TECHNICAL FIELD
The present disclosure relates to a lithium secondary battery activation
method and activation apparatus, and more particularly, to an activation protocol
generation method adapted to apply a specific voltage range, and an activation
method and activation apparatus using the activation protocol generation method.
The present application claims priority to Korean Patent Application No. 10-
2020-0134301 filed on October 16, 2020 in the Republic of Korea, the disclosures
of which are incorporated herein by reference.
BACKGROUND ART
Recently, as demand for portable electronic products such as notebook
computers, video cameras, and portable telephones is rapidly increasing, and
development of electric vehicles, energy storage batteries, robots, satellites, etc. is
in full swing, research into high-performance secondary batteries capable of being
repeatedly charged and discharged is being actively conducted.
Currently commercialized secondary batteries include nickel-cadmium
batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium secondary
batteries. Among them, compared to nickel-based secondary batteries, lithium
secondary batteries have almost no memory effect and thus are freely charged and
discharged and have a very low self-discharge rate and have a high energy
density. In general, such secondary batteries may be classified into cylindrical or
prismatic can-type secondary batteries and pouch-type secondary batteries
depending on outer casings or application forms.
A secondary battery may be used in the form of a single cell or in the
form of a module in which a plurality of cells are electrically connected,
depending on the type of external device using the second battery. For example,
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a small device such as a mobile phone can operate for a predetermined time
period with the output and capacity of one cell, whereas a medium-sized or largesized
device such as a notebook computer, a portable DVD, a small personal
computer (PC), an electric vehicle, and a hybrid electric vehicle needs to use a
module including a plurality of cells due to problems of output and capacity.
A module is manufactured by connecting a protection circuit or the like to
a core pack in which a plurality of cells are arranged in series and/or in parallel
and connected to one another. When a prismatic or pouch-type cell is used as a
unit cell, the unit cell can be easily manufactured by stacking wide surfaces to
face each other and then connecting electrode terminals to one another by using a
connecting member such as a bus bar. Accordingly, when a stereoscopic module
having a hexahedral structure is manufactured, a prismatic or pouch-type cell is
advantageous as a unit cell.
Because a pouch-type cell constitutes its exterior by using a pouch outer
casing formed as a multi-layer including a metal layer (foil) and a synthetic resin
layer coated on upper and lower surfaces of the metal layer, the pouch-type cell
can contribute to significant reduction in the weight of secondary batteries and are
changeable into various shapes, as compared with a cylindrical or prismatic cell
using a metal can. Moreover, usage of pouch-type cells is gradually increasing.
In general, pouch-type cells are manufactured through a process of
assembling a cell and a process of activating the cell.
A conventional pouch outer casing generally includes a lower outer
casing in which an electrode assembly is accommodated, and an upper outer
casing that seals an upper portion of the lower outer casing. A cell is assembled
by accommodating the electrode assembly in an accommodating portion of the
lower outer casing, making an edge around the accommodating portion of the
lower outer casing adhere to an edge of the upper outer casing corresponding to
the former edge, heat-sealing a closely adhered portion, putting the electrolyte in,
and vacuum-sealing the remaining portion.
Because the cell is assembled in a discharged state, it can function as a
battery only after being assembled and then being charged and activated. This is
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referred to as an activation or formation process.
In the activation process, a cell is mounted in an activation device, which
is predetermined activation process equipment, for smooth current flow, and
charging/discharging is performed under conditions necessary for activation.
Due to characteristics of a cell, this activation process must be preceded during a
first cycle in order to activate a positive electrode active material and generate a
solid electrolyte interface (SEI) on a negative electrode. In the activation
process, the SEI is finally formed on the surface of the negative electrode due to a
reaction between the negative electrode active material and the electrolyte, and
physical and mechanical soundness of this SEI determines performance of the cell
until the lifespans of the cell and a secondary battery including the cell end.
A cell manufacturing process including the activation process is as
follows. After the cell is assembled to have an air pocket, a jig formation
operation for SEI formation is performed. It takes an aging time so that an
electrolyte is sufficiently impregnated. An additional charge/discharge operation
is needed. Gas is generated inside the cell due to charging/discharging. To
remove this gas, the air pocket is punctured to suck in the gas, and a degassing
operation of cutting out an unnecessary portion of an outer casing and sealing the
outer casing is performed. Then, the cell is inspected and then shipped as a
finished product.
In the degassing operation, when the gas is sucked in, the electrolyte
inside the cell is also easily leaked. However, if a large number of pores are
formed in an electrode active material, the electrolyte is trapped in the pores and
thus is less leaked. The additional charge/discharge operation is performed to
form the pores in the electrode active material, and is thus very important.
However, when a lead time of the additional charge/discharge operation increases,
this leads to a delay in the progress of the entire activation process, and also leads
to a decrease in productivity. Therefore, there is a need for a method for
shortening the progress time of an activation process including an additional
charge/discharge operation.
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DISCLOSURE
Technical Problem
The present disclosure is designed to solve the problems of the related art,
and therefore the present disclosure is directed to providing an activation protocol
generation method capable of shortening a lead time of an additional
charge/discharge operation.
The present disclosure is designed to solve the problems of the related art,
and therefore the present disclosure is directed to providing an activation method
having a shortened lead time by using the activation protocol generation method.
The present disclosure is designed to solve the problems of the related art,
and therefore the present disclosure is directed to providing an activation
apparatus using the activation protocol generation method.
Technical Solution
In one aspect of the present disclosure, there is provided a method of
generating a charge/discharge protocol of an additional charging/discharging
operation included in an activation method, the activation method including a jig
formation operation, an aging operation, and the additional charging/discharging
operation with respect to assembled secondary batteries, the charge/discharge
protocol generation method including operation (a) of measuring a secondary
battery thickness increase rate over time while repeating charging/discharging
between a first voltage and a second voltage higher than the first voltage with
respect to any one of the assembled secondary batteries; operation (b) of
performing, at least once, an operation of performing operation (a) with respect to
another secondary battery that is the same model as the any one secondary battery,
after fixing the second voltage and changing the first voltage; operation (c) of
determining one of first voltages except for a first voltage at a lowest rate from
among measured secondary battery thickness increase rates as a lower limit
voltage; and operation (d) of setting a protocol so that charging/discharging is
repeated between the lower limit voltage and the second voltage.
The second voltage may be a full charge voltage of the secondary
6
batteries, and the first voltage may be a voltage greater than or equal to a full
discharge voltage of the secondary batteries.
The full charge voltage may be a voltage enabling an SOC of the
secondary batteries to have a determined value between 80% and 90%, and the
full discharge voltage may be a voltage when the SOC of the secondary batteries
is 0%.
The secondary battery thickness increase rate may be obtained by
subtracting a thickness of the secondary battery measured before
charging/discharging in operation (a) from a thickness of the secondary battery
measured after charging/discharging in operation (a) and by dividing a difference
between the two thicknesses by a total time taken for charging/discharging.
In one aspect of the present disclosure, there is provided a method of
generating a charge/discharge protocol of an additional charging/discharging
operation included in an activation method, the activation method including a jig
formation operation, an aging operation, and the additional charging/discharging
operation with respect to assembled secondary batteries, the charge/discharge
protocol generation method including measuring a secondary battery thickness
increase rate over time while repeating charging/discharging between a full
discharge voltage and a full charge voltage of the secondary batteries, with respect
to any one of the secondary batteries, and setting the measured secondary battery
thickness increase rate as a reference; measuring a secondary battery thickness
increase rate over time while repeating charging/discharging between a first
voltage higher than the full discharge voltage and the full charge voltage, with
respect to another secondary battery that is the same model as the any one
secondary battery; changing the first voltage, and then performing, at least once,
an operation of measuring a secondary battery thickness increase rate over time
while repeating charging/discharging between the changed first voltage and the
full charge voltage, with respect to another secondary battery that is the same
model as the any one secondary battery; determining a lower limit voltage from
among first voltages exhibiting greater rates than the reference from among the
measured secondary battery thickness increase rates; and setting a protocol so that
7
charging/discharging is repeated between the lower limit voltage and the full
charge voltage.
The present disclosure also proposes an activation method using this
additional charge/discharge activation protocol generation method. The
activation method according to the present disclosure includes a jig formation
operation for assembled secondary batteries; an aging operation; and an additional
charge/discharge operation, and the additional charge/discharge operation is
performed using a charge/discharge protocol obtained by an additional
charge/discharge activation protocol generation method according to the present
disclosure.
The present disclosure also provides an activation apparatus capable of
performing such an activation method. The activation apparatus according to the
present disclosure includes a charge/discharge device configured to perform
charging/discharging with respect to assembled secondary batteries; and a control
device configured to control an operation of the charge/discharge device
according to a charge/discharge protocol.
The control device includes a processing unit including a program module
for executing operation (a) of measuring a secondary battery thickness increase
rate over time while repeating charging/discharging between a first voltage and a
second voltage higher than the first voltage for any one of the assembled
secondary batteries; a program module for executing, at least once, an operation
of performing operation (a) with respect to another secondary battery that is the
same model as the any one secondary battery, after fixing the second voltage and
changing the first voltage; a program module for determining one of first voltages
except for a first voltage at the time of showing a lowest rate from among
measured secondary battery thickness increase rates as a lower limit voltage; and
a program module for setting a protocol to repeat charging/discharging between
the lower limit voltage and the second voltage. The control device controls the
charge/discharge device to perform an additional charging/discharging operation
for forming pores in an electrode active material, according to the protocol, after
performing jig formation charge/discharge for SEI formation on the secondary
8
batteries and then having an aging time to sufficiently impregnate an electrolyte.
The activation apparatus may further include a thickness measuring unit
configured to measure a thickness of the secondary battery. The control device
may control a driving and measuring timing of the thickness measuring unit, and
the program modules of the processing unit may calculate the secondary battery
thickness increase rate by using the thickness measured by the thickness
measuring unit.
Advantageous Effects
In an additional charge/discharge activation protocol generation method
and an activation method using the additional charge/discharge activation protocol
generation method, according to the present disclosure, a lead time of an
additional charge/discharge process may be shortened during an activation
process in a production process of a secondary battery including a pouch-type
cell. Accordingly, a lead time of the entire activation process may be shortened,
leading to an increase in productivity.
An additional charge/discharge activation process may sufficiently secure
pores in an electrode active material before degassing. According to the present
disclosure, because pores may be formed within a short period of time, a defect
rate of the residual amount of an electrolyte after degassing may be reduced.
An activation apparatus according to the present disclosure is optimized
for performing an additional charge/discharge activation protocol generation
method and an activation method using the same. The activation apparatus
needs only manpower sufficient to change secondary batteries to be charged and
discharged one by one, and is able to automatically perform almost the entire
charge/discharge process, thereby providing high productivity and efficiency.
DESCRIPTION OF DRAWINGS
The accompanying drawings illustrate a preferred embodiment of the
present disclosure and together with the foregoing disclosure, serve to provide
further understanding of the technical features of the present disclosure, and thus,
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the present disclosure is not construed as being limited to the drawing.
FIG. 1 is a flowchart of an additional charge/discharge activation protocol
generation method according to an embodiment of the present disclosure.
FIGS. 2 through 6 show various charge/discharge protocols that may be
taken as an example in the additional charge/discharge activation protocol
generation method according to an embodiment of the present disclosure.
FIG. 7 is a graph showing a secondary battery thickness increase rate
obtained for each secondary battery after charging/discharging is performed
according to FIGS. 2 through 6.
FIG. 8 is a schematic diagram of an activation apparatus according to
another embodiment of the present disclosure.
MODE FOR DISCLOSURE
Hereinafter, preferred embodiments of the present disclosure will be
described in detail with reference to the accompanying drawings. Prior to the
description, it should be understood that the terms used in the specification and
the appended claims should not be construed as limited to general and dictionary
meanings, but interpreted based on the meanings and concepts corresponding to
technical aspects of the present disclosure on the basis of the principle that the
inventor is allowed to define terms appropriately for the best explanation.
Therefore, the description proposed herein is just a preferable example for the
purpose of illustrations only, not intended to limit the scope of the disclosure, so it
should be understood that other equivalents and modifications could be made
thereto without departing from the scope of the disclosure.
In embodiments described below, a secondary battery are collectively
referred to as a battery in which lithium ions act as working ions during charging
and discharging to induce an electrochemical reaction at a positive electrode and a
negative electrode.
Even when the name of a secondary battery is changed depending on the
type of electrolyte or separator used in the secondary battery, the type of battery
case (or a packing material) used to pack the secondary battery, the internal or
10
external structure of the secondary battery, and the like, all batteries in which
lithium ions are used as working ions need to be interpreted as being included in
the category of the secondary battery.
In addition, the secondary battery is not limited by the number of
elements constituting the secondary battery. Therefore, the secondary battery
needs to be interpreted as including not only a single cell including an electrode
assembly of a positive electrode/separator/negative electrode and an electrolyte in
one battery case, but also an assembly of a single cell, a module in which a
plurality of assemblies are connected in series and/or in parallel, a pack in which a
plurality of modules are connected in series and/or in parallel, and a battery
system in which a plurality of packs are connected in series and/or parallel.
An example of a secondary battery assembly and activation process to
which a method according to the present disclosure is applicable is as follows.
An assembling operation includes receiving and sealing an electrode
assembly and an electrolyte in a battery case in a manufacturing room.
First, an electrode assembly including a positive electrode, a negative
electrode, and a separator interposed therebetween is manufactured. The
manufacturing of the electrode assembly includes applying an electrode slurry
including an active material and a binder to an electrode current collector to
manufacture the positive electrode and the negative electrode, respectively, and
then interposing the separator between the positive electrode and the negative
electrode. The manufacturing of the electrode assembly is not particularly
limited and may be performed according to a known method. In addition, the
electrode assembly is not particularly limited as long as it has a structure
including a positive electrode, a negative electrode, and a separator, and, the
structure may be, for example, a jelly-roll type, a stack type, or a stack/folding
type structure.
The negative electrode in the electrode assembly may include a carbonbased
negative electrode active material. The carbon-based negative electrode
active material may be artificial graphite or natural graphite.
The electrolyte may include an organic solvent and a lithium salt. The
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organic solvent is not limited as long as it can minimize decomposition due to an
oxidation reaction during charging/discharging of a battery and exhibit desired
properties. For example, the organic solvent may be a cyclic carbonate, a linear
carbonate, an ester, an ether, or a ketone. These may be used alone, or two or
more of them may be used in combination. Among the organic solvents, a
carbonate-based organic solvent may be preferably used. Examples of the cyclic
carbonate include ethylene carbonate (EC), propylene carbonate (PC) and
butylene carbonate (BC), and representative examples of the linear carbonate
include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate
(DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and
ethylpropyl carbonate (EPC). Lithium salts commonly used in electrolytes of
lithium secondary batteries, such as LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2,
LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4,
may be used as the lithium salt without limitations, and these may be used alone,
or two or more of them may be used in combination.
The battery case may preferably be a pouch made of an aluminum
laminate sheet.
Next, cells assembled as above are transferred to a formation room to
proceed with an activation process. The activation process includes a jig
formation operation for forming an SEI, an aging operation of sufficiently
impregnating an electrolyte, and an additional charge/discharge operation for
forming pores in an electrode active material. The present disclosure proposes,
particularly, a method of generating a charge/discharge protocol in an additional
charge/discharge operation.
The inventors of the present disclosure determine that an activation
voltage has a major influence on formation of pores in an electrode. The present
disclosure proposes a method of the most preferably determining a
charge/discharge voltage range from the viewpoint of productivity in the
additional charge/discharge operation by focusing on such a voltage range.
When a predetermined charge/discharge voltage range is determined as proposed
by the present disclosure and used as a charge/discharge protocol, sufficient pores
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may be secured within the same time period, thereby reducing both the lead time
of the additional charge/discharge operation and the lead time of the entire
activation process.
The inventors of the present disclosure have come to the present
disclosure by discovering that, when pores are formed in an electrode active
material, the thickness of a secondary battery increases, and, when the level of an
increase in the thickness of the secondary battery while changing a
charge/discharge voltage is ascertained, an appropriate charge/discharge range
may be determined.
A secondary battery has an upper limit that can be physically charged and
a lower limit that can be physically discharged. However, in an actual use
environment, charging/discharging is not performed up to the physical upper and
lower limits. Instead, within the physical upper and lower limits of the
secondary battery, a use area is appropriately set in terms of safety, lifespan, and
energy efficiency of the secondary battery, and charging and discharging are
performed only within the use area.
In other words, a lower limit of the use area is set higher than a physical
limit discharge point, and an upper limit of the use area is set lower than a
physical limit charge point. The use area may be variously set according to
characteristics of the secondary battery, usage environments, required
charge/discharge capacities, energy outputs, and the like. Hereinafter, it is
defined that the secondary battery is completely discharged (or fully discharged)
when the state of the secondary battery reaches the lower limit of the set use area
during a discharging process of the secondary battery. It is also defined that the
secondary battery is completely charged (or fully charged) when the state of the
secondary battery reaches the upper limit of the set use area during a charging
process of the secondary battery.
Conventionally, there is a case in which additional charging/discharging
is performed by repeating charging/discharging between a full charge voltage and
a full discharge voltage. Although the full charge voltage and the full discharge
voltage vary depending on the type of cell, there is, for example, a case where
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charging/discharging is performed in a 4.35 V to 3.0 V section. At this time, it
took 750 minutes to form pores in an electrode active material to a desired degree.
However, it was confirmed that, when additional charging/discharging was
performed with a charging/discharging voltage range obtained using the activation
protocol generation method proposed by the present disclosure, the time period to
form pores in an electrode active material could be reduced to 440 minutes. An
activation protocol generation method according to the present disclosure will
now be described in detail with specific examples.
FIG. 1 is a flowchart of an additional charge/discharge activation protocol
generation method according to an embodiment of the present disclosure.
Referring to FIG. 1, first, a secondary battery thickness increase rate over
time is measured while repeating charging/discharging between a first voltage and
a second voltage higher than the first voltage with respect to any one of assembled
secondary batteries [operation (a)].
The second voltage may be a full charge voltage of the secondary
batteries, and the first voltage may be a voltage greater than or equal to a full
discharge voltage of the secondary batteries. The full charge voltage and the full
discharge voltage may vary depending on how the use area is set as mentioned
above. For example, the full charge voltage may be a voltage enabling an SOC
of the secondary batteries to have a determined value between 80% and 90%, and
the full discharge voltage may be a voltage when the SOC of the secondary
batteries is 0%.
According to the present embodiment, a case in which the second voltage
is a full charge voltage of the secondary batteries and is a voltage enabling the
SOC of the secondary batteries to be 85% is taken as an example. The voltage
enabling the SOC to be 85% may vary depending on a secondary battery model.
However, in the secondary battery described in the present embodiment, the
voltage is 4.35 V. According to the present embodiment, a case in which the
first voltage is a full charge voltage of the secondary batteries and is a voltage
enabling the SOC of the secondary batteries to be 0% is taken as an example.
The voltage enabling the SOC to be 0% may vary depending on a secondary
14
battery model. However, in the secondary battery described in the present
embodiment, the voltage is 3.0 V.
Then, in operation (a), which is a first operation, while
charging/discharging between 3.0 V and 4.35 V with respect to any one secondary
battery is being repeated, a secondary battery thickness increase rate over time is
measured. The number of repetitions of charging/discharging may be arbitrarily
set to be one or more. The secondary battery thickness increase rate may be a
value obtained by subtracting a thickness of the secondary battery measured
before charging/discharging in operation (a) from a thickness of the secondary
battery measured after charging/discharging in operation (a) and by dividing a
difference between the two thicknesses by a total time taken for charging and
discharging.
For example, a charge/discharge protocol of operation (a) may be as
shown in FIG. 2. FIGS. 2 through 6 show various charge/discharge protocols
that may be taken as an example in the additional charge/discharge activation
protocol generation method according to an embodiment of the present disclosure.
After the secondary battery is aged in a state where the SOC is charged
to, for example, 65%, in the previous jig formation operation, additional
charging/discharging may be performed, and the additional charging/discharging
may be performed according to the additional charge/discharge protocol as shown
in FIG. 2. When the secondary battery reaches a full charge voltage of 4.35 V
by performing additional charging in an SOC 65% state, discharging is
performed. When the secondary battery reaches a full discharge voltage of 3.0
V, charging is performed until the secondary battery reaches the full charge
voltage again. When the secondary battery reaches the full charge voltage, the
secondary battery is discharged until the secondary battery reaches the full
discharge voltage again. For example, a cycle including one time of charging
and one time of discharging is repeated 4 times. A total time period to do this is
750 minutes. After charging/discharging is performed according to the
charge/discharge protocol shown in FIG. 2, the secondary battery thickness
increase rate is obtained. The secondary battery thickness increase rate is
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calculated by subtracting a thickness of the secondary battery measured before
charging/discharging from a thickness of the secondary battery measured after
charging/discharging and by dividing a difference between the two thicknesses
(thickness variation) by a total time taken for charging and discharging. The
charge/discharge profile of FIG. 2 may be, for example, a reference.
FIG. 7 is a graph showing a secondary battery thickness increase rate
obtained for a secondary battery after charging/discharging is performed
according to FIG. 2. For example, when the thickness variation (delta T) is
about 70 μm when a total time taken for charging/discharging is 750 minutes, a
circled dot is displayed as in FIG. 7, and the slope of a line connecting a zero
point to the circled point corresponds to the secondary battery thickness increase
rate.
Next, after the second voltage is fixed and the first voltage is changed, the
same operation as operation (a) is performed with respect to another secondary
battery that is the same model as the former secondary battery [operation (b)].
Operation (b) is performed at least once.
According to the present embodiment, a case where the second voltage is
4.35 V and the initial first voltage is 3.0 V is taken as an example. Because the
initial first voltage is the full discharge voltage, the changed first voltage may be
greater than the full discharge voltage. For example, the changed first voltage
may be 4.0 V as in FIGS. 3 and 4, or may be 3.9 V as in FIGS. 5 and 6. It is
only necessary that the first voltage is less than the second voltage.
When operation (b) is performed one or more times, operation (b) may be
performed by leaving the changed first voltage as it is and changing the number of
repetitions of charging/discharging. For example, the number of
charge/discharge cycles in FIGS. 3 and 5 is 4, which is the same as that of FIG. 2,
but FIGS. 4 and 6 show a case where the number of charge/discharge cycles is 9,
which is greater than that of FIG. 2. In other words, as shown in FIGS. 3
through 6, the secondary batteries are charged and discharged according to
various charge/discharge protocols having different first voltages or performing
different number of times of charging/discharging, and then different secondary
16
battery thickness increase rates are obtained for such different cases.
One or more secondary battery thickness increase rates obtained by
operation (b) may be added as data as further shown in FIG. 7. FIG. 7 is a graph
showing a secondary battery thickness increase rate obtained for each secondary
battery after charging/discharging is performed according to FIGS. 3 through 6.
Subsequently, one of first voltages except for a first voltage at a lowest
rate from among the measured secondary battery thickness increase rates is
determined as a lower limit voltage [operation (c)]. Referring to FIG. 7, when
charging/discharging is repeated 9 times between 3.9 V and 4.35 V according to
FIG. 6, the secondary battery thickness increase rate is the lowest (the slope of the
graph is the smallest). Therefore, the lower limit voltage is determined from
among first voltages of 4 V and 3.0 V except for 3.9 V. According to the present
embodiment, when the first voltage is 3.0 V, it takes 750 minutes to repeat
charging/discharging 4 times. However, when the first voltage is 4 V, it takes
230 minutes to repeat charging/discharging 4 times, and it takes 440 minutes to
repeat charging/discharging 9 times. Therefore, considering that it is
advantageous that the time taken to complete charging/discharging is short, 4 V
among 3.0 V and 4 V is suitable as the lower limit voltage and thus may be
determined as the lower limit voltage.
Next, a protocol is set to repeat charging/discharging between the lower
limit voltage and the second voltage [operation (d)]. Although using the same
lower limit voltage, when charging/discharging is repeated between 4 V and 4.35
V 4 times by referring to FIG. 7, a thickness variation is less than that when
charging/discharging is repeated between 4 V and 4.35 V 9 times. Therefore, the
case where the number of times of charging/discharging is 9 is suitable as a case
satisfying a condition that the thickness variation is large. The thickness
variation being large refers to many pores being formed in an electrode active
material and thus the volume of the electrode active material being expanded.
Therefore, a new charge/discharge protocol set in operation (d) is determined as
repeating charging/discharging 9 times between 4 V and 4.35 V. The additional
charge/discharge protocol determined in this way may be used as an established
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additional charge/discharge protocol in a next additional charge/discharge
process.
According to another embodiment, when operation (a) is performed, a
case in which a charge/discharge protocol as in FIG. 2 is followed may be
specially used as a reference, that is, a reference point. A result of measuring the
secondary battery thickness increase rate over time while repeating
charging/discharging between the full discharge voltage and the full charge
voltage is served as a reference.
Then, when operation (b) is performed, a secondary battery thickness
increase rate over time is measured while repeating charging/discharging between
the first voltage higher than the full discharge voltage and the full charge voltage,
with respect to another secondary battery that is the same model as the former
secondary battery. After further changing the first voltage, operation (b) is
further repeated.
When operation (c) is performed, a lower limit voltage may be
determined from among the first voltages exhibiting greater rates than the
reference from among the measured secondary battery thickness increase rates.
Operation (d) may be ended by setting a new additional charge/discharge protocol
to repeat charge/discharge between the determined lower limit voltage and the full
charge voltage.
When additional charge/discharge is performed according to the new
additional charge/discharge protocol obtained according to the present disclosure,
the secondary battery thickness increase rate is greater than that in a reference
case. In other words, when additional charge/discharge is performed according
to the new additional charge/discharge protocol obtained according to the present
disclosure, pores may be formed in an electrode active material within a shorter
time period than in the case of performing additional charging/discharging while
repeating charging/discharging between the full discharge voltage and the full
charge voltage. This results in increased productivity.
In other words, according to the present disclosure, a charge/discharge
voltage range is reduced compared to the reference case, leading to a reduction in
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the process lead time. The present disclosure is an activation protocol generation
method adapted to apply a specific voltage range. The present disclosure
proposes an additional charge/discharge protocol generation method that enables
sufficient pores to be secured within the same or shorter time period as or than in
the related art.
The present disclosure also proposes an activation method using this
additional charge/discharge activation protocol generation method. The
activation method according to the present disclosure includes a jig formation
operation for assembled secondary batteries; an aging operation; and an additional
charge/discharge operation, and the additional charge/discharge operation is
performed using a charge/discharge protocol obtained by an additional
charge/discharge activation protocol generation method according to the present
disclosure.
The present disclosure also provides an activation apparatus capable of
performing such an activation method. FIG. 8 is a schematic view of an
activation apparatus according to another embodiment of the present disclosure.
Referring to FIG. 8, an activation apparatus 100 includes a
charge/discharge device 110 and a control device 120.
The charge/discharge device 110 is capable of charging/discharging
assembled secondary batteries. The charge/discharge device 110 is a device for
charging/discharging a cell for activation, and may be an existing
charging/discharging device. The charge/discharge device 110 may include a
charging/discharging jig, a charging circuit, a discharging circuit, and the like.
The control device 120 controls an operation of the charge/discharge
device 110 according to a charge/discharge protocol. The control device 120 is
electrically connected to the charge/discharge device 110. The control device
120 controls the charging or discharging of the charge/discharge device 110 and,
at the same time, controls switching of a charging or discharging mode.
For example, the charging circuit of the charge/discharge device 110
supplies power for charging a cell in the charging mode, and the charging circuit
starts and stops an operation according to a start signal of the control device 120.
19
To perform CC charging, CV charging, or CC-CV charging, the charging circuit
includes a constant current circuit and a constant voltage circuit.
The discharging circuit of the charge/discharge device 110 functions to
discharge a cell in the discharging mode. The discharging circuit also starts and
stops an operation according to the start signal of the control device 120.
The control device 120 may include a processing unit 132, a memory unit
134, a display unit 136, and a control unit 138.
The processing unit 132 includes a program module for performing
operation (a) of measuring a secondary battery thickness increase rate over time
while repeating charging/discharging between a first voltage and a second voltage
higher than the first voltage with respect to any one secondary battery; a program
module for performing, at least once, an operation of performing operation (a)
with respect to another secondary battery that is the same model as the any one
secondary battery, after fixing the second voltage and changing the first voltage; a
program module for determining one of first voltages except for a first voltage at
the time of showing a lowest rate from among the measured secondary battery
thickness increase rates as a lower limit voltage; and a program module for setting
a protocol to repeat charging/discharging between the lower limit voltage and the
second voltage. These program modules are capable of implementing the abovedescribed
additional charge/discharge protocol generation method.
The memory unit 134 is a recording medium for storing control programs
and data related to calculation and judgment. For example, the memory unit 134
records a cell voltage measured for each time period while charging/discharging
the cell. The memory unit 134 may measure an electrode thickness before
charging/discharging starts and after charging/discharging ends, and store a
difference between the measured electrode thicknesses, that is, a variation in the
electrode thickness. The memory unit 134 may also record a total time taken for
charging/discharging. The display unit 136 may display, for example, a graph as
shown in FIG. 7 or a result such as the determined lower limit voltage. The
display unit 136 may be, for example, a display device such as a computer
monitor.
20
The control unit 138 controls the entire process of the activation
apparatus 100, based on the control programs stored in the memory unit 134.
In detail, as described above, the control unit 138 charges-maintainsdischarges
the cell by operating the charge/discharge device 110. The control
unit 138 measures the cell voltage for each time period and stores a result of the
measurement in the memory unit 134. The control unit 138 may display a
charge/discharge profile on the display unit 136, with the stored result. The
control unit 138 may implement an additional charge/discharge protocol
generation method according to the present disclosure by operating the processing
unit 132. The control unit 138 may store, in the memory unit 134, the lower
limit voltage as a determination result and the charge/discharge protocol including
the lower limit voltage, and may display the same on the display unit 136.
The activation apparatus 100 may further include a thickness measuring
unit 140 for measuring a thickness of the secondary battery. The control device
120 controls a driving and measuring timing of the thickness measuring unit 140,
and the thickness measured by the thickness measuring unit 140 may be stored in
the memory unit 134. The program module of the processing unit 132 may read
the thickness and the total time taken for charging/discharging from the memory
unit 134 to calculate the secondary battery thickness increase rate.
The activation apparatus 100 is not used only for generating an additional
charge/discharge protocol, but also controls the charge/discharge device 110 to
perform an additional charging/discharging operation for forming pores in an
electrode active material, according to the protocol, after performing jig formation
charge/discharge for SEI formation on secondary batteries and then having an
aging time to sufficiently impregnate an electrolyte.
For example, in the jig formation operation for SEI formation, when an
operator mounts a secondary battery on the charge/discharge device 110 of the
activation apparatus 100, the control device 120 controls the charge/discharge
device 110 to perform, for example, CC-CV charging, with respect to the
secondary battery. In the jig formation operation, there is a preset protocol, and
thus control is performed according to the preset protocol. For example, in order
21
to make a small number of SEI nuclei at the beginning of production and then
grow them to make a uniform SEI film, there may be a protocol for charging until
reaching 65% SOC by applying current at 0.1 C-rate for about 3 hours. As
another example, there may be a protocol for performing an operation of initially
applying a relatively high C-rate current to generate the nucleus of an SEI film
and a subsequent operation of maintaining a relatively low C-rate current to grow
the nucleus. The jig formation operation may vary at any time.
For the subsequent aging operation, the control device 120 stops driving
of the charge/discharge device 110. The operator takes out the secondary battery
and has an aging time in an aging room. When the operator mounts an agingcompleted
secondary battery on the charge/discharge device 110 of the activation
apparatus 100 again, the charge/discharge device 110 is driven according to the
additional charge/discharge protocol to perform an additional
charging/discharging operation for the secondary battery.
The present disclosure has been described in detail. However, it should
be understood that the detailed description and specific examples, while indicating
preferred embodiments of the disclosure, are given by way of illustration only,
since various changes and modifications within the scope of the disclosure will
become apparent to those skilled in the art from this detailed description.

WE Claim
1. A method of generating a charge/discharge protocol of an
additional charging/discharging operation included in an activation method, the
activation method comprising a jig formation operation, an aging operation, and
the additional charging/discharging operation with respect to assembled secondary
batteries, the charge/discharge protocol generation method comprising:
operation (a) of measuring a secondary battery thickness increase rate
over time while repeating charging/discharging between a first voltage and a
second voltage higher than the first voltage with respect to any one of the
assembled secondary batteries;
operation (b) of performing, at least once, an operation of performing
operation (a) with respect to another secondary battery that is a same model as the
any one secondary battery, after fixing the second voltage and changing the first
voltage;
operation (c) of determining one of first voltages except for a first voltage
at a lowest rate among measured secondary battery thickness increase rates, as a
lower limit voltage; and
operation (d) of setting a protocol to repeat charging/discharging between
the lower limit voltage and the second voltage.
2. The charge/discharge protocol generation method of claim 1,
wherein the second voltage is a full charge voltage of the secondary batteries, and
the first voltage is a voltage greater than or equal to a full discharge voltage of the
secondary batteries.
3. The charge/discharge protocol generation method of claim 2,
wherein the full charge voltage is a voltage enabling an SOC of the secondary
batteries to have a determined value between 80% and 90%, and the full discharge
voltage is a voltage when the SOC of the secondary batteries is 0%.
23
4. The charge/discharge protocol generation method of claim 1,
wherein the secondary battery thickness increase rate is obtained by subtracting a
thickness of the secondary battery measured before charging/discharging in
operation (a) from a thickness of the secondary battery measured after
charging/discharging in operation (a) and by dividing a difference between the
two thicknesses by a total time taken for charging/discharging.
5. The charge/discharge protocol generation method of claim 1,
wherein, when the lower limit voltage is determined, a first voltage when a total
time taken for charging/discharging is relatively short is determined as the lower
limit voltage.
6. The charge/discharge protocol generation method of claim 1,
wherein operation (b) is performed by changing the number of times of repetitions
of charging/discharging.
7. The charge/discharge protocol generation method of claim 6,
wherein, when the protocol is set, the number of times of repetitions of
charging/discharging when a variation in a secondary battery thickness is
relatively large is selected.
8. A method of generating a charge/discharge protocol of an
additional charging/discharging operation included in an activation method, the
activation method comprising a jig formation operation, an aging operation, and
the additional charging/discharging operation with respect to assembled secondary
batteries, the charge/discharge protocol generation method comprising:
measuring a secondary battery thickness increase rate over time while
repeating charging/discharging between a full discharge voltage and a full charge
voltage of the secondary batteries, with respect to any one of the secondary
batteries, and setting the measured secondary battery thickness increase rate as a
reference;
24
measuring a secondary battery thickness increase rate over time while
repeating charging/discharging between a first voltage higher than the full
discharge voltage and the full charge voltage, with respect to another secondary
battery that is a same model as the any one secondary battery;
changing the first voltage, and then performing, at least once, an
operation of measuring a secondary battery thickness increase rate over time
while repeating charging/discharging between the changed first voltage and the
full charge voltage, with respect to another secondary battery that is a same model
as the any one secondary battery;
determining a lower limit voltage from among first voltages having
greater rates than the reference among the measured secondary battery thickness
increase rates; and
setting a protocol to repeat charging/discharging between the lower limit
voltage and the full charge voltage.
9. An activation method comprising:
a jig formation operation with respect to assembled secondary batteries;
an aging operation; and
an additional charge/discharge operation,
wherein the additional charge/discharge operation is performed using a
charge/discharge protocol obtained according to the additional charge/discharge
activation protocol generation method of claim 1 or 8.
10. An activation apparatus comprising:
a charge/discharge device configured to perform charging/discharging
with respect to assembled secondary batteries; and
a control device configured to control an operation of the
charge/discharge device according to a charge/discharge protocol,
wherein the control device comprises:
a processing unit comprising a program module for executing
operation (a) of measuring a secondary battery thickness increase rate over time
25
while repeating charging/discharging between a first voltage and a second voltage
higher than the first voltage with respect to any one of the assembled secondary
batteries;
a program module for executing, at least once, an operation of
performing operation (a) with respect to another secondary battery that is a same
model as the any one secondary battery, after fixing the second voltage and
changing the first voltage;
a program module for determining one of first voltages except
for a first voltage at the time of showing a lowest rate from among measured
secondary battery thickness increase rates as a lower limit voltage; and
a program module for setting a protocol to repeat
charging/discharging between the lower limit voltage and the second voltage, and
the control device controls the charge/discharge device to perform an
additional charging/discharging operation for forming pores in an electrode active
material, according to the protocol, after performing jig formation
charge/discharge for SEI formation on the secondary batteries and then having an
aging time to sufficiently impregnate an electrolyte.
11. The activation apparatus of claim 10, further comprising a
thickness measuring unit configured to measure a thickness of the secondary
battery, wherein the control device controls a driving and measuring timing of the
thickness measuring unit, and the program modules of the processing unit
calculates the secondary battery thickness increase rate by using the thickness
measured by the thickness measuring unit.