Negative Electrode Slurry Blending to Eliminate Thick Edge Coating
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Solution Overview
Problem
The existing methods for manufacturing lithium-ion batteries face challenges in addressing the 'thick edge' issue during the coating process of electrode sheets, which leads to uneven thickness, increased pressure, and potential fractures, affecting the battery's performance and safety.
Innovation Solution
A solvent blending method is employed, combining water with an organic solvent having a lower surface tension and higher boiling point to create a surface tension gradient, counteracting capillary action and reducing the 'thick edge' effect, while also adding a thickener to maintain viscosity and improve spreadability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If water is used as the solvent in the slurry, then the slurry has good spreadability and low viscosity, but water evaporates faster at the edge due to larger surface area to volume ratio, causing slurry particles to move towards the edge under capillary force and form a thick edge
Solution Approach 1:
The patent changes the physical parameters of the solvent by using a mixed solvent system instead of pure water. The organic solvent component has higher surface tension and lower volatility, which modifies the evaporation rate and capillary force characteristics of the slurry, thereby preventing the thick edge effect while maintaining spreadability
Solution Approach 2:
The patent uses a composite solvent system comprising both water and organic solvent (such as ethanol or isopropanol). This composite solvent combines the advantages of water (good spreadability, low cost) with the advantages of organic solvent (higher surface tension, lower volatility), achieving both easy operation and uniform thickness
2Manufacturing precision
If the edge thickness is reduced to avoid thick edge, then the thick edge problem is alleviated, but the amount of active material at the edge is reduced, affecting the battery capacity and performance
Solution Approach 1:
By changing the solvent parameters (surface tension, volatility) through the mixed solvent system, the patent eliminates the need for edge thinning. The modified capillary force and evaporation rate allow uniform coating thickness to be achieved naturally, preserving the full amount of active material at the edges
3Manufacturing precision
If a mixed solvent system with organic solvent is used, then the surface tension gradient counteracts capillary action and reduces thick edge, but the viscosity and spreadability of the slurry need to be maintained
Solution Approach 1:
The patent carefully selects and adjusts the parameters of the mixed solvent system, including the type of organic solvent (ethanol, isopropanol), its proportion (typically 5-50% by volume), and the resulting surface tension and viscosity. This optimization ensures that the surface tension gradient is sufficient to counteract capillary action while the viscosity remains low enough for good spreadability
Solution Approach 2:
The mixed solvent system creates local quality differences in the slurry: the organic solvent concentrates slightly at the edge during evaporation, creating a local surface tension gradient that counteracts capillary force, while the bulk slurry maintains overall low viscosity for good spreadability
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
This approach effectively eliminates the 'thick edge' issue, enhancing the battery's energy density, stability, and safety by reducing lithium precipitation and improving the uniformity of the electrode sheet, thus improving the overall performance and safety of the battery cell.
Implementation Method 1
combining water with an organic solvent having a lower surface tension and higher boiling point to create a surface tension gradient
Implementation Method 2
counteracting capillary action and reducing the 'thick edge' effect
Implementation Method 3
drying the slurry
Implementation Method 4
organic solvent having a lower surface tension and higher boiling point
Data Source
AI summary
Provided is a method for preparing a secondary battery including a battery cell. The secondary battery includes a negative electrode. The method includes: preparing a negative electrode slurry, coating the negative electrode slurry on the negative current collector, and then drying and compacting the negative electrode slurry to form a negative electrode material coating, thereby obtaining the negative electrode. Preparing the negative electrode slurry includes: dry blending a negative electrode active material, a conductive agent and a dispersant to obtain a dry blend; kneading the dry blend with a part of the first solvent to obtain a kneaded material; subjecting the kneaded material, the remaining part of the first solvent, the second solvent to a first wet blending to obtain a first wet blend; and subjecting the first wet blend, a thickener and a binder to a second wet blending to obtain the negative electrode slurry.