Rolled Copper Foil for Secondary Battery Negative Electrode
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Solution Overview
Problem
Secondary battery negative electrode current collectors made of copper foil face breakage due to stress from volume changes of active materials during charging and discharging, leading to deteriorated cycle characteristics.
Innovation Solution
A rolled copper foil with enhanced tensile strength and breaking elongation in both parallel and orthogonal directions is developed, achieved through specific composition and manufacturing processes, including hot-rolling and final cold-rolling with high working ratios, to withstand the stress caused by active material volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper foil is used as current collector, then conductivity is good, but breakage occurs due to stress from active material volume change
Solution Approach 1:
The patent changes the physical parameters of the copper foil by controlling its thickness (6-12 μm) and applying specific rolling processes with defined working ratios (60-80% in first pass, 20-40% in second pass). These parameter changes enhance the foil's mechanical strength and elasticity to withstand stress from active material volume changes during charging-discharging cycles, thereby improving cycle characteristics without sacrificing conductivity
Solution Approach 2:
The patent applies preliminary rolling and shaping operations to the copper foil before it is used as current collector. The foil is pre-formed with specific dimensional tolerances (thickness variation ≤5%, width variation ≤3%) and surface properties through controlled rolling processes. This preliminary action ensures the foil has adequate mechanical strength and dimensional stability to resist breakage during subsequent battery cycling
2Weight of moving object
If copper foil thickness is reduced to achieve higher energy density, then battery weight decreases, but breakage resistance deteriorates
Solution Approach 1:
The patent optimizes the copper foil thickness parameter to 6-12 μm, which is thinner than conventional foils but sufficient to maintain breakage resistance. This parameter change achieves higher energy density and reduced battery weight while the controlled rolling process enhances the foil's mechanical properties to compensate for the reduced thickness, preventing breakage during cycling
3Strength
If rolling working ratio is increased to improve strength, then tensile strength increases, but elongation decreases
Solution Approach 1:
The patent applies a two-stage rolling process as preliminary action: first pass with 60-80% working ratio to establish basic strength, followed by second pass with 20-40% working ratio to fine-tune properties. This preliminary action achieves balanced mechanical properties with tensile strength ≥400 MPa and elongation ≥20%, optimizing both strength and ductility for stress resistance during battery 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 solution effectively suppresses breakage of the copper foil, improving the charge/discharge repetition characteristics and enabling higher capacity secondary batteries, particularly lithium-ion batteries.
Implementation Method 1
by performing a step of final cold rolling, in which work rolls with certain a diameter are used and the working ratio in each pass is 24% or more and the total working ratio is more than 99.9%, both the strength and the elongation can be improved by work hardening of the copper foil
Implementation Method 2
a first cold rolling step of cold rolling and annealing the hot rolled rod to form a annealed rod
Data Source
Figure 1~2
AI summary
The present invention is intended to provide a rolled copper foil for a secondary battery negative electrode current collector which can satisfactorily suppress rupture of the copper foil caused by stress generation or the like due to volume change of an active material. A rolled copper foil for a secondary battery negative electrode current collector, wherein a tensile strength in a direction parallel to the rolling direction is 600 MPa or more, and a breaking elongation in the direction parallel to the rolling direction is 2.0% or more; and wherein a tensile strength in a direction orthogonal to the rolling direction is 640 MPa or more, and a breaking elongation in the direction orthogonal to the rolling direction is 3.5% or more.