WO2016035280A1

WO2016035280A1 - Battery system, electric vehicle, and method for charging battery system

Info

Publication number: WO2016035280A1
Application number: PCT/JP2015/004251
Authority: WO
Inventors: 杉山　茂行; 青木　護
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2014-09-05
Filing date: 2015-08-25
Publication date: 2016-03-10

Abstract

In order to provide a battery system making it possible to perform appropriate charging according to the characteristics of each battery and capable of suppressing damage to a switch, the battery system is equipped with: a nonaqueous first battery; an aqueous second battery connected in parallel with the first battery; and a switch connected to the first battery in series. The charging of the first and second batteries is controlled by a constant-current/constant-voltage charging while the first and second batteries are connected in parallel with each other. When a decrease in the charging current is detected in a terminal phase of this charging, the connection of the first battery is cut by operating the switch so that the charging current flows through the second battery.

Description

Battery system, electric vehicle, and battery system charging method

The present invention relates to a battery system, an electric vehicle using the battery system, and a charging method for the battery system.

Conventionally, aqueous lead acid batteries that are relatively inexpensive and have a high track record of use have been widely used as power sources for electric vehicles. In recent years, non-aqueous liquid lithium ion batteries that have a longer life than lead-acid batteries, have a high voltage, and have a high energy density have been used. And these lithium ion batteries and lead acid batteries are charged by the charging method according to the characteristic of each battery.

By the way, a battery system is known in which a lithium ion battery and a lead storage battery are connected in parallel to increase capacity and improve performance. In this case, it is conceivable to employ a charging method according to the characteristics of the lithium ion battery or a charging method according to the characteristics of the lead storage battery.

However, if one of the charging methods according to the characteristics of the lithium-ion battery or the lead-acid battery is adopted, the battery system as a whole cannot be properly charged.

Therefore, in Patent Document 3, a lithium ion capacitor unit and a lead storage battery are connected in parallel, and during charging, the lithium ion capacitor unit and the lead storage battery are disconnected, and the lithium ion capacitor unit and the lead storage battery are separately provided. A DC power supply for charging has been proposed.

JP 2003-174734 A JP 2004-25979 A JP 2011-199951 A (paragraph number [0025])

However, the configuration and operation of the DC power supply device disclosed in Patent Document 3 may be complicated. In addition, a switch or the like used to disconnect the lithium ion capacitor unit from the lead storage battery may be damaged.

Embodiments of the present invention provide a battery system that can be appropriately charged according to the characteristics of each battery with a simple configuration and can suppress damage to a switch, an electric vehicle using the battery system, and a battery system. An object is to provide a charging method.

A battery system according to an embodiment of the present invention includes a first non-aqueous liquid battery, an aqueous second battery connected in parallel with the first battery, and the first battery in series. In the state where the first battery and the second battery are connected in parallel, the charging control is performed by constant current and constant voltage charging, and the charging current at the end of the charging is A battery system characterized by detecting a lowered state, operating the switch to cut off the connection of the first battery, and controlling the charging current to flow through the second battery.

According to the embodiments of the present invention, a battery system capable of appropriately charging according to the characteristics of each battery with a simple configuration and suppressing damage to a switch, an electric vehicle using the battery system, and A battery system charging method can be provided.

In the battery system which concerns on embodiment of this invention, it is a schematic block diagram which shows the state in which the 1st battery (lithium ion battery) and the 2nd battery (lead storage battery) were connected in parallel. It is a graph which shows the discharge characteristic at the time of use of the 1st battery and the 2nd battery. It is a graph which shows the discharge characteristic at the time of use in the case of connecting the 1st battery and the 2nd battery in parallel. It is a graph which shows the discharge characteristic of the battery system. It is the block block diagram. It is explanatory drawing which shows the sequence of the charging method of the battery system which concerns on embodiment of this invention. It is a graph which shows typically the charge system of the 1st battery. It is a graph which shows typically the charge system of the 2nd battery. It is a graph which shows typically the charging method of the battery system concerning the embodiment of the present invention. It is explanatory drawing which shows the Example of the 1st battery and 2nd battery which concern on embodiment of this invention (Example 1). It is explanatory drawing which shows the Example (Example 2). It is a graph which shows the discharge characteristic at the time of use in a general battery.

Hereinafter, a battery system according to an embodiment of the present invention will be described with reference to FIGS. 1 to 12. The battery system of the present embodiment is used by being mounted on an electric vehicle such as an electric vehicle, for example.

FIG. 1 is a configuration diagram showing an outline of a battery system. As shown in FIG. 1, the battery system 1 is configured by combining a first battery 10 and a second battery 20. The first battery 10 and the second battery 20 are electrically connected in parallel.

Specifically, a lithium ion battery is used as the first battery 10, and a lead storage battery is used as the second battery 20. These are connected in parallel via respective positive and negative terminals. A protective circuit 11 and a switch 12 are connected to the first battery 10 in series. The protection circuit 11 has a function of interrupting energization and protecting the first battery 10 when a large current discharge such as overcharge, overdischarge, or external short circuit occurs in the first battery 10. The switch 12 has a function of interrupting charging of the first battery 10 and stopping charging of the first battery 10.

The lithium ion battery is a type of non-aqueous liquid secondary battery, and is a secondary battery in which lithium ions in the electrolyte are responsible for electrical conduction. In a typical cell configuration, a lithium-containing metal oxide such as lithium cobaltate, lithium nickelate, or lithium iron phosphate is used for the positive electrode, a carbon material is used for the negative electrode, and an organic electrolyte is used for the electrolytic solution. It has a wound electrode body wound through a separator. The electrode body is soaked in a non-aqueous electrolyte and accommodated in a cylindrical battery can.

Such a lithium ion battery has a high voltage, high energy density, high charge / discharge energy efficiency, and rapid charge / discharge. On the other hand, it has a characteristic that is weak against overcharge and overdischarge. Further, when the battery is stored in a fully charged state, the deterioration rapidly progresses, and it has a characteristic that the capacity recoverability is better in the discharge storage than in the charge storage. The capacity recoverability is a property of recovering to a level compared to the initial capacity when charge / discharge is performed after storage.

The lead acid battery is an aqueous solution type secondary battery using lead dioxide for the positive electrode, spongy lead for the negative electrode, and dilute sulfuric acid as the electrolyte. Each cell chamber accommodates an electrode group in which a plurality of positive electrode plates and negative electrode plates are laminated via a glass fiber separator.

Lead-acid batteries are relatively inexpensive and have a long history of use. On the other hand, it is desirable to maintain a fully charged state because it deteriorates quickly when overdischarge is performed, and has a characteristic that capacity recovery is better when stored under charge than when stored during discharge. .

The nominal voltage of the first battery 10 and the second battery 20 is higher in the first battery 10 than in the second battery 20. In other words, the nominal voltage of the second battery 20 is lower than the nominal voltage of the first battery 10.

First, general discharge characteristics when using this type of battery will be described with reference to FIG. FIG. 12 shows a discharge curve in use in relation to the state of charge (SOC: State Of Charge) and voltage. The horizontal axis shows the state of charge (%) in the range of 100% to 0%, and the vertical axis shows the voltage (V).

As shown in FIG. 12, when the discharge continues in the discharge curve, the state of charge decreases, that is, the remaining charge capacity decreases, and the voltage decreases along with this. Here, unstable regions A and A ′ exist in the initial discharge portion and the final discharge portion, and a stable region B exists in an intermediate portion between the unstable regions A and A ′.

The unstable regions A and A ′ are regions with a large rate of change in which the voltage changes greatly with a slight change in the state of charge. In other words, this is a region where the discharge curve changes sharply and the voltage changes greatly with a slight change in discharge capacity.

Specifically, the unstable region A is a region in which the voltage is greatly decreased due to a slight decrease in the state of charge from the full charge to the initial stage of discharge. The unstable region A ′ is a region where the voltage is greatly reduced due to a slight decrease in the state of charge at the end of discharge to complete discharge.

The stable region B is a region with a small change rate with little change in voltage even when the state of charge changes, and the discharge curve changes slowly, and the change in voltage hardly changes even when the discharge capacity changes. It is an area.

Thus, the discharge curve is drawn as a curve that shifts from the unstable region A to the start portion of the stable region B and then shifts from the end portion of the stable region B to the unstable region A ′. Also, the actual voltage range is wider than the nominal voltage range of the battery. In actual use, there may occur an overcharge in which charging is performed to a voltage higher than the nominal voltage range or an overdischarge in which discharge is performed to a voltage lower than the nominal voltage range.

Next, discharge characteristics during use of the first battery 10 and the second battery 20 in the present embodiment will be described with reference to FIG. 2A shows the discharge characteristics of the first battery 10, and FIG. 2B shows the discharge characteristics of the second battery 20. FIG. 2 shows the discharge characteristics corresponding to FIG. 8 above. Similarly, the horizontal axis shows the state of charge (%) in the range of 100% to 0%, and the vertical axis shows the voltage (V). ing.

The first battery 10 and the second battery 20 have unstable regions A and A ′ in the initial discharge portion and the final discharge portion, respectively, in the same manner as in FIG. A stable region B exists in the portion.

Specifically, the first battery 10 and the second battery 20 have unstable regions A and A ′ in which the rate of change of the voltage with respect to the discharge capacity is steep at the beginning and end of discharge. In the middle part between A and the unstable region A ′ at the end of discharge, there is a stable region B in which the rate of change of the voltage with respect to the discharge capacity is relatively smaller than the unstable regions A and A ′.

The unstable region A occurs when the state of charge is approximately 100% to 80%, and the unstable region A ′ occurs when the state of charge is approximately 20% to 0%. Therefore, the stable region B occurs when the state of charge is approximately 80% to 20%. More specifically, the change rate of the voltage (V) with respect to the discharge capacity (%) in the stable region B is −0.5 or more, which is a substantially flat curve. That is, for example, when the state of charge changes by -10%, the battery voltage is changed from 3.7V to 3.6V, and the change rate of the voltage at that time is -2.7% with respect to 3.7V. Therefore, the rate of change is 0.27 [−]. That is, the rate of change is 0.5 or less. The unit at this time is [-] dimensionless. On the other hand, the voltage change in the unstable region A ′ changes by 0.3 V from 3.3 to 3.0 V when the state of charge changes from 10% to 0%, for example. This rate of change is 9%. Therefore, since the voltage changes by 9% when the state of charge changes by 10%, the rate of change at this time is 0.9 [-], which is larger than 0.5. This value of 0.5 is one example, and the ratio of the change in voltage (V) (%) to the actual change in discharge capacity (%) varies depending on the type of battery, but is generally 0.1-0. It is divided by the value of .9.

However, the discharge characteristics of the first battery 10 and the second battery 20 are mainly different in the following points.

(1) The voltage in the stable region B of the first battery 10 is higher than the voltage in the stable region B of the second battery 20. Conversely, the voltage in the stable region B of the second battery 20 is lower than the voltage in the stable region B of the first battery 10. Thus, there is a voltage difference in the stable region B.

(2) The voltage height in the unstable region A of the first battery 10 is narrow, whereas the voltage height in the unstable region A of the second battery 20 is wide. That is, in the unstable region A of the second battery 20, the voltage is greatly reduced by a slight change in the state of charge.

(3) While the voltage range in the unstable region A ′ of the first battery 10 is wide, the voltage range in the unstable region A ′ of the second battery 20 is narrow. That is, in the unstable region A ′ of the first battery 10, the voltage sharply decreases greatly due to a slight change in the state of charge.

Further, in addition to the discharge characteristics of the first battery 10 and the first battery 10, the final voltage Vt in the stable region B of the first battery 10 and the stable region B of the second battery 20 The initial voltage Vc is configured to substantially match. The coincidence between the voltage Vt at the end portion and the voltage Vc at the start portion can be realized, for example, by adjusting the number of cells connected in series in the first battery 10 and the second battery 20.

3, the discharge characteristics when the first battery 10 and the second battery 20 are electrically connected in parallel will be described. The first battery 10 is mainly preferentially discharged from the start of discharge until the voltage Vt at the end of the stable region B of the first battery 10 (shown voltages Vh to Vm). In this case, the second battery 20 is hardly discharged, and only the voltage changes following the voltage of the first battery 10.

This is based on the discharge characteristics of the first battery 10 and the second battery 20 that the voltage in the stable region B of the second battery 20 is lower than the voltage in the stable region B of the first battery 10. Further, the first battery 10 and the second battery 20 are connected in parallel, and this is because the voltages of the respective batteries become equal.

Next, the voltage Vt at the end of the stable region B of the first battery 10 shifts to the stable region B and the unstable region A ′ of the second battery 20, and discharges to near 0 V (shown voltages Vm to Vl). In this case, discharge is mainly performed by the second battery 20.

This discharge is based on the fact that the voltage Vt at the end portion of the stable region B of the first battery 10 and the voltage Vc at the start portion of the stable region B of the second battery 20 are substantially matched. Yes.

Therefore, discharge is performed mainly in the stable region B of the first battery 10 during the voltage Vh to Vm, and discharge is performed mainly in the stable region B of the second battery 20 during the voltage Vm to Vl. As a result, the discharge is transferred from the stable region B of the first battery 10 to the stable region B of the second battery 20.

FIG. 4 shows a state in which the discharge characteristics of the first battery 10 and the second battery 20 connected in parallel shown in FIG. 3 are synthesized. As shown in FIG. 4, the stable region B of the first battery 10 and the stable region B of the second battery 20 are connected so as to be continuous, and the individual batteries of the first battery 10 and the second battery 20 are connected. As compared with the case, the stable region B is expanded. In the range of voltages Vh to Vm, the first battery 10 is mainly discharged, and in the range of voltages Vm to Vl, the second battery 20 is mainly discharged.

In the configuration of the battery system 1 as described above, when the user actually uses the electric vehicle, the first battery 10 is preferentially discharged, so that the first battery 10 is charged and discharged with high frequency. become. That is, the frequency with which the second battery 20 is charged and discharged is lower than the frequency with which the first battery 10 is charged and discharged.

Therefore, by making the first battery 10 a battery having a capacity recoverability superior to the capacity recoverability during charge storage, the capacity recovery when the second battery 20 is stored under discharge can be restored. By making the battery more excellent in capacity recovery during storage when charged, the overall performance of the battery can be improved.

Next, the configuration of the battery system will be described with reference to the block diagram of FIG. As shown in FIG. 5, the battery system 1 includes a battery unit 30 and a control device 6. The battery unit 30 is provided with a first battery 10 and a second battery 20. The first battery 10 and the second battery 20 are connected in parallel.

Specifically, a series circuit in which the first battery 10, the protection circuit 11, the switch 12 and the current sensor 2a are connected and a series circuit in which the second battery 20 and the current sensor 2b are connected are connected in parallel. Has been. A load 3, that is, a motor of an electric vehicle is connected to both ends of these series circuits.

Further, the first battery 10 and the second battery 20 are connected to the commercial power source 5 via the charger 4 and charged as necessary. Further, the battery unit 30 is connected to the control device 6. The protection circuit 11, the switch 12 and the

current sensors

2a and 2b are controlled by the control device 6.

The control device 6 controls the entire system, has a charge control unit 61, and has a function of controlling charge / discharge states, voltages, currents, and the like of the first battery 10 and the second battery 20. is doing.

The protection circuit 11 includes a relay, a switching element, and the like. When the first battery 10 is overcharged or overdischarged, the protection circuit 11 operates to cut off the energization of the first battery 10 to ensure safety. It is like that. Specifically, the charging current and the discharging current are monitored by the current sensor 2a, and based on this, a control signal is output from the control device 6 to the protection circuit 11, and the protection circuit 11 is ON / OFF controlled.

The switch 12 operates to disconnect the first battery 10 from the charging circuit and stop the charging of the first battery 10. This switch 12 can be comprised by a relay or a switching element, for example.

The

current sensors

2a and 2b are composed of shunt resistors. Hall elements or magnetoresistive elements may be used for the

current sensors

2a and 2b.

A charging method of the battery system 1 configured as described above will be described with reference to FIGS.

First, it is desirable that the first battery 10 normally adopts a charging method using a constant current and a constant voltage. This charging method can be charged at a relatively high speed and is effective in preventing overcharging. That is, it is possible to prevent the danger that the organic electrolyte is decomposed to generate heat or ignite in an overcharged state with a high voltage.

In addition, it is desirable to adopt a charging method including equal charge for the second battery 20. In the case of the second battery 20, the distribution of the specific gravity of the electrolyte in the battery varies. In order to eliminate this variation, it is necessary to perform uniform charging.

In the case of the battery system 1 in which the first battery 10 and the second battery 20 are connected in parallel, if a charging method using a constant current and a constant voltage according to the characteristics of the first battery 10 is adopted, Although the battery 10 is appropriately charged, the second battery 20 is not uniformly charged, and the specific gravity distribution of the electrolyte cannot be made uniform. In addition, when a charging method according to the characteristics of the second battery 20 is adopted, a relatively large current flows continuously, so that the protection circuit 11 of the first battery 10 operates and the charging current is cut off, so that the charging capacity is reduced. A problem arises in that it cannot be sufficiently secured.

This embodiment provides a charging method capable of performing appropriate charging according to the characteristics of the first battery 10 and the second battery 20.

As shown in FIG. 6, the charging method of the present embodiment is generally performed in a sequence of five steps (S1 to S5) from the start of charging (S0). The first step (S1) is constant current charging, and the second step (S2) is constant voltage charging. The third step (S3) is a step of stopping the charging of the first battery 10, and the fourth step (S4) is a constant current charging of the second battery 20. Further, the fifth step (S5) is constant current charging and corresponds to equal charging.

In such a charging method, both the first battery 10 and the second battery 20 are charged in the first step (S1) and the second step (S2), and the fourth step (S4). ) And the fifth step (S5), only the second battery 20 is charged.

7 and 8 show charging methods suitable for the first battery 10 and the second battery 20, respectively. FIG. 7 shows a charging method for the first battery 10, and FIG. 8 shows a charging method for the second battery 20. The charging voltage (battery terminal voltage) and current change with time are shown, the horizontal axis shows charging time (h), and the vertical axis shows voltage (V) and current (A).

As shown in FIG. 7, the first battery 10 is initially charged with a constant current charge (CC), and after reaching a predetermined voltage, a constant voltage charge (CV) is performed with a recommended charge voltage (RV). is there. Overcharging can be prevented by not exceeding the recommended charging voltage. During the constant voltage charging (CV) period, the charging current changes so as to gradually decrease, and the charging current is substantially reduced at the end of charging. The recommended charging voltage (RV) is a voltage set based on the upper limit charging voltage in each temperature range (for example, standard temperature range 0 ° C. to 45 ° C., high temperature range 45 ° C. to 60 ° C.).

As shown in FIG. 8, the second battery 20 is initially subjected to constant current charging (CC), and thereafter, the charging current is reduced to perform equal charging (EC) with constant current, and the recommended charging voltage (RV). This is a charging method. Therefore, the charge capacity can be ensured and the specific gravity distribution of the electrolyte can be made uniform.

In this embodiment, as shown in FIG. 9, the first battery 10 charging method (FIG. 7) and the charging method of the second battery 20 (FIG. 8) are combined, and appropriate according to the characteristics of each battery. A simple charging method. FIG. 9 shows the time variation of the charging voltage and current as in FIGS. 7 and 8, the horizontal axis shows the charging time (h), and the vertical axis shows the voltage (V) and current (A ).

In FIG. 9, first, both the first battery 10 and the second battery 20 connected in parallel are charged by constant current charging (CC) (first step (S1)), followed by constant voltage charging. Charging is performed at (CV) (second step (S2)). Next, a state in which the charging current at the end of charging in the constant voltage charging (CV) is reduced is detected, and the charging circuit of the first battery 10 is cut off as the charging is completed, and the charging of the first battery 10 is stopped. (Third step (S3)).

In the first step (S1), the first battery 10 is charged with a standard 0.7 It. For example, if the first battery 10 has a capacity of 150 Ah, it is charged at 100 A. In the second step (S2), when the first battery 10 reaches 4 V / cell, the charging current changes so as to decrease, and when the charging reaches 0.05 It, it is determined that the charging is completed. Based on this determination, the charging circuit of the first battery 10 is shut off.

Specifically, as shown in FIG. 5, the voltage drop of the current sensor 2a is detected by the charging control unit 61 of the control device 6, and the charging control unit 61 determines that the charging current has decreased to a predetermined value. Based on this determination, the charging control unit 61 transmits a cutoff (OFF) signal to the switch 12. Then, the switch 12 is shut off and charging of the first battery 10 is stopped. In this case, since the switch 12 is operated with a low current, damage to the switch 12 can be suppressed.

As shown in FIG. 9 again, the second battery 20 is charged alone with the first battery 10 disconnected from the charging circuit (fourth step (S4) to fifth step). (S5)). In this step, since the second battery 20 is charged independently, the charge suitable for the characteristics of the second battery 20 can be performed.

First, the initial constant current charging (CC) is performed (fourth step (S4)), and then the charging current is decreased, and then the equal charging (EC) is performed with the constant current (fifth step (S5)). )).

In the fourth step (S4), since the second battery 20 is charged alone, the second battery 20 reaches a predetermined voltage in a short time, and then the charging current decreases. When the charging current is reduced to a certain level, equal charge (EC) is continuously performed at a constant current, and the electrolyte solution in the battery is circulated by the voltage at that time, and the distribution of the specific gravity of the electrolyte solution is made uniform. It becomes like this.

The charging control as described above is executed by a program stored in the control device 6. In the third step (S3), the fourth step (S3) is performed so that charging of the second battery 20 is started immediately after the charging circuit of the first battery 10 is shut off without leaving a time interval. You may make it transfer to S4). The program that can be executed by the charger 4 may be executed by the charger 4, and the control of both the control device 6 and the charger 4 may be combined to execute the above-described charging control.

As described above, according to the present embodiment, a battery system that can be appropriately charged according to the characteristics of the first battery 10 and the second battery 20 with a simple configuration and can suppress damage to the switch 12. 1. It is possible to provide an electric vehicle using the battery system and a battery system charging method.

Next, a specific example in which the first battery 10 and the second battery 20 according to the present embodiment are combined will be described with reference to FIGS. 10 and 11.

(Example 1)
As shown in FIG. 10, the first battery 10 is a LiFePO 4 type lithium ion battery. The battery has a nominal voltage of 3.2 V, and 18 cells are connected in series. Therefore, the nominal voltage as a lithium ion battery is 57.6V. Moreover, the protection circuit 11 (refer FIG. 5) which monitors charging / discharging is provided.

On the other hand, the second battery 20 is an open-type lead storage battery, the nominal voltage of the cell is 2V, and 24 cells are connected in series. Therefore, the nominal voltage as a lead storage battery is 48V.

By configuring the first battery 10 and the second battery 20 in parallel as described above, the above-described operation and effect can be realized.

(Example 2)
As shown in FIG. 11, the first battery 10 is a 18650 type lithium ion battery. This battery has a nominal voltage of 3.6 V, and 16 cells are connected in series. Therefore, the nominal voltage as a lithium ion battery is 57.6V. Moreover, the protection circuit 11 (refer FIG. 5) which monitors charging / discharging is provided. The second battery 20 is an open-type lead storage battery, and is the same as that of the first embodiment. Note that the first battery 10 does not necessarily need to be formed of a 18650 type lithium ion battery, and may be formed of a 3.6 V lithium ion battery such as a lithium polymer battery.

By configuring the first battery 10 and the second battery 20 to be connected in parallel, the battery system 1 that can realize the above-described effects can be obtained.

The present invention is not limited to the configuration of the above-described embodiment, and various modifications can be made without departing from the spirit of the invention. Moreover, the said embodiment is shown as an example and is not intending limiting the range of invention.

For example, as a means for stopping the charging of the first battery, a protection circuit may be used without providing a special switch.

The battery system and the battery system charging method of the present invention can be suitably used for electric vehicles such as electric vehicles, electric scooters and forklifts. Moreover, it is not limited to an electric vehicle, It can apply also to another apparatus and apparatus.

DESCRIPTION OF SYMBOLS 1 ...

Battery system

2a, 2b ... Current sensor 3 ... Load 4 ... Charger 5 ... Commercial power supply 6 ... Control apparatus 61 ... Charge control part 10 ... 1st Battery (lithium-ion battery)
DESCRIPTION OF SYMBOLS 11 ... Protection circuit 12 ... Switch 20 ... 2nd battery (lead acid battery)
30 ... Battery part A, A '... Unstable region B ... Stable region

Claims

A first non-aqueous liquid battery;
An aqueous second battery connected in parallel with the first battery;
A switch connected in series to the first battery;
In the state where the first battery and the second battery are connected in parallel, charging control is performed by constant current and constant voltage charging, and a state in which the charging current at the end of this charging is reduced is detected, A battery system characterized by operating a switch to disconnect the connection of the first battery and controlling the charging current to flow through the second battery.
The battery system according to claim 1, wherein the first battery is a lithium ion battery, and the second battery is a lead acid battery.
3. The battery system according to claim 2, wherein the lead storage battery of the second battery is an open type lead storage battery.
An electric vehicle using the battery system according to any one of claims 1 to 3.
In a battery system having a first nonaqueous liquid battery and an aqueous second battery connected in parallel with the first battery,
Charging the first battery and the second battery with a constant current;
A step of constant voltage charging following this constant current charging;
Shutting off the charging of the first battery by cutting off the first battery from the charging circuit in a state where the charging current at the end of the constant voltage charging is reduced;
Next, charging the second battery with a constant current;
After the constant current charging, charging the second battery evenly;
A charging method for a battery system, comprising: