JP2019176637A - Charge control device, power storage device, charge control method for power storage element, and computer program - Google Patents

Abstract

To provide a charge control device with good life properties, which has good fast chargeability and in which heat generation with increased resistance is suppressed and precipitation of metal Li is not caused at a negative electrode, a power storage device, a charge control method for a power storage element, and a computer program.SOLUTION: A charge control device 4 includes: a CC charging unit 47 charging a power storage element at a constant current, the power storage element including a positive electrode material represented by Li(NiM')O(M' represents a metal element other than Li and Ni, and 0.5≤a≤1 and 0<x≤1.1 are satisfied); a first calculation unit 45 calculating an SOC; and a CV charging unit 48 charging at a constant voltage when the SOC is equal to or more than a threshold.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a charge control device that controls charging of a power storage element, a power storage device, a charge control method for a power storage element, and a computer program.

  Storage elements such as lithium ion secondary batteries have been used as power sources for mobile devices such as notebook computers, mobile phones, and shavers. In recent years, it has been used in a wide range of fields such as EV (electric vehicle), HEV (hybrid electric vehicle), and PHEV (plug-in hybrid electric vehicle) power supplies, and further higher energy density is required.

Conventionally, a layered rock-salt type lithium transition metal oxide (hereinafter referred to as a layered oxide) has been used as a positive electrode active material, and a composition has been studied in order to realize a high energy density of a power storage device. That is, the amount of Li extracted until the charge upper limit voltage is reached is increased to increase the charge capacity. Of layered oxide, for example, in the case of NCM represented by _{Li x (Ni a Co b Mn} c) O 2 (a + b + c = 1,0 <x ≦ 1.1), by increasing the content of Ni, the power storage Without increasing the upper limit charging voltage of the device, the amount of Li extracted is increased to increase the capacity.
However, a storage element using a layered oxide with a large amount of Li extracted tends to increase the resistance of the storage element due to the positive electrode on the low SOC (State of Charge) side and the high SOC side.

  In recent years, there has been a demand for improvement in rapid chargeability (charge acceptability) of power storage elements. Examples of the charging method include CC-CV (Constant Current-Constant Voltage) charging (for example, Patent Document 1), multi-stage CC charging (for example, Patent Document 2), and the like. In CC-CV charging, after performing constant current charging in which charging is performed at a constant current, constant voltage charging is performed in which the charging current is gradually decreased so that the terminal voltage maintains a value near the charging upper limit voltage. In multi-stage CC (Constant Current) charging, after charging to a specified charging voltage with a constant current, CC charging is performed with the charging current reduced stepwise.

Japanese Patent Laid-Open No. 5-111184 Japanese Patent Application Laid-Open No. 7-296853

  When the above layered oxide is used as the positive electrode active material and the CC charge including the multi-stage CC charge of Patent Document 2 is performed, the resistance increases on the high SOC side, so that the second stage charging current is set small. Takes a long time to charge, and quick chargeability deteriorates. In addition, when the current is increased to shorten the charging time, the storage element deteriorates due to a rise in temperature of the storage element due to an increase in resistance or the deposition of metallic Li in the negative electrode, resulting in poor life characteristics. There is.

  The present invention provides a charge control device, a power storage device, and a charge control of a power storage element that have good quick chargeability, suppress heat generation due to an increase in resistance, do not cause deposition of metallic Li in the negative electrode, and have good life characteristics It is an object to provide a method and a computer program.

The charge control device according to the present invention is Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, A CC charging unit that charges a power storage element having a positive electrode active material represented by 0 ≦ c <1, a + b + c + d = 1, 0 <x ≦ 1.1, and a and c are not 0 at the same time with a constant current; A first calculation unit for calculating an SOC, and a CV for charging at a constant voltage when the SOC is equal to or greater than a threshold value set based on an SOC value when the positive electrode resistance is equal to or greater than a predetermined value. And a charging unit.

  In the present invention, when the SOC becomes equal to or higher than the threshold value during CC charging, switching to CV charging is performed before reaching the charging upper limit voltage, so that the charging time can be shortened and the quick chargeability is good. . Further, by making the current of CC charging smaller than that of CV charging, it is possible to avoid the temperature rise of the power storage element due to the charging so far, and during CV charging, the current gradually decreases and the heat generation becomes slow. Therefore, the deterioration of the power storage element is suppressed. In addition, since the current at the end of charging gradually decreases, no metal Li is deposited in the negative electrode, and the life characteristics are good.

It is an equivalent circuit schematic of the electrical storage element in charge. It is a graph which shows the relationship between the positive electrode of an electrical storage element, a negative electrode, and a terminal voltage. It is a block diagram which shows the structure of the vehicle and server which concern on 1st Embodiment. It is a perspective view of a battery module. It is a block diagram which shows the structure of BMU. It is an example of the graph which shows the relationship between SOC and resistance. Is a graph showing the relationship between the resistance and the li _x MeO ₂ of x. FIG. 8A is a graph showing the relationship between SOC and voltage during charging, FIG. 8B is a graph showing the relationship between SOC and current, and FIG. 8C is a graph showing the relationship between SOC and heat generation. It is a flowchart which shows the procedure of the update process of the battery capacity of a control part. It is a flowchart which shows the procedure of the charge control process of a control part. FIG. 11A is a graph showing the relationship between the SOC and the voltage when the charge control process of the first modification is performed, and FIG. 11B is a graph showing the relationship between the SOC and the current. FIG. 12A is a graph showing the relationship between the SOC and the voltage when the charge control process of the second modification is performed, and FIG. 12B is a graph showing the relationship between the SOC and the current. FIG. 13A is a graph showing the relationship between the SOC and the voltage when the charge control process of the third modification is performed, and FIG. 13B is a graph showing the relationship between the SOC and the current.

  Hereinafter, the present invention will be specifically described with reference to the drawings illustrating embodiments thereof.

(Outline of this embodiment)
The charge control device according to the present embodiment includes Li _x Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, A CC charging unit that charges a power storage element having a positive electrode active material represented by 0 <c <1, a + b + c + d = 1, 0 <x ≦ 1.1, and a and c are not 0 at the same time with a constant current; A first calculation unit for calculating an SOC, and a CV for charging at a constant voltage when the SOC is equal to or greater than a threshold value set based on an SOC value when the positive electrode resistance is equal to or greater than a predetermined value. A charging unit.

FIG. 1 is an equivalent circuit diagram of a storage element (battery) during charging, and FIG. 2 is a graph showing the relationship between the positive electrode, negative electrode, and terminal voltage of the storage element (battery).
1 and 2,
V: charger voltage,
V ₀ : Battery electromotive force (OCV)
R _p : positive electrode resistance R _n : negative electrode resistance η _p : positive electrode overvoltage η _n : negative electrode overvoltage I: current.
According to Kirchhoff's law, V−V ₀ = IR _p + IR _n always holds.

(1) In the case of CC charging: I = I ₁ and constant. At this time, the overvoltages of the positive electrode and the negative electrode are respectively η _p = I ₁ R _p ,
η _n = I ₁ R _n , which increases in proportion to the resistance.

(2) In the case of CV charging: V = V ₁ and constant. At this time, since V ₁ −V ₀ = IR _p + IR _n , I = (V ₁ −V ₀ ) / (R _p + R _n ).
η _p = (V ₁ −V ₀ ) × R _p / (R _p + R _n ),
η _n = (V ₁ −V ₀ ) × R _n / (R _p + R _n ). That is, the overvoltage η _n of the negative electrode depends on the magnitudes of both R _p and R _n .

It is assumed that the open circuit potential E _n0 (V vs. Li ^/ Li ⁺ ) of the negative electrode at the end of charging is constant. In the case of a graphite negative electrode, _{En 0} is approximately 0.1V. When the negative electrode potential, that is, (E _n0 −η _n ) is less than 0, metal Li begins to precipitate.

In the case of a conventional lithium ion secondary battery, the resistance of the positive electrode and the resistance of the negative electrode are almost the same. When CV charging is performed on this battery, as described above, the positive overvoltage η _p and the negative overvoltage η _n are applied according to the magnitude of the resistance. Therefore, when switching from a voltage lower than the charging upper limit voltage (hereinafter referred to as the upper limit voltage) to CV charging, an excessive overvoltage η _n is applied to the negative electrode, and the negative electrode potential (E _n0 −η _n ) is 0 V on the basis of Li. The metal Li is deposited. Therefore, conventionally, after CC charging up to the upper limit voltage, CV charging is performed at the upper limit voltage.

Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1, a + b + c + d = 1 , 0 <x ≦ 1.1, and a and c are not 0 at the same time), when the positive electrode active material is used, considering the composition, charging at the same charging upper limit voltage The amount of Li extracted can be increased and the charging capacity can be increased. At the end of charging when a large amount of Li is extracted, the Li concentration inside the positive electrode active material decreases and only the positive electrode resistance R _p increases.

At the end of charging, the negative electrode resistance R _n is smaller than the positive electrode resistance R _p . Even if switching to CV charging before reaching the upper limit voltage, coupled with the current gradually decreasing at the end of charging, the negative overvoltage η _n is small and the negative electrode potential (E _n0 −η _n ) is less than 0 Absent.
Therefore, when the SOC exceeds a threshold value set based on the SOC value when the resistance of the positive electrode exceeds a predetermined value, switching to CV charging can be performed, and the total charging time can be shortened. That is, quick chargeability is good.
By making the current of CC charging smaller than that of CV charging, the temperature of the power storage element due to the charging up to that time is avoided, and at the time of CV charging, the current gradually decreases and the heat generation becomes gentle. Deterioration of the power storage element is suppressed. In addition, as described above, since the negative electrode potential does not fall below 0, the deposition of metal Li does not occur and the life characteristics are good.

The charge control device according to the present embodiment includes Li _x (Ni _a M ′ _1-a ) O ₂ (M ′ is a metal element other than Li and Ni, 0.5 ≦ a ≦ 1, 0 <x ≦ 1.1). The CC charging unit that charges the storage element having the positive electrode active material represented by a constant current, a first calculation unit that calculates the SOC, and a constant voltage when the SOC exceeds a threshold value. A CV charging unit that performs charging.

The positive electrode active material having the above composition formula, where 0.5 ≦ a and the Ni content ratio is high, the amount of Li extracted when charged to the same upper limit voltage as compared with the positive electrode active material having a low Ni content ratio Is big. That is, at the end of charging, the Li concentration inside the positive electrode active material decreases and the positive electrode resistance _Rp increases.
Even when switching to CV charging when the upper limit voltage has not been reached, the negative electrode resistance R _n is small, and coupled with the gradual decrease in current at the end of charging, the negative electrode overvoltage η _n is small. Therefore, the negative electrode potential (E _n0 −η _n ) never falls below zero.
According to the above configuration, the SOC is equal to or higher than the threshold value, and switching to CV charging is performed before reaching the upper limit voltage. Therefore, the total charging time can be shortened, and quick chargeability is good.
The temperature rise of the power storage element during CC charging is limited, and the current gradually decreases during CV charging, so that the temperature rise of the power storage element due to the increase in resistance is suppressed, and the deterioration of the power storage element is suppressed. Is done. In addition, since the negative electrode potential never falls below 0, the deposition of metal Li does not occur and the life characteristics are good.

  In the charge control device according to the present embodiment, the threshold is set based on the SOC value when the resistance of the positive electrode is equal to or higher than a predetermined value.

  According to the above configuration, since the resistance is increased and switching to CV charging is performed when time is required for charging, the charging time can be effectively shortened and deterioration of the power storage element due to heat generation can be suppressed.

  In the charge control device according to the present embodiment, the CV charging unit performs charging at a voltage that is increased in one or more stages than the voltage when the SOC is equal to or higher than the threshold value.

  According to the above configuration, the charging time can be shortened and a sufficient amount of charged electricity can be obtained.

  In the charging control device according to the present embodiment, the CC charging unit continues charging at a current lower than the constant current when the SOC is equal to or higher than a first threshold, and the CV charging unit Is charged at a constant voltage when becomes equal to or greater than the second threshold. In the present invention, the voltage is made substantially constant within the range where the effects of the present invention are achieved. That is, charging may be performed with a voltage within a predetermined range when the SOC becomes equal to or higher than the second threshold. It is desirable to match the value of the constant voltage with the charge upper limit voltage of the battery.

  According to the above configuration, heat generation is suppressed.

  In the charge control device according to the present embodiment, when the SOC becomes equal to or higher than the threshold, the CV charging unit performs charging after the CC charging unit continues charging with a current higher than the constant current.

  According to the above configuration, the CC charging time can be shortened.

  The charge control device according to the present embodiment includes a first acquisition unit that acquires the current of the power storage element, a second acquisition unit that acquires the voltage of the power storage element, the current, the voltage, and the SOC-OCV characteristics. And a second calculator that calculates a capacity of the power storage element based on the first calculator. The first calculator calculates the SOC based on the capacity.

  According to the above configuration, the capacity of the power storage element is updated over time, so that the SOC is favorably calculated.

  The power storage device according to this embodiment includes the power storage element and any one of the above-described charge control devices.

  According to the said structure, quick charge property and a lifetime characteristic are favorable.

The charge control method for the electricity storage device according to this embodiment is Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1, a + b + c + d = 1, 0 <x ≦ 1.1, and a and c are not 0 at the same time) to charge a storage element having a positive electrode active material with a constant current, The SOC is calculated, and charging is performed at a constant voltage when the SOC is equal to or greater than a threshold value set based on the SOC value when the positive electrode resistance is equal to or greater than a predetermined value.

  According to the above configuration, the charging time can be shortened and the quick chargeability is good. By making the current of CC charging smaller than that of CV charging, avoiding the temperature rise of the electricity storage element due to the charging so far, and at the time of CV charging, the current gradually decreases and the heat generation becomes gentle, Deterioration of the power storage element is suppressed. In addition, since the current gradually decreases at the end of charging and only the resistance of the positive electrode increases at the end of charging, the negative overvoltage does not increase, the deposition of metallic Li does not occur in the negative electrode, and the life characteristics are good. .

The computer program according to the present embodiment causes _a computer to store Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b. <1, 0 ≦ c <1, a + b + c + d = 1, 0 <x ≦ 1.1, and a and c are not 0 at the same time). When the SOC becomes equal to or higher than a threshold value set based on the SOC value when the positive electrode resistance becomes equal to or higher than a predetermined value, a process of charging at a constant voltage is executed.

  According to the above configuration, the charging time can be shortened and the quick chargeability is good. By making the current of CC charging smaller than that of CV charging, avoiding the temperature rise of the electricity storage element due to the charging so far, and at the time of CV charging, the current gradually decreases and the heat generation becomes gentle, Deterioration of the power storage element is suppressed. In addition, since the current gradually decreases at the end of charging and only the resistance of the positive electrode increases, the overvoltage of the negative electrode does not increase, and no metal Li precipitates in the negative electrode, and the life characteristics are good.

(First embodiment)
Hereinafter, although the case where an electrical storage element is a lithium ion secondary battery used for motor vehicles is demonstrated, an electrical storage element is not limited to the lithium ion secondary battery of such a use.
FIG. 3 is a block diagram illustrating configurations of the vehicle 1 and the server 12 according to the first embodiment.
The vehicle 1 includes a storage element module (hereinafter referred to as a battery module) 3, a BMU (Battery Management Unit) 4, a load 5, a general ECU 6, a communication unit 7, a voltage sensor 8, and a current sensor 9. .
In the battery module 3, lithium ion secondary batteries (hereinafter referred to as batteries) 2 as a plurality of power storage elements are connected in series. The overall ECU 6 controls the entire power supply device of the vehicle 1. The overall ECU 6 also controls the engine when the vehicle 1 is an HEV vehicle or a gasoline vehicle.
The server 12 includes a communication unit 13 and a control unit 14.
The overall ECU 6 is connected to the control unit 14 via the communication unit 7, the network 11, and the communication unit 13. The overall ECU 6 transmits and receives data to and from the control unit 14 via the network 11.
In the present embodiment, any of the BMU 4, the overall ECU 6, and the control unit 14 functions as the charge control device of the present invention. Any of the BMU 4, the overall ECU 6, and the control unit 15 and the battery module 3 function as the power storage device of the present invention. In addition, when the control part 14 does not function as the said charge control apparatus, the vehicle 1 does not need to be connected to the server 12. FIG.
A plurality of battery modules 3 may be provided.
The BMU 4 may be a battery ECU.

The voltage sensor 8 is connected in parallel to the battery module 3 and outputs a detection result corresponding to the overall voltage of the battery module 3. The voltage sensor 8 is connected to terminals 23 and 23 to be described later of each battery 2, measures the terminal voltage V ₁ of each battery 2, and is a total value of V ₁ of each battery 2, which will be described later. The voltage V between the leads 33 and 33 to be detected is detected.
The current sensor 9 is connected in series with the battery module 3 and detects a current flowing through the battery module 3.

FIG. 4 is a perspective view of the battery module 3.
The battery module 3 includes a rectangular parallelepiped case 31 and a plurality of the batteries 2 accommodated in the case 31.

The battery 2 includes a rectangular parallelepiped case main body 21, a cover plate 22, a pair of terminals 23 and 23 provided on the cover plate 22 and having different polarities, a rupture valve 24, and an electrode body 25. The electrode body 25 is formed by laminating a positive electrode plate, a separator, and a negative electrode plate, and is accommodated in the case body 21.
The electrode body 25 may be obtained by winding a positive electrode plate and a negative electrode plate in a flat shape via a separator.

The positive electrode plate is obtained by forming a positive electrode active material layer on a positive electrode substrate foil that is a plate-like (sheet-like) or long strip-like metal foil made of aluminum, an aluminum alloy, or the like. The negative electrode plate is obtained by forming a negative electrode active material layer on a negative electrode substrate foil that is a plate-like (sheet-like) or long strip-like metal foil made of copper, a copper alloy, or the like. The separator is a microporous sheet made of a synthetic resin.
As a positive electrode active material used for the positive electrode active material layer, Li _x (Ni _a M ′ _1-a ) O ₂ (M ′ is a metal element other than Li and Ni, 0.5 ≦ a ≦ 1, 0 <x ≦ 1) The case where the layered oxide represented by .1) is used will be described. The positive electrode active material has a layered rock salt type crystal structure and contains a large amount of Ni at the transition metal site. For this reason, the resistance of the positive electrode is increased in the high SOC region.
The positive electrode active material is preferably NCM in which M ′ is Co or Mn and is represented by Li _x (Ni _a Co _b Mn _c ) O ₂ (a + b + c = 1, a ≧ 0.5, b ≧ 0). , C ≧ 0, 0 <x <1.1). a is more preferably 0.6 or more, and further preferably 0.8 or more.
The positive electrode active material may be NCA in which M ′ is Co and Al and is represented by Li _x (Ni _a Co _b Al _d ) O ₂ (a + b + c = 1, a ≧ 0.5, b ≧ 0). , C ≧ 0, 0 <x <1.1).
Note that M ′ is not limited to being made of two kinds of metals, and may be made of three or more kinds of metals. For example, a small amount of Ti, Nb, B, W, Zr, Ti, Mg, etc. may be included.

  Examples of the negative electrode active material used for the negative electrode active material layer include carbon materials such as graphite and amorphous carbon (non-graphitizable carbon and graphitizable carbon), or silicon monoxide (SiO), silicon (Si), and tin. It is a material that causes an alloying reaction with lithium ions, such as (Sn).

Adjacent terminals 23 of adjacent batteries 2 of the battery module 3 have different polarities, and the terminals 23 are electrically connected to each other by a bus bar 32, whereby a plurality of batteries 2 are connected in series.
Leads 33 and 33 for taking out electric power are provided at terminals 23 and 23 having opposite polarities of the battery 2 at both ends of the battery module 3.

  FIG. 5 is a block diagram showing a configuration of the BMU 4. The BMU 4 includes a control unit 41, a storage unit 49, an input unit 52, and an interface unit 53. These units are connected to each other via a bus so as to communicate with each other.

  The input unit 52 receives input of detection results from the voltage sensor 8 and the current sensor 9. The interface unit 53 includes, for example, a LAN interface and a USB interface, and communicates with other devices such as the overall ECU 6 by wire or wireless.

The storage unit 49 is configured by a hard disk drive (HDD), for example, and stores various programs and data. The storage unit 49 stores, for example, a charge control program 50 for executing a charge control process described later. The charging control program 50 is provided in a state stored in a computer-readable recording medium 60 such as a CD-ROM, DVD-ROM, or USB memory, and is stored in the storage unit 49 by being installed in the BMU 4. Alternatively, the charging control program 50 may be acquired from an external computer (not shown) connected to the communication network and stored in the storage unit 49.
The storage unit 49 also stores SOC-OCV data (SOC-OCV characteristics) 51 obtained in advance by experiments. This data may be updated by a regular method as appropriate.

  The control unit 41 includes, for example, a CPU, a ROM, a RAM, and the like, and controls the operation of the BMU 4 by executing a computer program such as the charging control program 50 read from the storage unit 49. For example, the control unit 41 functions as a processing unit that executes a charge control process described later by reading and executing the charge control program 50.

  Specifically, the control unit 41 includes a voltage acquisition unit 42, a current acquisition unit 43, a battery capacity calculation unit 44, an SOC calculation unit 45, a determination unit 46, a CC charging unit 47, and a CV charging unit 48.

Hereinafter, the charge control process according to the present embodiment will be described in detail. The case where the battery module 3 is used as one power storage element and the charging of the battery module 3 is controlled will be described.
The control unit 41 of the BMU 4 performs CC charging on the battery module 3 with a constant current, calculates the SOC, and performs CV charging with a constant voltage when the SOC exceeds a threshold value.
The threshold value is set based on the SOC value when the resistance of the positive electrode is equal to or greater than a predetermined value.

FIG. 6 is an example of a graph showing the relationship between SOC and positive electrode resistance. The horizontal axis of FIG. 6 is SOC (%), and the vertical axis is resistance (Ω). The positive electrode active material is NCM811, and the molar ratio of Ni, Co, and Mn is 8: 1: 1. As shown in FIG. 6, the resistance is high on the low SOC side and on the high SOC side.
As shown in FIG. 6, since the resistance starts to increase when the SOC reaches 80%, the threshold can be set to 80%. The threshold can be 85% or 90%.

FIG. 7 shows the quantity of electricity based on the SOC and the theoretical capacity of FIG. 6, and _x when Li _x MeO ₂ (Me is a molar ratio of Ni, Co, and Mn is 8: 1: 1) is obtained. It is a graph which shows the relationship with resistance. The horizontal axis is x, and the vertical axis is resistance (Ω). Since resistance increases rapidly when x is 0.25 or less, it can be seen that by performing the charging control process according to the present embodiment, the charging time can be effectively shortened and heat generation can be suppressed. .

The voltage acquisition unit 42 of the control unit 41 acquires the voltage V between the leads 33 and 33 of the battery module 3 from the voltage sensor 8 during charging.
The current acquisition unit 43 acquires the current I from the current sensor 9 during charging.

The battery capacity calculation unit 44 acquires the voltage V before and after the start of charging from the voltage acquisition unit 42. The battery capacity calculation unit 44 acquires the current I from the current acquisition unit 43 and calculates the amount of electricity q by integrating the energized current over time.
The battery capacity calculation unit 44 sets the difference between the voltages V before and after the start of charging as ΔOCV which is the difference in OCV, and obtains ΔSOC corresponding to ΔOCV with reference to the SOC-OCV data 54. The battery capacity calculation unit 44 performs current integration for a time corresponding to ΔSOC to obtain Δq. The battery capacity calculation unit 44 calculates the battery capacity based on ΔSOC and Δq. The battery capacity calculation method is not limited to this case.
The SOC calculation unit 45 acquires the current I from the current acquisition unit 43 at a predetermined interval or an arbitrary interval, obtains the electric quantity q by time-integrating the energization current, and divides the electric quantity q by the battery capacity to obtain the SOC. Is calculated.

The determination unit 46 determines whether the SOC is equal to or greater than a threshold value. The threshold value is set based on the SOC value when the resistance of the positive electrode becomes equal to or higher than a predetermined value with reference to the relationship between the resistance and the SOC described above.
When the determination unit 46 determines that the SOC is not equal to or greater than the threshold value, the CC charging unit 47 performs charging with a constant current.

  When the determination unit 46 determines that the SOC is equal to or greater than the threshold value, the CV charging unit 48 performs CV charging at a constant voltage. It is preferable that the CV charging unit 48 performs CV charging with a voltage that is larger in one or more steps than the voltage when the SOC becomes equal to or higher than the threshold value.

As described above, the positive electrode having a layered oxide with a large amount of extracted Li as the positive electrode active material has a high positive electrode resistance at the end of charging.
When CV charging is performed on a power storage element having this positive electrode, only the resistance of the positive electrode increases at the end of charging. When switching to CV charging when the SOC exceeds the threshold before reaching the upper limit voltage, the resistance of the negative electrode is smaller than the resistance of the positive electrode, so the current may gradually decrease at the end of charging. The overvoltage η _n is small. Therefore, no deposition of metal Li occurs on the negative electrode side. Although the total charging time is shortened, since the current is kept small in the charging up to that time, the temperature rise of the power storage element is limited, and the deterioration due to the temperature rise of the power storage element at the end of charging is suppressed.

FIG. 8A is a graph showing the relationship between SOC and voltage during charging, FIG. 8B is a graph showing the relationship between SOC and current, and FIG. 8C is a graph showing the relationship between SOC and heat generation. The horizontal axis of FIG. 8A is SOC (%), and the vertical axis is voltage (V). The horizontal axis of FIG. 8B is SOC (%), and the vertical axis is current (mA). The horizontal axis of FIG. 8C is SOC (%), and the vertical axis is the calorific value (j). Here, it is assumed that the resistance of the positive electrode increases when the SOC reaches 80%.
When the SOC reaches 80%, the current is increased at once and the voltage is increased to the upper limit voltage. The voltage may be a value smaller than the upper limit voltage or a larger value. The voltage is made higher than the voltage when the SOC reaches 80%. When the voltage is set higher than the upper limit voltage, the CV charging time is specified. Alternatively, current integration is performed so that the amount of charged electricity does not exceed a predetermined value.
Since the current until the SOC reaches 80% is small as shown in FIG. 8B, the heat generation amount is small as shown in FIG. 8C. Since the heat is dissipated, the amount of heat storage is small, and the temperature rise of the storage element at the time of switching to CV charging is limited. Thereafter, the calorific value decreases.

Hereinafter, the charge control process will be described as the process of the control unit 41.
First, the battery capacity update process will be described. FIG. 9 is a flowchart illustrating the procedure of the battery capacity update process of the control unit 41.
The control unit 41 performs a battery capacity update process at a predetermined interval or an arbitrary interval. The control unit 41 performs a battery capacity update process when charging is started in a state where there is no load and the open-circuit voltage is stable.

The control unit 41 acquires the voltage V before and after charging from the voltage sensor 8 and acquires the current I from the current sensor 9 (S1).
The control unit 41 refers to the SOC-OCV data 51 and reads ΔSOC corresponding to the difference (ΔOCV) between the voltages V before and after the start of charging. The control unit 41 calculates Δq by integrating the energized current for the time Δt corresponding to ΔSOC. The control unit 41 calculates the battery capacity based on Δq and ΔSOC (S2).
The control unit 41 stores the battery capacity in the storage unit 49, and the battery capacity is updated (S3).

Hereinafter, the charge control process will be described.
FIG. 10 is a flowchart showing the procedure of the charging control process of the control unit 41.
The control unit 41 performs CC charging with a constant current I (S11).
The control unit 41 acquires the current I from the current sensor 9 at a predetermined interval or an optional interval (S12).
The control unit 41 calculates the SOC by calculating the amount of electricity by time-integrating the current and dividing this by the battery capacity read from the storage unit 49 (S13).

The control unit 41 determines whether or not the SOC is greater than or equal to a threshold value (S14).
When it is determined that the SOC is not equal to or greater than the threshold (S14: NO), the control unit 41 returns the process to S11.
When it is determined that the SOC is equal to or higher than the threshold value (S14: YES), the control unit 41 increases the current so as to reach a predetermined voltage and performs CV charging with the voltage (S15).
For example, in the case of FIG. 6 and FIG. 7, when the voltage V of the battery module 3 is 4.15V when the SOC reaches 80%, the voltage is increased to 4.35V to perform CV charging, and the charge control processing Exit.

In this embodiment, before reaching the upper limit voltage, the resistance is increased and switching to CV charging is performed when charging takes time, so that it is avoided that CC charging is continued and charging takes a long time. Thus, the charging time can be shortened and the quick chargeability is good.
The temperature rise of the battery module 3 in CC charging is limited, and in CV charging, the current gradually decreases, so that the temperature rise of the battery module 3 due to the increase in resistance is suppressed, and the battery module 3 Deterioration is suppressed. In addition, since the negative electrode potential never falls below 0, the deposition of metal Li does not occur and the life characteristics are good.

[Modification 1]
In the first modification, the first threshold value and the second threshold value are set as the SOC threshold values (first threshold value <second threshold value), and when the determination unit 46 determines that the SOC is equal to or higher than the first threshold value, the CC charging unit 47 reduces the current and continues CC charging. When the determination unit 46 determines that the SOC is equal to or higher than the second threshold, the CV charging unit 48 increases the current to increase the voltage, and performs CV charging.
FIG. 11A is a graph showing the relationship between the SOC and the voltage when the charge control process of the first modification is performed, and FIG. 11B is a graph showing the relationship between the SOC and the current. In FIG. 11A, the horizontal axis represents SOC (%), and the vertical axis represents voltage (V). In FIG. 11B, the horizontal axis represents SOC (%), and the vertical axis represents current (mA). Here, it is assumed that the resistance of the positive electrode increases when the SOC reaches 80%, and further increases when the SOC reaches 90%.
When the SOC reaches 80%, the charging is continued by reducing the CC charging current. When the SOC reaches 90%, the current is increased and the voltage is increased to a value near the upper limit voltage to perform CV charging.
Note that CC charging is not limited to being performed in one stage, and may be performed in two or more stages.

[Modification 2]
In the second modification, the first threshold value and the second threshold value are set as the SOC threshold values (first threshold value <second threshold value), and CV charging is performed in a plurality of stages.
FIG. 12A is a graph showing the relationship between the SOC and the voltage when the charge control process of the second modification is performed, and FIG. 12B is a graph showing the relationship between the SOC and the current. The horizontal axis of FIG. 12A is SOC (%), and the vertical axis is voltage (V). The horizontal axis of FIG. 12B is SOC (%), and the vertical axis is current (mA). Here, it is assumed that the resistance of the positive electrode increases when the SOC reaches 80%, and further increases when the SOC reaches 90%.
When the SOC reaches 80%, the current is increased to increase the voltage, and switching to CV charging is performed for charging. When the SOC reaches 90%, the current is further increased to a value near the upper limit voltage for CV charging. Continue.
CV charging is not limited to being performed in two stages, and may be performed in three or more stages.

[Modification 3]
In the modification 3, when the S determination part 46 determines with SOC being more than a threshold value, the CC charge part 47 raises an electric current and continues CC charge. When the determination unit 46 determines to switch to CV charging, the CV charging unit 48 performs CV charging. The determination unit 46 determines, for example, whether or not the voltage is equal to or higher than a threshold value or whether or not the SOC is equal to or higher than a second threshold value.
FIG. 13A is a graph showing the relationship between the SOC and the voltage when the charge control process of the third modification is performed, and FIG. 13B is a graph showing the relationship between the SOC and the current. In FIG. 13A, the horizontal axis represents SOC (%), and the vertical axis represents voltage (V). In FIG. 13B, the horizontal axis represents SOC (%), and the vertical axis represents current (mA). Here, it is assumed that the resistance of the positive electrode increases when the SOC reaches 80%.
When the SOC reaches 80%, the CC charging current is increased to continue charging. When the voltage exceeds the threshold value, CV charging is performed.
Note that CC charging is not limited to being performed in one stage, and may be performed in two or more stages.

Examples of the present embodiment will be specifically described below, but the present embodiment is not limited to these examples. As shown below, Examples 1 to 4 and Comparative Example were charged, and quick chargeability and life characteristics were evaluated.
The quick chargeability was evaluated based on the length of time required for charging and the amount of charged electricity.
The life characteristics were evaluated based on whether or not the metal Li was deposited on the negative electrode and the life was reduced.

[Example 1]
As the positive electrode active material, NCM811 (Ni: Co: Mn (molar ratio) of the NCM is 8: 1: 1) was used. CC charging was performed at 1C, and switching to CV charging was performed when the SOC reached 80%.
In Example 1, the charging time was the shortest, the amount of charge was sufficient, and the quick chargeability was the best. No metal Li is deposited on the negative electrode, and the life characteristics are good.

[Example 2]
NCM811 was used as the positive electrode active material. CC charging was performed at 1C, and when the SOC reached 80%, switching to 0.2C was continued and CC charging was continued, and when the SOC reached 90%, switching to CV charging was performed.
Although charging time became longer than Example 1, it has improved greatly compared with the comparative example mentioned later. No metal Li is deposited on the negative electrode, and the life characteristics are good.

[Example 3]
NCM811 was used as the positive electrode active material. CC charging was performed at 1C, and switching to CV charging was performed when the SOC reached 90%.
Although charging time became longer than Example 1, it has improved greatly compared with the comparative example. No metal Li is deposited on the negative electrode, and the life characteristics are good.

[Example 4]
NCM901005 (Ni: Co: Mn (molar ratio) of the NCM is 90: 10: 5) was used as the positive electrode active material. CC charging was performed at 1C, and switching to CV charging was performed when the SOC reached 80%.
Although charging time became longer than Example 1, it has improved greatly compared with the comparative example. No metal Li is deposited on the negative electrode, and the life characteristics are good.

[Comparative Example 1] (When CC charge is performed with current I _const up to upper limit voltage V _max )
From Kirchhoff's law, V−V ₀ = I _const (R _p + R _n ).
Further, the electromotive force V ₀ (OCV) of the battery is a function of the SOC, and the higher the SOC, the larger the V ₀ .
Since charging is terminated at V = V _max , V ₀ = V _max −I _const (R _p + R _n ).
That more R _p or R _n is large, also, the larger Iconst, V ₀ decreases.
Therefore, charging is completed before the SOC is sufficiently increased, and a sufficient amount of charged electricity cannot be obtained.
When multistage charging is performed, it takes time to complete charging.

[Comparative Example 2] (Normal CC-CV charging)
CC charging is performed with current I _const up to upper limit voltage V _max , and CV charging is performed with V = V _max . At this time, I = (V _max −V ₀ ) / (R _p + R _n ). If the charging is continued, the SOC increases, so V _max gradually approaches V ₀ , and the charging is terminated when the charging end current I _cut or less. However, since V ₀ = V _max −I _cut (R _p + R _n ) at the end of charging, V ₀ decreases as R _p or R _n increases. That is, it cannot be charged to obtain a sufficient amount of electricity. Set small I _cut, if you choose to charge to the same SOC, as R _p or R _n is large, the I is reduced, the time to completion of charging becomes longer.

[Comparative Example 3] (CC-CV charging when charging current is increased)
When charging is performed until the inter-terminal voltage reaches V _max with a large current I _A , switching to CV charging is performed with a relatively low SOC. Therefore, it becomes possible to charge in a relatively short time. However, the power P consumed as heat in CC charging is P = I _A ² · R, and increases in proportion to the square of the current. On the other hand, since heat dissipation of the battery only occurs gradually in proportion to the difference between the battery surface temperature and the environmental temperature, the battery temperature rises significantly during CC charging, and the deterioration of the battery is accelerated.

[Comparative Example 4] (if charging has exceeded the upper limit voltage V _max)
At the time of charging, it is very difficult to control the current so that E _n0 −η _n <0 is not satisfied only by the voltage V between the battery terminals, the energizing current I, and the energizing time t that can be detected by the charger. It is difficult to avoid precipitation. Even if the precipitation of the metal Li can be avoided, the electric power P consumed as heat is P = I ² (R _p + R _n ), and the calorific value Q is Q = ∫P · dt. When NCM containing a large amount of Ni is used as the positive electrode active material, R _p increases at the end of charging, and the battery deteriorates.

In the case of the above-described embodiment, since R _n is small as compared with R _p , η _n is small, metal Li is not easily precipitated, and I during CV charging is moderately suppressed, so that heating of the battery Deterioration due to is difficult to occur.

  From the above, according to the charge control method of the present embodiment, it was confirmed that the quick chargeability was good. Moreover, since the rise of the battery temperature at the time of charge was suppressed, it was confirmed that battery deterioration due to temperature could be suppressed, metal Li was not deposited on the negative electrode, and the battery module 3 had good life characteristics.

  The present invention is not limited to the contents of the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

The power storage element according to the present invention is not limited to being mounted on a vehicle, but can be applied to other power storage devices such as a railway regenerative power storage device and a solar power generation system. The charge control device according to the present invention can also be applied to mobile devices such as notebook computers, mobile phones, and shavers.
And an electrical storage element is not limited to a lithium ion secondary battery. The storage element may be another secondary battery, a primary battery, or an electrochemical cell such as a capacitor.

  In the first embodiment, the case where the SOC-OCV data 51 is acquired and the charging of the battery module 3 is controlled using the battery module 3 as one power storage element is described, but the present invention is not limited to this. The SOC-OCV data 51 may be acquired for each battery 2 and the charging of the battery 2 may be controlled separately.

In the first embodiment, as the layered oxide, Li _x (Ni _a M ′ _1-a ) O ₂ (M ′ is a metal element other than Li and Ni, 0.5 ≦ a ≦ 1, 0 <x Although the case of using one represented by ≦ 1.1) is described, the present invention is not limited to this. Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1, a + b + c + d = 1 , 0 <x ≦ 1.1, and a and c are not 0 at the same time.

1 vehicle 2 battery (storage element)
3 Battery module (storage element)
4 BMU (Charge Control Device)
41 control unit 42 voltage acquisition unit (second acquisition unit)
43 Current acquisition unit (first acquisition unit)
44 Battery capacity calculation unit (second calculation unit)
45 SOC calculator (first calculator)
46 Determination Unit 47 CC Charging Unit 48 CV Charging Unit 49 Storage Unit 50 Charging Control Program 51 SOC-OCV Data 60 Recording Medium 6 Integrated ECU
7, 13 Communication unit 12 Server 14 Control unit

Claims (10)

Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a ≦ 1, 0 ≦ b <1, 0 ≦ c <1, a + b + c + d = 1 CC charging unit that charges a power storage element having a positive electrode active material represented by 0 <x ≦ 1.1 and a and c are not 0 at the same time with a constant current;
A first calculation unit for calculating the SOC;
A charge control device comprising: a CV charging unit that charges at a constant voltage when the SOC is equal to or greater than a threshold value set based on a value of SOC when the resistance of the positive electrode is equal to or greater than a predetermined value. Li _x (Ni _a M ′ _1-a ) O ₂ (M ′ is a metal element other than Li and Ni, and has a positive electrode active material represented by 0.5 ≦ a ≦ 1, 0 <x ≦ 1.1) A CC charging unit that charges the storage element with a constant current;
A first calculation unit for calculating the SOC;
A charging control device comprising: a CV charging unit that performs charging at a constant voltage when the SOC is equal to or greater than a threshold value.   The charge control device according to claim 2, wherein the threshold value is set based on a value of SOC when the resistance of the positive electrode becomes equal to or higher than a predetermined value.   The charging according to any one of claims 1 to 3, wherein the CV charging unit performs charging at a voltage that is one step or multistep larger than a voltage when the SOC is equal to or greater than the threshold value. Control device. The CC charging unit continues charging at a current lower than the constant current when the SOC is equal to or higher than a first threshold,
The said CV charge part is a charge control apparatus of any one of Claim 1 to 3 which charges with a fixed voltage, when the said SOC becomes more than a 2nd threshold value.   4. The device according to claim 1, wherein, when the SOC becomes equal to or greater than the threshold value, the CV charging unit performs charging after the CC charging unit continues charging at a current higher than the constant current. 5. The charge control device according to item. A first acquisition unit for acquiring a current of the power storage element;
A second acquisition unit for acquiring a voltage of the storage element;
A second calculator that calculates a capacity of the power storage element based on the current, the voltage, and an SOC-OCV characteristic;
The charge control device according to any one of claims 1 to 6, wherein the first calculation unit calculates the SOC based on the capacity. The power storage element;
A power storage device comprising: the charge control device according to any one of claims 1 to 7. Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1, a + b + c + d = 1 , 0 <x ≦ 1.1, and a and c are not 0 at the same time) to charge the storage element having a positive electrode active material with a constant current,
Calculate the SOC,
A charge control method for a storage element, wherein charging is performed at a constant voltage when the SOC is equal to or greater than a threshold value set based on an SOC value when the positive electrode resistance is equal to or greater than a predetermined value. On the computer,
Li _x (Ni _a Mn _b Co _c M _d ) O ₂ (M is a metal element other than Li, Ni, Mn, Co, 0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1, a + b + c + d = 1 , 0 <x ≦ 1.1, and a and c are not 0 at the same time) to charge the storage element having a positive electrode active material with a constant current,
Calculate the SOC,
A computer program for executing a process of charging at a constant voltage when the SOC is equal to or higher than a threshold value set based on a value of SOC when the resistance of the positive electrode is equal to or higher than a predetermined value.

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