JP6478112B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a nonaqueous electrolyte secondary battery.

  In recent years, nonaqueous electrolyte secondary batteries such as lithium secondary batteries have been used as so-called portable power sources such as personal computers and portable terminals and vehicle power sources. In particular, a lithium secondary battery (lithium ion secondary battery) that is lightweight and obtains a high energy density is preferably used as a high-output power source for driving vehicles such as electric vehicles and hybrid vehicles.

  In the manufacture of this type of non-aqueous electrolyte secondary battery, generally, an electrode body having a structure in which a positive electrode and a negative electrode face each other with a separator interposed therebetween, and an electrolyte (typically, an electrolytic solution) are used. After the battery assembly is constructed, an initial charging process for applying a current between the positive electrode and the negative electrode is performed in order to adjust the battery assembly to a state where it can actually be used as a battery. Then, the battery assembly after the initial charging is subjected to an aging process under a predetermined temperature condition (typically in a high temperature environment), and then the performance of the battery assembly is confirmed (for example, IV resistance or self-discharge). It is common to perform inspection of characteristics). In the self-discharge characteristic test, a battery assembly adjusted to a predetermined charge state is left for a certain period, and a voltage drop during the left-handed (self-discharge) period is measured. Whether or not has occurred. Japanese Patent Application Laid-Open No. 2004-228561 describes a technique for performing an aging process on a battery assembly after an initial charging process at a predetermined temperature for a predetermined time.

International Publication No. 2011/024250

By the way, when manufacturing such a nonaqueous electrolyte secondary battery, metal foreign matters such as copper and iron may be mixed from the outside (for example, a component of a manufacturing apparatus). The mixed metal foreign matter is ionized (for example, Cu ²⁺ , Fe ²⁺ ) when it exceeds the dissolution potential by charging the battery, and is eluted into the electrolyte. This metal ion generally moves toward the negative electrode side and may be reduced and deposited on the negative electrode. When such metal deposits penetrate the separator and reach the positive electrode, there is a possibility that a minute short circuit (so-called internal short circuit) may occur inside the battery. The occurrence of an internal short circuit is not preferable because the battery performance deteriorates (for example, the energy density decreases).

In manufacturing the non-aqueous electrolyte secondary battery, the battery assembly is constructed, and after the initial charge, the aging treatment is performed to deposit the metal foreign matter mixed in the battery assembly in advance on the negative electrode. be able to. Thereby, when the battery is used, it is possible to prevent the occurrence of an internal short circuit due to the metal foreign matter mixed in the battery.
On the other hand, a battery in which an internal short circuit has occurred during the aging process is determined as an inferior product in the manufacturing process in subsequent performance confirmation (typically, inspection of self-discharge characteristics), which may increase the defect rate in the manufacturing process. There is. Therefore, from the viewpoint of mass production of batteries (from the viewpoint of manufacturing efficiency), it is desired to reduce the occurrence of internal short circuits due to metal foreign matters mixed in the battery assembly during the aging process.

  The present invention has been made in view of such a point, and the object thereof is to improve the efficiency of a highly reliable non-aqueous electrolyte secondary battery (in which an internal short circuit due to precipitation of metallic foreign matter mixed in the battery is unlikely to occur). It is to provide a method that can be mass-produced well.

In order to achieve the above object, according to the present invention, there is provided a method for producing a non-aqueous electrolyte secondary battery, which comprises the following steps (i) to (v): Is done. That is, the manufacturing method disclosed here is:
(I) a step of constructing a battery assembly using a positive electrode, a negative electrode, and a non-aqueous electrolyte;
(Ii) initial charging the battery assembly;
(Iii) a low temperature aging step in which the battery assembly after the initial charging is left at 15 ° C. or higher and 30 ° C. or lower for 6 hours or longer;
(Iv) a high temperature aging step in which the battery assembly after the low temperature aging step is allowed to stand at 60 ° C. for at least 20 hours; and (v) a step of self-discharging the battery assembly after the high temperature aging step.

The lower the temperature at which aging is performed, the slower the rate at which metal foreign matter mixed inside the battery assembly dissolves in the non-aqueous electrolyte. Thereby, the ionized foreign metal (metal ion) diffuses in the non-aqueous electrolyte and is thinly deposited on the negative electrode.
That is, by performing the low-temperature aging, it is possible to reduce the concentration of precipitates derived from the metal foreign matter on the negative electrode facing the portion where the metal foreign matter is present, and by the precipitate deposited on the negative electrode. It is possible to suppress the occurrence of an internal short circuit through the separator. Thereby, the incidence rate of inferior goods in a manufacturing process (namely, the defective rate in a manufacturing process) can be reduced, and the manufacturing efficiency of a battery can be improved.
Further, even if the metal foreign matter mixed inside the battery assembly remains undissolved in the low temperature aging, by performing the high temperature aging, the metal foreign matter is dissolved in the non-aqueous electrolyte and is previously formed on the negative electrode. It can be deposited. Thereby, it can suppress that an internal short circuit generate | occur | produces at the time of battery use.
As described above, according to the present invention, it is possible to efficiently mass-produce nonaqueous electrolyte secondary batteries in which the occurrence of internal short circuits during use of the battery is suppressed while suppressing the defective rate in the manufacturing process.

It is a flowchart which shows the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one embodiment of this invention. It is a graph which shows the relationship between the conditions (temperature and time) of low temperature aging, and the occurrence frequency of an internal short circuit. It is a graph which shows the influence which the average thickness of a separator and the time of low-temperature aging have on the occurrence frequency of an internal short circuit.

  Hereinafter, a method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. 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 following drawings, members / parts having the same action are described with the same reference numerals, and redundant descriptions may be omitted or simplified. Further, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

  In the present specification, the “secondary battery” generally refers to a battery that can be repeatedly charged and discharged, such as a so-called chemical battery such as a lithium secondary battery, a sodium secondary battery, and a nickel hydride secondary battery, and an electric double layer capacitor. It is a term encompassing the physical battery. In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier (supporting salt, supporting electrolyte) and is charged and discharged by the movement of lithium ions between the positive and negative electrodes.

  As shown in FIG. 1, the manufacturing method of the nonaqueous electrolyte secondary battery disclosed here includes a battery assembly construction step (S10), an initial charging step (S20), a low temperature aging step (S30), a high temperature aging step ( S40) and a self-discharge step (S50). Hereinafter, each step will be described.

  First, the battery assembly construction step (S10) will be described. Such a process includes constructing a battery assembly using a positive electrode, a negative electrode, and a non-aqueous electrolyte. Here, the positive electrode, the negative electrode, and the nonaqueous electrolyte are not particularly limited, and those similar to those used in a general nonaqueous electrolyte secondary battery can be used without particular limitation. Although not intended to be particularly limited, a typical example of the battery assembly disclosed herein will be described using a lithium secondary battery as an example. The lithium secondary battery is an example, and the technical idea of the present invention is also applied to other non-aqueous electrolyte secondary batteries (for example, sodium secondary batteries) having other charge carriers (for example, sodium ions).

  The battery assembly is typically constructed by constructing an electrode body using a positive electrode and a negative electrode, and housing the electrode body and a non-aqueous electrolyte in a battery case (exterior body). The shape of the battery case is not particularly limited, and may be, for example, a cylindrical shape or a cubic shape (box shape). Such battery cases typically have positive and negative terminals for external connection, a safety valve set to release the internal pressure in the battery case, and an inlet for injecting a nonaqueous electrolyte into the case. Is provided. As a material of such a battery case, for example, a metal material (for example, aluminum) that is lightweight and has good thermal conductivity is suitable.

  The electrode body is constructed by superposing the positive electrode and the negative electrode with a separator interposed therebetween. In addition, the structure of this electrode body is not specifically limited, For example, it can be a laminated electrode body (laminated electrode body) or a wound electrode body (wound electrode body).

  The negative electrode includes a negative electrode current collector and a negative electrode active material layer including at least a negative electrode active material formed on one or both surfaces of the negative electrode current collector. As said negative electrode collector, copper foil etc. can be used conveniently, for example. As the negative electrode active material, one type or two or more types of materials conventionally used for lithium secondary batteries can be used without any particular limitation. For example, a particulate (or spherical or scale-like) carbon material including a graphite structure (layered structure) at least partially, a lithium transition metal composite oxide (for example, a lithium titanium composite oxide such as Li4Ti5O12), a lithium transition metal composite Nitride etc. are mentioned. Examples of the carbon material include natural graphite, artificial graphite (artificial graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and the like. Alternatively, carbon particles in a form in which graphite particles as a core are coated (coated) with an amorphous carbon material may be used. Note that the negative electrode active material layer can contain components other than the active material, such as a binder and a thickener. As the binder, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

  For such a negative electrode, for example, a negative electrode active material and a material used as necessary are dispersed in an appropriate solvent (for example, water) to prepare a paste-like (slurry) composition, and an appropriate amount of the composition Can be formed by drying after applying to the surface of the negative electrode current collector. Moreover, the properties (for example, average thickness, active material density, porosity, etc.) of the negative electrode active material layer can be adjusted by performing an appropriate press treatment as necessary.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer including at least a positive electrode active material formed on one or both surfaces of the positive electrode current collector. As said positive electrode electrical power collector, aluminum foil etc. can be used conveniently, for example. As the positive electrode active material, one kind or two or more kinds of materials conventionally used for lithium secondary batteries can be used without any particular limitation. For example, a lithium composite metal oxide such as a layered structure or a spinel structure (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiFePO _4, etc.). Note that the positive electrode active material layer may include components other than the active material, such as a conductive material and a binder. As the conductive material, carbon black such as acetylene black (AB) and other (such as graphite) carbon materials can be suitably used. As the binder, PVdF or the like can be used.

  For such a positive electrode, for example, a positive electrode active material and a material used as necessary are dispersed in a suitable solvent (for example, N-methyl-2-pyrrolidone) to prepare a paste-like (slurry) composition, It can be formed by applying an appropriate amount of the composition to the surface of the positive electrode current collector and then drying it. Moreover, the properties (for example, average thickness, active material density, porosity, etc.) of the positive electrode active material layer can be adjusted by performing an appropriate press treatment as necessary.

  Examples of the separator include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). Although the thickness (average thickness) of a separator is not specifically limited, The thing of 10 micrometers or more can be used conveniently from a viewpoint of ensuring the insulation of a positive electrode and a negative electrode. Moreover, according to the technique disclosed here, even when a thin separator is used, the occurrence of an internal short circuit can be suppressed. For example, the thickness (average thickness) of the separator is less than 30 μm (typically Is preferably a thin separator having a thickness of 24 μm or less. By using a thin separator, the separator volume occupying the volume inside the battery case can be reduced, and the capacity of the battery can be increased.

  The property of the nonaqueous electrolyte is not particularly limited, and may be liquid, gel, or solid. Typically, a nonaqueous electrolytic solution containing a supporting salt in an organic solvent (nonaqueous solvent) can be used. Such a non-aqueous electrolyte exhibits a liquid state at normal temperature (for example, 25 ° C.). In a preferred embodiment, the non-aqueous electrolyte always exhibits a liquid state under a battery usage environment (for example, a temperature environment of 0 ° C. to 60 ° C.).

As the non-aqueous solvent, organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones that are used in an electrolytic solution of a general lithium secondary battery can be used. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate.
As the supporting salt, the same salt as that of a general lithium secondary battery can be used. For example, a lithium salt of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ or the like (preferably LiPF ₆ ) can be used. Such a supporting salt can be used singly or in combination of two or more. Moreover, the suitable range of the density | concentration of the support salt in a nonaqueous electrolyte can be set to 0.7 mol / L-1.3 mol / L (for example, 1.1 mol / L).

  In addition, in the said nonaqueous electrolyte, unless the effect of this invention is impaired remarkably, components (additives) other than the nonaqueous solvent mentioned above and supporting salt may be included. Examples of such additives may include various additives such as a film forming agent (for example, lithium fluorosulfonate); a gas generating agent; a dispersant; a thickener;

Next, the initial charging step (S20) will be described. In the initial charging step, the battery assembly is charged. 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 is performed to a predetermined voltage. Such charging processing may be performed by constant current charging (CC charging), or may be performed by constant current constant voltage charging (CCCV charging). Although the charging rate at the time of constant current charge is not specifically limited, For example, what is necessary is just to be about 0.1C-10C (typically 1C-3C). Here, “1C” refers to a current value that can charge the battery capacity (Ah) predicted from the theoretical capacity in one hour. For example, when the battery capacity is 4 Ah, 1C = 4A.
In addition, the voltage between the positive and negative terminals (typically the highest voltage reached) in the charging process depends on the active material used, the type of non-aqueous solvent, etc., but the SOC (State of Charge) of the battery assembly. A voltage range that can be shown when the charging depth is in the range of about 80% or more (typically 90 to 105%) may be used. For example, in a battery that is fully charged at 4.2 V, it can be set to about 3.8 V to 4.2 V (for example, 3.95 V to 4.05 V). In addition, the said charge process may be performed once, for example, can also be repeatedly performed twice or more on both sides of a discharge process process.

Next, the low temperature aging step (S30) will be described. This step includes leaving (holding) the battery assembly after the initial charging step under a temperature condition of 15 ° C. or higher and 30 ° C. or lower for a predetermined time. For example, the battery assembly can be left (maintained) under a predetermined temperature condition by means for accommodating the battery assembly in a constant temperature bath (in a temperature controlled constant temperature bath) set to a predetermined temperature.
Here, if the temperature at which the battery assembly is left (held) is too low, the speed at which the metal foreign matter mixed in the battery assembly is dissolved in the non-aqueous electrolyte is too slow, and most of the metal foreign matter remains undissolved. May end up. Such undissolved metallic foreign matter tends to be dissolved in the non-aqueous electrolyte and locally deposited on the negative electrode in a high-temperature aging process described later, which may cause an internal short circuit. In addition, if the temperature at which the battery assembly is left (held) in the low temperature aging process is too high, the speed at which the metal foreign matter mixed in the battery assembly dissolves in the nonaqueous electrolyte becomes too high, Dispersion of dissolved metal foreign matter (metal ions) in the non-aqueous electrolyte tends to be insufficient. For this reason, since the metal foreign material (metal ion) melt | dissolved in the nonaqueous electrolyte deposits locally on a negative electrode and an internal short circuit may generate | occur | produce, it is unpreferable.

  In the low temperature aging process, the battery assembly is allowed to stand (hold) for 6 hours or more under the above temperature condition, so that the effect of suppressing the occurrence of an internal short circuit in the battery manufacturing process can be suitably exhibited. The time for performing such low-temperature aging is not particularly limited as long as it is 6 hours or longer. For example, it can be 12 hours or longer (for example, 24 hours or longer, typically 48 hours or longer). In consideration of the production efficiency of the battery, the time for the low temperature aging step can be, for example, 96 hours or less (typically 72 hours or less).

  Next, the high temperature aging step (S40) will be described. This step includes leaving (holding) the battery assembly after the low temperature aging for a predetermined time under a temperature condition higher than that of the low temperature aging step.

The temperature condition and the standing time in the high temperature aging process are not particularly limited, and may be set as appropriate according to the configuration of the battery. For example, the temperature condition for leaving (holding) the battery assembly may be 40 ° C. or higher (eg, 60 ° C. or higher, typically 60 ° C. ± 3 ° C.). If the temperature at which the battery assembly is left (held) in such a high temperature aging process is too high, the constituent materials of the battery assembly (for example, separators, non-aqueous electrolytes, etc.) are altered (deteriorated), which is not preferable. For this reason, the temperature condition in the high temperature aging step is a temperature lower than the heat resistance temperature of a material (typically a separator) that is most likely to change due to a temperature rise among the constituent materials of the battery assembly, for example, 100 ° C. or lower ( For example, it may be 90 ° C. or lower, typically 80 ° C. or lower). As a method for holding the battery assembly under the above temperature condition (high temperature condition), a conventionally known heating means can be preferably used. For example, the battery assembly is housed in a heating vessel such as a thermostat (temperature controlled thermostat) set at a predetermined temperature, or heated from the outside of the battery assembly using a heating means such as an infrared heater. Can be performed.
The time for which the battery assembly is left (held) can be, for example, 10 hours or longer (typically 15 hours or longer). If the time for which the battery assembly is left (held) is too long, the time required for manufacturing the battery is extended, and the manufacturing efficiency tends to decrease. For this reason, it can be, for example, 200 hours or less (typically 180 hours or less, generally 48 hours or less). Specifically, it may be left (held) for about 20 hours (generally 20 hours ± 2 hours) under the above temperature conditions.

  In the low temperature aging process and the high temperature aging process, it is preferable to maintain a relatively high terminal voltage range and / or a relatively high SOC range for the battery voltage throughout these processes. For example, it is preferable to perform the low temperature aging process and the high temperature aging process on a battery assembly in a charged state of SOC 65% or more (for example, SOC 80% or more) while maintaining the SOC range. Alternatively, for example, in a battery that is fully charged at 4.2 V, it is preferable to perform the low-temperature aging step and the high-temperature aging step within a range in which the voltage between the positive and negative electrodes is maintained at about 3.7 to 4.2 V. For this purpose, a voltage maintaining method such as constant voltage charging can be appropriately employed in these steps.

  Next, the self-discharge process (S50) will be described. Such a process includes adjusting the battery assembly after the high-temperature aging to a predetermined charging depth (typically, low SOC) and allowing it to stand for a certain period of time for self-discharge. Then, the battery assembly whose voltage has decreased in the self-discharge process can be determined (evaluated) as a battery assembly in which an internal short circuit has occurred. That is, the self-discharge process may include measuring a voltage drop amount (battery voltage difference before and after being left).

  In the self-discharge process, the battery assembly after the high-temperature aging is typically self-discharged for a certain time in a normal temperature range. Here, “normal temperature” means a temperature (room temperature, environmental temperature) defined in JIS Z8703 (1983). Specifically, it means a temperature in the range of 20 ° C. ± 15 ° C. (5 ° C. to 35 ° C.). Here, it is preferable to set the environmental temperature for performing the self-discharge in a range of 15 ° C to 25 ° C. Typically, during the self-discharge process, for example, it is preferable to always keep the temperature of the battery assembly constant by using a thermostat (temperature control thermostat) set to a predetermined temperature. Typically, such a self-discharge step causes the battery assembly to self-discharge (leave), for example, for several days or more (typically 2-3 days or more, generally 5 days or more). The standing time is preferably 20 days or less (more preferably 15 days or less) from the viewpoint of production efficiency. For example, it may be left for about 10 days.

  In the above self-discharge process, the rate at the time of discharge may be, for example, about 0.1 to 10C. The voltage between the positive and negative terminals at the start of the self-discharge process is a voltage range that can be shown when the SOC of the battery assembly is approximately 10% or less (typically 1 to 10%, for example 1 to 5%). It can be. For example, in the case of a battery that is fully charged at 4.2 V, it is preferable to adjust it to a range of about 3.1 to 3.5 V. Alternatively, after the high temperature aging process, the self-discharge process is started without adjusting the state of charge (typically, the discharge process) (that is, the terminal voltage between the positive and negative electrodes at the end of the high temperature aging process). Also good. For example, in a battery that is fully charged at 4.2 V, the self-discharge process may be started in a state where the voltage between the positive and negative electrodes is approximately 3.7 to 4.2 V. The discharge process may be performed once, for example, it may be repeated twice or more with the charge process interposed therebetween.

  Then, based on the measurement result of the voltage drop obtained in the self-discharge process, a reference value for non-defective product determination is set. The method for setting the reference value is not particularly limited. For example, an arithmetic average value, median value (median), or the like of the voltage drop amounts of a plurality of battery assemblies may be employed. Then, the difference between the reference value and the voltage drop amount of each battery assembly is calculated, and when the difference is equal to or less than a predetermined threshold value, the battery assembly is determined to be “no internal short circuit”, and the difference is determined to be a predetermined value. When the threshold value is exceeded, the battery assembly is determined as “with internal short circuit”. The threshold value may be set to a value corresponding to, for example, about 2σ to 4σ (σ means standard deviation), although depending on the standard of the target battery. By removing the battery assembly determined to be “with internal short circuit” based on the determination result, it is possible to prevent a defective product from flowing to a subsequent process, and to provide a highly reliable battery.

  According to the manufacturing method disclosed herein, it is possible to suppress the metal foreign matter from being concentrated on the negative electrode during battery manufacturing (typically the aging process), and to reduce the defective rate in the manufacturing process. Can do. Moreover, the nonaqueous electrolyte secondary battery manufactured by the method disclosed here is characterized by high reliability (internal short circuit is suppressed). That is, according to the manufacturing method disclosed herein, secondary batteries that are less likely to cause an internal short circuit can be mass-produced efficiently. A battery manufactured by such a manufacturing method can be used for various applications. For example, as a driving power source mounted on a vehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), or an electric vehicle (EV). It can be used suitably.

  Several examples (test examples) relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

  Lithium secondary batteries with different thicknesses (average thickness) of separators used for battery construction and low-temperature aging process conditions (temperature conditions and time) were constructed by the following materials and processes. Here, 10 lithium secondary batteries were constructed under the same conditions, and the number of batteries in which an internal short circuit occurred in the manufacturing process was counted.

[Construction of lithium secondary battery]
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are combined with LNCM: AB : PVdF = 90: 8: 2 was mixed with N-methylpyrrolidone (NMP) at a mass ratio to prepare a paste-like (slurry) positive electrode active material layer forming composition. This composition was applied to both sides of a long aluminum foil (positive electrode current collector) in a strip shape, dried and pressed to produce a positive electrode.

  Graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, at a mass ratio of C: SBR: CMC = 98: 1: 1 A paste-like (slurry) negative electrode active material layer forming composition was prepared by dispersing in water. The composition was applied in a strip shape on both sides of a long copper foil (negative electrode current collector), dried and pressed to prepare a negative electrode.

  The positive electrode and the negative electrode produced by the above method were overlapped in the longitudinal direction via two separators having a three-layer structure in which a porous polypropylene layer was formed on both sides of the porous polyethylene layer, and wound in the longitudinal direction. Later, flattened wound electrode bodies were fabricated by crushing and labbing. Here, as the separator, those having an average thickness of 10 μm, 16 μm, 24 μm, or 30 μm were prepared, and those having the same thickness were used in combination. Here, with respect to the battery assembly according to each example, in order to reproduce the state in which metal foreign matter is mixed between the positive electrode and the negative electrode, the average particle diameter is between the positive electrode and the negative electrode (here, between the positive electrode and the separator). Mixed with 50 μm copper powder.

Next, the wound electrode body and the nonaqueous electrolyte were accommodated in a rectangular battery case (made of aluminum) to construct a battery assembly. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 1: 1: 1 is used as a supporting salt. Of LiPF ₆ dissolved at a concentration of 1 mol / L was used.

  The battery assembly constructed as described above was initially charged. Here, under a temperature environment of 25 ° C., after performing constant current charging (CC charging) at a charging rate of 5 C (constant current) until the voltage between the positive and negative terminals reaches 3.97 V, the current value is Constant voltage charging (CV charging) was performed until the temperature reached 0.2C. Next, for the battery assembly after the initial charging, 0 hours, 3 hours, 6 hours, 12 hours, 24 hours under the temperature conditions of 10 ° C, 15 ° C, 25 ° C, 30 ° C, or 45 ° C, Low temperature aging was performed by standing for 48 hours or 72 hours. And each battery assembly after the said low-temperature aging was left to stand for 20 hours on 60 degreeC temperature conditions, and high temperature aging was performed.

  Each battery assembly after the high-temperature aging treatment was cooled to a normal temperature range (about 20 ° C. in this case), and then the battery assembly was left to stand for 5 days at 20 ° C. for self-discharge. Then, the voltage drop amount was calculated by subtracting the voltage value after self-discharge from the voltage value before self-discharge, and the occurrence of an internal short circuit was evaluated based on the voltage drop amount.

  FIG. 2 shows the relationship between the time of low temperature aging and the number of battery assemblies in which an internal short circuit occurred when each battery assembly constructed using two separators with a thickness of 16 μm was subjected to low temperature aging under different temperature conditions. Indicates. As shown in FIG. 2, the battery assembly after the initial charging is allowed to stand for 6 hours or more in a temperature condition of 15 ° C. or more and 30 ° C. or less before performing high temperature aging, thereby performing low temperature aging. It was confirmed that the frequency of occurrence of internal short circuits in the manufacturing process was significantly reduced.

FIG. 3 shows the relationship between the time of low temperature aging and the number of battery assemblies in which an internal short circuit occurred when each battery assembly constructed using separators having different thicknesses was subjected to low temperature aging under a temperature condition of 25 ° C. Show. As shown in FIG. 3, the battery assembly using a thin separator (for example, an average thickness of 10 μm to 24 μm) has a high frequency of internal short circuits when low temperature aging is not performed. However, even in a battery assembly constructed using these thin separators, internal short-circuiting can be performed in the battery manufacturing process by performing low-temperature aging for 6 hours or more after initial charging and before high-temperature aging. It has been confirmed that the occurrence of can be highly suppressed.
From these results, according to the technique disclosed herein, the non-aqueous electrolyte secondary battery in which internal short circuit caused by the metal foreign matter mixed in the battery assembly is highly suppressed can be efficiently performed (the defective rate in the manufacturing process). It was confirmed that it can be manufactured).

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

Claims (1)

A method of manufacturing a non-aqueous electrolyte secondary battery comprising:
Building a battery assembly using a positive electrode, a negative electrode, and a non-aqueous electrolyte;
Initial charging the battery assembly;
A low-temperature aging step in which the battery assembly after the initial charge is allowed to stand at 15 ° C. or higher and 30 ° C. or lower for 6 hours or longer in a SOC of 80% or higher ;
A high temperature aging step in which the battery assembly after the low temperature aging step is allowed to stand at 60 ° C. or higher for at least 20 hours in a range of SOC 80% or higher ; and a step of self-discharging the battery assembly after the high temperature aging step;
A method for producing a non-aqueous electrolyte secondary battery.

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