JP7161679B2 - Method for manufacturing non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery.

In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries and nickel-hydrogen batteries have been favorably used as so-called portable power sources for personal computers, portable terminals, and the like, and power sources for driving vehicles. In particular, lithium-ion secondary batteries, which are lightweight and provide high energy density, are used in vehicles such as electric vehicles and hybrid vehicles. ) is becoming increasingly important.

In the non-aqueous electrolyte secondary battery, a part of the non-aqueous electrolyte is reductively decomposed during the initial charge, and a film called an SEI film (Solid Electrolyte Interface) may be formed on the surface of the negative electrode active material. . Since the negative electrode is stabilized when this SEI film is formed, subsequent reductive decomposition of the electrolytic solution is suppressed.

Japanese Unexamined Patent Application Publication No. 2002-100000 discloses a technique related to the formation of the SEI film. In the initial charging method described in Patent Document 1, initial charging is started with the lithium-ion secondary battery restrained, low-speed charging is performed within a predetermined charging range, and restraint is released after the low-speed charging. Then, the lithium-ion secondary battery is restrained again and recharged at a higher rate than during low-speed charging. In the technique described in Patent Document 1, since inhibition of formation of the SEI film by gas can be suppressed by releasing and re-restricting during the initial charge, the SEI film can be formed evenly on the surface of the negative electrode active material. .

JP 2015-228289 A

By the way, since the formation of the SEI film by the reductive decomposition of the non-aqueous electrolyte is an irreversible reaction, it may cause the battery capacity to decrease. Therefore, in recent years, a technique has been proposed in which LiBOB (lithium bis(oxalato)borate), which decomposes at a potential lower than that of the electrolyte to form an SEI film, is added to the non-aqueous electrolyte.

However, in the non-aqueous electrolyte secondary battery to which LiBOB is added, the LiBOB-derived SEI film is further formed during the period from the completion of the manufacturing process to the shipment of the battery, which may increase the battery resistance. . As a result, there is a possibility that the battery resistance cannot be measured accurately by simply performing a resistance test after the completion of the manufacturing process.

The present invention was created to solve such problems, and its object is to provide a non-aqueous electrolyte secondary battery in which LiBOB is added to a non-aqueous electrolyte, in which an SEI film is formed after the manufacturing process is completed. Another object of the present invention is to provide a technology capable of suppressing an increase in battery resistance caused by a

In order to achieve the above objects, the present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "manufacturing method") having the following configuration.

The manufacturing method disclosed herein is a method of manufacturing a non-aqueous electrolyte secondary battery in which a wound electrode body and a non-aqueous electrolyte are accommodated in a battery case. Such a manufacturing method is a battery in which a wound electrode body and a non-aqueous electrolyte containing LiBOB are housed in a battery case, and surplus electrolyte exists between the wound electrode body and the battery case. an assembly building step of building an assembly; a binding step of binding the battery assembly with a predetermined pressure; an initial charging step of initially charging the battery assembly; an aging step of holding the battery assembly after initial charging for a predetermined time; encompasses The manufacturing method disclosed herein is characterized in that, after the initial charging step, a pumping step is performed to release the confining pressure on the battery assembly and then apply the confining pressure again.

The inventors of the present invention have studied the cause of the rise in battery resistance after the completion of the manufacturing process in a battery in which LiBOB is added to the non-aqueous electrolyte, and obtained the following findings. In a general non-aqueous electrolyte secondary battery, the retained electrolyte retained inside the wound electrode body exists between the wound electrode body and the battery case (exists outside the wound electrode body). ) containing excess electrolyte. LiBOB decomposed in the initial charge is LiBOB in the retained electrolyte, and LiBOB in the surplus electrolyte remains outside the wound electrode body without being decomposed in the initial charge. Therefore, when surplus electrolyte penetrates into the inside of the wound electrode body after the manufacturing process is completed, an SEI film derived from LiBOB remaining in the surplus electrolyte is formed to increase the battery resistance. For this reason, batteries using a non-aqueous electrolyte containing LiBOB may have battery resistance that fluctuates after the manufacturing process is completed. Therefore, it is necessary to conduct an inspection to measure the battery resistance immediately before shipment.

The manufacturing method disclosed herein has been made based on the above findings, and after the initial charging step, the confining pressure on the battery assembly is released, and then a pumping step is performed to apply the confining pressure again. As a result, the surplus electrolytic solution outside the wound electrode assembly and the retained electrolytic solution inside the wound electrode assembly can be mixed. In addition, since LiBOB remaining in the excess electrolyte can be decomposed in the aging process, it is possible to suppress an increase in battery resistance after the completion of the manufacturing process. Therefore, according to the manufacturing method disclosed herein, the battery resistance can be accurately measured in the resistance test immediately after the completion of the manufacturing process, which eliminates the need for the resistance test immediately before shipment, thereby improving the production efficiency.

It is a flow chart which shows each process of the manufacturing method concerning one embodiment of the present invention. 1 is a front view schematically showing the internal structure of a battery assembly manufactured by a manufacturing method according to one embodiment of the present invention; FIG. 4 is a graph showing the number (times) of pumping treatment and battery resistance (mΩ) in Samples 1 to 4. FIG.

Preferred embodiments of the present invention will be described below with reference to the drawings. Matters other than those specifically referred to in the present invention, which are necessary for carrying out the present invention, can be grasped as design matters by those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field.

Note that the dimensional relationships (length, width, thickness, etc.) in the drawings do not necessarily reflect the actual dimensional relationships. Also, in the following description, a lithium ion secondary battery will be described as an example of a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery manufactured by the manufacturing method disclosed herein is a battery that uses a non-aqueous electrolyte (typically, a non-aqueous electrolyte containing a supporting electrolyte in a non-aqueous solvent). If so, it is not limited to a lithium ion secondary battery, and may be, for example, a nickel metal hydride battery.

1. 1. Manufacturing Method According to this Embodiment FIG. 1 is a flow chart showing each step of a manufacturing method according to this embodiment. FIG. 2 is a front view schematically showing the internal structure of the battery assembly produced by the manufacturing method according to this embodiment.

As shown in FIG. 1, the method for manufacturing a non-aqueous electrolyte secondary battery according to the present embodiment includes an assembly construction step (S10), a binding step (S20), an initial charging step (S30), and an aging step. (S50). The manufacturing method according to this embodiment is characterized by performing the pumping step (S40) after the initial charging step (S30). As a result, an increase in battery resistance after completion of the manufacturing process can be suppressed, and accurate battery resistance can be measured in a resistance test immediately after completion of the manufacturing process. Each step will be described in detail below.

(1) Assembly Building Step In the assembly building step (S10), a battery assembly is built. In this specification, the term "battery assembly" refers to a non-aqueous electrolyte secondary battery before initial charging and aging. As shown in FIG. 2 , the battery assembly 100 constructed in this process includes a battery case 50 , a wound electrode body 10 and a non-aqueous electrolyte 20 .

Battery case 50 is a flat rectangular container made of a metal material such as aluminum, stainless steel, or nickel-plated steel. This battery case 50 includes a case body 52 and a lid 54 . The case body 52 is a flat box-shaped member with an open top, and the lid 54 is a plate-shaped member that closes the opening of the case body 52 . A positive electrode terminal 70 and a negative electrode terminal 72 are provided on a lid body 54 forming the upper surface of the battery case 50 . The positive terminal 70 and the negative terminal 72 are connected to an external device such as a vehicle motor or other battery.

The wound electrode body 10 is housed inside the battery case 50 . Although detailed illustration is omitted, the wound electrode assembly 10 includes a sheet-like positive electrode, a sheet-like negative electrode, and a separator (sheet-like insulating member). Then, the wound electrode assembly 10 is formed by winding a laminate obtained by laminating these sheet-like members.

The positive electrode is formed by applying a positive electrode mixture layer to the surface of a foil-shaped positive electrode current collector. The positive electrode mixture layer contains, as a positive electrode active material, a metal oxide (lithium-transition metal composite oxide, etc.) capable of reversibly intercalating and deintercalating charge carriers. In addition, a positive electrode current collector exposed portion to which the positive electrode mixture layer is not applied is formed at one side edge portion in the width direction of the sheet-like positive electrode. In this wound electrode body 10, a positive electrode connection portion 10A in which only the positive electrode current collector exposed portion is wound is formed at one end (left side in FIG. 2) in the width direction X, and the positive electrode connection A positive terminal 70 is electrically connected to the portion 10A.

On the other hand, the negative electrode is also formed by applying a negative electrode mixture layer to the surface of a foil-shaped negative electrode current collector. In addition, the negative electrode mixture layer contains a carbon material (such as graphite) capable of reversibly intercalating and deintercalating charge carriers as a negative electrode active material. In addition, a negative electrode current collector exposed portion to which the negative electrode mixture layer is not applied is formed on the other side edge portion in the width direction of the sheet-shaped negative electrode. A negative electrode connection portion 10B, in which only the negative electrode current collector exposed portion is wound, is formed at the other end (the right side in FIG. 2) in the width direction X, and the negative electrode connection portion 10B has a negative electrode terminal. 72 are electrically connected.

In addition, for each material constituting the above-described positive electrode, negative electrode, and separator, the same materials as those used in general lithium ion secondary batteries can be used without limitation, and this does not characterize the present invention. Detailed description is omitted.

The non-aqueous electrolyte 20 is housed inside the battery case 50 in the same manner as the wound electrode body 10 described above. The composition of such a non-aqueous electrolyte is not particularly limited. A solution containing a supporting electrolyte at a predetermined concentration (for example, about 1 mol/L) can be used. The supporting salts include fluorine-containing lithium compounds such as LiPF ₆ , LiBF ₄ and LiCF ₃ SO ₃ .

In this embodiment, the non-aqueous electrolyte 20 contains lithium bis(oxalato)borate (LiBOB). Such LiBOB is a type of film-forming agent, and in the initial charging step (S30) described later, it decomposes at a potential lower than that of other components of the non-aqueous electrolyte 20 to form an SEI film on the surface of the negative electrode active material. . Thereby, the negative electrode can be stabilized without lowering the battery capacity. The content of LiBOB when the total amount of the non-aqueous electrolyte 20 is 100% by mass is preferably 0.1% by mass or more from the viewpoint of forming an SEI film with a suitable thickness, and 0.1% by mass or more. It is more preferably 3% by mass or more. On the other hand, from the viewpoint of suppressing the increase in battery resistance due to the formation of the SEI film after the completion of the manufacturing process, the upper limit of the content of LiBOB is preferably 1.0% by mass or less, and 0.7% by mass. The following are more preferable.

Moreover, in the battery assembly 100 constructed by this process, the surplus electrolytic solution 20A exists between the wound electrode assembly 10 and the battery case 50 . Specifically, part of the non-aqueous electrolyte 20 described above is filled inside the wound electrode assembly 10 (in other words, between the positive and negative electrodes) as a retained electrolyte (not shown). Charge/discharge is performed by movement of charge carriers between the positive electrode and the negative electrode via the retained electrolyte. The non-aqueous electrolyte 20 that is not filled inside the wound electrode body 10 remains as surplus electrolyte 20A between the wound electrode body 10 and the battery case 50 (outside the wound electrode body 10). . By adjusting the injection amount of the non-aqueous electrolyte 20 so as to generate such a surplus electrolyte 20A, new electrolyte is injected into the wound electrode assembly 10 when the retained electrolyte in the wound electrode assembly 10 decreases. Since the non-aqueous electrolyte can be supplied, it is possible to suppress the deterioration of the battery performance due to the dryness of the electrolyte.

(2) Restraining Step Next, in the restraining step (S20), the battery assembly 100 described above is restrained with a predetermined pressure. As a result, the inter-electrode distance between the positive electrode and the negative electrode in the wound electrode body 10 is narrowed, and the charging reaction in the initial charging step (S30) described later can be stabilized. As long as the effect of the technology disclosed herein is not limited, the restraining step (S20) can employ a general procedure employed in the manufacture of conventional non-aqueous electrolyte secondary batteries. For example, the battery assembly 100 can be restrained by sandwiching the front and rear surfaces of the battery assembly 100 between a pair of restraining plates and connecting the pair of restraining plates with a bridging member. The restraining pressure at this time is preferably adjusted appropriately according to the size of the battery assembly 100, the number of windings of the wound electrode body 10, and the like. Also, the confining pressure in this step is preferably set to a pressure lower than the confining pressure in the pumping step, which will be described later, in consideration of expansion of the battery assembly 100 during initial charging. Such a confining pressure is set to, for example, approximately 1 kN to 12 kN (eg, 7 kN).

Non-aqueous electrolyte secondary batteries are sometimes used in the form of assembled batteries in which a plurality of such batteries are arranged. In this case, a cell group may be constructed by arranging the battery assemblies 100 along a predetermined arrangement direction, and the cell group having the plurality of battery assemblies 100 may be constrained together.

(3) Initial Charging Step In the initial charging step (S30), the restrained battery assembly 100 is initially charged (conditioned). Initial charging is a process of charging over the voltage range in which the manufactured non-aqueous electrolyte secondary battery is used. Thereby, the battery assembly 100 can be electrochemically activated. At this time, LiBOB contained in the retained electrolyte inside the wound electrode body 10 is decomposed, and an SEI film derived from the LiBOB is formed on the surface of the negative electrode active material.
Although the conditions for the initial charging are not particularly limited, the voltage between the positive terminal 70 and the negative terminal 72 is 2.5 V to 4.2 V (preferably 3.0 V) in a room temperature environment (for example, 25° C.). ~4.1V) until the SOC (State of Charge) reaches about 60% to 100% (typically about 80% to 100%) after charging at a constant current of about 0.1C to 10C. Constant-current constant-voltage charging (CC-CV charging), which charges at a constant voltage, can be used as the initial charging.

(4) Pumping Step In the manufacturing method according to the present embodiment, the pumping step (S40) is performed after the initial charging step (S30). In this step, a pumping process is performed in which the confining pressure applied to the battery assembly 100 is loosened and then the confining pressure is applied again. In this pumping process, the inter-electrode distance between the positive electrode and the negative electrode narrowed in the restraining step (S20) is increased by loosening the restraining pressure, and the surplus electrolytic solution 20A flows into the wound electrode body 10. Then, when the confining pressure is applied again, the inter-electrode distance narrows again, and part of the retained electrolyte flows out of the wound electrode body 10 to become surplus electrolyte 20A. As described above, in the manufacturing method according to the present embodiment, by performing the pumping step (S40), the retained electrolyte in which LiBOB is decomposed in the initial charging step (S30) and the surplus electrolyte in which LiBOB remains and the remaining LiBOB can be introduced into the wound electrode assembly 10 .

It should be noted that the pumping step (S40) may be performed at least once, and the number of times it is performed is not particularly limited. However, depending on the content of LiBOB in the non-aqueous electrolyte and the amount of excess electrolyte, it is preferable to perform the pumping step (S40) two or more times (preferably three or more times, more preferably four or more times). As a result, LiBOB remaining outside the wound electrode assembly 10 can be properly introduced into the wound electrode assembly 10 . Further, the number of times of the pumping step (S40) may be 10 times or less, 8 times or less, or 6 times or less. From the viewpoint of improving manufacturing efficiency by reducing the number of steps, the number of times of the pumping step (S40) is preferably 5 or less.

As in the above-described restraining step (S20), the restraining pressure in the pumping step (S40) is preferably adjusted appropriately according to the size of battery assembly 100, the number of windings of wound electrode assembly 10, and the like. For example, when a confining pressure of about 1 kN to 12 kN (for example, 7 kN) is applied in the confining step (S20), in the pumping step (S40), after loosening the confining pressure to 0 kN to 1 kN, about 1 kN to 12 kN ( For example, it is preferable to return the confining pressure to 9 kN). As a result, the retained electrolyte and the surplus electrolyte can be suitably mixed.

(5) Aging Step In the manufacturing method according to the present embodiment, the aging step (S50) is performed after the pumping step (S40). In this aging step (S50), the battery assembly 100 is stored in a predetermined high-temperature environment for a predetermined time while maintaining the state of charge after the initial charging step (S30). A general aging process is performed to modify the SEI film formed on the negative electrode. It is formed. As described above, in the manufacturing method according to the present embodiment, the pumping step (S40) is performed before the aging step (S50). has been introduced inside the Therefore, since the LiBOB remaining after the initial charging step (S30) can be decomposed in the aging step (S50), it is possible to suppress the formation of an SEI film derived from LiBOB after the completion of the manufacturing process and the increase in battery resistance. Therefore, according to the manufacturing method according to the present embodiment, the battery resistance can be accurately measured in the resistance test immediately after the completion of the manufacturing process. Therefore, the resistance test immediately before shipment becomes unnecessary, and the production efficiency can be improved.

The conditions of the aging process can be appropriately adjusted according to the composition of the SEI film and the like. As an example, the battery temperature (aging temperature) in the aging step (S50) can be 30° C. or higher, preferably 40° C. or higher, for example 50° C. or higher, further 60° C. or higher. Although the upper limit of the aging temperature is not particularly limited, for example, about 80° C. or less can be used as a guideline. A constant temperature bath, for example, can be used to manage the aging temperature. The time (aging time) of the aging step (S50) is preferably changed as appropriate according to the aging temperature. For example, when the aging temperature is about 45 to 70° C., the aging time is preferably about 20 to 28 hours (eg, 24 hours). Moreover, when the aging temperature is about 70 to 75° C., it is preferable to set the aging time to about 8 to 16 hours (eg, 12 hours).

2. Other Embodiments Although the method for manufacturing a non-aqueous electrolyte secondary battery according to one embodiment of the present invention has been described above, the manufacturing method disclosed herein is not limited to the above-described embodiment, and various modifications can be made. or change.

For example, after the aging step (S50), a pumping process under the same conditions as the pumping step (S40) may be performed. As a result, the LiBOB remaining in the surplus electrolytic solution 20A after the aging step (S50) can be introduced into the wound electrode body, so that the increase in battery resistance after the completion of the manufacturing process can be more suitably suppressed. However, according to experiments conducted by the present inventor, it has been confirmed that the pumping treatment is performed before the aging step, that is, in the pumping step (S40) in the above-described embodiment, to obtain a preferable effect. . Therefore, from the viewpoint of efficiency of the manufacturing process, it is preferable to increase the number of pumping processes in the pumping process rather than adding the pumping process after the aging process.

[Test example]
Test examples relating to the present invention will be described below, but the following test examples are not intended to limit the present invention.

1. _{Fabrication of Battery Assembly} for _Evaluation A sheet-like negative electrode using graphite as a material and a separator (porous polyolefin sheet) were prepared. Then, a laminate obtained by laminating these sheet-like members was wound to produce a wound electrode body.
Next, as the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of EC:DMC:EMC=30:40:30 is supported. A salt (LiPF ₆ ) dissolved at a concentration of 1.1 mol/L was used. Furthermore, LiBOB was added to the non-aqueous electrolyte in this test so as to be 0.5 wt %.
Then, the wound electrode body was housed inside a battery case made of aluminum, and the battery case was sealed. Then, by injecting the non-aqueous electrolyte into the case through the liquid inlet while the inside of the case is decompressed, the non-aqueous electrolyte is filled inside the wound electrode body, and then the liquid inlet is sealed. By doing so, a battery assembly for evaluation was produced. At this time, in this test, the injection amount was set to 40 g so that about 2 g of excess electrolytic solution was generated.

2. Preparation of each sample (1) Sample 1
After restraining the battery assembly for evaluation with a restraining pressure of 7 kN, initial charging was carried out by performing constant current and constant voltage charging (CCCV charging) at 1 C until the voltage reached 4.1V. After the initial charging, the confining pressure on the battery assembly was loosened to 0.5 kN, and a pumping process of reconstraining with a confining pressure of 9 kN was performed once. Then, an aging treatment was performed under conditions of a holding temperature of 60° C. and a holding time of 24 hours to obtain a test lithium ion secondary battery (Sample 1).

(2) Sample 2
A test lithium ion secondary battery (Sample 2) was produced under the same conditions as Sample 1, except that the pumping process was performed twice after the initial charge.

(3) Sample 3
A test lithium-ion secondary battery (Sample 3) was produced under the same conditions as Sample 1, except that the pumping treatment was performed three times after initial charging.

(4) Sample 4
A test lithium ion secondary battery (Sample 4) was fabricated under the same conditions as Sample 1, except that the pumping treatment was performed once after the aging treatment instead of after the initial charging.

(5) Sample 5
A test lithium ion secondary battery (Sample 5) was produced under the same conditions as Sample 1, except that the pumping treatment was performed once after the initial charging and then the pumping treatment was performed once after the aging treatment.

(6) Sample 6
A test lithium ion secondary battery (Sample 6) was produced under the same conditions as Sample 1, except that the pumping treatment was performed once after the initial charging and then the pumping treatment was performed twice after the aging treatment.

(7) Sample 7
A test lithium-ion secondary battery (Sample 7) was fabricated under the same conditions as Sample 1, except that the pumping treatment was not performed after the initial charging and after the aging treatment.

2. Evaluation Test The lithium-ion secondary battery of each sample was adjusted to a voltage of 3.70 V (equivalent to SOC 56%) in a temperature environment of 25°C. Then, CC discharge was performed for 5 seconds at a discharge rate of 10C. Then, the battery resistance (mΩ) was calculated by dividing the voltage change value (ΔV) for 5 seconds from the start of discharge by the discharge current value. FIG. 3 shows the measurement results of the battery resistance of each sample.

As shown in FIG. 3, when samples 1 to 7 were compared, an increase in battery resistance was confirmed in samples 1 to 3 and samples 5 and 6. From this, it was found that by performing the pumping process after the initial charging, it is possible to suppress the increase in the battery resistance due to the decomposition of LiBOB after the completion of the manufacturing process. Further, when samples 1 to 3 were compared, it was confirmed that samples 2 and 3 exhibited a more favorable increase in battery resistance. From this, it was found that the number of times of pumping treatment after initial charging is preferably two or more. Also, in samples 5 and 6, it was confirmed that the battery resistance tended to increase as the number of pumping processes increased, but samples 2 and 3 were confirmed to have higher battery resistance. From this, it was found that the LiBOB decomposition promoting effect by the pumping process is more preferably exhibited after the initial charging.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

REFERENCE SIGNS LIST 10 Wound electrode body 10A Positive electrode connection part 10B Negative electrode connection part 20 Non-aqueous electrolyte 20A Surplus electrolyte 50 Battery case 52 Case main body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 100 Battery assembly

Claims (1)

A method for manufacturing a non-aqueous electrolyte secondary battery in which a wound electrode body and a non-aqueous electrolyte are accommodated in a battery case, comprising:
A battery assembly in which the wound electrode assembly and a non-aqueous electrolyte containing LiBOB are housed in the battery case, and excess electrolyte exists between the wound electrode assembly and the battery case. an assembly building process for building a solid;
a restraining step of restraining the battery assembly with a predetermined pressure;
an initial charging step of initially charging the battery assembly;
an aging step of holding the battery assembly after the initial charge for a predetermined time;
encompasses
A method of manufacturing a non-aqueous electrolyte secondary battery, wherein, after the initial charging step and before the aging step , a pumping step is performed to loosen the confining pressure on the battery assembly and then apply the confining pressure again.

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