Cathode Binder Composition for High-Loading Lithium Batteries
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Solution Overview
Problem
Lithium batteries with high-capacity cathodes face issues of reduced flexibility and thermal stability due to increased thickness, leading to potential cracks during manufacturing and decreased lifespan, especially when using nickel-based cathode active materials.
Innovation Solution
A cathode is developed using a lithium transition metal oxide with nickel and another transition metal, combined with a linear carbon conductive material and a binder composition that includes a fluorine-containing binder and a polar functional group, enhancing adhesive strength, flexibility, and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the loading of cathode mixture is increased to provide high capacity, then the discharge capacity increases, but the thickness of the cathode increases leading to reduced flexibility and increased cracking
Solution Approach 1:
The patent uses a composite binder system comprising both fluorine-containing polymer (e.g., PVDF) and carboxymethyl cellulose (CMC) in specific weight ratios (PVDF: 1-10 parts, CMC: 90-90 parts by weight). This composite binder composition provides both adhesive strength and flexibility to the cathode structure, allowing high loading (up to 9 mAh/cm²) without cracking during winding or charge/discharge processes.
2Quantity of substance
If nickel-based cathode active material is used to provide high discharge capacity, then the capacity increases, but electrolyte side reactions deteriorate lifespan and thermal stability
Solution Approach 1:
The patent controls the nickel content in the cathode active material to be 30-80 mole percent based on total transition metals, and specifically maintains the Li:Ni molar ratio between 0.95:1 and 1.05:1. This parameter optimization balances high discharge capacity with reduced electrolyte side reactions, improving both lifespan and thermal stability while maintaining high performance.
3Quantity of substance
If the thickness of the cathode is increased to accommodate high loading, then the energy density increases, but cracks occur easily during winding or charge/discharge processes
Solution Approach 1:
The patent employs a composite binder system with carboxymethyl cellulose (CMC) and fluorine-containing polymer (PVDF) in specific ratios. CMC provides structural flexibility and adhesion to the current collector, while PVDF contributes to chemical stability and flexibility. This composite approach maintains structural integrity at high loadings (up to 9 mAh/cm²) and prevents cracking during winding and charge/discharge operations.
Solution Approach 2:
The patent applies different binder components to different functional requirements within the cathode structure. CMC is used primarily for adhesion to the current collector and providing flexibility, while PVDF is used for chemical stability and additional flexibility. This localized functional assignment optimizes the overall structural integrity at high loading.
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 solution improves the cycle characteristics, energy density, and thermal stability of lithium batteries by preventing cracks and maintaining high discharge capacity, even with increased loading, thereby extending the battery's lifespan and performance.
Implementation Method 1
a conductive material including a linear carbon conductive material, wherein an amount of the linear carbon conductive material is 0.1 weight percent or greater, based on a total combined weight of the cathode active material, the conductive material, and a binder
Implementation Method 2
a binder including a first binder including fluorine and a polar functional group, and a second binder, which does not include fluorine
Data Source
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AI summary
A cathode includes: a cathode active material comprising a lithium transition metal oxide; a conductive material; and a binder, wherein the lithium transition metal oxide includes nickel and a transition metal other than nickel, wherein the lithium transition metal oxide has a layered crystal structure, wherein a content of the nickel is 30 mole percent or greater, based on a total number of moles of transition metals of the lithium transition metal oxide, wherein the conductive material comprises a linear carbon conductive material, wherein the binder includes a first binder, wherein the first binder including fluorine and a polar functional group, and a second binder, which does not include fluorine, and wherein an amount of the linear carbon conductive material is 0.1 weight percent or greater, based on a total combined weight of the cathode active material, the conductive material, and the binder.