Fluorinated Negative Electrode Active Material for Lithium Ion Battery
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The production of lithium ion secondary batteries faces challenges in achieving high capacity retention rates due to binder migration and uneven distribution on the negative electrode surface, leading to reduced lithium ion diffusion and increased coating film defects when using traditional paste methods, while wet granule methods improve retention but suffer from low spreadability and defects like pinholes and streaks.
Innovation Solution
Incorporating fluorine into the negative electrode active material powder with a specific BET surface area and water contact angle to enhance water repellency, allowing for improved binder dissolution and granule spreadability, reducing coating film defects and increasing capacity retention by forming wet granules into a film form.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a paste containing a large amount of solvent is used to produce the negative electrode, then the negative electrode can be formed by applying and drying the paste, but thermal convection occurs during drying causing binder migration and uneven distribution, leading to reduced capacity retention rate
Solution Approach 1:
The patent changes the physical parameters of the granules by controlling their water content to 5-20 mass% and specific surface area to 0.03-0.15 m2/g, which fundamentally alters how the material behaves during film formation. This prevents binder migration while maintaining manufacturability, as the optimized granule parameters allow for direct film formation without the thermal convection issues that plague paste-based methods.
Solution Approach 2:
The patent replaces the thermal drying process (which causes binder migration through thermal convection) with a mechanical film formation process using optimized wet granules. The granules are directly compressed and formed into films without high-temperature drying, substituting a thermal-mechanical process with a purely mechanical one that avoids binder migration.
2Reliability
If wet granules are formed into a film form to reduce binder migration, then capacity retention rate improves, but low spreadability of wet granules causes coating film defects such as pinholes and streaks
Solution Approach 1:
The patent optimizes two critical parameters of the wet granules: water content (5-20 mass%) and specific surface area (0.03-0.15 m2/g). This dual-parameter optimization simultaneously improves spreadability (reducing coating defects) and maintains low binder migration (preserving capacity retention), resolving the contradiction between film quality and reliability.
Solution Approach 2:
The patent uses a small but sufficient amount of water (5-20 mass%) in the granules - not too little to cause poor spreadability and coating defects, not too much to cause binder migration. This partial action approach achieves the optimal balance for both film quality and capacity retention.
3Reliability
If water content in wet granules is reduced to minimize binder migration, then capacity retention rate improves, but spreadability of wet granules decreases causing coating film defects
Solution Approach 1:
The patent changes the water content parameter to an optimized range of 5-20 mass%, which is sufficient to maintain granule spreadability and prevent coating defects, yet low enough to minimize binder migration during film formation. This parameter optimization resolves the contradiction between reliability and ease of 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 method results in improved capacity retention and reduced coating film defects by enhancing the spreadability and water repellency of wet granules, ensuring better lithium ion diffusion and film formation, even under shear stress, thus enhancing the overall performance of lithium ion secondary batteries.
Implementation Method 1
Incorporating fluorine into the negative electrode active material powder with a specific BET surface area and water contact angle to enhance water repellency
Implementation Method 2
When the paste is dried, heat is applied to the paste. Thus, thermal convection occurs in the paste and a phenomenon in which a binder is lifted from a surface of a coating film
Implementation Method 3
the binder inhibits diffusion of lithium (Li) ions. When the binder is unevenly distributed on the surface of the negative electrode, Li ions do not easily diffuse into the negative electrode
Data Source
AI summary
A method of producing a lithium ion secondary battery includes the following (A) to (E). (A) A negative electrode active material powder having a BET specific surface area of 2.2 m2/g or more and 5.2 m2/g or less is prepared. (B) Fluorine is incorporated into the negative electrode active material powder. (C) Wet granules are prepared by mixing the negative electrode active material powder, a water-soluble binder powder, and water. (D) A negative electrode is produced by forming the wet granules into a film form. (E) A lithium ion secondary battery including the negative electrode, a positive electrode, and an electrolytic solution is produced. When the negative electrode active material powder is formed into a pellet having a density of 1.5 g/m3, fluorine is incorporated into the negative electrode active material powder so that the pellet has a water contact angle of 96° or more and 138° or less.