JP7812428B2 - Measuring units and measuring machines - Google Patents

Description

This disclosure relates to a unit, measuring device, and measurement method for measuring state changes that occur during interlayer short-circuiting (internal short-circuiting) in batteries with a stacked structure, as well as a method for evaluating the safety of batteries that have undergone interlayer short-circuiting, and in particular to measuring the state changes and evaluating the safety of such batteries by controlling the number of layers that are internally short-circuited.

In recent years, the use of rechargeable batteries has increased in a wide range of fields, including electronic devices, automobiles, and renewable energy. Internal short circuits can occur in such batteries due to the intrusion of foreign matter into the battery during manufacturing or from the outside during use. A method for evaluating the safety of batteries in the event of an internal short circuit is known (JP 2023-081127 A).

Japanese Patent Application Laid-Open No. 2023-081127

In the evaluation method described in Patent Document 1, an outer casing containing a stacked electrode group of positive electrodes, negative electrodes, and separators and small metal pieces is pressurized with a pressure jig, causing the small metal pieces to break through the separator, resulting in an internal short circuit. Because the small metal pieces have a height (dimension) of 0.3 mm or more in the direction of breaking through the separator, they may break through the relatively large number of stacked positive electrodes, negative electrodes, and separator layers, potentially preventing an internal short circuit from occurring in a relatively small number of layers, such as one or two layers. There is a need to evaluate the safety of batteries that have experienced an internal short circuit in a relatively small number of layers.

This disclosure was made based on the above-mentioned circumstances, and aims to provide a measurement unit that can cause an internal short circuit with a relatively small number of layers and evaluate the safety of the battery by measuring at least one of the voltage and current of the battery that has been internally shorted.

A measurement unit according to one aspect of the present disclosure is a unit that measures at least one of the voltage and current when an electrode layer in a battery is short-circuited, and includes a base on which the battery is placed, a needle for piercing a hole in the battery placed on the base, a holder that holds the needle and moves it so as to pierce the battery placed on the base, a displacement measuring device that measures the amount of displacement of the needle relative to the base, and a first measuring device that measures at least one of the voltage and current of the battery in which the hole has been pierced.

The measurement unit disclosed herein can generate an internal short circuit in a relatively small number of layers of a battery, and can measure at least one of the battery's voltage and current due to this internal short circuit to evaluate the safety of the battery.

FIG. 1 is a schematic front view showing a measurement unit according to an embodiment of the present disclosure. FIG. 2 is a schematic side view of the measurement unit of FIG. FIG. 3 is a cross-sectional view taken along line AA in FIG. FIG. 4 is a schematic front view of a needle provided in the measurement unit of FIG. FIG. 5 is a schematic side view of the needle of FIG. FIG. 6 is a schematic front view showing a measuring instrument according to an embodiment of the present disclosure. FIG. 7 is a schematic front view showing a state in which another battery is connected to a battery to be measured in a measurement method according to an embodiment of the present disclosure. FIG. 8 is a schematic front view showing a state in which a DC power supply is connected to a battery to be measured by this measurement method. FIG. 9 is a graph showing the change in voltage of a battery that has been internally short-circuited, measured by this measurement method. FIG. 10 is a graph showing the change in voltage between the battery shown in the graph of FIG. 9 and a needle that internally shorted the battery. FIG. 11 is a graph showing the voltage change of a battery that has been internally short-circuited using a measurement method according to one embodiment of the present disclosure, the temperature change of the battery, the voltage change between the internally short-circuited needle and the battery, and the displacement of the needle. Figure 12 is a graph showing the voltage change of an internally short-circuited battery, the current change between the internally short-circuited battery and a battery connected in parallel to this battery, the temperature change of the internally short-circuited battery, the voltage change between the internally short-circuited needle and the internally short-circuited battery, the needle displacement amount, and the needle load change, using a measurement method that is another embodiment of the present disclosure. FIG. 13 is a graph showing the relationship between the amount of energy of a current rushing from an external power source into a battery that has experienced an internal short circuit, and the amount of energy of the internal short circuit alone, and the time since the internal short circuit. FIG. 14 is a graph showing the relationship between the effective value of the current flowing from an external power source into a battery with an internal short circuit, the effective value of the current with only an internal short circuit, and the amount of energy in each case.

Description of the embodiments of the present disclosure
(1) A measurement unit according to one aspect of the present disclosure is a unit that measures at least one of the voltage and current when an electrode layer in a battery is short-circuited, and includes a base on which the battery is placed, a needle for piercing a hole in the battery placed on the base, a holder that holds the needle and moves it to pierce the battery placed on the base, a displacement measuring instrument that measures the amount of displacement of the needle relative to the base, and a first measuring instrument that measures at least one of the voltage and current of the battery in which the hole has been pierced.

The measurement unit is equipped with a displacement measuring device that measures the displacement of the needle used to puncture a battery placed on a base, making it possible to control the depth to which the needle penetrates into the battery. This makes it possible to control the number of layers that the needle penetrates in the battery's laminate, which includes the positive electrode layer, separator layer, and negative electrode layer, and to short-circuit a relatively small number of layers in the laminate. Furthermore, by controlling the needle's penetration depth, the measurement unit can control the needle's contact with, puncture, and penetration of each of the layers. The measurement unit is equipped with a measuring device that measures at least one of the voltage and current (hereinafter sometimes simply referred to as "voltage/current") of the punctured battery, making it possible to measure changes in the voltage/current of the battery that has experienced an internal short circuit.

(2) In (1) above, the measurement unit may further include a second measuring device that measures at least one of the voltage and current between the battery and the needle, or the first measuring device may be capable of further measuring at least one of the voltage and current between the battery and the needle. In other words, the measurement unit may be configured to measure the voltage/current between the needle and the battery in addition to measuring the voltage/current of the battery. By providing multiple measurement targets, it is possible to perform a multifaceted safety assessment of the battery.

(3) In (1) or (2) above, the displacement measuring device may have a first connection part connected to the needle and a second connection part connected to the base. This allows the amount of displacement of the needle to be measured easily and accurately.

(4) In (3) above, the base may have a main body on which the battery is placed, a pair of pillars standing on the main body, and a beam spanning the pair of pillars at a distance from the surface of the battery placed on the main body, and the second connection portion may be connected to the beam. This can improve the accuracy of the displacement measurement.

(5) In any of (1) to (4) above, a control unit may be further provided that controls the start and stop of movement of the needle by the holder, and the control unit may control the movement of the needle based on the measurement value of the measuring device. In this way, the movement and stop of the needle can be easily and accurately performed.

(6) In any of (1) to (5) above, the needle and the holder may be insulated. This can reduce measurement errors in the measuring device due to external disturbances.

(7) In any of (1) to (6) above, a current wire may be further provided that electrically connects the battery to be pierced and the needle. This can further reduce the measurement error caused by external disturbances.

(8) A measuring instrument according to one aspect of the present disclosure includes a measuring unit according to any one of (1) to (7) above, and a casing that houses at least a portion of the measuring unit.

The measuring device includes the measurement unit, allowing it to measure the voltage/current of the battery due to an internal short circuit in a relatively small number of layers of the battery. Furthermore, the measuring device includes a casing that houses at least a portion of the measurement unit, allowing it to perform the measurements while ensuring safety.

(9) A measurement method according to one aspect of the present disclosure is a method for measuring at least one of the voltage and current when an electrode layer in a battery is short-circuited, and includes the steps of placing the battery on a base, measuring at least one of the voltage and current of the battery placed on the base, moving a needle toward the battery being measured to make a hole, bringing the needle into contact with the outermost electrode layer in the battery where the hole has been made, and stopping the movement of the needle when it has come into contact with the electrode layer.

This measurement method involves bringing a needle that has pierced the battery into contact with the outermost electrode layer (outermost electrode layer) within the battery, thereby stopping the needle's movement. This measurement method therefore makes it possible to measure the change in the battery's voltage due to a short circuit between one electrode layer (the outermost electrode layer) and the needle.

(10) In (9) above, the measuring step may further measure at least one of the voltage and current between the needle and the battery. In this way, the change in voltage/current in the outermost electrode layer can be measured.

(11) In (8) or (9) above, the method may further include the steps of moving the needle, whose movement has been stopped, again toward the inside of the battery, piercing the outermost electrode layer with the needle that is being moved again, and halting the movement of the needle that has pierced the hole again. In this way, it is possible to measure changes in the voltage/current of the battery due to an interlayer short circuit between the outermost electrode layer and the electrode layer adjacent to this outermost electrode layer.

(12) In any of (9) to (11) above, the method may further include a step of connecting another battery to the battery, and the measuring step may measure at least one of the voltage and current of the battery to which the other battery is connected. In this way, it is possible to observe the effect of the other battery on the internally shorted battery.

(13) In any of (9) to (11) above, the method may further include a step of connecting a DC power supply to the battery, and the measuring step may measure at least one of the voltage and current of the battery connected to the DC power supply. In this way, the effect of the DC power supply on a battery that has an internal short circuit can be observed.

A safety evaluation method according to one aspect of the present disclosure is a method for evaluating the safety of a battery that has experienced an internal short circuit, and includes the steps of placing the battery on a base, connecting the battery to another battery or a DC power source, moving a needle toward the battery placed on the base, causing an internal short circuit by puncturing the battery with the moved needle, measuring the current I [A] that rushes into the internally short-circuited battery from the other battery or the DC power source, and calculating the amount of energy Ec [A ² ·s] added to the internal resistance of the battery using the following equation 1.
Ec = Irms ² × T (1)
Here, "Irms ² " is the effective value [A] of the current I, and "T" is the total time [s] that the current I flows into the battery.

This safety assessment method can predict the possibility of the battery being damaged by the amount of energy Ec applied to the battery, making it possible to easily and reliably assess the safety of the battery.

[Details of the embodiment of the present disclosure]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[Measurement unit]
A measurement unit according to one aspect of the present disclosure measures at least one of the voltage and current when the electrode layers in a battery are short-circuited. As shown in FIGS. 1 , 2 , and 3 , the measurement unit 1 includes a base 10 on which a battery B is placed, a needle 20 for piercing the battery B placed on the base 10, a holder 30 that holds the needle 20 and moves it to pierce the battery B placed on the base 10, a displacement measuring device 40 that measures the displacement of the needle 20 relative to the base 10, and a first measuring device (not shown) that measures at least one of the voltage and current of the pierced battery B. The measurement unit 1 of this embodiment also includes a control unit (not shown) that controls the start and stop of the movement of the needle 20 by the holder 30, and a second measuring device 50 that measures the voltage/current between the needle 20 and the battery B. In this embodiment, the first measuring device and the second measuring device 50 measure voltage. The second measuring device 50 is connected to either the positive or negative terminal B1 of battery B and the needle 20 (see FIG. 2), and measures the voltage between the needle 20 and battery B (needle-battery voltage). The first measuring device is connected to each of the positive and negative terminals B1 of battery B (not shown), and measures the voltage of battery B.

<Battery>
Battery B is not particularly limited as long as it has a laminate including a positive electrode layer, a negative electrode layer (hereinafter, these two electrode layers may be simply referred to as "electrode layers"), and a separator layer disposed between these electrode layers for electrical insulation, and an exterior housing that houses this laminate, and examples thereof include a lithium battery, a lithium ion battery, etc. Battery B may contain a liquid electrolyte, or may be an all-solid-state battery that contains a solid electrolyte.

The laminate may be a laminate of multiple electrode layers and multiple separator layers, or may be a laminate of a pair of strip-shaped electrode layers and one separator layer that are wound together. The exterior body may be made of a rigid material such as metal or resin, or a flexible material such as a laminate film. The shape of battery B is not particularly limited and may be, for example, a rectangular parallelepiped, cylindrical, or pouch-shaped.

<Foundation>
The base 10 of this embodiment includes a main body 11 on which a battery B is placed, a pair of columns 12 extending from the main body 11, and a beam 13 spanning the pair of columns 12 at a distance from the surface of the battery placed on the main body 11. The main body 11 is formed in a generally rectangular shape in a plan view, and the pair of columns 12 are spaced apart at the centers of two opposing sides of the main body 11. A through-hole 13a is provided in the center of the beam 13 in a plan view, and a needle 20 passes through this through-hole 13a. At least the surface of the main body 11 (the surface on which the battery B is placed) is preferably made of an insulator, or an insulating member is preferably disposed on the surface. The surface of the main body 11 may be provided with a shape or member for securing the placed battery B.

<Needle>
4 and 5, needle 20 has a cylindrical needle body 21 and an enlarged portion 22 that is enlarged in plan view. Needle 20 may be one in which needle body 21 and enlarged portion 22 are integrally formed, or may be formed separately and fixed together. A portion of needle body 21 is held by holder 30, and the end (tip) on the side not held by holder 30 is formed in a conical or pyramidal shape with a tip angle of 5 degrees to 90 degrees.

The material of the needle 20 is not particularly limited as long as it is conductive, and examples include iron and stainless steel. The diameter of the needle body 21 is not particularly limited, and can be, for example, 2 mm or more and 5 mm or less.

A known thermometer such as a thermocouple may be built into the needle body 21 to measure the temperature of battery B, which changes due to an internal short circuit.

<Holder>
The holder 30 is configured to be movable in the axial direction of the needle 20, and holds and moves the needle 20 that pierces the battery B. The needle 20 and the holder 30 are preferably insulated from each other. Insulating the needle 20 from the holder 30 can suppress disturbances (noise) to the first measuring device and the second voltage measuring device 50 during voltage measurement. The means for insulation is not particularly limited, and an insulating member may be placed in the portion of the holder 30 that holds the needle 20, or an insulating coating may be formed on the holding portion.

<Displacement measuring instrument>
The displacement measuring device 40 of this embodiment has a sensor unit 43, and a first connection unit 41 and a second connection unit 42 that extend in the same direction and have one end connected to the sensor unit 43. The displacement measuring device 40 is a so-called clip-type strain gauge. The first connection unit 41 is connected to the needle 20, and the second connection unit 42 is connected to the base 10. Specifically, the first connection unit 41 is connected to the widening unit 22, and the second connection unit 42 is connected to the beam unit 13. The sensor unit 43 is electrically connected to the control unit and transmits the measured displacement amount.

The central portion of the beam portion 13 and the widened portion 22 may be formed with engaging portions (not shown) that engage with the other ends (tips) of the first connecting portion 41 and the second connecting portion 42. The engaging portions are formed, for example, as notches or hooks, and are configured to hold the tips. The tips may also be formed with engaged portions (not shown) that engage with the engaging portions. By engaging the tips with the engaging portions, the widened portion 22 and beam portion 13 can easily hold the displacement measuring device 40, and the amount of displacement can be measured with high precision.

The number of displacement measuring devices 40 arranged in the measurement unit 1 may be one, but preferably multiple. By arranging multiple displacement measuring devices 40, the displacement amount of the needle 20 can be measured with high accuracy. In this embodiment, two displacement measuring devices 40 are provided, and are arranged so that the first connection portion 41 and the second connection portion 42 face each other.

The displacement measuring device 40 is preferably positioned close to the tip of the needle 20. Therefore, it is preferable that the position of the widened portion 22 on the needle body 21 of the needle 20 is close to the tip of the needle body 21. By positioning the displacement measuring device 40 close to the tip of the needle body 21, measurement errors due to deformation such as bending of the needle 20 when it presses against the battery B can be suppressed.

The resolution of the displacement measuring device 40 is preferably equal to or less than the thickness of the electrode layer. The upper limit of the resolution is preferably 0.0070 mm/μ, more preferably 0.0050 mm/μ, and even more preferably 0.0025 mm/μ. Having the resolution equal to or less than the upper limit allows one electrode layer to be short-circuited. The lower limit of the resolution is not particularly limited and may be, for example, 0.0001 mm/μ.

<Measuring instrument>
The first measuring device is connected to the positive and negative terminals B1 of battery B to measure the voltage of battery B. The second measuring device 50 is connected to either the positive or negative terminal B1 of battery B and the needle 20 to measure the needle-battery voltage. If the first measuring device is capable of measuring voltage in two systems, the second measuring device does not need to be provided. The first measuring device and second measuring device 50 (hereinafter, these two measuring devices may also be simply referred to as "measurements") are not particularly limited, and known voltmeters may be used.

For the needle-to-battery voltage, if the outermost electrode layer of the laminate housed in battery B is positive, connect the positive electrode cable of the measuring device to needle 20 and connect the negative electrode cable of the measuring device to the negative electrode terminal B1 of battery B. If the outermost electrode layer is negative, connect the negative electrode cable of the measuring device to needle 20 and connect the positive electrode cable of the measuring device to the positive electrode terminal of battery B. In Figure 2, both the positive electrode cable and the negative electrode cable are shown as electrode cables 51.

The measurement unit 1 preferably includes a current wire 60 that electrically connects the needle 20 to the battery B (see Figure 1). Specifically, the current wire 60 connects the needle 20 to the surface (outer surface) of the exterior body of the battery B. This reduces noise caused by the movement of the needle 20, enabling voltage to be measured with high accuracy.

<Control unit>
The control unit instructs the start and stop of movement of the holder 30 and receives the amount of displacement measured by the displacement measuring device 40. It is preferable that the control unit is electrically connected to the measuring device and receives the voltage value measured by the measuring device.

The control unit preferably controls the movement of the needle 20 based on the measurement value of the measuring device. That is, it preferably determines the stopping and starting of movement of the needle 20 (removal of the stop) based on the voltage value measured by the measuring device, and issues instructions to move and stop the holder 30. The voltage value used to control the stopping and starting of movement of the needle 20 may be set to any value.

[Measuring equipment]
As shown in FIG. 6 , the measuring device 100 includes a measuring unit 1 and a casing 70 that houses at least a portion of the measuring unit 1. The casing 70 is a rectangular box with an open side and a lid (not shown) that seals the opening. A through-hole (not shown) is provided in the other side of the casing 70 or in the lid, and the holder 30 passes through this through-hole, with a portion of the holder 30 housed within the casing 70. The measuring device does not need to be housed within the casing 70. Internally shorting the battery B within the casing 70 can improve operational safety. A thermometer may be placed within the casing 70 to measure temperature changes within the casing 70.

[Measurement method]
The measurement method includes the steps of placing a battery B on a base 10, measuring at least one of the voltage and current of the battery B placed on the base 10, moving a needle 20 toward the battery B whose voltage is being measured to make a hole, bringing the needle 20 into contact with the electrode layer located at the outermost layer within the holed battery B, and stopping the movement of the needle 20 that has come into contact with the electrode layer. Preferably, at least one of the voltage and current between the needle and the battery is further measured during the measuring step.

The measurement method may further include the steps of moving the stopped needle 20 again toward the inside of the battery B, and stopping the movement of the needle 20 again after it has penetrated the electrode layer. This measurement method is preferably performed using the measurement unit 1.

<Placing step>
The placing step may include a step of housing the measurement unit 1 excluding the measuring device in the casing 70. The placing step also includes a step of connecting the measuring device to each of the positive and negative terminals of the battery B placed on the base 10, and a step of connecting the displacement measuring device 40 to the control unit. It may also include a step of connecting the measuring device to the needle 20 and one terminal B1 of the battery B. If the needle 20 has the thermometer, it may also include a step of connecting the thermometer to the control unit.

<Measuring step>
In the measuring step, measurement of the voltage/current of battery B placed on base 10 is started. In this embodiment, voltage is measured. The measurement may include measurement of the voltage of battery B and measurement of the voltage between the needle and the battery.

<Hole drilling process>
In the hole-making step, the needle 20 is moved toward the battery B to make a hole. Specifically, a hole is made in the outer casing of the battery B and in the separator layer (outermost separator layer) disposed between the outer casing and the outermost electrode layer.

The speed at which the needle 20 moves toward the battery B is not particularly limited, but the upper limit of the speed may be, for example, 0.10 mm/sec, 0.05 mm/sec, or 0.01 mm/sec. The lower limit of the speed is not particularly limited, but may be, for example, 0.001 mm/sec. By keeping the speed within the above range, the accuracy of measuring the displacement of the needle 20 can be improved, and the needle 20 can be easily stopped.

The piercing process may include a first movement step in which the needle 20 is brought close to the battery B, and a second movement step in which the needle 20 pierces the exterior body and the outermost separate layer. In the first movement step, the needle 20 may be moved at a relatively fast speed until the distance between the battery B and the tip of the needle 20 is, for example, 1 mm or more and 5 mm or less, and in the second movement step after the first movement step, the needle 20 may be moved within the above speed range to pierce the exterior body and the outermost separate layer.

<Contacting step>
In the contacting step, the needle 20 is brought into contact with the outermost electrode layer. A short circuit caused by contact between the outermost electrode layer and the needle 20 changes the battery voltage and the voltage between the needle and the battery. By measuring this change, early symptoms of a short circuit can be observed. A thermometer may be built into the needle 20 to measure the temperature change of the short-circuited battery B.

<Stopping process>
In the stopping step, the movement of the needle 20 that has come into contact with the electrode layer is stopped. The movement of the needle 20 may be stopped after a predetermined time has elapsed after the contacting step, or the movement of the needle 20 may be stopped by control of the control unit when the voltage value measured by the measuring device reaches a predetermined value.

This measurement method can measure the voltage of Battery B when only one of the outermost electrode layers is short-circuited. This measurement method is suitable for evaluating the safety of Battery B because it allows observation of the behavior of Battery B when short-circuited at the smallest level.

<Removal step>
In the re-moving step, the needle 20 that has stopped moving is moved again toward the inside of the battery B. That is, the needle 20 that has stopped in contact with the outermost electrode layer is started to move so as to penetrate the outermost electrode layer. By re-moving the needle 20, the battery voltage and the needle-to-battery voltage change, and this change can be measured.

<Re-stopping process>
In the step of stopping again, the movement of the needle 20 that has penetrated the outermost electrode layer is stopped again. The needle 20 may be stopped again when it penetrates the outermost electrode layer, or when it comes into contact with an electrode layer adjacent to the outermost electrode layer.

By including the above-mentioned re-moving step and the above-mentioned re-stopping step, this measurement method can measure the voltage of battery B as a hole is created in the outermost electrode layer from contact between needle 20 and the outermost electrode layer and the hole expands, and can also measure the voltage of battery B when the hole is penetrated and a short circuit occurs only between the outermost electrode layer and the electrode layer adjacent to it.

<Step of connecting other batteries>
The above-described measurement method is a method for measuring voltage changes due to an internal short circuit in a single battery, but the measurement method may also be used to connect multiple batteries and measure the voltage/current changes when one of the batteries experiences an internal short circuit. Specifically, as shown in FIG. 7 , the measurement method may further include a step of connecting another battery Ba to battery B, and the voltage/current of battery B to which the other battery Ba is connected may be measured in the measurement step. The other battery Ba may be connected in parallel with battery B (see FIG. 7 ) or in series (not shown). The number of other batteries Ba connected to battery B is not particularly limited and may be one or two or more.

In products that use batteries, batteries may be installed in the form of a battery pack, in which multiple batteries are connected in parallel or series, or a battery unit, in which multiple battery packs are connected. If an internal short circuit occurs in one of the connected batteries, causing a voltage drop, current may inrush (enter) from the other batteries, potentially causing an event (such as explosion, rupture, fire, smoke, damage, or electrolyte leakage) in the battery with the internal short circuit. By connecting another battery (B) and intentionally short-circuiting it, and measuring the voltage/current of battery (B), it is possible to observe the signs, occurrence, and progress of the above-mentioned event in battery (B). In the measurement process, it is also recommended to measure the voltage between battery (B) and pin (20), the voltage of the other battery (B), the current between battery (B) and the other battery (B), and the temperature (surface temperature, internal temperature) of battery (B). Increasing the number of measurement targets allows for detailed observation of information related to the above-mentioned event (changes in battery (B)) and improves the ease and accuracy of evaluating the safety of the battery pack, battery unit, or product. A shunt (200) is recommended for measuring the current between battery (B) and the other battery (B).

An internal short circuit in battery B may be contact between the outermost electrode layer of battery B and the needle 20, or a short circuit between the needle 20 and the outermost electrode layer (positive electrode layer or negative electrode layer) of battery B and the adjacent electrode layer (negative electrode layer or positive electrode layer) (a short circuit between a single positive electrode layer and a single negative electrode layer), or a short circuit between the needle 20 and three or more electrode layers.

<Step of connecting the DC power supply>
As shown in Fig. 8, the measurement method may further include a step of connecting a DC power supply 300 to battery B, and the measuring step may measure the voltage/current of battery B connected to DC power supply 300. If an internal short circuit occurs in one or some of the batteries in a product equipped with the battery pack or battery unit, and high output is required from the product, a large current may rush from the other batteries into the battery with the internal short circuit, causing the above-mentioned event to occur and damaging the battery pack, battery unit, or product. The safety of battery B, the battery pack, the battery unit, or the product can be evaluated (CISC test) by connecting DC power supply 300 to battery B and injecting a constant current into the intentionally internally shorted battery B to measure the voltage/current (Constant-current Inrush during Internal Short Circuit: CISC).

In this measurement method (CISC test), battery B and DC power supply 300 are connected in parallel, and power supply control unit 400 is electrically connected to battery B and DC power supply 300. When power supply control unit 400 detects a voltage drop due to an internal short circuit in battery B, it instructs DC power supply 300 to supply current. DC power supply 300 may supply current immediately after the internal short circuit in battery B. Specifically, DC power supply 300 injects current several milliseconds to several hundred milliseconds after the internal short circuit in battery B. The current value supplied to battery B is not particularly limited and may be determined taking into account the maximum current value, wiring resistance, etc. of the product in which battery B is installed. The lower limit of the current value may be, for example, 1 A, 10 A, or 100 A. The upper limit of the current value may be, for example, 3000 A.

For the above CISC test, it is recommended to install a diode 310 in the wiring to protect the DC power supply 300 from reverse current. It is also recommended to install a switch 320 to stop the above CISC test in an emergency.

By connecting a DC power supply 300 to battery B and measuring the voltage/current of battery B that has been intentionally short-circuited internally, the safety of battery B, the battery pack, the battery unit, or the product can be evaluated.

[Safety evaluation method]
The safety evaluation method is a method for evaluating the safety of a battery that has experienced an internal short circuit, and includes the steps of placing the battery on a base, connecting another battery or a DC power source to the battery, moving a needle toward the battery placed on the base, causing an internal short circuit by puncturing the battery with the moved needle, measuring the current I [A] that rushes into the internally short-circuited battery from the other battery or the DC power source, and calculating the amount of energy Ec [A ² ·s] added to the internal resistance of the battery using the following equation 1.
Ec = Irms ² × T (1)
Here, "Irms ² " is the effective value [A] of the current I, and "T" is the total time [s] that the current I flows into the battery.

This safety assessment method evaluates safety based on the amount of energy Ec applied to an internally shorted battery B by another battery Ba or the DC power source 300. The current I that rushes into an internally shorted battery B from another battery Ba or the DC power source 300 can have a complex current waveform, making it difficult to calculate the amount of heat (Joule heat) generated by battery B. This safety assessment method evaluates the amount of energy Ec applied to battery B even when the rush current has a complex current waveform, making it possible to quantitatively evaluate the possibility of damage to battery B.

First, the effective value Irms [A] of the inrush current I [A] flowing through the internally shorted battery B is calculated using the following equation 2.
Here, "t" is the time [s] that has elapsed since the internal short circuit occurred in battery B.

Expanding the above equation 2 gives the following equation 3, where the left side is the product of the square of the effective value and time.

When the resistance (internal resistance) inside the internally short-circuited battery B is set to R, the following equation 4 is obtained.
(Irms ² × R) / (R × T) = (Ws × T) / R = J / R ... (4)
Here, "Ws" is the power [W] due to the inrush current I, and "J" is the heat generation amount [J] of the inrush current I.

From the above, the amount of energy Ec (Equation 1 above) applied to resistance R during an internal short circuit in Battery B can be used as a quantitative evaluation of Battery B after an internal short circuit occurs. As an example, Figures 13 and 14 show the results of a CISC test using multiple laminate cell batteries (maximum capacity 5.0 Ah) with NCM811 positive electrodes and graphite negative electrodes, in which an inrush current I of 1 A to 200 A was passed through each laminate cell battery using a DC power source.

In FIG. 13, the circles indicate damaged batteries, and the two-dot chain line is an approximation of the damaged batteries.
By cutting off the inrush current before it reaches the two-dot chain line (below the two-dot chain line in FIG. 13), it is possible to prevent the above-mentioned battery damage (event).

In FIG. 14, the circles indicate damaged batteries, and the two-dot chain line is an approximation of the damaged batteries.
By cutting off the inrush current before it reaches this two-dot chain line (to the left of the two-dot chain line in FIG. 14), damage to the battery can be prevented.

This safety evaluation method calculates the amount of energy Ec applied to battery B that has experienced an internal short circuit until the above-mentioned event occurs. If the current (energy) flowing into battery B is interrupted before the amount of energy applied to battery B reaches the calculated Ec, the above-mentioned event in battery B can be prevented.

In this safety evaluation method, the energy amount Ec may be calculated from the actual behavior (measurement) of the current I due to an internal short circuit in battery B, or the energy amount Ec may be calculated by simulation, and the calculation results from the measurements obtained by the above measurement may be compared with the calculation results from the above simulation. By using the energy amount Ec calculated by the above simulation, the number of measurements (number of tests) can be reduced, allowing for more efficient evaluation. Furthermore, the accuracy of the energy amount Ec calculated by the above measurement can be improved.

This safety evaluation test method simulates the conditions of Battery B used in the battery pack, battery unit, or as part of the product, and causes an internal short circuit in Battery B, making it possible to evaluate the safety of Battery B in the event of an internal short circuit under conditions and environments equivalent to those in which it is actually used.

[Other embodiments]
The above-described embodiments do not limit the configuration of the present invention. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as belonging to the scope of the present invention.

In the above embodiment, the displacement measuring device was described as a clip-type strain gauge, but the displacement measuring device is not particularly limited as long as it can measure the displacement of a needle.

The base is not limited to the above configuration and shape, as long as it can accommodate a battery and be configured to measure the needle displacement.

The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to these examples.

[Example 1]
A battery with an initial voltage of 4.2 V and the measurement unit 1 were prepared, and the battery was placed on the base 10. The measurement unit 1, excluding the voltage meter, was placed inside the casing 70. The needle 20 was moved to drill a hole in the battery and contact the outermost electrode layer. A displacement measuring device 40 with a resolution of 0.0025 mm was used. The control unit was set to stop needle 20 movement when the needle-to-battery voltage reached 4.0 V, restart needle 20 after a predetermined time had elapsed when the needle-to-battery voltage reached 4.0 V, and stop needle 20 movement again when the needle-to-battery voltage reached 4.05 V. Figure 9 shows the change in battery voltage due to the contact, and Figure 10 shows the change in needle-to-battery voltage. Figure 9 shows that the battery voltage dropped due to a short circuit caused by contact between the outermost electrode layer and needle 20. Figure 10 also shows that the needle-to-battery voltage dropped when the needle-to-battery voltage resumed movement. In FIG. 10, the needle-battery voltage waveform is disturbed before the needle 20 comes into contact with the battery exterior body, but this disturbance is noise (spatial noise) caused by the movement of the needle 20.

[Example 2]
A battery with an initial voltage of 4.2 V and a measurement unit 1 were prepared, and the battery was placed on a base 10. The measurement unit 1, excluding the voltage meter, was placed inside a casing 70, and a hole was pierced with a needle 20, which contacted the outermost electrode layer. A thermometer was built into the needle 20, and temperature changes of the battery were measured along with voltage changes. The control unit was set to stop movement of the needle 20 when the needle-to-battery voltage reached 4.0 V, restart the stopped needle 20 after a predetermined time had elapsed when the needle-to-battery voltage reached 4.2 V, stop the needle 20 again when the needle 20 contacted an electrode layer adjacent to the outermost electrode layer, and move the needle 20 away from the battery after a predetermined time had elapsed since the restart. The results are shown in Figure 11. While a short circuit between the outermost electrode layer and the needle 20 did not significantly change the temperature of the battery, a short circuit between the outermost electrode layer and the adjacent electrode layer (interlayer short circuit) caused a sudden rise in the battery temperature. The temperature of the battery returns to normal when the battery voltage and the voltage between the needle and the battery return to approximately 0 V. The battery voltage returns to approximately 3.7 V when the needle 20 moves away from the battery.

[Example 3]
As batteries to be subjected to an internal short circuit, a battery (test battery) with a reduced charge capacity and an initial voltage of 3.67 V, a battery (parallel battery) with an initial voltage of 3.67 V electrically connected in parallel to the test battery, and a measurement unit 1 were prepared. Also prepared were a voltage meter for measuring the voltage of the parallel battery and a current meter for measuring the current of the test battery. The test battery was placed on a base 10, and the measurement unit 1, excluding the voltage meter, was placed inside a casing 70. A hole was pierced in the test battery with a needle 20 to contact the outermost electrode layer.

The control unit is set to stop the movement of the needle 20 when the needle-battery voltage reaches 2.5V, to restart the movement of the needle 20 when a predetermined time has passed since the needle 20 was stopped and the battery voltage reached its initial voltage (3.67V), and to stop the movement of the needle 20 again when the battery voltage drops by 0.15V (reaching 3.52V).

A shunt was placed on the wire connecting the negative terminals of the parallel battery and the test battery, and the current between the test battery and the parallel battery was measured with the current measuring device ("6 - Current Between Batteries" in Figure 12). The voltage of the parallel battery was also measured ("8 - Parallel Battery Voltage" in Figure 12). A thermometer was built into the needle 20 to measure the temperature inside the test battery ("3 - Battery Temperature" in Figure 12). Two thermometers were placed near the point where the needle 20 pierced the test battery to measure the change in the surface temperature of the test battery ("1 - Battery Surface Temperature" and "2 - Battery Surface Temperature" in Figure 12). A thermometer was also placed inside the casing 70 to measure the change in temperature inside the casing 70 ("4 - Temperature Inside Casing" in Figure 12). The load of the needle 20 on the test battery ("5 - Load" in Figure 12) and the displacement of the holder 30 were also measured ("10 - Holder Displacement" in Figure 12). Figure 12 shows a graph of these measurements, along with the voltage of the test battery ("7 - Battery Voltage" in Figure 12), the needle-to-battery voltage ("9 - Needle-to-Battery Voltage" in Figure 12), and the displacement of needle 20 ("11 - Needle Displacement" in Figure 12).

Figure 12 shows that after the needle 20 was stopped again, a difference occurred between the displacement of the needle 20 and the displacement of the holder 30. This is thought to be because the displacement of the holder 30 includes various displacements caused by factors such as thermal expansion of the battery, base 10, needle 20, etc., making it difficult to measure the displacement with high accuracy. For this reason, it is preferable to measure the displacement of the needle 20 directly, and even more preferable to measure it at a location as close to the battery as possible. The needle-to-battery voltage is disrupted between 500 and 1400 seconds and between 1800 and 2400 seconds, and the ability to observe such disruption is significant in evaluating batteries that have experienced an internal short circuit. Note that the current between the batteries reached 0 A before 2600 seconds because the test battery was disconnected from the parallel battery.

The measurement unit disclosed herein can easily and accurately measure voltage changes due to internal short circuits in a battery, making it ideal for use in evaluating battery characteristics at battery development and manufacturing sites.

REFERENCE SIGNS LIST 1 Measurement unit 10 Base 11 Main body 12 Column portion 13 Beam portion 13a Through hole 20 Needle 21 Needle main body 22 Widening portion 30 Holder 40 Displacement measuring device 41 First connecting portion 42 Second connecting portion 43 Sensor portion 50 Second voltage measuring device 51 Electrode cable 60 Current line 70 Casing 100 Measuring device 200 Shunt 300 DC power supply 310 Diode 320 Switch 400 Power supply control unit B, Ba Battery B1 Terminal

Claims (5)

A unit for measuring at least one of a voltage and a current of a battery that is short-circuited by being pierced with a needle , and at least one of a voltage and a current between the needle and the short-circuited battery ,
a base on which the battery is placed;
a needle for piercing the battery placed on the base;
a holder that holds the needle and moves it so as to puncture the battery placed on the base;
a displacement measuring device for measuring the displacement of the needle;
a first measuring device for measuring at least one of the voltage and current of the battery ;
a second measuring device for measuring at least one of the voltage and the current between the battery and the needle;
a control unit that receives the displacement amount of the needle measured by the displacement measuring device, the measurement value measured by the first measuring device, and the measurement value measured by the second measuring device, and controls the displacement of the needle;
Equipped with
The above base is
a main body on which the battery is placed;
A pair of pillars standing on the main body;
a beam portion that is spaced apart from the surface of the battery placed on the main body and that is bridged across the pair of columns,
A measuring unit in which the displacement measuring device measures the displacement of the needle relative to the beam . 2. The measuring unit according to claim 1, wherein the displacement measuring device has a first connection part connected to the needle and a second connection part connected to the beam part of the base. The measurement unit of claim 1, wherein the needle and the holder are insulated. The measurement unit according to claim 1 , further comprising a current line that electrically connects the surface of the exterior body of the battery to the needle and suppresses noise generated by movement of the needle. The measurement unit according to any one of claims 1 to 4 ,
a casing that houses at least a portion of the measuring unit.