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Theoretical Limits of Energy Density in Silicon-Carbon Composite Anode Based Lithium Ion Batteries


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Silicon (Si) is under consideration as a potential next-generation anode material for the lithium ion battery (LIB). Experimental reports of up to 40% increase in energy density of Si anode based LIBs (Si-LIBs) have been reported in literature. However, this increase in energy density is achieved when the Si-LIB is allowed to swell (volumetrically expand) more than graphite based LIB (graphite-LIB) and beyond practical limits. The volume expansion of LIB electrodes should be negligible for applications such as automotive or mobile devices. We determine the theoretical bounds of Si composition in a Si–carbon composite (SCC) based anode to maximize the volumetric energy density of a LIB by constraining the external dimensions of the anode during charging. The porosity of the SCC anode is adjusted to accommodate the volume expansion during lithiation. The calculated threshold value of Si was then used to determine the possible volumetric energy densities of LIBs with SCC anode (SCC-LIBs) and the potential improvement over graphite-LIBs. The level of improvement in volumetric and gravimetric energy density of SCC-LIBs with constrained volume is predicted to be less than 10% to ensure the battery has similar power characteristics of graphite-LIBs.
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Scientific RepoRts | 6:27449 | DOI: 10.1038/srep27449
Theoretical Limits of Energy
Density in Silicon-Carbon
Composite Anode Based Lithium
Ion Batteries
Ranjan Dash1 & Sreekanth Pannala2
Silicon (Si) is under consideration as a potential next-generation anode material for the lithium ion
battery (LIB). Experimental reports of up to 40% increase in energy density of Si anode based LIBs
(Si-LIBs) have been reported in literature. However, this increase in energy density is achieved when
the Si-LIB is allowed to swell (volumetrically expand) more than graphite based LIB (graphite-LIB) and
beyond practical limits. The volume expansion of LIB electrodes should be negligible for applications
such as automotive or mobile devices. We determine the theoretical bounds of Si composition in
a Si–carbon composite (SCC) based anode to maximize the volumetric energy density of a LIB by
constraining the external dimensions of the anode during charging. The porosity of the SCC anode is
adjusted to accommodate the volume expansion during lithiation. The calculated threshold value of
Si was then used to determine the possible volumetric energy densities of LIBs with SCC anode (SCC-
LIBs) and the potential improvement over graphite-LIBs. The level of improvement in volumetric and
gravimetric energy density of SCC-LIBs with constrained volume is predicted to be less than 10% to
ensure the battery has similar power characteristics of graphite-LIBs.
For the past two decades, signicant eorts have been dedicated towards the development of high energy den-
sity LIBs1–3. e energy density of a LIB depends primarily on the specic capacities of cathode and anode, and
the operating voltage window at which the battery can be cycled1–3. Si has emerged as one of the promising
anode materials for high energy LIBs4,5. It is believed that a small amount of Si based material is currently used
in the anode of LIBs6. Si oers a suitable low voltage for an anode and a high theoretical specic capacity of
~4,200 mAh/g based on the formation of the Li22Si5 alloy, which is about 10 times higher than that of conventional
carbon based anodes (~372 mAh/g)4.
Today, the LIB capacity is limited by the capacity of cathode rather than the capacity of the anode1 with
the implication that any gains on anode capacity are proportionately reduced based on the overall cell compo-
sition. Commonly used cathodes such as lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide
(NMC), and lithium nickel cobalt aluminum oxide (NCA) have usable capacities of 140 mAh/g, 170 mAh/g,
and 185 mAh/g, respectively, which are lower than the widely used graphite anode (experimental capacity:
~330 mAh/g)7. us, despite Si having a signicantly larger capacity than graphite, the level of improvement in
gravimetric energy density on a cell level achieved using Si anode and existing cathodes is limited to a maximum
of ~41% (see Fig. S1a). is calculation does not take into account the issue of swelling; when mechanical eects
are taken into account, the possible capacity improvement becomes signicantly less.
Si has been a challenging anode material to work with because it expands volumetrically up to 400% upon full
lithium insertion to form the Li22Si5 alloy and conversely shrinks upon lithium extraction4,5,8,9. e other issue
with Si is its low ionic and electronic conductivity. Nano-sized Si particles combined with graphite and/or con-
ductive carbon (CC) are under investigation as a means to obtain a viable silicon based LIB anode4,10,11.
Signicant eort towards increasing the cycle life of Si anodes are currently being pursued with a reasonable
degree of success4. Up to 40% increase in gravimetric and volumetric energy density for Si-LIBs are reported in
various experimental works4,12; however, this improvement is achieved when the Si anode (and thus the cell) is
allowed to swell beyond practical limit. e increase in external volume (also referred to as swelling) of LIBs
1SABIC, 475 Creamery Way, Exton, PA 19341, USA. 2SABIC, 14100 Southwest Freeway, Sugar Land, TX 77478, USA.
Correspondence and requests for materials should be addressed to R.D. (email:
Received: 02 February 2016
accepted: 18 May 2016
Published: 17 June 2016
Scientific RepoRts | 6:27449 | DOI: 10.1038/srep27449
either arising from gas generation from electrolyte decomposition or volume expansion of electrode is not desir-
able for use in practical applications such as automotive and mobile computing as space is at a premium13,14.
Unusual swelling of LIBs in cell phones and laptops has also been reported to cause safety issues15–17. Similarly,
battery packs used in electric vehicles are in tight compression and thus external volume changes of LIBs are
undesirable16. Even though swelling of LIBs is undesirable, LIB module manufacturers have no choice but to
allow a volume expansion tolerance of ~5% to accommodate gases generated from electrolyte decomposition
without releasing these gases to the surrounding environment15. LIB swelling also causes structural damage
to the electrodes, delamination of the electrodes from the current collectors and separator, and other negative
eects, reducing cycle life. us, there is no room to allow for swelling of LIBs arising from volume expansion of
Figure1 provides a schematic to explain the swelling of graphite and SCC anode. Since the volume expansion
of graphite due to intercalation is low (~10%), any expansion may be incorporated within the porosity or void
spaces of the anode, which is typically about 30–35% (by volume)1 (see Fig.1a). e metal casing of LIBs cannot
withstand large dimensional changes and will rupture causing severe damage to the cell and triggering safety
issues15. e increase in volume of Si particles in an SCC anode with a low fraction of Si during charging can be
accommodated within the existing porosity of the anode so that there is no increase in thickness of anode upon
lithiation (see Fig.1b). However, the volume occupied by lithiated Si particles of an SCC anode with a large frac-
tion of Si cannot be incorporated within the existing porosity of anode, resulting in, an increase in the external
dimensions of the anode upon lithiation (see Figs1c and S1b).
e objective of this work is to determine the theoretical limits of the energy density of an LIB-SCC by
maximizing the fraction of Si (referred as “threshold value of Si”) that can be used in the anode without increas-
ing the external dimension of LIB beyond the accepted 5% swelling limit. e threshold or limiting value of Si
is calculated as the highest fraction of Si for which the anode does not change in size or shape due to the anode
particles’ increasing volume upon lithiation (Fig.1b). is requires that the porosity of the anode is adjusted to
accommodate the expansion of the Si. e threshold value of Si is determined by maximizing the volumetric
energy density of the LIB. As the threshold value of Si in the SCC anode will depend on the nal porosity of
lithiated anode, the threshold value is determined as a function of lithiated porosities. Based on the determined
threshold value of Si, the improvement in energy density over existing LIBs is calculated. e energy densities
of LIB were calculated for three types of cathode (LCO, NMC and NCA) and two types of anode (graphite and
SCC). is work is based on existing commercial cathode chemistries and does not address the improvements
that new and promising cathode chemistries can impart to the performance of LIBs. However, this work is easily
extensible to other cathode materials.
Figure 1. Schematic showing cross-section of anode before and aer charging for (a) graphite based anode,
(b) SCC anode with low amount of Si, and (c) SCC anode with high amount of Si. As can be seen, the anode
thickness remains unchanged for graphite and low Si based SCC anode. Swelling of anode is experienced for
anode with higher Si content (c).
Scientific RepoRts | 6:27449 | DOI: 10.1038/srep27449
is work does not focus on charge-discharge cycling stability of Si anode, which has been the focus of the
majority of published articles on Si anodes for LIBs. Instead, this work focuses on system level limitations of
Si-LIBs arising from issues related to swelling of Si particles18–20. Most of the scientic papers published in Si
anode have not reported the amount of swelling of the anode or LIB for a number of reasons. Coin cells, which
are typically used by LIB researchers, have sucient free volume internally and thus no external change in dimen-
sions of cell is noticed during electrochemical cycling. Tests made on single-layer, low-capacity (<100 mAh)
pouch cells undergoes reversible volume changes during cycling; however, the volume change is hard to see
with the naked eye and thus does not get reported. Furthermore, the volumetric energy density/capacity values
reported in scientic articles are based on the volumes of cells in the discharged state rather than in the fully
charged state. e swelling issues become evident and problematic when LIBs are made using multiple-layered
high-capacity (>5 Ah) commercial pouch cells. Experimental observations of swelling of low-capacity LIBs may
also require instrumentation and techniques that are not typically used in battery research21.
is work adopts a system-level approach22,23, which is used to determine the extent of benets of Si-LIBs, and
can supplement understanding generated using experimental material-level analysis. e current work extends
the analysis presented in Obrovac et al.22 to determine the amount of Si in a SCC anode that would maximize the
volumetric capacity of a SCC-LIB. e model uses well-established experimentally derived properties as inputs.
Results and Discussion
Using simple mass balance calculations24, the density (in g/cc) of anode, ρ
A, specific gravimetric capacity
(in mAh/g) of anode, GA, porosity (in %) of unlithiated SCC anode, PA, and specic volumetric capacity (in mAh/
cc) of anode, V
A can be expressed in the form of eqns(1), (2), (3) and (4), respectively.
100 P
Si A
Si A
(w s) (w s)
100 (2)
(w 280) (w 10)
=−⋅.+ ⋅. +⋅ ⋅+
[100 {(w28) (w 01)P }] {(ws)(ws)}
Si A
Si A
Where wSi-A, wG-A, wB-A, and wCC-A are the weight fractions (in wt.%) of Si, graphite, binder, and CC, respec-
tively in anode; ρ
S-A, ρ
G-A, ρ
B-A, and ρ
CC-A are the true densities (in g/cc) of Si, graphite, binder, and conductive
carbons, respectively; sSi and sG are the specic gravimetric capacity (in mAh/g) of Si and graphite, respectively;
and, PAL is the porosity (in %) of the lithiated anode.
By inputting the values, sSi = 3600 mAh/g, sG = 330 mAh/g, ρ
SiA = 2.3 g/cc, ρ
GA = 2.24 g/cc, and assigning a
variable for optimizing the relative weight of Si; wSiA = x, eqn. (4) can be rewritten as eqn. (5).
−⋅.+ −− −⋅.+
.⋅ +− −−⋅.
[100 {( 28)((100 ww )01) P}]
[( 36) ((100 w)33)]
100 ww
Figure2 is plotted using eqn. (5) for anode made using 5 wt.% SBR binder (ρ
BA = 1.1 g/cc) and assuming no
CC i.e., wCCA = 0 and complete expansion into the pores aer lithiation i.e., PAL = 0. As the Si content increases,
the porosity required to accommodate volume expansion of Si increases. As expected, the specic gravimetric
capacity of anode also increases linearly with Si content (see Eqn. (2)); however, the specic volumetric capacity
of anode increases with Si content up to a limiting value and then decreases (see Fig.2). Increase in Si content
beyond this limiting value, Sit = 12.02 wt.% leads to decrease in specic volumetric capacity because any further
increase in Si content warrants increase in porosity required to compensate the volume expansion and thereby
reducing the density of anode (see Eqns(1) and (3)). Further, the decrease in density of anode leads to the sig-
nicant decrease in the weight of graphite with minimal changes in weight of Si, thereby impacting the specic
volumetric capacity of anode (see Fig. S2).
e concept of this threshold value of Si is further explained using some illustrative values for anodes made
using no CC i.e., wCCA = 0 and no porosity aer lithiation i.e., PAL = 0. e density, specic gravimetric and
specic volumetric capacity of anode made using 5 wt.% Si, 5 wt.% SBR binder and 90 wt.% graphite is 1.64 g/cc,
477 mAh/g, and 783 mAh/cc, respectively (see Table S3 and Fig. S2). e weight of Si, graphite and binder for a
1 cc electrode volume are 0.08 g, 1.48 g, and 0.08 g, respectively. e porosity of anode required to avoid increase
in external dimension of anode is 23%. When the Si amount in the anode increases to let’s say, 20%, the porosity
required to avoid swelling increases to 64%, thereby reducing the anode density to 0.78 g/cc (see Eqns(1) and (3)).
e weight of graphite for a 1 cc electrode volume decreases signicantly to 0.59 g, while the weight of Si increased
Scientific RepoRts | 6:27449 | DOI: 10.1038/srep27449
slightly to 0.16 g. e specic gravimetric capacity increases to 968 mAh/g, whereas the specic volumetric capacity
decreases to 756 mAh/cc. Despite increase in the specic weight of Si from 0.08 g to 0.16 g, the specic volumetric
capacity decreases because of the decrease in the weight of graphite from 1.48 g to 0.59 g. At the threshold value
of Si, Sit = 12.02 wt.%, the specic volumetric capacity is maximum, i.e. 876 mAh/cc. e threshold value of Si is
independent of the thickness of Si anode and type of cathode material used but is dependent on the composition
of anode, density of binder and porosity of lithiated anode. e threshold value of Si decreases from 12.02 wt.% to
10.16%, 8.30% and 6.44%, for lithiated anode porosities of 10%, 20% and 30%, respectively (see Fig. S3).
e threshold value of Si that would maximize the volumetric capacity without any increase in the external
dimensions of anode can be determined by setting the rst derivative of eqn. (6) to zero:
′=⇒=fx x() 0Sit
Threshold value of Si was determined assuming sSi = 3600 mAh/g, sG = 330 mAh/g, ρ
SA = 2.3 g/cc and
GA = 2.24 g/cc. Figure S4 of Supplementary Information shows the threshold value of Si and volumetric capacity
of anode as a function of amount of binder and CC for dierent porosities of lithiated anode. e threshold value
of Si linearly increases with the amount of binder content with a constant slope of 0.068 and the intercept depends
on the amount of CC and porosities of lithiated anode. e threshold value of Si does not change drastically for
dierent amount of CCs. Calculations made using binder densities of 1.1 and 1.77 g/cc representing density of
SBR and PVDF, respectively, showed almost the same threshold value of Si. e threshold value depends more
on the amount of binder and porosity of lithiated anode than the type of binder. e threshold values for the
highest energy density is for the anode that does not contain binder and CC. e values are 11.68%, 9.82%,
7.96% and 6.10% for porosity of lithiated anode of 0%, 10%, 20% and 30%, respectively. e threshold value of
Si is independent of type and thickness of cathode assuming that the expansion of the anode is not absorbed by
the compression of the cathode. e maximum capacity of ~935 mAh/cc and ~712 mAh/g was obtained for SCC
anode with no binder and CC with the assumption that the porosity of the lithiated anode goes to 0. ese values
are more than twice of graphite anode (454 mAh/cc, 314 mAh/g). e threshold values for maximum volumetric
energy densities was found to be signicantly lower than what was determined without assuming no external
volume change. Such a low amount of Si can allow for exploration of more commercially viable manufacturing
approaches of Si. As the volume associated with Si content will be low (see Fig. S1b), the SCC material can be
porous Si mixed with graphite or porous Si-carbon composite.
Based on the determined threshold value of Si, the calculation was further extended to estimate the improve-
ment in capacity and energy density that can be achieved by moving from graphite to SCC anode for dierent
cathode materials (see Fig.3).
e specic electrolyte volume (in cc/cm2), vE and specic weight (in g/cc) of unit cell, wCell (in g) can be
expressed in the form of eqns(6) and (7), respectively.
.⋅+⋅ +⋅
f((t P) (t P) (t P))
10000 (6)
⋅ρ +⋅ρ+ ⋅ρ +⋅ρ+ ⋅ρ
(t /2)(t)(t )(t)(t /2)
Where f is electrolyte lling factor (in %); tC, tA, tS, tAl, and tCu are thickness (in μ m) of cathode, anode, separa-
tor, Al current collector, and Cu current collector, respectively; PC, PA, PAL, and PS are porosity (in %) of cathode,
SCC anode, unlithiated SCC anode, and separator, respectively; and, ρ
Cu, ρ
Al, ρ
E, and ρ
S are density (in g/cc) of
Cu current collector, Al current collector, electrolyte, and separator, respectively. e specic areal capacity (in
Figure 2. Relationship between specic capacity of anode and amount of Si in the anode, wSiA and
porosity of anode, PA for anode manufactured using 5 wt.% SBR binder (ρBA = 1.1 g/cc) and no CC.
Scientific RepoRts | 6:27449 | DOI: 10.1038/srep27449
mAh/cm2) of unit cell, SCell is determined by the capacity of 70 μ m thick cathode. e thickness of anode was
determined by equating the areal capacity of anode with that of cathode. e thickness of anode is determined
by the eqn. (8).
e specic gravimetric (in mAh/g), GCell and volumetric (in mAh/cc), VCell capacity of unit cell is determined
using eqn. (9) and eqn. (10), respectively.
Cell Cell
=++++ .V
(t /2)t tt (t /2)10000
Cell Cell
e energy density values are calculated by multiplication of capacity values with respective cell voltage. As the
Li+ intercalation potential of graphite (0.1 V) is lower than Si (0.37–0.45 V)10, the operational voltage for graphite
anode based LIBs will be higher than SCC anode based LIBs25,26. Because of the low amount of Si in SCC, it is
assumed that the operational voltage of graphite anode based LIB will be 0.1 V higher than SCC anode based LIB,
which is in agreement with experimental work5,27. e maximum improvement in capacity and energy density
that can be obtained by using SCC anode is for NCA based cathode. As the capacity and energy density of LIB
strongly depends on the porosity of the lithiated SCC anode, it is important that the particle size distribution and
other parameters that govern the packing density of lithiated anode is taken in to due consideration. Shape pre-
serving shell design of Si can be one of the potential approaches for maintaining the integrity of the Si particles via
conned porosity in its composite anode8,28. Minimal improvement in energy density and capacity of SCC-LIB
over graphite-LIB is seen when the porosity of lithiated SCC anode exceeds 30% (see Fig.3). e improvement in
capacity and energy density of SCC anode based LIBs over graphite anode based LIBs will be higher for thicker
cathodes and the value will depend on the thickness of cathode (see Fig. S5).
As the level of improvement that can be achieved with Si anode is limited because of its large volume and asso-
ciated electrode porosity change, other anode materials that can provide higher specic capacity than graphite
such as hard carbons, composite alloys, etc. will continue to be attractive as alternate anode materials27,29. Higher
capacity cathodes7 and approaches that can enable thicker cathode30 will increase the utilization of Si anode and
thus will provide higher level of improvement on a cell level.
e model was then extended to get an approximate eect of porosity changes on power density. At 22.5%
lithiated SCC anode porosity (equal to porosity of typical lithiated graphite anode), the power density of
SCC-LIBs will be equal to graphite anode based LIBs (see Fig.3). Currently, the power density of LIBs is limited
by lithium ion conductivity in the electrolyte and it is a strong function of electrode porosity. As the cathode
and separator porosities are assumed to be the same for SCC and graphite anode based LIBs, the power density
of SCC anode based LIB will be primarily limited by the porosity of lithiated anode. e decrease in porosity of
lithiated SCC anode will lead to decline in power density of SCC-LIB as compared to graphite-LIB. e decline
will be exponential and would depend on Bruggeman’s coecient31. e Bruggeman’s coecient and tortuosity
are dimensionless parameter and are related to electrode porosity as per eqn. (11).
(P )
Figure 3. Improvement in unit cell (a) capacity and (b) energy density of SCC-LIBs over graphite-LIBs for
three dierent cathode – LCO, NMC and NCA.
Scientific RepoRts | 6:27449 | DOI: 10.1038/srep27449
e conductivity of lithium ions and thus the power density of LIB is inversely proportional to tortuosity.
For electrode packed with spherical spheres, the Bruggeman’s coecient is 1.532. Based on experimental obser-
vation33, a Bruggemans coefficient of 2.5 (average of the anisotropic coefficients for graphite and note that
Bruggemans coecient in our denition includes the porosity in the numerator) is used to determine the decline
in power density (see Fig.4). us, in order to have similar power characteristics, the improvement in capacity
and energy density of various cathodes–SCC anode based LIBs over graphite-LIBs is between 7.5–12.5% and
5–10%, respectively (see Figs3 and 4). e improvement in capacity and energy density of SCC based LIB over
graphite-LIBs for lower lithiated anode porosity (< 22.5%) will come at a cost of lower power density.
A theoretical model was developed and used to obtain the amount of Si in SCC anodes required for maximizing
the volumetric energy density of LIBs without allowing for any increase in the external dimension of anode dur-
ing charging of the LIB. e result indicates that the amount of Si permitted in an anode is signicantly lower
than scenarios the external dimensional change of the anode is allowed. e threshold or limiting value of Si that
would maximize volumetric energy density was determined to be 11.68 wt.%. e maximum capacity of the SCC
anode with no volume expansion constraint was determined to be ~935 mAh/cc and ~712 mAh/g. e theoret-
ical limit for gravimetric and volumetric energy density of SCC-LIB was obtained for NCA based cathodes and
the values were ~14% and ~21%, respectively, higher than graphite-LIBs. Once a practical acceptable lithiated
porosity based on power requirements is introduced in the model, the level of improvement in gravimetric and
volumetric energy density of SCC-LIBs gains can further drop down to as low as ~7% and ~8%, respectively.
Calculations for threshold values of Si, capacity and energy density of LIBs were performed using Microso Excel
2013 and equations were derived based on simple mass/capacity balance. e unit cell of LIB dened in this work
consists of cathode, anode, separator and halves of positive and negative current collector. Halves of current
collectors are used because a single current collector is shared by two layers of cathodes or anodes. Table S1 of
Supplementary Information summarizes the values used in the model. It is assumed that electrolyte occupies 90%
of combined porosity of cathode, pre-lithiated anode, and separator. Table S2 of Supplementary Information sum-
marizes all the symbols and associated units used in the model. While a common cathode thickness30 of 70 μ m
was primarily used in the model, calculations were also performed for cathode thickness of 35 μ m, 100 μ m and
200 μ m (see Fig. S5).
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e authors would like to thank SABIC for providing support for this work and for agreeing to release the study
for broader distribution. e views and opinions of the authors expressed herein do not state or reect those
of SABIC. e authors would also like to thank Mark Armstrong and Deepak Doraiswamy for reviewing the
manuscript and helpful discussions.
Author Contributions
R.D. conceived, designed, and performed the research and wrote the paper. S.P. performed some aspects of the
research, and co-wrote the paper.
Additional Information
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Competing nancial interests: e authors declare no competing nancial interests.
How to cite this article: Dash, R. and Pannala, S. eoretical Limits of Energy Density in Silicon-Carbon
Composite Anode Based Lithium Ion Batteries. Sci. Rep. 6, 27449; doi: 10.1038/srep27449 (2016).
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... SiGr anodes are considered to be an effective way of increasing energy densities; [59][60][61] however, Si suffers from large volume changes upon cycling, destabilising the battery components and resulting in short lifespans. 60,62 Even though both nickel-rich positive electrodes and silicon-based negative electrodes still face severe challenges and short lifespans, the industry seems very optimistic that these novel materials will dominate the near-to medium-term future of LIBs. ...
... SiGr anodes are considered to be an effective way of increasing energy densities; [59][60][61] however, Si suffers from large volume changes upon cycling, destabilising the battery components and resulting in short lifespans. 60,62 Even though both nickel-rich positive electrodes and silicon-based negative electrodes still face severe challenges and short lifespans, the industry seems very optimistic that these novel materials will dominate the near-to medium-term future of LIBs. 39,63,64 Presently, carbon nanotubes (CNTs) and graphene are being studied intensively as replacements for graphite negative electrodes and carbon additives providing electronic conductivity for active materials in positive electrodes. ...
... Silicon is particularly promising because of its extremely high theoretical capacity, low discharge voltage, and natural abundance [17][18][19][20]. Silicon-carbon [21], silicon-graphite [22], silicon nanowirecarbon [23], and silicon-carbon nanotubes [24] composites have been extensively investigated for supercapacitor and battery applications, demonstrating that the introduction of Si could improve the energy density significantly. However, Si undergoes volume expansion during the charging and discharging process, leading to particle fracture and finally loss of capacity [17,18]. ...
... With attention to low-cost, environmentally friendly, abundant primary resources (second abundant element in earth's crust), high theoretical capacity (4200 vs. graphite: 372 mAh/g), and low electrochemical potential vs. lithium (0.37-0.45 V) silicon anode considered as a desirable alternative for LIB anodes which attracted lots of attention during last decades [10][11][12]. Despite these advantages, this material faces various challenges such as insufficient conductivity, irreversible volume change during lithiation/de-lithiation processes, and formation of unstable solid electrolyte interface (SEI) which leads to pulverization of active materials (Fig. 2) [13][14][15][16]. ...
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Lithium-ion batteries (LIBs) have always been known as promising energy sources for all kinds of electronic devices. These batteries are composed of graphitic anodes due to their high abundance, high conductivity, and low cost. But the low capacity of these anodes is considered the basic challenge that prevents their wide usage. Therefore, although silicon is known as a great promising anode material rather than graphite because of its high theoretical capacity, it has some challenges during the insertion-extraction of lithium ions such as extensive volume changes and formation of unstable solid electrolyte interface (SEI) which is led to active material pul- verization that confines the commercial application of silicon anodes. With this viewpoint, some research has been done to decrease and/or control these challenges; so, one of the best ways is to prepare silicon thin films as anode material with different chemical and physical deposition methods (e.g.: Chemical Vapor Deposition, Physical Vapor Deposition, ...) onto different substrates (e.g.: Copper foil, Nickel foam, ...). These methods have been spread to increase the utilization of silicon materials by producing multilayer and truly repeatable coatings for LIB anodes. In this article, the merits and issues of various methods to prepare silicon thin film anodes for LIBs with a focus on the function of each one have been reviewed.
... Furthermore, silicon oxide (SiO x ) is a commercially available Si-containing active material, which exhibits silicon domains in a stabilizing SiO 2 matrix [36]. A further approach is the co-utilization of Si with other active materials, e.g., graphite (C/Si composite), resulting in synergistic effects between a well-established anode component and an innovative anode constituent [37][38][39][40]. A blend of these materials implicates only a small increase in specific capacity, however, graphite can reduce the inter-particle electrical resistance and ensure sufficient electronic and indirectly also ionic conductivity within the composite electrode [41][42][43]. ...
Due to its high theoretical capacity, silicon is a promising active material candidate for the negative electrode of lithium ion batteries. One way to reduce the severe degradation of silicon during charge/discharge cycling, is to use blends of different active materials and a well-balanced ratio of active and inactive materials. To ensure high-energy densities while still maintaining good electronic conductivity and ionic mobility, the necessity of nano-scale conductive carbons within a graphite/silicon composite was evaluated in this study. In particular, the correlation of silicon particle size and the presence of conductive additive was studied in electrodes, predominantly consisting of graphite (15 wt% silicon). Carbon black as conductive additive has a high contact surface area, which can enhance the electronic conductivity within the electrode and thus the rate capability, however, it can also propagate parasitic side reactions. It was determined that composite electrodes containing micron-sized silicon particles depend on the addition of conductive additives with regard to electrochemical performance. Due to high contact area and small transport distances, electrodes based on nano-sized silicon showed comparable capacity retention and a higher specific discharge capacity. Omitting conductive particles from these composite electrodes allowed lower binder amounts, while maintaining a good mechanical electrode integrity.
... 435,436 Silicon anodes with a very large capacity of 3580 mAh g À1 (Li 15 Si 4 ) are suggested as an alternative, but large volume expansion during charging and discharging poses a serious safety problem. 437 As alternatives to the graphite anode materials, tin (Sn)-based composites, 438,439 phosphorous (P)-based composites, 440 and transition metal oxides (TMO) 441,442 have been studied, which have a higher capacity and superior rate capability compared to graphite. These materials suffer from significant volume changes upon the lithiation/delithiation 428 Copyright 2012, American Chemical Society processes, however, causing particle agglomeration or structural collapse during cycling, which eventually leads to a rapid capacity loss. ...
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Batteries are a promising technology in the field of electrical energy storage and have made tremendous strides in recent few decades. In particular, lithium‐ion batteries are leading the smart device era as an essential component of portable electronic devices. From the materials aspect, new and creative solutions are required to resolve the current technical issues on advanced lithium (Li) batteries and improve their safety. Metal‐organic frameworks (MOFs) are considered as tempting candidates to satisfy the requirements of advanced energy storage technologies. In this review, we discuss the characteristics of MOFs for application in different types of Li batteries. A review of these emerging studies in which MOFs have been applied in lithium storage devices can provide an informative blueprint for future MOF research on next‐generation advanced energy storage devices. In this review, we discuss the characteristics of metal‐organic frameworks (MOFs) applied to lithium storage devices containing Li‐ion, Li‐sulfur, Li‐metal, and Li‐O2. We summarize the origin, nomenclature, and synthesis method of MOFs, and report on recent studies in which MOFs and MOF‐derived materials are applied to lithium rechargeable batteries. This provides an informative roadmap for next‐generation advanced energy storage devices.
The demand for lithium-ion batteries has significantly increased due to the increasing adoption of electric vehicles (EVs). However, these batteries have a limited lifespan, which needs to be improved for the long-term use needs of EVs expected to be in service for 20 years or more. In addition, the capacity of lithium-ion batteries is often insufficient for long-range travel, posing challenges for EV drivers. One approach that has gained attention is using core-shell structured cathode and anode materials. That approach can provide several benefits, such as extending the battery lifespan and improving capacity performance. This paper reviews various challenges and solutions by the core-shell strategy adopted for both cathodes and anodes. The highlight is scalable synthesis techniques, including solid phase reactions like the mechanofusion process, ball-milling, and spray-drying process, which are essential for pilot plant production. Due to continuous operation with a high production rate, compatibility with inexpensive precursors, energy and cost savings, and an environmentally friendly approach that can be carried out at atmospheric pressure and ambient temperatures. Future developments in this field may focus on optimizing core-shell materials and synthesis techniques for improved Li-ion battery performance and stability.
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In this work, the reduced graphene oxide/NaTi2(PO4)3 (rGO/NTP) nanocomposite has been prepared by employing MXene as both the template and precursor for lithium ions battery with the enhanced performance. It is found that the NTP nanoparticles compact together and tightly decorate on the rGO layer. This novel structure benefits to shorten the diffusion path of Li⁺ and provide high conductivity, which are proved by the density functional calculations. Further, the Li⁺ diffusion coefficient of rGO/NTP is 3.68 × 10–9 cm²·s⁻¹ which is much higher than that of the NTP (7.18 × 10–10 cm²·s⁻¹). The results demonstrate that the rGO/NTP anode offers the high specific discharge capacity of 400.9 mAh·g⁻¹ after 200 cycles at 0.1 A·g⁻¹, which is nearly twice higher than that of NTP anode. Even the current density varied from 0.1 to 2 A·g⁻¹, the specific capacity rGO/NTP anode can reach to 149.2 mAh·g⁻¹. Further, the integrity of the lamellar structure rGO/NTP anode remained after 200 cycles, highlighting the superior stability.
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The 18650 and 21700 cell format are state of the art for high-energy cylindrical lithium-ion batteries, while Tesla proposed the new 4680 format with a continuous "tabless" design as the choice for electric vehicle applications. Using an experimentally validated multidimensional multiphysics model describing a high energy NMC811/Si-C cylindrical lithium-ion battery, the effects of tabless design and cooling topologies are evaluated for 18650, 21700, and 4680 cell formats under varying charging protocols. Mantle cooling is found to be the most efficient cooling topology for a segmented tab design, whereas tab cooling performs equally well for tabless cells and achieves better performance for the 4680 format. By massively reducing polarization drops (approx. 250 mV at 3C) and heat generation inside the current collectors (up to 99%), the tabless design increases cell homogeneity and enables format-independent scalability of fast-charging performance with a tab-cooling topology. In addition, the 0 to 0.8 SoC charge time can be reduced by 4 to 10 minutes compared to cells with a segmented tab design, resulting in 16.2 minutes for the 18650 and 21700, and 16.5 minutes for the larger 4680 cell format.
Battery-powered vehicles are among the few of important technology to lessen the environmental pollution triggered by the transport, energy, and industrial segments. It is necessary to implement energy production and energy storage in a sustainable way in order to effectively reduce greenhouse gas emissions. To achieve sustainability, batteries must operate beyond their current capabilities in terms of longevity, reliability, and safety. In addition, the chemicals and materials used in the battery must be cost-effective while achieving large-scale production. LIBs (Lithium-ion batteries) are the dominant recharging technology for batteries the next few years, but the problem with lithium-ion batteries is the cost of the materials used to make the LIB. Building batteries from cheaper materials is a challenging task, and investigators are carrying out extensive research on battery technology and battery materials that allow faster charging with superior capabilities. From the literature, it has been observed that nanoscale silicon is a promising material for achieving extremely high efficiency towards the anodic end in the cell because Si contributes the superior speculative anode capacity. This comprehensive review provides an indication of the cutting-edge research on the use of nanoscale silicon as the anode material in lithium-ion batteries.
L'impact du broyage du liant polymère dans la formulation d'encre d'électrode négative à base de silicium pour la technologie Li-ion a été pour la première fois étudiée. Nous avons démontré avec l'exemple de l'acide poly(acrylique) la dégradation du liant lors de la formulation d'électrode impliquant un broyage. Nous avons proposé de nouvelles formulations d'électrode s'affranchissant de ce broyage. La nouvelle formulation [(Si+C)SPEX+LP)MAG permet une augmentation de la rétention de capacité de 65 à 84 % à 20 cycles pour une électrode riche en silicium grâce à l'absence de dégradation du liant. Un nouveau polymère, l'acide polyfumarique, a été synthétisé et utilisé en tant que liant pour électrode négative. Les performances modestes des électrodes à base de ce nouveau liant sont améliorées par l'augmentation de sa masse molaire moyenne ainsi que par la formulation d'électrode développée lors de ces travaux. Bien que les résultats électrochimiques des électrodes à base de ce polymère restent modestes, des optimisations sont possibles pour améliorer ses performances en tant que liant.Enfin, la transposition de ces travaux a été réalisée sur deux matériaux d'électrodes négatives pour accumulateurs Li-ion : TiSnSb et le composite Si:Gr. Comme décrit dans la littérature, les améliorations apportées au silicium ne sont pas strictement transposables à TiSnSb et les électrodes à base de ce matériau ne bénéficient pas d'amélioration significative de leur durée de vie grâce à la formulation développée. L'étude des différents ratios massique Si:Gr montre que le que le silicium ne doit pas dépasser 30 % de la matière active pour permettre des rétentions de capacité intéressantes
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Si anodes exhibit a rapid capacity decay and increase in the internal resistance, which are caused by the large volume changes upon Li insertion and extraction. This unfortunately obstructs their practical applications. Therefore, managing the total volume change remains a critical challenge for effectively alleviating the mechanical fractures and instability of solid-electrolyte-interphase products. In this regard, we review the recent progress in volume-change-accommodating Si electrodes and investigate their ingenious structures with significant improvements in the battery performance, including size-controlled materials, patterned thin films, porous structures, shape-preserving shell designs, and graphene composites.Finally, we propose perspectives and future challenges to realize the practical application of Si anodes in LIB systems.
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Alloy-type anodes such as silicon and tin are gaining popularity in rechargeable Li-ion batteries, but their rate/cycling capabilities should be improved. Here by making yolk-shell nanocomposite of aluminium core (30 nm in diameter) and TiO2 shell (∼3 nm in thickness), with a tunable interspace, we achieve 10 C charge/discharge rate with reversible capacity exceeding 650 mAh g(-1) after 500 cycles, with a 3 mg cm(-2) loading. At 1 C, the capacity is approximately 1,200 mAh g(-1) after 500 cycles. Our one-pot synthesis route is simple and industrially scalable. This result may reverse the lagging status of aluminium among high-theoretical-capacity anodes.
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Silicon is receiving discernable attention as an active material for next generation lithium-ion battery anodes because of its unparalleled gravimetric capacity. However, the large volume change of silicon over charge-discharge cycles weakens its competitiveness in the volumetric energy density and cycle life. Here we report direct graphene growth over silicon nanoparticles without silicon carbide formation. The graphene layers anchored onto the silicon surface accommodate the volume expansion of silicon via a sliding process between adjacent graphene layers. When paired with a commercial lithium cobalt oxide cathode, the silicon carbide-free graphene coating allows the full cell to reach volumetric energy densities of 972 and 700 Wh l(-1) at first and 200th cycle, respectively, 1.8 and 1.5 times higher than those of current commercial lithium-ion batteries. This observation suggests that two-dimensional layered structure of graphene and its silicon carbide-free integration with silicon can serve as a prototype in advancing silicon anodes to commercially viable technology.
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Thicker electrode layers for lithium ion cells have a favorable electrode to current collector ratio per stack volume and provide reduced cell manufacturing costs due to fewer cutting and stapling steps. The aim of this work is to investigate the delivery of energy in such cells compared to cells with thinner electrodes. In this regard, lithium ion cells with single sided 70 μm and 320 μm NMC based cathodes and graphite based anodes with low binder and carbon black contents were prepared and tested in half cell and full cell configurations. Thick and thin electrodes showed capacity losses of only 6% upon cycling at C-rates of C/10 and C/5 while cycling at C/2 resulted in significant losses of 37% for the thick electrodes and only 8% for the thin electrodes. Pouch cells with thick electrodes showed 19% higher volumetric energy density at C/5 in comparison to thinner electrodes. This can be an innovative approach to reduce cell costs and to achieve more competitive prices per energy for applications where only medium to small C-rates are required.
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The expansion of battery material during lithium intercalation is a concern for the cycle life and performance of lithium ion batteries. In this paper, electrode expansion is quantified from in situ neutron images taken during cycling of pouch cells with lithium iron phosphate positive and graphite negative electrodes. Apart from confirming the overall expansion as a function of state of charge and the correlation with graphite transitions that have been observed in previous dilatometer experiments we show the spatial distribution of the expansion along the individual electrodes of the pouch cell. The experiments were performed on two cells with different electrode areas during low and high c-rate operation. The measurements show how charging straightened the cell layers that were slightly curved by handling of the pouch cell during setup of the experiment. Subsequent high charging rate, that exceeded the suggested operating voltage limits, was shown to have a strong influence on the observed expansion. Specifically, during high-rate cycling, the battery showed a much larger and irreversible expansion of around 1.5% which was correlated with a 4% loss in capacity over 21 cycles.
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We present an open source software application “BruggemanEstimator” that allows a user to estimate the tortuosity of a porous electrode. BruggemanEstimator determines the Bruggeman exponent based on the Differential Effective Medium approximation and as input requires only two microscope images: one of the top and one of a cross section through an electrode. These images, which can be easily acquired with a scanning electron or optical microscope, are used to extract a sampling of active particle shapes as well as the orientation of the particles within the electrode. We validate the accuracy of BruggemanEstimator by comparing the estimated Bruggeman exponents to values calculated by performing numerical diffusion simulations on three-dimensional microstructures obtained from tomographic techniques.
Dan Doughty and E. Peter Roth share their views on the safety measures to be taken for Li Ion batteries. They state that when discussing such battery safety, it is important to understand that batteries contain the oxidizer (cathode) and fuel (anode) in a sealed container. The fuel and oxidizer convert the chemical energy directly into heat and gas when allowed to react chemically in an electrochemical cell. Safety needs to be addressed at the cell, module, pack, and vehicle levels to address these issues. It is important to understand that failure at one level can quickly escalate to more severe failures at a higher level. Cell failures at each of these levels result in complete destruction of all components of the full battery system. It is also important to understand that failure at this level will result in loss of the complete vehicle.
Future generations of electrified vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium batteries is mandatory, maintaining at the same time similar, or improved, rate capability, lifetime, cost, and safety. Several new cathode materials have been claimed over the last decade to allow for this energy improvement. The possibility that some of them will find application in the future automotive batteries is critically evaluated here by first considering their theoretical and experimentally demonstrated energy densities at the material level. For selected candidates, the energy density at the automotive battery cell level for electric vehicle applications is calculated using an in-house developed software. For the selected cathodes, literature results concerning their power capability and lifetime are also discussed with reference to the automotive targets.