JP2002352864A - Method for testing secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for testing a secondary battery by which the secondary battery can be tested safely at low cost. SOLUTION: The method for testing the secondary battery of this invention includes a step of discharging and charging that carries out discharging and charging in the secondary battery treated initial discharging and charging treatment under a discharging and charging current larger than that of the initial discharging and charging current of the initial discharging and charging treatment. The test of the secondary battery is carried out in a short time so that the lowering of battery characteristics is induced by short-circuited a minute place and a place with a possibility of short-circuit in future in the battery are short-circuited by carrying out discharging and charging with a discharging and charging current larger than that of the initial discharging and charging current in the method of testing of the secondary battery of this invention.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery inspection method, and more particularly, to a secondary battery inspection method capable of inspecting a defective battery.

[0002]

2. Description of the Related Art To manufacture a secondary battery, first, a positive electrode and a negative electrode with a separator interposed are inserted into a battery case, and an electrolytic solution is injected into the battery case. Thereafter, the battery case is manufactured by sealing the opening of the case and sealing the battery case. Note that the battery in which the opening of the battery case is sealed is not subjected to the chemical conversion treatment, and thus is a secondary battery that is subjected to the initial charge / discharge treatment and can be charged / discharged.

[0003] A normal secondary battery is charged and discharged after the battery is manufactured, and the battery capacity is inspected. Further, the battery has been stored for a long time while being charged to some extent, and an inspection for measuring a decrease in battery voltage or battery capacity has been performed. That is, in order to improve the reliability of the secondary battery, it is essential to eliminate a battery having a low battery capacity and a secondary battery having a large decrease in battery voltage and a large self-discharge during storage.

For example, when a battery pack is formed by electrically connecting a plurality of secondary batteries, if there is a defective battery in the combined secondary batteries, the performance and safety of the battery pack will be extremely large. This is because a problem arises.

[0005] Conventional inspections for checking a decrease in the battery voltage or battery capacity of a secondary battery have been performed by storing the battery in a charged state for a long period of time. In addition, large storage equipment costs and storage periods have been required. The cost required for this preservation has increased the cost of the secondary battery.

In addition, in a lithium secondary battery, there is an irreversible reaction accompanied by the formation of a film on the negative electrode, and the state of the battery material of the positive and negative electrodes changes due to charging and discharging, so that the capacity characteristics and internal resistance change. For such reasons, a battery charge / discharge test for several cycles is initially performed.

In an evaluation method for storing a secondary battery for a long time in a state of being charged to some extent, there is a storage method in which the storage temperature of the secondary battery is set to a high temperature for the purpose of shortening the storage time in a charged state. That is, this is an evaluation method for promoting the electrode reaction of the secondary battery by increasing the temperature.

However, storage of a secondary battery at a high temperature has a safety problem since thermal energy is applied to a battery having a large energy. In other words, not only the energy charged in the battery but also the energy of the reaction between the electrolyte and the electrode material due to the thermal energy is added, and if there is an abnormality such as a short circuit, the battery may generate heat or increase in internal pressure. Get higher. In addition, the heating may cause a side reaction between the electrolyte and the electrode material, which may cause a decrease in battery capacity or an increase in resistance.

Further, storage of the secondary battery at a high temperature requires a heating device such as a heater, which has a problem of increasing equipment cost of storage equipment.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a secondary battery inspection method capable of inspecting a secondary battery safely and at low cost.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have repeatedly studied a method for inspecting a secondary battery, and as a result, a specific charge / discharge has been performed on a secondary battery which has been subjected to an initial charge / discharge process. It has been found that the above problem can be solved by using an inspection method having a charge / discharge step of performing charge / discharge under conditions.

That is, the inspection method of a secondary battery according to the present invention provides a method of charging a secondary battery that has been subjected to an initial charge / discharge process with a charge / discharge current having a current value larger than the initial charge / discharge current of the initial charge / discharge process. A charge / discharge step of performing discharge, and a measurement step of measuring a change in battery characteristics of the secondary battery subjected to the charge / discharge step,
It is characterized by having.

According to the inspection method for a secondary battery of the present invention, by performing charging / discharging with a charging / discharging current having a current value larger than the initial charging / discharging current, there is a possibility that a minute short-circuit portion in the battery and a short-circuit in the future may occur. Some parts are short-circuited. Since this short circuit causes deterioration of the battery characteristics, the inspection of the secondary battery can be performed in a short time.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A method for inspecting a secondary battery according to the present invention comprises:
It has a charge / discharge step and a measurement step.

The charging / discharging step is a step of charging / discharging the secondary battery which has been subjected to the initial charging / discharging process with a charging / discharging current having a current value larger than the charging / discharging current in the initial charging / discharging process. In other words, the charging / discharging step is a step of performing charging / discharging with the charging / discharging current, whereby the charging / discharging current concentrates on a portion of the battery where the current flows more easily, and forcibly short-circuits this portion. As a result, the characteristics of the secondary battery subjected to the charge / discharge process are deteriorated due to the short circuit.

More specifically, the charging / discharging step forcibly short-circuits a small short-circuit portion in the battery and a portion which may be short-circuited in the future.

Here, the minute short-circuited portion in the battery refers to a portion where a short-circuit occurs due to the stage of manufacture or initial charging / discharging, and the portion that may lead to a short-circuit in the future refers to a portion of the secondary battery. This indicates a portion that causes a short circuit when used and repeated charging and discharging.

Examples of the minute short-circuited portion in the battery include a short-circuited portion caused by a foreign substance remaining in the secondary battery at the time of manufacturing the secondary battery or a substance detached from the electrode. In addition, the portion that may lead to a short circuit in the future is that the electrolyte and impurities are deposited on the surface of the electrode by performing charging and discharging, and the portion where this precipitate causes a short circuit and the electrode causes a volume change This indicates a portion where a short circuit occurs.

The measuring step is a step of measuring a change in battery characteristics of the secondary battery subjected to the charging / discharging step. That is,
By measuring the change in the battery characteristics of the secondary battery in the measurement step, the secondary battery in which the short circuit has occurred in the charge / discharge step can be detected from the change in the battery characteristics.

That is, the battery characteristics of a secondary battery that has short-circuited in the charging / discharging process are lower than those of a secondary battery that has not short-circuited. For this reason, in the measurement process,
By measuring the change in the battery characteristics, the battery having the deteriorated battery characteristics can be determined as the short-circuited secondary battery.

According to the inspection method for a secondary battery of the present invention, in the charging / discharging process, a minute short-circuit portion in the secondary battery and a portion that may lead to a short-circuit in the future are forcibly short-circuited, and the short-circuit is detected in the measuring process. This is an inspection method that detects a deterioration in characteristics. In the method for inspecting a secondary battery according to the present invention, the secondary battery is forcibly short-circuited, so that a change in battery characteristics due to the short-circuit easily occurs. That is, since the change in the battery characteristics can be obtained in a short time, the long-term storage required in the conventional inspection method is not required. As a result, the inspection method of the secondary battery of the present invention can inspect the secondary battery in a short time.

The change in the battery characteristics is preferably a change in the battery voltage of the secondary battery or a change in the amount of self-discharge. Here, the change in the self-discharge capacity indicates a change in the capacity before and after storage. That is, the change in the battery characteristics measured in the measurement process is a change in the battery voltage or a change in the amount of self-discharge measured by the conventional inspection method, so that a short circuit inside the secondary battery is detected in the measurement process. it can.

The test method of the present invention is a test method for a secondary battery, and is particularly effective for testing a lithium secondary battery.

The lithium secondary battery is not particularly limited as long as it is a lithium secondary battery having a lithium metal oxide, and an ordinary lithium secondary battery can be used.

The lithium metal oxide is not particularly limited. Examples of the lithium metal oxide include LiCoO ₂ , LiNiO ₂ , and LiMnO.
₂ , compounds such as LiMn ₂ O ₄ .

The positive electrode of the lithium secondary battery is not particularly limited, and a positive electrode used for a normal lithium secondary battery can be used. For example, a positive electrode active material having a function of inserting and removing Li, a conductive agent such as carbon for imparting electron conductivity, and a P for maintaining an electrode shape.
A binder such as VDF is mixed with a solvent such as NMP to form a paste, applied to an aluminum current collector and dried,
A positive electrode manufactured by forming a slit for adjusting to the shape of the battery, improving the contact state between the particles and the current collector, or performing a pressing step to increase the electrode density can be given.

The negative electrode of the lithium secondary battery is not particularly limited, and a negative electrode used for a normal lithium secondary battery can be used. For example, a negative electrode active material such as carbon having a function of inserting / desorbing or depositing and eluting Li, and a binder such as PVDF for maintaining the electrode shape are mixed with a solvent such as NMP to form a paste, and then the current collection of Cu is performed. It is manufactured by applying a process of applying to the body, drying it, forming slits to match the battery shape, improving the contact state between the particles and the current collector, and pressing to increase the electrode density Negative electrode.

Further, as the lithium secondary battery, the positive and negative electrodes manufactured as described above are wound or laminated with a separator interposed therebetween, and the current collector and the electrode terminal are welded, inserted into the battery case, and then subjected to electrolysis. A battery manufactured by injecting a liquid and performing a process such as sealing the battery case by laser or caulking can be given.

In the lithium secondary battery manufactured as described above, foreign substances mixed in from the surroundings, burrs and chips at the time of slitting the current collector, and the active materials of the positive electrode and the negative electrode peeled off from the surface and the end face of the current collector. The substance penetrates through the separator in the initial stage and at the time of use, and the contact between the positive and negative electrodes causes a short circuit.

The lithium secondary battery has a layer structure of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , carbon, etc.
An active material formed by using LiMn ₂ O ₄ having a spinel structure as a main skeleton and adding various transition metals to suppress a change in crystal during charge and discharge is used.

The positive electrode active material mainly used for the lithium secondary battery has a different voltage change due to the movement of Li.
The potential used as a battery is about 3 to 4.1V.
The positive electrode active material used for the lithium secondary battery is L
The initial potential of the positive electrode without moving i is about 3.2 V, but when charging (de-insertion / re-insertion of Li) is started, the voltage rises steeply, and thereafter, the voltage is flat in the range of about 3.6 to 4 V. It is known that when the battery is further charged, the voltage rise curve becomes steeper again at around 4.1V.

It is also known that this change in voltage is caused by a change in the crystal system of the positive electrode active material. That is, the crystal system of the positive electrode active material of the lithium secondary battery is changed during charging and discharging.

For example, a LiCoO ₂ -based active material is L
When i is deinserted (charged) until the end of charging, its crystal system changes from hexagonal to monoclinic through the coexistence region of each crystal system. In addition, the LiNiO ₂ -based active material changes from a hexagonal system to a monoclinic system to a hexagonal system through a coexistence region of each crystal system as Li is desorbed (charged) from an initial state. Further, in the LiMn ₂ O ₄ -based active material, a region where a two-phase cubic crystal is present appears around 4 V with respect to the Li metal potential (the potential of a battery using counter electrode carbon is 3.7 to 4 V).

It is known that such a change in the crystal system of the positive electrode active material of the lithium secondary battery deteriorates the durability characteristics of the battery. In order to suppress the change of the crystal system, there is a method of adding an element such as a transition metal. However, when the evaluation was performed in detail by X-ray diffraction or the like, the change of the crystal system could not be completely eliminated.

Further, in a lithium secondary battery, it is known that carbon used as a negative electrode active material also causes a rapid change in potential in the initial state and the discharge state where the amount of inserted Li is small.

In a region where the potential change of the electrode active material of the lithium secondary battery is large, the potential distribution is likely to occur in the electrode. Therefore, when the charge and discharge are performed, the current concentrates on the potential portion where the current flows easily. At a potential where the crystal system is changing, microscopically, different portions of the crystal system are mixed in the electrode and the active material particles, and the battery reaction in the electrode is biased, resulting in a microscopic effect. Current concentration is likely to occur. Further, in a portion where the electrode protrudes, the electrode interval is narrowed, and the current is more likely to be concentrated.

As described above, when a local current concentration occurs microscopically in the electrode, for example, local heat generation occurs, and the separator that insulates between the positive electrode and the negative electrode is melted and short-circuited. Is more likely to occur.

In addition, during charging, the potential of the negative electrode is locally reduced, so that Li and impurities are deposited on the negative electrode, and a short circuit is caused by the precipitate penetrating the separator.

Further, if a rapid charge / discharge is performed at a potential at which a change in the crystal structure occurs, a change in the lattice constant of the crystal and a change in the volume of the active material occur. Short-circuits are likely to occur due to the occurrence of cracks.

The method for inspecting a secondary battery according to the present invention utilizes the above-mentioned phenomenon to make local current change in a specific voltage region where the battery voltage changes greatly or in a voltage region where the crystal system of the active material changes. Battery that has a small short circuit due to charge or discharge of the active material in the battery or foreign matter attached to it by charging and discharging with a specific current that causes concentration of the battery, or a battery that is likely to short circuit during use Is an inspection method that can be inspected in a short-term storage to forcibly short-circuit the data.

In the charging / discharging step, the voltage change ΔE / ΔQ (E: battery voltage of the lithium secondary battery, Q:
(The amount of Li transfer in the lithium metal oxide) is at least 1.0,
It is preferable to perform charging and discharging with a charging and discharging current having a charge of C or more. Here, the range where ΔE / ΔQ is 1.0 or more is a range in which two or more crystal phases of different lithium metal oxides are mixed, and is a range where there is a potential bias in the electrode. When charge / discharge is performed with a charge / discharge current having an electric charge of 3 C or more in this range, a potential portion where the current flows more easily in the electrode, that is, a sliding object of the electrode material or a conductive foreign matter is attached and short-circuited minutely. The current concentrates on a portion or a portion that can be short-circuited during use, and a short-circuit occurs at the concentrated portion. As a result, a short circuit can be detected in the subsequent measurement process.

In the charging / discharging step, it is preferable to perform charging / discharging with a charging / discharging current having a charge range of at least 3 C which is a voltage range that at least straddles a range in which the crystal system of the electrode active material changes during charging / discharging. That is, 3C in this range
When charge / discharge is performed with the charge / discharge current having the above charge, the potential portion of the electrode where the current flows more easily, that is, the portion where the sliding material of the electrode material or the conductive foreign matter adheres and is slightly short-circuited or used The current concentrates on a portion where a short circuit may occur, and a short circuit occurs at the concentrated portion. As a result, a short circuit can be detected in the subsequent measurement process.

In the charge / discharge step, the state of charge is the state of charge (SO
It is preferable that the charging and discharging be performed with a charging and discharging current having a charge range of at least 3 C, which is a voltage range that at least straddles a range where C) is 20% or less. That is, when charging and discharging are performed with a charging and discharging current having a charge of 3 C or more in this range,
The current concentrates on the potential portion of the electrode where the current flows more easily, that is, the portion where the sliding material of the electrode material or the conductive foreign matter adheres and the portion is short-circuited minutely or the portion that can be short-circuited during use,
A short circuit occurs at this concentrated portion. As a result, a short circuit can be detected in the subsequent measurement process.

In the charging / discharging step, the state of charge is the state of charge (SO
It is preferable that the charging / discharging be performed with a charging / discharging current having a charge of 3 C or more, which is a voltage range at least straddling the range where C) is 80% or more. That is, when charge / discharge is performed with a charge / discharge current having a charge of 3 C or more in this range,
The current concentrates on the potential portion of the electrode where the current flows more easily, that is, the portion where the sliding material of the electrode material or the conductive foreign matter adheres and the portion is short-circuited minutely or the portion that can be short-circuited during use,
A short circuit occurs at this concentrated portion. As a result, a short circuit can be detected in the subsequent measurement process.

The secondary battery has a lithium nickel oxide in the positive electrode, and the charge / discharge step is a voltage range in which the potential of the positive electrode with respect to Li metal is at least over a range of 3.7 to 3.9 V; It is preferable to perform charging and discharging with a charging and discharging current having the above-mentioned charge. That is, the potential of the positive electrode with respect to Li metal in the range of 3.7 to 3.9 V is a range in which lithium nickel oxide has two phases of hexagonal and monoclinic, and there is a potential bias in the electrode. Range. When charge / discharge is performed with a charge / discharge current having an electric charge of 3 C or more in this range, a potential portion where the current flows more easily in the electrode, that is, a sliding object of the electrode material or a conductive foreign matter is attached and short-circuited minutely. The current concentrates on a portion or a portion that can be short-circuited during use, and a short-circuit occurs at the concentrated portion.
As a result, a short circuit can be detected in the subsequent measurement process.

The secondary battery has a lithium nickel oxide for the positive electrode and carbon for the negative electrode, and the charging and discharging step is performed so that the battery voltage of the secondary battery at least straddles the range of 0.8 to 3.9 V. It is preferable to perform charging / discharging with a charging / discharging current having a range of 3C or more. That is,
The range of the battery voltage of the secondary battery in the range of 0.8 to 3.9 V is a range in which lithium nickel oxide has two phases of hexagonal and monoclinic, and a range in which a potential bias exists in the electrode. is there. When charge / discharge is performed with a charge / discharge current having a charge of 3 C or more in this range, a potential portion where the current flows more easily in the electrode,
In other words, current concentrates on a portion where a slip-off object of the electrode material or a conductive foreign substance is attached and a short circuit occurs, or a portion where a short circuit may occur during use, and a short circuit occurs at the concentrated portion. As a result, a short circuit can be detected in the subsequent measurement process.

The secondary battery has a lithium manganese oxide in the positive electrode, and the charge / discharge step is a voltage range in which the potential of the positive electrode with respect to Li metal is at least 3.9 to 4.1 V, and 3 C It is preferable to perform charging and discharging with a charging and discharging current having the above-mentioned charge. That is, the range of the potential of the positive electrode with respect to Li metal of 3.9 to 4.1 V is a range in which the lithium manganese oxide has two phases of hexagonal system and monoclinic system, and a potential bias exists in the electrode. Range. When charge / discharge is performed with a charge / discharge current having an electric charge of 3 C or more in this range, a potential portion where the current flows more easily in the electrode, that is, a sliding object of the electrode material or a conductive foreign matter is attached and short-circuited minutely. The current concentrates on a portion or a portion that can be short-circuited during use, and a short-circuit occurs at the concentrated portion.
As a result, a short circuit can be detected in the subsequent measurement process.

The secondary battery has a lithium manganese oxide for the positive electrode and carbon for the negative electrode, and the charge and discharge step is such that the battery voltage of the secondary battery at least straddles the range of 3.6 to 4.1 V. It is preferable to perform charging / discharging with a charging / discharging current having a range of 3C or more. That is,
The range of the battery voltage of the secondary battery in the range of 3.6 to 4.1 V is a range in which lithium nickel oxide has two phases of hexagonal system and monoclinic system, and a range in which a potential bias exists in the electrode. is there. When charge / discharge is performed with a charge / discharge current having a charge of 3 C or more in this range, a potential portion where the current flows more easily in the electrode,
In other words, current concentrates on a portion where a slip-off object of the electrode material or a conductive foreign substance is attached and a short circuit occurs, or a portion where a short circuit may occur during use, and a short circuit occurs at the concentrated portion. As a result, a short circuit can be detected in the subsequent measurement process.

The charge / discharge step is preferably performed at 10 ° C. or lower. When the charge and discharge process is performed at a temperature of 10 ° C. or less, the resistance of the electrolytic solution increases, and the reaction area between the electrolytic solution and the electrode material decreases. It will be easier. As a result, a short circuit can be detected in the subsequent measurement process.

The measuring step is preferably performed at 25 ° C. or higher. That is, by performing the measurement process at 25 ° C. or higher, self-discharge of the secondary battery is promoted, and the change in battery characteristics is further promoted. As a result, in the measurement step, a change in battery characteristics is more easily detected. Note that the upper limit of the temperature in the measurement step may be a temperature that does not cause damage due to overheating of the secondary battery.

According to the inspection method of the secondary battery of the present invention, by performing charging / discharging with a charging / discharging current having a current value larger than the initial charging / discharging in the charging / discharging process, a minute short-circuit portion in the battery and a short-circuit in the future may be caused. By short-circuiting a potential part and measuring the deterioration of the battery characteristics due to the short-circuit in the measuring step, the inspection of the secondary battery can be performed in a short time.

[0052]

The present invention will be described below with reference to examples.

As an example of the present invention, a 18650 size lithium secondary battery using lithium nickel oxide as a positive electrode active material and graphite as a negative electrode active material was manufactured, and subjected to a charge / discharge step and a measurement step.

(Production of lithium secondary battery) First, 85 parts by weight of LiNi _0.8 Co _0.15 Al _0.05 O ₂ as a positive electrode active material, 10 parts by weight of carbon as a conductive agent, and 5 parts by weight of PVDF as a binder Was dissolved in an N-methyl-2-pyrrolidone (NMP) solution to prepare a positive electrode active material paste. This paste was applied to both sides of an aluminum foil using a comma coater.

Next, a load was applied to the electrode by passing it through a roll press machine to prepare a positive electrode plate having an improved electrode density.
Thereafter, the positive electrode plate was cut into a predetermined size so that the electrode area became 900 cm ^2, and a sheet-shaped positive electrode was manufactured by scraping off the electrode mixture at a portion to be a lead tab weld for current extraction. .

Subsequently, 92.5 parts by weight of graphite as a negative electrode active material and 7.5 parts by weight of PVDF as a binder were dissolved in an NMP solution to prepare a negative electrode active material paste. This paste was applied to both surfaces of the copper foil surface using a comma coater in the same manner as the positive electrode. Thereafter, the copper foil to which the paste was applied was passed through a roll press to apply a load, thereby producing a negative electrode plate having an increased electrode density.

Next, the negative electrode plate was cut into a predetermined size, and the electrode mixture was scraped off at a portion to be a lead tab welding portion for extracting a current, thereby producing a sheet-shaped negative electrode.

Subsequently, the sheet-shaped positive electrode and the sheet-shaped negative electrode were wound with a separator made of a 25 μm-thick polyethylene microporous film interposed therebetween to form a wound electrode body. The obtained wound electrode body was inserted into the case and held in the case. At this time, the current collecting lead having one end welded to the lead tab welding portion of the sheet-shaped positive electrode and the sheet-shaped negative electrode was joined to the positive electrode terminal or the negative electrode terminal of the case.

Thereafter, the wound electrode body was held by an electrolytic solution obtained by dissolving LiPF ₆ as an electrolyte at a concentration of 1 mol / L in a mixed solvent of 30 vol% ethylene carbonate and 70 vol% diethyl carbonate. It was injected into the case, and the case was hermetically sealed.

By the above procedure, a cylindrical lithium secondary battery having a diameter of 18 mm and an axial length of 65 mm was manufactured.
In the manufacture of a normal lithium secondary battery, cleaning and foreign matter removal are usually performed after cutting or pressing an electrode, but in the lithium secondary battery of this embodiment, cleaning and foreign matter removal are not performed. Was.

In this embodiment, 1 C of the battery is 1
000 mA. The lithium secondary battery manufactured by the above-mentioned means was subjected to initial charge / discharge treatment and inspection under the conditions shown in Examples and Comparative Examples.

Example 1 First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge process was performed by performing charge / discharge of 5 cycles. Specifically, in the first cycle, constant current-constant voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant current discharging (current 1 / 3C, voltage 3V)
Charge and discharge in the second and third cycles, constant current-constant voltage charge (current 1C, voltage 4.1V, charge time 2.5H), constant current discharge (current 1C, voltage 3V) in the fourth cycle Are constant current-constant voltage charging (current 1C, voltage 4.1V, charging time 2.5H), constant current discharging (current 1 / 3C, voltage 3)
In the fifth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H) and constant current discharging (current 1/3 C, voltage 3 V) were performed. After each charge and discharge, a no-load period of 10 minutes was provided. After discharging the fourth cycle, the open circuit voltage of the battery is about 3.1 V
showed that.

The lithium secondary battery of the embodiment which had been subjected to the initial charge / discharge treatment described above was inspected by the inspection method of the present invention.

Specifically, the lithium secondary battery was charged with a large current of 6 C for 2 minutes, and then subjected to a constant current-constant voltage charge (current 1 C, voltage 3.75 V, charge time 6 H) treatment at 1 C. The open circuit voltage measured after charging with a large current of 6 C for 2 minutes was 3.47 V, and the SOC (charge seismic intensity) was about 20%. In addition, the SOC showed about 60% by charging at 3.75 V.

The charged and discharged lithium secondary battery 3
0 were left in a constant temperature bath at 25 ° C., and the standing time and the battery voltage were measured. The measurement results are shown in Table 1 and FIG.

The battery voltage was measured using a digital multimeter (Advantest) to measure the open circuit voltage of the battery.

Further, as Comparative Example 1, the battery of the example subjected to the following initial charge / discharge process was inspected by a conventional inspection method.

(Comparative Example 1) First, the batteries of the examples were subjected to an initial charge / discharge treatment.

The initial charge / discharge process was performed by performing charge / discharge of four cycles. Specifically, in the first cycle, constant current-constant voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant current discharging (current 1 / 3C, voltage 3V)
In the second and third cycles, constant current-constant voltage charging (current 1
C, voltage 4.1 V, charging time 2.5 H), constant current discharge (current 1 C, voltage 3 V), the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2) .5H) and constant current discharge (current 1C, voltage 3V). After each charge and discharge, a no-load period of 10 minutes was provided. The open circuit voltage of the battery after the discharge in the fourth cycle was about 3.1 V.

The lithium secondary battery of the embodiment which had been subjected to the above-mentioned initial charge / discharge treatment was inspected by a conventional secondary battery inspection method.

More specifically, a constant current-constant voltage charge (current 1
C, a voltage of 3.75 V and a charging time of 1.5 H), and 30 batteries were left in a thermostat at 25 ° C. in the same manner as in the inspection method of Example 1, and the time and battery voltage were measured. The measurement of the battery voltage was performed by the same means as in Example 1. The measurement results are shown in Table 1 and FIG.

[0073]

[Table 1]

As shown in Table 1 and FIG. 1, in the battery using the test method of Example 1, a sharp decrease in voltage was observed in three out of thirty cells, and the amount of decrease in the voltage was about three days. At 8
It was 0 mV or more. That is, when these batteries are charged with a large current of 6 C for 2 minutes, short-circuited portions in the batteries and portions that may be short-circuited in the future are forcibly short-circuited, and the voltage is reduced. In addition, a battery of 27 cells other than the three cells does not show a significant decrease in battery voltage even after being left for 30 days or more, and shows sufficient performance as a lithium secondary battery.

In the batteries tested under the conditions of Comparative Example 1, two out of thirty cells whose voltage gradually decreased existed. These batteries have only a small voltage drop,
On day 0, the battery voltage dropped by about 100 mV. That is,
As a result of being left unattended, a short-circuit portion in the battery and a portion likely to be short-circuited in the future caused a short-circuit, and the battery voltage dropped. In addition, a battery of 28 cells other than the two cells did not show a significant decrease in battery voltage even after being left for 30 days or more, and showed sufficient performance as a lithium secondary battery.

From the above, the inspection method of Comparative Example 1, which is the conventional inspection method, has a long time of about 30 days, but using the inspection method of Example 1 which is the inspection method of the present invention, It can be seen that batteries and defective batteries can be sorted in a short time.

(Example 2) First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge treatment was performed by performing the same charge / discharge as the initial charge / discharge up to the fourth cycle in Example 1. Specifically, in the first cycle, constant-current-constant-voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant-current discharging (current 1 / 3C, voltage 3V) is defined as 2
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3 V), and in the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment which had been subjected to the above-mentioned initial charge / discharge treatment was inspected by the inspection method of the present invention.

In detail, a constant current-constant voltage charge (current 1
C, voltage 3.8 V (SOC 70%), charging time 1.5
H), charged with a large current of 6 C for 2 minutes, discharged at a constant current of 1 C to 3 V, and then charged at a constant current-constant voltage at 1 C (current 1 C, voltage 3.75 V, charging time 1 H). .

When the open circuit voltage after charging with a large current of 6 C for 2 minutes was measured, it was 3.98 V, and the SOC was about 90%. In this battery, a change in the battery voltage occurs in a voltage range of about 3.8 to 3.98 V, and the change in the voltage is represented by ΔE / ΔQ (E: battery voltage, Q: Li movement amount in lithium metal oxide). Calculating, in this voltage range,
1.1 to 1.7.

The charged and discharged lithium secondary battery 3
0 were left in a constant temperature bath at 25 ° C., and the standing time and the battery voltage were measured. The measurement results are shown in Table 1.

(Comparative Example 2) First, the batteries of the examples were subjected to an initial charge / discharge treatment.

The initial charging / discharging process was performed by performing the same charging / discharging as the initial charging / discharging up to the fourth cycle in Example 1. Specifically, in the first cycle, constant-current-constant-voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant-current discharging (current 1 / 3C, voltage 3V) is defined as 2
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3 V), and in the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment which had been subjected to the above initial charge / discharge treatment was inspected by the following inspection method.

More specifically, a constant current-constant voltage charge (current 1
C, a voltage of 3.6 V (SOC 60%), a charging time of 1 H), a 2 minute charge with a large current of 6 C, and a constant current-constant voltage charging at 1 C (current 1 C, voltage 3.75 V, charging time 1).
H) was performed. Leave this battery in a 25 ° C constant temperature bath,
The standing time and voltage were measured. The open circuit voltage after charging with a large current of 6 C for 2 minutes was 3.75 V, and the SOC was about 60%.

In this battery, the change in the battery voltage is small in the voltage range of about 3.6 to 3.8 V, and the change in the voltage is Δ
Calculated from E / ΔQ (E: battery voltage, Q: Li movement amount in lithium metal oxide), this voltage range is 1.0
Was less than.

The charged / discharged lithium secondary battery 3
0 were left in a constant temperature bath at 25 ° C., and the standing time and the battery voltage were measured. Table 1 shows the measurement results.

As shown in Table 1, the batteries using the test method of Example 2 showed a sharp drop in the voltage of 4 cells out of 30 cells, and the voltage drop was 80 mV or more in about 3 days. Met. The 26-cell battery other than the 4-cell battery has a capacity of 3
Even when left for more than 0 days, no significant decrease in battery voltage was observed, indicating that the lithium secondary battery exhibited sufficient performance.

In the batteries tested under the conditions of Comparative Example 2, one out of every 30 cells had a voltage drop of 80 mV or more in about 3 days, but the voltage gradually dropped. There were also 2 cells out of 30 cells. In addition, a battery of 27 cells other than the three cells did not show a significant decrease in battery voltage even after being left for 30 days or more, and showed sufficient performance as a lithium secondary battery. Voltage drop is 80m in about 3 days
Although one cell out of 30 cells had a voltage drop of V or more, there were also two cells out of 30 cells whose voltage gradually decreased.

From the above, it was found that a good battery and a defective battery can be inspected in a short time by applying a large current in a voltage range where ΔE / ΔQ is 1.0 or more.

(Example 3) First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge treatment was performed by performing the same charge / discharge as the initial charge / discharge up to the fourth cycle in Example 1. Specifically, in the first cycle, constant-current-constant-voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant-current discharging (current 1 / 3C, voltage 3V) is defined as 2
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3 V), and in the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment, which had been subjected to the above-mentioned initial charge / discharge treatment, was inspected by an inspection method for charging under the following conditions.

More specifically, the lithium secondary battery which has been subjected to the initial charge / discharge treatment is charged with a large current of 2C for 6 minutes, 4C for 4 minutes, 6C for 2 minutes and 12C for 1 minute, and then charged at 1C. Current-constant voltage charging (current 1C, voltage 3.75V, charging time 1H) was performed. The open circuit voltage after charging with a large current under each condition showed about 3.73 V (SOC about 60%).

Each of the 30 lithium secondary batteries charged and discharged under each condition was allowed to stand in a constant temperature bath at 25 ° C., and the standing time and battery voltage were measured. The measurement results are shown in Table 1.

From Table 1, it can be seen that among the batteries which were charged under the condition that the charging current was 2 C, there was no battery whose voltage drop decreased by 80 mV or more in about 3 days, and the battery whose voltage gradually dropped There were also 2 cells out of 30 cells. In addition, under the condition that the charging current was 4C, 2 cells out of 30 cells dropped by 80 mV or more in 3 days. There was also one battery out of 30 cells whose voltage gradually decreased. In 6C and 12C, the amount of voltage drop is 8 in 3 days.
The batteries that drop 0 mV or more are 3 out of 30 cells,
There was no battery whose voltage gradually decreased.

As a result, it was found that the larger the current value was, the more effective it was.

(Example 4) First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charging / discharging process was performed by performing the same charging / discharging as the initial charging / discharging up to the fourth cycle in Example 1. Specifically, in the first cycle, charging and discharging of constant current-constant voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), and constant current discharging (current 1 / 3C, voltage 3V) are performed in two cycles.
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3V), and in the fourth cycle, constant current-constant voltage charging (current 1C, voltage 4.1V, charging time 2.5H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment which had been subjected to the above-mentioned initial charge / discharge treatment was inspected by an inspection method for charging under the following conditions.

More specifically, a lithium secondary battery that has been subjected to an initial charge / discharge treatment is treated at 6C for 10 seconds, 20 seconds, 40 seconds, and 1 second.
Charge for 2 minutes, 2 minutes and 4 minutes
To perform constant current-constant voltage charging (current 1C, voltage 3.75V, charging time 1H). The open circuit voltage after charging with a large current under each condition is about 3.15 V (about 1.7% SOC) for a battery with a charging time of 10 seconds, and about 3.2 V (SOC about 1.7%) for a battery with a charging time of 20 seconds. 3.3%), about 3.25 V (about 6.7% SOC) for a 40 second battery, about 3.4 V (about 10% SOC) for a 1 minute battery, and about 3.5 for a 2 minute battery.
V (SOC about 20%), about 3.6 V (S
OC about 40%).

Each of the 30 lithium secondary batteries charged and discharged under each condition was left in a thermostat at 25 ° C., and the time and battery voltage were measured. The measurement results are shown in Table 1.

From Table 1, it was found that among the batteries which were charged under the condition of the charging time of 10 seconds, there was no battery whose voltage drop decreased by 80 mV or more in about 3 days. Under the conditions, 2 cells out of 30 cells dropped by 80 mV or more in 3 days. Further, even in the batteries charged for 40 seconds, 1 minute, 2 minutes, and 4 minutes, the amount of the voltage drop of 80 mV or more in 3 days is 2 to 4 cells out of 30 cells, and the voltage gradually decreases. There were no batteries. Thus, it was found that the charge capacity at a large current was required to be 1/30 C or more of the battery capacity.

(Example 5) First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge process was performed by performing the same charge / discharge as the initial charge / discharge up to the fourth cycle of the first embodiment. Specifically, in the first cycle, constant-current-constant-voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant-current discharging (current 1 / 3C, voltage 3V) is defined as 2
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3 V), and in the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment, which had been subjected to the above-mentioned initial charge / discharge treatment, was inspected by an inspection method for charging under the following conditions.

More specifically, after charging a lithium secondary battery subjected to an initial charge / discharge treatment at a constant current of 6 C for 2 minutes,
After discharging for 2 minutes at a constant current of C and further charging for 2 minutes at a constant current of 6C, constant current-constant voltage charging at 1C (current 1
C, voltage 3.75 V, charging time 1 H).

Thirty lithium batteries thus charged and discharged were left in a thermostat at 25 ° C., and the time and battery voltage were measured. The measurement results are shown in Table 1.

From Table 1, it can be seen that the amount of voltage drop was 80 m in about 3 days.
There were 2 cells out of 30 cells that dropped by more than V, and the other cells did not drop in voltage. From this, it was found that the effect of causing a short circuit can be obtained not only by charging with a large current but also by an inspection method involving discharge.

(Example 6) First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge treatment was performed by performing the same charge / discharge as the initial charge / discharge up to the fourth cycle of the first embodiment. Specifically, in the first cycle, constant-current-constant-voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant-current discharging (current 1 / 3C, voltage 3V) is defined as 2
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3 V), and in the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment, which had been subjected to the above-mentioned initial charge / discharge treatment, was inspected by an inspection method for charging under the following conditions.

More specifically, a lithium secondary battery that has been subjected to an initial charge / discharge process is charged at a constant current of 6 C for 2 minutes in a constant temperature bath at 0 ° C., and then charged at a constant current-constant voltage at 1 C (current 1 C,
Voltage 3.75 V, charging time 1 H). The battery was left again at room temperature, and the time and the amount of decrease in voltage were measured.

From Table 1, it can be seen that the voltage drop of the battery charged and discharged under the conditions of Example 6 was larger than that of the battery charged with a large current at room temperature, and the voltage drop was 100 m in about 3 days.
There were 2 cells out of 30 cells that dropped by more than V, and the other cells did not drop in voltage. As a result, when a large current is applied at a low temperature, the current is more likely to be partially concentrated, so that the batteries can be sorted in a shorter time.

Example 7 First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge treatment was performed by performing the same charge / discharge as the initial charge / discharge up to the fourth cycle of the first embodiment. Specifically, in the first cycle, constant-current-constant-voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), constant-current discharging (current 1 / 3C, voltage 3V) is defined as 2
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3 V), and in the fourth cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment which had been subjected to the initial charge / discharge treatment was inspected by the inspection method for charging under the following conditions.

A battery whose battery voltage was adjusted to 3.75 V was
The sample was left at 45 ° C., and the standing time and the amount of decrease in voltage were measured.

From Table 1, it can be seen that the voltage drop of the battery charged / discharged under the conditions of Example 7 was larger than that of the battery charged with a large current at room temperature.
There were 2 cells out of 30 cells that dropped by mV or more. The other batteries did not drop in voltage. Than this,
By storing at a high temperature, the battery reaction was activated, and the batteries could be sorted in a shorter time.

(Example 8) First, the battery of the example was subjected to an initial charge / discharge treatment.

The initial charge / discharge treatment was performed by performing the same charge / discharge as the initial charge / discharge up to the fourth cycle of the first embodiment. Specifically, in the first cycle, charging and discharging of constant current-constant voltage charging (current 1 / 4C, voltage 4.1V, charging time 6H), and constant current discharging (current 1 / 3C, voltage 3V) are performed in two cycles.
In the third cycle, constant current-constant voltage charging (current 1 C, voltage 4.1 V, charging time 2.5 H), constant current discharging (current 1
C, voltage up to 3V), and in the fourth cycle, constant current-constant voltage charging (current 1C, voltage 4.1V, charging time 2.5H)
Was done. After each charge and discharge, a no-load period of 10 minutes was provided. After the discharge in the fourth cycle, the open circuit voltage of the battery was about 3.1 V.

The lithium secondary battery of the embodiment, which had been subjected to the above-mentioned initial charge / discharge treatment, was inspected by an inspection method for charging under the following conditions.

More specifically, the lithium secondary battery of the embodiment which had been subjected to the initial charge / discharge treatment was charged at a constant current of 6 C for 2 minutes, and then charged at a constant current-constant voltage at 1 C (current 1 C, voltage 3.
75V, charging time 1H).

Thirty lithium batteries thus charged and discharged were left in a thermostat at 25 ° C., and the time and battery voltage were measured. The measurement results are shown in Table 1.

From Table 1, it can be seen that the amount of voltage drop was 80 m in about 3 days.
There were 2 cells out of 30 cells that dropped by more than V, and the other cells did not drop in voltage. However, in the battery charged with a large current after the battery was assembled, the amount of voltage decrease was large, and the capacity was measured thereafter. As a result, it was found that the decrease was about 3%. This is presumably because, since the battery was charged with a large current, the reaction of forming a film on the negative electrode became non-uniform at the initial stage of charging, and a decrease in capacity due to an increase in side reactions and a voltage decrease due to a decomposition reaction of a film product occurred.

[0127]

According to the method for inspecting a secondary battery of the present invention, the battery characteristics are degraded by short-circuiting a minute short-circuit portion in the battery and a portion that may lead to a short-circuit in the future. Therefore, there is an effect that the inspection of the secondary battery can be performed in a short time.

[Brief description of the drawings]

FIG. 1 is a diagram showing inspection results of Example 1.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoru Suzuki 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. (72) Inventor Sugie sequentially 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Katsuyoshi Kawai 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 2G016 CB05 CB11 CB12 CB21 CB31 CC01 CC23 CF06 5G003 BA01 CA03 DA07 EA09 5H029 AJ14 AK03 AL06 AL07 AM03 AM05 AM07 BJ02 BJ14 HJ14 HJ18 HJ19 5H030 AA06 AA10 AS20 BB01 BB21 FF22 FF41 FF42FF43

Claims (13)

[Claims] 1. A secondary battery that has been subjected to an initial charge / discharge process is:
A charging / discharging step of performing charging / discharging with a charging / discharging current having a current value larger than the initial charging / discharging current of the initial charging / discharging process; and measuring a change in battery characteristics of the secondary battery subjected to the charging / discharging step. A method for inspecting a secondary battery, comprising: a measuring step. 2. The inspection method for a secondary battery according to claim 1, wherein the change in the battery characteristics is a change in a battery voltage and / or a change in a self-discharge amount of the secondary battery. 3. The inspection method for a secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery having a lithium metal oxide. 4. The charge / discharge step, wherein a voltage change ΔE / ΔQ of the lithium secondary battery (E: battery voltage of the lithium secondary battery, Q: Li movement amount in lithium metal oxide) is 1.0. The inspection method for a secondary battery according to claim 1, wherein the charging and discharging are performed with the charging and discharging current having a charge of 3 C or more, which is a voltage range at least straddling the above range. 5. The charging / discharging step includes performing charging / discharging with the charging / discharging current having a voltage range that at least straddles a range in which the crystal system of the electrode active material changes during charging / discharging and having a charge of 3 C or more. The inspection method for a secondary battery according to claim 1. 6. The charging / discharging step includes performing charging / discharging with a charging / discharging current having a charge state of at least 3C or more in a voltage range that at least straddles a range where a state of charge (SOC) is 20% or less. The inspection method for a secondary battery according to claim 1, wherein the inspection is performed. 7. The charging / discharging step includes performing charging / discharging with the charging / discharging current having a charge state of at least 3% or more in a voltage range over a range where a state of charge (SOC) is 80% or more. The inspection method for a secondary battery according to claim 1, wherein the inspection is performed. 8. The voltage range in which the secondary battery has a lithium nickel oxide in a positive electrode, and the charge / discharge step is such that a potential of the positive electrode with respect to Li metal at least spans a range of 3.7 to 3.9V. The inspection method for a secondary battery according to claim 1, wherein charging and discharging are performed with the charging and discharging current having a charge of 3 C or more. 9. The secondary battery has a lithium nickel oxide for a positive electrode and a carbon for a negative electrode, and the charge and discharge step includes a step of setting the battery voltage of the secondary battery to 0.8 to 0.8.
The method for inspecting a secondary battery according to claim 1, wherein the charging and discharging are performed with the charging and discharging current having a charge range of at least 3 C and a voltage range which at least straddles a range of 3.9 V. 10. A voltage range in which the secondary battery has a lithium manganese oxide in a positive electrode, and the charge / discharge step is such that a potential of the positive electrode with respect to Li metal at least spans a range of 3.9 to 4.1 V. The inspection method for a secondary battery according to claim 1, wherein charging and discharging are performed with the charging and discharging current having a charge of 3 C or more. 11. The secondary battery has a lithium manganese oxide for a positive electrode and carbon for a negative electrode, and the charge and discharge step is such that the battery voltage of the secondary battery is 3.6 to
The method for inspecting a secondary battery according to claim 1, wherein the charging and discharging are performed with the charging and discharging current having a charge of 3 C or more, which is a voltage range that at least spans a range of 4.1 V. 12. The inspection method for a secondary battery according to claim 1, wherein the charging / discharging step is performed at 10 ° C. or less. 13. The method according to claim 1, wherein the measuring step is performed at 25 ° C. or higher.