JP5521298B2 - Lithium secondary battery charge control method, charge control device, and vehicle - Google Patents

Description

  The present invention relates to a charge control method for a lithium secondary battery, a charge control device, and a vehicle equipped with the device.

  Lithium secondary batteries are used as driving power sources for automobiles and the like. When the lithium secondary battery is repeatedly charged and discharged, lithium ions are deposited on the negative electrode and grow into a dendritic body called a dendrite. As the dendrite grows, the amount of lithium decreases, so the battery capacity decreases.

  Further, when the dendrite grows and reaches the positive electrode, a short circuit is caused. If a short circuit occurs, it will not be possible to fully charge during CV charging in the CC-CV (constant current-constant voltage) charging cycle, and even if charging continues at a high voltage, the current value will remain stable and decrease further. Disappear. As the dendrite grows, the finally stable current value during CV charging increases. Therefore, when dendrite grows, the state of high voltage and high current continues for a long time. In this state, deterioration due to oxidation or the like of the electrolytic solution is promoted. This also causes a decrease in battery capacity.

  The decrease in battery capacity due to the growth of dendrites as described above is called natural deterioration, and is accepted by lithium secondary batteries as the battery life. Therefore, it is desired and studied to improve the total discharge amount (discharge integrated amount) until the battery capacity decreases to a value that cannot be used.

  The cause of the decrease in the battery capacity is considered other than natural degradation, and various techniques for reducing the cause have been proposed.

  For example, a method has been proposed in which a period after the completion of charging is measured and discharged so as to be a predetermined voltage or less depending on the period, thereby reducing characteristic deterioration during long-term storage (see Patent Document 1). .

Further, in order to extend the life of the battery, there is also known an apparatus that sets an end voltage at which discharge is terminated according to the discharge characteristics of the battery, and changes the setting of the end voltage according to the use state of the battery (Patent Document 2). reference).
Japanese Patent Laid-Open No. 2002-367681 JP 2005-269708 A

  However, in the above-described invention, although deterioration of the battery due to long-term storage can be reduced, the discharge capacity (discharge integrated amount) after long-term storage decreases due to natural deterioration due to elution of the positive electrode metal and precipitation of dendrites as described above. There's a problem.

  The present invention has been made in view of the above circumstances, and a lithium secondary battery charge control method, a charge control device, and a vehicle that reduce the natural deterioration of the battery due to the precipitation of dendrites and maximize the accumulated discharge amount of the battery. The purpose is to provide.

The lithium secondary battery charge control method according to the present invention includes a detection step of detecting a parameter value that increases due to natural deterioration of the lithium secondary battery due to charge and discharge, and whether the parameter value is higher than a threshold value. A determination step of determining whether or not. And when the value of a parameter becomes higher than a threshold value, the setting process which sets the target value of the full charge voltage at the time of charging a lithium secondary battery low is included. The parameter value is a current value that is constant and stable during constant voltage charging in a constant current-constant voltage charging cycle for charging a lithium secondary battery.

The charge control device for a lithium secondary battery according to the present invention includes a detector that detects a value of a parameter that increases due to natural deterioration of the lithium secondary battery due to charge and discharge, and whether the parameter value is higher than a threshold value. And a determination unit for determining whether or not. And when the value of a parameter becomes higher than the said threshold value, it has a setting part which sets the target value of the full charge voltage at the time of charging a lithium secondary battery low. The parameter value is a current value that is constant and stable during constant voltage charging in a constant current-constant voltage charging cycle for charging a lithium secondary battery.

  According to the charge control method and the charge control device for a lithium secondary battery, when the value of a parameter that increases due to natural deterioration exceeds a threshold value, the target value of the full charge voltage at the next charge is lowered. That is, since the potential in the deteriorated state is lowered, elution of the metal in the positive electrode active material layer in the next charge can be suppressed, and acceleration of natural deterioration can be prevented. At the same time, the growth of the dendrite of the negative electrode can be suppressed, and the decrease in capacity due to the decrease in lithium ions can be reduced. As a result, the accumulated discharge amount of the battery can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of a charge control device for a lithium secondary battery, and FIG. 2 is a diagram illustrating a voltage of a CC-CV charge / discharge cycle.

  A charge control device 20 is connected to the lithium secondary battery 10. The lithium secondary battery may be any secondary battery as long as lithium ions in the electrolyte conduct electricity. For example, a bipolar electrode in which a positive electrode active material layer is formed on one surface of a current collector and a negative electrode active material layer is formed on the other surface is a bipolar electrode in which a battery element in which an electrolyte layer is sandwiched is sealed Type secondary battery. Alternatively, a battery in which a positive electrode in which a positive electrode active material layer is formed on both surfaces of a positive electrode current collector and a negative electrode in which a negative electrode active material layer is formed on both surfaces of the negative electrode current collector are stacked via an electrolyte layer. This is a stacked secondary battery in which elements are sealed.

  The battery 10 is charged and discharged through a CC-CV (constant current-constant voltage) charge / discharge cycle shown in FIG. During CC charging, the voltage value is increased while the current value is fixed, and charging is performed until the battery 10 reaches the target value of the full charge voltage. During CV charging, the current value is reduced while the voltage value is fixed at the full charge voltage, and charging is performed until the battery reaches a predetermined capacity.

  The charging control device 20 is a device that controls charging / discharging of the battery 10, and includes a detector 21, a storage unit 22, and a control unit 23. The detector 21 is attached to the battery 10. The detector 21 increases a value (hereinafter referred to as a CV current value) when the current value decreases and stabilizes in CV charging of the CC-CV charging cycle shown in FIG. 2 due to natural deterioration of the battery 10. Detect as parameter value. As the natural degradation of the battery 10 progresses, dendrites grow and a partial short circuit occurs, and the internal resistance of the battery 10 decreases. Therefore, the CV current value increases as the natural degradation progresses. Therefore, the CV current value is a parameter value that increases due to the natural deterioration of the battery 10.

  The storage unit 22 stores Vm (V1, V2,...) As candidates for the target value V of the full charge voltage when charging the battery 10. Here, V1> V2> V3... Further, the storage unit 22 stores αm (α1, α2,...) As candidates for the threshold value α as a set with each target value V (V1, V2,...). Here, the values increase in the order of α1, α2,. The threshold value α is a value serving as a reference when changing a target value V of a full charge voltage described later.

  The control unit 23 is connected to the detector 21 and the storage unit 22, and is also directly connected to the battery 10. The control unit 23 also controls charging / discharging of the battery 10. As will be described later, the control unit 23 functions as a determination unit that determines whether the CV current value i is higher than the threshold value α. Furthermore, the control unit 23 also functions as a setting unit that sets a target value of a full charge voltage when charging the battery 10 based on the CV current value detected by the detector 21.

  The operation of the control unit 23 will be described in detail.

  FIG. 3 is a flowchart showing a flow of operation of the control unit.

  First, as an initial value, the control unit 23 substitutes 1 for the variable m (step S1), sets the target value of the full charge voltage to V = V1, and sets the threshold value α to α = α1 (step S2). ).

  The control part 23 starts CC charge with the start of charge (step S3). The controller 23 determines whether or not the voltage has reached the set target value V in CC charging (step S4). When the target value V has not been reached (step S4: NO), CC charging is continued.

  When the target value V is reached (step S4: YES), the control unit 23 starts CV charging (step S5). And the control part 23 determines whether the electric current value which flows into the battery 10 is constant (step S6). When the current value is not constant (step S6: NO), CV charging is continued. When the current value is constant (step S6: YES), the control unit 23 uses the detector 21 to measure the current value, that is, the CV current value at that time (step S7).

  Here, the control unit 23 determines whether or not the CV current value i is greater than or equal to the threshold value α (step S8). If the CV current value i is not equal to or greater than the threshold value α (step S8: NO), the CC-CV charge cycle is terminated as it is, and the process proceeds to a discharge cycle.

  When the CV current value i is greater than or equal to the threshold value α (step S8: YES), the control unit 23 increments the variable m by 1 (step S9). The control unit 23 calls new Vm and αm from the storage unit 22, and updates the target value V (= Vm) and threshold value α (= αm) of the full charge voltage (step S10). The target value Vm updated here is a value lower than the previous target value Vm-1.

  And the control part 23 discharges the battery 10 until it becomes a predetermined voltage (step S11). The control unit 23 determines whether or not to proceed to the next charge / discharge cycle (step S12). When the control unit 23 proceeds (step S12: YES), the processing from step S3 is repeated. If it does not proceed to the next charge / discharge cycle (step S12: NO), the system is terminated.

  According to the above lithium secondary battery charge control device, the following effects can be obtained.

  When the value of the parameter that rises due to natural degradation, that is, the CV current value i exceeds the threshold value α, the target value V of the full charge voltage at the next charge is lowered. That is, since the potential in the deteriorated state is lowered, elution of the metal in the positive electrode active material layer in the next charge can be suppressed, and acceleration of natural deterioration can be prevented. At the same time, the growth of the dendrite of the negative electrode can be suppressed, and the decrease in capacity due to the decrease in lithium ions can be reduced. As a result, as shown in FIG. 4, the accumulated discharge amount of the battery 10 can be improved.

  FIG. 4 is a diagram showing an example of the accumulated discharge amount of the battery.

  Referring to FIG. 4, when the target value of the full charge voltage is fixed at 4.3 V (V1), the discharge amount decreases linearly, and the integrated discharge amount is the amount indicated by cross hatching in FIG. It becomes. However, in the above embodiment, the target value is decreased in order, such as 4.3V, 4.2V, and 4.1V. Therefore, when the target value is fixed to 4.3V, 4.2V, and 4.1V, respectively. The integrated discharge amount of the present embodiment is obtained as the union of the integrated discharge amount. That is, in the example of FIG. 4, in addition to the cross hatched portion, the discharge amount integrated amount can be obtained in the hatched portion. As shown in FIG. 4, the threshold value αm is obtained in advance by experiments or the like so that the target value Vm is switched in order.

  In addition, according to the above-described embodiment, as the parameter value that increases due to natural degradation, the constant current value i at the time of constant voltage charging is used, so the value that directly increases due to the growth of dendrites is used. Thus, natural deterioration can be detected reliably, and the target value of the full charge voltage can be set low according to the natural deterioration.

  Since the target value of the full charge voltage is prepared in multiple stages of V1, V2,..., The deterioration of the battery can be reduced more effectively, and the discharge integrated amount of the battery can be improved.

  In addition, the said embodiment is applicable not only to the regular charging / discharging cycle which repeats charging / discharging of constant current but to all the charging / discharging cycles which may occur by use of the battery 10, such as the case where it recharges without using up capacity.

(Second Embodiment)
Next, a second embodiment of the charge control device and charge control method for a lithium secondary battery will be described. In 2nd Embodiment, it replaces with step S8, 9 of 1st Embodiment, and has a new process. Therefore, it demonstrates centering on the process different from 1st Embodiment.

  FIG. 5 is a flowchart showing steps unique to the second embodiment.

  The control part 23 performs the process of step S1-7 of FIG. 3, and progresses to step S20 of FIG. The controller 23 determines whether or not the CV current value i is greater than or equal to the threshold value α (step S20). When the CV current value i is not equal to or greater than the threshold value α (step S20: NO), the process proceeds to step S11 in FIG. When the CV current value i is greater than or equal to the threshold value α (step S20: YES), the control unit 23 calls the previous CV current value i from the storage unit 22, and the current CV current value i is compared to the previous CV current value i. The increased difference Δi is calculated (step S21).

  The controller 23 determines whether or not the difference Δi is larger than the predetermined value φ (step S22). Here, the predetermined value φ is a value obtained experimentally, and is an increase value of the CV current value that rises due to a cause other than natural degradation. When the difference Δi is equal to or larger than the predetermined value φ (step S22: YES), the control unit 23 multiplies the threshold value α by γ1 (γ1> 1) (step S23). As a result, the threshold value α is updated high.

  On the other hand, when the difference Δi is less than the predetermined value φ (step S22: NO), the control unit 23 increments the variable m by 1 (step S24). The control unit 23 calls new Vm and αm from the storage unit 22, and updates the target value V (= Vm) and threshold value α (= αm) of the full charge voltage (step S25).

  As described above, in the second embodiment, when the difference Δi between the current CV current value i and the previous CV current value i is greater than or equal to the predetermined value φ, the variable m is incremented by 1 and the target value V is not lowered. Conversely, the threshold value α is set higher. This makes it difficult to lower the target value V after the next charge / discharge cycle. This is because when the difference Δi is equal to or larger than the predetermined value φ, it is determined that the current value is abnormally increased beyond the range of natural degradation. Therefore, it is possible to prevent a cause that is not related to natural degradation, for example, a short circuit due to the inclusion of foreign matter and prevent the full charge voltage from being lowered unnecessarily. As a result, the accumulated discharge amount of the battery can be improved.

(Third embodiment)
The third embodiment has a new process in addition to the first embodiment or the second embodiment. Therefore, it demonstrates centering on the newly added process. In the third embodiment, the detector 21 also serves as a temperature detector that detects the temperature of the battery 10.

  FIG. 6 is a flowchart showing steps unique to the third embodiment.

  In the flowchart shown in FIG. 6, there are two blocks (A) and (B). In the block (A), the threshold value α is adjusted based on the temperature of the battery 10, and in the block (B), the threshold value α is adjusted based on the number N of charge / discharge cycles.

  After the process of step S10 in FIG. 3 or the processes of steps S23 and S25 in FIG. 5, the control unit 23 proceeds to step S30 in FIG. The control unit 23 detects the battery temperature T by the detector 21 (step S30). The control unit 23 determines whether or not the detected temperature T is equal to or higher than a predetermined temperature β (step S31).

  When the detected temperature T is not equal to or higher than the predetermined temperature β (step S31: NO), the process proceeds to step S40. When the detected temperature T is equal to or higher than the predetermined temperature β (step S31: YES), the threshold α is multiplied by γ2 (γ2> 1) (step S32). Thereby, the threshold value α is set to a higher value.

  Continuously, the control part 23 calls the charging / discharging cycle frequency N so far from the memory | storage part 22 (step S40). The storage unit 22 counts each time charging is repeated and stores the number of times.

  The controller 23 selects the coefficient εn (εn> 1) based on the number N of charge / discharge cycles (step S41). Here, the selected coefficient εn is stored in the storage unit 22 as a set of a plurality of coefficients (ε1, ε2,...). Whenever the number of times the battery 10 is used increases, the control unit 23 considers that the deterioration has progressed and selects an appropriate coefficient. For example, the coefficient εn is larger as n is larger, such as ε1 <ε2 <ε3 <. The control unit 23 may select the coefficient εn with the number of times N = n.

  The control unit 23 divides the threshold value α by εn (step S42). Thereby, the threshold value α is set to a lower value.

  As described above, in the block (A) of the third embodiment, the temperature of the battery 10 is detected, and when the temperature is equal to or higher than the predetermined temperature β, the threshold value α is reset higher. This is due to the following reason. When the temperature is high, the resistance value in the battery 10 decreases, and the stable current value of the constant voltage charging cycle also increases. This increase in the current value i is not related to the natural deterioration of the battery. Here, if the target value V of the full charge voltage is lowered based on the current value increased due to the high temperature, since it is not related to natural deterioration, the integrated discharge amount is lowered. Therefore, as in the above process, when the temperature is high, the threshold value α is set (corrected) higher to prevent the target value of the full charge voltage from being lowered regardless of natural deterioration.

  In the above embodiment, the coefficient γ1 is prepared for the predetermined temperature β. However, a plurality of sets of the predetermined temperature β and the coefficient γ1 may be prepared step by step. The higher the temperature, the greater the coefficient γ1 can be multiplied. Further, not only the coefficient γ1 is multiplied when the temperature is equal to or higher than the predetermined temperature, but may be divided by the coefficient γ1 when the temperature returns below the predetermined temperature. Thereby, the threshold value α can be determined following the temperature.

  The timing of temperature measurement of the battery 10 is not limited to the above embodiment. For example, the measurement may be performed at the stage of entering the CV charge, the maximum temperature during use of the battery 10 may be measured, the temperature when the battery 10 is discharged may be measured, or the voltage may be measured at an arbitrary voltage. . The timing at which the temperature is detected can be appropriately determined depending on the scale and structure of the battery.

  Further, in the block (B) of the above embodiment, since the progress of the natural degradation of the battery 10 is estimated based on the number N of charge / discharge cycles and the threshold value α is lowered, the natural degradation is not affected by the abnormal degradation. The threshold value α can be adjusted. As a result, natural deterioration and abnormal deterioration can be distinguished, and the accumulated discharge amount can be secured.

  In the above embodiment, the case where the coefficient εn is selected with the number N = n is described, but the present invention is not limited to this. For example, the value of n is such that n = 1 when the battery is used up to near the end voltage (charged state 25%), and n = 0.5 when recharged with the charged state remaining 50% or more. May be increased. As a result, the natural degradation can be estimated with high accuracy in consideration of the use situation. As a result, a larger amount of accumulated discharge can be secured.

  In 3rd Embodiment, although the case where (A) block and (B) block were included was demonstrated, it is not limited to this. Only one of them can be applied.

(Fourth embodiment)
4th Embodiment is a vehicle carrying the charging control apparatus of the lithium secondary battery of 1st-3rd embodiment.

  FIG. 7 is a schematic diagram of a vehicle equipped with a charge control device.

  As shown in FIG. 7, a lithium secondary battery 10 is mounted on a vehicle 30 such as an automobile. If the charging control device 20 is mounted on the vehicle to control charging / discharging, the same effects as those of the first to third embodiments can be obtained. Therefore, even after the vehicle is shipped, it can be continuously controlled so that the integrated discharge amount is maximized in accordance with the state of the vehicle. As a result, the time until replacement of the battery 10 can be prolonged, and the maintenance cost of the user can be reduced.

(First embodiment)
Next, Example 1 to which the charge control process of the first embodiment is applied will be described.

  First, the configuration of the battery 10 used in the first example is as follows.

<Battery 10>
A positive electrode active material was formed by mixing 85% by weight of nickel-based active material, 10% by weight of acetylene black as a conductive additive, and 5% by weight of PVdF as a binder. A positive electrode active material was applied to both surfaces of a positive electrode current collector made of an aluminum foil to form a positive electrode. Further, 90% by weight of hard carbon and 10% by weight of PVdF as a binder were mixed to constitute a negative electrode active material. A negative electrode active material was applied to both sides of a negative electrode current collector made of copper foil to form a negative electrode. The formed positive and negative electrodes are alternately laminated via separators, sandwiched between two laminate sheets, into which an electrolyte solution in which LiPF6 is dissolved as a lithium salt is poured, and a part of the current collector is drawn out And sealed. According to the above procedure, three same batteries were prepared and used as Comparative Example 1, Comparative Example 2, and Example 1, respectively.

<Measurement>
About each battery, 1 C discharge capacity and the stable CV electric current value were measured with the following method.

  For Comparative Example 1, charging / discharging was repeated 10 times with the target value of the full charge voltage being 4.3 V and the end voltage at which the discharge was terminated being 2.5 V.

  For Comparative Example 2, charging / discharging was repeated 10 times, with the target value of the full charge voltage being 4.2 V and the end voltage at which discharge was terminated being 2.5 V.

  About Example 1, charging / discharging was repeated 10 times, applying the charge control method of 1st Embodiment. Here, the target value V1 of the first full charge voltage is 4.3V, the target value V2 of the next full charge voltage is 4.2V, and the threshold value α1 is 0.01C (the current value is the C value indicating the discharge rate). Stored in the storage unit 22. Also in Example 1, the end voltage was set to 2.5V.

<Result>
The measurement results are as shown in FIGS.

  FIG. 8 is a diagram showing the relationship between the number of discharges and the discharge capacity, and FIG. 9 is a diagram showing the relationship between the number of discharges and the CV current value. 8 and 9, the graph is shown on the upper side and the measured value is shown on the lower side.

<Comparative Example 1>
The measurement results of Comparative Example 1 are shown as white circles in FIGS. 8 and 9.

  In Comparative Example 1, as shown in FIG. 8, the 1C discharge capacity decreased each time the number of times was increased. The degree of decrease was the largest compared to Comparative Example 2 and Example 1.

  As shown in FIG. 9, the CV current value of Comparative Example 1 increased rapidly after the fourth charge / discharge.

  The total discharge amount of Comparative Example 1 was 1015 mAh.

<Comparative example 2>
The measurement results of Comparative Example 2 are shown as crosses in FIGS.

  In Comparative Example 2, since the target value of the full charge voltage is as low as 4.2 V, the 1C discharge capacity is initially small as shown in FIG. However, the decrease rate of the 1C discharge capacity was small.

  As shown in FIG. 9, the CV current value of Comparative Example 2 gradually increased without increasing particularly rapidly.

  The total discharge amount of Comparative Example 2 was 1008 mAh.

<Example 1>
The measurement results of Example 1 are shown as white diamond marks in FIGS.

  In Example 1, as shown in FIG. 8, the 1C discharge capacity was initially large as in Comparative Example 1. This is because the target value of the full charge voltage is common at 4.3V.

  As shown in FIG. 9, during the fourth charge / discharge, the increase in the CV current value was 0.012C, which exceeded 0.01C (threshold α1). Accordingly, the target value of the full charge voltage is changed from V1 to V2 by the charge control method. That is, it was set to 4.2 V, which was the same as in Comparative Example 2. Since the voltage value decreased, the CV current value also decreased at the fifth time. As a result, referring to FIG. 8, the reduction rate of the 1C discharge capacity of Example 1 was substantially the same as the reduction rate of the 1C discharge capacity of Comparative Example 2.

  The total discharge amount of Example 1 was 1058 mAh.

<Discussion>
From the above, it can be seen that, as in Comparative Example 1, if the target value of the full charge voltage remains as high as 4.3 V, the rate of decrease of the 1C discharge capacity is large and the total discharge capacity is small. On the other hand, as in Comparative Example 2, when the target value of the full charge voltage is as low as 4.2 V from the beginning, the rate of decrease in the 1C discharge capacity is small. However, since the original 1C discharge capacity is small, it can be seen that the total discharge capacity is also small.

  Compared to Comparative Examples 1 and 2, in Example 1, when the target value of the full charge voltage is initially 4.3 V and the increase in the CV current value exceeds the threshold value 0.01 C, the target value of the full charge voltage is set. Was changed to 4.2V. Thus, as is apparent from the graph of FIG. 8, the 1C discharge capacity is reduced at the same rate as in Comparative Example 1, but the 1C discharge capacity is reduced at the same rate as in Comparative Example 2 after the fourth time. To do. That is, the variation of 1C discharge capacity is the same as that of Comparative Example 1 and Comparative Example 2. As a result, it was found that the total discharge capacity of Example 1 was the highest value of 1058 mAh.

(Second embodiment)
Next, a second example to which the charge control process of the first embodiment and the second embodiment is applied will be described.

  First, the configuration of the battery 10 used in the second example is as follows.

<Battery 10>
A positive electrode active material was formed by mixing 85% by weight of nickel-based active material, 10% by weight of acetylene black as a conductive additive, and 5% by weight of PVdF as a binder. A positive electrode active material was applied to both surfaces of a positive electrode current collector made of an aluminum foil to form a positive electrode. Further, 90% by weight of hard carbon and 10% by weight of PVdF as a binder were mixed to constitute a negative electrode active material. A negative electrode active material was applied to both sides of a negative electrode current collector made of copper foil to form a negative electrode. The formed positive electrode and negative electrode were alternately laminated via separators, sandwiched between two laminate sheets, and an electrolyte solution in which LiPF6 was dissolved as a lithium salt was poured into the inside thereof and sealed. According to the above procedure, three same batteries were prepared, which were referred to as Example 2, Example 3, and Example 4, respectively.

<Measurement>
About each battery, 1 C discharge capacity and the stable CV electric current value were measured with the following method.

  For Examples 2 and 3, charging and discharging were repeated 10 times by applying the charge control method of the second embodiment. Here, the target value V1 of the first full charge voltage is 4.3V, the target value V2 of the next full charge voltage is 4.2V, and the threshold value α1 is 0.01C (the current value is the C value indicating the discharge rate). Stored in the storage unit 22. Further, the predetermined value φ to be compared with the increase value Δi of the CV current value is stored in the storage unit 22 as 0.005C. When Δi exceeded φ (0.005C), 1.5 was stored in the storage unit 22 as the coefficient γ1 to be multiplied by the threshold value α. The end voltage was 2.5V.

  For Example 4, the charge control method of the first embodiment was applied, and charging / discharging was repeated 10 times. Here, the target value V1 of the first full charge voltage is 4.3V, the target value V2 of the next full charge voltage is 4.2V, and the threshold value α1 is 0.01C (the current value is the C value indicating the discharge rate). Stored in the storage unit 22. The end voltage was 2.5V. That is, the fourth embodiment is different from the second and third embodiments in that the increase value Δi of the CV current value is not calculated and is not compared with the predetermined value φ (0.005C).

<Result>
The measurement results are as shown in FIGS.

  10 is a diagram showing the relationship between the number of discharges and the discharge capacity, FIG. 11 is a diagram showing the relationship between the number of discharges and the CV current value, FIG. 12 is a diagram showing Δi for each time, and FIG. 13 is a diagram showing the threshold value α for each time. is there. 10 and 11, the graph is shown on the upper side and the measured value is shown on the lower side.

<Example 2>
The measurement results of Example 2 are shown as black diamond marks in FIGS. 10 and 11.

  As shown in FIG. 10, the 1C discharge capacity decreased as the number of times increased. Referring to FIG. 11, the CV current value became the threshold value α (0.01 C) or more at the eighth time. Here, since Δi is 0.002C as shown in FIG. 12, it is smaller than the predetermined value φ (0.005C). Therefore, the target value of the full charge voltage was lowered to 4.2 V by judging that the CV current value was not suddenly increased due to abnormal deterioration but natural deterioration.

  The total discharge amount of Example 2 was 1075 mAh.

<Example 3>
The measurement results of Example 3 are shown as US marks in FIGS. 10 and 11.

  As shown in FIG. 11, at the sixth time, the CV current value was 0.01 C, which was not less than the threshold value α (0.01 C). Here, since Δi is 0.006 as shown in FIG. 12, it is equal to or greater than a predetermined value φ (0.005C). Therefore, it was determined that the CV current value suddenly increased due to abnormal deterioration, and the target value of the full charge voltage was maintained at 4.3V. Then, the threshold value α is multiplied by a coefficient γ1 = 1.5. As shown in FIG. 13, the threshold value α is set to 0.015C after the seventh time. As shown in FIG. 11, even when the CV current value increased after the seventh time, the threshold value α (0.015) was not exceeded, and the target value of the full charge voltage remained at 4.3V.

  As a result, the total discharge amount of Example 3 was 1089 mAh.

<Example 4>
The measurement results of Example 4 are shown as black circles in FIGS. 10 and 11.

  As shown in FIG. 11, at the fifth time, the CV current value was 0.012 C, which was not less than the threshold value α (0.01 C). In Example 4, since the same charge control as that in the first embodiment is performed, the target value of the full charge voltage is changed from V1 to V2. That is, it was set to 4.2 V, which was the same as in Comparative Example 2. Since the voltage value decreased, the CV current value also decreased at the sixth time. As shown in FIG. 13, the threshold value α = α2 = 0.015C was set for the sixth and subsequent times.

  The total discharge amount of Example 4 was 1058 mAh.

<Discussion>
As described above, Examples 2 and 3 according to the charge control method of the second embodiment can obtain a higher total discharge amount than Example 4 according to the charge control method of the first embodiment. Recognize. This is because, in the charge control method of the second embodiment, even when the CV current value is equal to or greater than the threshold value α, if the increase width Δi is high, the target value of the full charge voltage is not lowered as abnormal deterioration. Since the target value of the full charge voltage could not be lowered, the 1C discharge amount increased and the total discharge amount also increased.

(Battery material)
The material of each part in the lithium secondary battery of the present invention may be a known material, and is not particularly limited. For reference, the material of the lithium ion secondary battery will be briefly described below.

[Current collector]
For example, a metal or a conductive polymer can be adopted as the current collector. Specifically, metal materials, such as aluminum, nickel, iron, stainless steel, titanium, copper, are mentioned, for example. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum and copper are preferable from the viewpoints of electron conductivity and battery operating potential.

[Positive electrode active material layer and negative electrode active material layer]
The positive electrode active material layer and the negative electrode active material layer contain an active material, and further contain other additives as necessary.

The positive electrode active material layer includes a positive electrode active material. Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Co—Mn) O _2, and lithium—such as those obtained by replacing some of these transition metals with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material. Of course, positive electrode active materials other than those described above may be used.

The negative electrode active material layer includes a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, and lithium-metal alloy materials. . In some cases, two or more negative electrode active materials may be used in combination. Preferably, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in each active material layer is not particularly limited, but is preferably 1 to 20 μm and more preferably 1 to 5 μm from the viewpoint of increasing output. However, it goes without saying that a form outside this range may be adopted. In the present specification, “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the active material particles. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

  Examples of the additive that can be contained in the positive electrode active material layer and the negative electrode active material layer include a binder, a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer.

  Examples of the binder include polyvinylidene fluoride (PVdF) and a synthetic rubber binder.

  The conductive auxiliary agent is an additive that is blended to improve the conductivity of the positive electrode active material layer 12 or the negative electrode active material layer 15. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The mixing ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous solvent secondary battery.

  The thickness of each active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. For example, the thickness of each active material layer is about 2 to 100 μm.

[Electrolyte layer]
As the electrolyte constituting the electrolyte layer, a liquid electrolyte or a polymer electrolyte can be used.

  The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). Further, as the supporting salt (lithium salt), a compound that can be added to the active material layer of the electrode, such as LiBETI, can be similarly employed.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

It is a figure which shows schematic structure of the charge control apparatus of a lithium secondary battery. It is a figure which shows the voltage of a CC-CV charging / discharging cycle. It is a flowchart which shows the flow of an effect | action of a control part. It is a figure which shows the example of the discharge integrated amount of a battery. It is a flowchart which shows the process peculiar to 2nd Embodiment. It is a flowchart which shows the process peculiar to 3rd Embodiment. It is the schematic of the vehicle carrying a charge control apparatus. It is a figure which shows the relationship between the frequency | count of discharge and discharge capacity. It is a figure which shows the relationship between the frequency | count of discharge and a CV electric current value. It is a figure which shows the relationship between the frequency | count of discharge and discharge capacity. It is a figure which shows the relationship between the frequency | count of discharge and a CV electric current value. It is a figure which shows (DELTA) i of each time. It is a figure which shows threshold value (alpha) of each time.

Explanation of symbols

10 Lithium secondary battery,
20 charge control device,
21 detectors,
22 storage unit,
23 control unit,
30 vehicles.

Claims (11)

A detection step of detecting a value of a parameter that increases due to natural deterioration of the lithium secondary battery due to charge and discharge;
A determination step of determining whether or not the value of the parameter is higher than a threshold;
When the value of the parameter is higher than the threshold value, a setting step of setting a target value of a full charge voltage when charging the lithium secondary battery,
Only including,
The charging control method for a lithium secondary battery, wherein the parameter value is a constant and stable current value during constant voltage charging in a constant current-constant voltage charging cycle for charging the lithium secondary battery. 2. The charging of the lithium secondary battery according to claim 1 , wherein the target value is prepared in a plurality of stages, and a lower target value is set in the setting step every time the stable current value exceeds the threshold value. Control method. In the setting step,
When the value of the stable current value is higher than the threshold value, the stable current value of the current constant current-constant voltage charging cycle, the stable current value of the previous constant current-constant voltage charging cycle, and Whether or not the difference is greater than or equal to a predetermined value,
If the difference is less than the predetermined value, set a target value of the full charge voltage when charging the lithium secondary battery,
If the difference is of the predetermined value or more, instead of setting low the target value, the charging control method for a lithium secondary battery according to claim 1 or claim 2 for setting higher the threshold. A temperature detection step of detecting a temperature in the vicinity of the lithium secondary battery;
A second threshold setting step for setting the threshold higher when the detected temperature is equal to or higher than a predetermined temperature;
The charge control method for a lithium secondary battery according to any one of claims 1 to 3 , further comprising: The constant current - by measuring the number of times of the constant voltage charging cycle, lithium secondary according to any one of claims 1 to 4, further comprising a third setting step of setting lower the threshold in accordance with the number of measurements Battery charge control method. A detector that detects the value of a parameter that increases due to natural degradation of the lithium secondary battery due to charge and discharge;
A determination unit for determining whether or not the value of the parameter is higher than a threshold;
When the value of the parameter is higher than the threshold value, a setting unit that sets a target value of a full charge voltage when charging the lithium secondary battery,
I have a,
The charging control device for a lithium secondary battery , wherein the value of the parameter is a constant and stable current value during constant voltage charging in a constant current-constant voltage charging cycle for charging the lithium secondary battery. A storage unit for storing the target value in a plurality of stages;
The charging control of the lithium secondary battery according to claim 6 , wherein the setting unit reads a lower target value from the storage unit and sets it as a new target value each time the stable current value exceeds the threshold value. apparatus. The setting unit
When the value of the stable current value is higher than the threshold value, the stable current value of the current constant current-constant voltage charging cycle, the stable current value of the previous constant current-constant voltage charging cycle, and Whether or not the difference is greater than or equal to a predetermined value,
If the difference is less than the predetermined value, set a target value of the full charge voltage when charging the lithium secondary battery,
The lithium secondary battery charge control device according to claim 6 or 7 , wherein when the difference is equal to or greater than the predetermined value, the threshold value is set higher instead of setting the target value low. A temperature detector for detecting a temperature in the vicinity of the lithium secondary battery;
The lithium secondary battery charge control device according to any one of claims 6 to 8 , wherein the setting unit sets the threshold higher when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature. The lithium secondary battery according to any one of claims 6 to 9 , wherein the control unit measures the number of the constant current-constant voltage charging cycles, and sets the threshold value lower according to the number of measurements. Charge control device. Vehicle equipped with a charge controller for lithium secondary battery according to any one of claims 6-10.

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