Secondary battery and preparation method thereof, energy storage system and electric equipment

Abstract

The invention relates to the technical field of secondary batteries, and provides a secondary battery and a preparation method thereof, an energy storage system and electric equipment, the secondary battery comprises a shell, an electrolyte and a battery cell assembly, the shell is provided with an accommodating space for accommodating the electrolyte and the battery cell assembly, the battery cell assembly is at least partially immersed in the electrolyte, and the shell is provided with a battery cell. The battery cell assembly comprises a positive pole piece, a negative pole piece and a diaphragm; the diaphragm is positioned between the positive pole piece and the negative pole piece; the liquid storage layer comprises a flexible porous framework, the flexible porous framework is provided with a plurality of pore channels, and the flexible porous framework comprises one of an organic metal framework, a covalent organic framework and a hydrogen bond organic framework; the pore channel has a first state and a second state, the pore channel deforms and changes from the first state to the second state under set conditions, in the process, the electrolyte flows out of the pore channel of the liquid storage layer, and the volume of the electrolyte contained in the pore channel in the second state is smaller than that of the electrolyte contained in the pore channel in the first state.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and a preparation method thereof, an energy storage system and an electrical device. Background Art

[0002] Secondary batteries refer to batteries that can be charged and discharged repeatedly, also known as rechargeable batteries or rechargeable batteries. They can undergo multiple charge and discharge cycles with acceptable energy loss, achieving sustainable utilization of resources. Currently common secondary batteries include lithium-ion batteries, nickel-metal hydride batteries, lead-acid batteries, etc.

[0003] The main components of a secondary battery include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet and the negative electrode sheet include active materials. The active materials in the positive and negative electrode sheets can undergo reversible electrochemical reactions during the charging and discharging process of the secondary battery, thereby releasing or receiving energy carriers (i.e., ions). The electrolyte is non-conductive but allows ions to move between the positive electrode sheet and the negative electrode sheet. The separator is located between the positive electrode sheet and the negative electrode sheet, and can be used to prevent the positive electrode sheet and the negative electrode sheet from direct contact, but allows ions to pass through.

[0004] During the charging process of secondary batteries, the voltage applied by the external power supply forces the active material at the positive electrode to undergo an oxidation reaction to release ions and electrons. The ions migrate from the positive electrode to the negative electrode in the electrolyte and are embedded in the active material at the negative electrode after reaching the negative electrode, thereby converting electrical energy into chemical energy and storing it in the battery. At the same time, electrons flow from the positive electrode to the negative electrode through the external circuit to maintain charge conservation.

[0005] During the discharge process of the secondary battery, the active material at the negative electrode undergoes an oxidation reaction to release electrons and ions. The electrons flow from the negative electrode to the positive electrode through an external circuit, so that the flow of electrons can form an electric current to drive external equipment to work, thereby converting the chemical energy stored in the battery into electrical energy for utilization. At the same time, inside the battery, ions migrate from the negative electrode to the positive electrode in the electrolyte and are embedded in the active material at the positive electrode after reaching the positive electrode.

[0006] However, during multiple charge and discharge cycles of secondary batteries, the electrolyte may react with the active materials of the positive and negative electrodes or undergo other side reactions, causing them to be consumed or decomposed, thereby reducing the amount of electrolyte that can be effectively utilized in the battery and reducing the conductivity of the battery, resulting in a shortened service life.

[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 certain information that does not form the prior art known in this country for those skilled in the art. Summary of the invention

[0008] The main purpose of the present application is to provide a secondary battery and a preparation method thereof, an energy storage system and an electrical device, so as to solve the problem of shortened service life of the secondary battery due to electrolyte loss in the prior art.

[0009] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a secondary battery is provided, the secondary battery comprising: a shell, an electrolyte and a battery cell assembly, wherein the shell has a containing space, the containing space is used to contain the electrolyte and the battery cell assembly, and the battery cell assembly is at least partially immersed in the electrolyte, the battery cell assembly comprises: a positive electrode sheet and a negative electrode sheet arranged opposite to each other; a diaphragm, located between the positive electrode sheet and the negative electrode sheet; at least one liquid storage layer, the liquid storage layer comprises a flexible porous frame, the flexible porous frame has a plurality of pores, and the flexible porous frame comprises one of an organic metal framework, a covalent organic framework, and a hydrogen bond organic framework; the pore has a first state and a second state, under set conditions, the pore is deformed and changes from the first state to the second state, and in the process of the pore changing from the first state to the second state, the electrolyte flows out of the pore of the liquid storage layer, and the volume of the electrolyte contained in the pore in the second state is smaller than the volume of the electrolyte contained in the pore in the first state.

[0010] In some embodiments of the present application, the at least one liquid storage layer includes at least one of the following: at least one first liquid storage layer, the first liquid storage layer is in contact with the negative electrode plate; at least one second liquid storage layer, the second liquid storage layer is in contact with the positive electrode plate.

[0011] In some embodiments of the present application, the first liquid storage layer is located between the negative electrode plate and the separator; and / or, the negative electrode plate includes a negative active material layer and a negative current collector, the negative current collector is located on the side of the negative active material layer away from the separator, and the first liquid storage layer is located between the negative current collector and the negative active material layer; and / or, the second liquid storage layer is located between the positive electrode plate and the separator; and / or, the positive electrode plate includes a positive active material layer and a positive current collector, the positive current collector is located on the side of the positive active material layer away from the separator, and the second liquid storage layer is located between the positive current collector and the positive active material layer.

[0012] In some embodiments of the present application, the set condition includes: the pressure on the liquid storage layer reaches a set threshold.

[0013] In some embodiments of the present application, the set threshold is greater than or equal to 30N, and the set threshold is less than or equal to 285N.

[0014] In some embodiments of the present application, the thickness of the liquid storage layer is greater than or equal to 0.01 μm, and the thickness of the liquid storage layer is less than or equal to 10 μm.

[0015] According to another aspect of the present application, a method for preparing a secondary battery is provided, the method for preparing the above-mentioned secondary battery, the method for preparing the secondary battery comprising: forming the shell, the positive electrode sheet, the negative electrode sheet and the diaphragm; coating a liquid storage layer slurry on a set surface of at least one set component, the set component comprising the positive electrode sheet, the negative electrode sheet and the diaphragm, the liquid storage layer slurry comprising a flexible porous frame material, a binder and a diluent; drying the liquid storage layer slurry to form the liquid storage layer on the surface of the set component, the liquid storage layer comprising a flexible porous frame having a plurality of pores; assembling the positive electrode sheet, the negative electrode sheet, the diaphragm and the liquid storage layer to form the battery cell assembly; placing the battery cell assembly in the accommodation space of the shell; injecting the electrolyte into the accommodation space, the electrolyte immersing at least a portion of the battery cell assembly and filling the pores.

[0016] In some embodiments of the present application, forming the negative electrode sheet includes: forming a negative electrode current collector and forming a negative electrode active material layer; coating a storage layer slurry on a set surface of at least one set component, including: coating the storage layer slurry on at least one of the surfaces of the negative electrode current collector facing the negative electrode active material layer, the surface of the negative electrode active material layer facing the negative electrode current collector, and the surface of the negative electrode active material layer away from the negative electrode current collector; and / or, forming the positive electrode sheet includes: forming a positive electrode current collector and forming a positive electrode active material layer; coating the storage layer slurry on a set surface of at least one set component, including: coating the storage layer slurry on at least one of the surfaces of the positive electrode current collector facing the positive electrode active material layer, the surface of the positive electrode active material layer facing the positive electrode current collector, and the surface of the positive electrode active material layer away from the positive electrode current collector.

[0017] According to another aspect of the present application, an energy storage system is provided, the energy storage system comprising a plurality of the above-mentioned secondary batteries.

[0018] According to another aspect of the present application, an electrical device is provided, wherein the electrical device includes the above-mentioned energy storage system.

[0019] The beneficial effects of this application are as follows:

[0020] The present application provides a secondary battery and a preparation method thereof, wherein the secondary battery comprises: a shell, an electrolyte and a battery cell assembly, wherein the shell has a containing space, the containing space is used to contain the electrolyte and the battery cell assembly, and the battery cell assembly is at least partially immersed in the electrolyte, and the battery cell assembly comprises: a positive electrode plate and a negative electrode plate arranged opposite to each other; a diaphragm, located between the positive electrode plate and the negative electrode plate; at least one liquid storage layer, the liquid storage layer comprises a flexible porous frame, the flexible porous frame has a plurality of pores, and the flexible porous frame comprises one of an organic metal framework, a covalent organic framework, and a hydrogen bond organic framework; the pores have a first state and a second state, under set conditions, the pores are deformed and change from the first state to the second state, and in the process of the pores changing from the first state to the second state, the electrolyte flows out of the pores of the liquid storage layer, and the volume of the electrolyte contained in the pores in the second state is smaller than the volume of the electrolyte contained in the pores in the first state. The multi-porous structure of the liquid storage layer can store more electrolyte and release the electrolyte during the charge and discharge cycle of the battery, maintaining the content of electrolyte that can be used to transport charge carriers in the accommodating space of the shell, thereby achieving more charge and discharge cycles and extending the service life of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0022] Figure 1 It is a structural schematic diagram of a battery core assembly;

[0023] Figure 2 A schematic diagram of a first state and a second state of a channel provided according to an embodiment of the present application;

[0024] Figure 3 A schematic diagram of the structure of a battery cell assembly provided according to an embodiment of the present application;

[0025] Figure 4 A schematic structural diagram of another battery cell assembly provided according to an embodiment of the present application;

[0026] Figure 5 A schematic structural diagram of another battery cell assembly provided according to an embodiment of the present application;

[0027] Figure 6 A schematic structural diagram of another battery cell assembly provided according to an embodiment of the present application;

[0028] Figure 7 A schematic structural diagram of another battery cell assembly provided according to an embodiment of the present application;

[0029] Figure 8 A schematic structural diagram of another battery cell assembly provided according to an embodiment of the present application;

[0030] Fig. 9 A graph showing the residual capacity retention rate of a secondary battery provided according to a comparative example and an embodiment of the present application;

[0031] Fig.10 A graph showing the recovery capacity retention rate of a secondary battery provided according to a comparative example and an embodiment of the present application;

[0032] Fig.11 A schematic flow chart of a method for preparing a secondary battery according to an embodiment of the present application is provided.

[0033] The above drawings include the following reference numerals:

[0034] 1. Battery cell assembly; 2. Positive electrode plate; 21. Positive electrode current collector; 22. Positive electrode active material layer; 3. Negative electrode plate; 31. Negative electrode current collector; 32. Negative electrode active material layer; 4. Diaphragm; 5. Pores; 6. First liquid storage layer; 7. Second liquid storage layer. DETAILED DESCRIPTION

[0035] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so as to describe the embodiments of the present invention described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0038] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be intermediate elements. Moreover, in the specification and claims, when it is described that an element is "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element through a third element.

[0039] As introduced in the background technology, in the prior art, electrolyte loss in secondary batteries during multiple charge and discharge cycles shortens the life of the secondary batteries. To solve the above problem, the embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage system and an electrical device.

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the relevant technologies and the drawings in the embodiments of the present application.

[0041] The secondary battery comprises: a shell, an electrolyte and a battery cell assembly, wherein the shell has a containing space for containing the electrolyte and the battery cell assembly, and the battery cell assembly is at least partially immersed in the electrolyte. Figure 1 A schematic diagram of the structure of a battery cell assembly is shown in FIG. Figure 1 As shown, the battery cell assembly 1 includes a positive electrode sheet 2 and a negative electrode sheet 3 that are arranged opposite to each other, and a separator 4 located between the positive electrode sheet 2 and the negative electrode sheet 3 .

[0042] Specifically, the positive electrode plate 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 can be used to provide and store charge carriers, and the positive electrode current collector 21 can be used to collect the current generated by the positive electrode active material layer 22 and transmit it to an external circuit. Taking a lithium-ion battery as an example, the positive electrode active material layer 22 can include lithium compounds, such as lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, etc., and the positive electrode current collector 21 can be made of metal, such as aluminum foil.

[0043] The negative electrode sheet 3 includes a negative electrode current collector 31 and a negative electrode active material layer 32. The negative electrode active material layer 32 can be used to store and release charge carriers, and the negative electrode current collector 31 can be used to collect the current generated by the negative electrode active material layer 32 and transmit it to an external circuit. Taking a lithium-ion battery as an example, the negative electrode active material layer 32 can include graphite, silicon-based materials (such as silicon or carbon silicon compounds), lithium metal, etc., and the negative electrode current collector 31 can also be made of metal, such as copper foil.

[0044] The separator 4 is used to separate the positive electrode sheet 2 and the negative electrode sheet 3 to prevent the two from directly contacting each other and causing a short circuit, and can selectively pass the charge carriers in the electrolyte so that the charge carriers can move between the positive electrode sheet 2 and the negative electrode sheet 3. Exemplarily, the separator 4 can be a polyethylene microporous separator, a polypropylene microporous separator, a ceramic coated separator, a composite separator, etc.

[0045] The secondary battery is connected to an external electrical appliance for discharge or to a power source for charging through the positive electrode sheet 2 and the negative electrode sheet 3. During the charging process, the charge carrier (such as lithium ion) moves from the positive electrode sheet 2 to the negative electrode sheet 3 and is embedded in the negative electrode active material layer 32, and during the discharging process, the charge carrier (such as lithium ion) moves from the negative electrode sheet 3 to the positive electrode sheet 2 and is embedded in the positive electrode active material layer 22. It can be seen that the charging and discharging process of the secondary battery is always accompanied by the embedding of charge carriers, and the embedding of charge carriers will cause the volume of the active material layer to expand, and due to the different materials of the active material layer, the expansion degree of the negative electrode active material layer 32 is usually greater than that of the positive electrode active material layer 22.

[0046] In view of the characteristic that the active material layer will expand during the charge and discharge process, the present application sets a liquid storage layer in the secondary battery to store the electrolyte and release the electrolyte under set conditions, thereby extending the service life of the secondary battery.

[0047] In the present application, the liquid storage layer includes a flexible porous frame, and the flexible porous frame has a plurality of pores. The sizes and shapes of different pores can be the same or different, and the embodiments of the present application are not limited here. The pores can have a first state and a second state. Under set conditions, the pores are deformed and change from the first state to the second state. In the process of the pores changing from the first state to the second state, the electrolyte flows out of the pores of the liquid storage layer, and the volume of the electrolyte contained in the pores in the second state is less than the volume of the electrolyte contained in the pores in the first state.

[0048] In the embodiment of the present application, on the one hand, the liquid storage layer stores electrolyte based on its multi-porous structure. When injecting electrolyte into the battery, the multi-porous structure can provide more accommodation space, thereby increasing the amount of electrolyte injected. In this way, even if the electrolyte is lost during multiple charge and discharge cycles, the secondary battery can support more charge and discharge cycles, thereby extending its service life. On the other hand, the liquid storage layer releases and replenishes the electrolyte based on the characteristic that the flexible porous frame can be deformed under set conditions. The electrolyte released by the liquid storage layer can make up for the electrolyte lost during the charge and discharge cycle, and maintain the content of electrolyte that can be used to transmit charge carriers in the accommodation space of the shell, thereby achieving more charge and discharge cycles and extending the service life of the secondary battery.

[0049] The above-mentioned set conditions that can cause the electrolyte to flow out of the pores of the liquid storage layer may include: the pressure on the liquid storage layer reaches a set threshold value.

[0050] Figure 2 A schematic diagram of a first state and a second state of a channel provided according to an embodiment of the present application.

[0051] like Figure 2 As shown, the first state of the pore 5 is a state in which the volume is relatively large, and the second state of the pore 5 is a state in which the volume is relatively small. When the pressure on the pore 5 increases, the pore 5 is squeezed and changes from the first state to the second state, so that the electrolyte in the pore 5 will be squeezed out of the pore 5; when the pressure on the pore 5 decreases, the pore 5 can change from the second state to the first state, and the pore 5 will expand to a certain extent, causing the pore 5 to absorb part of the electrolyte, but overall, when the pressure on the liquid storage layer is within the set threshold range, the pore 5 in the liquid storage layer is in a state of releasing the electrolyte.

[0052] In some embodiments of the present application, the above-mentioned threshold value is greater than or equal to 30N and less than or equal to 285N. Optionally, the above-mentioned threshold value may also be 115N~280N, 135N~265N, 140N~250N, 170N~225N. Exemplarily, the threshold value may include but is not limited to 30N, 50N, 100N, 115N, 120N, 135N, 140N, 150N, 160N, 170N, 180N, 190N, 200N, 210N, 220N, 225N, 235N, 240N, 250N, 260N, 265N, 270N, 275N, 280N, 285N, etc.

[0053] When the pressure on the liquid storage layer is within the range of the above-mentioned set threshold, on the one hand, the liquid storage layer can respond to the expansion of the battery cell assembly 1 at a lower pressure level and release the electrolyte stored in the pore 5 in time. On the other hand, the liquid storage layer can achieve fluid replenishment within a larger pressure range, thereby increasing the number of charge and discharge cycles of the battery and extending the life of the battery. When the pressure on the liquid storage layer is greater than the upper limit of the set threshold, the flexible porous frame in the liquid storage layer stops deforming.

[0054] It should be understood that the pressure on the above-mentioned liquid storage layer reaches the set threshold value, which means that the pressure on the liquid storage layer reaches any value within the above-mentioned pressure range, which can enable the liquid storage layer to achieve fluid replenishment based on the above-mentioned principle. That is to say, when the pressure of the liquid storage layer is within the above-mentioned range, the liquid storage layer can continuously release electrolyte to the outside.

[0055] In the embodiment of the present application, the pressure on the liquid storage layer is mainly caused by the expansion phenomenon of other components in the battery cell assembly 1 during the charge and discharge cycle, including but not limited to the pressure caused by the expansion of the positive electrode active material layer 22, the negative electrode active material layer 32 or the diaphragm 4. As the charge and discharge cycle continues, the electrolyte in the shell is continuously consumed, and the available electrolyte will become less and less, and the expansion force of the above-mentioned components will gradually increase. The increase in expansion force will cause the pressure on the pore 5 to increase, so that the pore 5 is further compressed and releases more electrolyte to make up for the loss of electrolyte after multiple charge and discharge cycles, increase the number of charge and discharge cycles of the battery, and extend the service life of the battery. Based on this, as the charge and discharge cycle proceeds, the liquid storage layer can release the electrolyte under the force of the original components in the battery cell assembly 1, and there is no need to set up other components, which is conducive to simplifying the product structure.

[0056] In an embodiment of the present application, the flexible porous framework may include one of metal-organic frameworks (MOF), covalent organic frameworks (COF), and hydrogen-bonded organic frameworks (HOF). The specific type can be selected according to actual needs and is not limited here.

[0057] Specifically, metal-organic frameworks (MOFs) are a type of porous material that is self-assembled by metal ions or clusters and organic ligands through coordination. When external conditions (such as pressure, temperature, or adsorption of specific chemical molecules) change, the framework structure of MOF can deform or the pore size can change, and it has a certain flexibility.

[0058] Covalent organic frameworks (COFs) are porous crystalline materials formed by organic ligands composed of light elements (such as carbon, hydrogen, oxygen, nitrogen, sulfur, etc.) connected by covalent bonds. By using flexible ligands with rotational freedom, COFs can exhibit a certain degree of flexibility at the molecular level.

[0059] Hydrogen-bonded organic frameworks (HOFs) are a type of porous material self-assembled by organic molecules through hydrogen bonding interactions. By adjusting the types of metal nodes and organic ligands, as well as the connectivity of the framework, HOFs can be made to have a certain degree of flexibility.

[0060] By using a porous framework such as MOF, COF or HOF with a certain degree of flexibility as a liquid storage layer in the battery, the liquid storage layer can release the electrolyte under the set temperature or pressure conditions to replenish the electrolyte in the shell, thereby extending the service life of the battery.

[0061] In the present application, the number and position of the liquid storage layer in the battery cell assembly 1 can be determined according to actual needs, and the number of the liquid storage layer can be at least one, and the at least one liquid storage layer includes at least one of the following: at least one first liquid storage layer in contact with the negative electrode plate 3, and at least one second liquid storage layer in contact with the positive electrode plate 2. Several possible arrangements of the liquid storage layer are described below in conjunction with the accompanying drawings.

[0062] Figure 3 A schematic diagram of the structure of a battery cell assembly provided according to an embodiment of the present application is shown in FIG. Figure 3 As shown, in some embodiments of the present application, the first liquid storage layer 6 may be located between the negative electrode plate 3 and the separator 4 .

[0063] Figure 4 A schematic diagram of the structure of another battery cell assembly provided according to an embodiment of the present application is shown in FIG. Figure 4 As shown, in some other embodiments of the present application, the negative electrode plate 3 includes a negative electrode active material layer 32 and a negative electrode current collector 31, the negative electrode current collector 31 is located on the side of the negative electrode active material layer 32 away from the separator 4, and the first liquid storage layer 6 can be located between the negative electrode current collector 31 and the negative electrode active material layer 32.

[0064] Figure 5 A schematic diagram of the structure of another battery cell assembly provided according to an embodiment of the present application is shown in FIG. Figure 5 As shown, in some other embodiments of the present application, the first liquid storage layer 6 may be disposed between the negative electrode active material layer 32 and the separator 4 , and between the negative electrode active material layer 32 and the negative electrode current collector 31 .

[0065] Similarly, Figure 6 A schematic diagram of the structure of another battery cell assembly provided according to an embodiment of the present application is shown in FIG. Figure 6 As shown, in some other embodiments of the present application, the second liquid storage layer 7 can be located between the positive electrode plate 2 and the separator 4.

[0066] Figure 7 A schematic diagram of the structure of another battery cell assembly provided according to an embodiment of the present application is shown in FIG. Figure 7 As shown, in some other embodiments of the present application, the positive electrode plate 2 includes a positive electrode active material layer 22 and a positive electrode current collector 21, the positive electrode current collector 21 is located on the side of the positive electrode active material layer 22 away from the separator 4, and the second liquid storage layer 7 can be located between the positive electrode current collector 21 and the positive electrode active material layer 22.

[0067] Figure 8 A schematic diagram of the structure of another battery cell assembly provided according to an embodiment of the present application is shown in FIG. Figure 8As shown, the second liquid storage layer 7 may be provided between the positive electrode active material layer 22 and the separator 4 , and between the positive electrode active material layer 22 and the positive electrode current collector 21 .

[0068] Depend on Figure 3~Figure 8 It can be seen that the liquid storage layer can be set on the surface of the electrode active material or on the surface of the current collector. In practical applications, the liquid storage layer can also be set on the surface of the diaphragm 4, and the above-mentioned settings of the liquid storage layer can be arbitrarily combined, so that according to the different expansion components contacted by the liquid storage layer, the structure of the flexible porous frame in each liquid storage layer can be adaptively designed, so that the liquid storage layer can adapt to the expansion state of the component it contacts and release the electrolyte in time, thereby ensuring the continuous electrochemical reaction and extending the service life of the battery.

[0069] In some embodiments of the present application, the thickness of the liquid storage layer is 0.01 μm to 10 μm. By selecting the thickness of the liquid storage layer within the above thickness range, the balance between the electrolyte storage capacity and the battery energy density can be achieved, avoiding the liquid storage layer being too thin, resulting in too low electrolyte reserves, and avoiding the liquid storage layer being too thick, occupying too much space inside the battery and reducing the battery energy density. Optionally, the thickness of the liquid storage layer can also be 0.1 μm to 2 μm. By selecting the thickness of the liquid storage layer within the above thickness range, the electrolyte storage capacity and the battery energy density can be better balanced. Exemplarily, the thickness of the liquid reservoir layer can be 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, etc.

[0070] In order to make the beneficial effects of the embodiments of the present application more clearly visible, the present application also provides the following test results on the performance of conventional secondary batteries and the secondary batteries in the present application.

[0071] Table 1 is a performance parameter table of the secondary batteries provided by the comparative examples and the embodiments of the present application after multiple charge and discharge cycles, wherein the comparative example is as follows Figure 1 The conventional secondary battery shown in the figure is a secondary battery in which a liquid storage layer is arranged on the surface of the negative electrode plate 3 facing the separator 4 in the embodiment of the present application.

[0072] Table 1

[0073]

[0074] Table 1 shows the expansion force and full-charge rebound rate of the negative electrode plate 3 after multiple charge and discharge cycles of the secondary battery, as well as the amount of free electrolyte in the battery and the cycle retention rate of the battery. The full-charge rebound rate of the negative electrode plate 3 represents the percentage of the expanded thickness of the negative electrode plate 3 relative to the original thickness of the negative electrode plate 3, the amount of free electrolyte represents the amount of electrolyte that can be used in the accommodating space of the shell, and the cycle retention rate represents the percentage of the remaining capacity of the secondary battery to the initial capacity.

[0075] As can be seen from Table 1, the amount of free electrolyte in the secondary battery in the embodiment of the present application is always greater than the amount of free electrolyte in the secondary battery in the comparative example, and the free electrolyte in the secondary battery in the comparative example is exhausted after 6000 charge and discharge cycles, while the free electrolyte in the secondary battery in the embodiment of the present application is still surplus after 15000 charge and discharge cycles. In addition, under the same number of cycles, the cycle retention rate of the secondary battery in the embodiment of the present application is always greater than the cycle retention rate of the secondary battery in the comparative example, and after 15000 charge and discharge cycles, it is still greater than or equal to 70%, that is, it can be used normally. In summary, it can be seen that by setting a liquid storage layer, the electrolyte available for the secondary battery in the embodiment of the present application is increased, thereby extending the service life of the secondary battery and maintaining good performance after more charge and discharge cycles.

[0076] Fig. 9 A graph showing the residual capacity retention rate of a secondary battery provided according to a comparative example and an embodiment of the present application; Fig.10 The graph is a graph showing the recovery capacity retention rate of a secondary battery provided according to a comparative example and an embodiment of the present application.

[0077] Fig. 9 and Fig.10 The residual capacity retention rate and the recovery capacity retention rate of the secondary battery in the comparative example and the embodiment of the present application at a high temperature of 55°C are shown respectively, wherein the residual capacity retention rate is the remaining capacity of the secondary battery after it is fully charged and stored for a certain number of days, and the recovery capacity retention rate is the remaining capacity of the secondary battery after it undergoes one charge and discharge cycle and is fully charged again and stored for a certain number of days, Figure 8 and Fig. 9 It can be seen that under the same number of storage days, the residual capacity retention rate and the recovery capacity retention rate of the secondary battery in the embodiment of the present application are higher than the residual capacity retention rate and the recovery capacity retention rate of the secondary battery in the comparative example, and the longer the storage time, the greater the difference in the residual capacity retention rate of the two, and the greater the difference in the recovery capacity retention rate of the two. It can be seen that providing a liquid storage layer in a secondary battery can improve the ability of the secondary battery to store electrical energy, and can also make the secondary battery have a longer service life at high temperature, thereby improving the reliability of the secondary battery.

[0078] Table 2 is a comparison table of the remaining amount of electrolyte after the secondary batteries provided by the comparative example and the embodiments of the present application were stored for a certain number of days.

[0079] Table 2

[0080]

[0081] As can be seen from Table 2, under the same storage time, the residual amount of electrolyte in the secondary battery provided by the embodiment of the present application is greater than the residual amount of electrolyte in the secondary battery provided by the comparative example, and the longer the storage time, the greater the difference in the residual amount of electrolyte between the two. It can be seen that providing a liquid storage layer in the secondary battery can also improve the ability of the secondary battery to store electrical energy, reduce the loss of electrolyte when storing the battery, and maintain the performance of the secondary battery in a better state during a longer storage time, so that the secondary battery has better stability and longer life. It should be understood that the residual amount of electrolyte in Table 2 refers to the residual amount of active ingredients in the electrolyte. When the electrolyte in the shell is lost and a concentration difference is generated with the electrolyte in the liquid storage layer, the electrolyte in the liquid storage layer can be released outside the liquid storage layer to maintain the concentration of the electrolyte that can be directly used in the battery.

[0082] As the secondary battery continues to cycle through charge and discharge, its operating temperature will gradually rise. Under high temperature conditions, the electrolyte may undergo a decomposition reaction, resulting in loss, and it is necessary to replenish the electrolyte. At this time, the concentration of the electrolyte in the housing space of the shell decreases, while the concentration of the electrolyte in the pore 5 is relatively high, so the electrolyte will spontaneously flow from the area with higher concentration (i.e., in the pore 5) to the area with lower concentration (i.e., in the housing space of the shell), so that the electrolyte stored in the liquid storage layer can flow out of the pore 5 and be used, effectively replenishing the electrolyte consumed by the battery during operation, and ensuring that the electrolyte in the battery remains sufficient.

[0083] In some embodiments of the present application, the working temperature of the liquid storage layer at which the electrolyte is released by the above principle is greater than or equal to 50°C and less than or equal to 150°C. For example, the above working temperature may include but is not limited to 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, and 150°C. It can be understood that the working temperature of the liquid storage layer reaches the above temperature, which means that the working temperature of the liquid storage layer reaches any value within the above temperature range, so that the liquid storage layer can achieve fluid replenishment based on the above principle. In other words, when the working temperature of the liquid storage layer is within the above range, the liquid storage layer can continuously release electrolyte to the outside. When the working temperature of the liquid storage layer reaches the above temperature, fluid replenishment can maintain the normal operation of the battery under high temperature conditions and extend the service life of the battery. In addition, the upper limit value of the above temperature range is relatively high, indicating that the flexible porous frame can also work normally at a higher temperature, and its reliability is better. When the temperature is higher than the upper limit value of the above temperature range, the flexible porous frame stops releasing the electrolyte.

[0084] Based on the same concept, the present application also provides a method for preparing a secondary battery. Fig.11 A schematic diagram of a method for preparing a secondary battery according to an embodiment of the present application is shown in FIG. Fig.11 As shown, the method for preparing a secondary battery includes the following steps:

[0085] Step S1, forming a shell, a positive electrode sheet 2, a negative electrode sheet 3 and a separator 4. The shell, the positive electrode sheet 2, the negative electrode sheet 3 and the separator 4 can all be prepared using conventional secondary battery materials and preparation methods. Taking lithium-ion batteries as an example, the shell can be made of materials including but not limited to aluminum, steel or aluminum-plastic film, etc. The positive electrode sheet 2 can be made by coating a positive electrode active material on a positive electrode collector 21, and the positive electrode current collector 21 can be made of materials including but not limited to aluminum foil. The positive electrode active material includes but is not limited to lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide and other lithium compounds. The negative electrode sheet 3 can be made by coating a negative electrode on the negative electrode collector 31. The negative electrode current collector 31 may be made of active materials, including but not limited to copper foil, the negative electrode active materials may be graphite, silicon-based materials (such as silicon or carbon silicon compounds), lithium metal, etc., and the materials used for the diaphragm 4 may include but are not limited to one or more of polyethylene, polypropylene, ceramics, etc. Among them, for polyolefin diaphragms 4 such as polyethylene and polypropylene, a biaxial stretching process may be used to form a continuous microporous structure, and the ceramic diaphragm 4 may be formed by coating a slurry of ceramic materials such as alumina on the polyolefin diaphragm 4, and then sintering or drying and curing. The preparation methods of the shell, the positive electrode sheet 2, the negative electrode sheet 3 and the diaphragm 4 can be selected according to different types of secondary batteries, and are not limited here.

[0086] Step S2, coating a liquid storage layer slurry on a set surface of at least one set component, the set component includes a positive electrode sheet 2, a negative electrode sheet 3 and a separator 4, and the liquid storage layer slurry includes a flexible porous framework material, a binder and a diluent. Exemplarily, the liquid storage layer slurry can be formed on the surface of the above-mentioned set component by a method such as cast coating or spraying, and the flexible porous framework material can be a MOF material, a COF material or a HOF material.

[0087] Specifically, the liquid storage layer slurry can be coated on at least one of the surfaces of the negative electrode collector 31 facing the negative electrode active material layer 32, the surface of the negative electrode active material layer 32 facing the negative electrode collector 31, the surface of the negative electrode active material layer 32 away from the negative electrode collector 31, the surface of the positive electrode collector 21 facing the positive electrode active material layer 22, the surface of the positive electrode active material layer 22 facing the positive electrode collector 21, and the surface of the positive electrode active material layer 22 away from the positive electrode collector 21 to form a liquid storage layer on the surface of the required components, thereby increasing the storage capacity of the secondary battery for electrolyte, facilitating subsequent liquid replenishment, and extending the service life of the secondary battery.

[0088] Step S3, drying the liquid storage layer slurry to form a liquid storage layer on the surface of the set component, the liquid storage layer comprising a flexible porous frame having a plurality of pores. After drying, the liquid storage layer is compounded with the component in contact with it, i.e., the set component mentioned above, and can be deformed and release electrolyte under the action of the expansion force of the component in contact with it.

[0089] Step S4, assembling the positive electrode sheet 2, the negative electrode sheet 3, the separator 4 and the liquid storage layer to form the battery cell assembly 1. Exemplarily, the positive electrode sheet 2, the negative electrode sheet 3, the separator 4 and the liquid storage layer can be stacked together in a set order, and then assembled by winding or laminating.

[0090] Step S5, placing the battery cell assembly 1 in the housing space of the housing. After placing the battery cell assembly 1 in the housing space of the housing, the housing may be vacuum dried to remove moisture and gas that may exist inside the housing to ensure that the inside of the battery is clean and dry.

[0091] Step S6, injecting electrolyte into the accommodation space, the electrolyte immerses at least part of the battery cell assembly 1 and fills the pores. Exemplarily, the injection can be performed by multiple vacuuming and then liquid injection. Each time the electrolyte is injected, it can enter the pores of the liquid storage layer and fill at least part of the space of the pores. After multiple injections, the pores can accommodate as much electrolyte as possible, thereby increasing the electrolyte content in the secondary battery product, which is beneficial to extending its service life. In addition, multiple vacuuming and liquid injection can also improve the uniformity of the electrolyte infiltration of each component in the battery cell assembly 1, thereby improving the electrical performance of the secondary battery product.

[0092] The following uses several MOF materials as examples to illustrate the preparation method of the liquid storage layer. The preparation method of the liquid storage layer using MOF materials includes the following steps:

[0093] Step S101, preparing a flexible MOF material. Exemplarily, the flexible MOF material may include but is not limited to MIL-53, SM-A, LIFM-28, SIFSIX-23-Cu, and the like.

[0094] Among them, MIL-53 can be obtained by dissolving aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and terephthalic acid (H2BDC) in a mixed solution of water and DMF, heating at 150°C for 24 hours, centrifuging and washing the reaction product, and then vacuum drying at 60°C.

[0095] Zn(CH3CO2)2·2H2O (0.043 g, 0.2 mmol) and 2,5-furandicarboxylic acid (2,5-FDA) (0.033 g, 0.2 mmol) were dissolved in 3 ml of DMF by a hydrothermal method, and then reacted at 120°C for 48 h. The reaction product was washed by centrifugation and then dried in vacuum at 60°C to obtain SM-A.

[0096] 100 mg ZrCl4 and 70 mg 2,-2'-ditrifluoromethyl-4-biphenyldicarboxylic acid are added into a 20 ml glass bottle, 20 ml DMF is added as a solvent, 0.6 ml trifluoroacetic acid is added as a regulator, the heat-resistant bottle is placed in an oven, the temperature is raised to 120°C for reaction for 72 hours, and then the temperature is lowered to room temperature at a rate of 10°C per hour, the reaction product is filtered and washed, and then vacuum dried at 60°C to obtain LIFM-28.

[0097] CuSiF6·H2O (22 mg, 0.1 mmol) can be dissolved in 5 ml of water, 6 ml of a mixed methanol-water solution (the volume ratio of methanol to water is 1:1) is added, and then 5 ml of a MeOH solution containing a bisimidazolyl ligand (42 mg, 0.2 mmol) is poured in, and SIFSIX-23-Cu is obtained after reacting for a period of time.

[0098] Step S102, forming a liquid storage layer slurry. For example, the flexible MOF and the binder can be dispersed in a solvent in a certain proportion, and then ultrasonically stirred for 2 to 4 hours to form a flexible MOF slurry. The binder includes but is not limited to conventional oil-based binders and water-based binders, and the solvent includes but is not limited to NMP, water or other solvents for dissolving the binder.

[0099] Step S103, coating the liquid storage layer slurry on the set component. For example, the uniformly mixed flexible MOF slurry can be scraped on the set component formed in the above step S1 with a scraper, and then dried in a 60°C vacuum oven for 4 hours, and dried in a 100°C vacuum oven for 12 hours, and a MOF coating, i.e., a liquid storage layer, is obtained after drying.

[0100] Based on the same concept, the present application also provides an energy storage system, which includes a plurality of the above-mentioned secondary batteries.

[0101] Based on the same concept, the present application also provides an electrical device, which includes the above-mentioned energy storage system.

[0102] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises: a shell, an electrolyte and a battery cell assembly, wherein the shell has a containing space, the containing space is used to contain the electrolyte and the battery cell assembly, and the battery cell assembly is at least partially immersed in the electrolyte, and the battery cell assembly comprises: A positive electrode sheet and a negative electrode sheet arranged opposite to each other; A diaphragm, located between the positive electrode sheet and the negative electrode sheet; At least one liquid storage layer, the liquid storage layer comprises a flexible porous framework, the flexible porous framework has a plurality of pores, and the flexible porous framework comprises one of an organic metal framework, a covalent organic framework, and a hydrogen bond organic framework; The pore has a first state and a second state. Under set conditions, the pore is deformed and changes from the first state to the second state. During the process of the pore changing from the first state to the second state, the electrolyte flows out of the pore of the liquid storage layer. The volume of the electrolyte contained in the pore in the second state is smaller than the volume of the electrolyte contained in the pore in the first state.

2. The secondary battery according to claim 1, characterized in that: The at least one liquid storage layer comprises at least one of the following: At least one first liquid storage layer, wherein the first liquid storage layer is in contact with the negative electrode plate; At least one second liquid storage layer, wherein the second liquid storage layer is in contact with the positive electrode plate.

3. The secondary battery according to claim 2, characterized in that: The first liquid storage layer is located between the negative electrode plate and the separator; and / or, The negative electrode plate comprises a negative electrode active material layer and a negative electrode current collector, the negative electrode current collector is located on a side of the negative electrode active material layer away from the separator, and the first liquid storage layer is located between the negative electrode current collector and the negative electrode active material layer; and / or, The second liquid storage layer is located between the positive electrode plate and the separator; and / or, The positive electrode sheet includes a positive electrode active material layer and a positive electrode current collector, the positive electrode current collector is located on a side of the positive electrode active material layer away from the separator, and the second liquid storage layer is located between the positive electrode current collector and the positive electrode active material layer.

4. The secondary battery according to claim 1, characterized in that: The set condition includes: the pressure on the liquid storage layer reaches a set threshold.

5. The secondary battery according to claim 4, characterized in that: The set threshold is greater than or equal to 30N, and the set threshold is less than or equal to 285N.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The thickness of the liquid storage layer is greater than or equal to 0.01 μm, and the thickness of the liquid storage layer is less than or equal to 10 μm.

7. A method for preparing a secondary battery, characterized in that: The method for preparing the secondary battery is used to prepare the secondary battery as claimed in claim 1, and the method for preparing the secondary battery comprises: forming the shell, the positive electrode sheet, the negative electrode sheet and the separator; Coating a liquid storage layer slurry on a setting surface of at least one setting component, wherein the setting component includes the positive electrode sheet, the negative electrode sheet and the separator, and the liquid storage layer slurry includes a flexible porous framework material, a binder and a diluent; Drying the liquid storage layer slurry to form the liquid storage layer on the surface of the setting component, wherein the liquid storage layer comprises a flexible porous frame having a plurality of pores; Assembling the positive electrode sheet, the negative electrode sheet, the separator and the liquid storage layer to form the battery cell assembly; Placing the battery cell assembly in the accommodating space of the shell; The electrolyte is injected into the accommodation space, and the electrolyte immerses at least a portion of the battery core assembly and fills the channel.

8. The method for preparing a secondary battery according to claim 7, characterized in that: Forming the negative electrode sheet includes: forming a negative electrode current collector and forming a negative electrode active material layer; coating a liquid storage layer slurry on a set surface of at least one set component, including: coating the liquid storage layer slurry on at least one of a surface of the negative electrode current collector facing the negative electrode active material layer, a surface of the negative electrode active material layer facing the negative electrode current collector, and a surface of the negative electrode active material layer away from the negative electrode current collector; and / or, Forming the positive electrode sheet includes: forming a positive electrode current collector and forming a positive electrode active material layer; coating a liquid storage layer slurry on a set surface of at least one set component, including: coating the liquid storage layer slurry on at least one of the surfaces of the positive electrode current collector facing the positive electrode active material layer, the surface of the positive electrode active material layer facing the positive electrode current collector, and the surface of the positive electrode active material layer away from the positive electrode current collector.

9. An energy storage system, characterized in that: The energy storage system comprises a plurality of secondary batteries according to any one of claims 1 to 6.

10. An electrical device, characterized in that: The electrical equipment includes the energy storage system as claimed in claim 9.

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