MG's case for semi-solid batteries beyond the bridge

Most of the industry treats the semi-solid-state battery as a waypoint. A chemistry good enough to sell today, engineered to be quietly retired once fully solid electrolytes are ready for the road. MG, or more precisely SAIC Motor, disputes that framing. Speaking to AMS at MG Tech Day II, Dr Li Zheng, the company's global chief battery scientist, argued that his SolidCore battery is not a placeholder at all, but a distinct product line with a commercial life of its own, one that will keep manufacturing space alongside, rather than beneath, the all-solid-state cells his teams are simultaneously building. In a separate presentation to the same audience, Zheng went further, setting out the materials science behind that claim and a case study in where it matters most on the factory floor, the plug-in hybrid.

That claim matters to a manufacturing audience because it changes the capital allocation question. If semi-solid is a bridge, gigafactories built for it are a sunk cost awaiting replacement. If however, as Zheng insists, it is a parallel product in its own right, those factories are in fact a long-term asset.

A bridge that intends to outlast the destination

Asked how much of the current SolidCore line could be carried over to a fully solid-state production process, Zheng was precise about the scale of the chemical change involved. "The all-solid-state is totally different compared with semi-solid," he said. "Semi-solid has about 80% similarity to the liquid. We only have a 20% change. And for the all-solid, they're only 40% similar compared with the liquid. So it's much different."

That gap explains why MG is not treating solid-state as an upgrade path so much as a second production system. On current capacity, Zheng said, "we already have about 10 gigawatt hours. And we think that for the following years, for 2027, we will increase our capability for the semi-solid state battery to about a 30-gigawatt-hour of capability."

Independent figures on Qingtao Energy Development, SAIC's semi-solid cell partner and the entity understood to be supplying SolidCore cells, put current Gen2 output at around 2GWh with a further 25.5GWh under construction, a total of roughly 27.5GWh based on figures the supplier has published on its own website.

That is broadly consistent with the trajectory Zheng described, even if the two figures cannot be reconciled precisely from public data alone, and AMS was unable to independently verify MG's own 10GWh current-capacity claim.

However, Zheng's rationale for building at that scale rather than treating semi-solid as transitional was indeed clear on the point.

"We think the semi-solid-state battery is not only a stage between the liquid and all-solid, it will long-term exceed, because they can solve certain problems that are hard to solve with all-solid state batteries, because of the quick-response capabilities that we see only in semi-solid state batteries."

The physics behind the speed

Zheng used his presentation slot to explain why that quick-response capability exists at all, and the answer sits at the level of crystal structure rather than pack design. SolidCore's manganese-based cathode material is built around what Zheng called a distinctive three-dimensional, high-speed conductive network for lithium-ion transport, in contrast with the structures used in conventional chemistries.

"We have a unique three-dimensional structure for lithium-ion transport. Compared with LFP and NMC battery materials, it has a fundamentally different material structure." The distinction lines up with independent reporting on the technology, which describes SolidCore's spinel cathode structure as three-dimensional against NCM's two dimensions and LFP's single dimension.

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Zheng's explanation of what that means in practice was blunt about the competing chemistry. "Because we have a three-dimensional structure," he said, "during the charging or discharging process the lithium ions can move into or out of the structure very quickly. With an LFP structure, by comparison, lithium ions effectively have to queue up to enter or leave the structure. That limits the speed of lithium-ion transport."

He then walked us through the underlying physics. Lithium-ion movement into a cathode particle is a diffusion process, governed, as Zheng put it, by Fick's second law, from which "we find that there can be an undesirable phenomenon known as polarisation."

The relationship he described was direct, greater polarisation means longer response time and a bigger delay, which in turn limits how much power the battery can deliver or absorb. Applying Fick's law resolves the practical question of how to reduce it. 

"We find that the polarisation, η, is inversely related to the diffusion coefficient, D. The diffusion coefficient, D, is completely different for different material structures. For our three-dimensional structure, the diffusion coefficient is much higher than it is for a one-dimensional LFP material structure."

For a manufacturing audience, the significance is less the equation itself than what it implies about the battery's dynamic response - the property that determines how quickly a pack can respond to a sudden demand for power, whether that demand comes from hard acceleration or from an engine management system asking the battery to fill a gap.

Two electrolytes, two different jobs

SolidCore's electrolyte is not a single material but two working in tandem, each solving a problem the other cannot. "We have the SolidCore cathode material, and we also have a semi-solid electrolyte. This electrolyte has two different components, one liquid and one solid," Zheng said. The solid component keeps the cathode material functional over repeated cycles.

"The solid component ensures that our SolidCore cathode material can operate effectively. Without the solid-electrolyte material, the cycle life of the cathode would be very low." It also does double duty on safety, a claim consistent with SAIC's own reporting elsewhere that SolidCore cells have passed nail-penetration and 200°C thermal-box testing without ignition.

The liquid fraction, meanwhile, exists to solve a different problem entirely, the physical interface between electrolyte and electrode. "The liquid component, meanwhile, provides very good interfacial contact," Zheng explained, contrasting it with a fully liquid battery, where "during the discharge process lithium ions must cross the interface and enter the cathode material. At this point, they can effectively queue up and slow down. However, this does not happen in the same way within our structure. Our interface enables much smoother and faster lithium-ion transport."

It is a useful corrective to any assumption that "semi-solid" simply means "mostly solid, with the liquid as a leftover." In MG's account, the liquid fraction is doing deliberate, load-bearing work.

Solving a PHEV's oldest anxiety

The clearest commercial case Zheng made for SolidCore was not about pure electric vehicles at all, but about plug-in hybrids, where MG plans to roll the battery out across its Hybrid+ range. His starting point was a structural weakness common to every PHEV. "A PHEV has two complex systems working together. One is the internal combustion engine system, and the other is the electric vehicle system," he said, and combining them risks combining their disadvantages rather than their strengths. "If we merely put these two different systems together, it could mean bringing together the disadvantages of both sides. That sounds terrible."

Two specific failure modes concerned him. The first is what happens as a conventional battery's state of charge falls. "When the state of charge of a conventional battery, what we call the battery SOC, is low, its discharge power output can be limited. For the vehicle, this means that when the battery is running low, acceleration performance and energy-saving performance can be greatly reduced. That can make users anxious."

The second is cold weather, where a PHEV's relatively small engine ends up doing more of the work than it was sized for. "We all know that conventional liquid-electrolyte batteries can struggle to operate at low temperatures. Under those conditions, we may have to rely on a relatively small engine to drive the whole vehicle. That can also create anxiety for users."

Zheng framed SolidCore's faster ion transport and improved cold-climate behaviour as a direct answer to both problems, allowing the electric side of a PHEV to keep contributing meaningfully even at low charge or low temperature, rather than handing the burden back to a downsized engine. His summary of the effect was characteristically compact. "We have better power performance, very good all-climate adaptability and higher energy efficiency. That is why we say one plus one is greater than two."

Solid-state timeline points to an early Start of Production (SOP)

MG's fully solid-state work continues in parallel, under a separate research team reporting to Zheng. "For the all-solid state battery, factory research and mass production is also our task," he said in interview. "We have solved long-range charging, higher energy density, those performance areas. However, we also have some issues which I think will be solved in the next year, because the lifecycle for the testing car is not enough for mass production. Actually there are so many things, like temperature, like pressure, that can affect the performance, and we still need to solve those problems. For mass production, the processing problem, I think nearly all of the problem is nearly solved already."

On timing, he was specific. "We already begin our mass production line construction, for the all-solid battery, and I'm sure that part will be SOP, I think, at the beginning of next year."

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That is a more aggressive timeline than SAIC has stated publicly elsewhere. The automaker has previously disclosed that Qingtao's all-solid-state line in Anting, Shanghai, completed full-process commissioning in late 2025, with prototype vehicle testing planned for 2026 and commercial mass delivery targeted for 2027, alongside phase-one production capacity at Anting planned at 0.5GWh. Readers should treat "beginning of next year" as Zheng's own framing rather than a confirmed SOP date, given the gap between it and SAIC's previously stated 2027 commercial target.

Moisture control, once the industry's hardest problem

For engineers weighing whether to follow MG into semi-solid production, the operational risk that usually dominates the conversation is moisture and atmospheric control on the line. Zheng dismissed it as a solved problem for MG specifically. "I think we already have some mature technology for mass production. I think there's no longer any difficulty for us. So I don't think we have a problem in this regard."

The harder constraint, he suggested, sits elsewhere, particularly as MG considers a European manufacturing footprint. "We also have a plan to build a new factory in Europe, maybe in the future, and there might be some problem, because we don't have enough engineering people. I think the experience of the people is very important. We are already training thousands of semi-solid-state battery engineers in China now, so that might be part of our treasure, and maybe our main advantage compared to other players."

That framing puts a workforce constraint, not a chemistry one, at the centre of MG's European expansion risk, a point worth noting given the company has already opened a new engineering centre in Frankfurt this year to support its "in Europe, for Europe" development strategy.

One platform for four powertrains

SolidCore is not being packaged as an EV-only technology, and the interview added a manufacturing dimension to the PHEV case Zheng had made in his presentation. MG intends to run the battery alongside internal combustion, hybrid and plug-in hybrid architectures on the same assembly lines, which raises an obvious question about mixed-model flexibility. Zheng described a standardisation strategy built around interfaces rather than parts.

"We are developing a very unique technology to combine the different parts of the whole powertrain system. The battery it's only one part, and we set up some standard interfaces together, and that means the heat environment and some other things are quite similar."

The genuine differentiator, he said, sits in software rather than hardware. "There's only one thing that's different compared with the semi-solid battery and the traditional liquid battery, and that's the software. Because the response capability is different. What we have is better, in that it's more effective. We have a shorter time delay for the signal, that means we can save more energy. So the software is totally different. We have a joint software team to achieve this."

The commercial payoff, according to Zheng, is design efficiency across the entire range. "For the EV cars and the PHEVs, for the whole lineup, we have a standard technology platform, to make all the ICE, EV, HEV and PHEV designs use it. So we have very high efficiency for car design, because no matter what kind of powertrain technology, they can design with a similar model, and we can adapt everything else accordingly."

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The 10,000-unit tipping point

MG's decision to debut SolidCore in a mass-market city car, the MG4 EV Urban, rather than a flagship model, breaks with the sequencing most rivals have followed. Zheng framed the choice as one of manufacturing economics rather than marketing strategy, and he gave AMS a specific number. "I think that the volume balance point is about 10,000 per month," he said, describing the threshold at which SolidCore production costs match or beat a conventional liquid lithium-ion pack.

"We have complementary production, so we can keep the balance. That's why we chose MG4 Urban in Europe, and with the MG4 itself in China alone, we can get over that number. So if the requirement number is larger than this number, that means the cost of semi-solid is lower."

That threshold looks achievable on current sales data. The semi-solid MG4 in China reportedly reached its 100,000th unit roughly eight months after launch, a pace the company has called a record for the fastest-selling pure electric hatchback, with monthly sales exceeding 13,000 units in April alone. If those volumes hold, MG's Chinese production alone clears Zheng's stated balance point without relying on European volumes to do the work.

Building a supply chain from nothing

Because SolidCore uses a chemistry with no established international supplier base, MG has had to internalise far more of the value chain than a conventional cell producer would. Zheng was direct about how much of it the company controls itself. "Most of our supply chain, the key supply chain, is ourselves. Everything from the solid electrolyte materials to the SolidCore cathode material is also made by us." Peripheral components followed existing liquid-cell suppliers more closely, he said, "like the shell, or some other small materials or components, like a binder, like a conductor, everything is quite similar to liquid," while anode materials draw on "the same mature liquid supplier."

Asked to confirm the scale of that vertical integration, Zheng gave a blunt explanation. "Basically, because this is a new technology, that means there's no mature supply chain for the difference." In practice, MG's speed to market has depended on owning the parts of the chain nobody else had yet built, an approach that concentrates both intellectual property and supply risk inside the group.

Stability across a three-month voyage

A centralised Chinese production base creates a logistics problem specific to semi-solid chemistry, namely whether a 95% solid electrolyte structure survives two to three months of maritime transit before reaching an overseas assembly line. Zheng said the answer lies in state of charge management rather than the electrolyte itself. 

"It's related to the state of charge. For transport, when all our products go out of our factory, we will make sure the state of charge, the SOC, is not very high. It's lower, I would say, which means it's less susceptible to issues. That's why, because we must make sure that during two or three months of storage, for the transport, for different environments, different temperatures, they all maintain the same level of voltage and resistance. That's very important for us. And also, having enough data to corroborate that our battery technology and the product is reliable enough, is also critical."

What Zheng wants Western manufacturers to know

Asked what he would want OEMs like Ford, GM and Stellantis to understand about MG, Zheng moved away from chemistry and margin entirely. "This one's easy. For us, despite all the technological expertise we have, the most important thing, is people."

It is a modest note to end on, given the scale of what precedes it, a battery whose speed advantage traces back to a diffusion coefficient, a PHEV strategy built to eliminate range and cold-weather anxiety rather than merely reduce it, a semi-solid-state platform already running at meaningful volume, and a solid-state line under construction behind it. Whether MG's 2027 solid-state timeline lands as early as Zheng suggested, or closer to the dates SAIC has previously disclosed, will be the clearest test yet of whether that dual-track manufacturing strategy holds up at scale.