JP2010016944A - Charging voltage control method, battery charger using the same, overcharge protection method, and battery pack using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to inject more electric charges into a battery charger for lithium ion secondary batteries. <P>SOLUTION: With respect to battery chargers for constant-current, constant-voltage (CC-CV) charging, the Battery Association of Japan recommends that charging voltage Vx should be 4.25 V at up to 45°C, 4.15 V at higher temperatures, and 4.10 V at 50°C or higher as indicated by reference code α1. In this invention, meanwhile, the charging voltage is determined from Vx=ä[(Tlim-Tx)/(Tlim-Tctl)]×(Vctl<SP>2</SP>-Ve<SP>2</SP>)+Ve<SP>2</SP>}<SP>1/2</SP>, where, Tx is the temperature of a battery cell; Tctl is the temperature (=45°C) at which the suppression of charging voltage should be started because of high temperature; Vctl is the maximum charging voltage permitted in the battery cell at temperature Tctl; Tlim is the maximum temperature permitted in the battery cell in terms of safety; and Ve is the discharge termination voltage of the battery cell. Therefore, the charging voltage is as indicated by reference code α2 and charging can be additionally carried out by the amount equivalent to the portion hatched with oblique lines. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for controlling a charging voltage of a battery pack including a secondary battery cell, a charger using the same, an overcharge protection method in the battery pack, and the battery pack using the same.

  Secondary batteries are being improved daily, and the amount of energy stored per unit volume and weight is increasing. And as a guideline for safely using such a battery with high energy density, there is Non-Patent Document 1. The non-patent document 1 defines a charging / discharging profile of a lithium ion secondary battery, and the charging profile is defined as shown in Table 1 and FIG. That is, T2 = 10 ° C. to T3 = 45 ° C. is the standard temperature range, the charging voltage in the standard temperature range is 4.25 V, and the charging current is a predetermined value Ic determined by each manufacturer, for example, 0.8 C. In contrast, in the low temperature range from T1 = 0 ° C. to T2 = 10 ° C., the charging voltage is 4.25V, but the charging current is Ic / 2, instead of lowering the charging voltage to 4.10V. The charging current is selected from the case where Ic remains unchanged. In the region exceeding the temperature T3, 4.15V until T4 = 50 ° C. and 4.10V until T4 ′ = 60 ° C., and the charging current remains Ic.

“Guidebook on the Safe Use of Lithium Ion Secondary Batteries in Notebook PCs” April 20, 2007 Japan Electronics and Information Technology Industries Association, Battery Industry Association (BAJ)

  However, in the standard according to Non-Patent Document 1, since the control of the charging voltage is rough, there is a possibility that the capacity of the secondary battery cannot be fully utilized. It became clear that charge could be injected.

  An object of the present invention is to provide a charging voltage control method capable of injecting more charges, a charger using the same, an overcharge protection method, and a battery pack using the same.

The charging voltage control method of the present invention is a charging voltage control method for charging a battery cell with a voltage Vx corresponding to the temperature Tx of the battery cell. The maximum charging voltage that the battery cell can accept at Tctl is Vctl, the maximum temperature that the battery cell can safely accept is Tlim, the discharge end voltage of the battery cell is Ve, and the temperature of the current battery cell that exceeds the temperature Tctl is When Tx, Vx = {[(Tlim−Tx) / (Tlim−Tctl)] · (Vctl ² −Ve ² ) + Ve ² } ^1/2 , the voltage Vx is set.

The charger of the present invention includes a charging current supply circuit, a temperature detection circuit, and a charge control circuit, and has a voltage Vx corresponding to the temperature Tx of the battery cell detected by the temperature detection circuit. In the charger in which the charging control circuit controls the charging voltage output from the charging current supply circuit, the temperature at which the suppression of the charging voltage is to be started due to the high temperature is Tct1, and the maximum allowable to the battery cell at the temperature Tctl The charging voltage is Vctl, the maximum temperature that the battery cell can safely accept is Tlim, the discharge end voltage of the battery cell is Ve, and the current temperature of the battery cell detected by the temperature detection circuit that exceeds the temperature Tctl is the Tx. when a, the charging control circuit, Vx = {[(Tlim- Tx) / (Tlim-Tctl)] · (Vctl 2 -Ve 2) + Ve 2 ^1/2, and sets the voltage Vx.

  According to said structure, in the charger which performs constant current constant voltage (CC-CV) charge, a temperature detection circuit is a signal showing the temperature of the battery cell from the battery pack side, or the temperature sensor provided in this charger From the detection result, the battery cell temperature Tx is detected, and the charging control circuit controls the charging current supply circuit according to the detection result, and the battery cell is charged at a constant voltage with the voltage Vx corresponding to the temperature Tx. In the charging control circuit, the charging voltage Vx for constant voltage charging at a high temperature is set to a temperature Tctl at which the suppression of the charging voltage should be started because of the high temperature, and the maximum charging voltage that the battery cell can tolerate at the temperature Tctl. Vctl, Tlim is the maximum temperature that the battery cell can safely accept, T Ve, the discharge end voltage of the battery cell is Ve, and the current temperature of the battery cell that exceeds the temperature Tctl is When the Tx, is determined by the following equation.

Vx = {[(Tlim-Tx) / (Tlim-Tctl)]
・ (Vctl ² −Ve ² ) + Ve ² } ^1/2
Therefore, as the battery cell temperature Tx rises, the charging voltage Vx for constant voltage charging is not reduced step by step relatively large at each step, but the battery cell temperature Tx by a minute voltage. Since it is lowered correspondingly, it can be charged extra by the difference from the level of the above stage.

Furthermore, the overcharge protection method of the present invention is the overcharge protection method for cutting off the charging current to the battery cell at a predetermined protection voltage Vz. At that temperature Tctl, the maximum charge voltage that the battery cell can accept is Vctl, the maximum temperature that the battery cell can safely accept is Tlim, the discharge end voltage of the battery cell is Ve, the predetermined margin is α, and the temperature exceeds the temperature Tctl. When the current battery cell temperature is Tx, Vz = {[(Tlim−Tx) / (Tlim−Tctl)] · (Vctl ² −Ve ² ) + Ve ² } ^1/2 + α, and the protection voltage Vz is It is characterized by setting.

The battery pack of the present invention further includes a battery cell, a voltage detection circuit, a switch element, and a protection circuit, and the voltage of the battery cell detected by the voltage detection circuit has a predetermined protection voltage Vz. When the battery pack exceeds, the battery pack that performs an overcharge protection operation that cuts off the switching element interposed in the charging path to the battery cell and cuts off the charging current further includes a temperature sensor, for high temperature The temperature at which charging voltage suppression should be started is Tctl, the maximum charging voltage that the battery cell can accept at the temperature Tctl, Vctl, the maximum temperature that the battery cell can safely accept is Tlim, and the discharge end voltage of the battery cell. Ve, where α is a predetermined margin, and Tx is the current temperature of the battery cell detected by the temperature sensor that exceeds the temperature Tctl. The protection circuit, Vz = from {[(Tlim-Tx) / (Tlim-Tctl)] · (Vctl 2 -Ve 2) + Ve 2} 1/2 + α, and sets the protection voltage Vz .

  According to the above configuration, when the voltage of the battery cell detected by the voltage detection circuit exceeds the predetermined protection voltage Vz, the protection circuit blocks the switch element interposed in the charging path to the battery cell. In the battery pack that performs the overcharge protection operation that cuts off the charging current, a temperature sensor is provided, and the protection circuit changes the protection voltage Vz in accordance with the temperature Tx of the battery cell, and further when the temperature is high. The protection voltage Vz at Tct is the temperature at which the suppression of the charging voltage due to the high temperature is Tctl, the maximum charging voltage that the battery cell can accept at the temperature Tctl is Vctl, and the maximum temperature that the battery cell can safely accept is Tlim, Ve is the discharge end voltage of the battery cell, α is a predetermined margin, and the current battery cell temperature exceeds the temperature Tctl. When the said Tx, determined by the following equation.

Vz = {[(Tlim-Tx) / (Tlim-Tctl)]
・ (Vctl ² −Ve ² ) + Ve ² } ^1/2 + α
Therefore, as the temperature Tx of the battery cell rises, the overcharge protection voltage Vz is finely decreased by a minute voltage, so that the battery is charged to the maximum capacity at that time (temperature Tx) while ensuring safety. can do.

  Furthermore, the charger of the present invention generates a current detection resistor for detecting a charging current, a counter for decoding data corresponding to the target charging current from the charging control circuit, and a voltage corresponding to the decoded value of the counter. A variable voltage first reference voltage source configured to include a digital / analog converter, and an error comparing the detection voltage of the current detection resistor with the first reference voltage of the first reference voltage source The charging control circuit is responsive to an output from the error amplifier during constant voltage charging, and charges the charging current supply circuit by a predetermined value when the detected voltage exceeds the first reference voltage. The current is reduced.

  According to said structure, in the constant voltage charge area | region of the said constant current constant voltage (CC-CV) charge, a charge control circuit reaches a full charge, making a charging current supply circuit maintain the said charging voltage Vx. When the current drooping control for decreasing the charging current is performed, the charging current is detected by the current detection resistor, the detection voltage of the current detection resistor, and the first reference voltage source of the first reference voltage source that becomes the control target value of the charging current 1 is compared with a reference voltage of 1 by an error amplifier, and when the detected voltage exceeds the first reference voltage, the charging current supply circuit reduces the charging current by a predetermined value, and further reduces the first reference voltage. Is repeated to perform the current drooping control. In such a configuration, the first reference voltage source includes a counter that decodes data corresponding to the target charging current from the charge control circuit, and a digital / analog converter that generates a voltage corresponding to the decoded value of the counter. It consists of a container.

  Therefore, it is possible to accurately set the control target value of the charging current instructed to be sequentially decreased with a simple configuration.

  In the battery pack of the present invention, the battery cells are provided in a plurality of stages in series with each other to form an assembled battery, and the protection circuit is provided in each stage, and a variable voltage first that sets the protection voltage Vz is provided. The second reference voltage source and the second reference voltage from the second reference voltage source are compared with the cell voltage of each stage, and if the cell voltage exceeds the second reference voltage, an overcharge determination signal is generated. A comparator that outputs, and a logic circuit that shuts off the switch element when the overcharge determination signal is output from at least one of the comparators, and further responds to an output from the temperature sensor. And a protection voltage control unit for changing the second reference voltage in the second reference voltage source.

  According to the above configuration, when the battery cell is provided in a plurality of stages in series to form an assembled battery, the overcharge protection circuit is provided in common with the second reference voltage source and the comparator provided in each stage. It can be realized with a simple configuration with a logic circuit.

As described above, the charging voltage control method and the charger according to the present invention are signals in which the temperature detection circuit indicates the temperature of the battery cell from the battery pack side in the charger that performs constant current constant voltage (CC-CV) charging. Alternatively, the temperature Tx of the battery cell is detected from the detection result of the temperature sensor provided in the charger, and in response to the detection result, the charge control circuit controls the charging current supply circuit and corresponds to the temperature Tx. When the battery cell is charged at a constant voltage with the voltage Vx, the charge control circuit sets the charging voltage Vx for constant voltage charging at a high temperature to a temperature Tctl at which the suppression of the charging voltage due to the high temperature is to be started, and the temperature Tctl. The maximum charging voltage that the battery cell can accept is Vctl, the maximum temperature that the battery cell can safely accept is Tlim, the discharge end voltage of the battery cell is Ve, and the temperature Tct Wherein when the Tx the current temperature of the battery cell exceeds, Vx = {[(Tlim- Tx) / (Tlim-Tctl)] · (Vctl 2 -Ve 2) + Ve 2} determined from ^1/2.

  Therefore, as the temperature Tx of the battery cell increases, the charging voltage Vx for constant voltage charging is not decreased step by step relatively large for each step, but the temperature of the battery cell is increased by a minute voltage. Since the voltage is lowered correspondingly to Tx, it is possible to charge extra by the difference from the level of the stage.

Furthermore, in the overcharge protection method of the present invention and the battery pack, as described above, when the voltage of the battery cell detected by the voltage detection circuit exceeds a predetermined protection voltage Vz, the protection circuit In a battery pack that performs an overcharge protection operation that cuts off a switching element interposed in a charging path to a battery cell and cuts off a charging current, a temperature sensor is provided, and the protection circuit supplies the protection voltage Vz to the battery cell. The protection voltage Vz at a high temperature is changed to correspond to the temperature Tx of the battery, and the temperature at which the suppression of the charging voltage is to be started due to the high temperature is Tctl, and the maximum charge that the battery cell can tolerate at the temperature Tctl The voltage is Vctl, the maximum temperature that the battery cell can safely accept is Tlim, the discharge end voltage of the battery cell is Ve, and a predetermined merge is performed. The alpha, when the temperature of the current of the battery cell exceeds the temperature TCTL and the Tx, Vz = {[(Tlim -Tx) / (Tlim-Tctl)] · (Vctl 2 -Ve 2) + Ve 2} 1 / Determine from ² + α.

  Therefore, as the temperature Tx of the battery cell rises, the overcharge protection voltage Vz is finely reduced by a minute voltage, so that the capacity is as high as possible at that time (temperature Tx) while ensuring safety. Can be charged.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

[Embodiment 1]
FIG. 1 is a block diagram of a charging system 1 according to the first embodiment of the present invention. The charging system 1 includes a battery pack 2 and a charger 3. As shown in FIG. 1, the battery pack 2 is not limited to a configuration in which the battery pack 2 is directly charged, but is charged in a state in which the battery pack 2 is built in a battery-driven device such as a portable personal computer, a digital camera, or a mobile phone. Also good. The battery pack 2 and the charger 3 are connected via connection terminals T1, T2, T3.

  The battery pack 2 performs a protective operation in response to a battery pack B in which secondary battery cells B1, B2, and B3 are connected in series, a control IC 11 that controls charging and discharging, and a control output from the control IC 11. The switch elements Q1 and Q2 and the temperature sensors 12 and 13 are provided. The temperature sensors 12 and 13 are in close contact with the assembled battery B (may be provided for each of the secondary battery cells B1, B2 and B3) to detect the temperature, and are composed of a thermistor or the like. It may be built in the control IC 11.

  The secondary battery cells B1, B2, B3 are lithium ion secondary batteries that are the subject of Non-Patent Document 1. Secondary battery cells B1, B2, and B3 may each have a plurality of secondary battery cells connected in parallel. The number of series stages is not limited to three. The assembled battery B is charged with a charging current supplied from the charger 2 via the connection terminals T1 and T3, and an overdischarge-preventing switch element Q1 and an overcharge are connected in series in the charge / discharge path. A switch element Q2 for prevention is interposed.

  The control IC 11 includes voltage dividing resistors R11, R12, R13; R21, R22, R23; R31, R32, R33, reference voltage sources E1, E2, E3, comparators CP11, CP12; CP21, CP22; CP31, CP32 And NAND gates G1 and G2. The cell voltages Vb1, Vb2, and Vb3 of the secondary battery cells B1, B2, and B3 are taken into the control IC 11 and are divided by the voltage dividing resistors R11, R12, R13; R21, R22, R23; R31, R32, R33. Divided pressure.

  The high-side divided voltages V11, V21, V31 between the voltage dividing resistors R11, R12; R21, R22; R31, R32 are input to one input terminal of overdischarge detection comparators CP11, CP21, CP31, It is compared with reference voltages Vref1, Vref2, and Vref3 from reference voltage sources E1, E2, and E3, which are second reference voltages input to the other input terminal. The comparison result is given to the NAND gate G1, and therefore the NAND gate G1 has at least one of the divided voltages V11, V21, V31 of the cell voltages Vb1, Vb2, Vb3 of the secondary battery cells B1, B2, B3. When the voltage drops below the reference voltages Vref1, Vref2, and Vref3, it is determined that the battery is overdischarged, and the switch element Q1 formed of a p-channel FET is cut off.

  Similarly, the divided voltage V12, V22, V32 on the low side between the voltage dividing resistors R12, R13; R22, R23; R32, R33 is applied to one input terminal of the overcharge detection comparators CP12, CP22, CP32. It is input and compared with reference voltages Vref1, Vref2, and Vref3 from the reference voltage sources E1, E2, and E3 input to the other input terminal. The comparison result is given to the NAND gate G2, and therefore the NAND gate G2 has at least one of the divided voltages V12, V22, V32 of the cell voltages Vb1, Vb2, Vb3 of the secondary battery cells B1, B2, B3. When the voltage drops below the reference voltages Vref1, Vref2, and Vref3, the overcharge state is determined, and the switch element Q2 formed of a p-channel FET is cut off.

  For example, the voltage dividing resistors R11, R21 and R31 are set to 1284 kΩ, the voltage dividing resistors R12, R22 and R32 are set to 1140 kΩ, the voltage dividing resistors R13, R23 and R33 are set to 1000 kΩ, and the reference voltages Vref1, Vref2 and Vref3 are set to 1. When the voltage is set to 25V, the divided voltages V11, V12, and V13 become 1.25V of the reference voltages Vref1, Vref2, and Vref3 because the cell voltages Vb1, Vb2, and Vb3 are 1.25 × 3424/2140 = 2V. It is time when. That is, when the cell voltages Vb1, Vb2, and Vb3 drop below 2V, the comparators CP11, CP21, and CP31 determine that overdischarge is performed, and the switch element Q1 is cut off via the NAND gate G1.

  In the same setting, the divided voltages V21, V22, V23 become 1.25V of the reference voltages Vref1, Vref2, Vref3 because the cell voltages Vb1, Vb2, Vb3 are 1.25 × 3424/1040 = 4. .28V. That is, when the cell voltages Vb1, Vb2, and Vb3 rise above 4.28V that is the overcharge protection voltage Vz, the comparators CP12, CP22, and CP32 determine that the overcharge occurs, and the NAND gate G2 The switch element Q2 is shut off via

  On the other hand, the charger 3 includes a DC power supply circuit 21, a DC-DC converter 22, a charge control circuit 23, a bias power supply E01 and a bias resistor RB, a current detection resistor RS, reference voltage sources E02 and E03, and an error. Amplifiers (error amplifiers) CP01 and CP02 are provided.

The DC power supply circuit 21 generates a DC voltage from commercial AC or the like, and the generated voltage is converted into a predetermined charging current at a predetermined charging voltage Vx (to be described later) by a step-up or step-down DC-DC converter 22. It is converted and given to the assembled battery B from the connection terminals T1, T3. These DC power supply circuit 21 and DC-DC converter 22 constitute a charging current supply circuit.

  The DC-DC converter 22 includes a switching element Q11, an inductor L1, and a smoothing capacitor C1 connected in series between the output terminals of the DC power supply circuit 21, and a diode D1 connected in parallel with the inductor L1 and the smoothing capacitor C1. And a PWM control circuit 24. The PWM control circuit 24 switches the switching element Q11 at a frequency and duty in response to the control output from the charge control circuit 23, so that a predetermined charge voltage is applied between the smoothing capacitor C1 and the connection terminals T1 and T3. A predetermined charging current is supplied at Vx.

  The voltage Vx between the connection terminals T1 and T3 is taken into the error amplifier CP01. The error amplifier CP01 compares the voltage Vx with the reference voltage Vref01 from the reference voltage source E02, and corresponds to the difference between them. By supplying the output to the charging control circuit 23, the charging control circuit 23 detects the charging voltage Vx. Further, the charging current flowing from the DC-DC converter 22 to the battery pack 2 is converted into a voltage by the current detection resistor RS, and the error amplifier CP02 generates a reference voltage Vref02 from a reference voltage source E03 which is a first reference voltage source. By comparing and providing an output corresponding to the difference to the charge control circuit 23, the charge control circuit 23 holds the charge current at a predetermined value.

  Furthermore, a bias voltage is applied to the connection terminal T2 from the bias power source E01 via the bias resistor RB. On the battery pack 2 side, there is a gap between the connection terminal T2 and the connection terminal T3 on the GND side. A temperature sensor 13 is connected. Therefore, a voltage obtained by dividing the bias voltage by the bias resistor RB and the temperature sensor 13 appears at the connection terminal T2, and the charge control circuit 23 generates a battery pack B (secondary battery cells B1, B1) from the divided voltage. The temperature of B2, B3) is detected. The bias power source E01, the bias resistor RB, and the temperature sensor 13 constitute a temperature detection circuit, but the temperature sensor 13 may be provided on the charger 3 side, and the detection result of the temperature sensor 12 connected to the control IC 11 May be obtained by communication.

In the charging system configured as described above, it should be noted that in the present embodiment, the charging control circuit 23 performs the constant current constant voltage (CC-CV) charging, the temperature sensor during constant voltage charging. The charging voltage Vx output from the DC-DC converter 22 is controlled so that the voltage Vx corresponds to the temperature Tx of the assembled battery B detected by the control unit 13. When the temperature is high, the non-patent document Unlike 1, the charging voltage Vx is determined according to the following equation. That is, the temperature at which the suppression of the charging voltage is to be started is Tctl, and the maximum charging voltage that can be allowed by the secondary battery cells B1, B2, and B3 at the temperature Tctl (corresponding to the upper limit charging voltage defined in Non-Patent Document 1). The upper limit value of the charging voltage possible per cell) is Vctl, the maximum temperature that the secondary battery cells B1, B2, and B3 can safely accept is Tlim, and the discharge end voltage of the secondary battery cells B1, B2, and B3 is Ve. When the current temperature of the secondary battery cells B1, B2, B3 detected by the temperature sensor 13 is Tx, which is a temperature exceeding the temperature Tctl, the charge profile is calculated by electrothermal engineering,
Vx = {[(Tlim-Tx) / (Tlim-Tctl)]
(Vctl ² −Ve ² ) + Ve ² } ^1/2 (1)
From the above, the voltage Vx is set. In the said nonpatent literature 1, the said temperature Tctl is 45 degreeC.

In the following, how to obtain Equation 1 will be described. First, assuming that the capacity of the secondary battery cells B1, B2, B3 is C, and the cell voltages at the temperatures Tctl, Tx are Vctl, Vx, the energy Ectl, Ex of the cell is
Ectl = (1/2) · C · Vctl ² − (1/2) · C · Ve ² (2)
Ex = (1/2) · C · Vx ² − (1/2) · C · Ve ² (3)
It is requested from.

Therefore, the energy ratio of the cell at the temperatures Tctl and Tx is
Ex / Ectl = [(1/2) · C · Vx ² − (1/2) · C · Ve ² ]
/ [(1/2) · C · Vctl ² − (1/2) · C · Ve ² ] ·· (4)
And then
^{Ex / Ectl = [Vx 2 -Ve} 2] / [Vctl 2 -Ve 2] ··· (5)
It becomes.

On the other hand, from Equation 4 above,
C · Vx ² −C · Ve ² = Ex · (C · Vctl ² −C · Ve ² ) / Ectl · (6)
And therefore
Vx ² = [Ex · (C · Vctl ² −C · Ve ² ) / Ectl · C] + Ve ² · (7)
It becomes. Here, the temperature rise ΔT is substantially proportional to the electric energy of the cell, and when the maximum temperature is Tlim, Equation 7 can be expressed as Equation 1.

In addition, when the equivalent circuit at the time of the internal short circuit of a cell is shown, it will become like FIG. 2 (a), and if it shows the model of the thermal circuit at that time, it will become like FIG.2 (b). Rq is a thermoelectromotive force generated by the electric resistance of the foreign matter that caused the internal short circuit, CT is a heat capacity of the battery, and R is a heat dissipation resistance of the battery. Therefore, the temperature rise ΔT is
ΔT = Rq (1−exp (−t / R · CT)) (8)
And when expanded,
ΔT = R · I ² · r (1-exp (−t / R · CT))
= R · P · (1-exp (−t / R · CT)) (9)
It becomes.

  Here, P is the electric power generated by the internal short circuit of the cell, and is the energy generated per unit time, the magnitude of which is derived from the energy E charged in the cell, so that the temperature rise ΔT as described above. Is approximately proportional to the electrical energy of the cell. Therefore, the limit temperature Tlim of the battery varies depending on the material, but when short-circuited inside the cell, the resistance generated by the short-circuit becomes a heating element (Rq), and the energy stored in the battery by overheating the battery itself It is sufficient that the charging energy can be controlled within a range in which the final temperature reached does not exceed the limit temperature determined by the battery material, even if the temperature rise ΔT occurs from the current temperature Tx, within the limit temperature Tlim. If it exists, safety can be ensured, and charging according to the above-mentioned formula 1 becomes possible.

  Here, the shape of the lithium ion battery includes a cylindrical shape, a rectangular shape, and a laminate (polymer) shape. An electrode plate group in which a positive electrode and a negative electrode are wound in a spiral shape through a separator is inserted into a battery case. It is manufactured by sealing after injecting a non-aqueous electrolyte. As the positive electrode active material, lithium cobaltate, lithium cobaltate modified, lithium nickelate, lithium nickelate modified, lithium manganate, lithium manganate modified, and the like are preferable. As each modified material, one containing an element such as aluminum or magnesium can be used, and one containing at least two of cobalt, nickel and manganese can also be used. On the other hand, as the negative electrode active material, various natural graphites, various artificial graphites, silicon-containing composite materials such as silicide, and various alloy materials can be used.

In addition, various lithium salts such as lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) can be used as the solute in the non-aqueous electrolyte. As the non-aqueous solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like are preferably used, but are not limited thereto. Although a nonaqueous solvent can also be used individually by 1 type, it is preferable to use 2 or more types in combination. Moreover, as an additive, vinylene carbonate, cyclohexylbenzene, diphenyl ether, etc. can also be used.

  A battery pack is a battery pack in which one or a plurality of lithium ion batteries and a protective circuit are placed in a resin case, and the solute consisting of the lithium salt moves between the positive and negative electrodes to charge and discharge. Therefore, even if the positive and negative electrode materials and the shapes are different, the above formula can be applied.

  3 and 4 are graphs showing the simulation results of the charging profile by the inventor of the present application. Both are simulations of the temperature Tctl = 45 ° C. or higher, and follow the example of Non-Patent Document 1 up to 45 ° C. FIG. 3 shows the case where the maximum temperature Tlim is 150 ° C., and FIG. 4 shows the case where the maximum temperature Tlim is 180 ° C. Reference numeral α1 is a charging profile according to the non-patent document, and reference numerals α2 and α3 are charging profiles according to the present invention.

  FIG. 5 is a graph showing the relationship between the battery temperature and the charging temperature Tx and voltage Vx based on the electrothermal optical calculation according to Equation 1. According to this, at the temperature Tctl = 45 ° C. at which the suppression of the charging voltage is to be started, even if the charging voltage Vx is already increased, the capacity does not change, and assuming that the capacity at this point is 100%, about 95 at 50 ° C. %, About 86% at 60 ° C. On the other hand, at 25 ° C., the capacity increases as the charging voltage Vx is increased, and is 100% at 4.25V. In addition, in order to perform numerical calculation in terms of electrical engineering and electrothermal engineering, when the battery is simulated by replacing the battery with a capacitor, the data at 25 ° C. is obtained. And in the said nonpatent literature 1, as shown by arrow F1, F2, F3, while charging voltage in each temperature is defined, in this Embodiment, it shows by arrow F1, F2 ', F3. Thus, the charging voltage is determined.

  Thus, as the temperature Tx of the secondary battery cells B1, B2, and B3 rises, the charge control circuit 23 decreases the constant voltage charging voltage Vx by a minute voltage corresponding to the temperature Tx. Thus, compared with the stepwise reduction according to Non-Patent Document 1, it is possible to charge an extra amount by the difference (the region shown by hatching in FIGS. 3 and 4 and F2′−F2 in FIG. 5). become able to.

  Also, it should be noted that, even on the battery pack 2 side, when the control IC 11 performs the overcharge protection operation using the comparators CP12, CP22, CP32 and the NAND gate G2, the temperature sensor 12 has a protection voltage control unit. 13 and the reference voltage sources E1, E2 and E3 are variable voltages. And the protection voltage control part 13 determines the protection voltage Vz of overcharge according to the following formula.

Vz = {[(Tlim-Tx) / (Tlim-Tctl)]
(Vctl ² −Ve ² ) + Ve ² } ^1/2 + α (10)
That is, while the equation 1 is the charging voltage Vx, the protection voltage Vz is a voltage to which a margin α is added. The margin α is, for example, 0.25V. The method for obtaining other than the margin α is as described above. The protection voltage control unit 13 changes the reference voltages Vref1, Vref2, and Vref3 by the reference voltage sources E1, E2, and E3 so that the determined protection voltage Vz is obtained. If the reference voltages Vref1, Vref2, and Vref3, which are overcharge determination levels, are changed, the overdischarge determination level also changes from 2V. However, the operation is different from charging and discharging, and the protection voltage control unit 13 The reference voltages Vref1, Vref2, and Vref3 may be changed only during charging. Alternatively, the reference voltages Vref1, Vref2, and Vref3 may be changed so that an appropriate overdischarge determination level corresponding to the temperature is obtained even during discharge. Furthermore, although the reference voltage sources E1, E2, E3 are shared for charging and discharging, they may be provided separately.

  By configuring in this way, the protection voltage control unit 13 finely lowers the overcharge protection voltage Vz by a minute voltage as the temperature Tx of the secondary battery cells B1, B2, B3 increases. While ensuring safety, the battery can be charged to the maximum capacity at that time (temperature Tx).

  Also, it should be noted that in the charger 3, a reference voltage source E03 that generates a reference voltage Vref02 serving as a reference for charge current control decodes data corresponding to the target charge current from the charge control circuit 23. And a digital / analog converter 26 for generating a voltage corresponding to the decoded value of the counter 25, and outputting the reference voltage Vref02 as a variable voltage. The digital / analog converter 26 operates with the power supply voltage from the power supply E04.

  In the constant voltage charge region of the constant current constant voltage (CC-CV) charge, the charge control circuit 23 maintains the charge voltage Vx in the DC-DC converter 22 and supplies the charge current until full charge. In performing the current drooping control, the charging current is detected by the current detection resistor RS, and the detected voltage of the current detection resistor RS is compared with the reference voltage Vref02 which is the control target value of the charging current by the error amplifier CP02. When the detected voltage exceeds the reference voltage Vref02, the current drooping control is performed by repeating the operation of reducing the charging current to the DC-DC converter 22 by a predetermined value and further reducing the reference voltage Vref02. . In such a configuration, the reference voltage source E03 is configured by the counter 25 and the digital / analog converter 26 as described above, so that the control target value of the charging current instructed to be sequentially decreased can be obtained with a simple configuration. It can be set with high accuracy.

[Embodiment 2]
FIG. 6 is a block diagram of a charging system 1a according to the second embodiment of the present invention. This charging system 1a is similar to the charging system 1 shown in FIG. 1 described above, and corresponding portions are denoted by the same reference numerals, and description thereof is omitted. It should be noted that in this charging system 1a, ID authentication chips 19 and 29 for eliminating non-genuine products or non-conforming products are mounted on the battery pack 2a and the charger 3a. The ID authentication chips 19 and 29 communicate via the connection terminals T2 and T3. If the ID authentication chip 29 on the charger 3a side cannot authenticate the battery pack 2a, the ID control chips 19 and 29 charge the charge control circuit 23a. When the operation is not performed, or when the ID authentication chip 19 on the battery pack 2a side cannot authenticate the charger 3a, the switch element Q2 is shut off and the charging operation is not performed, or between the ID authentication chips 19 and 29 The above operations may be performed together with mutual authentication.

  In the charging system 1a configured as described above, the ID authentication chip 19 on the battery pack 2a side includes the temperature sensor 12 and the protection voltage control unit 13a together with the authentication unit 19a that performs the authentication operation. For this reason, the protection voltage control unit 13 is not provided in the control IC 11a. In addition, the charging control circuit 23a on the charger 3a side acquires the temperature Tx of the assembled battery B through communication between the ID authentication chips 19 and 29.

  By configuring in this way, the ID authentication chip 19 can perform charging under the charging conditions and temperature profile recommended for its own secondary battery cells B1, B2, and B3 together with ID authentication.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used as a charging system used as a battery mounting device for electronic devices such as portable personal computers, digital cameras, and mobile phones, vehicles such as electric cars and hybrid cars, and the like.

1 is a block diagram of a charging system according to a first embodiment of the present invention. It is a figure which shows the equivalent circuit diagram at the time of the internal short circuit of a cell, and the model of a thermal circuit. It is a graph which shows the simulation result of the charge profile by this inventor. It is a graph which shows the simulation result of the charge profile by this inventor. It is a graph which shows the relationship between the charging temperature and voltage and battery energy by the electrothermal optical calculation of this Embodiment. It is a block diagram of the charging system which concerns on the 2nd Embodiment of this invention. It is a graph of the charge profile which concerns on background art.

Explanation of symbols

1, 1a Charging system 2, 2a Battery pack 3, 3a Charger 11, 11a Control IC
12, 13 Temperature sensor 19, 29 ID authentication chip 19a Authentication unit 21 DC power supply circuit 22 DC-DC converter 23, 23a Charge control circuit 25 Counter 26 Digital / analog converter B Batteries B1, B2, B3 Secondary battery cells CP01, CP02 Error amplifiers CP11, CP12; CP21, CP22; CP31, CP32 Comparator E01 Bias power supplies E02, E03 Reference voltage sources E1, E2, E3 Reference voltage sources G1, G2 NAND gates Q1, Q2 switch elements R11, R12, R13; R21 , R22, R23; R31, R32, R33 Voltage dividing resistor RB Bias resistor RS Current detection resistor T1, T2, T3 Connection terminal

Claims (6)

In a charging voltage control method for charging the battery cell with a voltage Vx corresponding to the temperature Tx of the battery cell,
The temperature at which charging voltage suppression should be started due to a high temperature is Tctl, the maximum charging voltage that can be allowed by the battery cell at the temperature Tctl, Vctl, the maximum temperature that the battery cell can safely accept is Tlim, and the discharge of the battery cell When the end voltage is Ve and the current battery cell temperature exceeding the temperature Tctl is the Tx,
Vx = {[(Tlim-Tx) / (Tlim-Tctl)]
・ (Vctl ² −Ve ² ) + Ve ² } ^1/2
To set the voltage Vx. In the overcharge protection method of cutting off the charging current to the battery cell at a predetermined protection voltage Vz,
The temperature at which charging voltage suppression should be started due to a high temperature is Tctl, the maximum charging voltage that can be allowed by the battery cell at the temperature Tctl, Vctl, the maximum temperature that the battery cell can safely accept is Tlim, and the discharge of the battery cell When the end voltage is Ve, the predetermined margin is α, and the current battery cell temperature exceeding the temperature Tctl is Tx,
Vz = {[(Tlim-Tx) / (Tlim-Tctl)]
・ (Vctl ² −Ve ² ) + Ve ² } ^1/2 + α
To set the protection voltage Vz. A charge current supply circuit; a temperature detection circuit; and a charge control circuit, wherein the charge control circuit supplies the charge current so that the voltage Vx corresponds to the temperature Tx of the battery cell detected by the temperature detection circuit. In the charger that controls the charging voltage output from the circuit,
The temperature at which charging voltage suppression should be started due to a high temperature is Tctl, the maximum charging voltage that can be allowed by the battery cell at the temperature Tctl, Vctl, the maximum temperature that the battery cell can safely accept is Tlim, and the discharge of the battery cell When the end voltage is Ve and the current temperature of the battery cell detected by the temperature detection circuit exceeding the temperature Tctl is Tx, the charge control circuit is
Vx = {[(Tlim-Tx) / (Tlim-Tctl)]
・ (Vctl ² −Ve ² ) + Ve ² } ^1/2
To set the voltage Vx. A current detection resistor for detecting the charging current;
A variable voltage first reference comprising: a counter that decodes data corresponding to a target charging current from the charge control circuit; and a digital / analog converter that generates a voltage corresponding to a decoded value of the counter. A voltage source;
An error amplifier that compares a detection voltage of the current detection resistor with a first reference voltage of the first reference voltage source;
The charging control circuit responds to an output from the error amplifier during constant voltage charging, and reduces the charging current by a predetermined value to the charging current supply circuit when the detected voltage exceeds the first reference voltage. The charger according to claim 3. A battery cell, a voltage detection circuit, a switch element, and a protection circuit, and when the voltage of the battery cell detected by the voltage detection circuit exceeds a predetermined protection voltage Vz, the protection circuit In a battery pack that performs an overcharge protection operation that cuts off the switch element interposed in the charging path to the battery cell and cuts off the charging current,
A temperature sensor,
The temperature at which charging voltage suppression should be started due to a high temperature is Tctl, the maximum charging voltage that can be allowed by the battery cell at the temperature Tctl, Vctl, the maximum temperature that the battery cell can safely accept is Tlim, and the discharge of the battery cell When the end voltage is Ve, the predetermined margin is α, and the current temperature of the battery cell detected by the temperature sensor exceeding the temperature Tctl is Tx, the protection circuit
Vz = {[(Tlim-Tx) / (Tlim-Tctl)]
・ (Vctl ² −Ve ² ) + Ve ² } ^1/2 + α
The battery pack is characterized in that the protection voltage Vz is set. The battery cells are provided in a plurality of stages in series with each other to form a battery pack,
The protection circuit is provided in each stage, and includes a second reference voltage source of variable voltage that sets the protection voltage Vz, a second reference voltage from the second reference voltage source, and a cell voltage of each stage. A comparator that outputs an overcharge determination signal when the cell voltage exceeds the second reference voltage, and the switch when the overcharge determination signal is output from at least one of the comparators. And a logic circuit that shuts off the element,
6. The battery pack according to claim 5, further comprising a protection voltage control unit that changes a second reference voltage in the second reference voltage source in response to an output from the temperature sensor.

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