To state the conclusion first: how an electrode assembly is stacked is not a matter of taste — it is a design decision about which defect to accept and which defect to eliminate.
Inside a cell, the cathode, separator, and anode are stacked in alternating layers. There are broadly three ways to create this stack: winding, which rolls a long strip up; stack and folding, which stacks individual sheets while wrapping them zigzag-fashion in a long separator; and lamination and stacking, which pre-bonds electrode and separator into unit cells before stacking them.
The tension comes from the format competition. Prismatic and cylindrical cells have rigid casings, so winding comes naturally, but a pouch cell’s soft exterior means the internal stacking structure itself determines the cell’s shape stability. On top of that, rising energy-density requirements are making cells thicker, and the thicker they get, the more the weaknesses of a “rolled-up” structure show. The question this article sets out to answer: what physical trade-off does each of the three methods make, and how is that difference protected from a patent perspective?
Basic Principle — Kimbap, Folding Screen, and Sandwich
The three methods can be split with everyday analogies.
- Winding is like making kimbap (Korean rice rolls). Two long electrode strips and a separator are rolled up together in one motion. The process is simple and fast, but curvature inevitably forms at the rolled edges.
- Stack and folding is like a folding screen. Individual electrode sheets are placed down and a long separator is folded zigzag-fashion around them to build up layers. Curvature remains only at the edges of the cell.
- Lamination and stacking is like a sandwich. The electrode and separator are pre-bonded with heat and pressure into “bi-cell” unit cells, which are then stacked layer by layer. There is, in principle, no curvature at all.
The key point here is the location of the curvature. Where an electrode is bent, stress concentrates at that spot as the electrode expands and contracts during charge and discharge. In particular, the inner corner where winding begins to curl has the smallest radius of curvature, so stress piles up there, making it the spot most likely to show active-material detachment or lithium plating first over repeated cycles.
Comparison — What the Three Methods Trade Off
| Item | Winding | Stack and Folding | Lamination and Stacking |
|---|---|---|---|
| Process speed | Fastest | Medium | Slow (adds a unit-cell fabrication step) |
| Internal curvature | Present throughout all layers | Confined to the edges | None in principle |
| Space utilization (prismatic case) | Dead space at corners | Good | Best |
| Suitability for thick cells | Unfavorable (inner stress concentration) | Moderate | Favorable |
| Alignment precision required | Low | Medium | High (per-layer alignment management) |
| Primary form factor | Cylindrical and prismatic | Pouch and prismatic | Mainly pouch |
Source: qualitative comparison compiled by the editorial team from the article analysis and published patents including KR100987300B1 and KR101795830B1
What this table tells us — the three methods trade “speed” against “structural stability.” For winding, hourly throughput is the bottleneck; for lamination and stacking, layer-alignment precision is. It is therefore only natural that even the same company would use different stacking methods on a low-cost LFP line versus a high-energy high-nickel line.
Source: concept diagram reconstructed by the editorial team from the article text
Patent Perspective — Structural Claims and Apparatus Claims Complement Each Other
The scope of rights in stacking technology is built up across two layers.
On the structural axis, granted patent KR100987300B1 (“Stack-folding type electrode assembly and manufacturing method thereof”) is the representative reference point. Judged by its core effect, the focus of the right is on a structure that combines the space efficiency of sheet stacking with the stability of a continuous separator, by wrapping and fixing unit cells with a long separator sheet. Follow-on filings that vary the unit-cell arrangement, such as WO2013137575A1 (“Electrode assembly of novel structure and battery cell comprising the same”), continue from there, forming a textbook patent thicket in which a single foundational structure is finely divided into filings by arrangement, dimension, and fixing method.
On the apparatus axis sit documents such as KR101795830B1 (“Battery lamination and stacking apparatus, and method thereof”) and WO2017146386A1 (“Roll press and lamination method using the roll press”), which claim the temperature/pressure-applying structure of the bonding rolls and the transport path. Looking at the finished cell alone, the exposure to infringement under apparatus claims is low, but for a business that wants to build or localize the equipment itself, this is where the real FTO risk lies.
Design-around approach (rebuttal scenario) — structural claims are generally specified by shape requirements such as “the separator wraps the unit cell,” so there may be room to avoid literal infringement by changing the wrapping order or the polarity arrangement of the unit cells. This workaround, however, is likely already preempted by follow-on filings in most cases. In practice, checking the family-wide term of the patent may be more effective than a design-around — a good many filings from the late 2000s have already expired or are close to expiring, so it is faster to first check whether the right is even still alive before spending resources on designing around it.
Limitations and Outlook
The optimistic outlook is the spread of lamination and stacking. As cells grow larger and thicker, the advantage of a curvature-free structure grows, and in a cell-to-pack structure, cell shape stability directly contributes to pack rigidity.
Opposing scenario — in the end, which stacking method wins out is decided by throughput per unit time. Lamination and stacking requires alignment at every layer, so tact time is long, and if alignment error accumulates, the risk of an edge short circuit actually grows. If winding equipment’s high-speed, high-precision control advances a notch further, and the stress problem of thick cells can be absorbed through case-constraint design, winding’s cost advantage could let it continue holding the low-cost, high-volume market.
Strategic alternative — rather than trying to standardize on a single stacking method, a two-track strategy split by product line is more realistic. Keep the high-energy, thick-electrode line on stacking and the cost-focused LFP line on winding, and aligning only the electrode specifications the two lines can share lets equipment-investment risk be spread out.
What planning and IP staff should check now — check whether the bonding-roll structure and transport method of the stacking equipment under consideration overlaps with the claim configuration of the apparatus-axis documents above, and at the same time look up the expiry date and family countries of those patents first. If the right has already expired, the design-around budget itself becomes unnecessary.
This article is a technical explainer based on publicly available patent documents and industry-disclosed material, and is not legal advice on whether any specific product infringes. Registration and litigation outcomes cannot be predicted with certainty.