Asymmetric current-collector coupling-area design is one of the central issues in a patent lawsuit LG Energy Solution filed against EVE Energy on July 21, 2026 in the US District Court for the Eastern District of Texas and at the ITC. Of the 5 patents-in-suit, 4 concern the tabless cylindrical cell structure, one of which — US12374762B2 — is analyzed here.
Patent Bibliographic Data
| Publication No. | US12374762B2 |
| Title | Cylindrical secondary battery comprising improved current collector plate, battery pack and vehicle including the same |
| Applicant | LG Energy Solution, Ltd. |
| Inventors | Byoung-Gu Lee, Duk-Hyun Ryu, Kwan-Hee Lee |
| Priority date | 2021-10-29 (KR priority 2021-12-24, KR1020210187847A) |
| Filing date | 2022-10-28 (PCT/KR2022/016740) |
| Publication/grant date | Granted 2025-07-29 (earlier publication US20240313364A1) |
| Family | US20240313364A1, KR20230062313A |
Mechanical Contradiction and the Question
The tabless structure eliminates the conventional tab by welding the entire uncoated portion directly to the current-collector plate. According to Samsung SDI’s 46-series materials, this transition alone reduces internal resistance by 90%. However, the uncoated-portion-to-current-collector-plate weld interface cannot be under the same conditions for the cathode and anode. The cathode foil is aluminum and the anode foil is copper, so their material properties and weld heat-generation behavior differ. This patent’s claims design the cathode uncoated-portion-to-current-collector-plate coupling area to be smaller than the anode’s. The central question is why the area is asymmetrically reduced.
Calculation / Formula Verification
The current capacity of a weld joint is a function of contact area and contact resistance. With contact resistance $R_c$ and contact area $A$, heat generation $Q$ is proportional to the square of current $I$.
$$Q = I^2 \times R_c,\quad R_c \propto \frac{1}{A}$$
The aluminum cathode foil has lower electrical conductivity than the copper anode foil (approximately 61% of copper’s) and shows greater contact-resistance variation during welding due to its oxide film. Simply increasing contact area reduces resistance but increases weld-spot density, lengthening the laser-head focal travel distance. The anode, thanks to copper’s low resistance, can favorably handle the same current with a smaller area. In other words, the asymmetric design is not a uniform reduction of current density but an approach that sets the optimal contact condition separately for each material. The safety factor is dual: the primary check is the heat-generation safety factor under normal discharge current; the secondary check is whether the weld joint fails first under overcurrent conditions such as an internal short. If the weld joint breaks first under overcurrent, it doubles as a current-interruption function, so the contact area must simultaneously satisfy both normal heat-generation management and fault-condition interruption design.
Shop-notes
If reflected in a domestic R2R assembly line, Option 1 is to avoid standardizing the laser-welding head for both cathode and anode and instead separate the focal-diameter and power profile by material. As an alternative, uniformly widening the weld area equally for cathode and anode to lower resistance across the board was also reviewed, but not adopted, since the increased spot count extends cycle time and could raise the uncoated-portion curling defect rate. Machinability note: uncoated-portion thickness is typically in the 10–15μm range (estimated — confirm after field measurement), thin enough that excessively narrowing the contact area increases the risk of localized melt-hole defects.
Design-Reflection Checklist
Whether cathode/anode weld-head profiles are separated; verification that the weld joint fails first under overcurrent (doubling as a fuse function); re-calculation of hole-defect risk using field-measured uncoated-portion thickness; internal standardization documentation of the asymmetric contact-area ratio.
Whether this patent is actually infringed by EVE Energy’s products is a matter for the court to decide; this article is a mechanical-design-perspective analysis based on the published specification.
One-Line Summary
The reason for setting an asymmetric cathode/anode coupling area in tabless current-collector welding is not resistance alone, but to simultaneously satisfy material-specific weld stability and overcurrent-interruption design.