Lithium Battery Composite Separator and Cathode Design
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Solution Overview
Problem
Lithium secondary batteries face challenges with high energy density, stability, and safety issues due to the use of LiCoO2 as a cathode material, including low charge/discharge capacity, unstable crystal structure, and risk of combustion, especially at high electric potentials and high temperatures, and conventional mixture-type cathode materials fail to achieve synergistic effects and prevent internal short circuits.
Innovation Solution
A lithium secondary battery design featuring a cathode composed of a mixture of two specific lithium transition metal oxides with a 50:50 to 90:10 ratio, combined with an organic/inorganic composite porous membrane that includes a polyolefin-based substrate coated with inorganic particles and a binder polymer, forming interconnected porous structures to enhance stability and prevent internal short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoO2 is used as cathode material to achieve high energy density, then charge/discharge capacity is improved, but crystal structure stability deteriorates at high voltage leading to combustion risk
Solution Approach 1:
The patent uses a composite cathode material consisting of LiCoO2 particles coated with LiMn2O4 spinel structure. This composite structure allows the battery to operate at high voltage (4.3V or higher) while the LiMn2O4 coating stabilizes the crystal structure and prevents combustion, resolving the contradiction between high energy density and structural stability.
2Power
If LiCoO2 is used to achieve high energy density, then power stability is improved, but resistance to internal short circuit deteriorates due to dendrite growth
Solution Approach 1:
The patent introduces an organic/inorganic composite porous membrane as an intermediary layer between electrodes. This membrane contains inorganic particles (such as alumina, silica, or titania) dispersed in a polymer matrix, forming a tortuous path that physically blocks dendrite growth while maintaining ionic conductivity, thus preventing internal short circuits without compromising power stability.
3Object-affected harmful factors
If conventional inorganic coating is applied to prevent internal short circuit, then dendrite growth is reduced, but capability to transfer lithium deteriorates
Solution Approach 1:
The patent employs a composite porous membrane combining organic polymer matrix with inorganic particles. The inorganic particles prevent dendrite growth and maintain structural integrity, while the porous polymer structure and controlled porosity (30-70%) ensure adequate ionic conductivity and lithium ion transport, resolving the contradiction between safety and performance.
4Reliability
If mixture-type cathode materials are used to improve stability, then crystal structure stability is improved, but synergistic effects deteriorate due to difficulty in obtaining superior performance
Solution Approach 1:
The patent applies local quality by coating only the surface of LiCoO2 particles with LiMn2O4 spinel structure, rather than creating a bulk mixture. This surface coating approach maintains the high-capacity bulk LiCoO2 core while providing stability and safety benefits from the LiMn2O4 shell, achieving synergistic effects with optimized performance.
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 battery achieves high energy density, superior capacity, and improved stability, maintaining discharge capacity and rate properties, while preventing combustion and internal short circuits, enabling safer and more efficient operation, especially at high temperatures.
Implementation Method 1
an organic/inorganic composite porous membrane comprising (a) a polyolefin-based membrane substrate and (b) an active layer in which one or more areas selected from the group consisting of the surface of the substrate and a portion of pores present in the substrate are coated with a mixture of inorganic particles and a binder polymer
Implementation Method 2
porous structures are formed by the interstitial volume between the inorganic particles
Data Source
Figure 1~2
Figure 3
AI summary
Disclosed is a secondary battery including a cathode, an anode, a membrane and an electrolyte, wherein the cathode contains a mixture of a first cathode material defined herein and a second cathode material selected from the group consisting of a second-(a) cathode material defined herein and a second-(b) cathode material defined herein, and a combination thereof, wherein a mix ratio of the two cathode materials (first cathode material: second cathode material) is 50:50 to 90:10, and the membrane is an organic/inorganic composite porous membrane including (a) a polyolefin-based membrane substrate and (b) an active layer in which one or more areas selected from the group consisting of the surface of the substrate and a portion of pores of the substrate are coated with a mixture of inorganic particles and a binder polymer, wherein the active layer has a structure in which the inorganic particles are interconnected and fixed through a binder polymer and porous structures are formed by the interstitial volume between the inorganic particles.