A sodium-ion cathode material, its preparation method and application

Abstract

The present invention discloses a sodium-ion cathode material, a preparation method thereof, and an application thereof. The sodium-ion cathode material of the present invention is an O3-type nickel-manganese-based layered transition metal oxide; the ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium-ion cathode material is ≥1.2. By regulating the ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium-ion cathode material, the integrity and stability of its crystal structure can be effectively improved, so as to maintain a good layered structure to promote the deintercalation and intercalation of sodium ions, thereby improving the rate performance and cycle stability of the sodium-ion cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of methods or devices for directly converting chemical energy into electrical energy, and more specifically, to a sodium ion cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the fact that sodium resources are more abundant and widely distributed, sodium ion batteries are more suitable as power batteries for large-scale energy storage or electric vehicles compared to lithium ion batteries. Among them, the cathode material of sodium ion batteries is a key factor affecting their energy density, cycle performance, and rate performance. Currently, commonly used cathode materials for sodium ion batteries include layered oxides, Prussian blue / white materials, and polyanion materials. Moreover, compared to polyanion materials or Prussian blue / white materials, layered oxides are considered the most promising sodium ion cathode materials due to their high specific capacity, high discharge average voltage, and excellent rate performance.

[0003] However, sodium elements in layered oxides will be lost during the high-temperature sintering process. Therefore, in existing preparation methods, generally, sodium salts higher than the theoretical value are added to reduce the influence of sodium element loss; however, excessive sodium salts will cause more "residual alkali" to remain on the surface of the sintered layered oxide cathode material, resulting in lower reversible capacity, poorer rate performance, and cycle stability of the cathode material. Moreover, the rate performance and cycle stability of the cathode material are not only affected by the content of residual alkali on its surface but also related to the structural stability of the layered oxide. A sodium ion battery cathode material, a preparation method thereof, and an application thereof disclosed in the prior art utilize an acidic solution to fully react with the residual alkali on the surface of the sodium ion cathode material to form a sodium salt coating layer with high ionic conductivity. Although it can reduce the content of residual alkali on the surface of the cathode material to a certain extent, it is difficult to effectively improve the structural stability and tap density of the layered oxide, resulting in poor rate performance, cycle stability, and low volume energy density of the cathode material. Summary of the Invention

[0004] The object of the present invention is to overcome the defects and deficiencies of the existing sodium ion layered oxide cathode material, such as poor structural stability, low tap density, resulting in poor rate performance, cycle stability, and low volume energy density, and to provide a sodium ion cathode material.

[0005] Another object of the present invention is to provide a preparation method of a sodium ion cathode material.

[0006] Another object of the present invention is to provide an application of a sodium ion cathode material in a sodium ion battery.

[0007] Another object of the present invention is to provide a positive electrode plate.

[0008] Another object of the present invention is to provide a sodium ion battery.

[0009] The above object of the present invention is achieved by the following technical solutions:

[0010] The present invention protects a sodium-ion cathode material, which is an O3-type nickel-manganese-based layered transition metal oxide; the ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium-ion cathode material is ≥1.2.

[0011] When the ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium-ion cathode material is regulated to be ≥1.2 in the present invention, the integrity and stability of its crystal structure can be effectively improved, so as to maintain a good layered structure to promote the extraction and insertion of sodium ions, and further improve the rate performance and cycle stability of the sodium-ion cathode material.

[0012] Preferably, the ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium-ion cathode material is 1.26 to 1.62. Specifically, it can be 1.62, 1.54, 1.43, 1.59, 1.47 or 1.26.

[0013] The present invention protects a sodium-ion cathode material, which is an O3-type nickel-manganese-based layered transition metal oxide, and the pH value of the suspension of the sodium-ion cathode material is ≤12.70.

[0014] Optionally, the pH value of the suspension of the sodium-ion cathode material is 12.35 to 12.66. Specifically, it can be 12.35, 12.62, 12.58, 12.40, 12.66 or 12.53.

[0015] Optionally, the D 10 = 2.9 to 3.8 μm, D 50 = 5.7 to 7.2 μm, D 90 = 11.3 to 19.5 μm. Preferably, D 10 = 2.98 to 3.76 μm, D 50 = 6.12 to 7.15 μm, D 90 = 11.31 to 19.42 μm. Specifically, D 10 = 3.48 μm, D 50 = 6.35 μm, D 90 = 11.31 μm; or D 10 = 3.24 μm, D 50 = 6.33 μm, D 90 = 18.69 μm; D 10 = 3.76 μm, D 50 = 7.15 μm, D 90 = 19.42 μm; or D 10= 3.31 μm, D 50 = 6.12 μm, D 90 = 15.33 μm; or D 10 = 3.11 μm, D 50 = 5.89 μm, D 90 = 17.66 μm; or D 10 = 2.98 μm, D 50 = 5.75 μm, D 90 = 18.03 μm.

[0016] Optionally, the surface of the sodium ion cathode material has a coating layer.

[0017] Optionally, the particle size of the sodium ion cathode material satisfies: (D 90 - D 10 ) / D 50 ≤ 2.7; preferably 1.23 ≤ (D 90 - D 10 ) / D 50 ≤ 2.62. Specifically, it can be 1.23, 2.44, 2.19, 1.96, 2.47 or 2.62.

[0018] Optionally, the pH value of the suspension of the sodium ion cathode material ≤ 12.60, preferably 12.35 - 12.58; specifically, it can be 12.35, 12.58, 12.40 or 12.53.

[0019] Specifically, the coating layer is nanoparticles with D50 = 1 - 500 nm attached to the surface of the nickel - manganese - based layered transition metal oxide, or a thin layer with a thickness of 1 - 500 nm wrapped on the surface of the nickel - manganese - based layered transition metal oxide.

[0020] Among them, the coating layer on the surface of the above - mentioned sodium ion cathode material refers to a coating structure attached to the surface of the nickel - manganese - based layered transition metal oxide. This coating structure mainly exists in the following two forms. One is in the form of nanoparticles (D 50 = 1 - 500 nm) attached to the surface of the nickel - manganese - based layered transition metal oxide, which can not only reduce the contact between the nickel - manganese - based layered transition metal oxide particles and air, but also inhibit the reaction of the nickel - manganese - based layered transition metal oxide particles with water and carbon dioxide in the air, resulting in the precipitation of sodium in the layered structure to form sodium bicarbonate, sodium carbonate, sodium hydroxide, etc. At the same time, it can also reduce the erosion of the electrolyte on the nickel - manganese - based layered transition metal oxide; the other is to form a coating layer with a uniform film - like shape (with a thickness of about 1 - 500 nm) on the surface of the nickel - manganese - based layered transition metal oxide particles. This coating layer has good ionic conductivity, can improve the interfacial properties of the nickel - manganese - based layered transition metal oxide, and thus improve the rate performance of the sodium ion cathode material.

[0021] Specifically, the chemical formula of the nickel-manganese-based layered transition metal oxide is

[0022] Na a Ni b Mn c M1 d M2 e O 2+f , where 0.9 ≤ a < 1, 0.1 ≤ b ≤ 0.8, 0.1 ≤ c ≤ 0.8, 0 < d + e ≤ 0.6, and a, b, c, d, e, f satisfy the principle of electrical neutrality numerically;

[0023] M1 and M2 are each independently selected from at least one of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg or Zn, and M1 is different from M2.

[0024] Optionally, the tap density of the sodium ion cathode material ≥ 1.95 g / cm 3 , preferably 1.98 - 2.11 g / cm 3 , specifically it can be 1.98, 2.00, 2.02, 2.03, 2.05, 2.06 or 2.11; it can be obtained by testing according to the GB / T5162 standard. When the tap density of the sodium ion cathode material ≥ 1.95 g / cm 3 , a higher tap density is more conducive to shortening the charge and ion transport paths of the cathode material, thereby improving the energy density of the battery.

[0025] The present invention also protects a preparation method of the above sodium ion cathode material, comprising the following steps:

[0026] S1. Mix the Ni source, Mn source, dopant M1 source and Na source, and perform a first calcination treatment at 800 - 1000 °C for 5 - 48 h, then crush and screen to obtain a primary sintered material;

[0027] S2. Mix the primary sintered material in S1 with the dopant M2 source, and perform a second calcination treatment at 700 - 950 °C for 5 - 24 h, then crush and screen to obtain the sodium ion cathode material; wherein, M1 is different from M2.

[0028] The role of the first calcination treatment is to form an oxide with a good layered structure from the Ni source, Mn source, M1 source, and Na source at a relatively high calcination temperature, and then crush and screen it to obtain a primary sintered material (oxide fine powder particles with an average particle size ≤ 1 mm), preparing for subsequent doping modification; while the role of the second calcination treatment is mainly to fuse the primary sintered material to generate larger single crystal particles, and doping modification is carried out by adding the dopant M2 source during the fusion process; moreover, since the oxide obtained from the first calcination treatment already has a layered structure, the dopant during the second calcination treatment can enter the oxide lattice at a lower temperature (compared with the temperature of the first calcination treatment), playing a role in stabilizing the layered structure and reducing phase transformation, and also being able to reduce energy consumption to a certain extent. More importantly, it is found that compared with the conventional one-step solid-phase sintering process, the above two-step sintering preparation method can effectively improve the tap density of the sodium-ion cathode material, thereby increasing its volumetric energy density, and further promoting the improvement of the energy density of the battery.

[0029] Preferably, the temperature of the first calcination treatment in S1 is 860 - 1000 °C, and the time is 5 - 30 h, specifically it can be 860 °C, 900 °C, 950 °C, or 1000 °C; the temperature of the second calcination treatment in S2 is 750 - 950 °C, and the time is 5 - 18 h, specifically it can be 750 °C, 800 °C, 850 °C, 900 °C, or 950 °C.

[0030] Specifically, the heating rate of the first calcination treatment in S1 or the second calcination treatment in S2 from room temperature to the required calcination temperature is 1 - 10 °C / min; preferably 1 - 8 °C / min.

[0031] The present invention also protects a preparation method of the above sodium-ion cathode material, including the following steps:

[0032] a1. After mixing the Ni source, Mn source, dopant M1 source, and Na source, perform the first calcination treatment at 800 - 1000 °C for 5 - 48 h, crush and screen to obtain a primary sintered cathode material;

[0033] a2. After mixing the primary sintered cathode material in a1 with the dopant M2 source, perform the second calcination treatment at 700 - 950 °C for 5 - 24 h, crush and screen to obtain a secondary sintered cathode material;

[0034] a3. After mixing the secondary sintered cathode material in a2 with the coating agent, perform the third calcination treatment at 100 - 800 °C for 1 - 12 h, crush and screen to obtain the sodium-ion cathode material; where M1 and M2 are different.

[0035] In the above preparation method, the role of the first calcination treatment is to form an oxide with a good layered structure from the Ni source, Mn source, M1 source and Na source at a relatively high calcination temperature, and then crush and screen it to obtain the primary sintered cathode material (oxide fine powder particles with an average particle size ≤ 1 mm), which is prepared for subsequent doping modification; while the role of the second calcination treatment is mainly to fuse the primary sintered cathode material to generate larger single crystal particles, and doping modification is carried out by adding the dopant M2 source during the fusion process; moreover, since the oxide obtained by the first calcination treatment already has a layered structure, the dopant in the second calcination treatment process can enter the oxide lattice at a lower temperature (compared with the temperature of the first calcination treatment), playing the role of stabilizing the layered structure and reducing phase transformation, and at the same time can also reduce energy consumption to a certain extent.

[0036] The role of the third calcination treatment is mainly to further fuse the secondary sintered cathode material to obtain particles with more uniform particle size, and form a good coating structure under the action of the coating agent. Moreover, part of the coating agent can form a coating layer or coating particles with lower alkalinity, better stability and ion-conducting performance with the free sodium on the surface of the secondary sintered cathode material, which can not only effectively consume the free sodium, but also reduce the contact with the electrolyte during the cycle and avoid the problem of low cycle capacity retention rate caused by electrolyte erosion on the surface of the cathode material. In addition, the above three-step calcination treatment (two-step sintering + coating treatment) can significantly improve the tap density of the sodium-ion cathode material, thereby promoting its volumetric energy density and the energy density of the battery.

[0037] Preferably, the temperature of the first calcination treatment in a1 is 860 - 1000 °C, and the time is 5 - 30 h, specifically it can be 860 °C, 900 °C, 950 °C or 1000 °C; the temperature of the second calcination treatment in a2 is 750 - 950 °C, and the time is 5 - 18 h, specifically it can be 750 °C, 800 °C, 850 °C, 900 °C or 950 °C; the temperature of the third calcination treatment in a3 is 200 - 800 °C, and the time is 1 - 10 h, specifically it can be 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C or 800 °C.

[0038] Specifically, the heating rate of the first calcination treatment in a1, the second calcination treatment in a2 or the third calcination treatment in a3 from room temperature to the required calcination temperature is 1 - 10 °C / min; preferably 1 - 8 °C / min.

[0039] Optionally, the mass ratio of the secondary sintered cathode material to the coating agent described in a3 is 100:(0.01 - 5), preferably 100:(0.05 - 2); specifically, it can be 100:0.1, 100:0.3, 100:0.5, 100:1 or 100:1.5.

[0040] The present invention also protects a method for preparing the above sodium ion cathode material, which includes the following steps:

[0041] After mixing the Ni source, Mn source, dopant M1 source, dopant M2 source and Na source, perform the first calcination treatment at 800 - 1000 °C for 5 - 48 h, crush and screen to obtain the sintered cathode material; then mix the sintered cathode material with the coating agent and perform the second calcination treatment at 100 - 800 °C for 1 - 12 h, crush and screen to obtain the sodium ion cathode material; where M1 and M2 are different.

[0042] Specifically, in the above preparation method, the mass ratio of the sintered cathode material to the coating agent is 100:(0.01 - 5), preferably 100:(0.05 - 2); specifically, it can be 100:0.1, 100:0.3, 100:0.5, 100:1 or 100:1.5.

[0043] It should also be noted that the M1 source and M2 source in the above preparation method can be independently selected from at least one of ferric oxide, ferrous oxide, ferroferric oxide, iron nitrate, iron sulfate, ferrous oxalate, iron hydroxide, titanium dioxide, copper oxide, tin dioxide, magnesium oxide, zinc oxide or lithium carbonate.

[0044] The Ni source can be at least one of nickel oxide, nickelous oxide, nickel nitrate, nickel sulfate, nickel oxalate, nickel acetate or nickel carbonate; the Mn source can be at least one of manganese dioxide, manganese monoxide, trimanganese tetroxide, manganese nitrate, manganese sulfate, manganese carbonate, manganese hydroxide, manganese oxalate or manganese acetate; the Na source can be at least one of sodium carbonate, sodium bicarbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium hydroxide or sodium sulfate.

[0045] The coating agent can be at least one of magnesium oxide, copper oxide, calcium oxide, manganese dioxide, titanium dioxide, zirconium dioxide, silicon dioxide, boron trioxide, aluminum oxide, aluminum phosphate, sodium phosphate, ammonium dihydrogen phosphate, boron oxide, boric acid, sodium borate, silicic acid, sodium silicate or silicon dioxide.

[0046] The application of the above sodium ion cathode material in a sodium ion battery is also within the protection scope of the present invention.

[0047] The present invention also protects a positive electrode plate, which includes a current collector and a positive electrode active material layer disposed on at least one side of the current collector. It is characterized in that the positive electrode active material layer contains the above-mentioned sodium ion positive electrode material.

[0048] The present invention also protects a sodium ion battery, which includes a positive electrode plate, a negative electrode plate, and an electrolyte located between the positive electrode plate and the negative electrode plate. It is characterized in that the positive electrode plate contains the above-mentioned sodium ion positive electrode material.

[0049] Compared with the prior art, the present invention has the following beneficial technical effects:

[0050] By regulating the ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium ion positive electrode material, the present invention can effectively improve the integrity and stability of its crystal structure, thereby maintaining a good layered structure to promote the extraction and insertion of sodium ions, and further improving the rate performance and cycle stability of the sodium ion positive electrode material. Description of the Drawings

[0051] Figure 1 It is the SEM diagram of the sodium ion positive electrode material in Example 1.

[0052] Figure 2 It is the SEM diagram of the sodium ion positive electrode material in Comparative Example 1.

[0053] Figure 3 It is the XRD diagram of the sodium ion positive electrode material in Example 1 and Comparative Example 1.

[0054] Figure 4 It is the rate performance diagram of the sodium ion positive electrode material in Example 1, Comparative Example 1, and Comparative Example 2.

[0055] Figure 5 It is the 200-cycle performance diagram of the sodium ion positive electrode material in Example 1 and Comparative Example 1 under the conditions of 2.0 - 4.0V and 0.5C.

[0056] Figure 6 It is the 100-cycle performance diagram of the sodium ion positive electrode material in Example 1 and Comparative Example 1 under the conditions of 2.0 - 4.2V and 1C. Detailed Embodiments

[0057] The present invention will be further described below in conjunction with the drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0058] Example 1

[0059] A sodium-ion cathode material, comprising a nickel-manganese-based layered transition metal oxide and a coating structure attached to the surface of the nickel-manganese-based layered transition metal oxide; the chemical formula of the nickel-manganese-based layered transition metal oxide is NaMn 0.3 Ni 0.3 Fe 0.3 Ti 0.05 Cu 0.05 O2.

[0060] The above sodium-ion cathode material can be prepared by the following preparation method:

[0061] S1. According to the stoichiometric ratio of each element in NaMn 0.3 Ni 0.3 Fe 0.3 Ti 0.05 Cu 0.05 O2, sodium carbonate (the actual addition amount of sodium carbonate is 104% of the theoretical addition amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide and iron(III) oxide are mixed evenly, and then subjected to a first calcination treatment at 900 °C in air for 20 h (the heating rate from room temperature to 900 °C is 4 °C / min), naturally cooled, crushed and sieved to obtain the primary sintered cathode material;

[0062] S2. The primary sintered cathode material obtained in S1 is mixed evenly with titanium dioxide and copper oxide according to the above stoichiometric ratio, and then subjected to a second calcination treatment at 850 °C in air for 10 h (the heating rate from room temperature to 850 °C is 4 °C / min), naturally cooled, crushed and sieved to obtain the secondary sintered cathode material;

[0063] S3. The secondary sintered cathode material obtained in S2 is mixed evenly with zirconia in a mass ratio of 100:0.2, and then subjected to a sintering treatment at 600 °C in air for 2 h (the heating rate from room temperature to 600 °C is 4 °C / min), naturally cooled, crushed and sieved to obtain the sodium-ion cathode material.

[0064] Example 2

[0065] A sodium-ion cathode material, comprising a nickel-manganese-based layered transition metal oxide, and the chemical formula of the nickel-manganese-based layered transition metal oxide is NaMn 0.3 Ni 0.3 Fe 0.3 Ti 0.05 Cu 0.05 O2.

[0066] The above sodium-ion cathode material can be prepared by the following preparation method:

[0067] S1. According to NaMn 0.3 Ni 0.3Fe 0.3 Ti 0.05 Cu 0.05 For the stoichiometric ratios of the elements in O₂, sodium carbonate (the actual addition amount of sodium carbonate is 104% of the theoretical addition amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide, and iron(III) oxide are mixed evenly and then subjected to the first calcination treatment at 900 °C in air for 20 h (the heating rate from room temperature to 900 °C is 4 °C / min), cooled naturally, crushed, and sieved to obtain the primary sintered material;

[0068] S2. After mixing the primary sintered material described in S1 with titanium dioxide and copper oxide evenly according to the above stoichiometric ratio, perform the second calcination treatment at 850 °C in air for 10 h (the heating rate from room temperature to 850 °C is 4 °C / min), cool naturally, crush, and sieve to obtain the sodium-ion positive electrode material.

[0069] Example 3

[0070] A sodium-ion positive electrode material includes a nickel-manganese-based layered transition metal oxide and a coating structure attached to the surface of the nickel-manganese-based layered transition metal oxide; the chemical formula of the nickel-manganese-based layered transition metal oxide is NaMn 0.3 Ni 0.3 Fe 0.3 Ti 0.05 Cu 0.05 O₂.

[0071] The above sodium-ion positive electrode material can be prepared by the following preparation method:

[0072] S1. According to the stoichiometric ratios of the elements in NaMn 0.3 Ni 0.3 Fe 0.3 Ti 0.05 Cu 0.05 O₂, sodium carbonate (the actual addition amount of sodium carbonate is 104% of the theoretical addition amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide, iron(III) oxide, titanium dioxide, and copper oxide are mixed evenly and then calcined at 900 °C in air for 20 h (the heating rate from room temperature to 900 °C is 4 °C / min), cooled naturally, crushed, and sieved to obtain the sintered positive electrode material;

[0073] S2. After mixing the sintered positive electrode material described in S1 with zirconia evenly at a mass ratio of 100:0.2, perform the sintering treatment at 600 °C in air for 2 h (the heating rate from room temperature to 600 °C is 4 °C / min), cooled naturally, crushed, and sieved to obtain the sodium-ion positive electrode material.

[0074] Example 4

[0075] A sodium-ion cathode material, comprising a nickel-manganese-based layered transition metal oxide and a coating structure attached to the surface of the nickel-manganese-based layered transition metal oxide; the chemical formula of the nickel-manganese-based layered transition metal oxide is Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 O2.

[0076] The above sodium-ion cathode material can be prepared by the following preparation method:

[0077] S1. According to the stoichiometric ratio of each element in Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 O2, sodium carbonate (the actual added amount of sodium carbonate is 104% of the theoretical added amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide and iron(III) oxide are mixed evenly, and then subjected to a first calcination treatment at 925 °C in air for 20 h (the heating rate from room temperature to 925 °C is 3 °C / min), cooled naturally, crushed and sieved to obtain the first sintered cathode material;

[0078] S2. The first sintered cathode material described in S1 is mixed evenly with tin dioxide and magnesium oxide according to the above stoichiometric ratio, and then subjected to a second calcination treatment at 860 °C in air for 10 h (the heating rate from room temperature to 860 °C is 3 °C / min), cooled naturally, crushed and sieved to obtain the second sintered cathode material;

[0079] S3. The second sintered cathode material described in S2 is mixed evenly with boron oxide in a mass ratio of 100:0.2, and then subjected to a sintering treatment at 500 °C in air for 1 h (the heating rate from room temperature to 500 °C is 3 °C / min), cooled naturally, crushed and sieved to obtain the sodium-ion cathode material.

[0080] Example 5

[0081] A sodium-ion cathode material, comprising a nickel-manganese-based layered transition metal oxide, and the chemical formula of the nickel-manganese-based layered transition metal oxide is Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 O2.

[0082] The above sodium-ion cathode material can be prepared by the following preparation method:

[0083] S1. According to the stoichiometric ratio of each element in Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 O₂, after mixing sodium carbonate (the actual addition amount of sodium carbonate is 104% of the theoretical addition amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide and ferric oxide evenly, conduct a primary calcination treatment at 925 °C in air for 20 h (the heating rate from room temperature to 925 °C is 3 °C / min), cool naturally, crush and sieve to obtain the primary sintered material;

[0084] S2. After mixing the primary sintered material described in S1 with tin dioxide and magnesium oxide according to the above stoichiometric ratio evenly, conduct a secondary calcination treatment at 860 °C in air for 10 h (the heating rate from room temperature to 860 °C is 3 °C / min), cool naturally, crush and sieve to obtain the sodium ion positive electrode material.

[0085] Example 6

[0086] A sodium ion positive electrode material includes a nickel-manganese-based layered transition metal oxide and a coating structure attached to the surface of the nickel-manganese-based layered transition metal oxide; the chemical formula of the nickel-manganese-based layered transition metal oxide is Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 O₂.

[0087] The above sodium ion positive electrode material can be prepared by the following preparation method:

[0088] S1. According to the stoichiometric ratio of each element in Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 O₂, after mixing sodium carbonate (the actual addition amount of sodium carbonate is 104% of the theoretical addition amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide, ferric oxide, tin dioxide and magnesium oxide evenly, conduct a primary calcination treatment at 925 °C in air for 20 h (the heating rate from room temperature to 925 °C is 3 °C / min), cool naturally, crush and sieve to obtain the sintered positive electrode material;

[0089] S2. Mix the sintered cathode material described in S1 with boron oxide in a mass ratio of 100:0.2 evenly, then conduct a sintering treatment at 500 °C in air for 1 h (the heating rate from room temperature to 500 °C is 3 °C / min), cool naturally, crush and sieve to obtain the sodium-ion cathode material.

[0090] Example 7

[0091] A sodium-ion cathode material includes a nickel-manganese-based layered transition metal oxide and a coating structure attached to the surface of the nickel-manganese-based layered transition metal oxide; the chemical formula of the nickel-manganese-based layered transition metal oxide is NaMn 0.45 Ni 0.35 Cu 0.1 Ti 0.05 Mg 0.05 O2.

[0092] The above sodium-ion cathode material can be prepared by the following preparation method:

[0093] S1. According to the stoichiometric ratio of each element in NaMn 0.45 Ni 0.35 Cu 0.1 Ti 0.05 Mg 0.05 O2, mix sodium carbonate (the actual added amount of sodium carbonate is 104% of its theoretical added amount obtained according to the above stoichiometric ratio), manganese dioxide, nickel oxide, and copper oxide evenly, then conduct a primary calcination treatment at 925 °C in air for 20 h (the heating rate from room temperature to 925 °C is 3 °C / min), cool naturally, crush and sieve to obtain the primary sintered cathode material;

[0094] S2. Mix the primary sintered cathode material described in S1 with titanium dioxide and magnesium oxide according to the above stoichiometric ratio evenly, then conduct a secondary calcination treatment at 860 °C in air for 10 h (the heating rate from room temperature to 860 °C is 3 °C / min), cool naturally, crush and sieve to obtain the secondary sintered cathode material;

[0095] S3. Mix the secondary sintered cathode material described in S2 with boron oxide in a mass ratio of 100:0.2 evenly, then conduct a sintering treatment at 500 °C in air for 1 h (the heating rate from room temperature to 500 °C is 3 °C / min), cool naturally, crush and sieve to obtain the sodium-ion cathode material.

[0096] Comparative Example 1

[0097] A sodium-ion cathode material can be prepared by the following preparation method:

[0098] According to NaMn 0.3 Ni 0.3Fe 0.3 Ti 0.05 Cu 0.05 According to the stoichiometric ratios of the elements in Na

[0099] Comparative Example 2

[0100] A sodium ion cathode material can be prepared by the following preparation method:

[0101] According to Na 0.95 Mn 0.3 Ni 0.3 Fe 0.3 Sn 0.75 Mg 0.025 According to the stoichiometric ratios of the elements in Na

[0102] Performance test

[0103] (1) Particle size distribution test: Tested according to GB / T19077.1 Particle size analysis - Laser diffraction method - Part 1, and the test results are shown in Table 1.

[0104] (2) Tap density: Tested according to GB / T5162 Test method for tap density of metallic powders, and the test results are shown in Table 1.

[0105] Table 1 Particle size distribution and tap density of sodium ion cathode materials in each example and comparative example

[0106] Number <![CDATA[D 10 (μm)]]> <![CDATA[D 50 (μm)]]> <![CDATA[D 90 (μm)]]> <![CDATA[(D 90 -D 10 ) / D 50 > <![CDATA[Td (g / cm 3 )]]> Example 1 3.48 6.35 11.31 1.23 2.11 Example 2 3.24 6.33 18.69 2.44 2.00 Example 3 3.76 7.15 19.42 2.19 2.03 Example 4 3.31 6.12 15.33 1.96 2.06 Example 5 3.11 5.89 17.66 2.47 2.02 Example 6 2.98 5.75 18.03 2.62 1.98 Example 7 3.25 6.09 16.21 2.12 2.05 Comparative Example 1 1.03 3.14 24.85 7.59 1.89 Comparative Example 2 1.10 3.05 26.94 8.47 1.81

[0107] According to the data in Table 1 and Figures 1 to 2 It can be seen that compared with the sodium ion cathode materials obtained by one-step solid-phase sintering in Comparative Example 1 or 2, the particle size distribution of the sodium ion cathode materials in Examples 1 - 7 is more uniform, and there are basically no fine powder particles or agglomerated large particles, having better cycle stability. At the same time, it can be known from the data in Table 1 that the tap densities of the sodium ion cathode materials in Examples 1 - 7 all reach 1.9 g / cm 3Above, it is significantly higher than the tap density of the sodium-ion cathode material in Comparative Example 1 or 2, indicating that compared with the common one-step solid-phase sintering, the preparation process of the present invention using two-step solid-phase sintering + coating treatment, two-step solid-phase sintering, or one-step solid-phase sintering + coating treatment is beneficial to improving the tap density of the sodium-ion cathode material, and thus beneficial to enhancing the volumetric energy density of the sodium-ion cathode material.

[0108] (3) pH value test: According to GB / T 1717 Determination of the pH Value of Aqueous Suspensions of Pigments, the test results are shown in Table 2.

[0109] (4) XRD test: Particle Size Analysis Laser Diffraction Method - Part 1: General Principles: The X-ray powder diffraction standard pattern (XRD) conforms to JCPDS (54-0887). It can be Figure 3 seen that the ratio of the XRD crystal plane diffraction intensity I(003) / I(104) of the sodium-ion cathode material in Example 1 is 1.62, while the ratio of the XRD crystal plane diffraction intensity I(003) / I(104) of Comparative Example 1 is 1.16. The larger the I(003) / I(104), the larger the effective area of the (003) plane of the cathode material scanned during the XRD test, and the wider the area perpendicular to the (003) plane, that is, the more lamellar structures rather than spherical-like structures of the cathode material. This shows that the sodium-ion cathode material of Example 1 of the present invention has a good layered crystal structure compared with that of Comparative Example 1, which can promote the deintercalation and intercalation of sodium ions.

[0110] (5) Electrochemical performance test: The sodium-ion cathode materials in Examples 1 to 7 and Comparative Examples 1 to 2 were respectively made into positive electrode sheets. At the same time, metallic sodium was used as the negative electrode sheet, glass fiber as the separator, and a carbonate solution of 1 mol / L NaClO4 (composed of ethylene carbonate and propylene carbonate in a volume ratio of 1:1) as the electrolyte to form a CR2032 coin cell. Charge-discharge tests were carried out at room temperature (25 °C), with a current density of 0.1 C and a voltage range of 2.0 - 4.0 V. Charge-discharge cycles were carried out 200 times under the condition of 0.5 C, and the cycle stability of the sodium-ion cathode material was evaluated by the capacity retention rate after 200 charge-discharge cycles. At 25 °C, the sodium-ion battery was first charged at a constant current of 1 C to a voltage of 4.2 V, and then discharged at a constant current of 1 C to a voltage of 2.0 V. This was a charge-discharge cycle process, and the discharge capacity of this time was the discharge capacity of the first cycle. The sodium-ion battery was subjected to 100 cycle charge / discharge tests according to the above method, and the discharge capacity of the 100th cycle was detected; similarly, at 25 °C, the sodium-ion battery was first charged at a constant current of 1 C to a voltage of 4.5 V, and then discharged at a constant current of 1 C to a voltage of 2.0 V. This was a charge-discharge cycle process, and the discharge capacity of this time was the discharge capacity of the first cycle. The sodium-ion battery was subjected to 100 cycle charge / discharge tests according to the above method, and the discharge capacity of the 100th cycle was detected; the rate performance of the sodium-ion cathode material was evaluated by the discharge capacity retention rate at 5 C and 0.1 C conditions (0.1 C cycle 5 laps → 0.5 C cycle 5 laps → 1 C cycle 5 laps → 2 C cycle 5 laps → 5 C cycle 5 laps → 0.1 C cycle 5 laps). The test results are shown in Table 2, Table 3 and Figures 4 to 5 as follows:

[0111] Capacity retention rate (%) after 200 charge-discharge cycles under 0.5 C condition = (Discharge capacity of the 200th time / Discharge capacity of the first time) * 100%.

[0112] Capacity retention rate (%) after 100 charge-discharge cycles under 1 C condition = (Discharge capacity of the 100th time / Discharge capacity of the first time) * 100%.

[0113] Table 2 Performance of sodium-ion cathode materials in each example and comparative example

[0114]

[0115] Table 3 Cycle performance of sodium-ion cathode materials in each example and comparative example at 1 C

[0116]

[0117]

[0118] It can be found from the data in Table 2 that the pH value of the sodium-ion cathode material suspension in Examples 1 to 7 is ≤ 12.66, which indicates that the surface residual alkali content of the sodium-ion cathode material of the present invention is relatively low. At the same time, it can also be seen that the XRD crystal plane diffraction intensity ratio I(003) / I(104) of the sodium-ion cathode material in Examples 1 to 7 is ≥ 1.26. The larger the I(003) / I(104), the larger the effective area of the (003) plane of the cathode material scanned during the XRD test, and the wider the area perpendicular to the (003) plane. That is, the lamellar structure of the cathode material is more rather than the spherical-like structure, indicating that the sodium-ion cathode material of the present invention has a good layered crystal structure, which can promote the deintercalation and intercalation of sodium ions, thereby improving the rate performance and cycle stability. Figure 4 and Figure 5 It also further proves that the sodium-ion cathode material of the present invention not only has better cycle stability (the capacity retention rate reaches more than 84% after 200 charge and discharge cycles under the condition of 0.5C), but also has better rate performance, especially the capacity is significantly improved under the condition of high rate (5C).

[0119] It can also be found through Example 2 and Comparative Example 1 that the pH value of the sodium-ion cathode material suspension in Example 2 is lower than that in Comparative Example 1, indicating that the surface residual alkali content of the sodium-ion cathode material in Example 2 is relatively low. That is, compared with the one-time calcination treatment, the two-time calcination treatment is more conducive to reducing the surface residual alkali content of the sodium-ion cathode material. The main reasons are as follows: (1) During each calcination treatment, there will be volatilization of sodium salts, and part of the residual alkali (sodium salts) that has not entered the crystal lattice will volatilize during the calcination process. The surface residual alkali content of the sodium-ion cathode material in Example 2 is lower than that in Comparative Example 1 after two-time calcination treatment; (2) After two-time calcination treatment of the sodium-ion cathode material in Example 2, the sodium salts remaining on the surface of the primary sintered material during the first calcination treatment can enter the sodium layer crystal lattice of the layered structure during the second calcination treatment, reducing the free sodium salts on the surface of the cathode material, that is, reducing the residual alkali content; (3) After two-time calcination treatment of the sodium-ion cathode material in Example 2, the second calcination treatment can further fuse some fine powder particles of the primary sintered material, reducing the specific surface area of the material and its contact area with air, thereby reducing the exchange of sodium in the cathode material structure with air and reducing the generation of residual alkali.

[0120] It can also be seen from Example 3 and Comparative Example 1 that the XRD crystal plane diffraction intensity ratio I(003) / I(104) of the sodium-ion cathode material in Example 3 is significantly greater than that in Comparative Example 1, indicating that the sodium-ion cathode material in Example 3 has a better layered crystal structure. That is, compared with the single calcination treatment, the single calcination treatment + coating treatment can enable the sodium-ion cathode material to have a better layered crystal structure. The main reason is that the calcination treatment of the cathode material is carried out in an air atmosphere. During the cooling process of the calcination treatment, water, carbon dioxide, etc. in the air exchange with the sodium layer in the cathode material structure, resulting in sodium dissolution. The sodium dissolution will also cause the transition metals in the transition metal layer to dissolve or segregate, thereby reducing the stability of the material's layered structure and the layered structure, which leads to a decrease in the degree of the layered structure of the sodium-ion cathode material obtained by the single calcination treatment. During the coating treatment process, heat treatment is required, and some of the dissolved sodium salts and transition metals will return to the crystal lattice during the heat treatment process, resulting in an improvement in both crystallinity and layered structure. Moreover, during the coating cooling process, due to the presence of the coating layer on the surface, the exchange of the sodium layer with water and carbon dioxide in the air can be reduced, thereby maintaining a good layered structure and crystallinity, that is, the XRD crystal plane diffraction intensity ratio I(003) / I(104) of the sodium-ion cathode material is larger.

[0121] Meanwhile, according to Table 3 and Figure 6 the data, it can be found that the capacity retention rates of the sodium-ion cathode materials in Examples 1 to 7 after 100 cycles under the conditions of 2.0 - 4.2 V and 1C reach more than 95%, and the capacity retention rates after 100 cycles under the conditions of 2.0 - 4.5 V and 1C reach more than 84%, which are significantly higher than the capacity retention rates of the sodium-ion cathode materials in Comparative Example 1 or 2 under the same test conditions. This shows that the sodium-ion cathode material of the present invention also has excellent cycle stability under high voltage and high-rate cycling conditions.

[0122] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A sodium-ion cathode material, which is an O3-type nickel-manganese-based layered transition metal oxide, characterized in that, The ratio of the XRD crystal plane diffraction intensities I(003) / I(104) of the sodium-ion cathode material is 1.57 to 1.62; The D of the sodium ion cathode material 10 = 3.25 to 3.48 μm, D 50 = 6.09 to 6.35 μm, D 90 = 11.31 to 16.21 μm.

2. The sodium ion cathode material according to claim 1, wherein The pH value of the suspension of the sodium-ion cathode material is ≤ 12.

70.

3. The sodium ion cathode material according to claim 2, wherein The pH value of the suspension of the sodium-ion cathode material is 12.35 to 12.

66.

4. The sodium ion cathode material according to claim 1 or 2, wherein The surface of the sodium-ion cathode material has a coating layer.

5. The sodium ion cathode material according to claim 1 or 2, characterized in that, The particle size of the sodium ion cathode material satisfies: (D 90 - D 10 ) / D 50 ≤ 2.

7.

6. The sodium ion cathode material according to claim 5, wherein The particle size of the sodium ion positive electrode material satisfies: 1.23 ≤ (D 90 - D 10 ) / D 50 ≤ 2.

62.

7. The sodium ion cathode material according to claim 4, wherein The pH value of the suspension of the sodium-ion cathode material is ≤ 12.

60.

8. The sodium ion positive electrode material according to claim 7, characterized in that, The pH value of the suspension of the sodium-ion cathode material is 12.35 to 12.

58.

9. The sodium ion cathode material according to claim 4, characterized in that The coating layer is nanoparticles with D50 = 1 to 500 nm attached to the surface of the nickel-manganese-based layered transition metal oxide, or a thin layer with a thickness of 1 to 500 nm wrapped on the surface of the nickel-manganese-based layered transition metal oxide.

10. The sodium ion cathode material according to claim 1 or 2, characterized in that, The chemical formula of the nickel-manganese-based layered transition metal oxide is Na a Ni b Mn c M1 d M2 e O 2+f , where 0.9 ≤ a < 1, 0.1 ≤ b ≤ 0.8, 0.1 ≤ c ≤ 0.8, 0 < d + e ≤ 0.6, and a, b, c, d, e, f satisfy the principle of electroneutrality numerically; M1 and M2 are each independently selected from at least one of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn, and M1 is different from M2.

11. A method for preparing the sodium ion cathode material according to any one of claims 1 to 10, characterized in that, It includes the following steps: a1. Mix the Ni source, Mn source, dopant M1 source, and Na source, and then perform the first calcination treatment at 800 to 1000 °C for 5 to 48 h, crush and screen to obtain the primary sintered cathode material; a2. Mix the primary sintered cathode material described in a1 with the dopant M2 source, and then perform the second calcination treatment at 750 to 950 °C for 5 to 24 h, crush and screen to obtain the secondary sintered cathode material; a3. Mix the secondary sintered cathode material described in a2 with the coating agent, and then perform the third calcination treatment at 100 to 800 °C for 1 to 12 h, crush and screen to obtain the sodium-ion cathode material; wherein, the M1 source and the M2 source are each independently selected from at least one of ferric oxide, ferrous oxide, ferroferric oxide, iron nitrate, iron sulfate, ferrous oxalate, iron hydroxide, titanium dioxide, copper oxide, tin dioxide, magnesium oxide, zinc oxide, or lithium carbonate; The temperature of the second calcination in a2 is lower than the temperature of the first calcination in a1.

12. According to the preparation method described in claim 11, characterized in that, The temperature of the first calcination treatment in a1 is 860 to 1000 °C, and the time is 5 to 30 h.

13. According to the preparation method described in claim 11, characterized in that, The temperature of the second calcination treatment in a2 is 750 to 950 °C, and the time is 5 to 18 h.

14. According to the preparation method described in claim 11, wherein, The temperature of the third calcination treatment in a3 is 200 to 800 °C, and the time is 1 to 10 h.

15. According to the preparation method described in claim 11, characterized in that, The mass ratio of the secondary sintered cathode material to the coating agent in a3 is 100:(0.01 to 5).

16. The preparation method according to claim 11, wherein The mass ratio of the secondary sintered cathode material to the coating agent in a3 is 100:(0.05 to 2).

17. The preparation method according to claim 11, wherein The coating agent is at least one of magnesium oxide, copper oxide, calcium oxide, manganese dioxide, titanium dioxide, zirconium dioxide, silicon dioxide, boron trioxide, aluminum trioxide, aluminum phosphate, sodium phosphate, ammonium dihydrogen phosphate, boron oxide, boric acid, sodium borate, silicic acid, sodium silicate, or silicon dioxide.

18. The application of the sodium-ion cathode material according to any one of claims 1 to 10 or the sodium-ion cathode material prepared by the preparation method according to any one of claims 11 to 17 in a sodium-ion battery.

19. A positive electrode sheet, comprising a current collector and a positive electrode active material layer provided on at least one side of the current collector, characterized in that, The positive electrode active material layer contains the sodium ion positive electrode material according to any one of claims 1 to 10, or the positive electrode active material layer contains the sodium ion positive electrode material prepared by the preparation method according to any one of claims 11 to 17.

20. A sodium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte located between the positive electrode sheet and the negative electrode sheet, characterized in that, The positive electrode sheet contains the sodium ion positive electrode material according to any one of claims 1 to 10, or the positive electrode sheet contains the sodium ion positive electrode material prepared by the preparation method according to any one of claims 11 to 17.

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