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Together with Xiaoxi He from IDTechEx (UK), Holger Althues from Fraunhofer IWS (Germany) & Marc Copley from Warwick University (UK), Pirmin Ulmann from b-science.net
joined the panel discussion on 'Solid-state battery feasibility: when & how will we get there?' with 273 attendees.
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Over the last few months, a close to unanimous industry consensus has formed that solid-state batteries will be adopted in EVs, albeit initially
based predominantly on solid electrolyte layers that might still contain some liquid electrolyte, along with Si-carbon negative electrodes.
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Presumably, solid-state battery EVs will start capturing market share at the high end in 2022 (NIO: 150 kWh battery, 10% or more liquid electrolyte, 90% or less solid electrolyte),
followed by gradual market share expansion over many years, driven by continuous cost reductions and further energy density improvements.
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Many questions came from the audience as to how these new battery chemistries will affect pack design. These projections
can be made:
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Solid-state EV batteries will almost exclusively be built with pouch or prismatic cell form factors in which electrode / electrolyte layers are arranged in a stacked, not wound manner.
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Operating temperatures for future solid-state battery chemistries
will allow for an increased maximal operating temperature of 80-140 °C in EVs (currently with liquid electrolytes: 50-60 °C).
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The feasibility of building bipolar cells at large scale is a major potential advantage of solid-state batteries, which is expected to reduce inactive
parts in EV packs from ca. 30% to 12% (ProLogium). Toyota is also pursuing bipolar cells, along with others. Both ProLogium and Toyota appear to pursue
Si-containing negative electrodes for now, which raises the question as to whether bipolar cells can be implemented with Li metal negative electrodes -
and if not yet - whether Li metal negative electrodes will deliver sufficient energy density improvements at pack level to compete with bipolar cells with Si-carbon negative electrodes.
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The debate as to whether oxides, sulfides and/or polymers will be used is still very much open considering that substantial breakthroughs have recently
been made at the materials level, while challenges remain:
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Oxides: suppression of lithium dendrite formation at high currents has been achieved (QuantumScape), but successful commercialization depends on an ambitious upscaling effort that is still to be accomplished.
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Sulfides: suppression of toxic hydrogen sulfide gas emissions in ambient air has been achieved (BASF together with Waterloo University, Prof. Linda Nazar and coworkers), but
the extent of hydrogen sulfide emissions upon contact with water is not clear (important in case of an accident and during recycling). This makes projections
on the necessary safety features at pack level difficult.
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Polymers: it is not yet clear if it will be possible to avoid liquid electrolytes if a polymer battery is to be operated at room temperature.
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