JP7176484B2 - battery system - Google Patents

Description

The present disclosure relates to battery systems.

Japanese Patent Laying-Open No. 2014-207107 (Patent Document 1) discloses a battery system. In the battery system, charging of the battery cells is controlled based on the surface pressure of the battery cells.

JP 2014-207107 A

Battery modules are used in various applications. A battery module includes one or more battery cells (single cells) and a restraining member. The restraint member physically restrains the periphery of the battery module. The binding member applies a binding load to the battery cells.

There is a demand for battery modules with high capacity. Therefore, active materials with large specific capacities (for example, silicon) are being studied. However, active materials with large specific capacities can generally expand significantly with charge-discharge cycles. As the active material expands, the battery cell also expands. The expansion of the battery cell increases the reaction force applied from the battery cell to the restraint member. The reaction force gradually increases according to the number of charge/discharge cycles. Over time, the reaction force may exceed the limit stress of the restraining member.

An object of the present disclosure is to provide a battery system suitable for a battery module containing an active material that easily expands.

The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action of this disclosure includes speculation. The correctness of the mechanism of action should not limit the scope of the claims.

A battery system includes a battery module, a measurement device, and a control device.
A battery module includes one or more battery cells and a restraining member. The binding member applies a binding load to the battery cells.
A measuring device measures the reaction force. The reaction force is a force acting from the battery cell to the restraint member in the direction opposite to the direction in which the restraint load acts.
The controller sets a first upper limit for the charging current of the battery module when the reaction force is zero. The controller sets a second upper limit for the charging current of the battery module when the reaction force is greater than zero. The first upper limit is smaller than the second upper limit.

FIG. 1 is a first conceptual diagram illustrating the relationship between the number of charge/discharge cycles and the reaction force.
Battery cell 10 includes housing 11 and electrode group 12 . The housing 11 accommodates the electrode group 12 . A reaction force is generated when the electrode group 12 contacts the housing 11 . Generally, the electrode group 12 is in contact with the housing 11 from the beginning. This is because the capacity per unit volume increases due to the small excess space in the housing 11 . As shown in the graph of FIG. 1, in the configuration in which the electrode group 12 is in contact with the housing 11 from the beginning, a reaction force is generated from the start of the charge/discharge cycle.

Here, the "upper limit SOC (state of charge)" in FIG. 1 corresponds to the time of full charge. The "lower limit SOC" in FIG. 1 corresponds to the time of complete discharge.

In each charge/discharge cycle, the reaction force is maximum at full charge and minimum at full discharge. This is because the electrode group 12 expands due to charging and contracts due to discharging. However, although the volume of the electrode group 12 shrinks during discharging, it does not return to the volume before expansion (before charging). Therefore, the volume of the electrode group 12 monotonically increases with an increase in the number of charge/discharge cycles. As a result, the reaction force also monotonically increases.

As shown in the graph of FIG. 1, the reaction force gradually increases with charge/discharge cycles. In the n-th charge/discharge cycle, the reaction force at the upper limit SOC reaches the limit stress of the restraint member. In order to prolong the period until the reaction force at the upper limit SOC reaches the critical stress, measures such as increasing the strength of the restraint member can be considered. However, increasing the strength of the restraining member may also result in increased cost.

FIG. 2 is a second conceptual diagram illustrating the relationship between the number of charge/discharge cycles and the reaction force.
For example, it is conceivable to provide a space 13 between the housing 11 and the electrode group 12 . Since the space 13 exists between the housing 11 and the electrode group 12 at the beginning, the reaction force at the start of the charge/discharge cycle is reduced. As a result, it is expected that the reaction force at the upper limit SOC will take longer to reach the critical stress.

However, the provision of the space 13 between the housing 11 and the electrode group 12 may also cause inconvenience. That is, the reaction force is zero within a predetermined SOC range from the first charge/discharge cycle to the m-th charge/discharge cycle. When the reaction force is zero, the electrode group 12 is considered substantially unconstrained. Since the electrode group 12 is not constrained, the inter-electrode distance between the positive electrode and the negative electrode can be increased. A long inter-electrode distance can increase the resistance. As a result, there is a possibility that the acceptability of the negative electrode side during charging (hereinafter also referred to as “charge acceptability”) will decrease. If the battery cell 10 is a lithium-ion battery, lithium (Li) may precipitate due to a decrease in charge acceptance.

In the battery system of the present disclosure, it takes a long time for the reaction force at the upper limit SOC to reach the critical stress, and the load applied to the negative electrode can be reduced. As a result, the battery module can have a long life. This is because, in the battery system of the present disclosure, charging control is changed depending on when the reaction force is zero and when the reaction force is greater than zero.

That is, the control device of the present disclosure sets the first upper limit to the charging current of the battery module when the reaction force is zero. The control device of the present disclosure sets a second upper limit for the charging current of the battery module when the reaction force is greater than zero. The first upper limit is smaller than the second upper limit.

In the battery system of the present disclosure, when the reaction force is zero (that is, when the charge acceptability is low), the upper limit of charging current is set low. Therefore, the load applied to the negative electrode can be reduced. When the battery cell 10 is a lithium-ion battery, deposition of Li can be suppressed.

From the above, it is considered that the battery system of the present disclosure is suitable for a battery module containing an active material that easily expands.

In a lithium ion battery, an alloy-based negative electrode active material, for example, can be considered as an active material that easily expands. The alloy-based negative electrode active material has a larger specific capacity than the carbon-based negative electrode active material (graphite, etc.). On the other hand, however, the alloy-based negative electrode active material expands more during charge-discharge cycles than the carbon-based negative electrode active material. Examples of alloy-based negative electrode active materials include silicon, silicon oxide, silicon-based alloys, tin, tin oxide, and tin-based alloys. That is, in the battery system of the present disclosure, the negative electrode active material may contain at least one selected from the group consisting of silicon, silicon oxide, silicon-based alloys, tin, tin oxide, and tin-based alloys.

FIG. 1 is a first conceptual diagram illustrating the relationship between the number of charge/discharge cycles and the reaction force. FIG. 2 is a second conceptual diagram illustrating the relationship between the number of charge/discharge cycles and the reaction force. FIG. 3 is a block diagram showing the battery system of this embodiment. FIG. 4 is a schematic side view showing a battery module. FIG. 5 is a first schematic cross-sectional view showing battery cells included in the battery module. FIG. 6 is a second schematic cross-sectional view showing battery cells included in the battery module. FIG. 7 is a flow chart showing the processing of the control device. FIG. 8 is an example of a current and reaction force profile.

Embodiments of the present disclosure (also referred to herein as “present embodiments”) are described below. However, the following description does not limit the scope of the claims.

<Battery system>
FIG. 3 is a block diagram showing the battery system of this embodiment.
The battery system 100 may be installed in an electric vehicle or the like, for example. The electric vehicle may be, for example, a hybrid electric vehicle (HEV). The electric vehicle may be, for example, an electric vehicle (EV). Battery system 100 includes battery module 101 , measuring device 102 and control device 103 . Each element included in the battery system 100 may be connected to each other by a predetermined cable or the like, for example. Each element included in the battery system 100 may be connected to each other by, for example, a wireless network.

《Battery module》
FIG. 4 is a schematic side view showing a battery module.
Battery module 101 includes one or more battery cells 10 and binding members 20 . The battery module 101 may include, for example, multiple battery cells 10 . The battery module 101 may include, for example, 2 or more and 100 or less battery cells 10 .

The plurality of battery cells 10 may be aligned in one predetermined direction. A plurality of battery cells 10 may be connected in series. A plurality of battery cells 10 may be connected in parallel.

(restraining member)
The binding member 20 physically binds the periphery of one or more battery cells 10 . The restraint member 20 may restrain the periphery of the plurality of battery cells 10 . The binding member 20 applies a binding load to the battery cell 10 . The restrained load may be a compressive load. The binding member 20 may apply a binding load to one battery cell 10 . The binding member 20 may apply a binding load to each of the plurality of battery cells 10 . The binding member 20 may apply a binding load to some of the plurality of battery cells 10 .

The restraining member 20 may be a single member. The restraining member 20 may include multiple members. The restraint member 20 may include, for example, a first restraint plate 21 , a second restraint plate 22 and a restraint band 23 . The first constraining plate 21 and the second constraining plate 22 are arranged at both ends in the alignment direction of the battery cells 10 (the y-axis direction in FIG. 4). The restraint band 23 bridges the first restraint plate 21 and the second restraint plate 22 . By tightening the restraint band 23, a compressive load can be generated from both ends in the alignment direction toward the center. Each of the first restraint plate 21, the second restraint plate 22 and the restraint band 23 may be made of metal, for example. Each of the first restraint plate 21, the second restraint plate 22 and the restraint band 23 may be made of resin, for example.

(battery cell)
FIG. 5 is a first schematic cross-sectional view showing battery cells included in the battery module.
In this embodiment, the battery cell 10 (single cell) is a lithium ion battery. However, the battery cell 10 may be a battery system other than a lithium ion battery as long as the charge acceptance tends to decrease when the reaction force is zero. The battery cell 10 may be a so-called liquid battery, a polymer battery, or an all-solid battery.

Battery cell 10 includes housing 11 and electrode group 12 . The housing 11 accommodates the electrode group 12 . A space 13 is initially provided between the housing 11 and the electrode group 12 in the y-axis direction of FIG. When space 13 exists, the reaction force is zero.

FIG. 6 is a second schematic cross-sectional view showing battery cells included in the battery module.
As the number of charge/discharge cycles increases, the electrode group 12 expands. The electrode group 12 eventually comes into contact with the housing 11 . Space 13 (FIG. 5) is thereby lost. Due to the loss of space 13, the reaction force becomes greater than zero.

The shape of the housing 11 may be, for example, rectangular (flat rectangular parallelepiped). The housing 11 may be, for example, a metal container. Electrode group 12 includes a positive electrode, a negative electrode, and an electrolyte.

Each of the positive electrode and the negative electrode may be, for example, a sheet-like member. The electrode group 12 may be of a laminated type. That is, the electrode group 12 may be formed by alternately stacking one or more positive electrodes and one or more negative electrodes. A porous resin film (so-called separator) may be arranged between the positive electrode and the negative electrode. The electrode group 12 may be of a wound type. That is, the electrode group 12 may be formed by spirally winding a positive electrode and a negative electrode.

The positive electrode contains at least a positive electrode active material. The positive electrode active material may contain, for example, a lithium-nickel-cobalt-manganese composite oxide. The negative electrode contains at least a negative electrode active material. The negative electrode active material may contain, for example, a carbon-based negative electrode active material. The negative electrode active material may contain, for example, at least one selected from the group consisting of graphite, soft carbon and hard carbon. Each of the positive electrode and the negative electrode may further contain, for example, a binder, a conductive material, a current collector, and the like.

The battery system 100 of this embodiment is suitable for a negative electrode active material that easily expands. The negative electrode active material may contain, for example, an alloy-based negative electrode active material. The negative electrode active material may contain, for example, at least one selected from the group consisting of silicon, silicon oxide, silicon-based alloys, tin, tin oxide, and tin-based alloys. The negative electrode active material may contain both a carbon-based negative electrode active material and an alloy-based negative electrode active material.

The electrolyte may be liquid, gel, or solid. The electrolyte may contain, for example, a carbonate-based solvent and a lithium salt. The electrolyte may contain, for example, a sulfide-based solid electrolyte.

"measuring device"
Measuring device 102 measures the reaction force. Measurement results are input to the control device 103 . The reaction force may be measured at regular intervals, for example. The reaction force may be measured at random intervals, for example. The reaction force may, for example, be measured constantly.

A reaction force is a force acting in a direction opposite to the direction in which the binding load acts. A reaction force acts on the binding member 20 from the battery cell 10 . The reaction force is generated when the electrode group 12 expands and contacts the housing 11 .

The measurement device 102 may include, for example, a surface pressure sensor or the like. The reaction force can be measured by, for example, a surface pressure sensor or the like. The surface pressure sensor may be, for example, a tactile sensor or the like. The surface pressure sensor includes a sensor sheet 30, for example. The sensor sheet 30 has a plurality of sensing points within its surface. The sensor sheet 30 can be inserted between the battery cells 10, for example. The measuring device 102 may include one sensor sheet 30 . The measurement device 102 may include multiple sensor sheets 30 .

"Control device"
The control device 103 controls at least the charging current of the battery module 101 . The control device 103 may perform other controls in addition to controlling the charging current. The controller 103 may further control, for example, discharge current, cooling conditions, and the like. The control device 103 may include, for example, an arithmetic device, a storage device, an input/output interface, and the like.

FIG. 7 is a flow chart showing the processing of the control device.
The control device 103 controls the charging current based on the reaction force measurement result. When the reaction force is 0 (zero) (when the determination is “YES”), control device 103 sets the charging current of battery module 101 to the first upper limit. When the reaction force is greater than zero (when the determination is “NO”), control device 103 sets the charging current of battery module 101 to the second upper limit. The first upper limit is smaller than the second upper limit.

When the reaction force is zero, charge acceptance tends to be low. If the reaction force is zero and the battery is charged with a large current, Li may precipitate on the negative electrode. Precipitation of Li can be suppressed when the first upper limit is small. The first upper limit value may be, for example, 0.1 times or more and 0.99 times or less the second upper limit value. The first upper limit value may be, for example, 0.2 times or more and 0.9 times or less of the second upper limit value. The first upper limit value may be, for example, 0.3 to 0.8 times the second upper limit value. The first upper limit value may be, for example, 0.4 times or more and 0.7 times or less of the second upper limit value.

The second upper limit value may be, for example, 0.5C or more and 50C or less. The second upper limit value may be, for example, 1C or more and 30C or less. The second upper limit value may be, for example, 5C or more and 20C or less. Note that with a charging current of "1C", the rated capacity of the battery module 101 is charged in one hour.

FIG. 8 is an example of a current and reaction force profile.
The profile in FIG. 8 is measured, for example, in an electric vehicle. In an electric vehicle, the electric discharge of the battery module 101 drives the motor. The battery module 101 is charged by the regenerative braking. The vertical axis on the left side of FIG. 8 indicates the current. The discharge current is shown in the area above the "current=0" line. In the upper region, the discharge current increases as it goes upward. The charging current is shown in the area below the "current=0" line. In the lower area, the lower the area, the higher the charging current.

The vertical axis on the right side of FIG. 8 indicates the reaction force. In FIG. 8, the reaction force decreases over time. For most of FIG. 8, the current is trending in the upper region. That is, the discharge capacity is larger than the charge capacity. Therefore, the SOC is gradually decreasing. Due to the decrease in SOC, the electrode group 12 contracts and the reaction force becomes smaller.

A charging current up to the second upper limit is allowed in a region where the reaction force is greater than zero. On the other hand, in the region where the reaction force is zero, the charging current is set to the first upper limit value. That is, the charging condition is changed such that charging with a charging current exceeding the first upper limit is prohibited. The first upper limit is smaller than the second upper limit. Therefore, it is considered that the load applied to the negative electrode can be reduced. As a result, it is considered that the battery module 101 can have a long life.

Embodiments of the present disclosure (also referred to herein as "the embodiments") are described below. However, the following description does not limit the scope of the claims.

<Charge-discharge cycle test>
Test systems 1 to 3 shown in Table 1 below were constructed. A charge/discharge cycle test was performed on the test systems 1 to 3.

《Test system 1》
The test system 1 corresponds to an example. In the test system 1 , a space 13 was initially provided between the housing 11 and the electrode group 12 . In test system 1, a first upper limit was set for the charging current when the reaction force was zero. A second upper limit was set on the charging current when the reaction force was greater than zero. The first upper limit was smaller than the second upper limit.

《Test system 2》
Test system 2 corresponds to a comparative example. In the test system 2 as well, a space 13 was initially provided between the housing 11 and the electrode group 12 . However, in the test system 2, the second upper limit was always set to the charging current regardless of the magnitude of the reaction force.

《Test system 3》
Test system 3 corresponds to a comparative example. In the test system 3 , no space 13 was provided between the housing 11 and the electrode group 12 . In the test system 3, the charging current was always set to the second upper limit.

<Results>
Table 1 above shows the reaction force at 100 cycles (100 cyc). The values shown in the "reaction force" column of Table 1 above are relative values assuming that the reaction force in the test system 1 is 100.

After 100 cycles, the battery cell 10 was disassembled and the presence or absence of deposition of Li was confirmed on the surface of the negative electrode. The confirmation results are shown in Table 1 above.

The reaction force at 100 cycles in Test System 2 is equivalent to the reaction force at 100 cycles in Test System 1 . However, in test system 2, precipitation of Li was confirmed. This is probably because when the reaction force is zero (that is, when the charge acceptability is low), control to reduce the upper limit of the charging current is not performed.

In test system 3, precipitation of Li was not confirmed. However, in test system 3, the reaction force at 100 cycles increased. This is probably because, in the system under test 3, the electrode group 12 is in contact with the housing 11 from the beginning, and there is no period during which the reaction force is zero.

Test system 1 had a small reaction force at 100 cycles. Moreover, in the test system 1, precipitation of Li was not confirmed after 100 cycles. This is probably because in the system under test 1, control was performed to reduce the upper limit of the charging current when the reaction force was zero.

This embodiment and this example are illustrative in all respects. This embodiment and this example are not restrictive. The technical scope defined by the description of the scope of claims includes all modifications equivalent to the scope of the claims. The technical scope defined by the description of the claims also includes all modifications within the scope of equivalents of the claims.

10 battery cell 11 housing 12 electrode group 13 space 20 restraining member 21 first restraining plate 22 second restraining plate 23 restraining band 30 sensor sheet 100 battery system 101 battery module 102 measuring device , 103 controller.

Claims (1)

battery module,
including a measuring device, and a control device;
the battery module includes one or more battery cells and a restraining member,
The binding member applies a binding load to the battery cell,
The measuring device measures the reaction force,
The reaction force is a force acting from the battery cell to the restraint member in a direction opposite to the direction in which the restraint load acts,
The control device is
setting a first upper limit to the charging current of the battery module when the reaction force is zero;
setting a second upper limit to the charging current of the battery module when the reaction force is greater than zero;
The first upper limit is smaller than the second upper limit,
battery system.

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