JP6930488B2 - Li precipitation evaluation method - Google Patents

Description

The present invention relates to a Li precipitation evaluation method for evaluating the precipitation of metallic Li generated on the surface of the negative electrode plate of a lithium ion secondary battery.

In a lithium ion secondary battery (hereinafter, also simply referred to as “battery”), metallic Li may be deposited on the surface of the negative electrode plate with the use of the battery. In a battery in which such metal Li precipitation occurs, problems such as an increase in the amount of heat generated by the battery occur. Further, the precipitated metal Li may be dendrited not only in the vicinity of the surface of the negative electrode plate. That is, dendrites of metallic Li may grow from the surface of the negative electrode plate, break through the separator, and reach the positive electrode plate, which may cause a minute internal short circuit in the battery. Therefore, there is a demand for a non-destructive and simple method for inspecting the degree of metal Li precipitation in a battery.

For example, Patent Document 1 discloses an inspection method for non-destructively determining whether or not metal Li is deposited in a battery. In this inspection method, the battery is charged at a constant voltage, and it is determined whether or not metal Li is deposited in the battery based on the presence or absence of a minimum value at which the charging current changes from a decrease to an increase.

Japanese Unexamined Patent Publication No. 2012-003863

However, for example, a battery mounted on a vehicle such as a vibrated car, a plug-in hybrid car, or an electric vehicle is frequently charged and discharged. On the other hand, in the inspection method of Patent Document 1, it is necessary to perform constant voltage charging as described above and examine the change in the charging current. For this reason, it may be difficult to perform the inspection method of Patent Document 1 for batteries and the like mounted on a vehicle, and another new inspection method has been required.

The present invention has been made in view of the current situation, and provides a Li precipitation evaluation method capable of nondestructively evaluating the precipitation of metallic Li generated on the surface of the negative electrode plate of a lithium ion secondary battery by a new method. The purpose is to do.

One aspect of the present invention for solving the above problems is a lithium ion secondary battery having an electrode body including an electrode body flat plate portion in which a positive electrode plate and a negative electrode plate are stacked in a flat plate shape in a flat plate shape via a separator. A Li precipitation evaluation method for evaluating the precipitation of metallic Li generated on the surface of the negative electrode plate, wherein the precipitated lithium ion secondary battery in which metal Li is precipitated on the surface of the negative electrode plate is the electrode body flat plate. When the precipitated lithium ion secondary battery is pressed in a form in which the portions are pressed in the stacking direction, the pressure at which the precipitated metal Li is not absorbed by the negative electrode plate is set to Pb1, and the precipitated metal is set to Pb1. When the pressure at which Li is absorbed by the negative electrode plate is Pb2 (Pb2> Pb1), the lithium ion secondary battery is pressed at the pressure Pb1 or the lithium ion secondary battery is not pressed. In this state, after the first voltage measuring step of measuring the first battery voltage V1 of the lithium ion secondary battery and the first voltage measuring step, the lithium ion secondary battery is pressed with the pressure Pb2. Based on the value of the ratio V2 / V1 of the second voltage measuring step for measuring the second battery voltage V2 of the lithium ion secondary battery and the ratio V2 / V1 of the second battery voltage V2 and the first battery voltage V1, the lithium ion This is a Li precipitation evaluation method including an evaluation step of evaluating the precipitation of metallic Li generated on the surface of the negative electrode plate in the secondary battery.

In a lithium ion secondary battery in which metal Li is not deposited on the surface of the negative electrode plate, the positive electrode potential in the state where the battery is pressed with the above-mentioned pressure Pb1 or the state where the battery is not pressed and the above-mentioned pressure Pb2 are used for the battery. The positive electrode potential in the state of pressing is almost the same. Further, the negative electrode potential when the battery is pressed with the pressure Pb1 or when the battery is not pressed is almost the same as the negative electrode potential when the battery is pressed with the pressure Pb2. Therefore, in a battery in which metal Li is not deposited, the battery voltage that appears as the difference between the positive electrode potential and the negative electrode potential is also the first battery voltage measured in the state of being pressed by the pressure Pb1 or in the state of not pressing the battery. V1 and the second battery voltage V2 measured in a state of being pressed by the pressure Pb2 have substantially the same value.

On the other hand, in the battery in which the metal Li is deposited on the surface of the negative electrode plate, the positive electrode potential is the state in which the battery is pressed with the pressure Pb1 or the battery is the same as the battery in which the metal Li is not deposited. The positive electrode potential is almost the same between the state in which the battery is not pressed and the state in which the battery is pressed with the pressure Pb2. However, regarding the negative electrode potential, in a battery in which metal Li is deposited, the battery is pressed at a pressure Pb2 rather than the negative electrode potential when the battery is pressed at the pressure Pb1 or the battery is not pressed. It has been found that the negative electrode potential is higher.

The reason is considered to be as follows. That is, the potential of the metal Li is lower than the potential of the negative electrode active material layer of the negative electrode plate (the potential of the negative electrode active material such as charged graphite). Further, since the battery reaction occurs particularly actively in the vicinity of the surface of the negative electrode active material layer of the negative electrode plate, which is close to the positive electrode plate, the negative electrode potential is easily affected by the vicinity of the surface of the negative electrode active material layer. Therefore, in a battery in which metal Li is deposited on the surface of the negative electrode plate (on the surface of the negative electrode active material layer), the metal Li is deposited when the battery is pressed with the pressure Pb1 or when the battery is not pressed. Since the metal Li is not absorbed by the negative electrode plate and the metal Li is present on the surface of the negative electrode active material layer, the negative electrode potential is lower than that of the battery in which the metal Li is not deposited.

It is considered that the precipitated metal Li is in contact with the surface of the negative electrode active material layer, but has few conductive paths. On the other hand, for a battery in which metal Li is deposited on the surface of the negative electrode plate, when the battery is pressed with the pressure Pb2, the deposited metal Li is absorbed by the negative electrode plate. Specifically, the precipitated metal Li more reliably contacts the surface of the negative electrode active material layer to increase the number of conductive paths, and the conductivity with the negative electrode active material layer becomes good. Then, it is considered that the precipitated metal Li is rapidly ionized (becomes lithium ion) and inserted into the negative electrode active material. Therefore, it is considered that the negative electrode potential when the battery is pressed with the pressure Pb2 is higher than the negative electrode potential when the battery is pressed with the pressure Pb1 or when the battery is not pressed.

Therefore, in a battery in which metal Li is deposited, the battery is pressed at a pressure Pb2 rather than the first battery voltage V1 when the battery is pressed at the pressure Pb1 or the battery is not pressed. 2 The battery voltage V2 is lower. Therefore, in the battery in which the metal Li is deposited, the value of the ratio V2 / V1 of the second battery voltage V2 and the first battery voltage V1 is smaller than that in the battery in which the metal Li is not deposited.

In the above-mentioned Li precipitation evaluation method, the first battery voltage V1 acquired in the first voltage measuring step (pressing the battery with the pressure Pb1 or not pressing the battery) and the second voltage measuring step (pressing the battery with the pressure Pb2). Based on the value of the ratio V2 / V1 with the second battery voltage V2 obtained in the above, the precipitation of metal Li generated on the surface of the negative electrode plate in the battery is evaluated. For example, as described above, in a battery in which metal Li is deposited on the surface of the negative electrode plate, the value of the battery voltage ratio V2 / V1 is smaller than that in a battery in which metal Li is not deposited. , The precipitation of metallic Li can be evaluated based on the value of the ratio V2 / V1. As described above, in the above-mentioned Li precipitation evaluation method, the precipitation of metallic Li generated on the surface of the negative electrode plate can be evaluated nondestructively by a new method.

In the "evaluation step", as a specific method of "evaluating the precipitation of metallic Li generated on the surface of the negative electrode plate based on the value of the battery voltage ratio V2 / V1", for example, the battery voltage ratio. When V2 / V1 is equal to or less than a predetermined reference ratio Ak (V2 / V1 ≦ Ak), a method of determining that metal Li is deposited on the surface of the negative electrode plate of the battery can be mentioned. Another method is to classify the inspected batteries into a plurality of groups according to the degree of precipitation of metallic Li by comparing the battery voltage ratio V2 / V1 with, for example, a plurality of reference ratios.

Further, as the "electrode body", for example, a flat-shaped winding type electrode body in which a band-shaped positive electrode plate and a band-shaped negative electrode plate are stacked via a pair of band-shaped separators and wound flat around an axis. Alternatively, a laminated electrode body in which a plurality of positive electrode plates and a plurality of negative electrode plates each having a rectangular shape or the like are alternately laminated via a separator can be mentioned.

It is explanatory drawing which shows the battery module which concerns on embodiment. It is the description which shows the battery assembly which concerns on embodiment. It is a perspective view of the battery which concerns on embodiment. It is a vertical sectional view of the battery which concerns on embodiment. It is a flowchart of the control method of the battery module which concerns on embodiment. It is a graph which shows the relationship between the pressure Pb which pressed the battery in measuring the 2nd battery voltage V2, and the ratio V2 / V1 of the battery voltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a battery module 1 according to this embodiment. Further, FIG. 2 shows a battery assembly 5 included in the battery module 1. Further, FIGS. 3 and 4 show a perspective view and a vertical cross-sectional view of the lithium ion secondary battery (hereinafter, also simply referred to as “battery”) 10. In the following description, the vertical direction BH, the horizontal direction CH, and the thickness direction DH of the battery 10 are defined as the directions shown in FIGS. 1 to 4.

The battery module 1 is an in-vehicle battery module mounted on a vehicle such as an electric vehicle or a plug-in hybrid car. The battery module 1 includes a battery assembly 5 in which a battery 10, a spacer 30, and a pressure sensor 40 are arranged in a row, and a pair of pressing members (first pressing member 50 and a pair of pressing members that press the battery assembly 5 in the rowing direction EH). A second pressing member 55), a moving device 60 for moving the first pressing member 50 in the rowing direction EH, and a control device 80 for controlling the moving device 60 are provided.
Of these, in the battery assembly 5, a plurality of square batteries 10 and a plurality of plate-shaped spacers 30 are alternately arranged in one of the arrangement directions EH (on the right side in FIGS. 1 and 2). , A plate-shaped pressure sensor 40 is arranged.

The battery 10 is a rectangular parallelepiped, sealed lithium-ion secondary battery. The plurality of batteries 10 included in the battery assembly 5 are arranged in a row in the thickness direction DH. The batteries 10 are connected in series via a bus bar 25. The battery 10 has an electrode body 15 housed together with an electrolytic solution 13 inside a battery case 11 having a rectangular parallelepiped box shape and made of metal (aluminum in the present embodiment). The electrode body 15 is formed by stacking a band-shaped positive electrode plate 16 and a band-shaped negative electrode plate 17 with each other via a pair of band-shaped separators 18 and 18 and winding them in a flat shape.

Of the electrode body 15, the portion where the positive electrode plate 16, the negative electrode plate 17, and the separators 18 and 18 overlap in a flat plate shape in the stacking direction FH is the electrode body flat plate portion 15f. The stacking direction FH of the electrode body flat plate portion 15f is the same as the thickness direction DH of the battery 10. On the other hand, of the electrode body 15, the positive electrode plate 16, the negative electrode plate 17, and the separators 18 and 18 are bent into a semi-cylindrical shape, respectively, located at both ends (upper end and lower end in FIGS. 3 and 4) of the electrode body flat plate portion 15f. The parts formed are the electrode body R portions 15r and 15r.

A positive electrode terminal member 21 made of aluminum and a negative electrode terminal member 23 made of copper are projected on the upper surface of the battery case 11 in a state of being insulated from the battery case 11, respectively. The positive electrode terminal member 21 is connected to and conducts with the positive electrode plate 16 of the electrode body 15 inside the battery case 11, while penetrating the upper surface of the battery case 11 and extending to the outside of the battery. Further, the negative electrode terminal member 23 is connected to and conducts with the negative electrode plate 17 of the electrode body 15 inside the battery case 11, while penetrating the upper surface of the battery case 11 and extending to the outside of the battery.

The spacer 30 has a rectangular plate shape and is made of an insulating resin. The spacer 30 is interposed between adjacent batteries 10 in a state where the battery assembly 5 is formed, and is also between the second pressing member 55 and the battery 10, and between the pressure sensor 40 and the battery 10. There are also intervenes between them.

The pressure sensor 40 is a rectangular plate-shaped pressure sensor. The pressure sensor 40 is arranged at one end (on the right side in FIGS. 1 and 2) of the battery assembly 5 in the rowing direction EH. A first pressing member 50, which will be described later, is arranged on the outside of the pressure sensor 40 (on the right side in FIGS. 1 and 2). As a result, the pressure sensor 40 can detect the pressure Pb that presses the battery 10 in the thickness direction DH. Further, the pressure sensor 40 is connected to the control device 80 so that an electric signal corresponding to the detected pressure Pb can be transmitted to the control device 80 described later.

The first pressing member 50 and the second pressing member 55 each have a rectangular plate shape and are made of metal (aluminum in this embodiment). The first pressing member 50 and the second pressing member 55 are arranged at both ends of the battery assembly 5 in the rowing direction EH, sandwich the battery assembly 5 including the battery 10, and move in the rowing direction EH at a pressure Pb = Pb0. Press. The pressure Pb = Pb0 is also referred to as "initial pressure". How the value of the initial pressure Pb = Pb0 was determined will be described later. As a result, the battery 10 is pressed against the thickness direction DH at an initial pressure Pb = Pb0, and the electrode body flat plate portion 15f of the electrode body 15 housed in the battery case 11 is pressed against the stacking direction FH. Of the pair of first pressing member 50 and second pressing member 55, one (right side in FIGS. 1 and 2) of the first pressing member 50 is moved in the rowing direction EH by the moving device 60 described later. It is configured to be possible.

Next, the moving device 60 will be described. The moving device 60 is a device that moves the first pressing member 50 in the rowing direction EH (stacking direction FH) to change the pressure Pb that presses the battery 10. The moving device 60 has a plurality of restraint rods 61 and a plurality of drive motors 63.
Each of the restraint rods 61 is a ball screw, and the first pressing member 50 and the second pressing member 55 are connected to restrain the battery assembly 5. Each of the restraint rods 61 is arranged so as to extend in the rowing direction EH of the battery assembly 5, and one end 61a of the restraint rod 61 is rotatably held by the second pressing member 55. Further, the restraint rod 61 penetrates the first pressing member 50, and the other end portion 61b of the restraint rod 61 is connected to the output shaft of the drive motor 63.
On the other hand, the first pressing member 50 is provided with a plurality of moving nuts 56 in a form penetrating the first pressing member 50, and a restraint rod 61, which is a ball screw, is screwed into each of these moving nuts 56. ing. As a result, when the restraint rods 61 are rotated by the drive motor 63, the first pressing member 50 moves in the rowing direction EH (stacking direction FH).

As described above, the drive motor 63 is a drive source for rotating the restraint rod 61, and is provided for each restraint rod 61 in the present embodiment. Each drive motor 63 is connected to a control device 80 described later, and is driven by an output signal from the control device 80.
By moving the first pressing member 50 in the direction closer to the second pressing member 55 (first direction FH1 in the stacking direction FH) by such a moving device 60, the pressure Pb for pressing the battery 10 can be increased. On the contrary, by moving the first pressing member 50 away from the second pressing member 55 (the second direction FH2 in the stacking direction FH), the pressure Pb for pressing the battery 10 can be lowered.

Next, the control device 80 will be described. The control device 80 is a device that controls the mobile device 60, and includes a storage unit and a calculation unit. As described above, the pressure sensor 40 and the drive motor 63 of the moving device 60 are connected to the control device 80. Further, the battery module 1 has a voltmeter 90 for detecting the battery voltage V for each battery 10, and these voltmeters 90 are also connected to the control device 80, respectively. Then, as will be described later, the control device 80 controls the drive motor 63 of the moving device 60 based on the battery voltage V detected by each voltmeter 90 and the pressure Pb detected by the pressure sensor 40.

(Preliminary test 1)
Here, the preliminary test 1 performed to determine the value of the above-mentioned initial pressure Pb = Pb0 will be described. A large number of new battery modules 1 are prepared, a charging / discharging device is connected to the battery module 1, and a "charging / discharging cycle test" is performed for each. Specifically, at an environmental temperature of −10 ° C., the starting SOC is set to SOC 50%, the battery is charged for 10 seconds at the charging current value Ix, and then the device is rested for 5 minutes. After that, the battery is discharged for 10 seconds with a discharge current value having the same magnitude as the charge current value Ix. With this charge / discharge as one cycle, the charge / discharge cycle is performed 5000 times. This charge / discharge cycle test was performed on a large number of battery modules 1 by changing the magnitude of the pressure Pb pressing the battery 10 and the magnitude of the charging current value Ix.

After that, the batteries 10 forming each battery module 1 are disassembled, the negative electrode plate 17 is taken out, and whether or not metal Li is deposited on the surface 17a of the negative electrode plate 17 (the surface 17ca of the negative electrode active material layer 17c) is checked. It was investigated visually. Then, from the investigation results of a large number of battery modules 1 in which the pressure Pb and the charging current value Ix are changed, the charging current value Ig at the limit (maximum) at which the metal Li does not precipitate on the surface 17a of the negative electrode plate 17 and the charging current value Ig, and At this limit charging current value Ig, the limit (minimum) pressure Pbg at which metal Li precipitation does not occur was determined, and these were used as the initial pressure Pb0 (= Pbg) and the reference current value Ik (= Ig).

(Preliminary test 2)
Next, the value of the pressure Pb1 that presses the battery 10 in the "first voltage measurement step S1" described later, the value of the pressure Pb2 that presses the battery 10 in the "second voltage measurement steps S2 and S3" described later, and the value of the pressure Pb2 that presses the battery 10 later. The preliminary test 2 performed in order to determine the value of the reference ratio Ak used as the criterion in the “evaluation step S4” will be described. First, a battery module 1 composed of a battery 10 in which metal Li is not deposited on the surface 17a of the negative electrode plate 17, and a precipitated lithium ion secondary battery in which metal Li is deposited on the surface 17a of the negative electrode plate 17 (precipitated lithium ion secondary battery). Precipitated batteries) A plurality of battery modules 1 made of 10y were prepared.

Specifically, as a battery module 1 composed of a battery 10 in which metal Li is not deposited, a plurality of battery modules 1 according to a new embodiment are prepared.
On the other hand, as the battery module 1 composed of the precipitation battery 10y in which the metal Li is precipitated, the battery module 1 in which the metal Li is precipitated on the surface 17a of the negative electrode plate 17 of the battery 10 by performing a "charge / discharge cycle test". I prepared multiple. This charge / discharge cycle test is performed with the battery 10 pressed at the initial pressure Pb = Pb0, the charging current value is 1.5 times (1.5 × Ik) the above-mentioned reference current value Ik, and the discharge current. The value was set to 1.5 times the reference current value Ik (1.5 × Ik). Other than that, it was the same as the charge / discharge cycle test described above. By increasing the charging current value (1.5 × Ik) in this way, the metal Li can be deposited on the surface 17a of the negative electrode plate 17 of the battery 10. However, although precipitation of metallic Li occurs, it has been confirmed that an internal short circuit due to the growth of dendrites of metallic Li does not occur.

Next, for each of the battery module 1 made of the battery 10 in which the metal Li is not deposited and the battery module 1 made of the precipitated battery 10y in which the metal Li is deposited, the battery is first set at an initial pressure Pb = Pb0. The first battery voltage V1 of the battery 10 was measured with the 10 pressed. After that, the magnitude of the pressure Pb pressing the battery 10 was changed in the range of Pb = 1.0 × Pb0 to Pb = 1.8 × Pb0. Then, the second battery voltage V2 was measured for the battery 10 after the pressure Pb was changed. Then, the ratio V2 / V1 was obtained from the first battery voltage V1 and the second battery voltage V2 of each battery 10. The result is shown in FIG. The horizontal axis of FIG. 6 indicates the pressure Pb that presses the battery 10 when measuring the second battery voltage V2, and the vertical axis indicates the ratio V2 / V1 of the battery voltage.

As is clear from the graph of FIG. 6, in the battery 10 (marked with □ in FIG. 6) in which the metal Li is not deposited, regardless of the magnitude of the pressure Pb pressing the battery 10 when measuring the second battery voltage V2. However, the ratio V2 / V1 of the battery voltage is about 1.00.
On the other hand, in the precipitation battery 10y (marked with ◆ in FIG. 6) in which metal Li is deposited, the pressure Pb that presses the battery 10 when measuring the second battery voltage V2 is Pb ≦ 1.4 × Pb0. , The battery voltage ratio V2 / V1 is close to 1.00 (a value exceeding 0.98), but when Pb ≧ 1.5 × Pb0, the battery voltage ratio V2 / V1 becomes less than 0.94. It went down a lot. The reason why such a result occurred is considered to be as follows.

In the battery 10 in which the metal Li is not deposited, the positive electrode potential is substantially the same regardless of the magnitude of the pressure Pb pressing the battery 10. Further, the negative electrode potential is almost the same regardless of the magnitude of the pressure Pb that presses the battery 10. Therefore, in the battery 10 in which the metal Li is not deposited, the first battery voltage V1 and the second battery voltage V2 are substantially the same value. Therefore, the ratio V2 / V1 of the battery voltage is about 1.00 regardless of the magnitude of the pressure Pb that presses the battery 10 when measuring the second battery voltage V2.

On the other hand, in the precipitation battery 10y in which the metal Li is precipitated, the positive electrode potential is substantially the same regardless of the magnitude of the pressure Pb pressing the precipitation battery 10y. However, regarding the negative electrode potential, the negative electrode potential when the precipitation battery 10y is pressed at a pressure Pb ≧ 1.5 × Pb0 is compared with the negative electrode potential when the precipitation battery 10y is pressed at a pressure Pb ≦ 1.4 × Pb0. Will be higher.
The reason is that the potential of the metal Li is lower than the potential of the negative electrode active material layer 17c of the negative electrode plate 17 (the potential of the charged negative electrode active material (graphite)). Further, since the battery reaction occurs particularly actively in the vicinity of the surface 17ca of the negative electrode active material layer 17c of the negative electrode plate 17 which is close to the positive electrode plate 16, the negative electrode potential is the negative electrode active material layer 17c of the negative electrode plate 17. It is easily affected by the vicinity of the surface 17ca. Therefore, in the precipitation battery 10y, when the precipitation battery 10y is pressed at a pressure Pb ≦ 1.4 × Pb0, the precipitated metal Li is not absorbed by the negative electrode plate 17, and the surface of the negative electrode active material layer 17c is not absorbed. Since the metal Li is present on 17ca, the negative electrode potential is lower than that of the battery 10 in which the metal Li is not deposited.

It is considered that the precipitated metal Li is in contact with the surface 17ca of the negative electrode active material layer 17c of the negative electrode plate 17, but the conductive path is small. On the other hand, with respect to the precipitation battery 10y, when the precipitation battery 10y is pressed at a pressure Pb ≧ 1.5 × Pb0, the deposited metal Li more reliably contacts the surface 17ca of the negative electrode active material layer 17c, and a conductive path is formed. The number increases, and the conductivity with the negative electrode active material layer 17c becomes good. Then, the precipitated metal Li is rapidly ionized (becomes lithium ion) and inserted into graphite, which is a negative electrode active material. That is, the precipitated metal Li is absorbed by the negative electrode plate 17. Therefore, the negative electrode potential when the precipitation battery 10y is pressed at the pressure Pb ≧ 1.5 × Pb0 is higher than the negative electrode potential when the precipitation battery 10y is pressed at the pressure Pb ≦ 1.4 × Pb0. Conceivable.

Therefore, in the precipitation battery 10y, the precipitation battery 10y is pressed at a pressure Pb ≧ 1.5 × Pb0 as compared with the second battery voltage V2 when the precipitation battery 10y is pressed at a pressure Pb ≦ 1.4 × Pb0. The second battery voltage V2 at the above becomes low. As a result, in the precipitation battery 10y, as described above, when the pressure Pb at the time of measuring the second battery voltage V2 is Pb ≦ 1.4 × Pb0, the ratio V2 / V1 of the battery voltage is close to 1.00 (0). It was a value exceeding .98). On the other hand, when the pressure Pb is Pb ≧ 1.5 × Pb0, it is considered that the ratio V2 / V1 of the battery voltage is reduced to less than 0.94.

From the results of such a preliminary test 2, when the pressure Pb pressing the precipitation battery 10y is Pb ≦ 1.4 × Pb0, the metal Li deposited on the surface 17a of the negative electrode plate 17 is not absorbed by the negative electrode plate 17. On the other hand, when the pressure Pb is Pb ≧ 1.5 × Pb0, it is considered that the metal Li deposited on the surface 17a of the negative electrode plate 17 is absorbed by the negative electrode plate 17.
Therefore, the pressure Pb1 for pressing the battery 10 in the "first voltage measuring step S1" described later is set to Pb1 ≦ 1.4 × Pb0, and in this embodiment, Pb1 = Pb0. Further, the pressure Pb2 for pressing the battery 10 in the "second voltage measuring steps S2 and S3" described later was set to Pb2 ≧ 1.5 × Pb0, and in this embodiment Pb2 = 1.5 × Pb0. Further, the reference ratio Ak used as the determination criterion in the “evaluation step S4” described later was set to Ak = 0.94.

Next, a control method of the battery module 1 mounted on the vehicle will be described with reference to FIG. When the driver changes the key switch of the vehicle from the on position to the off position, in step S1, the first battery voltage V1 of each battery 10 included in the battery module 1 is measured. This step S1 corresponds to the above-mentioned "first voltage measurement step". Specifically, in step S1, the first battery voltage V1 detected by the voltmeter 90 connected to each battery 10 is taken into the control device 80.

Each battery 10 forming the battery module 1 is pressed by the above-mentioned initial pressure Pb = Pb0 (= Pb1) even before the driver changes the key switch from the on position to the off position. Therefore, the first battery voltage V1 measured in step S1 is the battery voltage in a state where the battery 10 is pressed at the pressure Pb = Pb1 = Pb0. As described above, the initial pressure Pb = Pb1 = Pb0 is a pressure such that the metal Li deposited on the surface 17a of the negative electrode plate 17 is not absorbed by the negative electrode plate 17.

Next, in step S2, the pressure Pb for pressing the battery 10 is changed from the initial pressure Pb = Pb1 (= Pb0) to Pb = Pb2 (= 1.5 × Pb0). As described above, the pressure Pb = Pb2 = 1.5 × Pb0 is a pressure such that the metal Li deposited on the surface 17a of the negative electrode plate 17 is absorbed by the negative electrode plate 17. Specifically, the control device 80 drives each drive motor 63 of the moving device 60, and the moving device 60 brings the first pressing member 50 closer to the second pressing member 55 (first direction of the stacking direction FH). It is moved to FH1), and the pressure Pb detected by the pressure sensor 40 is set to Pb = Pb2 (= 1.5 × Pb0).

Next, in step S3, the second battery voltage V2 of each battery 10 included in the battery module 1 is measured. The above-mentioned step S2 and this step S3 correspond to the above-mentioned "second voltage measurement step". Specifically, in step S3, the second battery voltage V2 detected by the voltmeter 90 connected to each battery 10 is taken into the control device 80.
Each battery 10 forming the battery module 1 is pressed at a pressure Pb = Pb2 (= 1.5 × Pb0) by performing step S2. Therefore, the second battery voltage V2 measured in step S3 is the battery voltage in a state where the battery 10 is pressed by the pressure Pb2.

Next, in step S4, for each battery 10, the value of the ratio V2 / V1 of the second battery voltage V2 and the first battery voltage V1 is a predetermined reference ratio Ak (Ak = 0.94 in this embodiment). ) The following (V2 / V1 ≦ Ak) or not is determined respectively. The reference ratio Ak = 0.94 is a predetermined value based on the result of the preliminary test 2 (see FIG. 6) as described above.
If YES in step S4, that is, if the value of the battery voltage ratio V2 / V1 is equal to or less than the reference ratio Ak (V2 / V1 ≦ Ak), the metal Li is placed on the surface 17a of the negative electrode plate 17 of the battery 10. It is determined that precipitation has occurred, and the process proceeds to step S5. On the other hand, when NO in step S4, that is, when the value of the battery voltage ratio V2 / V1 is larger than the reference ratio Ak (V2 / V1> Ak), the metal Li is placed on the surface 17a of the negative electrode plate 17 of the battery 10. It is determined that no precipitation has occurred, and the process proceeds to step S6. This step S4 corresponds to the above-mentioned "evaluation step".

When it is determined in step S4 that metal Li is deposited in the battery, in step S5, the warning light in the meter of the vehicle is turned on. This allows the driver to know that there is a problem with the battery module 1.
Further, in step S5, the pressure Pb for pressing the battery 10 is changed from Pb = Pb2 (= 1.5 × Pb0) to Pb = 0.5 × Pb0, which is lower than the initial pressure Pb = Pb1 (= Pb0). do. Specifically, the control device 80 drives each drive motor 63 of the moving device 60, and the moving device 60 moves the first pressing member 50 away from the second pressing member 55 (the second direction of the stacking direction FH). It is moved to FH2), and the pressure Pb detected by the pressure sensor 40 is set to Pb = 0.5 × Pb0. By lowering the pressure Pb in this way, the distance between the electrodes of the electrode body 15 (the gap between the positive electrode plate 16 and the negative electrode plate 17 in the electrode body flat plate portion 15f) is widened, so that the dendrite of the metal Li is formed on the surface 17a of the negative electrode plate 17. It is possible to prevent a minute internal short circuit from occurring in the battery 10 by breaking through the separator 18 and reaching the positive electrode plate 16. After that, this control is terminated.

On the other hand, when it is determined in step S4 that metal Li is not deposited in the battery, in step S6, the pressure Pb for pressing the battery 10 is initially changed from Pb = Pb2 (= 1.5 × Pb0). The pressure is returned to Pb = Pb1 (= Pb0). Specifically, the control device 80 drives each drive motor 63 of the moving device 60, and the moving device 60 moves the first pressing member 50 away from the second pressing member 55 (the second direction of the stacking direction FH). It is moved to FH2), and the pressure Pb detected by the pressure sensor 40 is set to the initial pressure Pb = Pb1 (= Pb0). After that, this control is terminated.

As described above, in the above-described embodiment, the first battery voltage V1 of each battery 10 acquired in the first voltage measurement step (step S1) and the acquisition in the second voltage measurement step (step S2 and step S3). In the evaluation step (step S4), the precipitation of metal Li in each battery 10 is evaluated based on the value of the ratio V2 / V1 of each battery 10 to the second battery voltage V2. In the precipitation battery 10y in which metal Li is deposited on the surface 17a of the negative electrode plate 17, the value of the battery voltage ratio V2 / V1 is higher than that in the battery 10 in which metal Li is not deposited, as described above. Since it becomes smaller, the precipitation of metal Li can be evaluated based on the value of the ratio V2 / V1. As described above, in the Li precipitation evaluation method of the embodiment, the precipitation of metallic Li in the battery 10 generated on the surface 17a of the negative electrode plate 17 of the battery 10 can be evaluated nondestructively by a new method.

Although the present invention has been described above in accordance with the embodiment, it goes without saying that the present invention is not limited to the above-described embodiment and can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the flat wound type electrode body 15 is exemplified as the electrode body, but the form of the electrode body is not limited to this. The electrode body may be, for example, a laminated electrode body in which a plurality of rectangular positive electrode plates and a plurality of negative electrode plates are alternately laminated via a separator.

Further, in the embodiment, in the first voltage measuring step S1, the first battery voltage V1 is measured with the battery 10 pressed at the pressure Pb1 = Pb0, but the present invention is not limited to this. As can be seen from the results of the preliminary test 2, the pressure Pb1 that presses the battery 10 when measuring the first battery voltage V1 may be Pb1 ≦ 1.4 × Pb0. Further, the first battery voltage V1 may be measured in a state where the battery 10 is not pressed at all (pressure Pb1 = 0).
Further, in the embodiment, in the second voltage measuring steps S2 and S3, the second battery voltage V2 is measured with the battery 10 pressed at a pressure Pb2 = 1.5 × Pb0, but the present invention is not limited to this. As can be seen from the results of the preliminary test 2, the pressure Pb2 that presses the battery 10 when measuring the second battery voltage V2 may be Pb2 ≧ 1.5 × Pb0.

1 Battery module 10 Lithium-ion secondary battery (battery)
10y Precipitated lithium ion secondary battery (precipitated battery)
15 Electrode body 15f Electrode body flat plate portion 16 Positive electrode plate 17 Negative electrode plate 17a (Negative electrode plate) Surface 17c Negative electrode active material layer 17ca (Negative electrode active material layer) Surface 18 Separator 30 Spacer 40 Pressure sensor 50 First pressing member 55 Second Pressing member 60 Moving device 80 Control device 90 Voltage gauges Pb, Pb1, Pb2 Pressure EH Rowing direction FH Stacking direction S1 First voltage measuring process S2, S3 Second voltage measuring step S4 Evaluation step

Claims (1)

For a lithium ion secondary battery having an electrode body including an electrode body flat plate portion in which a positive electrode plate and a negative electrode plate are stacked in a flat plate shape in a flat plate shape via a separator, precipitation of metal Li generated on the surface of the negative electrode plate is evaluated. Li precipitation evaluation method
Regarding a precipitated lithium ion secondary battery in which metal Li is deposited on the surface of the negative electrode plate, when the precipitated lithium ion secondary battery is pressed in a form in which the flat plate portion of the electrode body is pressed in the stacking direction. The pressure at which the precipitated metal Li is not absorbed by the negative electrode plate is defined as Pb1, and the pressure at which the precipitated metal Li is absorbed by the negative electrode plate is defined as Pb2 (Pb2> Pb1). When
A first voltage measuring step of measuring the first battery voltage V1 of the lithium ion secondary battery with the lithium ion secondary battery pressed at the pressure Pb1 or without pressing the lithium ion secondary battery. ,
After the first voltage measuring step, a second voltage measuring step of measuring the second battery voltage V2 of the lithium ion secondary battery while pressing the lithium ion secondary battery with the pressure Pb2, and
An evaluation step for evaluating the precipitation of metallic Li generated on the surface of the negative electrode plate in the lithium ion secondary battery based on the value of the ratio V2 / V1 of the second battery voltage V2 and the first battery voltage V1. A Li precipitation evaluation method comprising.

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