Laminated Sulfur Cathode Structure for High-Loading Lithium Batteries
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Solution Overview
Problem
Conventional methods for manufacturing lithium-sulfur secondary battery positive electrodes result in reduced energy density due to the use of electrically conductive materials and binders, and involve time-consuming and costly processes.
Innovation Solution
A laminated positive electrode structure comprising a wet sulfur-carbon composite layer and a dry carbon-containing sulfur melt layer, formed through a combination of wet and dry processes, to enhance capacity and reduce internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a slurry process with electrically conductive material and binder is used to manufacture the positive electrode, then the electrode structure is stable and manufacturable, but the loading amount of positive electrode active material is reduced and energy density is lowered
Solution Approach 1:
The positive electrode is divided into two distinct layers: a wet positive electrode active material layer containing sulfur-carbon composite, binder, and electrically conductive material; and a dry positive electrode active material layer composed of carbon-containing sulfur melt. This segmentation allows each layer to serve specific functions while maximizing active material content.
Solution Approach 2:
The invention changes the physical state parameter of the positive electrode active material from entirely wet (slurry-based) or entirely dry to a laminated structure combining both wet and dry layers. The dry layer is formed by heating sulfur and carbon material to create a sulfur melt, then cooling it to form a free-standing film, representing a parameter change from solid to liquid and back to solid state.
2Productivity
If a slurry process is used to manufacture the positive electrode, then the electrode can be formed with uniform structure, but the manufacturing time and cost are increased due to detailed processes such as mixing, coating, drying, and rolling
Solution Approach 1:
The manufacturing process is segmented into two independent parts: (1) preparing a slurry and forming a wet positive electrode active material layer on a current collector, and (2) preparing a dry positive electrode active material layer as a free-standing film and attaching it to the wet layer. This segmentation allows each layer to be optimized independently while simplifying the overall process.
Solution Approach 2:
The dry positive electrode active material layer is prepared in advance as a free-standing film through a separate process involving mixing sulfur and carbon material, heating to form sulfur melt, cooling, and punching into shape. This preliminary preparation allows the dry layer to be ready for attachment without interfering with the slurry coating process, improving manufacturing efficiency.
3Use of energy by moving object
If sulfur is used as positive electrode active material to achieve high energy density, then the theoretical energy density is five times higher than conventional materials, but the electrical conductivity is extremely low at 5x10^-30 S/cm
Solution Approach 1:
Sulfur is combined with carbon-based materials to form sulfur-carbon composite positive electrode active material. The carbon material provides electrical conductivity while sulfur provides high energy density. This composite structure allows the electrode to benefit from both the high energy density of sulfur and the electrical conductivity of carbon, resolving the contradiction between these two properties.
Solution Approach 2:
Electrically conductive materials serve as intermediaries between sulfur particles, creating conductive pathways that enable electron transport throughout the electrode. The conductive material acts as a mediator that connects isolated sulfur particles, allowing the electrode to maintain both high sulfur content for energy density and sufficient electrical conductivity for reliable operation.
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
The laminated structure improves capacity, high-rate characteristics, and lifespan of lithium secondary batteries by minimizing binder-related resistance and optimizing sulfur loading.
Implementation Method 1
comprising the steps of (a) mixing sulfur and a porous carbon material; (b) heat-treating the mixture formed in step (a)
Implementation Method 2
during the discharging which is a reduction reaction, as the sulfur-sulfur bond is cut off, the oxidation number of sulfur decreases, and during the charging which is an oxidation reaction, as the oxidation number of sulfur increases, the sulfur-sulfur bond is re-formed. Through this oxidation-reduction reaction, electrical energy is stored and generated.
Data Source
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AI summary
The present disclosure relates to a cathode for a lithium secondary battery, a manufacturing method therefor, and a lithium secondary battery comprising same. More specifically, the cathode for a lithium secondary battery has a structure including a wet cathode active material layer, which has loadability low enough not to increase the moisture content in the battery, and a dry cathode active material layer prepared by a dry process, and thus can produce a lithium secondary battery with improved capacity, overvoltage, and lifespan characteristics, compared with a battery with a cathode containing only a wet cathode active material layer or only a dry cathode active material layer.