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Pure Silicon Anodes Boosting the Energy Density of Li-ion Batteries

Periodic Reporting for period 1 - LeydenJar (Pure Silicon Anodes Boosting the Energy Density of Li-ion Batteries)

Reporting period: 2019-04-01 to 2020-03-31

LeydenJar Technologies BV is a Dutch high tech venture and spin off company from applied research institute TNO. It is applying a solar cell production technology to produce a pure silicon anode for use in Lithium-Ion battery cells. The current generation of Li-ion battery cells does not have a sufficient energy density (the amount of energy stored per liter or kg of battery cell) for a wide range of applications, from consumer electronics to electric vehicles, from e-flight to renewable energy storage. In all these applications an increased energy density could lead to substantial customer value, such as a longer range for electric vehicles, more powerful applications for a smart phone, and smaller battery cells for small products. It could even enable new industries such as e-flight.

The current generation of Li-ion battery cells is based on graphite anodes. The maximum theoretical capacity of graphite to contain Lithium ions has been reached. An alternative material is silicon, as it can theoretically contain 10 times as much Lithium ions. However, silicon swells when Lithium ions enter it, up to 300%. In a normal case a pure silicon anode would crack after charging it, as an alloy is created, which expands, and the active anode layer is broken. This is why the battery industry is developing silicon particles that can withstand the swelling, and that can be used in the traditional production process of anode roll manufacturing. State of the art cells now have a maximum of 5% silicon in the graphite anode, increasing the energy density incrementally.

LeydenJar in stead has created a pure silicon anode that remains mechanically stable when it is used as battery material. This is because we create a porous silicon anode. We produce the anode in a single thin film process step (PECVD) in which silicon is grown in a columnar structure. The space between the pillars and inside the pillars allow the silicon to absorb the swelling and to remain intact. These pure silicon anodes can replace the traditional coated anodes in a Li-ion battery cell and can substantially improve the energy density, enabling battery cells with the highest energy density in the world.

The objective of this LEYDENJAR project is a) to engineer pure silicon anodes that can enable an energy density at stack level of 1.200 Wh/l (50% more energy density in an industry that can improve the energy density by 3% per year), b) to build a demonstration roll to roll production machine that can make pure silicon anode rolls, c) to validate this roll in a battery production plant.

This technology is strategically important for Europe. First because battery technology is an enabler for innovation in a range of industries. Second because the European industry needs to rely on the emerging European battery production infrastructure in order not to become too dependent on Asian suppliers. Thirdly because we can offer this production technology to European battery producers so that they can produce superior battery cells at similar cost and with reduced CO2 footprint.
In the first year of this LEYDENJAR project (two years in total) we have focused on four work packages. In work package 1 we have engineered high capacity pure silicon anode material. We worked on improving the plasma deposition parameters, leading to an optimized silicon morphology, did cell balancing, improved formation loss and mechanical stability. This has led to very good results, beyond what we originally expected. We have demonstrated energy density at stack level beyond 1.200 Wh/l and cycle life close to 500. In order to demonstrate this performance in larger cells, we are currently optimizing the quality of the copper substrate foil. We expect to demonstrate our milestone for this work package in time.

In parallel we have worked in work package 2 on realizing the demo plant for pure silicon anode roll production. Instead of designing and building a roll to roll PECVD tool ourselves, we have been able to acquire an existing roll to roll PECVD tool and made it fit for our purpose by adjusting the gas infrastructure and software. We have already made battery cells out of the material with good performance, and are now optimizing the homogeneity of the silicon layers. We have saved a lot of time and substantially reduced the operational risks of the demo plant in this way. We expect to demonstrate our milestone for this work package in time.

Also at the same time we worked in work package 5 on exploitation, IP, and communication. The strong progress in both work packages 1 and 2 have enabled us to attract a lot of industry attention, both from OEM's using battery cells in their products, as from battery cell manufacturers. We have started a first consortium with a European OEM and a European battery cell manufacturer on building prototype cells for a specialty application. Furthermore we have started first sampling projects to let OEM's and battery cell manufacturers test our pure silicon anode sheets in their battery labs. We made an invention in the adhesion of the silicon on the copper foil, for which we applied for a patent in August 2019. We have also actively communicated about our project, for instance we were exhibitors at the CES fair in Las Vegas in Jan 2020. Please see attached short movie clip that we have made for communication purposes.

In work package 6 we established and maintained project management. We have set up a tracking system to trace hours spend on the project, an accounting system to trace eligible actual cost versus budget, planning and review sessions and worked on the various deliverables during the tenor of the project.
As stated, we believe we can reach 1.200 Wh/l at stack level for battery energy density using our pure silicon anode. Fraunhofers leading battery roadmap 2030 has estimated the best energy density for pouch cells in 2020 to be 600 Wh/l. The difference between energy density at stack level and at cell level, is that the non active packaging is taken into account in the weight or volume at cell level. Typically the energy density at pouch cell level is 88% over stack level. So if we demonstrate 1.200 Wh/l at stack level, this implies 1.056 Wh/l at pouch cell level. This means that we have outperformed the state of the art as forecasted by Fraunhofer by 76%!

The roll to roll PECVD production process for silicon anode rolls is scalable, has the potential to reach cost parity with the traditional anode production method, fits in existing battery plant design, and can be produced at 40% lower CO2 footprint. In combination with the impact on the energy density at battery level, our technology has a serious and disruptive impact on the emerging European battery infrastructure, and could offer substantial benefits to European OEM's, including the automotive industry to innovate their products.

As follow up to the project we are planning to build an optimized version of our roll to roll PECVD machine, so that we can scale up to the huge production output required at gigafactories. For that we aim to raise a € 15 mln Series A round this year. After the EASME phase 2 grant agreement was signed, we successfully closed follow on funding (equity and debt) in September 2019 and February 2020 (totaling € 2,8 mln).
LeydenJar's demo plant
pouch cell by LeydenJar
LeydenJar's battery lab
automatically charging and discharging battery cells