Core-Shell Sulfur-Carbon Cathode for High-Loading Li-S Batteries
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Solution Overview
Problem
Existing lithium-sulfur batteries face challenges in maximizing the reactivity of sulfur-carbon composites due to reduced specific surface area and pore volume when increasing sulfur content, which hinders improved electrical conductivity and lithium ion transport.
Innovation Solution
A core/shell structure is developed for a lithium secondary battery using a sulfur-carbon composite with thermally expanded-reduced graphene oxide as the core and carbon nanotubes as the shell, enhancing specific surface area and pore volume to improve sulfur loading and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiCoO3 is used as the positive electrode active material to achieve high output characteristics, then the battery capacity can reach theoretical values, but cobalt resources are limited and production costs increase
Solution Approach 1:
The patent uses a composite material system consisting of LiCoO3 particles coated with a multi-layer structure of Li2SiO3 and Li3PO4. This composite approach allows the battery to achieve high capacity (4.0-4.7 mAh at 0.2C rate) while reducing cobalt content requirements and lowering production costs through the use of abundant silicon and phosphorus materials.
2Quantity of substance
If LiCoO3 is used as the positive electrode active material to achieve high output characteristics, then the battery capacity can reach theoretical values, but the supply of cobalt is insufficient
Solution Approach 1:
The patent creates a composite structure where LiCoO3 particles are coated with Li2SiO3 and Li3PO4 layers. This composite material system reduces the amount of cobalt needed per battery while maintaining high capacity (4.0-4.7 mAh), thereby addressing cobalt supply insufficiency through material substitution and optimization.
3Reliability
If the surface of LiCoO3 particles is treated with a protective coating to improve cycle characteristics, then battery durability increases, but the manufacturing process becomes more complex
Solution Approach 1:
The patent employs a porous-like amorphous coating structure of Li2SiO3 and Li3PO4 on LiCoO3 particles. This coating provides protective functions improving cycle characteristics (maintaining 80% capacity after 500 cycles at 45°C) while using a relatively simple sol-gel process that doesn't significantly complicate manufacturing.
Solution Approach 2:
The dual-layer composite coating of Li2SiO3 and Li3PO4 provides synergistic protection: Li2SiO3 offers structural stability and ion transport pathways, while Li3PO4 provides chemical stability and surface protection. This composite approach achieves superior cycle life (80% retention after 500 cycles) through functional differentiation without excessive process complexity.
4Reliability
If a thick protective coating is applied to LiCoO3 particles to improve cycle characteristics, then battery durability increases, but Li ion permeability decreases
Solution Approach 1:
The patent uses an amorphous coating structure with inherent porosity and nanoscale thickness (optimal ratio 0.03-0.07) that allows efficient Li ion diffusion. The porous/amorphous structure provides ion transport pathways while maintaining protective functions, achieving 80% capacity retention after 500 cycles without significantly impeding Li ion permeability.
Solution Approach 2:
The patent optimizes the thickness and composition ratio of the coating layers to achieve the desired balance. By controlling the Li2SiO3:Li3PO4 ratio (0.03-0.07) and using sol-gel processing parameters, the coating provides protection while maintaining Li ion permeability for high-rate discharge (4.0-4.7 mAh at 0.2C rate).
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 structure results in a lithium secondary battery with enhanced initial discharging capacity and improved performance in high-rate sections by facilitating even sulfur loading and ion transport.
Implementation Method 1
a sol-gel process using tetraethyl orthosilicate and trimethyl phosphate
Implementation Method 2
The sol-gel process forms a protective coating layer on the surface of LiCoO3 particles through chemical reactions, creating Li2SiO3 and Li3PO4 compounds
Implementation Method 3
the protective coating layer formed on the surface of the LiCoO3 particles in a specific amount prevents formation of a spinel structure and stabilization of a monoclinic structure
Implementation Method 4
occlusion and release of lithium ions in charge and discharge
Data Source
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AI summary
The present invention relates to a positive electrode active material having a core/shell structure, which comprises a sulfur-carbon composite containing thermally expanded-reduced graphene oxide, a carbon material as a core, and carbon nanotube as a shell, and a preparation method thereof and a lithium secondary battery comprising the same.