8
Figure 14 shows one of the pressure-time plots where
the venting of three cells was captured as distinct jumps in
pressure.
Even though the volume of venting gas appeared higher
for the three-cell configuration, the peak pressure seen in
this configuration falls in line with the inverse power rela-
tionship as seen in Figure 13. In Figure 15 this new data
for LTO-type batteries were compared to past NIOSH data
looking at NMC-type and LFP-type cells.
Figure 15 shows how similar the LTO cells are to the
LFP cells, and how much more reactive the NMC cells are.
Even though the LTO and LFP peak pressures look the
same, the LFP-type batteries have a higher energy density
which manufacturers will want to consider.
LIMITATIONS
The limitations of the study that need to be considered
are as follows. The LTO cells were tested at a full state of
charge. It is known that the thermal runaway severity is
positively correlated with the state of charge [31]. Only one
cell type from one manufacturer was used. There are other
manufacturers that may use different cathode, separator, or
electrolyte chemistries that fall under the category of LTO
that were not tested. Differences in cell additives can influ-
ence failure response [32].
CONCLUSIONS
A very similar inverse power relationship was observed
from the maximum thermal runaway pressures of LTO-
type cells with the free space to cell volume ratio. This
relationship of pressure to free space per cell volume most
closely represented plots of an LFP-type cell. A container
with an internal volume of 1,175 ml was necessary for a
cell with a volume of 16.5 ml to meet the MSHA pressure
generation threshold specification. The vented gases that
were recorded during venting and thermal runaway were
approximately 3 L per cell with a volume of 16.5 ml. Given
the known energy density of the LTO cell, this results in
the highest volume of gas per the energy of the cell. The
temperatures recorded during thermal runaway were under
Figure 13. Pressure versus free space per cell volume for LTO
type LIB in sealed containers
Figure 14. Triple-cell venting event in a 1,175-ml container
showing additive pressures
Figure 15. Comparison of peak thermal runway pressures
from LTO, LFP [14], NMC [14] cells
Figure 14 shows one of the pressure-time plots where
the venting of three cells was captured as distinct jumps in
pressure.
Even though the volume of venting gas appeared higher
for the three-cell configuration, the peak pressure seen in
this configuration falls in line with the inverse power rela-
tionship as seen in Figure 13. In Figure 15 this new data
for LTO-type batteries were compared to past NIOSH data
looking at NMC-type and LFP-type cells.
Figure 15 shows how similar the LTO cells are to the
LFP cells, and how much more reactive the NMC cells are.
Even though the LTO and LFP peak pressures look the
same, the LFP-type batteries have a higher energy density
which manufacturers will want to consider.
LIMITATIONS
The limitations of the study that need to be considered
are as follows. The LTO cells were tested at a full state of
charge. It is known that the thermal runaway severity is
positively correlated with the state of charge [31]. Only one
cell type from one manufacturer was used. There are other
manufacturers that may use different cathode, separator, or
electrolyte chemistries that fall under the category of LTO
that were not tested. Differences in cell additives can influ-
ence failure response [32].
CONCLUSIONS
A very similar inverse power relationship was observed
from the maximum thermal runaway pressures of LTO-
type cells with the free space to cell volume ratio. This
relationship of pressure to free space per cell volume most
closely represented plots of an LFP-type cell. A container
with an internal volume of 1,175 ml was necessary for a
cell with a volume of 16.5 ml to meet the MSHA pressure
generation threshold specification. The vented gases that
were recorded during venting and thermal runaway were
approximately 3 L per cell with a volume of 16.5 ml. Given
the known energy density of the LTO cell, this results in
the highest volume of gas per the energy of the cell. The
temperatures recorded during thermal runaway were under
Figure 13. Pressure versus free space per cell volume for LTO
type LIB in sealed containers
Figure 14. Triple-cell venting event in a 1,175-ml container
showing additive pressures
Figure 15. Comparison of peak thermal runway pressures
from LTO, LFP [14], NMC [14] cells