Tin Pillar Negative Electrode for Li-Ion Battery
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Solution Overview
Problem
Lithium ion secondary batteries face issues with cracking at the root of pillar-shaped negative electrodes due to volume expansion during alloying, leading to poor charge/discharge cycle characteristics and peeling of the tin film on patterned organic substrates.
Innovation Solution
A negative electrode with a tin structure featuring protrusions that have a smaller cross-sectional area at the tip than the base, increasing the surface area and reducing cracking by allowing for volume expansion at the tip without affecting the base, combined with a method of forming this structure using electrolytic or electroless tin plating and molding techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a tin film is formed on a patterned organic film to increase surface area, then output voltage and energy density are enhanced, but volume expansion during alloying causes cracking at the pillar root and peeling of the tin film
Solution Approach 1:
The tin film is divided into multiple independent pillar-shaped protrusions rather than a continuous film. Each pillar is separated from others, allowing independent volume expansion during lithium alloying without causing stress concentration at pillar roots or peeling between pillars. This segmentation resolves the contradiction by maintaining high surface area for energy density while preventing structural failure during cycling.
Solution Approach 2:
The pillar structure creates local geometric features where the tip has a smaller cross-sectional area than the base. This local quality difference allows the tip to accommodate volume expansion during alloying while the broader base provides structural support and prevents cracking. The local geometric variation enables both high surface area utilization and structural stability during charge/discharge cycles.
2Power
If the tin film surface area is increased to enhance output voltage, then energy density improves, but cracking occurs at the pillar root due to volume expansion
Solution Approach 1:
The pillar structure employs asymmetric geometry where the cross-sectional area varies along the height, with the tip having a smaller area than the base. This asymmetric design allows the tip to expand during lithium alloying while the larger base provides structural strength and prevents cracking. The asymmetric shape optimizes both power output through increased surface area and mechanical strength against cracking.
Solution Approach 2:
The solution transitions from a two-dimensional flat tin film to a three-dimensional pillar structure with varying cross-sectional area. This dimensional change enables the structure to accommodate volume expansion in the vertical dimension while maintaining structural integrity through the broader base, thereby increasing surface area for higher power output without sacrificing cracking resistance.
3Ease of manufacture
If a patterned organic film is used as substrate, then tin film adhesion is improved, but peeling occurs during repeated charging/discharging
Solution Approach 1:
The continuous tin film is segmented into discrete pillar structures, which prevents peeling by eliminating the continuous stress pathways that would propagate through a uniform film. Each pillar acts as an independent unit that can expand and contract without causing delamination from the patterned organic substrate, thereby maintaining film adhesion during repeated cycling while retaining ease of manufacture through standard plating processes.
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 enhances initial charge characteristics and extends charge/discharge cycle life by distributing volume expansion stress effectively, preventing cracking and maintaining electrode stability during repeated charging/discharging.
Implementation Method 1
a method of forming this structure using electrolytic or electroless tin plating and molding techniques
Implementation Method 2
a method of forming this structure using electrolytic or electroless tin plating and molding techniques
Data Source
AI summary
An object of the present invention is to provide a negative electrode for a lithium ion secondary battery, capable of obtaining a lithium ion secondary battery which is excellent in initial charge characteristics and is also excellent in charge/discharge cycle characteristics, and a method for producing the same, as well as a lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery. A negative electrode for a lithium ion secondary battery according to the present invention comprises a current collector layer, and a negative electrode active material layer composed of a tin structure, the tin structure includes a plurality of protrusions which protrude approximately perpendicularly to a main surface of the current collector layer, and a cross-sectional area of the tip portion parallel to the main surface of the current collector layer of the protrusion is smaller than that of the base end portion.