US-12626922-B2 - Secondary battery

US12626922B2US 12626922 B2US12626922 B2US 12626922B2US-12626922-B2

Abstract

This secondary battery comprises a positive electrode, a negative electrode, and an electrolyte solution. The electrolyte solution includes a solvent containing water as a main component, and a lithium salt. The negative electrode has a negative electrode active material that includes a carbon material. The Raman spectrum of the carbon material, which is obtained by Raman spectroscopy, indicates that the peak intensity ratio between the D-band and the G-band (D/G) is 0.3 or greater. This secondary battery can suppress the reductive decomposition of the water-based electrolyte solution.

Inventors

Kazuhiro Iida
Masanobu Takeuchi

Assignees

PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20200728
Priority Date: 20190927

Claims (4)

1 . A secondary battery, comprising: a positive electrode; a negative electrode; and an electrolyte liquid, wherein the electrolyte liquid includes: a solvent mainly composed of water; and a lithium salt, the negative electrode has a negative electrode active material including a carbon material, the carbon material has a peak intensity ratio of a D band to a G band (D/G value) of 0.3 or more and 0.8 or less in a Raman spectrum obtained by Raman spectroscopy, and has a full width at half maximum of a diffraction peak of a (004) surface of 1.0° or smaller as determined by X-ray diffraction measurement, and the carbon material is a surface-modified carbon material comprising graphite and an amorphous carbon coating a surface of the graphite.
2 . The secondary battery according to claim 1 , wherein the electrolyte liquid includes a dicarbonyl group-containing compound.
3 . The secondary battery according to claim 2 , wherein the dicarbonyl group-containing compound includes at least one of succinic acid and maleic anhydride.
4 . The secondary battery according to claim 1 , wherein the carbon material has a peak intensity ratio of a D band to a G band (D/G value) of 0.3 or more and 0.45 or less in a Raman spectrum obtained by Raman spectroscopy.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a National Phase Application filed under 35 U.S.C. § 371 of International Application No. PCT/JP2020/028823 filed on Jul. 28, 2020 which claims the benefit of priorities under 35 U.S.C. § 119 (a) of Japanese Patent Application No. 2019-177964 filed in Japan on Sep. 27, 2019, the contents of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure generally relates to a secondary battery. BACKGROUND ART Commonly used as a secondary battery with a high output and a high energy density is a lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte liquid, and performing charge and discharge by allowing lithium ions to travel between the positive electrode and the negative electrode. In the conventional secondary battery, an organic solvent-based electrolyte liquid is used for achieving the high energy density. However, organic solvents are generally flammable, and pose an important challenge of ensuring safety. In addition, organic solvents have a lower ion conductivity than an aqueous solution, and therefore causes a problem of not-sufficient rapid charge-discharge characteristics. In view of such problems, a secondary battery using an electrolyte liquid containing water (hereinafter, which may be referred to as an aqueous electrolyte liquid) has been studied. For example, Patent Literature 1 proposes use of an aqueous solution including an alkaline salt at a high concentration as an aqueous electrolyte liquid of a secondary battery. Patent Literature 2 proposes a use of an aqueous electrolyte liquid in which an organic carbonate is added into an aqueous solution including an alkaline salt at a high concentration. CITATION LIST Patent Literature PATENT LITERATURE 1: JP 6423453 BPATENT LITERATURE 2: JP 2018-073819A SUMMARY In a secondary battery having an aqueous electrolyte liquid, use of a carbon material as a negative electrode active material may lead to lowered operation voltage and potentially increased capacity. However, a conventional carbon material, unfortunately, may enhance a reductive decomposition of the aqueous electrolyte liquid and inhibit charge and discharge reactions. A secondary battery of an aspect of the present disclosure comprises: a positive electrode; a negative electrode; and an electrolyte liquid, wherein the electrolyte liquid includes: a solvent mainly composed of water; and a lithium salt, the negative electrode has a negative electrode active material including a carbon material, the carbon material has a peak intensity ratio of a D band to a G band (D/G value) of 0.3 or more in a Raman spectrum obtained by Raman spectroscopy. According to the secondary battery according to the present disclosure, the reductive decomposition of the aqueous electrolyte liquid may be inhibited. BRIEF DESCRIPTION OF DRAWING The Drawing is a schematic sectional view illustrating an example of a secondary battery of the present embodiment. DESCRIPTION OF EMBODIMENTS Generally, the reductive decomposition of an aqueous electrolyte liquid including a solvent including water and a lithium salt occurs at a potential between near or lower than approximately 2 V with reference to Li, and charge and discharge reactions of a carbon material occur at a potential equal to or lower than the reductive decomposition of the aqueous electrolyte liquid. Thus, a vigorous reductive decomposition of the aqueous electrolyte liquid during a charge process consumes a charging current, which inhibits progress of a charge reaction of a negative electrode active material. The present inventors have made intensive investigation, and as a result, have found that a crystallinity of a carbon material (negative electrode active material) may inhibit the reductive decomposition of the aqueous electrolyte liquid, and have reached a secondary battery of the following aspect. A secondary battery of an aspect of the present disclosure comprises: a positive electrode; a negative electrode; and an electrolyte liquid, wherein the electrolyte liquid includes: a solvent mainly composed of water; and a lithium salt, the negative electrode has a negative electrode active material including a carbon material, the carbon material has a peak intensity ratio of a D band to a G band (D/G value) of 0.3 or more in a Raman spectrum obtained by Raman spectroscopy. According to the secondary battery of an aspect of the present disclosure, the reductive decomposition of the aqueous electrolyte liquid is inhibited. In a Raman spectrum obtained by Raman spectroscopy, “D band” denotes a Raman band near 1360 cm−1 derived from a defect or an amorphous carbon component. “G band” denotes a Raman band near 1580 cm−1 derived from a C═C bond. Thus, a peak intensity ratio of the D band to the G band (hereinafter, which may be referred to simply as a D/G value) of 0.3 or more indicates an amorphous surface of the carbon material. When