Sodium ion battery cell, secondary battery, and electric device

Abstract

The invention provides a sodium ion battery monomer, a secondary battery and a power utilization device. The sodium ion battery monomer comprises an electrode assembly and a shell, the shell is cylindrical, a containing cavity is formed in the shell, and the electrode assembly is located in the containing cavity; the electrode assembly comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the density of the negative electrode current collector is smaller than or equal to 5.0 g / cm < 3 >, the group margin of the sodium ion battery monomer meets the condition that the group margin is larger than or equal to 0.95 and smaller than 1, and the group margin is the ratio of the diameter of the electrode assembly to the diameter of the containing cavity. According to the present invention, the sodium ion battery monomer adopts the negative electrode current collector with the low density, is matched with the large group margin, and adopts the cylindrical structure, such that the battery monomer can give consideration to the high mass energy density, the high volume energy density and the good cycle performance so as to easily promote the development of the miniaturization and the light weight of the battery monomer.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a sodium ion battery cell, a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Sodium-ion batteries have good cost advantages, which are conducive to broadening the scope of use of sodium-ion batteries. However, it is difficult to effectively balance the mass energy density and volume energy density of sodium-ion batteries, which restricts the development of miniaturization and lightweight of sodium-ion batteries. Summary of the invention

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a sodium ion battery cell, comprising an electrode assembly and a shell, wherein the shell is cylindrical, and the shell has a receiving cavity inside, and the electrode assembly is located inside the receiving cavity; the electrode assembly comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, and the density of the negative electrode current collector is ≤5.0g / cm 3 , the group margin of the sodium ion battery cell satisfies: 0.95≤group margin<1, wherein the group margin is the ratio of the diameter of the electrode assembly to the diameter of the accommodating cavity.

[0005] The sodium ion battery cell adopts a negative electrode current collector with a lower density, a larger group margin, and a cylindrical structure, so that the battery cell has a higher mass energy density and volume energy density while taking into account better cycle performance.

[0006] In some embodiments, the density of the negative electrode current collector is 1.3 g / cm 3 ~3.5g / cm 3 The density of the negative electrode current collector within this range can further reduce the weight of the negative electrode current collector, thereby further improving the mass energy density of the battery cell.

[0007] In some embodiments, the group margin of the sodium ion battery monomer is 0.95 to 0.97. Within this range, the group margin of the sodium ion battery monomer can take into account both higher energy density and better cycle performance.

[0008] In some embodiments, the elongation of the negative electrode current collector is ≥ 3%. The negative electrode current collector has a large elongation, which can have better pressure resistance when preparing the negative electrode pole piece, can reduce the risk of the negative electrode pole piece breaking during the cold pressing process, and is conducive to promoting the improvement of the compaction density of the negative electrode active layer. Optionally, the elongation of the negative electrode current collector is 3.5% to 5.0%.

[0009] In some embodiments, the ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer is ≤ 0.2. In this case, the thickness of the negative electrode active layer can be further increased, which is conducive to further improving the mass energy density and volume energy density of the battery cell. Optionally, the ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer is 0.03 to 0.15.

[0010] In some embodiments, the thickness of the negative electrode current collector is 6 μm to 12 μm. The thickness of the negative electrode current collector within this range can make the negative electrode current collector play its own role, make the negative electrode plate have a more appropriate thickness, and thus make the battery cell have a suitable volume energy density. Optionally, the thickness of the negative electrode current collector is 6.5 μm to 10 μm.

[0011] In some embodiments, the negative electrode current collector includes aluminum foil or a metal / polymer composite current collector.

[0012] In some embodiments, the metal / polymer composite current collector comprises a polymer substrate layer and a metal layer located on at least one surface of the polymer substrate layer. Optionally, the polymer substrate layer comprises at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene and polyethylene. Optionally, the metal layer comprises at least one of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0013] In some embodiments, the sodium ion battery cell further comprises an electrolyte, and the electrolyte is located inside the accommodating cavity; the sodium ion battery cell satisfies: m / C0≤6g / Ah, wherein m represents the mass of the electrolyte, in g, and C0 represents the rated capacity of the sodium ion battery cell, in Ah. m / C0 within this range can enable the battery cell to have a larger group margin while maintaining good electrical performance, which is conducive to further improving the volume energy density of the battery cell. Optionally, 4g / Ah≤m / C0≤5g / Ah.

[0014] In some embodiments, the compaction density of the negative electrode active layer is 0.7 g / cm 3 ~1.3g / cm 3The compaction density of the negative electrode active layer within this range can make the battery monomer have a higher energy density. Optionally, the compaction density of the negative electrode active layer is 0.8 g / cm 3 ~1.2g / cm 3 .

[0015] In some embodiments, a ratio of the height of the battery cell to the diameter of the battery cell is greater than or equal to 3.5, and can be optionally 4-6.

[0016] In some embodiments, the height of the battery cell is greater than or equal to 60 mm, and can be optionally 70 mm to 300 mm.

[0017] In some embodiments, the diameter of the battery cell is greater than or equal to 21 mm, and can be 30 mm to 60 mm.

[0018] A second aspect of the present application provides a secondary battery, comprising the sodium ion battery cell.

[0019] A third aspect of the present application provides an electrical device comprising at least one of the sodium ion battery cell and the secondary battery. DETAILED DESCRIPTION

[0020] For ease of understanding of the present application, the present application will be described more fully below with reference to the relevant embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0022] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0023] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0024] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0025] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0026] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0027] In this application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A includes not only a1, a2 and a3, but also other members".

[0028] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0029] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0030] An embodiment of the present application provides a sodium ion battery cell. The sodium ion battery cell comprises an electrode assembly and a shell, the shell is cylindrical, the shell has a receiving cavity inside, and the electrode assembly is located inside the receiving cavity; the electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, and the density of the negative electrode current collector is ≤5.0g / cm 3 , the group margin of the sodium ion battery cell satisfies: 0.95≤group margin<1, wherein the group margin is the ratio of the diameter of the electrode assembly to the diameter of the accommodating cavity.

[0031] The sodium ion battery monomer in this embodiment can effectively improve the mass energy density of the battery by adopting a negative electrode current collector with a lower density. However, the thickness of the current collector with a lower density in the prior art is usually designed to be thicker, which has a certain impact on the volume energy density of the battery. In order to improve the volume energy density, the group margin of the battery can be increased, but after the group margin is increased, the battery cell may be subjected to excessive stress locally during the expansion process, which affects the cycle performance of the battery. If a cylindrical structure is adopted, the stress on the battery cell inside the battery is more balanced, which can effectively alleviate this problem. Furthermore, by adopting the specific battery structure, the mutual cooperation of the negative electrode current collector and the group margin in this embodiment, the battery can have better cycle performance while taking into account higher mass energy density and volume energy density.

[0032] It is understandable that in a sodium ion battery cell, the accommodating cavity can be represented as a cavity formed by the shell. It is also understandable that the sodium ion battery cell further includes a cover plate, which cooperates with the shell to seal the accommodating cavity.

[0033] In some embodiments, the density of the negative electrode current collector is 1.3 g / cm 3 ~3.5g / cm 3 The density of the negative electrode current collector within this range can further reduce the weight of the negative electrode current collector, thereby further improving the mass energy density of the battery cell. Optionally, the density of the negative electrode current collector can be 1.3 g / cm 3 , 1.5g / cm 3 , 1.8g / cm 3 , 2g / cm 3 , 2.3g / cm 3 , 2.5g / cm 3 , 2.8g / cm 3 , 3g / cm 3 、3.2g / cm 3 , 3.5g / cm 3 wait.

[0034] In some embodiments, the group margin of the sodium ion battery cell is 0.95 to 0.97. The group margin of the sodium ion battery cell within this range can improve the space utilization of the accommodation cavity and further improve the volume energy density of the battery cell. Optionally, the group margin of the sodium ion battery can be 0.955, 0.96, 0.965, 0.97, etc.

[0035] In some embodiments, the elongation of the negative electrode current collector is ≥ 3%. The negative electrode current collector has a large elongation, which can have better pressure resistance when preparing the negative electrode pole piece, can reduce the risk of the negative electrode pole piece breaking during the cold pressing process, and is conducive to further improving the energy density and cycle performance. Optionally, the elongation of the negative electrode current collector is 3.5% to 5.0%. For example, the elongation of the negative electrode current collector can be 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0036] The elongation of the negative electrode current collector can be tested by the following method: record the initial length H1 of the negative electrode current collector. Use a high-speed rail tensile test machine to perform a tensile test, apply tension to both ends of the length direction of the negative electrode current collector, and the stretching speed is 2mm / min. The two ends of the stretching machine need to be tightly attached with wrinkle glue to prevent the negative electrode current collector from loosening and falling off during stretching. The negative electrode current collector should remain vertical and straight during stretching. The negative electrode current collector must break somewhere in the middle, and the data of breaks at both ends of the fixture are discarded. Until the negative electrode current collector breaks, record the length H2 of the negative electrode current collector at the time of break. Calculate the elongation δ of the negative electrode current collector, elongation δ = (H2-H1) / H1×100%. Optionally, H1 is 50mm.

[0037] In some embodiments, the ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer is ≤0.2. This can further increase the thickness of the negative electrode active layer, which is conducive to further improving the mass energy density and volume energy density of the battery cell. Optionally, the ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer is 0.03 to 0.15. For example, the ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, etc.

[0038] In some embodiments, the negative electrode current collector comprises aluminum foil or a metal / polymer composite current collector, and the metal / polymer composite current collector comprises a polymer substrate layer and a metal layer located on at least one surface of the polymer substrate layer. Optionally, the polymer substrate layer comprises one or more substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. Optionally, the metal layer comprises at least one of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0039] In some embodiments, the polymer substrate layer of the metal / polymer composite current collector includes polypropylene, and the metal layer includes at least one of copper or a copper alloy.

[0040] In some embodiments, the polymer substrate layer of the metal / polymer composite current collector includes at least one of polyethylene terephthalate and polybutylene terephthalate, and the metal layer includes at least one of aluminum or an aluminum alloy.

[0041] The density of the composite current collector can be adjusted by adjusting the type or ratio of the polymer and the metal. Optionally, when the metal layer includes copper or a copper alloy, the density of the composite current collector can be between 1.0 g / cm 3 -8.9g / cm 3 When the metal layer includes aluminum or an aluminum alloy, the density of the composite current collector can be adjusted within a range of 1.4 g / cm 3 -2.7g / cm 3 within the range of adjustment.

[0042] Optionally, as some examples of the thickness of the negative electrode current collector, the thickness of the negative electrode current collector is 6μm to 12μm. The thickness of the negative electrode current collector within this range can make the negative electrode current collector play its own role, so that the negative electrode pole piece has a more appropriate thickness, and thus the battery cell has a suitable volume energy density. Optionally, the thickness of the negative electrode current collector can be 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, etc. Further optionally, the thickness of the negative electrode current collector is 6.5μm to 10μm.

[0043] It is understandable that the sodium ion battery cell also includes an electrolyte, which is located inside the receiving cavity. Optionally, the electrolyte may be an electrolyte solution.

[0044] In some embodiments, the sodium ion battery cell satisfies: m / C0≤6g / Ah, where m represents the mass of the electrolyte, and C0 represents the rated capacity of the sodium ion battery cell, in Ah. m / C0 within this range can enable the battery cell to have a larger group margin while maintaining good electrical performance, which is conducive to further improving the volume energy density of the battery cell. Optionally, 4g / Ah≤m / C0≤5g / Ah. Further optionally, m / C0 can be 3g / Ah, 3.5g / Ah, 4g / Ah, 4.5g / Ah, 5g / Ah, 5.5g / Ah, 6g / Ah, etc. It can be understood that C0 can be measured by the following method: discharge the battery cell to 1.5V at 0.33C and leave it for 10min; then charge it to 3.9V at 0.33C and leave it for 10min; then discharge it to 1.5V at 0.33C, and record the discharge capacity at this time as the rated capacity.

[0045] It can also be understood that the mass m of the electrolyte in the battery cell can be measured by the following method: take a battery cell sample, weigh the initial mass m1 of the battery cell, disassemble the battery cell, wash the shell and electrode assembly with dimethyl carbonate for more than three times, dry the shell and electrode assembly after washing, and weigh the mass m2 of the shell and the mass m3 of the electrode assembly respectively. The mass m of the electrolyte = m1-m2-m3.

[0046] In some embodiments, the compaction density of the negative electrode active layer is 0.7 g / cm 3 ~1.3g / cm 3 The compaction density of the negative electrode active layer within this range can make the battery cell have a higher energy density. Optionally, it is 0.8 g / cm 3 ~1.2g / cm 3 Alternatively, the compaction density of the negative electrode active layer may be 0.8 g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 wait.

[0047] In some embodiments, the ratio of the height of the battery cell to the diameter of the battery cell is greater than or equal to 3.5. Optionally, the ratio of the height of the battery cell to the diameter of the battery cell is 4 to 6. Further optionally, the ratio of the height of the battery cell to the diameter of the battery cell can be 3.5, 4, 4.5, 5, 5.5, 6, etc.

[0048] Optionally, the height of the battery cell is greater than or equal to 60 mm. Further optionally, the height of the battery cell is 70 mm to 300 mm. For example, the height of the battery cell can be 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 90 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, etc.

[0049] Optionally, the diameter of the battery cell is greater than or equal to 21 mm. Further optionally, the diameter of the battery cell is 30 mm-60 mm. For example, the diameter of the battery cell can be 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, etc.

[0050] The electrode assembly further comprises a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector. The positive electrode active layer comprises a positive electrode active material.

[0051] Optionally, the positive electrode active material includes at least one of a sodium-containing transition metal oxide, a Prussian blue material, and a polyanion material.

[0052] Further optionally, the sodium-containing transition metal oxide comprises a chemical formula of Na x Cu y Fe z Mn a M 1-y-z-a O2 material, sodium iron composite oxide, sodium cobalt composite oxide, sodium chromium composite oxide, sodium manganese composite oxide, sodium nickel composite oxide, sodium nickel titanium composite oxide, sodium nickel manganese composite oxide, sodium iron manganese composite oxide, sodium nickel iron manganese composite oxide and sodium nickel cobalt manganese composite oxide. Among them, Na x Cu y Fe z Mn a M 1-y-z-a In O2, M includes at least one of Li, Ni, Mg, Zn, Co, Al, Zr and Ti, 0<x≤1, 0<y≤0.5, 0<z≤0.5, 0<a≤0.5. It can be understood that the values ​​of x, y, z and a satisfy the charge balance of the chemical formula.

[0053] Further optionally, the Prussian blue material comprises a chemical formula of A x M[M′(CN)6] y ·zH2O, where A is an alkali metal cation, an alkaline earth metal cation, Zn 2+ 、Al 3+ One or more of, M is a transition metal, M' is a transition metal, 0 <x≤2;0.8≤y<1;0<z≤20。

[0054] Further optionally, the polyanion material includes at least one of phosphate, fluorophosphate, pyrophosphate and sulfate. Further optionally, the polyanion material includes at least one of sodium iron phosphate, sodium manganese phosphate and sodium cobalt phosphate. Further optionally, the polyanion material includes NaFePO4, Na3V2(PO4)3, NaM"PO4F and Na3(VO c )2(PO4)2F 3-2c At least one of. Wherein, M" includes at least one of V, Fe, Mn and Ni, and 0≤c≤1.

[0055] In some embodiments, the compaction density of the positive electrode active layer is 2 g / cm 3 ~3.3g / cm 3 Optionally, the compaction density of the positive electrode active layer can be 2 g / cm 3 , 2.1g / cm 3, 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3 、3.1g / cm 3 、3.2g / cm 3 Optionally, the compaction density of the positive electrode active layer is 2.5 g / cm 3 ~3g / cm 3 .

[0056] Another embodiment of the present application provides a secondary battery, which includes any of the above-mentioned sodium ion battery cells.

[0057] Another embodiment of the present application provides an electric device, which includes at least one of the above-mentioned sodium ion battery monomer or the above-mentioned secondary battery.

[0058] The secondary battery and the electric device of the present application are described below.

[0059] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0060] Positive electrode

[0061] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material.

[0062] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0063] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector may be obtained by forming a metal material on a polymer substrate layer. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer substrate layer may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0064] In some embodiments, the positive electrode active material may adopt a positive electrode active material for sodium ion batteries known in the art. As an example, the positive electrode active material may be used alone or in combination of two or more. Among them, the positive electrode active material may be selected from sodium iron composite oxide, sodium cobalt composite oxide, sodium chromium composite oxide, sodium manganese composite oxide, sodium nickel composite oxide, sodium nickel titanium composite oxide, sodium nickel manganese composite oxide, sodium iron manganese composite oxide, sodium nickel iron manganese composite oxide, sodium nickel cobalt manganese composite oxide, sodium iron phosphate compound, sodium manganese phosphate compound, sodium cobalt phosphate compound, Prussian blue material, polyanion material, etc., but the present application is not limited to these materials, and the present application may also use other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries. Optionally, sodium iron composite oxide includes NaFeO2. Sodium cobalt composite oxide includes NaCoO2. Sodium chromium composite oxide includes NaCrO2. Sodium manganese composite oxide includes NaMnO2. Sodium nickel composite oxide includes NaNiO2. Sodium nickel titanium composite oxide includes NaNi 1 / 2 Ti 1 / 2 O2. Sodium nickel manganese composite oxides include NaNi 1 / 2Mn 1 / 2 O2. Sodium iron manganese composite oxide includes Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2. Sodium nickel cobalt manganese composite oxides include NaNi 1 / 3 Co 1 / 3Mn 1 / 3 O2. Sodium iron phosphate includes NaFePO4. Sodium manganese phosphate includes NaMnPO4. Sodium cobalt phosphate includes NaCoPO4. The polyanion material includes at least one of phosphate, fluorophosphate, pyrophosphate and sulfate.

[0065] In some of these embodiments, the positive electrode active layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0066] In some embodiments, the positive electrode active layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0067] In some of the embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector.

[0068] Negative electrode

[0069] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material.

[0070] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0071] The negative electrode current collector may be the aforementioned metal foil or metal / polymer composite current collector.

[0072] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. In some embodiments, the negative electrode active material includes hard carbon.

[0073] In some embodiments, the negative electrode active layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0074] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some of the embodiments, the negative electrode active layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0076] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector.

[0077] Electrolytes

[0078] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0079] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0080] In some of the embodiments, the electrolyte salt may include one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorophosphate (NaPO2F2), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0081] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0082] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0083] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0084] Isolation film

[0085] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0086] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0087] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process.

[0088] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode plate, a separator, a negative electrode plate and an electrolyte. During the battery charging and discharging process, active ions are embedded and removed back and forth between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, which can insulate electrons and prevent internal short circuits, while allowing active ions to pass through and move between the positive and negative electrodes. The electrolyte plays the role of conducting active ions between the positive electrode plate and the negative electrode plate.

[0089] In some embodiments, the secondary battery may be a battery module or a battery pack.

[0090] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0091] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0092] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0093] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0094] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0095] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0096] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0097] As an example, the electric device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0098] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery cell may be used as a power source.

[0099] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail in conjunction with the embodiments below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0100] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0101] The preparation methods of the battery cells in the examples and comparative examples are as follows:

[0102] (1) Preparation of positive electrode sheet

[0103] The positive electrode active material NaNi 0.22 Cu 0.11 Fe 0.33 Mn 0.34 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 97:2:1 and added to a solvent N-methylpyrrolidone (NMP) to make a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector aluminum foil, dried and cold pressed, and then die-cut and striped to make a positive electrode sheet.

[0104] (2) Preparation of negative electrode sheet

[0105] The negative electrode active material hard carbon, the conductive agent acetylene black, the thickener sodium hydroxymethyl cellulose, and the binder styrene butadiene rubber are added to the solvent water in a mass ratio of 96:2:1:1 and mixed evenly to form a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode collector, dried and cold pressed, and then die-cut and slit to form a negative electrode sheet. The types of negative electrode collectors are detailed in Table 1.

[0106] (3) Preparation of electrolyte

[0107] Sodium hexafluorophosphate is dissolved in a mixed solvent of ethyl methyl carbonate (EMC) and propylene carbonate (PC) (the volume ratio of ethyl methyl carbonate to propylene carbonate is 58:42), and fluoroethylene carbonate (FEC) additive is added to obtain an electrolyte. The concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L, and the mass percentage of FEC is 5wt%.

[0108] (4) Isolation film

[0109] Polyethylene separator is used.

[0110] (5) Preparation of battery cells

[0111] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in a cylindrical shell, and after packaging, liquid injection, formation, exhaust and other processes, a sodium ion battery cell is obtained. The size of the battery cell is 32.6mm×130mm.

[0112] The diameter L1 of the electrode assembly in the battery cell of Example 1, the diameter L2 of the housing cavity of the shell, the group margin L1 / L2, the density of the negative electrode collector, etc. are detailed in Table 1.

[0113] The preparation methods of Examples 2 to 10 are similar to those of Example 1, and the differences are detailed in Table 1.

[0114] Comparative Example 1

[0115] The preparation method is similar to that of Example 1, except that in the preparation of the battery cell, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive and negative electrodes to play a role of isolation, and the electrode assembly is wound. The electrode assembly is placed in a square shell, and after packaging, liquid injection, formation, exhaust and other processes, a sodium ion battery cell is obtained. The size of the battery cell is 15mm×100mm×80mm.

[0116] The length L3 of the electrode assembly in the battery cell of Comparative Example 1, the length L4 of the housing cavity of the shell, the group margin L3 / L4, the density of the negative electrode current collector, etc. are detailed in Table 1.

[0117] The preparation methods of Comparative Examples 2 to 4 are similar to those of Comparative Example 1, and the differences are detailed in Table 1.

[0118] Test Case

[0119] (1) Volume energy density test of battery cells: Discharge the battery cells at 0.33C to a cut-off voltage of 1.5V, and leave it for 10 minutes; charge at 0.33C to a cut-off voltage of 3.9V, leave it for 10 minutes, and then discharge at 0.33C to a cut-off voltage of 1.5V. The discharge energy is the energy E of the battery cell. Measure the volume V of the battery cell shell. The volume energy density of the battery cell = E / V, in Wh / L. The test results are shown in Table 1.

[0120] (2) Test of mass energy density of battery cells: Discharge the battery cells at 0.33C to a cut-off voltage of 1.5V, and leave it for 10 minutes; charge at 0.33C to a cut-off voltage of 3.9V, leave it for 10 minutes, and then discharge at 0.33C to a cut-off voltage of 1.5V. The discharge energy is the energy E of the battery cells. Measure the mass M of the battery cells. The volume energy density of the battery cells = E / M, in units of Wh / kg. The test results are shown in Table 1.

[0121] (3) Battery cycle performance test: At 25°C, charge the battery at 0.33C to a cut-off voltage of 3.9V, leave it for 5 min, and discharge it at 0.33C to a cut-off voltage of 1.5V. Record the capacity C1 of this cycle. Repeat this cycle until C n / C1×100%=80%, record the cycle number n at this time. The test results are shown in Table 1.

[0122] Table 1

[0123]

[0124] In Table 1, L1 is the diameter of the electrode assembly in the battery cell, in mm. L2 is the diameter of the housing cavity of the shell, in mm. L3 is the length of the electrode assembly in the battery cell, in mm. L4 is the length of the housing cavity of the shell, in mm. L1 / L2 is the group margin of the cylindrical battery. L3 / L4 is the group margin of the square battery. The unit of the thickness of the negative electrode collector is μm. The unit of the density of the negative electrode collector is g / cm3. The unit of volume energy density is Wh / L. The unit of mass energy density is Wh / kg. The unit of the number of cycles is times.

[0125] It can be seen from the comparison of Examples 1 to 10 with Comparative Examples 1 to 4 that when the sodium ion battery cell adopts a negative electrode current collector with a lower density, a larger group margin, and a cylindrical shell, the battery cell has a higher volume energy density and mass energy density while taking into account better cycle performance.

[0126] It can be seen from Examples 1 to 5 that when the group margin of the battery cell is between 0.95 and 0.97, better cycle performance can be achieved.

[0127] It can be seen from the comparison between Example 6 and Example 1 that when the negative electrode current collector adopts a metal / polymer composite current collector, the battery cell has higher volume energy density, mass energy density and cycle performance.

[0128] From the comparison of Example 3 and Example 7 to Example 10, it can be seen that when the elongation of the negative electrode current collector is within a suitable range, especially when it is 3.5% to 5.0%, the battery cell can simultaneously take into account higher volume energy density, mass energy density and cycle performance.

[0129] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A sodium ion battery cell, characterized in that: The invention comprises an electrode assembly and a shell, wherein the shell is cylindrical, the shell has a receiving cavity inside, and the electrode assembly is located inside the receiving cavity; the electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, and the density of the negative electrode current collector is ≤5.0g / cm 3 , the group margin of the sodium ion battery cell satisfies: 0.95≤group margin<1, wherein the group margin is the ratio of the diameter of the electrode assembly to the diameter of the accommodating cavity.

2. The sodium ion battery cell according to claim 1, characterized in that: The density of the negative electrode current collector is 1.3 g / cm 3 ~3.5g / cm 3 .

3. The sodium ion battery cell according to any one of claims 1 to 2, characterized in that: The group margin of the sodium ion battery monomer is 0.95-0.

97.

4. The sodium ion battery cell according to any one of claims 1 to 3, characterized in that: The elongation of the negative electrode current collector is ≥3%; optionally, the elongation of the negative electrode current collector is 3.5% to 5.0%.

5. The sodium ion battery cell according to any one of claims 1 to 4, characterized in that: The ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer is ≤0.2; Optionally, the ratio of the thickness of the negative electrode current collector to the thickness of the negative electrode active layer is 0.03 to 0.

15.

6. The sodium ion battery cell according to any one of claims 1 to 5, characterized in that: The thickness of the negative electrode current collector is 6 μm to 12 μm, and optionally 6.5 μm to 10 μm.

7. The sodium ion battery cell according to any one of claims 1 to 6, characterized in that: The negative electrode current collector includes at least one of a metal foil material and a metal / polymer composite current collector.

8. The sodium ion battery cell according to any one of claims 1 to 7, characterized in that: The metal / polymer composite current collector comprises a polymer substrate layer and a metal layer located on at least one surface of the polymer substrate layer; Optionally, the polymer substrate layer comprises at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene and polyethylene; Optionally, the metal layer includes at least one of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

9. The sodium ion battery cell according to any one of claims 1 to 8, characterized in that: The sodium ion battery monomer also includes an electrolyte, which is located inside the accommodating cavity; the sodium ion battery monomer satisfies: m / C0≤6g / Ah, wherein m represents the mass of the electrolyte, in g, and C0 represents the rated capacity of the sodium ion battery monomer, in Ah; optionally, 4g / Ah≤m / C0≤5g / Ah.

10. The sodium ion battery cell according to any one of claims 1 to 9, characterized in that: The compaction density of the negative electrode active layer is 0.7 g / cm 3 ~1.3g / cm 3 , optionally 0.8 g / cm 3 ~1.2g / cm 3 .

11. The sodium ion battery cell according to any one of claims 1 to 10, characterized in that: The ratio of the height of the battery cell to the diameter of the battery cell is greater than or equal to 3.5, and can be optionally 4-6.

12. The sodium ion battery cell according to any one of claims 1 to 11, characterized in that: The height of the battery cell is greater than or equal to 60 mm, and may be 70 mm to 300 mm; and / or, The diameter of the battery cell is greater than or equal to 21 mm, and can be optionally 30 mm to 60 mm.

13. A secondary battery, characterized in that: The invention comprises the sodium ion battery monomer according to any one of claims 1 to 12.

14. An electrical device, characterized in that: The invention comprises at least one of the sodium ion battery monomer according to any one of claims 1 to 12 or the secondary battery according to claim 13.

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