JP6120083B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a secondary battery (nonaqueous electrolyte secondary battery) provided with a nonaqueous electrolyte.

  Lithium ion secondary batteries (for example, Patent Document 1) and other non-aqueous electrolyte secondary batteries are becoming increasingly important as power sources for vehicles or as power sources for personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle. In manufacturing this type of battery, an electrode body composed of a positive electrode and a negative electrode is accommodated in a battery case, a nonaqueous electrolyte is injected into the battery case, and then the electrode body is impregnated with the nonaqueous electrolyte. Build the battery assembly. Next, the battery assembly thus constructed is subjected to a conditioning process (initial charge), subjected to a high-temperature aging process in a high-temperature environment, and then self-discharged at room temperature to measure a voltage drop amount. Selection (self-discharge characteristic inspection) of large batteries (short-circuit batteries) is performed.

Japanese Patent Laid-Open No. 2004-220956

  However, in the battery manufacturing method described above, initial gas is generated when the battery assembly is initially charged. Therefore, if charging and discharging is performed as it is, charging unevenness occurs in the gas biting portion of the electrode body, and battery characteristics are obtained. Can be a factor of lowering. In order to cope with this problem, Patent Document 1 describes that the above-described malfunction due to gas generation is suppressed by sealing under reduced pressure after preliminary charging. However, according to the inventor's knowledge, the initial gas is more likely to be generated at a higher voltage and temperature, so that only a part of the initial gas is generated by the initial charging, and can be increased to a high voltage and high temperature after sealing. The remaining initial gas is generated. According to the method of Patent Document 1, the influence of the initial gas generated before the preliminary charging / sealing can be eliminated, but the influence of the initial gas generated after the preliminary charging / sealing (for example, during high temperature aging treatment) is eliminated. I can't. The present invention solves the above problems.

  As a result of intensive studies to solve the above problems, the present inventor left the battery assembly after the self-discharge process in a low voltage region of 3.45 V or less for a certain period of time, thereby performing an initial charging process or a high temperature aging process. The inventors have found that a high-performance nonaqueous electrolyte secondary battery can be obtained by eliminating the influence of the gas generated in the above, and the present invention has been completed.

  That is, the method for manufacturing a non-aqueous electrolyte secondary battery provided by the present invention is a battery assembly construction for constructing a battery assembly in which an electrode body including a positive electrode and a negative electrode and a non-aqueous electrolyte solution are housed in a battery case. An initial charging step for charging the battery assembly to a predetermined voltage value in a normal temperature range; a high temperature aging step for holding the battery assembly in a predetermined high temperature range for a predetermined time; and the battery set A self-discharge step of self-discharging the solid for a predetermined time in a normal temperature range, and discharging the battery assembly after the self-discharge step to a low voltage range of 3 V to 3.45 V, and then 1 to 3 hours in the low voltage range And a low voltage leaving step of leaving. According to such a manufacturing method, the battery assembly after the self-discharge process is allowed to stand for a certain period of time in a low voltage region of 3.45 V or less, so that the gas biting portion of the electrode body (typically the initial charging process or high-temperature aging). The electrolyte solution impregnates the liquid uneven part of the electrode body caused by the initial gas generated in the process. Therefore, the malfunction (for example, reduction of battery capacity) by this gas biting part can be controlled.

FIG. 1 is a diagram showing a manufacturing flow of a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a graph showing a change in voltage change of the manufacturing method according to the embodiment. FIG. 3 is a graph showing the relationship between the standing time and the initial capacity. FIG. 4 is a graph showing the transition of voltage after voltage adjustment. FIG. 5 is a graph showing the relationship between the standing time and the voltage stabilization days. FIG. 6 is a diagram for explaining the state of the positive electrode and the negative electrode in each manufacturing process.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. The “non-aqueous electrolyte secondary battery” refers to a battery provided with a non-aqueous electrolyte (typically, an electrolyte containing a supporting salt (supporting electrolyte) in a non-aqueous solvent). The “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of lithium ions between positive and negative electrodes. The electrode active material refers to a material capable of reversibly occluding and releasing chemical species (lithium ions in a lithium ion secondary battery) serving as a charge carrier.

  The manufacturing method disclosed here is a manufacturing method characterized by having a low voltage standing step after the self-discharge step, and specifically includes steps S10 to S60 shown in the flowchart of FIG. Moreover, transition of the change of the voltage of the battery assembly in each process S10-S60 is shown in FIG. Hereinafter, each process will be described in order with reference to these.

<Battery assembly construction process (S10)>
The battery assembly construction step of Step S10 is a step of constructing a battery assembly in which an electrode body including a positive electrode sheet and a negative electrode sheet and a nonaqueous electrolyte solution are accommodated in a battery case. Typically, in a normal temperature range, the electrode body is accommodated in a battery case, and then a non-aqueous electrolyte is poured into the battery case. The battery assembly may be constructed by impregnating the electrode body with a non-aqueous electrolyte. The method for impregnating the electrode body with the nonaqueous electrolytic solution is not particularly limited. For example, after pouring the electrolytic solution, the inside of the battery case may be depressurized (negative pressure) and impregnated in the electrode body. In this embodiment, the positive electrode terminal is joined to the end portion of the positive electrode sheet of the electrode body, the negative electrode terminal is joined to the end portion of the negative electrode sheet, and the electrode body is accommodated in a rectangular parallelepiped hard case, and then a nonaqueous electrolyte is injected. To do. Then, in a state in which the inside of the hard case is evacuated to a negative pressure, a battery is assembled by attaching a lid to the opening of the case and joining by laser welding. As the battery case, for example, a lightweight metal material such as aluminum can be preferably used. The battery assembly as used herein refers to all batteries assembled up to the stage prior to the initial charging process, and typically refers to a battery that is sealed (typically a battery case is sealed). .

The positive electrode sheet includes a strip-shaped positive electrode current collector and a positive electrode active material layer. For the positive electrode current collector, for example, a metal foil (for example, aluminum foil) suitable for the positive electrode can be suitably used. In this embodiment, the positive electrode current collector has a positive electrode active material layer non-formation part in which a positive electrode active material layer is not formed at one end in the width direction orthogonal to the longitudinal direction of the positive electrode current collector. In addition, a positive electrode active material layer is formed so that a positive electrode active material layer non-formation portion is not substantially provided at the other end. The positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder. Examples of positive electrode active materials include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (lithium nickel cobalt manganese composite oxide), LiNiO ₂ (lithium nickel oxide), LiCoO ₂ (lithium cobalt oxide). And lithium transition metal composite oxides such as LiMn ₂ O ₄ (lithium manganese oxide). A powdery carbon black material such as acetylene black (AB) can be mixed as the conductive material. In addition to the positive electrode active material and the conductive material, a binder such as polyvinylidene fluoride (PVDF) can be added.

  The negative electrode sheet includes a strip-shaped negative electrode current collector and a negative electrode active material layer. For the negative electrode current collector, for example, a metal foil (for example, copper foil) suitable for the negative electrode can be suitably used. In this embodiment, the negative electrode current collector has a negative electrode active material layer non-formation part in which a negative electrode active material layer is not formed at one end in the width direction orthogonal to the longitudinal direction of the negative electrode current collector. Further, the negative electrode active material layer is formed at the other end so that the negative electrode active material layer non-formation portion is not substantially provided. The negative electrode active material layer contains a negative electrode active material and a binder. Examples of the negative electrode active material include carbon-based materials such as graphite carbon and amorphous carbon. In addition to the negative electrode active material, a binder such as styrene butadiene rubber (SBR) can be added. Furthermore, in addition to the negative electrode active material and the binder, a thickener such as carboxymethyl cellulose (CMC) can be added.

  In this embodiment, the electrode body is formed by stacking and winding the positive electrode active material layer and the negative electrode active material layer while interposing a separator between the positive electrode active material layer and the negative electrode active material layer. A rotating electrode body). Further, in the winding axis direction of the wound electrode body, the positive electrode current collector and the negative electrode current collector are arranged so that the respective electrode active material layer non-forming portions protrude on the opposite side in the winding axis direction. ing. And the width | variety of a negative electrode active material layer is wider than the width | variety of a positive electrode active material layer. In this case, the negative electrode active material layer has a portion facing the positive electrode active material layer (opposite portion) and a portion not facing the positive electrode active material layer in the winding axis direction (width direction) of the wound electrode body. (Non-opposing part).

As the separator, a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. The non-aqueous electrolyte typically has a composition in which a supporting salt is contained in a suitable non-aqueous solvent. As the non-aqueous solvent, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like can be used. Moreover, as said support salt, lithium salts, such as LiPF ₆ , can be used, for example. As an example, a nonaqueous electrolytic solution in which LiPF ₆ is contained in a mixed solvent of ethylene carbonate and diethyl carbonate (for example, a mass ratio of 1: 1) at a concentration of about 1 mol / L can be given.

<Initial charging step (S20)>
The initial charging step of step S20 is a step of charging the battery assembly constructed as described above up to a predetermined voltage value in the normal temperature range. Typically, an external power source is connected between the positive electrode (positive electrode terminal) and the negative electrode (negative electrode terminal) of the assembly, and charging to a predetermined voltage (typically constant current and constant voltage charging) is performed. Here, the normal temperature region in the initial charging step refers to a temperature region that is typically normal temperature, and refers to 20 ° C. ± 15 ° C. The temperature to which the battery assembly is exposed in the initial charging process can be selected from a temperature range of 5 ° C to 35 ° C, for example, and preferably 20 ° C to 30 ° C. Further, the voltage between the positive and negative terminals (typically the highest voltage reached) in the initial charging process may vary depending on the active material used, the type of the non-aqueous solvent, and the like, but the SOC (State of Charge) of the battery assembly: A voltage range that can be indicated when the (charge depth) is in the range of approximately 80% or more (typically 90 to 105%) of the full charge (typically the rated capacity of the battery) may be used (see FIG. 2). ). For example, in the case of a battery that is fully charged at 4.2 V, it is preferable to adjust to a range of about 3.8 to 4.2 V. The charging rate in the initial charging process may be the same as a conventionally known charging rate that can be generally adopted when initially charging a conventional battery assembly, and may be about 0.1 to 10 C, for example. Such a charging process may be performed once, but may be performed twice or more, for example, with a discharging process interposed therebetween.

<High temperature aging process (S30)>
The high temperature aging process of step S30 is a process of holding (typically resting) the battery assembly after the initial charging process in a predetermined high temperature range for a certain period of time. By holding the battery assembly in a high temperature region in this way, even if metal foreign matter is mixed into the battery from the outside, the metal foreign matter can be dissolved as metal ions and deposited and grown on the negative electrode. Thus, a minute internal short-circuit can be generated in the electrode body, and by detecting in the next self-discharge process, it is possible to prevent the short-circuit cell from flowing out due to contamination of foreign matter. In such a high temperature aging step, the battery assembly is preferably maintained at a temperature of 40 ° C. to 85 ° C. (for example, 55 ° C. to 70 ° C.) higher than the room temperature region. When the holding temperature is lower than 40 ° C., the metal foreign matter may not be sufficiently dissolved. The holding time in the high temperature aging step is preferably 5 hours or more and 250 hours or less (for example, the total time from the start of temperature increase is 100 to 200 hours, preferably 150 to 180 hours). As a means for heating the battery assembly, for example, a thermostatic bath or an infrared heater can be used as appropriate. The battery voltage preferably maintains a relatively high voltage range between terminals and / or a relatively high SOC range throughout the high temperature aging process (see FIG. 2). For example, in a battery that is fully charged at 4.2 V, it is preferable to perform charging and discharging within a range in which the voltage between the positive and negative electrodes is maintained at approximately 3.7 to 4.2 V.

<Cell self-discharge process (S40)>
The cell self-discharge process of step S40 is a process in which the battery assembly that has finished the high-temperature aging process is left in the normal temperature range and self-discharged for a predetermined time. By measuring the voltage drop amount (battery voltage difference before and after being left) at this time, it is possible to grasp the presence or absence of an internal short circuit due to some influence (for example, high temperature aging process) derived from manufacturing conditions. That is, a battery in which an internal short circuit has occurred has a large amount of voltage drop since it has a large self-discharge amount if left for a certain period of time. Therefore, it can be determined whether or not an internal short circuit has occurred in the battery based on the voltage drop amount. For example, a threshold value that is used as a criterion for determining whether or not there is an internal short circuit is set in advance, and when the voltage drop amount exceeds the threshold value, the battery assembly is determined as “with an internal short circuit”, and the voltage drop amount is equal to or less than the threshold value. In this case, the battery assembly may be determined as “no internal short circuit”. By removing the battery assembly determined to be “with internal short circuit” based on the determination result, it is possible to prevent the defective product from flowing to the subsequent process. In addition, the temperature at which the battery assembly is exposed in the cell self-discharge process may be a temperature range that is normal temperature, for example, 20 ° C. ± 15 ° C., preferably 15 ° C. to 25 ° C. In addition, the standing time in the cell self-discharge process is not particularly limited, but it is suitably about 36 hours to 200 hours, preferably 48 hours to 150 hours, and particularly preferably 60 hours to 120 hours.

<Low voltage leaving step (S50)>
The low voltage leaving step of step S50 is a step of discharging the battery assembly after the self-discharge step to a low voltage region of 3.45 V or less and then leaving it in the low voltage region for 1 to 3 hours. According to the knowledge of the present inventor, initial gas is generated when the battery assembly is subjected to initial charging and high temperature aging treatment. If charging / discharging is performed as it is, charging unevenness occurs in the gas biting portion of the electrode body, which may be a factor of deterioration of battery characteristics. On the other hand, according to the above configuration, the initial gas is generated in the initial charging or the high temperature aging process by leaving the battery assembly after the self-discharge process in a low voltage region of 3.45 V or less. However, since the electrolytic solution is impregnated in the gas biting portion of the electrode body, it is difficult for a situation in which uneven charging occurs in the subsequent charge / discharge treatment. Therefore, an event that battery performance (for example, battery capacity) decreases due to the uneven charging can be suppressed, and a high-performance battery can be manufactured.

  It is appropriate that the voltage between the positive and negative terminals (stand voltage) in the low voltage standing step is about 3 V to 3.45 V or less. If the neglected voltage is too higher than 3.45 V, it is difficult to impregnate the gas biting portion of the electrode body with the electrolytic solution, and the above-described battery performance improvement effect (for example, battery capacity improvement effect) may be insufficient. On the other hand, if the neglected voltage is too lower than 3V, there is not much merit because it takes a long discharge time. The standing voltage in the low voltage standing step is generally 3 V or more and 3.45 V or less, preferably 3.1 V or more and 3.4 V or less, and particularly preferably 3.2 V or more and 3.3 V or less.

  It is appropriate that the standing time in the low voltage standing step is approximately 1 hour or more and 3 hours or less. If the standing time is shorter than 1 hour, the gas biting portion of the electrode body is not sufficiently impregnated with the electrolytic solution, and the above-described battery performance improvement effect may not be obtained. From the viewpoint of improving the impregnation of the electrolytic solution, the standing time is generally 1 hour or longer, preferably 1.5 hours or longer, particularly preferably 2 hours or longer. On the other hand, if the standing time is longer than 3 hours, the time until the voltage stabilizes in the stack self-discharge process, which will be described later, becomes long, and the stack self-discharge process may not be performed quickly. From the viewpoint of voltage stability, the standing time is generally 3 hours or less, and preferably 2.5 hours or less. In addition, the temperature at which the battery assembly is exposed in the low voltage standing step may be a temperature range that is normal temperature, for example, 20 ° C. ± 15 ° C., and preferably 15 ° C. to 30 ° C.

  Note that the low-voltage leaving step may be performed in a state where the battery assembly is sandwiched with a jig and the battery assembly is pressed and restrained. In this case, the low voltage leaving step maintains a low voltage state of 3.45 V or less, and a load (constraint pressure) applied to the battery assembly is 300 kgf or less (for example, 100 kgf to 200 kgf, preferably 180 kgf or less, for example, 120 kgf to It is desirable that the setting is 180 kgf). As described above, by leaving the battery assembly under a low voltage and a low load, the impregnation property of the electrolytic solution into the gas biting portion of the electrode body is further improved, and a battery with higher performance can be obtained.

<Stack self-discharge process (S60)>
In the stack self-discharge process of step S60, a plurality of batteries (single batteries) that have been subjected to the low-voltage standing process are prepared, and after adjusting the voltage of each battery (for example, adjusting SOC 50% to 80%), An assembled battery is constructed by arranging batteries and restraining them in the arrangement direction. Then, the assembled battery is left in a normal temperature range and self-discharged for a certain time. At this time, by measuring the voltage drop amount (battery voltage difference before and after being left) for each unit cell constituting the assembled battery, for example, it is possible to grasp the presence or absence of an internal short circuit due to some influence derived from the manufacturing conditions. it can. That is, since the unit cell in which an internal short circuit has occurred is left untreated, the amount of self-discharge increases, and the amount of voltage drop also increases. Therefore, based on the amount of voltage drop, it can be determined whether or not an internal short circuit has occurred for each unit cell constituting the assembled battery. By removing the single cell determined as “internal short circuit” based on the determination result, it is possible to prevent a defective product from flowing into the market and to provide a highly reliable assembled battery.

  In the stack self-discharge process, as described above, a short-circuited cell is detected based on the voltage drop amount. Therefore, if the voltage is measured in a region where the voltage changes rapidly, the voltage drop amount may vary and the detection accuracy of the short-circuit cell may be reduced. There is. Therefore, in the stack self-discharge process, it is preferable to start measuring the voltage drop after a certain time has elapsed until the voltage is stabilized after adjusting the voltage (for example, adjusting SOC of 50% to 80%). The fixed time until the voltage stabilizes is appropriately 24 hours or less, and preferably 18 hours or less.

  The non-aqueous electrolyte secondary battery and the assembled battery manufactured by the method disclosed herein can be excellent in reliability. Therefore, it can be suitably used for various applications. Among these, it can be suitably used as a power source (drive power source) for a motor mounted on a vehicle such as a plug-in hybrid vehicle (PHV).

  An evaluation cell (lithium ion secondary battery) was constructed using the production method according to the present invention, and the initial capacity of the battery was evaluated. In this evaluation cell, a positive electrode sheet in which a positive electrode active material layer is formed on a positive electrode current collector and a negative electrode sheet in which a negative electrode active material layer is formed on a negative electrode current collector are arranged through a separator. A wound electrode body is provided. In the winding axis direction of the wound electrode body, the width of the negative electrode active material layer is wider than the width of the positive electrode active material layer. Therefore, the negative electrode active material layer has a portion facing the positive electrode active material layer and a portion not facing the positive electrode active material layer in the winding axis direction (width direction).

Here, the positive electrode sheet used LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as the positive electrode active material particles contained in the positive electrode active material layer. Acetylene black (AB) was used as the conductive material, and PVDF was used as the binder. LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , AB and PVDF were mixed with N-methylpyrrolidone (NMP) so that the mass ratio was 91: 6: 3 to prepare a slurry-like composition. . This composition was applied to both sides of a long aluminum foil (positive electrode current collector) to form a positive electrode active material layer. The obtained positive electrode was dried and pressed to produce a positive electrode sheet.

  The negative electrode sheet used graphite powder as negative electrode active material particles contained in the negative electrode active material layer. Styrene butadiene rubber (SBR) was used as the binder, and carboxymethyl cellulose (CMC) was used as the thickener. Graphite, SBR, and CMC were mixed with ion-exchanged water so that the mass ratio was 98: 1: 3 to prepare a slurry composition. This composition was applied to both sides of a long copper foil (negative electrode current collector) to form a negative electrode active material layer. The obtained negative electrode was dried and pressed to prepare a negative electrode sheet.

The separator used was a three-layer structure in which a polypropylene (PP) layer was laminated on both sides of a polyethylene (PE) layer. Further, a nonaqueous electrolytic solution in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 3: 5: 2 and 1 mol of LiPF ₆ was dissolved was used.

  The battery assembly was constructed as follows. First, the positive electrode sheet and the negative electrode sheet were overlapped and wound through two separators, and the obtained wound electrode body was formed into a flat shape by crushing it from the side surface and dragging it. And the positive electrode terminal was joined to the edge part of the positive electrode collector of this winding electrode body, and the negative electrode terminal was joined to the edge part of the negative electrode collector, respectively. This electrode body was housed in a rectangular parallelepiped hard case, and a non-aqueous electrolyte was injected. Then, in a state where the inside of the hard case was evacuated to a negative pressure, a battery was assembled by attaching a lid to the opening of the case and joining by laser welding.

  Next, the battery assembly constructed above was charged with a constant current at a constant current of 5 A until the voltage between the positive and negative terminals reached 4.0 V, and then at a constant voltage until the current reached 0.1 A. Charging was performed (initial charging step). Next, the battery assembly after the initial charging step was placed in a thermostatic chamber, the temperature was raised to 60 ° C., and an aging treatment was performed until the elapsed time from the start of the temperature rising reached 160 hours (high temperature aging step). . Next, after the temperature of the battery assembly was lowered to 20 ° C., it was left to self-discharge for 5 days (self-discharge process).

  Next, the battery assembly having undergone the above self-discharge process was charged and discharged at a constant current at a constant current of 5 A until the voltage between the positive and negative terminals reached a predetermined leaving voltage, and left in that state for a certain period of time (low voltage Neglect process). Here, a plurality of battery assemblies were prepared, and the low voltage standing step was performed by changing the standing voltage and the standing time from each other. Specifically, the leaving voltage is set to 3V, 3.2V, 3.45V, 3.6V, 3.8V, 3.9V, and the leaving time is 0.5 hours, 1 hour, 3 hours, It was set to 5 hours, 12 hours, 24 hours, or 48 hours. Thus, an evaluation battery was produced. The initial capacity of the evaluation battery was evaluated. The results are shown in FIG.

  As shown in FIG. 3, in the low voltage standing step, each sample having a standing voltage of 3 V to 3.45 V and a standing time of 1 hour or more had a larger initial capacity than the other samples. From this result, it was confirmed that in the low voltage leaving step, the initial capacity can be improved by setting the leaving voltage to 3 V to 3.45 V and setting the standing time to 1 hour or more.

  Also, a plurality of batteries of each sample were prepared and adjusted to SOC 60%, and then an assembled battery was constructed in which the batteries were arranged and restrained in the arrangement direction. Thereafter, the assembled battery in a restrained state was left in a room temperature range, and the change in voltage change of each battery was measured. The results are shown in FIG. Sample 1 in FIG. 4 has a neglected voltage of 3.45 V and a standing time of 3 hours in the low voltage leaving step, sample 2 has a standing voltage of 3.45 V and a standing time of 5 hours, and sample 3 has a standing voltage. Was 3.45 V, and the standing time was 48 hours. As shown in FIG. 4, when the batteries of Samples 1 to 3 were left after voltage adjustment, a rapid voltage drop was observed. However, in sample 1 in which the standing time in the low voltage standing step is 3 hours, the voltage is stable enough to accurately determine whether or not there is a short-circuited cell in the stack self-discharge step in about one day. The number of days (hereinafter referred to as voltage stabilization days) until the end of the rapid voltage drop was shorter than in Samples 2 and 3.

  The graph of FIG. 5 shows the relationship between the standing time in the low voltage standing step and the voltage stabilization days for each sample in which the standing voltage in the low voltage standing step is 3V, 3.2V, and 3.45V. As shown in FIG. 5, the voltage stabilization days tended to decrease as the standing time decreased. In particular, by setting the standing time to 3 hours or less, it was possible to achieve an extremely short voltage stabilization day of approximately 1 day or less. The shorter the voltage stabilization days, the shorter the time until the voltage stabilizes in the stack self-discharge process, and the stack self-discharge process can be performed quickly. From this result, the standing time in the low voltage standing step is preferably about 3 hours or less, and more preferably 2 hours or less.

  The reason why the number of days for voltage stabilization is shortened as the standing time in the low voltage standing step is shorter is estimated as follows. That is, according to the knowledge of the present inventor, as shown in FIG. 6A, when the battery assembly is initially charged, lithium ions are released from the positive electrode active material layer 10 into the electrolytic solution. . At this time, in the negative electrode, lithium ions in the electrolytic solution enter the negative electrode active material layer 20 and are occluded in the negative electrode active material layer 20. In addition, lithium ions are occluded in a portion (opposing portion) 22 facing the positive electrode active material layer 10 in the negative electrode active material layer 20 at the beginning of charging, and face the positive electrode active material layer 10 as charging progresses. It is thought that it diffuses also to the part (non-opposing part) 24 which is not. That is, lithium ions are also occluded in the non-facing portion 24 of the negative electrode active material layer 20.

  On the other hand, when the discharge treatment is performed in the low voltage standing step, lithium ions occluded in the negative electrode active material layer 20 are released into the electrolytic solution as shown in FIG. 6B. At that time, first, lithium ions are preferentially released from the facing portion 22 of the negative electrode active material layer 20. As the lithium ions are released (as the discharge progresses), the potential of the facing portion 22 of the negative electrode active material layer 20 increases. Then, the potential difference between the facing portion 22 and the non-facing portion 24 of the negative electrode active material layer 20 gradually increases. In order to eliminate this potential difference, lithium ions move from the non-facing portion 24 of the negative electrode active material layer 20 to the facing portion 22 (see arrows in FIG. 6B). Such movement of lithium ions from the non-facing portion 24 to the facing portion 22 tends to increase as the standing time of the low-voltage standing step increases. That is, the longer the standing time in the low voltage standing step, the smaller the remaining amount of lithium ions in the non-facing portion 24.

  Thereafter, when voltage adjustment (charging process) for performing the stack self-discharge process is performed, lithium ions enter the negative electrode active material layer 20 again as shown in FIG. The opposite site 22 is occluded. As charging proceeds, the negative electrode active material layer 20 occludes lithium ions, and the potential of the facing portion 22 of the negative electrode active material layer 20 decreases. For this reason, in the negative electrode active material layer 20, the potential difference between the facing portion 22 and the non-facing portion 24 increases. In order to eliminate this potential difference, lithium ions move from the facing portion 22 of the negative electrode active material layer 20 to the non-facing portion 24.

  Here, when the remaining amount of lithium ions in the non-facing portion 24 of the negative electrode active material layer 20 is small, the potential difference between the facing portion 22 and the non-facing portion 24 is large. Ions move. Therefore, it takes a long time for the battery voltage to stabilize. On the other hand, if the remaining amount of lithium ions in the non-facing portion 24 of the negative electrode active material layer 20 is large, the potential difference between the facing portion 22 and the non-facing portion 24 is small. Do not move. Therefore, the battery voltage is stabilized in a relatively short time. For this reason, it is considered that the battery voltage is stabilized in a shorter time as the leaving time in the low voltage leaving step is longer.

  Although the lithium ion secondary battery according to one embodiment of the present invention has been described above, the secondary battery according to the present invention is not limited to any of the above-described embodiments, and various modifications can be made.

  As described above, the present invention can contribute to improving the performance of a battery (for example, a lithium ion secondary battery). The present invention is suitable for a lithium ion secondary battery for a vehicle driving power source such as a driving battery for a hybrid vehicle or an electric vehicle. That is, for example, the lithium ion secondary battery can be suitably used as a vehicle driving power source for driving a motor (electric motor) of a vehicle such as an automobile. The power source for driving the vehicle may be an assembled battery in which a plurality of secondary batteries are combined.

DESCRIPTION OF SYMBOLS 10 Positive electrode active material layer 20 Negative electrode active material layer 22 Opposite part 24 of negative electrode active material layer Non-opposite part of negative electrode active material layer S10 Battery assembly construction process S20 Initial charging process S30 High temperature aging process S40 Cell self-discharge process S50 Process S60 stack self-discharge process

Claims (1)

A method of manufacturing a non-aqueous electrolyte secondary battery comprising:
A battery assembly construction process for constructing a battery assembly in which an electrode body including a positive electrode and a negative electrode and a nonaqueous electrolyte solution are housed in a battery case;
An initial charging step for charging the battery assembly to a predetermined voltage value in a normal temperature range;
A high temperature aging step of holding the battery assembly in a predetermined high temperature region for a predetermined time;
A self-discharge step of self-discharging the battery assembly for a predetermined time in a normal temperature range; and
The battery assembly after the self-discharge step is discharged to a low voltage range of 3V to 3.45V, and then left in the low voltage range for 1 to 3 hours;
A method for producing a non-aqueous electrolyte secondary battery.

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