O3-P2 layered double-phase sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses an O3-P2 layered double-phase sodium ion battery positive electrode material and a preparation method thereof, and belongs to the technical field of sodium ion batteries. The chemical formula is Na (1.0-x) MxNiaMnbMe1-a-bO2, x is more than 0 and less than 0.5, a is more than 0.1 and less than 0.9, b is more than 0.1 and less than 0.9, a + b is more than 0.2 and less than 1, M is a metal element, and Me is a transition metal element. Through doping of metal ions, an impurity phase component in an original positive electrode material is converted into a layered P2 phase component, and the O3 and P2 layered two-phase sodium ion battery positive electrode material is formed. The composite phase structure obtained through metal ion doping enhances the structural stability of the material, so that the positive electrode material has the advantages of low cost, low strain, high capacity, good cycling stability and rate capability, simple preparation process, high repeatability and great potential for large-scale production.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to an O3-P2 layered dual-phase sodium ion battery positive electrode material and a preparation method. BACKGROUND

[0002] The global energy demand continues to grow, and traditional fossil energy not only faces pollution problems, but also is non-renewable, which makes it difficult to meet the demand. Therefore, developing sustainable electric energy storage materials has become a key issue. Among them, secondary batteries have become a research hotspot due to their excellent conversion efficiency and high energy density. Since commercialization, lithium ion batteries have been favored due to long cycle life and high energy density. However, the low crust abundance and uneven distribution of lithium resources have led to a rising price as demand increases.

[0003] Sodium ion batteries, which are rich in resources and have similar electrochemical properties, have gradually become an important research direction due to their cost advantage. The positive electrode material, as an important part of the sodium ion battery, has a very important influence on the overall performance of the battery. The positive electrode layered transition metal oxide of the sodium ion battery mainly includes P2 type, O3 type and P3 type structures. Among them, "P" and "O" respectively represent the coordination environment of sodium ions as prismatic (Prismatic) and octahedral (Octahedral). P2-phase Na x Mn 1-y MyO2 (0.5<=x<=0.8) material has a low Na + diffusion barrier and a high ion migration rate, but its initial charge capacity is usually low. In contrast, O3-Na x Mn 1-y M y O2 (0.8<=x<=1) material has a high initial charge capacity, but the structure reversibility is poor. SUMMARY

[0004] The purpose of the present application is to provide an O3 and P2 layered dual-phase sodium ion battery positive electrode material and a preparation method, to solve the problems in the technical background, to convert the impurity phase components in the original positive electrode material into layered components through dual-site synergistic doping, to form an O3 and P2 layered dual-phase sodium ion battery positive electrode material, to enhance the material structure stability, to make the positive electrode material have low cost, low strain, high capacity and good cycle stability, to have a simple preparation process, high repeatability and great potential for large-scale production.

[0005] To achieve the above purpose, the present application provides an O3 and P2 layered dual-phase sodium ion battery positive electrode material, the chemical formula of the sodium ion battery positive electrode material is Na 1.0-x M x Ni a Mn bMe 1-a-b O2, wherein M is a metal element substituted for sodium sites, Me is a transition metal element substituted for transition metal sites, 0

[0006] Preferably, M is any one or more of Li, Mg, Al, Zn, B, K, Ca, Ba, Sr, and Me is any one or more of Co, Cu, Fe, Ti, Sc, V, Mo, Sb, Ru, W, Ta, Ce, Zr, Y, La.

[0007] Preferably, the sodium ion battery positive electrode material is a layered O3 and P2 layered dual-phase composite structure.

[0008] The application also provides a preparation method of the above-mentioned O3 and P2 layered dual-phase sodium ion battery positive electrode material, comprising the following steps: S1、Ni a Mn b Me 1-a-b (OH)2 precursor preparation The metal salt solutions of Ni, Mn and Me are simultaneously dropped into the reaction kettle with lye, and continuous stirring is performed, so that Ni a Mn b Me 1-a-b (OH )2 The precipitate is filtered to be free of impurity ions, and is placed into a 120℃ oven for drying for 6h, to obtain the Ni a Mn b Me 1-a-b (OH)2 precursor; S2、Na 1.0-x M x Ni a Mn b Me 1-a-b O2 preparation According to the molar ratio of each element in the chemical formula Na 1.0-x M x Ni a Mn b Me 1-a-b O2, the sodium source, the M-containing compound and the Ni a Mn b Me 1-a-b (OH)2 precursor are weighed, and are mixed uniformly in a ball mill to obtain a mixture, and then the mixture is transferred to a porcelain boat and is placed into an air muffle furnace for gradient temperature calcination, and then is naturally reduced to room temperature, to obtain the Na 1.0-x M x Ni a Mn bMe 1.0-a-b O2.

[0009] Preferably, step S1 specifically comprises the following steps: S1-1, according to the chemical formula Ni a Mn b Me 1-a-b The molar ratio of each element in (OH)2 is taken to weigh the precursors of Ni, Mn, and Me, mixed in a beaker, and deionized water is added to dissolve and prepare a metal salt solution; S1-2, in another beaker, NaOH solution is prepared by dissolving in deionized water, and ammonia water is added to adjust the pH value to about 12.5 to prepare a lye; S1-3, in a flask, N2 is introduced to form an inert atmosphere, and under nitrogen protection, the metal salt solution and the lye are simultaneously dropped into the reaction kettle at a certain liquid feeding speed, the dropping speed of the lye is controlled, the pH in the reaction kettle is kept in the range of 9.0~11.5, the temperature of the flask is kept at 30℃~90℃, and the stirring speed is 300~1200 rpm until the metal salt solution is completely dropped; S1-4, after the feeding is completed, continue to stir for 3~12h or more to allow the precursors to age; the precipitate after reaction is filtered with a circulating water pump until no impurity ions are detected in the filtrate, and then placed in a 120℃ oven for drying for 6h to obtain Ni a Mn b Me 1-a-b (OH)2 precursor.

[0010] Preferably, in step S1, the metal salt solution is any one of the water-soluble salts of Ni, Mn, and Me, including sulfate, nitrate, and chloride; In step S1-2, the concentration of NaOH solution is 0.5~8mol / L; In step S1-3, the dropping speed of the metal salt solution is 0.1~10mL / s.

[0011] Preferably, in step S1-2, the calcination temperature is 300~600℃, the calcination time is 1~12h, and the heating rate is 1~10℃ / min.

[0012] Preferably, in step S3, the sodium source is any one of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium nitrate, and sodium oxalate; The M-containing compound is any one of the M-containing oxides, carbonates, hydroxides, nitrates, and oxalates.

[0013] Preferably, in step S3, the ball milling time is 2~20h; the gradient temperature calcination is 300~600℃ for 1~12h, and then raised to 700~1000℃ for 2~24h.

[0014] The O3 and P2 layered dual-phase sodium-ion battery positive electrode material provided by the application is applied to a sodium-ion battery positive electrode material.

[0015] Therefore, the application has the following beneficial effects: 1. The O3 and P2 layered dual-phase sodium-ion battery positive electrode material is formed by doping metal ions to convert the positive electrode material into a layered component, presents an O3 and P2 mixed-phase structure, and combines the advantages of P2 and O3 single-phase materials, wherein the O3 and P2 mixed-phase structure provides high-rate performance and structural stability, the O3 phase contributes high initial capacity, and the balance between high capacity and long cycle life can be achieved, the material is applied to a sodium-ion battery positive electrode material, and the capacity, voltage and stability of the material can be comprehensively improved.

[0016] 2. The co-precipitation preparation method provided by the application does not require complex equipment or harsh conditions, has low raw material cost, simple synthesis steps, high experimental repeatability, stable performance after repeated verification, and strong industrial production feasibility.

[0017] 3. The application provides a relationship between the double-site doping ratio and the phase composition in the dual-phase sodium-ion battery positive electrode material: when a+b≤0.7 and 0<x<0.5, both are O3 and P2 layered mixed-phase structures; when a+b>0.7 and x>0.1, an impurity-free phase O3 and P2 layered mixed-phase structure is formed; when a+b>0.7 and x<0.1, an impurity phase NiO and O3 layered mixed-phase structure is formed; Therefore, through the relationship, an ideal phase structure can be accurately, simply and controllably obtained, so that the performance of the battery is comprehensively optimized.

[0018] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM images of a Na 0.9 Mg 0.1 Ni 0.5 Fe 0.25 Mn 0.25 O2 positive electrode material in Example 1 of the application, wherein the scale of (a) is 200 nm, and the scale of (b) is 500 nm; Figure 2 SEM images of Na 1.0 Ni 0.5 Fe 0.25 Mn 0.25 O2 positive electrode material in Comparative Example 1 of the application, wherein the scale of (a) is 200 nm, and the scale of (b) is 500 nm; Figure 3 Na 0.8 Li 0.2 Ni 0.5 Fe 0.25 Mn 0.25 SEM images of O2 cathode material, wherein the scale of (a) is 200 nm, and the scale of (b) is 500 nm; Figure 4 XRD patterns of cathode materials prepared in Example 1 and Comparative Example 1 of the present application, respectively; Figure 5 First charge-discharge curves of cathode materials prepared in Example 1 and Comparative Example 1 of the present application at 0.1C rate, respectively; Figure 6 Cycle performance of cathode materials prepared in Example 1 and Comparative Example 1 of the present application at 1.0C rate, respectively; Figure 7 Rate performance of cathode materials prepared in Example 1 and Comparative Example 1 of the present application, respectively. DETAILED DESCRIPTION

[0020] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0021] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those with ordinary skills in the art to which the present application pertains.

[0022] In addition, it should be understood that although the present specification is described in terms of embodiments, each embodiment does not necessarily contain only one independent technical solution, and the description of the specification is only for the sake of clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each example can be appropriately combined to form other embodiments that those skilled in the art can understand. These other embodiments are also covered by the protection scope of the present application.

[0023] Example 1 The present embodiment provides a layered sodium-ion battery cathode material, with a chemical formula of Na 0.9 Mg 0.1 Ni 0.5 Mn 0.25 Fe 0.25 O2. The cathode material is prepared by a co-precipitation method, and its preparation includes the following steps: (1) According to the chemical formula Ni 0.5 Fe 0.25 Mn 0.25The nickel sulfate, iron sulfate and manganese sulfate reagents were weighed according to the molar ratio of each element, mixed in a beaker, and deionized water was added to dissolve and prepare a metal salt solution.

[0024] (2) In another beaker, NaOH was dissolved in deionized water to prepare a NaOH solution with a concentration of 2 mol / L, and ammonia water was added to the NaOH solution to adjust the pH value to about 12.5, and 1 L of lye was prepared.

[0025] (3) In a flask, N2 was introduced to form an inert atmosphere, and under nitrogen protection, the metal salt solution and lye were simultaneously dropped into the reaction kettle at a rate of 1 drop / s using a peristaltic pump, the pH in the reaction kettle was controlled in the range of 10.48-10.52, the temperature of the flask was maintained at 60°C, and the stirring speed was 1000 rpm until the metal liquid was completely dropped.

[0026] (4) After the feeding was completed, the stirring was continued for more than 6 h to allow the precursor to age. The precipitate after the reaction of step (3) was filtered with a circulating water pump, and no impurity ions were detected in the filtrate. After being placed in a 120°C oven and dried for 6 h, the Ni 0.5 Fe 0.25 Mn 0.25 (OH)2 precursor was obtained.

[0027] (5) According to the molar ratio of doping, sodium carbonate, magnesium oxide and Ni 0.5 Fe 0.25 Mn 0.25 (OH)2 precursor were weighed and placed in a ball mill for ball milling for 4-5 hours.

[0028] (6) The salt ball-milled in step (5) was transferred to a porcelain boat and placed in an air muffle furnace at 500°C for 6 h, with a heating rate of 5°C / min; then it was heated at 900°C for 12 h, with a heating rate of 5°C / min, and then slowly cooled to room temperature to obtain a transition metal-doped Na 0.9 Mg 0.1 Ni 0.5 Mn 0.25 Fe 0.25 O2 positive electrode material, numbered a.

[0029] Comparative Example 1 This comparative example provides a sodium-ion battery positive electrode material with the chemical formula Na 1.0 Ni 0.5 Mn 0.25 Fe 0.25 O2, numbered b, and the preparation steps are the same as in Example 1, except that no M (i.e. MgO in Example 1) containing compound is added in step (5).

[0030] Example 2 The embodiment provides a sodium ion battery positive electrode material, chemical formula is Na 0.8 Li 0.2 Ni 0.5 Mn 0.25 Fe 0.25 O2, the preparation steps are same with those of example 1, and the difference is that the component and the adding amount of the M-containing compound (Li2CO3) in step (5) are different.

[0031] Example 3 The embodiment provides a sodium ion battery positive electrode material, chemical formula is Na 0.8 Mg 0.2 Ni 0.4 Mn 0.3 Fe 0.1 Cu 0.2 O2, the preparation steps are same with those of example 1, and the difference is that the component and the adding amount of the M-containing compound (Li2CO3) in step (5) are different.

[0032] The element ratio and the synthesis condition of example 1, example 2, example 3 and comparative example 1 are shown in table 1: Table 1 ;

[0033] The materials synthesized in the above examples and comparative examples are observed by SEM and XRD to observe the morphology and structure. The material after doping modification forms a mixed phase, and there are more O3 phases in the mixed phase, and the lattice parameter c of the O3 phase is greater than that of the P2 phase, which is more beneficial to the diffusion of Na + . Figure 1 、 2 、3 are SEM images of example 1, comparative example 1 and example 3 respectively, and it is found that the grain size of the example gradually decreases, about 1 µm, and the shape becomes more regular, showing a sheet-shaped stacked spherical morphology. Figure 4 The XRD images of the example and the comparative example in the middle are compared, and it is found that the (110) peak type of the modified example changes from single peak to double peak, which shows that the O3-P2 mixed phase has been produced in the material.

[0034] Performance test: The positive electrode materials prepared by example 1 and comparative example 1 are assembled into a button cell, and are weighed and mixed according to the ratio of active material: carbon black: PVDF = 8:1:1, N-methyl pyrrolidone solution (NMP) is added for stirring and homogenization, then the obtained slurry is uniformly coated on an aluminum foil, dried in a vacuum oven at 70 DEG C for 12h, and the dried film is rolled twice by using a button cell roll machine, and the rolled film is cut into 1.13 cm2 The fully dried electrode sheet was placed in a super-clean glove box in MIRAE, and a piece of metallic sodium was used as the negative electrode. A mixed solution system of NaPF6 solute and ethylene carbonate (EC) and diethyl carbonate (DEC) solvent was used as the electrolyte, and glass fiber paper was used as the separator. The battery was assembled in the order of negative electrode shell, sodium sheet, separator, electrolyte (40 L), positive electrode sheet, gasket, spring, and positive electrode shell. After assembly, the assembled battery was packaged by a battery sealing machine, and the pressure was about 600 Pa. A CR2025 type button half-cell was obtained. The assembled button half-cell was allowed to stand for 24 h, and then tested. -1 A mixed solution system of NaPF6 solute and ethylene carbonate (EC) and diethyl carbonate (DEC) solvent was used as the electrolyte, and glass fiber paper was used as the separator. The battery was assembled in the order of negative electrode shell, sodium sheet, separator, electrolyte (40 L), positive electrode sheet, gasket, spring, and positive electrode shell. After assembly, the assembled battery was packaged by a battery sealing machine, and the pressure was about 600 Pa. A CR2025 type button half-cell was obtained. The assembled button half-cell was allowed to stand for 24 h, and then tested.

[0035] The half-cell assembled from the above materials was tested on a test system, and the voltage window was 2.5-4.2 V, and 1C=150 mA / g. The results are shown in Figure 5 The results show that the first circle discharge specific capacity of Example 1 is improved compared with that of Comparative Example 1.

[0036] The half-cells of Example 1 and Comparative Example 1 were tested for rate performance at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C. The results are shown in Figure 6 The results show that the discharge specific capacity of Example 1 at different current densities is higher than that of the sample of Comparative Example 1, and the sample of Example 1 can still maintain a discharge specific capacity of 71 mAh g -1 at a high rate of 5C, indicating that the sample obtained in Example 1 has good rate performance.

[0037] Figure 7 The 100 cycle performance of Example 1 and Comparative Example 1 samples at 1C is shown in the figure. The test results show that the capacity retention rate of Example 1 sample is greater than 95% after 100 cycles, indicating that the material with a composite phase structure exhibits excellent cycle stability and rate reversibility.

[0038] The above is only a preferred embodiment of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. An O3-P2 layered dual-phase sodium ion battery cathode material, characterized in that: The chemical formula of the sodium ion battery positive electrode material is Na 1.0-x M x Ni a Mn b Me 1-a-b O2, wherein M is a metal element substituted for the sodium site, Me is a transition metal element substituted for the transition metal site, 0<x<0.5, 0.1<a<0.9, 0.1<b<0.9, 0.2<a+b<1.

2. The O3-P2 layered dual-phase sodium ion battery cathode material according to claim 1, characterized in that: M is any one or more of Li, Mg, Al, Zn, B, K, Ca, Ba, and Sr, and Me is any one or more of Co, Cu, Fe, Ti, Sc, V, Mo, Sb, Ru, W, Ta, Ce, Zr, Y, and La.

3. The O3-P2 layered dual-phase sodium ion battery cathode material according to claim 2, characterized in that: The sodium ion battery positive electrode material is a layered O3 and P2 layered two-phase composite structure.

4. The O3-P2 layered dual-phase sodium ion battery cathode material according to claim 3, characterized in that: The structure and chemical formula of the sodium ion battery positive electrode material are Na 1.0-x M x Ni a Mn b Me 1-a-b The values ​​of a, b, and x in O2 are related to: When a+b≤0.7 and 0<x<0.5, the positive electrode material of the sodium ion battery is a layered mixed phase structure of O3 and P2; When a+b>0.7 and 0.5>x>0.1, the sodium ion battery positive electrode material forms an impurity-free O3 and P2 layered mixed phase structure; When a+b>0.7 and 0<x<0.1, the structure of the sodium ion battery positive electrode material forms a layered mixed phase structure of impurity phase NiO and O3.

5. A method for preparing the O3-P2 layered dual-phase sodium ion battery positive electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1、Ni a Mn b Me 1-a-b Preparation of (OH)2 precursor Add the metal salt solution of Ni, Mn and Me and the alkali solution into the reactor at the same time, stirring continuously to make Ni a Mn b Me 1-a-b The (OH)2 precursor was aged, and the precipitate was filtered until there was no impurity ions, and then dried in an oven at 120°C for 6 hours to obtain Ni a Mn b Me 1-a-b (OH)2 precursor; S2、Na 1.0-x M x Ni a Mn b Me 1-a-b O2 production According to the chemical formula Na 1.0-x M x Ni a Mn b Me 1-a-b The molar ratio of each element in O2, weigh the sodium source, M-containing compound and Ni a Mn b Me 1-a-b (OH)2 precursor, mixed and put into ball mill to mix evenly, after obtaining the mixed material, the mixed material is transferred to a porcelain boat, placed in an air muffle furnace and calcined at a gradient temperature, and then naturally cooled to room temperature, thus obtaining Na O3 and P2 layered dual-phase sodium ion battery positive electrode material. 1.0-x M x Ni a Mn b Me 1.0-a-b O2.

6. The method for preparing an O3-P2 layered dual-phase sodium ion battery cathode material according to claim 5, characterized in that: Step S1 specifically includes the following steps: S1-1, according to the chemical formula Ni a Mn b Me 1-a-b The molar ratio of each element in (OH)2 was calculated by weighing the precursors of Ni, Mn, and Me respectively, mixing them in a beaker, and adding deionized water to dissolve them to prepare a metal salt solution; S1-2. In another beaker, dissolve 2% HCl in deionized water to prepare a NaOH solution, and add ammonia water to the NaOH solution to adjust the pH to about 12.5 to prepare an alkaline solution. S1-3. N2 is introduced into the flask to form an inert atmosphere. Under nitrogen protection, the metal salt solution and the alkali solution are simultaneously added dropwise into the reactor at a certain liquid addition rate using a peristaltic pump. The alkali solution addition rate is controlled to keep the pH in the reactor within the range of 9.0-11.

5. The flask temperature is maintained at 30°C-90°C and the stirring speed is maintained at 300-1200 rpm until all the metal salt solution is added dropwise; S1-4, after the feeding is completed, continue stirring for more than 3 to 12 hours to allow the precursor to age; filter the precipitate after the reaction with a circulating water pump until no impurity ions are detected in the filtrate, and place it in a 120°C oven to dry for 6 hours to obtain Ni a Mn b Me 1-a-b (OH)2 precursor.

7. The method for preparing an O3-P2 layered dual-phase sodium ion battery positive electrode material according to claim 6, characterized in that: In step S1, the metal salt solution is any one of sulfate, nitrate, and chloride salts containing Ni, Mn, and Me that is soluble in water; In step S1-2, the concentration of the NaOH solution is 0.5-8 mol / L; In step S1-3, the metal salt solution is added at a rate of 0.1 to 10 mL / s.

8. The method for preparing an O3-P2 layered dual-phase sodium ion battery cathode material according to claim 5, characterized in that: In step S1-2, the calcination temperature is 300-600°C, the calcination time is 1-12 h, and the heating rate is 1-10°C / min.

9. The method for preparing an O3-P2 layered dual-phase sodium ion battery cathode material according to claim 6, characterized in that: In step S3, the sodium source is any one of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium nitrate, and sodium oxalate; The M-containing compound is any one of an oxide, carbonate, hydroxide, nitrate, and oxalate containing M.

10. The method for preparing an O3-P2 layered dual-phase sodium ion battery cathode material according to claim 6, characterized in that: In step S3, the ball milling time is 2-20 hours; the gradient temperature calcination is 300-600° C. for 1-12 hours, and then the temperature is raised to 700-1000° C. for a holding time of 2-24 hours.

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