U.S. patent application number 09/728804 was filed with the patent office on 2002-08-01 for lithium-ion battery electrode composition.
Invention is credited to Anani, Anaba, Deng, Guoping, Kerzhner-Haller, Inna, Maleki, Hossein.
Application Number | 20020102458 09/728804 |
Document ID | / |
Family ID | 26877765 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020102458 |
Kind Code |
A1 |
Maleki, Hossein ; et
al. |
August 1, 2002 |
Lithium-ion battery electrode composition
Abstract
A lithium-ion battery having at least an anode that includes
phenol formaldehyde in a range of 0.1% to 10% by weight as a binder
material. The phenol formaldehyde, or a mixture of phenol
formaldehyde with polyvinylidene fluoride (PVDF), is used as a
binding material in a Li-ion battery negative electrode to decrease
the exothermic reaction of the battery during charging and
discharging, which accordingly lessens the risk of thermal runaway
and rupture of the battery.
Inventors: |
Maleki, Hossein;
(Lawrenceville, GA) ; Deng, Guoping;
(Lawrenceville, GA) ; Anani, Anaba;
(Lawrenceville, GA) ; Kerzhner-Haller, Inna;
(Auburn, GA) |
Correspondence
Address: |
Motorola Energy Systems Group
Intellectual Property Department
1700 Belle Meade Court
Lawrenceville
GA
30043
US
|
Family ID: |
26877765 |
Appl. No.: |
09/728804 |
Filed: |
December 2, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60182080 |
Feb 11, 2000 |
|
|
|
Current U.S.
Class: |
429/217 ;
429/231.8 |
Current CPC
Class: |
H01M 4/623 20130101;
Y02E 60/10 20130101; H01M 2004/027 20130101; H01M 50/109 20210101;
H01M 10/0525 20130101; H01M 10/4235 20130101; H01M 4/621
20130101 |
Class at
Publication: |
429/217 ;
429/231.8 |
International
Class: |
H01M 004/62; H01M
004/58 |
Claims
What is claimed is:
1. A lithium-ion battery having at least one anode and at least one
cathode, wherein at least the anode includes phenol formaldehyde in
a range of 0.1% to 10% by weight.
2. The battery of claim 1, wherein the cathode includes phenol
formaldehyde in a range of 0.1% to 10% by weight.
3. The battery of claim 1, wherein the anode is comprised of
graphite, and includes phenol formaldehyde at 8% by weight as a
binder.
4. The battery of claim 1, wherein the anode further includes
polyvinylidene fluoride (PVDF).
5. The battery of claim 4, wherein the anode includes phenol
formaldehyde at 6.5% by weight and polyvinylidene fluoride at 1.5%
by weight.
6. The battery of claim 4, wherein the anode includes phenol
formaldehyde at 5% by weight and polyvinylidene fluoride at 3% by
weight.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 60/182,080, filed Feb. 11, 2000, the
disclosures of which, including all attached documents and
appendices, are incorporated by reference in their entirety for all
purposes.
TECHNICAL FIELD
[0002] This invention relates generally to rechargeable batteries
and their construction. More particularly, the present invention
relates to a composition for an electrode of a lithium-ion battery
that has a low exothermic reaction to create a more reliable Li-ion
battery.
BACKGROUND
[0003] As the term is used in electrochemistry, a battery is any of
a class of devices that convert chemical energy directly into
electrical energy. The mechanism by which a battery generates an
electric current involves the arrangement of constituent chemicals
in such a manner that electrons are released from one part of the
battery and made to flow through an external circuit to another
part. The part of the battery at which the electrons are released
to the circuit is called the anode, or the negative electrode, and
the part of the battery that receives the electrons from the
circuit is known as the cathode, or the positive electrode. Some
batteries, known as "rechargeable" batteries, are constructed such
that a reverse current applied to the electrodes causes the battery
to recharge and hold a new capacity to discharge.
[0004] One of the most common rechargeable batteries is a
lithium-ion battery. Conventional negative electrodes (or anodes)
in rechargeable Li-ion batteries contain active conductive
materials such as hard carbons, graphite, or MCMB, with
polyvinylidene fluoride (PVDF) as a "binder" material.
[0005] The electrochemical reaction in a Li-ion battery is
exothermic and thus the battery generates heat in both the charge
and discharge cycle. Further, significant exothermic heat
generation occurs in the Li-ion battery under abusive conditions,
such as a short circuit, overcharging, over-discharging, and
operation at high temperatures. The exothermic heat generation is
attributed to a combination of effects including the reaction of
the PVDF in the electrodes with "lithiated" carbon, reaction of
electrolyte with oxygen liberated due to decomposition of positive
electrode (cathode) material, and breakdown of the electrodes
passivation layers. Insufficient heat dissipation in the Li-ion
battery can compromise the performance of the battery and may
result in the release of combustible gasses at high temperatures,
known as "thermal runaway".
[0006] Accordingly, the minimization of the exothermic heat
generation from the electrochemical operation of the Li-ion battery
is desirable because increasing the reliability of the battery
decreases the likelihood that the battery will suffer from thermal
runaway and rupture. It is thus to the provision of such a battery
having an electrode composition that has minimal exothermic heat
generation during electrical charge and discharge of the battery
that the present invention is primarily directed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is an exemplary embodiment of a lithium-ion battery
with the anode and cathode in a coin-on-coin configuration in
accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0008] A preferred embodiment of the invention is now described in
detail. Referring to the drawings, like numbers indicate like parts
throughout the views. As used in the description herein and
throughout the claims, the following terms take the meanings
explicitly associated herein, unless the context clearly dictates
otherwise: the meaning of "a," "an," and "the" includes plural
reference, the meaning of "in" includes "in" and "on."
[0009] With reference to FIG. 1, there is illustrated a lithium-ion
battery 10 having electrodes in a coin-on-coin configuration. The
battery 10 has an upper component 12 and a lower component 14,
which are constructed of one or more conductive materials. Within
the upper component 12 is an anode 16, and within lower component
14 is a cathode 20, with separator 18 between anode 16 and cathode
20. The insulator 22 insures that the anode 16 is only in
conductive connection with the upper component 12, and the cathode
20 is in conductive connection with the lower component 14 whereby
conductive contact with both the upper component 12 and lower
component 14 will close a circuit and allow current to flow due to
the electrochemical reaction of the anode 16 and cathode 20. The
coin-on-coin Li-ion battery configuration and other electrode and
component configurations are well known in the art and the present
inventive battery can be readily configured to any type of Li-ion
or Li-polymer battery as would be apparent to one of skill in the
art.
[0010] The present invention provides an alternative binder
material for use in the composition of at least the anode 16 of a
Li-ion battery. Alternately, the binder material can be used in the
cathode of the battery. While conventional Li-ion batteries use
polyvinylidene fluoride (PVDF) as a binder for the conductive
elements of the negative electrode, the present invention uses
phenol formaldehyde (PF) as the binder ingredient at least in the
negative electrode (and alternately the cathode) in a range of 0.1%
to 10% by weight, either as the sole binder or in mixture with
PVDF. The use of PF as the binder lessens the exothermic reaction
in the battery from the electrochemical reaction. And most
importantly, the heat generation of the negative electrode is
independent of the degree of lithiation.
[0011] Electrochemical cells that are assembled with PF as a
component of the anode binder exhibit a lower self-heating rate
than cells solely using PVDF as the binder material in the anode.
As is more fully shown herein, even under abusive and fully
lithiated conditions, the battery with the PF anode exhibits
reduced heat generation when compared to electrodes with the
typical PVDF binder. In addition, the electrode formulation results
in battery cells with higher thermal stability with minimal, if
any, consequences to cell performance in voltage and cycling
characteristics.
[0012] The experimental cells used to verify the efficacy of the
present invention were constructed as follows. For the construction
of the half cell electrodes, a solvent, SFG44 graphite, and either
PVDF or PF binder were mixed for 3 minutes to form a slurry which
was then coated on a conductive substrate. The coating was then
cured under a vacuum at 100.degree. C. and allowed to sit for 12
hours. Then the coated substrate was heated to 700.degree. C. for 4
hours. The single cells were comprised of an anode 16 and cathode
20, where the anode 16 is comprised of SFG44 and MCMB in a 50/50
mixture with either PF at 5% by weight and PVDF at 3% by weight, or
PF at 6.5% by weight and PVDF at 1.5% by weight, and the mixture
included a solvent. The cathode 20 included LiNiO2 and PVDF at 1.5%
by weight and PF at 2.5% by weight, with a solvent. Each of the
compositions were mixed for 3 minutes and then coated upon a
substrate and calendared. The coated substrate was heated to
100.degree. C. under a vacuum for 12 hours. If pre-carbonization of
the electrodes were desired, it could be performed at this stage,
prior to the electrodes being placed in an electrochemical
cell.
[0013] The SFG44 Negative Electrode Containing Phenol Formaldehyde
electrode was lithiated at current density of 0.4 mA/cm2
(equivalent to C/10) to 0.005 V, followed by tapering current to
C/30. The delithiation was carried to 2.0 V at C/5 rate. Table 1
illustrates a 1st cycle efficiency and a 2nd cycle reversible
capacity comparison for the negative electrodes containing SFG44
graphite in half-cell configuration.
1TABLE 1 1.sup.st Cycle Reversible Capacity Anodes Efficiency (%)
(mA/g) Binder SFG44 87.5 336 PVDF Binder SFG44 83.0 300 Phenol
Formaldehyde
[0014] Comparison of DSC spectra for fully lithiated SFG44
electrodes containing solely PVDF binder (8.0% by weight) and
pre-carbonized PF binder (8.0% by weight), and of SPG44/MCMB
electrode made with PVDF (8.0% by weight), PVDF (3.0% by weight)-PF
(5% by weight), or PVDF (1.5% by weight)-PF (6.5% by weight),
revealed in each instance, that anodes having only PVDF binder
exhibited higher heat generation. Thus, the results show that heat
generation in the negative electrode (anode) is primarily due to
the reaction of lithiated carbon with PVDF, and also that heat
generation increases with an increasing content of PVDF binder in
the anode. Conversely, the heat generation of cells with
PF-containing negative electrodes remained substantially constant
regardless of the extent of lithiation. Therefore, the inclusion of
PF into the anode will give the cell increased thermal stability
and will lessen the risk of thermal runaway.
[0015] To illustrate the invention on a full battery cell, full
T-cells were constructed with the negative electrode containing
SFG44/MCMB in a 50/50 mixture, and PF/PVDF mixture binder
materials. The positive electrode (cathode) is constructed with
LiNiO2, a Li-paste electrolyte (LiPF6 in 40:30:30 EC:DEC:DMC) as
known in the art, and a glass-fiber separator. The binder in the
cathode is PVDF at 1.5% by weight and PF at 2.5% by weight, and the
binder in the anode is PVDF 3% by weight and PF at 5% by
weight.
[0016] The T-cells were cycled at 1.0 mA/cm2 charge rate and 2.0
mA/cm2 discharge rate. All of the cells demonstrate 62% first cycle
efficiency and cathode capacity utilization of 112 mAh/g. Thus, the
charge and discharge rates are almost identical to the cell with
anode consisting solely of PVDF.
[0017] Lithium-ion polymer cells were likewise constructed with the
same combination of elements in the positive and negative
electrodes as the T-cells. Table 2 summarizes the cell performance
when cycled by charging at 250 mA to 4.1 V, and tapering at
constant 4.1 V to 20 mA, and discharging at 500 mA to 3.0 V
cut-off.
2TABLE 2 1.sup.st Cycle 5.sup.th Cycle Binder Efficiency Discharge
Capacity Cell in the Anode (%) (mAh) FN54101-FN54103 PVDF, Phenol
62.4 529 Formaldehyde FN49915-FN49921 PVDF 62.2 535
[0018] As can be seen in Table 2, the efficiency and discharge
capacity between the cells with PVDF anode and PVDF/PF anode are
negligible. Therefore, the safety benefit of the inclusion of PF in
the anode does not significantly adversely effect the performance
of the fully assembled cell. The cycle efficiency and cell capacity
are similar in the T-cells and polymer cells containing the same
positive/negative electrode material.
[0019] The thermal runaway profile of the polymer cell having a PF
binder is significantly less than a typical cell without any PF
binder. Accelerated rate calorimeter (ARC) experiments reveal that
the self-heating rate profile of a standard polymer cell, e.g.
LiNiO2 mixture with no PF as a binder material, is exponential from
the onset of thermal runaway until cell rupture. When the polymer
cell is embodied with the anode containing a binder mixture of 5%
by weight of PF and 3% by weight of PVDF, the cell begin to
experience thermal runaway at the same onset temperature, but
reaches a maximum self-heating rate and then the self-heating rate
decreases to almost 0. Consequently, while both cells undergo
thermal runaway at about the same temperature, the cell having PF
in the binder of the anode stabilizes and does not exponentially
heat until cell rupture. Thus, the PF binder would be especially
advantageous in providing a safer Li-ion battery that is routinely
subjected to abusive conditions, such as extremes of ambient
heat.
[0020] While the preferred embodiments of the invention have been
illustrated and described, it is clear that the invention is not so
limited. Numerous modifications, changes, variations,
substitutions, and equivalents will occur to those skilled in the
art without departing from the spirit and scope of the present
invention as defined by the following claims.
* * * * *