Sodium secondary battery and electric device

Abstract

The present application provides a sodium secondary battery and an electric device. The sodium secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a sodium reactant.

Description

Sodium secondary battery and electric device TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a sodium secondary battery and an electric device. BACKGROUND

[0002] With the increasing prominence of energy and environmental problems, new energy industries have received more and more attention. In recent years, secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. due to their high energy density and good cycle performance.

[0003] Sodium has the advantages of abundant reserves and low cost, and compared with lithium secondary batteries, sodium secondary batteries are a more environmentally friendly energy solution. However, sodium secondary batteries are prone to dendrite growth, which can cause the risk of piercing the separator and causing internal short circuit of the battery cell, resulting in safety hazards, which limits the development of sodium secondary batteries.

[0004] SUMMARY

[0005] The present application is made in view of the above-mentioned problems, and aims to provide a sodium secondary battery with good safety and cycle stability.

[0006] The first aspect of the present application provides a sodium secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, the separator comprising a sodium reactive agent.

[0007] The sodium reactive agent in the separator reacts with sodium dendrites or free cluster sodium, causing the sodium dendrites to change into ion-conducting sodium salt, eliminating or blocking the dendrites, reducing the risk of dendrite growth piercing the separator, and improving the cycle performance and safety performance of the sodium secondary battery.

[0008] In any embodiment, the sodium reactive agent comprises a sodium-containing hydrate.

[0009] The sodium-containing hydrate can directly react with sodium to form ion-conducting sodium salt, reducing the risk of sodium dendrites continuing to grow and piercing the separator, and improving the cycle performance and safety performance of the sodium secondary battery.

[0010] In any embodiment, the sodium-containing hydrate comprises a composition of formula I x M y Q z ·σH2O formula I

[0011] M comprises one or more of Sb, Bi, Sn; Q comprises one or more of O, Cl, S, F, Br; sigma is any value from 1 to 9, x is any value from 1 to 5, y is any value from 0 to 2, and z is any value from 1 to 5.

[0012] The sodium hydrate can react with sodium dendrites or free sodium clusters in an electrochemical environment, and can eliminate free sodium.

[0013] In any embodiment, the sodium reaction agent has a particle volume distribution particle size Dv50 of 100 nm to 5 microns.

[0014] The particle volume distribution particle size Dv50 of the sodium reaction agent is within a suitable range, which on the one hand reduces the risk of clogging the pores on the surface of the material layer due to too small particle size of the particles, so that the separator maintains good air permeability and ion transmission performance, and on the other hand does not cause deterioration of the processing performance due to too large particle size of the particles of the sodium reaction agent, improves the uniformity of the distribution of the sodium reaction agent in the separator, and also reduces the "powder dropping" phenomenon of the sodium reaction agent with too large particle size during processing, which affects the effect of the sodium reaction agent on absorbing sodium dendrites, and improves the fast charging performance and safety performance of the sodium secondary battery.

[0015] In any embodiment, the sodium hydrate comprises one or more of Na3SbS4·7H2O, NaBiO3·5H2O, and NaSnCl3·6H2O.

[0016] In any embodiment, the separator comprises a base film and a functional layer arranged on at least one side of the base film, and optionally, the functional layer comprises the sodium reaction agent; and / or the base film comprises the sodium reaction agent.

[0017] In any embodiment, the functional layer containing the sodium reaction agent is arranged on both sides of the base film.

[0018] The above arrangement can effectively eliminate dead sodium and block the growth of sodium dendrites in a timely and effective manner, and can also play the role of a bottom line for the sodium reaction agent, thereby achieving a dual protection function and improving the cycle stability of the sodium secondary battery.

[0019] In any embodiment, the base film comprises one or more of polyethylene (PE), polypropylene (PP), glass fiber, non-woven fabric, and polyvinylidene fluoride, and / or the functional layer comprises one or more of ceramic material and polymer material.

[0020] In any embodiment, the separator has a pore size of 0.2 microns to 1 micron, and / or the separator has an air permeability Gurley value of 100 seconds to 500 seconds.

[0021] When the pore size and / or the Gurley value of the separator is in the above range, it indicates that the addition of the sodium reactant does not cause excessive deterioration of the performance of the separator, the separator can still form uniform ion transmission channels, so that the ion retains a good transmission rate, and the internal resistance and safety of the sodium secondary battery are considered, the safety risk caused by too large pore size is reduced, and the fast charging performance of the sodium secondary battery is improved.

[0022] In any embodiment, the sodium secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, and the mass ratio of the sodium reactant in the unit area separator to the mass of the unit area single-sided positive electrode film layer is 0.1%-5%, optionally 1%-3%.

[0023] The mass ratio of the sodium reactant in the unit area separator to the mass of the unit area single-sided positive electrode film layer is in a suitable range, so that there is enough sodium hydrate in the separator for absorbing sodium dendrites, achieving the purpose of improving the cycle performance of the sodium secondary battery, while also reducing the influence of excessive sodium hydrate content on the compatibility of the separator, reducing the interface effect, controlling the growth rate of the battery impedance, and comprehensively improving the cycle performance and rate performance of the sodium secondary battery.

[0024] In any embodiment, the sodium secondary battery comprises one or more of a sodium ion battery and a sodium metal battery.

[0025] In any embodiment, the sodium metal battery comprises a negative electrode-free battery.

[0026] A second aspect of the present application provides a power utilization device comprising the sodium secondary battery provided in the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a schematic diagram of a separator according to an embodiment of the present application.

[0028] FIG. 2 is a schematic diagram of a sodium secondary battery according to an embodiment of the present application.

[0029] FIG. 3 is an exploded view of the sodium secondary battery according to an embodiment of the present application shown in FIG. 2.

[0030] FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0031] FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0032] FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5.

[0033] FIG. 7 is a schematic diagram of a power utilization device using the sodium secondary battery according to an embodiment of the present application as a power source.

[0034] Explanation of Reference Numerals: 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: sodium secondary battery; 51: case; 52: electrode assembly; 53: top cap assembly; 10: separator; 101: base film; 102: functional layer. DETAILED DESCRIPTION

[0035] Hereinafter, specific embodiments of the sodium secondary battery and the electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed description is omitted. For example, there are cases where detailed description of matters that are well known, repeated description of substantially 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 accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0036] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way are generally inclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained within the range, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing those numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0038] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0039] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0040] If not specified otherwise, the terms "comprising" and "including" as used in the present application are open-ended. For example, the terms "comprising" and "including" can mean that other components not listed can also be included or can mean that only the listed components are included.

[0041] If not specified otherwise, the term "or" in the present application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": 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).

[0042] With the development of the current society, people's requirements for the safety of sodium secondary batteries are also getting higher and higher. However, after multiple cycles, sodium secondary batteries are prone to grow sodium dendrites or precipitate free sodium clusters on the surface of the negative electrode. Metal sodium dendrites and free sodium clusters can pierce the separator, causing the positive electrode and the negative electrode to come into contact with each other, resulting in internal short circuit of the battery cell, especially in the fast charging process and low temperature use scenarios, dendrites are particularly prone to occur, affecting the cycle performance and safety performance of the sodium secondary battery.

[0043] [Secondary battery]

[0044] The first aspect of the present application provides a sodium secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a sodium reactive agent.

[0045] In the present application, the sodium secondary battery includes but is not limited to sodium ion battery, sodium metal battery. It can be understood that the negative electrode-free sodium battery belongs to one of the sodium metal batteries.

[0046] In the present application, the sodium reactive agent refers to a substance capable of reacting with sodium, including but not limited to compounds, compositions, composites, etc.

[0047] The sodium reaction agent reacts with sodium dendrites or free sodium clusters in the diaphragm to convert the sodium dendrites into ionic sodium salt, eliminate or block the dendrites, reduce the risk of dendrite growth piercing the diaphragm, and improve the cycle performance and safety performance of the sodium secondary battery.

[0048] In some embodiments, the sodium reaction agent includes a sodium-containing hydrate.

[0049] The sodium-containing hydrate can directly react with sodium element to generate ionic sodium salt, reduce the risk of sodium dendrite growth piercing the diaphragm, and improve the cycle performance and safety performance of the sodium secondary battery.

[0050] In some embodiments, the sodium-containing hydrate includes a composition of formula I. x M y Q z ·σH2O formula I

[0051] M includes one or more of Sb, Bi, and Sn; Q includes one or more of O, Cl, S, F, and Br; σ is any value in the range of 1-9, x is any value in the range of 1-5, y is any value in the range of 0-2, and z is any value in the range of 1-5.

[0052] In some embodiments, σ can be selected as 1, 2, 3, 4, 5, 6, 7, 8, 9, or any numerical range between any two of them; x can be selected as 1, 2, 3, 4, 5, or any numerical range between any two of them; y can be selected as 0, 1, 2, or any numerical range between any two of them; and z can be selected as 1, 2, 3, 4, 5, or any numerical range between any two of them. It should be noted that the selection of x, y, z, and σ here is not limited to integers.

[0053] The above sodium-containing hydrate can react with sodium dendrites or free sodium clusters in an electrochemical environment to eliminate free sodium element, and the specific reaction principle is shown in the following formula: nNa+Na x M y Q z ·σH2O→zNa s1 Q+yNa s2 M+2σNaH+σNa2O.

[0054] In some embodiments, the particle volume distribution particle size Dv50 of the sodium reaction agent is 100 nm-5 μm.

[0055] The volume distribution particle size Dv50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50% from the small particle size side in the particle size volume distribution graph.

[0056] In the present application, the particle size Dv50 of the particle volume distribution of the sodium reactant can be tested by methods known in the art, for example, referring to GB / T 19077-2016, and determined by a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0057] In some embodiments, the particle size Dv50 of the particle volume distribution of the sodium reactant can be selected as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any numerical range between any two of them.

[0058] The particle size Dv50 of the particle volume distribution of the sodium reactant within a suitable range, on the one hand, reduces the risk of clogging the pores on the surface of the material layer due to too small particle size, so that the separator maintains good air permeability and ion transmission performance, and on the other hand, does not cause deterioration of the processing performance due to too large particle size of the sodium reactant, improves the uniformity of the distribution of the sodium reactant in the separator, and also reduces the “powder dropping” phenomenon of the sodium reactant with too large particle size during processing, which affects the effect of sodium dendrite absorption by the sodium reactant, and improves the fast charging performance and safety performance of the sodium secondary battery.

[0059] In some embodiments, the sodium-containing hydrate includes one or more of Na3SbS4·7H2O, NaBiO3·5H2O, and NaSnCl3·6H2O.

[0060] In some embodiments, the separator includes a base film and a functional layer disposed on at least one side of the base film, and optionally, the functional layer includes the sodium reactant; and / or the base film includes the sodium reactant.

[0061] FIG. 1 is a schematic diagram of an embodiment of the separator of the present application, which includes a base film 101 and a functional layer 102 disposed on at least one side of the base film 101.

[0062] In some embodiments, the base film includes one or more of polyethylene (PE), polypropylene (PP), glass fiber, non-woven fabric, and polyvinylidene fluoride.

[0063] In some embodiments, the functional layer includes one or more of ceramic material and polymer material.

[0064] In some embodiments, the base film includes the sodium reactant. The sodium reactant can be co-formed with the base film in any manner.

[0065] In some embodiments, the sodium reactive agent is included in the functional layer. The sodium reactive agent can be formed in the functional layer by blending with a ceramic slurry or a polymer slurry of the functional layer, or can be deposited on the surface of the base film by layer-by-layer deposition, and then a ceramic slurry or a polymer slurry is coated on the surface of the sodium reactive agent to prepare a composite functional layer.

[0066] In some embodiments, the functional layer containing the sodium reactive agent is arranged on the positive electrode side of the base film.

[0067] The sodium reactive agent arranged on the positive electrode side can play a role in eliminating sodium dendrites after the dendrites pierce the separator, serving as the last line of defense and reducing the probability of direct internal short-circuiting fire of the sodium secondary battery.

[0068] In some embodiments, the functional layer containing the sodium reactive agent is arranged on the negative electrode side of the base film.

[0069] The above arrangement can effectively play the role of the sodium reactive agent in eliminating dead sodium, blocking the growth of sodium dendrites, and improving safety, thereby improving the cycle stability of the sodium secondary battery.

[0070] In some embodiments, the functional layer containing the sodium reactive agent is arranged on both sides of the base film.

[0071] The above arrangement can not only effectively play the role of the sodium reactive agent in eliminating dead sodium and blocking the growth of sodium dendrites, but also enable the sodium reactive agent to serve as the bottom line of defense, thereby playing a dual protection function and improving the cycle stability of the sodium secondary battery.

[0072] In some embodiments, the pore size of the separator is 0.2 μm to 1 μm, and / or the air permeability Gurley value of the separator is 100 s to 500 s.

[0073] In this document, the term "Gurley value" reflects the permeability of the separator. That is, the time required for a certain volume of gas to pass through a separator with an area of 1 square inch under a certain pressure condition. In this application, the Gurley value refers to the time required for 100 mL of air to pass through a base film with an area of 6.45 cm 2 under a pressure of 1.24 KPa, and the unit is s.

[0074] In this application, the air permeability Gurley value of the separator can be tested by methods known in the art, for example, by referring to the standard GB / T 36363-2018 for testing. As an example, a gas permeability tester Gurley 4320N can be used for testing. Specifically, for example, the separator is cut into an area of 6.45 cm 2The test sample is placed in a gas permeability tester, and the time for 100 mL of air to pass through the diaphragm under a pressure of 1.24 KPa is measured, which is the Gurley value. The average of the test results of multiple (for example, 3) parallel samples can be taken as the Gurley value of the diaphragm.

[0075] In some embodiments, the air permeability Gurley value of the diaphragm can be selected to be 100 s, 120 s, 140 s, 160 s, 180 s, 200 s, 220 s, 240 s, 260 s, 280 s, 300 s, 320 s, 340 s, 360 s, 380 s, 400 s, 420 s, 440 s, 460 s, 480 s, 500 s, or a numerical range between any two of them.

[0076] In some embodiments, the pore size of the diaphragm can be selected to be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or a numerical range between any two of them.

[0077] In this application, the pore size of the diaphragm can be tested by any method known in the art. As an example, the gas displacement method can be used for testing. The diaphragm with an apparent volume of V1 is rolled into a ball and inserted into a sample cup. The sample cup containing the sample is placed in a true density tester, and the system is closed. Helium is introduced according to the program. The porosity of the sample to be tested is calculated according to the Boyle law (PV = nRT) by detecting the pressure of the gas in the sample chamber and the expansion chamber. Specifically, the sample cup volume is 3.5 cm 3 , and the percentage of the sample hole volume to the total volume is [(V1-V2) / V1]x100%, V1 is the apparent volume of the sample, and V2 is the true volume of the sample.

[0078] When the pore size and / or the Gurley value of the diaphragm are within the above ranges, it indicates that the addition of the sodium reactant does not cause excessive degradation of the performance of the diaphragm. The diaphragm can still form uniform ion transmission channels, so that the ion has a good transmission rate, and the internal resistance and safety of the sodium secondary battery are considered. The safety risk caused by the excessively large pore size is reduced, and the fast charging performance of the sodium secondary battery is improved.

[0079] In some embodiments, the sodium secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, and the mass ratio of the sodium reactant in the diaphragm per unit area to the mass of the single-sided positive electrode film layer per unit area is 0.1%-5%, which can be selected to be 1%-3%.

[0080] In some embodiments, the mass ratio of the sodium reactant in the separator per unit area to the mass of the single-sided positive electrode film layer per unit area can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any numerical range between any two of the above values.

[0081] The mass ratio of the sodium reactant in the separator per unit area to the mass of the single-sided positive electrode film layer per unit area is within a suitable range, so that there is enough sodium hydrate in the separator for absorbing sodium dendrites, achieving the purpose of improving the cycle performance of the sodium secondary battery, while also reducing the influence of excessive sodium hydrate content on the compatibility of the separator, reducing the interface effect, controlling the growth rate of the battery impedance, and comprehensively improving the cycle performance and rate performance of the sodium secondary battery.

[0082] In some embodiments, the sodium secondary battery includes one or more of a sodium-ion battery, a sodium metal battery.

[0083] In some embodiments, the sodium metal battery includes a negative electrode-free battery.

[0084] A negative electrode-free secondary battery refers to a battery that is not actively provided with a negative electrode active material layer on the negative electrode side during the manufacturing process of the battery, for example, a battery that is not provided with a metal or carbon-based active material layer on the negative electrode by coating or deposition process during the manufacturing process of the battery. During the first charging, active ions obtain electrons on the anode side to deposit in the form of metal on the surface of the current collector to form a metal phase. During discharging, the metal can be converted into active ions to return to the positive electrode, realizing cyclic charging and discharging. Therefore, the negative electrode-free battery is also a kind of metal battery. Compared with other secondary batteries, the negative electrode-free secondary battery can obtain higher energy density because it does not need to pre-provide a negative electrode active material layer.

[0085] Although the negative electrode-free secondary battery does not need to provide a metal or carbon-based active material layer by coating or deposition process to form a negative electrode active material layer, the negative electrode-free secondary battery often has a primer layer containing conductive material to achieve the function of inducing deposition.

[0086] [Positive electrode sheet]

[0087] In some embodiments, the sodium secondary battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on at least part of the surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, which can include at least one of a layered transition metal oxide, a polyanion compound, and a Prussian blue compound.

[0088] The transition metal in the layered transition metal oxide can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Alternatively, the layered transition metal oxide is, for example, NaxMO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x < 1.

[0089] The polyanionic compound can be a compound having a metal ion, a transition metal ion and a tetrahedral (YO4) n- The metal ion can be selected from one of sodium ion, lithium ion, potassium ion and zinc ion; the transition metal can be selected from at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ge, Ga, Sn, Hf, Ta, W and Pb; Y can be selected from at least one of P, S and Si; and n represents the valence of (YO4) n- .

[0090] As an alternative embodiment of the present application, the chemical formula of the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4)2 c F z-d Q d , wherein the A element represents an alkali metal element doped to substitute the Na element, the M element represents a metal element doped to substitute the V element, the D element represents a doping element doped to substitute the P element, and the Q element represents a doping element doped to substitute the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 < x < 4.5, 0 < a < 0.15x, 0.8 < y < 1.1, 0 < b < 0.3y, 0 < c < 0.15, 0.8 < z < 1.1, 0 < d < 0.2z. Alternatively, the A element includes at least one of K and Li; and the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu and Co.

[0091] As an alternative embodiment of the present application, the chemical formula of the polyanionic compound can be Na x R y (PO4)2P2O7, wherein x = 3.5-4.5, y = 2.75-3.25, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb.

[0092] As an optional embodiment of the present application, the chemical formula of the polyanionic compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein 0 < x < 0.5, 0 < y < 0.5, 0 < m < 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0093] As an optional embodiment of the present application, the chemical formula of the polyanionic compound can be Na m Fe x (PO4) y P2O7 / C; wherein 3.6 < m < 4.4, 2.8 < x < 3, and 2 < y < 2.1. The Prussian blue compound can be a compound having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, Na a Me b Me’ c (CN)6, wherein Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a < 2, 0 < b < 1, and 0 < c < 1.

[0094] In some embodiments, the positive electrode active material layer can further include a conductive agent to improve the conductivity of the positive electrode. The conductive agent can be selected from one or more of Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0095] In some embodiments, the positive electrode active material layer can further include a binder to firmly bind the positive electrode active material and the optional conductive agent to the positive electrode current collector. The binder can be selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0096] In some embodiments, the positive current collector can adopt conductive carbon sheets, metal foils, carbon-coated metal foils, porous metal plates, or composite current collectors. The conductive carbon material of the conductive carbon sheets can be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foils, carbon-coated metal foils, and porous metal plates is independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil and a polymer-based film.

[0097] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and performing processes such as drying, cold pressing, and the like to obtain the positive electrode sheet.

[0098] [Electrolyte]

[0099] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0100] In some embodiments, the electrolyte adopts an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0101] In some embodiments, the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethanesulfonylimide, sodium triflate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0102] In some embodiments, the electrolyte solution includes an ester-based solvent, and the ester-based solvent includes at least one selected from ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, and fluoroethylene carbonate.

[0103] In some embodiments, the electrolyte solution includes an ether-based solvent, and the ether-based solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether, and optionally includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0104] In some embodiments, the electrolyte can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, and the like.

[0105] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be formed into an electrode assembly through a winding process or a stacking process.

[0106] In some embodiments, the sodium secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0107] In some embodiments, the outer package of the sodium secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the sodium secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, and the like can be listed.

[0108] The shape of the sodium secondary battery according to the present application is not particularly limited, and can be cylindrical, square, or any other shape. For example, FIG. 2 is a sodium secondary battery 5 having a square structure as an example.

[0109] In some embodiments, referring to FIG. 3, the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate can enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the sodium secondary battery 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0110] In some embodiments, the sodium secondary battery can be assembled into a battery module, and the number of sodium secondary batteries included in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0111] FIG. 4 is a battery module 4 as an example. Referring to FIG. 4, in the battery module 4, a plurality of sodium secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arrangements can also be used. Further, the plurality of sodium secondary batteries 5 can be fixed by fasteners.

[0112] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of sodium secondary batteries 5 can be received in the receiving space.

[0113] In some embodiments, the battery module described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0114] Figs. 5 and 6 are a battery pack 1 as an example. Referring to Figs. 5 and 6, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0115] In addition, the present application also provides a power utilization device, which includes at least one of the sodium secondary battery, the battery module, or the battery pack provided by the first aspect of the present application. The sodium secondary battery, the battery module, or the battery pack can be used as a power source of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook 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 and a satellite, an energy storage system, etc., but is not limited thereto.

[0116] As the power utilization device, the sodium secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0117] Fig. 7 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high power and high energy density of the sodium secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0118] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and the sodium secondary battery can be used as a power source.

[0119] Embodiments

[0120] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0121] Embodiment 1

[0122] 1) Preparation of the positive electrode sheet

[0123] 95wt% of the positive electrode active material sodium pyrophosphate, 2.5wt% of the conductive agent conductive carbon black, 2.0wt% of the binder polyvinylidene fluoride, and 0.5wt% of the dispersant polypropylene pyrrole PVP were mixed, then N-methyl pyrrolidone was added for stirring and dispersion to prepare a positive electrode slurry.

[0124] The viscosity of the positive electrode slurry was adjusted to 8000-20000 mPa.s, and then the positive electrode slurry was coated on an Al foil by a double-sided double-cavity coating device. After the double-sided coating was completed, drying, cold pressing, and slitting were performed to prepare a positive electrode sheet.

[0125] 2) Preparation of a negative electrode sheet

[0126] Sodium metal was used as the negative electrode sheet

[0127] 3) Preparation of an electrolyte

[0128] In an argon atmosphere glove box with a water content <10 ppm, a first sodium salt sodium hexafluorophosphate and a second sodium salt sodium perchlorate were added to an ethylene glycol dimethyl ether solvent to obtain a mixed solution, the molar concentration of the sodium hexafluorophosphate was 1 mol / L, and the molar concentration of the sodium perchlorate was 1 mol / L.

[0129] 4) Preparation of a separator

[0130] The base film of the separator was polyethylene PE, and a PVDF polymer slurry containing Na3SbS4·7H2O was coated on both sides of the separator by a gravure process, the coating mass of the slurry on both sides was 1:1, and after drying to form a film, the mass of Na3SbS4·7H2O in the separator was 1% of the mass of the single-sided positive electrode film layer, the total thickness of the separator was 20 μm, the thickness of the base film was 12 μm, and the thickness of the single-sided functional layer formed by the PVDF polymer slurry was 4 μm.

[0131] The Dv50 of the Na3SbS4·7H2O particles was 5 μm.

[0132] 5) Preparation and design of a battery

[0133] The positive electrode sheet, the separator, and the negative electrode sheet were placed in order to assemble a wound battery for testing.

[0134] The preparation method of Example 2-7 was basically the same as that of Example 1, except that the type, position, or addition amount of the sodium reagent was adjusted, as shown in Table 1.

[0135] Comparative Example 1

[0136] The preparation method of Comparative Example 1 was basically the same as that of Example 1, except that Na3SbS4·7H2O was not added to the separator.

[0137] Table 1

[0138] II. Performance test

[0139] 1. Cycle number test

[0140] The battery was tested at 25℃, rested for 30 min, discharged to 1.5V at 0.33C rate, rested for 30 min again, charged to 3.65V at 0.33C rate, charged to the cut-off current 0.05C at constant voltage, and recorded as the charge capacity C. After resting for 30 min, it was discharged to 1.5V at 0.33C rate, and recorded as the discharge capacity D. This was one charge-discharge cycle, and the above operation was repeated to record the cycle number when the discharge capacity decayed to 80% SOH of the charge capacity.

[0141] 2. C / D average value test

[0142] The battery was tested at 25℃, rested for 30 min, discharged to 1.5V at 0.33C rate, rested for 30 min again, charged to 3.65V at 0.33C rate, charged to the cut-off current 0.05C at constant voltage, and recorded as the charge capacity C. After resting for 30 min, it was discharged to 1.5V at 0.33C rate, and recorded as the discharge capacity D. This was one charge-discharge cycle, and the above operation was repeated to record the cycle number when the discharge capacity decayed to 80% SOH of the charge capacity.

[0143] III. Analysis of test results of each example and comparative example

[0144] The batteries of each example and comparative example were prepared according to the above method, and each performance parameter was measured, and the results are shown in Table 2 below.

[0145] Table 2

[0146] Test results

[0147] The C / D average value can be used to characterize the degree of lithium loss during the cycle process. The higher the C / D value, the higher the content of lithium converted into dead lithium during the cycle process, and the faster the growth rate of lithium dendrites.

[0148] According to the comparison of the examples and comparative examples of the present application, it can be seen that the sodium secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, and the separator comprises a sodium reactant, which can comprehensively improve the safety performance and cycle performance of the sodium secondary battery.

[0149] According to Examples 1, 3-4 of the present application, it can be seen that the sodium reactant disposed on both sides of the separator is beneficial to further improve the cycle stability of the sodium secondary battery.

[0150] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. In addition, other modes constructed by combining part of the configurations of the embodiments in a manner that a person skilled in the art can think of within the scope of the present application are also included in the scope of the present application.

Claims

1. A sodium secondary battery characterized by comprising: The sodium secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a sodium reaction agent.

2. The sodium secondary battery according to claim 1, characterized by, The sodium reaction agent comprises a sodium-containing hydrate.

3. The sodium secondary battery according to claim 2, characterized by, The sodium-containing hydrate comprises a composition of general formula as in Formula I x M y Q z • σH2O Formula I M comprises one or more of Sb, Bi, and Sn; Q comprises one or more of O, Cl, S, F, and Br; σ is any value in the range of 1-9; x is any value in the range of 1-5; y is any value in the range of 0-2; and z is any value in the range of 1-5.

4. The sodium secondary battery according to any one of claims 1 to 3, characterized by, The sodium reaction agent has a particle volume distribution particle size Dv50 in the range of 100 nm-5 μm.

5. The sodium secondary battery according to any one of claims 2 to 4, characterized by, The sodium-containing hydrate comprises one or more of Na3SbS4·7H2O, NaBiO3·5H2O, and NaSnCl3·6H2O.

6. The sodium secondary battery according to any one of claims 1 to 5, characterized by, The separator comprises a base film and a functional layer arranged on at least one side of the base film, and the functional layer optionally comprises the sodium reaction agent; and / or the base film comprises the sodium reaction agent.

7. The sodium secondary battery according to any one of claims 1 to 6, characterized by, The functional layer comprising the sodium reaction agent is arranged on both sides of the base film.

8. The sodium secondary battery according to claim 6 or 7, characterized by, The base film comprises one or more of polyethylene (PE), polypropylene (PP), glass fiber, non-woven fabric, and polyvinylidene fluoride, and / or the functional layer comprises one or more of ceramic material and polymer material.

9. The sodium secondary battery according to any one of claims 1 to 8, characterized by, The separator has a pore size in the range of 0.2 μm-1 μm, and / or the separator has a Gurley value in the range of 100 s-500 s.

10. The sodium secondary battery according to any one of claims 1 to 9, characterized by, The sodium secondary battery comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, and the mass ratio of the sodium reaction agent in the unit area of the separator to the mass of the unit area of the single-sided positive electrode film layer is in the range of 0.1%-5%, and optionally in the range of 1%-3%.

11. The sodium secondary battery according to any one of claims 1 to 10, characterized by, The sodium secondary battery comprises one or more of a sodium-ion battery and a sodium-metal battery.

12. The sodium secondary battery according to claim 11, characterized by, The sodium-metal battery comprises a negative-electrode-free battery.

13. An electrical device, comprising: The electric device comprises the sodium secondary battery of any one of claims 1-12.

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