KR-102964287-B1 - An cathode for lithium-sulfur battery and a lithium ion secondary battery comprising the same

Abstract

The present invention relates to a cathode for a lithium-sulfur battery, wherein the cathode comprises two types of sulfur-carbon composites as cathode active materials. The cathode according to the present invention utilizes two types of carbon materials having different specific surface areas and pore volumes, and a secondary battery to which the cathode is applied has the effect of reducing the initial irreversible capacity and improving output characteristics and lifespan characteristics.

Inventors

• 박인태
• 김용휘
• 박성효
• 송명준
• 이현수
• 최란

Assignees

• 주식회사 엘지에너지솔루션

Dates

Publication Date

20260513

Application Date

20221031

Priority Date

20211029

Claims (10)

1. A positive active material comprising a mixture of a first sulfur-carbon complex and a second sulfur-carbon complex, and The above-mentioned first sulfur-carbon composite comprises a first carbon material and sulfur, and The first carbon material has a BET specific surface area of 2,900 m² /g or more, and pores with a diameter of less than 3 nm account for 80 vol% or more of the total pores of the first carbon material. The above-mentioned second sulfur-carbon composite comprises a second carbon material and sulfur, and The above second carbon material has a BET specific surface area of 1,000 m² /g or more and less than 1,600 m² /g, and among the total pores of the second carbon material, pores with a diameter of less than 3 nm account for 50 vol% or less, and The above first sulfur-carbon composite is 50 wt% to 85 wt% or less relative to 100 wt% of the first sulfur-carbon composite and the second sulfur-carbon composite. A cathode for a lithium-sulfur battery, wherein the first sulfur-carbon composite has an SCP value of Equation 1 below greater than 0.65 and less than 1, and the second sulfur-carbon composite has an SCP value of Equation 1 below greater than 0.55 and less than 0.85: [Equation 1] SCP = Sulfur content ratio (A) ÷ Pore volume ratio of carbon material (B) In the above Equation 1, A represents the ratio of the mass of sulfur to the mass of the carbon-sulfur composite, and B represents the ratio of the pore volume of the carbon material to the apparent volume of the carbon material.
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3. In paragraph 1, The above-mentioned first carbon material is a positive electrode for a lithium-sulfur battery comprising activated carbon.
4. In paragraph 1, A cathode for a lithium-sulfur battery, wherein the first carbon material comprises 95 wt% or more of activated carbon relative to 100 wt% of the first carbon material.
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7. In paragraph 1, A cathode for a lithium-sulfur battery, wherein the above-mentioned cathode active material comprises 70 wt% or more of the first sulfur-carbon composite and the second sulfur-carbon composite relative to 100 wt% of the cathode active material.
8. In paragraph 1, The above-mentioned first sulfur-carbon composite and second sulfur-carbon composite are a positive electrode for a lithium-sulfur battery having one or more of the following states: sulfur and carbon material are simply mixed and composited, have a core-shell structured coating form, or sulfur is filled into the internal pores of the carbon material.
9. In paragraph 1, The above positive active material is a positive electrode for a lithium-sulfur battery that further comprises a binder resin and a conductive material.
10. A lithium-sulfur battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte comprises one or more of cyclic ether, linear ether, and fluorinated ether, and the positive electrode conforms to claim 1.

Description

An cathode for lithium-sulfur battery and a lithium ion secondary battery comprising the same The present invention relates to a lithium-ion secondary battery having high energy density and suppressed polysulfide leaching, and a positive electrode for said battery. This application is a priority claim application for Korean Patent Application No. 10-2021-0147384 filed on October 29, 2021, and all contents disclosed in the specification and drawings of said application are incorporated by reference into this application. Lithium-sulfur (Li-S) batteries utilizing the existing catholyte system rely on a liquid phase reaction (catholyte type) through the generation of polysulfide, an intermediate product of the Li 2 S X type, which fails to fully utilize the high theoretical discharge capacity (1675 mAh/g) of sulfur and has a problem in that the battery life characteristics are degraded due to battery degradation caused by the leaching of polysulfide. Recently, a sparingly solvating electrolyte (SSE) system that suppresses polysulfide leaching has been proposed, and it has been confirmed that more than 90% of the theoretical capacity can be utilized when applying a carbon material with a BET specific surface area of 1,500 ( m² /g) or more. However, there is a need to improve the low lifespan and output characteristics. Accordingly, in order to build a battery system with a high energy density of 400 Wh/kg, 600 Wh/L or higher, an electrolyte and cathode active material system capable of operating even with a porosity of 4.0 mAh/ cm² or higher and 60 vol% or lower is required. Figure 1 is a graph showing the results of the capacity retention rate of a battery according to an embodiment and a comparative example of the present invention. The present invention will be described in more detail below. Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Throughout this specification, when a part is described as "comprising" or "having" a certain component, unless specifically stated otherwise, this means that it does not exclude other components but may include additional components. Additionally, terms such as “about,” “substantially,” as used throughout this specification, are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values are mentioned to aid in understanding this invention. Throughout this specification, the description “A and/or B” means “A or B or both.” In the present invention, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BEL SORP-mino II from BEL Japan. The term “polysulfide” as used in this specification is a concept that includes both “polysulfide ions ( Sx²⁻ , x = 8, 6, 4, 2))” and “lithium polysulfide ( Li₂Sx or LiSx⁻ , x = 8, 6, 4, 2)”. As used in this specification, the term “composite” refers to a material in which two or more materials are combined to form physically and chemically different phases, thereby exhibiting a more effective function. The term “porosity” as used in this specification refers to the ratio of the volume occupied by pores to the total volume of a structure, and uses % as its unit; it may be used interchangeably with terms such as porosity and porosity. In the present invention, "particle size D 50 " refers to the particle size at the 50% reference of the volume-cumulative particle size distribution of the particle powder to be measured. The particle size D 50 can be measured using a laser diffraction method. For example, after dispersing the particle powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of approximately 28 kHz at an output of 60 W, and then obtained a volume-cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume-cumulative amount can be measured. Furthermore, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and thus the present invention is not necessarily limited to what is illustrated. Thicknesses have been enlarged in the drawings to clearly represent various layers and regions. Additionally, for convenience of explanation, the thickness of some layers and regions has been exaggerated in the drawings. Furthermore, throughout the specification, when a part is described