Automotive Engineering - May 2022 - 22

NIOBIUM:
magic metal for
battery anodes?
ELECTRIFICATION FEATURE
" Niobium's ability to assume multiple oxidative states is
basic to the expanded capabilities. "
A Toshiba NTO battery
cell, developed in
partnership with CBMM.
and are more thermally stable. Another strategy is the
hybrid battery, which seeks a " rounder wheel " by combining
one battery of high specific energy chemistry
with another having high current chemistry, with the
latter being recharged by the former.
Anodes such as LTO (lithium titanium oxide), with
an open-spinel chemical structure, allow high current
and rapid charging with good safety and outstanding
cycle life (thousands, not hundreds of cycles). But
their specific energy storage capability is much inferior
to that of batteries favored for camera/laptop/phone
or EV applications. These qualities have given it a
place in powering electric city buses on short, repetitive
routes. High charge/discharge current and very
high cycle life allow a 6-minute charge at either end of
a route to provide adequate power and longevity.
Curb your enthusiasm
And what of niobium? Toshiba in Japan has marketed
its LTO battery since 2008, while research into openstructured
anodes has continued in many places. It has
been discovered that a niobium titanium oxide (NTO)
structure has a theoretical volume capacity (mAh/cm3
three times that of LTO, making NTO a potential competitor
in the EV market. It is claimed that the resulting
battery maintains 90% of its initial capacity after
22 May 2022
)
Niobium-based anodes are also gaining favor among electric motorcycle OEMs. U.S.based
Lightning Motorcycles, maker of the Strike Carbon superbike shown, partnered
with CBMM on NTO cells it used to set the world speed record (215.907 mph) for
electric two-wheelers. Another electric-bike maker, Brazil-based Horwin, is working
with CBMM and expects to launch its first NTO-battery-powered bike by 2024.
5,000 charge/discharge cycles, retaining LTO's ability to be rapidly
recharged in temperature as low as 14°F (-10°C).
These new anode materials are described as Wadsley-Roth crystallographic
shear structures, open enough to offer rapid, low resistance
charge/discharge, containing many lattice vacancies for lithium ions,
yet not changing volume during charge/discharge as carbon does.
Niobium's ability to assume multiple oxidative states is basic to the
expanded capabilities. The intensive and detailed study that has
gone into such development gives hope that increasingly, improved
battery electrode capabilities can be actively engineered - perhaps
even by computational methods - rather than passively discovered
by that old stand-by of research, trying everything.
Rapid charging capability sounds good but restrain enthusiasm
until you calculate the amperage required. Can foreseeable charging
stations deliver it - even with the liquid-cooled cables now being
discussed? Creating a new anode composition such as NTO is only a
beginning. A whole range of existing and possible future techniques
must be applied to optimize the performance of its chemistry. As
noted in one paper, such work " requires deep understanding of crystal
and electronic structure. "
A primary supplier of ferroniobium (used in tiny amounts as a grain
refining agent in HSLA [high-strength low-alloy] steels) and niobium
oxide is CBMM (Companhia Brasiliera Metalugia e Mineracao) in Araxa,
Brazil. On Sept. 24, 2021, CBMM signed an agreement with Toshiba and
Sojitz Corp., a Japanese trading company, to develop a Li-ion battery
with NTO anode having higher specific energy yet retaining the rapid
charging and long life of its LTO predecessor.
AUTOMOTIVE ENGINEERING
FROM LEFT: CBMM; LIGHTNING MOTORCYCLES
Automotive Engineering - May 2022

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