CN117276472A - Positive pole piece of sodium ion battery, preparation method of positive pole piece and sodium ion battery - Google Patents

Positive pole piece of sodium ion battery, preparation method of positive pole piece and sodium ion battery Download PDF

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CN117276472A
CN117276472A CN202311551118.9A CN202311551118A CN117276472A CN 117276472 A CN117276472 A CN 117276472A CN 202311551118 A CN202311551118 A CN 202311551118A CN 117276472 A CN117276472 A CN 117276472A
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positive electrode
sodium
polyacrylonitrile
ion battery
sodium ion
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CN117276472B (en
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李享
杨亦双
李健平
张伟清
杨庆亨
王健
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Zhongxing Pylon Battery Co Ltd
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Zhongxing Pylon Battery Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes

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Abstract

The invention discloses a positive plate of a sodium ion battery, a preparation method of the positive plate and the sodium ion battery, and relates to the technical field of sodium ion batteries. The polyacrylonitrile itself has extremely high oxidation resistance, so that the polyacrylonitrile forms a coating layer on the surface of the ferric sodium sulfate base material, the high voltage oxidation resistance of the positive electrode interface can be improved, and the decomposition of electrolyte under high voltage can be reduced. the-C.ident.N in the polyacrylonitrile is taken as a polar group with strong electron withdrawing, can form chelate with transition metal ions with strong binding force, and can chelate iron ions after the polyacrylonitrile is coated on the surface of the sodium ferric sulfate, thereby relieving Fe 2+ Fe (Fe) 3+ Is dissolved out. In addition, the-C (identical to) N group of polyacrylonitrile is a polar structural unit with strong electron withdrawing, and has good bonding effect on active material particles and a current collector after being coated on the surface of the positive electrode material, so that the stripping strength of the pole piece can be improved, and the falling off of the pole piece in the manufacturing process is avoided.

Description

Positive pole piece of sodium ion battery, preparation method of positive pole piece and sodium ion battery
Technical Field
The invention relates to the technical field of sodium ion batteries, in particular to a positive pole piece of a sodium ion battery, a preparation method thereof and the sodium ion battery.
Background
Sodium ion batteries are one of the emerging energy storage solutions, and are developed very rapidly at present due to the fact that the sodium ion batteries are rich in raw material resources and low in cost. The current positive electrode materials of sodium ion batteries are mainly classified into the following three types: layered oxide, polyanion and Prussian white derivative materials. Among them, the polyanion material has been attracting attention because the polyanion polyhedron and the transition metal ion polyhedron are connected by strong covalent bonds to form a three-dimensional network structure, which has excellent structural stability and long cycle potential.
Current polyanionic materials mainly include: vanadium-based phosphates (NaVPO) 4 F、Na 3 V 2 (PO 4 ) 3 Etc.), iron-based pyrophosphate (Na 2 FeP 2 O 7 、Na 3.32 Fe 2.34 (P 2 O 7 ) 2 Etc.), iron-based sulfate (Na x Fe y (SO 4 ) z ，Na 2 Fe 2 (SO 4 ) 3 Etc.). Wherein the working potential of the vanadium-based phosphate is higher (can reach 4.0V vs. Na + Na), vanadium is toxic and expensive, but practical application is limited. The iron-based polyanion type positive electrode material has rich iron content, is environment-friendly and has rapid development. Wherein, the iron-based pyrophosphate positive electrodeThe working potential of the material is lower (3.0V vs. Na) + Na), the energy density is lower. The working potential of the iron-based sulfate material is higher (3.7V vs. Na) + Na) can bring about a higher energy density and is therefore of interest.
However, the iron-based sulfate material has high working voltage and charging voltage close to 4.2-4.5V vs. Na + Na, which is liable to cause oxidative decomposition of the electrolyte at the positive electrode, causes continuous increase of gas production of the battery, continuous increase of internal resistance of the battery, and accelerates capacity decay and failure of the battery. In addition, the iron-based sulfate is prepared under high voltage due to Na + All deviate from, the crystal structure is deformed, and collapse of the structure and Fe are easily caused 3+ Dissolution, results in a loss of active material capacity. And dissolved Fe 3+ And the electrolyte can migrate to the negative electrode to reduce to form elemental iron, block the pores of the negative electrode hard carbon, catalyze the decomposition of the electrolyte, and cause the aggravation of gas production and the rise of battery impedance.
Therefore, there is a need for an effective method to alleviate the problem of iron ion elution of iron-based sulfate at high positive voltage, and at the same time avoid capacity loss caused by continuous decomposition of electrolyte.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide a positive pole piece of a sodium ion battery, a preparation method thereof and the sodium ion battery, which aim to reduce the problem of iron ion dissolution under the high-voltage condition and reduce the capacity loss caused by electrolyte decomposition.
The invention is realized in the following way:
the invention provides a positive electrode plate of a sodium ion battery, which comprises a positive electrode current collector, wherein a positive electrode active coating is attached to the positive electrode current collector, the positive electrode active coating contains a sodium ferric sulfate positive electrode active material, and the sodium ferric sulfate positive electrode active material comprises a sodium ferric sulfate base material and a polyacrylonitrile coating layer coated on the sodium ferric sulfate base material;
the chemical formula of the ferric sodium sulfate substrate is Na (2+2x) Fe (2-x) (SO 4 ) 3 Wherein 0 is<x<0.5。
In an alternative embodiment, the mass ratio of the sodium iron sulfate substrate to the polyacrylonitrile coating layer is 100: (0.1-10); preferably 100: (0.5-5.0).
In an alternative embodiment, the positive electrode active coating layer further comprises a conductive agent and a binder;
wherein the conductive agent is at least one selected from conductive carbon black and carbon nanotubes;
the binder is at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.
In an alternative embodiment, the mass ratio of the sodium iron sulfate substrate, the conductive agent, and the binder is (100): (0.5-5): (0.5-5).
In an alternative embodiment, the positive current collector is aluminum foil;
preferably, the thickness of the positive electrode current collector is 6 μm to 20 μm.
In a second aspect, the present invention provides a method for preparing a positive electrode sheet of a sodium ion battery according to any one of the foregoing embodiments, including: and forming a positive electrode active coating on the positive electrode current collector by utilizing positive electrode slurry, wherein the positive electrode slurry contains sodium ferric sulfate and polyacrylonitrile.
In an alternative embodiment, in the positive electrode slurry, the mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100: (0.1-10); preferably 100: (0.5-5.0).
In an alternative embodiment, the preparation process of the positive electrode slurry includes: mixing and homogenizing sodium iron sulfate, a conductive agent, a binder and polyacrylonitrile, wherein the mass ratio of the sodium iron sulfate to the conductive agent to the binder is (100): (0.5-5): (0.5-5);
preferably, the solvent used in the homogenization process is N-methylpyrrolidone (NMP).
In an alternative embodiment, the prepared positive electrode slurry is coated on a positive electrode current collector, and the double-sided density is controlled to be 20g/cm 2 -46g/cm 2 And drying and rolling after coating.
In a third aspect, the present invention provides a sodium ion battery, including a sodium ion battery positive electrode sheet according to any one of the foregoing embodiments or a sodium ion battery positive electrode sheet prepared by any one of the foregoing embodiments.
The invention has the following beneficial effects: the polyacrylonitrile has extremely high oxidation resistance, so that the polyacrylonitrile forms a coating layer on the surface of the ferric sodium sulfate substrate, the high voltage oxidation resistance of the positive electrode interface can be improved, and the decomposition of electrolyte under high voltage is reduced. the-C.ident.N in the polyacrylonitrile is taken as a polar group with strong electron withdrawing, can form chelate with transition metal ions with strong binding force, and can chelate iron ions after the polyacrylonitrile is coated on the surface of the sodium ferric sulfate, thereby relieving Fe 2+ Fe (Fe) 3+ Is dissolved out. In addition, the-C (identical to) N group of polyacrylonitrile is a polar structural unit with strong electron withdrawing, and has good bonding effect on active material particles and a current collector after being coated on the surface of the positive electrode material, so that the stripping strength of the pole piece can be improved, and the falling off of the pole piece in the manufacturing process is avoided.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an SEM image of a sodium iron sulfate pole piece without polyacrylonitrile added in comparative example 1;
fig. 2 is an SEM image of a sodium iron sulfate pole piece added with polyacrylonitrile of experimental example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The embodiment of the invention provides a preparation method of a positive electrode plate of a sodium ion battery, which comprises the steps of introducing polyacrylonitrile during preparation of positive electrode slurry, dissolving the polyacrylonitrile in a solvent used for homogenate, and removing the solvent during later drying, so that the polyacrylonitrile can be uniformly coated on sodium ferric sulfate. The method comprises the following specific steps:
s1, preparing positive electrode slurry
Polyacrylonitrile is introduced as an additive in the preparation of the positive electrode slurry, and the polyacrylonitrile is dissolved in a solvent after homogenization. In the actual operation process, the preparation process of the positive electrode slurry comprises the following steps: mixing sodium iron sulfate, a conductive agent, a binder and polyacrylonitrile, and adding a solvent for homogenizing.
In some embodiments, the conductive agent is at least one selected from conductive carbon black and carbon nanotubes, and may be any one or more of the above; the binder is at least one selected from polyvinylidene fluoride and styrene-butadiene rubber, and can be any one or more of the above; the solvent used in the homogenization process was N-methylpyrrolidone (NMP).
To effectively inhibit Fe 2+ Fe (Fe) 3+ The amount of each raw material is optimized: the mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100: (0.1-10), preferably 100: (0.5-5.0); the mass ratio of the sodium iron sulfate, the conductive agent and the binder is (100): (0.5-5): (0.5-5). Specifically, the mass ratio of sodium iron sulfate to polyacrylonitrile can be 100:0.1, 100:1.0, 100:2.0, 100:3.0, 100:4.0, 100:5.0, 100:6.0, 100:7.0, 100:8.0, 100:9.0, 100:10.0, etc. The amount of the solvent is not limited, so as to have a homogenizing effect and effectively dissolve the polyacrylonitrile. The mass ratio of sodium iron sulfate, conductive agent and binder may be 100:0.5:0.5, 100:1.0:1.0, 100:2.0:3.0, 100:3.0:2.0, 100:4.0:4.0, 100:5.0:5.0, etc.
S2, forming an anode active coating
The positive electrode slurry is used to form a positive electrode active coating on the positive electrode current collector, the specific process is not limited, and a traditional coating process can be adopted.
In some embodiments, the prepared positive electrode slurry is coated on a positive electrode current collector, and the double-sided density is controlled to be 20g/cm 2 -46g/cm 2 Drying and rolling after coating, dissolving in the drying processThe agent is removed, and most of polyacrylonitrile is uniformly coated on the surface of the sodium iron sulfate.
Specifically, the drying temperature can be controlled to 80-130 ℃, and the drying operation can be performed in a baking mode. After controlled rolling, the compaction density of the pole piece is 1.8-2.3 g/cm 3 。
In some embodiments, the positive electrode current collector may be an aluminum foil, and the positive electrode current collector has a thickness of 6 μm to 20 μm.
The embodiment of the invention provides a positive electrode plate of a sodium ion battery, which comprises a positive electrode current collector, wherein a positive electrode active coating is attached to the positive electrode current collector, the positive electrode active coating contains a sodium ferric sulfate positive electrode active material, and the sodium ferric sulfate positive electrode active material comprises a sodium ferric sulfate base material and a polyacrylonitrile coating layer coated on the sodium ferric sulfate base material.
In some embodiments, the mass ratio of the sodium iron sulfate substrate to the polyacrylonitrile coating layer is 100: (0.1-10); preferably 100: (0.5-5.0), the mass of the sodium iron sulfate substrate and the polyacrylonitrile coating layer is approximately the same as that of sodium iron sulfate and polyacrylonitrile used in preparing the positive electrode slurry. The mass ratio of the ferric sodium sulfate base material, the conductive agent and the binder is (100): (0.5-5): (0.5-5), the same amount of raw materials as in the preparation of the slurry.
The embodiment of the invention provides a sodium ion battery, which comprises the positive electrode plate of the sodium ion battery in the embodiment, and can also comprise a negative electrode plate, electrolyte, a diaphragm and other structures to form a complete battery structure. The improvement of the positive pole piece is beneficial to prolonging the cycle life of the battery.
The features and capabilities of the present invention are described in further detail below in connection with the examples.
The raw material sodium iron sulfate used in the following examples has the chemical formula of Na (2+2x) Fe (2-x) (SO 4 ) 3 Wherein 0 is<x<0.5, the specific preparation method is as follows: ferrous sulfate (FeSO) with molar ratio of (2-x): (1+1x) 4 ) And sodium sulfate (Na) 2 SO 4 ) After being evenly mixedSintering for 12h at 300 ℃ in inert atmosphere to obtain sodium iron sulfate Na 2.4 Fe 1.8 (SO4) 3 。
Example 1
The embodiment provides a preparation method of a positive plate of a sodium ion battery, which comprises the following steps:
(1) Sodium iron sulfate Na 2.4 Fe 1.8 (SO 4 ) 3 Mixing conductive agent (conductive carbon black, available from TIMCAL, model: super P Li, the same applies below), binder (polyvinylidene fluoride, available from ARKEMA, model: PVDF-900, the same applies below) according to a mass ratio of 95:2:3, adding polyacrylonitrile (number average molecular weight greater than 1 ten thousand, available from aladin, model: P303197, the same applies below), and the mass ratio of sodium iron sulfate to polyacrylonitrile is 100:2, adding a solvent N-methyl pyrrolidone (NMP) for homogenating, and controlling the mass ratio of the solvent to the sodium iron sulfate to be 50:50.
(2) Coating the slurry obtained in the step (1) on the front and back sides of an aluminum foil with the thickness of 13 mu m, and controlling the density of the coated two sides to be 30 mg/cm 2 The compacted density after rolling is 1.9 g/cm 3 And then dried through a drying tunnel at 120 c for 0.5. 0.5 h.
Example 2
The embodiment provides a preparation method of a positive plate of a sodium ion battery, which comprises the following steps:
(1) Sodium iron sulfate Na 2.4 Fe 1.8 (SO 4 ) 3 Mixing a conductive agent (conductive carbon black) and a binder (polyvinylidene fluoride) according to a mass ratio of 98:1:1, adding polyacrylonitrile, wherein the mass ratio of sodium iron sulfate to polyacrylonitrile is 100:2, then adding a solvent N-methylpyrrolidone (NMP) for homogenizing, and controlling the mass ratio of the solvent to sodium iron sulfate to be 50:50.
(2) For specific steps, refer to step (2) of example 1.
Example 3
The embodiment provides a preparation method of a positive plate of a sodium ion battery, which comprises the following steps:
(1) Sodium iron sulfate Na 2.4 Fe 1.8 (SO 4 ) 3 Conductive agentMixing (conductive carbon black) and a binder (polyvinylidene fluoride) according to a mass ratio of 90:5:5, adding polyacrylonitrile, wherein the mass ratio of sodium iron sulfate to polyacrylonitrile is 100:2, then adding a solvent N-methyl pyrrolidone (NMP) for homogenizing, and controlling the mass ratio of the solvent to sodium iron sulfate to be 60:40.
(2) For specific steps, refer to step (2) of example 1.
Example 4
The only difference from example 1 is that: the mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100:0.5.
Example 5
The only difference from example 1 is that: the mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100:5.
Example 6
The only difference from example 1 is that: the mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100:0.2.
Example 7
The only difference from example 1 is that: the mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100:8.
Comparative example 1
The only difference from example 1 is that: in the step (1), polyacrylonitrile is not added, and is replaced by equivalent sodium iron sulfate.
Comparative example 2
The only difference from example 1 is that: the polyacrylonitrile in the step (1) is replaced by styrene butadiene rubber.
Test example 1
SEM images of the pole pieces prepared in comparative example 1 and example 1 were tested, and the results are shown in fig. 1 and 2.
It can be seen that fig. 2 (sodium iron sulfate pole piece with polyacrylonitrile added) shows a more uniform pore distribution compared with fig. 1 (sodium iron sulfate pole piece without polyacrylonitrile added), indicating that the addition of polyacrylonitrile improves the bonding and dispersing effects between particles, and the pore distribution is more uniform.
Test example 2
The performance of the positive electrode sheet prepared in the test examples and comparative examples is shown in Table 1.
And (3) testing the electrochemical performance of the pole piece:
(1) The sodium ferric sulfate pole piece prepared in the above example is used as the positive electrode of a sodium ion battery, the metal sodium pole piece is used as the negative electrode, the 25 um PP film is used as the battery diaphragm, and 1.0mol/L NaPF is used 6 The solution dissolved in PC: EMC: fec=4:6:0.5 was used as an electrolyte, and assembled into a button cell in a glove box filled with argon.
(2) Capacity test: charging the assembled battery to 4.5V at 0.1C, and discharging to 2.0V at 0.1C to obtain capacity V 0 。
(3) And (3) multiplying power performance test: charging the assembled battery to 4.5V at 0.1C, and discharging to 2.0V at 2C to obtain capacity V 2C . The rate capability of the battery can be calculated according to the capacity retention rate of the battery under 2C discharge, namely V 2C /V 0 。
(4) Cycle life test: the assembled battery was charged to 4.5V at 0.5C and discharged to 2.0V at 0.5C, and the capacity retention was recorded by 100 cycles.
(5) And (3) gas production testing: the sodium ferric sulfate pole piece prepared in the above example is used as the positive electrode of a sodium ion battery, the pole piece made of hard carbon is used as the negative electrode, a 25 μm PP film is used as the battery diaphragm, and 1.0mol/L NaPF is used 6 The solution dissolved in PC: EMC: fec=4:6:0.5 was used as an electrolyte, and assembled into a pouch cell in a glove box filled with argon. The manufacturing method of the hard carbon negative plate comprises the following steps: hard carbon, SP, CMC, SBr according to 90:5:2:3, homogenizing in deionized water, coating on 13um aluminum foil, and oven drying to obtain double-sided density of 9 mg/cm 2 A compacted density of 0.9g/cm 3 Sodium ion battery negative electrode sheet. The prepared soft package battery is charged and discharged at 45 ℃ according to the multiplying power of 0.5C and the voltage of 2.0-4.3V, and the gas yield is tested according to a drainage method after 100 circles of circulation.
(6) And testing gas production by a drainage method: suspending the assembled and sealed untested soft-package battery into a container containing water with a fixed volume, wherein the total test mass is M1; after 100 circles of cycle life test, the battery is suspended and immersed in a container containing water with a fixed volume, and the total test mass is M2. The gas yield is (M2-M1)/ρ Density of water 。
(7) Peel strength test: the sodium iron sulfate pole piece prepared in the above example was cut into 300mm×30mm samples, a flat sheet was taken, and the pole piece was completely adhered to the sheet (stainless steel sheet having a length and width of 500mm×100 mm and a thickness of about 5 mm) with double-sided tape (commercially available, model 30403). And (3) mounting the bonded sample on a peeling strength tester, and testing the peeling strength of the pole piece after calibrating and clearing.
Table 1 results of performance tests of positive electrode sheets prepared in examples and comparative examples
From the above table, comparative example 1 and comparative example 1 show that the peel strength of the sodium iron sulfate positive plate added with polyacrylonitrile is significantly improved, the multiplying power and the cycle performance are significantly improved, and the gas yield is also reduced.
In comparative examples 1 and 2, the performance parameters of the pole piece added with polyacrylonitrile are all obviously dominant, which shows that the functional groups of the additive have obvious influence on the performance of the pole piece.
The combination properties of example 1 are best for comparative examples 1, 4, 5 and examples 6, 7. In comparative examples 4 and 6, the cycle performance, gas generation and peel strength of example 4 were all good. The capacity, rate and cycle of example 5 are all advantageous for comparison of examples 5 and 7. It is indicated that the addition amount of polyacrylonitrile is most suitable within the scope of the claims.
Compared with the comparative example, the positive pole piece prepared by the embodiment of the invention has obviously improved peeling strength, rate capability, cycle performance and gas production condition.
In summary, the embodiment of the invention forms the protective layer resistant to high voltage oxidation on the surface of the active material particles by using polyacrylonitrile, and has the following advantages:
(1) Polyacrylonitrile coats the surface of the positive electrode material, and the-C.ident.N group and the transition metal ion form chelate, thereby effectively relieving Fe 2+ Fe (Fe) 3+ To reduce the capacity of the positive electrode active materialAnd loss, and the cycle life of the battery is prolonged.
(2) The electrolyte can be reduced from decomposing under high voltage, gas production is reduced, thicker CEI film is avoided from being formed, and the impedance increase of the battery in the circulation process is greatly reduced.
(3) the-C.ident.N group of polyacrylonitrile favors Na + The ionic transmission improves the rate capability of the battery;
(4) The polyacrylonitrile has a-C (identical to N) group, is a polar structural unit with strong electron withdrawing, is coated on the surface of the positive electrode material, has good bonding effect on active material particles and a current collector, can improve the peeling strength of a pole piece, and can prolong the cycle life of a battery.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The positive pole piece of the sodium ion battery is characterized by comprising a positive current collector, wherein a positive active coating is attached to the positive current collector, the positive active coating contains a sodium ferric sulfate positive active material, and the sodium ferric sulfate positive active material comprises a sodium ferric sulfate base material and a polyacrylonitrile coating layer coated on the sodium ferric sulfate base material;
the chemical formula of the sodium iron sulfate substrate is Na (2+2x) Fe (2-x) (SO 4 ) 3 Wherein 0 is<x<0.5。
2. The positive electrode plate of the sodium ion battery according to claim 1, wherein the mass ratio of the ferric sodium sulfate base material to the polyacrylonitrile coating layer is 100: (0.1-10).
3. The positive electrode plate of the sodium ion battery according to claim 2, wherein the positive electrode active coating further comprises a conductive agent and a binder;
wherein the conductive agent is at least one selected from conductive carbon black and carbon nanotubes;
the binder is at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.
4. The positive electrode sheet of sodium ion battery according to claim 3, wherein the mass ratio of the ferric sodium sulfate base material, the conductive agent and the binder is (100): (0.5-5): (0.5-5).
5. The positive electrode sheet of a sodium ion battery of claim 1, wherein the positive electrode current collector is aluminum foil;
the thickness of the positive electrode current collector is 6-20 mu m.
6. A method for preparing the positive electrode plate of the sodium ion battery as claimed in any one of claims 1 to 5, comprising: and forming the positive electrode active coating on the positive electrode current collector by utilizing positive electrode slurry, wherein the positive electrode slurry contains sodium ferric sulfate and polyacrylonitrile.
7. The production method according to claim 6, wherein in the positive electrode slurry, a mass ratio of the sodium iron sulfate to the polyacrylonitrile is 100: (0.1-10).
8. The method of manufacturing according to claim 6, wherein the process of manufacturing the positive electrode slurry includes: mixing and homogenizing sodium iron sulfate, a conductive agent, a binder and polyacrylonitrile, wherein the mass ratio of the sodium iron sulfate to the conductive agent to the binder is (100): (0.5-5): (0.5-5);
the solvent used in the homogenization process was N-methylpyrrolidone.
9. The method according to claim 8, wherein the positive electrode slurry obtained by the preparation is applied to the positive electrode current collectorOn the surface, the density of the double-sided surface is controlled to be 20 mg/cm 2 -46 mg/cm 2 And drying and rolling after coating.
10. A sodium ion battery, characterized by comprising the sodium ion battery positive electrode sheet according to any one of claims 1 to 5 or the sodium ion battery positive electrode sheet prepared by the preparation method according to any one of claims 6 to 9.
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