Flow battery energy storage system and method coupled with phase change heat storage

Abstract

According to the flow battery energy storage system and method coupled with phase change heat storage, the system comprises a cathode liquid storage tank, an anode liquid storage tank, a high-temperature area phase change cavity, a low-temperature area phase change cavity, an electric pile and a control system, under the control of the control system, electrolyte selectively flows through the high-temperature area phase change cavity and the low-temperature area phase change cavity; by coupling the phase-change material to absorb heat generated by battery operation and solar energy, the system always operates in an optimal temperature range, so that the energy efficiency and the thermal stability of the system are effectively improved, and the thermal management energy consumption of the system is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow battery electrochemistry, and in particular relates to a liquid flow battery energy storage system and method coupled with phase change heat storage. Background Art

[0002] Driven by the "dual carbon" goals, the energy structure is transforming towards low-carbonization, and the development of renewable energy power generation technology has become particularly important. However, the instability of renewable energy power generation, such as "extremely hot and no wind, no light at night", has led to a continuous widening of the peak-to-valley difference in new energy power generation load, and long-term energy storage technology is urgently needed for regulation. All-vanadium liquid flow battery (VRFB) has a place in energy storage technology due to its advantages such as long life, high safety, and separation of output power and capacity. Despite this, all-vanadium liquid flow batteries still face some challenges in practical applications: (1) The stability of vanadium ions in the electrolyte is poor, which limits the operating temperature range of the battery (10°C~40°C). The accumulation of heat can easily lead to the precipitation of vanadium ions, affecting the performance and life of the battery. (2) Due to the low operating temperature, the solubility of vanadium ions in the electrolyte is limited and the viscosity is high, resulting in low energy efficiency and poor charge and discharge performance; (3) The all-vanadium liquid flow battery energy storage system requires an active thermal management system, which consumes relatively high energy; (4) Compared with traditional liquid flow battery energy storage systems, all-vanadium liquid flow batteries have low energy density and require a larger footprint and storage space. These technical bottlenecks limit the performance and application scope of all-vanadium liquid flow battery energy storage systems and urgently need to be overcome through technological innovation. Summary of the invention

[0003] In view of the problems of low energy density, poor thermal stability, high energy consumption of thermal management system and low system energy efficiency in the existing all-vanadium liquid flow battery energy storage system, the first purpose of the present invention is to provide a liquid flow battery energy storage system coupled with phase change heat storage. The second purpose of the present invention is to provide a liquid flow battery energy storage method coupled with phase change heat storage, which aims to couple phase change material storage to utilize solar thermal energy and waste heat from liquid flow battery operation, so that the system always operates within the optimal temperature range, thereby effectively improving the energy efficiency and thermal stability of the system and reducing the thermal management energy consumption of the system.

[0004] The present invention solves the above problems by the following technical means: A liquid flow battery energy storage system coupled with phase change heat storage, comprising a cathode liquid storage tank, an anode liquid storage tank, a high temperature phase change cavity, a low temperature phase change cavity, a battery stack and a control system; The high-temperature zone phase change cavity is provided with a high-temperature zone cathode heat exchange tube and a high-temperature zone anode heat exchange tube, and the high-temperature zone phase change cavity is filled with a high-temperature zone phase change material; the low-temperature zone phase change cavity is provided with a low-temperature zone cathode heat exchange tube and a low-temperature zone anode heat exchange tube, and the low-temperature zone phase change cavity is filled with a low-temperature zone phase change material; The outlet pipe of the cathode liquid storage tank is connected to one end of the cathode heat exchange pipe in the low temperature zone, and a cathode booster pump is arranged on it. The other end of the cathode heat exchange pipe in the low temperature zone is connected to the cathode side inlet pipe of the stack. The cathode side outlet pipe of the stack is connected to the return pipe of the cathode liquid storage tank and one end of the cathode heat exchange pipe in the high temperature zone through a cathode electromagnetic three-way valve. The other end of the cathode heat exchange pipe in the high temperature zone is connected to the cathode liquid storage tank. The outlet pipe of the anode liquid storage tank is connected to one end of the anode heat exchange tube in the low temperature zone, and an anode booster pump is arranged on it. The other end of the anode heat exchange tube in the low temperature zone is connected to the anode side inlet pipe of the stack. The anode side outlet pipe of the stack is connected to the return pipe of the anode liquid storage tank and one end of the anode heat exchange tube in the high temperature zone through the anode electromagnetic three-way valve. The other end of the anode heat exchange tube in the high temperature zone is connected to the anode liquid storage tank. In the specific implementation process, heat exchange fins are added to the heat exchange tubes; The control system is electrically connected to the cathode electromagnetic three-way valve, the anode electromagnetic three-way valve, the cathode booster pump, and the anode booster pump respectively.

[0005] Furthermore, the control system comprises: A temperature sensor is used to detect the electrolyte temperature and generate an electrical signal; A position controller receives an electrical signal from a temperature sensor; The DC contactor receives the electrical signal from the position controller, responds based on the control of the position controller, controls the on-off of the circuit between the DC power supply and the electromagnetic three-way valve, thereby changing the outlet of the electromagnetic three-way valve and the flow direction of the electrolyte; A PID controller receives an electrical signal from the temperature sensor and is used to control the speed of the boost pump; Switching power supply, supplying power to PID controller and position controller; Computer, connected with PID controller and position controller.

[0006] Furthermore, the control system has two control loops. The first control loop is the opening control of the electromagnetic three-way valve. When the temperature sensor detects that the electrolyte temperature exceeds the set value, the position controller controls the DC contactor to connect the circuit between the DC power supply and the electromagnetic three-way valve, and the electromagnetic three-way valve is energized to turn the opening to the pipeline directly connected to the liquid storage tank; conversely, when the temperature sensor detects that the electrolyte temperature is lower than the set value, the position controller controls the DC contactor to disconnect the circuit between the DC power supply and the electromagnetic three-way valve, and the electromagnetic three-way valve is deenergized to turn the opening to the pipeline connected to the high-temperature zone heat exchange pipe. , so that the electrolyte flows through the phase change material heated by solar energy, so that the electrolyte is heated; the second control loop is the control loop of the electrolyte flow rate. The PID controller in this loop can compare the temperature of the electrolyte with the set temperature in the PID controller. When the difference between the two is large, the PID controller will increase the speed of the boost pump to enhance the heat transfer coefficient of the electrolyte heat exchange and realize rapid heat exchange between the electrolyte and the phase change material. Conversely, when the difference between the two is small, the PID controller will reduce the speed of the boost pump to better maintain the temperature of the electrolyte at the set value.

[0007] Furthermore, it also includes a container, wherein the cathode liquid storage tank, the anode liquid storage tank, the battery stack and the low-temperature phase change cavity are all arranged in the container, and the high-temperature phase change cavity is arranged on the top of the container.

[0008] Furthermore, the high temperature zone cathode heat exchange tube and the high temperature zone anode heat exchange tube are arranged in the high temperature zone phase change cavity in a serpentine manner.

[0009] Furthermore, the low temperature zone cathode heat exchange tube and the low temperature zone anode heat exchange tube are arranged in the low temperature zone phase change cavity in a serpentine manner.

[0010] Furthermore, photothermal conversion materials for enhancing the photothermal conversion capability are added to the high-temperature phase change material to achieve full utilization of solar thermal energy and increase the temperature of the high-temperature phase change material. Metal nanoparticles such as carbon black, copper oxide, iron oxide, and graphene with high light absorption rates all have this effect.

[0011] Furthermore, the melting point of the phase change material in the high temperature zone is higher than the optimal operating temperature of the system, and the melting point of the phase change material in the low temperature zone is lower than the optimal operating temperature of the system.

[0012] A method for storing energy using the above-mentioned liquid flow battery energy storage system with coupled phase change heat storage. When the system is running, the booster pump is powered on and rotated to pump electrolyte from the electrolyte storage tank. Under the action of the booster pump, the electrolyte first flows through the low-temperature zone heat exchange tube to exchange heat with the low-temperature zone phase change material, and then enters the battery stack. After the electrolyte undergoes an oxidation-reduction reaction in the battery stack, it flows through the electromagnetic three-way valve, which is controlled by the control system. When the electrolyte temperature is lower than the set temperature, the electromagnetic three-way valve controls the electrolyte to flow through the high-temperature zone heat exchange tube to absorb the light and heat stored in the high-temperature zone phase change material. Conversely, when the electrolyte temperature is higher than the set temperature, the electromagnetic three-way valve controls it to bypass the high-temperature zone phase change material and flow directly into the storage tank, thereby completing a cycle.

[0013] The battery stack is the place where the electrochemical reaction of the liquid flow battery occurs. The battery stack used in this system is a general all-vanadium liquid flow battery stack. Multiple battery stacks are placed side by side on a support frame, and the battery stacks are charged / discharged in series.

[0014] In this operating mode, the system can flexibly switch the flow channels so that the electrolyte can selectively absorb and dissipate heat with the phase change material. This can save the system from additional thermal management equipment, reduce the complexity and operating costs of the energy storage system, achieve low-cost passive temperature control of the energy storage system, and ensure safe and efficient operation of the system.

[0015] Furthermore, in order to further improve the safety of the operation of the energy storage system and improve the energy density and energy efficiency of the battery, the present invention proposes a high-efficiency and stable operation technology for all-vanadium liquid flow batteries. Among them, in terms of electrolyte, the electrolyte concentration ratio used in the present invention is 1.7M vanadium ions, 4M sulfate ions, and 1.5% mass concentration of diammonium phosphate additives. Phosphoric acid additives can form complexes with vanadium ions, thereby effectively inhibiting the precipitation of vanadium ions and improving the thermal stability of the electrolyte. In terms of additive selection, additives such as hydrochloric acid or organic matter have similar effects on improving the thermal stability of the electrolyte. The introduction of thermally stable electrolytes effectively improves the safety of the energy storage system and provides a basis for the stable operation of the system at high temperatures. The use of intelligent integrated monitoring and control systems allows the electrolyte to make full use of the thermal energy stored in the phase change material, providing temperature conditions for the efficient operation of the battery at high temperatures, thereby effectively improving the energy density and energy efficiency of the system.

[0016] Based on the structure of the flow battery energy storage container, this system adds a high-temperature phase change cavity and a low-temperature phase change cavity. Among them, the high-temperature phase change material can use common phase change materials with a phase change temperature between 50-60°C, such as polyethylene glycol 4000, polyethylene glycol 2000, paraffin, etc. In addition, an appropriate concentration of additives is additionally introduced into the high-temperature phase change material to enhance its light-to-heat conversion ability. Here, the additives can be common light-to-heat conversion materials, such as carbon black, graphite, graphene, etc. The low-temperature phase change material can use common phase change materials with a phase change temperature between 40-50°C, such as lauric acid, sodium thiosulfate 5-hydrate, paraffin, etc. The electrolyte pipes and heat exchange fins are laid inside the high-temperature and low-temperature phase change materials, which can fully conduct convective heat exchange with the cathode and anode electrolytes.

[0017] The key points of the present invention are: (1) Operation mode and device of liquid flow battery for combined heat and power storage. The present invention modifies the device structure and pipeline layout of the containerized liquid flow battery energy storage system so that the system can passively adjust the flow pattern of the electrolyte under different temperature conditions. When the electrolyte temperature is low, the system controls it to flow through the phase change material in the high temperature zone to increase the temperature; when the electrolyte temperature is high, the system controls it to flow through the phase change material in the low temperature zone to cool down. The pipe sections laid between the phase change materials adopt serpentine pipe layout to improve their heat exchange effect. The selection of phase change materials needs to ensure that the optimal operating temperature of the system setting is between the melting point temperature of the phase change material in the high temperature zone and the melting point temperature of the phase change material in the low temperature zone.

[0018] (2) Low-cost passive temperature control technology coupled with phase change material heat storage. This system adds grooves for storing high-temperature phase change materials and containers for storing low-temperature phase change materials in the enclosure structure of the existing containerized liquid flow battery energy storage system. Photothermal conversion materials are added to the high-temperature phase change materials to improve their light absorption, so that the high-temperature phase change materials can absorb solar heat and heat up. The electrolyte pipeline is laid in the phase change material, and the heat generated by battery operation and solar heat are recycled through heat exchange, realizing the joint storage of thermal energy and electrical energy, thereby improving the energy density of the system.

[0019] (3) High-temperature stabilization technology of vanadium electrolyte based on inorganic additives. The present invention prepares an electrolyte with thermal stability by introducing inorganic additives into the electrolyte. The electrolyte concentration ratio used in the present invention is 1.7M vanadium ions, 4M sulfate ions, and 1.5% mass concentration of diammonium phosphate additives. Phosphoric acid additives can form complexes with vanadium ions, thereby effectively inhibiting the precipitation of vanadium ions and enhancing the thermal stability of the electrolyte, thereby improving the suitable operating temperature range of the liquid flow battery, providing basic conditions for the long-term, efficient and stable operation of the system in a high-temperature environment.

[0020] (4) Intelligent integrated monitoring and control system. The control system constructed by the present invention can accurately monitor the operating status of the battery in real time, collect key parameters such as electrolyte temperature and flow rate in real time, and can use PID controller and position controller to automatically adjust the system's operating strategy and the flow distribution of the pipeline network. In addition, the parameters of the PID controller in the present invention are measured by the controller's own self-tuning function to improve the accuracy, rapidity and stability of the control system, ensuring that the energy storage system operates efficiently and stably under high temperature conditions.

[0021] Beneficial effects of the present invention: When the system is working, the phase change material in the high temperature zone can absorb and store solar heat to maintain a high temperature; the phase change material in the low temperature zone can absorb and store the heat generated by the operation of the flow battery to maintain a low temperature. When the temperature of the flow battery is too low, the electrolyte can conduct convective heat exchange with the phase change material in the high temperature zone, absorb the solar heat stored inside, and the temperature rises; when the temperature of the flow battery is too high, the electrolyte can conduct convective heat exchange with the phase change material in the low temperature zone, transfer the heat generated by the operation of the flow battery and store it in the phase change material in the low temperature zone, and the temperature drops. In the above process, the system does not require active thermal management equipment to keep the operating temperature of the flow battery within the ideal range, realizing passive thermal management of the flow battery energy storage system, reducing the operating energy consumption of the flow battery energy storage system, and solving the problem of high thermal management energy consumption of the flow battery energy storage system.

[0022] In addition, this system realizes the combined heat and power storage mode of liquid flow battery coupled with photothermal effect. After introducing phase change materials in high temperature zone and low temperature zone, this system realizes the new combined heat and power storage operation mode of "liquid flow battery electricity storage + phase change material heat storage", and improves the energy density of liquid flow battery energy storage system through the joint storage of thermal energy and electrical energy, solving the problem of low energy density of liquid flow battery energy storage system.

[0023] In summary, the advantages of the present invention are as follows: 1. A new type of liquid flow battery system coupled with phase change heat storage can achieve passive thermal management of the liquid flow battery system and reduce energy consumption by coupling phase change materials to absorb heat generated by battery operation and solar energy.

[0024] 2. The combined heat and power storage mode of liquid flow batteries coupled with the photothermal effect improves energy density through the combined storage of thermal energy and electrical energy.

[0025] 3. The high-temperature operation mode of the flow battery based on high thermal stability electrolyte and intelligent temperature control strategy effectively improves the operating efficiency of the system.

[0026] 4. The new liquid flow battery energy storage device coupled with phase change heat storage has the advantages of high safety, high efficiency and intelligence. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] Figure 1 A schematic diagram of a preferred embodiment of an energy storage system of the present invention; Figure 2 Schematic diagram of the three-dimensional structure of the phase change cavity in the high temperature zone; Figure 3 It is a top view of the phase change cavity in the high temperature zone; Figure 4 Schematic diagram of the three-dimensional structure of the phase change cavity in the low temperature zone; Figure 5 It is a top view of the phase change cavity in the low temperature zone; Figure 6 is a schematic diagram of the control system; Figure 7 This is the thermal stability experimental device diagram; Figure 8 This is a diagram of the placement of reagent bottles and the sediment inside the bottles for the thermal stability experiment; Fig. 9 The curve of charge and discharge performance of thermally stable electrolyte changing with temperature; Fig.10 This is a comparison chart of the energy efficiency of 55℃ electrolyte. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0030] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0031] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0032] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0033] like Figures 1 to 6 As shown, on the one hand, this embodiment provides a liquid flow battery energy storage system coupled with phase change heat storage, and the liquid flow battery energy storage system coupled with phase change heat storage includes a cathode liquid storage tank 1, an anode liquid storage tank 5, a high temperature zone phase change cavity 7, a low temperature zone phase change cavity 3, a battery stack 14 and a control system; The high-temperature zone phase change cavity is provided with a high-temperature zone cathode heat exchange tube 12 and a high-temperature zone anode heat exchange tube 13, and the high-temperature zone phase change cavity is filled with a high-temperature zone phase change material; the low-temperature zone phase change cavity is provided with a low-temperature zone cathode heat exchange tube 10 and a low-temperature zone anode heat exchange tube 11, and the low-temperature zone phase change cavity is filled with a low-temperature zone phase change material; The outlet pipe of the cathode liquid storage tank is connected to one end of the cathode heat exchange pipe in the low temperature zone, and a cathode booster pump 2 is arranged on it. The other end of the cathode heat exchange pipe in the low temperature zone is connected to the cathode side inlet pipe of the stack. The cathode side outlet pipe of the stack is connected to the return pipe of the cathode liquid storage tank and one end of the cathode heat exchange pipe in the high temperature zone through the cathode electromagnetic three-way valve 9. The other end of the cathode heat exchange pipe in the high temperature zone is connected to the cathode liquid storage tank. The outlet pipe of the anode liquid storage tank is connected to one end of the anode heat exchange tube in the low temperature zone, and an anode booster pump 4 is arranged on it. The other end of the anode heat exchange tube in the low temperature zone is connected to the anode side inlet pipe of the stack. The anode side outlet pipe of the stack is connected to the reflux pipe of the anode liquid storage tank and one end of the anode heat exchange tube in the high temperature zone through the anode electromagnetic three-way valve 8. The other end of the anode heat exchange tube in the high temperature zone is connected to the anode liquid storage tank. It also includes a container 6, wherein the cathode liquid storage tank, the anode liquid storage tank, the battery stack and the low temperature zone phase change cavity are all arranged in the container, and the high temperature zone phase change cavity is arranged on the top of the container.

[0034] The high temperature phase change cavity is located on the top of the container. It is the carrier and phase change site of the high temperature phase change material. Its structure is as follows: Figure 2 and Figure 3As shown. The high-temperature phase change cavity is generally a groove-type structure. The high-temperature phase change material is stored in the groove. The top surface of the groove is equipped with transparent glass, which can effectively absorb solar heat and undergo phase change. The interior of the high-temperature phase change material is evenly laid with high-temperature cathode heat exchange tubes, high-temperature anode heat exchange tubes and corresponding heat exchange fins, which can fully exchange heat with the cathode and anode electrolytes. It should be noted that since the phase change material will gradually change into a liquid state during the process of absorbing solar heat, sealing measures should be taken for the inlet and outlet parts of the pipes in the high-temperature phase change cavity.

[0035] The low temperature phase change cavity is the carrier container and phase change place of the low temperature phase change material. Its structure is as follows: Figure 4 and Figure 5 As shown. The low temperature zone phase change cavity is a closed shell, in which the low temperature zone phase change material is stored. The low temperature zone cathode heat exchange tube, the low temperature zone anode heat exchange tube and the corresponding heat exchange fins are buried in the low temperature zone phase change material, and can fully exchange heat with the low temperature zone phase change material. Consistent with the high temperature zone phase change cavity, the pipeline inlet and outlet parts of the low temperature zone phase change cavity also need to be provided with a sealing structure to prevent leakage of liquid phase change material. It should be pointed out that the low temperature zone phase change cavity can be installed in a container or in the surrounding protective structure, and can be arranged in a large range and set up flexibly.

[0036] The phase change cavity in the high temperature zone and the phase change cavity in the low temperature zone need to use phase change materials with different melting points so that the optimal operating temperature of the system is within the melting point range of the phase change material in the high temperature zone and the phase change material in the low temperature zone. Taking the present invention as an example, the optimal operating temperature of the battery in the system is 45°C. Therefore, the phase change temperature of the phase change material in the high temperature zone needs to be higher than 45°C, and phase change materials such as polyethylene glycol 4000 (melting point 50~60°C) and polyethylene glycol 2000 (melting point 64~66°C) meet the requirements; the phase change temperature of the phase change material in the low temperature zone needs to be less than 45°C, and phase change materials such as lauric acid (melting point 43~44°C) and low melting point paraffin meet the requirements. In addition, in order to fully utilize solar energy and increase the temperature of the phase change material at the top of the high temperature zone, the present invention needs to add additional photothermal fillers to the phase change material at the top of the high temperature zone. Metal nanoparticles such as carbon black, copper oxide, iron oxide, and graphene with high light absorption rate have this effect.

[0037] In order to make the temperature control of the electrolyte more precise, the system is equipped with a program-controlled electromagnetic three-way valve. One interface of the electromagnetic three-way valve is connected to the battery stack through a pipeline, one interface is connected to the high-temperature heat exchange pipe section, and one interface is connected to the pipe section without phase change material. The control system can select the opening of the three-way valve. Specifically, Figure 6 As shown, the control system includes: a temperature sensor for detecting the electrolyte temperature and generating an electrical signal; A position controller receives the electrical signal from the temperature sensor; a DC contactor receives the electrical signal from the position controller, responds based on the control of the position controller, controls the on-off of the circuit between the DC power supply and the electromagnetic three-way valve, thereby changing the outlet of the electromagnetic three-way valve and the flow direction of the electrolyte; a PID controller receives the electrical signal from the temperature sensor and is used to control the speed of the boost pump; a switching power supply supplies power to the PID controller and the position controller; and a computer is connected to the PID controller and the position controller.

[0038] The control system has two control loops. The first control loop is the opening control of the electromagnetic three-way valve. When the temperature sensor detects that the electrolyte temperature exceeds the set value, the position controller controls the DC contactor to connect the circuit between the DC power supply and the electromagnetic three-way valve, and the electromagnetic three-way valve is energized to turn the opening to the pipeline directly connected to the liquid storage tank; conversely, when the temperature sensor detects that the electrolyte temperature is lower than the set value, the position controller controls the DC contactor to disconnect the circuit between the DC power supply and the electromagnetic three-way valve, and the electromagnetic three-way valve is powered off, and the opening is turned to connect to the high-temperature zone heat exchange pipe, so as to The electrolyte is made to flow through the phase change material heated by solar energy to increase the temperature of the electrolyte. The second control loop is the control loop for the electrolyte flow rate. The PID controller in this loop can compare the temperature of the electrolyte with the set temperature in the PID controller. When the difference between the two is large, the PID controller will increase the speed of the boost pump to enhance the heat transfer coefficient of the electrolyte and achieve rapid heat exchange between the electrolyte and the phase change material. Conversely, when the difference between the two is small, the PID controller will reduce the speed of the boost pump to better maintain the temperature of the electrolyte at the set value.

[0039] The high temperature zone cathode heat exchange tube and the high temperature zone anode heat exchange tube are arranged in a serpentine manner in the high temperature zone phase change cavity. The low temperature zone cathode heat exchange tube and the low temperature zone anode heat exchange tube are arranged in a serpentine manner in the low temperature zone phase change cavity.

[0040] Photothermal conversion materials are added to the high-temperature phase change materials to enhance the photothermal conversion capacity, so as to fully utilize the solar thermal energy and increase the temperature of the high-temperature phase change materials. Metal nanoparticles such as carbon black, copper oxide, iron oxide, and graphene with high light absorption rates all have this effect.

[0041] The melting point of the high temperature zone phase change material is higher than the optimal operating temperature of the system, and the melting point of the low temperature zone phase change material is lower than the optimal operating temperature of the system. Among them, the high temperature zone phase change material can use common phase change materials with a phase change temperature between 50-60°C, such as polyethylene glycol 4000, polyethylene glycol 2000, paraffin, etc. In addition, an appropriate concentration of additives is additionally introduced into the high temperature zone phase change material to enhance its photothermal conversion ability. Here, the additives can be common photothermal conversion materials, such as carbon black, graphite, graphene, etc. The low temperature zone phase change material can use common phase change materials with a phase change temperature between 40-50°C, such as lauric acid, sodium thiosulfate 5-hydrate, paraffin, etc. The electrolyte pipes and heat exchange fins are laid inside the high temperature zone and low temperature zone phase change materials, which can fully carry out convective heat exchange with the cathode and anode electrolytes.

[0042] On the other hand, the present embodiment provides an energy storage method of a liquid flow battery energy storage system using the above-mentioned coupled phase change heat storage. When the system is running, the booster pump is powered on and rotated to pump electrolyte from the electrolyte storage tank. Under the action of the booster pump, the electrolyte first flows through the heat exchange tube in the low temperature zone to exchange heat with the phase change material in the low temperature zone, and then enters the battery stack. After the electrolyte undergoes an oxidation-reduction reaction in the battery stack, it flows through the electromagnetic three-way valve, which is controlled by the control system. When the electrolyte temperature is lower than the set temperature, the electromagnetic three-way valve controls the electrolyte to flow through the heat exchange tube in the high temperature zone to absorb the light and heat stored in the phase change material in the high temperature zone. Conversely, when the electrolyte temperature is higher than the set temperature, the electromagnetic three-way valve controls it to bypass the phase change material in the high temperature zone and flow directly into the storage tank, thereby completing a cycle.

[0043] To be more specific, taking the cathode side as an example, when the system is running, the cathode boost pump is energized and rotated to pump the electrolyte out of the cathode storage tank. Under the action of the cathode boost pump, the electrolyte first flows through the cathode heat exchange tube in the low-temperature zone, exchanges heat with the phase change material in the low-temperature zone, and then enters the fuel cell stack. After the electrolyte undergoes redox reaction in the fuel cell stack, it flows through the cathode solenoid three-way valve, and the cathode solenoid three-way valve is controlled by the control system. When the electrolyte temperature is lower than the set temperature, the cathode solenoid three-way valve controls the electrolyte to flow through the cathode heat exchange tube in the high-temperature zone, absorbing the light and heat stored in the phase change material in the high-temperature zone. Conversely, when the electrolyte temperature is higher than the set temperature, the cathode solenoid three-way valve controls it to bypass the phase change material in the high-temperature zone and flow directly into the anode storage tank, thereby completing a cycle.

[0044] The battery stack is the place where the electrochemical reaction of the liquid flow battery occurs. The battery stack used in this system is a general all-vanadium liquid flow battery stack. Multiple battery stacks are placed side by side on a support frame, and the battery stacks are charged / discharged in series.

[0045] In this operating mode, the system can flexibly switch the flow channels so that the electrolyte can selectively absorb and dissipate heat with the phase change material. This can save the system from additional thermal management equipment, reduce the complexity and operating costs of the energy storage system, achieve low-cost passive temperature control of the energy storage system, and ensure safe and efficient operation of the system.

[0046] In order to further improve the safety of energy storage system operation and improve the energy density and energy efficiency of the battery, the present invention proposes a high-efficiency and stable operation technology for all-vanadium liquid flow batteries. Among them, in terms of electrolyte, the electrolyte concentration ratio used in the present invention is 1.7M vanadium ions, 4M sulfate ions, and 1.5% mass concentration of diammonium phosphate additives. Phosphoric acid additives can form complexes with vanadium ions, thereby effectively inhibiting the precipitation of vanadium ions and improving the thermal stability of the electrolyte. In terms of additive selection, additives such as hydrochloric acid or organic matter have similar effects on improving the thermal stability of the electrolyte. The introduction of thermally stable electrolytes effectively improves the safety of the energy storage system and provides a basis for the stable operation of the system at high temperatures. The use of intelligent integrated monitoring and control systems allows the electrolyte to make full use of the thermal energy stored in the phase change material, providing temperature conditions for the efficient operation of the battery at high temperatures, thereby effectively improving the energy density and energy efficiency of the system.

[0047] Thermal stability effect Phosphate ions can form complexes with pentavalent vanadium ions to inhibit the high-temperature precipitation and precipitation of vanadium pentoxide. Based on this characteristic, the team conducted an experimental comparative analysis of the effects of different phosphoric acid additives on the thermal stability of the electrolyte under high-temperature conditions. The experiment selected ammonium dihydrogen phosphate and diammonium hydrogen phosphate as additives. The experimental setup is as follows: Figure 7 and Figure 8 shown.

[0048] By observing the bottom of the reagent bottle, the team obtained the time when precipitation was first observed for each group of electrolytes, as shown in Table 1.

[0049]

[0050] After the sample precipitated, the experiment further observed the effect of additives on the high-temperature stability of vanadium ions. Based on the results in Table 1, after the introduction of 1.5% diammonium phosphate additive, the time for the first precipitation of the electrolyte at 55 and 50°C increased from 4h and 8h to 35h and 62h, respectively, an increase of about 8 times, and excellent thermal stability.

[0051] Operation effect Based on the results of the thermal stability experiment, the charge and discharge performance test of the flow battery monomer under different temperature environments was further designed. The charge and discharge test system consists of a battery stack monomer, a liquid storage tank, a peristaltic pump, a battery test system and a water bath.

[0052] The thermally stable electrolyte of the flow battery adopts a concentration ratio of 1.7M V+4M H2SO4+0.15% NH4H2PO4, 30mL for the cathode and 30mL for the anode, and a pumping speed of 40r / min. The upper and lower limits of the cut-off voltage of the battery are 1.7V and 0.7V respectively, the charge and discharge current density is constant at 100mA / cm2, and the operating temperature is controlled by a water bath.

[0053] The charge and discharge characteristics of the thermally stable electrolyte and the conventional electrolyte (without additives) were tested at room temperature, 45, 50, and 55°C, and the coulombic efficiency CE, voltage efficiency VE, and energy efficiency EE of the battery at different temperatures were calculated by equations (1) to (3). The specific results are as follows: Fig. 9 and Fig.10 shown.

[0054] (1) (2) (3) comprehensive Fig. 9 and Fig.10 It can be seen that after the introduction of 1.5% diammonium dihydrogen phosphate, the flow battery can operate stably at 55°C, and compared with the blank group, the energy efficiency increased from 61.90% to 65.54%, an increase rate of 5.88%, and the cycle performance is good. In addition, the team observed that the operating performance of the thermally stable electrolyte changes with temperature and reaches a peak at 45°C, at which time the cycle coulomb efficiency, voltage efficiency, and energy efficiency are 95.03%, 74.00%, and 68.22%, respectively.

[0055] After coupling phase change material heat storage, the energy density increment of the system can be calculated according to formula (4): (4) The energy stored in the original system is chemical energy stored in flow batteries. The energy stored in the current system includes the energy of waste heat and solar thermal energy absorbed and stored by phase change materials on the basis of the energy stored in the original system.

[0056] The results show that compared with the commercial containerized liquid flow battery energy storage system, the energy density of this system is increased by 0.35Wh / L, with an increase rate of 5.96%, alleviating the problem of low energy density of liquid flow battery energy storage.

[0057] Invention Examples Cyclic charge and discharge test example 1: Use a pipette to measure 60 ml of V 3.5+Solution, add 1.5% ammonium dihydrogen phosphate additive, and place them in the cathode and anode storage tanks of the cyclic charge and discharge test device in a 1:1 ratio. Start the peristaltic pump and set the speed to 40r / min. After the flow stabilizes, nitrogen is introduced into the cathode storage tank to form a protective atmosphere, and the magnetic stirrer is started. Start the electrochemical workstation and set the working steps to 1) constant current charging, with a current of 40mA / cm 2 , the cut-off voltage is 1.7V; 2) constant current discharge, the current size is 40mA / cm 2 , the cut-off voltage is 0.7V; 3) constant current charging, the current size is 100mA / cm 2 , the cut-off voltage is 1.7V; 4) constant current discharge, the current size is 100mA / cm 2 , the cut-off voltage is 0.7V; 5) Step 3 and step 4 are cycled for 10 times. The average energy efficiency, coulomb efficiency and voltage efficiency are 67.63%, 94.92% and 73.29% respectively.

[0058] Cyclic charge and discharge test example 2: Compared with Example 1, only the temperature and the number of cycles were changed.

[0059] Use a pipette to measure 60 ml of V 3.5+ Solution, add 1.5% ammonium dihydrogen phosphate additive, and place them in the anode and cathode storage tanks of the cyclic charge and discharge test device in a 1:1 ratio. Start the peristaltic pump and set the speed to 40r / min. After the flow stabilizes, nitrogen is introduced into the cathode storage tank to form a protective atmosphere, and the magnetic stirrer is started. Start the water bath heating device and set the temperature to 45°C. Start the electrochemical workstation and set the working steps to 1) constant current charging, with a current of 40mA / cm 2 , the cut-off voltage is 1.7V; 2) constant current discharge, the current size is 40mA / cm 2 , the cut-off voltage is 0.7V; 3) constant current charging, the current size is 100mA / cm 2 , the cut-off voltage is 1.7V; 4) constant current discharge, the current size is 100mA / cm 2 , the cut-off voltage is 0.7V; 5) Steps 3 and 4 are cycled for 5 times. The average energy efficiency, coulomb efficiency and voltage efficiency are 68.22%, 95.03% and 74.00% respectively. This shows that high temperature promotes the charge and discharge performance of the battery.

[0060] Cyclic charge and discharge test example 3: Compared with Example 1, only the temperature and the number of cycles were changed.

[0061] Use a pipette to measure 60 ml of V 3.5+Solution, add 1.5% ammonium dihydrogen phosphate additive, and place them in the anode and cathode storage tanks of the cyclic charge and discharge test device in a 1:1 ratio. Start the peristaltic pump and set the speed to 40r / min. After the flow stabilizes, nitrogen is introduced into the cathode storage tank to form a protective atmosphere, and the magnetic stirrer is started. Start the water bath heating device and set the temperature to 50°C. Start the electrochemical workstation and set the working steps to 1) constant current charging, with a current of 40mA / cm 2 , the cut-off voltage is 1.7V; 2) constant current discharge, the current size is 40mA / cm 2 , the cut-off voltage is 0.7V; 3) constant current charging, the current size is 100mA / cm 2 , the cut-off voltage is 1.7V; 4) constant current discharge, the current size is 100mA / cm 2 , the cut-off voltage is 0.7V; 5) Steps 3 and 4 are cycled for 5 times. The average energy efficiency, coulomb efficiency and voltage efficiency are 66.87%, 93.26% and 73.84% respectively. This shows that at 50℃, the battery performance is slightly lower than that at room temperature.

[0062] Cyclic charge and discharge test example 4: Compared with Example 1, only the temperature and the number of cycles were changed.

[0063] Use a pipette to measure 60 ml of V 3.5+ Solution, add 1.5% ammonium dihydrogen phosphate additive, and place them in the anode and cathode storage tanks of the cyclic charge and discharge test device in a 1:1 ratio. Start the peristaltic pump and set the speed to 40r / min. After the flow stabilizes, nitrogen is introduced into the cathode storage tank to form a protective atmosphere, and the magnetic stirrer is started. Start the water bath heating device and set the temperature to 55°C. Start the electrochemical workstation and set the working steps to 1) constant current charging, with a current of 40mA / cm 2 , the cut-off voltage is 1.7V; 2) constant current discharge, the current size is 40mA / cm 2 , the cut-off voltage is 0.7V; 3) constant current charging, the current size is 100mA / cm 2 , the cut-off voltage is 1.7V; 4) constant current discharge, the current size is 100mA / cm 2 , the cut-off voltage is 0.7V; 5) Step 3 and step 4 are performed cyclically for 5 times. The average energy efficiency, coulomb efficiency and voltage efficiency of the cycle are 65.54%, 93.62% and 72.24% respectively. It shows that at 55°C, the battery performance is slightly reduced compared with room temperature. Combined with Examples 1-4, it is shown that the optimal operating temperature of the battery is about 45°C.

[0064] Cyclic charge and discharge test comparative example 1: Compared with Example 4, the only difference is whether the electrolyte contains additives.

[0065] Use a pipette to measure 60 ml of V 3.5+ The solution was placed in the cathode and anode liquid storage tanks of the cyclic charge and discharge test device in a 1:1 ratio. Start the peristaltic pump and set the speed to 40r / min. After the flow stabilizes, nitrogen is introduced into the cathode liquid storage tank to form a protective atmosphere, and the magnetic stirrer is started. Start the water bath heating device and set the temperature to 55°C. Start the electrochemical workstation and set the working steps to 1) constant current charging with a current of 40mA / cm 2 , the cut-off voltage is 1.7V; 2) constant current discharge, the current size is 40mA / cm 2 , the cut-off voltage is 0.7V; 3) constant current charging, the current size is 100mA / cm 2 , the cut-off voltage is 1.7V; 4) constant current discharge, the current size is 100mA / cm2, the cut-off voltage is 0.7V; 5) cyclic execution of step 3 and step 4, the number of cycles is 5 times. The average energy efficiency, coulomb efficiency and voltage efficiency of the cycle are 61.90%, 90.73% and 70.35% respectively. This shows that the vanadium electrolyte containing additives has better charge and discharge performance at high temperature. The specific results can still be seen Fig. 9 and Fig.10 .

[0066] Thermal stability test example 1: Use a pipette to measure 13.5 ml of V 5+ solution and 1.5 ml V 4+ The solution was mixed evenly and divided into three equal portions, each with 5 ml, and placed in a liquid storage bottle. 0.5%, 1% and 1.5% of diammonium phosphate additive were added to the three solutions respectively. The liquid storage bottle was placed in an ultrasonic cleaning device for 10 minutes. The liquid storage bottle was taken out and placed in a 50°C water bath. It was observed that the time for the first precipitation of the vanadium solution containing 0.5%, 1% and 1.5% diammonium phosphate additive was 25, 50 and 62 hours. This shows that at 50°C, with the increase of diammonium phosphate concentration, the high temperature resistance of the vanadium electrolyte is enhanced.

[0067] Thermal stability test example 2: Compared with Example 1, only the type of additive was changed.

[0068] Use a pipette to measure 13.5 ml of V 5+ solution and 1.5 ml V 4+The solution was mixed evenly and divided into three equal parts, each with 5 ml, and placed in a liquid storage bottle. 0.5%, 1% and 1.5% of diammonium hydrogen phosphate additive were added to the three solutions respectively. The liquid storage bottle was placed in an ultrasonic cleaning device for 10 minutes. The liquid storage bottle was taken out and placed in a 50°C water bath. It was observed that the time for the first precipitation of the vanadium solution containing 0.5%, 1% and 1.5% diammonium hydrogen phosphate additive was 25, 47 and 56 hours. The explanation shows that at 50°C, with the increase of diammonium hydrogen phosphate concentration, the high temperature resistance of the vanadium electrolyte is enhanced, but the effect is not as good as that of diammonium hydrogen phosphate.

[0069] Thermal stability test example 3: Compared with Example 1, only the test temperature was changed.

[0070] Use a pipette to measure 13.5 ml of V 5+ solution and 1.5 ml V 4+ The solution was mixed evenly and divided into three equal parts, each with 5 ml, and placed in a liquid storage bottle. 0.5%, 1% and 1.5% of diammonium phosphate additive were added to the three solutions respectively. The liquid storage bottle was placed in an ultrasonic cleaning device for 10 minutes. The liquid storage bottle was taken out and placed in a 55°C water bath. It was observed that the time for the first precipitation of the vanadium solution containing 0.5%, 1% and 1.5% diammonium phosphate additive was 10, 22 and 35 hours. This shows that at 55°C, with the increase of diammonium phosphate concentration, the high temperature resistance of the vanadium electrolyte is enhanced.

[0071] Thermal stability test example 4: Compared with Example 2, only the test temperature was changed.

[0072] Use a pipette to measure 13.5 ml of V 5+ solution and 1.5 ml V 4+ The solution was mixed evenly and divided into three equal parts, each with 5 ml, and placed in a liquid storage bottle. 0.5%, 1% and 1.5% of diammonium hydrogen phosphate additive were added to the three solutions respectively. The liquid storage bottle was placed in an ultrasonic cleaning device for 10 minutes. The liquid storage bottle was taken out and placed in a 55°C water bath. It was observed that the time for the first precipitation of the vanadium solution containing 0.5%, 1% and 1.5% diammonium hydrogen phosphate additive was 8, 9 and 22 hours. This shows that at 55°C, with the increase of diammonium hydrogen phosphate concentration, the high temperature resistance of the vanadium electrolyte is enhanced, but the effect is not as good as that of diammonium hydrogen phosphate.

[0073] Thermal stability test comparative example 1: Compared with Example 1, the only difference is whether additives are contained.

[0074] Use a pipette to measure 4.5 ml of V 5+ solution and 0.5 ml V4+ The solution was placed in a liquid storage bottle. The liquid storage bottle was placed in an ultrasonic cleaning device for 10 minutes. The liquid storage bottle was taken out and placed in a 50°C water bath. It was observed that the first precipitation of the vanadium solution occurred in 8 hours. Comparison between Example 1 and Example 2 shows that the additive effectively promotes the high temperature resistance of the vanadium electrolyte.

[0075] Thermal stability test comparative example 2: Compared with Example 3, the only difference is whether additives are contained.

[0076] Use a pipette to measure 4.5 ml of V 5+ solution and 0.5 ml V 4+ The solution was placed in a liquid storage bottle. The liquid storage bottle was placed in an ultrasonic cleaning device for 10 minutes. The liquid storage bottle was taken out and placed in a 55°C water bath. It was observed that the first precipitation of the vanadium solution occurred in 4 hours. Comparison between Example 3 and Example 4 shows that the additive effectively promotes the high temperature resistance of the vanadium electrolyte.

[0077] Based on the above thermal stability test results, the use of 1.5% diammonium phosphate additive can maximize the high temperature resistance of vanadium electrolyte.

[0078] High temperature operation simulation experiment of energy storage system Take V 4+ 、V 3+ The solution was mixed in a 1:1 ratio to obtain 0.85 mol / L VO 2++ 0.85mol / LV 3++ 4mol / LH2SO4 solution, referred to as V 3.5+ Solution.

[0079] To the V 3.5+ Add 0-1.5% of any common electrolyte additive such as dihydrogen phosphate to the solution, and place it in an ultrasonic cleaning device for ultrasonic treatment for 10-15 minutes to obtain V containing the additive. 3.5+ Solution.

[0080] The V containing additives 3.5+ The solution was placed in the anode and cathode storage tanks of the cyclic charge and discharge test device in a 1:1 ratio.

[0081] The cyclic charge-discharge test device comprises the cyclic electrolysis device and a water bath device. The cathode and anode liquid storage tanks in the cyclic electrolysis device are both placed in a water bath pot.

[0082] Start the peristaltic pump, set the speed to 40-60r / min, and introduce nitrogen into the cathode liquid storage tank to form a protective atmosphere. After the flow stabilizes, start the water bath heating device and set the temperature to 25-55°C.

[0083] After the water bath temperature stabilizes, start the electrochemical workstation and set the process to 1) constant current charging with a current of 40-60 mA / cm 2 , the cut-off voltage is 1.7-1.9V; 2) constant current discharge, the current size is 40-60mA / cm 2 , the cut-off voltage is 0.6-0.7V; 3) constant current charging, the current size is 80-100mA / cm 2 , the cut-off voltage is 1.7-1.9V; 4) constant current discharge, the current size is 80-100mA / cm 2 , the cut-off voltage is 0.6-0.7V; 5) cyclically perform step 3 and step 4, and the number of cycles is 5-10 times. Record the voltage-time curve during the cyclic charge and discharge process, and calculate the charge and discharge energy efficiency, voltage efficiency and coulomb efficiency. Experiments show that the present invention has good cycle performance. Under the operating condition of 55°C, the energy density of the battery is increased by 5.96% and the energy efficiency is increased by 5.88% compared with before the improvement.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A liquid flow battery energy storage system coupled with phase change thermal storage, characterized in that: It includes a cathode liquid storage tank, an anode liquid storage tank, a high temperature phase change chamber, a low temperature phase change chamber, a battery stack and a control system; The high-temperature zone phase change cavity is provided with a high-temperature zone cathode heat exchange tube and a high-temperature zone anode heat exchange tube, and the high-temperature zone phase change cavity is filled with a high-temperature zone phase change material; the low-temperature zone phase change cavity is provided with a low-temperature zone cathode heat exchange tube and a low-temperature zone anode heat exchange tube, and the low-temperature zone phase change cavity is filled with a low-temperature zone phase change material; The outlet pipe of the cathode liquid storage tank is connected to one end of the cathode heat exchange pipe in the low temperature zone, and a cathode booster pump is arranged on it. The other end of the cathode heat exchange pipe in the low temperature zone is connected to the cathode side inlet pipe of the stack. The cathode side outlet pipe of the stack is connected to the return pipe of the cathode liquid storage tank and one end of the cathode heat exchange pipe in the high temperature zone through a cathode electromagnetic three-way valve. The other end of the cathode heat exchange pipe in the high temperature zone is connected to the cathode liquid storage tank. The outlet pipe of the anode liquid storage tank is connected to one end of the anode heat exchange tube in the low temperature zone, and an anode booster pump is arranged on it. The other end of the anode heat exchange tube in the low temperature zone is connected to the anode side inlet pipe of the stack. The anode side outlet pipe of the stack is connected to the return pipe of the anode liquid storage tank and one end of the anode heat exchange tube in the high temperature zone through the anode electromagnetic three-way valve. The other end of the anode heat exchange tube in the high temperature zone is connected to the anode liquid storage tank. The control system is electrically connected to the cathode electromagnetic three-way valve, the anode electromagnetic three-way valve, the cathode booster pump, and the anode booster pump respectively.

2. The liquid flow battery energy storage system coupled with phase change heat storage according to claim 1 is characterized in that: The control system comprises: A temperature sensor is used to detect the electrolyte temperature and generate an electrical signal; A position controller receives an electrical signal from a temperature sensor; The DC contactor receives the electrical signal from the position controller, responds based on the control of the position controller, controls the on-off of the circuit between the DC power supply and the electromagnetic three-way valve, thereby changing the outlet of the electromagnetic three-way valve and the flow direction of the electrolyte; A PID controller receives an electrical signal from the temperature sensor and is used to control the speed of the boost pump; Switching power supply, supplying power to PID controller and position controller; Computer, connected with PID controller and position controller.

3. The liquid flow battery energy storage system coupled with phase change heat storage according to claim 2 is characterized in that: The control system has two control loops. The first control loop is the opening control of the electromagnetic three-way valve. When the temperature sensor detects that the electrolyte temperature exceeds the set value, the position controller controls the DC contactor to connect the circuit between the DC power supply and the electromagnetic three-way valve, and the electromagnetic three-way valve is energized to turn the opening to the pipeline directly connected to the liquid storage tank; conversely, when the temperature sensor detects that the electrolyte temperature is lower than the set value, the position controller controls the DC contactor to disconnect the circuit between the DC power supply and the electromagnetic three-way valve, and the electromagnetic three-way valve is powered off, and the opening is turned to connect to the high-temperature zone heat exchange pipe, so as to The electrolyte is made to flow through the phase change material heated by solar energy to increase the temperature of the electrolyte. The second control loop is the control loop for the electrolyte flow rate. The PID controller in this loop can compare the temperature of the electrolyte with the set temperature in the PID controller. When the difference between the two is large, the PID controller will increase the speed of the boost pump to enhance the heat transfer coefficient of the electrolyte and achieve rapid heat exchange between the electrolyte and the phase change material. Conversely, when the difference between the two is small, the PID controller will reduce the speed of the boost pump to better maintain the temperature of the electrolyte at the set value.

4. The liquid flow battery energy storage system coupled with phase change heat storage according to claim 3 is characterized in that: It also includes a container, wherein the cathode liquid storage tank, the anode liquid storage tank, the battery stack and the low-temperature phase change cavity are all arranged in the container, and the high-temperature phase change cavity is arranged on the top of the container.

5. The liquid flow battery energy storage system coupled with phase change heat storage according to claim 4 is characterized in that: The high temperature zone cathode heat exchange tube and the high temperature zone anode heat exchange tube are both arranged in the high temperature zone phase change cavity in a serpentine manner.

6. The liquid flow battery energy storage system coupled with phase change thermal storage according to claim 5 is characterized in that: The low temperature zone cathode heat exchange tube and the low temperature zone anode heat exchange tube are both arranged in the low temperature zone phase change cavity in a serpentine manner.

7. The liquid flow battery energy storage system coupled with phase change heat storage according to claim 6 is characterized in that: Adding photothermal conversion materials to the high temperature phase change materials to enhance the photothermal conversion capability.

8. The liquid flow battery energy storage system coupled with phase change heat storage according to claim 7 is characterized in that: The melting point of the high temperature zone phase change material is higher than the optimal operating temperature of the system, and the melting point of the low temperature zone phase change material is lower than the optimal operating temperature of the system.

9. An energy storage method using the liquid flow battery energy storage system coupled with phase change heat storage as claimed in claim 1, characterized in that: When the system is running, the boost pump is powered on and rotates to pump electrolyte from the electrolyte storage tank. Under the action of the boost pump, the electrolyte first flows through the low-temperature zone heat exchange tube to exchange heat with the low-temperature zone phase change material, and then enters the fuel cell stack. After the electrolyte undergoes redox reaction in the fuel cell stack, it flows through the electromagnetic three-way valve, which is controlled by the control system. When the electrolyte temperature is lower than the set temperature, the electromagnetic three-way valve controls the electrolyte to flow through the high-temperature zone heat exchange tube to absorb the light and heat stored in the high-temperature zone phase change material. Conversely, when the electrolyte temperature is higher than the set temperature, the electromagnetic three-way valve controls it to bypass the high-temperature zone phase change material and flow directly into the storage tank, thus completing a cycle.

10. The energy storage method according to claim 9, characterized in that: The electrolyte concentration ratio is 1.7M vanadium ion, 4M sulfate ion, and 1.5% mass concentration of diammonium phosphate additive.

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