Sodium-ion battery positive electrode material, preparation method and sodium-ion battery thereof

Abstract

The invention provides a sodium ion battery positive electrode material, a preparation method and a sodium ion battery thereof. The sodium carbonate, the zinc oxide and the nickel-iron-manganese hydroxide are mixed according to the stoichiometric ratio, ground, calcined and ground, and the sodium ion battery positive electrode material is obtained. The chemical formula of the doped positive electrode material is Na [alpha] Ni [x] Fe [y] Mn [z] Zn [beta] O [gamma], alpha < = 1, 0lt; x is less than or equal to 1, 0lt; y < = 1 / 2, 0lt; z < = 1 / 2, 0lt; beta is less than or equal to 0.1, 0.2 lt; gamma < = 3, and x + y + z + beta = 1. The sodium ion battery disclosed by the invention has the advantages of high specific capacity, excellent rate capability, good stability and very high energy density and power density; the assembled sodium ion battery is good in cycling stability, green, pollution-free and low in manufacturing cost, and is a very excellent electrochemical energy storage system; and the raw materials adopted by the positive electrode material are low in price and easy to obtain, the preparation process is extremely simple, and large-scale production is easy to realize.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a cathode material for a sodium-ion battery, a preparation method thereof, a cathode for a sodium-ion battery, and a sodium-ion battery. Background Art

[0002] Since the Industrial Revolution, the large-scale use of fossil fuels has not only accelerated the pace of industrialization but also caused serious pollution and damage to the environment. Facing this challenge, the development of renewable energy sources such as wind energy and solar energy has become the key to solving the energy crisis and environmental problems. However, the generation of these energy sources is limited by natural conditions and has the characteristics of instability and intermittency. Directly integrating them into the power grid may lead to power grid stability problems. Under the goal of carbon peaking and carbon neutrality, developing an efficient energy storage system to achieve the efficient storage of clean energy is a difficult problem that needs to be solved urgently. This can not only improve the utilization efficiency of renewable energy but also contribute to building a green, low-carbon, and energy-saving sustainable development society. In the past few decades, lithium-ion batteries (LIBs) have become the preferred energy storage solution for portable electronic devices and electric vehicles due to their high energy density, long life cycle, and mature production process. However, due to the sharp increase in these demands, the scarcity of lithium resources, and the increase in mining costs, these factors have gradually become bottlenecks hindering their development. Therefore, researchers have begun to search for new energy solutions, and sodium-ion batteries (SIBs) have attracted attention due to their advantages such as low raw material costs, rich resources, high safety, and more reliable high-temperature / low-temperature performance.

[0003] The working mechanism of sodium-ion batteries is similar to that of lithium-ion batteries. The material system matching principle and key technologies can also draw on the existing experience of lithium-ion batteries. After years of development, some material systems have emerged continuously. Among them, the selection of cathode materials plays a crucial role in the overall performance of SIBs. Currently, the cathode materials for SIBs mainly include polyanion compounds, Prussian blue analogs, layered transition metal oxides, and organic compounds, etc. Among them, layered transition metal oxides have become one of the most promising commercial options attracting much attention in the industry due to their simple preparation process, easy large-scale production, significant battery capacity, and simple structure.

[0004] Layered transition metal oxide NaTMO 2 has a typical layered structure, formed by edge-sharing TMO 6 octahedral units to form NaTMO 2 sheets, and sodium ions are in NaTMO 2Coordination occurs at octahedral (O), tetrahedral (T), or prismatic (P) sites between the flakes. O3 and P2-type nickel-iron-manganese-based layered oxides have attracted great interest due to the low cost and environmentally friendly characteristics of Mn and Fe, as well as the high capacity provided by Ni. They are a promising cathode material for sodium-ion batteries, but their cycling stability still needs to be optimized and improved through strategies such as new electrolytes or by substituting different elemental sites. Compared with the P2 phase, the O3 phase has the advantage of accommodating more Na + into the layered structure, has a higher charge-discharge capacity, and the potential to achieve high-rate charge and discharge, but also faces the problem of lower stability. At the same time, P2-phase materials have been proven to have better sodium-ion conductivity than the O3 phase and generally have better cycling performance.

[0005] The literature first reported (Electrochemistry Communications, 18, 2012, 66 - 69) the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 cathode material, with a first-cycle discharge capacity reaching 123 mAh / g. Full-cell tests showed that this cathode material has good cycling stability, but the first-cycle Coulombic efficiency is low and further improvement in the preparation process is needed. NaNi 1 / 3 Fe 1 / 3 Co 1 / 3 O 2 cathode material (Electrochemistry Communications, 38, 2014, 79 - 81) exhibits a specific capacity of 150 mAh / g, but due to the cobalt-containing material, its cost is relatively high and it is not suitable for application in large-scale energy storage batteries. Chinese Patent CN104505507A discloses a Ti-doped NaNi y Ti 1-y O 2 cathode material. By doping Ti, the stability of the material is improved, but the discharge capacity it shows is only 110 mAh / g. Chinese Patent CN102522553A discloses a three-dimensional framework structure transition metal complex cathode material, which exhibits excellent cycling stability, but the discharge capacity of this cathode material at 1C rate is only 78 mAh / g. Therefore, how to improve the charge-discharge specific capacity of the material while taking into account the cycling stability of the cathode material has become one of the challenges in current sodium-ion battery research. Summary of the Invention

[0006] Based on the deficiencies in the prior art, the present invention provides a cathode material for a sodium-ion battery and a sodium-ion battery to improve the charge-discharge specific capacity of the material and take into account the cycle stability of the cathode material. The cathode material for the sodium-ion battery is a transition metal oxide sodium salt, has a layered structure, and a preparation method thereof is provided.

[0007] The present invention provides a cathode material for a sodium-ion battery, characterized in that the molecular formula of the cathode material for the sodium-ion battery is Na α Ni x Fe y Mn z Zn β O γ , where 0 < α ≤ 1, 0 < x ≤ 1, 0 < y ≤ 1 / 2, 0 < z ≤ 1 / 2, 0 < β ≤ 0.1, 0.2 < γ ≤ 3, and x + y + z + β = 1.

[0008] Preferably, x = y = z = 0.33, β = 0.01 or x = y = z = 0.327, β = 0.0196 or x = y = z = 0.324, β = 0.029.

[0009] The cathode material of the present invention with the above characteristics has a uniform particle size distribution and exhibits a spherical powder with a good morphology. Its structure is tightly formed and can provide a three-dimensional continuous and effective path for electron transfer.

[0010] When the cathode material is a powder with a uniform particle size distribution and spherical shape, during the charge-discharge cycle of the sodium-ion battery, the diffusion path of sodium ions in the material is more regular and stable, thereby improving the cycle performance. The good spherical morphology increases the specific surface area of the particles, and at the same time, the uniform particle size is conducive to constructing a stable conductive network. Sodium ions can contact and react with the material more efficiently and can complete the charge-discharge process in a shorter time compared with materials with irregular shapes, thereby improving the rate performance of the battery. In addition, when the volume change of the electrode material is caused by the charge-discharge cycle, the spherical particles can better withstand the stress brought by this volume change, reduce the pulverization and shedding of the electrode material, and thus maintain the integrity and good conductivity of the electrode, further improving the performance and service life of the battery.

[0011] The present invention also provides a preparation method for the cathode material of the sodium-ion battery, including the following steps:

[0012] Step 1: Synthesize a nickel-iron-manganese ternary precursor by a coprecipitation method;

[0013] Step 2: Mix and grind a Zn source with the nickel-iron-manganese ternary precursor and a sodium source;

[0014] Step 3: Perform a heat treatment reaction on the mixed raw materials to obtain the cathode material for the sodium-ion battery.

[0015] Preferably, step 1 further includes the following steps: Weigh nickel, iron, and manganese salts in proportion and dissolve them in water to form a mixed solution, and prepare a precipitant solution separately; Mix the two and stir, control the temperature at 60 °C. At this temperature, the reaction between metal ions and the precipitant can proceed at an appropriate rate; The pH is about 9-10 to ensure that nickel, iron, and manganese ions precipitate simultaneously and the precipitation is relatively complete; After precipitation, stir and age for 2 hours to allow the precipitate to further grow and perfect the crystal structure, filter and wash with deionized water, and finally dry at 100 °C to obtain nickel-iron-manganese ternary precursor powder. Without damaging the precursor structure, remove the moisture to make the powder in a dry state, which is convenient for subsequent processing and treatment.

[0016] Preferably, in step 2, the sodium source is sodium carbonate; the zinc source is zinc oxide; the nickel-iron-manganese ternary precursor is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH) 2 precursor.

[0017] Preferably, the molar doping ratios of Zn relative to the nickel-iron-manganese ternary precursor are 1%, 2%, and 3% respectively.

[0018] Introducing an appropriate amount of Zn element promotes the reversibility of the structure and has a positive impact on the electrode-electrolyte interface, avoiding adverse side reactions and providing additional Na + deintercalation / insertion sites. In addition, introducing an appropriate amount of Zn element improves the capacity retention rate of the cathode material. At the same time, with the increase of the Zn doping amount, the polarization is alleviated and good reversible electrochemical characteristics are obtained. However, when the content of Zn that cannot provide capacity 2+ further increases to 4%, the excessive Zn 2+ will occupy a large number of sites in the TM-O layer, which may damage the original lattice structure and cause additional irreversible structural changes during charge and discharge, reducing the discharge specific capacity of NFM. Therefore, in the present invention, the doping molar ratios of Zn relative to the nickel-iron-manganese ternary precursor are set to 1%, 2%, and 3% respectively.

[0019] Preferably, the grinding method is to grind evenly into powder in an agate mortar; the grinding time is controlled within 15-30 min. Controlling the grinding time within 15-30 min can grind the material to a suitable particle size, and at the same time, it will not introduce too many impurities or damage the material properties due to too long grinding time.

[0020] Preferably, step 3 further includes the following steps: calcine the mixture in a muffle furnace at 500 °C for 4 hours. At this temperature, some structural and chemical changes may occur to the material, such as removing moisture and some organic impurities in the material, or promoting the preliminary decomposition and crystallization of the precursor material, etc. The 4-hour calcination time is to ensure that these processes proceed sufficiently to make the material reach a relatively stable intermediate state. Then calcine at 850 °C for 14 hours. At this temperature, more significant structural transformations will occur to the material to form the desired crystal structure and phase state. The longer 14-hour calcination time is to ensure the growth and perfection of the crystal structure and the sufficient reaction between components to form stable compounds, thereby obtaining the final cathode material sample. After natural cooling to 200 °C, take it out immediately to avoid the degradation of performance or structural changes of the material due to staying at high temperature for a long time. After forming powder, place it in a glove box filled with argon to prevent the material from reacting with oxygen, moisture, etc. in the air.

[0021] The present invention also provides a cathode, which includes a cathode current collector and the sodium-ion battery cathode material provided above disposed on one or both surfaces of the cathode current collector.

[0022] The present invention also provides a sodium-ion battery, including the cathode described above.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] 1) Compared with other existing cathode materials, the cathode material in the present invention realizes both good charge-discharge performance and good cycle stability by introducing Zn element into the transition metal layered oxide. As Figure 2 shown, the cathode material obtained in Comparative Example 1 only retains a specific capacity of 51 mAh / g after 300 cycles, and the capacity retention rate is 31.4%. However, under the same cycling conditions, the cathode material obtained in Example 3 maintains a reversible capacity of 84 mAh / g, and the capacity retention rate is as high as 50%. As Figure 3 shown, when the rate ranges from 0.1C to 5C, the gap between the discharge capacities of the cathode material obtained in Comparative Example 1 and the cathode material obtained in Example 3 becomes larger. At a high rate of 5C, the capacity of Comparative Example 1 is only

[0025] 109.6 mAh / g, while the cathode material of Example 3 maintains a high capacity of 114.4 mAh / g. Compared with 50 times the initial current density, the capacity retention rate of Comparative Example 1 is 64.2%, while that of Example 3 is increased to 66.1%. The cathode material in Example 3 shows higher capacity retention rate, reversibility and lower voltage polarization rate than Comparative Example 1 at various rates.

[0026] 2) The core of the layered-structured cathode material of the present invention is Naα Ni x Fe y Mn z Zn β O γ Among them, the Ni element can improve the capacity of the material, the Mn element can reduce the material cost and improve the safety and stability of the material, the Fe element can improve the high-temperature resistance and cycle life of the material, and the Zn doping element can also improve the structural stability of the material, so as to inhibit the phase change in the high sodium extraction state.

[0027] 3) The synthesis process of the present invention is simple, the raw materials are cheap and easy to obtain, the process is simple, and it is easy to control, which can significantly reduce the production and preparation cost. Description of the Drawings

[0028] Figure 1 It is the SEM diagram of the positive electrode material of the sodium-ion battery obtained in Example 1 of the present invention;

[0029] Figure 2 It is the long-term cycle stability test diagram of the positive electrode materials obtained in Examples 1 to 3 and Comparative Example 1 of the present invention at 2.0 - 4.2V and 1C;

[0030] Figure 3 It is the rate performance of the positive electrode materials obtained in Comparative Example 1 and Example 3 of the present invention in the range of 0.1 - 10C. Detailed Embodiments

[0031] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and those skilled in the art can think of other obvious variations.

[0032] Example 1:

[0033] A preparation method of a positive electrode material for a sodium-ion battery, comprising the following steps:

[0034] 1) Synthesize a nickel-iron-manganese ternary precursor by the co-precipitation method

[0035] Weigh nickel, iron, and manganese salts in proportion and dissolve them in water to form a mixed solution, and prepare a precipitant solution separately; mix the two and stir, control the temperature at 60°C, and the pH is about 9 - 10 to ensure that the nucleation and growth rates of the precipitate can reach a relatively balanced state to precipitate metal ions; after precipitation, stir and age for 2 hours, filter and wash with deionized water to remove impurity ions; finally, dry at 100°C to obtain the nickel-iron-manganese ternary precursor powder.

[0036] 2) Design a 1% molar ratio of Zn doping. Mix the Zn source with the nickel-iron-manganese ternary precursor and the sodium source, and grind them. Take 0.01105 mol of sodium carbonate and 0.00022 mol of zinc oxide as the Na and Zn sources respectively, and take 0.0221 mol of Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH) 2 precursor. Then, uniformly grind the nickel-iron-manganese ternary precursor, sodium carbonate, and zinc oxide in an agate mortar into a black powder, thereby reducing the particle size of the reactants and increasing the contact area between the reactants. The increase in the contact area is beneficial to improving the reaction rate; the fine and uniform powder obtained through grinding can better fill the voids during the subsequent sintering process, improving the density and uniformity of the green body; the grinding time is controlled within 15 - 30 min. If the grinding time is too short, it may lead to insufficient mixing of each component, and in the subsequent reaction or processing, the product quality will be affected due to uneven composition distribution. At the same time, limiting the grinding time can avoid over-grinding, and over-grinding may introduce impurities. Especially when the mortar itself has a certain degree of wear, the fine particles of the mortar material may be mixed into the reactants.

[0037] 3) Conduct a heat treatment reaction on the mixed raw materials to obtain the cathode material for sodium-ion batteries.

[0038] Calcine the mixture in a muffle furnace at 500 °C for 4 hours. During this process, the atoms or ions in the precursor obtain sufficient energy for rearrangement, making the crystal structure more ordered and stable. It can also remove the impurities and volatile components in the precursor. At the same time, after calcination, a better balance can be achieved between the chemical activity and stability of the material; then calcine at 850 °C for 14 hours. During the 14-hour high-temperature calcination at 850 °C, the thermal motion of atoms intensifies, further improving the crystal structure of the material. A more perfect crystal structure can effectively shorten the diffusion path of ions and provide more active sites. At the same time, it can further remove the small amount of residual volatile impurities and some difficult-to-decompose impurities in the material, and the long-time high-temperature calcination makes the physical and chemical properties of the material more stable, ensuring that the battery can have relatively stable performance under different usage conditions. Obtain the cathode material sample; after naturally cooling to 200 °C, immediately take it out, which can reduce the contact time between the material and the furnace atmosphere, prevent the surface of the material from being oxidized or forming other impurity phases, thereby maintaining the chemical composition and performance stability of the material and ensuring that it can exhibit good electrochemical performance when used as the cathode material of the battery later. After forming a powder, place it in a glove box filled with argon. Obtain the final sample.

[0039] Comparative Example 1:

[0040] The difference between Comparative Example 1 and Example 1 is only that Zn doping was not designed in Step 2, and the metal salts in Step 2 were 0.01658 mol Na 2 CO 3 , 0.03315 mol ZnO. The remaining steps remained unchanged. The final sample was obtained.

[0041] Example 2:

[0042] Compared with Example 1, the designed molar ratio of Zn doping in Step 2 was 2%, and the metal salts in Step 2 were 0.01105 mol Na 2 CO 3 , 0.00044 mol ZnO. The remaining steps remained unchanged. The final sample was obtained.

[0043] Example 3:

[0044] Compared with Example 1, the designed molar ratio of Zn doping in Step 2 was 3%, and the metal salts in Step 2 were 0.01105 mol Na 2 CO 3 , 0.00066 mol ZnO. The remaining steps remained unchanged. The final sample was obtained.

[0045] The following conclusions were obtained through analysis: Refer to Figure 2 As shown, the specific capacity of the positive electrode material obtained in Comparative Example 1 was only 51 mAh / g after 300 cycles, and the capacity retention rate was 31.4%. However, under the same cycling conditions, the positive electrode material obtained in Example 3 maintained a reversible capacity of 84 mAh / g, and the capacity retention rate was as high as 50%.

[0046] Refer to Figure 3 As shown, from a rate of 0.1C to 5C, the gap between the discharge capacities of the positive electrode materials obtained in Comparative Example 1 and Example 3 became larger. At a high rate of 5C, the capacity of Comparative Example 1 was only 109.6 mAh / g, while the positive electrode material of Example 3 maintained a high capacity of 114.4 mAh / g. Relative to 50 times the initial current density, the capacity retention rate of Comparative Example 1 was 64.2%. While that of Example 3 increased to 66.1%. The positive electrode material in Example 3 showed a higher capacity retention rate, reversibility, and lower voltage polarization rate than Comparative Example 1 at various rates.

[0047] Example 4

[0048] A positive electrode, which includes a positive electrode current collector and the above-mentioned sodium-ion battery positive electrode material provided on one or both surfaces of the positive electrode current collector or obtained by using the preparation method of the above-mentioned sodium-ion battery positive electrode material.

[0049] Example 5

[0050] A sodium-ion battery, characterized in that it includes the above-mentioned positive electrode.

[0051] The present invention aims at the problems in the prior art, provides a cathode material for a sodium-ion battery and a preparation method thereof, and assembles a sodium-ion battery using the same. Compared with the reported layered metal oxide cathode materials: by doping Zn elements with different molar ratios in the present invention, the reversibility of the material structure is promoted, good rate performance and cycling performance are obtained, and a cathode material with high charge / discharge specific capacity can be obtained; by comparing and exploring the effects of different molar ratios of Zn doping, it is found that in Example 3, when the molar ratio of Zn doping is 3%, the prepared cathode material has the best electrochemical performance; the solid-phase synthesis method is used to prepare the cathode material for the sodium-ion battery to obtain a precursor powder with a uniform three-dimensional spherical morphology, and at the same time, the process is simple, the cost is low, and the repeatability is good, which is conducive to realizing the large-scale production of the composite cathode material for the sodium-ion battery.

[0052] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the principle and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A sodium ion battery positive electrode material, characterized in that: The molecular formula of the sodium ion battery positive electrode material is Na α Ni x Fe y Mn z Zn β O γ , where 0<α≤1, 0 <x≤1,0<y≤1 / 2,0<z≤1 / 2,0<β≤0.1,0.2<γ≤3,x+y+z+β=1。 2. The sodium ion battery positive electrode material according to claim 1, characterized in that: x=y=z=0.33, β=0.001 or x=y=z=0.327, β=0.0196 or x=y=z=0.324, β=0.

029.

3. A method for preparing the positive electrode material for a sodium ion battery according to claim 1 or 2, characterized in that: The following steps are involved: Step 1: synthesizing nickel-iron-manganese ternary precursor by coprecipitation method; Step 2: Mix and grind the Zn source with the nickel-iron-manganese ternary precursor and the sodium source; Step 3: subjecting the mixed raw materials to a heat treatment reaction to obtain a positive electrode material for a sodium ion battery.

4. The method for preparing a sodium ion battery positive electrode material according to claim 3, characterized in that: The step 1 further comprises the following steps: weighing nickel, iron and manganese salts in proportion and dissolving them in water to prepare a mixed solution, and separately preparing a precipitant solution; mixing and stirring the two, controlling the temperature at 60° C. and the pH at 9 to 10 to precipitate the metal ions; stirring and aging for 2 hours after precipitation, filtering and washing with deionized water, and finally drying at 100° C. to obtain a nickel-iron-manganese ternary precursor powder.

5. The method for preparing a sodium ion battery positive electrode material according to claim 3, characterized in that: In step 2, the sodium source is sodium carbonate; the Zn source is zinc oxide; the nickel-iron-manganese ternary precursor is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor.

6. The method for preparing a sodium ion battery positive electrode material according to claim 3, characterized in that: The molar ratio of Zn doped with respect to the nickel-iron-manganese ternary precursor is selected as: 1%, 2%, and 3%.

7. The method for preparing a sodium ion battery positive electrode material according to claim 3, characterized in that: The grinding method is to evenly grind into powder in an agate mortar; the grinding time is controlled within 15 to 30 minutes.

8. The method for preparing a sodium ion battery positive electrode material according to claim 3, characterized in that: The step 3 further includes the following steps: calcining the mixed raw materials in a muffle furnace at 500°C for 4 hours, and then calcining at 850°C for 14 hours to obtain a positive electrode material sample; after naturally cooling to 200°C, taking it out immediately, grinding it into powder and placing it in a glove box filled with argon.

9. A positive electrode, comprising a positive electrode collector and a sodium ion battery positive electrode material according to any one of claims 1 to 2 arranged on one side or both sides of the positive electrode collector, or obtained by the preparation method of the sodium ion battery positive electrode material according to any one of claims 3 to 8.

10. A sodium ion battery, characterized in that: Comprising the positive electrode as claimed in claim 9.

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