KR101719685B1 - Method for charge and discharge of redox flow battery - Google Patents

Abstract

A charge / discharge control method for a secondary battery including a unit cell including a positive electrode, a negative electrode and an electrolyte, the method comprising: charging the secondary battery including zinc metal ions; Performing a high-current discharge when the charged state meets a predefined condition, and recharging the secondary battery when the unevenness between the positive electrode and the negative electrode is dissolved by the high-current discharge.

Description

METHOD FOR CHARGE AND DISCHARGE OF REDOX FLOW BATTERY [0002]

The present invention relates to a charge / discharge control method for a secondary battery, and more particularly, to a charge / discharge control technique for a secondary battery including zinc and a flow cell.

The most basic battery operation and control method is a method of operating a redox flow battery (RFB) by charging and discharging the battery by charging and discharging, Performance and Efficiency.

However, the Zinc-Bromine Redox Flow Battery has different charging and discharging characteristics from other batteries (lithium ion, lead battery, etc.).

When a general battery charge / discharge control method is used, zinc at the anode generated at the time of charging is deposited on the electrode and irregularly deposited on the electrode surface. During the discharge, zinc deposited on the surface of the anode electrode is dissociated through an electrochemical reaction, and is then reacted with bromine ions and then reversibly reacted with the ZnBr2 solution.

Figure 1 shows a unit cell of a zinc-bromine flow cell stack in the prior art.

1, a unit cell 10 of a stack of a zinc-bromine flow cell includes a positive electrode 11, a negative electrode 13, a separator 15, electrolyte 17 and 19, 21).

It can be seen that the deposition of zinc (Zn) on the positive electrode 11 is made non-uniform when the general charging system is used.

KR 2014-0060315 P KR 1506951 P

Disclosure of Invention Technical Problem [6] The present invention provides a method for controlling charging and discharging of a secondary battery that controls charging conditions of a secondary battery to uniformly deposit zinc under the optimum charge and discharge conditions to increase the efficiency of the stack upon discharging.

According to one aspect of the present invention, a charge / discharge control method for a secondary battery includes a unit cell including a positive electrode, a negative electrode, and an electrolyte, the method comprising: step; Performing a high-current discharge when the charged state meets a predefined condition, and recharging the secondary battery when the unevenness between the positive electrode and the negative electrode is dissolved by the high-current discharge.

Wherein the performing comprises:

If the state of charge (SOC) of the secondary battery satisfies 50% or 90%, the high current discharge can be performed.

Wherein the performing comprises:

When the condition (SOC) of the secondary battery is 20% to 30%, the high-current discharge can be performed.

Wherein the performing comprises:

When the condition (SOC) of the secondary battery is 40% to 50%, the high current discharge can be performed.

Wherein the performing comprises:

When the condition (SOC) of the secondary battery is 70% to 80%, the high current discharge can be performed.

Wherein the performing comprises:

If the condition (SOC) of the secondary battery is 80% to 90%, the high current discharge can be performed.

The secondary battery includes:

A zinc-fluorine-flow cell.

The secondary battery includes:

A zinc-chlorine-flow battery.

The secondary battery includes:

Zinc-iodine < / RTI > flow cell.

The secondary battery includes:

Zinc-air.

According to the present invention, the efficiency of the stack and the module can be improved compared to the conventional one by controlling the specific charging state at the time of charging. Particularly, when the secondary battery including zinc, for example, a zinc-bromine flow cell, is filled with zinc uniformly on the positive electrode, the battery can be uniformly discharged at a high current in a specific charging state, One zinc can be dissolved to increase the discharge of the stack, increase the energy efficiency of the stack and module, and improve the durability.

In addition, uniform zinc deposition can prevent damage to the membrane due to dendrite inside the stack and pin-hole damage, thereby increasing the durability of the stack, resulting in a more economical effect .

In addition, when a high current discharge is performed in a state of being charged with a specific battery during charging, the zinc of the positive electrode is dissolved and has a uniform layer and is excellent in discharging characteristics during discharging, which is very efficient in increasing the efficiency of the flow cell including zinc.

Figure 1 shows a unit cell of a zinc-bromine flow cell stack in the prior art.
2 is a view showing a configuration of a control system of a secondary battery according to an embodiment of the present invention.
FIG. 3 is a view illustrating a form of zinc deposition on the anode side of a stack according to charge control operation of a secondary battery according to an embodiment of the present invention.
FIG. 4 shows a stack voltage curve according to a charge control operation of a conventional zinc-bromine flow cell.
FIG. 5 shows a stack voltage curve according to charge control operation of a zinc-bromine flow cell according to an embodiment of the present invention.
FIG. 6 shows a stack voltage curve according to charge control operation of a zinc-bromine flow cell according to another embodiment of the present invention.

The invention will be described in more detail in the following examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

2 is a diagram showing a configuration of a control system of a secondary battery according to an embodiment of the present invention

Referring to FIG. 2, the control system 100 is an apparatus for controlling the secondary battery 101. In particular, it is possible to control a flow cell containing zinc.

The control system 100 controls the charge and discharge currents of the secondary battery 101 based on the charging and discharging currents flowing through the secondary batteries 101 detected by the ammeter 107 and the terminal voltages of the secondary batteries 101 detected by the voltmeter 105. [ Control of charging and discharging, and calculation of the state of charge (SOC) of the secondary battery 101 are performed. After the first charge, if the charge state (SOC) satisfies the predefined condition, the secondary charge is performed.

FIG. 3 is a view illustrating a form of zinc deposition on the anode side of a stack according to charge control operation of a secondary battery according to an embodiment of the present invention. In particular, a zinc-bromine flow cell is shown.

3, the unit cell 109 of the stack of the zinc-bromine flow cell includes a positive electrode 111, a negative electrode 113, a separator 117, an electrolyte 119, and a collecting plate 121 at both ends. Respectively.

At this time, it can be seen that zinc deposition on the positive electrode 111 during the charge control operation is relieved and the deposition of the zinc can be uniformly maintained.

During the charging and discharging of the zinc-bromine flow cell, zinc deposition and bromine ion generation occur in the positive electrode 111 and the negative electrode 113, respectively, and the charging progresses. The discharge proceeds in a reversible range due to its reverse process do. The uniform deposition of zinc on the positive electrode 111 during charging will improve the durability of the flow energy storage device including the stack and the module. However, the positive electrode 111 includes a very irregular active range, and deposition of zinc is made to form irregularities.

According to the embodiment of the present invention, after a primary charge, a portion where zinc (Zn +) is irregularly deposited on an anode electrode 111 is divided into a state of charge (SOC) of 50% or a state of charge of 90% Current, that is, a high-current discharge is performed. At this time, the zinc-bromine flow cell is operated at the maximum current that can be stable inside the stack at the time of discharging.

Particularly, when a high current is discharged at 50% and 90% of the specific battery state (SOC), the positive electrode 101 is electrochemically dissolved from the part where the deposition of zinc on the positive electrode 101 is performed to the electrolyte 109, The portion is planarized with the other zinc deposition portions. Here, the operating temperature is room temperature, and ranges from 10 degrees to 40 degrees.

50% of the state of charge (SOC) refers to the total amount of charge from 40 kWh to 42 kWh when calculating 8 charges of 6.25 kWh class of 50 kWh module. 90% of the state of charge (SOC) is from 71 kWh to 73 kWh Tells the total charge. And the discharge is from 15 A to 38 A, which does not overload the stack 109, and the high current is 30 A or more.

Then, irregularly deposited zinc (Zn +) deposited on the positive electrode 111 can be dissolved from the uneven portion 117. Once all of the dissolution is achieved, the zinc is refilled to uniformly control the zinc deposition.

However, the charging condition is not limited to 50% and 90%, but the specific charging state (SOC) corresponding to the charging condition is 20% to 30%, 40% to 50%, 70% to 80%. It can be set from 80% to 90%.

In addition, the specific state of charge (SOC) corresponding to the charging condition can be set to 30% to 60% and 70% to 90%.

As such, the specific state of charge (SOC) can be variously specified in a range including 50% and 90%.

As described above, it is confirmed that the charging condition of the zinc-bromine flow cell is controlled to uniformize the deposition of zinc under the optimum operation (charge and discharge) conditions, thereby increasing the efficiency of the stack at the time of discharging and increasing the durability at the same time .

Also, zinc (Zn +) uniformly deposited on the positive electrode 101 can be confirmed to have a constant oxidation / reduction reaction of zinc-bromine upon discharge.

Here, although the zinc-bromine flow battery has been described, the optimum charge control operation according to the embodiment of the present invention can be applied to a secondary battery module system including zinc metal ions generating irregularities. For example, it can be a zinc-fluorine flow cell, a zinc-chlorine flow cell, a zinc-iodine flow cell, and a zinc-air flow cell. In addition, it may be a flow battery including a metal such as lead, zinc, and cerium.

FIG. 4 shows a stack voltage curve according to charge control operation of a conventional zinc-bromine flow cell, and FIG. 5 shows a stack voltage curve according to charge control operation of a zinc-bromine flow cell according to an embodiment of the present invention. And FIG. 6 shows a stack voltage curve according to charge control operation of a zinc-bromine flow cell according to another embodiment of the present invention.

Referring to FIGS. 4, 5 and 6, when the stack internal voltage curve according to the charge control of the zinc-bromine flow cell is checked, the charge state of FIG. 5 is 50% When the charge state is 90%, zinc is dissolved in the portion of the electrode which is severely irregularly formed in the positive electrode through the high current discharge, and charging is performed while uniformly depositing the same again, thereby progressing the more efficient battery discharge.

As shown in FIG. 4, according to the charge control operation, when the charging according to the conventional method is performed as shown in FIG. 4, the zinc of the positive electrode is sequentially deposited and discharged through the high current discharge.

On the other hand, in the control # 1 system in the case of the charging state (SOC) of 50% or in the control # 2 system of the state of charge (SOC) of 90% as shown in FIG. 6, the unevenness of the zinc of the positive electrode is flattened And the discharge time and stack efficiency are improved by the discharge slope of the voltage curve.

4, the control # 1 is a charge / discharge graph in which the high current discharge is performed once at the charge state of 50% to eliminate the uniform distribution of the zinc deposit. The control # 2 of FIG. 5 includes the high # 4 control # Discharging graph in which the high current discharge is once performed at 50% of the state and the high current discharge is once again performed at the charge state of 90% to eliminate zinc deposition unevenness. Accordingly, FIG. 4 shows a high current discharge once at 50% of the charged state and FIG. 5 shows a high current discharge at 50% and 90% of the charged state. Thereafter, when the SOC reached 95%, the discharge proceeded.

Meanwhile, in the following Examples and Comparative Examples, the performance of the zinc-bromine flow battery according to the operation method through charge control was compared using a 50 kWh module.

In the zinc-bromine flow cell, the electrolytic solution contained zinc bromine (ZnBr2) (30-35 wt%), complexing agent (QBr) (10-15 wt%) and conductive agent (ZnCl2) The dissolved solution was used.

In addition, the charging voltage was 25 Kw, and 10 ~ 25 kW was applied during discharging to discharge.

Also, the energy efficiency, the charge efficiency, and the voltage efficiency were calculated and compared.

≪ Example 1 >

Table 1 shows the results of the experiment when charge control was performed with a high current discharge at a charge state (SOC) of 50%. A, B, C, D, and E are data of successive cycles.

Charge amount (Wh) Discharge amount (Wh) Energy efficiency (%) Charge efficiency (%) Voltage efficiency (%) A 78,390 53,890 68.7 86.7 79.2 B 77,510 53,400 69.0 86.8 79.5 C 77,710 54,570 70.3 88.6 79.4 D 78,280 53,490 69.2 86.6 80.0 E 78,220 54,130 69.3 87.4 79.3 Average 78,022 53,896 69.3 87.2 79.5

≪ Example 2 >

Table 2 shows the experimental results when charging is controlled by high current discharge at 50% and 90% of the state of charge (SOC). A, B, C, D, and E are data of successive cycles.

Charge amount (Wh) Discharge amount (Wh) Energy efficiency (%) Charge efficiency (%) Voltage efficiency (%) A 77,840 53,730 69.9 87.8 79.5 B 77,910 53,960 69.8 88.0 79.4 C 78,760 54,110 70.0 89.9 77.8 D 78,160 54,050 69.5 87.4 79.6 E 77,500 54,030 70.2 88.9 79.0 Average 78,034 53,976 69.8 88.4 79.1

<Comparative Example>

Table 3 shows the results of the experiment without charge control regardless of the state of charge (SOC). A, B, C, D, and E are data of successive cycles.

Charge amount (Wh) Discharge amount (Wh) Energy efficiency (%) Charge efficiency (%) Voltage efficiency (%) A 76,620 51,220 66.9 84.6 79.0 B 77,590 52,020 67.1 82.6 81.2 C 75,990 51,120 67.3 87.0 77.4 D 77,420 53,260 68.8 85.4 80.6 E 78,170 52,090 66.6 82.5 80.8 Average 77,158 51,942 67.3 84.4 79.8

The data in Tables 1, 2 and 3 are the final data calculated by applying the embodiment of the present invention, and the charged amount and the discharged amount are the charging amounts that can be obtained from the 50 kWh class module. Each of the energy efficiency, voltage efficiency, and current efficiency is calculated based on the charge amount. Energy efficiency is basically the efficiency that can evaluate the performance of the stack or cell, and the voltage efficiency and the current efficiency are the efficiencies that can detect the charge amount and the state of the stack.

Therefore, Table 1, Table 2 and Table 3 are basically important energy efficiency standards. Table 1 shows high current discharge at SOC 50% once, Table 2 shows SOC at 50% and 90% The discharge was carried out twice each. Table 3 shows the general progress (discharging after charging to SOC 0 ~ 95%). Energy efficiency is best in Table 2 and is lowered in the order of Table 1 and Table 3. Thus, it can be seen that conducting a high current discharge in a short time in a specific SOC part is a good way to make the zinc deposition uniform, and it is more effective to proceed twice or more.

As described above, the discharging amount of the module in the charging control according to the embodiment and the comparative example is increased, and it is judged that the electrochemical discharging amount is increased by the uniform zinc deposition. Charge efficiency increased during charge control, but voltage efficiency decreased and energy efficiency improved.

Claims (10)

A charge / discharge control method for a redox flow battery (RFB) including a unit cell including a positive electrode, a negative electrode, and an electrolyte,
Performing a first charge of the redox flow cell comprising zinc metal ions;
Performing at least one high current discharge if the state of charge (SOC) of the redox flow cell satisfies a predefined specific value, and
And performing secondary charging of the redox-flow battery when the unevenness between the positive electrode and the negative electrode is dissolved in accordance with the at least one high-current discharge,
The primary charge, the at least one high current discharge, and the secondary charge,
The redox flow cell is charged in one charging process,
The step of performing the at least one high-
Performing the high-current discharge once when the state of charge (SOC) is 50% or
Performing a second high current discharge when the state of charge (SOC) is 90% after performing a first high current discharge when the state of charge (SOC) is 50%
Wherein the current value at the time of the high current discharge is set to at least 30 amperes (A) or more. delete delete delete delete delete The method according to claim 1,
The redox flow battery comprises:
A method for controlling charging / discharging of a redox flow cell comprising a zinc-fluorine-flow battery. The method according to claim 1,
The redox flow battery comprises:
A charge / discharge control method for a redox flow cell comprising a zinc-chlorine-flow battery. The method according to claim 1,
The redox flow battery comprises:
A method for controlling charging / discharging of a redox flow cell comprising a zinc-iodine flow battery. The method according to claim 1,
The redox flow battery comprises:
Charge / discharge control method of a redox flow cell including zinc - air.

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