ALD Coating of VACNT Electrodes for High-Aspect-Ratio Uniformity
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Solution Overview
Problem
Conventional lithium ion batteries with vertically aligned carbon nanotubes (VACNTs) face challenges in achieving thorough and uniform coating of high aspect ratio structures due to steric hindrance, leading to increased manufacturing costs and reduced energy density.
Innovation Solution
Utilizing atomic layer deposition (ALD) in conjunction with patterned substrates and open-cell foam structures to facilitate uniform coating of VACNTs, reducing aspect ratios and enhancing gas diffusion, thereby improving coating efficiency and maintaining high electrode loadings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high aspect ratio VACNT structures are used to increase electrode loading, then energy density is improved, but coating uniformity deteriorates due to steric hindrance
Solution Approach 1:
The patent segments the coating process into multiple sequential ALD cycles, where each cycle deposits a thin conformal layer on the VACNT surfaces. This segmentation allows the coating precursor to access and coat the high aspect ratio structures in manageable steps, achieving uniform coverage even on difficult-to-reach surfaces while maintaining high electrode loading.
Solution Approach 2:
The patent employs periodic ALD deposition cycles with alternating precursor and purge steps. This periodic action enables thorough penetration of the coating material into the VACNT forest over time, ensuring complete and uniform coating of high aspect ratio structures without requiring excessive deposition time in any single step.
2Manufacturing precision
If long ALD deposition times are used to coat high aspect ratio structures, then coating completeness is improved, but manufacturing cost increases
Solution Approach 1:
The patent optimizes ALD process parameters including deposition temperature, precursor flow rates, and cycle timing to achieve maximum coating efficiency. By carefully controlling these parameters, the process achieves complete coating of high aspect ratio VACNTs in fewer cycles than conventional approaches, reducing deposition time while maintaining coating completeness.
Solution Approach 2:
The patent applies a controlled number of ALD cycles that provides sufficient coating coverage without excessive deposition. This partial action approach achieves the minimum required coating thickness for performance while avoiding the time and cost penalties of over-deposition, optimizing the balance between completeness and efficiency.
3Manufacturing precision
If multiple sol-gel coatings are used to achieve uniform coverage, then coating completeness is improved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces the complex multi-step sol-gel coating process with atomic layer deposition, a vapor-phase deposition technique. This substitution eliminates the need for multiple sequential coating applications, drying steps, and thermal treatments required by sol-gel methods, achieving uniform coating in a single controlled ALD process with reduced complexity.
4Productivity
If low aspect ratio structures are used to improve coating speed, then manufacturing efficiency is improved, but electrode loading decreases
Solution Approach 1:
The patent utilizes the three-dimensional vertical structure of high aspect ratio VACNTs growing perpendicular to the substrate. This dimensional approach provides extensive surface area for coating in the vertical dimension while maintaining a compact footprint, enabling high electrode loading without compromising coating accessibility or speed.
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
Achieves high energy and power densities by ensuring complete conformal coating of VACNTs with active materials, reducing manufacturing time and costs while maintaining structural integrity.
Implementation Method 1
The invention utilizes atomic layer deposition (ALD) in conjunction with patterned substrates and open-cell foam structures to facilitate uniform coating of VACNTs
Implementation Method 2
Chemical Vapor Deposition (CVD)
Data Source
AI summary
Battery electrodes using VACNT forests to create 3D electrode nanostructures, and methods of making, are described. The VACNTs are electrically and mechanically attached to the anode or cathode substrates, providing a large area of 3D surfaces for coating with active materials and high-conductivity electron pathways to the cell current collectors. A number of different active materials suitable for anodes and cathodes in lithium-ion batteries may be used to coat the individual carbon nanotubes. The high surface area provided by the VACNT forest and the nano-dimensions of the coated active materials enable both high energy-density and high power-density to be achieved with the same battery. Complete conformal coating of the individual CNTs may be achieved by a number of different methods, and coating with multiple active materials may be used to create nanolaminate coatings having improved electrochemical characteristics over single materials.