Electrolytic Copper Foil for Si Alloy Battery Current Collectors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium-ion secondary batteries using Si or Sn alloy-based active materials face challenges with poor electron conductivity, volume changes during charge-discharge cycles, and detachment of the copper foil from the active material due to inadequate adhesiveness and surface roughness, leading to reduced cycle life and overcharge characteristics.
Innovation Solution
An electrodeposited copper foil with a roughened glossy surface and controlled surface area ratio, produced using a copper sulfate-based electrolyte with specific additives and chlorine ion concentrations, maintains tensile strength above 300 MPa and elongation rate of 3.0% after heat treatment at 350°C for 1 hour, preventing breakage and ensuring adhesiveness with the active material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a copper foil for FPC is used as a current collector, then the copper foil has high tensile strength initially, but the crystals become coarse after heat treatment at 350°C for 1 hour and the tensile strength cannot be maintained at 300 MPa or higher
Solution Approach 1:
The patent applies parameter changes by controlling the electrolyte composition (adding specific additives like gelatin or starch at 0.01-5 g/L, and controlling chlorine ion concentration at 1-50 ppm) and electrodeposition conditions (current density 10-50 A/dm², temperature 20-60°C) to produce a copper foil with fine crystal structure that maintains tensile strength of 300 MPa or higher after heat treatment at 350°C for 1 hour
2Shape
If the copper foil surface is made smooth, then the surface roughness is low, but the adhesiveness between the copper foil and active material is insufficient causing detachment during charge-discharge cycles
Solution Approach 1:
The patent applies local quality by creating a copper foil surface with controlled roughness (Rz: 1-20 μm, Ra: 0.5-10 μm) through specific electrodeposition conditions, providing localized surface characteristics that enhance adhesion while maintaining overall structural integrity and electrical conductivity
Solution Approach 2:
The patent applies preliminary action by pre-treating the copper foil surface during the electrodeposition process itself, forming a surface with appropriate roughness and chemical composition that ensures strong adhesion to the active material before the active material is applied, eliminating the need for additional surface treatment steps
3Quantity of substance
If Si or Sn alloy-based active materials are used, then the charge and discharge capacity exceeds the theoretical capacity of carbon materials, but the materials undergo large volume changes causing pulverization and detachment
Solution Approach 1:
The patent applies beforehand cushioning by creating a copper foil with enhanced mechanical properties (tensile strength ≥300 MPa, elongation rate ≥3%) and controlled surface roughness before applying the active material, providing a resilient substrate that can accommodate the volume expansion and contraction of Si or Sn alloy during charge-discharge cycles without causing pulverization or detachment
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 copper foil effectively withstands the thermal and mechanical stresses of the charge-discharge cycle, maintaining adhesiveness and preventing breakage, thus enhancing the cycle life and overcharge characteristics of lithium-ion secondary batteries.
Implementation Method 1
a copper sulfate-based electrolyte containing from 1 to 20 ppm of organic additives of one or more compounds selected from compounds having a structure with an SH group binding to a heterocycle containing N or thiourea-based compounds, and from 10 to 80 ppm of chlorine ions
Implementation Method 2
an electrodeposited copper foil having a roughened glossy surface
Data Source
AI summary
The present invention provides an electrodeposited copper foil having a tensile strength of at least 300 MPa and elongation rate of at least 3.0% after heat treatment at 350° C. for 1 hour and provides a copper foil which prevents the breakage of a current collector (copper foil) while maintaining adhesiveness between the current collector (copper foil) and the active material in response to substantial expansion and contraction of a Si or Sn alloy-based active material. The foil is an electrodeposited copper foil having a roughened surface, the tensile strength of the copper foil being at least 300 MPa after heating at 350° C. for 1 hour, the elongation rate being at least 3.0% after heating at 350° C. for 1 hour, and respective surface area ratios (actual surface area/geometric surface area) of both sides of the copper foil (the side that is roughened and the side that is not roughened) being from 1.6 to 2.2. The electrodeposited copper foil is produced with an electrolyte in which from 3 to 20 ppm of organic additives of one or more compounds selected from compounds having a structure with an SH group binding to a heterocycle containing N or thiourea-based compounds is added to a copper sulfate-based electrolyte, and then from 0 to 12 ppm of hydroxyethyl cellulose or a low-molecular weight glue, and from 10 to 80 ppm of chlorine ions are added thereto.