Battery cell and preparation method and application thereof

Abstract

The invention provides a battery cell and a preparation method and application thereof.The battery cell comprises a positive pole piece, a diaphragm and a negative pole piece, the diaphragm is located between the positive pole piece and the negative pole piece, and a functional coating is arranged between the positive pole piece and the diaphragm; the functional coating comprises a functional compound, and the functional compound comprises vinyl sodium salt. According to the battery cell disclosed by the invention, the functional coating is arranged between the positive pole piece and the diaphragm, and the functional coating contains vinyl sodium salt, so that diffusion of metal ions can be inhibited, HF generated by side reaction of an electrolyte can be eliminated, sodium ions can be additionally supplemented, and electrochemical performance such as first-circle coulombic efficiency and cycle performance of the battery cell can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a battery core and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in all aspects of life, from mobile phones and computers to electric vehicles. However, with the continuous development of electronic devices or electric vehicles, the disadvantages of lithium resources are becoming increasingly apparent. Sodium is abundant, easy to obtain and cheap, so the sodium-ion batteries derived from it have been widely studied, but the performance of sodium-ion batteries needs to be further improved. It is necessary to find a suitable battery cell to improve the electrochemical performance and safety performance of sodium-ion batteries and extend the service life of sodium-ion batteries. Summary of the invention

[0003] The object of the present invention is to provide a battery cell and a preparation method and application thereof, wherein a functional coating is arranged between the positive electrode plate and the diaphragm of the battery cell, and the functional coating contains sodium vinyl salt, which can inhibit the diffusion of metal ions, eliminate HF generated by the side reaction of the electrolyte, additionally supplement sodium ions, and improve the electrochemical properties of the battery cell such as the first-cycle coulomb efficiency and cycle performance.

[0004] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a battery cell, comprising a positive electrode plate, a separator and a negative electrode plate, wherein the separator is located between the positive electrode plate and the negative electrode plate, and a functional coating is provided between the positive electrode plate and the separator; the functional coating comprises a functional compound, and the functional compound comprises sodium vinyl salt.

[0006] Preferably, the vinyl sodium salt includes any one of sodium vinyl sulfonate, sodium 4-styrene sulfonate, tetrasodium vinyl diphosphonate or heptasodium diethylenetriamine penta (methylene phosphonate) or a combination of at least two thereof.

[0007] Preferably, the vinyl sodium salt is tetrasodium vinyl diphosphonate and / or heptasodium diethylene triamine penta (methylene phosphonate).

[0008] Preferably, the functional coating further comprises a first conductive agent and a first binder;

[0009] Preferably, the first conductive agent includes any one of Super P (conductive carbon black), acetylene black, Ketjen black, conductive graphite, and carbon nanotubes, or a combination of at least two thereof.

[0010] Preferably, the first conductive agent is Super P (conductive carbon black) and / or carbon nanotubes.

[0011] Preferably, the mass ratio of the functional compound, the first conductive agent and the first binder is (90-94):(1-6):(2-4).

[0012] Preferably, the positive electrode plate comprises a current collector and a positive electrode active layer disposed on at least one side surface of the current collector, and the thickness ratio of the functional coating to the positive electrode active layer is 1:(10-20).

[0013] Preferably, the thickness of the functional coating is 2-6 μm.

[0014] Preferably, the positive electrode plate comprises a current collector and a positive electrode active layer disposed on at least one side surface of the current collector, and the positive electrode active layer comprises a positive electrode active material, a second conductive agent and a second binder.

[0015] Preferably, the mass ratio of the positive electrode active material, the second conductive agent and the second binder is (90-94):(1-6):(2-4).

[0016] Preferably, the positive electrode active material includes any one of a polyanion compound, a transition metal oxide or a Prussian blue compound, or a combination of at least two thereof.

[0017] Preferably, the diaphragm includes any one of a polypropylene diaphragm, a polyethylene diaphragm or a multi-layer composite diaphragm, or a combination of at least two of them.

[0018] Preferably, the diaphragm is a polypropylene diaphragm.

[0019] In a second aspect, the present invention provides a method for preparing the battery cell according to the first aspect, the method comprising the following steps:

[0020] The functional coating slurry is applied to at least one side of the surface of the positive electrode sheet, and after drying, a functional coating is obtained on at least one side of the surface of the positive electrode sheet, a separator is arranged on the surface of the functional coating, and then a negative electrode sheet is arranged on the side of the separator away from the functional coating to obtain the battery cell;

[0021] Alternatively, a functional coating slurry is coated on at least one side of the surface of the diaphragm, and after drying, a functional coating is obtained on at least one side of the surface of the diaphragm to obtain a composite diaphragm, a positive electrode sheet is arranged on one side of the composite diaphragm, and a negative electrode sheet is arranged on the other side, wherein the positive electrode sheet is arranged on the side of the functional coating away from the diaphragm to obtain the battery cell;

[0022] The functional coating slurry includes a functional compound, and the functional compound includes a vinyl sodium salt.

[0023] In a third aspect, the present invention provides a battery, comprising the battery cell as described in the first aspect, or comprising the battery cell prepared by the preparation method as described in the second aspect.

[0024] In a fourth aspect, the present invention provides an electrical device, wherein the electrical device comprises the battery as described in the third aspect.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a functional coating containing sodium vinyl salt between the positive electrode plate and the separator, so that the vinyl group can form a coordination bond with the transition metal ions in the positive electrode active material in the form of a π bond, thereby inhibiting the diffusion of metal ions, thereby inhibiting the dissolution of metal ions in the positive electrode active material and improving the cycle performance; at the same time, HF generated by the side reaction of the electrolyte can be eliminated, and sodium ions can be additionally supplemented during the first cycle of the battery cell to compensate for the irreversible capacity loss in the first cycle and improve the first cycle coulomb efficiency of the battery cell. DETAILED DESCRIPTION

[0027] Studies have found that the poor performance of sodium-ion batteries during use is mainly due to the following reasons: (1) During the charge and discharge process, the positive electrode active material will dissolve, and the dissolved metal ions will diffuse to the negative electrode surface and be reduced, accelerating the growth of SEI. At the same time, the generated metal element will affect the battery safety performance during subsequent use; (2) The electrolyte will inevitably undergo some side reactions, generating harmful substances such as HF, which will reduce the electrochemical performance of the battery and cause the cycle performance to decline; (3) During the first cycle of charge and discharge, sodium-ion batteries will consume sodium ions to form the SEI film, resulting in the irreversible loss of some sodium ions, which in turn causes a decrease in the first cycle coulombic efficiency.

[0028] Therefore, in order to improve the performance of sodium-ion batteries, it is necessary to solve the problems of metal ion dissolution in the positive electrode active materials of sodium-ion batteries, the impact of electrolyte side reaction products on the performance of sodium-ion batteries, and the irreversible loss of sodium ions during the first cycle of charge and discharge of sodium-ion batteries.

[0029] The present invention adds vinyl sodium salt to the functional coating between the positive electrode plate and the diaphragm. The vinyl sodium salt can not only inhibit the dissolution of metal ions and react with the side reaction products of the electrolyte, but also additionally supplement sodium ions to compensate for the irreversible loss of sodium ions, thereby effectively solving the above technical problems and effectively improving various aspects of the performance of the sodium ion battery.

[0030] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0031] In a first specific embodiment, the present invention provides a battery cell, which includes a positive electrode plate, a separator and a negative electrode plate, wherein the separator is located between the positive electrode plate and the negative electrode plate, and a functional coating is arranged between the positive electrode plate and the separator; the functional coating includes a functional compound, and the functional compound includes sodium vinyl salt.

[0032] The battery cell of the present invention is provided with a functional coating between the positive electrode plate and the separator, wherein the functional coating contains vinyl sodium salt, wherein the vinyl sodium salt contains vinyl groups, which can form coordination bonds with transition metal ions in the positive electrode active material in the form of π bonds, thereby inhibiting the diffusion of metal ions, thereby inhibiting the dissolution of metal ions in the positive electrode active material. At the same time, the vinyl sodium salt has the properties of a Lewis base, and can eliminate HF generated by the side reaction of the electrolyte; in addition, the vinyl sodium salt contains sodium ions, which can additionally supplement sodium ions during the first cycle of the battery cell, compensate for the irreversible capacity loss in the first cycle, and improve the first cycle coulomb efficiency of the battery cell.

[0033] The functional compound of the present invention needs to be a vinyl sodium salt. Only the vinyl sodium salt has the properties of a Lewis base, which can enable the vinyl sodium salt to neutralize HF and coordinate with other substances as an electron donor. Specifically, the vinyl group coordinates with the transition metal ions in the positive electrode active material with π bond electrons, and forms a coordination bond with the transition metal ions in the positive electrode active material to form a "Zeise salt". This bonding method makes the vinyl sodium salt a Lewis base. If the functional compound is a sodium salt such as propenyl or butenyl instead of the vinyl sodium salt of the present invention, the sodium salt such as propenyl or butenyl has no Lewis base properties and cannot neutralize the HF generated during the use of the battery, and the safety of the battery is not guaranteed.

[0034] Preferably, the vinyl sodium salt includes any one of sodium vinyl sulfonate, sodium 4-styrene sulfonate, tetrasodium vinyl diphosphonate or heptasodium diethylenetriamine penta (methylene phosphonate) or a combination of at least two thereof.

[0035] Preferably, the vinyl sodium salt is tetrasodium vinyl diphosphonate and / or heptasodium diethylene triamine penta (methylene phosphonate).

[0036] The vinyl sodium salt of the present invention is preferably tetrasodium vinyl diphosphonate and / or heptasodium diethylenetriamine penta(methylenephosphonate). The sodium content in a single molecule of tetrasodium vinyl diphosphonate and / or heptasodium diethylenetriamine penta(methylenephosphonate) is relatively high, and the sodium supplementation effect is better. Heptasodium diethylenetriamine penta(methylenephosphonate) contains two vinyl groups, and has more sites for coordination with metal ions, and has a better effect of inhibiting the dissolution of metal ions.

[0037] Preferably, the functional coating further includes a first conductive agent and a first binder.

[0038] Preferably, the first conductive agent includes any one of Super P (conductive carbon black), acetylene black, Ketjen black, conductive graphite, and carbon nanotubes, or a combination of at least two thereof.

[0039] Preferably, the first conductive agent is Super P (conductive carbon black) and / or carbon nanotubes.

[0040] The first conductive agent of the present invention is preferably Super P (conductive carbon black) and / or carbon nanotubes. Since Super P (conductive carbon black) and / or carbon nanotubes have a large specific surface area and a high porosity, the functional coating is conducive to the diffusion of ions and can effectively reduce the impact of the functional coating on the performance of the positive electrode active material.

[0041] Preferably, the first binder includes any one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate or polyacrylic acid binders, or a combination of at least two thereof.

[0042] Preferably, the mass ratio of the functional compound, the first conductive agent and the first binder is (90-94):(1-6):(2-4), for example, it can be 90:6:4, 92:4:4, 94:4:2 or 94:2:4, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the positive electrode plate includes a current collector and a positive electrode active layer arranged on at least one side surface of the current collector, and the thickness ratio of the functional coating to the positive electrode active layer is 1:(10-20), for example, it can be 1:10, 1:12, 1:14, 1:16, 1:18 or 1:20, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] The functional coating of the present invention can form coordination bonds with transition metal ions in the positive electrode plate in the form of π bonds, thereby inhibiting the diffusion of metal ions. Therefore, when the thickness of the functional coating is within a specific range relative to the thickness of the positive electrode active layer, the functional coating can effectively play a better role and promote the normal performance of the positive electrode active material.

[0045] Preferably, the thickness of the functional coating is 2-6 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the positive electrode plate comprises a current collector and a positive electrode active layer disposed on at least one side surface of the current collector, and the positive electrode active layer comprises a positive electrode active material, a second conductive agent and a second binder.

[0047] Preferably, the mass ratio of the positive electrode active material, the second conductive agent, and the second binder is (90-94):(1-6):(2-4). For example, it can be 90:6:4, 92:4:4, 94:4:2, or 94:2:4, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0048] Preferably, the second conductive agent includes any one or a combination of at least two of Super P (conductive carbon black), acetylene black, Ketjen black, conductive graphite, and carbon nanotubes.

[0049] Preferably, the second binder includes any one or a combination of at least two of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate binder, or polyacrylic acid binder.

[0050] Preferably, the positive electrode active material includes any one or a combination of at least two of polyanion compounds, transition metal oxides, or Prussian blue compounds.

[0051] Preferably, the chemical general formula of the polyanion compound is Na x M y [(XO m ) n- z , where M is a transition metal atom with different valence states (such as Fe, Co, Ni, V, or Cu), and X includes any one or a combination of at least two of B, P, and W.

[0052] Preferably, the chemical general formula of the transition metal oxide is Na x MO2, where M includes transition metal elements, such as any one or a combination of at least two of Ni, Fe, or Mn.

[0053] Preferably, the chemical general formula of the Prussian blue compound is Na x M1[M2(CN)6] y ·zH2O, where 0 < x ≤ 2, for example, it can be 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, or 2, 0.8 ≤ y < 1, for example, it can be 0.8, 0.85, 0.9, 0.95, or 0.99, 0 < z ≤ 20, for example, it can be 1, 5, 10, 15, or 20, and M1 and M2 are transition metal elements, such as any one or a combination of at least two of Fe, Mn, Cu, Ni, or Co.

[0054] Preferably, the separator includes any one or a combination of at least two of polypropylene separator, polyethylene separator, or multilayer composite separator.

[0055] ​Preferably, the diaphragm is a polypropylene diaphragm.

[0056] The diaphragm of the present invention is preferably a polypropylene diaphragm. The polypropylene diaphragm has good thermal stability and good permeability. When used in combination with sodium vinyl salt, it can have good ductility and mechanical properties, which is beneficial to prolonging the service life of the battery.

[0057] Preferably, the negative electrode plate comprises a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, and the negative electrode active layer comprises a negative electrode active material, a third conductive agent and a third binder.

[0058] Preferably, the mass ratio of the negative electrode active material, the third conductive agent and the third binder is (90-96):(1-6):(2-4), for example, it can be 90:6:4, 92:4:4, 94:4:2 or 96:1:3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0059] Preferably, the negative electrode active material includes any one of carbon-based materials, titanium-based compounds, alloy materials, metal compounds or organic compounds, or a combination of at least two thereof.

[0060] Preferably, the third conductive agent includes any one of Super P (conductive carbon black), acetylene black, Ketjen black, conductive graphite, and carbon nanotubes, or a combination of at least two thereof.

[0061] Preferably, the third binder includes any one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate or polyacrylic acid binders, or a combination of at least two thereof.

[0062] In a second specific embodiment, the present invention provides a method for preparing a battery cell as described in the first specific embodiment, the preparation method comprising the following steps:

[0063] The functional coating slurry is applied to at least one side of the surface of the positive electrode sheet, and after drying, a functional coating is obtained on at least one side of the surface of the positive electrode sheet, a separator is arranged on the surface of the functional coating, and then a negative electrode sheet is arranged on the side of the separator away from the functional coating to obtain the battery cell;

[0064] Alternatively, a functional coating slurry is coated on at least one side of the surface of the diaphragm, and after drying, a functional coating is obtained on at least one side of the surface of the diaphragm to obtain a composite diaphragm, a positive electrode sheet is arranged on one side of the composite diaphragm, and a negative electrode sheet is arranged on the other side, wherein the positive electrode sheet is arranged on the side of the functional coating away from the diaphragm to obtain the battery cell;

[0065] The functional coating slurry includes a functional compound, and the functional compound includes a vinyl sodium salt.

[0066] The functional coating of the present invention is arranged between the positive electrode plate and the diaphragm. Specifically, the functional coating can be directly coated and arranged on the positive electrode plate, and then the diaphragm is arranged on the surface where the functional coating is arranged, so that the functional coating is located between the positive electrode plate and the diaphragm; the functional coating can also be directly coated and arranged on the diaphragm, and then the positive electrode plate is arranged on the surface where the functional coating is arranged, so that the functional coating is located between the positive electrode plate and the diaphragm.

[0067] In the present invention, the functional coating is preferably directly coated on the positive electrode plate, which can more quickly inhibit the diffusion of metal ions and enable sodium ions to be better transported within the battery cell.

[0068] In a third specific embodiment, the present invention provides a battery, which includes the battery cell as described in the first specific embodiment, or includes the battery cell prepared by the preparation method as described in the second specific embodiment.

[0069] In a fourth specific embodiment, the present invention provides an electrical device, wherein the electrical device includes the battery as described in the third specific embodiment.

[0070] The technical scheme of the present invention is further illustrated by the following examples. It should be understood by those skilled in the art that the examples are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0071] Example 1

[0072] This embodiment provides a battery cell, the battery cell comprising a positive electrode sheet, a separator and a negative electrode sheet, the separator is located between the positive electrode sheet and the negative electrode sheet, and a functional coating is provided between the positive electrode sheet and the separator;

[0073] The functional coating comprises a functional compound, Super P (conductive carbon black) and polyvinylidene fluoride in a mass ratio of 94:4:2, the functional compound is heptasodium diethylenetriamine penta(methylenephosphonic acid), and the thickness of the functional coating is 4 μm;

[0074] The positive electrode plate includes an aluminum foil and a positive electrode active layer disposed on one side of the aluminum foil, wherein the positive electrode active layer includes Na3V2(PO4)3, Super P (conductive carbon black) and polyvinylidene fluoride in a mass ratio of 94:4:2, and a thickness ratio of the functional coating to the positive electrode active layer is 1:12.5;

[0075] The diaphragm is a polypropylene film with a thickness of 12 μm;

[0076] The negative electrode plate includes a copper foil and a negative electrode active layer disposed on one side of the copper foil, wherein the negative electrode active layer includes a hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) in a mass ratio of 95.5:2:1.5:1, and the thickness of the copper foil is 8 μm;

[0077] The method for preparing the battery cell comprises the following steps:

[0078] (1) According to the formula, the functional compound, Super P (conductive carbon black) and polyvinylidene fluoride are mixed, and then N-methylpyrrolidone is added in an amount of 1:2 in a mass ratio of the functional compound to N-methylpyrrolidone, and the mixture is dispersed at a high speed and mixed evenly to obtain a functional layer slurry;

[0079] (2) Na3V2(PO4)3, Super P (conductive carbon black) and polyvinylidene fluoride are mixed according to the formula, and N-methylpyrrolidone is added in an amount of Na3V2(PO4)3 to N-methylpyrrolidone in a mass ratio of 1:2.2, and the mixture is dispersed at a high speed and mixed evenly to obtain a positive electrode active layer slurry;

[0080] (3) Setting the coating machine parameters so that the coating thickness is 50 μm, the positive electrode active layer slurry is evenly coated on a 12 μm aluminum foil, and the electrode piece after coating is dried under a drum vacuum at 110° C. for 0.5 h to obtain an electrode piece A, wherein the positive electrode active layer is disposed on the surface of the electrode piece A;

[0081] (4) The functional layer slurry is evenly coated on the positive electrode active layer of the electrode piece A, so that the coating thickness of the functional coating is 4 μm, and the coated electrode piece is vacuum dried at 120° C. for 11 h to obtain a positive electrode piece provided with a functional coating;

[0082] (5) Mix the hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) according to the formula, disperse them in water, apply them on a copper foil of 8 μm, and dry them to obtain a negative electrode sheet;

[0083] (6) A separator is disposed on the surface of the functional coating in step (4), and then the negative electrode sheet in step (5) is disposed on the surface of the separator away from the functional coating. After winding, the battery cell is obtained.

[0084] Example 2

[0085] This embodiment provides a battery cell, the battery cell comprising a positive electrode sheet, a separator and a negative electrode sheet, the separator is located between the positive electrode sheet and the negative electrode sheet, and a functional coating is provided between the positive electrode sheet and the separator;

[0086] The functional coating comprises a functional compound, Super P (conductive carbon black) and polyvinylidene fluoride in a mass ratio of 90:6:4, the functional compound is diethylenetriamine pentasodium methylenephosphonate, and the thickness of the functional coating is 2 μm;

[0087] The positive electrode plate includes an aluminum foil and a positive electrode active layer arranged on one side of the aluminum foil, wherein the positive electrode active layer includes Na 1.73 Fe[Fe(CN)6]·3.8H2O, Super P (conductive carbon black) and polyvinylidene fluoride; the thickness ratio of the functional coating to the positive electrode active layer is 1:20;

[0088] The diaphragm is a polypropylene film with a thickness of 12 μm;

[0089] The negative electrode plate includes a copper foil and a negative electrode active layer disposed on one side of the copper foil, wherein the negative electrode active layer includes a hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) in a mass ratio of 95.5:2:1.5:1, and the thickness of the copper foil is 8 μm;

[0090] The method for preparing the battery cell comprises the following steps:

[0091] (1) According to the formula, the functional compound, Super P (conductive carbon black) and polyvinylidene fluoride are mixed, and then N-methylpyrrolidone is added in an amount of 1:2 in a mass ratio of the functional compound to N-methylpyrrolidone, and the mixture is dispersed at a high speed and mixed evenly to obtain a functional layer slurry;

[0092] (2) According to the formula, Na 1.73 Fe[Fe(CN)6]·3.8H2O, Super P (conductive carbon black) and polyvinylidene fluoride were mixed according to Na 1.73 Fe[Fe(CN)6]·3.8H2O and N-methylpyrrolidone were added in a mass ratio of 1:2, and N-methylpyrrolidone was dispersed at a high speed and mixed evenly to obtain a positive electrode active layer slurry;

[0093] (3) Setting the coating machine parameters so that the coating thickness is 40 μm, the positive electrode active layer slurry is evenly coated on a 12 μm aluminum foil, and the electrode piece after coating is dried under a drum vacuum at 110° C. for 0.5 h to obtain an electrode piece A, wherein the positive electrode active layer is disposed on the surface of the electrode piece A;

[0094] (4) The functional layer slurry is evenly coated on the positive electrode active layer of the electrode piece A, so that the coating thickness of the functional coating is 2 μm, and the coated electrode piece is vacuum dried at 120° C. for 11 h to obtain a positive electrode piece provided with a functional coating;

[0095] (5) Mix the hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) according to the formula, disperse them in water, apply them on a copper foil of 8 μm, and dry them to obtain a negative electrode sheet;

[0096] (6) A separator is disposed on the surface of the functional coating in step (4), and then the negative electrode sheet in step (5) is disposed on the surface of the separator away from the functional coating. After winding, the battery cell is obtained.

[0097] Example 3

[0098] This embodiment provides a battery cell, the battery cell comprising a positive electrode sheet, a separator and a negative electrode sheet, the separator is located between the positive electrode sheet and the negative electrode sheet, and a functional coating is provided between the positive electrode sheet and the separator;

[0099] The functional coating comprises a functional compound, Super P (conductive carbon black) and polyvinylidene fluoride in a mass ratio of 92:5:3, the functional compound is diethylenetriamine pentasodium methylenephosphonate, and the thickness of the functional coating is 6 μm;

[0100] The positive electrode plate includes an aluminum foil and a positive electrode active layer arranged on one side of the aluminum foil, wherein the positive electrode active layer includes NaMn with a mass ratio of 92:5:3. 0.5 Ni 0.5 O2, Super P (conductive carbon black) and polyvinylidene fluoride; the thickness ratio of the functional coating to the positive electrode active layer is 1:10;

[0101] The diaphragm is a polypropylene film with a thickness of 12 μm;

[0102] The negative electrode plate includes a copper foil and a negative electrode active layer disposed on one side of the copper foil, wherein the negative electrode active layer includes a hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) in a mass ratio of 95.5:2:1.5:1, and the thickness of the copper foil is 8 μm;

[0103] The method for preparing the battery cell comprises the following steps:

[0104] (1) According to the formula, the functional compound, Super P (conductive carbon black) and polyvinylidene fluoride are mixed, and then N-methylpyrrolidone is added in an amount of 1:2 in a mass ratio of the functional compound to N-methylpyrrolidone, and the mixture is dispersed at a high speed and mixed evenly to obtain a functional layer slurry;

[0105] (2) According to the formula, NaMn 0.5 Ni 0.5 O2, Super P (conductive carbon black) and polyvinylidene fluoride are mixed according to NaMn 0.5Ni 0.5 N-methylpyrrolidone was added in an amount of O2 and N-methylpyrrolidone in a mass ratio of 1:2.2, and the mixture was dispersed at a high speed and mixed evenly to obtain a positive electrode active layer slurry;

[0106] (3) Setting the coating machine parameters so that the coating thickness is 60 μm, the positive electrode active layer slurry is evenly coated on a 12 μm aluminum foil, and the electrode piece after coating is dried under a drum vacuum at 110° C. for 0.5 h to obtain an electrode piece A, wherein the positive electrode active layer is disposed on the surface of the electrode piece A;

[0107] (4) The functional layer slurry is evenly coated on the positive electrode active layer of the electrode piece A, so that the coating thickness of the functional coating is 6 μm, and the coated electrode piece is vacuum dried at 120° C. for 12 h to obtain a positive electrode piece provided with a functional coating;

[0108] (5) Mix the hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) according to the formula, disperse them in water, apply them on a copper foil of 8 μm, and dry them to obtain a negative electrode sheet;

[0109] (6) A separator is disposed on the surface of the functional coating in step (4), and then the negative electrode sheet in step (5) is disposed on the surface of the separator away from the functional coating. After winding, the battery cell is obtained.

[0110] Example 4

[0111] This embodiment provides a battery cell, the battery cell comprising a positive electrode sheet, a separator and a negative electrode sheet, the separator is located between the positive electrode sheet and the negative electrode sheet, and a functional coating is provided between the positive electrode sheet and the separator;

[0112] The functional coating comprises a functional compound, Super P (conductive carbon black) and polyvinylidene fluoride in a mass ratio of 94:4:2, the functional compound is heptasodium diethylenetriamine penta(methylenephosphonic acid), and the thickness of the functional coating is 4 μm;

[0113] The positive electrode plate includes an aluminum foil and a positive electrode active layer disposed on one side of the aluminum foil, wherein the positive electrode active layer includes Na3V2(PO4)3, Super P (conductive carbon black) and polyvinylidene fluoride in a mass ratio of 94:4:2, and a thickness ratio of the functional coating to the positive electrode active layer is 1:12.5;

[0114] The diaphragm is a polypropylene film with a thickness of 12 μm;

[0115] The negative electrode plate includes a copper foil and a negative electrode active layer disposed on one side of the copper foil, wherein the negative electrode active layer includes a hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) in a mass ratio of 95.5:2:1.5:1, and the thickness of the copper foil is 8 μm;

[0116] The method for preparing the battery cell comprises the following steps:

[0117] (1) According to the formula, the functional compound, Super P (conductive carbon black) and polyvinylidene fluoride are mixed, and then N-methylpyrrolidone is added in an amount of 1:2 in a mass ratio of the functional compound to N-methylpyrrolidone, and the mixture is dispersed at a high speed and mixed evenly to obtain a functional layer slurry;

[0118] (2) Na3V2(PO4)3, Super P (conductive carbon black) and polyvinylidene fluoride are mixed according to the formula, and N-methylpyrrolidone is added in an amount of Na3V2(PO4)3 to N-methylpyrrolidone in a mass ratio of 1:2, and the mixture is dispersed at a high speed and mixed evenly to obtain a positive electrode active layer slurry;

[0119] (3) Setting the coating machine parameters so that the coating thickness is 40 μm, the positive electrode active layer slurry is evenly coated on a 12 μm aluminum foil, and the electrode sheet after coating is dried under a drum vacuum at 110° C. for 0.5 h to obtain a positive electrode sheet;

[0120] (4) The functional layer slurry is evenly coated on the polypropylene film to make the coating thickness of the functional coating layer 2 μm, and the coated electrode is vacuum dried at 120° C. for 11 h to obtain a polypropylene film with a functional coating layer;

[0121] (5) Mix the hard carbon material, styrene-butadiene rubber, sodium carboxymethyl cellulose and Super P (conductive carbon black) according to the formula, disperse them in water, apply them on a copper foil of 8 μm, and dry them to obtain a negative electrode sheet;

[0122] (6) The positive electrode sheet of step (3) is arranged on the surface of the functional coating on one side of the polypropylene film of step (4), and then the negative electrode sheet of step (5) is arranged on the surface of the other side of the polypropylene film of step (4). After winding, the battery cell is obtained.

[0123] Example 5

[0124] This embodiment provides a battery cell, which is the same as that of Embodiment 1 except that the functional compound is tetrasodium vinyl diphosphonate.

[0125] Example 6

[0126] This embodiment provides a battery cell, which is the same as that of Embodiment 1 except that the functional compound is sodium vinyl sulfonate.

[0127] Example 7

[0128] This embodiment provides a battery cell, which is the same as that of Embodiment 1 except that the functional compound is sodium 4-styrenesulfonate.

[0129] Example 8

[0130] This embodiment provides a battery cell, which is the same as that of Embodiment 1 except that the thickness ratio of the functional coating to the positive electrode active layer is 1:30 and the thickness of the functional coating is adaptably adjusted to 1.67 μm.

[0131] Example 9

[0132] This embodiment provides a battery cell, which is the same as that of Embodiment 1 except that the thickness ratio of the functional coating to the positive electrode active layer is 1:5 and the thickness of the functional coating is adaptably adjusted to 10 μm.

[0133] Example 10

[0134] This embodiment provides a battery cell, which is the same as that of Embodiment 1 except that the separator is a polyethylene separator.

[0135] Comparative Example 1

[0136] This comparative example provides a battery cell, which is the same as Example 1 except that it does not include a functional coating.

[0137] Comparative Example 2

[0138] This comparative example provides a battery cell, which is the same as Example 1 except that the functional compound is sodium carbonate.

[0139] Comparative Example 3

[0140] This comparative example provides a battery cell, which is the same as Example 1 except that the functional compound is sodium propylene sulfonate.

[0141] The battery cells obtained in the above embodiments and comparative examples are installed in an aluminum shell and injected with electrolyte to seal, thereby obtaining a square aluminum shell sodium ion battery, wherein the electrolyte is a 1 mol / L NaPF6 solution in diethylene glycol dimethyl ether.

[0142] The obtained sodium ion battery was subjected to electrochemical performance test, and the test method was as follows:

[0143] First cycle capacity test: The sodium ion batteries prepared in the above embodiments and comparative examples were subjected to first cycle capacity test under the test conditions of 25° C., 0.2C rate, charge cut-off voltage, and discharge cut-off voltage.

[0144] 1C / 1C cycle life test: The sodium ion batteries prepared in the above embodiments and comparative examples were respectively divided into different capacities under the test condition of 0.1C rate at 25°C, and then subjected to 1C / 1C cycle test at 25°C.

[0145] HF gas content test: The sodium ion batteries prepared in the above embodiments and comparative examples were subjected to a needle-piercing gas production test after three weeks of circulation to measure the gas production amount and the gas production composition. The test process was as follows: placed at 25°C for 5 minutes, discharged at 1C to the cut-off voltage, placed for 10 minutes, charged at 1C constant current and constant voltage to the cut-off voltage, the cut-off current was 0.05C, placed for 10 minutes, the battery was placed at 25°C for 2 hours, the single-point internal pressure was tested by needle-piercing, the gas was collected, and the gas composition was tested.

[0146] Among them, during the test, the charge cut-off voltage of the polyanion compound was 4.2V, and the discharge cut-off voltage was 1.6V; the charge cut-off voltage of the Prussian blue analogue was 2.0V, and the discharge cut-off voltage was 0.5V; the charge cut-off voltage of the layered oxide was 4.0V, and the discharge cut-off voltage was 2.0V.

[0147] The test results are shown in the following table:

[0148] Table 1

[0149]

[0150]

[0151] From the above table we can see that:

[0152] (1) It can be seen from Example 1 and Comparative Examples 1-3 that the functional coating of the present invention is provided, and the functional compound is vinyl sodium salt, which can inhibit the diffusion of metal ions, eliminate HF, and supplement sodium ions, thereby improving the first-cycle coulomb efficiency and cycle performance of the battery, while reducing the content of HF gas without significantly affecting the first-cycle charge and discharge specific capacity of the battery; It can be seen from Example 1 and Example 4 that the functional coating of the present invention can be directly coated and provided on the positive electrode plate, or directly coated and provided on the diaphragm. The present invention is preferably provided on the positive electrode, which can better play the role of the functional compound, so that the sodium ions can be better transmitted inside the battery cell, thereby better improving the first-cycle coulomb efficiency and cycle performance of the battery, and reducing the content of HF gas.

[0153] (2) It can be seen from Examples 1 and 5-7 that the functional compound of the present invention is preferably tetrasodium vinyl diphosphonate and / or heptasodium diethylene triamine penta (methylene phosphonate), which contain more sodium ions and vinyl content in their monomer molecules and can play a better role, thereby better improving the first-cycle coulomb efficiency and cycle performance of the battery, reducing the content of HF gas, and obtaining a better first-cycle charge and discharge specific capacity of the battery; It can be seen from Examples 1 and 8-9 that the thickness ratio of the functional coating of the present invention to the positive electrode active layer is within a suitable range, which can promote the role of the functional coating, and obtain a better first-cycle charge and discharge specific capacity of the battery, improve the first-cycle coulomb efficiency and cycle performance of the battery, and reduce the content of HF gas; It can be seen from Examples 1 and 10 that the battery cell of the present invention is preferably a polypropylene separator, which can be better used with sodium vinyl salt, which is beneficial to extending the cycle life of the battery.

[0154] In summary, the present invention provides a battery cell and a preparation method and application thereof. The battery cell is provided with a functional coating between the positive electrode plate and the diaphragm. The functional coating contains vinyl sodium salt, which can inhibit the diffusion of metal ions, eliminate HF generated by the side reaction of the electrolyte, additionally supplement sodium ions, and improve the first-cycle coulomb efficiency and cycle performance of the battery cell and other electrochemical properties.

[0155] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A battery cell, characterized in that: The battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and a functional coating is arranged between the positive electrode sheet and the separator; the functional coating comprises a functional compound, and the functional compound comprises sodium vinyl salt.

2. The battery cell according to claim 1, characterized in that: The vinyl sodium salt includes any one of sodium vinyl sulfonate, sodium 4-styrene sulfonate, tetrasodium vinyl diphosphonate or heptasodium diethylenetriamine penta (methylene phosphonate) or a combination of at least two thereof; Preferably, the vinyl sodium salt is tetrasodium vinyl diphosphonate and / or heptasodium diethylene triamine penta (methylene phosphonate).

3. The battery cell according to claim 1, characterized in that: The functional coating further includes a first conductive agent and a first binder; Preferably, the first conductive agent includes any one of Super P, acetylene black, Ketjen black, conductive graphite, and carbon nanotubes, or a combination of at least two thereof; Preferably, the first conductive agent is Super P and / or carbon nanotubes; Preferably, the mass ratio of the functional compound, the first conductive agent and the first binder is (90-94):(1-6):(2-4).

4. The battery cell according to any one of claims 1 to 3, characterized in that: The positive electrode plate includes a current collector and a positive electrode active layer disposed on at least one side of the current collector, and the thickness ratio of the functional coating to the positive electrode active layer is 1:(10-20); Preferably, the thickness of the functional coating is 2-6 μm.

5. The battery cell according to any one of claims 1 to 3, characterized in that: The positive electrode sheet comprises a current collector and a positive electrode active layer disposed on at least one side of the current collector, wherein the positive electrode active layer comprises a positive electrode active material, a second conductive agent and a second binder; Preferably, the mass ratio of the positive electrode active material, the second conductive agent and the second binder is (90-94):(1-6):(2-4).

6. The battery cell according to claim 5, characterized in that: The positive electrode active material includes any one of a polyanion compound, a transition metal oxide or a Prussian blue compound, or a combination of at least two of them.

7. The battery cell according to any one of claims 1 to 3, characterized in that: The diaphragm includes any one of a polypropylene diaphragm, a polyethylene diaphragm or a multi-layer composite diaphragm or a combination of at least two thereof; Preferably, the diaphragm is a polypropylene diaphragm.

8. A method for preparing a battery cell according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: The functional coating slurry is applied to at least one side of the surface of the positive electrode sheet, and after drying, a functional coating is obtained on at least one side of the surface of the positive electrode sheet, a separator is arranged on the surface of the functional coating, and then a negative electrode sheet is arranged on the side of the separator away from the functional coating to obtain the battery cell; Alternatively, a functional coating slurry is coated on at least one side of the surface of the diaphragm, and after drying, a functional coating is obtained on at least one side of the surface of the diaphragm to obtain a composite diaphragm, a positive electrode sheet is arranged on one side of the composite diaphragm, and a negative electrode sheet is arranged on the other side, wherein the positive electrode sheet is arranged on the side of the functional coating away from the diaphragm to obtain the battery cell; The functional coating slurry includes a functional compound, and the functional compound includes a vinyl sodium salt.

9. A battery, characterized in that: The battery comprises the battery cell according to any one of claims 1 to 7, or comprises the battery cell prepared by the preparation method according to claim 8.

10. An electrical device, characterized in that: The electric device comprises the battery as claimed in claim 9.

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