US-12626911-B2 - Cathode mixture

US12626911B2US 12626911 B2US12626911 B2US 12626911B2US-12626911-B2

Abstract

To provide a cathode mixture configured to increase the discharge capacity of a lithium secondary battery. The cathode mixture is a cathode mixture for lithium secondary batteries, comprising: a cathode active material containing an S element, and diphenyl disulfide as an additive, wherein a content of the diphenyl disulfide in the cathode mixture is less than 13.0 mass % of a total mass (100 mass %) of the cathode mixture.

Inventors

Shigenori Hama
Keisuke Omori
Mitsutoshi Otaki
Donghai Wang
Atif S. ALZAHRANI
Daiwei WANG

Assignees

TOYOTA JIDOSHA KABUSHIKI KAISHA
THE PENN STATE RESEARCH FOUNDATION

Dates

Publication Date: 20260512
Application Date: 20220610

Claims (3)

1 . A cathode mixture for lithium secondary batteries, comprising: a cathode active material containing an S element, and diphenyl disulfide as an additive, wherein a content of the diphenyl disulfide in the cathode mixture is 0.8 mass % or more and 3.7 mass % or less of a total mass (100 mass %) of the cathode mixture.
2 . A lithium secondary battery comprising: a cathode comprising a cathode layer containing the cathode mixture defined by claim 1 , an anode comprising an anode layer containing an anode active material, and an electrolyte layer containing an electrolyte.
3 . The lithium secondary battery of claim 2 , having a discharge capacity of 1100 mAh/g or higher.

Description

TECHNICAL FIELD The disclosure relates to a cathode mixture. BACKGROUND The development of a lithium secondary battery in which sulfur is used as a cathode active material (in other words a lithium-sulfur battery) is under development. Sulfur is characterized in that the theoretical capacity is 1675 mAh/g and very high. As a technique for enhancing the electric conductivity of the inside of an electrode, the cycle characteristics of a battery and the capacity of the battery, Patent Literature 1 discloses a sulfur-carbon composite and a cathode active material for a lithium-sulfur battery, which comprises an amphiphilic polymer comprising hydrophilicity parts and hydrophobicity parts. Patent Literature 2 discloses a cathode material composed of an electrically conductive material and a complex of sulfur and/or a sulfur compound having a S—S bonding. Patent Literature 3 discloses a cathode electrode comprising a current collector and a cathode active material layer containing a sulfur composite in which a sulfur surface is coated with a metal layer or a metal sulfide layer. Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2016-506055 Patent Literature 2: JP-A No. 2006-092881 Patent Literature 3: JP-A No. 2014-035944 A conventional lithium secondary battery in which sulfur is used as the cathode active material, has the following problems: components other than the cathode active material account for a large proportion of the cathode layer of the lithium secondary battery; the energy density of the cathode layer is low; and the discharge capacity of the lithium secondary battery is low. SUMMARY The disclosed embodiments were achieved in light of the above circumstances. An object of the disclosed embodiments is to provide a cathode mixture configured to increase the discharge capacity of a lithium secondary battery. In a first embodiment, there is provided a cathode mixture for lithium secondary batteries, comprising: a cathode active material containing an S element, anddiphenyl disulfide as an additive,wherein a content of the diphenyl disulfide in the cathode mixture is less than 13.0 mass % of a total mass (100 mass %) of the cathode mixture. In the cathode mixture of the disclosed embodiments, the content of the diphenyl disulfide may be 0.8 mass % or more and 3.7 mass % or less of the total mass (100 mass %) of the cathode mixture. In another embodiment, there is provided a lithium secondary battery comprising: a cathode comprising a cathode layer containing the cathode mixture, an anode comprising an anode layer containing an anode active material, and an electrolyte layer containing an electrolyte. According to the disclosed embodiments, a cathode mixture configured to increase the discharge capacity of a lithium secondary battery, is provided. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic sectional view of an example of the lithium secondary battery of the disclosed embodiments. DETAILED DESCRIPTION The cathode mixture of the disclosed embodiments is a cathode mixture for lithium secondary batteries, comprising: a cathode active material containing an S element, anddiphenyl disulfide as an additive,wherein a content of the diphenyl disulfide in the cathode mixture is less than 13.0 mass % of a total mass (100 mass %) of the cathode mixture. It was found that the discharge capacity of a lithium secondary battery comprising a cathode layer containing the cathode mixture, is specifically increased by adding diphenyl disulfide, which reacts with Li during charging, to the cathode mixture. The diphenyl disulfide represented by the following chemical formula (1) is known to react with Li+, cause a ring-opening reaction and produce a substance represented by the following chemical formula (2), that is, lithium thiophenolate (LiTP). Since the LiTP has Li ion conductivity, the ion conductivity of the cathode layer is thought to be increased by reacting the Li with the diphenyl disulfide during charging of the lithium secondary battery. Accordingly, the discharge capacity of the lithium secondary battery is thought to be increased since the diphenyl disulfide is contained in the cathode layer. The cathode mixture contains as least a cathode active material and, as an additive, diphenyl disulfide. As needed, it may contain a solid electrolyte, a conductive additive and a binder, for example. The cathode active material contains an S element. The cathode active material containing the S element may be selected from various kinds of materials. As the cathode active material, examples include, but are not limited to, an elemental sulfur and LiXS. As the elemental sulfur, examples include, but are not limited to, S8 sulfur. S8 sulfur can be three types of crystal systems (i.e., α sulfur (orthorhombic sulfur), β sulfur (monoclinic sulfur) and γ sulfur (monoclinic sulfur)). The cathode active material containing the S element may be any of the crystal systems. The form of the cathode acti