CN116364854A - A kind of positive pole piece and sodium ion battery - Google Patents

Abstract

The invention provides a positive pole piece and a sodium ion battery. The invention provides a positive electrode plate, which comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a sodium supplementing agent, and the sodium supplementing agent comprises sodium borohydride and a carbon layer coated on the surface of the sodium borohydride. The sodium supplementing agent provided by the invention has a core-shell structure, sodium borohydride is used as an inner core, and sodium element can be irreversibly decomposed and released in the charging process, so that the sodium supplementing effect is realized, and the first coulomb efficiency and the energy density of the sodium ion battery are improved; in addition, because the conductivity and the stability of sodium borohydride in air are poor, the carbon layer is coated on the surface of the sodium borohydride, so that the conductivity and the stability of the sodium borohydride are effectively improved, and the sodium supplementing effect of the sodium borohydride is improved.

Description

A kind of positive pole piece and sodium ion battery

technical field

The invention relates to a positive pole piece and a sodium ion battery, and relates to the technical field of sodium ion batteries.

Background technique

As an energy storage device with high energy density and long service life, lithium-ion batteries have been widely used in electronic devices such as mobile phones and notebook computers. However, lithium resources are limited and expensive, and lithium-ion batteries are difficult to meet the growing demand. The needs of the mobile electronics and automotive industries. Compared with lithium, sodium has more abundant reserves, which can significantly reduce the cost of batteries, and sodium-ion batteries have broad application prospects.

Because sodium and lithium have similar electrochemical properties, during the first charging and discharging process of a sodium-ion battery, some sodium ions will react on the surface of the negative electrode to form a solid electrolyte film (SEI), resulting in irreversible sodium loss, making the sodium-ion battery The first coulombic efficiency and energy density of the sodium ion battery are reduced. By adding a sodium supplement to the positive active material layer, the loss of sodium ions during the first cycle can be supplemented, and the first coulombic efficiency and energy density of the sodium ion battery can be improved. Therefore, developing a sodium supplement that effectively compensates for the loss of this part of sodium ions is one of the hotspots that those skilled in the art continue to pay attention to.

Contents of the invention

The invention provides a positive pole piece and a sodium ion battery, which include a sodium replenishing agent for improving the first coulombic efficiency and energy density of the sodium ion battery.

The first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, the positive electrode active material layer includes a sodium replenishing agent, and the sodium replenishing agent Including sodium borohydride and a carbon layer coated on the surface of the sodium borohydride;

The particle size of the sodium borohydride is 0.5-6 μm, and the thickness of the carbon layer is 10-100 nm.

As for the above-mentioned positive electrode sheet, the sodium supplement is prepared by the following preparation method:

Reaction of boric acid and methanol to obtain trimethyl borate, reaction of metal sodium and hydrogen to obtain sodium hydride;

reacting the trimethyl borate with sodium hydride to obtain sodium borohydride;

The sodium supplement agent is obtained by heat-treating the sodium borohydride and a gaseous carbon source.

As mentioned above, the positive electrode sheet is prepared by reacting metal sodium with hydrogen to obtain sodium hydride, which specifically includes:

Sodium metal is dispersed in an oily medium, hydrogen gas is introduced into the oily medium, and the reaction is carried out at 200-500° C. for 4-12 hours to prepare sodium hydride.

As for the above-mentioned positive electrode sheet, the sodium borohydride and the gaseous carbon source are heat-treated to obtain the sodium replenishing agent, which specifically includes:

Under an inert atmosphere, the sodium borohydride is dispersed in an oily medium, and a gaseous carbon source is passed through, so that simple carbon is deposited on the surface of the sodium borohydride to form a carbon layer, and the sodium supplement agent is obtained.

As for the positive electrode sheet above, the gaseous carbon source includes one or more of methane, ethane, propane, ethylene, propylene, acetylene, and propyne.

As for the above positive electrode sheet, the molar ratio of the sodium borohydride to the gaseous carbon source is 50-200:1.

For the above-mentioned positive electrode sheet, the heat treatment temperature of the sodium borohydride and the gaseous carbon source is 250-280° C., and the time is 2-12 hours.

As for the above-mentioned positive electrode sheet, the positive electrode active material layer also includes a positive electrode active material, a conductive agent and a binder, and the quality of the sodium replenishing agent is the total mass of the positive electrode active material, conductive agent and binder. 5-20%.

In the above-mentioned positive electrode sheet, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 8˜9:1:1.

The second aspect of the present invention provides a sodium-ion battery, which comprises any one of the above-mentioned positive pole pieces.

Implementation of the present invention has at least the following advantages:

1. The positive electrode sheet provided by the present invention includes a sodium supplement agent with a core-shell structure, and uses sodium borohydride as the core, which can irreversibly decompose and release sodium ions during the charging process of the sodium ion battery, so as to realize the sodium supplement effect and increase the sodium Specific capacity and coulombic efficiency of ion battery; In addition, because the electrical conductivity of sodium borohydride and the stability in air are relatively poor, the present invention coats carbon layer on the surface of sodium borohydride, effectively improves the electrical conductivity and the stability of sodium borohydride Stability improves the sodium supplementation effect of sodium borohydride.

2. By limiting the particle size of sodium borohydride and the thickness of the carbon coating, the present invention helps to further improve the sodium supplementation effect of sodium borohydride, and improve the specific capacity and coulombic efficiency of the sodium ion battery.

3. The preparation method of the sodium supplement provided by the present invention is simple, the raw material is easy to obtain, the pollution is small, the post-treatment is simple, and it can be compatible with the manufacturing process of the existing sodium ion battery, which is conducive to large-scale production and application.

4. The sodium ion battery provided by the present invention includes the above-mentioned sodium replenishing agent, which can effectively improve the specific capacity and coulombic efficiency of the sodium ion battery.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is a schematic structural view of a positive pole piece provided by an embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a sodium supplement provided by an embodiment of the present invention.

Explanation of reference signs:

1- positive current collector;

2-positive active material layer;

31-sodium borohydride;

32 - carbon layer.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the implementation of the present invention. example, not all examples. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Fig. 1 is a schematic structural view of a positive electrode sheet provided by an embodiment of the present invention. As shown in Fig. 1, the positive electrode sheet includes a positive electrode current collector 1 and a positive electrode active material layer 2 arranged on the surface of the positive electrode current collector. It can be understood that Fig. 1 Both the upper and lower surfaces of the positive electrode current collector are provided with a positive electrode active material layer. In addition, the positive electrode active material layer can also be separately provided on the upper or lower surface of the positive electrode current collector. means to carry out.

The positive current collector 1 refers to the base metal used to attach the active material in the positive electrode of the battery, for example, it may be a conventional material such as aluminum foil.

The positive electrode active material layer 2 includes a sodium supplement agent. FIG. 2 is a schematic structural diagram of a sodium supplement agent provided by an embodiment of the present invention. As shown in FIG. 2 , the sodium supplement agent includes sodium borohydride 31 and the sodium borohydride coated The carbon layer 32 on the surface, the inventors of the present application have found that sodium borohydride has the ability to transport sodium ions and dissociate sodium ions, so it is used as a sodium supplement; in order to improve the conductivity and stability of sodium borohydride, the The carbon element is deposited on the surface of the sodium borohydride 31 by van der Waals force in the state of extremely fine powder, forming the coated carbon layer 32 .

Specifically, the particle size of sodium borohydride is 0.5-6 μm, and the particle size refers to the size of sodium borohydride particles, which can be obtained by testing with a particle size analyzer.

The thickness of the carbon layer 32 is 10-100nm. The thickness of the carbon layer 32 refers to the distance between the outermost layer of the carbon layer 32 and the surface of the sodium borohydride 31. The distance interval is 10-100nm. The carbon layer 32 and its thickness can be obtained by SEM, EDS, TEM, XPS and other ways to determine.

In a specific embodiment, the sodium supplement is prepared by the following preparation method:

Step 1, reacting boric acid with methanol to prepare trimethyl borate, and reacting metallic sodium with hydrogen to obtain sodium hydride;

First, boric acid and methanol are used as raw materials to react to prepare trimethyl borate. The involved reaction formula is: B(OH) ₃ +3CH ₃ OH=B(OCH ₃ ) ₃ +3H ₂ O, the reaction between boric acid and methanol The molar ratio is 1:3, the reaction temperature is 25-100°C, and the reaction time is 1-2h.

Simultaneously, react with metal sodium and hydrogen as raw materials to prepare sodium hydride. Because the activity of metal sodium is very high, it is very easy to react with air and water. Therefore, the present invention disperses metal sodium in the oily medium, and feeds hydrogen into the oily medium. Specifically, the mixture of metal sodium and hydrogen The molar ratio is 1:1, the reaction temperature is 200-500°C, and the reaction time is 4-12 hours to prepare sodium hydride.

Further, the oily medium is paraffin oil.

Step 2, reacting the trimethyl borate with sodium hydride to obtain sodium borohydride;

Secondly, react with trimethyl borate and sodium hydride prepared in step 1 as raw materials, the molar ratio of trimethyl borate and sodium hydride is 1:4, the reaction temperature is 200-400°C, and the reaction time is 2-12h, After the reaction, the solid product was collected to obtain sodium borohydride.

The prepared sodium borohydride is crushed, and its particle size is controlled to be 0.5-6 μm.

Step 3, heat-treating the sodium borohydride and a gaseous carbon source to obtain the sodium supplement.

The sodium borohydride obtained in step 2 is used as a raw material, and the sodium borohydride is dispersed in an oily medium under an inert atmosphere, and a gaseous carbon source is passed through to react, and the sodium supplement agent is prepared after the reaction is completed.

Further, the gaseous carbon source includes one or more of methane, ethane, propane, ethylene, propylene, acetylene, and propyne.

Further, the molar ratio of the sodium borohydride to the gaseous carbon source is 50-200:1.

Further, the heat treatment temperature of the sodium borohydride and the gaseous carbon source is 250-280° C. for 2-12 hours, so that the carbon element is deposited on the surface of the sodium borohydride to form a coating layer.

It can be understood that, in addition to the sodium replenishing agent, the positive electrode active material layer 2 also includes a positive electrode active material, a conductive agent and a binder, wherein the quality of the sodium replenishing agent is the total mass of the positive electrode active material, the conductive agent and the binder. 5-20%.

Further, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 8˜9:1:1.

The selection of positive electrode active material, conductive agent and binder is not special, and can be conventional selection in this field. For example, the positive electrode active material can be sodium-containing layered oxide material, Prussian white material, sodium-containing polyanion material, etc.; for example, the positive electrode active material can be nickel-containing NaNi _0.3 Fe _0.25 Mn _0.45 O ₂ , copper-containing One or more of NaCu _0.20 Fe _0.40 Mn _0.40 O ₂ , polyanionic NaV ₂ (PO ₄ ) ₃ ; the conductive agent is selected from conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nano One or more of tubes, single-walled carbon nanotubes, multi-armed carbon nanotubes, carbon fibers, the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), lithium polyacrylate (PAALi) one or more of.

During the preparation process, the positive electrode active material, sodium replenishing agent, conductive agent and binder are dispersed in a solvent, and stirred evenly to obtain a positive electrode slurry; subsequently, the positive electrode slurry is uniformly coated on the positive electrode current collector 1 to obtain a positive electrode active The material layer 2 is dried and cut to obtain the positive electrode sheet.

The second aspect of the present invention provides a sodium-ion battery, which includes any one of the positive electrode sheets described above.

Based on the positive pole piece provided by the invention, the sodium ion battery comprising the positive pole piece has better specific capacity and coulombic efficiency.

It can be understood that the sodium ion battery provided by the present invention also includes a negative electrode sheet, a separator and an electrolyte, all of which are conventional choices in the field.

The sodium supplement, the positive electrode sheet and the sodium ion battery provided by the present invention will be described below in conjunction with specific examples.

Example 1

This embodiment provides a preparation method of sodium supplement, which specifically includes the following steps:

Step 1. Add boric acid and methanol into the reaction kettle at a molar ratio of 1:3, heat to 80°C for 2 hours to prepare trimethyl borate;

Step 2. Dispersing sodium metal in paraffin oil, heating to 300°C, introducing hydrogen according to the molar ratio of sodium metal:hydrogen = 1:1, and reacting at 400°C for 6h to prepare sodium hydride;

Step 3, mixing trimethyl borate and sodium hydride in a molar ratio of 1:4, and reacting at 350° C. for 5 hours to obtain sodium borohydride;

Step 4, placing sodium borohydride in a mortar and grinding for 20 minutes to obtain sodium borohydride with a particle size of 3.79 μm;

Step 5. Put trimethyl borate and sodium hydride in paraffin oil, continuously feed nitrogen as a protective gas, heat to 250°C, and then feed methane under nitrogen protection for 2 hours to obtain sodium supplement NaBH ₄ @C, The thickness of the carbon layer is 16 nm.

Example 2

The preparation method of the sodium supplement provided in this example can refer to Example 1, the difference is that in step 3, the reaction time of introducing methane is 5 hours, and the thickness of the carbon layer is 43nm.

Example 3

The preparation method of the sodium supplement provided in this example can refer to Example 1, the difference is that in Step 3, the reaction time of introducing methane is 8 hours, and the thickness of the carbon layer is 68nm.

Example 4

The preparation method of the sodium supplement provided in this example can refer to Example 1, the difference is that in Step 3, the reaction time of introducing methane is 11 hours, and the thickness of the carbon layer is 95nm.

Example 5

The preparation method of the sodium supplement provided in this example can refer to Example 1, the difference is that in step 3, the carbon source introduced is replaced by ethylene from methane, and the thickness of the carbon layer is 21nm.

Example 6

The preparation method of the sodium supplement provided in this example can refer to Example 1, the difference is that in step 3, the carbon source introduced is replaced by acetylene from methane, and the thickness of the carbon layer is 19nm.

Comparative example 1

The preparation method of the sodium supplement provided in this comparative example can refer to Example 1, the difference is that in Step 3, the reaction time of introducing methane is 20h, and the thickness of the carbon layer is 200nm.

Comparative example 2

The preparation method of the sodium supplement provided in this comparative example can refer to Example 1, the difference is that the particle size of sodium borohydride is 8.06 μm.

Example 7

This embodiment provides a positive electrode sheet, including a positive electrode current collector aluminum foil and a positive electrode active material layer arranged on the surface of the positive electrode current collector aluminum foil, the positive electrode active material layer includes 8 parts by mass of positive electrode active material (NaNi _0.3 Fe _0.25 Mn _0.45 O ₂ ), the sodium supplement agent that the embodiment 1 of 1 mass part provides, the conductive agent acetylene black of 1 mass part and the polyvinylidene fluoride (PVDF) of 1 mass part.

The preparation method of the positive electrode active material (NaNi _0.3 Fe _0.25 Mn _0.45 O ₂ ) includes:

Step 1. Mix the precursor and lithium hydroxide evenly in a coulter mixer, and then sinter at 900°C for 20 hours;

Step 2. Crushing, sieving, washing, and drying the materials after primary sintering, and then transferring them to a rotary kiln for sintering at 600°C for 16 hours;

Step 3: Sieve the material after secondary sintering and remove iron to obtain polycrystalline ternary positive electrode active material (NaNi _0.3 Fe _0.25 Mn _0.45 O ₂ ).

The preparation method of the positive pole piece comprises:

Step 1. Disperse the positive electrode active material, sodium supplement, acetylene black and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solution, and stir evenly to obtain a positive electrode slurry;

Step 2. Evenly coat the positive electrode slurry on the aluminum foil, dry in a vacuum drying oven for 24 hours, and cut to obtain positive electrode sheets.

Example 8

The positive electrode sheet provided in this embodiment can refer to the embodiment 7, the difference is that the sodium supplement agent provided in the embodiment 2 is included in the positive electrode active material layer.

Example 9

The positive electrode sheet provided in this embodiment can refer to the embodiment 7, the difference is that the sodium supplement agent provided in the embodiment 3 is included in the positive electrode active material layer.

Example 10

The positive electrode sheet provided in this embodiment may refer to Example 7, the difference is that the positive electrode active material layer includes the sodium supplement provided in Example 4.

Example 11

The positive electrode sheet provided in this embodiment can refer to the embodiment 7, the difference is that the sodium supplement agent provided in the embodiment 5 is included in the positive electrode active material layer.

Example 12

The positive electrode sheet provided in this embodiment can refer to the embodiment 7, the difference is that the sodium supplement agent provided in the embodiment 6 is included in the positive electrode active material layer.

Comparative example 3

The positive electrode sheet provided in this comparative example can refer to Example 7, the difference is that the positive electrode sheet does not include a sodium supplement.

Comparative example 4

The positive pole piece provided in this comparative example can refer to Example 7, the difference is that the sodium replenishing agent is sodium borohydride coated with no carbon layer.

The preparation method of the sodium borohydride coated without carbon layer comprises:

Step 1. Add boric acid and methanol into the reaction kettle at a molar ratio of 1:3, heat to 80°C for 2 hours to prepare trimethyl borate;

Step 2. Dispersing sodium metal in paraffin oil, heating to 300°C, introducing hydrogen according to the molar ratio of sodium metal:hydrogen = 1:1, and reacting at 400°C for 6h to prepare sodium hydride;

Step 3. Mix trimethyl borate and sodium hydride at a molar ratio of 1:4, and react at 350° C. for 5 hours to obtain sodium borohydride.

Comparative example 5

The positive electrode sheet provided in this comparative example may refer to Example 7, the difference is that the positive electrode active material layer includes the sodium supplement provided in Comparative Example 1.

Comparative example 6

The positive electrode sheet provided in this comparative example may refer to Example 7, the difference is that the positive electrode active material layer includes the sodium replenishing agent provided in Comparative Example 2.

Comparative example 7

The positive electrode sheet provided in this comparative example can refer to Example 7, the difference is that the sodium replenishing agent is Na ₂ O.

Place the positive pole pieces and the hard carbon negative electrodes provided in Examples 7 to 12 and Comparative Examples 3 to 7 on both sides of the diaphragm respectively, and add an appropriate amount of sodium ion battery electrolyte (the solute is sodium hexafluorophosphate, and the solvent is ethylene carbonate (EC ) and dimethyl carbonate (DMC), and its volume ratio is EC:DMC=1:1), assembled into a pouch battery. Then, the discharge specific capacity and first coulombic efficiency of the battery were tested. The test method is as follows, and the test results are shown in Table 1.

The test method of discharge specific capacity and first coulombic efficiency: at 25°C, 1.5~4.2V, charge and discharge at 0.1C/0.1C to test the charge and discharge performance, and then according to the formula: first discharge efficiency = first cycle discharge specific capacity / first cycle Charge specific capacity * 100%, calculate the first Coulombic efficiency.

The performance test results of the batteries provided by Table 1 Examples 7-12 and Comparative Examples 3-7

Discharge specific capacity (mAh/g) First Coulombic Efficiency (%) Example 7 117.7 86.2% Example 8 120.3 87.3% Example 9 121.9 88.6% Example 10 119.6 87.1% Example 11 118.2 85.9% Example 12 117.0 86.0% Comparative example 3 105.9 75.6% Comparative example 4 111.3 81.4% Comparative example 5 112.7 81.9% Comparative example 6 114.1 82.6% Comparative example 7 108.9 79.5%

According to the data provided in Comparative Example 3, it can be known that adding sodium supplementation agent in the positive pole piece helps to improve the discharge specific capacity and first Coulombic efficiency of the battery; To improve the discharge specific capacity and the first coulombic efficiency of the sodium-ion battery; according to the data provided in Comparative Examples 5 to 6, it can be known that by controlling the particle size of sodium borohydride and the thickness of the coated carbon layer, it is helpful to further improve the discharge of the sodium-ion battery Specific capacity and first coulombic efficiency; according to comparative example 7, it can be known that the sodium supplementation effect of sodium borohydride is better than that of _Na2O ; according to examples 7-10, with the increase of gaseous carbon source introduction time, the thickness of the carbon layer continues to increase. However, the discharge specific capacity and first coulombic efficiency of the sodium-ion battery first increase and then decrease. Therefore, the introduction time of the gaseous carbon source is controlled at 5-8h, and the thickness of the carbon layer is controlled at 40-70nm, which will help to further increase the sodium ion battery. Discharge specific capacity and first coulombic efficiency of ion batteries; According to Examples 11-12, the type of gaseous carbon source has little effect on the performance of sodium ion batteries, which is conducive to large-scale production and application.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (10)

1. The positive electrode plate is characterized by comprising a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a sodium supplementing agent, and the sodium supplementing agent comprises sodium borohydride and a carbon layer coated on the surface of the sodium borohydride;

the granularity of the sodium borohydride is 0.5-6 mu m, and the thickness of the carbon layer is 10-100 nm.

2. The positive electrode sheet according to claim 1, wherein the sodium supplementing agent is prepared by the following preparation method:

reacting boric acid with methanol to obtain trimethyl borate, and reacting metallic sodium with hydrogen to obtain sodium hydride;

the trimethyl borate reacts with sodium hydride to prepare sodium borohydride;

and carrying out heat treatment on the sodium borohydride and a gaseous carbon source to obtain the sodium supplement.

3. The positive electrode sheet according to claim 2, wherein sodium hydride is prepared by reacting metallic sodium with hydrogen gas, and specifically comprises:

dispersing metallic sodium in an oily medium, introducing hydrogen into the oily medium, and reacting for 4-12 h at 200-500 ℃ to prepare sodium hydride.

4. The positive electrode sheet according to claim 2, wherein the sodium borohydride is heat-treated with a gaseous carbon source to obtain the sodium supplement, specifically comprising:

and dispersing the sodium borohydride in an oily medium under an inert atmosphere, and introducing a gaseous carbon source to deposit a carbon simple substance on the surface of the sodium borohydride to form a carbon layer, so as to obtain the sodium supplement.

5. The positive electrode sheet of claim 2 or 4, wherein the gaseous carbon source comprises one or more of methane, ethane, propane, ethylene, propylene, acetylene, propyne.

6. The positive electrode sheet according to claim 2 or 4, characterized in that the molar ratio of sodium borohydride to gaseous carbon source is 50-200:1.

7. The positive electrode sheet according to claim 2 or 4, wherein the heat treatment temperature of the sodium borohydride and the gaseous carbon source is 250-280 ℃ for 2-12 hours.

8. The positive electrode sheet according to claim 1, wherein the positive electrode active material layer further comprises a positive electrode active material, a conductive agent and a binder, and the mass of the sodium supplement agent is 5 to 20% of the total mass of the positive electrode active material, the conductive agent and the binder.

9. The positive electrode sheet according to claim 8, wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is 8 to 9:1:1.

10. a sodium ion battery, characterized in that it comprises the positive electrode sheet according to any one of claims 1 to 9.

Images