High-capacity sodium-ion battery positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a high-capacity sodium ion battery positive electrode material and a preparation method and application thereof, and relates to the technical field of sodium ion batteries, the molecular formula of the material is NaxNiyFezMmMnnO2, x is greater than or equal to 0.8, y is greater than or equal to 0.1 and less than or equal to 0.2, y + z = 0.6, m is less than or equal to 0.1, m + n = 0.4, and M represents a divalent transition metal element. According to the invention, a bivalent transition metal element is used for replacing a high-valence manganese element, so that the volume-phase sodium content can be increased, the Mn < 3 + > content can be reduced, the ginger Taylor effect can be reduced, and the cycle performance can be improved; the composition of transition metal elements in the layered oxide is favorably adjusted, the oxidation reduction of nickel in the charge-discharge process is deeply activated, and the reversible capacity is improved; according to the invention, low-nickel, high-iron and high-manganese are used as main elements, so that the material cost is reduced. In the preparation process, a process of firstly carrying out wet vacuum mixing and then carrying out tabletting and sintering is adopted, so that the crystallinity and purity of the material are improved, and large-size single crystals are formed.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion batteries, in particular to a high-capacity sodium ion battery positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium battery technology has been continuously breaking through, and the proportion of lithium batteries in global electrochemical energy storage is as high as 86%. However, lithium is the core raw material of lithium batteries, but the lithium resource reserves are limited. In the face of the dual challenges of lithium resource shortage and supply chain safety, the development of sodium batteries with abundant raw material reserves has become an important strategic choice. The development of sodium batteries has become an important technical reserve to cope with the shortage of lithium resources, and is also a key solution to promote the cost reduction and efficiency improvement of the energy storage market.

[0003] As a key component of sodium ion batteries, the positive electrode material plays a crucial role in determining the energy density and cost competitiveness of the battery. Among various candidate materials, layered transition metal oxides are of great interest due to their high theoretical capacity and mature manufacturing process. In particular, the O3 phase structure is extremely attractive due to its high sodium content (x > 0.7) and good reversibility, suitable for achieving high energy density. However, O3 phase layered transition metal oxides usually have insufficient content in the safe voltage window (2.0-4.0V vs. Na + / Na), which greatly hinders their commercial application.

[0004] Precise adjustment of the composition of the transition metal layer is particularly important, as it can activate additional reversible redox reactions, thereby increasing the specific capacity. Layered oxides rich in nickel exhibit high capacity due to their high active element content, but are limited by their high cost, while layered oxides rich in manganese are more economical, but their structure is degraded due to the Jahn-Teller effect of Mn 3+ , and their rate performance is also poor. In contrast, low-nickel O3-type layered oxides strike a good balance between high sodium content and potential cost advantage, and are therefore expected to become candidate materials for the next generation of positive electrodes. At present, there is still little known about the phase transition mechanism and sodium storage dynamics of low-nickel layered oxides, and there is no report on how to regulate the transition metal composition to fully activate the oxidation of Ni to improve the capacity.

[0005] A low-nickel high-capacity sodium ion battery positive electrode material, a preparation method and a sodium ion battery are disclosed in Chinese Patent CN119092657A. The positive electrode material of the invention is in the form of irregular blocks and has a layered structure. The material can be prepared by sintering a co-precipitated precursor or a high-temperature solid-phase method, which shows higher discharge capacity than the NFM111 system material, average discharge voltage and lower material cost, and maintains good rate and cycle performance. However, the invention introduces Zn doping to guide high-potential Ni 3+ / Ni4+ or O 2 The redox reaction of the material is advanced, leading to irreversible phase transition of the material at high voltage, and a small amount of Zn migrates to the Na site during the cycle process, causing cycle performance degradation, and the zinc element does not have chemical activity, has a greater obstacle to electron transmission, and has a greater negative impact on the rate performance.

[0006] Chinese patent CN115911331A discloses a preparation method of a low-nickel copper-manganese-based sodium ion battery positive electrode material. The invention mixes a nickel source, a manganese source and a copper source by wet grinding, adds a carbonate, and performs a co-precipitation reaction to obtain a carbonate precursor. The precursor is mixed with carbon nanotubes and then a sodium source is added. The mixture is calcined to obtain a positive electrode material. The invention significantly hinders the promotion of grain and grain boundary due to the doping of carbon nanotubes during sintering, maintains the stability of the crystal phase structure, solves the problem of crystal phase transformation, and forms a network structure of electron conduction structure after sintering. The carbon nanotubes reduce the contact between the positive electrode material and the electrolyte, inhibit the occurrence of side reactions, and maintain structural stability under high voltage conditions. However, the specific surface area of carbon nanotubes is too large, which makes it difficult to mix uniformly, and the large specific surface area increases the side reactions during charging and discharging, increases the risk of gas production, and reduces the long cycle performance.

[0007] Chinese patent CN117936734A discloses a low-nickel high-capacity sodium ion battery positive electrode material, a preparation method and application thereof. The invention controls the nickel content component to be 0.08-0.12, which is lower than NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 O2 can significantly reduce production costs, and by optimizing the composition and coating a point array coating layer with a special morphology on the surface of the layered oxide, high capacity, high median voltage and high compaction density can be achieved while reducing costs. However, the iron content of this system is high, and local enrichment of iron elements occurs in the prepared layered material, which is prone to Fe 4+ migration at high voltage, causing irreversible phase transition and structural damage, and reducing long cycle performance.

[0008] In view of this, the present invention is proposed. SUMMARY

[0009] The purpose of the present invention is to provide a high-capacity sodium ion battery positive electrode material and a preparation method and application thereof.

[0010] The present invention is implemented as follows:

[0011] In a first aspect, the present invention provides a high-capacity sodium ion battery positive electrode material, the molecular formula of the high-capacity sodium ion battery positive electrode material being Na x Ni y Fe z M mMn n O2, x≥0.8, 0.1≤y≤0.2, y+z=0.6, m≤0.1 and m+n=0.4, M represents a transition divalent metal element.

[0012] In an alternative embodiment, x>0.96; m:n=1:3.5-5.

[0013] In an alternative embodiment, the ions corresponding to M are selected from at least one of Mg 2+ , Cu 2+ , Zn 2+ , Co 2+ , Ca 2+ , Ba 2+ and Sr 2+ .

[0014] In an alternative embodiment, the ions corresponding to M are selected from Mg 2+ and Cu 2+ ; the doping amount ratio of Mg 2+ and Cu 2+ is 1:1-2.

[0015] In an alternative embodiment, the high-capacity sodium-ion battery anode material has at least one of the parameters characterized by (1)-(5):

[0016] Characteristics (1): the average particle size of the high-capacity sodium-ion battery anode material is 5-20 μm;

[0017] Characteristics (2): the ratio of Mn 3+ / Mn 4+ in the high-capacity sodium-ion battery anode material is 1:3-4;

[0018] Characteristics (3): the high-capacity sodium-ion battery anode material has a layered structure, and the compaction density is ≥3.0 g cm -3 ;

[0019] Characteristics (4): the average sodium-ion diffusion coefficient of the high-capacity sodium-ion battery anode material during the charging and discharging process is greater than 1×10 -10 cm 2 s -1 ;

[0020] Characteristics (5): the cycle life of the high-capacity sodium-ion battery anode material in a full battery is >1000 cycles.

[0021] In a second aspect, the present application provides a preparation method of the high-capacity sodium-ion battery anode material as described in the foregoing embodiments, which comprises adding a sodium source, a nickel source, an iron source, a manganese source and a M source in stoichiometric ratio into a solvent for stirring, followed by ball milling and high-temperature sintering.

[0022] In optional embodiments, the method for preparing the high-capacity sodium-ion battery cathode material comprises at least one of features (6)-(18):

[0023] Feature (6): the solvent comprises at least one of anhydrous ethanol and acetone;

[0024] Feature (7): the rotation speed of the ball milling is 300-500 rpm, and the mixing time is 6-10 h;

[0025] Feature (8): the ball milling is performed under vacuum conditions;

[0026] Feature (9): the high-temperature sintering comprises first heating from room temperature to 1000-1050 °C, holding for 10-20 h, then cooling to 180-220 °C, and subsequently cooling to room temperature in a box filled with inert gas;

[0027] Feature (10): the heating rate during the high-temperature sintering is 1-3 °C / min, and the cooling rate is 1-3 °C / min;

[0028] Feature (11): after the ball milling and before the high-temperature sintering, further comprising tabletting the mixture under a pressure of 8-12 MPa for 2-5 min;

[0029] Feature (12): after the high-temperature sintering, further comprising grinding the sintered material and passing through a 300-400 mesh sieve;

[0030] Feature (13): the sodium source is at least one of sodium carbonate, sodium acetate, sodium nitrate, sodium fluoride, and sodium chloride;

[0031] Feature (14): the nickel source is at least one of nickel oxide, nickel sesquioxide, nickel carbonate, nickel acetate, nickel chloride, nickel sulfate, and nickel nitrate;

[0032] Feature (15): the iron source is at least one of ferrous oxide, iron oxide, ferrous carbonate, iron acetate, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferrous nitrate, and ferric nitrate;

[0033] Feature (16): the manganese source is at least one of manganese monoxide, manganese sesquioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate, and manganese nitrate;

[0034] Feature (17): the M source comprises Mg 2+ , Cu 2+ , Zn 2+ , Co 2+ , Ca 2+ , Ba 2+and Sr 2+ at least one corresponding metal oxide of the at least one metal;

[0035] Feature (18): the sodium source is anhydrous sodium carbonate, the nickel source is nickel oxide, the iron source is diiron trioxide, the manganese source is dimanganese trioxide, and the M source is at least one of magnesium oxide and copper oxide.

[0036] In a third aspect, the present application provides a high-capacity sodium-ion battery cathode material or a high-capacity sodium-ion battery cathode material prepared by the preparation method of the high-capacity sodium-ion battery cathode material according to any one of the preceding embodiments for use in the preparation of a sodium-ion battery cathode material.

[0037] In a fourth aspect, the present application provides a sodium-ion battery comprising a cathode sheet, wherein the cathode sheet comprises the high-capacity sodium-ion battery cathode material according to any one of the preceding embodiments or the high-capacity sodium-ion battery cathode material prepared by the preparation method of the high-capacity sodium-ion battery cathode material according to any one of the preceding embodiments as a cathode material.

[0038] In a fifth aspect, the present application provides an electric device comprising the sodium-ion battery according to the preceding embodiments.

[0039] The present application has the following beneficial effects:

[0040] The high-capacity sodium-ion battery cathode material provided by the present application is beneficial to increasing the content of sodium in the bulk phase, reducing the content of Mn 3+ , reducing the Jahn-Teller effect, and improving the cycle performance by replacing the high-valence manganese element with a divalent transition metal element. The specific metal introduced into the transition metal layer is beneficial to adjusting the composition of the transition metal elements in the layered oxide, deeply activating the oxidation and reduction of nickel in the charging and discharging process, and improving the reversible capacity. In the present application, low-nickel high-iron high-manganese is used as the main element, which is beneficial to reducing the cost of the material. In the preparation process of the present application, a process of first wet vacuum mixing and then tabletting and sintering is adopted to improve the crystallinity and purity of the material and form a large-size single crystal. In the sintering process, a controllable slow cooling rate is adopted, which is beneficial to forming a high-purity cathode material and reducing the surface residual alkali. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0042] Figure 1SEM image of high-capacity sodium-ion battery cathode material provided for Example 1;

[0043] Figure 2 SEM image of high-capacity sodium-ion battery cathode material provided for Example 2;

[0044] Figure 3 SEM image of high-capacity sodium-ion battery cathode material provided for Example 3;

[0045] Figure 4 SEM image of sodium-ion battery cathode material provided for Comparative Example 1;

[0046] Figure 5 SEM image of sodium-ion battery cathode material provided for Example 5;

[0047] Figure 6 SEM image of sodium-ion battery cathode material provided for Example 7. DETAILED DESCRIPTION

[0048] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. In the embodiments, the specific conditions not noted are implemented according to conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments not noted by the manufacturers are all conventional products that can be purchased in the market.

[0049] The present application provides a high-capacity sodium-ion battery cathode material, and the molecular formula of the high-capacity sodium-ion battery cathode material is Na x Ni y Fe z M m Mn n O2, x≥0.8, 0.1≤y≤0.2, y+z=0.6, m≤0.1 and m+n=0.4, and M represents a transition divalent metal element.

[0050] In the formula, the ion corresponding to M is selected from at least one of Mg 2+ , Cu 2+ , Zn 2+ , Co 2+ , Ca 2+ , Ba 2+ and Sr 2+ ; preferably, the ion corresponding to M is selected from at least one of Mg 2+ and Cu 2+ .

[0051] In some embodiments, x > 0.96; m:n = 1:3.5-5. By controlling the ratio of m and n in the present application, the doping amount of the transition divalent metal element can be limited, which is conducive to better substitution of the divalent element to adjust the electronic structure and effectively improve the cycle performance and rate performance of the material. Among them, the transition divalent metal element M replaces Mn ions, and the local charge distribution in the crystal structure is adjusted to increase the bulk sodium content. The ratio of Mn 3+ / Mn 3+ is 1:3-4.

[0052] When multiple ions corresponding to M are selected, the sum of the doping amounts of the multiple M ions is m, and further, the ions corresponding to M are selected from Mg 2+ and Cu 2+ ; the doping amount ratio of Mg 2+ and Cu 2+ is 1:1-2. By further limiting the doping amount of Mg 2+ and Cu 2+ in the present application, the aggregation of Mn 3+ and the occurrence of Jahn-Teller effect can be inhibited, and the material structure stability is improved.

[0053] In addition, the average particle size of the high-capacity sodium ion battery positive electrode material is 5-20 μm; and the high-capacity sodium ion battery positive electrode material has a layered structure. The high-capacity sodium ion battery positive electrode material has a compaction density ≥ 3.0 gcm -3 .

[0054] Further, the present application provides a preparation method of the above-mentioned high-capacity sodium ion battery positive electrode material, which comprises adding a sodium source, a nickel source, an iron source, a manganese source and an M source into a solvent for stirring, followed by ball milling and high-temperature sintering.

[0055] Specifically, the method comprises the following steps:

[0056] S1, mixing.

[0057] The sodium source, the nickel source, the iron source, the manganese source and the M source are added into a solvent for stirring, followed by vacuum ball milling.

[0058] Among them, the sodium source includes but is not limited to at least one of sodium carbonate, sodium acetate, sodium nitrate, sodium fluoride and sodium chloride; the nickel source includes but is not limited to at least one of nickel oxide, nickel sesquioxide, nickel carbonate, nickel acetate, nickel chloride, nickel sulfate and nickel nitrate; the iron source includes but is not limited to at least one of ferrous oxide, iron oxide, ferrous carbonate, iron acetate, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferrous nitrate and ferric nitrate; the manganese source includes but is not limited to at least one of manganese monoxide, manganese sesquioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate and manganese nitrate. The M source includes Mg2+ Cu 2+ Zn 2+ Co 2+ Ca 2+ Ba 2+ Sr 2+ at least one corresponding metal oxide of the at least one of Na, Ni, Fe, Mn, Co, Ca, Ba, and Sr;

[0059] Preferably, the sodium source is anhydrous sodium carbonate, the nickel source is nickel oxide, the iron source is diiron trioxide, the manganese source is dimanganese trioxide, the M source is at least one of magnesium oxide and copper oxide.

[0060] In the present application, solvent wet vacuum mixing is adopted, and the uniformity of the material is better. The solvent includes at least one of anhydrous ethanol and acetone; the rotation speed of the vacuum ball mill is 300-500 rpm, and the mixing time is 6-10 h.

[0061] S2, tabletting.

[0062] The mixture obtained in step S1 is subjected to tabletting under a pressure of 8-12 MPa for 2-5 min.

[0063] In the present application, tabletting is to compress loose powder raw materials into dense tablet-like structures by mechanical pressure, so as to reduce the voids between particles and make the particles closely contact. This helps to promote solid-phase diffusion in the subsequent high-temperature sintering process, increase the contact area between particles, accelerate the diffusion of atoms or ions, and shorten the sintering time. At the same time, the porosity is reduced, the internal defects of the material after sintering are reduced, and the overall density is improved.

[0064] After mixing, the raw materials may have the problem of local uneven composition. Tabletting makes different components uniformly distributed by external force, avoiding uneven performance (such as conductivity, capacity difference) caused by composition segregation during sintering. The green body after tabletting has a certain mechanical strength, which is convenient for handling and subsequent processing, and can maintain the preset geometric shape (such as tablet, block) during sintering, preventing deformation or cracking at high temperature. For multi-component positive electrode materials, tabletting can force different raw materials (such as lithium source, transition metal oxide) to closely contact, ensure that the high-temperature solid-phase reaction proceeds fully, and avoid the influence of unreacted residues on the electrochemical performance.

[0065] It should be understood that in some other embodiments, the step of tabletting can also be omitted, and the material after vacuum ball milling can be directly subjected to high-temperature sintering.

[0066] S3, high-temperature sintering.

[0067] The high-temperature sintering can make the material form a positive electrode material with stable crystal structure, high purity and good electrochemical performance, wherein the high-temperature sintering comprises the following steps: firstly, heating from room temperature to 1000-1050 DEG C, and keeping the temperature for 10-20 hours; secondly, cooling to 180-220 DEG C; thirdly, cooling to room temperature in a box filled with inert gas; preferably, the heating rate in the high-temperature sintering process is 1-3 DEG C / min, and the cooling rate is 1-3 DEG C / min.

[0068] In the present application, by controlling the temperature, the heating rate and the cooling rate of the high-temperature sintering, a positive electrode material with high purity can be formed, and gas production can be reduced. In the present application, slow heating can make the reaction more uniform, avoid local overheating and cause composition segregation. It is beneficial to the gradual decomposition of organic matter or residual solvent, and reduces pores and cracks. In the present application, slow cooling can reduce thermal stress, avoid particle cracking or lattice distortion, and also promote the ordered arrangement of atoms and improve the crystallinity.

[0069] In the present application, by using the process of wet vacuum mixing and then tablet sintering, the crystallinity and purity of the material can be improved, and a large-size single crystal can be formed.

[0070] S4, grinding.

[0071] After the high-temperature sintering of step S3, the sintered material is further ground and sieved through a 300-400 mesh sieve.

[0072] In the present application, the sintered material is usually clumped or forms larger particles, and grinding can break it to the target particle size (such as microns or sub-microns), increase the specific surface area, and improve the lithium ion diffusion rate. By grinding, the particle size distribution is more uniform, avoiding large particles leading to uneven electrode coating or small particles causing agglomeration, thereby optimizing the compaction density and cycle stability of the electrode. Further, grinding can remove the sintered hard shell on the surface of the sintered material, expose fresh surface, increase the contact area and reaction activity of the material and electrolyte. Grinding can also slightly modify the surface morphology of the particles, reduce sharp edges and corners, and reduce the risk of puncturing the separator during electrode preparation. Small and uniform particles are easier to disperse in the electrode slurry, reduce slurry settlement or clumping, improve coating uniformity, and increase compaction density, which is beneficial to promoting the uniform mixing of the material and the conductive agent (such as carbon black) and the binder (such as PVDF), forming a continuous conductive network, reducing the internal resistance of the electrode, and also playing a role in regulating the electrochemical performance. The particle size of the high-capacity sodium ion battery positive electrode material in the present application after grinding can reach 5-20 μm.

[0073] In addition, the present application provides the use of the above-mentioned high-capacity sodium ion battery positive electrode material in the preparation of a sodium ion battery positive electrode material.

[0074] For example, the present application provides a sodium-ion battery, which comprises a positive electrode sheet, and the positive electrode sheet uses the above high-capacity sodium-ion battery positive electrode material as a positive electrode material. The present application also provides an electric device comprising the sodium-ion battery of the foregoing embodiments.

[0075] The features and properties of the present application are further described in detail below in conjunction with the embodiments.

[0076] Embodiment 1

[0077] The present embodiment provides a preparation method of a sodium-ion battery layered oxide positive electrode material, and the chemical formula of the sodium-ion battery layered oxide positive electrode material is Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Mg 0.08 O2, and the steps are as follows:

[0078] Na2CO3, NiO, Mn2O3, Fe2O3, and MgO are mixed in a marver mortar according to the stoichiometric ratio, transferred into a ball mill, vacuum packaged after adding an appropriate amount of anhydrous ethanol, and mixed at 400 rpm for 8 h; the uniformly ground raw materials are poured into the mold of a tablet press, and the mold is placed in the tablet press, with a pressure of 10 MPa for 2 min to press into a 20 mm round tablet; the pressed raw material round tablet is placed in a corundum canister and placed in a muffle furnace, with a control heating rate of 3 ℃ / min to heat to 1020 ℃, and after holding for 15 h, the temperature is lowered to 200 ℃ at a rate of 2 ℃ / min; after heat treatment, the material is immediately placed in an Ar-filled glove box to prevent contact with any moisture until it is cooled to room temperature; then the material is transferred to a low-humidity drying room (dew point of -70 ℃, relative humidity <1%, same below), and the material is ground into powder using a mortar, and sieved using a 325 mesh sieve, thereby obtaining Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Mg 0.08 O2 positive electrode material.

[0079] Please refer to Figure 1 , from Figure 1 It can be seen that the obtained sample is a large single crystal in the form of a plate with a size of 5 15 μm.

[0080] Embodiment 2

[0081] The present embodiment provides a preparation method of a sodium-ion battery layered oxide positive electrode material, and the chemical formula of the sodium-ion battery layered oxide positive electrode material is Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Cu 0.08O2, the steps are as follows:

[0082] Na2CO3, NiO, Mn2O3, Fe2O3 and CuO were mixed in a maroon mortar according to the stoichiometric ratio, transferred into a ball mill, vacuum packaged after adding an appropriate amount of anhydrous ethanol, mixed at 400 rpm for 8 h; the uniformly ground raw materials were poured into the mold of a tablet press, and the mold was placed in the tablet press, with a pressure of 10 MPa for 2 min, to press into 20 mm round tablets; the pressed raw material round tablets were placed in a corundum canister and placed in a muffle furnace, with a control heating rate of 3 ℃ / min to 1020 ℃, and then held for 15 h, and then cooled at a rate of 2 ℃ / min to 200 ℃; after heat treatment, the material was immediately placed in an Ar-filled glove box to prevent contact with any moisture until it was cooled to room temperature; then the material was transferred to a low-humidity drying room, and the material was crushed into powder using a mortar, sieved using a 325 mesh screen, to obtain Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Cu 0.08 O2 cathode material.

[0083] See Figure 2 , from Figure 2 It can be seen that the obtained sample is also a large single crystal in the form of a plate, with a size of 515 μm.

[0084] Example 3

[0085] The embodiment provides a preparation method of a sodium ion battery layered oxide cathode material, and the chemical formula of the sodium ion battery layered oxide cathode material is Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Mg 0.04 Cu 0.04 O2, the steps are as follows:

[0086] Na2CO3, NiO, Mn2O3, Fe2O3, MgO and CuO were mixed in a maroon mortar according to the stoichiometric ratio, transferred into a ball mill, vacuum packaged after adding an appropriate amount of anhydrous ethanol, mixed at 400 rpm for 8 h; the uniformly ground raw materials were poured into the mold of a tablet press, and the mold was placed in the tablet press, with a pressure of 10 MPa for 2 min, to press into a 20 mm round tablet; the pressed raw material round tablet was placed in a corundum capsule and placed in a muffle furnace, with a controlled heating rate of 3 ℃ / min to 1020 ℃, and then cooled to 200 ℃ at a rate of 2 ℃ / min after 15 h of heat preservation; after heat treatment, the material was immediately placed in an Ar-filled glove box to prevent contact with any moisture until it cooled to room temperature; then the material was transferred to a low-humidity drying room, and the material was crushed into powder using a mortar and sieved using a 325 mesh screen, thereby obtaining a Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Mg 0.04 Cu 0.04 O2 cathode material.

[0087] See Figure 3 , from Figure 3 It can be seen that the obtained sample is a large single crystal in the form of a plate, with a smoother surface and a size of 5 15 μm.

[0088] Example 4

[0089] The present embodiment provides a preparation method of a sodium ion battery layered oxide cathode material, the chemical formula of the sodium ion battery layered oxide cathode material being Na 0.96 Ni 0.2 Mn 0.32 Fe 0.4 Mg 0.02 Cu 0.06 O2. The preparation process is basically the same as that of Example 3.

[0090] Example 5

[0091] The present embodiment provides a preparation method of a sodium ion battery layered oxide cathode material, the chemical formula of the sodium ion battery layered oxide cathode material being Na 0.98 Ni 0.2 Mn 0.31 Fe 0.4 Mg 0.09 O2, and the preparation process is basically the same as that of Example 1.

[0092] Example 6

[0093] The present embodiment provides a preparation method of a sodium ion battery layered oxide cathode material, the chemical formula of the sodium ion battery layered oxide cathode material being Na0.92 Ni 0.2 Mn 0.34 Fe 0.4 Mg 0.06 O2, which was prepared by substantially the same process as in Example 1.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing a sodium-ion battery layered oxide cathode material with a chemical formula of Na 096 Ni 02 Mn 04 Fe 04 O2, by the following steps:

[0096] Na2CO3, NiO, Mn2O3, and Fe2O3 were mixed in a marver mortar in stoichiometric ratio, and then transferred into a ball mill, and vacuum packaged after adding an appropriate amount of anhydrous ethanol, and mixed at 400 rpm for 8 h; the uniformly ground raw materials were poured into the mold of a tablet press, and the mold was placed in the tablet press, and pressed at a pressure of 10 MPa for 2 min to form a 20 mm round tablet; the pressed raw material round tablet was placed in a corundum canister, and placed in a muffle furnace, and the temperature was raised to 1020°C at a rate of 3°C / min, and held for 15 h, and then cooled to 200°C at a rate of 2°C / min; after heat treatment, the material was immediately placed in an Ar-filled glove box to prevent contact with any moisture until it was cooled to room temperature; then the material was transferred to a low-humidity drying room (-70°C dew point, relative humidity <1%, same below), and the material was crushed into powder using a mortar, and sieved using a 325 mesh sieve, thereby obtaining Na 0.96 Ni 0.2 Mn 0.4 Fe 0.4 O2 cathode material.

[0097] See Figure 4 , from Figure 4 It can be seen that the obtained sample is a large single crystal in the form of a plate, with a rough surface and many secondary particles, and the size is 5-20 μm.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a sodium-ion battery layered oxide cathode material with a chemical formula of Na1Ni 0.2 Mn 0.3 Fe 0.4 Mg 0.1 O2, which was prepared by substantially the same process as in Example 1.

[0100] Comparative Example 3

[0101] The comparative example 1 provides a preparation method of a sodium ion battery layered oxide cathode material, and the chemical formula of the sodium ion battery layered oxide cathode material is Na 0.8 Ni 0.2 Mn 0.32 Fe 0.4 Ti 0.08 O2, and the preparation process is basically the same as that of example 1.

[0102] Comparative example 4

[0103] The comparative example 1 provides a preparation method of a sodium ion battery layered oxide cathode material, and the chemical formula of the sodium ion battery layered oxide cathode material is Na 0.8 Ni 0.2 Mn 0.32 Fe 0.4 Cu 0.04 Ti 0.04 O2, and the preparation process is basically the same as that of example 1.

[0104] Comparative example 5

[0105] The difference between the comparative example 1 and example 1 is that, after high-temperature sintering, the comparative example 1 is naturally cooled to 200 DEG C, and the cooling rate is not controlled, and other steps and parameters remain unchanged.

[0106] Please refer to Figure 5 , from Figure 5 It can be seen that the obtained sample is extremely uneven, the surface is rough and there are a large number of secondary particles, and the size is 1 30 μm.

[0107] Comparative example 6

[0108] The difference between the comparative example 1 and example 1 is that, after high-temperature sintering, the comparative example 1 is naturally cooled to 200 DEG C, and the cooling rate is not controlled, and other steps and parameters remain unchanged.

[0109] Comparative example 7

[0110] The difference between the comparative example 1 and example 1 is that, after high-temperature sintering, the comparative example 1 is naturally cooled to 200 DEG C, and the cooling rate is not controlled, and other steps and parameters remain unchanged.

[0111] Please refer to Figure 6 , from Figure 6 It can be seen that the obtained sample is extremely uneven, the surface is rough and there are a large number of secondary particles, and the size is 1 30 μm.

[0112] Experimental example one

[0113] The high-capacity sodium-ion battery positive electrode materials prepared in the above Examples 1-6 and Comparative Examples 1-7 were subjected to performance detection, wherein the detection methods included: laser particle size analyzer for analyzing average particle size, in-situ differential electrochemical mass spectrometer for detecting first circle gas production of charging and discharging, thickness gauge for measuring the roll-pressed positive plate to calculate the compaction density, potential titrator for determining residual alkali content, X-ray photoelectron spectroscopy for analyzing Mn 3+ / Mn 4+ ratio, X-ray diffraction refinement for calculating Na-O bond length.

[0114] Table 1: Related parameters of the positive electrode materials prepared

[0115]

[0116]

[0117] As can be seen from the above table, the present application can prepare corresponding high-compaction-density large-size single-crystal layered oxide positive electrode materials through vacuum wet mixing and solid-phase high-temperature calcination. The Mn 3+ / Mn 4+ ratio is adjusted by low-valence element substitution to reduce surface residual alkali and reduce the gas production behavior of the positive electrode material. The Na-O bond energy is enhanced, and the structural stability is increased.

[0118] In Comparative Example 1 of the present application, no divalent transition metal element doping was performed, and the data thereof were compared with those of Example 1. It can be seen that the gas production, residual alkali CO3 2- content of Example 1 were significantly higher, and the compaction density was significantly lower than that of Example 1, and the Mn 3+ / Mn 4+ ratio adjustment effect was poor.

[0119] In Comparative Example 2, the ratio of Mg and Mn was 1:3, which was not within the range of m:n = 1:3.5-5 of the present application, and the doping amount of Mg was large, which would cause the gas production and residual alkali CO3 2- content to increase to a certain extent, and the compaction density to decrease to a certain extent, and the overall performance was poorer than that of Example 1 but better than that of Comparative Example 1 which was not doped.

[0120] In Comparative Example 3, the doping element was Ti. It can be seen that, compared with the doping of Mg in Example 1, the comprehensive performance was significantly reduced, which was due to the fact that the substitution of tetravalent Ti could not increase the bulk sodium content and could not adjust the Mn 3+ / Mn 4+ ratio, fully proving that not all transition metals can meet the performance requirements of the present application.

[0121] The doping elements in Comparative Example 4 are a combination of Cu and Ti, and it can be seen that the performance thereof is not much different from that of Comparative Example 3, and it can be seen that the combination of Cu and Ti does not have a synergistic effect. However, in the present application, the effect of the simultaneous doping of Cu and Mg in Example 3 is obviously better than that of the single doping of Mg in Example 1 and the single doping of Cu in Example 2, fully proving that the combination of Cu and Mg has a synergistic effect.

[0122] In Comparative Example 5, natural cooling to 200°C is used after high-temperature sintering, and the cooling rate is not controlled, which will cause the sample to be non-uniform. During natural cooling, sodium ions fail to fully embed into the crystal lattice and remain on the surface to form Na2O, which reacts with H2O / CO2 in the air to generate Na2CO3. Na2CO3 decomposes during the charging and discharging process of the battery to release CO2(gas production). The crystal lattice defects (such as oxygen vacancies) caused by cooling stress can become active sites for electrolyte decomposition, further increasing gas production. Therefore, the gas production and residual alkali CO3 2- content is significantly higher than that of Example 1, and the compaction density is lower than that of Example 1.

[0123] In Comparative Example 6, a higher cooling rate is used after high-temperature sintering, which will cause part of the Na + to remain at high-energy sites (such as grain boundaries or surfaces), increasing the risk of surface residual alkali (Na2O / NaOH) generation. Rapid cooling causes thermal stress accumulation, which can cause microcracks or oxygen vacancies, exposing more active surfaces (such as Mn 3+ ), aggravating residual alkali generation and gas production. Therefore, the gas production and residual alkali CO3 2- content are significantly higher than those of Example 1, and the compaction density is lower than that of Example 1.

[0124] In Comparative Example 7, dry mixing is used, which will cause the sample to be non-uniform in size, with a rough surface and irregular morphology. The gas production and residual alkali CO3 2- content are significantly higher than those of Example 1, and the compaction density is lower than that of Example 1.

[0125] Experimental Example Two

[0126] The positive electrode materials provided in Examples 1-6 and Comparative Examples 1-7 above are prepared into batteries. The preparation method includes: adding a certain amount of NMP to mix and homogenize 8:1:1 of positive electrode material: conductive carbon black (Super P): PVDF, and then coating and drying to obtain a positive electrode sheet with a surface density of 10 mg / cm 3 After rolling with a roller, the compaction of the positive electrode sheet is about 3.3 g / cm 3, cutting into 14mm circular pole piece, placed in the glove box for standby; sodium sheet as the battery counter electrode, sodium hexafluorophosphate electrolyte, glass fiber diaphragm, cutting into 18mm round piece, according to the sequence of positive shell, positive pole piece, diaphragm, negative pole piece, gasket, spring and negative shell, assembled into CR2025 button cell, the test voltage is 2.0-4.0V, and the test equipment is Xinnwei. The electrochemical performance test adopts constant current charge and discharge test, that is, a constant current is set to make the battery perform charging and discharging cycles under the current condition for a specified number of times, which is used to evaluate the cycle life and rapid charge and discharge capacity of the battery.

[0127] Table 2 Electrochemical performance table of prepared positive electrode materials

[0128]

[0129] As can be seen from the above table, the layered oxide positive electrode material prepared by divalent element substitution in the application examples 1-6 has higher discharge capacity, rate performance and cycle stability, and exhibits excellent comprehensive electrochemical performance, and is significantly better than the comparative examples 1-7.

[0130] In summary, the high-capacity sodium ion battery positive electrode material provided by the application has the advantages of high-capacity sodium ion battery positive electrode material, which is beneficial to improve the body phase sodium content, reduce the Mn 3+ content, reduce the Jahn-Teller effect, and improve the cycle performance; the divalent metal element is introduced into the transition metal layer, which further adjusts the Mn 3+ / Mn 4+ ratio in the layered oxide, which is beneficial to deeply activate the oxidation and reduction of nickel in the charging and discharging process, and is beneficial to improve the reversible capacity; in the application, low-nickel high-iron high-manganese is used as the main element, which is beneficial to reduce the material cost. In the preparation process of the application, the process of first wet vacuum mixing and then tabletting and sintering is adopted, which improves the crystallinity and purity of the material and forms a large-size single crystal; in the sintering process, a controllable slow cooling rate is adopted, which is beneficial to form a positive electrode material with high purity and reduce gas production.

[0131] The above only describes the preferred embodiments of the application and is not intended to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A high-capacity sodium-ion battery cathode material, characterized in that, The molecular formula of the high-capacity sodium-ion battery cathode material is Na. x Ni y Fe z M m Mn n O2, x≥0.8, 0.1≤y≤0.2, y+z=0.6, m≤0.1 and m+n=0.4, M represents a divalent transition metal element.

2. The high-capacity sodium-ion battery cathode material according to claim 1, characterized in that, x＞0.96； m:n = 1:3.5-5.

3. The high-capacity sodium-ion battery cathode material according to claim 1, characterized in that, The ion corresponding to M is selected from Mg. 2+ Cu 2+ Zn 2+ Co 2+ Ca 2+ Ba 2+ and Sr 2+ At least one of them.

4. The high-capacity sodium-ion battery cathode material according to claim 1, characterized in that, The ion corresponding to M is selected from Mg. 2+ and Cu 2+ ;Mg 2+ and Cu 2+ The doping ratio is 1:1-2.

5. The high-capacity sodium-ion battery cathode material according to claim 1, characterized in that, The high-capacity sodium-ion battery cathode material is characterized by at least one parameter of features (1)-features (5): Feature (1): The average particle size of the high-capacity sodium-ion battery cathode material is 520 μm; Feature (2): The high-capacity sodium-ion battery cathode material contains Mn 3+ / Mn 4+ The ratio is 1:3-4; Feature (3): The high-capacity sodium-ion battery cathode material has a layered structure and a compaction density ≥3.0 g cm⁻¹. -3 ; Feature (4): The high-capacity sodium-ion battery cathode material has an average sodium-ion diffusion coefficient greater than 1×10⁻⁶ during charging and discharging. -10 cm 2 s -1 ; Feature (5): The high-capacity sodium-ion battery cathode material has a cycle life of >1000 cycles in a full cell.

6. A method for preparing a high-capacity sodium-ion battery cathode material as described in any one of claims 1-5, characterized in that, It involves adding sodium, nickel, iron, manganese and M sources to a solvent in stoichiometric ratios, stirring, followed by ball milling and high-temperature sintering.

7. The method for preparing the high-capacity sodium-ion battery cathode material according to claim 6, characterized in that, The method for preparing the high-capacity sodium-ion battery cathode material includes at least one of features (6)-features (18): Feature (6): The solvent includes at least one of anhydrous ethanol and acetone; Feature (7): The ball mill rotates at a speed of 300-500 rpm and the mixing time is 6-10 h; Feature (8): The ball milling is performed under vacuum conditions; Feature (9): The high-temperature sintering includes first heating from room temperature to 1000-1050℃, holding for 10-20h, then cooling to 180-220℃, and then placing it in a box filled with inert gas to cool to room temperature; Feature (10): The heating rate during the high-temperature sintering process is 1℃ / min to 3℃ / min; the cooling rate is 1℃ / min to 3℃ / min. Feature (11): After ball milling and before high-temperature sintering, the mixture is further compressed into tablets at a pressure of 8-12 MPa for 2-5 minutes; Feature (12): After the high-temperature sintering, the sintered material is further ground and passed through a 300-400 mesh sieve; Feature (13): The sodium source is at least one of sodium carbonate, sodium acetate, sodium nitrate, sodium fluoride and sodium chloride; Feature (14): The nickel source is at least one of nickel oxide, nickel trioxide, nickel carbonate, nickel acetate, nickel chloride, nickel sulfate and nickel nitrate; Feature (15): The iron source is at least one of ferrous oxide, ferric oxide, ferrous carbonate, ferric acetate, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferrous nitrate, and ferric nitrate; Feature (16): The manganese source is at least one of manganese monoxide, manganese trioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate and manganese nitrate; Feature (17): The M source includes Mg 2+ Cu 2+ Zn 2+ Co 2+ Ca 2+ Ba 2+ and Sr 2+ At least one corresponding metal oxide; Feature (18): The sodium source is anhydrous sodium carbonate, the nickel source is nickel oxide, the iron source is ferric oxide, the manganese source is manganese oxide, and the M source is at least one of magnesium oxide and copper oxide.

8. The application of the high-capacity sodium-ion battery cathode material prepared by the preparation method of the high-capacity sodium-ion battery cathode material according to any one of claims 1-5 or any one of claims 67 in the preparation of sodium-ion battery cathode materials.

9. A sodium-ion battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet is prepared using a high-capacity sodium-ion battery positive electrode material prepared by the preparation method of the high-capacity sodium-ion battery positive electrode material according to any one of claims 1-5 or according to any one of claims 67.

10. An electrical device, characterized in that, Including the sodium-ion battery as described in claim 9.

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