Ø
Large Lithium Ion (Li-Ion) Batteries
Solid polymer
electrolytes (SPEs) serve two principal roles in a Li battery. It is the separator that insulates
the anode from the cathode in the battery and it is the medium through
which ions are transported between the anode and cathode during discharge
and charge. Consequently, the
SPE should not only have high ionic conductivity, but it also should be an
electronic insulator. In addition, it should have adequate mechanical
strength to withstand the stack pressure changes and stresses of the
electrodes during discharge/charge cycling of the battery. Preferably, the mechanical
strength of the polymer electrolytes should be comparable to that of the
porous polyolefin separators used in conventional Li batteries utilizing
organic liquid electrolytes.
In general,
conductivity and mechanical strength of a polymer electrolyte follow an
inverse trend, i.e., mechanical strength decreases as conductivity
increases. We recognized this behavior as early as 1988 when we attempted
to fabricate rechargeable solid-state Li batteries with MEEP-based SPEs
(1). Although these classical
polymer electrolytes based on poly[bis((methoxy ethoxy)
ethoxy)phosphazene] (MEEP)
have room temperature ionic conductivities exceeding 10-5S/cm,
they are glutinous materials with a tendency to flow under mild pressure.
Consequently, Li batteries could not be constructed with these
electrolytes unless their mechanical strength was increased. We developed two approaches to
prepare mechanically strong MEEP electrolytes.
In the first approach,
mechanically strong electrolytes were prepared by forming interpenetrating
polymer network (IPN) structures and composites with morphologically rigid
polymers such as poly (ethylene glycol diacrylate) (PEGDA), poly (vinyl
pyrrolidinone) (PVP),
poly(ethylene oxide) (PEO), or poly(propylene oxide) (PPO)
(2). In the second approach
we encapsulated MEEP electrolytes in thin, highly porous, fiber glass
separator mats (1). A Li cell
of the configuration, Li/MEEP-(LiX)-fiberglass/TiS2, was
constructed and cycled at room temperature. This represents one of the early
demonstrations of room temperature performance of conventional solid
polymer electrolyte-based rechargeable Li batteries. Because of the relatively low
conductivities, however, these solid polymer electrolytes, derived from Li
salt complexes of long chain polymer hosts, are not suitable for the
development of Li batteries capable of high power performance at and below
room temperature
Solid Polymer
electrolytes with conductivities exceeding 10-3 S/cm at room
temperature have been prepared as gel electrolytes (3,4). They are formed
by absorbing organic liquid electrolytes into polymer structures. Examples include gel electrolytes
obtained by immobilizing LiPF6 solutions in mixtures of
ethylene carbonate (EC) and propylene carbonate(PC) in polymers such
as polyacrylonitrile (PAN),
poly(vinylidene fluoride) PVF), poly(methyl-methacrylate) (PMMA),
poly(vinyl pyrrolidinone) (PVP) and poly(ethylene glycol diacrylate)
(PEGDA)-based electrolytes(3,4).
The mechanical strength of these gel electrolytes is usually
adequate for use as separators in Li-ion batteries, but their soft
morphology often is unsuitable for the high speed processing employed in
large volume manufacturing of batteries. The flow properties of some of
these electrolytes can also lead to internal short-circuits and safety
hazards.
In order to develop
highly conductive polymer electrolytes which can be handled like
conventional separators, we set out to prepare microporous
membrane-bonded polymer electrolytes. As an example of this concept, we
encapsulated PEGDA-based gel electrolytes into the pores of several types
of Celgard® membranes(5). We found that ionic conductivities of
these polymer electrolytes can be modulated by controlling the thickness
and porosity of the separator.
This was an extension of the work we had carried out previously
with unsupported PEGDA-based electrolytes having the compositoin of
PEGDA-EC/PC-LiX (LiX=LiClO4, LiAsF6) with a room
temperature
conductivity of about 3x10-3 S/cm (4).
Conductivities of a
few of these separator-bonded electrolytes are shown in Table 1. The
PEGDA-based electrolytes were formed by in-situ polymerizing the
tetra-ethylene glycol diacrylate (TEGDA)-containing electrolyte solutions
on Celgard membranes. The pores of the membranes were fully covered by the
solid electrolytes. As
expected, membranes with higher porosity gave electrolytes with higher
conductivity. In addition to
good mechanical strength, the resulting electrolyte showed excellent
electrochemical stability with a voltage window spanning 0.0V to 4.3V
versus Li+/Li.
Li/LiMn2O4 cells using these electrolytes as
the separators showed
excellent cycling behavior at room temperature (5).
Incorporation of
polymer electrolytes into porous separator membranes lowers their
conductivity to a degree determined by the solid fraction of the membrane.
However, mechanically strong thin electrolyte films can be prepared which
are useful to the construction of rugged batteries. The conductivity loss
of the electrolyte due to the porous membrane is compensated for by its
smaller thickness. It should be noted that in this work we used
commercially available separator membranes to demonstrate the
concept. By suitably
optimizing the thickness and porosity of the porous membrane, it should be
possible to prepare solid polymer electrolytes with conductivities
comparable to that of unsupported polymer electrolytes, (i.e., without the
membranes). It is not necessary to fully cover the pores of the membrane
with the polymer electrolyte. A fraction of the pore may be left open to
store liquid electrolytes to provide high ionic conductivity in the cell.
The polymer electrolyte layer can be used to bond the separator to the
electrodes to achieve a monolithic cell package suitable for the
construction of thin prismatic batteries with dimensional stability.
Various
modifications of this concept have been adopted to fabricate practical
batteries which are being introduced commercially. Das Gupta and Jacob (6) reported
on Li-ion batteries with bonded electrolytes in which a microporous
separator and electrodes were coated with a liquid electrolyte solution
and a layer of a polymer adhesive plasticized with a liquid electrolyte
solution. The separator and
the electrodes were then bonded.
Another variant is a process in which an adhesive layer (e.g. PVdF)
is applied to the separator and used to bond the electrode and separator
films (7,8). Sony described
liquid electrolyte plasticized polyacrylonitrile layer directly applied
either to the electrode or the separator (9). Note that practical utility of
polyacrylonitrile-based electrolytes for Li and Li-ion batteries were
reported by us in many publications since 1990 (3,4,10). In Sanyo’s work (11) on separator
bonded electrolytes, they added polymer precursor solutions to
spirally-wound liquid electrolyte-based Li-ion cells and solidified the
cell package by thermal polymerization. Researchers from Telecordia
technologies (12) described a process wherein propylene
carbonate-plasticized electrodes were permanently bonded to several
different untreated microporous polyolefin separators. Batteries fabricated using this
process reportedly exhibited excellent performance: 3 C rates with 75-80% capacity
utilization at room temperature and 50% capacity at C/2 at
–20oC, very low internal impedance and high specific energy
(>180 Wh/kg).
In conclusion our work to improve the
mechanical strength of gel polymer electrolytes by bonding them to
micro-porous membranes has been transitioned into a successful technology
for the fabrication of commercial Li-ion polymer batteries.
References:
1. M. Alamgir, R. K. Reynolds and
K. M. Abraham in “Materials and Processes for Lithium Batteries,”
The Electrochemical Society, PV 89-4, K. M. Abraham and B. B.
Owens, Editors, The Electrochemical Society, Pennington New Jersey,
(1989), pp. 321.
2. K. M. Abraham and M.
Alamgir, Chem. Mater. 3, 339
(1991).
3. K. M. Abraham and M. Alamgir,
J. Power Sources, 43-44, 195 (1993).
4. K. M. Abraham and M.
Alamgir, J. Electrochem. Soc. 136, 1657 (1990) (See also U. S.
Patent 5,252,413 (1993).
5. K. M. Abraham, M. Alamgir
and D. K. Hoffman, J. Electrochem. Soc. 142, 683 (1995).
6. U. S. Patents 5,437,692 (1995);
5,498,489 (1996) and 5,512,389 (1966).
7. G. Venugopal, J. Moore, J. Howard
and S. Pendalwar. J. Power
Sources, 77, 34 (1999).
8. U. S. Patent, 5,981,107 (1999),
6,024,773 (2000) and 6,051,342 (2000).
9. K. Kezuka, T. Hatazawa and
K. Nakajima in Proceedings of the 10th IMLB, Como, Italy, May,
2000 (Abstract # 4).
10. K. M. Abraham, H. S.
Choe and D. M. Pasquariello, Electrochim Acta. 43, 2399 (1998)
11. T. Fujii, Proceedings of the
17th International Seminar and Exhibit on Primary and Secondary
Batteries, Boca Raton, Fl, March, 2000.
12. A.S. Gozdz, I. Plitz, A.
DuPasquier and T. Zhang. In
Rechargeable Lithium Batteries, The Electrocheical Society Proceedings
Volume, PV 2000-21, pp 336, 2001
Table1. Conductivities of Porous
Membrane-based Solid Electrolytes at 25oC
Membrane
Electrolyte
Thickness
Conductivity
Porosity Thickness
( micron)
( ohm
-1 cm-1)
(%)
( micron)
70
25
30(m/o)EC-30 PC tetraglyme-2 PEGDA-8 LiAsF6
37.5 1.1
x 10-4
55
25
74(m/o) EC-16 PC-2 PEGDA-8
LiAsF6
40.0 1.7 x 10-4
35
25
74 (m/o) EC-16 PC-2 PEGDA-8 LiAsF6
40.0 3.0 x 10-5
34
25
30 (m/o) EC-30 PC-30 tetraglyme-2 PEGDA-8 LiAsF6
37.5 1.2 x 10-5
42
25
30 (m/o) EC-30 PC-30 tetraglyme-2 PEGDA-8 LiAsF6
37.5 1.7
x 10-5
-------------------------------------------------------------------------------------------------------------------------------------------------------
Unsupported Electrolyte: 3(m/o) PEGDA-68
EC/15 PC-14 LiPF6
100
3 x 10-3
For an in-depth
discussion of Li-ion polymer batteries and solutions to practical
problems, consult Dr. K. M. Abraham at
E-KEM Sciences
High Power
Li-ion batteries capable of being fully discharged and charged in several
seconds to a few minutes are needed for hybrid electric vehicles, directed
energy weapons, power tools and many other high power applications. The
selection of appropriate electrode and electrolytes materials and porous
separator, and the design of optimum electrodes, current collectors, cell
stacks and battery packs with low resistances and polarization losses in
order to sustain the very high current drains are key to the successful
development of such batteries.
The
power, P, of a Li-ion cell is given by P=V2/R, where V is the
cell’s load voltage and R is its internal resistance, high voltage cells
with low internal resistances are the most desirable for high power
batteries. In additional to the polarization losses associated with the
resistances of the various cell components, mass transport in the solid
electrode lattice and in the electrolyte solution/separator phase have to
be understood and optimized to obtain the highest continuous power output
from the cell. A pragmatic methodology to design such batteries is needed.
It can be shown that an electrode material with a relatively high
solid-state Li diffusion coefficient of the order of 10-10
cm2/sec (e.g., LiCoO2 and
Li2Mn2O4) can be fully discharged in 100
seconds using about one micron size particles. On the other hand, if the
diffusion coefficient of the electrode material is a much lower
10-14 cm2 /sec, (e.g., LiFePO4)
approximately ten nanometer size particles are needed to achieve full
discharge in the same time period. The use of very small electrode
particles having the latter dimensions may introduce potential issues such
as difficulty to fabricate low impedance electrodes, enhanced electrode
surface reactions with the electrolyte leading to the loss of active
material and increases internal resistances, and penetration of particles
through the separator pores to cause high rates of self discharge. An
awareness of the latter problem is especially important as separator
porosity and electrolyte conductivity show a direct relationship to the
discharge rate capability of high power Li-ion cells (1). Rationally selecting both active
and inactive materials and incorporating them in optimally designed
electrodes, and building cell stacks with minimal internal resistances and
optimal ion transport profiles to produce high power Li-
ion batteries are key to the development of high power Li-ion
batteries (1-3).
Small high power Li-ion cells with
LiMn2O4, LiFePO4 and LiMn-Ni-oxide
cathode materials are commercially available. Interestingly, high power
Li-ion batteries are not fabricated with LiCoO2. What is the
reason?
For an in-depth review and discussion of high
power Li-ion batteries, including which Li-ion battery to choose for an
application; performance, safety and life issues of high power Li-ion
batteries for power tools; and, applications of large format high power
Li-ion batteries for hybrid EV consult Dr. K. M. Abraham at
E-KEM Sciences
References:
1.
K.M. Abraham, D.M. Pasquariello and E.M. Willstaedt;
Discharge rate capability of LiCoO2 electrode, J.
Electrochem. Soc., 145, 482-486 (1998)
2.
K.M. Abraham and M. Alamgir, "Solid-State Carbon/LiNiO2 Pulse Power Batteries", in
Proceedings of the 36th International Power Sources Symposium, published
by IEEE, New York, NY (1994), p. 257.
3.
H.S. Choe and K.M. Abraham, “Synthesis and Characterization of
LiNiO2 as a Cathode Material for Pulse Power Batteries”, in
Proceedings of the Symposium, Materials For Electrochemical Energy
Storage and Conversion II - Batteries, Capacitors and Fuel Cells,
Fall MRS Meeting, Boston, Ma. December 1-5,
1997.
The electrolytes influence the rates of
discharge, low temperature performance, high temperature stability, and
cycle and calendar life of lithium and lithium ion batteries.
Consequently, knowledge of the ion transport mechanisms in electrolytes is
important in designing new and improved electrolytes. Our recent results
show that there are strong similarities between the ion transport
processes in Li ion conducting liquid and polymer electrolytes so that
there is a limit to the conductivity that can be achieved for conventional
solid polymer electrolytes. Our data also have provided insights into the
design of improved polymer electrolytes (1,2).
We measured the conductivities (K) of
solutions of LiPF6,
LiN(SO2C2F5)2,
LiBF4 and LiC(SO2CF3)3 in a
variety of carbonate solvents as a function of temperature (T). The
conductivity data from – 40 to +85 oC provided insights into
the ion conduction mechanism in Li-ion conducting electrolytes. The
K versus 1/T plots fit well to the Vogel-Tamman-Fulcher (VTF)
relationship shown in equation 1 describing the dependence of ion
conductivity to free volume in solution. In this equation, A and B are
constants; A is a pre-exponential function, B is the energy needed to
create free volume for ion movement in solution, and To is the
temperature at which solvent structural relaxation becomes
nonexistent.
K = AT-1/2 exp{-B/T-To}
(1)
The closeness between the measured glass transition
temperature Tg of the solutions and their To values calculated
from conductivity data provides strong support for solvent coupled motion
of ions in Li-ion conducting electrolytes. The solvent-assisted transport
of ions in Li battery electrolytes is further supported by 13C
NMR data that show that the Li-ion are solvated by the solvent molecules
and their mobility is coupled to the mobility of the solvent
molecules.
The
conductivity-temperature behavior of the liquid electrolytes we have
observed is similar to the well-established behavior of Li-ion conducting
solid polymer electrolytes. The polymer segmental mobility assisted
mechanism of ion transport in polymer electrolytes is well recognized.
This suggests that ions conduct via similar solvent–assisted mechanisms in
both liquid and solid polymer electrolytes.
A good understanding of the ion
transport mechanism in liquid and polymer electrolytes has allowed us to
design improved electrolytes with superior low temperature performance,
high temperature stability, and long life in Li-ion and Li-ion polymer
batteries
For an in-depth review and discussion of
electrolytes for Li-ion and Li-ion polymer batteries, consult Dr. K. M. Abraham at
E-KEM Sciences
References:
1. G.Y. Gu, R. Laura and K. M. Abraham,
Electrochem. and Solid-State
Lett., 2, 486 (1999).
2. B. Ravdel, K.M. Abraham, R.L. Gitzendanner and C. Marsh, in Batteries
and Supercapacitors, The Electrochemical Society Proceeding Volume,
PV2001-21 (2003)
Almost all of the applications of Li-ion
batteries are currently filled by small cells, prominently the 18650 size
cells having a capacity of ~2Ah, and small batteries constructed by the
series/ parallel combination of a few of them. Despite their superiority
in practically every aspect of performance of a battery, Li-ion batteries
have not penetrated the high-capacity market dominated by Lead-Acid for
applications such as backup power systems because of higher cost and
safety concerns. Even for applications that are not cost sensitive,
potential safety concerns have remained as a deterrent to the widespread
use of large Li-ion batteries with hundreds to thousands of watt-hours
(Wh) of stored energy. Traditionally such large Li-ion batteries have been
constructed from the series/parallel stacking of large monolithic cells,
each with tens to hundreds of ampere-hours (Ah) of capacity. Large
monolithic Li-ion cells are more prone to safety hazards because they are
unable to quickly dissipate the internally generated heat from such abuses
such as internal short circuit and overcharge to prevent pressure buildup
and the associated cell rupture and venting. Large cells also tend to be
more expensive because of higher manufacturing costs.
Small commercial Li-ion cells with a
capacity of 1-2 ampere-hours, such as the 18650 cells, have several layers
of protection against hazards from short circuit and overcharge, and that
account for their widespread consumer acceptance. High volume
manufacturing has lowered the price of small Li-ion cells to levels very
attractive for high energy applications such as telecom and cable TV
backup power. What has been lacking until now is a reliable way to build
large batteries from small cells.
Modular Energy Devices, Inc.
of Westerly, RI has developed Li-ion battery modules and packs with
capacities ranging from 80 to 200 Ah for Cable TV/Telecom power backup
applications. The modules are constructed from small, highly reliable and
safe 18650 Li-ion cells using the proprietary electronic technology called
Massively Parallel Modular Architecture. The battery modules are readily
combined in series and parallel to produce 24, 36 and 48 and 96 V battery
packs with appropriate capacities for cable TV/Telecom applications. The
use of small cells in combination with the superior electronic
architecture makes the batteries safe, reliable and low cost.
There are
increased efforts to use large Li-ion batteries for aerospace applications
in satellites, military and commercial airplanes, unmanned aerial vehicles
and many others. The most famous recent aerospace application of Li-ion
batteries is in the Mars Rovers, Spirit and Opportunity, which
significantly exceeded the pre-launch life expectations. The 28 V Li-ion
batteries performed more than one year on the Martian surface. Large Li-ion batteries are also
developed for many other civilian and military applications. In all of
these concerns arise about their performance, safety, life and
temperature-dependent performance.
For
additional discussion and consulting on large format Li-ion batteries
constructed from small and large cells including their performance, safety
and applications consult Dr. K. M. Abraham at E-KEM
Sciences
Reference:
K. M.
Abraham, Stephen
Eaves and Farshid Bhaktyari, “Low Cost Lithium-Ion Batteries for Cable
TV/Telecom Power Backup”, in Proceedings of the 2004 Intelec Meeting,
Chicago, September 20004
The dense packing of energy makes Li-ion batteries
susceptible to safety hazards when abused. Of particular concern are
conditions that dramatically increase the internal temperature of the
cell. Two conditions that are potentially unsafe are short circuit and
severe overcharge.
Short Circuit of Li-Ion Batteries: It is obvious
that short-circuiting an energy dense battery cell will increase its
internal temperature to high values in a relatively short time.
Manufacturers of small 18650 Li-ion cells have been able to overcome
safety hazards from short circuit through several design features of the
cell. The key to the design of a safe cell is to incorporate features that
would prevent the buildup of excessive heat that can vaporize the organic
solvents in the cell, resulting in internal pressure build-up, cell
rupture and venting.
Generally this problem is mostly attributed to large Li-ion cells
rather than 18650 cells, since the large cells are unable to quickly
dissipate the internally generated heat and prevent pressure buildup.
Small cells such as the 18650 Li-ion cells with a
capacity of about 2 ampere-hours have several layers of protection against
hazards from short circuit. First of all, the small size of the 18650 cell
enables the heat generated during a short circuit to be dissipated fast
enough from the inside to the outside to prevent buildup. In addition, the
cell incorporates a current limiting device, referred to as a PTC
(positive temperature coefficient), that erves as a reversible thermal
fuse and over-temperature protection device. As a back-up to the PTC, shut-down
separators and/or current interrupting devices (CID) can permanently limit
current flow during internal short circuit and prevent excessive pressure
build-up and cell rupture. If all of these safety features fail the cell
incorporates a pressure relief disc to safely vent the gases generated.
The gases generated are non-toxic organic compounds, hydrocarbons and
carbon dioxide.
Overcharge of Li-Ion
Batteries: A Li-ion cell is
usually charged to a potential of about 4.2 V. The cell generates very
little heat during this normal charging process. Experiments have revealed
that it can be safely charged to a potential of at least 4.5 V without
excessive heat buildup. Excessive heating of and pressure buildup and
heating in the cell can occur if the voltage exceeds 4.5 V and hovers
around 5 V. Such a severe
overcharge of Li-ion cell leads to the plating of elemental Li on the
carbon anode and the formation of chemically unstable cobalt oxide. Our
work indicates that the safety hazard upon overcharge does not originate
from the plated Li but from the unstable cobalt oxide cathode although the
plated Li on the anode may have a role in exacerbating the ensuing runaway
reaction. A cell would encounter this situation if the charger fails and
the electronic circuitry in the cell fails. In a battery built with cells
connected in series, overcharge can occur if each of the cells is not
electronically protected against this condition.
The 18650 cells are safeguarded against excessive heat buildup
from the rare event of an overcharge by means of all of the above features
that are also used to protect it against short circuit. When these cells
are combined to form batteries, each cell is further protected against
overcharge with electronic circuitry. Large Li-ion batteries may not
contain all the necessary safety features, and also suffer from the basic
problem of using large monolithic cells for which adequate internal
protection mechanisms have not yet been developed. When such large
batteries experience a safety hazard, there is a tendency to blame Li-ion
batteries as a whole.
For additional discussion and
consulting on the safety pf Li-ion batteries consult Dr. K. M.
Abraham at E-KEM Sciences
References:
1.
S.N. Iaconetti, B. Ravdel, S. Santee, K. M. Abraham and J. F.
DiCarlo “Overcharging Characteristics of 7 Ah Prismatic Lithium-Ion
Batteries”, in Proceedings of 40th Power sources Conference,
Cherry Hill, NJ 2002, pp
37
2.
C.L Campion, W. Li, W.B. Euler, B. L. Lucht, B. Ravdel, J.F. DiCarlo, R.
Gitzendanner and K. M. Abraham, “Suppression of toxic Compounds
Formed in the Decomposition of lithium-Ion Battery Electrolytes”,
Electrochem. and Solid-State Lett., 7, A194 (2004)
The calendar life and cycle life of Li-ion batteries
are sensitive to the environmental temperature. An examination of
commercial 18650 cell specifications reveal that all cells do not behave
in the same manner. Typically, a Li-ion cells shows two types of capacity
loss on storage at elevated temperature; a reversible capacity loss and an
irreversible capacity loss. Interestingly, the values of each of these
capacity fades are manufacturer dependent suggesting that they are both
construction and material dependent. Similarly, the capacity fade rate on
charge/discharge cycling of 18650 Li-ion cells can also vary from
manufacturer to manufacturer.
Our recent studies of Li-ion cells with reference electrodes have
provided insight into the origin of these capacity losses
The accelerated test is usually based on the
Arrhenius relationship and relies upon the assumption that the logarithm
of rate of capacity fade, K, is proportional to the inverse of
temperature, T (in Kelvin).
K = A.
e-E/RT
(1)
Or,
log K = log
A – E/ 2.303RT
(2)
Here, A is a proportionality constant, E is the
activation energy for the capacity fade reaction and R is the gas
constant, 1.987. According to equation 2, a plot of logarithm of capacity
fade rate versus 1/T will give a straight line from which the activation
energy can be determined which then can be used to determine the life at
an unknown temperature. It
should be noted the fade reaction mechanism is assumed to remain the same
over this temperature range
First of all we can show that that for an
activation of energy of ~15 kCal/mole, the life of a cell would double for
a 10 degree decrease in temperature.
For this we differentiate equation 2 with respect to temperature
and integrate between two temperature limits, giving
Log
K2
=
E
(T2-T1) (3)
K1
2.303 R
(T1T2)
It can be shown that the value of E, the activation
energy, determines whether the Li-ion battery capacity fade will double,
triple, or follow some other order, for every 10 degree rise in
temperature. We can put in some numbers into equation (3) to see this
outcome.
For the two temperatures of 40 and 50 oC
with an activation energy, E, of 15 k Cal (15,000 Cal) /mole the fade rate
will approximately double when going from 40 to 50 oC. (Note temperature
is in Kelvin). Thus,
Log
K50
=
15,000 (323 – 313)
K40
2.303 x 1.987 (323x313)
= 150,000 =
0.32
462635
Therefore, K50 = 10
0.32 =
2.1
K40
That is the fade rate at 50 oC will be
about 2.1 times faster than that at 40 oC for an E of 15,000
Cal /mole or conversely the life at 40 oC will be about twice
as long as the life at 50 oC. If the activation energy is higher than 15
kCal/mole, the fade rate will increase more than twice from 40 to 50
oC or the life at 40 oC will be more than twice that
at 50 oC. It is
clear that a very good understanding of the relevant capacity fade
reactions and their kinetics are needed for a comprehensive understanding
of the thermal stability of Li-ion cells.
For a comprehensive discussion of how temperature
influences the performance of Li-ion batteries and to find out if the
common rule of thumb principles employed in the accelerated testing of
conventional batteries can be extended to Li-ion batteries, and to
ascertain what studies should be carried out to determine and predict
Li-ion battery life, consult Dr. K. M. Abraham at
E-KEM Sciences
References:
1. J.S. Gnanaraj, R.W. Thompson, S.N. Iaconneti, J.F.
DiCarlo and K. M. Abraham, “The Formation and Growth of Surface
Films on Graphitic Anode Materials for Li-ion Batteries” Electrochem.
and Solid-State Lett., 8, 128, 2005).
2.
W.
Li, C.L Campion, B. L. Lucht, B. Ravdel, J.F. DiCarlo, and
K. M. Abraham, “Additives
to Stabilize LiPF6-Based Electrolytes Against Thermal
Decomposition ”, J.
Electrochem. Soc., 152, 1361(2005)
3. B. Ravdel, S.A. Trebukhova, K. M.
Abraham and J. F. DiCarlo, “Coin Cell with Two Reference Electrodes
for Fundamental Study of Lithium-Ion Cells”, Fall Meeting of The
Electrochemical Society, Los Angeles, Ca. , September 2005. Abstract No.
246
For
Comprehensive Information on All Aspects of Lithium Ion (Li-Ion)
Batteries
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