JP7122938B2 - Micro-short circuit detection method and micro-short circuit detection device - Google Patents

Description

The present invention relates to a micro-short circuit detection method and a micro-short circuit detection device.

Lithium secondary batteries are generally constructed by using a metal oxide into which lithium can be intercalated and deintercalated for the positive electrode, and a graphite material into which lithium can be intercalated and deintercalated, for the negative electrode. , lithium ions are desorbed from the positive electrode and inserted into the negative electrode. Lithium secondary batteries are widely used as power supply sources for various electronic devices because they are relatively superior in terms of energy density, output voltage, battery life, and the like.

By the way, in a lithium secondary battery, needle-like crystals of lithium called dendrites may be deposited on the surface of the negative electrode during charging. However, there is a risk that a short circuit may occur and the electrolyte or the separator may ignite. Moreover, in this case, the lithium oxide used as the positive electrode of the lithium secondary battery releases highly active oxygen ions when it reaches a high temperature, which may cause violent combustion due to thermal runaway.

As a countermeasure against short-circuit failures such as those described above, Patent Document 1 discloses a conventional technique for determining the occurrence of a minute short-circuit as a sign of short-circuiting between electrodes during charging of a lithium secondary battery. . More specifically, in the prior art, dendrite deposition is considered to occur when the reciprocal of the amount of change in the battery voltage of a lithium secondary battery during charging becomes a value greater than a preset specified value. Judging.

JP 2013-89363 A

However, the amount of change in battery voltage of a lithium secondary battery varies depending on various conditions such as battery characteristics and charging conditions. Therefore, if the amount of change in the battery voltage for judging a small short circuit is obtained under conditions different from the data previously obtained for setting the specified value, it is possible to correctly judge a small short circuit. can't Therefore, in the conventional technology described above, the conditions for correctly determining the occurrence of a micro-short are restricted, and versatility is reduced. In addition, the measured battery voltage may show a value that deviates greatly from the true voltage value due to the influence of noise that occurs stochastically due to the measurement system. may be erroneously determined.

The present invention has been made in view of such circumstances, and its object is to improve the versatility and accuracy of detection of micro-short circuits in lithium secondary batteries. is to provide

<First aspect of the present invention>
A first aspect of the present invention is a micro-short circuit detection method for detecting a micro-short circuit in a charging period of a lithium secondary battery by constant current charging, wherein the ratio of the battery capacity to the charging current of the lithium secondary battery per unit time a voltage acquisition step of acquiring the battery voltage of the lithium secondary battery in the charging period every unit time; and a change of calculating a voltage change amount of the battery voltage every unit time. and a slight short circuit determination step of determining that a slight short circuit has occurred when the amount of voltage change during the charging period of the lithium secondary battery is less than a predetermined threshold, wherein the threshold is the The micro-short circuit detection method is set as Th=μ−α×σ using the coefficient α corresponding to the unit time and the previously obtained average value μ and standard deviation σ of the voltage change amount.

In the method for detecting a slight short circuit according to the first aspect of the present invention, in the charging period of the lithium secondary battery, the unit time is defined by the ratio of the battery capacity to the charging current, and the battery voltage obtained every unit time. By calculating the amount of change, it is possible to calculate an index for detecting a slight short circuit that does not depend on the battery voltage and charging current of the lithium secondary battery. Furthermore, in the method for detecting a small short circuit according to the first aspect of the present invention, the threshold value is set using the coefficient α corresponding to the unit time and the average value μ and standard deviation σ of the voltage change amount obtained in advance. , it is possible to detect a slight short circuit while suppressing the occurrence of erroneous detection due to stochastically generated noise. As a result, according to the method for detecting a minute short circuit according to the first aspect of the present invention, it is possible to improve the versatility and the accuracy of determination in detecting a minute short circuit in a lithium secondary battery.

<Second aspect of the present invention>
According to a second aspect of the present invention, in the first aspect of the present invention described above, the coefficient α is such that the reciprocal of the number of calculations of the voltage change amount in the charging period is from the interval of the distribution defined by the threshold value. It is a micro short circuit detection method that is set to be lower than the probability of disconnection.

According to the second aspect of the present invention, the coefficient α used for calculating the threshold value for detecting a small short circuit is set as a value that suppresses erroneous detection of a small short circuit caused by stochastically occurring noise. Therefore, it is possible to further improve the detection accuracy of a micro short circuit.

<Third aspect of the present invention>
According to a third aspect of the present invention, in the above-described first or second aspect of the present invention, when the number of times it is determined that a slight short circuit has occurred is equal to or greater than a predetermined number of times in the minute short circuit determination step, In the method for detecting a slight short circuit, charging of the lithium secondary battery is stopped.

According to the third aspect of the present invention, charging of the lithium secondary battery is not immediately stopped even in the unlikely event that the occurrence of a small short circuit is erroneously determined due to noise that occurs stochastically. As a result, the risk of erroneously discarding a normal lithium secondary battery can be reduced.

<Fourth aspect of the present invention>
A fourth aspect of the present invention includes a charging circuit for charging a lithium secondary battery, an ammeter for measuring the charging current of the lithium secondary battery, a voltmeter for measuring the battery voltage of the lithium secondary battery, a control unit that charges the lithium secondary battery by controlling the charging circuit, wherein the control unit controls the lithium secondary battery with respect to the charging current during a charging period of the lithium secondary battery by constant current charging. The amount of voltage change in the battery voltage is calculated for each unit time defined by the ratio of the battery capacity of the battery, and when the amount of voltage change is below a predetermined threshold, it is determined that a slight short circuit has occurred in the lithium secondary battery. and the threshold value is set as Th=μ-α×σ using the coefficient α corresponding to the unit time and the pre-obtained average value μ and standard deviation σ of the voltage change amount. It is a short circuit detection device.

A slight short circuit detection device according to a fourth aspect of the present invention is a charging period of a lithium secondary battery, in which the unit time is defined by the ratio of the battery capacity to the charging current, and the battery voltage voltage obtained every unit time By calculating the amount of change, it is possible to calculate an index for detecting a slight short circuit that does not depend on the battery voltage and charging current of the lithium secondary battery. Furthermore, in the micro-short detection device according to the fourth aspect of the present invention, the threshold value is set using the coefficient α corresponding to the unit time and the pre-obtained average value μ and standard deviation σ of the voltage change amount. , it is possible to detect a slight short circuit while suppressing the occurrence of erroneous detection due to stochastically generated noise. As a result, according to the micro-short circuit detection device according to the fourth aspect of the present invention, it is possible to improve versatility and determination accuracy in detecting micro-short circuits in lithium secondary batteries.

<Fifth aspect of the present invention>
According to a fifth aspect of the present invention, in the fourth aspect of the present invention described above, the coefficient α is such that the reciprocal of the number of calculations of the voltage change amount in the charging period is from the interval of the distribution defined by the threshold value. It is a micro-short circuit detection device that is set to be lower than the probability of disconnection.

According to the fifth aspect of the present invention, the coefficient α used for calculating the threshold value for detecting a small short circuit is set as a value that suppresses erroneous detection of a small short circuit caused by stochastically occurring noise. Therefore, it is possible to further improve the detection accuracy of a micro short circuit.

<Sixth aspect of the present invention>
According to a sixth aspect of the present invention, in the fifth or sixth aspect of the present invention described above, when the number of times it is determined that a slight short circuit has occurred is equal to or greater than a predetermined number of times, the lithium secondary It is a micro-short circuit detection device that stops charging of the next battery.

According to the sixth aspect of the present invention, charging of the lithium secondary battery is not stopped immediately even in the unlikely event that the occurrence of a small short circuit is erroneously determined due to stochastically generated noise. As a result, the risk of erroneously discarding a normal lithium secondary battery can be reduced.

According to the present invention, it is possible to provide a micro-short-circuit detection method and a micro-short-circuit detection device that improve versatility and determination accuracy in detecting micro-short circuits in lithium secondary batteries.

1 is a configuration diagram schematically showing a circuit configuration of a charger according to the present invention; FIG. 4 is a flow chart showing a procedure executed by a control unit; 4 is a graph showing battery voltage and voltage change when the battery capacity is 5 [mAh] and the charging current is 1 [mA]. 4 is a graph showing battery voltage and voltage change when battery capacity is 5 [mAh] and charging current is 5 [mA]. 4 is a graph showing battery voltage and voltage change when the battery capacity is 5 [mAh] and the charging current is 15 [mA]. 4 is a graph showing battery voltage and voltage change when battery capacity is 10 [mAh] and charging current is 2 [mA]. 4 is a graph showing battery voltage and voltage change when battery capacity is 10 [mAh] and charging current is 10 [mA]. 4 is a graph showing battery voltage and voltage change when the battery capacity is 10 [mAh] and the charging current is 30 [mA]. 5 is a graph showing a first example of battery voltage and voltage change amount of a lithium secondary battery in which a slight short circuit has occurred; 7 is a graph showing a second example of battery voltage and voltage change amount of a lithium secondary battery in which a slight short circuit has occurred;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the content described below, and can be arbitrarily changed and implemented without changing the gist of the present invention. In addition, all of the drawings used for describing the embodiments schematically show constituent members, and are partially emphasized, enlarged, reduced, or omitted for the purpose of deepening understanding. It may not represent the scale, shape, etc. accurately.

FIG. 1 is a configuration diagram schematically showing the circuit configuration of a charger 1 according to the present invention. In this embodiment, the charger 1 charges the lithium secondary battery 3 with power supplied from the external power supply 2 by being connected to the external power supply 2 and the lithium secondary battery 3 respectively. In addition, the charger 1 functions as a "minor short circuit detection device" that detects the occurrence of a minor short circuit in the lithium secondary battery 3 during the charging period in which the lithium secondary battery 3 is charged with a constant current.

The charger 1 more specifically includes a charging circuit 10 , a control section 20 , an ammeter 30 , a voltmeter 40 , an input section 50 and an output section 60 .

The charging circuit 10 converts the power input from the external power supply 2 into charging power for the lithium secondary battery 3 and outputs the charging power under the control of the control unit 20 . Here, when AC power is supplied from the external power supply 2, the charging circuit 10 converts the AC power into DC power.

The control unit 20 is composed of, for example, a known microcomputer control circuit or an electronic computer such as a personal computer, and performs charging control while monitoring the state of the lithium secondary battery 3. Detects the occurrence of micro-shorts.

Ammeter 30 is provided in series on a circuit connecting charging circuit 10 and lithium secondary battery 3 , measures the charging current supplied to lithium secondary battery 3 , and outputs the measured charging current to control unit 20 .

The voltmeter 40 is provided in parallel on a circuit connecting the charging circuit 10 and the lithium secondary battery 3 , measures the battery voltage of the lithium secondary battery 3 , and outputs the measured voltage to the control unit 20 .

Here, the ammeter 30 and the voltmeter 40 respectively measure the current and voltage as analog signals with built-in AD converters, convert them into digital signals at sampling intervals according to their specifications, and output them to the control unit 20. do. Therefore, the cycle in which the control unit 20 acquires the current and voltage may differ from the cycle in which the ammeter 30 and the voltmeter 40 measure the current and voltage.

The input unit 50 is used to input various parameters required for charging control of the lithium secondary battery 3 and control for determining the occurrence of a small short circuit, and outputs various input parameters to the control unit 20 . The input unit 50 may be, for example, a keyboard or buttons for selecting parameters.

The output unit 60 is used to present various information output from the control unit 20 to the user, and notifies the state of charge of the lithium secondary battery 3, the occurrence of a slight short circuit, and the like. The output unit 60 may be, for example, a display, or may be a display lamp that presents various information by lighting an LED.

Next, the operation of the controller 20 in the charger 1 will be described. FIG. 2 is a flow chart showing the procedure executed by the control unit 20. As shown in FIG. The control unit 20 detects a minute short circuit while charging the lithium secondary battery 3 by the minute short circuit detection method shown in FIG.

In this embodiment, the charger 1 performs constant current charging (CC charging) until the lithium secondary battery 3 reaches a target voltage (here, 4.2 [V]), and then charges the lithium secondary battery 3 with a constant voltage. It is assumed that so-called CCCV charging (Constant Current Constant Voltage), which is switched to charging (CV charging), is performed. Since the detection of a slight short circuit according to the present invention is performed during the charging period of CC charging, detailed description of CV charging will be omitted below.

Various parameters of the lithium secondary battery 3 are input to the controller 20 of the charger 1 as a preparation for starting the flow chart of FIG. More specifically, the control unit 20 controls the battery capacity A [Ah] of the lithium secondary battery 3 to be charged, which is input via the input unit 50, and the charging current B [Ah] for charging the lithium secondary battery 3. ] settings.

When various parameters are read, the control unit 20 starts the procedure according to the flow chart, and defines the unit time dt, which is the calculation cycle for determining a slight short circuit (step S1, unit time defining step). More specifically, the controller 20 defines the unit time dt as the ratio of the battery capacity A to the charging current B of the lithium secondary battery 3 according to the following equation (1). Here, the numerical value 3600 in the formula is due to the fact that the unit of the battery capacity A is [Ah], and can be appropriately changed depending on the notation of the unit.
dt=A/(B×3600) Expression (1)

Next, the control unit 20 calculates a threshold TH for successively determining the occurrence of a micro short circuit (step S2). Here, the threshold TH is a threshold for the amount of voltage change dV/dt of the battery voltage V during the charging period of the lithium secondary battery 3, and the details of the calculation method thereof will be described later.

When the unit time dt has been defined and the threshold value TH has been calculated, the control unit 20 controls the charging circuit 10 to perform constant current charging of the lithium secondary battery 3 at the read set value of the charging current B[A]. is started (step S3).

When charging is started, the control unit 20 determines whether or not the unit time dt defined in step S1 has passed (step S4). That is, in step S4, in order to determine whether there is a slight short circuit every unit time dt, the subsequent processing is temporarily suspended (No in step S4).

After the unit time dt has elapsed, the control unit 20 acquires the battery voltage V at this timing from among the battery voltages V of the lithium secondary battery 3 continuously measured by the voltmeter 40 (step S5). That is, the control unit 20 acquires the battery voltage V of the lithium secondary battery 3 every unit time dt (voltage acquisition step).

Then, the control unit 20 determines whether or not the obtained battery voltage V has reached the target voltage of 4.2[V] (step S6).

When the battery voltage V reaches the target voltage (Yes in step S6), the control unit 20 terminates the constant current charging including the detection of the slight short circuit to the lithium secondary battery 3, and continues to the constant voltage charging described above. do. Here, the control unit 20 may present to the user via the output unit 60 that the constant current charging has ended normally or that a slight short circuit was not detected during the charging period of the constant current charging.

On the other hand, if the battery voltage V has not reached the target voltage in step S6 (No in step S6), the control unit 20 calculates the voltage change amount dV/dt of the battery voltage V every unit time dt (step S8, variation calculation step).

Then, the control unit 20 compares the calculated voltage change amount dV/dt with the threshold value TH calculated in step S2 to determine whether or not a slight short circuit has occurred in the lithium secondary battery 3 ( step S9, minute short-circuit determination step).

Here, when a slight short circuit occurs in the lithium secondary battery 3, the positive electrode and the negative electrode are instantaneously connected to cause the battery voltage V to decrease, thereby decreasing the value of the voltage change amount dV/dt. will let you Therefore, when the voltage change amount dV/dt is less than the threshold value TH (Yes in step S9), the control unit 20 determines that a slight short circuit has occurred in the lithium secondary battery 3, and performs constant current charging in step S7. finish. In this case, the control unit 20 presents to the user via the output unit 60 that constant current charging has been forcibly terminated due to the occurrence of a slight short circuit.

In step S9, when it is determined that the voltage change amount dV/dt is equal to or greater than the threshold TH (No in step S9), the control unit 20 determines that the minor short circuit of the lithium secondary battery 3 has not been detected. Returning to step S4, the constant current charging of the lithium secondary battery 3 is continued. As a result, the control unit 20 continues the slight short-circuit determination every unit time dt during the charging period of the constant current charging.

Next, actual measurement data of the battery voltage V and the amount of voltage change dV/dt will be described. Measured data obtained when the above-described constant-current charging was performed under a plurality of conditions for a newly manufactured lithium secondary battery 3 is illustrated here. First, a lithium secondary battery 3 was produced by the following procedure.

(positive electrode)
On one side of the aluminum current collector, a slurry prepared by adjusting 94 parts by weight of LiNiCoAlO2 as an active material, 3 parts by weight of acetylene black as a conductive material, and 3 parts by weight of PVdF as a binder was applied to one side in an amount of 11 [mg/ cm ² ], dried and pressed, and then cut into a size of 17×17 [mm] (excluding the terminal welded portion) to obtain a positive electrode.

(negative electrode)
On one side of the copper current collector, a slurry adjusted to a composition of 100 parts by weight of graphite, 1.5 parts by weight of CMC (carboxymethyl cellulose) as a thickener, and 3.0 parts by weight of SBR (styrene butadiene rubber) as a binder was applied to one side. It was applied at a coating amount of 7.0 [mg/cm ² ], dried and pressed, and then cut into a size of 18×18 [mm] (excluding the terminal welded portion) to obtain a negative electrode.

(separator)
As the separator, an olefin-made or cellulose-made separator used in a general lithium-ion secondary battery can be used.

(Creating a cell)
A laminate was prepared by laminating the positive electrode, the separator, and the negative electrode in this order. The obtained laminate was inserted into an aluminum laminate film as an exterior material to assemble a cell. An electrolytic solution (1 [mol/l] concentration of LiPF6 dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a weight ratio of 1:2) was injected into the cell, impregnated under reduced pressure, and then vacuum-sealed. stopped. The sealing width of the aluminum laminate was set to 2.5 [mm], and the four sides were sealed with a heat bar of 180 [°C] having a PTFE sheet on the surface to prepare a cell. The battery capacity A at this time was about 5 [mAh].

Further, a lithium secondary battery 3 having a battery capacity A of about 10 [mAh] was produced by the same production method as above.

3 to 8 show the battery voltage V and voltage change amount dV/dt when the lithium secondary battery 3 manufactured as described above is charged with a plurality of charging currents B, respectively. 3 to 8 show the data series of the battery voltage V and voltage change amount dV/dt when the lithium secondary battery 3 is charged to the target voltage, with the horizontal axis representing the time [s] from the start of charging.

More specifically, for the battery voltage V and the voltage change amount dV/dt of the lithium secondary battery 3 with a battery capacity A of 5 [mAh], the figure shows the case where the charging current B is 1 [mA] (0.2C). 3, the case (1C) in which the charging current B is 5 [mA] is shown in FIG. 4, and the case (3C) in which the charging current B is 15 [mA] is shown in FIG.

FIG. 6 shows the battery voltage V and voltage change amount dV/dt of the lithium secondary battery 3 with a battery capacity A of 10 [mAh] when the charging current B is 2 [mA] (0.2 C). FIG. 7 shows (1C) when the charging current B is 10 [mA], and FIG. 8 shows (3C) when the charging current B is 30 [mA].

As can be seen from FIGS. 3 to 8, the lithium secondary battery 3 varies in the time required to reach the target voltage and the variation in data depending on the magnitude of the charging current B. Since the amount of voltage change dV/dt is calculated based on the battery voltage V obtained every unit time dt, it is confirmed that the value of the amount of voltage change dV/dt is approximately -0.0005 under any conditions. can. That is, the lithium secondary battery 3 calculates the voltage change amount dV/dt for each unit time dt of the formula (1) as long as a slight short circuit does not occur, thereby obtaining the battery capacity A of the lithium secondary battery 3 and the Regardless of the charging current B, a stable voltage change amount dV/dt can be calculated.

Next, a method for calculating the above-described threshold value TH for detecting a slight short circuit will be described in more detail. The threshold value TH calculated by the controller 20 of the charger 1 is calculated by previously obtaining the voltage change amount dV/dt as shown in any one of FIGS. Here, a case where the voltage change amount dV/dt shown in FIG. 3 is obtained in advance will be described as an example.

When the lithium secondary battery 3 is charged at a constant current, the battery voltage V rises relatively sharply at the initial stage, and thereafter the battery voltage V rises toward the target voltage at a relatively slow and constant pace. go. In FIG. 3, it can be confirmed that the voltage change amount dV/dt of the lithium secondary battery 3 converges to a substantially constant value from about 2000 seconds after the start of charging. Therefore, it is assumed that the data series of the voltage change amount dV/dt after about 2000 seconds follows a normal distribution, and the average μ and standard deviation σ thereof are calculated. In the example of the voltage variation dV/dt in FIG. 3, the average μ=0.0005 and the standard deviation σ=1.8.

Then, the control unit 20 in the charger 1 stores the above-described average μ and standard deviation σ of the voltage change amount dV/dt obtained in advance, and calculates the coefficient α corresponding to the unit time dt defined in step S1. is used to calculate the threshold value TH according to the following equation (2).
TH=μ−α×σ (2)

Here, the coefficient α is a parameter for adjusting the allowable amount for variations in voltage variation dV/dt of the lithium secondary battery 3 . That is, the calculated voltage change amount dV/dt may greatly deviate from the original value due to, for example, the influence of noise that stochastically occurs due to the measurement system. To some extent, it is more likely to be erroneously detected that a minute short circuit has occurred with respect to the variation. On the other hand, the greater the value of the set coefficient α, the more likely it is that the occurrence of a micro-short will be overlooked. Therefore, the coefficient α is set as follows in consideration of the noise occurrence probability.

For example, when the charger 1 charges the lithium secondary battery 3 having a battery capacity A of 5 [mAh] with a charging current B of 2.5 [mA] (0.5 C), in the unit time regulation step of step S1, the above The unit time dt=2 [s] is defined by the formula (1). At this time, the number n of calculations of the voltage change amount dV/dt calculated until the lithium secondary battery 3 reaches the target voltage is 9000 times. Even if the unit time dt is calculated as another value, the number of calculations n can be calculated by the same method. show.

Further, the voltage change amount dV / dt of the lithium secondary battery 3 is assumed to follow the normal distribution of the data series, so the probability that it is included in the interval μ ± α × σ according to the coefficient α and the interval can be calculated. Table 2 shows the respective probabilities for values of the coefficient α.

Based on the above probability, in step S2, the control unit 20 of the charger 1 determines that the reciprocal of the number n of calculations of the voltage change amount dV/dt during the charging period is the interval of the distribution defined by the threshold TH, that is, μ±α The coefficient α is set so as to be lower than the probability of deviating from the interval defined by xσ, and the threshold TH is calculated based on the above equation (2).

More specifically, in the case of this embodiment, since the number n of calculations of the voltage change amount dV/dt is 9000, the calculated value of the voltage change amount dV/dt is stochastically generated due to the measurement system. The coefficient α is set so that the probability of deviation from the interval defined by μ±α×σ due to the influence of noise is less than 1/9000. Here, by setting the coefficient α to, for example, 5, it is possible to suppress the occurrence probability of erroneous detection by one digit more than the noise occurrence probability. Similarly, when the unit time dt = 20 [s], the number of calculations n = 900. Therefore, by setting the coefficient α to, for example, 4, the probability of false detection is reduced by one digit more than the probability of noise occurrence. The occurrence probability can be suppressed.

In this embodiment, the controller 20 of the charger 1 determines that a slight short circuit has occurred when the voltage variation dV/dt is below the threshold TH, as seen in step S9 in the flowchart of FIG. The number of times that a slight short circuit is determined to have occurred is counted, and when the number of times is equal to or greater than a predetermined number (for example, three times), charging of the lithium secondary battery 3 is performed. may be stopped. In addition, the control unit 20 of the charger 1 stops charging the lithium secondary battery 3 when the number of times it is determined that a slight short circuit has occurred exceeds a predetermined number of times within an arbitrarily set time period. You may

Here, actual measurement data when a slight short circuit occurs during charging of the lithium secondary battery 3 will be described. 9 and 10 are graphs plotting the battery voltage V and voltage variation dV/dt of the lithium secondary battery 3 in which a slight short circuit occurred during the charging period.

More specifically, FIGS. 9 and 10 show battery voltage V and voltage variation dV when the lithium secondary battery 3 with battery capacity A=5 [mA] is charged with charging current B=5 [mA]. /dt. Here, even after it is determined that a slight short circuit has occurred, charging is continued and data is acquired. Note that the threshold value TH is expressed by the above equation (2) with the coefficient α=5 set as described above based on the values of the average μ=0.0005 and the standard deviation σ=1.8 in FIG. 3 and the unit time dt. is calculated as TH=-0.0004.

9 and 10, the lithium secondary battery 3 has a voltage change amount dV/dt stable around 0.0005 from about 300 [s] to 2700 [s] from the start of charging, but at T1 At the indicated timing, the voltage change amount dV/dt starts to vary and falls below the threshold value Th, so that it is determined that a slight short circuit has occurred. Then, it can be confirmed that the short-circuit state is reached at the timing indicated by T2, and the battery voltage V rapidly drops. That is, the charger 1 judges the minor short circuit of the lithium secondary battery 3 based on the voltage change amount dV/dt and the threshold value TH set as described above, thereby preventing the lithium secondary battery 3 from reaching the short circuit state. Charging of the battery 3 can be stopped.

As described above, according to the present invention, in detecting a slight short circuit in the lithium secondary battery 3, the unit time dt is defined by the ratio of the battery capacity A to the charging current B, and the coefficient α corresponding to the unit time dt is obtained in advance. By setting the threshold value TH using the average value μ and standard deviation σ of the voltage change amount dV/dt, regardless of the battery capacity A and charging current B conditions of the lithium secondary battery 3 to be charged, It is possible to detect a slight short circuit while suppressing the occurrence of erroneous detection caused by stochastically generated noise. Therefore, according to the present invention, it is possible to improve versatility and determination accuracy in detecting a minor short circuit in the lithium secondary battery 3 .

1 Charger 2 External Power Supply 3 Lithium Secondary Battery 10 Charging Circuit 20 Control Section 30 Ammeter 40 Voltmeter 50 Input Section 60 Output Section

Claims (6)

A slight short circuit detection method for detecting a slight short circuit during a charging period of a lithium secondary battery by constant current charging,
a unit time defining step of defining the unit time by the ratio of the battery capacity to the charging current of the lithium secondary battery;
a voltage acquisition step of acquiring the battery voltage of the lithium secondary battery during the charging period every unit time;
A change amount calculation step of calculating a voltage change amount of the battery voltage every unit time;
a slight short circuit determination step of determining that a slight short circuit has occurred when the amount of voltage change is below a predetermined threshold during the charging period of the lithium secondary battery;
The threshold value is set as Th=μ-α×σ using the coefficient α corresponding to the unit time and the pre-obtained average value μ and standard deviation σ of the voltage change amount. . 2. The micro-short circuit according to claim 1, wherein the coefficient α is set so that the reciprocal of the number of times the voltage change amount is calculated during the charging period is lower than a probability of deviating from the section of the distribution defined by the threshold value. Detection method. 3. The micro-short circuit according to claim 1, wherein in the micro-short-circuit determination step, charging of the lithium secondary battery is stopped when the number of times the occurrence of the micro-short circuit is determined to be a predetermined number or more. Detection method. a charging circuit for charging a lithium secondary battery;
an ammeter for measuring the charging current of the lithium secondary battery;
a voltmeter for measuring the battery voltage of the lithium secondary battery;
a control unit that charges the lithium secondary battery by controlling the charging circuit;
The control unit calculates a voltage change amount of the battery voltage for each unit time defined by a ratio of the battery capacity of the lithium secondary battery to the charging current during a charging period of the lithium secondary battery by constant current charging. and determining that a slight short circuit has occurred in the lithium secondary battery when the amount of voltage change is below a predetermined threshold,
The threshold value is set as Th=μ−α×σ using the coefficient α corresponding to the unit time and the pre-obtained average value μ and standard deviation σ of the voltage change amount. . 5. The micro-short circuit according to claim 4, wherein the coefficient α is set so that the reciprocal of the number of calculations of the voltage change amount during the charging period is lower than the probability of being out of the distribution section defined by the threshold value. detection device. 6. The micro-short circuit detection device according to claim 4, wherein said control unit stops charging said lithium secondary battery when the number of times it is determined that a micro-short circuit has occurred is equal to or greater than a predetermined number.

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