Positive electrode composite coating, positive electrode plate and application of positive electrode plate

Abstract

The invention relates to a positive electrode composite coating, a positive electrode plate and application thereof, the positive electrode composite coating comprises a first coating and a second coating, the first coating comprises a conjugated microporous polymer, and the second coating comprises porous inorganic oxide particles and a conductive polymer. The positive electrode composite coating disclosed by the invention can effectively prevent metal ions from being dissolved out under normal-temperature and high-temperature conditions, and can remarkably improve the high-temperature cycling stability of the battery, so that the safety of the battery is improved, and the high-quality development of the battery industry is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode composite coating, a positive electrode sheet and applications thereof. Background Art

[0002] Sodium-ion batteries have been widely studied due to their excellent cost-effectiveness. Among them, electrode materials have always been one of the key factors affecting the performance of sodium-ion batteries. Compared with negative electrode materials, positive electrode materials are relatively mature. At present, there are layered oxides, Prussian blue and polyanion positive electrode materials. However, these positive electrode materials are sodium-containing compounds with transition metal elements (Mn, Fe, Co, Ni, etc.) as the main framework. As the cycle proceeds, some metal ions will separate from the positive electrode material and dissolve in the electrolyte, which will not only cause the destruction of the positive electrode structure and reduce the active substances of the positive electrode, but also the dissolved metal ions diffuse through the electrolyte and deposit on the negative electrode under various environmental factors (concentration, electrochemistry, electric field gradient, etc.), thereby accelerating the decomposition of the electrolyte, forming an overly thick SEI film, increasing the interface impedance, and causing the performance of the sodium-ion battery to decay, thereby reducing the electrochemical performance of the battery.

[0003] In order to solve the problem of metal dissolution in the positive electrode of sodium ion batteries, a large number of studies have been conducted to inhibit the dissolution of transition metal ions by coating and doping the positive electrode materials and constructing a stable electrode / electrolyte interface through interface engineering. However, under extreme conditions, especially under high temperature conditions, the inhibitory effect of traditional modification methods will be significantly weakened and cannot effectively inhibit the migration of metal ions. Moreover, the dissolved metal ions will also remain in the electrolyte, affecting the thermal stability of the electrolyte, thereby increasing the safety risk of the battery. Summary of the invention

[0004] Based on this, it is necessary to provide a positive electrode composite coating, a positive electrode sheet and its application to address the above-mentioned problems; the positive electrode composite coating can effectively block the dissolution of metal ions under both normal temperature and high temperature conditions, and can significantly improve the high-temperature cycle stability of the battery, thereby improving the safety of the battery, which is conducive to promoting the high-quality development of the battery industry.

[0005] A positive electrode composite coating comprises a first coating and a second coating, wherein the first coating comprises a conjugated microporous polymer, and the second coating comprises porous inorganic oxide particles and a conductive polymer.

[0006] In one embodiment, the conjugated microporous polymer satisfies at least one of the following conditions:

[0007] (1) The pore volume of the conjugated microporous polymer is 0.5 cm 3 / g-1.5cm 3 / g;

[0008] (2) The pore size of the conjugated microporous polymer is less than or equal to 2 nm;

[0009] (3) The specific surface area of ​​the conjugated microporous polymer is 500 m 2 / g-1500m 2 / g;

[0010] (4) The conjugated microporous polymer includes at least one of polyfuran, polyindole, polynaphthalene sulfide, polyphenylene sulfide, dihydrophenazine-based polymer, and triazine-based polymer.

[0011] In one embodiment, the porous inorganic oxide particles satisfy at least one of the following conditions:

[0012] (1) The pore volume of the porous inorganic oxide particles is 0.5 cm 3 / g-1.5cm 3 / g;

[0013] (2) The pore size of the porous inorganic oxide particles is 2nm-10nm;

[0014] (3) The median particle size of the porous inorganic oxide particles is 50 nm to 300 nm;

[0015] (4) The specific surface area of ​​the porous inorganic oxide particles is 1000 m 2 / g-2000m 2 / g;

[0016] (5) The porous inorganic oxide particles include at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, and molybdenum oxide.

[0017] In one embodiment, the conductive polymer includes at least one of polyacetylene, polyaniline, polythiophene, polypyrrole, poly(p-phenylene vinylene), and poly(3,4-ethylenedioxythiophene).

[0018] In one embodiment, the thickness of the first coating layer is greater than or equal to the thickness of the second coating layer.

[0019] In one embodiment, the thickness of the first coating layer is less than or equal to 5 μm;

[0020] And / or, the thickness of the second coating layer is less than or equal to 5 μm.

[0021] In one embodiment, the first coating layer further includes a first binder, and the mass ratio of the conjugated microporous polymer to the first binder is 9:1-9.5:0.5.

[0022] In one embodiment, the second coating layer further includes a second binder, and the mass ratio of the porous inorganic oxide particles to the conductive polymer and the second binder is 8:1:1-9:0.5:0.5.

[0023] A positive electrode plate comprises a current collector, and a positive electrode active material layer and the positive electrode composite coating layer stacked in sequence on the surface of the current collector, wherein the first coating layer in the positive electrode composite coating layer is arranged between the second coating layer and the positive electrode active material layer.

[0024] An energy storage device comprises the positive electrode plate as described above.

[0025] The present invention provides a positive electrode composite coating as a protective barrier for metal dissolution, and utilizes the synergistic effect of the first coating and the second coating. On the one hand, the positive electrode composite coating can quickly adsorb dissolved metal ions through electrostatic action, coordination action, hydrogen bonding action and other methods while allowing sodium ions to pass through, and stabilize the metal ions on the positive electrode side, thereby effectively inhibiting metal dissolution; on the other hand, it can not only enhance the electron transmission force of the positive electrode composite coating, reduce interface side reactions, thereby reducing the coating interface impedance, but also block the dissolution of metal ions in a high temperature environment, thereby significantly improving the electrochemical performance of the battery under high temperature conditions, especially the high temperature cycle stability, thereby improving the safety of the battery.

[0026] Therefore, the positive electrode composite coating provided by the present invention can effectively block the dissolution of metal ions under both normal and high temperature conditions, which not only overcomes the problem of easy dissolution of positive electrode metals in traditional batteries under extreme high temperature conditions, but also significantly improves the high-temperature cycle stability of the battery, thereby improving the safety of the battery, which is conducive to promoting the high-quality development of the battery industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet in one embodiment of the present invention;

[0029] Figure 2 This is a 1C cycle performance diagram of Example 4 of the present invention at room temperature;

[0030] Figure 3 This is a 1C cycle performance diagram of Example 4 of the present invention under a high temperature condition of 55°C;

[0031] Figure 4 This is a 1C cycle performance diagram of Comparative Example 1 of the present invention at room temperature;

[0032] Figure 5 This is a 1C cycle performance diagram of comparative example 1 of the present invention under high temperature conditions of 55°C.

[0033] Among them, 10, current collector; 20, positive electrode active material layer; 30, positive electrode composite coating; 301, first coating; 302, second coating. DETAILED DESCRIPTION

[0034] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific implementation methods or embodiments, and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the combinations include any two related listed items, any more related listed items, or all related listed items.

[0036] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0037] The invention provides a positive electrode composite coating, comprising a first coating and a second coating.

[0038] Among them, the first coating layer includes a conjugated microporous polymer. The first coating layer serves as an electron donor layer. By utilizing the rich pore structure and nitrogen-rich and oxygen-rich groups of the conjugated microporous polymer (GMPs) in the first coating layer, while allowing sodium ions to pass through, it can quickly adsorb dissolved metal ions through electrostatic action, coordination action, hydrogen bonding action and other methods, and stabilize the metal ions on the positive electrode side, thereby effectively inhibiting metal dissolution.

[0039] The second coating layer includes porous inorganic oxide particles and conductive polymers. The second coating layer serves as a physical barrier layer. On the one hand, the porous inorganic oxide particles can not only construct an interface layer with strong adaptability, so that it can effectively block the direct contact between the positive electrode material and the electrolyte and reduce the possibility of metal dissolution, but also can further adsorb the dissolved metal ions. At the same time, its excellent high temperature resistance is beneficial to block the dissolution of metal ions in a high temperature environment, thereby significantly improving the electrochemical performance of the battery under high temperature conditions, especially the cycle stability of the battery under high temperature conditions; on the other hand, the introduction of conductive polymers can not only enhance the electron transmission force of the positive electrode composite coating, reduce interface side reactions, thereby reducing interface impedance, but also help to further inhibit the dissolution of metal ions in a high temperature environment, thereby improving the high temperature electrochemical performance of the sodium ion battery and improving the safety of the battery.

[0040] In one embodiment of the present invention, the pore volume of the conjugated microporous polymer is 0.5 cm 3 / g-1.5cm 3 / g, including but not limited to 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.5cm 3 Any point value in / g or any range of values ​​between them.

[0041] In one embodiment of the present invention, the pore size of the conjugated microporous polymer is less than or equal to 2 nm, including but not limited to any point value among 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm or any range value between two of them.

[0042] In one embodiment of the present invention, the specific surface area of ​​the conjugated microporous polymer is 500 m 2 / g-1500m 2 / g, including but not limited to 500m 2 / g、600m 2 / g、800m 2 / g、1000m 2 / g、1200m 2 / g、1500m 2 Any point value in / g or any range of values ​​between them.

[0043] By regulating the pore size, pore volume and specific surface area of ​​the conjugated microporous polymer, it is beneficial to further improve the adsorption effect of the conjugated microporous polymer on dissolved metal ions.

[0044] In one embodiment of the present invention, the conjugated microporous polymer includes but is not limited to at least one of polyfuran (PTHF), polyindole (PBZ), polynaphthalene sulfide (PTIN), polyphenylene sulfide (PPs), dihydrophenazine-based (GMPs) polymers, and triazine-based (GMPs) polymers, wherein the dihydrophenazine-based polymers include but are not limited to dihydrophenazine-biphenyl polymers (PhPz), and the triazine-based polymers include but are not limited to aniline-pyrene conjugated polymers.

[0045] In one embodiment of the present invention, the pore volume of the porous inorganic oxide particles is 0.5 cm 3 / g-1.5cm 3 / g, including but not limited to 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.5cm 3 Any point value in / g or any range of values ​​between them.

[0046] In one embodiment of the present invention, the pore size of the porous inorganic oxide particles is 2nm-10nm, including but not limited to any point value among 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm or any range value between two thereof.

[0047] In one embodiment of the present invention, the median particle size (D50) of the porous inorganic oxide particles is 50nm-300nm, including but not limited to any point value among 50nm, 100nm, 150nm, 200nm, 250nm, 300nm or any range value between two thereof.

[0048] In one embodiment of the present invention, the specific surface area of ​​the porous inorganic oxide particles is 1000 m 2 / g-2000m 2 / g, including but not limited to 1000m 2 / g、1200m 2 / g、1500m 2 / g、1600m 2 / g、1800m 2 / g, 2000m 2 Any point value in / g or any range of values ​​between them.

[0049] By regulating the pore size, pore volume, specific surface area and particle size distribution of the porous inorganic oxide particles, it is beneficial to further improve the effect of the porous inorganic oxide particles in blocking the dissolution of metal ions under high temperature environments and ensure the high-temperature cycle stability of the battery.

[0050] In one embodiment of the present invention, the porous inorganic oxide particles include but are not limited to at least one of aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon dioxide (SiO2), zirconium dioxide (ZrO2), magnesium oxide (MgO), and molybdenum trioxide (MoO3).

[0051] In one embodiment of the present invention, the conductive polymer includes but is not limited to at least one of polyacetylene (PA), polyaniline (PANI), polythiophene (PTh), polypyrrole (PPy), polyparaphenylene vinylene (PPV), and poly(3,4-ethylenedioxythiophene) (PEDOT).

[0052] In one embodiment of the present invention, the thickness of the first coating layer is greater than or equal to the thickness of the second coating layer, which is beneficial to further balance the thermal stability and electrochemical performance and achieve better overall performance.

[0053] In one embodiment of the present invention, the thickness of the first coating layer is less than or equal to 5 μm.

[0054] Specifically, the thickness of the first coating layer includes but is not limited to any point value among 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm, or a range value between any two of them, and is preferably 1 μm-3 μm.

[0055] In one embodiment of the present invention, the thickness of the second coating layer is less than or equal to 5 μm.

[0056] Specifically, the thickness of the second coating layer includes but is not limited to any point value among 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm, or a range value between any two of them, and is preferably 1 μm-3 μm.

[0057] In one embodiment of the present invention, the first coating layer further includes a first binder, and the mass ratio of the conjugated microporous polymer to the first binder is 9:1-9.5:0.5.

[0058] Specifically, the first binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC).

[0059] It should be noted that the present invention does not limit the preparation method of the first coating, and a conventional method can be used. For example, a conjugated microporous polymer and a first binder are uniformly mixed in a solvent to form a first dispersion, and then the first dispersion is applied to the surface of the positive electrode active material layer of the positive electrode plate, and then dried to form a first coating, wherein the mass concentration of the solute in the first dispersion is preferably 1%-10%, and the coating method includes but is not limited to spraying, electrospinning, inkjet printing, and ultrasonic spraying.

[0060] In one embodiment of the present invention, the second coating layer further includes a second binder, and the mass ratio of the porous inorganic oxide particles to the conductive polymer and the second binder is 8:1:1-9:0.5:0.5.

[0061] Specifically, the second binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC).

[0062] It can be understood that the first adhesive and the second adhesive can be the same or different, and the present invention is not limited to this.

[0063] It should be noted that the present invention does not limit the preparation method of the second coating, and conventional methods can be used. For example, porous inorganic oxide particles, conductive polymers, and a second binder are uniformly mixed in a solvent to form a second dispersion, and then the second dispersion is applied to the surface of the first coating, and the second coating is formed after drying. The mass concentration of the solute in the second dispersion is preferably 10%-50%, and the coating method includes but is not limited to spraying, electrospinning, inkjet printing, and ultrasonic spraying.

[0064] The present invention provides a positive electrode plate, combined with Figure 1 As shown, the positive electrode plate described in the present invention includes a current collector 10, and a positive electrode active material layer 20 and a positive electrode composite coating 30 as described above, which are sequentially stacked on the surface of the current collector 10, wherein the first coating 301 in the positive electrode composite coating 30 is arranged between the second coating 302 and the positive electrode active material layer 20.

[0065] The present invention arranges the first coating 301 in the positive electrode composite coating 30 between the second coating 302 and the positive electrode active material layer 20, and utilizes the second coating 302 to suppress the volume expansion of the conjugated microporous polymer in the first coating 301 due to the charge and discharge temperature during the cycle process, thereby further improving the high temperature cycle stability of the battery.

[0066] It is understandable that the present invention does not limit the positive electrode active material in the positive electrode active material layer 20 , and existing conventional positive electrode active materials may be used, such as lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide or lithium cobalt oxide.

[0067] The present invention also provides an energy storage device, comprising the positive electrode sheet as described above. It is understood that the energy storage device includes but is not limited to a battery.

[0068] The energy storage device provided by the present invention has excellent high-temperature cycle stability and safety, which is conducive to promoting the high-quality development of energy storage industries such as batteries.

[0069] In one embodiment of the present invention, the energy storage device includes a 32700 cylindrical battery with a capacity of 4.5Ah, and the structure of the cylindrical battery mainly includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a metal shell.

[0070] Among them, the preparation method of the positive electrode plate includes: adding the positive electrode active material and auxiliary materials such as a binder and a conductive agent into a mixer according to a certain mass ratio, then adding a certain amount of solvent, vacuuming and stirring at high speed for several hours, mixing the mixture into a uniform slurry with consistent fluidity, and then evenly coating the slurry on a foil current collector through a coating machine, and rolling and cutting the coated plate and then drying it to obtain a positive electrode plate.

[0071] The preparation method of the negative electrode plate comprises: adding the negative electrode active material and auxiliary materials such as a binder and a conductive agent into a mixer according to a certain mass ratio, then adding a certain amount of solvent, vacuuming and stirring at a high speed for several hours, mixing the mixture into a uniform slurry with consistent fluidity, and then uniformly coating the slurry on a foil current collector through a coating machine, and rolling and slitting the coated plate and then baking it to obtain the negative electrode plate.

[0072] Specifically, the positive electrode active material includes but is not limited to at least one of layered oxides, Prussian blue and polyanionic compounds, preferably a ternary layered oxide; the negative electrode active material includes but is not limited to at least one of hard carbon, soft carbon and graphite, preferably hard carbon; the binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC), the positive electrode is preferably polyvinylidene fluoride (PVDF), and the negative electrode is preferably sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR); the conductive agent includes but is not limited to carbon nanotubes (CNT), conductive At least one of electric carbon black (SP), acetylene black, Ketjen black and conductive graphite; the solvent includes but is not limited to at least one of deionized water, N-methylpyrrolidone (NMP) and dimethylformamide (DMF), wherein the solvent used to prepare the positive electrode sheet is preferably N-methylpyrrolidone (NMP), and the solvent used to prepare the negative electrode sheet is preferably deionized water; the foil current collector includes but is not limited to at least one of aluminum foil, copper foil, carbon-coated aluminum foil and carbon-coated copper foil, wherein the foil current collector used to prepare the positive electrode sheet is preferably aluminum foil, and the foil current collector used to prepare the negative electrode sheet is preferably copper foil; the drying temperature is preferably 60°C-120°C, and the drying time is preferably 1h-20h.

[0073] The electrolyte mainly comprises: 80%-85% of non-aqueous solvent, 10%-15% of sodium salt and 3%-5% of additives, wherein the non-aqueous solvent includes but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), diethylene glycol dimethyl ether (DEGDME), ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (EGDE), tetraethylene glycol dimethyl ether (TEGDME), and diethylene glycol diethyl ether; the additive includes but is not limited to at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (1,3-PS), and vinyl sulfate (DTD); the sodium salt includes but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), and sodium fluorosulfonimide (NaFSI) salt.

[0074] The diaphragm includes but is not limited to a polypropylene diaphragm (PP), a polyimide diaphragm (PI), a polyethylene diaphragm (PE), and a PE ceramic film (a polyethylene film having a ceramic coating), preferably a PE ceramic film.

[0075] The cylindrical battery assembly method comprises: arranging a positive electrode sheet, a first diaphragm, a negative electrode sheet, and a second diaphragm in order, then winding them to form a bare battery cell, vacuum baking the bare battery cell, and when the moisture content of the positive and negative electrodes is less than 200 ppm, sequentially performing the processes of shelling, spot welding, grooving, liquid injection, capping, sealing, etc., and then standing, forming, and dividing the capacity to obtain a cylindrical battery.

[0076] The positive electrode composite coating, positive electrode sheet and its application will be further described by the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained commercially.

[0077] Example 1

[0078] Step 1: Prepare the first dispersion: Polyfuran (pore volume is about 0.5 cm 3 / g, pore size is about 2nm, specific surface area is about 500m 2 / g) and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a ratio of 9.5:0.5 to prepare a uniform dispersion with a mass concentration of 1% for later use.

[0079] Step 2: Prepare the second dispersion: Add aluminum oxide (pore volume is about 0.65 cm 3 / g, pore size is about 5nm, median particle size is about 100nm, specific surface area is about 1000m 2 / g), polyacetylene and polyvinylidene fluoride are dispersed in N-methylpyrrolidone in a mass ratio of 8:1:1 to prepare a uniform dispersion with a mass concentration of 10% for later use.

[0080] Step 3: Prepare the positive electrode: Select ternary NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used as a positive electrode active material, and is uniformly mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 96.5:2:1.5. After being coated on the surface of an aluminum foil and rolled, a positive electrode active material layer is formed on the surface of the aluminum foil. The first dispersion is sprayed onto the surface of the positive electrode active material layer, and a first coating layer with a thickness of about 1 μm is formed after baking. The second dispersion is then sprayed onto the surface of the first coating layer, and a second coating layer with a thickness of about 1 μm is formed after drying to obtain a positive electrode sheet. The surface density loading of the positive electrode sheet is 20 mg / cm 2 .

[0081] Example 2

[0082] The difference between Example 2 and Example 1 is that the mass concentration of the first dispersion prepared in step 1 is 2%, and in step 2, aluminum oxide, polyacetylene and polyvinylidene fluoride are dispersed in N-methylpyrrolidone in a mass ratio of 8.5:0.5:1 to prepare a second dispersion with a mass concentration of 20%.

[0083] Example 3

[0084] The difference between Example 3 and Example 2 is that the thickness of the first coating prepared in step 3 is about 3 μm.

[0085] Example 4

[0086] Step 1: Prepare the first dispersion: dihydrophenazine-biphenyl polymer (pore volume is about 0.85 cm 3 / g, pore size is about 1.5nm, specific surface area is about 1000m 2 / g) and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a ratio of 9.5:0.5 to prepare a uniform dispersion with a mass concentration of 3% for later use.

[0087] Step 2: Prepare the second dispersion: Add silica (pore volume is about 0.8 cm 3 / g, pore size is about 3nm, median particle size is about 70nm, specific surface area is about 1500m 2 / g), polyaniline and polyvinylidene fluoride are dispersed in N-methylpyrrolidone in a mass ratio of 9:0.5:0.5 to prepare a uniform dispersion with a mass concentration of 30% for later use.

[0088] Step 3: Prepare the positive electrode: Select ternary NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used as a positive electrode active material and is uniformly mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 96.5:2:1.5. After being coated on the surface of an aluminum foil and rolled, a positive electrode active material layer is formed on the surface of the aluminum foil. A first dispersion is sprayed onto the surface of the positive electrode active material layer and baked to form a first coating layer with a thickness of about 3 μm. A second dispersion is then sprayed onto the surface of the first coating layer and dried to form a second coating layer with a thickness of about 3 μm to obtain a positive electrode sheet.

[0089] Example 5

[0090] The difference between Example 5 and Example 4 is that the thickness of the second coating prepared in step 3 is about 5 μm.

[0091] Example 6

[0092] The difference between Example 6 and Example 4 is that in step 1, aniline-pyrene conjugated polymer (pore volume of about 0.95 cm3 / g, pore size is about 1nm, specific surface area is about 1500m 2 / g) instead of dihydrophenazine-biphenyl polymer, and polypyrrole instead of polyaniline in step 2.

[0093] Comparative Example 1

[0094] Select ternary NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, as a positive electrode active material, is uniformly mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 96.5:2:1.5, and after being coated on the surface of an aluminum foil and rolled, a positive electrode active material layer is formed on the surface of the aluminum foil to obtain a positive electrode sheet.

[0095] Comparative Example 2

[0096] Step 1: Prepare dispersion: dihydrophenazine-biphenyl polymer (pore volume is about 0.85 cm 3 / g, pore size is about 1.5nm, specific surface area is about 1000m 2 / g) and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a ratio of 9.5:0.5 to prepare a uniform dispersion with a mass concentration of 3% for later use.

[0097] Step 2: Prepare the positive electrode: Select ternary NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used as a positive electrode active material and is uniformly mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 96.5:2:1.5. After being coated on the surface of an aluminum foil and rolled, a positive electrode active material layer is formed on the surface of the aluminum foil. The dispersion is sprayed onto the surface of the positive electrode active material layer and baked to form a coating with a thickness of about 3 μm to obtain a positive electrode sheet.

[0098] Comparative Example 3

[0099] Step 1: Prepare dispersion: Add silica (pore volume is about 0.8 cm 3 / g, pore size is about 3nm, median particle size is about 70nm, specific surface area is about 1500m 2 / g), polyaniline and polyvinylidene fluoride are dispersed in N-methylpyrrolidone in a mass ratio of 9:0.5:0.5 to prepare a uniform dispersion with a mass concentration of 30% for later use.

[0100] Step 2: Prepare the positive electrode: Select ternary NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2 is used as a positive electrode active material and is uniformly mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 96.5:2:1.5. After being coated on the surface of an aluminum foil and rolled, a positive electrode active material layer is formed on the surface of the aluminum foil. The dispersion is sprayed onto the surface of the positive electrode active material layer and baked to form a coating with a thickness of about 3 μm to obtain a positive electrode sheet.

[0101] The positive electrode sheets prepared in Examples 1-6 and Comparative Examples 1-3 were assembled into batteries according to the following preparation method:

[0102] (1) Preparation of negative electrode sheet: Kuraray hard carbon (Type 2) was selected as the main negative electrode material, and was evenly mixed with CMC, SBR, and SP in a mass ratio of 94.5:1.5:2.5:1.5. The negative electrode sheet was then obtained by coating, rolling, slitting, and baking. The surface density loading of the negative electrode sheet was 10.03 mg / cm 2 ;

[0103] (2) Preparation of electrolyte: The solvent is a mixed solution of EC, DEC and PC, wherein the mass content of EC is 10%, the mass content of DEC is 55% and the mass content of PC is 17%; the sodium salt is NaDFOB, with a mass content of 13%; the additives are FEC, DTD and VC, wherein the mass content of FEC is 1%, the mass content of DTD is 3% and the mass content of VC is 1%.

[0104] (3) Assembling batteries: Arrange the positive electrode sheet, PE ceramic film, negative electrode sheet, and PE ceramic film in order, then wind them to form a bare cell, and vacuum bake the bare cell. When the moisture content of the positive and negative electrodes is less than 200 ppm, the cell is sequentially shelled, spot welded, grooved, injected, capped, and sealed. Then, it is left to stand, formed, and divided into different capacities to obtain the desired sodium-ion battery.

[0105] After assembling the battery of Examples 1-6 and Comparative Examples 1-3, the performance test was carried out:

[0106] (1) Battery cycle performance test: The assembled battery was charged at a constant current of 0.5C (1C = 4500mA) to a cut-off voltage of 3.9V, and then charged at a constant voltage until the current dropped to 0.05C. Then, it was discharged at a constant current of 1C to a discharge cut-off voltage of 2.0V. The above steps were repeated to complete the cycle performance test.

[0107] (2) Metal ion dissolution test: According to the above-mentioned cycle performance test method, after the battery is cycled for 500 cycles, the battery is disassembled, and then the negative electrode sheet of the same mass is dissolved in an equal volume (100 mL) of deionized water. After filtering, the metal ion components in the test solution are detected using inductively coupled plasma emission spectrometry (ICP) to test the content of metal dissolved ions in the positive electrode of each embodiment. In particular, the electrode sheet of the embodiment and the comparative example after cycling for 150 cycles at a high temperature of 55°C is subjected to a metal dissolution test.

[0108] (3) High temperature storage performance test: The assembled battery is charged to 3.9V at a constant current of 0.2C (1C = 4500mA) at a high temperature of 55°C, and then charged at a constant voltage until the current drops to 0.05C. In the discharge phase, the battery is discharged to 1.5V at the same current of 0.2C. The capacity C1 at this time is recorded, and then the charging is completed in the same manner, and the battery is left to rest in a constant temperature oven at 55°C for 7 days. After that, the battery is discharged to 1.5V at a constant current of 0.2C, and the capacity C2 at this time is recorded. The capacity retention rate before and after the 7-day rest at 55°C is calculated, that is, C2 / C1×100%.

[0109] The test results are as follows Figures 2 to 5 As shown in Table 1 and Table 2.

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114]

[0115] According to Tables 1 and 2, the positive electrode composite coating provided by the present invention can effectively block the dissolution of metal ions under both normal temperature and high temperature conditions, and can significantly improve the high-temperature cycle stability of the battery, thereby improving the safety of the battery, which is conducive to promoting the high-quality development of the battery industry.

[0116] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0117] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A positive electrode composite coating, characterized in that: The invention comprises a first coating layer and a second coating layer, wherein the first coating layer comprises a conjugated microporous polymer, and the second coating layer comprises porous inorganic oxide particles and a conductive polymer.

2. The positive electrode composite coating according to claim 1, characterized in that: The conjugated microporous polymer satisfies at least one of the following conditions: (1) The pore volume of the conjugated microporous polymer is 0.5 cm 3 / g-1.5cm 3 / g; (2) The pore size of the conjugated microporous polymer is less than or equal to 2 nm; (3) The specific surface area of ​​the conjugated microporous polymer is 500 m 2 / g-1500m 2 / g; (4) The conjugated microporous polymer includes at least one of polyfuran, polyindole, polynaphthalene sulfide, polyphenylene sulfide, dihydrophenazine-based polymer, and triazine-based polymer.

3. The positive electrode composite coating according to claim 1, characterized in that: The porous inorganic oxide particles satisfy at least one of the following conditions: (1) The pore volume of the porous inorganic oxide particles is 0.5 cm 3 / g-1.5cm 3 / g; (2) The pore size of the porous inorganic oxide particles is 2nm-10nm; (3) The median particle size of the porous inorganic oxide particles is 50 nm to 300 nm; (4) The specific surface area of ​​the porous inorganic oxide particles is 1000 m 2 / g-2000m 2 / g; (5) The porous inorganic oxide particles include at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, and molybdenum oxide.

4. The positive electrode composite coating according to claim 1, characterized in that: The conductive polymer includes at least one of polyacetylene, polyaniline, polythiophene, polypyrrole, poly(p-phenylene vinylene), and poly(3,4-ethylenedioxythiophene).

5. The positive electrode composite coating according to claim 1, characterized in that: The thickness of the first coating layer is greater than or equal to the thickness of the second coating layer.

6. The positive electrode composite coating according to claim 1 or 5, characterized in that: The thickness of the first coating is less than or equal to 5 μm; And / or, the thickness of the second coating layer is less than or equal to 5 μm.

7. The positive electrode composite coating according to claim 1, characterized in that: The first coating layer also includes a first binder, and the mass ratio of the conjugated microporous polymer to the first binder is 9:1-9.5:0.

5.

8. The positive electrode composite coating according to claim 1, characterized in that: The second coating layer further includes a second binder, and the mass ratio of the porous inorganic oxide particles to the conductive polymer and the second binder is 8:1:1-9:0.5:0.

5.

9. A positive electrode sheet, characterized in that: A positive electrode composite coating comprising a current collector, and a positive electrode active material layer sequentially stacked on the surface of the current collector, and the positive electrode composite coating according to any one of claims 1 to 8, wherein the first coating in the positive electrode composite coating is arranged between the second coating and the positive electrode active material layer.

10. An energy storage device, characterized in that: Comprising the positive electrode sheet as claimed in claim 9.

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