Flow cell stack structure packaging design method

Abstract

The invention relates to the technical field of flow cell stack design, and provides a flow cell stack structure packaging design method, which comprises the following steps of: dividing a flow cell stack model into a stack core area and a stack sealing area positioned on the periphery of the stack core area, and respectively calculating equivalent stiffness k stack core area and k stack sealing area by adopting # imgabs0 #; the overall equivalent stiffness k galvanic pile of the flow cell pile model is equal to k galvanic pile core area + k galvanic pile sealing area, the clamping force F galvanic pile core area borne by the galvanic pile core area and the clamping force F galvanic pile sealing area borne by the galvanic pile sealing area are calculated, and the clamping force or / and the parameters of the flow cell pile model are adjusted according to the sealing performance or / and the electrochemical performance of the flow cell pile. According to the flow cell stack structure packaging design method provided by the invention, the overall equivalent stiffness of the flow cell stack is regarded as the combination of the equivalent stiffness of each component, and the flow cell stack under the acting force of the clamping force is simplified into an equivalent stiffness mechanical model, so that the design efficiency can be improved.

Description

[0001] This application is a divisional application of an invention patent application with an application date of July 18, 2024, Chinese application number 202410963242.4, and invention name “A method for designing liquid flow battery stack structure packaging”. Technical Field

[0002] The present invention belongs to the technical field of liquid flow battery stack design, and in particular relates to a liquid flow battery stack structure packaging design method. Background Art

[0003] Liquid flow battery technology has made great progress in the past few decades. As the electrolyte of liquid flow batteries has no cross contamination and has a long cycle life, it is favored by more people. Nowadays, liquid flow batteries are gradually being commercialized. The liquid flow battery stack is the core component of the liquid flow battery. The efficiency and cycle stability of the battery are closely related to the stack. How to ensure its stable and efficient operation is the focus of the industry.

[0004] During the assembly process of the flow battery stack, the final clamping force is an important factor affecting its working efficiency and system stability. When the clamping force is too small, the contact resistance of the component interface will increase, the electrolyte will mix inside and outside, and the capacity will decay. When the clamping force is too large, the parts will be plastically deformed or even destroyed, causing mechanical damage to the graphite plate and frame of the battery. What's more, excessive clamping force will cause the porous electrode to penetrate the ion exchange membrane, causing the battery to short-circuit and affecting the normal use of the flow battery.

[0005] In the prior art, although the clamping force can be calculated using the finite element analysis method, in order to reduce the calculation time, people often simplify the internal details of the battery stack, such as ignoring the flow field shape, simplifying all parts into simple flat plates, and increasing the grid size to reduce the number of grids and nodes, thereby reducing the calculation time, which makes the calculation result have a certain error with the clamping force required by the actual battery stack. In engineering practice, people often rely on experience or repeated experiments to design the packaging structure and adjust the clamping force, and it is difficult to effectively ensure the stability of the battery stack. Each assembly and adjustment takes a lot of time, and the assembly and adjustment efficiency is low.

[0006] Therefore, there is an urgent need for a method that can simply, efficiently and accurately determine the optimal clamping force while ensuring the performance of the flow battery stack.

[0007] The above information disclosed in the background technology section is only used to enhance the understanding of the background technology of the technology described in this article. Therefore, the background technology may contain some information that does not form the known prior art for those skilled in the art. Summary of the invention

[0008] The purpose of the present invention is to overcome at least one of the above-mentioned deficiencies of the prior art and to provide a method for designing a liquid flow battery stack structure packaging, which can simply, efficiently and relatively accurately determine the optimal clamping force of the liquid flow battery stack, thereby improving the design efficiency of the liquid flow battery stack.

[0009] The technical solution of the present invention is: a method for designing a liquid flow battery stack structure packaging, comprising the following steps:

[0010] Partition setting step: obtaining a liquid flow battery stack model, wherein the liquid flow battery stack model comprises at least two electrode plates, a membrane located between two adjacent electrode plates, and a screw passing through each electrode plate, and the liquid flow battery stack model is divided into an electrode stack core area and an electrode stack sealing area located outside the electrode stack core area, the electrode plates in the liquid flow battery stack model are correspondingly divided into an electrode plate core area and an electrode plate sealing area, and the membrane located between two electrode plates in the liquid flow battery stack model is correspondingly divided into a membrane core area and a membrane sealing area;

[0011] Equivalent stiffness calculation steps: Use Calculate the equivalent stiffness k of the core area of ​​the stack separately 电堆核心区 and the equivalent stiffness k of the stack sealing area 电堆密封区 , the overall equivalent stiffness k of the flow battery stack model 电堆 =k 电堆核心区 +k 电堆密封区 , E represents the elastic modulus of the component material, A represents the cross-sectional area of ​​the component perpendicular to the clamping force direction, and L represents the thickness of the component in the clamping force direction;

[0012] Clamping force calculation steps: Calculate the clamping force F on the core area of ​​the stack 电堆核心区 and the clamping force F borne by the stack sealing area 电堆密封区 ,

[0013]

[0014] Where C is the number of screws and δ is the elongation of the screw;

[0015] Model correction steps: adjust the clamping force and / or adjust the parameters of the flow battery stack model according to the sealing and / or electrochemical performance of the flow battery stack.

[0016] Specifically, the flow battery stack model also includes a gasket located between the membrane and the plate. The model correction step includes a first correction step: correcting the clamping force range based on the sealing of the flow battery stack; the first correction step includes: calculating the average contact pressure P according to the clamping force 密封 , and calculate the minimum pressure to prevent leakage The maximum average contact pressure at which the gasket material will not fail The calculation formula is:

[0017]

[0018] Check the average contact pressure P 密封 Whether it meets: Among them, P 电解液 is the pressure of the electrolyte in the battery stack, b is the thickness of the gasket, ξ is the transient coefficient of the gasket material from elastic deformation to plastic deformation, σ 垫片 is the yield stress of the gasket.

[0019] Specifically, the clamping force calculation step includes a bolt tightening torque calculation step. After the clamping force is applied to the end plate of the flow battery stack model through a nut threadedly connected to the screw rod, the battery stack core area and the battery stack sealing area in the plate have the same compression displacement, and the relationship between the bolt tightening torque and the clamping force is:

[0020]

[0021] Where T is the tightening torque of a single nut and d is the nominal diameter of the screw.

[0022] Specifically, the flow battery stack model also includes electrodes, and the model correction step also includes a second correction step, the second correction step: determining the clamping force range based on the electrochemical performance of the battery stack, the second correction step includes: calculating the contact resistance R between the electrode and the plate 接触 , the contact resistance between the electrode and the plate R 接触 The relationship formula with pressure change is:

[0023]

[0024] Among them, P 接触 is the contact pressure between the electrode and the bipolar plate.

[0025] Specifically, the model correction step further includes a third correction step: determining the clamping force range based on the actual permeability of the electrode. The third correction step includes: calculating the actual permeability of the electrode, and the calculation formula of the actual permeability of the electrode is:

[0026]

[0027] Among them, θ is the actual porosity of the electrode, θ0 is the initial porosity of the electrode, and ε V is the strain rate of the electrode, γ is the actual permeability of the electrode, d f is the diameter of the carbon fiber in the electrode, γ CK is the Carman–Kozeny constant.

[0028] Specifically, the core area of ​​the plate is divided into a flow channel rib part and a plate base part, and the equivalent stiffness of the core area of ​​the plate is obtained by superimposing the equivalent stiffness of each flow channel rib in parallel with the equivalent stiffness of the plate base part.

[0029] Specifically, the liquid flow battery stack model includes two end plates located at both ends of the liquid flow battery stack model, and the end plate at one end is set to be fixed, and the end plate at the other end is set to withstand pressure and generate displacement; the screw rod serves as an equivalent spring model, one end of the screw rod is connected to the fixed end plate, and there is a gap between the other end of the screw rod and the displaceable end plate, and the size of the gap is equal to the deformation variable δ of the screw rod.

[0030] Specifically, the equivalent stiffness k of the sealing area is 电堆密封区 It is the superposition of the equivalent stiffness of the plate sealing area, gasket, and membrane sealing area.

[0031] Specifically, the value range of ξ is 2 to 4.

[0032] Specifically, adjusting the parameters of the flow battery stack model includes adjusting at least one of the elastic modulus of the material, adjusting the cross-sectional area of ​​the component perpendicular to the direction of the clamping force, and adjusting the thickness of the component in the direction of the clamping force;

[0033] After the model modification step, a practical validation step is performed on the battery stack model.

[0034] A liquid flow battery stack structure packaging design method provided by the present invention can regard the overall equivalent stiffness of the liquid flow battery stack as a combination of the equivalent stiffnesses of each component by constructing an equivalent stiffness model. Under the action of the clamping force, the overall stack structure is compressed and deformed mainly along the direction of the screw. The liquid flow battery stack under the clamping force is simplified into an equivalent stiffness mechanical model by using mechanical theory, and the corresponding relationship between the deformation of the parts and the clamping force acting on the surface is derived. Then, the optimal liquid flow battery stack packaging parameters are determined according to specific design requirements, and corrections are made for the situation where the thickness of the front electrode and the sealing gasket of the liquid flow battery stack are different. The clamping force can be calculated more effectively, and then the range of the clamping force is determined based on the sealing of the stack and the electrochemical properties of the stack. The mechanical response of the stack under the clamping force can be accurately and quickly obtained, thereby completing the determination of the optimal clamping force range, saving a lot of time and calculation costs, and greatly improving the design efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 Schematic diagram of a single-stage liquid flow battery in a liquid flow battery stack model of a liquid flow battery stack structure packaging design method in an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the regional division of the proton exchange membrane in the flow battery stack model of the flow battery stack structure packaging design method in an embodiment of the present invention.

[0038] Figure 3 Schematic diagram of the overall equivalent stiffness of a flow battery stack in a flow battery stack structure packaging design method in an embodiment of the present invention.

[0039] Figure 4 Schematic diagram of the equivalent stiffness model of the assembled battery stack in the method for designing the structure packaging of the flow battery stack in an embodiment of the present invention.

[0040] Figure 5 It is a structural diagram of a liquid flow battery stack assembled according to the liquid flow battery stack structure packaging design method in an embodiment of the present invention.

[0041] Figure 6 It is a schematic diagram of the relationship between the bolt tightening torque, contact resistance and permeability according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention 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 invention and are not intended to limit the present invention.

[0043] It should be noted that the terms “setting” and “connection” should be understood in a broad sense. For example, it can be directly setting or connecting, or it can be indirectly setting or connecting through a central component or a central structure.

[0044] In addition, in the embodiments of the present invention, if there are terms indicating orientation or positional relationships such as "longitudinal", "transverse", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., they are based on the orientation or positional relationships or conventional placement states or usage states shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the structure, feature, device or element referred to must have a specific orientation or positional relationship, nor must it be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0045] The various specific technical features and embodiments described in the specific implementation methods can be combined in any suitable manner unless there is any contradiction. For example, different implementation methods can be formed by combining different specific technical features / embodiments. In order to avoid unnecessary repetition, the various possible combinations of the specific technical features / embodiments in the present invention will not be described separately.

[0046] like Figures 1 to 4 As shown, a method for designing a liquid flow battery stack structure packaging according to an embodiment of the present invention comprises the following steps:

[0047] Partition setting step: obtain a liquid flow battery stack model, and the components of the liquid flow battery stack model include at least two electrode plates 20, a membrane 5 located between two adjacent electrode plates 20 (in actual applications, it can be a proton exchange membrane or an ion exchange membrane) and a screw passing through each electrode plate 20. In the liquid flow battery stack model, the electrode plates 20, membrane 5 and other components have set dimensions and material properties, and different materials have corresponding elastic modulus parameters. In the above-mentioned partition setting step, the liquid flow battery stack model is divided into a battery stack core area 8 and a battery stack sealing area 7 located outside the battery stack core area 8. The electrode plates 20 in the liquid flow battery stack model are correspondingly divided into a electrode plate core area (corresponding to the battery stack core area 8) and an electrode plate sealing area (corresponding to the battery stack sealing area 7). The membrane 5 located between two electrode plates 20 in the liquid flow battery stack model is correspondingly divided into a membrane core area and a membrane sealing area.

[0048] Equivalent stiffness calculation steps: Use Calculate the equivalent stiffness k of the core area 8 of the stack separately 电堆核心区8 and the equivalent stiffness k of the stack sealing area 7 电堆密封区7 And the equivalent stiffness k of the screw 螺杆 , the overall equivalent stiffness k of the flow battery stack model 电堆 =k 电堆核心区8 +k 电堆密封区7 , k represents the equivalent stiffness of the component, E represents the elastic modulus of the component material, and A represents the cross-sectional area of ​​the component perpendicular to the clamping force direction (unit: m 2 ), L represents the thickness of the component in the direction of the clamping force (unit: m), where the equivalent stiffness k of the screw 螺杆 In the calculation, A is calculated from the screw minor diameter (thread bottom diameter).

[0049] Clamping force calculation steps: Calculate the clamping force F on the core area 8 of the stack 电堆核心区8 and the clamping force F borne by the stack sealing area 7 电堆密封区7 .

[0050]

[0051] Where, C is the number of screws, δ is the elongation (deformation) of the screw (unit: m);

[0052] The deformation of a single part or a divided area in the direction of the clamping force is given by the formula Calculate, where F i is the force on this part or area. Select F according to the location of the part. 电堆核心区 With F 电堆密封区 Calculate k i is the equivalent stiffness of this part or area. Calculate the maximum force (determined by the strength limit of the material) and the minimum force required to clamp this part. and The deformation displacements of the parts in the core area and the sealing area of ​​the stack are accumulated respectively, and the deformation ranges of the core area and the sealing area are calculated:

[0053]

[0054] The above two conditions should be met at the same time, and the final range of deformation value should be determined accordingly.

[0055] Z 最小 <Z 电堆 <Z 最大 According to the displacement coordination condition and the static load balance condition in the clamping direction, the structural load balance equation can be written as:

[0056] C.k 螺杆 (δ-Z 电堆 ) = k 电堆 ·Z 电堆 The range of the elongation δ of the screw is determined thereby. δ can be selected within the above range, for example, the median is first selected within the above range, and then adjusted upward or downward in steps within the above range according to the calculation and verification results.

[0057] Model correction steps: According to the sealing and / or electrochemical performance of the flow battery stack, adjust the clamping force and / or adjust the flow battery stack model. In specific applications, the clamping force F that the core area 8 of the stack is subjected to is calculated. 电堆核心区8 and the clamping force F borne by the stack sealing area 7 电堆密封区7Afterwards, actual manufacturing, assembly and experimental verification can be carried out according to the component structure, size and material in the flow battery stack model. In this way, the initial clamping force data of the flow battery stack is obtained through the previous calculation, and then the flow battery stack is actually manufactured according to the flow battery stack model, and the initial clamping force data is used to clamp the flow battery stack, and then the actual performance of the flow battery stack is analyzed through the set test. If the actual performance of the flow battery stack meets the requirements, it can be verified that the packaging design process and parameters are reasonable. If the actual performance of the flow battery stack does not meet the requirements, the clamping force can be increased or reduced according to the performance characterization to make the actual performance of the flow battery stack meet the requirements, avoid the problem of increased contact resistance of the component interface, internal and external mixing of the electrolyte, and capacity attenuation caused by too small clamping force, and avoid deformation and damage of components caused by excessive clamping force, avoid battery short circuit, and help ensure the normal use of the flow battery. The above design method is simple, easy and accurate, does not consume a lot of computing resources, and does not need to rely on experience or repeated experiments to design the packaging structure and adjust the clamping force. The overall design efficiency is high, which is conducive to shortening the design cycle and reducing the design cost.

[0058] In a specific application, in the equivalent stiffness model established by the above design method, the equivalent stiffness (k 电堆核心区8 ) is the equivalent stiffness superposition (series connection) of the components in the core area 8 of the stack (including the stacked components such as the plate 20 and the membrane 5). Similarly, the equivalent stiffness (k 电堆密封区7 ) is the equivalent stiffness superposition (series connection) of each layer of components (including the electrode plate 20, the membrane 5 and other stacked components) in the stack sealing area 7. The equivalent stiffness of the core area of ​​the stack 8 corresponding to each layer of components can be calculated separately, that is, the equivalent stiffness of the core area of ​​the stack corresponding to each component is adopted Calculate them separately, then sum the equivalent stiffness of each core area of ​​the stack, and superimpose the equivalent stiffness of the multi-layer components. And calculate the equivalent stiffness of the stack sealing area 7 corresponding to each layer of components, that is, the equivalent stiffness of the stack sealing area corresponding to each component is calculated using Calculate them separately, and then sum the equivalent stiffness of each stack sealing area to obtain the equivalent stiffness k of the stack core area 8 电堆核心区8 and the equivalent stiffness k of the stack sealing area 7 电堆密封区7 In this embodiment, the core area 8 of the battery stack is the active area where the electrochemical reaction occurs, and the sealing area 7 of the battery stack is the area around the electrode plate 20 that is in contact with the sealing component (gasket) (outside the active area). In specific applications, the electrode plate 20 includes a plate body 1 and a flow channel rib 2 arranged on one side of the plate body 1. The flow channel rib 2 can be arranged in a circuitous manner to form a flow channel of the liquid flow battery. The flow channel rib 2 is located in the core area 8 of the battery stack. In specific applications, such as Figures 1 to 3As shown, the planar shape of the liquid flow battery stack is rectangular, the battery stack core area 8 can be rectangular, and the battery stack sealing area 7 is a rectangular frame area arranged around the outer side of the battery stack core area 8, that is, the battery stack core area 8 and the battery stack sealing area 7 are arranged in a "U" shape. Specifically, the equivalent stiffness model of the liquid flow battery stack is ultimately equivalent to: the equivalent springs corresponding to the battery stack core area 8 and the battery stack sealing area 7 have no initial displacement, and both ends of the equivalent springs are connected to the end plate 11. The equivalent springs (equivalent stiffness) corresponding to the battery stack core area 8 and the battery stack sealing area 7 are connected in parallel to form the overall equivalent stiffness of the battery stack; since the end plate 11 on one side is fixed, the end plate 11 on the other side will be under pressure and produce a compressive displacement. One end of the equivalent stiffness spring 12 corresponding to the screw used for packaging is connected to the fixed end plate 11, and there is a gap (δ) between the other end and the movable end plate 11. The size of the gap represents the deformation amount (δ) of the screw, as shown Figure 3 According to the equivalent mechanical model, the overall packaging equivalent stiffness of the flow battery stack is k 电堆 =k 电堆核心区8 +k 电堆密封区7 Specifically, when the clamping force is applied, the clamping force causes the equivalent stiffness spring 12 of the screw to stretch and connect with the movable end plate 11. Under the restriction of the end plate 11, the screw, the battery core area 8 and the battery sealing area 7 will perform a force balance and displacement coordination process, and the total displacement of the flow battery stack can be obtained. After the packaging is completed, the entire flow battery stack system is in a stable state, such as Figure 4 As shown, 15 is the deformation of the battery core area after packaging; 16 is the deformation of the battery seal area. The pressure borne by a single structure can be calculated based on the product of the equivalent stiffness of this area and its own displacement, that is, F = kx. The number of screws is C, and their elongation is δ. After assembly, the clamping force borne by the battery core area 8 and the battery seal area 7 is calculated using the following formula:

[0059]

[0060] Specifically, the flow battery stack model also includes a gasket 6 (sealing gasket) located between the membrane 5 and the electrode plate 20. To correct the unequal thickness of the electrode and the gasket, the initial thickness of the electrode in the flow battery stack is generally greater than the thickness of the sealing gasket (gasket 6, also called sealing gasket). At this time, the spring model corresponding to the sealing area in the equivalent stiffness model and the fixed end plate 11 should have a gap 4. In the initial packaging, only the core area 8 of the stack is subject to the clamping load; when the clamping force gradually increases to eliminate the gap 4, that is, when the displacement generated by the stack sealing area 7 is equal to the gap 4, the core area 8 of the stack and the stack sealing area 7 will jointly bear the clamping force. At this time, the total clamping force borne by the core area 8 of the stack is the product of its equivalent stiffness 13 and the total displacement of the stack, and the total clamping force borne by the stack sealing area 7 is the product of its equivalent stiffness and the difference between the total displacement of the stack and the gap.

[0061] In specific applications, the bolt deformation process is divided into two stages:

[0062] δ=δ 间隙 +δ 预紧

[0063] where δ 间隙 is the preload displacement before the gap disappears in the initial stage of assembly, δ 预紧 is the design displacement variable of the clamping bolt after the gap disappears.

[0064] Z 间隙 =L 电极 -L 垫片

[0065] Where L 电极 is the thickness of the electrode, L 垫片 is the thickness of the gasket, Z 间隙 is the initial gap.

[0066]

[0067] Where M is the number of cells connected in series in the stack.

[0068] at this time

[0069]

[0070] Specifically, the model correction step includes a first correction step: correcting the clamping force range based on the sealing performance of the flow battery stack. The first correction step includes: 密封 Calculation of clamping force F 密封 =

[0071] P 密封 A 密封 , and calculate the minimum pressure to prevent leakage The maximum average contact pressure at which the gasket material will not fail The calculation formula is:

[0072]

[0073] Check the average contact pressure P 密封 Whether it meets: Among them, P 电解液 is the pressure of the electrolyte in the battery stack, b is the thickness of the gasket 6, ξ is the transient coefficient of the gasket 6 material from elastic deformation to plastic deformation, σ 垫片is the yield stress of gasket 6. The value range of ξ can be 2 to 4. Gasket 6 can be made of polymer material. For gasket 6 made of polymer material, ξ is 3. The clamping force has a great influence on whether the battery stack can work normally. Excessive clamping force will cause the stress of the parts to exceed their strength limit, resulting in damage and cracking; too small clamping force will make the battery stack less sealed and cause electrolyte leakage. If the average contact pressure P 密封 Greater than The clamping force F on the stack sealing area 7 can be reduced. 电堆密封区7 , if the average contact pressure P 密封 Less than The clamping force F that the stack sealing area 7 can bear can be increased. 电堆核心区8 .

[0074] Specifically, the clamping force calculation step includes a bolt tightening torque calculation step. After the clamping force is applied to the end plate 11 by a nut threadedly connected to the screw, the stack core area 8 and the stack sealing area 7 in the electrode plate 20 have the same compression displacement, and the relationship between the bolt tightening torque and the clamping force is:

[0075]

[0076] Where T is the tightening torque of a single nut (Nm), and d is the nominal diameter of the screw (mm). In this way, a torque wrench can be used to directly tighten the nut to the set tightening torque, making assembly and debugging simple and easy. The above two formulas are equivalent and refer to the tightening torque of the bolts. When assembling the battery stack, control the tightening torque of each bolt to be the same.

[0077] Specifically, the model correction step also includes the design based on the structural strength of the parts, the stress of all parts in the battery stack, Where F is the pressure on the part in the clamping direction (N), A is the area of ​​the part (m 2 ). To ensure that the parts will not be crushed, σ≤[σ], where [σ] is the ultimate strength of the parts (Pa).

[0078] Specifically, the model correction step further includes a second correction step: determining the clamping force range based on the electrochemical performance of the battery stack. The second correction step: calculating the contact resistance R between the electrode and the electrode plate 20 接触 According to the experimental results, the relationship between contact resistance and pressure is fitted as follows:

[0079]

[0080] Among them, P 接触 is the contact pressure between the electrode and the bipolar plate. 接触 It is obtained by dividing the contact pressure between the electrode and the bipolar plate by the contact area. The formula is an empirical formula obtained by fitting the pressure-contact resistance curve obtained from experimental tests through polynomial fitting.

[0081] If R 接触 If the clamping force F of the core area 8 of the stack is greater than the set range, the clamping force F of the core area 8 of the stack can be increased. 电堆核心区8 The actual contact area between the electrode and the plate 20 (bipolar plate) increases with the increase of the clamping force, and the contact resistance gradually decreases. For a flow battery stack, the clamping force should be large enough to reduce the contact resistance to an acceptable level.

[0082] Specifically, the model correction step includes a third correction step: determining the clamping force range based on the actual electrode permeability. The third correction step: calculating the electrode permeability. The electrode permeability decreases with the increase of the clamping force. For a flow battery stack, the electrode permeability cannot be too small to increase the pump work. The calculation formula of the actual electrode permeability is:

[0083]

[0084] Among them, θ is the actual porosity of the electrode, θ0 is the initial porosity of the electrode, and ε V is the strain rate of the electrode, γ is the actual permeability of the electrode, d f is the diameter of the carbon fiber in the electrode, γ CK is the Carman–Kozeny constant. If the actual electrode permeability is greater than the set range, the clamping force F on the core area 8 of the stack can be reduced. 电堆核心区8 If the actual electrode permeability is less than the set range, the clamping force F of the stack sealing area 7 can be increased. 电堆核心区8 .

[0085] Specifically, the strain rate ε of the electrode V =Δl / l,Δl=F 电极 / k 电极 , where Δl is the change in size of the electrode and l is the initial size of the electrode. Calculate k 电极 . F 电极 =F 电堆核心区 .

[0086] Specifically, the order of the first correction step, the second correction step and the third correction step can be adjusted as needed, and the adjustment of any correction step requires repeating the entire model correction step (the first correction step, the second correction step and the third correction step) to ensure the rationality and accuracy of the design, so as to ensure that the actual performance of the liquid flow battery stack meets the design and use requirements.

[0087] Specifically, in the partition setting step, the core area of ​​the plate is divided into a flow channel rib part (flow channel rib 2) and a base part of the plate (plate body 1). The equivalent stiffness of the core area of ​​the plate is obtained by connecting the equivalent stiffness of each flow channel rib 2 in parallel and then superimposing (connecting in series) the equivalent stiffness of the base part of the plate. There is no need to consider the complex internal details of the flow channel rib 2, which significantly reduces the calculation time. Since the flow channel rib 2 (bipolar plate rib) will contact the electrode, and the gap between the ribs will not contact the electrode, the flow channel rib 2 and the base part of the bipolar plate (plate body 1) are separated, and the flow channel rib 2 can be simplified into multiple equivalent springs in parallel, and then connected in series with the base part of the bipolar plate (plate body 1), which is convenient for calculating stiffness. And because the equivalent stiffness is strongly related to the material and thickness, the design method in this application has a small error in the calculation result and the clamping force required by the actual battery stack.

[0088] Specifically, the liquid flow battery stack model in the partition setting step includes two end plates 11 located at both ends of the liquid flow battery stack model, and the end plate 11 at one end is set to be fixed, and the end plate 11 at the other end is set to withstand pressure and generate displacement; the screw rod serves as an equivalent spring model 12, one end of the screw rod is connected to the fixed end plate 11, and there is a gap between the other end of the screw rod and the displaceable end plate 11, and the size of the gap is equal to the deformation amount δ of the screw rod.

[0089] In this embodiment, the equivalent stiffness k of the sealing area 电堆密封区7 ( Figure 2 The sealing area equivalent stiffness spring model 14) is formed by the equivalent stiffness of the plate sealing area, gasket 6, and membrane sealing area connected in series (added).

[0090] In specific applications, adjusting the parameters of the liquid flow battery stack model includes adjusting the elastic modulus of the material, adjusting the cross-sectional area of ​​the component perpendicular to the clamping force direction, and adjusting at least one of the thickness of the component in the clamping force direction; after the model correction step, it also includes: a model verification step, in which the liquid flow battery stack model (corresponding liquid flow battery stack sample) is actually verified to verify the design results, and the design can be adjusted accordingly based on the actual verification results.

[0091] In this embodiment, in the present invention, springs are used to characterize the structural stiffness of a single part, and the equivalent stiffness model of the flow battery stack (electrical stack) can be regarded as a combination of multiple springs of different stiffness connected in series and in parallel. Specifically, the electrode plate 20 (bipolar plate) of the flow battery stack is divided into two major parts: the stack core area 8 and the stack sealing area 7. The equivalent stiffness of these two areas in the direction of the clamping force is independent of each other. The stack core area 8 is the active area where the electrochemical reaction occurs, and the stack sealing area 7 is the area around the bipolar plate that is in contact with the sealing gasket 6. Similarly, the ion exchange membrane is also divided into a membrane core area and a membrane sealing area. The plate core area corresponding to the plate 20 is further divided in detail to improve the calculation accuracy: the array-arranged flow channel ribs 2 are divided independently, and the remaining part is the base part of the plate. The final plate (bipolar plate) 20 is divided into three parts (i.e., the plate sealing area, the flow channel rib part and the plate base part), the flow channel rib part and the plate base part are superimposed to form the plate core area, and the plate core area is independent of the plate sealing area, such as Figure 1 As shown. That is, the equivalent stiffness of the core area of ​​the plate ( Figure 2 The core area equivalent stiffness spring model 13) is formed by connecting the equivalent stiffness of the flow channel rib part (each flow channel rib 2) in parallel and then connecting the equivalent stiffness of the plate base part (plate body 1) in series.

[0092] In specific applications, the flow battery stack is also divided into two parts: the stack core area 8 and the stack sealing area 7. The equivalent stiffness of the stack core area ( Figure 2 The core area equivalent stiffness spring model 13) is composed of the equivalent stiffness of the plate core area, positive electrode, ion exchange membrane core area, and negative electrode components connected in series; the equivalent stiffness of the stack sealing area ( Figure 2 The sealing area equivalent stiffness spring model 14) is composed of the plate sealing area, gasket 6, and ion exchange membrane sealing area components connected in series. The above design method is simple, easy and accurate, does not consume a lot of computing resources, and does not need to rely on experience or repeated experiments to design the packaging structure and adjust the clamping force. The overall design efficiency is high, which is conducive to shortening the design cycle and reducing design costs.

[0093] Example 1: Taking the calculation of the clamping force of a single-stage flow battery with an active area (i.e., the area of ​​the core region 8 of the battery stack) of 265 mm×500 mm as an example, a specific embodiment of the present invention is described in detail.

[0094] (1) The specific steps are as follows: According to the material of each component, find the elastic modulus of each part, measure the required dimensions of each part, and use Calculate the equivalent stiffness value of each component.

[0095] (2) Using the equivalent stiffness model established by the present invention, the equivalent stiffness of each part is combined in series and parallel, and then k 电堆 =k 电堆核心区8 +k电堆密封区7 Calculate the equivalent stiffness of the entire flow battery stack.

[0096] (3) Using F 密封 =P 密封 A 密封 Determine F according to sealing requirements 电堆密封区 The value range of

[0097] and Calculate the relationship between contact resistance and permeability and force respectively, and select the appropriate F according to their changing trends. 电堆核心区 Value range, and then use:

[0098]

[0099] To calculate the bolt torque range.

[0100] (4) If the calculated torque range of the battery stack is too wide, the size of the parts, such as thickness, can be adjusted to obtain a new design solution, and then steps (1) to (4) are repeated until the optimal structure and optimal clamping force range of the battery stack are designed.

[0101] Example 2: The structural equivalent stiffness of the single-stage flow battery in Example 1 was verified using the finite element method. To save calculation time, the finite element model selected a 1 / 8 battery structure and divided the grid. The total number of nodes was 2235961 and the total number of units was 1396985. The computing platform used a 2.9GHz six-core 12-thread CPU, 16GB memory, 1TB hard disk, and six cores for 2 hours of parallel computing. The calculation results are compared in Table 1.

[0102] Table 1 Comparison of equivalent stiffness of each component calculated in Example 2 with three-dimensional finite element calculation results

[0103]

[0104] It can be seen that the relative error between the two is very small, and the relative error of the equivalent stiffness of the overall battery structure is below 2%, thereby verifying the correctness of the equivalent stiffness model established in Example 1 of the present invention. When calculating the equivalent stiffness of a single-stage liquid flow battery, this embodiment only takes 10 minutes, while the finite element method, in addition to the time spent on calculation, also requires a lot of time for dividing the grid and setting boundary conditions, which is time-consuming and labor-intensive. Moreover, if it is expanded to a large liquid flow battery stack structure, the finite element method may not be able to obtain the calculation results in a short time, and may even cause the calculation results to not converge, but the design method in the present invention can still be used to conveniently and quickly design the clamping force of the liquid flow battery stack.

[0105] Example 3: Figure 5As shown in the figure, a small flow battery stack of a certain model with an active area of ​​100mm×150mm, 6 cells, and 12 M12 screws is assembled. First, the relationship between the contact resistance and permeability with force is calculated respectively. By comparing their changing trends, the tightening torque range based on performance is determined to be 9.8 to 17.2Nm. Then, based on the sealing requirements of the battery stack, the tightening torque is used.

[0106]

[0107] The calculated tightening torque range is 14.7 to 32Nm. Then, based on the requirements of the structural strength of the parts, it is calculated whether the stress applied to each part is less than its strength limit. When the tightening torque reaches 17.2Nm, the stress on the bipolar plate sealing area exceeds the strength limit of the material, and there is a risk of crushing. Combining the above calculation results, it is concluded that the optimal tightening torque range is 14.7 to 17.2Nm. The flow battery stack is assembled with a nut tightening torque of 16Nm. After assembly, air is filled into the inner cavity of the flow battery stack to make the air pressure reach 150kPa. After standing for 6 hours, the pressure does not drop and the sealing test is passed. The flow battery stack is connected to the test system for water flow test, and the flow rate is set to 2L / min. At this time, the pipeline pressure is 82kPa, the flow battery stack has no leakage, and the flow battery stack can work normally.

[0108] Example 4: After reducing the bolt tightening torque of the flow battery stack in Example 3 to 13Nm, an air tightness test was performed. The flow battery stack was filled with gas to a pressure of 150kPa and left to stand for 6 hours. The results showed that the pressure dropped to 110kPa, indicating poor sealing. Further water flow tests revealed that there was a slight leakage at the bottom of the flow battery stack. At this time, the pressure on the sealing gasket in the flow battery stack was less than the formula The minimum pressure determined in Example 3 causes the flow battery stack to fail to achieve a good sealing state. Based on the calculation in Example 3, if the flow battery stack is to work properly, the tightening force needs to be increased to at least 14.7 Nm to ensure that the pressure on the sealing gasket is greater than the required minimum sealing pressure. Figure 6 The figure shows the relationship between bolt tightening torque, contact resistance and permeability.

[0109] Example 5: The bolt tightening torque of the flow battery stack in Example 3 was increased to 20 Nm, and the air tightness test was repeated. Air was filled into the flow battery stack to make the pressure reach 150 kPa. After standing for 6 hours, the pressure remained stable and passed the air tightness test. The flow battery stack was then connected to the charge and discharge test system for water flow test, and the flow rate was set to 2 L / min. At this time, the pipeline pressure was 108 kPa, which was significantly higher than 82 kPa in Example 3. This is because the tightening torque of the bolts exceeded the maximum torque of 17.2 Nm obtained in Example 3. According to the formula and Calculations show that excessive clamping force reduces the electrode porosity, thereby reducing the electrode permeability and increasing the internal flow resistance of the flow battery stack, which will increase the pump work and reduce the system efficiency. Therefore, it is necessary to reduce the bolt tightening torque so that the system can operate within the high efficiency range.

[0110] Example 6: The bolt tightening torque of the flow battery stack in Example 3 was increased to 25Nm. During the assembly process, the lower right corner of the second bipolar plate was cracked and the assembly was stopped. At this time, the nut at the lower right corner of the battery stack was tightened with a torque wrench. When the tightening torque reached a certain value, the force at this position of the bipolar plate exceeded its strength limit, causing the bipolar plate to crack. At this time, the bipolar plate could no longer be used. If the electrolyte was passed in, serious leakage would occur. Therefore, a new bipolar plate must be replaced and the tightening torque must be reduced before reassembly before the battery stack can be used normally.

[0111] Example 7: In the liquid flow battery stack of Example 3, the original bipolar plate was replaced and a new bipolar plate with higher strength was adopted. The elastic modulus of the original bipolar plate is 3.44GPa, while the elastic modulus of the new bipolar plate reaches 5GPa. Recalculated according to the above design method, the bolt tightening torque range is 21.2Nm to 25.4Nm. In this case, a tightening torque of 25Nm is selected for the assembly of the liquid flow battery stack. After assembly, air is filled into the liquid flow battery stack to make the air pressure reach 150kPa, and after 6 hours of static testing, the results show that the pressure has not dropped and the sealing test has passed. Subsequently, the liquid flow battery stack is connected to the test system for water flow test, and the flow rate is set to 2L / min. At this time, the pipeline pressure is 87kPa, which is a normal level. After testing, the liquid flow battery stack has no leakage and can work normally.

[0112] The equivalent stiffness model constructed by the design method provided by the present invention, the overall equivalent stiffness of the liquid flow battery stack can be regarded as a combination of the equivalent stiffness of each component. Under the action of the clamping force, the overall stack structure is compressed and deformed mainly along the direction of the screw, and the deformation in the other two directions is very small and can be ignored. Based on the above conditions, the mechanical theory is used to simplify the liquid flow battery stack under the clamping force into an equivalent stiffness mechanical model, and the corresponding relationship between the deformation of the parts and the clamping force acting on the surface is derived, and then the optimal liquid flow battery stack packaging parameters are determined according to the specific design requirements. The geometric structure of the parts can be reflected in detail. For example, the bipolar plate engraved with the flow channel is structurally decomposed and regarded as the base part, the sealing part, and the flow field part formed by multiple ribs in parallel, which can greatly improve the calculation accuracy. The present invention also makes corrections for the situation where the thickness of the front electrode and the sealing gasket of the all-vanadium liquid flow battery stack are different, and the clamping force can be determined more effectively. The range of the clamping force is then determined based on the sealing of the stack and the electrochemical properties of the stack. The embodiment of the present invention mainly takes the structure of an all-vanadium liquid flow battery stack as an example, and is also applicable to other liquid flow battery stacks with similar structures. It can very accurately and quickly obtain the mechanical response of the battery stack under the clamping force, thereby determining the optimal clamping force range, saving a lot of time and calculation costs, and can greatly improve design and production efficiency.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing a liquid flow battery stack structure packaging, characterized in that: The following steps are involved: Partition setting step: obtaining a liquid flow battery stack model, the liquid flow battery stack model comprising at least two electrode plates, a membrane located between two adjacent electrode plates, and a screw passing through each electrode plate to apply a clamping force to the liquid flow battery stack model, dividing the liquid flow battery stack model into a battery stack core area and a battery stack sealing area located outside the battery stack core area, the electrode plates in the liquid flow battery stack model are correspondingly divided into a electrode plate core area and a electrode plate sealing area, and the membrane located between two electrode plates in the liquid flow battery stack model is correspondingly divided into a membrane core area and a membrane sealing area; Equivalent stiffness calculation steps: Use Calculate the equivalent stiffness k of the core area of ​​the stack separately 电堆核心区 and the equivalent stiffness k of the stack sealing area 电堆密封区 , the overall equivalent stiffness k of the flow battery stack model 电堆 =k 电堆核心区 +k 电堆密封区 , E represents the elastic modulus of the component material, A represents the cross-sectional area of ​​the component perpendicular to the clamping force direction, and L represents the thickness of the component in the clamping force direction; Clamping force calculation steps: Calculate the clamping force F on the core area of ​​the stack 电堆核心区 and the clamping force F borne by the stack sealing area 电堆密封区 , Where C is the number of screws and δ is the elongation of the screw; Model correction steps: adjust the clamping force and / or adjust the parameters of the flow battery stack model according to the sealing and / or electrochemical performance of the flow battery stack.

2. A method for designing a liquid flow battery stack structure package as claimed in claim 1, characterized in that: The flow battery stack model further comprises a gasket between the membrane and the electrode plate, and the model correction step comprises: First calibration step: calibrating the clamping force range based on the sealing of the flow battery stack; The first calibration step comprises: Calculation of the average contact pressure P from the clamping force 密封 , and calculate the minimum pressure to prevent leakage The maximum average contact pressure at which the gasket material will not fail The calculation formula is: Check the average contact pressure P 密封 Whether it meets: Among them, P 电解液 is the pressure of the electrolyte in the battery stack, b is the thickness of the gasket, ξ is the transient coefficient of the gasket material from elastic deformation to plastic deformation, σ 垫片 is the yield stress of the gasket.

3. A method for designing a liquid flow battery stack structure package as claimed in claim 1, characterized in that: The clamping force calculation step comprises: Bolt tightening torque calculation steps: After applying a clamping force to the end plate of the flow battery stack model through a nut threadedly connected to the screw, the stack core area and the stack sealing area in the plate have the same compression displacement, and the relationship between the bolt tightening torque and the clamping force is: Where T is the tightening torque of a single nut and d is the nominal diameter of the screw.

4. A method for designing a liquid flow battery stack structure package as claimed in claim 2, characterized in that: The flow battery stack model also includes electrodes, and the model correction step further includes: Second calibration step: determining the clamping force range based on the electrochemical performance of the battery stack; The second correction step comprises: Calculate the contact resistance R between the electrode and the plate 接触 , the contact resistance between the electrode and the plate R 接触 The relationship formula with pressure change is: Among them, P 接触 is the contact pressure between the electrode and the bipolar plate.

5. A method for designing a liquid flow battery stack structure package as claimed in claim 4, characterized in that: The model correction step also includes: The third calibration step: determining the clamping force range based on the actual electrode permeability; The third correction step includes: calculating the actual permeability of the electrode, and the calculation formula of the actual permeability of the electrode is: Among them, θ is the actual porosity of the electrode, θ0 is the initial porosity of the electrode, and ε V is the strain rate of the electrode, γ is the actual permeability of the electrode, d f is the diameter of the carbon fiber in the electrode, γ CK is the Carman–Kozeny constant.

6. A method for designing a liquid flow battery stack structure package according to any one of claims 1 to 5, characterized in that: The core area of ​​the plate is divided into a flow channel rib part and a plate base part. The equivalent stiffness of the core area of ​​the plate is obtained by superimposing the equivalent stiffness of each flow channel rib in parallel with the equivalent stiffness of the plate base part.

7. A method for designing a liquid flow battery stack structure package according to any one of claims 1 to 5, characterized in that: The liquid flow battery stack model also includes two end plates located at both ends of the liquid flow battery stack model, and the end plate at one end is set to be fixed, and the end plate at the other end is set to withstand pressure and generate displacement; the screw rod serves as an equivalent spring model, one end of the screw rod is connected to the fixed end plate, and there is a gap between the other end of the screw rod and the displaceable end plate, and the size of the gap is equal to the deformation variable δ of the screw rod.

8. A method for designing a liquid flow battery stack structure package according to any one of claims 1 to 5, characterized in that: Equivalent stiffness of sealing area k 电堆密封区 It is composed of the equivalent stiffness of the plate sealing area, gasket and membrane sealing area connected in series.

9. A method for designing a liquid flow battery stack structure package as claimed in claim 2, characterized in that: The value of ξ ranges from 2 to 4.

10. A method for designing a liquid flow battery stack structure package as claimed in claim 1, characterized in that: Adjusting the parameters of the flow battery stack model includes adjusting at least one of the elastic modulus of the material, adjusting the cross-sectional area of ​​the component perpendicular to the clamping force direction, and adjusting the thickness of the component in the clamping force direction; After the model modification step, it also includes: Model verification step: actual verification of the flow battery stack model.

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