Tech Briefs Magazine - February 2022 - BT-17

Typically, liquid cooling is
employed for automotive applications,
but BYD uses a special thermally
conductive adhesive between the cooling
system and the cell stack in the Blade
battery. (Photo: BYD)
enabling faster power delivery for
improved vehicle acceleration. Discharge
voltage of LFP is very consistent.
Strategically, their chemistry does not
include cobalt or nickel. And the lack of
those metals makes them inexpensive,
with LFP costs under $100/kWh in China.
That cost advantage has prompted
Tesla, Ford, and Volkswagen to announce
a shift to LFP cathodes in order to move
away from cobalt and nickel. This is both
for ethical/mining reasons as well as to
offer significant cost reduction for some
EV models that do not require high performance
and +200-mile driving ranges
(that will be covered by high-manganese
content lithium battery chemistries with
higher specific energy). Ford, however, has
indicated that LFP cathodes may also end
up in the batteries of its electric F-Series.
Eliminate the Modules
Prior to its emergence as a consumer
electronics giant and an automaker,
China's BYD had been developing lithium-
and nickel-based battery technologies
since 1995. LFP became a major
R&D focus, leading to the " Blade " battery,
an innovation in lower cost, safer EV battery
packs. As Chen explains it, " The blade
battery originates from a concept called
CTP - cell to pack. CTP technology
directly integrates the battery cells into
the pack, without the use of modules.
BYD is, I believe, the pioneer to make this
battery concept available to the market,
Battery & Electrification Technology, February 2022
Thermal stability comparison of materials
considering that most competitors still
use different sizes of modules. "
Going beyond the CTP concept, BYD
recently showed a new battery concept
called CTC (cell-to-chassis). In CTC, the
inherent safety of the LFP chemistry
enables the Blade batteries to be integrated
directly into vehicle body structure.
BYD's 'e-platform 3.0' is an electric
vehicle structure that uses the battery to
increase the rigidity of the vehicle.
BYD engineers and chemists began
work on the CTP Blade concept about
three years ago, Chen said. It was purpose-designed
for automotive, to give
BYD a competitive weapon against NCM's
superior energy density and cold-weather
performance. " We have a big stake in
the LFP technology so we sat down to
determine how we can compete with
NCM, particularly NCM811 which is " a big
competitor " to the Blade battery.
The 811 number of the nickel-rich layered
oxide NMC811 denotes 80 percent
nickel and 1 percent each cobalt and
magnesium. According to battery experts,
while the chemistry offers high specific
energy density for EVs, its downsides
include rapidly-depleting capacity and
voltage. In terms of chemistry, " there isn't
a lot of innovation you can do in a short
time, " Chen said. " We did patent the cell
structure and mainly focused on structure
optimization. After a thorough analysis,
we decided to remove the module level;
that was the main breakthrough. "
Viewing an LFP battery's Module level
as unnecessary, the engineers removed it.
" In doing so we eliminate some mechanical
parts, reinforcements, and some harnesses, "
Chen noted. " With the Blade battery
we reduce weight, decrease overall
pack volume by about 50 percent, and
increase the energy density. This makes a
very solid point for our chemistry.
It's
more robust than a module-based pack,
it's lighter per cell and it's about 20 percent
cheaper. "
A Robust Design
The accompanying exploded view of
the Blade battery shows its simplicity.
Typical dimensions of the compact, single-cell
design are 905  118  13.5 mm
(35.6  4.6  .53 in.). The size can be customized.
The thin, blade-like cells are
inserted into the pack in a blade-type
array. BYD engineers have also decreased
the cubic volume of the battery installation
by 50 percent, improving overall
vehicle packaging.
Thermal stability comparison of materials
containing electrolyte
NCM
LFP
NCM
LFP
100
300
500
T/°C
180
230
280
T/°C
A thermal stability comparison for materials in NCM and LFP batteries. (Photo: BYD)
17
Heat production rate
Heat production rate
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