JPWO2014122776A1 - Control device and control method for lithium ion secondary battery - Google Patents

Abstract

An object of the present invention is to provide a discharge control device and a control method that prevent overdischarge of a lithium ion secondary battery and obtain the maximum output. The present invention is a control device (27) for setting two or more discharge end voltages of a lithium ion secondary battery (20) having two or more plateaus in a discharge voltage curve. For example, when the first discharge end voltage is lower than the second discharge end voltage and a secondary plateau (voltage change rate: 0.1 mV / s to 10 mV / s) is detected at 2.5 V to 3 V during discharge When discharging to the first discharge end voltage value and no secondary plateau is detected at the time of discharge, discharging is performed to the second discharge end voltage.

Description

  The present invention relates to a control device and a control method for a lithium ion secondary battery that detects, for example, the voltage of a lithium ion secondary battery and controls charging and discharging based on the detected voltage.

  Development of power supply devices such as lithium ion secondary batteries or capacitors has been extensive for application to hybrid vehicles. In recent years, from the viewpoint of environmental problems such as carbon dioxide reduction, the expectation of practical application to hybrid vehicles has increased, and the improvement of battery performance and battery control technology has been remarkable. Attention has been focused on the reliability and safety of lithium ion batteries.

  For example, if the negative electrode potential is about 3.0 V or more due to overdischarge (battery voltage is about 0.6 V or less, positive electrode 3.6 V or less), the copper that constitutes the current collector plate will elute, causing abnormalities in the positive electrode or There are concerns about dissolution, leakage, ignition and rupture.

  As a countermeasure against overdischarge of a lithium ion secondary battery, voltage control is performed by a secondary device such as a protection element or a protection circuit.

JP 2002-164053 A

  However, in the case of a battery using a general carbon-based negative electrode and a lithium transition metal oxide-based positive electrode, the resistance is high at the end of discharge (for example, 3 V or less), and the discharge rate increases as the voltage decreases. It becomes difficult to detect and control overdischarge.

  In such a state, if a delay occurs in detection during overdischarge, there is a high possibility that the voltage will be 0.6 V or less at which copper elution is a concern. Therefore, the lower limit voltage at the time of discharge must be set higher, and the output is particularly lowered.

  The objective of this invention provides the control apparatus and control method which can prevent the overdischarge of a lithium ion secondary battery and can take out output to the maximum.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by giving two or more plateaus to the discharge voltage curve and appropriately controlling the discharge end voltage according to the state of the discharge curve. The headline and the present invention were completed.

  The lithium ion secondary battery control method of the present invention discharges to the second discharge end voltage when the secondary plateau is detected during discharge, and discharges to the first discharge end voltage when the secondary plateau is not detected. It is characterized by letting.

  ADVANTAGE OF THE INVENTION According to this invention, the discharge control apparatus and control method which prevent overdischarge by setting discharge end voltage with the discharge curve of a lithium ion secondary battery, and take out the maximum can be provided.

The block circuit diagram which shows the outline of the secondary battery module of this embodiment. Sectional drawing which shows typically the cylindrical lithium ion secondary battery which comprises the secondary battery module of this embodiment. The flowchart explaining operation | movement of the secondary battery module of this embodiment. FIG. 3 is a diagram for explaining a discharge curve at each current value in Example 1;

  A first aspect of the present invention is a lithium secondary battery having, for example, two or more plateaus in a discharge voltage curve at a current value of 1 C, and having two or more discharge end voltages, and controlling the secondary battery System.

  In the first aspect, by giving two or more plateaus to the discharge voltage curve, the discharge rate of 3 V or less at the end of discharge is alleviated, so that the discharge is performed until just before the elution voltage of copper used for the negative electrode current collector. Therefore, the discharge end voltage can be set low.

  On the other hand, when the current value is large (10C), the plateau of 3V or less disappears due to the influence of resistance, so the discharge end voltage is set high. That is, it is possible to provide a discharge control method that prevents overdischarge and sets the output to the maximum by setting the discharge end voltage according to the discharge curve. In addition, a battery system having only one plateau at 3 V or less is not preferable because the battery has a low average voltage and low energy density and output.

  In the second aspect, the lithium secondary battery has two discharge end voltage values, the second discharge end voltage value being lower than the first discharge end voltage value, and the voltage change rate is 0.1 mV during discharge. The first plateau (primary plateau) that is 10 mV / s to 10 mV / s is detected, and the battery voltage is 2.5 V to 3 V, and the voltage change rate is 0.1 mV / s to 10 mV / s. When the plateau of the eye (secondary plateau) is detected, discharge is performed up to the second discharge end voltage value, and when the second plateau is not detected during discharge, discharge is performed up to the first discharge end voltage. A control method for a secondary battery.

  A third aspect includes a battery unit configured by one or more of the lithium ion secondary batteries of the first aspect, and battery control for detecting a voltage of each lithium ion secondary battery and controlling a battery state. And a secondary battery control system.

The positive and negative electrode materials of the lithium battery of the first aspect are olivine manganese iron alone, or olivine manganese iron, olivine iron, solid solution positive electrode active material (Li ₂ MO ₃ -LiM′O ₂ solid solution (M is Mn, Ti, 1 or more elements selected from Zr, M ′ is a mixture of at least one element selected from Ni, Co, Mn, Fe, Ti, Zr, Al, Mg, Cr, and V)) More than two kinds of positive electrode materials are used, or graphite or amorphous carbon alone, or at least one of graphite or amorphous carbon, at least one of lithium titanate, iron oxide, silicon, tin oxide is mixed The negative electrode material is used. That is, by providing two or more plateaus in the discharge curve, the discharge end voltage can be set by changing the discharge voltage, and it is possible to provide a discharge control device and a control method for preventing overdischarge and taking out the maximum output. .

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a secondary battery system including a cylindrical lithium ion secondary battery to which the present invention is applied will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1, the secondary battery module 40 includes a battery unit 25 configured by a cylindrical lithium ion secondary battery 20 and a battery control unit 27 for controlling the battery state of each lithium ion secondary battery 20. And.

  In this example, the battery unit 25 is configured by connecting six lithium ion secondary batteries 20 in series. The battery control unit 27 is a central processing unit CPU, a basic control program, a ROM that stores various setting values and the like, a RAM that functions as a work area for the CPU and temporarily stores various data, and an internal connection between them. It consists of a microcomputer A having a bus. The microcomputer A is operated by a power source from a power supply unit (not shown).

  The voltage etc. of each lithium ion secondary battery 20 constituting the battery unit 25 is detected by the battery control unit 27. That is, the negative electrode terminal of the lowest-order lithium ion secondary battery 20 is connected to the ground. The positive terminal of the uppermost lithium ion secondary battery 20 is connected to one end of the switch SW2. The positive electrode terminal of each lithium ion secondary battery 20 and the negative electrode terminal of the lowest lithium ion secondary battery 20 constituting the battery unit 25 are input side terminals of a voltage measurement circuit 29 that measures the voltage of each lithium ion secondary battery 20. It is connected to the.

  The voltage measurement circuit 29 can be configured by a differential amplifier circuit or the like that converts the voltage of each lithium ion secondary battery 20 into a voltage based on the negative electrode terminal. The output side terminal of the voltage measurement circuit 29 is connected to the A / D input port of the microcomputer A for A / D converting the voltage of the lithium ion secondary battery 20. Further, the voltage measurement circuit 29 is connected to the battery designation port of the microcomputer A in order to receive designation of the lithium ion secondary battery 20 to be voltage measured from the microcomputer A. Therefore, the microcomputer A can capture the voltage data of each lithium ion secondary battery 20.

  The positive terminal of each lithium ion secondary battery 20 is connected to one end of a bypass resistor R for capacity adjustment (the same resistance value for each lithium ion secondary battery), and the other end of the bypass resistor R is a lithium ion secondary. It is connected to one end of a switch SW1 that adjusts the capacity of the battery 20. The other end of the switch SW1 is connected to the negative terminal of each lithium ion secondary battery 20.

  The switch SW1 is connected to an output port of the microcomputer A that outputs a control signal (high level signal, low level signal). Therefore, when the switch SW1 is turned on by the control signal from the microcomputer A, the current flowing through the lithium ion secondary battery 20 is consumed by the bypass resistor R, and the capacity of each lithium ion secondary battery 20 can be adjusted. is there.

  Further, the microcomputer A has an output port that outputs a control signal to the switch SW2. The other end of the switch SW2 is connected to one end of the external load 32, and the other end of the external load 32 is connected to the ground. For this reason, the switch SW <b> 2 is turned on by the control signal from the microcomputer A, whereby the electric power from the secondary battery module 40 is supplied to the external load 32.

  As the switches SW1 and SW2, for example, FETs that function as switching elements can be used. That is, the output port of the microcomputer A is connected to the gate of the FET. Accordingly, when a weak high level signal is input from the output port of the microcomputer A to the gate of the FET, a current flows between the drain and the source, and the switches SW1 and SW2 are turned on.

  As shown in FIG. 2, the lithium ion secondary battery 20 constituting the battery unit 25 includes a bottomed cylindrical battery can 4 made of steel plated with nickel. The battery can 4 accommodates an electrode group G in which the positive electrode plate 1 and the negative electrode plate 2 are wound with the separator 3 interposed therebetween.

  On the upper side of the electrode group G, a positive electrode current collecting lead portion 7 made of aluminum for collecting a potential from the positive electrode plate 1 is disposed on a substantially extension line of the winding center. The positive electrode current collecting lead portion 7 is ultrasonically bonded to the end portion of the positive electrode current collecting lead piece 5 led out from the positive electrode plate 1. A disk-shaped battery lid 9 serving as a positive electrode external terminal is disposed above the positive electrode current collecting lead portion 7.

  The battery lid 9 is composed of a steel disk-shaped terminal plate whose central portion protrudes upward, and an aluminum annular plate having a gas discharge opening formed in the central portion. An annular positive terminal portion 11 is disposed between the protruding portion of the terminal plate and the flat plate. The upper surface and the lower surface of the positive electrode terminal portion 11 are in contact with the lower surface of the terminal plate and the upper surface of the flat plate, respectively. The inner diameter of the positive electrode terminal portion 11 is larger than the inner diameter of the opening formed in the flat plate.

  On the upper side of the opening of the flat plate, a rupture valve 10 that cleaves when the battery internal pressure rises is disposed so as to close the opening. The peripheral edge portion of the rupture valve 10 is sandwiched between the lower surface of the inner edge portion of the positive electrode terminal portion 11 and the flat plate. The peripheral part of the terminal plate and the peripheral part of the flat plate are fixed. The upper surface of the positive electrode current collector lead portion 7 is joined to the lower surface of the flat plate, that is, the bottom surface of the battery lid 9 (surface on the electrode group G side) by resistance welding.

  On the other hand, a negative electrode current collecting lead portion 8 made of nickel for collecting a potential from the negative electrode plate 2 is disposed below the electrode group G. The negative electrode current collecting lead portion 8 is ultrasonically bonded to the end portion of the negative electrode current collecting lead piece 6 led out from the negative electrode plate 2. The negative electrode current collecting lead portion 8 is joined by resistance welding to the inner bottom portion of the battery can 4 that also serves as a negative electrode external terminal.

In addition, a non-aqueous electrolyte is injected into the battery can 4. In this example, the non-aqueous electrolyte is 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) in a mixed organic solvent having a volume ratio of 1: 2 of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). What was dissolved so that it might become the density | concentration of a liter is used. A battery lid 9 is caulked and fixed to the upper part of the battery can 4 via a gasket 12. For this reason, the inside of the lithium ion secondary battery 20 is sealed.

  The electrode group G accommodated in the battery can 4 is such that the positive electrode plate 1 and the negative electrode plate 2 are not in contact with each other via a microporous separator 3 made of polyethylene or the like. Has been wounded. The positive electrode current collecting lead piece 5 and the negative electrode current collecting lead piece 6 are respectively disposed on opposite end surfaces of the electrode group G. The entire outer peripheral surface of the electrode group G is provided with an insulating coating to prevent electrical contact with the battery can 4.

  The positive electrode plate 1 has an aluminum foil as a positive electrode current collector. The thickness of the aluminum foil is set to 20 μm in this example. On both surfaces of the aluminum foil, a positive electrode mixture containing a positive electrode active material is applied substantially evenly. In this example, olivine manganese iron is used as the positive electrode active material. In addition to the positive electrode active material, the positive electrode composite material is mixed with graphite as a conductive material and polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder). In this example, the mixing ratio of the positive electrode active material, graphite, and PVDF is adjusted to a weight ratio of 80: 15: 5. Olivine manganese iron has a characteristic that there are two plateaus (primary plateau and secondary plateau) in the discharge curve. The electrode plate 1 is formed by applying a positive electrode mixture kneaded by a kneader to an aluminum foil, and after being dried, is rolled and formed by a press machine. A positive electrode current collecting lead piece 5 is led out to a side edge on one side in the longitudinal direction of the aluminum foil.

  On the other hand, the negative electrode plate 2 has a copper foil as a negative electrode current collector. The thickness of the copper foil is set to 10 μm in this example. A negative electrode mixture containing a negative electrode active material is applied to both sides of the copper foil substantially evenly. In this example, graphite is used for the negative electrode active material. A binder PVDF is blended in addition to the negative electrode active material. In this example, the mixing ratio of the negative electrode active material and PVDF is adjusted to a weight ratio of 90:10.

(Battery assembly)
In the manufacture of the lithium ion secondary battery 20, the produced positive electrode plate 1 and negative electrode plate 2 are vacuum dried at 100 ° C. for 24 hours, and then wound through the separator 3 to produce the electrode group G. At this time, the positive electrode plate 1 and the negative electrode plate 2 are wound so that the positive electrode current collecting lead piece 5 and the negative electrode current collecting lead piece 6 are positioned in opposite directions.

  Next, all of the positive electrode current collector lead pieces 5 are ultrasonically bonded to the positive electrode current collector lead part 7, and all of the negative electrode current collector lead pieces 6 are ultrasonically bonded to the negative electrode current collector lead part 8. Insulate the surrounding area. Then, the electrode group G to which the positive current collecting lead portion 7 and the negative current collecting lead portion 8 are connected is inserted into the battery can 4 with the negative current collecting lead portion 8 facing the bottom side.

  Then, the electrode rod is passed through the winding center portion of the electrode group G, and the negative electrode current collector lead portion 8 and the inner bottom portion of the battery can 4 are resistance welded, and then the positive electrode current collector lead portion 7 and the battery lid 9 are resistance welded. Join. Then, after pouring a non-aqueous electrolyte into the battery can 4, the battery lid 9 is caulked and fixed to the battery can 4 via the gasket 12, thereby completing the lithium ion secondary battery 20 having a battery capacity of 1 Ah. Let

(Operation)
Next, charge / discharge control of the secondary battery module 40 will be described focusing on battery state control of the lithium ion secondary battery 20.

  When charging each lithium ion secondary battery 20 constituting the battery unit 25, a power supply unit (not shown) is connected in parallel with the battery unit 25. Each lithium ion secondary battery 20 is charged with electric power from the power supply unit. Calculation of the state of charge SOC of the lithium ion secondary battery 20 at this time will be described.

  The microcomputer A detects open circuit voltage (OCV) data for each lithium ion secondary battery 20 at a rate of once every fixed time (for example, 30 seconds). In other words, the microcomputer A designates the lithium ion secondary battery 20 to be measured from the battery designation port to the voltage measurement circuit 29, whereby the measurement target lithium ion secondary battery is designated from the voltage measurement circuit 29 via the A / D input port. The open circuit voltage of the battery 20 is taken in.

  The microcomputer A calculates the state of charge SOC of each lithium ion secondary battery 20 from the data of each open circuit voltage using a battery state map (or relational expression) stored in advance in the ROM and expanded in the RAM in the initial setting. . In this battery state map, the open circuit voltage and the state of charge SOC are developed in the RAM in a corresponding state. Moreover, the microcomputer A calculates the average charge state of all the lithium ion secondary batteries as the charge state SOC of the battery unit 25. It is also possible to detect the temperature data of the battery unit 25 with a thermistor or the like and add temperature correction when calculating the state of charge SOC.

  In addition, for each lithium ion secondary battery 20, the microcomputer A has a (charge state SOC of the lithium ion secondary battery 20−average charge state of all lithium ion secondary batteries 20) exceeding 5 points (capacity adjustment target) It is determined whether or not the lithium ion secondary battery 20 is present. If the determination is affirmative, the capacity adjustment time t depending on the resistance value of the bypass resistor R is calculated only for the lithium ion secondary battery. . The switch SW1 is turned on for the capacity adjustment time t and the bypass resistance R is connected to the lithium ion secondary battery 20 to be capacity adjusted, thereby averaging the capacity difference between the batteries. When the average charge state of the battery unit 25 is 100%, that is, when the battery unit 25 reaches the full charge state, the microcomputer A determines that the charge is finished, and notifies the outside of the charge by a not-shown notification means. At this time, the connection between the power supply unit (not shown) and the battery unit 25 is released.

  Next, control during discharge will be described.

  FIG. 3 is a flowchart illustrating a method for controlling the lithium ion secondary battery.

  When the microcomputer A determines that the average charging state of all the lithium ion secondary batteries 20 is 30% or more, the microcomputer A outputs a control signal from the output port to turn on the switch SW2. Thereby, the electric power from the battery unit 25 is supplied to the external load 32.

  Normally, in a lithium ion secondary battery, when discharged from a fully charged state, the battery voltage gradually decreases as the state of charge SOC decreases, that is, the discharge depth DOD increases. When the discharge proceeds and reaches the end of discharge (a state where the depth of discharge DOD exceeds approximately 90%), the battery voltage rapidly decreases, and when the battery is further discharged, an overdischarge state occurs.

  On the other hand, in the lithium ion secondary battery 20 using olivine manganese iron as the positive electrode mixture, the olivine of olivine manganese iron is obtained when the battery voltage is 3 V or less and 2.5 V or more at a current value of 1 C on the low current value side. Occlusion and release of lithium ions in iron. That is, the discharge capacity from 3V to 2.5V increases. For this reason, the discharge rate with respect to the voltage fluctuation from 3V to 2.5V becomes moderate compared with the conventional lithium ion secondary battery.

  In the secondary battery module 40, the voltage measurement circuit 29 detects the open circuit voltage of the lithium ion secondary battery 20 (step S101), and outputs the information to the microcomputer A. Then, the voltage change rate is calculated from the voltage information obtained by the microcomputer A (step S102), and a plateau is detected based on the voltage change rate (step S103). The plateau is a stagnant portion where the voltage change is relatively small and relatively flat in the discharge curve. In this embodiment, the plateau is a plateau when the voltage change rate is 0.1 mV / s or more and 10 mV / s or less. To be judged.

  Then, it is determined whether or not the plateau is a secondary plateau (step S104). A plateau where the voltage change rate is 0.1 mV / s or more and 10 mV / s or less is detected between the start of discharge and the preset first discharge end voltage, and the battery voltage is 2.5 V or more. When a second plateau having a voltage change rate of 0.1 mV / s to 10 mV / s at a battery voltage of 3 V or less is detected, it is determined that the second plateau is a secondary plateau. When a plurality of plateaus are detected after the second, all are determined to be secondary plateaus.

  And when it determines with it being a secondary plateau (it is YES at step S104), a 2nd discharge end voltage (for example, 1.75V) is set to 1V or more and less than 2V which is a voltage lower than a 1st discharge end voltage, Discharge to the second discharge end voltage. On the other hand, for example, when the plateau is less than one at the current value 10C on the high current value side, it is determined that the plateau is not a secondary plateau (NO in step S104), and there is a risk of overdischarge. The first discharge end voltage of 2.5 V or higher is discharged, and the discharge is stopped when the first discharge end voltage is reached (step S106).

  When the discharge of the battery unit 25 is stopped, power is supplied to the external load 32 from another battery unit configured in the same manner as the battery unit 25, and each lithium ion secondary battery 20 of the battery unit 25 is charged. To control.

  The battery output is calculated by the following equation (1).

Battery output = (− end-of-discharge voltage ² + OCV × end-of-discharge voltage) / DC resistance (1)
From the above formula (1), it can be seen that the battery output is maximized when the end-of-discharge voltage is ½ of OCV.

For example, in a conventional lithium ion secondary battery in which the positive electrode is made of a lithium transition metal composite oxide, the negative electrode is made of graphite, and the OCV is 3.6, the end-of-discharge voltage is set to 1.8 V, which is 1/2 of OCV. When set, the battery output is given by equation (1) above.
Battery output = (− (1.8V) ² + 3.6V × 1.8V) /0.05Ω=65W.

However, in order to avoid overdischarge due to a sudden voltage drop, conventionally, the discharge end voltage has been set higher. For example, when the discharge end voltage is set to 2.7 V, the battery output is According to the above formula (1),
Battery output = (− (2.7V) ² + 3.6V × 2.7V) /0.05Ω=48W.

  On the other hand, in the present embodiment, the discharge end voltage is lowered from the primary discharge end voltage 2.7 V to the second discharge end voltage 1.8 V by detecting the secondary plateau. The maximum efficiency improvement of about 35% was achieved (65 ÷ 48 × 100 = 13.5%).

  Next, examples of the lithium ion secondary battery 20 constituting the secondary battery module 40 of the present embodiment will be described. A comparative example manufactured for comparison is also shown. Further, the present invention is not limited to the examples described below.

Example 1
In Example 1, the lithium ion secondary battery 20 was manufactured by blending olivine manganese iron into the positive electrode material and blending graphite into the negative electrode material.

(Example 2)
Example 2 is the same as Example 1 except that lithium cobalt oxide and olivine iron are blended in a ratio of 90:10 to the positive electrode material.

(Example 3)
Example 3 is the same as Example 1 except that lithium cobaltate and a solid solution positive electrode active material are blended in the ratio of 90:10 to the positive electrode material. The solid solution positive electrode active material is Li ₂ MO ₃ —LiM′O ₂ solid solution (M is one or more elements selected from Mn, Ti, Zr, M ′ is Ni, Co, Mn, Fe, Ti, Zr, Al , One or more elements selected from Mg, Cr, and V).

Example 4
In Example 4, a lithium ion secondary battery 20 in which lithium cobaltate was used as the positive electrode material and graphite and lithium titanate were blended in the ratio of 90:10 as the negative electrode material was manufactured.

(Example 5)
Example 5 is the same as Example 4 except that the negative electrode material is mixed with graphite and iron oxide in a ratio of 90:10.

(Example 6)
Example 6 is the same as Example 4 except that the negative electrode material is mixed with graphite and tin oxide in a ratio of 90:10.

(Example 7)
Example 7 is the same as Example 4 except that the negative electrode material is mixed with graphite and silicon in a ratio of 90:10.

(Comparative Example 1)
In Comparative Example 1, a lithium ion secondary battery in which lithium cobaltate was blended into the positive electrode material and graphite was blended into the negative electrode material was produced. That is, Comparative Example 1 is a conventional lithium ion secondary battery.

(Evaluation)
About the lithium ion secondary battery of each Example and the comparative example, the voltage change rate with respect to the discharge depth DOD in each electric current value was evaluated. That is, after each lithium ion secondary battery is initialized, it is discharged from a fully charged voltage of 4.2 V to a discharge end voltage of 1 V at a current rate of 1 C (1 hour rate of rated electrical capacity), and the voltage with respect to the depth of discharge DOD. And measure how many plateaus (regions where the voltage change rate is 0.1 mV / s or more and 10 mV / s or less), and the second plateau (secondary plateau) becomes 2.5V or more and 3V or less. I checked.

  As a representative of FIG. 4, the discharge curve at each current value in Example 1 is shown. In Example 1, it was found that the second plateau (secondary plateau) was 2.5 V or more and 3 V or less up to 3 C on the low current value side.

  Others are summarized in Table 1. As shown in Table 1, olivine manganese iron alone, or two or more kinds of positive electrode materials (positive electrode active materials) mixed with at least one of olivine manganese iron, olivine iron, and solid solution are used, or graphite or non- Example 1 using crystalline carbon alone or two or more kinds of negative electrode materials (negative electrode active materials) in which at least one of graphite or amorphous carbon, lithium titanate, iron oxide, silicon, and tin oxide is mixed. ~ 7, there is a second plateau (region where the voltage change rate is 0.1 mV / s or more and 10 mV / s or less) at a battery voltage of 2.5 V or more and 3 V or less up to a certain current value (1 to 3 C). I understood. In Comparative Example 1, there was one plateau (area where the voltage change rate was 0.1 mV / s or more and 10 mV / s or less) at any current value.

  Therefore, as compared with the conventional lithium ion secondary battery, the discharge rate at the time of discharging from the voltage of 2.5 V to 3 V is moderately (slow) to the above current value region. Then, it became clear that the discharge end voltage was low and could be controlled.

  Table 2 shows the battery output at each current value. The battery output was measured at an open circuit voltage of 3.5V. As a result, in Examples 1 to 7, since the discharge end voltage can be controlled to be low at a current value in which there is a plateau (voltage change rate of 0.1 mV / s to 10 mV / s) in the range of 2.5 V to 3 V, the battery It turns out that the output improves. That is, it has been found that the secondary battery module 40 including the lithium ion secondary battery 20 exhibits an excellent effect for overdischarge countermeasures, secures safety and reliability, and can maximize output.

1 Positive electrode plate (positive electrode)
2 Negative electrode plate (negative electrode)
4 Battery can
9 Battery cover
20 Cylindrical lithium ion secondary battery
25 Battery part
27 Battery control unit
40 Secondary battery module

Claims (11)

On the high current value side, a primary plateau in which the voltage change of the discharge voltage is within a predetermined speed range is exhibited, and on the low current value side, the primary plateau and the primary plateau after the primary plateau is developed are again within the speed range. A control device for a lithium ion secondary battery having a discharge characteristic that expresses a secondary plateau,
When the secondary plateau is detected, the battery is discharged to a second discharge final voltage lower than a preset first discharge final voltage. When the secondary plateau is not detected, the secondary plateau is discharged to the first discharge final voltage. The control apparatus of the lithium ion secondary battery characterized by the above-mentioned. Voltage detecting means for detecting the discharge voltage;
Change rate calculation means for calculating the change rate of the discharge voltage detected by the voltage detection means;
Plateau detection means for detecting the plateau based on the change speed calculated by the change speed calculation means;
Plateau determination means for determining whether or not the plateau detected by the plateau detection means is the secondary plateau;
When the plateau determination means determines that the plateau is the secondary plateau, the discharge end voltage is set to a second discharge end voltage lower than a preset first discharge end voltage, and the secondary plateau A discharge end voltage setting means for setting the discharge end voltage to the first discharge end voltage when it is determined that the discharge end voltage is not,
The control device for a lithium ion secondary battery according to claim 1, comprising:   3. The lithium ion according to claim 2, wherein the plateau detection unit determines that the plateau is detected when a change rate of the discharge voltage is in a range of 0.1 mV / s to 10 mV / s. Secondary battery control device.   The plateau determination means determines that the plateau is the secondary plateau when the change rate of the discharge voltage is in a range of 0.1 mV / s to 10 mV / s and the discharge voltage is 2.5 V to 3 V. The control apparatus for a lithium ion secondary battery according to claim 3. The positive electrode active material is composed of olivine manganese iron alone, or olivine manganese iron, olivine iron, Li ₂ MO ₃ —LiM′O ₂ solid solution (M is one or more elements selected from Mn, Ti, Zr, M 'includes a mixture of at least one element selected from Ni, Co, Mn, Fe, Ti, Zr, Al, Mg, Cr, and V). The control apparatus of the lithium ion secondary battery as described in any one of Claims 4-5.   The negative electrode active material includes a material made of amorphous carbon alone or a mixture of at least one of amorphous carbon, lithium titanate, iron oxide, silicon, and tin oxide. The lithium secondary battery according to claim 5. On the high current value side, a primary plateau in which the voltage change of the discharge voltage is within a predetermined speed range is exhibited, and on the low current value side, the primary plateau and the primary plateau after the primary plateau is developed are again within the speed range. A battery module comprising: a lithium ion secondary battery having a discharge characteristic that expresses a secondary plateau, and a battery control unit that detects the voltage of the lithium ion secondary battery and controls charge and discharge;
When the battery control unit detects the secondary plateau, the battery control unit discharges to a second discharge cutoff voltage lower than a preset first discharge cutoff voltage, and does not detect the secondary plateau. A battery module that performs control to discharge to the first discharge end voltage. On the high current value side, a primary plateau in which the voltage change of the discharge voltage is within a predetermined speed range is exhibited, and on the low current value side, the primary plateau and the primary plateau after the primary plateau is developed are again within the speed range. A control method of a lithium ion secondary battery having a discharge characteristic that expresses a secondary plateau,
When the secondary plateau is detected, the battery is discharged to a second discharge cutoff voltage lower than a preset first discharge cutoff voltage, and when the secondary plateau is not detected, the first discharge cutoff voltage is detected. A method for controlling a lithium ion secondary battery, wherein A voltage detection step of detecting the discharge voltage;
A change rate calculating step for calculating a change rate of the detected discharge voltage;
A plateau detection step of detecting the plateau based on the calculated rate of change;
A plateau determination step of determining whether or not the detected plateau is the secondary plateau;
When it is determined that the plateau is the secondary plateau, the discharge end voltage is set to a second discharge end voltage lower than a preset first discharge end voltage, and is determined not to be the secondary plateau. A discharge end voltage setting step for setting the discharge end voltage to the first discharge end voltage when
The method for controlling a lithium ion secondary battery according to claim 8, wherein:   10. The lithium ion according to claim 9, wherein in the plateau detection step, it is determined that the plateau is detected when a change rate of the discharge voltage is in a range of 0.1 mV / s to 10 mV / s. Secondary battery control method.   In the plateau determination step, the secondary plateau is determined when the change rate of the discharge voltage is in a range of 0.1 mV / s to 10 mV / s and the discharge voltage is 2.5 V to 3 V. The method for controlling a lithium ion secondary battery according to claim 10.

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