CN114790013B - Sodium ion battery positive electrode active material capable of self-supplementing sodium, preparation method and application thereof - Google Patents

Abstract

The present invention relates to a self-supplementing sodium positive electrode active material for a sodium ion battery and its preparation method and application. The self-supplementing sodium positive electrode active material for a sodium ion battery is a sodium-rich manganese-based layered oxide material with a general chemical formula of: Na _x Ni _a Cu _b Fe _c Mn _d M _e 0 _2±δ ; among them, Ni, Cu, Fe, and Mn are transition metal elements, and M is an ion doping and substituting the transition metal site; Mn ion is positive trivalent or positive trivalent. A mixed valence state of valence and positive tetravalence; in the structure of sodium-rich manganese-based layered oxide materials, the ions at the transition metal site form an octahedral structure with the adjacent six oxygens, and are alternately arranged with the octahedral-coordinated NaO ₆ layers , constituting the sodium-rich manganese-based layered oxide material of O3 type with space group R-3m; during the first cycle of charging, the Mn ³⁺ /Mn ⁴⁺ oxidation in the low voltage range is accompanied by the detachment of sodium ions, which effectively compensates for the first The active sodium ions are consumed in the process of forming the SEI film around the negative electrode, and the voltage range is controlled during the discharge process to inhibit the reduction of Mn ⁴⁺ , reduce the generation of Ginger Taylor effect, and significantly improve the battery cycle performance.

Description

Self-replenishing sodium positive electrode active material for sodium ion batteries and preparation method and application thereof

Technical field

The present invention relates to the field of material technology, and in particular to a self-supplementing sodium positive electrode active material for sodium ion batteries and its preparation method and application.

Background technique

Due to its low cost and abundant sources, sodium-ion batteries have shown great application potential in stationary grid storage systems and have therefore received widespread attention. Various prototype batteries based on sodium ion _{layered oxide} Na Although these advanced cathode/anode materials each achieve high power and energy density, the irreversible loss of sodium due to the solid electrolyte interface (SEI) formed on the anode side in the full battery limits the further improvement of the energy density of the full battery.

In response to this issue, current reports have explored several pre-sodiumization methods to introduce additional sodium sources into the battery system.

1) Electrochemical pre-sodiumization of the negative electrode. By assembling a half-cell on the negative electrode and performing electrochemical pre-cycling, the SEI is preformed on the negative electrode. Then the battery is disassembled and the pre-sodiumized negative electrode is taken out and rematched with the positive electrode to assemble a full battery. Although this method significantly improves the first-cycle Coulombic efficiency, energy density and subsequent cycle stability of the battery system, the complex operation process brings challenges to practical applications.

2) Direct mixed contact of the anode material with sodium metal also seems to be an effective pre-sodiumization strategy, because there have been reports in the literature that stable lithium metal powder was successfully incorporated into graphite and silicon anodes for prelithiation. However, Na metal is more reactive than Li metal and is sensitive to ambient atmosphere/dry air, which indicates that these composite electrodes are not conducive to scale-up or require high-cost manufacturing processes.

3) Pre-sodiumization of the positive electrode is another way to compensate for the irreversible capacity loss of the negative electrode. The introduction of sacrificial sodium-rich salts as additives to the cathode side with appropriate electrochemical decomposition voltage and chemical stability can effectively offset the initial sodium loss. However, previous studies have shown that the release of sodium ions in additives will produce by-products, such as N ₂ , CO or CO ₂ , and create pores in the passivation layer of the composite positive electrode or negative electrode, which is absolutely critical for batteries. Undesirable.

Therefore, to further improve the energy density of sodium-ion batteries, another novel sodium compensation strategy is needed that is compatible with existing industrial battery manufacturing processes and introduces few by-products.

Contents of the invention

Embodiments of the present invention provide a self-supplementing sodium positive electrode active material for a sodium ion battery and its preparation method and application.

In a first aspect, embodiments of the present invention provide a self-supplementing sodium-ion battery cathode active material. The self-supplementing sodium-ion battery cathode active material is a sodium-rich manganese-based layered oxide material, and the general chemical formula is: Na _x Ni _a Cu _b Fe _c Mn _d M _e 0 _2±δ ;

Among them, Ni, Cu, Fe, and Mn are transition metal elements, and M is an ion doping and substituting the transition metal position; the Mn ion is a positive trivalent or a mixed valence state of positive trivalent and positive tetravalent; in the sodium-rich manganese base layer In the structure of the oxide material, the ions at the transition metal site form an octahedral structure with the six adjacent oxygens, and are alternately arranged with the octahedral coordinated NaO ₆ layers to form the O3 type with the space group R-3m. Sodium-rich manganese-based layered oxide materials;

The M specifically includes Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ , B ³⁺ , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , and Zr ^{4 +} , Sn ⁴⁺ , Si ^{4 +} , Nb ⁵⁺ ; x, a, b, c, d, e and 2±δ are respectively the number of moles of the corresponding elements. In the general chemical formula Each component satisfies charge conservation and stoichiometry conservation, among which, 0.67≤x≤1, 0≤a<0.5, 0≤b≤0.35, 0≤c≤0.35, 0.1≤d≤0.6, 0≤e≤0.35, 0 ≤δ≤0.1, and a, b, c are not 0 at the same time.

In a second aspect, embodiments of the present invention provide a method for preparing the self-supplementing sodium-ion battery cathode active material described in the first aspect. The preparation method is a solid-phase method, including:

Mix the required stoichiometric sodium source of 100wt%-105wt% and the required stoichiometric amount of oxides, hydroxides or nitrates containing nickel, copper, iron, manganese and M in proportion, add absolute ethanol or Precursor powder is obtained after uniform grinding of acetone; the sodium source includes one or more of sodium carbonate, sodium nitrate, sodium peroxide, sodium superoxide, sodium hydroxide and sodium oxalate;

The obtained precursor powder is pressed into tablets in a crucible, calcined in a sintering atmosphere of air or oxygen at 700°C-900°C for 10-24 hours, rapidly cooled to room temperature within 1s-300s, and then ground to obtain the sodium Ion battery cathode active materials;

Among them, M is the element doping and substituting the transition metal site, specifically including Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al 3+ , ^{B 3+} , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ one or more.

In a third aspect, embodiments of the present invention provide a method for preparing the self-supplementing sodium-ion battery cathode active material described in the first aspect. The preparation method is a co-precipitation-high-temperature solid phase method, including:

Prepare a mixed solution of water-soluble Ni salt, Cu salt, Fe salt, Mn salt and M salt according to the required ratio of Ni, Cu, Fe, Mn and M to be the first solution; wherein the cation concentration in the first solution is 1 -3mol/L; M is the element doping and substituting the transition metal site, specifically including Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ , B ³⁺ , Co ³⁺ , One or more of V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ ;

Dissolve NaOH or KOH in deionized water to a concentration of 2-4mol/L, then add an appropriate amount of ammonia to form a second solution;

During the stirring process, add the first solution and the second solution into the reaction vessel at the same time, and perform a co-precipitation reaction under the conditions of 50°C-60°C. During the reaction, the pH value is maintained at 10-12;

After the co-precipitation reaction is completed, it is aged for 0-24 hours, and the precipitate is filtered, washed and dried to obtain a uniformly distributed hydroxide precursor of the transition metal element;

After the hydroxide precursor is evenly mixed with a sodium source with a stoichiometric amount of sodium of 100wt%-105wt%, it is kept at 400°C-500°C for 3-6 hours in an air atmosphere, and then calcined at 700°C-900°C for 10- 24 hours, and after rapidly cooling to room temperature within 1s-300s, grind to obtain the sodium ion battery cathode active material; wherein, the sodium source includes: sodium nitrate, sodium peroxide, sodium superoxide, sodium carbonate, hydrogen One or more of sodium oxide and sodium oxalate.

In a fourth aspect, embodiments of the present invention provide a method for preparing the self-supplementing sodium-ion battery cathode active material described in the first aspect, which is a sol-gel method, including:

According to the required stoichiometric ratio, weigh 100wt%-105wt% sodium ions, soluble salts of transition metal ions and an appropriate amount of citric acid and dissolve them in deionized water to form a mixed solution slurry; wherein the transition metal ions include Ni , Cu, Fe, Mn; the transition metal ions also include element M that is doped and substituted for the transition metal position; M specifically includes Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ , B ³⁺ , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ one or more;

The obtained slurry is heated and evaporated to dryness in an oil bath to form a xerogel;

Place the obtained xerogel in a crucible and pretreat it at 400°C-500°C for 3-6 hours. Then grind the pretreated powder and place it into tablets in a crucible at 700°C-900°C, air or oxygen. The sodium ion battery cathode active material is obtained by calcining in an atmosphere for 10-24 hours, rapidly cooling to room temperature within 1s-300s, and then grinding.

In a fifth aspect, embodiments of the present invention provide an electrode material for a sodium-ion secondary battery, including: a conductive additive, a binder, and the self-replenishing sodium-ion battery cathode active material described in the first aspect.

Preferably, the conductive additive includes: one or more of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon;

The binder includes one or more of polyvinylidene fluoride PVDF, sodium alginate, sodium carboxymethylcellulose CMC, and styrene-butadiene rubber SBR.

In a sixth aspect, embodiments of the present invention provide a positive electrode sheet including the electrode material of the sodium ion secondary battery described in the fifth aspect.

In a seventh aspect, embodiments of the present invention provide a sodium ion secondary battery including the positive electrode sheet described in the sixth aspect.

The self-supplementing sodium-ion battery cathode active material provided by the embodiment of the present invention introduces a large number of trivalent manganese ions into the material through composition optimization design, and through quenching treatment, Mn ³⁺ ions and Na ⁺ are retained in the material body at the same time. Mutually. The self-supplementing sodium-ion battery cathode active material of the present invention has the following advantages: 1) Containing more sodium ions in the bulk phase can compensate for the sodium ions consumed in the formation of the negative electrode solid electrolyte interface (SEI) film and reduce surface alkalinity The formation of sodium carbonate; 2) Mn ³⁺ in the low-oxidation platform can provide charge compensation for the removal of sodium ions, avoid the consumption of other active ions, significantly reduce material costs and increase the energy density of the system.

The sodium-ion full battery constructed by using the positive electrode matched with the hard carbon negative electrode provided by the present invention has the characteristics of high average energy storage voltage, high energy density and power density, and can be used as green and clean energy for power generation, smart grid peak shaving, distributed power stations, Energy storage equipment for backup power supplies, communication base stations or low-speed electric vehicles has excellent safety performance, rate performance and cycle performance.

Description of the drawings

The technical solutions of the embodiments of the present invention will be described in further detail below through the accompanying drawings and examples.

Figure 1 is an X-ray diffraction (XRD) pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in the embodiment of the present invention and the conventional manganese-based oxide cathode material in the comparative example;

Figure 2 is a scanning electron microscope (SEM) image of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 4 of the present invention;

Figure 3 is an SEM image of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 6 of the present invention;

Figure 4 is an SEM image of a conventional manganese-based oxide cathode material prepared in a comparative example of the present invention;

Figure 5 is a charge-discharge curve for the first two weeks of half-cell testing using the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 4 of the present invention;

Figure 6 is a charge-discharge curve for the first two weeks of the half-cell test using the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 5 of the present invention;

Figure 7 is a charge-discharge curve for the first two weeks of half-cell testing using the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 6 of the present invention;

Figure 8 is a charge-discharge curve for the first two weeks of the half-cell test using conventional manganese-based oxide cathode materials prepared in the comparative example of the present invention;

Figure 9 shows the charge and discharge curves of the full battery in the first two weeks using the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 6 of the present invention and the conventional manganese-based oxide cathode material prepared in the comparative example, respectively, and the hard carbon negative electrode. picture;

Figure 10 is a cycle performance curve of a full battery using the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 6 of the present invention and the conventional manganese-based oxide cathode material prepared in the comparative example and the hard carbon negative electrode respectively.

Detailed ways

The present invention will be further described below through the drawings and specific examples. However, it should be understood that these examples are only for more detailed description and should not be understood as limiting the present invention in any form, that is, they are not intended to limit the present invention. to limit the scope of protection of the present invention.

The self-supplementing sodium-ion battery cathode active material of the present invention is a sodium-rich manganese-based layered oxide material, and its general chemical formula is: Na _x Ni _a Cu _b Fe _c Mn _d M _e 0 _2±δ ; wherein, Ni, Cu, Fe, and Mn are transition metal elements, and M is an ion doping and substituting the transition metal position; the Mn ion is positive trivalent or a mixed valence state of positive trivalent and positive tetravalent; the structure of the sodium-rich manganese-based layered oxide material , the ions at the transition metal position form an octahedral structure with the six adjacent oxygens, and are alternately arranged with the octahedral coordinated NaO ₆ layers to form the Na-rich manganese-based layered oxidation of the O3 type with the space group R-3m. material;

M specifically includes Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ , B ³⁺ , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , One or more of Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ ; x, a, b, c, d, e and 2±δ are respectively the number of moles occupied by the corresponding elements. Each group in the general chemical formula It satisfies charge conservation and stoichiometry conservation, among which, 0.67≤x≤1, 0≤a<0.5, 0≤b≤0.35, 0≤c≤0.35, 0.1≤d≤0.6, 0≤e≤0.35, 0≤δ ≤0.1, and a, b, c are not 0 at the same time.

The sodium-rich manganese-based layered oxide material of the sodium ion battery of the present invention can be used as a positive electrode active material of a sodium ion secondary battery. A large number of trivalent manganese ions are introduced into the material through composition optimization design, and Mn ³⁺ ions and Na ⁺ are retained in the bulk phase of the material at the same time through quenching treatment. This material has the following advantages: 1) More sodium ions in the bulk phase can compensate for the sodium ions consumed by the SEI formation of the negative electrode and reduce the formation of alkaline sodium carbonate on the surface; 2) Mn ³⁺ in the low-oxidation platform can be sodium ions The detachment provides charge compensation, avoids the consumption of other active ions, significantly reduces material costs and increases the energy density of the system. The sodium-ion full battery constructed by matching the positive electrode with the hard carbon negative electrode has the characteristics of high average energy storage voltage, high energy density and power density. The sodium-ion full battery constructed by using the positive electrode matched with the hard carbon negative electrode provided by the present invention has the characteristics of high average energy storage voltage, high energy density and power density, and can be used as green and clean energy for power generation, smart grid peak shaving, distributed power stations, Energy storage equipment for backup power supplies, communication base stations or low-speed electric vehicles has excellent safety performance, rate performance and cycle performance.

Embodiments of the present invention also provide a method for preparing the above-mentioned sodium-rich manganese-based layered oxide cathode material used as a self-supplementing sodium-ion battery cathode active material. Specifically, solid phase method, co-precipitation-high temperature solid phase method or sol can be used. Prepared by gel method.

The method steps prepared by solid phase method specifically include:

Step 110, combine the required stoichiometric sodium source of 100wt%-105wt%, the required stoichiometric nickel oxide, copper oxide, iron oxide, manganese oxide and M oxide, hydroxide Mix the precursor or nitrate in proportion, add absolute ethanol or acetone and grind evenly to obtain the precursor powder;

Wherein, the sodium source includes one or more of sodium nitrate, sodium peroxide, sodium superoxide, sodium carbonate, sodium hydroxide and sodium oxalate; M is as mentioned above and will not be described again.

Step 120: Place the obtained precursor powder into tablets in a crucible, calcine in a sintering atmosphere of air or oxygen at 700°C-900°C for 10-24 hours, rapidly cool to room temperature within 1s-300s, and then grind to obtain The sodium-rich manganese-based layered oxide cathode material.

The method steps prepared by co-precipitation-high temperature solid phase method specifically include:

Step 210, prepare a mixed solution of water-soluble Ni salt, Cu salt, Fe salt, Mn salt and M salt according to the required ratio of Ni, Cu, Fe, Mn and M as the first solution; wherein the cations in the first solution The concentration is 1-3mol/L;

Among them, M is as mentioned above and will not be described again.

Step 220: Dissolve NaOH or KOH in deionized water with a concentration of 2-4 mol/L, and then add an appropriate amount of ammonia to form a second solution;

Step 230: Add the first solution and the second solution into the reaction vessel at the same time during the stirring process, and perform a co-precipitation reaction under the conditions of 50°C-60°C. The pH value is maintained at 10-12 during the reaction;

Step 240: After the co-precipitation reaction is completed, the mixture is aged for 0-24 hours, and the precipitate is filtered, washed and dried to obtain a uniformly distributed hydroxide precursor of the transition metal element;

Step 250: Mix the hydroxide precursor and a sodium source with a stoichiometric amount of 100wt%-105wt% of sodium evenly, keep it at 400°C-500°C for 3-6 hours in an air atmosphere, and then calcine it at 700°C-900°C for 10 -24 hours, and after rapidly cooling to room temperature within 1s-300s, grind to obtain the sodium-rich manganese-based layered oxide cathode material;

The sodium source includes: one or more of sodium nitrate, sodium peroxide, sodium superoxide, sodium carbonate, sodium hydroxide and sodium oxalate.

The method steps prepared by the sol-gel method specifically include:

Step 310: Weigh stoichiometrically 100wt%-105wt% sodium ions, soluble salts of transition metal ions and an appropriate amount of citric acid and dissolve them in deionized water to form a mixed solution slurry according to the required stoichiometric ratio; wherein, the transition metal Ions include Ni, Cu, Fe, Mn;

Among them, the transition metal ion also includes an element M that is doped and substituted at the transition metal site; M is as mentioned above and will not be described again.

Step 320, heat and evaporate the obtained slurry in an oil bath to dryness to form a xerogel;

Step 330: Place the obtained xerogel in a crucible, pretreat it at 400°C-500°C for 3-6 hours, then grind the powder obtained by the pretreatment, press it into tablets and place it in the crucible at 700°C-900°C. The sodium-rich manganese-based layered oxide cathode material is obtained by calcining in an air or oxygen atmosphere for 10-24 hours, rapidly cooling to room temperature within 1s-300s, and then grinding.

In each of the above preparation methods, a rapid cooling method is adopted after high-temperature calcination. The specific implementation can include: 1) quickly placing the calcined high-temperature sample in liquid nitrogen; 2) quickly placing the calcined high-temperature sample in two clean between metal plates with high specific heat capacity (>0.1KJ/Kg); 3) Quickly place the calcined high-temperature sample into a metal tank filled with argon gas. Of course, it is not limited to the above methods, other methods with mature existing technology that can quickly reduce the material temperature can also be used.

The preparation method provided by the invention effectively maintains Mn in the designed Mn ³⁺ valence state or Mn ³⁺ /Mn ⁴⁺ mixed valence state through a precisely controlled quenching process. The material is used to match the negative electrode plate of the full battery. During the first week of charging, the oxidation of Mn ³⁺ /Mn ⁴⁺ in the low voltage range along with the release of sodium ions can effectively compensate for the active sodium ions consumed during the formation of the SEI film on the negative electrode in the first week. The voltage range during the discharge process is controlled to suppress Mn ⁴⁺ Reduction reduces the occurrence of the Ginger Taylor effect and significantly improves battery cycle performance. The self-replenishing sodium positive electrode material of the present invention is used in sodium-ion batteries. It is simple to operate and does not require adjustment of the existing battery production process. It can effectively compensate for the loss of active sodium ions caused by some irreversible reactions in the full battery system, thereby significantly improving the performance of the full battery. Energy Density.

In order to better understand the technical solutions provided by the present invention, the self-supplementing sodium-ion battery positive electrode active material of the present invention—sodium-rich manganese-based layered oxide material, its preparation method and performance will be further described below with reference to some specific examples. Elaborate.

Example 1

In this example, a co-precipitation-high-temperature solid phase method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material NaNi _0.3 Fe _0.2 Mn _0.5 O ₂ . The specific steps include:

According to the proportion of Ni, Fe and Mn in the molecular formula NaNi _0.3 Fe _0.20 Mn _0.5 O ₂ , prepare a deionized water solution of NiSO ₄ ·6H ₂ O, FeSO ₄ ·7H ₂ O and MnSO ₄ ·H ₂ O, with a concentration of 2mol/L ;

Use sodium hydroxide, ammonia and deionized water to prepare alkali solution, where the concentration of sodium hydroxide is 4mol/L and the concentration of ammonia is 1mol/L;

Add an appropriate amount of deionized water to the reaction kettle and pass in nitrogen, heat it to 60°C and keep it warm, then add sodium hydroxide and ammonia water to the reaction kettle to adjust the pH to 11.7, the ammonia concentration to 0.4mol/L, and operate at 500r/min. Stir at high speed, then add transition metal solution and alkali solution dropwise at the same time, and maintain the pH at about 11.7;

After the reaction is completed, filter and wash the precipitate until the pH of the filtered water is ≤ 9.5, and dry it at 120°C for 12 hours to obtain a uniformly distributed hydroxide precursor of the transition metal element;

After the obtained hydroxide precursor and excess 2% sodium carbonate are mixed evenly according to the stoichiometric ratio, the temperature is maintained at 450°C for 5 hours in an air atmosphere, and calcined at 850°C for 15 hours. The sample at high temperature is quickly placed on two blocks. The temperature between the copper plates is lowered to room temperature, and the sodium-rich manganese-based layered oxide cathode material NaNi _0.3 Fe _0.2 Mn _0.5 O ₂ is obtained.

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m.

Example 2

In this example, a solid-phase method is used to prepare a self-supplementing sodium-rich manganese-based layered oxide cathode material NaNi _0.3 Fe _0.2 Mn _0.5 O ₂ . The specific steps include: weighing Na ₂ CO ₃ (excess 2%) according to the stoichiometric ratio; Put NiO, Fe ₂ O ₃ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor. Press the precursor into a 15mm diameter disc under a pressure of 10Mpa, and place it in an air atmosphere of 900 After treatment at ℃ for 15 hours, the sample at high temperature was quickly placed between two copper plates to cool down. After cooling to room temperature, the sodium-rich manganese-based layered oxide cathode material NaNi _0.3 Fe _0.2 Mn _0.5 O ₂ was obtained.

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m.

Example 3

In this example, a solid-phase method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material NaNi _0.2 Cu _0.1 Fe _0.20 Mn _0.50 O ₂ . The specific steps include: weighing Na ₂ CO ₃ according to the stoichiometric ratio (excess 2% ), NiO, CuO, Fe ₂ O ₃ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor, and press the precursor into a 15mm diameter disc under a pressure of 10Mpa. Treat the sample at 900°C for 15 hours in an air atmosphere. The sample at high temperature is quickly placed between two copper plates to cool down. After cooling to room temperature, the sodium-rich manganese-based layered oxide cathode material NaNi _0.2 Cu _0.1 Fe _0.20 is obtained. Mn _0.50 O ₂ .

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that its main phase is O3 phase, the space group is R-3m, and it contains a small amount of copper oxide. Miscellaneous.

Example 4

In this example, a solid-phase method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Cu _0.22 Fe _0.30 Mn _0.48 O ₂ . The specific steps include: weighing Na ₂ CO ₃ according to the stoichiometric ratio (excess 2% ), CuO, Fe ₂ O ₃ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor, press the precursor into a 15mm diameter disc under a pressure of 10Mpa, and place it in the air The atmosphere was treated at 900°C for 15 hours. The high-temperature sample was quickly placed between two copper plates to cool down. After cooling to room temperature, the sodium-rich manganese-based layered oxide cathode material Na _0.9 Cu _0.22 Fe _0.30 Mn _0.48 was obtained. O ₂ .

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that the main phase is O3 phase and the space group is R-3m. The SEM picture is shown in Figure 2. The particle size is about 4 microns and the crystallinity is good.

Example 5

In this example, a solid-phase method is used to prepare a self-supplementing sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.48 O ₂ . The specific steps include: weighing Na ₂ CO ₃ (excess 2%), NiO, CuO, Fe ₂ O ₃ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor, which is pressed into a 15mm diameter circle under a pressure of 10Mpa. The piece was processed for 15 hours in an air atmosphere at 900°C. The high-temperature sample was quickly placed between two copper plates to cool down. After cooling to room temperature, the sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 was obtained. Cu _0.11 Fe _0.30 Mn _0.48 O ₂ .

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m.

Example 6

In this example, a solid-phase method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _{0.1 1} Fe _0.30 Mn _0.38 Ti _0.10 O ₂ . The specific steps include: weighing Na ₂ CO according to the stoichiometric ratio. ₃ (excess 2%), NiO, CuO, Fe ₂ O ₃ , TiO ₂ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor, put the precursor under a pressure of 10Mpa Press it into a 15mm diameter disc and treat it in an air atmosphere at 900°C for 15 hours. The high-temperature sample is quickly placed between two copper plates to cool down. After cooling to room temperature, a sodium-rich manganese-based layered oxide with sodium supplementation is obtained. Cathode material Na _{0. 9} Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.38 Ti _0.10 O ₂ .

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m. The SEM picture is shown in Figure 3. The particle size is about 2 microns and the crystallinity is good.

Example 7

In this example, a solid-phase method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _{0.1 1} Fe _0.30 Mn _0.28 Ti _0.20 O ₂ . The specific steps include: weighing Na ₂ CO according to the stoichiometric ratio. ₃ (excess 2%), CuO, Fe ₂ O ₃ , TiO ₂ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor, which is pressed under a pressure of 10Mpa. A 15mm diameter disc is processed in an air atmosphere at 900°C for 15 hours. The high temperature sample is quickly placed between two copper plates to cool down. After cooling to room temperature, a sodium-rich manganese-based layered oxide cathode material is obtained. Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.28 Ti _0.20 O ₂ .

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m.

Example 8

In this example, a solid-phase method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _{0.1 1} Fe _0.30 Mn _0.0.38 Ti _0.10 O ₂ . The specific steps include: weighing Na according to the stoichiometric ratio ₂ CO ₃ (excess 2%), NiO, CuO, Fe ₂ O ₃ , TiO ₂ and Mn ₂ O ₃ are placed in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor. Put the precursor at 10Mpa. Press into 15mm diameter discs under pressure, and process for 15 hours at 900°C in an air atmosphere. The high-temperature sample is quickly placed in liquid nitrogen to cool down. After the liquid nitrogen evaporates, a sodium-rich manganese-based layered oxide is obtained. Cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.0.38 Ti _0.10 O ₂ .

The XRD pattern of the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m.

Example 9

In this embodiment, a sol-gel method is used to prepare a self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Cu _0.11 Ni _0.11 Fe _0.30 Mn _0.48 O ₂ . The specific steps include:

Weigh sodium nitrate, manganese acetate, nickel acetate, copper acetate, ferric nitrate and an appropriate amount of citric acid according to the required stoichiometric ratio and dissolve them in deionized water to form a mixed solution; heat and evaporate the resulting slurry to dryness in an oil bath to form a dry condensation Glue; collect the xerogel obtained and place it in a crucible, pretreat it at 450°C for 3-6 hours, grind the powder obtained by pretreatment, press it into tablets and place it in the crucible and calcine it at 800°C for 20 hours. The sintering atmosphere is In the air, the high-temperature sample was quickly placed between two copper plates to cool down. After cooling to room temperature, the sodium-rich manganese-based layered oxide cathode material Na-supplemented Na _0.9 Cu _0.11 Ni _0.11 Fe _0.30 Mn _0.48 O ₂ was obtained.

Comparative ratio

In this example, the conventional manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.38 Ti _0.10 O ₂ is prepared using a solid-phase method. The specific steps include: weighing Na ₂ CO ₃ according to the stoichiometric ratio (excess 2% ), NiO, CuO, Fe ₂ O ₃ , TiO ₂ and Mn ₂ O ₃ in an agate mortar, add an appropriate amount of absolute ethanol, mix and grind evenly to obtain a precursor, which is pressed into a 15mm diameter tube under a pressure of 10Mpa. The disc is treated at 900°C in an air atmosphere for 15 hours, and then cooled to room temperature with the furnace to obtain the conventional manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.38 Ti _0.10 O ₂ .

The XRD pattern of the conventional manganese-based layered oxide cathode material prepared in this example is shown in Figure 1. Comparing with the standard card, it can be seen that it is a pure O3 phase material with a space group of R-3m. The SEM picture is shown in Figure 4. The particle size is about 2 microns and the surface is rough.

Further research found that the amorphous substance covering the surface is sodium carbonate, indicating that during the cooling process of the material, the sodium ions in the granular phase will slowly desorb to form amorphous sodium carbonate, accompanied by the oxidation of bulk manganese ions.

The self-supplemented sodium-rich manganese-based layered oxide cathode materials prepared in the above embodiments of the present invention and the materials in the comparative examples were tested.

Half-cell assembly: The self-supplemented sodium-rich manganese-based layered oxide cathode material in each example was mixed with conductive carbon black (Super P) and vinylidene fluoride (PVDF) in an inert atmosphere at a mass ratio of 75: 15:10 is slurried in N-methylpyrrolidone (NMP) solution and coated on aluminum foil. After vacuum drying, it is cut into pole pieces with a diameter of 12mm (loading capacity is about 5-10mg/cm ² ), and metallic sodium is used. The sheet is the negative electrode, 1 mol/L NaClO ₄ /polycarbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio 1:1:1) solution is used as the electrolyte, and the glass fiber separator is used. CR2032 coin cell half cells were assembled in an argon glovebox. By matching the above pole pieces with hard carbon negative electrodes, a full battery can be assembled, in which the hard carbon first efficiency is 80% and the reversible specific capacity is 350mAh·g ^-1 .

Charge and discharge test: The voltage range of button half cell charge and discharge is 2.5-4.0V, and the full battery voltage range is 1.0-4.0V. Before the cycle test, a smaller current density of 15mA/g (0.1C) is used for two activations. , followed by cycling at 1C rate in the same voltage range, and all electrochemical performance tests were conducted at room temperature.

Figure 5 shows the charge and discharge curves of the first 2 weeks of the self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Cu _0.22 Fe _0.30 Mn _0.48 O ₂ prepared in Example 4. During the first week of charging, it can be found that about 2.5V There is a voltage platform, which is mainly caused by the oxidation of Mn ³⁺ in the material body and is accompanied by the release of sodium ions. Although the Mn ⁴⁺ /Mn ^{3 +} redox process is reversible, the platform voltage is too low (matching hard carbon results in a wider charge and discharge interval), and the Ginger Taylor effect caused by Mn ³⁺ deteriorates the structural stability of the material. . Therefore, manganese ions can be stabilized at positive tetravalent valence only through the first week of charging, and the released sodium ions are used to compensate for the consumption of active sodium ions caused by the formation of SEI in the negative electrode in the first week to achieve the effect of self-replenishing sodium, thereby reducing the consumption of positive electrode materials in the entire battery system. , significantly improving the overall energy density. The cathode material has a first-week charge specific capacity of 129mAh·g ^-1 and a reversible specific capacity of 97mAh·g ^-1 .

Figure 6 shows the first ₂ -week charge-discharge curve of the self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.48 O 2 prepared in Example 5, in the voltage range of 2.5-4.0V Its first-week charging specific capacity is 130mAh·g ^-1 and its reversible specific capacity is 100mAh·g ^-1 .

Figure 7 shows the first 2-week charge-discharge curve of the self-supplemented sodium-rich manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.38 Ti _0.10 O ₂ prepared in Example 6, at a voltage of 2.5-4.0V Within the range, its first-week charging specific capacity is 133mAh·g ^-1 and its reversible specific capacity is 106mAh·g ^-1 .

Figure 8 shows the first 2-week charge-discharge curve of the conventional manganese-based layered oxide cathode material Na _0.9 Ni _0.11 Cu _0.11 Fe _0.30 Mn _0.38 Ti _0.10 O ₂ prepared in the comparative example. Its first cycle in the voltage range of 2.5-4.0V The charge specific capacity is 124mAh·g ^-1 , which obviously lacks the low-voltage Mn ³⁺ oxidation platform, and the reversible specific capacity is 99mAh·g ^-1 .

Figure 9 shows the first cycle of charge and discharge of a full battery using the self-supplemented sodium-rich manganese-based layered oxide cathode material prepared in Example 6 of the present invention and the conventional manganese-based oxide cathode material prepared in the comparative example, respectively matched with the hard carbon negative electrode. curve. It can be seen that the lower voltage platform during the charging process of the embodiment is mainly provided by Mn ³⁺ oxidation, but there is no such platform in the comparative example. The reversible specific capacity of the cathode system with self-replenishing sodium effect has been significantly improved (104mAh·g ^-1 higher than the 90mAh·g ^-1 of conventional manganese-based materials). It can also be seen from Figure 10 that the full battery matched with self-supplemented sodium materials also achieves better cycle performance.

The self-supplementing sodium-ion battery cathode active material provided by the present invention introduces a large number of trivalent manganese ions into the material through composition optimization design, and through quenching treatment, Mn ³⁺ ions and Na ⁺ are retained in the bulk phase of the material at the same time. The carrier phase of this material contains more sodium ions to compensate for the sodium ions consumed by the SEI formation of the negative electrode and reduce the formation of alkaline sodium carbonate on the surface. At the same time, the Mn ³⁺ in the low-oxidation platform can provide charge compensation for the detachment of sodium ions and avoid The consumption of other active ions significantly reduces material costs and increases the energy density of the system. The sodium-ion full battery constructed using this positive electrode matched with a hard carbon negative electrode has the characteristics of high average energy storage voltage, high energy density and power density. It can be used as green and clean energy for power generation, smart grid peak shaving, distributed power stations, backup power, Energy storage equipment for communication base stations or low-speed electric vehicles has excellent safety performance, rate performance and cycle performance.

The above-described specific embodiments further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (8)

1. A self-supplementing sodium-ion battery cathode active material, characterized in that the self-supplementing sodium-ion battery cathode active material is a sodium-rich manganese-based layered oxide material, and the general chemical formula is: Na _x Ni _a Cu _b Fe _c Mn _d M _e 0 _2±δ ; Among them, Ni, Cu, Fe, and Mn are transition metal elements, and M is an ion doping and substituting the transition metal position; the Mn ion is a positive trivalent or a mixed valence state of positive trivalent and positive tetravalent; in the sodium-rich manganese base layer In the structure of the oxide material, the ions at the transition metal site form an octahedral structure with the six adjacent oxygens, and are alternately arranged with the octahedral coordinated NaO ₆ layers to form the O3 type with the space group R-3m. Sodium-rich manganese-based layered oxide material; first obtain a cathode active material precursor, and then calcine the cathode active material precursor at high temperature and then immediately quench it to retain Mn ³⁺ and Na ⁺ in the sodium-rich manganese-based layered oxide material. The physical phase of matter; The M specifically includes Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ , B ³⁺ , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , and Zr ^{4 +} , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ ; x, a, b, c, d, e and 2±δ are respectively the number of moles of the corresponding elements. In the general chemical formula Each component satisfies charge conservation and stoichiometry conservation, among which, 0.67≤x≤1, 0≤a<0.5, 0≤b≤0.35, 0≤c≤0.35, 0.1≤d≤0.6, 0≤e≤0.35, 0 ≤δ≤0.1, and a, b, c are not 0 at the same time. 2. A method for preparing the self-supplementing sodium-ion battery cathode active material according to claim 1, characterized in that the preparation method is a solid-phase method, including: Mix the required stoichiometric sodium source of 100wt%-105wt% and the required stoichiometric oxide, hydroxide or nitrate containing nickel, copper, iron, manganese and M in proportion, add absolute ethanol or Precursor powder is obtained after uniform grinding of acetone; the sodium source includes one or more of sodium carbonate, sodium nitrate, sodium peroxide, sodium superoxide, sodium hydroxide and sodium oxalate; The obtained precursor powder is pressed into tablets in a crucible, calcined in a sintering atmosphere of air or oxygen at 700°C-900°C for 10-24 hours, rapidly cooled to room temperature within 1s-300s, and then ground to obtain the sodium Ion battery cathode active materials; Among them, M is the element doping and substituting the transition metal site, specifically including Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al 3+ , ^{B 3+} , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ one or more. 3. A method for preparing the self-supplementing sodium-ion battery cathode active material according to claim 1, characterized in that the preparation method is a co-precipitation-high temperature solid phase method, including: Prepare a mixed solution of water-soluble Ni salt, Cu salt, Fe salt, Mn salt and M salt according to the required ratio of Ni, Cu, Fe, Mn and M to be the first solution; wherein the cation concentration in the first solution is 1 -3 mol/L; M is the element doping and substituting the transition metal site, specifically including Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , Al ³⁺ , B ³⁺ , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ one or more; Dissolve NaOH or KOH in deionized water to a concentration of 2-4 mol/L, then add an appropriate amount of ammonia to form a second solution; During the stirring process, add the first solution and the second solution into the reaction vessel at the same time, and perform a co-precipitation reaction under the conditions of 50°C-60°C. During the reaction, the pH value is maintained at 10-12; After the co-precipitation reaction is completed, it is aged for 0-24 hours, and the precipitate is filtered, washed and dried to obtain a uniformly distributed hydroxide precursor of the transition metal element; After the hydroxide precursor is evenly mixed with a sodium source with a stoichiometric amount of sodium of 100 wt%-105 wt%, it is kept at 400°C-500°C for 3-6 hours in an air atmosphere, and then calcined at 700°C-900°C. 10-24 hours, and after rapidly cooling to room temperature within 1s-300s, grind to obtain the sodium ion battery positive active material; wherein, the sodium source includes: sodium nitrate, sodium peroxide, sodium superoxide, and sodium carbonate , one or more of sodium hydroxide and sodium oxalate. 4. A method for preparing the self-supplementing sodium-ion battery cathode active material according to claim 1, characterized in that the preparation method is a sol-gel method, including: According to the required stoichiometric ratio, weigh sodium ions with a stoichiometric amount of 100 wt%-105 wt%, soluble salts of transition metal ions and an appropriate amount of citric acid and dissolve them in deionized water to form a mixed solution slurry; wherein, the transition metal ions Including Ni, Cu, Fe, Mn; the transition metal ions also include the element M that is doped and substituted for the transition metal position; M specifically includes Li ⁺ , Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Zn ²⁺ , and Al One or more of ³⁺ , B ³⁺ , Co ³⁺ , V ³⁺ , Y ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Nb ⁵⁺ ; The obtained slurry is heated and evaporated to dryness in an oil bath to form a xerogel; Place the obtained xerogel in a crucible and pretreat it at 400°C-500°C for 3-6 hours. Then grind the pretreated powder and place it into tablets in a crucible at 700°C-900°C, air or oxygen. The sodium ion battery cathode active material is obtained by calcining in an atmosphere for 10-24 hours, rapidly cooling to room temperature within 1s-300s, and then grinding. 5. An electrode material for a sodium-ion secondary battery, characterized in that the electrode material includes: a conductive additive, a binder and the self-supplementing sodium-ion battery cathode active material of claim 1. 6. The electrode material of sodium ion secondary battery according to claim 5, characterized in that the conductive additive includes: carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon. one or several kinds; The binder includes one or more of polyvinylidene fluoride PVDF, sodium alginate, sodium carboxymethylcellulose CMC, and styrene-butadiene rubber SBR. 7. A positive electrode sheet comprising the electrode material of the sodium ion secondary battery according to claim 5 or 6. 8. A sodium ion secondary battery comprising the positive electrode sheet according to claim 7.