Sodium ion battery, battery and electric device

Abstract

The invention provides a sodium ion battery, a battery and an electric device. The sodium ion battery comprises a negative pole piece and a positive pole piece containing a positive active material, wherein the negative pole piece comprises a negative current collector and a sodium metal layer arranged on at least one surface of the negative current collector; the slope of the SOC-OCV curve of the sodium ion battery is k, and the SOC-OCV curve of the sodium ion battery meets the following conditions: the accumulated SOC is greater than or equal to 20%, and k is greater than or equal to 5mV / 1% SOC.

Description

Sodium ion batteries, batteries and electrical devices Technical Field

[0001] The present application relates to a sodium ion battery, a battery and an electrical device. Background Art

[0002] Sodium-ion batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric aircraft, electric boats, electric toy cars, electric toy boats, electric toy airplanes and power tools, etc.

[0003] As battery applications become increasingly widespread, the performance requirements for sodium-ion batteries are becoming increasingly stringent. Because sodium-ion batteries have virtually no voltage change at the negative electrode, they are not conducive to correcting the state of charge, and thus hindering the control of battery management systems.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a sodium ion battery, a battery and an electrical device.

[0006] A first aspect of the present application provides a sodium ion battery, comprising a negative electrode sheet and a positive electrode sheet containing a positive electrode active material, the negative electrode sheet comprising a negative electrode current collector and a sodium metal layer disposed on at least one surface of the negative electrode current collector; the slope of a state of charge (SOC)-open circuit voltage (OCV) curve of the sodium ion battery is k, and the state of charge (SOC)-open circuit voltage (OCV) curve of the sodium ion battery satisfies: cumulative SOC ≥ 20%, k ≥ 5 mV / 1% SOC.

[0007] Therefore, when the sodium ion battery of the embodiment of the present application meets the above range, within the range of 0 to 100% SOC, at least a cumulative 20% SOC has a significant platform change, that is, the SOC-OCV curve has a significant slope change and has k ≥ 5mV / 1% SOC, which is beneficial to the control of the battery management system BMS.

[0008] In some embodiments, the state of charge (SOC)-open circuit voltage (OCV) curve of the sodium ion battery satisfies: 90%≤SOC≤100%, k≥5mV / 1%SOC.

[0009] In some embodiments, the state of charge (SOC)-open circuit voltage (OCV) curve of the sodium ion battery satisfies: 25%≤SOC≤50%, k≥5mV / 1%SOC.

[0010] In some embodiments, the positive electrode plate includes a positive electrode active material comprising at least one of a layered oxide and a sodium-containing polyanionic compound and a modified compound thereof. By combining these two types of materials, the embodiments of the present application can adjust the state of charge (SOC)-open circuit voltage (OCV) curve of the sodium-ion battery, facilitating further precise control of the battery management system (BMS).

[0011] In some embodiments, the layered oxide comprises a molecular formula of Na x M y One or more compounds of O2 and modified compounds thereof, wherein 0<x≤4.5, 0<y≤1, M is selected from one or more of Ti, V, Cr, Fe, Co, Mn, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; further optionally, M is selected from one or more of Ti, V, Cr, Fe, Co, Mn, Ni, Cu and Zn.

[0012] In some embodiments, the layered oxides include NaFeO2, NaTiO2, NaMnO2, Na2NiO2, Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O2、Na 2 / 3 [Cu 1 / 3 Mn 2 / 3 ]O2、Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 ]O2、Na 2 / 3 [Co 2 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]One or more of O2.

[0013] In some embodiments, the anion of the polyanionic compound comprises PO4 3- 、P2O7 4- 、(PO4)2P2O7 10- 、(SO4)2 4- and (SO4)3 6- One or more of; further optionally, the anion of the polyanionic compound further includes F - .

[0014] In some embodiments, the polyanionic compound includes cations of one or more elements from the following group: Ni, V, Co, Fe, Mn, Ti, Cr, Zn, and Cu.

[0015] In some embodiments, the polyanionic compound includes NaCoPO4, NaMnPO4, Na3V2(PO4)3, NaCoPO4F, Na2CoP2O7, Na2FeP2O7, Na2MnP2O7, Na4Co3(PO4)2P2O7, Na4Fe3(PO4)2P2O7, Na4Mn3(PO4)2P2O7, and Na2Fe(SO4) 2、 One or more of Na2Fe2(SO4)3.

[0016] In some embodiments, based on the total molar amount of anions of the polyanionic compound, PO4 3- The molar percentage is recorded as A mol %,P2O7 4- The molar percentage is recorded as B mol %; the polyanionic compound satisfies: 0.1≤A / B≤5.0; optionally, 0.1≤A / B≤3.0.

[0017] In some embodiments, based on the total mass of the layered oxide and the polyanionic compound, the mass percentage of the layered oxide is C wt %, 0<C≤70.

[0018] The second aspect of the present application further provides a battery, comprising the sodium ion battery described in any embodiment of the first aspect of the present application.

[0019] The third aspect of the present application further provides an electrical device comprising the battery described in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0021] FIG1 is a schematic diagram of an embodiment of a secondary battery of the present application.

[0022] FIG. 2 is an exploded schematic diagram of an embodiment of the secondary battery of FIG. 1 .

[0023] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0024] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0025] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0026] FIG6 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.

[0027] FIG7 is an open circuit voltage OCV-state of charge SOC curve of the sodium ion battery in Comparative Example 1 and Example 1.

[0028] The drawings are not necessarily drawn to scale.

[0029] The reference numerals are as follows: 1. battery pack; 2. upper case; 3. lower case; 4. battery module; 5. secondary battery; 51. housing; 52. electrode assembly; 53. cover plate; 6. electrical device. DETAILED DESCRIPTION

[0030] The following detailed description specifically discloses the embodiments of the sodium ion battery, battery, and electrical device of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the 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.

[0031] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0034] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0035] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0036] In this application, the terms "plurality" and "multiple" refer to two or more.

[0037] To characterize the battery's condition, the battery's state of charge (SOC) is generally measured to reflect the battery's capacity. When not charging, the battery's capacity is considered A0, corresponding to 0% SOC. When fully charged, the battery is considered to have reached its rated capacity, A, corresponding to 100% SOC. During charging, when the battery's capacity is x% (A-A0), it corresponds to x% SOC, where x% is any value between 0 and 100. For example, if x is 70, the battery is charged to 70% of its capacity (A-A0), corresponding to 70% SOC.

[0038] In the related art, the open circuit voltage method is often used to correct the state of charge of the battery. The open circuit voltage (OCV) of the battery is tested by a detection unit. The detection unit transmits the open circuit voltage OCV to the battery management system BMS. The battery management system BMS obtains the state of charge of the battery according to the SOC-OCV curve of the battery, and obtains the first state of charge change of the battery according to the state of charge and the state of charge obtained last time. At the same time, the battery management system BMS obtains the current in the battery circuit and calculates the second state of charge change of the battery through ampere-hour integration. Finally, the first state of charge change obtained by the open circuit voltage method is used to correct the second state of charge change obtained by ampere-hour integration to obtain the state of charge of the battery.

[0039] However, in the related art, the negative electrode plate of the sodium ion battery includes a negative electrode current collector and a sodium metal layer. During the charge and discharge process, the sodium metal layer has basically no voltage change. In addition, since the positive electrode plate of the sodium ion battery may have full-platform characteristics, it is not easy to determine the negative electrode SOC state and the SOC state of the entire battery through the SOC-OCV curve, thereby making it impossible to perform closed-loop correction, and is not conducive to the control of the battery management system BMS.

[0040] In response to the above problems, the inventors improved the positive electrode active material so that the SOC-OCV curve has a certain slope change, which is beneficial to the control of the battery management system BMS.

[0041] Sodium-ion batteries

[0042] In a first aspect, the present application proposes a sodium ion battery, comprising a negative electrode sheet and a positive electrode sheet containing a positive electrode active material, the negative electrode sheet comprising a negative electrode current collector and a sodium metal layer disposed on at least one surface of the negative electrode current collector, the slope of the state of charge (SOC)-open circuit voltage (OCV) curve of the sodium ion battery being k, and the state of charge (SOC)-open circuit voltage (OCV) curve of the sodium ion battery satisfying: cumulative SOC ≥ 20%, k ≥ 5 mV / 1% SOC.

[0043] The sodium metal layer of the negative electrode plate can be a sodium metal sheet disposed on the negative electrode current collector. The sodium metal sheet can be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. Alternatively, the sodium metal layer can be sodium metal deposited on the negative electrode current collector during charging.

[0044] The positive electrode active material in the positive electrode plate has a slope change characteristic. The positive electrode active material is used in combination with the above-mentioned negative electrode plate, so that it has an OCV change characteristic during the charging process.

[0045] When the sodium ion battery of the embodiment of the present application meets the above range, within the range of 0 to 100% SOC, at least a cumulative 20% SOC has a significant platform change, that is, the SOC-OCV curve has a significant slope change and has k ≥ 5mV / 1% SOC, which is beneficial to the control of the battery management system BMS.

[0046] The following is an embodiment of the method for testing the state of charge (SOC)-open circuit voltage (OCV) curve of the present application, comprising the following steps:

[0047] S101: charging the sodium ion battery using a nominal current constant current and constant voltage until the nominal upper limit cut-off voltage of the sodium ion battery is reached, so that the sodium ion battery is fully charged;

[0048] S102: leaving the fully charged sodium ion battery at rest for 2 hours to allow the electrolyte in the sodium ion battery to fully infiltrate the separator and active material, so that the voltage of the sodium ion battery tends to be stable;

[0049] S103: Discharging the battery at a discharge rate of 0.33C to a lower cutoff voltage of the sodium ion battery to obtain an actual discharged capacity C0 of the sodium ion battery. The actual discharged capacity C0 is the actual capacity of the sodium ion battery.

[0050] S104: leaving the discharged sodium ion battery to stand for 2 hours to allow the electrolyte in the sodium ion battery to fully infiltrate the separator and the active material, so that the voltage of the sodium ion battery tends to be stable;

[0051] S105: Using 0.04C0 to charge the sodium ion battery at a constant current to obtain a capacity C1;

[0052] S106: Using C1 as the denominator, convert the capacity-open circuit voltage curve into a state of charge (SOC)-open circuit voltage (OCV) curve.

[0053] In addition, the nominal current can be freely selected according to the capacity of the battery. For example, when the capacity of the battery is 50Ah, the nominal current can be 50A; for another example, when the capacity of the battery is 100Ah, the nominal current can be 100A.

[0054] In the embodiments of the present application, the cumulative SOC refers to the interval difference of the horizontal axis. For example, if the interval range of the horizontal axis SOC includes (10% to 50%), the cumulative SOC is 50%-10%=40%, that is, the cumulative SOC is 40%. For another example, if the interval range of the horizontal axis SOC includes (10% to 50%) and (70% to 80%), the cumulative SOC is (50%-10%)+(80%-70%)=50%, that is, the cumulative SOC is 50%. The cumulative SOC is 50%.

[0055] The slope k represents the degree of inclination of the tangent of the curve with respect to the horizontal axis, and can be expressed by the ratio of the difference between the vertical coordinates of two points to the difference between the horizontal coordinates. For example, k is 5mV / 1%SOC, which means that the interval difference of the horizontal coordinate is 1%SOC and the interval difference of the vertical coordinate is 5mV.

[0056] The cumulative SOC is 40%, k≥5mV / 1%SOC, which means that within the interval difference of 40% SOC, the curve slope k is greater than or equal to 5mV / 1%SOC.

[0057] Illustratively, if the cumulative SOC is ≥20%, k≥5mV / 1%SOC; or if the cumulative SOC is ≥35%, k≥5mV / 1%SOC; or if the cumulative SOC is ≥40%, k≥5mV / 1%SOC; or if the cumulative SOC is ≥45%, k≥5mV / 1%SOC.

[0058] In some embodiments, the SOC-OCV curve of the sodium-ion battery satisfies the following conditions: 90% ≤ SOC ≤ 100%, k ≥ 5 mV / 1% SOC; 90% ≤ SOC ≤ 100% means that within the SOC range of 90% to 100% on the horizontal axis, the slope of the curve is greater than or equal to 5 mV / 1% SOC. When the SOC-OCV curve of the sodium-ion battery satisfies the above range, the risk of overcharging of the sodium-ion battery can be reduced to a certain extent, and full charging can be more easily controlled.

[0059] In some embodiments, the SOC-OCV curve of a sodium-ion battery satisfies the following conditions: 25% ≤ SOC ≤ 50%, k ≥ 5mV / 1% SOC. 25% ≤ SOC ≤ 50% means that within the SOC range of 25% to 50% on the horizontal axis, the slope of the curve is greater than or equal to 5mV / 1% SOC. When the SOC-OCV curve of a sodium-ion battery satisfies this range, it facilitates step-through testing and SOC and SOH correction.

[0060] [Positive electrode]

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

[0062] The positive electrode film layer may be disposed on one surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector.

[0063] When the positive electrode active material of the sodium ion battery of the embodiment of the present application meets at least one of the following conditions, the slope change characteristics of the SOC-OCV curve of the positive electrode active material are more significant, which is beneficial to the control of the battery management system BMS.

[0064] In some embodiments, the positive electrode active material comprises a layered oxide. Alternatively, the layered oxide comprises a x M y One or more compounds of O2 and modified compounds thereof, wherein 0<x≤2.1, 0<y≤2.1, M is selected from one or more of Ti, V, Cr, Fe, Co, Mn, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; further optionally, M is selected from one or more of Ti, V, Cr, Fe, Co, Mn, Ni, Cu and Zn.

[0065] Illustratively, the layered oxides include NaFeO2, NaTiO2, NaMnO2, Na2NiO2, Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O2、Na 2 / 3 [Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 ]O2、Na 2 / 3 [Cu 1 / 3 Mn 2 / 3 ]O2、Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 ]O2、Na 2 / 3 [Co 2 / 3 Mn1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]One or more of O2.

[0066] In some embodiments, the positive electrode active material further includes a sodium-containing polyanionic compound and a modified compound thereof. The polyanionic compound has various types, such as phosphate, pyrophosphate, mixed polyanionic compounds, sulfate, and the like.

[0067] In some embodiments, the cations of the polyanionic compound may include cations of one or more elements from the following group in addition to sodium ions: Ni, V, Co, Fe, Mn, Ti, Cr, Zn, and Cu.

[0068] In some embodiments, the anion of the polyanionic compound comprises PO4 3- 、P2O7 4- 、(PO4)2P2O7 10- 、(SO4)2 4- and (SO4)3 6- One or more of .

[0069] In some embodiments, the anion of the polyanionic compound further comprises F - .

[0070] In some embodiments, based on the total molar amount of anions of the polyanionic compound, PO4 3- The molar percentage is recorded as A mol %,P2O7 4- The molar percentage is recorded as B mol %, the polyanionic compound satisfies: 5.0≤A / B≤0.1; alternatively, 3.0≤A / B≤0.1. Specifically, the polyanionic compound may include a mixture of phosphate and pyrophosphate, or the polyanionic compound may include a mixed polyanion. Exemplarily, A / B may be 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, or a range consisting of any two of the foregoing values.

[0071] Illustratively, the phosphate includes one or more of NaCoPO4, NaMnPO4, Na3V2(PO4)3, and NaCoPO4F.

[0072] Illustratively, the pyrophosphate includes one or more of Na2CoP2O7, Na2FeP2O7, and Na2MnP2O7.

[0073] Illustratively, the mixed polyanionic compound includes one or more of Na4Co3(PO4)2P2O7, Na4Fe3(PO4)2P2O7, and Na4Mn3(PO4)2P2O7.

[0074] Illustratively, the sulfate includes at least one of Na2Fe(SO4)2 and Na2Fe2(SO4)3.

[0075] In some embodiments, the positive electrode active material may include a layered oxide and a polyanionic compound, and the mass percentage of the layered oxide is C based on the mass of the positive electrode active material. wt %,0<C≤70;Exemplarily, the mass percentage of the layered oxide C wt % can be 1 wt %, 2 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, 45 wt %, 50 wt %, 60 wt %, 70 wt % or a range consisting of any two of the above values.

[0076] On the basis of ensuring that the positive electrode active material meets the above conditions, the modified compound of the embodiment of the present application includes a surface coating modified compound and / or a doping modified compound; the surface coating modified compound can be provided with a coating layer on at least part of the surface of the material particles, and the coating layer can include at least one layer of a carbon layer, an oxide layer, an inorganic salt layer, and a conductive polymer layer; the surface coating modification can improve the cycle performance of the sodium ion battery. The doping modified compound can add at least one of the elements such as Li, Zn, and Cu to the material, and the structural stability of the sodium ion battery can be improved through doping modification.

[0077] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present application embodiment does not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is ≤5 wt % based on the mass of the positive electrode film layer.

[0078] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of the positive electrode binder. As an example, the positive electrode 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 acrylic resin. In some embodiments, based on the mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5wt%.

[0079] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0080] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly.

[0081] [Negative electrode]

[0082] In some embodiments, the negative electrode plate includes a negative electrode current collector. During charging, sodium ions gain electrons on the surface of the negative electrode current collector to form a sodium metal layer.

[0083] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foil, aluminum foil or copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0084] Furthermore, the negative electrode plate further includes a conductive layer disposed on the negative electrode current collector, the conductive layer including a negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In other embodiments, the negative electrode plate includes a negative electrode current collector and a sodium metal sheet disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector, and the sodium metal sheet is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0086] The material of the negative electrode current collector is as described above and will not be repeated here.

[0087] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application embodiment does not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is ≤5 wt% based on the total weight of the negative electrode film layer.

[0088] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application embodiment does not particularly limit the type of the negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin SR-1B, a water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0089] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, or the like. In some embodiments, the other additives may comprise ≤ 2 wt % of the total weight of the negative electrode film layer.

[0090] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until uniformly mixed. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0091] [Electrolyte]

[0092] During the charge and discharge process of a battery cell, sodium ions are intercalated and released back and forth between the positive and negative electrodes, and the electrolyte acts as a conductor of active ions between the positive and negative electrodes. The present application does not impose any particular restrictions on the type of electrolyte, and the electrolyte can be selected based on actual needs.

[0093] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0094] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0095] As an example, the electrolyte salt may include, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bisfluorosulfonyl imide (NaFSI), sodium bistrifluoromethanesulfonyl imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobisoxalatophosphate (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0096] As an example, the solvent may include, but is not limited to, at least one of 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 (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0097] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0098] [Isolation film]

[0099] In some embodiments, the battery cell further includes a separator. The embodiments of the present application have no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0100] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0101] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0102] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square or any other shape. FIG1 shows a battery cell 5 of a square structure as an example.

[0103] In some embodiments, as shown in Figures 1 and 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

[0104] The preparation methods of the battery cells of the embodiments of the present application are well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The battery cell is then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0105] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0106] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0107] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0108] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0109] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0110] The battery according to the embodiment of the present application may further include one or more battery cells. When the battery includes a plurality of battery cells, the battery may include a battery module or a battery pack.

[0111] Electrical devices

[0112] The embodiments of the present application also provide an electrical device, which includes at least one of the battery cells, battery modules, and battery packs of the present application. The battery cells, battery modules, and battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as 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.

[0113] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0114] Figure 6 is a schematic diagram of an exemplary electrical device. Electrical device 6 can be a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or battery module can be used. Another exemplary electrical device can be a mobile phone, tablet computer, or laptop computer. These electrical devices typically require a thin and lightweight design and can utilize battery cells as their power source.

[0115] Example

[0116] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are intended only to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be purchased commercially.

[0117] Example 1

[0118] 1. Preparation of positive electrode sheet:

[0119] Aluminum foil with a thickness of 12 μm was used as the positive electrode current collector.

[0120] The positive electrode active material (50 wt% layered oxide Na 2 / 3 [Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 A positive electrode slurry was prepared in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2, containing 50 wt% of the polyanionic compound Na₃V₂(PO₄)₃, a conductive agent Super P, and a binder of polyvinylidene fluoride. The slurry was coated onto a current collector aluminum foil, dried at 85°C, and then cold-pressed. The cathode was then trimmed, cut, and slit, and then dried at 85°C under vacuum for 4 hours to form the positive electrode sheet.

[0121] 2. Preparation of negative electrode sheet:

[0122] A copper foil with a thickness of 8 μm was used as the negative electrode current collector.

[0123] 3. Preparation of electrolyte

[0124] In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents diethylene glycol dimethyl ether and triethylene glycol dimethyl ether are mixed in a volume ratio of 1:1 to obtain an electrolyte solvent, and then the electrolyte sodium salt sodium hexafluorophosphate and the mixed solvent are mixed to prepare an electrolyte with a sodium salt concentration of 1 mol / L.

[0125] 4. Preparation of sodium ion batteries:

[0126] A 16μm polyethylene film (PE) was used as a separator. The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes were then wound to form an electrode assembly. The electrode assembly was placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, a sodium-ion battery (the soft-pack sodium-ion battery had a thickness of 4.0mm, a width of 60mm, and a length of 140mm) was obtained.

[0127] Comparative Example 1

[0128] A sodium ion battery was prepared by a method similar to that of Example 1. The difference from Example 1 was that the positive electrode active material of Comparative Example 1 was Na3V2(PO4)3.

[0129] The parameters of the embodiments and comparative examples are shown in Table 1.

[0130] Test Method

[0131] 1. Test of element content in positive electrode

[0132] The contents of carbon, metals, and other non-metallic elements were obtained by inductively coupled plasma emission spectroscopy (ICP) using an Agilent ICP-OES730, and the carbon, metals, and other non-metallic elements were calculated based on the ICP results.

[0133] 2. SOC-OCV curve

[0134] S101: charging the sodium ion batteries prepared in the examples and comparative examples using a nominal current constant current and constant voltage until the nominal upper limit cut-off voltage of the sodium ion battery is reached, so that the sodium ion battery is fully charged;

[0135] S102: leaving the fully charged sodium ion battery at rest for 2 hours to allow the electrolyte in the sodium ion battery to fully infiltrate the separator and active material, so that the voltage of the sodium ion battery tends to be stable;

[0136] S103: Discharging the battery at a discharge rate of 0.33C to a lower cutoff voltage of the sodium ion battery to obtain an actual discharged capacity C0 of the sodium ion battery. The actual discharged capacity C0 is the actual capacity of the sodium ion battery.

[0137] S104: leaving the discharged sodium ion battery to stand for 2 hours to allow the electrolyte in the sodium ion battery to fully infiltrate the separator and the active material, so that the voltage of the sodium ion battery tends to be stable;

[0138] S105: Using 0.04C0 to charge the sodium ion battery at a constant current to obtain a capacity C1;

[0139] S106: Using C as the denominator, convert the capacity-open circuit voltage curve into a state of charge (SOC)-open circuit voltage (OCV) curve.

[0140] Test results

[0141] The test results are shown in Table 1.

[0142] Table 1

[0143] As can be seen from Figure 7, Figure 7 is the open circuit voltage OCV-state of charge SOC curve of Comparative Example 1 and Example 1. It can be seen from the curve and Table 1 that compared with Comparative Example 1, the OCV-SOC curve of the positive electrode active material in Example 1 has a significant slope change, which is beneficial to the control of the battery management system BMS.

[0144] The positive electrode active material of the embodiment of the present application is more conducive to precise control of the battery management system BMS when it meets 90%≤SOC≤100%, k≥5mV / 1%SOC; and / or 25%≤SOC≤50%, k≥5mV / 1%SOC.

[0145] The embodiment of the present application adjusts the type of positive electrode active material, for example, the anion of the polyanion active material is adjusted to PO4 3- and / or (PO4)2P2O7 10- , or the cations (non-sodium ions) of the polyanion active material are adjusted to other cations such as Ni, V, Co, etc., and the OCV-SOC curve of the positive electrode active material as a whole has a significant slope change, which is beneficial to the control of the battery management system BMS. The embodiment of the present application can also adjust the type of layered oxide, for example, adjusting the cations of the layered oxide to Ti, V, Cr, Co, etc., so that the OCV-SOC curve of the positive electrode active material as a whole has a significant slope change, which is beneficial to the control of the battery management system BMS. Of course, the present application can also adjust the OCV-SOC curve change trend by adjusting the molar ratio of different anions and / or the molar ratio of different cations.

[0146] The embodiment of the present application can also adjust the mass ratio of the layered oxide and the polyanionic compound to regulate the change trend of the OCV-SOC curve of the entire positive electrode active material, so as to enable further precise control of the battery management system BMS.

[0147] Although this application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of this application. In particular, the various technical features described in the various embodiments may be combined in any manner, provided there are no structural conflicts. This application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A sodium ion battery, comprising a negative electrode sheet and a positive electrode sheet containing a positive electrode active material, wherein the negative electrode sheet comprises a negative electrode current collector and a sodium metal layer disposed on at least one surface of the negative electrode current collector; The slope of the state of charge SOC-open circuit voltage OCV curve of the sodium ion battery is k, and the state of charge SOC-open circuit voltage OCV curve of the sodium ion battery satisfies: cumulative SOC≥20%, k≥5mV / 1%SOC.

2. The sodium ion battery according to claim 1, wherein The state of charge SOC-open circuit voltage OCV curve of the sodium ion battery satisfies: 90%≤SOC≤100%, k≥5mV / 1%SOC; and / or 25%≤SOC≤50%, k≥5mV / 1%SOC.

3. The sodium ion battery according to claim 1 or 2, wherein: The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes at least one of a layered oxide and a sodium-containing polyanionic compound and a modified compound thereof; Optionally, the layered oxide comprises a molecular formula of Na x M y O2 and its modified compounds, wherein 0<x≤4.5, 0<y≤1, M is selected from one or more of Ti, V, Cr, Fe, Co, Mn, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; further optionally, M is selected from one or more of Ti, V, Cr, Fe, Co, Mn, Ni, Cu and Zn; Optionally, the anion of the polyanionic compound comprises PO4 3- 、P2O7 4- 、(PO4)2P2O7 10- 、(SO4)2 4- and (SO4)3 6- One or more of; further optionally, the anion of the polyanionic compound also includes F - .

4. The sodium ion battery according to claim 3, wherein: The layered oxides include NaFeO2, NaTiO2, NaMnO2, Na2NiO2, Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O2、Na 2 / 3 [Cu 1 / 3 Mn 2 / 3 ]O2、Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 ]O2、Na 2 / 3 [Co 2 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 ]One or more of O2.

5. The sodium ion battery according to claim 3 or 4, wherein: The polyanionic compound includes cations of one or more elements from the following group: Ni, V, Co, Fe, Mn, Ti, Cr, Zn and Cu.

6. The sodium ion battery according to any one of claims 3 to 5, wherein The polyanionic compound includes one or more of NaCoPO4, NaMnPO4, Na3V2(PO4)3, NaCoPO4F, Na2CoP2O7, Na2FeP2O7, Na2MnP2O7, Na4Co3(PO4)2P2O7, Na4Fe3(PO4)2P2O7, Na4Mn3(PO4)2P2O7 and Na2Fe(SO4)2, Na2Fe2(SO4)3.

7. The sodium ion battery according to any one of claims 3 to 6, wherein Based on the total molar amount of anions of the polyanionic compound, PO4 3- The molar percentage is recorded as A mol %P2O7 4- The molar percentage is recorded as B mol %; the polyanionic compound satisfies: 0.1≤A / B≤5.0; optionally, 0.1≤A / B≤3.

0.

8. The sodium ion battery according to any one of claims 3 to 7, wherein Based on the total mass of the layered oxide and the polyanionic compound, the mass percentage of the layered oxide is C wt %,0<C≤70.

9. A battery comprising the sodium ion battery according to any one of claims 1 to 8.

10. An electrical device comprising the battery according to claim 9.

Images