Diaphragm, sodium ion battery, battery pack and energy storage system

Abstract

The invention provides a diaphragm, a sodium ion battery, a battery pack and an energy storage system.The diaphragm comprises a base membrane and a first coating arranged on the surface of the base membrane, the first coating is located on the side, facing a positive electrode, of the base membrane, and the first coating comprises a first active stabilizer; the first active stabilizer is selected from at least one of a sodium-based polyanionic compound, a sodium-based layered transition metal oxide and Prussian blue. Since the first active stabilizer can realize deintercalation of sodium ions, when the first active stabilizer is applied to the sodium ion battery, the amount of the sodium ions in the sodium ion battery can be increased, so that the capacity of the sodium ion battery is increased. Moreover, the first coating can protect the base membrane and improve the thermal stability, heat shrinkage resistance and mechanical strength of the diaphragm, so that the use safety of the sodium-ion battery can be improved, short circuit of a positive electrode and a negative electrode caused by thermal shrinkage or melting of the diaphragm is avoided, and the use risk of the sodium-ion battery is reduced.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a diaphragm, a sodium ion battery, a battery pack, and an energy storage system. Background Art

[0002] Sodium ion batteries can include: positive electrode, negative electrode, separator and electrolyte. The separator is located between the positive electrode and the negative electrode, and the electrolyte infiltrates the positive electrode, the separator and the negative electrode. The separator can effectively prevent the electron transfer between the positive electrode and the negative electrode, and the Na + It can ensure transmission in the diaphragm, so the diaphragm cannot transmit electrons but can transmit ions. At present, diaphragms are usually made of polyolefin compounds. Polyolefin diaphragms have the advantages of low cost, good chemical stability and high mechanical strength. However, due to the low melting point, polyolefin diaphragms will shrink or even melt under high temperature conditions. In severe cases, it will cause a short circuit between the positive and negative electrodes, causing the safety performance of sodium ion batteries to be greatly reduced. In addition, polyolefin diaphragms generally do not participate in chemical reactions, such as Na + Therefore, how to improve the thermal stability and heat shrinkage resistance of the separator and increase the capacity of the sodium ion battery has become an urgent problem to be solved. Summary of the Invention

[0003] The present application provides a diaphragm, a sodium-ion battery, a battery pack, and an energy storage system, which are used to improve the thermal stability and heat shrinkage resistance of the diaphragm and increase the capacity of the sodium-ion battery.

[0004] In a first aspect, an embodiment of the present application provides a sodium ion battery, which includes a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode, and the separator includes: a base membrane, and a first coating disposed on the surface of the base membrane, the first coating being located on the side of the base membrane facing the positive electrode, and the first coating including a first active stabilizer, the first active stabilizer being selected from at least one of a sodium-based polyanion compound, a sodium-based layered transition metal oxide, and Prussian blue. Since the first active stabilizer can achieve sodium ion intercalation and deintercalation, when applied to a sodium ion battery, the amount of sodium ions in the sodium ion battery can be increased, thereby increasing the capacity of the sodium ion battery. In addition, the first coating can protect the base membrane, improve the thermal stability, heat shrinkage resistance, and mechanical strength of the separator, thereby improving the safety of the sodium ion battery, preventing the positive and negative electrodes from short-circuiting when the separator shrinks or melts, and reducing the risk of using the sodium ion battery.

[0005] Optionally, different substances have different voltage windows when deintercalating sodium ions, that is, a large amount of sodium ions will be deintercalated in the corresponding voltage interval, so this voltage interval can be considered as the main deintercalation interval; but when it is outside this voltage interval, sodium ions will also be deintercalated, but the amount of deintercalation is small. Based on this, the main deintercalation interval of the first active stabilizer and the main deintercalation interval of the positive electrode active material in the positive electrode have an intersection, that is, the first active stabilizer has Na + The voltage range during the deintercalation reaction is related to the Na + There is an intersection in the voltage range of the deintercalation reaction, which can provide more Na for sodium ion batteries. + , thereby greatly improving the capacity of sodium ion batteries.

[0006] Optionally, the median particle size D50 of the first active stabilizer can be set to 0.1μm-5μm, such as but not limited to: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm and other values. The further median particle size D50 is 1μm-3μm, which can be set according to actual needs and is not specifically limited here. When D50 is small, it means that the specific surface area of ​​the first active stabilizer is large, and a large specific surface area will increase the occurrence of particle agglomeration, resulting in unstable performance of the diaphragm; when D50 is large, it means that the particles of the first active stabilizer are large, which may cause uneven stress in the first coating, which may scratch the base film and cause damage to the diaphragm. Therefore, setting D50 within an appropriate range can not only make the diaphragm have better performance, but also avoid damage to the diaphragm and improve the reliability of the diaphragm.

[0007] Optionally, the specific surface area of ​​the first active stabilizer can be set to 8m 2 / g-25m 2 / g, such as but not limited to: 8m 2 / g、9m 2 / g、10m 2 / g、12m 2 / g、14m 2 / g、16m 2 / g、18m 2 / g, 20m 2 / g、22m 2 / g、24m 2 / g, 25m 2 / g and other values, and further the specific surface area is 9m 2 / g-20m 2 / g, which can be set according to actual needs and is not specifically limited here. If the specific surface area of ​​the first active stabilizer is too large, the particles will increase the occurrence of agglomeration and cannot be effectively dispersed, resulting in unstable performance of the diaphragm. If the specific surface area of ​​the first active stabilizer is too small, it means that the particles of the first active stabilizer are large, which will cause uneven stress in the first coating layer and scratch the base film. Therefore, setting the specific surface area of ​​the first active stabilizer within a suitable range can not only improve the performance of the diaphragm, but also avoid damage to the diaphragm and improve the reliability of the diaphragm.

[0008] Alternatively, since the sodium-based layered transition metal oxide is unstable due to the collapse of its layered structure after the sodium ions in it are deintercalated, the sodium-based layered transition metal oxide remains stable after the sodium ions are removed from the sodium-based polyanion compound and Prussian blue. Therefore, the first active stabilizer can be further selected from sodium-based polyanion compounds and Prussian blue to improve the stability of the first active stabilizer. Since Prussian blue is less commonly used and sodium-based polyanion compounds are more common and easier to obtain, the first active stabilizer can be further selected from sodium-based polyanion compounds. Among them, the sodium-based polyanion compound can be a compound with a NASICON structure. The sodium-based polyanion compound with a NASICON structure has a three-dimensional ion transport channel, and the volume change is small during the transmission of sodium ions, which can further improve the stability of the first active stabilizer; and the sodium-based polyanion compound is selected from: at least one of NaFeSO4, Na3Fe2(PO4)3, Na2FeP2O7, Na3Fe2(PO4)P2O7, Na3V2(PO4)3, Na3V2Fe(PO4)3, Na3VMn2Fe(PO4)3, Na3VTiFe(PO4)3, Na3Fe2Fe(PO4)3, and Na3MnTiFe(PO4)3, and can be specifically selected according to actual needs and is not limited here.

[0009] Optionally, in addition to the first coating, the diaphragm may also include a second coating, the second coating being located on the side of the base film facing the negative electrode, the second coating including a second active stabilizer, and the second active stabilizer being selected from amorphous carbon. Since the second active stabilizer can also realize the deintercalation of sodium ions, when applied to a sodium ion battery, the amount of sodium ions in the sodium ion battery can be further increased, thereby increasing the capacity of the sodium ion battery. In addition, the second coating can protect the base film, improve the thermal stability, heat shrinkage resistance and mechanical strength of the diaphragm, thereby improving the safety of the use of the sodium ion battery, avoiding the short circuit between the positive and negative electrodes caused by thermal shrinkage or melting of the diaphragm, and reducing the risk of using the sodium ion battery.

[0010] Among them, the median particle size D50 of the second active stabilizer is 0.1μm-5μm, such as but not limited to: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm and other values. The further median particle size D50 is 1μm-3μm, which can be set according to actual needs and is not specifically limited here. When D50 is small, it means that the specific surface area of ​​the second active stabilizer is large, and a large specific surface area will increase the occurrence of particle agglomeration, resulting in unstable performance of the diaphragm; when D50 is large, it means that the particles of the second active stabilizer are large, which may cause uneven stress in the second coating, which may scratch the base film and cause damage to the diaphragm. Therefore, setting D50 within an appropriate range can not only make the diaphragm have better performance, but also avoid damage to the diaphragm and improve the reliability of the diaphragm.

[0011] The thickness of the first coating layer and / or the second coating layer is 0.5 μm-5 μm, that is, the thickness of the first coating layer can be set to 0.5 μm-5 μm, such as but not limited to: 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 and other thicknesses. Further, the thickness of the first coating layer is 3 μm-4 μm, which can be set according to actual needs and is not specifically limited here. The thickness of the second coating layer can be set to 0.5 μm-5 μm, such as but not limited to: 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 and other thicknesses. Further, the thickness of the second coating layer is 3 μm-4 μm, which can be set according to actual needs and is not specifically limited here. It should be understood that the thicknesses of the first coating layer and the second coating layer can be set to be the same or different. When the thickness is too large, it will affect the Na + transmission, resulting in Na + If the thickness is too small, the base film may not be effectively covered, which will reduce the heat shrinkage resistance of the separator and ultimately reduce the stability of the separator and the safety of the battery. Therefore, setting the thickness within the appropriate range can not only support high-rate discharge and improve battery reliability, but also improve the performance of the separator and enhance the safety of battery use.

[0012] The porosity of the first coating and / or the second coating is 25%-90%, that is, the porosity of the first coating can be set to 25%-90%, such as but not limited to: 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and other values. Further, the porosity of the first coating is 30%-50%, which can be set according to actual needs and is not specifically limited here. The porosity of the second coating can be set to 25%-90%, such as but not limited to: 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and other values. Further, the porosity of the second coating is 30%-50%, which can be set according to actual needs and is not specifically limited here. It should be understood that the porosity of the first coating and the second coating can be set to be the same or different. When the porosity is too small, it will hinder the Na + The transmission of Na2PO4 cannot support high rate discharge, and will increase heat generation, which will reduce the reliability of the battery. Therefore, setting the porosity larger is beneficial to Na2PO4 + The transmission of sodium ions and the increase of electrolyte retention can effectively improve the transmission capacity of sodium ions, support high-rate discharge, and improve battery reliability.

[0013] In addition to the first active stabilizer, the first coating layer may also include a first conductive adhesive. The first conductive adhesive is used to bond the first active stabilizer to the base film, so that the first active stabilizer can be firmly fixed on the base film to prevent the first active stabilizer from loosening or falling off during use. In addition, the first conductive adhesive can also increase the transmission of electrons in the first active stabilizer, thereby promoting Na + In addition to the second active stabilizer, the second coating may also include a second conductive adhesive, which is used to bond the second active stabilizer to the base film, so that the second active stabilizer can be firmly fixed on the base film to prevent the second active stabilizer from loosening or falling off during use; and the second conductive adhesive can also increase the transmission of electrons in the second active stabilizer, thereby promoting Na + The first conductive adhesive and the second conductive adhesive can be independently selected from at least one of the following or their derivatives: polyaniline, polypyrrole, polyethylene dioxythiophene, polyphenanthrenequinone, and polyfluorene polymers. The specific selection can be based on actual needs and is not limited here. Thus, the first conductive adhesive and the second conductive adhesive can be set to be the same or different.

[0014] Furthermore, the first coating layer may further include a conductive agent to further increase the transport of electrons in the first active stabilizer, thereby further promoting the Na +When the first coating layer includes: a first active stabilizer, a first conductive binder, and a conductive agent, the mass percentage of the first active stabilizer in the first coating layer is 75%-95%, the mass percentage of the first conductive binder in the first coating layer is 5%-30%, and the mass percentage of the conductive agent in the first coating layer is 0%-5%. Furthermore, the mass ratio of the first active stabilizer, the first conductive binder, and the conductive agent is 87.5%:10%:2.5%. Of course, the second coating layer may also include a conductive agent to further increase the transmission of electrons in the second active stabilizer, thereby further promoting Na + Deintercalation; when the second coating layer includes: a second active stabilizer, a second conductive binder and a conductive agent, the mass percentage of the second active stabilizer in the second coating layer is 80%-95%, the mass percentage of the second conductive binder in the second coating layer is 5%-20%, and the mass percentage of the conductive agent in the second coating layer is 0%-5%. Further, the mass ratio of the second active stabilizer, the second conductive binder and the conductive agent is 90%:7.5%:2.5%. Among them, the conductive agent in the first coating layer and the conductive agent in the second coating layer can be independently selected from conductive agents commonly used in sodium ion batteries, such as but not limited to: conductive carbon black, graphite, carbon nanotubes and other carbon materials. In addition, the types of conductive agents in the second coating layer and the first coating layer can be the same or different, and can be designed according to actual needs and are not limited here.

[0015] Optionally, the base membrane can be set as a porous membrane, and the presence of pores in the porous membrane can realize Na + For transmission, the thickness of the base film can be set to 3μm-25μm, such as but not limited to: 3μm, 5μm, 10μm, 15μm, 20μm, 25μm and other thicknesses. It can be set according to actual needs and is not specifically limited here.

[0016] The base membrane is a non-conductive but ion-conducting membrane, and its manufacturing material may include at least one of the following: polypropylene, polyethylene, nitrocellulose membrane, cellulose acetate membrane, polyamide membrane, polyethylene terephthalate, polyester membrane, thermoplastic polyimide, thermosetting polyimide, polyamide-imide copolymer, polyetherimide, milled fiber membrane, polyphthalamide membrane, metal membrane, alloy membrane, ceramic membrane, polymer technology combined membrane, molecular sieve composite membrane, zeolite membrane, glass membrane, etc. It can be specifically set according to actual needs and is not specifically limited here.

[0017] In a second aspect, an embodiment of the present application further provides a diaphragm, comprising: a base film, and a first coating provided on the surface of the base film, the first coating being located on the side of the base film facing the positive electrode, the first coating comprising a first active stabilizer, the first active stabilizer being selected from at least one of a sodium-based polyanion compound, a sodium-based layered transition metal oxide, and Prussian blue. Since the first active stabilizer can achieve the deintercalation of sodium ions, when applied to a sodium-ion battery, the amount of sodium ions in the sodium-ion battery can be increased, thereby increasing the capacity of the sodium-ion battery. In addition, the first coating can protect the base film, improve the thermal stability, heat shrinkage resistance, and mechanical strength of the diaphragm, thereby improving the safety of the sodium-ion battery, avoiding short circuits between the positive and negative electrodes caused by thermal shrinkage or melting of the diaphragm, and reducing the risk of using the sodium-ion battery.

[0018] It should be understood that since the principle of the diaphragm to solve the problem is similar to the principle of the aforementioned sodium ion battery to solve the problem, the implementation and technical effects of the diaphragm can refer to the implementation and technical effects of the aforementioned sodium ion battery, and the repeated parts will not be repeated.

[0019] In a third aspect, embodiments of the present application further provide a battery pack, which may include: a housing; and multiple sodium-ion batteries, each of which is disposed within the housing. The sodium-ion batteries may be those described in the first aspect and any of the embodiments of the first aspect. In this manner, while improving the performance of the sodium-ion batteries, the performance of the battery pack is also improved.

[0020] It should be understood that since the principle of solving the problem by this battery pack is similar to the principle of solving the problem by the aforementioned sodium ion battery, the implementation and technical effects of this battery pack can refer to the implementation and technical effects of the aforementioned sodium ion battery, and the repeated parts will not be repeated.

[0021] Fourthly, embodiments of the present application further provide an energy storage system, comprising a battery pack and a power converter as described in the third aspect above. The power converter is configured to convert AC power outputted by an external AC power source into DC power for output to the battery pack, and / or the power converter is configured to convert DC power outputted by the battery pack into AC power for output to a load or power grid. In this way, while improving the performance of the battery pack, the performance of the energy storage system is also improved.

[0022] It should be understood that since the principle of solving the problem by the energy storage system is similar to the principle of solving the problem by the aforementioned battery pack, the implementation and technical effects of the energy storage system can refer to the implementation and technical effects of the aforementioned battery pack, and the repeated parts will not be repeated. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the structure of the energy storage system provided in an embodiment of the present application;

[0024] Figure 2 A schematic diagram of the structure of the battery pack provided in an embodiment of the present application;

[0025] Figure 3 A schematic structural diagram of a sodium ion battery provided in an embodiment of the present application;

[0026] Figure 4 A schematic diagram of the structure of the diaphragm provided in an embodiment of the present application;

[0027] Figure 5 This is a scanning electron microscope image of the diaphragm provided in the embodiment of the present application;

[0028] Figure 6 A schematic diagram of cyclic discharge data provided in an embodiment of the present application;

[0029] Figure 7 A comparison chart of thermal stability provided by the examples of this application;

[0030] Figure 8 A comparison diagram of the adiabatic accelerating rate calorimeter provided in the embodiments of the present application;

[0031] Figure 9 This is a photo of the diaphragm in Example 1 provided in the examples of the present application after being folded in half five times. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application clearer, this application will be further described in detail below with reference to the accompanying drawings.

[0033] It should be noted that the same reference numerals in the drawings of this application represent the same or similar structures, and thus their repeated description will be omitted. The words expressing positions and directions described in this application are all explained using the drawings as examples, but they can be modified as needed, and such modifications are included in the scope of protection of this application. The drawings of this application are only for illustrating relative positional relationships and do not represent true proportions.

[0034] In order to facilitate understanding of the technical solution provided by the embodiments of the present application, its application scenario is first explained below.

[0035] The technical solutions provided in the embodiments of this application can be widely used in energy storage systems, which can be applied to, but not limited to, household energy storage, site energy, smart photovoltaics, and data center energy scenarios, for storing and providing electrical energy. Figure 1 The energy storage system shown in the figure is a schematic diagram of an energy storage system. The energy storage system may include: a battery cluster and a power converter 200. The battery cluster includes a plurality of battery packs 100 connected in series. Figure 1Only one battery pack 100 is shown as an example. The power converter 200 can convert the AC power output by an external AC power source (such as the power grid 300) into DC power and output it to the battery pack 100 in the battery cluster to charge the battery pack 100. It can also convert the DC power output by the battery pack 100 in the battery cluster into AC power and output it to the load 400 or the power grid 300 to discharge the battery pack 100.

[0036] See also Figure 2 The battery pack 100 is a schematic diagram of a structure of a battery pack 100, which may include: a housing 101, and a plurality of sodium ion batteries 102. Each sodium ion battery 102 is arranged in the housing 101. Each sodium ion battery 102 may be connected in series, in parallel, or in a combination of series and parallel connections, so that the battery pack 100 has a higher capacity and a higher voltage, and is thus applicable to various application scenarios. Figure 3 The structure diagram of the sodium-ion battery 102 shown in FIG. 1 shows a sodium-ion battery 102. The sodium-ion battery 102 may include a positive electrode 11, a negative electrode 12, a separator 13, and an electrolyte 14. The separator 13 is disposed between the positive electrode 11 and the negative electrode 12, and the electrolyte 14 infiltrates the positive electrode 11, the separator 13, and the negative electrode 12. When the sodium-ion battery 102 is charged, sodium ions are released from the positive electrode 11, pass through the separator 13, and are embedded in the negative electrode 12. When the sodium-ion battery 102 is discharged, sodium ions are released from the negative electrode 12, pass through the separator 13, and are embedded in the positive electrode 11. Therefore, the performance of the separator affects the performance of the sodium-ion battery.

[0037] The separator can effectively prevent electron transfer between the positive and negative electrodes, while allowing sodium ions to transfer through the separator, making it unable to transfer electrons but able to transfer ions. Currently, separators are usually made of polyolefin compounds. Polyolefin separators have the advantages of low cost, good chemical stability and high mechanical strength. However, due to their low melting point, polyolefin separators will shrink or even melt under high temperature conditions. In severe cases, this can cause a short circuit between the positive and negative electrodes, greatly reducing the safety performance of sodium-ion batteries.

[0038] To solve this problem, the current common practice is to use ceramic materials, metal-organic frameworks or blended polymers to make a coating on the surface of polyolefins to obtain a composite diaphragm. However, these materials generally do not participate in chemical reactions, such as the deintercalation and intercalation of sodium ions, and have no contribution to the capacity of sodium-ion batteries. In addition, they increase the weight and cost of the diaphragm.

[0039] Based on this, an embodiment of the present application provides a diaphragm, which not only has high thermal stability and resistance to heat shrinkage to improve the stability of the sodium ion battery, but also can increase the capacity of the sodium ion battery.

[0040] Exemplarily, the diaphragm includes: a base film, and a first coating provided on the surface of the base film, the first coating being located on the side of the base film facing the positive electrode, the first coating including a first active stabilizer, the first active stabilizer being selected from at least one of a sodium-based polyanion compound, a sodium-based layered transition metal oxide, and Prussian blue. Since the first active stabilizer can achieve sodium ion deintercalation, when applied to a sodium ion battery, the amount of sodium ions in the sodium ion battery can be increased, thereby increasing the capacity of the sodium ion battery. In addition, the first coating can protect the base film, improve the thermal stability, heat shrinkage resistance, and mechanical strength of the diaphragm, thereby improving the safety of the sodium ion battery, preventing the positive and negative electrodes from short-circuiting due to thermal shrinkage or melting of the diaphragm, and reducing the risk of using the sodium ion battery.

[0041] The first active stabilizer can be set as follows:

[0042] 1. Since the layered structure of sodium-based layered transition metal oxides collapses after sodium ions are deintercalated, sodium-based layered transition metal oxides are unstable. However, the structures of sodium-based polyanion compounds and Prussian blue remain stable after the sodium ions are removed. Therefore, the first active stabilizer can be further selected from sodium-based polyanion compounds and Prussian blue to improve the stability of the first active stabilizer. Since Prussian blue is less commonly used and sodium-based polyanion compounds are more common and easier to obtain, the first active stabilizer can be further selected from sodium-based polyanion compounds. Among them, the sodium-based polyanion compound can be a compound with a NASICON structure. The sodium-based polyanion compound with a NASICON structure has a three-dimensional ion transport channel, and the volume change is small during the transmission of sodium ions, which can further improve the stability of the first active stabilizer; and the sodium-based polyanion compound is selected from: at least one of NaFeSO4, Na3Fe2(PO4)3, Na2FeP2O7, Na3Fe2(PO4)P2O7, Na3V2(PO4)3, Na3V2Fe(PO4)3, Na3VMn2Fe(PO4)3, Na3VTiFe(PO4)3, Na3Fe2Fe(PO4)3, and Na3MnTiFe(PO4)3, and can be specifically selected according to actual needs and is not limited here.

[0043] 2. Different substances have different voltage windows when deintercalating sodium ions. That is, a large amount of sodium ions will be deintercalated in the corresponding voltage range, so this voltage range can be considered as the main deintercalation range; but when it is outside this voltage range, sodium ions will also be deintercalated, but the amount of deintercalation is small. Based on this, the main deintercalation range of the first active stabilizer and the main deintercalation range of the positive electrode active material in the positive electrode have an intersection, that is, the first active stabilizer has Na + The voltage range during the deintercalation reaction is related to the Na+ There is an intersection in the voltage range of the deintercalation reaction, which can provide more Na for sodium ion batteries. + , thereby greatly improving the capacity of sodium ion batteries.

[0044] 3. The median particle size D50 of the first active stabilizer can be set to 0.1μm-5μm, such as but not limited to: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm and other values. The median particle size D50 is further 1μm-3μm. It can be set according to actual needs and is not specifically limited here. When D50 is small, it means that the specific surface area of ​​the first active stabilizer is large, and a large specific surface area will increase the occurrence of particle agglomeration, resulting in unstable performance of the diaphragm; when D50 is large, it means that the particles of the first active stabilizer are large, which may cause uneven stress in the first coating, which may scratch the base film and cause damage to the diaphragm. Therefore, setting D50 within an appropriate range can not only make the diaphragm have better performance, but also avoid damage to the diaphragm and improve the reliability of the diaphragm.

[0045] 4. The specific surface area of ​​the first active stabilizer can be set to 8m 2 / g-25m 2 / g, such as but not limited to: 8m 2 / g、9m 2 / g、10m 2 / g、12m 2 / g、14m 2 / g、16m 2 / g、18m 2 / g, 20m 2 / g、22m 2 / g、24m 2 / g, 25m 2 / g and other values, and further the specific surface area is 9m 2 / g-20m 2 / g, which can be set according to actual needs and is not specifically limited here. If the specific surface area of ​​the first active stabilizer is too large, the particles will increase the occurrence of agglomeration and cannot be effectively dispersed, resulting in unstable performance of the diaphragm. If the specific surface area of ​​the first active stabilizer is too small, it means that the particles of the first active stabilizer are large, which will cause uneven stress in the first coating layer and scratch the base film. Therefore, setting the specific surface area of ​​the first active stabilizer within a suitable range can not only improve the performance of the diaphragm, but also avoid damage to the diaphragm and improve the reliability of the diaphragm.

[0046] For the first coating, the following settings can be made:

[0047] 1. The thickness of the first coating layer can be set to 0.5μm-5μm, such as but not limited to: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm and other thicknesses. Further, the thickness of the first coating layer is 3μm-4μm, which can be set according to actual needs and is not specifically limited here. When the thickness is too large, it will affect the Na + transmission, resulting in Na + If the thickness is too small, the base film may not be effectively covered, which will reduce the heat shrinkage resistance of the separator and ultimately reduce the stability of the separator and the safety of the battery. Therefore, setting the thickness within the appropriate range can not only support high-rate discharge and improve battery reliability, but also improve the performance of the separator and enhance the safety of battery use.

[0048] 2. The porosity of the first coating layer can be set to 25%-90%, such as but not limited to: 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and other values. Further, the porosity of the first coating layer is 30%-50%, which can be set according to actual needs and is not specifically limited here. When the porosity is too small, it will hinder the Na + The transmission of Na2PO4 cannot support high rate discharge, and will increase heat generation, which will reduce the reliability of the battery. Therefore, setting the porosity larger is beneficial to Na2PO4 + The transmission of sodium ions and the increase of electrolyte retention can effectively improve the transmission capacity of sodium ions, support high-rate discharge, and improve battery reliability.

[0049] 3. In addition to the first active stabilizer, the first coating layer may also include a first conductive adhesive. The first conductive adhesive is used to bond the first active stabilizer to the base film, so that the first active stabilizer can be firmly fixed on the base film to prevent the first active stabilizer from loosening or falling off during use. In addition, the first conductive adhesive can also increase the transmission of electrons in the first active stabilizer, thereby promoting Na + The first conductive binder can be selected from at least one of the following or its derivatives: polyaniline, polypyrrole, polyethylene dioxythiophene, polyphenanthrenequinone, polyfluorene polymers, and can be selected according to actual needs and is not limited here. Furthermore, the first coating can also include a conductive agent to further increase the transmission of electrons in the first active stabilizer, thereby further promoting Na +The conductive agent can be selected from commonly used conductive agents in sodium-ion batteries, such as, but not limited to, conductive carbon black, graphite, carbon nanotubes, and other carbon materials. When the first coating layer includes a first active stabilizer, a first conductive binder, and a conductive agent, the mass percentage of the first active stabilizer in the first coating layer is 75%-95%, the mass percentage of the first conductive binder in the first coating layer is 5%-30%, and the mass percentage of the conductive agent in the first coating layer is 0%-5%. Furthermore, the mass ratio of the first active stabilizer, the first conductive binder, and the conductive agent is 87.5%:10%:2.5%.

[0050] Exemplarily, in addition to the first coating, the diaphragm may also include a second coating, the second coating being located on the side of the base film facing the negative electrode, the second coating including a second active stabilizer, and the second active stabilizer being selected from amorphous carbon. Since the second active stabilizer can also realize the deintercalation of sodium ions, when applied to a sodium ion battery, the amount of sodium ions in the sodium ion battery can be further increased, thereby increasing the capacity of the sodium ion battery. In addition, the second coating can protect the base film, improve the thermal stability, heat shrinkage resistance and mechanical strength of the diaphragm, thereby improving the safety of the sodium ion battery, avoiding the short circuit between the positive and negative electrodes caused by thermal shrinkage or melting of the diaphragm, and reducing the risk of using the sodium ion battery.

[0051] Among them, the median particle size D50 of the second active stabilizer is 0.1μm-5μm, such as but not limited to: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm and other values. The further median particle size D50 is 1μm-3μm, which can be set according to actual needs and is not specifically limited here. When D50 is small, it means that the specific surface area of ​​the second active stabilizer is large, and a large specific surface area will increase the occurrence of particle agglomeration, resulting in unstable performance of the diaphragm; when D50 is large, it means that the particles of the second active stabilizer are large, which may cause uneven stress in the second coating, which may scratch the base film and cause damage to the diaphragm. Therefore, setting D50 within an appropriate range can not only make the diaphragm have better performance, but also avoid damage to the diaphragm and improve the reliability of the diaphragm.

[0052] Moreover, the thickness of the second coating layer can be set to 0.5μm-5μm, such as but not limited to: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm and other thicknesses. Further, the thickness of the second coating layer is 3μm-4μm, which can be set according to actual needs and is not specifically limited here. When the thickness is too large, it will affect the Na + transmission, resulting in Na +The transmission rate is reduced, which makes it impossible to support high-rate discharge, and it will also increase heat generation, which will reduce the reliability of the battery. If the thickness is too small, it may not be able to effectively cover the base film, which will lead to a decrease in the heat shrinkage resistance of the diaphragm, and ultimately lead to a decrease in the stability of the diaphragm and a decrease in the safety of the battery. Therefore, setting the thickness within an appropriate range can not only support high-rate discharge and improve battery reliability, but also improve the performance of the diaphragm and improve the safety of battery use. It should be understood that the thickness of the first coating layer and the second coating layer can be set to the same or different.

[0053] The porosity of the second coating layer can be set to 25%-90%, such as but not limited to: 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and other values. Further, the porosity of the second coating layer is 30%-50%, which can be set according to actual needs and is not specifically limited here. When the porosity is too small, it will hinder the Na + The transmission of Na2PO4 cannot support high rate discharge, and will increase heat generation, which will reduce the reliability of the battery. Therefore, setting the porosity larger is beneficial to Na2PO4 + The transmission of sodium ions and the increase in electrolyte retention effectively enhance the transmission capacity of sodium ions, support high-rate discharge, and improve battery reliability. It should be understood that the porosity of the first coating and the second coating can be set to be the same or different.

[0054] In addition to the second active stabilizer, the second coating layer may also include a second conductive adhesive. The second conductive adhesive is used to bond the second active stabilizer to the base film, so that the second active stabilizer can be firmly fixed on the base film to prevent the second active stabilizer from loosening or falling off during use. In addition, the second conductive adhesive can also increase the transmission of electrons in the second active stabilizer, thereby promoting Na + The second conductive adhesive can be selected from at least one of the following or its derivatives: polyaniline, polypyrrole, polyethylene dioxythiophene, polyphenanthrenequinone, polyfluorene polymers, and can be selected according to actual needs and is not limited here; it should be understood that the types of the first conductive adhesive and the second conductive adhesive can be set to be the same or different. Of course, the second coating can also include a conductive agent to further increase the transmission of electrons in the second active stabilizer, thereby further promoting Na + The type of conductive agent in the second coating layer and the first coating layer may be the same or different, and may be specifically designed according to actual needs and is not limited thereto.

[0055] When the second coating layer includes: a second active stabilizer, a second conductive adhesive and a conductive agent, the mass percentage of the second active stabilizer in the second coating layer is 80%-95%, the mass percentage of the second conductive adhesive in the second coating layer is 5%-20%, and the mass percentage of the conductive agent in the second coating layer is 0%-5%. Furthermore, the mass ratio of the second active stabilizer, the second conductive adhesive and the conductive agent is 90%:7.5%:2.5%.

[0056] The following settings can be made for the basement membrane:

[0057] The base membrane can be set as a porous membrane, and the presence of pores in the porous membrane can realize Na + For transmission, the thickness of the base film can be set to 3μm-25μm, such as but not limited to: 3μm, 5μm, 10μm, 15μm, 20μm, 25μm and other thicknesses. It can be set according to actual needs and is not specifically limited here.

[0058] The base membrane is a non-conductive but ion-conducting membrane, and its manufacturing material may include at least one of the following: polypropylene, polyethylene, nitrocellulose membrane, cellulose acetate membrane, polyamide membrane, polyethylene terephthalate, polyester membrane, thermoplastic polyimide, thermosetting polyimide, polyamide-imide copolymer, polyetherimide, milled fiber membrane, polyphthalamide membrane, metal membrane, alloy membrane, ceramic membrane, polymer technology combined membrane, molecular sieve composite membrane, zeolite membrane, glass membrane, etc. It can be specifically set according to actual needs and is not specifically limited here.

[0059] The performance of sodium ion batteries is tested below.

[0060] Example 1:

[0061] Production process.

[0062] The manufacturing process of the diaphragm may include: dissolving 7wt% polyaniline in N-methylpyrrolidone, then adding 2wt% conductive carbon black and 91wt% Na3Fe2(PO4)P2O7 powder to the solution, stirring for 24 hours to obtain a slurry; coating the slurry on one side of the base film to form a first coating layer with a thickness of 3μm, and drying at 90°C to obtain a diaphragm coated with the first coating layer containing the first active stabilizer (i.e., Na3Fe2(PO4)P2O7), such as Figure 4 In the schematic diagram shown, 10 represents the base film, 20 represents the first coating layer, and 21 represents the first active stabilizer in the first coating layer 20.

[0063] The production process of the positive electrode may include: mixing the positive electrode active material, conductive agent, and adhesive in a certain mass percentage, stirring and dispersing them in an organic solvent to obtain a uniform and stable positive electrode slurry, uniformly coating the positive electrode slurry on the surface of the current collector, drying, rolling, slitting, and die-cutting to obtain the positive electrode.

[0064] The production process of the negative electrode may include: mixing the negative electrode active material, conductive agent, and adhesive in a certain mass percentage and dispersing them in deionized water to obtain a uniform negative electrode slurry, uniformly coating the negative electrode slurry on the surface of the current collector, drying, rolling, slitting, and die-cutting to obtain the negative electrode.

[0065] The production process of a sodium ion battery may include: winding the positive electrode produced by the above process, the negative electrode produced by the above process, and the separator to obtain a battery cell, placing the battery cell in an aluminum-plastic film and baking it, then injecting an electrolyte, and undergoing processes such as standing, formation, aging, and capacity separation to obtain a sodium ion battery.

[0066] Example 2: The difference from Example 1 is that the first active stabilizer is Na3V2(PO4)3.

[0067] Example 3: The difference from Example 1 is that the two opposite surfaces of the base film are respectively provided with a first coating and a second coating.

[0068] The manufacturing process of the diaphragm may include: dissolving 7wt% of polyaniline in N-methylpyrrolidone, then adding 2wt% of conductive carbon black and 91wt% of Na3Fe2(PO4)P2O7 powder to the solution, and stirring for 24 hours to obtain a slurry; applying the slurry on one side of the base film to form a first coating layer, the thickness of the first coating layer is 3μm, and drying at 90°C; dissolving 10wt% of polyaniline in N-methylpyrrolidone, then adding 2wt% of conductive carbon black and 88wt% of amorphous carbon powder to the solution, and stirring for 24 hours to obtain a slurry; applying the slurry on the other side of the base film to form a second coating layer, the thickness of the second coating layer is 3μm, and drying at 90°C, so that the first coating layer and the second coating layer are respectively located on two opposite surfaces of the base film to form a diaphragm.

[0069] Comparative Example 1: The difference from Example 1 is that a base film is used as the diaphragm.

[0070] Characterize the data.

[0071] The surface morphology of the diaphragms of Example 1 and Comparative Example 1 was characterized using a scanning electron microscope. Figure 5 The characterization results shown, where Figure 5 (a) is the morphology of the surface of the membrane provided with the first coating in Example 1. Figure 5 (b) is the morphology of the membrane surface in Comparative Example 1. Figure 5The results shown in show that the surface of the base membrane is smooth and porous, while the surface of the diaphragm provided with the first coating has a lot of granular substances, which are the first active stabilizers, indicating that the first active stabilizer is evenly coated on the surface of the base membrane.

[0072] Test data.

[0073] About discharge capacity: Figure 6 From the cyclic discharge data shown in , the discharge specific capacity of Examples 1 to 3 is always higher than that of Comparative Example 1, which shows that the first coating and the second coating in the diaphragm can increase the discharge specific capacity. In other words, the first active stabilizer in the first coating and the second active stabilizer in the second coating can achieve Na + The deintercalation and insertion of Na2+ provides more Na2+ for Na2+ batteries. + , thereby increasing the capacity of the sodium-ion battery. Furthermore, as the cycle time increases, the discharge specific capacity of Examples 1 to 3 is relatively stable, with a smaller decrease in discharge specific capacity. This indicates that the presence of the first and second coatings gives the separator greater stability, thereby enabling the sodium-ion battery to have better cycle stability.

[0074] Regarding thermal stability: Figure 7 The thermal stability comparison chart of each embodiment and comparative example is shown in Table 1. The relevant temperatures of each embodiment and comparative example are given in Table 1, wherein T1 in Table 1 represents the starting temperature of self-heating, T2 represents the starting temperature of thermal runaway, and T3 represents the highest temperature during the thermal runaway process; Figure 7 From the results shown in Table 1, it can be seen that in Examples 1 to 3, the lowest T1 of the sodium ion battery is 146°C, and the lowest T2 of the sodium ion battery is 201°C, while the T1 of Comparative Example 1 is 131°C and T2 is 196°C. Therefore, the T1 and T2 of each example are higher than those of the comparative example. Since T1 and T2 are key temperatures that characterize the thermal stability of the battery, the higher the T1 and T2, the better the thermal stability of the battery. Therefore, adding the first active stabilizer and the second active stabilizer to the diaphragm can improve the thermal stability of the sodium ion battery. In addition, the highest T3 in Examples 1 to 3 is 347°C, which is much lower than the 380°C of Comparative Example 1. The lower the T3, the lower the harm caused. Therefore, adding the first active stabilizer and the second active stabilizer to the diaphragm can reduce the heat released during the thermal runaway process, thereby improving the thermal stability of the sodium ion battery and reducing the harm caused by thermal runaway.

[0075] Table 1

[0076] T1 / ℃ T2 / ℃ T3 / ℃ Example 1 146 201 347 Example 2 146 204 338 Example 3 148 205 323 Comparative Example 1 131 196 380

[0077] About heat shrinkage resistance: Figure 8This is a comparison chart of the adiabatic accelerating calorimeter of Example 1 and Comparative Example 1. After Example 1 and Comparative Example 1 were heat treated at 60°C, 90°C, 120°C and 150°C for 1 hour respectively, the base film in Comparative Example 1 began to melt at 120°C and shrank over a large area. When the temperature reached 150°C, the base film almost shrank completely, but the diaphragm in Example 1 remained almost intact at 150°C, which shows that adding the first active stabilizer to the diaphragm can increase the heat shrinkage resistance of the diaphragm.

[0078] Regarding mechanical strength: Figure 9 The photo shows the diaphragm in Example 1 after being folded in half five times. It was found that there was no powder falling off the surface of the diaphragm, indicating that the first active stabilizer was well fixed on the surface of the base film, and further indicating that the diaphragm had good stability.

[0079] Obviously, those skilled in the art may make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the embodiments of the present application. Thus, if these modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalents, the present application also intends to include such modifications and variations.

Claims

1. A sodium ion battery, characterized in that include: A positive electrode, a negative electrode and a separator, wherein the separator is arranged between the positive electrode and the negative electrode, and the separator comprises: a base film, and a first coating arranged on the surface of the base film, wherein the first coating is located on the side of the base film facing the positive electrode, and the first coating comprises a first active stabilizer, which is selected from at least one of a sodium-based polyanion compound, a sodium-based layered transition metal oxide, and Prussian blue.

2. The sodium ion battery according to claim 1, wherein The positive electrode includes a positive electrode active material, and the first active stabilizer generates Na + The voltage range during the deintercalation reaction is related to the positive electrode active material undergoing Na + There is an intersection in the voltage ranges of the intercalation and deintercalation reactions.

3. The sodium ion battery according to claim 1 or 2, wherein: The median particle size D50 of the first active stabilizer is 0.1 μm-5 μm.

4. The sodium ion battery according to any one of claims 1 to 3, wherein The specific surface area of ​​the first active stabilizer is 8m 2 / g-25m 2 / g.

5. The sodium ion battery according to any one of claims 1 to 4, wherein The sodium-based polyanion compound is a compound having a NASICON structure.

6. The sodium ion battery according to any one of claims 1 to 5, wherein The sodium-based polyanion compound is selected from at least one of: NaFeSO4, NaFePO4, Na2FeP2O7, Na3Fe2(PO4)P2O7, Na3V2Fe(PO4)3, Na3VMn2Fe(PO4)3, Na3VTiFe(PO4)3, Na3Fe2Fe(PO4)3, and Na3MnTiFe(PO4)3.

7. The sodium ion battery according to any one of claims 1 to 6, wherein The separator further includes a second coating layer, which is located on a side of the base film facing the negative electrode. The second coating layer includes a second active stabilizer, which is selected from amorphous carbon.

8. The sodium ion battery according to claim 7, wherein The median particle size D50 of the second active stabilizer is 0.1 μm-5 μm.

9. The sodium ion battery according to claim 7 or 8, characterized in that The thickness of the first coating layer and / or the second coating layer is 0.5 μm-5 μm.

10. The sodium ion battery according to any one of claims 7 to 9, wherein: The porosity of the first coating layer and / or the second coating layer is 25%-90%.

11. The sodium ion battery according to any one of claims 7 to 10, wherein: The first coating layer further includes a first conductive adhesive, and the first conductive adhesive is used to bond the first active stabilizer to the base film; And / or, the second coating layer further comprises a second conductive adhesive, and the second conductive adhesive is used to bond the second active stabilizer to the base film; The first conductive adhesive and the second conductive adhesive are independently selected from at least one of polyaniline, polypyrrole, polyethylenedioxythiophene, polyphenanthrenequinone, and polyfluorene polymers.

12. A diaphragm, characterized in that: include: A base film and a first coating provided on the surface of the base film, wherein the first coating comprises a first active stabilizer selected from at least one of a sodium-based polyanion compound, a sodium-based layered transition metal oxide, and Prussian blue.

13. A battery pack, characterized in that: include: A box, and a plurality of sodium ion batteries according to any one of claims 1 to 11, each of the sodium ion batteries being arranged in the box.

14. An energy storage system, characterized in that: The energy storage system includes a battery pack and a power converter as described in claim 13, wherein the power converter is used to convert the AC power output by an external AC power source into DC power and output it to the battery pack, and / or the power converter is used to convert the DC power output by the battery pack into AC power and output it to a load or a power grid.

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