What’s at Stake: Diversifying a Pressing Process That Relied on the Isostatic Press Alone
The bottleneck in all-solid-state battery mass production lies more in the pressing process than in chemistry, and the range of pressing options is widening now that Korean equipment maker M Plus announced on April 9, 2026 that it had completed development of planar-pressure press and roll-press technologies to replace the warm isostatic press (WIP) and had won a pilot equipment order. From a patent perspective, the focus of competition is shifting from “how to press” to “who secures rights to the surrounding structures that make pressing possible.”
To start with the industry backdrop: sulfide-based solid electrolytes do not deliver proper ionic conductivity in powder form, and normal charge-discharge is possible only when sufficient physical interfacial contact is secured between the cathode, solid electrolyte, and anode. The standard method for creating this contact has been the warm isostatic press (WIP). A paper on an all-solid-state cell with a silver-carbon composite anode, published in Nature Energy on March 9, 2020 by researchers at the Samsung Advanced Institute of Technology, also stated that a WIP technique was introduced to improve contact between the electrode and the electrolyte. The paper reported an energy density above 900 Wh/L and 1,000 cycles in a 0.6 Ah pouch cell.
The tension lies in the fact that WIP is batch-type equipment. Because the structure places cells inside a large pressure chamber and applies high temperature and pressure, it is hard to fit into a continuous production line, and both equipment cost and cycle time have held back the transition to mass production. This piece lays out how the three pressing methods differ structurally, and what these differences mean for all-solid-state battery production costs and the patent landscape.
Basic Mechanism: A Balloon Under Water, an Iron, and a Rolling Pin
The easiest analogy for understanding the isostatic press (WIP) is pressing a balloon under water. Because a fluid transmits pressure uniformly in all directions, the balloon is compressed evenly no matter which side is pressed. WIP likewise immerses the cell in a high-temperature, high-pressure fluid medium and applies the same pressure from every direction. As a result, the solid-electrolyte powder layer is densely compacted and interfacial contact resistance falls. However, because this is a batch process in which cells must be loaded into and unloaded from the chamber one at a time (or in small lots), it is a poor match for roll-to-roll continuous production.
Source: reconstructed by the editorial team from the original comparison table and press reports of the M Plus announcement (2026-04-09)
A planar-pressure press compresses the cell from above and below with two flat plates. Because pressure is applied in one direction, like ironing a sheet of paper, it is not as uniform as isostatic pressure, but it is easy to place in a continuous line and allows a short cycle time. A roll press goes a step further, compressing the cell (or electrode-solid electrolyte stack) as it passes between rotating rollers. It resembles rolling out dough with a rolling pin, and it applies to solid-state pressing the equipment concept used in conventional battery electrode processes (calendering).
The three methods sit on a trade-off that sacrifices some pressure directionality and uniformity in exchange for throughput and line integration. In this announcement, M Plus explained that cell makers can now choose among three options, WIP, planar-pressure press, and roll press, according to process characteristics and production scale. In the same announcement, the company also disclosed a plan to develop a dry coater (equipment that coats active material directly onto the current collector without solvent) so that it can supply the electrode process on a turnkey basis in addition to the assembly process.
- WIP: uniformity first; batch process
- Planar-pressure press: between uniformity and speed; batch to semi-continuous
- Roll press: speed and line integration first; continuous process
Comparison: Three Pressing Methods and Related Patents
The table below keeps the original comparison table as is. Because it is a qualitative rather than a quantitative comparison, it is safer to read it for direction.
| Category | Pressure application | Process type | Interfacial contact uniformity | Suitability for continuous lines | Capital investment characteristics |
|---|---|---|---|---|---|
| Isostatic press (WIP) | Equal pressure from all sides (fluid medium) | Batch | High | Low | High chamber cost and maintenance |
| Planar-pressure press | Uniaxial flat-plate compression | Batch to semi-continuous | Medium | Medium | Existing press equipment can be adapted |
| Roll press | Line pressure between rollers | Continuous (roll-to-roll) | Medium to low (improvement under way) | High | An extension of existing calendering equipment |
Source: compiled by the editorial team from the original comparison table and press reports of the M Plus announcement (2026-04-09)
What this table says: In the three methods, interfacial contact quality and production speed stand in inverse proportion. The very fact that M Plus seeks to offer all three options reflects an industry perception that “each solid-state cell maker requires a different optimal process.” Actual interfacial resistance figures for each method cannot be confirmed from public sources.
Next, two published patents touching on the pressing process are checked against their Google Patents bibliographic records. It is notable that both claim the surrounding structures rather than the “pressing method” itself.
| Publication number | Applicant | Priority / Publication | Status | Gist of claim 1 (restated) | Pressing-method disclosure |
|---|---|---|---|---|---|
| WO2023224342A1 | LG Energy Solution Ltd | 2022-05-16 / 2023-11-23 | International phase ended (Ceased) | Method of making an all-solid-state battery by overlapping two electrode substrates with alternating single- and double-sided electrodes, cross-folding them into a stack, and pressing at high temperature | High-temperature pressing by CIP, WIP, or upper/lower plates; notes porosity problems from repeated roll-to-roll pressing |
| US20260088331A1 | Solid Power Operating Inc | 2024-09-26 / 2026-03-26 | Pending | A frame of two mated plates, rigid at the perimeter and flexible inside, that transmits isostatic-press pressure onto the cell’s stacked faces while keeping pressing force off the cell ends | Names WIP explicitly but states other isostatic presses may be used |
Source: reconstructed by the editorial team from the Google Patents records and claims of WO2023224342A1 and US20260088331A1
What this table says: The LG Energy Solution application lists CIP, WIP, and upper/lower plates side by side as alternatives, and the Solid Power application claims a protective frame for isostatic pressing. This shows that the center of gravity of the rights lies in stack structures, jigs, and frames rather than the principle of the pressing equipment.
Patent Perspective: The Surroundings of Pressing, Not the Pressing “Method,” Become the Rights
The diversification of pressing processes is likely to lead to competition over the scope of rights (the technical substance a claim protects). However, for M Plus’s newly announced planar-pressure and roll-press developments, individual patent publication numbers and claim elements are not identified at the level of currently published reports, so this piece does not cite specific claims. The number of patents held by M Plus cited in the original article (78 registered, 34 pending) is also set aside as an item requiring verification, because its original source could not be confirmed in this review.
A May 2025 report posted on the M Plus website stated that the company was developing a high-pressure hot press and a multi-stage roll press as WIP replacements, targeting commercialization in 2027. The April 2026 announcement means this roadmap moved into the “development completed, pilot order won” stage in about a year. The faster an equipment maker develops, the more likely it is that questions over ownership of rights in joint-development results between cell makers and equipment makers will grow as well.
Source: reconstructed by the editorial team from Nature Energy 5, 299–308 (2020), Google Patents WO2023224342A1 and US20260088331A1, and reports on M Plus
Looking at the two patents in the table above yields one interpretation of our own. LG Energy Solution’s WO2023224342A1 lists CIP, WIP, and upper/lower plates side by side in its specification as means of high-temperature pressing. Because such a disclosure itself becomes prior art for later filings, it may become increasingly difficult to obtain new, broad claims at the method level, such as “pressing a stack with flat plates.” New rights are therefore likely to come from “pressing-surround structures” such as pressure-profile control, roll arrangement, and frames and jigs that protect the cell. Solid Power’s frame application is exactly such a case.
There is also a point of caution. The Solid Power application states that, while using an isostatic press, it applies a “substantially uniaxial load” to the cell’s flat surfaces. This means the boundary between isostatic and planar pressure may be defined not by the equipment’s name but by the direction of the load actually applied to the cell. That is why it is hard to conclude that switching to a planar-pressure press automatically escapes WIP-related claims.
Design-around scenarios (including counterarguments) are as follows.
- Differentiating roll shape and pressure profile: if a particular company secures its own claim to “a method of compressing a solid-electrolyte layer by line pressure between rollers,” competitors could consider a scenario of avoiding literal infringement by designing the press roll’s shape (for example, crowning or a multi-stage roll arrangement) or the pressure-profile control method differently. This, however, is a hypothetical scenario applying general design-around principles, not a judgment based on any specific claim.
- Replacing frames and jigs: solving cell-end protection through cell design (for example, a change in end structure) rather than a frame leaves room to fall outside frame-type claims. As a counterargument, if the claim is written functionally, the right holder may argue that alternative structures also fall within the scope of rights.
Limits and Outlook: Can Speed Be Gained While Keeping Uniformity?
Optimistically, if the planar-pressure and roll-press alternatives are validated, the CAPEX (capital expenditure) burden of all-solid-state batteries could fall, and the entry barrier for small and mid-sized cell makers to build pilot lines could be lowered. M Plus stated that it has already supplied equipment to the pilot lines of multiple global all-solid-state battery makers and expects large additional orders when they move to mass production.
A counter-scenario also exists. If interfacial contact uniformity is lower than with WIP, there is a risk of degraded capacity development in early cycles or long-term life characteristics, in which case automakers and cell makers may ultimately return to the WIP process for safety margin or choose a hybrid line mixing the two methods, a possibility that cannot be ruled out. It should also be remembered that a pilot order is only the start of performance validation and does not mean adoption for mass production.
As a strategic alternative, cell makers can consider a phased transition strategy that keeps WIP in the early mass-production stage while validating the roll-press method in parallel only for specific cell formats (for example, small pouches). When conducting joint validation with equipment makers, it is sensible from a risk-management standpoint to settle, at the contract stage, the process-condition data (pressure and temperature profiles) and the ownership of rights in improvement inventions.
Practical action: IP staff are advised to add new filings on pressing processes by domestic and overseas equipment makers, including M Plus, to their regular monitoring on KIPRIS and Google Patents, broadening search queries beyond method keywords such as “isostatic press” and “roll press” to surrounding-structure keywords such as “frame,” “jig,” and “pressing profile.”
Items requiring verification
- The number of patents held by M Plus (stated in the original article as 78 registered and 34 pending) and the original source and reference date
- Individual patent publication numbers and claim structure for M Plus’s planar-pressure and roll-press technologies
- The customer for the pilot equipment order and the applicable cell format
- Comparative data on interfacial resistance and capacity development for the WIP, planar-pressure, and roll-press methods
Sources
- Financial News (fnnews), “M Plus develops core technology for all-solid-state battery mass production,” 2026-04-09
- Edaily, Money Today, Etoday, and Digital Today, reports on M Plus’s solid-state pressing equipment development and pilot order, 2026-04-09
- Report (on-site feature) posted on the M Plus website on developing a high-pressure hot press and multi-stage roll press with a 2027 commercialization target, 2025-05
- Y.-G. Lee et al., “High-energy long-cycling all-solid-state lithium metal batteries enabled by silver–carbon composite anodes,” Nature Energy 5, 299–308, 2020
- Google Patents, WO2023224342A1 “All-solid-state battery and manufacturing method therefor” (LG Energy Solution Ltd)
- Google Patents, US20260088331A1 “Flexible frame for use in applying high pressure in the manufacture of a solid-state battery cell” (Solid Power Operating Inc)