Sodium ion batteries, battery modules, battery packs, and electric devices

Abstract

The present application provides a sodium ion battery, a battery module, a battery pack, and an electric device. The sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; and the separator is disposed between the positive electrode sheet and the negative electrode sheet; and the porosity (α) of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator satisfy 0 ≤ (β-α) / γ ≤ 1.5 and α ≤ γ. By simultaneously controlling the porosity of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator, the sodium ion battery of the present application can improve the charge and discharge performance of the sodium ion battery and improve the capacity performance and charge / discharge power of the sodium ion battery.

Description

Technology Field

[0001] The present application belongs to the field of battery technology, and specifically relates to sodium ion batteries, battery modules, battery packs, and electric devices. Background Technology

[0002] Lithium-ion batteries occupy the major market for rechargeable batteries due to their high energy density and long cycle life. Currently, most advanced energy storage systems utilize lithium-ion battery technology. However, due to fluctuations in lithium-ion battery prices, particularly the consumption of lithium resources and potential future shortages, there is an urgent need in the battery sector to find alternative products or technologies to meet the growing global demand for energy storage.

[0003] Sodium and lithium are elements of the same main group in the periodic table and have similar physicochemical properties; furthermore, sodium is abundant in natural reserves, and especially has huge reserves in the ocean, so it can be considered as an active ion for batteries, which can solve the problem of lithium resource shortage.

[0004] However, since the radius and relative atomic mass of sodium ions are relatively high, when they are applied to batteries as active ions, the performance of sodium ion batteries, such as charge and discharge power, is relatively poor. Therefore, it is urgent to improve the performance of sodium ion batteries to obtain high-performance sodium ion batteries.

[0005] This application has been made in consideration of the above-mentioned problem and aims to provide a sodium ion battery, a battery module, a battery pack, and an electric device.

[0006] A first aspect of the present application provides a sodium ion battery, wherein the sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; and the separator is disposed between the positive electrode sheet and the negative electrode sheet; and the porosity (α) of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator satisfy 0 ≤ (β-α) / γ ≤ 1.5 and α ≤ γ.

[0007] Thus, the present application simultaneously controls the porosity of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator to satisfy 0 ≤ (β-α) / γ ≤ 1.5 and α ≤ γ, thereby allowing sodium ions in the positive electrode active material layer to detach from the positive electrode sheet, rapidly pass through the separator, and move into the negative electrode active material layer during charging, and allowing sodium ions to be sufficiently and rapidly accommodated in the negative electrode active material layer, thereby improving the capacity performance of the sodium ion battery. During discharge, sodium ions in the negative electrode active material layer to detach from the negative electrode sheet, rapidly pass through the separator, and move into the positive electrode active material layer, and allowing sodium ions to be sufficiently and rapidly accommodated in the positive electrode active material layer, thereby improving the capacity performance of the sodium ion battery and improving the charging and discharging performance of the sodium ion battery, and thereby improving the capacity performance and charge / discharge power of the sodium ion battery.

[0008] In any embodiment, 0.4 ≤ (β-α) / γ ≤ 1.0. When the porosity of the positive electrode active material layer, the porosity of the negative electrode active material layer (β), and the porosity of the separator (γ) satisfy the above-described range, the charge / discharge performance of the sodium ion battery can be further improved.

[0009] In any embodiment, the porosity (α) of the positive electrode active material layer satisfies 20% ≤ α ≤ 40%, and optionally 28% ≤ α ≤ 38%.

[0010] Thus, when the porosity (α) of the positive electrode active material layer of the present application satisfies the range described above, the porosity of the positive electrode active material layer is suitable, which is advantageous for sodium ions to escape from the positive electrode active material layer and advantageous for sodium ions to be inserted into the positive electrode active material layer; furthermore, the electrolyte can be sufficiently infiltrated into the positive electrode active material layer, thereby improving the infiltration properties of the interface of the positive electrode active material layer.

[0011] In any embodiment, the porosity (β) of the negative electrode active material layer satisfies 40% ≤ β ≤ 66%, and optionally 45% ≤ β ≤ 58%.

[0012] Thus, when the porosity of the negative electrode active material layer of the present application satisfies the range described above, the porosity (β) of the negative electrode active material layer is suitable, which is advantageous for sodium ions to escape from the negative electrode active material layer and for sodium ions to be inserted into the negative electrode active material layer; furthermore, the electrolyte can be sufficiently infiltrated into the negative electrode active material layer, thereby improving the infiltration properties of the negative electrode active material layer interface.

[0013] In any embodiment, the porosity (γ) of the separator satisfies 30% ≤ γ ≤ 55%, and optionally 33% ≤ γ ≤ 50%.

[0014] Thus, when the porosity of the separator of the present application satisfies the range described above, the porosity (γ) of the separator is suitable, which is advantageous for sodium ions to move through the separator into the positive electrode active material layer or the negative electrode active material layer.

[0015] In any embodiment, the compression density of the positive electrode active material layer (PD1) and the compression density of the negative electrode active material layer (PD2) satisfy 0.44 ≤ PD1 / PD2 ≤ 2.3.

[0016] Thus, the present application adjusts the compression density (PD1) of the positive electrode active material layer and the compression density (PD2) of the negative electrode active material layer to match, so that the relationship between them satisfies 0.44 ≤ PD1 / PD2 ≤ 2.3, thereby allowing sodium ions released from the positive electrode active material layer to be sufficiently inserted into the negative electrode active material layer during charging; and sodium ions released from the negative electrode active material layer to be sufficiently inserted into the positive electrode active material layer during discharging. Since the kinetic performance of the positive electrode sheet and the negative electrode sheet is matched, the ion release rate and the ion insertion rate are basically the same, and the Cask Effect caused by the deterioration of the kinetic performance of one of the electrode sheets can be reduced. Therefore, problems such as performance loss and energy density loss caused by concentration polarization can be reduced, and the charge / discharge power of the sodium ion battery can be improved.

[0017] In any embodiment, the compression density (PD1) of the positive electrode active material layer satisfies 0.8≤PD1≤1.7, optionally 0.9≤PD1≤1.6, and more optionally 1.1≤PD1≤1.5.

[0018] Thus, since the compression density (PD1) of the positive electrode active material layer of the present application is relatively suitable, the thickness of the positive electrode active material layer can be appropriately reduced and the sodium ion transport path can be shortened to improve the charge / discharge power of the sodium ion battery, while at the same time, problems such as sodium precipitation and sodium dendrites caused by the concentration polarization phenomenon can be reduced.

[0019] In any embodiment, the compression density (PD2) of the negative electrode active material layer satisfies 0.7≤PD2≤1.8, optionally 0.8≤PD2≤1.3, and more optionally 0.9≤PD2≤1.0.

[0020] Thus, since the compression density (PD2) of the negative electrode active material layer of the present application is relatively suitable, the thickness of the negative electrode active material layer can be appropriately reduced, and the sodium ion transport path can be shortened to improve the charge / discharge power of the sodium ion battery, while allowing sodium ions to be sufficiently inserted into the negative electrode active material layer, and reducing problems such as sodium precipitation and sodium dendrites caused by concentration polarization.

[0021] In any embodiment, the positive electrode active material layer comprises a positive electrode active material, and the negative electrode active material layer comprises a negative electrode active material, wherein the difference between the capacity per gram of the positive electrode active material (CAP1) and the capacity per gram of the negative electrode active material (CAP2) is

[0022] or Satisfying,

[0023] Here, h1 represents the thickness of the positive electrode active material layer when the sodium ion battery is at 0% SOC, and h2 represents the thickness of the negative electrode active material layer when the sodium ion battery is at 0% SOC.

[0024] Thus, the present application can ensure that the capacity per gram of the positive electrode active material (CAP1) and the capacity per gram of the negative electrode active material (CAP2) are smaller than the capacity per gram of the negative electrode active material (CAP2) when the relationship between them is adjusted to satisfy the above-described relationship. Since sodium ions detached from the positive electrode active material can basically be inserted into the negative electrode active material, sodium ions are not easily accumulated on the surface of the negative electrode active material. Therefore, the risk of sodium precipitation caused by sodium ions accumulating on the surface of the negative electrode sheet to form metallic sodium can be reduced, and at the same time, the risk of metallic sodium caused by sodium precipitation penetrating the separator and causing an internal short circuit in the sodium ion battery can be reduced, thereby improving the cycle performance of the sodium ion battery.

[0025] The capacity per gram of the negative electrode active material (CAP2) is slightly increased compared to the capacity per gram of the positive electrode active material (CAP1), but not too large, for example, 2 ≤ CAP2 / CAP1 ≤ 3, so the risk of excess energy density reduction of the positive electrode sheet caused by the capacity per gram of the negative electrode active material (CAP2) being too large can be reduced and the energy density of the sodium ion battery can be improved.

[0026] In any embodiment, the capacity per gram (CAP1) of the positive electrode active material satisfies 110 mAh / g ≤ CAP1 ≤ 160 mAh / g, and more optionally satisfies 120 mAh / g ≤ CAP1 ≤ 155 mAh / g. When the capacity per gram (CAP1) of the positive electrode active material satisfies the above-described range, the capacity performance of the sodium-ion battery can be improved.

[0027] In any embodiment, the capacity per gram (CAP2) of the negative electrode active material satisfies 300mAh / g≤CAP2≤360mAh / g, and more optionally 320mAh / g≤CAP2≤355mAh / g.

[0028] Thus, when the capacity per gram (CAP2) of the negative electrode active material of the present application satisfies the above-described range, the capacity performance of the sodium ion battery can be improved; furthermore, it is possible to ensure that sodium ions detached from the positive electrode active material can be basically inserted into the negative electrode active material, and the cycle performance of the sodium ion battery can be improved.

[0029] In any embodiment, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises one or more types of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and sodium alloys; optionally, the negative electrode active material comprises hard carbon.

[0030] Thus, using the negative electrode active material described above in this application is advantageous for the movement of sodium ions, and in particular, when hard carbon is used as the negative electrode active material, the layer spacing of the hard carbon is relatively high, so the insertion and exit speeds of sodium ions are relatively fast, and thus the charge and discharge power of the sodium ion battery can be improved.

[0031] In any embodiment, the negative electrode active material layer comprises a negative electrode active material, and the particle size distribution of the negative electrode active material satisfies 0.5≤(DV90-DV10) / DV50≤2.

[0032] Thus, the difference between the particle size distribution of the negative electrode active material of the present application and the average particle size is not too large, and since the movement path of sodium ions in the negative electrode active material is close during the process in which sodium ions detached from the positive electrode active material are inserted into the negative electrode active material, sodium ions can be uniformly inserted into the negative electrode active material, and thus the risk of concentration polarization can be reduced.

[0033] In any embodiment, 1 μm ≤ DV50 ≤ 20 μm, and more optionally, 5 μm ≤ DV50 ≤ 15 μm.

[0034] In any embodiment, the positive electrode active material layer comprises a positive electrode active material having the molecular formula Na2MFe(CN)6, and M comprises one or more of Mg, K, Ca, V, Cr, Mn, Co, Ni, Cu, and Zn, and the molar ratio of M to Fe satisfies 0.95 to 1.05.

[0035] In any embodiment, the thickness of the separator satisfies 5μm to 15μm, and optionally 7μm to 13μm.

[0036] Thus, when the thickness of the separator of the present application satisfies the above-described range, the thickness of the separator is appropriate and the transport path of sodium ions is relatively short, so the charge and discharge power of the sodium ion battery can be improved; additionally, the separator can maintain a constant thickness and mechanical strength, so problems such as excessive self-discharge caused by a short circuit in the sodium ion battery due to the separator being too thin can be reduced.

[0037] Thus, the positive electrode active material of the present application has relatively high structural stability and is advantageous for the release and insertion of sodium ions.

[0038] A second aspect of the present application provides a battery module comprising a sodium ion battery of any one embodiment of the first aspect of the present application.

[0039] A third aspect of the present application provides a battery pack comprising a battery module of the second aspect of the present application.

[0040] A fourth aspect of the present application provides an electric device comprising a sodium ion battery of any one embodiment of the first aspect of the present application, a battery module of any one embodiment of the second aspect of the present application, or a battery pack of the third aspect of the present application. Brief explanation of the drawing

[0041] Below, the drawings used in the embodiments of the present application are briefly described to more clearly explain the technical solution means of the embodiments of the present application. Of course, the drawings described below are merely some embodiments of the present application, and those skilled in the art can obtain other drawings from the attached drawings without creative effort. FIG. 1 is a schematic diagram of a sodium ion battery according to one embodiment of the present application. FIG. 2 is an exploded view of a sodium ion battery of one embodiment of the present application shown in FIG. 1. FIG. 3 is a schematic diagram of a battery module of one embodiment of the present application. FIG. 4 is a schematic diagram of a battery pack according to one embodiment of the present application. FIG. 5 is an exploded view of a battery pack of one embodiment of the present application shown in FIG. 4. FIG. 6 is a schematic diagram of an electric device of one embodiment of the present application. Specific details for implementing the invention

[0042] Embodiments of the sodium-ion battery, battery module, battery pack, and electric device of the present application are described and disclosed in detail below. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters or repetitive descriptions of substantially identical structures may be omitted. This is intended to prevent the following description from becoming unnecessarily long and to make it easier for those skilled in the art to understand. Furthermore, the attached drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0043] The “ranges” disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by the selection of one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of a specific range. A range defined in this manner may or may not include endpoint values ​​and may be arbitrarily combined. That is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it should be understood that ranges of 60–110 and 80–120 are also considered. Furthermore, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4, and 5 are listed, all ranges of 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5 are expected. In this application, unless otherwise specified, numeric ranges “a–b” represent a shortened expression of a combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0 to 5” indicates that all real numbers between “0 to 5” are listed in this specification, and “0 to 5” is merely an abbreviated expression for combinations of such numerical values. Additionally, if a specific parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with one another to form a new technical solution. Unless otherwise specified, all technical configurations and optional technical configurations of this application may be combined with one another to form a new technical solution.

[0045] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, and sequentially is preferred. For example, the statement that the method comprises steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the statement that the mentioned method further comprises step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms “comprehensive” and “include” as used in this application may indicate an open or closed form. For example, the terms “comprehensive” and “include” may indicate that other unlisted components may be further included or included, or that only the listed components may be included or included.

[0047] Unless otherwise specified, the term “or” in this application is inclusive. For example, the phrase “A or B” indicates “A, B, or both A and B.” More specifically, “A or B” satisfies any one of the conditions that A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0048] Sodium ions in a sodium ion battery are used as active ions, and during the charging process, sodium ions detach from the positive electrode active material and enter the negative electrode active material via a separator, while electrons flow from the positive electrode sheet to the negative electrode sheet through an external circuit; the discharging process is the opposite of the charging process described above. Since the ionic radius of sodium ions is relatively large, the requirements for the ion transport path during the charging and discharging process are relatively high; otherwise, the transport efficiency of sodium ions becomes relatively low, and thus the charging and discharging power of the sodium ion battery may decrease.

[0049] In order to increase the charge and discharge power of a sodium-ion battery, the inventors started from the perspective of increasing the transport efficiency of sodium ions and ensured the smooth movement of sodium ions by adjusting the porosity of the materials among the positive and negative electrode sheets, thereby realizing an improvement in the transport efficiency of sodium ions. The present application is described in detail below.

[0050] [Sodium Ion Battery]

[0051] In a first aspect, an embodiment of the present application provides a sodium ion cell. The sodium ion cell comprises a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0052] [Straight Play Sheet]

[0053] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material.

[0054] As an example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode active material layer is disposed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0055] In some embodiments, the positive electrode current collector may use 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 material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0056] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. For example, the positive electrode active material may include one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds.

[0057] As an example of the sodium transition metal oxide described above, the sodium transition metal oxide may be Na1-xCuhFekMnlM1mO2-y, where M1 may be one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, and 0 <x≤0.33, 0<h≤0.24, 0≤k≤0.32, 0<l≤0.68, 0≤m<0.1, h+k+l+m=1, 0≤y<0.2이다.

[0058] As another example of the sodium transition metal oxide described above, the sodium transition metal oxide may be Na0.67Mn0.7NizM20.3-zO2, where M2 may be one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn, and Ba, and 0 <z≤0.1이다.

[0059] As another example of the sodium transition metal oxide described above, the sodium transition metal oxide may be NaaLibNicMndFeeO2, where 0.67 <a≤1, 0<b<0.2, 0<c<0.3, 0.67<d+e<0.8, b+c+d+e=1이다.

[0060] As an example of the polyanionic compound described above, the polyanionic compound may be A1fM3g(PO4)iOjX13-j, where A may be one or more of H, Li, Na, K, and NH4, M3 may be one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, and X1 may be one or more of F, Cl, and Br, and 0 <f≤4, 0<g≤2, 1≤i≤3, 0≤j≤2이다.

[0061] As another example of the polyanionic compound described above, the polyanionic compound may be NanM4PO4X2, where M4 may be one or more of Mn, Fe, Co, Ni, Cu, and Zn, and X2 may be one or more of F, Cl, and Br, and 0 <n≤2이며; NapM5q(SO4)3일 수 있으며, 여기서 M5는 Mn, Fe, Co, Ni, Cu 및 Zn 중 한 종류 또는 여러 종류일 수 있으며, 0<p≤2, 0<q≤2이다.

[0062] As another example of the aforementioned polyanionic compound, the polyanionic compound may be NasMntFe3-t(PO4)2(P2O7), where 0 <s≤4, 0≤t≤3이며, 예를 들어 t는 0, 1, 1.5, 2 또는 3이다.

[0063] As an example of the above-described Prussian blue compound, the Prussian blue compound may be AuM6v[M7(CN)6]w·xH2O, where A may be one or more of H+, NH4+, alkali metal cations, and alkaline earth metal cations, and M6 and M7 may each independently be one or more of transition metal cations, and 0 <u≤2, 0<v≤1, 0<w≤1, 0<x<6이다. 예를 들어 A는 H+, Li+, Na+, K+, NH4+, Rb+, Cs+, Fr+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+ 및 Ra2+ 중 한 종류 또는 여러 종류일 수 있으며, M6 및 M7은 각각 독립적으로 Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn 및 W 중 한 종류 또는 여러 종류의 전이 금속 원소의 양이온이다. 바람직하게, A는 Li+, Na+ 및 K+ 중 한 종류 또는 여러 종류이고, M6은 Mn, Fe, Co, Ni 및 Cu 중 한 종류 또는 여러 종류의 전이 금속 원소의 양이온이고, M7은 Mn, Fe, Co, Ni 및 Cu 중 한 종류 또는 여러 종류의 전이 금속 원소의 양이온이다.

[0064] In addition, the positive electrode active material layer includes a positive electrode active material with the molecular formula Na2MFe(CN)6, and M includes one or more of Mg, K, Ca, V, Cr, Mn, Co, Ni, Cu, and Zn, and the molar ratio of M to Fe satisfies 0.95 to 1.05.

[0065] The positive electrode active material of the above-described embodiment has relatively high structural stability and is advantageous for the release and insertion of sodium ions. For example, the molar ratio of M to Fe is 0.95, 1.0, or 1.05; of course, it may be a range consisting of any two of the above-described values.

[0066] In some embodiments, the positive electrode active material layer may also optionally further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0067] In some embodiments, the positive electrode active material layer may also optionally further include a conductive agent. As an example, the conductive agent may include at least one type selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In some embodiments, a positive electrode sheet can be manufactured in the following manner: the above-described components for manufacturing a positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated onto a positive electrode current collector, and a positive electrode sheet is obtained after undergoing processes such as drying and cold rolling.

[0069] [Polar Sheet]

[0070] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material.

[0071] As an example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer is disposed on either one or both of the two opposing surfaces of the negative electrode current collector.

[0072] In some embodiments, the negative electrode current collector may use a metal foil or a composite current collector. For example, copper foil is used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and sodium alloys. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other existing 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 types.

[0074] In some embodiments, the negative electrode active material may include hard carbon. Since the layer spacing of the hard carbon is relatively large, the insertion and removal rates of sodium ions are relatively fast, so the charge and discharge power of the sodium ion battery can be improved.

[0075] In some embodiments, the particle size distribution of the negative electrode active material satisfies 0.5 ≤ (DV90 - DV10) / DV50 ≤ 2. Since the difference between the particle size distribution of the negative electrode active material and the average particle size is not too large, the migration paths of sodium ions within the negative electrode active material are close during the process in which sodium ions detached from the positive electrode active material are inserted into the negative electrode active material; thus, sodium ions can be inserted uniformly into the negative electrode active material, thereby reducing the risk of concentration polarization. For example, when the negative electrode active material is hard carbon, the migration paths of sodium ions within the hard carbon are close, so sodium ions can be inserted uniformly into the hard carbon. The Dv50 value of the negative electrode active material represents the intermediate particle size of the negative electrode active material. Specifically, a specific Dv50 value indicates that the particle diameter occupying 50% of the total volume is larger than that value, and the particle diameter occupying another 50% of the total volume is smaller than that value. The Dv50 value of the negative electrode active material can be measured by referring to the method specified in GB / T19077-2016. The Dv10 value represents the particle size corresponding to 10% of the volume distribution among the particles, specifically indicating that the particle diameter occupying 10% of the total volume among the particles is larger than the value, and the particle diameter occupying 90% of the total volume is smaller than the value. The Dv10 value of the negative electrode active material can be measured by referring to the method specified in GB / T19077-2016. The Dv90 value represents the particle size corresponding to 90% of the volume distribution among the particles, indicating that the particle diameter occupying 90% of the total volume is larger than the value, and the particle diameter occupying 10% of the total volume is smaller than the value. The Dv90 value of the negative electrode active material can be measured by referring to the method specified in GB / T19077-2016.

[0076] For example, assuming the negative electrode active material is hard carbon, the following process is used to control the particle size distribution so that it satisfies the range described above: straw, which is a biomass precursor, is used as a raw material, and a first drying is performed by heating at a high temperature under an air atmosphere; after the first drying, it is ground, and then, the straw after grinding is heated under an oxygen-free environment to perform a second drying; after the second drying, the straw after drying is ball-milled using a ball mill for a grinder, whereby three types of different particle sizes (e.g., 50 mm, 20 mm, 5 mm) are used to grind the straw according to a certain water ratio, and hard carbon with a desired particle size distribution is obtained after grinding. The control of the particle size distribution of other negative electrode active materials can also be performed by referring to the method described above.

[0077] In some embodiments, the intermediate particle size of the negative electrode active material satisfies 1 μm ≤ DV50 ≤ 20 μm.

[0078] When the average particle size of the negative electrode active material satisfies the range described above, the insertion and exit paths of sodium ions can be shortened, thereby securing the first Coulomb efficiency of the sodium ion battery. For example, when the negative electrode active material is hard carbon, the layer spacing of the hard carbon is relatively large, so the insertion and exit speeds of sodium ions are relatively fast, which is advantageous for improving the charge and discharge power of the sodium ion battery; at the same time, if the particle size of the hard carbon is controlled to satisfy the range described above, the insertion and exit paths of sodium ions can be shortened. Optionally, 5μm≤DV50≤15μm, and exemplarily, DV50 may be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, or 20μm.

[0079] In some embodiments, the negative electrode active material layer may also optionally further include a binder. The binder may be selected from at least one 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).

[0080] In some embodiments, the negative electrode active material layer may also optionally further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In some embodiments, the negative electrode active material layer may also optionally include other auxiliary agents, such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0082] In some embodiments, a negative electrode sheet can be manufactured by the following method: the above-described components for manufacturing a negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is coated onto a negative electrode current collector, and a negative electrode sheet is obtained after undergoing processes such as drying and cold rolling.

[0083] [Separator]

[0084] The present application does not specifically limit the type of separator, and any known porous separator having good chemical stability and mechanical stability may be selected.

[0085] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and there are no particular limitations. When the separator is a multilayer composite film, the material of each layer may be the same or different, and there are no particular limitations.

[0086] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

[0087] In some embodiments, the thickness of the separator satisfies 5μm to 15μm.

[0088] When the thickness of the separator satisfies the range described above, the separator thickness is appropriate and the transport path of sodium ions is relatively short, so the charge / discharge power of the sodium ion battery can be improved; additionally, since the separator can maintain a constant thickness and mechanical strength, problems such as excessive self-discharge caused by a short circuit in the sodium ion battery due to the separator being too thin can be reduced. The thickness of the separator is optionally 7 μm to 13 μm; for example, the thickness of the separator may be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm; and the thickness of the separator may be a range consisting of any two values ​​described above.

[0089] In some embodiments, the porosity (α) of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator may satisfy 0 ≤ (β-α) / γ ≤ 1.5, and also α ≤ γ.

[0090] The porosity (α) of the positive electrode active material layer refers to the ratio of the volume of pores within the positive electrode active material layer to the total volume of the positive electrode active material. The porosity (β) of the negative electrode active material layer refers to the ratio of the volume of pores within the negative electrode active material layer to the total volume of the negative electrode active material. The porosity (γ) of the separator refers to the ratio of the volume of pores within the separator to the total volume of the separator.

[0091] The measurement of each porosity described above can be performed by referring to the porosity measurement method of GB / T 24586-2009. For example, the measurement can be performed using the AccuPyc II 1340 type fully automatic true density meter of Micromeritics, USA. The above measurement method includes the following steps: a sample (e.g., a positive electrode sheet) is cut into 30 small discs with a diameter of 14 mm, and according to the principle of gas adsorption, an inert gas, such as helium or nitrogen gas, is used as the medium; after measuring the true volume of the 30 small discs with a diameter of 14 mm, the porosity is calculated based on the relationship between the apparent volume and the true volume of the positive electrode sheet calculated according to the area, thickness, and number of the small discs. Since the measurement method for the porosity of the negative electrode sheet and the porosity of the separator is the same as the measurement method for the porosity of the positive electrode sheet, it is not repeated here.

[0092] When (β-α) / γ<0, the porosity of the separator is relatively high, and since the separator has a relatively large number of pore channels, the siphon effect of the electrolyte passing through the separator is weakened, preventing the reflux of the electrolyte from occurring in time, so that sodium ions cannot be sufficiently released to the opposing electrode sheet through the electrolyte; furthermore, if the separator has a relatively high porosity, the insulation effect of the separator decreases, making it difficult to effectively insulate the positive electrode sheet and the negative electrode sheet, and the self-discharge of the sodium ion battery is relatively large.

[0093] When (β-α) / γ > 1.5, the porosity of the separator is relatively small, so the movement speed of sodium ions is limited by the separator. For example, during the process in which sodium ions are inserted into the negative electrode sheet after being separated from the positive electrode sheet, the porosity of the separator is limited, and since it is difficult for the separator to provide sufficient pore passages for the movement of sodium ions, the charge and discharge power of the sodium ion battery is limited.

[0094] The embodiments of the present application allow the porosity of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator to be controlled such that 0 ≤ (β-α) / γ ≤ 1.5 and α ≤ γ simultaneously. This enables, when charging, sodium ions in the positive electrode active material layer to detach from the positive electrode sheet, rapidly pass through the separator, and move into the negative electrode active material layer. Since sodium ions are sufficiently and rapidly accommodated in the negative electrode active material layer, the capacity of the sodium ion battery can be improved. When discharging, sodium ions in the negative electrode active material layer can detach from the negative electrode sheet, rapidly pass through the separator, and move into the positive electrode active material layer. Since sodium ions are sufficiently and rapidly accommodated in the positive electrode active material layer, the capacity of the sodium ion battery can be improved, and the charging and discharging performance of the sodium ion battery can be improved. This, in turn, improves the capacity performance and charge / discharge power of the sodium ion battery. Optionally, 0.4≤(β-α) / γ≤1.0, and exemplarily, (β-α) / γ may be 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5; (β-α) / γ may be a range consisting of any two values ​​mentioned above.

[0095] In some embodiments, the porosity (α) of the positive electrode active material layer satisfies 20% ≤ α ≤ 40%. When the porosity (α) of the positive electrode active material layer satisfies the above-described range, the porosity of the positive electrode active material layer is suitable, which is advantageous for sodium ions to escape from the positive electrode active material layer and advantageous for sodium ions to be inserted into the positive electrode active material layer; additionally, the electrolyte can sufficiently infiltrate the positive electrode active material layer, thereby improving the infiltration properties of the positive electrode active material layer interface. Optionally, 28% ≤ α ≤ 38%; exemplarily, α may be 20%, 25%, 28%, 30%, 32%, 35%, 38%, 39%, or 40%; and α may be a range consisting of any two of the above-described values.

[0096] In some embodiments, the porosity (β) of the negative electrode active material layer satisfies 40% ≤ β ≤ 66%. When the porosity of the negative electrode active material layer satisfies the above-described range, the porosity (β) of the negative electrode active material layer is suitable, which is advantageous for sodium ions to escape from the negative electrode active material layer and advantageous for sodium ions to be inserted into the positive electrode active material layer; additionally, the electrolyte can sufficiently infiltrate the negative electrode active material layer, thereby improving the infiltration properties of the negative electrode active material layer interface. Optionally, 45% ≤ β ≤ 58%; exemplarily, β may be 40%, 43%, 45%, 50%, 55%, 58%, 60%, 62%, or 66%; and β may be a range consisting of any two of the above-described values.

[0097] In some embodiments, the porosity (γ) of the separator satisfies 30% ≤ γ ≤ 55%. When the porosity of the separator satisfies the range described above, the porosity (γ) of the separator is suitable, so it is advantageous for sodium ions to move through the separator into the positive electrode active material layer or the negative electrode active material layer. Optionally, 33% ≤ γ ≤ 50%, and exemplarily, γ may be 30%, 32%, 33%, 35%, 40%, 45%, 50%, 52%, or 55%; γ may be a range consisting of any two values ​​described above.

[0098] In each of the above-described embodiments, the positive electrode active material layer, the negative electrode active material layer, and the separator combine their respective porosities to promote sufficient insertion of sodium ions separated from one of the electrode sheets into another electrode sheet, thereby securing the charge / discharge power of the sodium ion battery.

[0099] In some embodiments, the compression density of the positive electrode active material layer (PD1) and the compression density of the negative electrode active material layer (PD2) satisfy 0.44 ≤ PD1 / PD2 ≤ 2.3.

[0100] Compressive density is the ratio of the mass of the active material layer to its volume, and the arrangement of the active material can be controlled by adjusting the compressive density of the active material layer. The volume of the active material layer is the product of its thickness and its area.

[0101] The embodiments of the present application adjust the compression density (PD1) of the positive electrode active material layer and the compression density (PD2) of the negative electrode active material layer to match, such that the relationship between them satisfies 0.44 ≤ PD1 / PD2 ≤ 2.3, and during charging, sodium ions released from the positive electrode active material layer can be sufficiently inserted into the negative electrode active material layer; and during discharging, sodium ions released from the negative electrode active material layer can be sufficiently inserted into the positive electrode active material layer. Since the kinetic performance of the positive electrode sheet and the negative electrode sheet is matched, the ion release rate and the ion insertion rate are essentially the same, and the Cask Effect caused by the deterioration of the kinetic performance of one of the electrode sheets can be reduced. Therefore, problems such as performance loss and energy density loss caused by concentration polarization can be reduced, and the charge / discharge power of the sodium-ion battery can be improved. Optionally, 1.1 ≤ PD1 / PD2 ≤ 1.9; For example, PD1 / PD2 may be 0.44, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 1.0, 1.2, 1.5, 1.8, 2.0, 2.1, 2.2, or 2.3; or PD1 / PD2 may be a range consisting of any two of the above-mentioned values.

[0102] Optionally, the compression density (PD1) of the positive electrode active material layer satisfies 0.8≤PD1≤1.7.

[0103] If the compression density (PD1) of the positive electrode active material layer is relatively appropriate, the thickness of the positive electrode active material layer can be appropriately reduced, and the sodium ion transport pathway can be shortened to improve the charge / discharge power of the sodium ion battery, while simultaneously reducing problems such as sodium precipitation and sodium dendrites caused by concentration polarization. In addition, a positive electrode active material layer satisfying the above-described compression density range is advantageous for improving the capacity performance of the sodium ion battery and reducing internal resistance, thereby extending the cycle life of the sodium ion battery. Optionally, 0.9 ≤ PD1 ≤ 1.6, and more optionally, 1.1 ≤ PD1 ≤ 1.5; exemplarily, PD1 may be 0.8, 0.85, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.65, or 1.7; or PD1 may be a range consisting of any two of the above-described values.

[0104] The compressive density (PD2) of the negative electrode active material layer satisfies 0.7≤PD2≤1.8.

[0105] If the compression density (PD2) of the negative electrode active material layer is relatively appropriate, the thickness of the negative electrode active material layer can be appropriately reduced, and the sodium ion transport path can be shortened to improve the charge / discharge power of the sodium ion battery, while allowing sodium ions to be sufficiently inserted into the negative electrode active material layer and reducing problems such as sodium precipitation caused by concentration polarization. Optionally, 0.8≤PD2≤1.3, and more optionally, 0.9≤PD2≤1.0; exemplarily, PD2 may be 0.7, 0.75, 0.8, 0.85, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8; PD2 may be a range consisting of any two values ​​described above.

[0106] In some embodiments, the positive electrode active material layer comprises a positive electrode active material, and the negative electrode active material layer comprises a negative electrode active material, wherein the difference between the capacity per gram of the positive electrode active material (CAP1) and the capacity per gram of the negative electrode active material (CAP2) is

[0107] also Satisfying,

[0108] Here, h1 represents the thickness of the positive electrode active material layer when the sodium ion battery is in a 0% State of Charge (SOC), and h2 represents the thickness of the negative electrode active material layer when the sodium ion battery is in a 0% SOC. 0% SOC indicates that the sodium ion battery is completely discharged. The thickness of the positive electrode active material layer or the negative electrode active material layer may vary under different SOC conditions, and in particular, the thickness of the negative electrode active material layer increases with increasing SOC.

[0109] Capacity per gram refers to the ratio of the electrical capacity that can be released from the active material inside a sodium-ion battery to the mass of the active material. Capacity per gram can be expressed in milliampere-hours per gram (mA·h / g).

[0110] In an embodiment of the present application, when the capacity per gram of the positive electrode active material (CAP1) and the capacity per gram of the negative electrode active material (CAP2) are adjusted to satisfy the relationship described above, the capacity per gram of the positive electrode active material (CAP1) can be secured to be smaller than the capacity per gram of the negative electrode active material (CAP2). Since sodium ions detached from the positive electrode active material can basically be inserted into the negative electrode active material, it is not easy for sodium ions to accumulate on the surface of the negative electrode active material. Therefore, the risk of sodium precipitation caused by sodium ions accumulating on the surface of the negative electrode sheet to form metallic sodium can be reduced, and at the same time, the risk of metallic sodium caused by sodium precipitation penetrating the separator and causing an internal short circuit in the sodium ion battery can be reduced, thereby improving the cycle performance of the sodium ion battery.

[0111] In addition, the capacity per gram of the negative electrode active material (CAP2) is slightly increased compared to the capacity per gram of the positive electrode active material (CAP1), but not too large, for example, 2 ≤ CAP2 / CAP1 ≤ 3, and thus the risk of a decrease in excess energy density of the positive electrode sheet caused by the capacity per gram of the negative electrode active material (CAP2) being too large can be reduced and the energy density of the sodium ion battery can be improved.

[0112] In some embodiments, the capacity per gram (CAP1) of the positive electrode active material satisfies 110mAh / g≤CAP1≤160mAh / g.

[0113] When the capacity per gram (CAP1) of the positive electrode active material satisfies the range described above, the capacity performance of the sodium-ion battery can be improved. Optionally, 120mAh / g ≤ CAP1 ≤ 155mAh / g, and exemplarily, CAP1 may be 110mAh / g, 115mAh / g, 120mAh / g, 125mAh / g, 130mAh / g, 135mAh / g, 140mAh / g, 150mAh / g, 155mAh / g, or 160mAh / g; and CAP1 may be a range consisting of any two values ​​described above.

[0114] In some embodiments, the capacity per gram (CAP2) of the negative electrode active material satisfies 300mAh / g ≤ CAP2 ≤ 360mAh / g.

[0115] When the capacity per gram (CAP2) of the negative electrode active material satisfies the range described above, the capacity performance of the sodium ion battery can be improved; additionally, sodium ions released from the positive electrode active material can be secured to be inserted into the negative electrode active material, and the cycle performance of the sodium ion battery can be improved. Optionally, 320 mAh / g ≤ CAP2 ≤ 355 mAh / g; exemplarily, CAP2 may be 300 mAh / g, 310 mAh / g, 320 mAh / g, 325 mAh / g, 330 mAh / g, 335 mAh / g, 340 mAh / g, 345 mAh / g, 350 mAh / g, or 355 mAh / g; and CAP2 may be a range consisting of any two values ​​described above.

[0116] [Electrolyte]

[0117] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of electrolyte and may be selected as needed. For example, the electrolyte may be in liquid form, gel form, or completely solid form.

[0118] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0119] In some embodiments, the electrolyte salt may be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0120] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0121] In some embodiments, the electrolyte may also optionally include additional additives. For example, the additives may include negative electrode film forming additives and positive electrode film forming additives, and may further include additives that can improve some performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0122] [Outer Packaging]

[0123] In some embodiments, the sodium ion battery may include an outer packaging. The outer packaging may be used to package the electrode assembly and electrolyte described above.

[0124] In some embodiments, the outer packaging of the sodium ion battery may be a rigid case, for example, a rigid plastic case, an aluminum case, a steel case, etc. The outer packaging of the sodium ion battery may be a soft pack, for example, an envelope-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. The present application does not particularly limit the shape of the sodium ion battery and may be cylindrical, rectangular, or any other shape. For example, FIGS. 1 and 2 are a sodium ion battery (1) with a rectangular structure as an example.

[0125] In some embodiments, the sodium ion battery (1) includes an outer packaging (11). The outer packaging (11) includes an upper cover assembly (111) and a case (112). A positive electrode sheet, a negative electrode sheet, and a separator constitute an electrode assembly (12) and are housed within the case (112), and an electrolyte is also housed within the case (112). The positive electrode sheet or the negative electrode sheet includes a tab. During the charging and discharging process of the sodium ion battery (1), metal ions reciprocate between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is placed between the positive electrode sheet and the negative electrode sheet and serves primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing active ions to pass through. Specifically, the sodium ion battery (1) may be a wound or stacked battery, but is not limited thereto.

[0126] Optionally, the case (112) may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity. The case (112) has an opening communicating with the receiving cavity, and a top cover assembly (111) covers the opening to seal the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator form an electrode assembly (12) through a winding process or a lamination process. The electrode assembly (12) is packaged within the receiving cavity. An electrolyte is infiltrated into the electrode assembly (12). The number of electrode assemblies (12) included in the sodium ion battery (1) may be one or more, and a person skilled in the art may select as needed.

[0127] In some embodiments, the sodium ion battery (1) may be assembled into a battery. The battery may be a battery module or a battery pack. For example, the number of sodium ion batteries (1) included in the battery module may be one or several, and the specific number may be adjusted according to the application and capacity of the battery module.

[0128] FIG. 3 is a battery module (10) as an example. As shown in FIG. 3, in the battery module (10), a plurality of sodium ion batteries (1) may be arranged sequentially along the longitudinal direction of the battery module (10). Of course, they may also be arranged in any other arbitrary manner. Additionally, the plurality of sodium ion batteries (1) may be secured through fasteners. Optionally, the battery module (10) may further include a housing having a receiving space, and the plurality of sodium ion batteries (1) are received in the receiving space.

[0129] In some embodiments, the battery module (10) may also be assembled into a battery pack, and the number of battery modules (10) included in the battery pack may be one or multiple, and the specific number may be adjusted by a person skilled in the art according to the application and capacity of the battery pack. Of course, the battery pack may be directly composed of multiple sodium-ion batteries (1).

[0130] FIGS. 4 and FIGS. 5 are examples of a battery pack (20). As illustrated in FIGS. 4 and FIGS. 5, the battery pack (20) may include a battery box and a plurality of battery modules (10) disposed in the battery box. The battery box includes an upper box body (21) and a lower box body (22), and the upper box body (21) may cover the lower box body (22) to form a sealed space for accommodating the battery modules (10). The plurality of battery modules (10) may be arranged within the battery box in any manner.

[0131] Additionally, the present application also provides an electric device, the electric device comprising at least one type of a sodium-ion battery, a battery module, or a battery pack according to the present application. The sodium-ion battery, battery module, or battery pack may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., 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.), an electric train, a ship, a satellite, an energy storage system, etc. As the electric device, a sodium-ion battery, a battery module, or a battery pack may be selected as needed.

[0132] FIG. 6 is an example of an electric device (30). The electric device (30) is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To satisfy the requirements for high power and high energy density for a sodium ion battery, the electric device (30) may use a battery pack or a battery module. Other exemplary electric devices may be mobile phones, tablet computers, laptop computers, etc. Since the device generally requires lightweight and thin design, a sodium ion battery may be used as a power source.

[0133] Examples

[0134] The following describes embodiments of the present application. The embodiments described below are illustrative and are intended only for the interpretation of the present application and should not be understood as a limitation thereof. Where specific techniques or conditions are not specified in the embodiments, they may be performed according to techniques or conditions described in literature of the art or according to product descriptions. Unless the manufacturer is specified, the reagents or equipment used may all be commercially available conventional products.

[0135] Example 1

[0136] 1. Manufacture of positive electrode sheet

[0137] An aluminum foil with a thickness of 10 μm can be used as a positive electrode current collector.

[0138] Na2MnFe(CN)6, a positive electrode active material; Super P, a conductive agent; and polyvinylidene fluoride (PVDF), a binder, are mixed in a mass ratio of 96:2.5:1.5 and added to N-methylpyrrolidone (NMP), a solvent, and uniformly stirred under the action of a vacuum stirrer to obtain a positive electrode slurry. The solid content of the slurry is 60% by weight.

[0139] The positive electrode slurry prepared above is coated onto an aluminum foil with a thickness of 8 μm, and after undergoing processes such as drying, a positive electrode sheet is obtained.

[0140] The process for measuring the porosity of a positive electrode sheet is as follows: the positive electrode sheet is cut into 30 small discs with a diameter of 14 mm, and according to the principle of gas adsorption, helium gas is used as the medium. The true volume of the 30 small discs is measured using an AccuPyc II 1340 type fully automatic true density meter from Micromeritics, USA, and then the porosity is calculated based on the relationship between the apparent volume and the true volume of the positive electrode sheet calculated according to the area, thickness, and number of small discs.

[0141] 2. Manufacture of negative electrode sheet

[0142] A copper foil with a thickness of 6 μm is used as the negative electrode current collector.

[0143] A negative electrode active material, a conductive agent Super P, a thickening agent sodium carboxymethylcellulose (CMC), and a binder styrene-butadiene rubber emulsion (SBR) are mixed in a mass ratio of 97:0.7:1.8:0.5 and added to deionized water as a solvent, and uniformly stirred under the action of a vacuum stirrer to obtain a negative electrode slurry. The solid content of the negative electrode slurry is 56% by weight.

[0144] The negative electrode slurry prepared above is coated onto a copper foil with a thickness of 8 μm, and after undergoing processes such as drying, a negative electrode sheet is obtained.

[0145] The process for measuring the porosity of the negative electrode sheet is as follows: the negative electrode sheet is cut into 30 small discs with a diameter of 14 mm, and according to the gas adsorption principle, helium gas is used as the medium. The true volume of the 30 small discs is measured using an AccuPyc II 1340 type fully automatic true density meter from Micromeritics, USA, and then the porosity is calculated based on the relationship between the apparent volume and the true volume of the negative electrode sheet calculated according to the area, thickness, and number of small discs.

[0146] 3. Preparation of Electrolytes

[0147] In an argon atmosphere glove box with a moisture content <10 ppm, a sufficiently dried sodium salt (NaPF6) is dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:20:60, and then vinylene carbonate (VC) is added as an additive and mixed uniformly to obtain an electrolyte. Here, the concentration of the sodium salt is 1 mol / L.

[0148] 4. Manufacture of Separator

[0149] A polyethylene (PE) film with a thickness of 7 μm is used as the base film for a separator, and aluminum oxide, sodium carboxymethylcellulose (CMC), and acrylate are added in a weight ratio of 93%:3%:4% in deionized water and uniformly stirred under the action of a vacuum stirrer to obtain a slurry. The solid content of the slurry is 55 wt%. The obtained slurry is uniformly coated on both sides of the base film so that the thickness of one side is 2 μm to obtain a separator.

[0150] The process for measuring the porosity of a separator is as follows: the separator is cut into 30 small discs with a diameter of 14 mm, and according to the principle of gas adsorption, helium gas is used as the medium. The true volume of the 30 small discs is measured using an AccuPyc II 1340 fully automatic true density meter from Micromeritics, USA, and then the porosity is calculated based on the relationship between the apparent volume and the true volume of the separator calculated according to the area, thickness, and number of the small discs.

[0151] 5. Manufacture of sodium-ion batteries

[0152] A positive electrode sheet, a separator (PP / PE / PP composite film), and a negative electrode sheet are stacked in sequence and wrapped in an aluminum plastic film to form a stacked battery core; 0.3g of the electrolyte is injected into the battery core at 60°C, vacuum hot rolling packaging is performed on the aluminum plastic film, the battery is left standing at 60°C for at least 6 hours, the temperature is lowered to 30°C, and the battery is left standing at 30°C for at least 6 hours until the electrolyte hardens, after which a sodium ion battery is obtained through processes such as superheated cold rolling and formation.

[0153] Examples 2 to 12

[0154] The difference from Example 1 is that at least one of the porosity of the positive electrode active material layer, the negative electrode active material layer, and the separator in Examples 2 to 12 is different from that of Example 1.

[0155] Examples 13 to 21

[0156] The difference from Example 1 is that at least one of the compression density of the positive electrode active material layer and the compression density of the negative electrode active material layer in Examples 13 to 21 is different from Example 1.

[0157] Examples 22 to 26

[0158] The difference from Example 1 is that at least one of the compression density, capacity per gram, and thickness of the positive electrode active material layer in Examples 22 to 26, and the compression density, capacity per gram, and thickness of the negative electrode active material layer is different from Example 1.

[0159] Examples 27 to 31

[0160] The difference from Example 1 is that the particle size of the negative electrode active material in the negative electrode active material layer of Examples 27 to 31 is different.

[0161] Comparative Example 1

[0162] The difference from Example 1 is that the porosity of the positive electrode active material layer, the negative electrode active material layer, and the separator is different.

[0163] Each material and related parameter of Examples 1 to 31 and Comparative Example 1 is as shown in Tables 1 to 3.

[0164]

[0165]

[0166] In Table 2, the thickness of the positive electrode active material layer (h1) represents the thickness of the positive electrode active material layer when the sodium ion battery is in a 0% state of charge (SOC). The thickness of the negative electrode active material layer (h2) represents the thickness of the negative electrode active material layer when the sodium ion battery is in a 0% state of charge (SOC).

[0167] negative electrode active material layer (D V 90-D V 10) / D V 50 Dv10 / μm Dv50 / μm Dv90 / μm negative electrode active material Example 1 2.2 5.3 9.3 Hard carbon 1.34 Example 27 3.5 5.0 6.0 Hard carbon 0.50 Example 28 5.0 10.0 15.0 Hard carbon 1.00 Example 29 6.5 15.0 21.5 Hard carbon 1.00 Example 30 0.6 1.0 1.6 Hard carbon 1.00 Example 31 5.5 20.0 45.5 Hard carbon 2.00

[0168] The process for controlling the particle size distribution (DV90-DV10) / DV50 of the negative electrode active material of the above-described example is as follows: Straw, which is a biomass precursor, is used as a raw material. First, the precursor is heated for 5 hours in a high-temperature furnace at 200°C under an air atmosphere to perform a first drying process to remove moisture from inside the precursor. After cooling, it is ground. Then, the material after grinding is placed in an oxygen-free environment and dried at 1600°C for 5 hours. After cooling, ball milling is performed for 4 hours using a ball mill for a grinder to obtain hard carbon with a desired particle size distribution. Here, the particle sizes of the ball mill beads are 50 mm, 20 mm, and 5 mm, respectively, and the ratio of the number of ball mill beads is approximately 5:30:55.

[0169] Test section

[0170] Porosity test of positive electrode active material layer, negative electrode active material layer, and separator

[0171] Referring to the GB / T 24586-2009 porosity test method, the test method is as follows: a sample cup containing the sample is placed in a true density tester, the test system is sealed, helium gas is introduced, the gas pressure in the sample chamber and the expansion chamber is detected, and then the true volume is calculated according to Boyle's Law (PV=nRT) to obtain the porosity of the test sample.

[0172] Test method for the compression density of the positive electrode active material layer and the negative electrode active material layer

[0173] At 25°C, the sodium ion battery is discharged to 0% SOC with a current of 0.1C, and then the sodium ion battery is disassembled to separate the positive electrode sheet, the negative electrode sheet, and the separator. After disassembly, the electrode sheet is placed in a 60°C air-drying oven for 60 minutes to completely evaporate the electrolyte on the electrode sheet, then the electrode sheet is removed, the temperature is lowered to room temperature, and the remaining electrolyte on the electrode sheet is washed by soaking it in anhydrous ethanol for 30 minutes, and then the electrode sheet is dried by placing it in a 60°C air-drying oven for 60 minutes. A button-type electrode sheet is punched into a small disc with a diameter of 14 mm using a button-type electrode sheet punching machine, the area of ​​the small disc is S, the weight of the small disc (W1) and the weight of the current collector (W2) are weighed, and the thickness of the electrode sheet (H1) and the thickness of the current collector (H2) are tested using a micrometer.

[0174] The compressive density of the electrode sheet is PD=(W1-W2) / ((H1-H2)*S), and the unit is g / cm³.

[0175] Test of active material thickness when sodium-ion battery is at 0% SOC

[0176] When the sodium ion battery is at 0% SOC, a positive electrode sheet or a negative electrode sheet is used as a sample, and the thickness of the electrode sheet is measured at at least 12 different positions in the thickness direction of the electrode sheet using a micrometer, and then the average value is taken. By using the average value and subtracting the thickness of the current collector, the thickness of the active material can be obtained.

[0177] Dv10, Dv50, and Dv90 measurements of negative electrode active material

[0178] Using a laser diffraction particle size distribution meter (Malvern Mastersizer 3000), the particle size distribution is measured according to the particle size distribution laser diffraction method GB / T19077-2016 to obtain Dv10, Dv90, and Dv50, and (Dv90-Dv10) / Dv50 is calculated.

[0179] To explain the Dv50 test as an example, specifically, the Dv50 test method for a negative electrode active material is as follows: (1) Sample pretreatment: A clean beaker is taken and an appropriate amount of the test sample is placed in it. Sodium dodecyl sulfate, a surfactant, is added dropwise, and deionized water is added as a dispersant. Ultrasonic treatment (120W / 5 min) is performed to ensure that the sample is completely dispersed in the dispersant. (2) Test process: Dv50 measurement is performed using an LS-909 laser particle size meter (manufactured by OMAX). After pouring the sample into the sample injection tower, the sample is circulated through the solution to the test optical path system. A laser beam is irradiated to receive scattered light emitted from the particles, and its energy distribution is measured to obtain the particle size distribution characteristics (light shielding degree: 8~12%), and finally, the Dv50 value of the material can be obtained.

[0180] Measurement of sodium ion battery cycle counts

[0181] The cycle performance of a sodium-ion battery is evaluated under 0.5C / 0.5C conditions at 25℃.

[0182] Specifically, the sodium-ion battery is charged with a constant current and constant voltage of 0.5C until the charge cutoff voltage reaches 3.75V, and after standing for 5 minutes, it is discharged with a constant current of 0.5 until the discharge cutoff voltage reaches 2V, the discharge capacity is recorded, and then it is stood for 5 minutes, and this is considered a cycle. The number of cycles is recorded when the discharge capacity maintains 80% or more of the initial capacity.

[0183] Measurement of 60s pulse discharge power of a sodium ion battery

[0184] At 25℃, the sodium-ion battery is charged with a constant current and constant voltage of 0.5C multiplier until the charge cutoff voltage reaches 3.75V, and after standing for 5 minutes, it is discharged with a specific power so that the battery voltage reaches 2V at 60s and the discharge is stopped, and the power at this time is the 60s pulse discharge power.

[0185] By measuring the 60s pulse discharge power of a sodium ion battery, the power performance of the battery can be determined.

[0186] Test results

[0187] The effect of the present application in improving the charge / discharge performance and energy density of sodium ion batteries is as shown in Tables 4 to 6.

[0188] Sodium ion battery cycle count Sodium-ion battery power performance / W Example 1 3450 529.82 Example 2 3340 512.93 Example 3 3360 516.00 Example 4 3300 506.78 Example 5 3100 476.07 Example 6 3150 483.75 Example 7 3055 469.09 Example 8 2920 448.41 Example 9 2381 365.70 Example 10 2240 344.00 Example 11 1588 243.93 Example 12 1344 206.40 Comparative Example 1 845 129.77

[0189] As can be seen from Table 4, in Comparative Example 1 and Examples 1 to 12, positive electrode active material layers, negative electrode active material layers, and separators with different porosities were used, and the migration speed of sodium ions can be controlled during the sodium ion charging and discharging process. When 0≤(β-α) / γ≤1.5 and α≤γ, particularly when 0.4≤(β-α) / γ≤1.5, the sodium ion migration speed is relatively fast and the sodium ion charge / discharge power is relatively high.

[0190] Sodium ion battery cycle count Sodium-ion battery power performance / W Example 1 3450 529.82 Example 13 3725 572.05 Example 14 3990 612.75 Example 15 4260 654.21 Example 16 4435 681.09 Example 17 4300 660.36 Example 18 4100 629.64 Example 19 3890 597.39 Example 20 3300 506.80 Example 21 3380 519.07 Example 22 3670 563.61 Example 23 3790 582.04 Example 24 3900 598.93 Example 25 3542 543.95 Example 26 3345 513.70

[0191] As can be seen from Table 5, in Examples 1, 13 to 21, the compression density (PD1) of the positive electrode active material layer and the compression density (PD2) of the negative electrode active material layer were controlled, and when 0.44 ≤ PD1 / PD2 ≤ 2.3, particularly 1.2 ≤ PD1 / PD2 ≤ 1.5, the kinetic performance of the positive electrode active material layer and the negative electrode active material layer is matched with each other, and sodium ions released from the active material can be sufficiently inserted into the active material with opposite polarity, which can reduce adverse effects caused by concentration polarization and improve the charge / discharge power of the sodium ion battery.

[0192] In Examples 23 to 26, the performance of the sodium ion battery was controlled by simultaneously adjusting the compression density, capacity per gram, and thickness of the active material layer.

[0193] also When that happens, sodium-ion batteries have relatively good performance.

[0194] Sodium ion battery cycle count Sodium-ion battery power performance / W Example 1 3450 529.82 Example 27 3500 537.50 Example 28 3560 546.71 Example 29 3690 566.75 Example 30 3460 531.40 Example 31 3386 520.00

[0195] As can be seen from Table 6, in Examples 1, 27 to 31, the particle size and particle size distribution of the negative electrode active material were controlled, and in particular, when 0.5 ≤ (DV90 - DV10) / DV50 ≤ 2, the migration speed of sodium ions at each location of the negative electrode active material is basically consistent and the migration paths are close, so that sodium ions can be uniformly inserted into the negative electrode active material and the risk of concentration polarization can be reduced.

[0196] Although the present application has been described with reference to preferred embodiments, various modifications may be made and components thereof replaced with equivalents without departing from the scope of the present application. In particular, all technical configurations mentioned in each embodiment may be combined arbitrarily, provided there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein and includes all technical solutions within the scope of the claims. Explanation of the symbols

[0197] 1: Sodium ion battery 1: Outer packaging 11: Top cover assembly 12: Case 2: Electrode assembly 10: Battery module 20: Battery pack 21: Upper box body 22: Lower box body 30: Electrical device

Claims

Claim 1 A sodium ion battery comprising: a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the porosity (α) of the positive electrode active material layer, the porosity (β) of the negative electrode active material layer, and the porosity (γ) of the separator satisfy 0 ≤ (β-α) / γ ≤ 1.5 and α ≤ γ, and the compressive density (PD1) of the positive electrode active material layer and the compressive density (PD2) of the negative electrode active material layer satisfy 0.44 ≤ PD1 / PD2 ≤ 1.

26. Claim 2 A sodium ion battery according to claim 1, wherein 0.4 ≤ (β-α) / γ ≤ 1.

0. Claim 3 A sodium ion battery according to claim 1, wherein the porosity (α) of the positive electrode active material layer satisfies 20% ≤ α ≤ 40%; and / or the porosity (β) of the negative electrode active material layer satisfies 40% ≤ β ≤ 66%; and / or the porosity (γ) of the separator satisfies 30% ≤ γ ≤ 55%. Claim 4 A sodium ion battery according to claim 1, wherein the compression density (PD1) of the positive electrode active material layer satisfies 0.8 ≤ PD1 ≤ 1.7; and / or the compression density (PD2) of the negative electrode active material layer satisfies 0.7 ≤ PD2 ≤ 1.

8. Claim 5 In claim 4, the positive electrode active material layer comprises a positive electrode active material, and the negative electrode active material layer comprises a negative electrode active material, wherein the difference between the capacity per gram of the positive electrode active material (CAP1) and the capacity per gram of the negative electrode active material (CAP2) is also A sodium ion battery satisfying, wherein h1 represents the thickness of the positive electrode active material layer when the sodium ion battery is at 0% SOC and h2 represents the thickness of the negative electrode active material layer when the sodium ion battery is at 0% SOC; the capacity per gram of the positive electrode active material (CAP1) satisfies 110 mAh / g ≤ CAP1 ≤ 160 mAh / g; and / or the capacity per gram of the negative electrode active material (CAP2) satisfies 300 mAh / g ≤ CAP2 ≤ 360 mAh / g. Claim 6 A sodium ion battery according to claim 1, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises one or more types of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and sodium alloys. Claim 7 A sodium ion battery according to claim 1, wherein the negative electrode active material layer comprises a negative electrode active material, and the particle size distribution of the negative electrode active material satisfies 0.5 ≤ (DV90 - DV10) / DV50 ≤ 2; and 1 μm ≤ DV50 ≤ 20 μm. Claim 8 A sodium ion battery according to claim 1, wherein the positive electrode active material layer comprises a positive electrode active material having the molecular formula Na2MFe(CN)6, M comprises one or more types of Mg, K, Ca, V, Cr, Mn, Co, Ni, Cu, and Zn, and the molar ratio of M to Fe satisfies 0.95 to 1.

05. Claim 9 A sodium ion battery according to claim 1, wherein the thickness of the separator satisfies 5μm to 15μm. Claim 10 A battery module comprising a sodium ion battery according to any one of claims 1 to 9. Claim 11 A battery pack comprising the battery module of claim 10. Claim 12 An electric device comprising the battery pack of claim 11.

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