Silicon is a highly desirable anode material for EV batteries as it has over nine times the energy density of current graphite anodes, allowing for faster charging rates. Significantly changing the energy density of a battery, silicon anodes close the gap in cost, charging time, and driving range between EV and ICE vehicles.
Automakers are committed to using silicon in batteries.
“Silicon is awesome and inexpensive,” as was stressed during the Tesla Battery Day 2020 presentation.
“It is necessary to change the cell chemistry from graphite to silicon…higher energy density, lower lithium plating, faster charging,” said Oliver Blume, Chairman of the Executive Board, Porsche AG at Volkswagen Power Day 2021.
“… silicon can connect more lithium ions than just the graphite” was stated at Volkswagen Power Day 2021 by Frank Blome, Head of Business Unit Battery Cell and System at Volkswagen Group Components.
There is a fundamental and unresolved problem with silicon related to its expansion during battery charging and discharging, which leads to cracking and loss of contact between the silicon material particles.
As a result, a battery with silicon goes out of service very quickly. This problem made it impossible to use silicon, the best material in terms of energy density, in the formulations of modern Li-ion batteries.
TUBALL™ graphene nanotubes cover the surface of the silicon particles and create highly conductive and durable connections between them. These connections are so dense, long, conductive, and strong that even when the silicon particles in the anode expand and the material starts to crack, the particles stay well connected to each other through the TUBALL™ graphene nanotubes.
This prevents the anode from going out of service—the hugely improved cycle life is enough to meet even the strictest EV manufacturer requirements.
When added to the silicon anode, graphene nanotubes bind silicon particles together, even during their expansion, and maintain electrical connection. This prevents battery degradation.
TUBALL™ is the only material today that creates long, flexible, conductive, and strong bridges to keep silicon anode particles well connected to each other even during severe volume expansion and cracking.
Leading Li-ion manufacturers have proven that TUBALL™ nanotubes make it possible today to create anodes containing 20% SiO and thus reach record-breaking battery energy densities—up to 300 Wh/kg and 800 Wh/l. This enables fast-charging capabilities. Such battery cells can deliver up to +15% higher range than the best Li-ion battery cells on the market.
OCSiAl’s R&D team’s results show that TUBALL™ allows for the maximization of SiO content in the anode to up to 90%, which will result in energy density of 350 Wh/kg.
Batteries with TUBALL™ are already in serial production by a number of leading Li-ion battery makers.
To facilitate the use of graphene nanotubes in battery applications, OCSiAl has developed the ready-to-use product TUBALL™ BATT that contains well-dispersed nanotubes in various liquid carriers and that can be simply mixed in during standard manufacturing processes.
TUBALL™ BATT H2O is an ultrafine TUBALL™ dispersion in water for high-energy Si anodes. It creates a robust network inside the Si anode and solves the key problem of its degradation, allowing Li-ion battery makers to use record high quantities of silicon in the recipes of their cells for the first time and reach the desired energy density targets, as well as unlocking fast-charging capabilities.
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The pitch-derived soft carbon and SWCNTs provided an excellent conductivity, and the porous structure of the composite accommodated the stress produced by the Si expansion.
The all‐nanomat full cell shows exceptional improvement in battery energy density – 479 Wh/kg battery, and Si-anode capacity – 1166 mAh/g.
High thickness and specific capacity leads to areal capacities of up to 45 and 30 mAh cm−2 for anodes and cathodes, respectively. Combining optimized composite anodes and cathodes yields full cells with state-of-the-art areal capacities (29 mAh cm−2) and specific/volumetric energies (480 Wh kg−1 and 1,600 Wh l−1).
Areal capacities greater than 10 mAh/cm2 and volumetric capacities greater than 1400 mAh/cm3 can be achieved.
The use of SWCNT conductive additive enables graphite-free SiO electrodes with 74% higher volumetric energy and superior full-cell cycling compared to graphite electrodes.
The best results overall are obtained with 0.5%wt SWCNT added to the active powder, which produced 800mAh/g after 250 cycles.
