JP2012084346A - Method for producing lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a lithium ion secondary battery prepared with an electrolyte containing a difluorophosphate in which the duration of a cell-voltage rise after left to stand is short in a second self-discharge step.SOLUTION: The method for producing a lithium ion secondary battery satisfies at least one of the following requirements (1) and (2). (1) In a first self-discharge step (S5), a prescribed standing duration of a cell is in the range of 1 to 7 days. (2) A voltage difference ΔVbe obtained by subtracting a final voltage Ve of discharge in a step (S6) of measuring the amount of discharge from an initiation voltage Vb of standing in the first self-discharge step, satisfies the following relation, 0.25 V≤ΔVbe≤0.55 V.

Description

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

In recent years, lithium ion secondary batteries have been used as driving power sources for portable electronic devices such as hybrid vehicles, notebook computers, and video camcorders.
Patent Document 1 proposes a lithium ion secondary battery using an electrolytic solution containing difluorophosphate. It is described that low temperature discharge characteristics (low temperature output characteristics) and the like are improved by using an electrolytic solution containing difluorophosphate.

JP 2006-143572 A

  By the way, a lithium ion secondary battery using an electrolytic solution containing difluorophosphate is manufactured as follows, for example. First, in the assembling step, a battery in which an electrode body having a positive electrode active material and a negative electrode active material and an electrolytic solution containing difluorophosphate is housed in a battery case is manufactured. Next, in the initial charging step, the battery produced in the assembly step is initially charged. Thereafter, in the aging process, the battery that has finished the initial charging process is aged at a predetermined temperature for a fixed time.

  Next, in the first self-discharge process, the battery that has finished the aging process is left to stand for a predetermined period to be self-discharged. Thereafter, in the discharge amount measurement step, the battery that has finished the self-discharge step is forcibly discharged, and the amount of discharge electric current between the battery voltage value from the predetermined measurement start voltage value to the discharge end voltage value is measured. . Next, in the internal resistance measurement step, the internal resistance of the battery that has finished the discharge amount measurement step is measured.

Next, in the battery row restraint step, a plurality of batteries that have completed the discharge amount measurement step are prepared, and these batteries are arranged in one row or a plurality of rows to form one or a plurality of battery rows. Then, it is held in a restrained state by being sandwiched by pressing jigs from both ends. Thereafter, in the second self-discharge step, the batteries in the battery array are self-discharged by leaving the battery array in a restrained state.
In the second self-discharge process, the battery voltage value before and after being left is measured for each battery in the battery array, and it is determined whether or not an internal short circuit has occurred in each battery based on the battery voltage difference before and after being left. To do. A battery with an internal short circuit has a larger self-discharge amount due to neglected than a battery with no internal short circuit (normal battery), so the battery voltage value is smaller, and the battery voltage difference before and after leaving is greater. It is considered to be. Therefore, it is possible to determine whether or not an internal short circuit has occurred in the battery based on the battery voltage difference before and after being left.

  However, a lithium ion secondary battery using an electrolytic solution containing difluorophosphate has a tendency for the battery voltage to increase for a while after starting to stand in the second self-discharge process. For example, the battery voltage may increase for about a week after the start of standing, and then the battery voltage value may decrease. While the battery voltage value is rising, the self-discharge characteristics of the battery cannot be grasped (it cannot be distinguished from a battery that is not internally short-circuited), so wait for the battery voltage value to finish rising, After that, it was necessary to leave the battery array in a restrained state for a specified period and determine whether an internal short circuit occurred in the battery.

  Thus, when producing a lithium ion secondary battery using an electrolytic solution containing difluorophosphate, in the second self-discharge step, the battery voltage rises for a while after starting to stand, A long process time has been a problem. For this reason, in the 2nd self-discharge process, it was calculated | required to shorten as much as possible the battery voltage rise period after a leaving start.

  The present invention has been made in view of such problems, and in a method for manufacturing a lithium ion secondary battery using an electrolytic solution containing a difluorophosphate, after the start of standing in the second self-discharge step described above. An object of the present invention is to provide a method of manufacturing a lithium ion secondary battery that can shorten the battery voltage increase period.

One embodiment of the present invention is an assembly process for manufacturing a battery in which an electrode body having a positive electrode active material and a negative electrode active material, and an electrolytic solution containing a difluorophosphate is contained in a battery case, and the assembly process described above. An initial charging step for initial charging the finished battery, an aging step for aging the battery after the initial charging step for a predetermined time at a predetermined temperature, and the battery after the aging step for a predetermined time. A first self-discharge step for self-discharge by leaving for a period of time, and the battery that has finished the first self-discharge step, forcibly discharged until the battery voltage value reaches a predetermined discharge end voltage value, A discharge amount measuring step for measuring the amount of discharge electricity of the battery between a battery voltage value from a predetermined measurement start voltage value to the discharge end voltage value, and after the discharge amount measurement step A plurality of the internal resistance measuring step for measuring the internal resistance of the battery and the batteries after the internal resistance measuring step are prepared, and these batteries are arranged in one or a plurality of rows to form one or a plurality of rows of batteries. In addition, a battery row restraining step for sandwiching the battery row from both ends with a pressing jig and restraining the battery row, and leaving the battery row in the restrained state, leaving each battery constituting the battery row A second self-discharge step for self-discharge, a method of manufacturing a lithium ion secondary battery, wherein in the first self-discharge step, a leave start voltage value that is a battery voltage value when the leave of the battery is started When the battery voltage difference ΔVbc obtained by subtracting the battery voltage value Vc, which is the battery voltage value when the battery is left for the predetermined period from Vb, is equal to or greater than a predetermined threshold value, an internal short circuit has occurred in the battery. Judgment In the second self-discharge step, when the battery voltage value rises after starting to leave the battery row, the restraint state of the restraint state is increased after a lapse of the battery voltage value rise period. In the case where the battery voltage is decreased without increasing after the battery array is left to stand or the battery array is left to stand, the restraint state is kept for the specified period from the start of the battery array. The battery array is left as it is, and the battery forming the battery array is self-discharged. The manufacturing method includes a lithium ion secondary that satisfies at least one of the following conditions (1) and (2): It is a manufacturing method of a battery.
(1) In the first self-discharge step, the predetermined period is a period within a range of 1 to 7 days.
(2) The voltage difference value ΔVbe obtained by subtracting the discharge end voltage value Ve in the discharge amount measurement step from the neglect start voltage value Vb in the first self-discharge step has a relationship of 0.25V ≦ ΔVbe ≦ 0.55V. Meet.

  By the way, in an assembly process, metal powder (such as Cu powder) may be mistakenly mixed into the electrode body. In such a battery, dendrite derived from metal powder is generated in the aging process, and an internal short circuit occurs (the positive electrode plate and the negative electrode plate electrically insulated by the separator are electrically connected through the dendrite). There is. For this reason, in the subsequent first self-discharge step, a battery in which an internal short circuit has occurred is detected and not shipped (removed as a defective product).

  In the first self-discharge process, the lithium ion secondary battery that has finished aging is self-discharged by being left for a predetermined period (for example, 5 days). Further, in the first self-discharge step, the leaving end voltage value Vc, which is the battery voltage value when the predetermined period of time has been left, is subtracted from the leaving start voltage value Vb, which is the battery voltage value when starting to leave the battery. If the battery voltage difference ΔVbc (= Vb−Vc) is greater than or equal to a predetermined threshold value, it is determined that an internal short circuit has occurred in the battery.

  In a battery with an internal short circuit, the amount of self-discharge due to neglect is larger than that of a battery without a short circuit (normal battery). growing. Therefore, based on the battery voltage difference ΔVbc before and after being left, it can be determined whether or not an internal short circuit has occurred in the battery. Therefore, in the first self-discharge process, it is determined whether or not an internal short circuit has occurred in the battery depending on whether or not the battery voltage difference ΔVbc is equal to or greater than a predetermined threshold value Tbc. A battery determined to have an internal short circuit is removed, for example, as a defective product (for example, discarded). Note that the threshold Tbc is, for example, a value between the battery voltage difference ΔVbc of both batteries obtained by examining the battery voltage difference ΔVbc of a battery in which an internal short circuit has occurred and a battery in which no internal short circuit has occurred. It ’s fine.

In the method for manufacturing a lithium ion secondary battery described above, at least one of the above conditions (1) and (2) is satisfied.
Specifically, (1) In the first self-discharge step, a predetermined period in which the battery is left is set to a period within a range of 1 to 7 days. That is, in the first self-discharge process, the battery after the aging process is left for a period of 1 day to 7 days to self-discharge.

  As a result of an investigation by the present inventor, it has been found that the shorter the battery leaving period in the first self-discharge step, the shorter the battery voltage increase period after the start of the leaving in the second self-discharge step. However, if the battery leaving period in the first self-discharge process is too short, the detection accuracy of the battery in which an internal short circuit has occurred (determination accuracy of whether or not an internal short circuit has occurred) is low in the first self-discharge process. Turned out to be. This is because if the leaving period is too short, the difference in battery voltage difference ΔVbc between the battery in which an internal short circuit has occurred and the battery in which no internal short circuit has occurred is not clear (is an approximate value).

  As a result of the investigation, in the first self-discharge process, the period in which the battery is left (predetermined period) is set to a period (1 day to 7 days) within the range of 1 to 7 days. The battery voltage increase period after the start of leaving can be shortened, and a battery having an internal short circuit can be detected with high accuracy.

  Further, (2) a voltage difference value ΔVbe (= Vb−Ve) obtained by subtracting the discharge end voltage value Ve in the discharge amount measurement step from the standing start voltage value Vb in the first self-discharge step is 0.25 V ≦ ΔVbe ≦ 0. It is better to satisfy the relationship of .55V. That is, the voltage difference value ΔVbe (= Vb−Ve) is preferably set to a value within the range of 0.25V to 0.55V.

  As a result of investigation by the present inventor, it has been found that the battery voltage increase period after the start of standing in the second self-discharge process can be shortened as the voltage difference value ΔVbe is reduced. However, it has been found that if the voltage difference value ΔVbe is too small, the internal resistance of the battery increases. As a result of the investigation, by setting the voltage difference value ΔVbe to a value within the range of 0.25 V or more and 0.55 V or less, it is possible to shorten the battery voltage increase period after the start of standing in the second self-discharge process, and The internal resistance of the battery can also be reduced.

  Note that the measurement start voltage value in the discharge amount measurement step is set to a value equal to or lower than the standing end voltage value Vc in the first self-discharge step. Further, the discharge end voltage value Ve is set to a value smaller than the measurement start voltage value.

  Furthermore, it is good to set it as the manufacturing method of said lithium ion secondary battery, Comprising: About the conditions of said (1), the said predetermined period is made into the period within the range of 1-4 days. .

  In the first self-discharge process, the predetermined period of time during which the battery is left is set to a period within the range of 1 to 4 days (1 day to 4 days), thereby increasing the battery voltage after the start of the leave in the second self-discharge process. The period can be set to “0”. In other words, by setting the leaving period (predetermined period) in the first self-discharge process to a period (1 day to 4 days) within the range of 1 to 4 days, the leaving is started in the second self-discharge process. After that, the battery voltage value decreases without increasing. Thereby, the period concerning a 2nd self-discharge process can be shortened very much.

  Furthermore, any one of the above-described lithium ion secondary battery manufacturing methods may be a lithium ion secondary battery manufacturing method that satisfies the relationship of 0.25 V ≦ ΔVbe ≦ 0.45 V with respect to the condition (2). .

  By satisfying the relationship of 0.25V ≦ ΔVbe ≦ 0.45V for the condition (2) described above, the battery voltage increase period after the start of standing in the second self-discharge process can be set to “0”. it can. In other words, by setting the voltage difference value ΔVbe (= Vb−Ve) to a value within the range of 0.25V to 0.45V, the battery voltage value increases after starting to stand in the second self-discharge process. Decrease without. Thereby, the period concerning a 2nd self-discharge process can be shortened very much.

  Furthermore, in any one of the above-described lithium ion secondary battery manufacturing methods, after the assembly process, before the initial charging process, the battery that has finished the assembly process is sandwiched between pressing jigs, and is constrained A battery restraining step, and after the internal resistance measuring step and before the battery row restraining step, a restraint releasing step for releasing the restraint of the battery performed in the battery restraining step, the initial charging step, In any of the aging process, the first self-discharge process, the discharge amount measurement process, and the internal resistance measurement process, the battery may be a method for manufacturing a lithium ion secondary battery in the restrained state.

  In the above-described manufacturing method, the initial charging step, the aging step, the first self-discharge step, the discharge amount measuring step, and the internal resistance measuring step are performed with the battery held in a restrained state with a pressing jig. By placing the battery in a restrained state with a pressing jig, the electrode body can be compressed, and unevenness in the distance between the positive electrode plate and the negative electrode plate can be reduced (made uniform). For this reason, in each said process, since the nonuniformity of a battery reaction (a charge reaction, a discharge reaction) can be made small, it is preferable.

It is a perspective view of the lithium ion secondary battery manufactured by the manufacturing method of embodiment. It is a perspective view of the positive electrode plate of the lithium ion secondary battery. It is a perspective view of the negative electrode plate of the lithium ion secondary battery. It is an expanded sectional view of the same negative electrode plate, and corresponds to the AA sectional view of FIG. It is a flowchart which shows the flow of the manufacturing method of the lithium ion secondary battery concerning embodiment. It is a perspective view which shows the state which pinched | interposed the battery which finished the assembly | attachment process in the battery restraint process, and was made into the restraint state. In a battery row | line | column restraint process, it is a figure which shows the state made into the restraint state by pinching | interposing a battery row | line | column with the pressing jig from the both ends. It is a graph which shows the relationship between the leaving period and battery voltage difference (DELTA) Vbc when it is left on the same conditions as a 1st self-discharge process about the normal battery which is not internally short-circuited, and the battery which is internally short-circuited. It is a graph which shows the relationship between the leaving period when the battery row | line | column is left as it is on the same conditions as a 2nd self-discharge process, and the variation | change_quantity of battery voltage about the normal battery which is not an internal short circuit, and the battery which is an internal short circuit . It is a graph which shows the relationship between voltage difference value (DELTA) Vbe and the battery voltage rise period in a 2nd self-discharge process. It is a graph which shows the relationship between the leaving period in a 1st self-discharge process, and the battery voltage rise period in a 2nd self-discharge process.

First, the lithium ion secondary battery 100 manufactured by the manufacturing method of this embodiment will be described.
As illustrated in FIG. 1, the lithium ion secondary battery 100 includes an electrode body 110 and a battery case 180 that accommodates the electrode body 110. The electrode body 110 includes a positive electrode plate 130, a negative electrode plate 120, and a separator 150. The separator 150 is made of polyethylene, and is interposed between the positive electrode plate 130 and the negative electrode plate 120 to separate them. The separator 150 is impregnated with an electrolytic solution 160 having lithium ions.

  The battery case 180 is made of aluminum and has a rectangular parallelepiped shape. The battery case 180 has a battery case main body 181 and a sealing lid 182. Among these, the battery case main body 181 has a bottomed rectangular box shape. Note that an insulating film (not shown) made of a resin and bent in a box shape is interposed between the battery case main body 181 and the electrode body 110. The battery case 180 has a pair of wide side surfaces 180b and 180c facing away from each other. The wide side surface 180b is a surface facing the front side in FIG. 1, and the wide side surface 180c is a surface facing the back side in FIG. 1 (a surface located on the back side of the wide side surface 180b).

  The sealing lid 182 has a rectangular plate shape, closes the opening of the battery case body 181, and is welded to the battery case body 181. A rectangular plate-shaped safety valve 197 is sealed on the sealing lid 182.

  Further, a plate-like positive electrode current collecting member 191 bent in a crank shape is welded to the positive electrode plate 130 of the electrode body 110 (see FIG. 1). Further, a plate-like negative electrode current collecting member 192 bent in a crank shape is welded to the negative electrode plate 120. Of the positive electrode current collecting member 191 and the negative electrode current collecting member 192, the positive electrode terminal portion 191A and the negative electrode terminal portion 192A located at the respective tips penetrate the sealing lid 182 and protrude from the lid surface 182A. Insulating members 195 made of electrically insulating resin are interposed between the positive electrode terminal portion 191A and the sealing lid 182 and between the negative electrode terminal portion 192A and the sealing lid 182, respectively.

The electrolyte solution 160 is LiPF ₆ added as a solute to a mixed organic solvent in which ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) are adjusted to a volume ratio of 3: 4: 3. Furthermore, it is a non-aqueous electrolyte to which difluorophosphate is added. The concentration of LiPF ₆ in the electrolytic solution 160 is 1 mol / L.

  The electrode body 110 is a wound electrode body in which a belt-like positive electrode plate 130 and a negative electrode plate 120 are wound into a flat shape via a belt-like separator 150 (see FIG. 1). Specifically, the strip-shaped positive electrode plate 130, the negative electrode plate 120, and the separator 150 extending in the longitudinal direction DA are wound in the longitudinal direction DA to form a wound electrode body 110 (FIGS. 1 to 4). reference). In the electrode body 110, the positive electrode active material layer 131 of the positive electrode plate 130 and the negative electrode active material layer 121 of the negative electrode plate 120 face each other with the separator 150 interposed therebetween (see FIG. 4).

  As shown in FIG. 2, the positive electrode plate 130 has a belt-like shape extending in the longitudinal direction DA. The positive electrode current collector plate 138 made of aluminum foil and both main surfaces of the positive electrode current collector plate 138 extend in the longitudinal direction DA. It has two positive electrode active material layers 131 and 131 arranged in a strip shape. The positive electrode active material layer 131 includes a positive electrode active material 137, a conductive material made of acetylene black, PEO (polyethylene oxide), and CMC (carboxymethylcellulose) in a weight ratio of 88: 10: 1: 1. Yes.

Note that as the positive electrode active material 137, Li _x MO ₂ (M is Ni, or in addition to Ni as a main component, Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, 1.04 ≦ X ≦ 1.15) containing at least one of Ga, Zr, and Si is used.
In addition, carbon layers 139 are provided on both surfaces of the aluminum foil forming the positive electrode current collector plate 138. The carbon layer 139 contains acetylene black and polyvinylidene fluoride in a weight ratio of 3: 7.

  Further, as shown in FIG. 3, the negative electrode plate 120 is formed on a negative electrode current collector plate 128 made of a copper foil in a strip shape extending in the longitudinal direction DA, and on both main surfaces 128 F and 128 F of the negative electrode current collector plate 128. It has two negative electrode active material layers 121 and 121 arranged in a strip shape extending in the direction DA. The negative electrode active material layer 121 includes the negative electrode active material 127, SBR (styrene butadiene rubber), CMC, and (carboxymethyl cellulose) in a weight ratio of 98: 1: 1.

  In addition, as the negative electrode active material 127, a material in which particles of the negative electrode active material are composed of graphite and amorphous carbon (for example, a surface of graphite covered with amorphous carbon) is used. A metal oxide insulating layer 129 is provided on the surface of the negative electrode active material layer 121. The metal oxide insulating layer 129 contains aluminum oxide (alumina) and polyvinylidene fluoride in a weight ratio of 95: 5.

  As shown in FIGS. 3 and 4 (AA cross-sectional view of FIG. 3), the negative electrode active material layer 121 includes a facing portion 122 that faces the positive electrode active material layer 131 through the separator 150, and a separator 150. It consists of a non-facing portion 123 where the facing positive electrode active material layer 131 does not exist. Specifically, the negative electrode active material layer 121 has a larger area than the positive electrode active material layer 131, and the non-opposing portion 123 is positioned around the opposing portion 122. Note that the position of the boundary between the non-facing portion 123 and the facing portion 122 in the negative electrode active material layer 121 is determined when the electrode body 110 is formed by winding the negative electrode plate 120, the separator 150, and the positive electrode plate 130. In FIG. 4, for reference, the positions of the positive electrode plate 130 and the separator 150 when the electrode body 110 is formed are indicated by a two-dot chain line.

Next, a manufacturing method of the lithium ion secondary battery according to the present embodiment will be described. FIG. 5 is a flowchart showing a flow of a manufacturing method of the lithium ion secondary battery according to the present embodiment.
First, in step S <b> 1 (assembly process), a battery in which the electrode body 110 and the electrolytic solution 160 are housed in the battery case 180 is manufactured. Specifically, first, the positive electrode active material 137, acetylene black, PEO (polyethylene oxide), and CMC (carboxymethylcellulose) are mixed at a weight ratio of 88: 10: 1: 1, and water (solvent) is mixed therewith. Were mixed to prepare a positive electrode slurry. Next, this positive electrode slurry was applied to the surface of a positive electrode current collector plate 138 made of aluminum foil (having a carbon layer 139 on the surface), dried, and then pressed. Thereby, the positive electrode plate 130 was obtained.

A carbon layer 139 is formed in advance on the surface of the aluminum foil that forms the positive electrode current collector plate 138. The carbon layer 139 contains acetylene black and polyvinylidene fluoride in a weight ratio of 3: 7. By providing the carbon layer 139 on the surface of the aluminum foil, when the positive electrode slurry is applied, contact between the positive electrode slurry (being alkaline) and the aluminum foil constituting the positive electrode current collector plate 138 can be prevented. Thereby, corrosion of the aluminum foil which comprises the positive electrode current collecting plate 138 can be prevented.
The thickness of the carbon layer 139 is preferably 1 to 5 μm.

  Moreover, the negative electrode active material 127, SBR (styrene butadiene rubber), CMC, and (carboxymethylcellulose) were mixed in water in the ratio of 98: 1: 1 (weight ratio), and the negative electrode slurry was produced. Next, this negative electrode slurry was applied on both main surfaces 128F of the negative electrode current collector plate 128 made of copper foil, dried, and then pressed. Thereby, the negative electrode plate 120 was obtained.

  The negative electrode active material 127 can be produced, for example, as follows. Spherical shaped graphite and pitch (petroleum pitch) are mixed and fired. By this firing, the pitch (petroleum pitch) becomes amorphous carbon. Thereafter, the fired body is pulverized, whereby the negative electrode active material 127 (graphite surface coated with amorphous carbon) can be obtained.

Note that as the negative electrode active material 127, it is preferable to use a negative electrode active material in which the ratio of amorphous carbon (amorphous carbon content) is in the range of 2.5 to 7.1 wt%. As the negative electrode active material 127, it is preferable to use a negative electrode active material in which the BET specific surface area of the negative electrode active material particles is in the range of 2.8 to 5.2 m ² / g. In the present embodiment, the value of the specific surface area obtained by a known BET method (specifically, the N ₂ gas adsorption method) is adopted as the value of the BET specific surface area.

A metal oxide insulating layer 129 is formed on the surface of the negative electrode active material layer 121. Specifically, aluminum oxide (alumina) and polyvinylidene fluoride are mixed at a weight ratio of 95: 5, and a solvent is mixed with this to obtain a paste. The paste is applied to the surface of the negative electrode active material layer 121 and dried, whereby the metal oxide insulating layer 129 can be formed.
Note that the thickness of the metal oxide insulating layer 129 is preferably 2 to 8 μm.

  Further, the capacity ratio (negative electrode capacity / positive electrode capacity) between the positive electrode capacity and the negative electrode capacity is preferably in the range of 1.4 to 1.9. Note that the capacity ratio between the positive electrode capacity and the negative electrode capacity (the ratio of the negative electrode capacity to the positive electrode capacity) is the capacity ratio between the positive electrode active material layer 131 and the facing portion 122 of the negative electrode active material layer 121. This capacity ratio can be adjusted within the range of 1.4 to 1.9 by adjusting the thickness of the negative electrode active material layer 121 (opposing portion 122) (that is, the coating amount of the negative electrode slurry).

  Thereafter, the electrode body 110 is formed by winding the separator 150 between the negative electrode plate 120 and the positive electrode plate 130. Note that the separator 150, the negative electrode plate 120, the separator 150, and the positive electrode plate 130 are disposed so that the positive electrode active material layer 131 of the positive electrode plate 130 faces the facing portion 122 of the negative electrode active material layer 121 of the negative electrode plate 120 through the separator 150. The layers are wound in the order of (see FIG. 4).

  Thereafter, the negative electrode current collecting member 192 is welded to the negative electrode plate 120 (negative electrode current collecting plate 128), and the positive electrode current collecting member 191 is welded to the positive electrode plate 130 (positive electrode current collecting plate 138). Next, after the electrode body 110 welded to the negative electrode current collecting member 192 and the positive electrode current collecting member 191 is inserted into the battery case main body 181, the electrolytic solution 160 is injected. Thereafter, the sealing lid 182 and the battery case main body 181 are welded in a state where the opening of the battery case main body 181 is closed with the sealing lid 182 to complete the assembly of the lithium ion secondary battery.

Incidentally, the electrolytic solution 160, the ethylene carbonate (EC) and methyl ethyl carbonate (MEC) and dimethyl carbonate (DMC), 3 in volume ratio: 4: a mixed organic solvent was adjusted to 3, added LiPF ₆ as a solute Furthermore, it is a non-aqueous electrolyte to which difluorophosphate is added. The concentration of LiPF ₆ in the electrolytic solution 160 is 1 mol / L.
Moreover, it is preferable that the density | concentration of the difluorophosphate in the electrolyte solution 160 shall be in the range of 0.01-0.076 mol / L. In this embodiment, LiPF ₂ O ₂ is used as the difluorophosphate.

  Next, the process proceeds to step S2 (battery restraint process) (see FIG. 5), and the lithium ion secondary battery 100 manufactured in the above assembly process (step S1) is sandwiched between the pressing jigs 30 and 40 to be in a restraint state. (See FIG. 6). Specifically, as illustrated in FIG. 6, the lithium ion secondary battery 100 is sandwiched between the pressing jigs 30 and 40 so that the wide side surfaces 180 b and 180 c of the battery case 180 are pressed by the pressing jigs 30 and 40. Then, the lithium ion secondary battery 100 is brought into a restrained state. Specifically, the pressing jig 30 disposed on the wide side surface 180 b side of the battery case 180 and the pressing jig 40 disposed on the wide side surface 180 c side are fastened using the cylindrical rod 51 and the nut 53. Then, the lithium ion secondary battery 100 is sandwiched between the pressing jigs 30 and 40, and the wide side surfaces 180 b and 180 c of the battery case 180 are pressed with the pressing jigs 30 and 40. Thus, a predetermined load (for example, 400 to 800 kgf) is applied to the battery case 180.

  As shown in FIG. 7, the pressing jig 30 includes a metal pressing main body portion 35 and a resin close contact pressing plate 36. The pressing jig 40 has a metal pressing main body 45 and a resin-made close pressing plate 46. The close-contact pressing plates 36 and 46 have a comb-shaped cross section (see FIG. 7).

  Next, it progresses to step S3 (initial charge process) (refer FIG. 5), and the lithium ion secondary battery 100 of the state (state shown in FIG. 6) restrained with the pressing jigs 30 and 40 is initially charged. Specifically, charging is performed with a constant current of 1 C (5 A) until the battery voltage value reaches a predetermined charging end voltage value Va, and then charging is performed while the battery voltage value is maintained at Va. When the voltage drops to 1A, the initial charging is terminated. The lithium ion secondary battery 100 can be activated by this initial charging. In addition, an SEI (film) can be formed on the surface of the negative electrode active material 127.

The charge end voltage value Va is set to, for example, 4.1 V (corresponding to the battery voltage value when SOC is 100%). Here, SOC is an abbreviation for State Of Charge.
Further, 1C is a current value at which the discharge having a rated capacity value (nominal capacity value) is constant-current discharged and discharge is completed in one hour. Since the rated capacity (nominal capacity) of the lithium ion secondary battery 100 is 5.0 Ah, 1C = 5.0 A.

  Next, the process proceeds to step S4 (aging process), and the lithium ion secondary battery 100 (battery voltage value is Va) in the restraint state (state shown in FIG. 6) after the initial charge (process of step S3) is completed. Aging is performed at a predetermined temperature (for example, 50 ° C.) for a certain period of time (for example, 15 hours).

  By the way, in the assembly process (step S1), metal powder (such as Cu powder) may be mixed in the electrode body 110 by mistake. In such a battery, dendrite derived from metal powder is generated in the aging process, and an internal short circuit occurs (the positive electrode plate 130 and the negative electrode plate 120 that are electrically insulated by the separator 150 are electrically connected through the dendrite. Sometimes). For this reason, in step S5 (first self-discharge process) described later, a battery in which an internal short circuit has occurred is detected so as not to be shipped (removed as a defective product).

In step S5 (first self-discharge process), the lithium ion secondary battery 100 in a restrained state (state shown in FIG. 6) after aging (the process of step S4) is kept in a temperature environment of 25 ° C. for a predetermined period ( For example, it is self-discharged by leaving it for 5 days.
In step S5 (first self-discharge step), the battery voltage value when starting to leave the lithium ion secondary battery 100 (leaving start voltage value Vb) and the battery voltage value when finishing leaving for a predetermined period of time. (Leaving end voltage value Vc) is measured.

  Further, in step S5 (first self-discharge process), a battery voltage difference ΔVbc (= Vb−Vc) obtained by subtracting the leaving end voltage value Vc from the leaving start voltage value Vb is calculated, and the battery voltage difference ΔVbc is set to a predetermined threshold value. It is determined whether it is equal to or higher than Tbc. When the battery voltage difference ΔVbc is equal to or greater than the threshold value Tbc, it is determined that an internal short circuit has occurred in the battery 100.

  In a battery with an internal short circuit, the amount of self-discharge due to neglect is larger than that of a battery without a short circuit (normal battery). growing. Therefore, based on the battery voltage difference ΔVbc before and after being left, it can be determined whether or not an internal short circuit has occurred in the battery. Therefore, in step S5 (first self-discharge process), it is determined whether or not an internal short circuit has occurred in the lithium ion secondary battery 100 depending on whether or not the battery voltage difference ΔVbc is equal to or greater than a predetermined threshold value Tbc. A battery determined to have an internal short circuit is removed as a defective product (for example, discarded).

  Note that the threshold Tbc is, for example, a value between the battery voltage difference ΔVbc of both batteries obtained by examining the battery voltage difference ΔVbc of a battery in which an internal short circuit has occurred and a battery in which no internal short circuit has occurred. It ’s fine.

  In addition, the period (predetermined period) in which the battery 100 is left in step S5 (first self-discharge process) is preferably a period (1 day to 7 days) within a range of 1 to 7 days. As will be described later, the battery voltage increase period after the start of standing in the second self-discharge process (step S10) can be shortened, and the period required for the second self-discharge process (step S10) can be shortened. is there.

  Next, it progresses to step S6 (discharge amount measurement process), and the battery voltage value of the lithium ion secondary battery 100 determined that the internal short circuit has not occurred (is normal) in step S5 is a predetermined discharge end voltage. The battery is forcibly discharged until the value Ve is reached. For example, using a known charging / discharging device, the battery 100 is discharged at a constant current of 1 C (5 A) until the battery voltage value of the battery 100 reaches the end-of-discharge voltage value Ve. Further, during the discharge period, the discharge electric quantity Qde of the battery 100 during the period from the battery voltage value to the discharge end voltage value Ve from the predetermined measurement start voltage value Vd is measured. Thereafter, it is determined whether or not the discharge electricity amount Qde is smaller than a predetermined threshold value Tde, and the battery having the discharge electricity amount Qde smaller than the threshold value Tde is removed as a defective product (for example, discarded).

In step S6 (discharge amount measurement step), the measurement start voltage value Vd is set to a value equal to or lower than the leaving end voltage value Vc in the first self-discharge step. Further, the discharge end voltage value Ve is set to a value smaller than the measurement start voltage value Vd. In the present embodiment, the discharge end voltage value Ve is set to 3.55 V (corresponding to the battery voltage value when the SOC is 30%). However, the value of the discharge end voltage value Ve is not limited to 3.55V.
Moreover, also in step S6 (discharge amount measuring step), the lithium ion secondary battery 100 remains in the state of being restrained by the pressing jigs 30 and 40 (the state shown in FIG. 6).

  Further, in the present embodiment, a voltage difference value ΔVbe (= Vb−Ve) obtained by subtracting the discharge end voltage value Ve in the discharge amount measurement step (step S6) from the neglect start voltage value Vb in the first self-discharge step (step S5). ) Satisfy the relationship of 0.25V ≦ ΔVbe ≦ 0.55V. That is, the voltage difference value ΔVbe (= Vb−Ve) is set to a value within the range of 0.25V to 0.55V. As will be described later, the battery voltage increase period after the start of standing in the second self-discharge process (step S10) can be shortened, and the period required for the second self-discharge process (step S10) can be shortened. is there.

  In order to satisfy the relationship of 0.25V ≦ ΔVbe ≦ 0.55V, for example, in step S5 (first self-discharge step), the battery 100 is charged or discharged before starting to leave the battery 100. Thus, the battery voltage value of the battery 100 may be adjusted. Specifically, the battery voltage value of the battery 100 is 0.25 to 0.55 V higher than the preset discharge end voltage value Ve (3.55 V) (this is the neglect start voltage value Vb). ) To satisfy the relationship of 0.25V ≦ ΔVbe ≦ 0.55V. However, in this case, the battery 100 that has undergone the process of step S5 (first self-discharge process) is started to be discharged in step S6 (discharge amount measurement process) without being charged or discharged.

  In addition, the charge end voltage value Va in step S3 (initial charge step) may be set so as to satisfy the relationship of 0.25V ≦ ΔVbe ≦ 0.55V. Specifically, for example, in step S4 (aging process), when the aging process is performed at a temperature of 50 ° C. for 15 hours, the battery voltage value decreases by about 0.04 V during the aging process. Yes. Accordingly, the battery voltage that is higher by 0.29 to 0.59 V than the preset value (3.55 V) of the discharge end voltage value Ve in step S3 (initial charge step). By setting the value, the neglect start voltage value Vb becomes higher by 0.25 to 0.55 V than the discharge end voltage value Ve (3.55 V). Thereby, the relationship of 0.25V ≦ ΔVbe ≦ 0.55V can be satisfied. However, in this case, the battery 100 that has been subjected to aging (the process of step S4) is left to stand for a predetermined period in step S5 (first self-discharge step) without being charged or discharged. Furthermore, about the battery 100 which finished the process of step S5 (1st self-discharge process), the discharge in step S6 (discharge amount measurement process) is started as it is, without charging / discharging.

  Next, the process proceeds to step S7 (internal resistance measurement process), and the internal resistance (IV resistance) of the lithium ion secondary battery 100 in the restraint state (state shown in FIG. 6) after the discharge amount measurement process (step S6) is completed. taking measurement. Specifically, the lithium ion secondary battery 100 is charged, and the battery voltage value is set to 3.6 V (SOC 40%). Thereafter, the lithium ion secondary battery 100 is discharged at a constant current of 20 A for 4 seconds, and the battery voltage value Vg at the end of discharge (moment of completion) is measured. Next, a value (= ΔV / 20) obtained by dividing the battery voltage change amount ΔV (= 3.6-Vg) changed by the discharge by the current value 20A is acquired as an IV resistance value (internal resistance value). A battery whose IV resistance value is out of the allowable range is removed as a defective product (for example, discarded).

  Then, it progresses to step S8 (restraint cancellation | release process), and the restraint state of the lithium ion secondary battery 100 which finished the internal resistance measurement process (step S7) is cancelled | released. Specifically, the pressing jigs 30 and 40 that have been pressed with the lithium ion secondary battery 100 interposed therebetween are removed.

  Next, in step S9 (battery row restraint process), a plurality of lithium ion secondary batteries 100 that have finished the restraint release process (step S8) are prepared, and these batteries are put together into a restraint state. Specifically, first, a plurality (for example, 20) of lithium ion secondary batteries 100 that have finished the restraint releasing step (step S8) are prepared. Thereafter, for example, as shown in FIG. 7, these lithium ion secondary batteries 100 are arranged in a row to form a battery row 200. Further, the battery array 200 is held in a restrained state by being sandwiched between the pressing jigs 30 and 40 from both ends (left and right ends in FIG. 7). In the example shown in FIG. 7, the batteries 100 adjacent to each other in the row direction are arranged in a row with the wide side surfaces 180 b and 180 c of the battery case 180 in the opposite direction to form the battery row 200.

  Specifically, a battery case in which the close contact pressing plate 36 is disposed between the lithium ion secondary batteries 100 adjacent to each other in the row direction (left and right direction in FIG. 7) and is positioned at one end (right end in FIG. 7) of the battery row 200. The pressing jig 30 is arranged on the wide side surface 180c side (right end in FIG. 7) of 180, and the wide side surface 180c side (left end in FIG. 7) of the battery case 180 located at the other end (left end in FIG. 7) of the battery array 200. The pressing jig 40 is disposed on the surface. In this state, the pressing jig 30 and the pressing jig 40 are fastened by using the cylindrical rod 52 and the nut 53, whereby the battery row 200 is sandwiched between the pressing jigs 30 and 40 to form the battery row. The wide side surfaces 180b and 180c of the battery case 180 of each battery 100 to be pressed are pressed by the pressing jigs 30 and 40. As a result, a predetermined load (a larger load than the battery restraining step, for example, 2000 to 3000 kgf) is applied to the battery array 200.

  In the above example, the case where the battery row is one row has been described, but the battery row may be a plurality of rows (for example, two rows of battery rows in which 10 batteries are arranged in one row). good. Therefore, a plurality of battery rows may be put together into a restrained state.

  By the way, if the battery row 200 is brought into a restrained state in step S9 (battery row restraining step), a large compressive force is applied to the electrode bodies 110 of each lithium ion secondary battery 100 constituting the battery row 200, and each electrode body 110 is placed. Is compressed. If a metal foreign object is mixed in the electrode body 110 (for example, if a metal foreign object is mistakenly mixed in the electrode body 110 in the assembling process and the metal foreign object still remains), as described above. When the electrode body 110 is compressed, the metal foreign matter penetrates the separator 150 and an internal short circuit occurs (the positive electrode plate 130 and the negative electrode plate 120 electrically insulated by the separator 150 are electrically connected through the metal foreign matter. Connection). For this reason, in step S10 (second self-discharge process) described later, a battery in which an internal short circuit has occurred is detected so as not to be shipped (removed as a defective product).

  In step S10 (second self-discharge step), each of the lithium ion secondary batteries forming the battery array 200 is left by leaving the battery array 200 in a restrained state (the state shown in FIG. 7) in a temperature environment of 25 ° C. 100 is self-discharged. Further, in step S10 (second self-discharge step), each lithium ion secondary battery 100 is internally short-circuited based on the change in battery voltage of each lithium ion secondary battery 100 when self-discharged. It is determined whether or not.

  However, in step S10 (second self-discharge process), when the battery voltage value of each lithium ion secondary battery 100 increases after the battery array 200 is left unattended, the battery voltage value increase period has elapsed. Later, the battery array 200 in a restrained state is left for a specified period (for example, 3 days). On the other hand, when the battery voltage value of each lithium ion secondary battery 100 decreases without increasing after the start of leaving the battery array 200, the specified period (for example, 3) Days), the battery array 200 in a restrained state is left unattended.

  Further, in step S10 (second self-discharge step), the battery voltage value Vh of each lithium ion secondary battery 100 immediately before the battery array 200 is left for the specified period (for example, 3 days) and the battery array 200 are specified. The battery voltage value Vi immediately after being left for a period (for example, 3 days) is measured, and the battery voltage difference ΔVhi (= Vh−Vi) is calculated.

  A battery with an internal short circuit has a larger self-discharge amount due to neglected than a battery without normal internal short circuit (normal battery). The voltage difference ΔVhi also increases. Therefore, it can be determined whether or not an internal short circuit has occurred in the battery based on the battery voltage difference ΔVhi.

Therefore, in step S10 (second self-discharge process), an internal short circuit occurs for each lithium ion secondary battery 100 constituting the battery array 200 depending on whether or not the battery voltage difference ΔVhi is equal to or greater than a predetermined threshold value Thi. It is determined whether or not. A battery 100 having a battery voltage difference ΔVhi that is equal to or greater than a predetermined threshold value Thi is determined to have an internal short circuit, and is removed as a defective product (for example, discarded).
The threshold value Thi is, for example, a value between the battery voltage difference ΔVhi of the two batteries, which is obtained by previously investigating the battery voltage difference ΔVhi for the battery in which the internal short circuit has occurred and the battery in which the internal short circuit has not occurred. It ’s fine.

  In this way, each lithium ion secondary battery 100 constituting the battery array 200 is left to stand for a specified period (for example, 3 days) in which the battery voltage value is reliably reduced by self-discharge, and each lithium ion before and after the specified period is left. By determining whether or not each lithium ion secondary battery 100 is internally short-circuited based on the battery voltage difference ΔVhi of the secondary battery 100, appropriate internal short-circuit determination can be performed.

  Whether or not the battery voltage value of the lithium ion secondary battery 100 increases in step S10 (second self-discharge process), the length of the battery voltage increase period when the battery voltage value increases, and the internal short circuit The length of the specified period during which presence / absence can be properly determined is previously determined by a neglect test. Specifically, under the same conditions as in step S10 (second self-discharge process), the battery row 200 including the battery 100 in which the internal short circuit has occurred and the battery 100 in which the internal short circuit has not occurred is left to stand, A battery voltage value of 100 is measured. Based on this measurement result (see FIG. 9 to be described later), whether or not there is an internal short-circuit when starting to leave the specified period in step S10 (second self-discharge step) (when measuring the battery voltage value Vh) The value of the threshold value Thi is determined in advance when the predetermined period that can be discriminated at the end of the period, and when the leaving of the specified period ends (when the battery voltage value Vi is measured). Note that a method for determining these values will be specifically described later with reference to FIG.

  If it is determined in step S10 (second self-discharge step) that no internal short circuit has occurred in any of the batteries 100 constituting the battery array 200, the assembled battery 300 (see FIG. 7) remains in the above-described restrained state. Will be shipped as. As shown in FIG. 7, the assembled battery 300 is configured such that the battery array 200 is sandwiched between pressing jigs 30 and 40 from both ends (left and right ends in FIG. 7).

  On the other hand, if it is determined in step S10 (second self-discharge step) that an internal short circuit has occurred in any of the batteries 100 constituting the battery array 200, the restraint state is once released and the internal short circuit is performed. Remove the battery 100. Then, the battery 100 determined not to be internally short-circuited is taken out from the other battery array 200 that has finished step S10 (second self-discharge process), and this battery 100 is replaced with the battery 100 that is internally short-circuited. Arrange. In this way, the battery array 200 is configured by only the batteries 100 that are determined not to have an internal short circuit, and then the battery array 200 is placed in a restrained state in the same manner as in step S9 (battery train restraining step). The battery is shipped as an assembled battery 300 (see FIG. 7).

  The battery 100 of this embodiment is used as the assembled battery 300 (in the state of the assembled battery 300). This assembled battery 300 is used, for example, as a driving power source for a hybrid vehicle or an electric vehicle.

Example 1
In the first embodiment, the lithium ion secondary battery 100 is manufactured as follows.
First, in step S1 (assembly process), a battery in which the electrode body 110 and the electrolytic solution 160 are housed in the battery case 180 is manufactured as described above.

In the first embodiment, the thickness of the carbon layer 139 of the positive electrode plate 130 is 2 μm.
Further, as the positive electrode active material 137, Li _X MO ₂ having an _X value of 1.08 is used. That is, Li _1.08 MO ₂ is used as the positive electrode active material 137. Specifically, Li _1.08 Ni _0.8 Co _0.15 Al _0.05 O ₂ is used as the positive electrode active material 137. As described above, in Example 1, “ _1.0 ” of Li _1.08 MO ₂ containing Co and Al in addition to Ni as the main component is used as the positive electrode active material 137.

Further, as the negative electrode active material 127, a negative electrode active material in which the ratio of amorphous carbon (amorphous carbon content) is 6 wt% and the BET specific surface area of the negative electrode active material particles is 3.3 m ² / g. Is used. The thickness of the metal oxide insulating layer 129 of the negative electrode plate 120 is 4 μm. The capacity ratio (negative electrode capacity / positive electrode capacity) between the positive electrode capacity and the negative electrode capacity is 1.5. Moreover, the density | concentration of the difluorophosphate in the electrolyte solution 160 shall be 0.038 mol / L.

Next, as described above, steps S2 to S9 are performed.
In the first embodiment, the end-of-charge voltage value Va in step S3 (initial charging step) is set to 4.1V. In step S4 (aging process), the lithium ion secondary battery 100 is aged at an environmental temperature of 50 ° C. for 15 hours. Furthermore, in step S5 (first self-discharge process), the battery 100 that has been subjected to aging (the process of step S4) is left to stand without being charged or discharged. Further, in step S6 (discharge amount measurement process), the battery 100 that has undergone the process in step S5 (first self-discharge process) is started to be discharged without being charged or discharged.

  In this way, a voltage difference value ΔVbe (= Vb−Ve) obtained by subtracting the discharge end voltage value Ve in the discharge amount measurement step (step S6) from the neglect start voltage value Vb in the first self-discharge step (step S5). ) Can satisfy the relationship of 0.25V ≦ ΔVbe ≦ 0.55V. Specifically, when the end-of-charge voltage value Va in step S3 (initial charging process) is 4.1 V, and the battery 100 is left at an environmental temperature of 50 ° C. for 15 hours in step S4 (aging process), the battery voltage The value is approximately 4.06V. Therefore, the neglect start voltage value Vb is 4.06V. Since the discharge end voltage value Ve is set to 3.55 V, the voltage difference value ΔVbe (= Vb−Ve) is 0.51 V (= 4.06 V−3.55 V).

In the first embodiment, the period (predetermined period) in which the battery 100 is left in step S5 (first self-discharge process) is 5 days. As will be described later, by setting the leaving period to 5 days, it is possible to accurately detect a battery in which an internal short circuit has occurred.
By the way, in step S5 (first self-discharge process), a battery voltage difference ΔVbc (= Vb−Vc) obtained by subtracting the leaving end voltage value Vc from the leaving start voltage value Vb is calculated, and the battery voltage difference ΔVbc is a predetermined threshold value. It is determined whether it is equal to or higher than Tbc. When the battery voltage difference ΔVbc is equal to or greater than the threshold value Tbc, it is determined that an internal short circuit has occurred in the battery 100. As will be described later, by setting the threshold value Tbc to, for example, 13 mV, it is possible to accurately detect a battery in which an internal short circuit has occurred.

Thereafter, as described above, the process of step S10 (second self-discharge process) is performed.
However, as will be described later, the battery of Example 1 (battery manufactured in the assembly process as described above) has a battery voltage value of nearly two days after the start of leaving the battery array 200 (up to a maximum). 2 days) is known to rise. For this reason, in step S10 (second self-discharge process) of the first embodiment, the battery voltage value Vh of each lithium ion secondary battery 100 is measured two days after the start of leaving the battery array 200, Thereafter, the battery array 200 is left for a specified period, and when the specified period has elapsed, the battery voltage value Vi of each lithium ion secondary battery 100 is measured.

  Thereafter, for each lithium ion secondary battery 100, a battery voltage difference ΔVhi (= Vh−Vi) that is a difference value between the battery voltage value Vh and the battery voltage value Vi is calculated, and the battery voltage difference ΔVhi is greater than or equal to the threshold value Thi. It is determined whether or not there is. The lithium ion secondary battery 100 whose battery voltage difference ΔVhi is equal to or greater than the threshold Thi determines that an internal short circuit has occurred. On the other hand, regarding the lithium ion secondary battery 100 in which the battery voltage difference ΔVhi is less than the threshold value Thi, it is determined that an internal short circuit has not occurred.

  In the first embodiment, the “specified period” is 3 days. As will be described later, from the result of the neglect test, after two days have passed since the start of leaving the battery array 200, it is allowed to stand for another three days, so that whether or not there is an internal short circuit appropriately based on the battery voltage difference ΔVhi. This is because it is understood that it can be determined. Further, the threshold value Thi may be set to 0.5 mV, for example. As will be described later, from the result of the neglect test, in the battery 100 in which the internal short circuit has not occurred, the value of ΔVhi is about 0.3 mV, and in the battery 100 in which the internal short circuit has occurred, the value of ΔVhi is about 0.8 mV. I know that Therefore, the presence or absence of an internal short circuit can be appropriately determined by setting the threshold value Thi to a value between these values.

(First neglect test)
Here, a description will be given of a neglect test performed in step S5 (first self-discharge process) for investigating the conditions (the number of days to be neglected and the value of the threshold Tbc) for accurately detecting a battery in which an internal short circuit has occurred. .

  Specifically, first, 60 batteries 100 (normal batteries in which no internal short circuit occurred) manufactured under the same conditions as in Example 1 were prepared. Among them, for 30 batteries 100, a battery simulating an internal short circuit (hereinafter referred to as an internal short circuit battery) was manufactured by connecting a resistance element of 300 kΩ between the positive terminal part 191A and the negative terminal part 192A. . After that, under the same conditions as in step S5 (first self-discharge process), 30 batteries 100 (hereinafter referred to as normal batteries) and 30 internal short-circuit batteries in which no internal short circuit has occurred are allowed to stand, The battery voltage difference ΔVbc was calculated. The result is shown in FIG.

  In FIG. 8, among the 30 normal batteries, the measurement result of the battery having the minimum battery voltage difference ΔVbc is shown by a solid curve C1, and the measurement result of the battery having the maximum battery voltage difference ΔVbc is shown by a solid curve. This is indicated by C2. Although the curves showing the measurement results of the remaining 28 batteries 100 are not shown, they exist in a region between the curves C1 and C2 (a region indicated by hatching in FIG. 8).

  On the other hand, among the 30 internal short-circuit batteries, the measurement result of the battery having the smallest battery voltage difference ΔVbc is shown by a dashed-dotted curve C3, and the measurement result of the battery having the largest battery voltage difference ΔVbc is shown by the dashed-dotted line. This is indicated by a curve C4. The curves showing the measurement results of the remaining 28 internal short-circuit batteries are not shown, but are present in the region between the curves C3 and C4 (the region indicated by hatching in FIG. 8).

  As can be seen from FIG. 8, when the leaving period is less than one day, the difference in the value of the battery voltage difference ΔVbc between the normal battery and the internal short-circuit battery is not clear. In detail, in the leaving period of less than one day, a part of the range of the battery voltage difference ΔVbc of the normal battery overlaps with a part of the range of the battery voltage difference ΔVbc of the internal short circuit battery. When the value of the battery voltage difference ΔVbc is the value of the overlapping portion, it cannot be determined whether the battery is a normal battery or an internal short-circuit battery. Therefore, when the leaving period is less than one day, the normal battery and the internal short-circuit battery cannot be properly identified based on the battery voltage difference ΔVbc.

On the other hand, when the leaving period is one day or longer, the difference in the value of the battery voltage difference ΔVbc between the normal battery and the internal short circuit battery becomes clear. Specifically, in the standing period of one day or more, the range of the battery voltage difference ΔVbc of the normal battery and the range of the battery voltage difference ΔVbc of the internal short-circuited battery can be clearly distinguished without overlapping.
Therefore, in step S5 (first self-discharge process), it can be said that the battery in which an internal short circuit has occurred can be accurately detected by setting the leaving period to one day or longer.

  Moreover, in Example 1, let the leaving period in step S5 (1st self-discharge process) be 5 days. In this case, the value of the threshold value Tbc for accurately detecting a battery in which an internal short circuit has occurred is examined. As can be seen from FIG. 8, when the standing period is 5 days, the maximum value (value of curve C2) of the battery voltage difference ΔVbc of the normal battery is about 12 mV. On the other hand, the minimum value of the battery voltage difference ΔVbc of the internal short circuit battery is about 15 mV.

  Therefore, it can be said that by setting the threshold value Tbc to a value within the range of 12 to 15 mV (for example, 13 mV), it is possible to accurately detect a battery in which an internal short circuit has occurred. Specifically, in step S5 (first self-discharge process), if the value of the battery voltage difference ΔVbc is equal to or greater than the threshold value Tbc (13 mV), it can be determined that an internal short circuit has occurred. On the other hand, when the value of the battery voltage difference ΔVbc is less than the threshold value Tbc (13 mV), it can be determined that an internal short circuit has not occurred.

(Second neglect test)
Next, FIG. 9 shows the result of the standing test performed to determine the conditions in step S10 (second self-discharge step) of Example 1. Specifically, the processes from Steps S1 to S9 were performed under the conditions of Example 1, and a plurality of batteries 100 in which an internal short circuit occurred and a plurality of batteries 100 in which no internal short circuit occurred were prepared. After that, under the same conditions as in step S10 (second self-discharge step), the battery train 200 including the battery 100 in which the internal short circuit has occurred and the battery 100 in which the internal short circuit has not occurred is left for 11 days, 100 battery voltage values were measured. In FIG. 9, among these measurement results, the measurement results of two batteries 100 (the battery 100 in which an internal short circuit has occurred and the battery 100 in which no internal short circuit has occurred) are used with reference to the battery voltage value at the time of starting to stand. The amount of change is shown.

  In FIG. 9, the battery voltage change amount of the battery 100 in which the internal short circuit has not occurred is indicated by ◯, and the battery voltage change amount of the battery 100 in which the internal short circuit has occurred is indicated by the Δ mark. Whether or not an internal short circuit has occurred is confirmed by disassembling each battery 100 after the 11-day standing test has been completed.

As shown in FIG. 9, the battery voltage values of the two batteries 100 have risen nearly two days after the battery array 200 has been left unattended. The other batteries 100 were almost the same, and it was found that the voltage increase period from the start of standing was 2 days at the longest.
Further, it can be seen that after the voltage increase period (2 days) has elapsed, the battery voltage value of the battery 100 in which the internal short circuit has occurred is greatly reduced as compared with the battery 100 in which the internal short circuit has not occurred. Then, after the voltage increase period (2 days) has elapsed, the battery 100 that has undergone internal short-circuiting and the battery 100 that has not undergone internal short-circuiting have been left for another 3 days. It can be seen that there is a large difference in the amount of change in battery voltage from

  Specifically, in the battery 100 in which no internal short circuit has occurred, the battery is a difference value between the battery voltage value when the voltage increase period (2 days) has elapsed and the battery voltage value when left for another 3 days thereafter. The voltage difference ΔVhi was about 0.3 mV. On the other hand, in the battery 100 in which the internal short circuit occurs, the battery voltage difference ΔVhi is about 0.8 mV, which is a considerably large value compared to the battery 100 in which the internal short circuit does not occur. If such a large difference occurs in the battery voltage difference ΔVhi, it is possible to appropriately determine the presence or absence of an internal short circuit based on the battery voltage difference ΔVhi. Therefore, the “specified period” in the second self-discharge process of Example 1 is set to 3 days.

  Therefore, in step S10 (second self-discharge step) of Example 1, the battery voltage value Vh of each lithium ion secondary battery 100 is measured two days after the start of leaving the battery array 200, and then The battery array 200 was left unattended for 3 days (specified period), and when the 3 days (specified period) passed, the battery voltage value Vi of each lithium ion secondary battery 100 was measured.

  As described above, according to the manufacturing method of Example 1, in step S10 (second self-discharge step), the battery voltage increase period after the start of standing can be shortened to within 2 days (maximum 2 days). The entire period of the second self-discharge process can be shortened to 5 days.

(Preferred value of voltage difference value ΔVbe)
Next, a preferred value of the voltage difference value ΔVbe was investigated.
Specifically, first, a battery 100 was manufactured in the same manner as steps S1 to S9 in Example 1. However, 10 types of batteries 100 were manufactured by changing only the voltage difference value ΔVbe within a range of 0.15 V to 0.85 V (see FIG. 10). Specifically, the value of the voltage difference value ΔVbe is set to 0.15V by setting the value of the charge end voltage value Va in step S3 (initial charging process) to a different value within the range of 3.74V to 4.44V. Differentiated within the range of ~ 0.85V.

  For example, when the end-of-charge voltage value Va in step S3 (initial charge process) is set to 3.74V, the battery voltage value is reduced to 3.7V in step S4 (aging process). Therefore, the leaving start voltage value Vb in step S5 (first self-discharge process) is 3.7V. Since the final discharge voltage value Ve in step S6 (discharge amount measurement step) is 3.55V, the voltage difference value ΔVbe is 0.15V (= 3.7V−3.55V).

  Thereafter, the second neglect test described above (same as in the second self-discharge process) was performed, and the battery voltage increase period from the start of the neglect was investigated for each battery 100. The result is indicated by a circle in FIG. 10 as the relationship between the voltage difference value ΔVbe and the battery voltage increase period.

  Further, the internal resistance (IV resistance) of each of the ten types of batteries 100 described above was measured. Specifically, each battery 100 is charged (or discharged) to set each battery voltage value to 3.6 V (SOC 40%). Thereafter, each battery 100 is discharged at a constant current of 100 A for 10 seconds in a temperature environment of 25 ° C., and the battery voltage value Vk at the end of discharge (moment of completion) is measured. Next, a value (= ΔV / 100) obtained by dividing the battery voltage change ΔV (= 3.6-Vk) changed by the discharge by the current value 100A was obtained as an IV resistance value (internal resistance value). These results are shown by Δ in FIG. 10 as the relationship between the value of the voltage difference value ΔVbe and the battery internal resistance (IV resistance).

  As can be seen from FIG. 10, the battery voltage increase period after the start of standing in the second self-discharge process can be shortened by decreasing the voltage difference value ΔVbe. However, when the voltage difference value ΔVbe is too small, the internal resistance of the battery increases. A battery having a large internal resistance is not preferable. From the above results, the voltage difference value ΔVbe is set to a value within the range of 0.25V to 0.55V (so that the relationship of 0.25V ≦ ΔVbe ≦ 0.55V is satisfied). It can be said that the battery voltage increase period after the start of standing in the two self-discharge process can be shortened (within 2 days), and the battery internal resistance can be reduced.

  In particular, by setting the voltage difference value ΔVbe to a value within the range of 0.25 V to 0.45 V (so that the relationship of 0.25 V ≦ ΔVbe ≦ 0.45 V is satisfied), the second self-discharge is performed. The battery voltage increase period after the start of standing in the process can be extremely shortened (the voltage increase period is set to 0). In other words, by satisfying the relationship of 0.25V ≦ ΔVbe ≦ 0.45V, in the second self-discharge process, the battery voltage value decreases without increasing after starting to leave the battery array. become. Thereby, the period concerning a 2nd self-discharge process can be shortened very much.

  On the other hand, by satisfying the relationship of 0.45V <ΔVbe ≦ 0.55V, in particular, the internal resistance of the battery can be reduced (see Δ mark in FIG. 10). Thereby, the battery 100 excellent in output characteristics can be obtained.

(Preferred value of the leaving period in the first self-discharge process)
Next, the preferred value (number of days) of the standing period in the first self-discharge process (step S5) was investigated.
Specifically, first, a battery 100 was manufactured in the same manner as steps S1 to S9 in Example 1. However, 10 types of batteries 100 were manufactured by changing only the leaving period of the battery 100 in the first self-discharge process (step S5) (see FIG. 11). Thereafter, the second neglect test described above (same as in the second self-discharge process) was performed, and the battery voltage increase period from the start of the neglect was investigated for each battery 100. The result is shown by a circle in FIG. 11 as the relationship between the leaving period and the battery voltage increase period.

Moreover, based on FIG. 8, the internal short circuit detection rate (%) in the first self-discharge step (step S5) was obtained for each leaving period shown in FIG. This internal short circuit detection rate (%) is based on the battery voltage difference ΔVbc before and after being left (= left start voltage value Vb − left end voltage value Vc) in the first self-discharge step (step S5). This corresponds to the probability that a battery can be detected. Specifically, out of the range of the battery voltage difference ΔVbc of the internal short circuit battery (the hatched area range between the curves C3 and C4 in FIG. 8), the range of the battery voltage difference ΔVbc of the normal battery (the curve in FIG. 8). The ratio of the range not included in the hatched area between C1 and C2) is the internal short circuit detection rate (%).
The result is shown by Δ in FIG. 11 as the relationship between the standing period and the internal short circuit detection rate in the first self-discharge process.

  As can be seen from FIG. 11, the battery voltage increase period after the start of standing in the second self-discharge process can be shortened by shortening the standing period in the first self-discharge process. However, if the leaving period in the first self-discharge process is made too short, the internal short circuit detection rate decreases. Specifically, if the standing period in the first self-discharge process is less than 1 day, the internal short circuit detection rate is less than 100%, and there is a possibility that the internal short-circuited battery cannot be detected appropriately. In other words, by setting the leaving period in the first self-discharge process to be 1 day or longer, the internal short circuit detection rate becomes 100%, and the battery that is internally short-circuited can be detected appropriately.

  From the above results, in the first self-discharge step, the period in which the battery is left (predetermined period) is set to a period (1 day to 7 days) within the range of 1 to 7 days. It is possible to accurately detect a battery in which an internal short circuit has occurred in the battery and to shorten the battery voltage increase period after the start of standing in the second self-discharge process (within 2.5 days). .

  In particular, by setting the leaving period in the first self-discharge process to a period within the range of 1 to 4 days (1 day or more and 4 days or less), the battery voltage increase period after the start of leaving in the second self-discharge process, It can be made extremely short (the voltage rise period is set to 0) (see FIG. 11). In other words, by setting the leaving period in the first self-discharge process to a period of 1 day or more and 4 days or less, the battery voltage value does not increase after the start of leaving the battery array in the second self-discharge process. It begins to decline. Thereby, the period concerning a 2nd self-discharge process can be shortened very much.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, although step S2 (battery restraint process) and step S8 (restraint release process) are provided in the embodiment, a lithium ion secondary battery may be manufactured without providing these processes. That is, you may make it perform the process of step S3-S7, without putting the lithium ion secondary battery 100 produced in the assembly | attachment process (step S1) between the pressing jigs 30 and 40, and making it a restraint state.

30, 40 Pressing jig 100 Lithium ion secondary battery (battery)
DESCRIPTION OF SYMBOLS 110 Electrode body 120 Negative electrode plate 121 Negative electrode active material layer 127 Negative electrode active material 128 Negative electrode current collecting plate 130 Positive electrode plate 131 Positive electrode active material layer 137 Positive electrode active material 138 Positive electrode current collecting plate 150 Separator 160 Electrolytic solution 180 Battery case 200 Battery array

Claims (4)

An assembly process for producing a battery in which an electrode body having a positive electrode active material and a negative electrode active material and an electrolytic solution containing difluorophosphate are housed in a battery case;
An initial charging step for initially charging the battery after the assembly step;
An aging process in which the battery after the initial charging process is aged at a predetermined temperature for a fixed time; and
A first self-discharge step in which the battery that has finished the aging step is self-discharged by being left for a predetermined period;
While the battery having undergone the first self-discharge process is forcibly discharged until the battery voltage value reaches a predetermined discharge end voltage value, the battery voltage value is changed from the predetermined measurement start voltage value to the discharge end voltage. A discharge amount measuring step for measuring the amount of discharge electricity of the battery until reaching a value;
An internal resistance measuring step of measuring the internal resistance of the battery after the discharge amount measuring step;
A plurality of the batteries having undergone the internal resistance measurement step are prepared, and these batteries are arranged in one or a plurality of rows to form one or a plurality of battery rows, and the battery row is pressed from both ends. A battery array restraining step to be in a restrained state sandwiched between tools,
A second self-discharge step of self-discharging each of the batteries constituting the battery row by leaving the battery row in the restrained state, and a method of manufacturing a lithium ion secondary battery,
In the first self-discharge step, a leaving end voltage value Vc that is a battery voltage value at the end of the predetermined period is determined from a leaving start voltage value Vb that is a battery voltage value at the start of leaving the battery. If the subtracted battery voltage difference ΔVbc is greater than or equal to a predetermined threshold, it is determined that an internal short circuit has occurred in the battery,
The second self-discharge step is
If the battery voltage value rises after starting to leave the battery row, leave the battery row in the restrained state for a specified period after the rising period of the battery voltage value, or
If the battery voltage value decreases without increasing after starting to leave the battery row, leave the battery row in the restrained state for the specified period after starting to leave the battery row,
A step of self-discharging the battery forming the battery row;
The manufacturing method is a method for manufacturing a lithium ion secondary battery that satisfies at least one of the following conditions (1) and (2).
(1) In the first self-discharge step, the predetermined period is a period within a range of 1 to 7 days.
(2) The voltage difference value ΔVbe obtained by subtracting the discharge end voltage value Ve in the discharge amount measurement step from the neglect start voltage value Vb in the first self-discharge step has a relationship of 0.25V ≦ ΔVbe ≦ 0.55V. Meet. It is a manufacturing method of the lithium ion secondary battery according to claim 1,
Regarding the condition (1), a method for producing a lithium ion secondary battery, wherein the predetermined period is a period within a range of 1 to 4 days. It is a manufacturing method of the lithium ion secondary battery according to claim 1 or 2,
A manufacturing method of a lithium ion secondary battery satisfying the relationship of 0.25V ≦ ΔVbe ≦ 0.45V with respect to the condition (2). It is a manufacturing method of the lithium ion secondary battery as described in any one of Claims 1-3,
After the assembling step, before the initial charging step, the battery that has finished the assembling step is provided with a battery restraining step that is sandwiched between pressing jigs,
After the internal resistance measurement step, before the battery row restraint step, comprising a restraint release step of releasing the restraint of the battery performed in the battery restraint step,
In all of the initial charging step, the aging step, the first self-discharge step, the discharge amount measuring step, and the internal resistance measuring step, the battery is a method for manufacturing a lithium ion secondary battery in the restrained state.

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