JP7088038B2 - Lithium-ion battery manufacturing method - Google Patents

Description

The present disclosure relates to a method for manufacturing a lithium ion battery.

Japanese Unexamined Patent Publication No. 2018-11258 (Patent Document 1) discloses a fast-charging lithium-ion battery.

Japanese Unexamined Patent Publication No. 2018-11258

The performance of a lithium-ion battery (hereinafter, may be abbreviated as "battery") gradually deteriorates due to repeated use. For example, in a battery that has been used for a predetermined period of time, the lithium acceptability of the negative electrode may decrease. In a battery having a reduced lithium acceptability of the negative electrode, if rapid charging (that is, high-rate charging) is performed, lithium may be deposited on the negative electrode. In a battery in which lithium is deposited on the negative electrode, heat generation during overcharging may increase.

An object of the present disclosure is to reduce heat generation during overcharging in a battery that has been used for a predetermined period of time.

Hereinafter, the technical configuration and the action and effect of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The scope of claims should not be limited by the correctness of the mechanism of action.

The method for manufacturing a lithium ion battery of the present disclosure includes the following (A), (B) and (C).
(A) Prepare a first lithium-ion battery that has been used for the first period in the first posture.
(B) The first lithium ion battery is held in the second posture for the second period.
(C) After the lapse of the second period, the second lithium ion battery is manufactured by repeatedly charging and discharging the first lithium ion battery while holding the first lithium ion battery in the second posture.
The first lithium ion battery includes at least a battery case, a group of electrodes, and a surplus electrolytic solution.
A part of the electrode group is immersed in the excess electrolytic solution in the battery case.
The second posture is a posture in which the first posture is rotated by 180 ° with an arbitrary straight line parallel to the horizontal direction as the axis of rotation.

In the manufacturing method of the present disclosure, a first lithium ion battery (hereinafter, may be abbreviated as "first battery") used for a predetermined period is prepared. In the first battery, it is considered that the lithium acceptability of the negative electrode is lower than that in the state before the start of use. When the first battery is rapidly charged, lithium may precipitate on the negative electrode. The first battery contains a surplus electrolytic solution. "Excess electrolytic solution" indicates an electrolytic solution that is not impregnated in the electrode group. A part of the electrode group is immersed in the excess electrolytic solution.

In the manufacturing method of the present disclosure, the posture of the first battery is changed from the first posture to the second posture. The first posture is the posture when the first battery is used. The second posture is a posture in which the first posture is turned upside down in the vertical direction. Due to the change from the first posture to the second posture, the portion of the electrode group that has not been soaked in the surplus electrolytic solution is immersed in the surplus electrolytic solution. As a result, the excess electrolytic solution permeates the electrode group.

After the posture is changed, charging and discharging are repeated to manufacture a second lithium ion battery (hereinafter, may be abbreviated as "second battery"). The second battery is considered to be a new product that lacks the same identity as the first battery. The second battery is expected to generate less heat during overcharging after rapid charging than the first battery. The reason can be considered as follows, for example.

FIG. 1 is a first conceptual diagram illustrating the mechanism of action of the present disclosure.
It is considered that the film 2a is formed on the surface of the negative electrode active material 1 by using the first battery. The coating 2a can inhibit the movement of lithium ions. When rapid charging is carried out, lithium 3a is deposited on the surface of the coating film 2a. Due to the precipitation of lithium 3a, heat generation during overcharging may increase. It is considered that lithium 3a is active.

FIG. 2 is a second conceptual diagram illustrating the mechanism of action of the present disclosure.
It is considered that the composition of the electrolytic solution impregnated in the electrode group has changed due to the use of the first battery. On the other hand, the composition of the surplus electrolytic solution is considered to be close to the initial composition. It is considered that the coating film 2b is dispersed and formed on the surface of the negative electrode active material 1 by repeating charging and discharging after the excess electrolytic solution permeates the electrode group due to the change in posture. As a result, it is considered that the entire coating film (coating film 2a and coating film 2b) has large irregularities.

When rapid charging is carried out, it is considered that lithium 3b is concentrated and deposited on the convex portion (coating 2b). It is considered that the lithium 3b deposited on the convex portion tends to be finely granular. Since the fine granular lithium 3b has a large specific surface area, it is considered that it is easily deactivated. Since lithium 3b is easily deactivated, it is expected that heat generation will be reduced during subsequent overcharging.

FIG. 1 is a first conceptual diagram illustrating the mechanism of action of the present disclosure. FIG. 2 is a second conceptual diagram illustrating the mechanism of action of the present disclosure. FIG. 3 is a flowchart showing an outline of the method for manufacturing the lithium ion battery of the present embodiment. FIG. 4 is a schematic view showing an example of the configuration of the first lithium ion battery of the present embodiment. FIG. 5 is a schematic view showing an example of the configuration of the electrode group of the present embodiment.

Hereinafter, embodiments of the present disclosure (referred to as "the present embodiment" in the present specification) will be described. However, the following explanation does not limit the scope of claims.

<Manufacturing method of lithium-ion battery>
FIG. 3 is a flowchart showing an outline of the method for manufacturing the lithium ion battery of the present embodiment. The method for manufacturing a lithium ion battery of the present embodiment includes "(A) battery preparation", "(B) posture change", and "(C) charge / discharge cycle".

<< (A) Battery preparation >>
The method for manufacturing a lithium ion battery of the present embodiment includes preparing a first battery that has been used for the first period in the first posture.

The conditions of use of the first battery should not be particularly limited. The first battery may be used, for example, as a drive battery for an electric vehicle. The first battery may be used, for example, as an auxiliary battery for a vehicle. The first period may have a length such that the lithium acceptability of the negative electrode is lowered to some extent. When the first battery is mounted on the electric vehicle, the first period may have a length of, for example, a year. The first period may have a length of, for example, one year or more. The first period may have a length of, for example, 3 years or more. The first period may have a length of, for example, 3 years or more and 7 years or less.

The first period may be changed according to the usage conditions, usage environment, etc. of the first battery. For example, when the usage time in a high temperature environment is long, the first period may have a length of less than one year (for example, a length of 30 days or more and 180 days or less).

FIG. 4 is a schematic view showing an example of the configuration of the first lithium ion battery of the present embodiment.
The first battery 100 includes at least a battery case 90, an electrode group 50, and a surplus electrolytic solution. The battery case 90 is hermetically sealed. The battery case 90 is square. The battery case 90 may be made of metal, for example.

The alternate long and short dash line in FIG. 4 indicates the position of the liquid level of the excess electrolytic solution. A part of the electrode group 50 is immersed in the excess electrolytic solution. The electrolyte contains at least a solvent and a lithium salt. The solvent may contain, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. The lithium salt may contain, for example, LiPF ₆ or the like. It is considered that the composition of the electrolytic solution impregnated in the electrode group 50 changes due to the use of the first battery 100. For example, the component ratio may change due to the decomposition of the solvent.

The electrode group 50 is a winding type. In the first posture of the present embodiment, the winding axis of the electrode group 50 and the vertical direction are substantially orthogonal to each other. In FIG. 4, the winding axis of the electrode group 50 is parallel to the x-axis. In FIG. 4, the vertical direction is parallel to the z-axis.

FIG. 5 is a schematic view showing an example of the configuration of the electrode group of the present embodiment.
The electrode group 50 includes a positive electrode 10, a negative electrode 20, and a separator 30. Each of the positive electrode 10, the negative electrode 20, and the separator 30 has a strip-shaped planar shape. The electrode group 50 is formed by stacking a positive electrode 10, a separator 30, and a negative electrode 20 in this order, and further winding them in a spiral shape.

The positive electrode 10 is a sheet-shaped component. The positive electrode 10 contains at least a positive electrode active material. The positive electrode active material should not be particularly limited. The positive electrode active material may contain, for example, lithium cobalt manganate or the like.

The negative electrode 20 is a sheet-shaped component. The negative electrode 20 contains at least a negative electrode active material. The negative electrode active material should not be particularly limited. The negative electrode active material may contain, for example, graphite, silicon oxide, silicon and the like.

The separator 30 is a porous film. The separator 30 may contain, for example, a porous film made of polyolefin or the like.

The electrode group of this embodiment should not be limited to the winding type. The electrode group may be, for example, a stacked type. In the laminated electrode group, each of the positive electrode, the negative electrode, and the separator has, for example, a single-wafer-shaped planar shape. The laminated electrode group is formed by alternately laminating one or more positive and negative electrodes. A separator is arranged between each of the positive electrode and the negative electrode.

<< (B) Posture change >>
The method for manufacturing a lithium ion battery of the present embodiment includes holding the first battery in the second posture for a second period.

The second posture is a posture in which the first posture is rotated by 180 ° with an arbitrary straight line parallel to the horizontal direction as the axis of rotation. For example, the first battery 100 may be rotated by 180 ° about a straight line parallel to the x-axis of FIG. 4 as a rotation axis. For example, the first battery 100 may be rotated by 180 ° about a straight line parallel to the y-axis of FIG. 4 as a rotation axis. By changing from the first posture to the second posture, the first battery 100 is turned upside down in the vertical direction. It should be noted that "180 °" in this embodiment indicates that it is substantially 180 °, and does not indicate only geometrically perfect 180 °. For example, the range of 180 ° ± 5 ° is considered to be substantially 180 °.

In the second period, for example, the excess electrolytic solution may have a length that allows the excess electrolytic solution to pass through the electrode group 50. The second period may be, for example, 5 hours or more. The second period may be, for example, 8 hours or more. The second period may be, for example, 15 hours or less.

<< (C) Charge / discharge cycle >>
In the method for manufacturing a lithium ion battery of the present embodiment, after the lapse of the second period, the second battery (not shown) is obtained by repeatedly charging and discharging the first battery 100 while holding the first battery 100 in the second posture. ) Includes manufacturing.

The second battery has substantially the same structure as the first battery 100. However, it is considered that the state of the coating film inside the battery is different between the first battery 100 and the second battery. That is, in the second battery, it is considered that a film having large irregularities is formed on the surface of the negative electrode active material. It is considered that the deposited lithium tends to become fine particles during rapid charging due to the large unevenness of the coating film. Fine-grained lithium is considered to be easily deactivated. Since the precipitated lithium is finely granular, it is expected that heat generation will be reduced during subsequent overcharging.

For example, charging / discharging may be repeated in a range where the SOC (state of charge) is in the range of 0% to 100%. For example, charging / discharging may be repeated in the range of SOC of 0% to 80%. That is, the width of the SOC range of charge / discharge may be 80% or more and 100% or less. The upper limit of the SOC of charge / discharge may be 80% or 100%. The lower limit of SOC for charge / discharge may be 0%. The "SOC" of the present embodiment is the ratio of the remaining capacity at that time to the fully charged capacity.

The number of cycles may be, for example, 5 or more and 100 or less. The number of cycles may be, for example, 30 or less. Note that one cycle indicates a cycle of one charge and one discharge.

The charging / discharging current rate may be, for example, 0.1 C or more and 10 C or less. "C" is a unit of current rate. At a current rate of 1C, the rated capacity is charged (or discharged) in 1 hour. The charging / discharging current rate may be, for example, 1C or more and 5C or less. The current rate during charging and the current rate during discharging may be the same or different from each other.

Hereinafter, examples of the present disclosure (referred to as “the present examples” in the present specification) will be described. However, the following explanation does not limit the scope of claims.

<Manufacturing of lithium-ion batteries>
No. in Table 1 below. 1 to No. The second battery was manufactured by the manufacturing method up to 23.

<< (A) Battery preparation >>
A drive battery for an electric vehicle was prepared as the first battery. The first battery was a square battery. The basic configuration of the first battery is as follows.

Positive electrode active material: Nickel cobalt Lithium manganate Negative electrode active material: Graphite Electrolyte: EC / DMC / EMC, LiPF ₆ (concentration 1.0 mol / L)

The first battery was placed in the first posture in a constant temperature bath set at 60 ° C. The first posture of this embodiment was the posture shown in FIG. In that state, the first battery was stored for the first period. Batteries are stored in a high temperature environment assuming the use of batteries.

The discharge capacity was measured before and after storage. The capacity retention rate was calculated by dividing the discharge capacity after storage by the discharge capacity before storage. The capacity retention rate was 80%. Resistance was measured before and after storage. The resistance increase rate was calculated by dividing the resistance after storage by the resistance before storage. The resistance increase rate was 105%.

<< (B) Posture change >>
After the lapse of the first period, the first battery was taken out of the constant temperature bath. In a room temperature environment, the posture of the first battery was changed from the first posture to the second posture as shown in Table 1 below. The "rotation angle" in Table 1 below indicates the rotation angle when the first battery is rotated with the straight line parallel to the y-axis of FIG. 4 as the rotation axis. The rotation angle of 0 ° indicates that there is no change in posture. In a room temperature environment, the first battery was held in the second posture for the second period in Table 1 below.

<< (C) Charge / discharge cycle >>
After the lapse of the second period, the charge / discharge cycle was carried out under the conditions shown in Table 1 below. As a result, the second battery was manufactured. The charge / discharge cycle of this example was carried out in a room temperature environment.

<Evaluation>
《Low temperature quick charge》
The second battery was placed in the first posture in a constant temperature bath set at −10 ° C. The second battery was charged at a current rate of 30C. It is considered that this caused lithium to precipitate on the surface of the negative electrode active material. Rapid charging in a low temperature environment is a condition in which lithium is likely to precipitate.

《Overcharge test》
After low-temperature rapid charging, the second battery was placed in the first posture in a constant temperature bath set at 10 ° C. At a current rate of 10C, the second battery was charged until the separator shut down. In this test, the time when a voltage surge was detected during charging was considered to be the shutdown of the separator. After shutdown, the temperature of the battery case was measured. The results are shown in Table 1 below.

In the column of the overcharge test in Table 1 below, "S" indicates that the amount of temperature rise of the battery case after shutdown was less than 10 ° C. “L” indicates that the amount of temperature rise of the battery case after shutdown was 10 ° C. or higher. If the result is "S", it is considered that the heat generation at the time of overcharging is small.

<Result>
In Table 1 above, for example, No. From the results of 2, 5, 8 and 11, when the second posture is a posture in which the first posture is rotated by 180 °, the heat generation at the time of overcharging tends to be small.

In Table 1 above, for example, No. From the results of 14, 17, and 22, it can be seen that the heat generation during overcharging tends to be small when the second period is 5 hours or more.

In Table 1 above, No. In 17, the charge / discharge is carried out for 5 cycles in the range of SOC of 0% to 100%, so that the heat generation at the time of overcharging tends to be small. No. At 20, there is a tendency that heat generation during overcharging tends to be reduced by performing 30 cycles of charging / discharging in the range of SOC of 0% to 80%. Therefore, it is expected that heat generation during overcharging will be reduced by performing charging / discharging with a width of the SOC range of 80% or more and 100% or less for 5 cycles or more and 30 cycles or less.

The present embodiment and the present embodiment are exemplary in all respects and are not restrictive. The technical scope defined by the description of the scope of claims includes all changes within the meaning and scope equivalent to the scope of claims.

1 Negative electrode active material, 2a, 2b coating, 3a, 3b lithium, 10 positive electrode, 20 negative electrode, 30 separator, 50 electrode group, 90 battery case, 100 1st battery (1st lithium ion battery).

Claims (1)

Preparing a first lithium-ion battery that has been used for the first period in the first position,
Holding the first lithium-ion battery in the second posture for the second period,
After the lapse of the second period, the second lithium ion battery is manufactured by repeatedly charging and discharging the first lithium ion battery while holding the first lithium ion battery in the second posture.
Including
The first lithium ion battery contains at least a battery case, a group of electrodes, and a surplus electrolytic solution.
A part of the electrode group is immersed in the surplus electrolytic solution in the battery case.
The second posture is a posture in which the first posture is rotated by 180 ° with an arbitrary straight line parallel to the horizontal direction as a rotation axis.
A method for manufacturing a lithium-ion battery.

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