JP6056125B2 - Battery pack and power storage device - Google Patents

Description

  The present invention relates to an assembled battery in which a plurality of unit cells, which are secondary batteries, are connected in series, and a power storage device having a function of determining a charge / discharge state of the assembled battery.

  Among technologies such as EV cars and smart grids using natural energy power generation, secondary batteries have a major role as power storage devices. In particular, lithium ion secondary batteries are excellent in both capacity and output, and contribute greatly to miniaturization of the system. On the other hand, the lithium ion secondary battery is likely to deteriorate in an overcharged state / overdischarged state and needs to be used within a predetermined voltage range. Therefore, it is important to grasp in detail the state of charge of the lithium ion secondary battery.

  In general, the evaluation of the state of charge of single cells and assembled batteries is performed by measuring the voltage of an open circuit and comparing it with a value measured in advance. For example, Patent Document 1 discloses that the open circuit voltage-residual capacity characteristic of at least one single cell among the single cells is a voltage that proportionally changes the open circuit voltage according to the discharge state of the secondary battery. A technique for measuring the open circuit voltage of the unit cell and evaluating the charging depth of the assembled battery is disclosed.

JP 2004-311308 A

  However, when charging / discharging with a large current, there is a tendency that sufficient accuracy cannot be obtained by the conventional evaluation method. For example, in the evaluation method of Patent Document 1, when a large current is passed, a voltage rise or a voltage drop due to the internal resistance of the unit cell is taken into account, and the charge depth determined by the magnitude of the charge / discharge current is greatly different. End up. For this reason, in order to operate the assembled battery safely, it is necessary to narrow the charge / discharge range by a voltage fluctuation caused by the maximum current that can be assumed, resulting in a decrease in the capacity of the assembled battery.

  The present invention was created to solve such problems of the prior art, and even when a large current is input / output with respect to the assembled battery capacity, the charging depth of the assembled battery can be detected with high accuracy, It is to provide a power storage device.

  The assembled battery of the present invention comprises one or more lithium ion secondary batteries and two or more charge depth detection lithium ion secondary batteries connected in series, and the two or more charge depth detection lithium ion secondary batteries. The battery is characterized by having an inflection region where the voltage changes sharply in different charging depth regions. Here, the “charge depth detection lithium ion secondary battery” is a lithium ion secondary battery having an inflection region in which the voltage changes sharply at a predetermined charge depth. Here, “charging depth” refers to the proportion of the amount of electricity charged, and the fully charged state is assumed to be 100%. However, it is not limited to the value at the time of charge, and includes both the amount of electricity at the time of charge and at the time of discharge. “Two or more charging depth detection lithium ion secondary batteries” mean two or more charging depth detection lithium ion secondary batteries that exhibit inflection regions at different charging depths. The “inflection region” refers to a region where the cell voltage shows a steep change with respect to the change in the charging depth. FIG. 4 shows a charge / discharge curve representing the relationship between the charge depth (X axis) and the single cell voltage (Y axis) of the lithium ion secondary battery for detecting the charge depth that can be used in the present invention. In FIG. 4, a change region 90 in which the cell voltage changes sharply with respect to the change in the charging depth is an example of the “inflection region” in the present invention.

  According to the lithium ion secondary battery for detecting the charging depth of the present invention, an “inflection region” in which a sudden change in voltage is detected at a predetermined charging depth appears. In the “inflection region”, an active material that completes charging at a predetermined voltage A and an active material that completes discharging at a voltage A are mixed, and at least one of one positive electrode and one negative electrode is mixed. It can be made to express by producing and using this for the lithium ion secondary battery for charge depth detection.

  At this time, by connecting in series the two or more charging depth detection lithium ion secondary batteries whose inflection areas are expressed at different charging depths, the charging depth of the entire assembled battery is accurately stepwise. It becomes possible to detect. If two or more charge depth detection lithium ion secondary batteries differ in the proportion of the active material in the electrode, two or more charge seismic intensity detection lithium ion secondary batteries are inflected to different charge depths. Express the region. In a battery pack composed of series connections, the voltage of two or more charge depth detection lithium ion secondary batteries is monitored, and if a sudden voltage fluctuation is observed in one charge depth detection lithium ion secondary battery, the battery pack The charging depth of the battery is a charging depth corresponding to the inflection region of one lithium ion secondary battery for detecting the charging depth.

Furthermore, in the present invention, the lithium ion secondary battery for charge depth detection is used as the positive electrode or negative electrode active material, with respect to the above charge depth,
(1) One active material in which the charge depth is 100%, and the state of charge is 95% to 100% at the charge depth,
(2) The discharge depth determined by this charge depth is set to 100% discharge capacity, and the discharge state is 95% to 100% at the discharge depth, and other active materials,
It is desirable that the lithium ion secondary battery has a positive electrode or a negative electrode made of a mixed active material, in which at least two kinds of active materials are mixed for at least one of the positive electrode and the negative electrode.

  According to this configuration, the amount of change in charge depth in the inflection region can be expressed within 10% of the battery capacity of the lithium ion secondary battery for charge depth detection. Of 10% or less. Here, it is generally considered that about 90% of the capacity of the assembled battery should be used for actual use. In order to prevent overdischarge, it is desirable to suppress the detection of the charging depth to 10% or less of the capacity of the lithium ion secondary battery for detecting the charging depth. According to said structure, there exists a tendency for the charge depth measurement precision of an assembled battery to be improved. In addition, since it is not necessary to set the capacity of the assembled battery low in advance, it can substantially contribute to the improvement of the assembled battery capacity.

  For example, two or more kinds of active material materials in which the charge depth at the predetermined voltage A is within ± 5% are mixed to produce either a positive electrode or a negative electrode. Thereby, the amount of change in charge depth in the inflection region of the lithium ion secondary battery for charge depth detection can be converged within 10% of the battery capacity. For example, when the charging depth at voltage A is 100%, the active material that completes charging at 95% or more and the active material that completes discharging at 5% or less when the charging depth at voltage A is 0% Are mixed as a positive electrode active material or a negative electrode active material, the inflection region of the lithium ion secondary battery for charge depth detection can be converged to 10% or less with respect to the battery capacity.

  At this time, the active material in which the charging depth at the predetermined voltage A is in the actual use range is desirably 10% or less as the electric capacity ratio of all active materials in the electrode. For example, if the active material having a charging depth of 20% to 80% at voltage A is set to 10% or less, the inflection region of the lithium ion secondary battery for detecting the charging depth is set to 10% or less with respect to the battery capacity. Can converge.

  In the present invention, it is desirable that the amount of voltage change in the inflection region of the lithium ion secondary battery for detecting the charge depth is 100 mV or more.

  By selecting two or more kinds of active material materials to be mixed as the positive electrode active material or the negative electrode active material as a combination of active material materials in which the potential difference caused by each intrinsic potential is 100 mV or more, the above inflection region The amount of voltage change at can be 100 mV or more.

  For example, the cell voltage during charging / discharging at a relatively large current of about 1 C (1 C is the amount of current that completes discharging in one hour when discharging from a fully charged lithium ion secondary battery at a constant current) is: When charging at a minute current, the voltage rise and voltage drop due to the internal resistance of the battery are taken into account and observed to be about 100 mV greater than the cell voltage at the time of discharging. Therefore, by using a single cell for depth of charge detection in which the amount of voltage change in the inflection region is 100 mV or more as in this configuration, even when charging / discharging about 1 C, the voltage rise caused by the internal resistance of the battery, The voltage drop is smaller than the voltage change amount in the inflection region, and the charging depth of the assembled battery can be detected with high accuracy by an error in the inflection region.

  Moreover, in this invention, it is desirable that the voltage change amount in the inflection area | region of the lithium ion secondary battery for charge depth detection is 300 mV or more.

  By selecting two or more active material materials to be mixed as the positive electrode active material or the negative electrode active material as a combination of active material materials in which the potential difference caused by each intrinsic potential is 300 mV or more, the above inflection region The amount of voltage change at can be set to 300 mV or more.

  For example, the cell voltage during charging / discharging with a large current larger than 5C (5C is the amount of current that completes discharging in 12 minutes when discharged from a fully charged lithium ion secondary battery at a constant current) is very small. When charging at the time of electric current, compared to the cell voltage at the time of discharging, a voltage increase and a voltage drop due to the internal resistance of the battery are taken into account and are observed to be increased by about 300 mV. Therefore, by using a single cell for charge depth detection whose voltage change amount in the inflection region is 300 mV or more as in this configuration, the internal resistance of the battery is caused even in charge / discharge at a large current of about 5C. The voltage rise and drop that occur is smaller than the amount of voltage change in the inflection region, and the charge depth of the assembled battery can be detected accurately with an error in the inflection region.

  The lithium ion secondary battery for charge depth detection desirably has a positive electrode in which a plurality of types of positive electrode active materials are mixed and / or a negative electrode in which a plurality of types of negative electrode active materials are mixed.

  Each of the positive electrode and negative electrode active materials of the lithium ion secondary battery has a specific potential. The overall voltage of the lithium ion secondary battery is a potential difference between the potentials inherent in the positive electrode active material and the negative electrode active material. By combining a plurality of types of active materials in one positive electrode or negative electrode to form an electrode, an inflection region having a steep potential difference can be provided at the potential break between the active materials. At this time, an inflection region can be designed at an arbitrary charging depth by appropriately selecting and combining a plurality of types of positive electrode active materials or a plurality of types of negative electrode active materials and adjusting the ratio of the active materials. .

  Moreover, it is desirable that the two or more types of lithium ion secondary batteries for detecting the depth of charge are composed of a combination of positive electrode active materials of the same type. That is, two or more charge depth detection lithium ion secondary batteries have a positive electrode in which the same plural types of positive electrode active materials are mixed and / or a negative electrode in which the same plural types of negative electrode active materials are mixed. The mixing ratios of the positive electrode active materials and / or the mixing ratios of the plurality of types of negative electrode active materials are different.

  By using two or more types of lithium-ion secondary batteries for detecting the depth of charge as the same positive electrode / negative electrode active material combination, only the charging depth at which the inflection region appears is different, and the battery characteristics of each single cell are almost equal. It can be. Thereby, there exists a tendency which can implement | achieve the assembled battery which can measure a charging depth with high precision. At this time, it is preferable that the kind of positive electrode / negative electrode active material of the lithium ion secondary battery for charge depth detection is four or less. When it is limited to four types or less, the inflection region does not appear more than necessary, the battery characteristics can be made almost uniform, and there is a tendency that a higher performance assembled battery can be provided.

  In addition, the plurality of types of positive electrode active materials and / or the plurality of types of negative electrode active materials in the lithium ion secondary battery for charge depth detection use two types of positive electrode active materials and / or two types of negative electrode active materials. It is desirable.

  By limiting the number of positive electrode / negative electrode active materials to only two types, it is possible to design a lithium ion secondary battery for charge depth detection with a clear expression of the inflection region and to provide a higher performance assembled battery. is there.

  The positive electrode active material of the lithium ion secondary battery for detecting the charge depth is 10% or less in terms of the electric capacity ratio of the positive electrode active material as a whole, the amount of the positive electrode active material containing 3.5 V in the actual usage range based on metallic lithium. It is desirable that

  Lithium ions for detecting the depth of charge by setting the positive electrode active material containing a potential of 3.5 V on the basis of metallic lithium in the actual usage range (for example, charging depth 20% to 80%) to 10% or less as the ratio of electric capacity Since the amount of change in charge depth required for voltage fluctuation in the inflection region of the secondary battery is 10% or less, the charge depth can be detected with higher accuracy.

The positive electrode active material of the lithium ion secondary battery for charge depth detection is a low-voltage positive electrode active material of at least one of LiTiO ₂ and LiFePO ₄ , and the high-voltage positive electrode material is Li (Ni _1-xy Co). _x Mn _y ) O ₂ (where 0.1 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.5), Li _a (Ni _1- bc Co _b Al _c ) O ₂ (where 0 .9 ≦ a ≦ 1.3, 0 <b ≦ 0.5, 0 <c ≦ 0.7), LiMn ₂ O ₄ , LiVPO ₄ , LiVOPO ₄ , LiCoO ₂ , LiMnPO ₄ , LiCoPO ₄ , LiNiPO ₄ It is desirable to be at least one of the following.

According to this configuration, LiTiO ₂ and LiFePO ₄ can be selected as a low-voltage positive electrode active material whose voltage near the end of charging is in the vicinity of 3.5 V or less, and Li (Ni _1-xy Co _x Mn _y ) O2 (where 0.1 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.5), Li _a (Ni _1- bc Co _b Al _c ) O ₂ (where 0.9 ≦ a ≦ 1.3, 0 <b ≦ 0.5, 0 <c ≦ 0.7), LiMn ₂ O ₄ , LiVPO ₄ , LiVOPO ₄ , LiCoO ₂ , LiMnPO ₄ , LiCoPO ₄ , LiNiPO ₄ are near the start of discharge Can be selected as a high voltage positive electrode active material. Since the amount of change in the charge seismic intensity in the inflection region can be proposed by these selections, the charge depth of the assembled battery can be detected with high accuracy.

At least one of the state of charge low voltage positive electrode active material of the detection for a lithium ion secondary battery is LiFePO _4, the high voltage positive electrode active material _{is LiVPO 4, LiVOPO 4, LiCoO 2} , LiMnPO 4, LiCoPO 4, LiNiPO 4 It is desirable that

  According to this configuration, the positive electrode active material having an olivine skeleton has a relatively flat charge / discharge curve, and the charge / discharge curves at the end of discharge and the end of charge change sharply. By using a positive electrode active material having an olivine skeleton for both the low-voltage positive electrode active material and the high-voltage positive electrode active material, the amount of change in charge depth in the inflection region can be easily reduced to 10% or less, and the charge depth can be accurately adjusted. Can be detected.

  The lithium ion secondary battery for charge depth detection includes a negative electrode active material, and the negative electrode active material is a mixture of one or more low-voltage negative electrode active materials and one or more high-voltage negative electrode active materials as a plurality of types of negative electrode active materials. The low-voltage negative electrode active material is at least one or more of negative electrode active materials having a potential near the upper limit of less than 0.5 V with respect to metallic lithium, and the high-voltage negative electrode active material contains metallic lithium. As a reference, it is desirable that the potential near the lower limit is at least one of negative electrode active materials having a potential of 0.5 V or more.

  According to this configuration, the discharge is almost finished at less than about 0.5 V with respect to metallic lithium (for example, the charge depth is 5% or less) and the charge is almost finished at about 0.5 V (for example, A charging depth of 95% or more) and a high voltage negative electrode active material are combined in the negative electrode. Thereby, the variation | change_quantity of the charge depth in the inflection area | region of the lithium ion secondary battery for charge depth detection can be made into 10% or less, and a charge depth can be detected further accurately.

The negative electrode active material has at least one selected from graphite as a low voltage negative electrode active material, hard carbon, LiTiO ₂ , SiO _w (w is 1 to 4), and Al ₂ O ₃ as a high voltage negative electrode active material. Is desirable.

According to this configuration, graphite has a voltage near the end of discharge of 0.5 V or less, and can be selected as a low-voltage negative electrode active material. Hard carbon, LiTiO ₂ , SiO _w (w is 1 to 4), Al ₂ O ₃ has a voltage near the start of charging of 0.5 V or more and can be selected as a high-voltage negative electrode active material. By using it in combination with a lithium ion secondary battery for detecting the charging depth, the charging depth can be detected with high accuracy. .

  The assembled battery of the present invention is preferably used as a power storage device. Here, the power storage device includes the assembled battery, a voltage detection device provided in parallel for at least each of the lithium ion secondary batteries for charge depth detection, and a charge depth detection device configured by a logic circuit. The depth detection device determines the charging depth of the assembled battery based on the voltage value detected in the lithium ion secondary battery for detecting the charging depth.

  By using the power storage device in which the charge depth detection device is connected to the assembled battery, the power storage device itself can detect the charge depth, and can be used safely as a power storage device for electric vehicles or a stationary power storage device.

  The logic circuit determines the end of charging when it detects a voltage in the inflection region that is greater than the inflection region intermediate voltage during charging, and determines that the charging is complete when the voltage is in the inflection region during discharging. It is desirable to determine the end of discharge when a smaller voltage is detected.

  The direction of the voltage applied to the lithium ion secondary battery differs between charging and discharging. According to the direction of the applied voltage, the charge depth detection voltage during charging is a voltage within the inflection region and greater than the inflection region intermediate voltage, and the charge depth detection voltage during discharge is the voltage within the inflection region. However, by making the voltage smaller than the inflection region intermediate voltage, there is a tendency that the amount of change in voltage in the inflection region can be used effectively and the charging depth of the assembled battery can be detected accurately even at a large current.

  According to the present invention, even when a large current is input / output with respect to the assembled battery capacity of the power storage device, it becomes possible to detect the charging depth of the assembled battery with high accuracy, and to prevent a deterioration in the performance of the assembled battery. Is possible.

FIG. 1 is a diagram schematically showing an assembled battery according to an embodiment to which the present invention is applicable. FIG. 2 is a diagram schematically showing a power storage device according to an embodiment to which the present invention is applicable. FIG. 3 is a schematic sectional view showing a configuration example of a lithium ion battery according to an embodiment to which the present invention is applicable. FIG. 4 is a graph showing a change in voltage with respect to the charging depth of the lithium ion secondary battery for detecting the charging depth according to the embodiment to which the present invention is applicable.

  Exemplary embodiments of a battery pack and a power storage device according to the present invention will be described below in detail with reference to the accompanying drawings. However, the assembled battery and the power storage device of the present invention are not limited to the following embodiments. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

  The individual batteries that can be connected in series with each other to constitute the assembled battery of the present invention are “lithium ion secondary batteries”. Unless specifically limited, batteries having electrode materials and electrolytes of various compositions are included.

  As described above, an example of the charge / discharge curve representing the relationship between the voltage and the charge depth of the lithium ion secondary battery of the present embodiment is shown in FIG. The inflection region in the charge / discharge curve is predetermined at the time of manufacture, and can be set to an arbitrary charge depth region by adjusting the electrode material, for example. In this case, the voltage developed in the inflection region is determined by the selection of the electrode material.

  The charging depth of the assembled battery according to the present embodiment is obtained from a value obtained by measuring a voltage using a voltage sensor connected in parallel to the lithium ion secondary battery for detecting the charging depth. When the assembled battery is charged / discharged and the voltage of the lithium ion secondary battery for detecting the charging depth reaches a predetermined voltage, it can be determined that the assembled battery is in a predetermined charging depth state. At this time, since the voltage changes sharply in the inflection region, the amount of change in the charge depth is less than the amount of change in the voltage, and it is possible to determine the accurate greedy charge depth. Further, by selecting the battery material, the absolute amount of voltage change can be increased, and the determination error due to the voltage difference generated during charging / discharging due to the contact resistance and the battery internal resistance can be reduced. That is, even when the assembled battery is being charged or discharged from the assembled battery to the device, the depth of charge can be known with high accuracy, and overcharge / overdischarge can be effectively prevented.

  FIG. 1 schematically shows an example of the assembled battery of the present embodiment. The assembled battery 10 includes a first charge depth detection lithium ion secondary battery 14 and a second charge depth detection lithium ion having an inflection region at a charge depth different from that of the charge depth detection lithium ion secondary battery. The secondary battery 16 and one or more non-charging depth detection lithium ion secondary batteries 12 have a structure in which they are connected in series. The “non-charge depth detection lithium ion secondary battery” refers to a lithium ion secondary battery that does not contribute to charge depth detection but contributes only to charge / discharge of the assembled battery. “Lithium-ion secondary battery for charge depth detection” is not limited to the two indicated as “first” and “second”, but should be incorporated according to the number of stages where the charge depth is to be detected. Can do. The first charging depth detection lithium ion secondary battery 14 and the second charging depth detection lithium ion secondary battery 16 of the present embodiment are inflection regions in which voltage fluctuations are steep in different charging depths. Indicates. It is desirable that the lithium-ion secondary battery for detecting the charging depth is connected in more types than the number of charging depths to be detected.

  In the assembled battery 10 of the present embodiment, the arrangement of each battery alone is not particularly limited as long as a plurality of non-charging depth detection lithium ion batteries 12 and a charging depth detection lithium ion secondary battery are connected in series. . For example, a non-charging depth detection lithium ion secondary battery may be further connected in series and in parallel to the non-charging depth detection lithium ion secondary battery 12. Moreover, the lithium ion secondary battery for charge depth detection which has the characteristic equivalent to each in the lithium ion secondary battery for charge depth detection 14 and the lithium ion secondary battery 16 for charge depth detection of 2nd in parallel is parallel. You may connect. Further, in order to improve the detection accuracy of the charge depth, some other charge depth detection lithium ion secondary batteries having the same characteristics as the lithium ion secondary battery for detecting the charge depth may be connected in series. Furthermore, the assembled battery 10 of FIG. 1 may be further connected in series and in parallel.

  When the assembled battery 10 of the present embodiment is used for a large power supply system, it is desirable to use a large number of non-charging depth detection lithium ion secondary batteries 12 from the viewpoint of obtaining high output. In this case, the output and energy density of the assembled battery 10 as a whole are mainly determined by the output and the energy density of the lithium ion secondary battery 12 for detecting a non-contained charge depth. In the battery pack 10 of the present embodiment, since the charge depth of the entire battery pack is detected by a plurality of charge depth detection lithium ion secondary batteries, the inactive charge depth detection lithium ion secondary battery is used within the range of charge depths used. There is no need to increase the voltage change or internal resistance of the battery itself. Therefore, a battery having a small voltage change and a low internal resistance can be used as the lithium ion secondary battery 12 for detecting a non-capacity charge depth constituting the assembled battery. As a result, the assembled battery of this embodiment can provide a stable high output to a device in a wide charging depth range. In order to enhance this effect, it is desirable that the lithium ion secondary batteries 12 for non-charging depth detection have their initial battery capacities within a range of manufacturing variation (5%). Moreover, it is desirable that the initial battery capacity of the lithium ion secondary battery for detecting the charging depth is larger than the lithium ion secondary battery for detecting the non-charging depth.

  In FIG. 2, one preferable embodiment of the electrical storage apparatus incorporating the assembled battery of this embodiment is typically shown. The power storage device 40 of the present embodiment includes the assembled battery 10 of FIG. 1 and a voltage detection device and charge depth detection devices 30 and 35 connected in parallel to the lithium ion secondary battery for detection of charge depth. The charge depth is calculated by the charge depth detection device using the voltage value measured by a voltage detection device connected in parallel to the battery, by measuring the voltage of the lithium ion battery for charge depth detection.

  FIG. 3 shows an example of a charge depth detection lithium ion secondary battery according to this embodiment. The lithium ion secondary battery 50 includes a positive electrode 60 and a negative electrode 70 made of a material capable of occluding and releasing lithium ions, a lithium ion conductive electrolyte, and a separator 80 between the positive electrode and the negative electrode.

The lithium ion secondary battery for detecting the charge depth has an inflection region 90 in which the voltage changes sharply in a certain charge depth region. The expression of the inflection region 90 is obtained in the following cases.
(1) When the positive electrode mixture layer 61 is formed by mixing a plurality of positive electrode active materials,
(2) When the negative electrode mixture layer 71 is formed by mixing a plurality of negative electrode active materials,
(3) In both cases The positive electrode active material and the negative electrode active material each have a unique potential. The voltage of the lithium ion secondary battery is a potential difference caused by the intrinsic potential of the positive electrode active material and the negative electrode active material. By using a mixture of a plurality of types of active material in one electrode, an inflection region 90 having a steep potential difference is generated at the potential break between the active materials. However, like LiMnFePO ₄ , one type of active material may develop an inflection region.

As described above, the inflection region is for detecting the depth of charge by mixing an active material that completes charging at a predetermined voltage and an active material that completes discharging at the same voltage to produce one electrode. It can be expressed in a lithium ion secondary battery. Also,
(A) An active material that is charged at 95% or more when the charging depth at that voltage is 100% (hereinafter referred to as “low-voltage active material”. Voltage active material ”(hereinafter sometimes referred to as“ high voltage active material ”). "High voltage positive electrode active material" and "high voltage negative electrode active material"))
(B) The active material whose charging depth at the voltage is in the actual use range is 10% or less as the electric capacity ratio of all active materials in the electrode,
Thus, the change in the charging depth in the inflection region can be converged to 10% or less.

  In the case of the above (1) and (3), it is generally desirable that the voltage range of the positive electrode active material for a lithium ion battery is a voltage range of about 3.0 to about 4.0 V with respect to metallic lithium. For example, when the median value of 3.5 V is used as a reference, a low-voltage positive electrode active material whose voltage is smaller than 3.5 V and near 3.5 V is fully charged, and greater than 3.5 V and near 3.5 V Can be combined with a high-voltage positive electrode active material whose voltage is the discharge end voltage. It is desirable that the potentials of the plural types of positive electrode active materials related to the combination do not overlap. This is because the inflection area may be made gentle and the measurement system may be lowered.

Specifically, examples of the low voltage positive electrode active material include LiTiO ₂ and LiFePO ₄ . Moreover, as a high-voltage positive electrode active material, Li (Ni _1-xy Co _x Mn _y ) O ₂ (where 0.1 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.5), Li _{a (N 1-b-c Co} b Al c) O 2 ( however, 0.9 ≦ a ≦ 1.3,0 <b ≦ 0.5,0 <c ≦ 0.7), LiMn 2 O 4, LiVPO ₄ , LiVOPO ₄ , LiCoO ₂ , LiMnPO ₄ , LiCoPO ₄ , LiNiPO _{4 and the} like. By combining any one of the low-voltage positive electrode active material and the high-voltage positive electrode active material shown here to form the positive electrode mixture layer 61, the inflection region can be expressed starting from the positive electrode 60.

Low voltage positive electrode active LiFePO ₄ of material, of the high voltage positive electrode active _{material, LiVPO 4, LiVOPO 4, LiMnPO} 4, LiCoPO 4, LiNiPO 4 , etc., has an olivine structure, small voltage change in normal use range It is known that the voltage changes abruptly at the beginning and end of charging. By using a positive electrode active material having such an olivine structure, the amount of change in charge depth with respect to the amount of change in voltage in the inflection region 90 can be reduced, and the detection accuracy can be improved.

In the case of (2) or (3) where the inflection region originates from the negative electrode 70, the inflection region can be obtained by selecting a plurality of types of negative electrode active materials in the negative electrode mixture layer 71. The selection of the active material is preferably a combination in which the potential difference of the negative electrode active material is large. In the case of the negative electrode, a low voltage active material and a high voltage active material can be distinguished with about 0.5 V as a boundary. Graphite can be used as the low voltage negative electrode active material. As the high voltage negative electrode active material, hard carbon, LiTiO ₂ , SiO _w (w is 1 to 4), Al ₂ O ₃ or the like can be used as appropriate.

  The charging depth at which the inflection region appears can be adjusted by changing the mixing ratio of the low voltage active material and the high voltage active material. Therefore, two or more lithium ion secondary batteries for detecting the charge depth can be adjusted to different charge depths by making the mixing ratio of the low voltage active material and the high voltage active material different. Thereby, multiple types of lithium ion secondary batteries 14 and 16 for charge depth detection are obtained.

On the other hand, the charging depth of two or more lithium ion secondary batteries for detecting the charging depth can be adjusted by changing the type of the low voltage active material or the type of the high voltage active material. However, it is effective to adjust the charging depth by changing only the mixing ratio for the same low-voltage active material and the same high-voltage active material. This is because, when the type of the active material is changed, it may be necessary to detect the charge depth in consideration of characteristics other than the potential difference. For example, a case of different depth of charge of the inflection area by the adjustment of the positive electrode, if the LiFePO ₄ as a low-voltage positive electrode active material, selects the LiMnPO ₄ as a high voltage positive electrode active material, two or more charging depth detector The lithium ion secondary battery is preferably adjusted only by the difference in the mixing ratio between LiFePO ₄ and LiMnPO ₄ . The same applies when adjusting the negative electrode.

Moreover, the lithium ion secondary battery for charge depth detection is not necessarily limited to mixing two types of active materials (one low voltage active material and one high voltage active material). For example, LiFePO ₄ and LiMnO, and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ can be combined in the positive electrode. However, when various kinds of active materials are combined, a large number of inflection regions appear and affect each other, so that the inflection regions tend to be gentle. Also, there is a tendency that the influence of characteristics other than the potential difference appears remarkably. Therefore, it is desirable that the number of types of positive electrode active materials be four or less. The same applies to the negative electrode.

The low-voltage positive electrode active material, the high-voltage positive electrode active material, and the low-voltage negative electrode active material so that the inflection region originating from the positive electrode active material and the inflection region originating from the negative electrode active material are aligned at substantially the same charging depth. If a high-voltage negative electrode active material is selected, the potential difference developed in the inflection region can be increased. As an example of such a combination, LiFePO ₄ is selected as the low voltage positive electrode active material, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ is selected as the high voltage positive electrode active material, and graphite is selected as the low voltage negative electrode active material. There is a configuration in which hard carbon is selected as the high-voltage negative electrode active material. In this case, it is desirable to align the ratio of the positive electrode active material and the ratio of the negative electrode active material with reference to the capacity of the active material.

  The positive electrode of the lithium ion secondary battery for detecting the charge depth can be produced using a positive electrode paint in which a high voltage positive electrode active material, a low voltage positive electrode active material, a conductive additive and a binder are mixed in a solvent. This paint is applied on the current collector 62 and dried to form the positive electrode mixture layer 61, thereby forming the positive electrode 60. About a negative electrode, a high voltage negative electrode active material and a low voltage negative electrode active material are mixed with a solvent with a conductive support agent and a binder, and a negative electrode coating material is created. This paint is applied on the current collector 72 and dried to form the negative electrode mixture layer 71, thereby forming the negative electrode 70. The formation of the electrode is not limited to that using such a coating technique. For example, the positive electrode paint or the negative electrode paint may be solidified into a sheet shape and attached onto the current collector. Further, they may be bonded via a mesh-like current collector.

  As the binder, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like can be appropriately selected and used. As the solvent, various solvents for dissolving the binder can be used. Specifically, N-methylpyrrolidone (NMP), pure water, or the like can be used.

  As the current collector, various known materials used in lithium ion secondary batteries can be used. Specifically, a copper foil can be used as the negative electrode current collector 72, and an aluminum foil can be used as the positive electrode current collector 62.

As the electrolyte, an inorganic material having lithium ion conductivity, an organic polymer material, an aqueous electrolyte material, a nonaqueous electrolyte material, or the like can be used as appropriate. For example, when using a non-aqueous electrolyte, various lithium ion conductive solvents are desirable, and cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) are used alone or in appropriate combination. can do. In addition, in order to obtain an electrolytic solution with high electrical conductivity and appropriate viscosity, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), difluoro carbonate (FEC), etc. are used in combination. Also good. Examples of the electrolyte in the non-aqueous electrolyte include LiPF ₆ , LiBF ₄ , and LiClO ₄ .

  As the separator, a microporous film of a polyolefin resin such as polyethylene or polypropylene can be used. When the electrolyte is a non-aqueous electrolyte, it is desirable that the separator 80 be impregnated.

  The obtained positive electrode 60 and negative electrode 70 are laminated via a separator 80 to form a battery element. The battery element may be formed as a laminate or may be formed as a wound body. Furthermore, the wound body may be formed in a cylindrical shape, or may be formed in a flat (elliptical) shape.

  The battery element is inserted into the exterior body and sealed. As the exterior body, a metal cylindrical can, a flat can, a laminated exterior bag, and the like can be appropriately selected.

  In addition, about the lithium ion secondary battery for non-charging depth detection, the positive electrode 60 and the negative electrode 70 should just be formed using one type of positive electrode active material and one type of negative electrode active material. In this case, the selection of the positive electrode active material and the negative electrode active material is not particularly limited.

(Creation of assembled battery)
A plurality of depth-of-charge-detection lithium-ion secondary batteries and non-charge-depth-detection lithium-ion secondary batteries that are created as described above and have different charging depths in the inflection region are connected in series to obtain an assembled battery. be able to. The assembled battery is incorporated in various devices as a power source. The assembled battery may be mounted on various devices as it is, or an assembled battery module may be mounted on each device by combining a plurality of assembled batteries and a control circuit. When producing an assembled battery module, the assembled batteries may be connected in series and / or in parallel, whereby an assembled battery module having high output and excellent cycle characteristics can be obtained.

  Since only the voltage change in the inflection region becomes a problem in the lithium ion secondary battery for detecting the charging depth, the position in the assembled battery is not a problem in the measurement function in principle. On the other hand, when the outside air temperature is low, if the lithium ion secondary battery for detecting the depth of charge is placed in the center of the assembled battery, the lithium ion secondary battery for detecting the depth of charge in the center is warmed by self-heating. Since the influence caused by the external environment can be eliminated, the charging depth of the assembled battery can be detected with higher accuracy.

  On the other hand, if the external environment is controlled and constant, if the lithium ion secondary battery for detecting the charge depth is placed outside the assembled battery, the temperature of the lithium ion secondary battery for detecting the charge depth is external. Since it becomes almost constant depending on the environment, it is possible to detect the charging depth of the assembled battery with higher accuracy.

  When an assembled battery using the lithium ion secondary battery for charge depth detection is used as a power storage device, a voltage sensor for detecting the charge depth of the power storage device from the voltage of the lithium ion secondary battery for charge depth detection, Connect in parallel to the lithium-ion battery for detection. The voltage sensor is preferably connected to a logic circuit having a charge depth detection function. This logic circuit is preferably a logic circuit that evaluates the charging depth of the entire assembled battery from the voltage values of two or more types of lithium ion secondary batteries for detecting the charging depth in the power storage device.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
[Preparation of A lithium ion secondary battery for charge depth detection]
Two types of positive electrode active materials, LFP and NCM, were used as the positive electrode active material. LFP was prepared using a hydrothermal synthesis method. Natural graphite was used as the negative electrode active material.

-Battery electrode preparation and positive electrode preparation As a positive electrode active material, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (hereinafter referred to as “NCM” manufactured by Toda Kogyo Co., Ltd.), (LiFePO ₄ (hereinafter referred to as “LFP”) And carbon black (hereinafter referred to as “CB”, manufactured by Denki Kagaku Kogyo Co., Ltd., model number DAB50) and graphite (hereinafter referred to as “Gr”, manufactured by Timkal Co., Ltd., model number KS-). 6) A positive electrode was prepared using polyvinylidene fluoride (hereinafter referred to as “PVDF” (Kureha Co., Ltd., KF7305)) as a binder, 42.5 g of NCM, 42.5 g of LFP, 5 g of CB, graphite. 5 g of PVDF in NMP (N-methyl-2-pyrrolidone) (50 g, 10 wt%) was added and mixed to make about 145 g of paint. After coating with the doctor blade method to the aluminum foil (thickness 20 [mu] m) is a collector, and dried at 90 ° C., and rolled.

-Preparation of negative electrode After dry-mixing 45 g of natural graphite as a negative electrode active material and 2.5 g of CB as a conductive additive, 22.5 g of the PVDF solution was added as a binder to prepare a negative electrode paint. This paint was applied to a copper foil (thickness 16 μm) as a current collector by a doctor blade method, dried (90 ° C.) and rolled.

-Preparation of battery The prepared positive electrode and negative electrode were cut into predetermined dimensions. In addition, a separator (polyolefin microporous membrane) was cut to a predetermined size. The positive electrode and the negative electrode were provided with portions to which no electrode paint (active material + conductive aid + binder) was applied in order to weld the external lead terminals. A positive electrode, a negative electrode, and a separator were laminated in this order. The number of laminations was such that the capacity of the lithium ion secondary battery was 200 mAh. When laminating, a small amount of hot melt adhesive (ethylene-methacrylic acid copolymer, EMAA) was applied and fixed so that the positive electrode, the negative electrode, and the separator did not shift. An aluminum foil (width 4 mm, length 40 mm, thickness 100 μm) and nickel foil (width 4 mm, length 40 mm, thickness 100 μm) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals. Polypropylene (PP) grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. This is to improve the sealing performance between the external terminal and the exterior body. A battery outer package enclosing a battery element in which a positive electrode, a negative electrode, and a separator are stacked is made of an aluminum laminate material, and a configuration of PET (12) / Al (40) / PP (50) is prepared. PET is polyethylene terephthalate and PP is polypropylene. The value in parentheses represents the thickness of each layer (unit: μm). At this time, bags were made so that PP was inside. A battery element is put in this outer package, and an appropriate amount of electrolyte (LiPF6 is dissolved in 1M in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 30: 70 vol%)). The outer package was vacuum-sealed to prepare a lithium ion secondary battery. Aging was performed at 10 mA (0.05 C) for 10 hours.

  The initial average discharge capacity was about 200 mAh. In addition, as an evaluation of the charge / discharge curve at the time of open circuit, measurement was performed at 10 mA (0.05 C) where the contact resistance and the like can be ignored and the current value is sufficiently small. The charge / discharge curve has an inflection region where the voltage changes greatly in a region where the charging depth is about 40%.

[Preparation of lithium ion secondary battery for charge depth detection B]
Preparation of battery electrode / preparation of positive electrode A battery electrode was prepared in the same manner as the preparation of the lithium ion secondary battery A for detecting the charge depth, except that 63.8 g of NCM and 21.3 g of LFP were used.

-Creation of negative electrode The electrode equivalent to the lithium ion secondary battery A for charge depth detection was used.

○ Preparation of battery / prepared in the same manner as lithium-ion secondary battery A for charge depth detection.
The initial average discharge capacity was about 200 mAh. In addition, as an evaluation of the charge / discharge curve at the time of open circuit, measurement was performed at 10 mA (0.05 C) where the contact resistance and the like were negligible and the current value was sufficiently small. The charge / discharge curve has an inflection region where the voltage changes greatly in a region where the charging depth is about 12%.

[Creation of lithium ion secondary battery C for depth of charge detection]
Two types of positive electrode active materials, LFP and NCM, were used as the positive electrode active material. LFP was prepared using a hydrothermal synthesis method. Natural graphite was used as the negative electrode active material.

Preparation of battery electrode / preparation of positive electrode A battery electrode was prepared in the same manner as the preparation of the lithium ion secondary battery A for detecting the charge depth, except that 17.0 g of NCM and 68.0 g of LFP were used.

-Creation of negative electrode The electrode equivalent to the lithium ion secondary battery A for charge depth detection was used.

○ Preparation of battery / prepared in the same manner as lithium-ion secondary battery A for charge depth detection.
The initial average discharge capacity was about 200 mAh. In addition, as an evaluation of the charge / discharge curve at the time of open circuit, measurement was performed at 10 mA (0.05 C) where the contact resistance and the like were negligible and the current value was sufficiently small. The charge / discharge curve has an inflection region where the voltage changes greatly in a region where the charging depth is about 70%.

[Creation of lithium ion secondary battery D for depth of charge detection]
Two types of positive electrode active materials of LiMn ₂ O ₄ (hereinafter referred to as “LMO”; manufactured by Toda Kogyo Co., Ltd.) were used as the positive electrode active material. Hard carbon was used as the amorphous carbon for the negative electrode active material.

○ Battery electrode preparation / preparation of positive electrode The battery electrode was prepared in the same manner as the lithium ion secondary battery A for charge depth detection except that 85 g of LMO was used.

-Preparation of negative electrode An electrode was prepared in the same manner as the lithium ion secondary battery A for charge depth detection, except that hard carbon was used as amorphous carbon instead of natural graphite.

○ Preparation of battery / prepared in the same manner as lithium-ion secondary battery A for charge depth detection.
The initial average discharge capacity was about 200 mAh. In addition, as an evaluation of the charge / discharge curve at the time of open circuit, measurement was performed at 10 mA (0.05 C) where the contact resistance and the like were negligible and the current value was sufficiently small. The charge / discharge curve has no inflection region, and has a shape with an inclination over the entire area as disclosed in Patent Document 1.

[Production of lithium-ion secondary battery for non-charging depth detection]
LFP was used as the positive electrode active material. LFP was prepared using a hydrothermal synthesis method. Natural graphite was used as the negative electrode active material.

○ Battery electrode preparation / preparation of positive electrode Except that 85 g of LFP was used, it was prepared in the same manner as lithium ion secondary battery A for charge depth detection.

-Creation of negative electrode A battery equivalent to a battery for detecting the depth of charge was created.

○ Preparation of battery / prepared in the same manner as lithium-ion secondary battery A for charge depth detection.
The initial average discharge capacity was about 200 mAh. In addition, as an evaluation of the charge / discharge curve at the time of open circuit, measurement was performed at 10 mA (0.05 C) where the contact resistance and the like were negligible and the current value was sufficiently small. The inflection region did not appear in the charge / discharge curve. Table 1 shows the charging depth at which the inflection region of the created battery appears and the intermediate potential of the inflection region. As shown in Table 1, the inflection region does not appear in the lithium ion secondary battery for non-charging depth detection and D, whereas the inflection region can be developed at any charging depth in batteries A to C. I understood.

  Hereinafter, examples will be described in which each of the created batteries is connected in series to form a battery pack and actually charged and discharged.

(Example 2)
In Example 2, four non-charging depth detection lithium ion secondary batteries, a charging depth detection lithium ion secondary battery A, and a charging depth detection lithium ion secondary battery B, which are in the same state of charge, are connected in series. An assembled battery of 20V class lithium ion batteries was prepared.

  From about 5% charge state, charge at 200 mA (1C), and when the battery of the single lithium ion secondary battery A for charge depth detection reaches 3.6 V, the charge is terminated, and the assembled battery is made one by one again. Four batteries for non-charging depth detection were evaluated for their true state of charge with a charger / discharger. The charging depth was a little less than 38%, and the detection error of the charging depth was 1%.

  Similarly, when the true charge state of the four non-charging depth detection batteries when the lithium ion secondary battery B for detecting the charging depth of the assembled battery reaches 3.6 V, the charging depth is less than 12%. The detection error was 1%.

  Furthermore, when the same thing as 600mA (3C) charge, 1000mA (5C) charge, 200mA (1C) discharge, 600mA (3C) discharge, and 1000mA (5C) discharge was performed, it was as shown in Table 2. The results at the time of charging and discharging are shown only together because the absolute amounts are almost the same except for the sign of the detection error.

(Example 3)
In Example 3, nine lithium ion secondary batteries for non-charge depth detection, lithium ion secondary battery A for charge depth detection, lithium ion secondary battery B for charge depth detection, and lithium ion secondary battery for charge depth detection A 40V class assembled battery was prepared using C one by one. Similarly to Example 2, 1C charge / discharge, 3C charge / discharge, 5C charge / discharge, and when each charge depth detection lithium ion secondary battery reaches a predetermined voltage, a non-charge depth detection lithium ion secondary battery When the true charge / discharge state was evaluated and the detection error was calculated, it was as shown in Table 2.

Comparative example

(Comparative Example 1)
In Comparative Example 1, an assembled battery of a 20V class lithium ion battery was prepared using five lithium ion secondary batteries for non-charge depth detection and one lithium ion secondary battery D for charge depth detection. The open circuit voltage at which the state of charge obtained from the charge / discharge curve of the lithium ion secondary battery for detecting the charge depth was 12%, 38%, and 70% was obtained in advance and set as a predetermined voltage. In the same manner as in Example 2, the detection error from the true charge / discharge state for detecting the non-charge depth when the predetermined voltage is reached during charge / discharge of 1C, 3C, and 5C is as shown in Table 2. became. As shown in Table 2, the assembled batteries of Examples 2 and 3 had a detection error within 10% in all of 1C, 3C, and 5C, whereas the assembled battery of Comparative Example 1 was 10 under any conditions. It was a detection error exceeding%.

  The present invention provides an assembled battery and a power storage device of a lithium ion secondary battery that do not require a complicated determination circuit even during charging and discharging with a large current and can accurately evaluate the depth of charge, and an assembled battery of a lithium ion secondary battery Since it contributes to the manufacture and use of power storage devices, it has industrial applicability.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 12 Lithium ion secondary battery for non-charging depth detection 14 Lithium ion secondary battery for first charging depth detection 16 Lithium ion secondary battery for second charging depth detection 30 Voltage detection device and charge depth detection device 35 Voltage detection device and charge depth detection device 40 Storage device of lithium ion secondary battery 50 Lithium ion secondary battery 60 Positive electrode 61 Positive electrode mixture layer 62 Positive electrode current collector foil 70 Negative electrode 71 Negative electrode mixture Layer 72 Negative electrode current collector foil 90 Inflection region

Claims (14)

One or more lithium ion secondary batteries and two or more lithium ion secondary batteries for charge depth detection are connected in series,
Two or more lithium ion secondary batteries for detecting the charge depth have inflection regions where the voltage changes sharply in different charge depth regions. The lithium ion secondary battery for charge depth detection is used as a positive electrode or negative electrode active material, with respect to the charge depth,
(1) One active material in which the charge depth is 100%, and the state of charge is 95% to 100% at the charge depth,
(2) The discharge depth determined by this charge depth is set to 100% discharge capacity, and the discharge state is 95% to 100% at the discharge depth, and other active materials,
The assembled battery according to claim 1, wherein the batteries are mixed and used in at least one of a positive electrode and a negative electrode.   The assembled battery according to claim 1, wherein the amount of change in voltage in the inflection region is 100 mV or more.   The assembled battery according to claim 1, wherein the amount of change in voltage in the inflection region is 300 mV or more.   The lithium ion secondary battery for charge depth detection has a positive electrode in which a plurality of types of positive electrode active materials are mixed and / or a negative electrode in which a plurality of types of negative electrode active materials are mixed. Battery pack. Two or more lithium ion secondary batteries for charge depth detection have a positive electrode in which the same plural types of positive electrode active materials are mixed and / or a negative electrode in which the same plural types of negative electrode active materials are mixed,
The assembled battery according to claim 1, wherein a mixing ratio of the plurality of types of positive electrode active materials and / or a mixing ratio of the plurality of types of negative electrode active materials is different.   The plurality of types of positive electrode active materials and / or the plurality of types of negative electrode active materials use two types of positive electrode active materials and / or two types of negative electrode active materials. Battery pack. The lithium ion secondary battery for charge depth detection includes a positive electrode active material,
The positive electrode active material is a mixture of one or more low-voltage positive electrode active materials and one or more high-voltage positive electrode active materials as the plurality of types of positive electrode active materials,
The low-voltage positive electrode active material is at least one or more of positive electrode active materials having a potential near the upper limit of less than 3.5 V based on metallic lithium,
The high-voltage positive electrode active material is at least one or more of positive electrode active materials having a potential near a lower limit of 3.5 V or more with respect to metallic lithium as a reference. Assembled battery. The low-voltage positive electrode active material is at least one of LiTiO ₂ and LiFePO ₄ , and the high-voltage positive electrode active material is Li (Ni _1-xy Co _x Mn _y ) O ₂ (provided that 0. 1 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.5), Li _a (Ni _1- bc Co _b Al _c ) O 2 (where 0.9 ≦ a ≦ 1.3, 0 <b ≦ 0.5,0 <c ≦ _0.7), according to _{LiMn 2 O 4, LiVPO 4,} LiVOPO 4, LiCoO 2, LiMnPO 4, LiCoPO 4, claim 8 is at least one of LiNiPO ₄ Assembled battery. The low-voltage positive electrode active material is LiFePO _4, the high-voltage positive electrode active _material according to claim 9, wherein at least one of _{LiVPO 4, LiVOPO 4, LiCoO 2} , LiMnPO 4, LiCoPO 4, LiNiPO 4 Assembled battery. The lithium ion secondary battery for charge depth detection includes a negative electrode active material,
The negative electrode active material is a mixture of one or more low-voltage negative electrode active materials and one or more high-voltage negative electrode active materials as the plurality of types of negative electrode active materials,
The low-voltage negative electrode active material is at least one or more of negative electrode active materials having a potential near the upper limit of less than 0.5 V based on metallic lithium,
The assembled battery according to claim 5, wherein the high-voltage negative electrode active material is at least one of negative electrode active materials having a potential near a lower limit of 0.5 V or more with respect to metallic lithium. The low voltage negative electrode active material is graphite,
The assembled battery according to claim 11, wherein the high-voltage negative electrode active material is at least one of hard carbon and LiTiO ₂ . An assembled battery according to any one of claims 1 to 12,
A voltage detection device provided in parallel for each lithium ion secondary battery for at least charge depth detection;
A charge depth detection device configured by a logic circuit,
A power storage device including a charge depth detection device that determines a charge depth of an assembled battery based on a voltage value detected in the lithium ion secondary battery for charge depth detection. The charge depth detection voltage of the charge depth detection device is different between charging and discharging,
The charge depth detection voltage at the time of charging is a voltage within the inflection region and a voltage greater than the inflection region intermediate voltage,
The power storage device according to claim 13, wherein the charge depth detection voltage at the time of discharging is a voltage within the inflection region and is smaller than the inflection region intermediate voltage.

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