JP2014225368A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a reliable battery for a short time which enables the highly accurate detection and rejection of defective products.SOLUTION: A method for manufacturing a nonaqueous electrolyte secondary battery comprises: a step (S10) of constructing a battery assembly; a conditioning step (S20) of performing a charging treatment on the battery assembly; a first inspection step (S30) of detecting an IV resistance by charging and discharging the battery assembly while raising the temperature of the assembly to a high-temperature region of 40°C or higher; a high-temperature aging step (S40) of holding the battery assembly in the high-temperature region; a second inspection step (S50) of detecting the IV resistance by charging and discharging the battery assembly after lowering the temperature of the battery assembly; and a step (S60) of making comparison between results of the first and a second inspection step to make determination on whether each battery assembly is defective or not, and removing a battery assembly determined to be defective.

Description

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

  Nonaqueous electrolyte secondary batteries such as lithium-ion batteries are lighter and have higher energy density than existing batteries, and thus have been preferably used in recent years for high-output power supplies mounted on vehicles. In manufacturing this type of battery, it is common to perform a conditioning process (initial charge) on the constructed battery assembly and then perform an aging process in a high-temperature environment. When a battery assembly is held under a high temperature environment, for example, when the assembly has some trouble, a decrease in performance appears remarkably. Therefore, a method of inspecting a battery assembly using such an aging process is widely used. It has been. For example, Patent Document 1 discloses an inspection method in which the voltage between terminals before and after the aging process is measured, and the presence or absence of conductive foreign matter is determined based on whether or not the difference (voltage drop amount) is within a predetermined threshold. ing.

Japanese Patent Laid-Open No. 2005-158643

  However, according to the study of the present inventor, in the method of Patent Document 1, a battery assembly whose performance is deteriorated due to some influence (typically high temperature aging) derived from the manufacturing process flows into the subsequent process. was there. For this reason, it is required to accurately detect a decrease in performance derived from the manufacturing process. In addition, since the conditioning process is usually performed in a room temperature range, it is necessary to raise the temperature of the battery assembly to a high temperature range during the aging process. Since this heating requires a relatively long time, shortening the heating time has been a problem.

  The present invention has been created in view of such a conventional situation, and its purpose is to manufacture a highly reliable non-aqueous electrolyte secondary battery that can detect and eliminate defective products with high accuracy and in a shorter time. Is to provide a way to do.

In order to achieve the above object, according to the present invention, the following steps (1) to (6):
(1) A battery assembly construction process in which an electrode body having a positive electrode and a negative electrode and a nonaqueous electrolyte are housed in a battery case in a normal temperature range;
(2) A conditioning process in which the battery assembly is charged in a normal temperature range;
(3) A first inspection step of detecting IV resistance by performing at least one constant current charge / discharge on the assembly while raising the battery assembly to a high temperature range of 40 ° C. or higher;
(4) A high-temperature aging step of holding the battery assembly in the high-temperature range for at least 5 hours;
(5) a second inspection step of detecting IV resistance by performing at least one constant current charge / discharge on the battery assembly after the battery assembly is cooled to a normal temperature range;
(6) A step of comparing the result of the first inspection step with the result of the second inspection step to determine the quality of the battery assembly and removing the battery assembly determined to be defective (hereinafter referred to as “non-defective product determination step”). ").);
A method for producing a non-aqueous electrolyte secondary battery is provided.

In the manufacturing method disclosed herein, before and after the high-temperature aging process, that is, in the first inspection process and the second inspection process, one or more charge / discharge tests are performed to detect the IV resistance value. Then, in the non-defective product determination step, the obtained IV resistance values are compared. As a result, it is possible to quantitatively accurately grasp the deterioration in performance resulting from the manufacturing process (typically high temperature aging). Therefore, according to this manufacturing method, it is possible to prevent a defective product from flowing into a subsequent process and efficiently remove it before shipping. Thereby, a battery with higher reliability can be provided. In addition, by performing charging and discharging at the same time as the temperature increase after the conditioning process, it is possible to shorten the time required for the temperature increase as compared with the conventional case. This is preferable from the viewpoint of work efficiency and productivity.
Here, the normal temperature range refers to 20 ° C. ± 15 ° C. (that is, for example, 5 to 35 ° C., preferably 10 to 30 ° C., more preferably 20 to 30 ° C.).

It is a flowchart of the manufacturing method which concerns on one Embodiment. It is a graph which shows a time-dependent change of temperature and voltage in the 1st inspection process-the 2nd inspection process. It is a graph which shows the relationship between the required time of a 1st test process, and a charging current.

  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 implementation 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.

  The manufacturing method disclosed here is a manufacturing method including a step of charging and discharging the battery assembly simultaneously with the temperature rise before the high temperature aging treatment, and specifically, shown in the flowchart of FIG. 1 (S10) to (S60). These steps are included. Hereinafter, each process is demonstrated in order.

(S10) Battery Assembly Construction Step Here, an electrode body having at least a positive electrode and a negative electrode and a non-aqueous electrolyte are accommodated in a battery case in a normal temperature range to construct a battery assembly. As the battery case, for example, a lightweight metal material such as aluminum can be preferably used. Note that the battery assembly refers to a general assembly that has been assembled up to the stage prior to the conditioning process, and the type and configuration of the battery are not particularly limited. For example, the battery case may be before sealing or after sealing.

The electrode body is constructed by laminating a positive electrode and a negative electrode, typically via a separator.
As a positive electrode, the thing of the form which adhered the positive electrode active material on the positive electrode electrical power collector as a composition with a electrically conductive material, a binder, etc., and formed the positive electrode active material layer can be used. As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum) can be suitably employed. Examples of the positive electrode active material include lithium composite metal oxides such as layered and spinel (for example, LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO _4, etc.) can be suitably employed. As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be adopted. As the binder, various polymer materials such as polyvinylidene fluoride (PVdF) and polyethylene oxide (PEO) can be adopted.

  As the negative electrode, it is possible to use a negative electrode active material layer in which a negative electrode active material is deposited on a negative electrode current collector as a composition together with a binder or the like. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper) can be suitably used. As the negative electrode active material, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), or the like can be used, and among them, graphite can be preferably used. As the binder, various polymer materials such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE) can be adopted.

  As the separator, a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. Especially, what equips one side or both surfaces of the said porous resin sheet with a porous heat resistant layer is preferable. Note that in a battery using a solid electrolyte (lithium polymer battery), the electrolyte can also serve as a separator.

As the nonaqueous electrolyte, typically, a nonaqueous solvent containing a supporting salt is used. Alternatively, the liquid non-aqueous electrolyte may be added with a polymer to form a solid (typically a so-called gel). As the supporting salt, lithium salt, sodium salt, magnesium salt and the like can be used, and among them, lithium salts such as LiPF ₆ and LiBF ₄ can be preferably used. As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used.

(S20) Conditioning Step Here, at least one charge process is performed on the constructed battery assembly in a 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 (typically constant current charging) is performed to a predetermined voltage range. As a result, a part of the non-aqueous electrolyte (typically a non-aqueous solvent) is reduced and decomposed at the negative electrode, and a film made of the decomposition product is formed on the surface of the negative electrode active material. The rate at the time of charge at this time can be about 0.1-10C, for example. Further, the voltage between the positive and negative terminals (typically the highest voltage reached) depends on the type of the non-aqueous solvent used, but can be about 3.9 to 4.2 V, for example. The charging process may be performed once. For example, the charging process may be repeated twice or more with the discharge process interposed therebetween. The end voltage may be a voltage range that can be indicated when the state of charge (SOC) of the battery assembly is in the range of approximately 90 to 105%. For example, in the case of a battery that is fully charged at 4.2 V, it is preferable to adjust the voltage between the positive and negative electrodes after the end of this step to a range of approximately 3.8 to 4.2 V. For example, in the Example mentioned later, the voltage between positive / negative electrodes after the completion | finish of this process is 3.95V.

(S30) First Inspection Step Here, the battery assembly after the conditioning step is heated to a high temperature range of 40 ° C. or higher (eg, 40 to 80 ° C., preferably 60 to 70 ° C.) while the battery assembly is heated. Constant current charge / discharge is performed at least once (for example, 2 to 10 times). This makes it possible to detect and grasp the performance before high-temperature aging (for example, the IV resistance calculated based on the current (I) -voltage (V) curve and the discharge capacity in a predetermined voltage range). In addition, the time required for this step can be shortened by raising the temperature while charging and discharging at a constant current. As a method for raising the temperature of the battery assembly, for example, heating means such as a temperature controlled thermostat or an infrared heater can be used.

  FIG. 3 shows the relationship between the time required for this step and the charging current. As is clear from FIG. 3, the time required for raising the temperature of the battery assembly can be shortened by setting the current during charging higher. For example, when the charging current is set to 60 A, the time required for the temperature rise is about 100 minutes (for example, 95 to 100 minutes). For example, when the charging current is set to 120 A, the time required for temperature increase is about 60 minutes (for example, 55 minutes to 60 minutes). For this reason, it is preferable to determine the electric current value at the time of charging / discharging considering the viewpoint of work efficiency and the viewpoint of measurement accuracy, and although it does not specifically limit, For example, it can be set as about 0.1C-5C. The rate may be the same during charging and discharging, or may be different.

  The voltage between the positive and negative electrodes is preferably set to a relatively high voltage range between terminals and / or a relatively high SOC range throughout the process. 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. In other words, it is preferable to set the charge / discharge conditions so that the maximum value (maximum voltage) and the minimum value (minimum voltage) of the inter-terminal voltage in this step are within the above voltage range. Moreover, after a constant current charge and / or after a constant current discharge, a constant voltage charging / discharging process or a rest can be appropriately sandwiched. For example, in the embodiment described later, first, constant voltage charging is performed for a certain period of time, then constant current discharging is performed until the voltage between the positive and negative electrodes reaches a predetermined voltage, and after a short pause, constant current charging is performed until the voltage at the start of charging. To do. This is one cycle and is repeated four times here.

(S40) High temperature aging process Here, the battery assembly after the first inspection process is at least 5 hours in the high temperature range (for example, a total time from the start of temperature increase (S30) is 5 to 48 hours, preferably Hold (leave) until 10-24 hours. As a result, the film formed on the surface of the negative electrode active material can be modified to a good quality, and the resistance of the negative electrode can be effectively reduced. Therefore, excellent battery performance (for example, cycle characteristics) can be realized. As a method for holding the battery assembly in the high temperature range, the same means as in the first inspection step can be used.

(S50) Second Inspection Step Here, after the temperature of the battery assembly after the high-temperature aging step is lowered to a normal temperature range, the battery assembly is charged and discharged at a constant current at least once. Thereby, the performance (typically IV resistance) after high temperature aging can be detected and grasped. In addition, the charging / discharging conditions (for example, a voltage range and charging / discharging electric current value) in this process can be made the same as that of the said 1st test process.

(S60) Non-defective Product Determination Step Here, first, the result of the first inspection step (IV resistance value) and the result of the second inspection step (IV resistance value) are compared to determine the quality of the battery assembly. For example, the IV resistance value before the process is subtracted from the IV resistance value after the high temperature aging process to calculate the increase amount of the IV resistance. Thereby, it is possible to quantitatively evaluate and grasp a change in battery performance due to some influence (typically high-temperature aging) derived from manufacturing conditions.
Thereafter, a non-defective product reference value that serves as a reference value for non-defective product determination is set based on the calculation result of the resistance increase amount. The method for setting the non-defective product reference value is not particularly limited. For example, an arithmetic average value or a median value (median) of resistance increase amounts of a plurality of battery assemblies may be employed. Then, the difference between the non-defective product reference value and the resistance increase 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 “good”, Is exceeded, the battery assembly is determined to be “defective”. The threshold value may be set to a value corresponding to, for example, about 2σ to 3σ (σ means standard deviation), although depending on the standard of the target battery. According to such a method, it becomes easy to find a defect of an individual battery assembly. For this reason, it is possible to prevent a defective product from being determined as a non-defective product and generating a defective product more than necessary in a later process. Then, by removing the battery assembly determined as “defective” 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. .

  The nonaqueous electrolyte secondary battery manufactured by the method disclosed herein can be excellent in reliability. Therefore, it can be suitably used for various applications. In particular, it can be suitably used as a power source (drive power source) for a motor mounted on a high capacity battery having a theoretical capacity of about 10 to 100 Ah, such as a plug-in hybrid vehicle (PHV).

  Hereinafter, the manufacturing method of the battery disclosed here will be described in more detail by taking as an example the case of manufacturing a lithium ion battery as one embodiment.

Li _1.005 Ni _0.38 Co _0.32 Mn _0.30 Zr _0.005 O ₂ powder as the positive electrode active material powder, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder in a mass ratio of 91: 6 : It mixed with N-methylpyrrolidone (NMP) so that it might be set to 3, and the slurry-like composition was prepared. This composition was applied to a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm to form a positive electrode active material layer. The obtained positive electrode was dried and pressed to produce a sheet-like positive electrode (positive electrode sheet).

  Next, ion exchange is performed so that the amorphous carbon (fired at 1300 ° C.) powder, the styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) as the negative electrode active material have a mass ratio of 98: 1: 1. A slurry-like composition was prepared by mixing with water. This composition was applied to a long copper foil (negative electrode current collector) having a thickness of about 10 μm to form a negative electrode active material layer. The obtained negative electrode was dried and pressed to prepare a sheet-like negative electrode (negative electrode sheet).

Next, the positive electrode sheet and the negative electrode sheet prepared above are combined with a separator (here, a porous heat-resistant layer on one side of a base material having a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer) And is wound so that the porous heat-resistant layer faces the positive electrode.) And the resulting wound electrode body is crushed from the lateral direction and ablated. Was formed into a flat shape. 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 accommodated in a battery case and a non-aqueous electrolyte was injected. 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 30:40:30, and LiPF ₆ as an electrolyte are approximately. Those dissolved at a concentration of 1 mol / L were used. Then, a battery assembly was constructed by attaching a lid to the opening of the battery case and welding and joining (S10 in FIG. 1).

  Next, the battery assembly constructed as described above was conditioned at a constant current and a constant voltage up to 4.2 V at a charging rate of 0.3 C, and at a temperature of 25 ° C. The charge-discharge process of repeating the operation of discharging at a constant current and constant voltage up to 3.0 V at a discharge rate of 3 times was performed, and then the voltage between the positive and negative electrodes was adjusted to 3.95 V (S20 in FIG. 1). In this way, two nonaqueous electrolyte secondary batteries having the same conditions for S10 and S20 were produced.

<Example>
In this example, the battery assembly constructed as described above was placed in a temperature-controlled thermostat and heated to 60 ° C., and constant current charge / discharge was performed in a pattern as shown in FIG. 2 to detect IV resistance. Specifically, first, constant voltage charging is performed for approximately 10 minutes, then constant current discharging is performed at 60 A until the voltage between the positive and negative electrodes reaches 3.75 V, and after a short pause of several minutes, charging is started. The battery was charged at a constant current of 60 A up to a voltage (3.95 V). This was defined as one cycle, and was repeated four times here (S30 in FIG. 1). As a result, it took about 98 minutes to raise the temperature to 60 ° C.

<Comparative example>
In this example, the battery assembly constructed as described above was installed in a temperature-controlled thermostat and only the temperature was raised. As a result, the time required to raise the temperature to 60 ° C. was 150 minutes, which is approximately 1.5 times that of the example. From the above results, the temperature of the battery assembly is raised to a desired temperature in a relatively short time by passing through the first inspection process disclosed herein (that is, charging and discharging at the same time as the temperature rise). I knew it could be.

Next, as shown in FIG. 2, the battery structures according to the above examples and comparative examples are held in an environment of 60 ° C. until the elapsed time from the start of temperature increase reaches 20 hours, and a high temperature aging treatment is performed. (S40 in FIG. 1).
Next, as shown in FIG. 2, after the battery assembly is cooled to a normal temperature range, the battery assembly is charged and discharged at a constant current with the same charge / discharge pattern as that at the time of the temperature increase (first inspection step). The IV resistance was detected (S50 in FIG. 1). Then, by calculating the amount of increase in resistance due to the high temperature aging process from the obtained IV resistance value, it was possible to quantitatively evaluate and grasp the change in battery performance (S60 in FIG. 1).

  The non-aqueous electrolyte secondary battery (for example, lithium ion battery) according to the present invention is capable of outputting a large current and is excellent in reliability as described above, so that it is particularly used for a motor (electric motor) mounted on a vehicle such as an automobile. It can be suitably used as a power source.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims (1)

A method of manufacturing a non-aqueous electrolyte secondary battery comprising:
A process for constructing a battery assembly in which an electrode body having a positive electrode and a negative electrode and a nonaqueous electrolyte are housed in a battery case in a normal temperature range;
A conditioning process in which the battery assembly is charged in a room temperature range;
A first inspection step of detecting IV resistance by performing at least one constant current charging / discharging of the battery assembly while raising the temperature of the battery assembly to a high temperature range of 40 ° C. or higher;
A high temperature aging step of holding the battery assembly in the high temperature region for at least 5 hours;
A second inspection step of detecting IV resistance by performing at least one constant current charge / discharge on the battery assembly after the battery assembly is cooled to a normal temperature range; and a result of the first inspection step; Comparing the results of the second inspection step and determining the quality of the battery assembly and removing the battery assembly determined to be defective;
A method for producing a non-aqueous electrolyte secondary battery.

Images