JP5775725B2 - Charge control system - Google Patents

Description

  The present invention relates to a charge control system that charges a lithium ion secondary battery.

  Lithium ion secondary batteries have a high energy density, so for example, batteries used in vehicles such as railways and automobiles, or used for storing electric power generated by solar power generation or wind power generation and supplying it to an electric power system. It is attracting attention as. For example, when a lithium ion secondary battery (hereinafter referred to as “battery” as appropriate) is mounted on an automobile and used, such automobiles include a zero emission electric vehicle without an engine, both an engine and a secondary battery. There are also hybrid electric vehicles equipped with a plug-in hybrid electric vehicle that is directly charged from a system power source. In addition, it is expected to be used as a stationary power storage system that supplies power in an emergency when the power system is cut off.

  For such various uses, excellent durability is required for the battery. For example, even when the environmental temperature becomes high or the charge / discharge cycle is repeated, the reduction rate of the rechargeable battery capacity (that is, the battery capacity) is low, and the battery capacity maintenance rate is required to be high over a long period of time. Further, due to radiant heat from the road surface or heat conduction from the inside of the vehicle, for example, storage characteristics and cycle life in a high temperature environment of 60 ° C. or higher are important required performances.

  However, when a lithium ion secondary battery is left in a high temperature environment or a charge / discharge cycle is performed, the battery capacity decreases. This decrease in capacity becomes more prominent when left at a high voltage or cycled over a wide voltage range.

  As a method for suppressing such a decrease in battery capacity, for example, a technique for expanding the voltage drive range so that the battery capacity becomes constant even when the battery deteriorates is known (see, for example, Patent Document 1).

JP-A-8-214469

  However, in the method of expanding the voltage driving range as described above, the charging / discharging voltage of the battery becomes excessively wide, so that lithium metal may be deposited on the negative electrode or the internal resistance of the battery may increase excessively. is there.

According to a first aspect of the present invention, there is provided a charge control system comprising: a charge control unit that charges a lithium ion secondary battery up to a charge end voltage; and the battery voltage of the lithium ion secondary battery becomes a charge end voltage by charging by the charge control unit. A determination unit that determines whether the battery state of the lithium ion secondary battery satisfies a predetermined charge end voltage change condition, and the determination unit determines whether the battery state of the lithium ion secondary battery A charge end voltage change unit that changes the charge end voltage to a higher charge end voltage when it is determined that the voltage change condition is satisfied, and the charge end voltage change unit changes the charge end voltage. If that, the charge control section, have further line charging of the lithium ion secondary battery until the battery voltage reached a charge termination voltage after the change, charge voltage changing conditions, lithium during determination The potential of the negative electrode of the ion secondary battery is higher than the lower limit value of said potential, characterized in that it comprises a change condition.
According to a second aspect of the present invention, there is provided a charge control system comprising : a charge control unit that charges a lithium ion secondary battery up to a charge end voltage; and the battery voltage of the lithium ion secondary battery becomes a charge end voltage by charging by the charge control unit. A determination unit that determines whether the battery state of the lithium ion secondary battery satisfies a predetermined charge end voltage change condition, and the determination unit determines whether the battery state of the lithium ion secondary battery A charge end voltage change unit that changes the charge end voltage to a higher charge end voltage when it is determined that the voltage change condition is satisfied, and the charge end voltage change unit changes the charge end voltage. If that, the charge control unit further performs charging of the lithium ion secondary battery until the battery voltage reached a charge termination voltage after the change, charge voltage changing conditions, lithium during determination That the potential of the positive electrode of the ion secondary battery is less than said potential of allowable upper limit value, characterized in that it comprises a change condition.
According to a third aspect of the present invention, in the charge control system according to the first or second aspect of the present invention, the charge end voltage changing condition is that the ratio between the charge capacity of the lithium ion secondary battery and the initial battery capacity at the time of determination is a predetermined value or less. It is characterized in that it is included as a change condition.
According to a fourth aspect of the present invention, in the charge control system according to any one of the first to third aspects, the charge end voltage changing condition includes an elapsed use time of the lithium ion secondary battery as the changing condition. And
According to a fifth aspect of the present invention, in the charge control system according to any one of the first to fourth aspects, the charge end voltage changing unit is configured to determine the potential of the positive electrode or the negative electrode at the time of determining the charge end voltage change condition, The charge end voltage is changed based on the allowable potential.
According to a sixth aspect of the present invention, in the charge control system according to any one of the first to fourth aspects, the charge end voltage changing unit changes the charge end voltage to a charge end voltage that is higher by a preset predetermined voltage. The charging end voltage change control unit is further provided to make the determination by the determination unit again after the end voltage is changed.
A seventh aspect of the present invention is the charge control system according to any one of the first to sixth aspects, wherein the positive electrode potential when the charge end voltage is the initial value is lower than the allowable upper limit value of the positive electrode potential. It is characterized by setting.
The invention of claim 8 is the charge control system according to any one of claims 1 to 7 , wherein the positive electrode of the lithium ion secondary battery includes a lithium composite oxide represented by the following formula (1). It is characterized by.
_{LiNi a Mn b Co c M d} O 2 ··· (1)
In the formula (1), M represents at least one selected from the group consisting of Fe, V, Ti, Cu, Al, Sn, Zn, Mg, B, and W, and a, b, c, and d are Are values satisfying 0.2 ≦ a ≦ 0.8, 0.1 ≦ b ≦ 0.4, 0 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.1, and a + b + c + d = 1. There is a relationship that satisfies.
The invention according to claim 9 is the charge control system according to claim 8 , wherein the positive electrode potential when initially charged to the end-of-charge voltage is set to 3.8 V or more and 4.1 V or less. .
A tenth aspect of the invention is characterized in that, in the charge control system according to the eighth or ninth aspect , the changed positive electrode potential is set to fall within a range of 3.9V to 4.3V.
An eleventh aspect of the present invention is the charge control system according to any one of the eighth to tenth aspects, wherein the negative electrode of the lithium ion secondary battery includes graphite, and a graphite interlayer distance of the graphite is 0.335 nm or more and 0.00. It is characterized by being 338 nm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of battery capacity can be suppressed, suppressing the increase in internal resistance of a battery, and the improvement of the cycling characteristics of a battery can be aimed at.

It is a circuit diagram showing the structure of the charge control system which concerns on this embodiment. It is a figure which shows the relationship between the capacity | capacitance of positive and negative electrodes, and an electric potential, and the relationship between battery capacity and a battery voltage. FIG. 3 is an enlarged schematic diagram showing a portion where the potentials of negative electrode potential curves 102 and 105 in FIG. 2 are in the vicinity of α. It is a flowchart which shows a charging method. It is a figure explaining the case where the charge end voltage is increased by ω. It is the figure which showed typically the internal structure of the lithium ion secondary battery. It is a figure which shows the evaluation result of Example 1 and Comparative Examples 1-3. It is a figure which shows an example of the power supply device which can apply the charge control system of this Embodiment, and is a block diagram which shows the drive system of a hybrid vehicle.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “this embodiment” as appropriate) will be described in detail with reference to the drawings. However, this embodiment is not limited to the following contents. Any change can be made without departing from the scope of the invention.

[Configuration of charge control system]
FIG. 1 is a circuit diagram illustrating a configuration of a charge control system according to the present embodiment. A charge control system 201 according to the present embodiment controls charging of a lithium ion secondary battery 204 (hereinafter referred to as a battery) having a positive electrode and a negative electrode, and an arithmetic processing unit having a charge end voltage correcting unit 202. 205, a charge / discharge control circuit 203, a current measuring unit 208, and a voltage measuring unit 209. An external load 206 is connected to the battery 204 via a switch 210a, and a charging power source 207 for charging the battery 204 is connected via a switch 210b. Note that the battery 204 may be a single battery made of one battery or an assembled battery in which two or more batteries are arbitrarily combined.

  The charge / discharge control circuit 203 controls charge / discharge of the battery 204 based on a command to the arithmetic processing unit 205. When charging the discharged battery 204, the charge / discharge control circuit 203 charges the battery 204 until the battery voltage of the battery 204 after starting charging reaches a predetermined charge end voltage. The end-of-charge voltage is set to V0 in advance, but is changed to the corrected end-of-charge voltage V1 by the end-of-charge voltage correcting unit 202, as will be described later. When the charge end voltage is changed from V0 to the corrected charge end voltage V1, the charge / discharge control circuit 203 performs further charging from the charge end voltage V0 to the corrected charge end voltage V1.

  Information on the current and battery voltage of the battery 204 measured by the current measuring unit 208 and the voltage measuring unit 209 is input to the arithmetic processing unit 205. The arithmetic processing unit 205 measures and integrates the battery voltage, current, charging time, rest time (standby time), non-use time, etc. of the battery 204, and performs calculations, processing, etc. according to the integrated time. The arithmetic processing unit 205 determines charging / discharging control parameters (for example, discharging or charging time, discharging or charging voltage, discharging or charging current, etc.) of the battery 204 based on the results of these calculations, processing, and the like. By transmitting the discharge control parameter to the charge / discharge control circuit 203, the charging of the battery 204 by the charge / discharge control circuit 203 is controlled.

  At the time of discharging, the arithmetic processing unit 205 transmits a control parameter such that the charging voltage and charging current of the battery 204 are as desired, to the charging / discharging control circuit 203, and a signal for closing the switch 210a and a signal for opening the switch 210b. It transmits to each switch 210a, 210b. As a result, the battery 204 and the external load 206 are electrically connected, and the battery 204 can be discharged.

  On the contrary, at the time of charging, the arithmetic processing unit 205 transmits a control parameter such that the charging voltage and charging current become desired to the charging / discharging control circuit 203, and also outputs a signal for opening the switch 210a and a signal for closing the switch 210b. Send to each switch. As a result, the battery 204 and the charging power source 207 are electrically connected, and the battery 204 can be charged.

  The end-of-charge voltage correcting unit 202 measures the potentials of the positive electrode and the negative electrode of the battery 204. Although there is no restriction | limiting in the measuring method of an electric potential, For example, it can measure using the battery voltage value of the battery 204, the electric current value which is flowing, and temperature etc. as needed. For example, the calculation is performed using the positive and negative charge / discharge curves and the voltage change of the battery voltage curve stored in the end-of-charge voltage correction unit 202 in advance.

  Alternatively, the calculation may be performed by incorporating lithium metal or the like into the battery 204 in advance and using the difference in potential between the lithium metal or the like and each electrode. However, in this case, since the structure of the battery 204 needs to be changed, the above-described potential measurement method is preferable from the viewpoint that a general battery can be used as the battery 204.

  In the case of the potential measurement method using the charge / discharge curve of the positive electrode and the negative electrode and the voltage change of the battery voltage curve, for example, the unique unipolar curve (each charge / discharge curve) of the positive electrode and the negative electrode that are measured and stored in advance and the actual measurement value The potential can be calculated from the battery voltage curve when the battery 204 is charged or discharged. At that time, the accuracy of the potential can be improved by using the voltage change rate obtained from the charge / discharge curve = (potential change ΔV) / (battery capacity change ΔQ). Here, the integrated value of the battery capacity change ΔQ is calculated as the product of the current value flowing through the battery 204 and time (= measurement cycle). As an apparatus for measuring the battery capacity change ΔQ, for example, any known electronic element can be used. A more detailed method is described in, for example, Japanese Patent Application Laid-Open No. 2009-80093.

  Although not shown, a temperature measuring means for measuring the temperature of the battery 204, such as a thermocouple or a thermistor, may be provided. The arithmetic processing unit 205 can control the charging of the battery 204 according to the temperature by acquiring the temperature measured by the temperature measuring unit, thereby enabling more accurate charging control.

  Furthermore, you may provide the recording part (not shown) for recording the various measured information. There is no particular limitation on the specific configuration of such a recording unit, for example, a magnetic recording medium such as a floppy (registered trademark) disk (FD) or a hard disk drive (HDD); a random access memory (RAM), a flash memory (USB memory) Semiconductor media such as: compact discs (CD-R, CD-RW, etc.), digital versatile discs (DVD-R, DVD + R, DVD + RW, DVD-RW, DVD-RAM, etc.), HD-DVD, Blu-ray disc, etc. An optical recording medium can be used.

  When charging a secondary battery such as the battery 204, it is necessary to suppress the charging voltage to a voltage that does not degrade the life characteristics, and the upper limit voltage is the above-described charging end voltage. This end-of-charge voltage varies depending on the type of secondary battery. The battery capacity is represented by the amount of electricity (Ah) that can be taken out during discharge from the end-of-charge voltage to the end-of-discharge voltage. In the present embodiment, the end-of-charge voltage correcting unit 202 changes (that is, corrects) the end-of-charge voltage V0 of the battery 204 to the corrected end-of-charge voltage V1, and then the end-of-charge voltage V0 is corrected to the end of the corrected charge. The significance of changing to the voltage V1 will be described.

  FIG. 2 is a graph showing the relationship between positive and negative electrode capacities and potentials and the relationship between battery capacities and battery voltages for the battery 204. 2, the horizontal axis represents battery capacity (Ah), and the vertical axis represents potential ((V) or voltage value (V), where the vertical axis represents the potential when the current is 0. Curves 101, 102, and 103 are curves in the initial state where the battery 204 is not deteriorated, the curve 101 is a positive potential curve of the battery, the curve 102 is a negative potential curve, and the curve 103 is a battery voltage curve. Show.

  In this embodiment, the difference between the “potential” of the positive electrode and the “potential” of the negative electrode is defined as the “voltage” of the battery. In FIG. 2, the potential curves 101 and 102 are described so that the difference between the positive electrode potential and the negative electrode potential at the same position with respect to the horizontal axis becomes the voltage value of the battery voltage curve 103. Further, the potential of the electrode in the present embodiment is a value based on the Li metal. α, β, and γ will be described later.

  The positive electrode potential curve 101 shows the relationship between the capacity and potential of the positive electrode. When the battery 204 is discharged from the charged state, the potential decreases to the positive electrode as the capacity decreases. The decreasing tendency is almost linear as a whole, but the degree of reduction is large near zero capacity. On the other hand, in the case of the negative electrode potential curve 102, the potential of the negative electrode increases substantially linearly with a decrease in capacity due to discharge, and the potential rapidly increases near zero capacity.

  As shown in FIG. 2, the battery voltage curve 103 showing the difference between the positive electrode potential and the negative electrode potential decreases as the battery capacity decreases. FIG. 2 shows a battery voltage curve having a voltage value in the range of V2 to V0. The battery 204 can be used outside the range shown in FIG. 2 (voltage values less than V2 and greater than or equal to V0). However, in the predetermined voltage range, the battery is liable to be deteriorated and the life is shortened. V0 and V2 are set. This V0 is a charge stop voltage, and V2 is a discharge stop voltage.

  The potential curves 101 and 102 in FIG. 2 are potential curves in the initial state (there is no deterioration). However, in reality, irreversible capacity is generated during the first charge / discharge cycle of the battery. 101 and the negative electrode potential curve 102 may be displaced. However, here, for convenience of explanation, it is assumed that the irreversible capacity is constant between the positive electrode and the negative electrode, and that the positive electrode potential curve 101 and the negative electrode potential curve 102 in the initial state are treated as being out of position.

By the way, with respect to a lithium ion secondary battery, it is known that by repeating the charge / discharge cycle, a phenomenon in which the battery capacity is reduced particularly by repetition at a high temperature. According to the study by the present inventors, it has been found that the following two points are mainly responsible for such a decrease in battery capacity.
(A) Lithium ions are inactivated, and the battery capacity decreases due to the potential range of the positive electrode and negative electrode of the battery shifting.
(B) A decrease in battery capacity due to a decrease in electrode materials (for example, a positive electrode active material and a negative electrode active material) that contribute to charge and discharge of the positive electrode and the negative electrode.
It was also found that the cause of the decrease in the charge capacity during the high charge state was derived from the negative electrode.

  In the phenomenon (b), the length of the potential curve of the positive electrode or the negative electrode is shortened because the amount of the electrode material that contributes to charge / discharge changes.

  On the other hand, in the phenomenon (a) (deactivation of lithium ions), since the amount of the electrode material that contributes to charging / discharging does not change, the potential curves of the positive electrode and the negative electrode are merely shifted. The length of the curve does not change.

  It was also found that such lithium ion inactivation occurs mainly at the positive and negative electrodes in a high charge state with a large charge depth. Therefore, it is necessary to manage the potentials of the positive electrode and the negative electrode at full charge within an appropriate range. In the present embodiment, the “charge depth” represents a value indicating the charge capacity as a percentage of the rated capacity of the battery (that is, the battery capacity at the time of full charge).

  Further, it has been found that lithium ion inactivation tends to occur particularly on the negative electrode side. Therefore, lithium ions occluded in the negative electrode react with, for example, a decomposition product of the nonaqueous electrolytic solution to be inactivated, and the potential range of the positive electrode and the negative electrode becomes narrow. Since such a reaction is mainly a reduction reaction, the reaction tends to be larger in a high charge state. In the present embodiment, such a phenomenon is referred to as “negative electrode capacity shift”, and hereinafter, a countermeasure against a decrease in battery capacity due to a negative electrode capacity shift will be described.

  As described above, it is necessary to manage the potential of the positive electrode and the negative electrode at full charge within an appropriate range. However, in the battery 204 of this embodiment, the positive electrode potential is managed to be γ or less, and the negative electrode potential is controlled. Is managed to be greater than or equal to α. Then, the charge end voltage V0, the active material application amount of the positive electrode and the negative electrode are set so that the potential of the negative electrode when the battery voltage is the charge end voltage V0 is α and the potential of the positive electrode is lower than γ at that time. doing.

  However, when the battery 204 whose initial state is indicated by the curves 101 to 103 deteriorates due to the above-described negative electrode capacity shift, the negative electrode potential curve after the deterioration becomes a curve represented by reference numeral 105, and the battery voltage is The curve is represented by reference numeral 106. A curve 104 shows a positive electrode potential curve after battery deterioration.

  The negative electrode potential curve 105 deviates from the negative electrode potential curve 102 in the initial state in the right direction in the figure by a capacity corresponding to inactivation of lithium ions. Therefore, when the capacity of the negative electrode decreases due to discharge, the potential of the negative electrode potential curve 105 after deterioration rises earlier than the negative electrode potential curve 102 in the initial state, and the battery voltage curve 106 after deterioration shows the battery voltage in the initial state. The discharge end voltage V2 is reached earlier than the curve 103. As a result, the battery capacity from the end-of-charge voltage V0 to the discharge stop voltage V2 is A0 in the initial state, but decreases to A1 (<A0) after deterioration due to the capacity deviation of the negative electrode. Thus, there arises a problem that the battery capacity of the battery 204 decreases due to the capacity shift of the negative electrode.

  FIG. 3 is an enlarged schematic view showing a portion where the potentials of the negative electrode potential curves 102 and 105 are in the vicinity of α in FIG. Before the capacity deviation occurs, the use area of the negative electrode is set to be α or more. However, if the capacity shift of the negative electrode occurs, as can be seen from FIG. 3, the negative electrode potential at the end of charging becomes α + ΔV and is not used up to the potential α, and the use area of the negative electrode decreases. Therefore, in the present embodiment, when battery deterioration (negative electrode capacity shift) occurs and the battery voltage becomes as shown by curve 106, by changing the charge end voltage V0 to the corrected charge end voltage V1, Charging can be performed until α, which is an available potential of the negative electrode, is reached. As a result, even when the battery 204 is deteriorated (capacity deviation of the negative electrode), a decrease in charge capacity can be suppressed.

  The above-described change of the charging end voltage is performed when the potential difference between the positive electrode and the negative electrode of the battery 204 (that is, the battery voltage measured by the voltage measuring unit 209 shown in FIG. 1) becomes the charging end voltage V0 of the battery 204. This is performed by the voltage correction unit 202. The end-of-charge voltage V0 is changed by the end-of-charge voltage correcting unit 202 when a predetermined end-of-charge voltage changing condition described later is satisfied.

  The condition for changing the end-of-charge voltage is an indicator of the capacity deviation of the negative electrode. For example, the potential of the positive electrode and the negative electrode estimated directly or indirectly, the number of charge / discharge cycles of the battery 204, the elapsed time, and the current time The amount of capacity deviation estimated from the ambient temperature, the degree of deterioration of the battery, or the like may be used, but is not limited thereto.

  Moreover, it is particularly preferable that the charge end voltage changing condition includes that the potential of the negative electrode is not less than α shown in FIG. By correcting the end-of-charge voltage based on the potential of the negative electrode, a decrease in battery capacity can be easily suppressed.

  The value α shown in FIG. 2 is a threshold at which battery deterioration occurs abruptly when the negative electrode is used at a potential below this value. This value is a parameter that can be arbitrarily determined by the user, and is not particularly limited. For example, it is determined according to battery capacity, battery life, electrolyte solvent or lithium salt, battery deterioration degree, positive electrode and negative electrode materials, and the like. do it. However, it is preferable to set α based on the likelihood of a capacity shift at the negative electrode potential.

  Furthermore, it is preferable that the charge end voltage changing condition includes that the potential of the positive electrode of the battery 204 is not more than the predetermined value γ shown in FIG. Γ shown in FIG. 2 is an upper limit potential that causes battery deterioration to increase when a value higher than this is used as the positive electrode potential. This value γ is a parameter that can be arbitrarily determined by the user and is not particularly limited. For example, the value γ is determined according to the battery capacity, the battery life, the electrolyte solvent or lithium salt, the deterioration degree of the battery, the positive electrode and negative electrode materials, and the like. do it. However, it is preferable to set γ based on the likelihood of a capacity shift at the positive electrode potential.

  The setting method of the positive electrode potential and the negative electrode potential at the end-of-charge voltage V0 is also a parameter that can be arbitrarily determined by the user, and is not particularly limited. For example, the battery capacity, battery output, battery life, battery deterioration degree, positive electrode and negative electrode What is necessary is just to determine according to a material, a combination, etc. of these. However, in order to correct the capacity deviation between the positive and negative electrodes, it is necessary to set the potential of the positive electrode to a value lower than γ and set the potential of the negative electrode to a value higher than α. The amount of difference is a parameter that can be arbitrarily determined by the user, and is not particularly limited. For example, it is determined according to battery capacity, battery output, battery life, battery deterioration, positive and negative electrode materials and combinations, etc. do it. In this case, it should be considered that the lower the positive electrode potential at VO, the lower the initial battery capacity, while the recharge is possible when the capacity is shifted. In FIG. 2, the initial charge negative electrode potential and α are matched, but this is not a limitation.

  In FIG. 2, the corrected charge end voltage V1 is obtained by adding β to the charge end voltage V0, that is, a value satisfying V1 = V0 + β. The management value β is also a parameter that can be arbitrarily determined by the user, and is not particularly limited. Like the management value α, for example, the battery capacity, the battery life, the electrolyte solvent or lithium salt, the deterioration degree of the battery, the positive electrode And may be determined according to the material or combination of the negative electrode. For example, if the curves 101, 102, 104, 105, the management value α, and the negative electrode potential at the end of charge voltage V0 are known, β and V1 can be estimated from them. For example, ΔV in FIG. 3 is calculated from the negative electrode potential at the end-of-charge voltage V0, the charge capacity until the negative electrode potential reaches the control value α is estimated from the magnitude of ΔV, and further from the estimated ΔV Estimate the battery voltage rise β.

[Charge control method in charge control system]
Next, a charging method in the above-described charging control system will be described with reference to the flowchart of FIG. The processing shown in FIG. 4 is performed by the arithmetic processing unit 205. In step S101, it is determined whether or not a charging trigger instructing the start of charging has been received. If it is determined that the charging trigger has been received, the process proceeds to step S102. The charging trigger is not particularly limited, but is generated when electricity is supplied from an external power source (charging power source 207 in FIG. 1). In step S <b> 102, the arithmetic processing unit 205 transmits a charge command signal for charging the battery 204 to the charge / discharge control circuit 203. The charging trigger may be transmitted directly to the charge / discharge control circuit 203 instead of the arithmetic processing unit 205, and charging may be started without going through the arithmetic processing unit 205.

  If charging of the battery 204 is started, in step S103, the charging end voltage correcting unit 202 measures the potential of the positive electrode and the negative electrode of the battery 204, and the measured potential is calculated by the arithmetic processing unit 205 or the charging end voltage correcting unit. The data is stored in a storage unit (not shown) provided in 202. This potential measurement is repeatedly performed at a predetermined timing. The potential measurement timing is not particularly limited, but if the measurement time interval is too long, the battery voltage of the battery 204 reaches the charge end voltage V0, and there is a possibility that the time wasted after the charge is stopped. Further, when the measurement time interval is too short, there is a possibility that the load on the end-of-charge voltage correction unit 202 becomes excessive in order to perform measurement excessively.

  In step S104, it is determined whether or not the battery voltage of the battery 204 measured by the voltage measurement unit 209 has reached the end-of-charge voltage V0. Here, the voltage measurement unit 209 determines whether or not the battery voltage has reached the end-of-charge voltage V0, but may be determined by the end-of-charge voltage correction unit 202. If YES is determined in step S104, the positive electrode potential Vp and the negative electrode potential Vn of the battery 204 are measured again in step S105. In step S106, it is determined whether or not the negative electrode potential Vn measured in step S105 is greater than a preset management value α.

  If it is determined in step S106 that Vn> α, the process proceeds to step S107, and if it is determined that Vn ≦ α, the process proceeds to step S109. If it is determined in step S106 that Vn ≦ α, if the charging is continued, battery deterioration or the like becomes remarkable. Therefore, a charge stop signal is transmitted to the charge / discharge control circuit 203 in step S109. As a result, charging of the battery 204 is stopped.

  If it is determined in step S106 that Vn> α and the process proceeds to step S107, it is determined in step S107 whether the positive electrode potential Vp is less than a predetermined management value γ (that is, Vp <γ). If it is determined in step S107 that Vp ≧ γ, battery deterioration or the like becomes significant when charging is continued. Therefore, the process proceeds to step S109, and a charge stop signal is transmitted to the charge / discharge control circuit 203. As a result, charging of the battery 204 is stopped.

  On the other hand, when it is determined in step S107 that Vp <γ, since the negative electrode potential Vn is larger than the management value α and the positive electrode potential Vp is smaller than the management value γ, the battery 204 is in a state where it can be further charged. Therefore, in this case, the process proceeds from step S107 to step S108, the charge end voltage correction unit 202 corrects the charge end voltage, and then the process returns to step S104. In step S108, the current end-of-charge voltage V0 is corrected to V0 + ω by the end-of-charge voltage correction unit 202, so that charging is further continued. Then, when the battery end voltage V0 (= initial V0 + ω) at which the battery voltage is set in step S104 is reached again, the processing from step S105 is executed again.

  That is, the process from step S104 to step S108 is repeated until the negative electrode potential is equal to or lower than the control value α or the positive electrode potential is equal to or higher than the control value γ. Will be increased. When either Vn ≦ α or Vp ≧ γ is satisfied, the charging operation of the battery 204 ends. The step width ω when correcting the end-of-charge voltage is usually preferably set within a range of 0.1 mV to 100 mV.

  FIG. 5 is a diagram illustrating a case where the charge end voltage is increased by ω as in the flowchart of FIG. In FIG. 5, when the process of step S108 is performed twice, that is, when the charging end voltage is increased for the second time and charged to the battery voltage A0 + 2ω, the potential of the negative electrode becomes equal to or lower than the control value α, finish. As a result, the battery capacity is increased by ΔA = A2−A1 as compared with the case where the charge is terminated at the initial charge end voltage V0. In addition, by changing the charge end voltage in small increments while confirming that the potentials of the negative electrode and the positive electrode are within the control range in this way, the potentials of the positive electrode and the negative electrode at the end of the charge are greatly shifted out of the control range. Can be prevented. Therefore, it is possible to provide a charge control system that can improve cycle characteristics particularly at high temperatures, such as suppressing an increase in internal resistance of the lithium ion secondary battery 204 and suppressing a decrease in battery capacity.

  In the flowchart shown in FIG. 4, it is determined whether or not to change the discharge end voltage V0 using the positive electrode potential, but the battery deterioration degree, material, elapsed time, and time at that time are changed to the positive and negative electrode potentials. Whether or not to change to the corrected charge end voltage V1 may be determined using the voltage or temperature as a criterion. When using these methods, it is necessary to consider the capacity deviation in advance. For example, when the degree of deterioration of the battery is used, it is preferable to change the percentage of the capacity reduction by correcting the charging voltage after considering the ratio of the capacity deviation in the battery capacity reduction in advance.

  In the above description, the charging control system 201 has been described as having the arithmetic processing unit 205 as shown in FIG. However, since the charge / discharge control circuit 203 or the end-of-charge voltage correction unit 202 has the function of the calculation processing unit 205, the calculation processing unit 205 may not be provided.

  In FIG. 2, the length of the potential curve of the positive electrode and the negative electrode is fixed for convenience of explanation, and the above description has been made. However, in actuality, the decrease in the electrode material that contributes to the charge and discharge of the positive electrode and the negative electrode of the battery Side reactions in the positive electrode and the negative electrode can also occur. Therefore, since the positive electrode potential curve 101 also changes, when a method of simply making the charging capacity constant is applied, a region of γ or more is also used as the positive electrode utilization region at the time of charging / discharging, so that the high-temperature cycle characteristics of the battery deteriorate. Resulting in.

[Configuration of lithium ion secondary battery]
The charge control system according to the present embodiment can be applied to any known lithium ion secondary battery. Here, an embodiment of a lithium ion secondary battery will be described with reference to FIG. Of course, the configuration described below is merely an example, and the lithium ion secondary battery to which the charge control system according to the present embodiment is applied is not limited to the structure illustrated in FIG. 6.

  FIG. 6 is a diagram schematically showing the internal structure of the lithium ion secondary battery. A battery 204 according to this embodiment shown in FIG. 6 includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container (that is, a battery can) 13, a positive electrode current collecting tab 14, a negative electrode current collecting tab 15, an inner lid 16, and an internal pressure release valve. 17, a gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axis 21. The battery lid 20 is an integrated part composed of the inner lid 16, the internal pressure release valve 17, the gasket 18, and the PTC resistance element 19. A positive electrode 10, a separator 11, and a negative electrode 12 are wound around the shaft center 21.

The positive electrode 10 includes a positive electrode active material, a conductive agent, a binder, and a current collector. Illustrative examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . _{Other, LiMnO 3, LiMn 2 O 3} , LiMnO 2, Li 4 Mn 5 O 12, LiMn 2-X M X O 2 ( where selected from the group consisting of M = Co, Ni, Fe, Cr, Zn, Ti Li ₂ Mn ₃ MO ₈ (however, at least one selected from the group consisting of M = Fe, Co, Ni, Cu, Zn), Li _{1− X} A _X Mn ₂ O ₄ (provided that, A = Mg, B, Al , Fe, Co, Ni, Cr, Zn, at least one selected from the group consisting of Ca, x = 0.01~0.1), _{LiNi 1-X M X O 2} ( however, M = Co, Fe, at least one selected from the group consisting of _{Ga, x = 0.01~0.2), LiFeO} 2, Fe 2 (SO 4) 3, _{LiCo 1-X M X O 2} ( where At least one selected from the group consisting of M = Ni, Fe, Mn, x = 0.01 to 0.2), LiNi1-xMxO2 (where M = Mn, Fe, Co, Al, Ga, Ca, Mg) At least one selected from the group consisting of x = 0.01 to 0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , and LiMnPO ₄ can be listed.

  The particle size of the positive electrode active material is usually defined so as to be equal to or less than the thickness of the mixture layer formed from the positive electrode active material, the conductive agent, and the binder. When there are coarse particles having a size equal to or greater than the thickness of the mixture layer in the positive electrode active material powder, the coarse particles can be removed in advance by sieving classification or wind classification to produce particles having a thickness of the mixture layer thickness or less. preferable.

  In addition, since the positive electrode active material is generally oxide-based and has high electrical resistance, a conductive agent made of carbon powder for supplementing electrical conductivity is used. Since both the positive electrode active material and the conductive agent are usually powders, a binder can be mixed with the powders, and the powders can be bonded together and simultaneously bonded to the current collector.

  For the current collector of the positive electrode 10, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, or a metal foam plate is used. . In addition to aluminum, materials such as stainless steel and titanium are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

  A positive electrode slurry in which a positive electrode active material, a conductive agent, a binder, and an organic solvent are mixed is attached to a current collector by a doctor blade method, a dipping method, or a spray method, and then the organic solvent is dried and applied by a roll press. The positive electrode 10 can be produced by pressure forming. In addition, a plurality of mixture layers can be laminated on the current collector by performing a plurality of times from application to drying.

The negative electrode 12 includes a negative electrode active material, a binder, and a current collector. When high rate charge / discharge is required, a conductive agent may be added. Examples of the negative electrode active material that can be used in the present invention include graphite, non-graphite carbon, metals such as aluminum, silicon, and tin, and alloys thereof, lithium-containing transition metal nitrides Li _(3-X) M _X N, silicon A material for forming an alloy with lithium or a material for forming an intermetallic compound of Li _X SiO _Y (0 ≦ x, 0 <y <2) and a lower oxide of Li _X SnO _Y be able to.

  The material of the negative electrode active material is not particularly limited and can be used other than the above materials. However, when a part of the material such as a material having a large expansion and contraction is selected, if the range used by the negative electrode is too large, Resistance rise may be large. In this case, it is preferable to confirm whether or not the negative electrode potential is below a certain level as a condition for changing the battery voltage.

However, it is preferable that graphite is included, and the graphite has a graphite interlayer distance (d ₀₀₂ ) of 0.335 nm or more and 0.338 nm or less. By including such graphite in the negative electrode 12, since the potential curve of graphite has a stage structure, the cycle characteristics of the lithium ion secondary battery can be further improved. The graphite used for the negative electrode 12 is natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor grown carbon fiber, pitch-based carbonaceous material, needle coke capable of chemically occluding and releasing lithium ions. , Petroleum coke, and polyacrylonitrile-based carbon fiber. The graphite interlayer distance (d ₀₀₂ ) can be measured by using XRD (X-Ray Diffraction Method) or the like.

  The non-graphite carbon used for the negative electrode 12 is a carbon material excluding the above graphite, and can occlude or release lithium ions. This includes a carbon material that has a graphite layer spacing of 0.34 nm or more and changes to graphite by high-temperature heat treatment at 2000 ° C. or more, a 5-membered or 6-membered cyclic hydrocarbon, or a cyclic oxygen-containing material. Amorphous carbon materials synthesized by pyrolysis of organic compounds are included.

As described above, a material that forms an alloy with lithium or a material that forms an intermetallic compound may be added to the negative electrode 12 having a voltage change rate different from that of the positive electrode 10 as a third negative electrode active material. Examples of the third negative electrode active material include metals such as aluminum, silicon, and tin, and alloys thereof, lithium-containing transition metal nitrides Li _(3-X) M _X N, silicon lower oxide Li _X SiO _Y ( 0 ≦ x, 0 <y <2), and a lower oxide of tin Li _X SnO _Y. There is no restriction | limiting in particular in the material of a 3rd negative electrode active material, It can utilize also other than said material.

  Since the negative electrode active material generally used is a powder, a binder is mixed with the negative electrode active material so that the powders are bonded together and simultaneously bonded to the current collector. In the negative electrode 12 included in the battery according to the present embodiment, it is desirable that the particle size of the negative electrode active material be equal to or less than the thickness of the mixture layer formed from the negative electrode active material and the binder. When there are coarse particles having a size equal to or greater than the thickness of the mixture layer in the negative electrode active material powder, the coarse particles may be removed in advance by sieving classification or wind classification, and particles having a thickness of the mixture layer thickness or less may be used. preferable.

  For the current collector of the negative electrode 12, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to copper, materials such as stainless steel, titanium, or nickel are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

  A negative electrode slurry in which a negative electrode active material, a binder, and an organic solvent are mixed is attached to a current collector by a doctor blade method, a dipping method, a spray method, or the like, and then the organic solvent is dried and pressure-molded by a roll press. Thereby, the negative electrode 12 can be produced. Moreover, it is also possible to form a multilayer mixture layer on a current collector by carrying out a plurality of times from application to drying.

  Further, it is preferable that the amount of the active material applied to the positive electrode and the negative electrode is designed so that it is in the vicinity of the negative electrode potential α and slightly less than the positive electrode potential γ at the end-of-charge voltage V0. Specifically, the positive electrode utilization rate is preferably 70% or more and 98% or less with respect to the positive electrode potential γ, particularly the positive electrode utilization rate is preferably 75% or more and 95% or less, and the positive electrode utilization rate is 80%. % Or more and 90% or less is preferable.

The positive electrode active material of the positive electrode 10 preferably contains a lithium composite oxide represented by the following formula (1) from the viewpoint of facilitating measurement of the potential, and in particular, LiNi _1/3 Mn _1/3 Co _{1 / Preferably} it contains _3O2 .
_{LiNi a Mn b Co c M d} O 2 ··· (1)
(In the above formula (1), M represents at least one selected from the group consisting of Fe, V, Ti, Cu, Al, Sn, Zn, Mg, B and W, and a, b, c and d are Are values satisfying 0.2 ≦ a ≦ 0.8, 0.1 ≦ b ≦ 0.4, 0 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.1, and a + b + c + d = 1. Note that, in each of the above examples, for example, there are characters that are duplicated in each of the examples such as “M” and “x”, but these characters are independent in each example. It shall be. The same applies to the following description unless otherwise specified.

  In the positive electrode active material described above, the positive electrode potential at the end-of-charge voltage V0 is preferably 3.8 V or more and 4.1 V or less, and the positive electrode utilization rate is particularly preferably 3.9 V or more and 4.05 V or less. Furthermore, the positive electrode utilization rate is preferably 3.95 V or more and 4.0 V or less. When the voltage becomes higher than the design potential, the correctable amount at the time of capacity shift decreases, and conversely, when the voltage becomes lower, the initial battery capacity decreases.

  In the positive electrode active material described above, the positive electrode potential γ is preferably 3.9 V or more and 4.3 V or less, particularly the positive electrode utilization rate is preferably 3.95 V or more and 4.2 V or less, and the positive electrode utilization rate is further increased. It is preferable that it is 4.0V or more and 4.1V or less. If it becomes higher than the above design potential, the high-temperature cycle characteristics will deteriorate, and if it becomes lower, the amount that can be corrected at the time of capacity shift will decrease.

  The negative electrode potential α varies depending on the material, but must be set to 0 V or more. When it is less than 0 V, Li metal is precipitated, and the high-temperature cycle characteristics are greatly deteriorated.

  The separator 11 is inserted between the positive electrode 10 and the negative electrode 12 produced by the above method to prevent a short circuit between the positive electrode 10 and the negative electrode 12. The separator 11 can be a polyolefin polymer sheet made of polyethylene, polypropylene, or the like, or a two-layer structure in which a polyolefin polymer and a fluorine polymer sheet typified by tetrafluoropolyethylene are welded. It is. A mixture of ceramics and a binder may be formed in a thin layer on the surface of the separator 11 so that the separator 11 does not shrink when the battery temperature increases. Since these separators 11 need to allow lithium ions to permeate during charging and discharging of the battery, they can generally be used for lithium ion secondary batteries if the pore diameter is 0.01 to 10 μm and the porosity is 20 to 90%. It is.

  Such a separator 11 is inserted between the positive electrode 10 and the negative electrode 12, and an electrode group wound around the axis 21 is produced. As the axis 21, any known one can be used as long as it can support the positive electrode 10, the separator 11, and the negative electrode 12. In addition to the cylindrical shape shown in FIG. 6, the electrode group has various shapes such as a laminate of strip-shaped electrodes, or a positive electrode 10 and a negative electrode 12 wound in an arbitrary shape such as a flat shape. Can do. The shape of the battery case 13 may be selected from shapes such as a cylindrical shape, a flat oval shape, a flat oval shape, and a square shape according to the shape of the electrode group.

  The material of the battery case 13 is selected from materials that are corrosion-resistant to the nonaqueous electrolyte, such as aluminum, stainless steel, and nickel-plated steel. Further, when the battery container 13 is electrically connected to the positive electrode 10 or the negative electrode 12, the material is not deteriorated due to corrosion of the battery container 13 or alloying with lithium ions in the portion in contact with the nonaqueous electrolyte. Thus, the material of the battery container 13 is selected.

  The electrode group is housed in the battery container 13, the negative electrode current collecting tab 15 is connected to the inner wall of the battery container 13, and the positive electrode current collecting tab 14 is connected to the bottom surface of the battery lid 20. The electrolyte is injected into the battery container interior 13 before the battery is sealed. As a method for injecting the electrolyte, there are a method of adding directly to the electrode group in a state where the battery cover 20 is released, or a method of adding from an injection port installed in the battery cover 20.

  Thereafter, the battery lid 20 is brought into close contact with the battery container 13 to seal the entire battery. If there is an electrolyte inlet, seal it as well. As a method for sealing the battery, there are known techniques such as welding and caulking.

As a typical example of the electrolytic solution that can be used in the present invention, lithium hexafluorophosphate (LiPF ₆ ) or lithium borofluoride as an electrolyte in a solvent obtained by mixing dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate with ethylene carbonate There is a solution in which (LiBF ₄ ) is dissolved. The present invention is not limited to the type of solvent and electrolyte, and the mixing ratio of solvents, and other electrolytes can be used.

  Examples of non-aqueous solvents that can be used in the electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2 -Methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphate triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2- There are nonaqueous solvents such as oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, or chloropropylene carbonate. Other solvents may be used as long as they do not decompose on the positive electrode 10 or the negative electrode 12 incorporated in the battery of the present invention.

In addition, examples of the _{electrolyte, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 3SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, or imide salts such as lithium represented by lithium trifluoromethane sulfonimide, multi There are different types of lithium salts. A nonaqueous electrolytic solution obtained by dissolving these salts in the above-mentioned solvent can be used as a battery electrolytic solution. An electrolyte other than this may be used as long as it does not decompose on the positive electrode 10 and the negative electrode 12 included in the battery according to the present embodiment.

  When a solid polymer electrolyte (polymer electrolyte) is used, an ion conductive polymer such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, polyhexafluoropropylene, and polyethylene oxide can be used for the electrolyte. When these solid polymer electrolytes are used, there is an advantage that the separator 11 can be omitted.

Furthermore, an ionic liquid can be used. For example, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ ), lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), a mixed complex of triglyme and tetraglyme, a cyclic quaternary ammonium cation (N- methyl-N-propylpyrrolidinium is exemplified) and an imide anion (bis (fluorosulfonyl) imide is exemplified), and a combination that does not decompose at the positive electrode 10 and the negative electrode 12 is selected, and this embodiment is used. It can be used for such a battery.

  The lithium ion secondary battery having the above configuration is used as the battery 204, and the charge control system according to this embodiment can be applied to such a battery.

  Hereinafter, the case where the battery 204 having the configuration shown in FIG. 6 is charged by the above-described charging control system of the present embodiment (Example 1) and Comparative Examples 1 to 3 will be described.

[Example 1]
First, a lithium ion secondary battery (battery) having the structure shown in FIG. 6 was produced. At this time, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material, and natural graphite (graphite interlayer distance (d ₀₀₂ ) = 0.336 nm by X-ray structural analysis) was used as the negative electrode active material. . Further, an aluminum foil was used as the positive electrode, and a copper foil was used as the negative electrode.

  In preparing the battery, the application amount ratio of the positive electrode and the negative electrode was adjusted so that the end-of-charge voltage V0 was 4.00 V, the initial positive electrode potential at that time was 4.10 V, and the negative electrode potential was 0.10 V.

  The produced battery was used as the battery 204, charged by the charge control system shown in FIG. 1, and the battery characteristics were evaluated by the following method.

  The produced battery was charged to 4.00 V at a current equivalent to 0.3 C around room temperature (25 ° C.), and then constant voltage charging was performed until the current reached 0.03 C at 4.10 V. After 30 minutes of rest, constant current charging was performed to 3.00 V with a constant current corresponding to 0.3C. This was initialized by performing 4 cycles, and the battery capacity at the 4th cycle was measured, and the measured battery capacity was defined as the initial battery capacity. The initial battery capacity was 0.932 Ah.

  Next, discharge was performed at 25 ° C. for 10 seconds in the order of currents 4 CA, 8 CA, 12 CA, and 16 CA. The relationship between the discharge current at that time and the voltage at 10 seconds was plotted, and the initial DC resistance was obtained from the slope of the obtained straight line. The measured initial DC resistance was 54.5 mΩ.

  Next, 500 charge / discharge cycles were performed at 50 ° C. In each cycle, the battery was charged to 4.0 V with a current corresponding to 0.3 C, and then constant voltage charging was performed until the current became 0.03 C at 4.10 V. Thereafter, constant current discharge was performed at a constant current equivalent to 0.3C. There was a pause for 3 hours between charge and discharge. Charging was performed according to the flowchart shown in FIG. 4, and the charge end voltage V0 = 4.00V, α = 0.10V, γ = 4.2V and ω = 0.01V.

  Then, after leaving at 25 ° C. for 12 hours, the battery capacity of the battery after 500 cycles was measured and found to be 0.803 Ah. Further, when the DC resistance after 500 cycles was determined in the same manner as the measurement of the initial DC resistance, it was 64.7Ω.

Using the results obtained above, the battery capacity retention rate and the DC resistance increase rate were calculated according to the following formula. The result is shown in FIG.
Battery capacity retention rate (%) = (battery capacity after 500 cycles) / (initial battery capacity)
DC resistance increase rate (%) = (DC resistance after 500 cycles) / (initial DC resistance)

[Comparative Example 1]
In the 500 charge / discharge cycles, the battery capacity retention rate and the DC resistance increase rate were calculated in the same manner as in Example 1 except that the cycle was performed without changing the charge end voltage. The results are shown in Table 1. The initial battery capacity was 0.932 Ah, the initial DC resistance was 54.5 mΩ, the battery capacity after 500 cycles was 0.701 Ah, and the DC resistance after 500 cycles was 64.5 mΩ.

[Comparative Example 2]
Comparative Example 1 except that the charge end voltage V0 was 4.10V, the initial positive electrode potential was adjusted to 4.20V, and the negative electrode potential was adjusted to 0.10V. In the same manner, the battery capacity maintenance rate and the DC resistance increase rate were calculated. The results are shown in Table 1. The initial battery capacity was 1.053 Ah, the initial DC resistance was 54.3 mΩ, the battery capacity after 500 cycles was 0.745 Ah, and the DC resistance after 500 cycles was 75.7 mΩ.

[Comparative Example 3]
In the 500 charge / discharge cycles, the battery capacity retention rate and the DC resistance increase rate were calculated in the same manner as in Example 1 except that the corrected upper limit positive electrode potential γ was changed to 4.40V. The results are shown in Table 1. The initial battery capacity was 0.932 Ah, the initial DC resistance was 54.5 mΩ, the battery capacity after 500 cycles was 0.855 Ah, and the DC resistance after 500 cycles was 107.91 mΩ.

  As shown in FIG. 7, in Example 1 in which the end-of-charge voltage was changed, compared with Comparative Example 1 in which the end-of-charge voltage was not changed, while maintaining the same DC resistance increase rate, The battery capacity maintenance rate was greatly improved. Furthermore, for Comparative Example 2 in which the end-of-charge voltage was set to 4.10 V, although the absolute value of the initial battery capacity was inferior, in any of the absolute value of capacity after 500 cycles, the capacity maintenance rate, and the resistance increase rate, Excellent value was shown. Compared to Comparative Example 3 in which γ was set to 4.40 V, although the capacity was inferior, in Comparative Example 3, a remarkable increase in resistance was observed due to excessively high positive electrode potential.

  As described above, according to the present invention, even after 500 cycles of charge / discharge, it is possible to suppress an increase in resistance inside the lithium ion secondary battery and a decrease in battery capacity, and to improve cycle characteristics. A discharge control system can be provided.

  As described above, the charge control system according to the present embodiment includes the charge / discharge control circuit 203 that charges the lithium ion secondary battery 204 to the end-of-charge voltage, and the lithium ion secondary battery 204 that is charged by the charge / discharge control circuit 203. An arithmetic processing unit 205 that determines whether or not the battery state of the lithium ion secondary battery 204 satisfies a predetermined end-of-charge voltage changing condition when the battery voltage of the battery becomes the end-of-charge voltage V0; If it is determined by 205 that the battery state of the lithium ion secondary battery 204 satisfies a predetermined charge end voltage change condition (for example, Vn> α, Vp <γ), the charge end voltage is charged to a higher voltage. And a charge end voltage correction unit 202 that changes to the end voltage (for example, the voltage V1 or V0 + ω).

  When the charge end voltage is changed by the charge end voltage correction unit 202, the charge / discharge control circuit 203 further charges the lithium ion secondary battery until the battery voltage becomes the changed charge end voltage. As a result, even when the battery is deteriorated due to the capacity deviation of the negative electrode, it is possible to suppress a decrease in the battery capacity.

  Further, in the charge end voltage change condition, the potential of the negative electrode of the lithium ion secondary battery 204 at the time of determination is higher than the lower limit value α of the potential, or the potential of the positive electrode of the lithium ion secondary battery 204 at the time of determination is By including that the potential is less than the allowable upper limit value γ as the change condition, an increase in the internal resistance of the lithium ion secondary battery 204 due to the change of the charge end voltage can be suppressed to a low level.

  As the charge end voltage change condition, the charge end voltage is changed when the ratio A1 / A0 between the charge capacity A1 and the initial battery capacity A0 of the lithium ion secondary battery 204 at the time of determination is equal to or less than a predetermined value. Anyway, the determination becomes simple. The predetermined value in this case may be set arbitrarily.

  Further, as shown in FIG. 5, the charge end voltage may be changed to a charge end voltage that is higher by a preset predetermined voltage ω, and the determination by the arithmetic processing unit 205 may be performed again after the end voltage is changed. . By doing so, it is possible to change the end-of-charge voltage in small increments while confirming that the potential of the negative electrode and the positive electrode is within the control range, and the potential of the positive electrode and the negative electrode at the end of charge greatly deviates outside the control range. Can be prevented.

  Further, when changing (correcting) the charge end voltage, instead of using ω described above, β shown in FIG. 2 is estimated based on the potential of the positive electrode or the negative electrode and their allowable potential, and the charge end voltage V1 is set. You may make it set.

  Moreover, it is preferable to set the initial value V0 of the charge end voltage so that the potential of the positive electrode of the lithium ion secondary battery 204 is lower than γ which is the allowable upper limit value.

  FIG. 8 is a diagram showing an example of a power supply device to which the charge control system of the present embodiment can be applied, and is a block diagram showing a drive system for a hybrid vehicle. The drive system shown in FIG. 8 includes a battery module 9, a battery monitoring device 100 that monitors the battery module 9, an inverter device 220 that converts DC power from the battery module 9 into three-phase AC power, and a motor 230 for driving the vehicle. ing. Motor 230 is driven by the three-phase AC power from inverter device 220. The inverter device 220 and the battery monitoring device 100 are connected by CAN communication, and the inverter device 220 functions as a host controller for the battery monitoring device 100. Further, the inverter device 220 operates based on command information from a host controller (not shown).

  The inverter device 220 includes a power module 226, an MCU 222, and a driver circuit 224 for driving the power module 226. The power module 226 converts the DC power supplied from the battery module 9 into three-phase AC power for driving the motor 230. Although not shown, a large-capacity smoothing capacitor of about 700 μF to about 2000 μF is provided between the high voltage lines HV + and HV− connected to the power module 226. The smoothing capacitor serves to reduce voltage noise applied to the integrated circuit provided in the battery monitoring device 100.

  When the inverter device 220 starts operating, the charge of the smoothing capacitor is substantially zero, and when the relay RL is closed, a large initial current flows into the smoothing capacitor. The relay RL may be fused and damaged due to the large current. In order to solve this problem, the MCU 222 charges the smoothing capacitor by changing the precharge relay RLP from the open state to the closed state at the start of driving of the motor 230 in accordance with a command from the higher-order controller, and then turns on the relay RL. The power supply from the battery module 9 to the inverter device 220 is started from the open state to the closed state. When charging the smoothing capacitor, charging is performed while limiting the maximum current via the resistor RPRE. By performing such an operation, the relay circuit can be protected, and the maximum current flowing through the battery cell and the inverter device 220 can be reduced to a predetermined value or less, and high safety can be maintained.

  Inverter device 220 controls the phase of AC power generated by power module 226 with respect to the rotor of motor 230, and causes motor 230 to operate as a generator during vehicle braking. That is, regenerative braking control is performed, and the battery module 9 is charged by regenerating the power generated by the generator operation to the battery module 9. When the charging state of the battery module 9 is lower than the reference state, the inverter device 220 operates using the motor 230 as a generator. The three-phase AC power generated by the motor 230 is converted into DC power by the power module 226 and supplied to the battery module 9. As a result, the battery module 9 is charged.

  On the other hand, when powering the motor 230, the MCU 222 controls the driver circuit 224 to generate a rotating magnetic field in the advance direction with respect to the rotation of the rotor of the motor 230 in accordance with a command from the host controller. Control the behavior. In this case, DC power is supplied from the battery module 9 to the power module 226. When the battery module 9 is charged by regenerative braking control, the MCU 222 controls the driver circuit 224 so as to generate a rotating magnetic field that is delayed with respect to the rotation of the rotor of the motor 230, and Controls the switching operation. In this case, electric power is supplied from the motor 230 to the power module 226, and DC power of the power module 226 is supplied to the battery module 9. As a result, the motor 230 acts as a generator.

  The power module 226 of the inverter device 220 conducts and cuts off at high speed and performs power conversion between DC power and AC power. At this time, since a large current is interrupted at a high speed, a large voltage fluctuation occurs due to the inductance of the DC circuit. In order to suppress this voltage fluctuation, the above-described large-capacity smoothing capacitor is provided.

  The battery module 9 includes two battery blocks 9A and 9B connected in series. Each battery block 9A, 9B is provided with 16 battery cells connected in series. The battery block 9A and the battery block 9B are connected in series via a maintenance / inspection service disconnect SD in which a switch and a fuse are connected in series. By opening this service disconnect SD, the direct circuit of the electric circuit is cut off, and even if a connection circuit is formed at one place between the battery blocks 9A and 9B and the vehicle, no current flows. With such a configuration, high safety can be maintained. With such a configuration, high safety can be maintained. Further, even if a human touches between HV + and HV− during inspection, it is safe because a high voltage is not applied to the human body.

  A high voltage line HV + between the battery module 9 and the inverter device 220 is provided with a battery disconnect unit BDU including a relay RL, a resistor RP, and a precharge relay RLP. A series circuit of the resistor RP and the precharge relay RLP is connected in parallel with the relay RL.

  The battery monitoring device 100 mainly performs measurement of each cell voltage, measurement of total voltage, measurement of current, cell temperature, cell capacity adjustment, and the like. For this purpose, ICs (integrated circuits) 1 to IC6 as cell controllers are provided. The 16 battery cells provided in each of the battery blocks 9A and 9B are divided into three cell groups, and one integrated circuit is provided for each cell group. The cell controller has a function of managing each cell, and performs cell voltage monitoring, overcharge / overdischarge detection, voltage equalization between cells, and the like. The charge / discharge control circuit 203 and the voltage measurement unit 209 in FIG. 1 are provided in this cell controller.

  IC1 to IC6 include a communication system 602 and a 1-bit communication system 604. In the communication system 602 for reading cell voltage values and transmitting various commands, serial communication with the microcomputer 30 is performed in a daisy chain manner via an insulating element (for example, photocoupler) PH. The 1-bit communication system 604 transmits an abnormal signal when cell overcharge is detected. In the example shown in FIG. 1, the communication system 602 is divided into an upper communication path for IC1 to IC3 of the battery block 9A and a lower communication path for IC4 to IC6 of the battery block 9B.

  The microcomputer 30 has a function as an upper controller of the cell controllers (IC1 to IC6), and monitors the battery module 9 (total voltage monitor, current monitor, temperature monitor, information acquisition from the cell controller, etc.), Perform external circuit control (relay control, etc.), battery status detection (SOC calculation, SOH calculation, allowable charge / discharge current calculation, etc.), various diagnoses (overcharge protection, overdischarge protection, leakage detection, failure detection, etc.) . The arithmetic processing unit 205 in FIG. 1 is provided in the microcomputer 30.

  A current sensor Si such as a Hall element is installed in the battery disconnect unit BDU, and the output of the current sensor Si is input to the microcomputer 30. Signals relating to the total voltage and temperature of the battery module 9 are also input to the microcomputer 30 and are measured by an AD converter (ADC) of the microcomputer 30. Temperature sensors are provided at a plurality of locations in the battery blocks 9A and 9B.

  For example, when the battery module 9 is charged at night, the battery module 9 is charged by the above-described charging method. Since the voltage for each battery cell is measured by the cell controllers (IC1 to IC6), the determination of the end-of-charge voltage changing condition described with reference to FIG. 4 can be performed for each battery cell. For example, when it is determined NO in steps S106 and S107 for any one battery cell, the process proceeds to step S109 and the charging operation is terminated.

  In the above-described embodiment, the lithium ion secondary battery for mounting on a vehicle has been described as an example.However, the present invention is not limited to mounting on a vehicle, and stores power generated by solar power generation or wind power generation. The present invention can also be applied to a charging control system for a lithium ion secondary battery used for applications to be supplied to an electric power system.

  Each of the embodiments described above may be used alone or in combination. This is because the effects of the respective embodiments can be achieved independently or synergistically. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

  10: positive electrode, 12: negative electrode, 101, 102, 104, 105: potential curve, 103, 106: battery voltage curve, 201: charge control system, 202: charge end voltage correction unit, 203: charge / discharge control circuit, 204: Lithium ion secondary battery, 205: arithmetic processing unit, 206: external load, 207: power supply for charging, 208: current measuring unit, 209: voltage measuring unit, 210a, 210b: switch

Claims (11)

A charge control unit for charging the lithium ion secondary battery to a charge end voltage;
Whether or not the battery state of the lithium ion secondary battery satisfies a predetermined charge end voltage change condition when the battery voltage of the lithium ion secondary battery becomes the charge end voltage by charging by the charge control unit A determination unit for determining whether or not
When the determination unit determines that the battery state of the lithium ion secondary battery satisfies a predetermined charge end voltage change condition, the charge end voltage changes the charge end voltage to a higher charge end voltage. A change unit, and
When the end-of-charge voltage is changed by the end-of-charge voltage changing unit, the charge control unit further performs charging of the lithium ion secondary battery until the battery voltage becomes the changed end-of-charge voltage,
The charge control system, wherein the charge end voltage change condition includes, as a change condition, that the potential of the negative electrode of the lithium ion secondary battery at the time of determination is higher than a lower limit value of the potential. A charge control unit for charging the lithium ion secondary battery to a charge end voltage;
Whether or not the battery state of the lithium ion secondary battery satisfies a predetermined charge end voltage change condition when the battery voltage of the lithium ion secondary battery becomes the charge end voltage by charging by the charge control unit A determination unit for determining whether or not
When the determination unit determines that the battery state of the lithium ion secondary battery satisfies a predetermined charge end voltage change condition, the charge end voltage changes the charge end voltage to a higher charge end voltage. A change unit, and
When the end-of-charge voltage is changed by the end-of-charge voltage changing unit, the charge control unit further performs charging of the lithium ion secondary battery until the battery voltage becomes the changed end-of-charge voltage,
The charging end voltage changing condition includes, as a changing condition, that the potential of the positive electrode of the lithium ion secondary battery at the time of determination is less than an allowable upper limit value of the potential. In the charge control system according to claim 1 or 2 ,
The charging end voltage changing condition includes, as a changing condition, a ratio between a charging capacity and an initial battery capacity of the lithium ion secondary battery at the time of determination being a predetermined value or less. In the charge control system according to any one of claims 1 to 3 ,
The charging end voltage changing condition includes an elapsed usage time of the lithium ion secondary battery as a changing condition. In the charge control system according to any one of claims 1 to 4 ,
The charge end voltage change unit changes the charge end voltage based on a potential of a positive electrode or a negative electrode in the determination of the charge end voltage change condition and an allowable potential thereof. In the charge control system according to any one of claims 1 to 4 ,
The charge end voltage changing unit changes the charge end voltage to a charge end voltage that is higher by a predetermined voltage set in advance,
A charge control system, further comprising a charge end voltage change control unit that makes the determination by the determination unit again after the end voltage is changed. In the charge control system according to any one of claims 1 to 6 ,
A charge control system, wherein a positive electrode potential when the charge end voltage is an initial value is set to be lower than an allowable upper limit value of the positive electrode potential . In the charge control system according to any one of claims 1 to 7 ,
The positive electrode of the said lithium ion secondary battery contains the lithium complex oxide represented by following Formula (1), The charge control system characterized by the above-mentioned.
_{LiNi a Mn b Co c M d} O 2 ··· (1)
In the formula (1), M represents at least one selected from the group consisting of Fe, V, Ti, Cu, Al, Sn, Zn, Mg, B, and W, and a, b, c, and d are Are values satisfying 0.2 ≦ a ≦ 0.8, 0.1 ≦ b ≦ 0.4, 0 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.1, and a + b + c + d = 1. There is a relationship that satisfies. The charge control system according to claim 8 ,
A charge control system, wherein a positive electrode potential when initially charged to a charge end voltage is set to 3.8 V or more and 4.1 V or less. The charge control system according to claim 8 or 9 ,
A charge control system, wherein the changed positive electrode potential is set to fall within a range of 3.9V to 4.3V. In the charge control system according to any one of claims 8 to 10 ,
The negative electrode of the lithium ion secondary battery contains graphite,
A charge control system, wherein a graphite interlayer distance of the graphite is 0.335 nm or more and 0.338 nm or less.

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