Secondary battery with low expansion rate, preparation method and battery pack

Abstract

According to the secondary battery with the low expansion rate, the negative electrode end comprises the porous current collector or the porous modification layer on the surface of the current collector, and the change of the electrode thickness in the charging and discharging process of the battery is controlled through the physical confinement of the porous current collector or the porous modification layer and the synergistic effect of related electrochemical reactions; and the service life of the sodium ion battery can be prolonged without additionally customizing a battery assembly suitable for the negative-electrode-free sodium battery. Compared with a traditional sodium-ion battery which is not protected by a stable host material on the negative electrode side, and deposition / stripping of sodium metal on the negative electrode side can cause change of the volume of the battery, so that the problem of battery expansion is caused, the expansion rate of the battery is reduced under the action of the porous current collector or the current collector with a porous modification layer on the surface, and the service life of the battery is prolonged. Therefore, the safety and the cycle life of the sodium ion battery in the use process are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a secondary battery with low expansion rate, a preparation method and a battery pack. BACKGROUND

[0002] Among many battery technologies, lithium ion batteries, as green and environmentally friendly energy storage devices, have been widely used in the electronic market, new energy vehicles and other energy storage fields due to their high energy density, long cycle life, safety and non-pollution, etc. advantages, greatly improving the production and living standards of human beings. However, the global reserves of lithium resources are limited, and the content of lithium element in the earth's crust is only 0.0065%. With the rapid increase in demand for batteries with the development of new energy vehicles, the resource bottleneck gradually appears, and the high cost limits the large-scale application and sustainable development of lithium ion batteries.

[0003] Sodium ion batteries have become one of the focuses of research and development of new generation battery technologies due to their sustainability and economy. However, sodium ion batteries do not have a stable host material on the negative side to protect the sodium metal deposition / peeling on the negative side, which can cause changes in the volume of the battery, thereby causing the battery to swell. Especially under long-term use or high-intensity conditions, the swelling of the battery not only affects the appearance, but also can cause damage to the internal components of the battery, leading to a decrease in cycle life, and even causing serious safety problems such as battery leakage / short circuit.

[0004] Therefore, how to reduce the expansion rate of sodium ion batteries has become a problem that needs to be solved. SUMMARY

[0005] The embodiments of the present application aim at the problem that the deposition / peeling of sodium metal on the negative side of the existing sodium ion battery can cause changes in the volume of the battery, thereby causing the battery to swell and causing damage to the internal components of the battery, leading to a decrease in cycle life and causing serious safety problems such as battery leakage / short circuit. The present application provides a secondary battery with low expansion rate, a preparation method and a battery pack and application, which reduces the expansion rate of sodium ion batteries.

[0006] To achieve the above-mentioned purpose, the technical solutions adopted by the embodiments of the present application are as follows:

[0007] In a first aspect, the embodiments of the present application provide a secondary battery with low expansion rate, comprising: a positive electrode end, a negative electrode end and a separator, the negative electrode end comprising a porous current collector or a porous modification layer on the surface of the current collector; the separator is arranged between the positive electrode end and the negative electrode end, and the separator is used to store electrolyte.

[0008] In a possible implementation, the pore volume of the porous current collector or the porous modification layer on the surface of the current collector is greater than the volume of the sodium metal deposited in the secondary battery, and the positive electrode end and the negative electrode end each comprise at least one layer; the capacity provided by the negative electrode end is not greater than 20% of the capacity of the battery.

[0009] In a possible implementation, the porous current collector comprises at least one of foamed nickel, foamed nickel alloy, foamed copper, foamed copper alloy, foamed aluminum, foamed aluminum alloy, foamed iron, foamed iron alloy, foamed zinc, foamed zinc alloy, copper mesh, copper foil, copper alloy mesh, aluminum mesh, aluminum alloy mesh, titanium mesh, titanium alloy mesh, stainless steel mesh, nickel mesh, nickel alloy mesh, foamed carbon, carbon aerogel, carbon cloth, carbon paper, and carbon felt.

[0010] In a possible implementation, the porous modification layer on the surface of the current collector comprises at least one of a metal, an alloy of the metal, and halide, sulfide, oxide, nitride, selenide, and hydride of the metal, and one or more of a carbon material; the metal comprises one or more of Mg, Zn, Bi, Sn, Ge, Si, Pb, Sb, In, Ca, Ni, Ga, and Ti.

[0011] In a possible implementation, the areal loading of the porous modification layer on the surface of the current collector is 0.05-2.0 mg / cm 2 .

[0012] In a possible implementation, the porous modification layer on the surface of the current collector is loaded on the surface of the current collector by means of scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing.

[0013] In a second aspect, an embodiment of the present application provides a preparation method of a secondary battery with low expansion rate, comprising:

[0014] After mixing and stirring the positive electrode active material, the conductive agent, and the binder according to a first preset mass ratio, a solvent is added to prepare a positive electrode slurry with uniform distribution; the positive electrode slurry is uniformly coated on two surfaces of the positive electrode current collector aluminum foil, dried at a first preset temperature, and then cold-pressed to obtain a positive electrode end coated with the positive electrode slurry on both surfaces; preferably, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 90:5:5; preferably, the areal loading is 20.0 mg / cm 2 ;

[0015] The negative electrode material is mixed and stirred according to a second preset mass ratio, a solvent is added, and a negative electrode slurry is prepared; the negative electrode slurry is uniformly coated on two surfaces of the negative electrode current collector aluminum foil, and is dried at a second preset temperature, to obtain a negative electrode end coated with the negative electrode slurry on both surfaces, the negative electrode material can include mesoporous carbon CMK-3 and sodium polyacrylate (NaPAA), and further, the negative electrode material can further include aluminum fluoride;

[0016] The positive electrode end, the separator and the negative electrode end are sequentially stacked in order, with the separator being between the positive electrode end and the negative electrode end, and after the positive electrode end and the negative electrode end are respectively stacked, an electrode assembly is obtained; the electrode assembly is loaded into a shell assembly, and water is removed again, the prepared electrolyte is injected, and a secondary battery is processed. The number of stacked layers of the positive electrode end and the negative electrode end is selected according to actual conditions, and preferably, the positive electrode end and the negative electrode end are respectively stacked by 10 layers.

[0017] In a third aspect, an embodiment of the present application provides a battery pack comprising the secondary battery according to the first aspect of the present application

[0018] The secondary battery provided by the embodiment of the present application has a capacity of the negative electrode not higher than 20% of the capacity of the battery, and the capacity of the battery is mainly derived from the positive electrode. The negative electrode end has a porous structure containing a modification layer, which is used to accommodate the deposited sodium metal during charging of the battery. When the current collector with the porous modification layer on the surface contains ordered mesoporous carbon and sodium polyacrylate at a preset ratio, stable cycling of the secondary battery can be achieved, and the cycle life reaches 10,000 times.

[0019] The preparation method of the secondary battery provided by the embodiment of the present application reduces the expansion rate of the sodium ion battery, improves the cycle life and use safety of the battery. Compared with the sodium ion battery without the protection of the stable host material on the negative electrode side in the prior art, the deposition / exfoliation of the sodium metal on the negative electrode side can cause the change of the volume of the battery, thereby causing the expansion of the battery. Especially under long-time use or high-intensity conditions, the expansion of the battery not only affects the appearance, but also can cause damage to the internal components of the battery, thereby reducing the cycle life, and even causing serious safety problems such as battery leakage / short circuit. The porous current collector or the current collector with the porous modification layer on the surface is introduced in the present application. By controlling the size of the pore volume, the capacity provided by the negative electrode is 0-20% of the capacity of the battery, thereby reducing the expansion rate of the sodium ion battery, and improving the service life and safety performance.

[0020] The battery pack of the secondary battery with low expansion rate provided by the embodiment of the present application has the same advantages as the secondary battery, and can meet the use requirements in the fields of renewable energy, consumer electronics and electric vehicles. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The secondary battery with low expansion rate is prepared by the embodiment 1 of the present application. DETAILED DESCRIPTION

[0022] The following non-limiting examples can provide a more complete understanding of the application to one of ordinary skill in the art, but are not intended in any way to limit the scope of the application. The following merely illustrates the scope of the application, and the application should be construed to cover any alterations and modifications of the application, and any applications falling within the scope of the application.

[0023] When numerical ranges are given, understand that the range is inclusive of the two endpoints and any number in between. Unless otherwise defined, all technical and scientific terms used in the application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0024] The application is further described in the following specific examples. The various chemical reagents used in the examples are obtained from commercial sources unless otherwise stated.

[0025] Among the many battery technologies, lithium-ion batteries, as green and environmentally friendly energy storage devices, have been widely used in the electronic market and new energy vehicles due to their high energy density, long cycle life, safety and non-pollution, etc. These advantages have greatly improved the level of human production and life. However, the global reserves of lithium resources are limited, and the content of lithium element in the earth's crust is only 0.0065%. With the rapid increase in demand for batteries due to the development of new energy vehicles, the resource bottleneck gradually appears, and the high cost limits the large-scale application and sustainable development of lithium-ion batteries. Under this background, sodium-ion batteries, which have many advantages, show sustainability and economy, making them one of the focuses of research and development of new generation battery technologies. However, they have not yet been widely used, mainly due to low energy density, which is still not comparable to existing lithium-ion batteries. An anode-free sodium battery without negative active material can improve the energy density of the battery to the limit while reducing the production cost of the battery, and is an ideal high-energy-density system.

[0026] However, without the protection of a stable host material on the negative side, the deposition / stripping of sodium metal on the negative side can cause changes in the volume of the battery, leading to battery swelling, especially under long-term use or high-intensity conditions. The swelling of the battery not only affects the appearance, but also can cause damage to the internal components of the battery, leading to a decrease in cycle life, and even serious safety problems such as battery leakage / short circuit. The cycle life and safety of metal lithium batteries without a negative electrode face great challenges. In addition, for certain specific fields such as aerospace / medical devices, there are strict requirements for the size and weight of the battery, and the swelling problem of the battery is more prominent. Therefore, the research of low-swelling battery has become one of the hotspots in the field of battery technology. Low-swelling batteries not only improve the stability and safety of the battery, but also prolong the service life of the battery, reduce maintenance costs, and promote the popularization and development of electric vehicles / portable electronic devices and other products. However, to realize the commercial application of low-swelling batteries, many technical problems need to be solved, including challenges in material selection / structure design / production process / electrolyte optimization, etc.

[0027] To solve the above technical problems, the present application provides a low-swelling secondary battery, a preparation method and a battery pack. To solve the problem of volume swelling and short cycle life caused by the deposition / stripping of sodium metal on the surface of the negative current collector in the existing technology of the secondary sodium battery without a negative electrode, thereby maintaining high energy density while improving the service life and stability of the battery.

[0028] The low-expansion secondary battery in the embodiment of the application comprises a positive electrode end, a negative electrode end, and a separator, the negative electrode end comprises a porous current collector or a porous modification layer on the surface of the current collector; the separator is arranged between the positive electrode end and the negative electrode end, and the separator is used to store electrolyte. The pore volume of the porous current collector or the porous modification layer on the surface of the current collector is greater than the volume of the deposited sodium metal in the secondary battery, the positive electrode end and the negative electrode end each comprise at least one layer; the capacity provided by the negative electrode end is not greater than 20% of the capacity of the battery. The porous current collector comprises at least one of foamed nickel, foamed nickel alloy, foamed copper, foamed copper alloy, foamed aluminum, foamed aluminum alloy, foamed iron, foamed iron alloy, foamed zinc, foamed zinc alloy, copper mesh, copper alloy mesh, copper foil, aluminum mesh, aluminum alloy mesh, titanium mesh, titanium alloy mesh, stainless steel mesh, nickel mesh, nickel alloy mesh, foamed carbon, carbon aerogel, carbon cloth, carbon paper, and carbon felt. Further, the porous modification layer on the surface of the current collector comprises at least one of a metal, an alloy of the metal, and a halide, a sulfide, an oxide, a nitride, a selenide, and a hydride of the metal, and one or more of a carbon material; the metal comprises one or more of Mg, Zn, Bi, Sn, Ge, Si, Pb, Sb, In, Ca, Ni, Ga, and Ti. The preferred porous modification layer on the surface of the current collector is a carbon material, and the carbon material can be ordered mesoporous carbon CMK-3. The surface loading of the porous modification layer on the surface of the current collector is 0.05-2.0 mg / cm 2 The porous modification layer is loaded on the surface of the current collector by means of scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing.

[0029] The following further illustrates the embodiment in detail.

[0030] Embodiment 1

[0031] The embodiment provides a preparation method of a low-expansion secondary sodium battery, comprising the following steps:

[0032] Preparation of the positive electrode end

[0033] The positive electrode end was prepared as follows. The positive electrode active material (sodium iron pyrophosphate in this example), conductive agent Super P, and binder polyvinylidene difluoride (PVDF) were weighed according to the mass ratio of 90:5:5 (e.g., 90 g of sodium iron pyrophosphate, 5 g of Super P, and 5 g of PVDF), and then added to a 2 L stirring tank for mechanical mixing. Subsequently, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75%. After stirring for 2 hours, the slurry was uniformly coated on one surface of an aluminum foil positive electrode current collector with a thickness of 12 μm, and then dried at 100°C to obtain a positive electrode end with a single-side coated positive electrode slurry. The surface loading of sodium iron pyrophosphate on the surface of the electrode sheet was 20.0 mg / cm 2 The thickness of the dry film of the positive electrode end was measured to be 150 μm. The above steps were then repeated on the other surface of the positive electrode end to obtain a positive electrode end with a double-side coated positive electrode slurry (sodium iron pyrophosphate). The positive electrode end was cold-pressed and then cut into a 56 mm x 43 mm size for use.

[0034] Preparation of the negative electrode end (preparation of the porous modification layer on the surface of the current collector)

[0035] The ordered mesoporous carbon CMK-3 and sodium polyacrylate (NaPAA) were weighed according to the mass ratio of 90:10 (e.g., 90 g of ordered mesoporous carbon CMK-3 and 10 g of NaPAA), and then added to a 2 L stirring tank for mechanical mixing. Deionized water was added as a solvent to prepare a slurry with a solid content of 45%. After stirring for 2 hours, the slurry was uniformly coated on one surface of a stainless steel foil with a thickness of 12 μm, and then dried at 80°C to obtain an electrode sheet with a single-side coated ordered mesoporous carbon CMK-3 slurry. The surface loading of ordered mesoporous carbon CMK-3 (porous modification layer on the surface of the current collector) was 0.15 mg / cm 2 . The above steps were then repeated on the other surface of the electrode sheet to obtain an electrode sheet with a double-side coated ordered mesoporous carbon CMK-3 slurry. After coating, the electrode sheet was cut into a 58 mm x 45 mm size for use. Unlike the positive electrode sheet, the electrode sheet with the porous modification layer was not subjected to a rolling operation, and the pore volume was measured to be 0.5 mL / g.

[0036] Preparation of the electrolyte

[0037] In a glove box under dry argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm), organic solvents ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether after water removal by molecular sieves were mixed in a volume ratio of 1:1:2, then a certain amount of sodium triflate was dissolved and mixed uniformly in the mixed organic solvent to obtain an electrolyte with a sodium salt concentration of 1 mol / L.

[0038] Separator

[0039] A polypropylene (PP) film (provided by Celgard) with a thickness of 15 μm was used. The packaging material was a 113 μm aluminum-plastic composite film.

[0040] Preparation of secondary battery

[0041] The above-prepared positive electrode end, separator, and negative electrode end (current collector surface porous modification layer) were sequentially stacked in order with the separator between the positive electrode end and the negative electrode end to play a separating role. After 10 layers of positive and negative electrodes were stacked, an electrode assembly was obtained. The electrode assembly was loaded into an aluminum-plastic composite film, and water was removed at 80°C. The prepared electrolyte was injected, and vacuum packaging, standing, formation, shaping, and other processes were performed to obtain a soft-packaged secondary battery, as shown in Figure 1 .

[0042] Example 2

[0043] In this example, the positive electrode end, electrolyte, separator, and secondary battery were prepared as in Example 1, and the difference from Example 1 was that the negative electrode end (current collector surface porous modification layer) was prepared as follows:

[0044] Ordered mesoporous carbon CMK-3, aluminum fluoride (AlF3), and sodium polyacrylate (NaPAA) were weighed in a mass ratio of 90:6:4.0 (e.g., 90 g of ordered mesoporous carbon CMK-3, 6.0 g of aluminum fluoride, and 4.0 g of NaPAA), added to a 2 L stirring tank, and mechanically mixed. Deionized water was added as a solvent to prepare a slurry with a solid content of 40%, and the slurry was stirred for 2 hours to make it uniformly dispersed. The stirred modification layer slurry was uniformly coated on one surface of a stainless steel foil with a thickness of 12 μm, and dried at 80°C to obtain a single-sided coated porous modification layer electrode tab with a surface ordered mesoporous carbon CMK-3 and aluminum fluoride composite coating (current collector surface porous modification layer) with a surface loading of 0.2 mg / cm 2 . Then, the above steps were repeated on the other surface of the electrode tab to obtain a double-sided coated porous composite modification layer slurry electrode tab. After coating, the electrode tab was cut into a 58 mm x 45 mm specification for use. Unlike the positive electrode tab, the modification layer-containing electrode tab was not subjected to a rolling operation, and the pore volume was measured to be 0.45 mL / g.

[0045] Example 3

[0046] In this embodiment, the positive electrode, electrolyte, separator and preparation of the secondary battery are the same as in Example 1, except that the negative electrode (porous modification layer on the surface of the current collector) is prepared differently from Example 1:

[0047] The ordered mesoporous carbon CMK-3 and sodium polyacrylate (NaPAA) are weighed according to a mass ratio of 90:10 (for example, 90 g of ordered mesoporous carbon CMK-3 and 10 g of NaPAA), and then added to a 2 L stirring tank for mechanical mixing. Deionized water is added as a solvent to prepare a slurry with a solid content of 40%, and stirring is performed for 2 hours to ensure uniform dispersion. The stirred slurry is uniformly coated on one surface of a stainless steel foil with a thickness of 12 μm, and then dried at 80°C to obtain a pole piece coated with ordered mesoporous carbon CMK-3 slurry on one side, with a surface loading of ordered mesoporous carbon CMK-3 (porous modification layer on the surface of the current collector) of 0.05 mg / cm 2 . Then, the above steps are repeated on the other surface of the pole piece to obtain a pole piece coated with ordered mesoporous carbon CMK-3 slurry on both sides. After completion of the coating, the pole piece is cut into a size of 58 mm x 45 mm for use. Unlike the positive pole piece, the pole piece containing the modification layer is not subjected to a rolling operation, and the pore volume is measured to be 0.1 mL / g.

[0048] Example 4

[0049] In this embodiment, the positive electrode, electrolyte, separator and preparation of the secondary battery are the same as in Example 1, except that the negative electrode (porous modification layer on the surface of the current collector) is prepared differently from Example 1:

[0050] The ordered mesoporous carbon CMK-3 and sodium polyacrylate (NaPAA) are weighed according to a mass ratio of 90:10 (for example, 90 g of ordered mesoporous carbon CMK-3 and 10 g of NaPAA), and then added to a 2 L stirring tank for mechanical mixing. Deionized water is added as a solvent to prepare a slurry with a solid content of 40%, and stirring is performed for 2 hours to ensure uniform dispersion. The stirred slurry is uniformly coated on one surface of a stainless steel foil with a thickness of 12 μm, and then dried at 80°C to obtain a pole piece coated with ordered mesoporous carbon CMK-3 slurry on one side, with a surface loading of ordered mesoporous carbon CMK-3 (porous modification layer on the surface of the current collector) of 0.05 mg / cm 2 . Then, the above steps are repeated on the other surface of the pole piece to obtain a pole piece coated with ordered mesoporous carbon CMK-3 slurry on both sides. After completion of the coating, the pole piece is cut into a size of 58 mm x 45 mm for use. Unlike the positive pole piece, the pole piece containing the modification layer is not subjected to a rolling operation, and the pore volume is measured to be 0.1 mL / g.

[0051] Example 5

[0052] In this embodiment, the preparation of the positive electrode, electrolyte, separator and secondary battery is the same as in Example 1, except that the preparation of the negative electrode (porous current collector) is different from that in Example 1:

[0053] A 12-μm copper foil was placed in a 0.5-mol / L FeCl3solution, removed after etching for 10 min, rinsed with deionized water and ethanol three times in turn, and dried and cut into a 58-mm x 45-mm size for use. The pore volume of the Cu foil after etching was measured to be 0.1 mL / g.

[0054] Example 6

[0055] In this embodiment, the preparation of the positive electrode, electrolyte, separator and secondary battery is the same as in Example 1, except that the preparation of the negative electrode (porous current collector) is different from that in Example 1:

[0056] A 12-μm copper foil was placed in a 0.5-mol / L ZnCl2solution, removed after etching for 10 min, rinsed with deionized water and ethanol three times in turn, and dried and cut into a 58-mm x 45-mm size for use. The pore volume of the Cu foil after etching was measured to be 0.1 mL / g.

[0057] Example 7

[0058] In this embodiment, the preparation of the positive electrode, electrolyte, separator and secondary battery is the same as in Example 1, except that the preparation of the negative electrode (porous modification layer on the surface of the current collector) is different from that in Example 1:

[0059] Ordered mesoporous carbon CMK-3 and sodium polyacrylate (NaPAA) were weighed according to a mass ratio of 94.0:4.7, and then added to a 2-L stirring tank for mechanical mixing. Deionized water was added as a solvent, and a slurry with a solid content of 43% was prepared. The slurry was stirred for 2 hours to make it uniformly dispersed. The stirred slurry was uniformly coated on one surface of a 12-μm-thick stainless steel foil, and dried at 80°C to obtain a pole piece coated with ordered mesoporous carbon CMK-3 slurry on one surface. The surface loading of ordered mesoporous carbon CMK-3 (porous modification layer on the surface of the current collector) was 0.3 mg / cm 2 . Then, the above steps were repeated on the other surface of the pole piece to obtain a pole piece coated with porous modification layer slurry on both surfaces. After coating, the pole piece was cut into a 58-mm x 45-mm size for use. Unlike the positive pole piece, the pole piece containing the porous layer was not subjected to a rolling operation, and the pore volume was measured to be 1.3 mL / g.

[0060] Example 8

[0061] In this example, the positive electrode, electrolyte, separator and preparation of the secondary battery are the same as in Example 1, except that the negative electrode (porous modification layer on the surface of the current collector) is prepared as follows:

[0062] The ordered mesoporous carbon CMK-3 and sodium polyacrylate (NaPAA) were weighed according to a mass ratio of 95:5 (e.g. 95 g of ordered mesoporous carbon CMK-3 and 3.8 g of NaPAA), and then added to a 2 L stirring tank for mechanical mixing. Deionized water was added as a solvent to prepare a slurry with a solid content of 43%, and the slurry was stirred for 2 hours to ensure uniform dispersion. The stirred slurry was uniformly coated on one surface of a stainless steel foil with a thickness of 12 μm, and then dried at 80°C to obtain a pole piece coated with ordered mesoporous carbon CMK-3 slurry on one side, with a surface loading of ordered mesoporous carbon CMK-3 (porous modification layer on the surface of the current collector) of 2 mg / cm 2 . Then, the above steps were repeated on the other surface of the pole piece to obtain a pole piece coated with porous modification layer slurry on both sides. After completion of the coating, the pole piece was cut into a size of 58 mm x 45 mm for use. Unlike the positive pole piece, the pole piece containing the porous layer was not subjected to a rolling operation, and the pore volume was measured to be 1.2 mL / g.

[0063] Comparative Example 1

[0064] In this example, the positive electrode, electrolyte, separator and preparation of the secondary battery are the same as in Example 1, except that the negative electrode is prepared as follows:

[0065] The stainless steel current collector was directly cut into a size of 58 mm x 45 mm for use.

[0066] Comparative Example 2

[0067] In this example, the positive electrode, electrolyte, separator and preparation of the secondary battery are the same as in Example 1, except that the negative electrode is prepared as follows:

[0068] Aluminum fluoride and sodium polyacrylate were weighed according to a mass ratio of 96:4 (e.g. 96 g of aluminum fluoride and 4.0 g of NaPAA), and then added to a 2 L stirring tank for mechanical mixing. Deionized water was added as a solvent to prepare a slurry with a solid content of 35%, and the slurry was stirred for 2 hours to ensure uniform dispersion. The stirred slurry was uniformly coated on one surface of a stainless steel foil with a thickness of 12 μm, and then dried at 80°C to obtain a pole piece coated with aluminum fluoride on one side, with a surface loading of the aluminum fluoride coating layer of 0.15 mg / cm 2 . Then, the above steps were repeated on the other surface of the pole piece to obtain a pole piece coated on both sides. After completion of the coating, the pole piece was cut into a size of 58 mm x 45 mm for use. Unlike the positive pole piece, the pole piece containing the porous layer was not subjected to a rolling operation, and the pore volume was measured to be 0.1 mL / g.

[0069] Comparative Example 3

[0070] In this example, the positive electrode, electrolyte, and separator, and the preparation of the secondary battery are the same as in Example 1, except that the negative electrode is prepared as follows:

[0071] A 30% sodium polyacrylate solution was stirred for 2 hours to disperse uniformly. The stirred slurry was uniformly coated on one surface of a stainless steel foil having a thickness of 12 μm, and dried at 80°C to obtain an electrode sheet having a single adhesive layer on one surface, with a surface loading of 0.3 mg / cm 2 . Thereafter, the above procedure was repeated on the other surface of the electrode sheet to obtain an electrode sheet having a double adhesive layer. After completion of the coating, the electrode sheet was cut into a size of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the electrode sheet having the adhesive layer was not subjected to a rolling operation, and the pore volume was measured to be 0.06 mL / g.

[0072] In the case where the capacity provided by the negative electrode is not higher than 20% of the capacity of the battery, the initial efficiency, the expansion rate, the energy density, and the cycle number of the examples and comparative examples are shown in Table 1, where SS indicates a stainless steel current collector.

[0073] Table 1

[0074]

[0075] As can be seen from Example 1, Example 2, and Comparative Examples 1-3, the expansion rate, the energy density, and the cycle life of the electrochemical device are related to the modification layer, CMK-3 having a rich pore structure can provide the space required for sodium deposition, inhibit the volume change of the negative electrode during sodium metal deposition during charging, maintain the stability of the internal structure of the battery, and improve the cycle life of the battery; sodium-philic AIF3 can reduce the overpotential of sodium deposition, but when used alone, the volume change of the zinc-sodium alloy results in a large expansion of the negative electrode. Therefore, the two need to be used in combination, so that the energy density of the sodium battery is above 200 Wh / kg, the expansion rate is less than 2.2%, and the cycle life is 10,000 times.

[0076] As can be seen from Example 1, Example 3, and Example 4, the expansion rate, the energy density, and the cycle life of the electrochemical device are related to the pore volume of the modification layer, the pore volume of the modification layer is too small, which is not sufficient to provide the space required for sodium deposition, the expansion rate of the battery is high, and the cycle life is shortened; the pore volume of the modification layer is too large, which increases the contact area with the electrolyte, increases the formation of the solid electrolyte interphase (SEI), and reduces the initial coulombic efficiency. Therefore, the pore volume of the modification layer needs to be optimized. For the modification layer containing CMK-3, the pore volume is preferably around 0.5 mL / g.

[0077] Through electrode structure design and optimization, the mass energy density of the secondary sodium battery cell formed can reach 200 Wh / kg, the battery expansion rate is only 2% at 100% SOC (when the battery is fully charged), no additional customization of the battery assembly suitable for the anode-free sodium battery is needed, and the cycle life reaches 1000 h.

[0078] Finally, it should be noted that the above is only used to illustrate the technical solutions of the present application, and is not a limitation on the scope of protection of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

[0079] The above is only the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement and improvement 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 with low swelling, characterized by comprising: The secondary battery comprises a positive electrode terminal, a negative electrode terminal and a separator, the negative electrode terminal comprises a porous current collector or a porous modification layer on the surface of the current collector; the separator is arranged between the positive electrode terminal and the negative electrode terminal, and the separator is used to store electrolyte.

2. The low expansion rate secondary battery according to claim 1, characterized by, The pore volume of the porous current collector or the porous modification layer on the surface of the current collector is greater than the volume of the deposited sodium metal in the secondary battery, and the positive electrode terminal and the negative electrode terminal each comprises at least one layer; the capacity provided by the negative electrode terminal is not greater than 20% of the capacity of the battery.

3. The low-expansion secondary battery according to claim 1, characterized by The porous current collector comprises at least one of foamed nickel, foamed nickel alloy, foamed copper, foamed copper alloy, foamed aluminum, foamed aluminum alloy, foamed iron, foamed iron alloy, foamed zinc, foamed zinc alloy, copper mesh, copper foil, copper alloy mesh, aluminum mesh, aluminum alloy mesh, titanium mesh, titanium alloy mesh, stainless steel mesh, nickel mesh, nickel alloy mesh, foamed carbon, carbon aerogel, carbon cloth, carbon paper and carbon felt.

4. The low expansion secondary battery of claim 1, wherein The porous modification layer on the surface of the current collector comprises at least one of a metal, an alloy of the metal and a halide, a sulfide, an oxide, a nitride, a selenide and a hydride of the metal and one or more of a carbon material; The metal comprises one or more of Mg, Zn, Bi, Sn, Ge, Si, Pb, Sb, In, Ca, Ni, Ga and Ti.

5. The low-expansion secondary battery according to claim 1, characterized by The current collector surface porous modification layer face load is: 0.05-2.0 mg / cm 2 .

6. The low-expansion secondary battery according to claim 1, characterized by The porous modification layer on the surface of the current collector is loaded on the surface of the current collector by scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation or 3D printing.

7. A method of producing a low-expansion secondary battery as claimed in any one of claims 1 to 6, characterized by, The method comprises: After mixing and stirring the positive electrode active material, the conductive agent and the binder according to a first preset mass ratio, a solvent is added to prepare a positive electrode slurry with uniform distribution; the positive electrode slurry is uniformly coated on two surfaces of the positive electrode current collector aluminum foil, dried at a first preset temperature, and then cold-pressed to obtain a positive electrode terminal coated with the positive electrode slurry on both surfaces; After mixing and stirring the negative electrode material according to a second preset mass ratio, a solvent is added to prepare a negative electrode slurry; the negative electrode slurry is uniformly coated on two surfaces of the negative electrode current collector aluminum foil, dried at a second preset temperature, and then cold-pressed to obtain a negative electrode terminal coated with the negative electrode slurry on both surfaces; The positive electrode terminal, the separator and the negative electrode terminal are sequentially stacked in order with the separator between the positive electrode terminal and the negative electrode terminal, and the positive electrode terminal and the negative electrode terminal are respectively stacked to obtain an electrode assembly; the electrode assembly is loaded into a housing assembly, and water is removed, the prepared electrolyte is injected, and the secondary battery is processed.

8. A battery pack, characterized by, The secondary battery comprises any one of the secondary batteries in claims 1 to 7.

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