The SOLiD project is developing next-generation lithium-metal batteries, combining safety and performance with recyclability for Europe’s clean energy future
On the path to a climate-neutral future, few technologies are as indispensable and as closely scrutinised as the battery. Powering everything from smartphones to electric vehicles (EVs), batteries sit at the heart of the energy transition. But as demand increases, so do concerns about sustainability, cost, and the physical limits of today’s dominant lithium-ion technology.
SOLiD is an ambitious EU-funded project aimed at redesigning the rules of battery manufacturing. Launched in September 2022, SOLiD brings together 13 partners across eight countries, ranging from industrial powerhouses to nimble SMEs and leading research institutes. The goal of the project is to create a sustainable pilot-scale process for the next generation of solid-state lithium-metal batteries, which promise higher energy density, improved safety, longer lifespan, and recyclability by design.
Four years after SOLiD’s outset, the project has reached almost the end. Its breakthroughs in electrode dry processing, polymer electrolyte formulation, and digital quality control are paving the way for Europe to scale solid-state batteries beyond the lab and into real-world production. And with them comes the promise of safer, lighter and energy-efficiently manufactured batteries for EVs and a path toward European battery sovereignty.
Beyond lithium-ion: The need for a new generation
Lithium-ion batteries have carried the electrification revolution this far. They power millions of EVs on Europe’s roads and are central to the continent’s plans for renewable energy storage. Yet, their limitations are increasingly clear. Liquid electrolytes are volatile and flammable, graphite anodes limit energy density, and dependence on critical raw materials, especially cobalt, poses both supply risks and ethical concerns.
Solid-state lithium-metal batteries (SSBs) offer a way forward. By enabling the use of NMC811 as cathode active material, replacing liquid electrolytes with solid polymers and swapping graphite for lithium metal anodes, these batteries can store up to 70% more energy in the same volume. They also reduce fire risks, perform better at higher voltages, and create design possibilities for lighter, more compact batteries. Most importantly, they can drastically cut dependence on cobalt and lithium by using advanced protective layers and thinner electrode coatings.
The problem, until now, has been scalability. Most SSB research remains confined to the lab, where carefully produced cells work in small numbers, but falter under industrial conditions. SOLiD was launched with the aim of bringing scalable manufacturing, recycling-ready design, and digital quality control into the DNA of solid-state batteries.
Reinventing the battery factory
SOLiD goes beyond better materials: it’s redefining battery manufacturing. Traditional electrode fabrication is a wet and wasteful process, relying on toxic solvents and energy-intensive drying steps. SOLiD is pioneering roll-to-roll (R2R) dry extrusion coating, which blends active cathode material, polymer binder electrolyte, and conductive additives into uniform films without the use of solvents and excess material waste.
Dry coating is a ‘game-changer.’ It’s cleaner, faster, and eliminates the need for costly solvent recovery and drying infrastructure, which is better for the environment and for production costs. The use of ALD-protected NMC811 enables dry extrusion coating under ambient conditions and eliminates the need for a dry room.
On the anode side, the project has scaled up the pulsed laser deposition (PLD) process of a thin lithium layer below 10 micrometres in thickness and a thin protective lithium-alloy layer on lithium metal to ensure compatibility with the cathode and electrolyte layers. This meticulous interfacial control is crucial for preventing dendrites, which are tiny needle-like formations that can pierce the electrolyte and short-circuit the battery.
Meanwhile, the solid polymer electrolyte (SPE) itself is being reinvented. Early work focused on polyethylene glycol-based systems, but, by mid-2025, the team unveiled a polyester-based formulation, PESDA, that vastly outperformed its predecessors. With tensile yields up to 250% before failure and stable cycling performance, retaining 95% of capacity after 120 cycles in prototype cells, PESDA is proving to be the electrolyte of choice for scaling into pouch cells.
From lab bench to pilot line
Pilot-scale production has already started. Extruded cathode films with improved thickness control and uniformity have been prepared, while slot-die-coated separator polymer electrolytes have been tested for consistency and repeatability. Protective coating for cathode active material has been ALD-processed to enable kilo scale production and roll-to-roll PLD-deposited lithium has been validated at coin cells both with liquid and solid polymer electrolyte.
The first smart inspection tools, combining particle detection, optical monitoring, and electrochemical impedance spectroscopy, have been integrated and verified in pilot lines and are now fully operational, enabling near real-time quality assurance.
This is where SOLiD’s digital edge comes in. The project is developing a digital twin, which is an AI-driven feedback and feedforward system that links inspection data directly to process control. In effect, the factory learns as it produces, reducing defects, improving yields, and cutting costs. This battery production line digital twin could become a template for future gigafactories, seeking to minimise waste and maximise efficiency.
Building for sustainability from day one
As SOLiD advances its next-generation SSB technology, sustainability is being engineered alongside performance. A comprehensive life cycle assessment of the cell manufacturing process has been conducted, evaluating environmental impacts from raw material extraction through the production and cell assembly. Because many of SOLiD’s materials and processes are novel and absent from conventional life cycle (LCI) inventory databases, process-specific LCI datasets in accordance with ISO 14040 and ISO 14044 standards are developed.
Milestones and momentum
By the fourth year of the project, the list of achievements is impressive:
- Pilot-scale dry extrusion of cathodes with binder solid polymer electrolyte.
- Pilot-scale slot-die coating of solid polymer electrolytes on a separator with a cross-linking capability.
- Roll-to-roll scale pulsed laser deposition of thin lithium-metal anode and lithium alloy.
- Effective protective barrier on lithium metal by atomic layer deposition.
- Kilo-scale atomic layer deposition of a protective layer on NMC811 powder.
- Validation of polyester-based electrolytes with superior mechanical and electrochemical properties.
- Validation of extruded cathode and PLD anode functionality in cells with SPE.
- Reference ‘Gen 2b’ cells built and tested in multiple formats.
- Inline inspection and quality control tools integrated and verified in a pilot line.
- Finalising a digital twin for the polymer electrolyte deposition with closed-loop control.
- Finalising a three-dimensional project-specific lifecycle sustainability assessment.
- Peer-reviewed publications and conference presentations disseminating results to the global battery community.
These advances are not only technical, but also strategic. With global demand for batteries expected to grow 14-fold by 2030, Europe faces stiff competition from Asia and North America. By developing both the materials and the manufacturing methods for next-generation SSBs, SOLiD is helping to secure Europe’s place in the global battery race.
Europe’s strategic battery sovereignty
Behind SOLiD’s technical breakthroughs lies a larger strategic goal: to ensure Europe’s energy independence. Today, most advanced batteries are produced in Asia, with China, South Korea, and Japan dominating the supply chain. This imbalance exposes Europe to supply risks and undermines its ability to fully control the environmental and ethical footprint of its energy transition.
By investing in projects such as SOLiD, the EU is working to shift this balance. The technologies developed, including dry extrusion, pulsed laser and atomic layer deposition, and inline characterisation systems, are more than laboratory successes. They are the building blocks of a homegrown European battery industry that can scale sustainably and competitively. In practical terms, this means reducing reliance on imported batteries and critical raw materials, while creating skilled jobs in European factories and research centres.
If Europe wants to meet its Green Deal targets and remain competitive in the global clean-tech race, building this battery sovereignty is not optional, but essential.
Looking ahead: Scaling and impact
As SOLiD enters its final eight months, attention is turning to scaling innovations into pouch cells and their safety testing, along with refining digital quality control with a feedback loop feature. The ambition is clear: to create a cost-efficient, high-yield, and environmentally responsible pilot-scale production line that can be transferred to industrial partners.
If successful, the project’s impact will be felt across the value chain:
- For EV drivers, ultrahigh energy density batteries mean longer driving ranges and faster charging.
- For manufacturers, dry processing and inline monitoring methods reduce costs while improving safety and reliability.
- For the environment, reduced reliance on cobalt and lithium eases pressure on critical raw materials and ecosystems.
- For society, safer batteries open up new applications in renewable integration and grid storage.
In many ways, SOLiD is building more than a battery – it’s building a blueprint for the factory of the future.
The bigger picture
The story of SOLiD is also the story of Europe’s determination to lead in clean technologies. As the continent pushes toward the Green Deal’s climate-neutrality targets, batteries are recognised as a strategic priority. Projects like SOLiD not only advance the science but also ensure that production capacity, sustainability, and resource efficiency are embedded in the very architecture of the industry.
With consortium leadership from VTT Technical Research Centre of Finland and strong participation from academia, SMEs, and industry, SOLiD is a microcosm of European collaboration. It reflects the continent’s recognition that the energy transition is not just a technological challenge, but also a social and economic one.
Final thoughts
The journey from lab prototype to industrial reality is rarely straightforward. However, as the SOLiD project demonstrates, it is possible to integrate cutting-edge materials science, innovative production methods, and sustainability principles into a coherent roadmap. The project has already proven that solid-state batteries can be manufactured more cleanly, safely, and efficiently.
As SOLiD’s pouch cell prototypes come to life and digital quality control systems go live, Europe moves one step closer to a future of stronger, more sustainable batteries. SOLiD is creating more than just energy storage. It’s advancing Europe’s energy independence, driving cleaner mobility, and establishing the groundwork for a circular economy – a testament to the fact that electrification’s future can be both powerful and sustainable.
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