An operation strategy for zinc-based flow batteries

Abstract

The present invention discloses an operation strategy of a zinc-based liquid flow battery, wherein the charging process adopts the following method: (1) after assembling the zinc-based liquid flow battery, first charge the battery at 0.1-50 mAh cm ‑2 The method is as follows: (1) the battery is charged at a constant capacity at a charging capacity of 10000, and the operation is repeated for 3-10 cycles; (2) the current density is kept constant, and the charging time is increased by 1-20 min based on the previous step, and the operation is repeated for 3-10 cycles; (3) step (2) is repeated until the battery reaches the highest achievable charging capacity, and then enters normal operation; the discharge process adopts the cut-off voltage mode. This strategy first charges the zinc-based flow battery at a constant capacity at a low charging capacity, and then gradually increases the capacity to a higher capacity, so that the zinc-based flow battery can operate efficiently and stably at a high charging capacity. This method is simple and effective, and can improve the performance and stability of zinc-based flow batteries under high charging capacity conditions, solving the problem of limited capacity of traditional zinc-based flow batteries.

Description

Technical Field

[0001] The present invention belongs to the field of liquid flow batteries, and in particular relates to an operation strategy of a zinc-based liquid flow battery. Background Art

[0002] With the increasing depletion of fossil energy, the development and utilization of renewable energy such as wind energy and solar energy has become the focus of attention of all countries. Since wind energy and solar energy are discontinuous and unstable due to factors such as weather, this will cause impact on the power grid during the process of renewable energy power generation and grid connection, affecting the power supply quality and grid stability. Energy storage technology can solve this problem and ensure the efficient and stable operation of renewable energy power generation and grid connection. Energy storage technology is mainly divided into two categories: physical energy storage and chemical energy storage. Among them, chemical energy storage represented by all-vanadium liquid flow batteries and zinc-based liquid flow batteries has the most advantages in large-scale energy storage due to its many advantages such as independent power and capacity, rapid response, simple structure, easy design, long cycle life, and environmental friendliness.

[0003] Zinc-based flow batteries have the advantages of low cost, high potential and high energy density, and are suitable for user-side energy storage. However, the negative electrode of the zinc-based flow battery undergoes a zinc deposition and dissolution reaction, and the deposited zinc element is unevenly distributed. During the battery charging process, zinc will deposit in the direction of the membrane, blocking the ion transmission path of the membrane, increasing the polarization of the battery; and excessive zinc growth will pierce the membrane and cause the battery to short-circuit. The above problems seriously affect the performance and stability of zinc-based flow batteries, limiting their charging capacity. Under the condition that the current density remains unchanged, a high charging capacity means a long charging time, that is, a longer time for zinc deposition and growth, and it is more likely to have problems with deposited zinc blocking membrane pores and zinc dendrites piercing the membrane. Therefore, traditional zinc-based flow batteries are often difficult to operate stably directly at high charging capacities. Summary of the invention

[0004] In view of the above problems, the present invention adopts a new operation strategy, firstly charging the zinc-based flow battery at a low charge capacity at a constant capacity, and then gradually increasing the capacity to a higher capacity, so that zinc can gradually deposit toward the current collector rather than the membrane, so that the zinc-based flow battery can operate efficiently and stably at a high charge capacity. This method is simple and effective, and can improve the performance and stability of zinc-based flow batteries under high capacity conditions, solving the problem of limited capacity of traditional zinc-based flow batteries.

[0005] The technical solution of the present invention is specifically as follows:

[0006] A zinc-based liquid flow battery operation strategy, the operation process of the zinc-based liquid flow battery includes a charging process and a discharging process, and the charging process adopts the following method:

[0007] (1) After assembling the zinc-based flow battery, first -2-50mAh cm -2 Perform constant capacity charging at a charging capacity of , and run 3-10 cycles;

[0008] (2) Keeping the current density unchanged, based on the previous step, increase the charging time by 1-20 min and run 3-10 cycles;

[0009] (3) Repeat step (2) until the battery reaches the highest achievable charge capacity and then enters normal operation; the maximum charge capacity is 55-120 mAh cm -2 ;

[0010] The discharge process adopts a cut-off voltage mode.

[0011] The charging mode of the zinc-based liquid flow battery described in the present invention is a constant capacity mode, that is, the charging capacity of each cycle is equal; the discharging mode is a cut-off voltage mode, that is, when the battery voltage drops to the cut-off voltage, the discharging process stops; the charging capacity is equal to the product of the current density and the charging time.

[0012] Based on the above solution, preferably, in the discharge mode, the cut-off voltage is between 0-1V.

[0013] Based on the above scheme, preferably, in step (1), the charging capacity is 0.1-40 mA cm -2 .

[0014] Based on the above scheme, preferably, during the constant capacity charging process in step (1), the current density is 20-80 mA cm -2 , the charging time is 0.5-1h.

[0015] Based on the above scheme, preferably, in the charging mode, within 3-10 cycles, if the coulombic efficiency of the zinc-based liquid flow battery remains above 90% and fluctuates between 0-8%, the next step can be carried out; otherwise, it is deemed that the zinc-based liquid flow battery cannot operate stably at this capacity, and the charging capacity in the previous charge and discharge mode is the maximum capacity that can be achieved by this zinc-bromine liquid flow battery.

[0016] The coulombic efficiency of zinc-based flow batteries is defined as: Coulombic efficiency = charge capacity / discharge capacity × %

[0017] Under the condition of constant charging capacity, small fluctuation of coulomb efficiency means small fluctuation of discharge capacity, that is, small attenuation of battery capacity and high stability.

[0018] Based on the above scheme, preferably, the zinc-based liquid flow battery can be either a dual-flow battery or a single-flow battery; in a dual-flow battery, the positive electrode electrolyte storage tank is connected to the positive electrode liquid inlet of the battery through a pipeline via a pump, and the negative electrode electrolyte storage tank is connected to the negative electrode liquid inlet of the battery through a pipeline via a pump; in a single-flow battery, the positive electrode electrolyte storage tank is not connected to the positive electrode liquid inlet, and the negative electrode electrolyte storage tank is connected to the negative electrode liquid inlet of the battery through a pipeline via a pump.

[0019] Based on the above scheme, preferably, the zinc-based flow battery includes zinc-iron flow battery, zinc-iodine flow battery, zinc-bromine flow battery, zinc-manganese flow battery, zinc-nickel flow battery, zinc-chlorine flow battery, etc.

[0020] Beneficial effects of the present invention:

[0021] (1) The capacity of the zinc-based flow battery operated by the method of the present invention is increased by more than 10% compared with the normal operation mode. Using this strategy to operate the battery can make the negative electrode zinc element deposit more uniformly and deposit in the direction of the current collector, thereby increasing the deposition depth, avoiding the blocking of the membrane ion transmission path by the deposited zinc and the piercing of the membrane by zinc dendrites, thereby improving the performance and stability of the battery and also increasing the capacity of the battery.

[0022] (2) This method has no additional cost, is quick to take effect, and is easy to operate. It solves the problem of limited capacity of traditional zinc-based flow batteries in a short time and efficiently, and promotes the development of zinc-based flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a cycle performance diagram of the zinc-bromine flow battery using the operating strategy of the present invention in Example 1.

[0024] Figure 2 For comparative example 1, when the battery is directly charged at 80 mAh cm -2 Cycling performance diagram of zinc-bromine flow battery when charging and discharging at a charging capacity of .

[0025] Figure 3 (a) is the zinc deposition morphology of comparative example 1; (b) is the zinc deposition morphology of example 1.

[0026] Figure 4 (a) is the SEM image of the electrode of the battery of comparative example 1 after charging; (b) is the SEM image of the electrode of the battery of embodiment 1 after charging. DETAILED DESCRIPTION

[0027] The present invention is described in detail below in conjunction with embodiments, but the present invention is not limited to these embodiments.

[0028] Example 1

[0029] The present invention takes zinc-bromine flow battery as an example. First, a zinc-bromine flow battery (double flow) is assembled, wherein the catalyst layer is activated carbon felt, the bipolar plate is a graphite plate, and the membrane is a commercial perfluorosulfonic acid ion exchange membrane (Nafion 115), and the membrane effective area is 36 cm 2 The electrolyte composition is: 2 mol / L zinc bromide + 3 mol / L potassium chloride + 0.8 mol / L N, N-methylethylpyrrolidine bromide (complexing agent).

[0030] (1) After assembling the zinc-bromine flow battery, the operation mode of the zinc-bromine flow battery is set to: the charging process adopts a constant capacity charging mode with a current density of 40 mA cm -2 The charging time is 60 minutes, and the charging capacity is constant at 40 mAh cm -2 ; The discharge process adopts the voltage cut-off mode, and the cut-off voltage is 0.8V;

[0031] (2) After charging for 5 cycles, the charging mode for the 6th cycle was set to: the charging process adopted the constant capacity charging mode with a current density of 40 mA cm -2 The charging time is 65 min and the charging capacity is constant at 43.33 mAh cm -2 ; The discharge process adopts the voltage cut-off mode, and the cut-off voltage is 0.8V;

[0032] (3) After charging for 5 cycles, the charging mode for the 11th cycle was set to: the charging process adopted a constant capacity charging mode with a current density of 40 mA cm -2 The charging time is 70 min and the charging capacity is constant at 46.67 mAh cm -2 ; The discharge process adopts the voltage cut-off mode, and the cut-off voltage is 0.8V;

[0033] (4) Repeat the above steps until the battery coulombic efficiency is less than 90%, or the coulombic efficiency fluctuation is greater than 8%. The charging capacity in the previous charging and discharging mode is the maximum capacity that this zinc-bromine liquid flow battery can achieve (defined as AmAh cm -2 ), and this capacity is greater than 40 mAh cm -2 .

[0034] After the above steps, we get A=80.

[0035] (5) Repeat steps (1) to (3) until the charging mode is changed to: the charging process adopts constant capacity charging mode with a current density of 40 mA cm -2 The charging time is 2h and the charging capacity is constant at 80mAh cm -2 ; The discharge process adopts the voltage cut-off mode, and the cut-off voltage is 0.8V. Under this condition, the coulomb efficiency of the battery is 98.12%, and the efficiency fluctuation is within 8%, which can operate normally ( Figure 1 ). After that, the battery can continue to operate under this charge and discharge condition.

[0036] Comparative Example 1

[0037] The zinc-bromine flow battery was assembled according to the method described in Example 1, except that the charging and discharging mode of the battery was kept constant. The specific process was as follows: the charging process adopted a constant capacity charging mode with a current density of 40 mA cm -2 The charging time is 2h and the charging capacity is constant at 80mAh cm -2 ; The discharge process adopts the voltage cut-off mode, and the cut-off voltage is 0.8V. Under this condition, the coulombic efficiency of the zinc-bromine flow battery is less than 90%, and it cannot operate normally and stably ( Figure 2 ).

[0038] Figure 3 (a) is the zinc deposition morphology of Comparative Example 1, and (b) is the zinc deposition morphology of Example 1. It can be seen from the SEM image of the zinc deposition morphology of Comparative Example 1 that during the charging process of Comparative Example 1, the electrode deposits too much zinc in a short period of time, and the deposition is uneven and deposited toward the membrane. The overgrown zinc blocks the ion transmission path of the membrane, which greatly increases the battery polarization. The battery performance and stability are greatly reduced and cannot operate normally and stably. Unlike Comparative Example 1, the operating strategy described in Example (1) is adopted. As the charging capacity increases, zinc gradually deposits toward the collector side rather than the membrane side, and the zinc deposition depth increases. Therefore, the problem of blocking the membrane ion transmission path is solved, the zinc deposition is more uniform, and the battery polarization is also smaller, so that the battery can operate efficiently and stably.

[0039] Figure 4 It is the SEM picture of the electrodes of the batteries of Example 1 and Comparative Example 1 after charging. It can be seen from the figure that due to the change in the direction of zinc deposition, the amount of zinc deposited on the electrode of Comparative Example 1 after charging using the operating mode of the prior art is extremely small. This is because a large number of uneven zinc dendrites are deposited on the surface of the membrane. The charging strategy of the present invention promotes more uniform growth of zinc on the surface of the carbon felt, thereby achieving higher battery performance and cycle life.

[0040] Comparative Example 2

[0041] The zinc-bromine flow battery was assembled according to the method described in Example 1, except that the charging capacity of the battery in step (1) was kept constant at 70 mAh cm -2 .

[0042] Under this condition, the coulombic efficiency of the zinc-bromine flow battery is less than 90%, and it cannot operate normally and stably. This is because the initial capacity of the battery is too high, and the long charging process causes too much zinc to be deposited on the electrode. The deposition is uneven and deposited toward the membrane. The excessive growth of zinc blocks the ion transmission path of the membrane, which greatly increases the polarization of the battery. The battery performance and stability are greatly reduced, and it cannot operate normally and stably.

[0043] Comparative Example 3

[0044] The zinc-bromine flow battery was assembled according to the method described in Example 1, except that the charging capacity of the battery in step (1) was kept constant at 0.01 mAh cm -2 .

[0045] Under this condition, the zinc-bromine flow battery can operate normally with a capacity of 80 mAh cm -2 , the coulomb efficiency is 96.35%, and the fluctuation is within 8%. However, the time taken is too long and does not meet the actual application requirements.

[0046] Comparative Example 4

[0047] A zinc-bromine flow battery was assembled according to the method described in Example 1, except that the number of cycles in steps (1)-(4) was changed to 15 times.

[0048] Under this condition, the zinc-bromine flow battery can operate normally with a capacity of 80 mAh cm -2 , the coulomb efficiency is 96.32%, and the fluctuation is within 8%. However, the time taken is too long and does not meet the actual application requirements.

[0049] Comparative Example 5

[0050] A zinc-bromine flow battery was assembled according to the method described in Example 1, except that the number of cycles in steps (1)-(4) was changed to 2.

[0051] Under this condition, the cycle time is too short to determine the fluctuation of the battery's coulombic efficiency and to verify whether the battery can operate normally at a certain capacity.

Claims

1. A zinc-based liquid flow battery operation strategy, wherein the operation process of the zinc-based liquid flow battery includes a charging process and a discharging process, characterized in that: The charging process is as follows: (1) After assembling the zinc-based flow battery, first -2 Perform constant capacity charging at a charging capacity of , and run 3-10 cycles; (2) Keeping the current density unchanged, increase the charging time by 1-20 min based on the previous step and run 3-10 cycles; (3) Repeat step (2) until the battery reaches the highest achievable charge capacity and then enters normal operation with a maximum charge capacity of 55-120 mAh cm -2 ; The discharge process adopts a cut-off voltage mode; In the charging mode, within 3-10 cycles, if the coulombic efficiency of the zinc-based liquid flow battery remains above 90% and fluctuates between 0-8%, the next step can be carried out; otherwise, it is considered that the zinc-based liquid flow battery cannot operate stably at this capacity. At this time, the charging capacity in the previous charging and discharging mode is the maximum charging capacity that this zinc-bromine liquid flow battery can achieve.

2. The operation strategy according to claim 1, characterized in that: In discharge mode, the cut-off voltage is between 0-1 V.

3. The operation strategy according to claim 1, characterized in that: In step (1), the charge capacity is 0.1-40 mAcm -2 .

4. The operation strategy according to claim 1, characterized in that: Step (1) During constant capacity charging, the current density is 20-80 mA cm -2 , the charging time is 0.5-1 h.

5. The operation strategy according to claim 1, characterized in that: The zinc-based flow battery is a dual-flow battery or a single-flow battery.

6. The operation strategy according to claim 1, characterized in that: The zinc-based liquid flow battery is a zinc-iron liquid flow battery, a zinc-iodine liquid flow battery, a zinc-bromine liquid flow battery, a zinc-manganese liquid flow battery, a zinc-nickel liquid flow battery or a zinc-chloride liquid flow battery.

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