Researchers at Germany’s Fraunhofer ISE say their in-house silicon-rich anode pouch cells kept more than 83% of their capacity after more than 1,000 full cycles, but only under high mechanical pressure.
Fraunhofer ISE said it has cycled 25 Ah pouch cells with silicon-rich anodes more than 1,000 times, with the cells retaining over 83% of their original capacity at a cell-level gravimetric energy density of 280 Wh/kg.
The 40-layer cells were built on a semi-automatic production line in the cleanroom of the institute’s Center for Electrical Energy Storage in Freiburg, Germany, using commercially available electrode foils. They pair a silicon-carbon/graphite anode with a nickel-rich nickel-manganese-cobalt (NMC) cathode. The silicon-carbon composite made up 51% of the anode active material, and the anodes reached a specific capacity of more than 1,000 mAh/g and an areal capacity of more than 5 mAh/cm².
“Cycle life is one of the key hurdles to the widespread industrial use of silicon-rich anodes,” said Lukas Dold, team leader for battery materials technology and scaling at Fraunhofer ISE. “More than 1,000 cycles with a capacity retention of at least 80 percent is considered an important performance target here.”
The cell-level 280 Wh/kg was achieved in the institute’s non-optimized PrecISE research cell format. Dold said an industrially optimized pouch format is expected to reach about 330 Wh/kg.
Pressure dependence
The researchers cycled the cells at 1C at two axial contact pressures, 300 kPa and 1,000 kPa. The 83% retention figure applies to cells held at 1,000 kPa.
“At a lower contact pressure of 300 kPa, a significantly greater decline in usable capacity over time is observed, particularly during 1C operation,” said Marc Kissling, group leader for battery cell production and technology evaluation. “Mechanical cell pressure is therefore an important parameter for the stable operation of silicon-rich pouch cells.”
Fraunhofer ISE did not publish a retention figure for the 300 kPa cells. It also reported that as the cells aged, capacity measured in periodic check-ups at low discharge rates increasingly diverged from the capacity available during regular 1C cycling. The institute said performance under real-world operating conditions must be considered alongside capacity retention when evaluating silicon-rich cells.
Silicon’s theoretical specific capacity is 10 times that of graphite, and Fraunhofer ISE said silicon-carbon composites could reduce global dependence on graphite and shift raw-material value creation toward the European Union.
The StrOboBatt project is led by PCC Thorion with Fraunhofer ISE and Glatt Ingenieurtechnik, with LG Chem Europe, E-Lyte Innovations and UniverCell Holding among its partners. It received €2.6 million in federal funding and is scheduled to run for three years, PCC said when the project launched in 2024. The partners cited stationary storage of surplus solar and wind power as a target application, along with electric mobility and aerospace.
Other silicon-carbon anode developers are moving toward commercial scale. In July, the Australian Renewable Energy Agency (ARENA) awarded up to AUD 45 million ($31.6 million) to Himadri-backed Sicona for a commercial-scale demonstration plant at BlueScope Steel’s Port Kembla precinct in New South Wales. ARENA said Sicona’s material could raise lithium-ion energy density by up to 20% and enable charging up to 40% faster than conventional graphite anodes.
From ESS News
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