or a full-width at half-maximum of a G-band of greater than 28 cm-1, and containing a second graphite having a D/G ratio or a full-width at half-maximum of the G-band of the corresponding value or less at an amount of from 0 mass% to 10 mass% per 100 mass% of the total amount of the first graphite and the second graphite; and a positive electrode.