Preparation method of lithium-sodium dual-ion positive electrode material, lithium-sodium dual-ion positive electrode material and secondary battery

Abstract

The application belongs to the technical field of positive electrode materials, and particularly relates to a preparation method of lithium-sodium dual-ion positive electrode material, the lithium-sodium dual-ion positive electrode material and a secondary battery. x Na y )Ni a Co b M 1‑a‑b O2, wherein 0.15<=x<=0.85, 0.15<=y<=0.85, x+y=1, 0<=a<=1, 0.1<b<=1, M is a doping element, in the lithium-sodium dual-ion positive electrode material, Li + is mainly distributed in the inside, and Na + is mainly distributed in the outside. The positive electrode material can store and release energy by deintercalating lithium ions and sodium ions, and the application can form a gradient distribution in the particles, better exert the advantages of the two, and combine the advantages of high energy density, good structural stability and voltage of lithium ion batteries and the good rate, low temperature and safety performance of sodium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a method for preparing a lithium-sodium dual-ion cathode material, the lithium-sodium dual-ion cathode material, and a secondary battery. Background Technology

[0002] With the booming development of the new energy industry, energy storage devices, represented by lithium-ion batteries, have begun to be widely used in all aspects of social production due to their advantages such as high energy density, high discharge voltage, no memory effect, and lightweight and convenient design. However, the large-scale application of lithium-ion batteries has raised serious concerns about the Earth's lithium resources. The content of lithium resources in the Earth's crust is only 17 ppm, and its distribution is extremely uneven. This makes lithium mining difficult and expensive, and it is also prone to causing regional instability and resource conflicts, just like oil.

[0003] As the only lithium-containing material in lithium-ion batteries, the cathode material's performance essentially determines the battery's properties. Currently, widely used cathode materials generally have high energy densities, resulting in strong activity in the high-delithiation state, which poses a risk of combustion and explosion in lithium-ion batteries. Furthermore, the poor solvation ability of lithium ions leads to rapid capacity decay and poor rate performance in low-temperature environments.

[0004] To address the scarcity of lithium resources and the safety, low-temperature performance, and poor rate capability of lithium-ion batteries, scientists have been proposing new types of ion batteries in recent years to supplement or replace lithium-ion batteries. Among these, the "rocking chair battery," represented by the sodium-ion battery, has attracted considerable attention from researchers. The working principle of a sodium-ion battery is essentially the same as that of a lithium-ion battery, primarily relying on the movement of ions between the positive and negative electrodes to store and release energy. Sodium resources are abundant in the Earth's crust, with a content as high as 23,000 ppm, making it virtually inexhaustible. Furthermore, compared to lithium-ion batteries, sodium ions have stronger migration capabilities after solvation, resulting in excellent low-temperature and rate performance. Sodium ions are also easily deactivated, providing excellent safety. However, due to the large radius, high standard electrode potential, and large atomic mass of sodium ions, the ability of sodium ions to be inserted and extracted in the positive and negative electrode materials is poor, leading to extreme structural instability during cycling. Consequently, sodium-ion batteries have relatively low operating voltage and energy density, and their cycle performance is difficult to meet industrial requirements. These factors severely limit the industrialization potential of sodium-ion batteries.

[0005] Therefore, if the advantages of high energy density, good structural stability and voltage of lithium-ion batteries can be combined with the good rate capability, low temperature and safety performance of sodium-ion batteries to develop a lithium-sodium dual-ion battery cathode material, it can not only solve the problem of resource shortage, but also significantly reduce the cost of lithium-ion batteries and promote the development of the dual-ion battery industry.

[0006] CN107591531A discloses a lithium / sodium dual-ion manganese-based oxide cathode material and its preparation method and application. The preparation method includes the following steps: (1) dispersing a transition metal salt in a solvent to obtain a metal salt solution; (2) dispersing lithium salt and sodium salt in a solvent to obtain a mixed solution I; (3) adding the metal salt solution obtained in step (1) to an oxalic acid solution for reaction to obtain a reaction solution II; (4) dispersing the mixed solution I obtained in step (2) into the reaction solution II obtained in step (3), then freeze-drying and grinding into powder to obtain a precursor powder; (5) calcining the precursor powder obtained in step (4) to obtain the lithium / sodium dual-ion manganese-based oxide cathode material. It leverages the advantages of both lithium-ion and sodium-ion batteries, achieving synergistic effects of dual ions, resulting in good product crystallization and exhibiting excellent electrochemical performance, high specific capacity, and good cycle stability. However, the process methods used in this patent, such as solution reaction and freeze-drying, are characterized by low efficiency and complex processes, making them unsuitable for large-scale production. Meanwhile, since this method does not control the insertion order of lithium and sodium ions, on the one hand, it will induce lithium or sodium ions to react with metal oxides to generate cathode materials, resulting in phase separation and the product being a mixed phase; on the other hand, the main advantages of sodium ions, such as safety performance or strong solvation ability, depend on the surface structure. Sodium ions in the bulk phase not only have difficulty exerting their advantages, but will also hinder the insertion and extraction of lithium ions, affecting the overall electrochemical performance. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, the present invention aims to provide a method for preparing a lithium-sodium dual-ion cathode material, the lithium-sodium dual-ion cathode material itself, and a secondary battery. This invention provides a lithium-sodium dual-ion cathode material that can store and release energy through the insertion and extraction of both lithium and sodium ions. It exhibits high rate performance, low-temperature performance, and safety performance, while also possessing high energy density, good cycle performance, and a high operating voltage. Besides solving the problem of resource scarcity, it can also significantly reduce the cost of lithium-ion batteries.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a lithium-sodium dual-ion cathode material, wherein the chemical formula of the lithium-sodium dual-ion cathode material is (Li x Na y )Ni a Co b M 1-a-bO2, wherein 0.15≤x≤0.85, 0.15≤y≤0.85, x+y=1, 0≤a≤1, 0.1<b≤1, M is a doping element, and in the lithium-sodium dual-ion cathode material, Li + is mainly distributed in the interior, and Na + is mainly distributed in the exterior.

[0010] In the present invention, that Li + is mainly distributed in the interior means: based on the total molar amount of said Li + , the molar proportion of Li + in the interior is greater than 50% and less than 100%, such as 52%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 97%. That Na + is mainly distributed in the exterior means: based on the total molar amount of said Na + , the molar proportion of Na + in the exterior is greater than 50% and less than 100%, such as 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 98%.

[0011] wherein x can be, for example, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.80 or 0.85, y can be, for example, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.80 or 0.85, a can be, for example, 0, 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, and b can be, for example, 0.15, 0.20, 0.25, 0.30, 0.40, 0.45, 0.50, 0.55, 0.60, 0.70, 0.75, 0.80, 0.85, 0.90 or 1.

[0012] In the present invention, in the statement "Li + is mainly distributed in the interior, and Na + is mainly distributed in the exterior", the interior refers to a region close to the center of primary particles of the cathode material, the exterior refers to a region close to the surface of primary particles of the cathode material, and the interior and the exterior are relative concepts.

[0013] In the lithium-sodium dual-ion cathode material of the present invention, sodium ions are mainly distributed on the outside, which can improve the solvation ability of ions and improve the rate performance, low temperature performance and safety performance of the material; lithium ions are mainly distributed on the inside, which can ensure that the material has a high energy density and good cycle stability, and the working voltage is also higher than that of a simple sodium-ion battery.

[0014] Preferably, M is selected from at least one of Mn, Al, Ti, Zr, Mg, W, Sr, or Y.

[0015] Preferably, the lithium-sodium dual-ion cathode material is a layered O3 phase with space group R-3m; as shown in the schematic diagram. Figure 6 As shown, the Li in the lithium-sodium dual-ion cathode material + and Na + All elements are located at position 3a, i.e., the alkali metal layer; Ni, Co, and M elements are all located at position 3b, and are distributed in a disordered manner in the transition metal layer; O element is located at position 6c. Since the material is still the O3 phase, it is no different from the current mainstream layered cathode materials for lithium-ion batteries, and is suitable for large-scale industrial production.

[0016] As a preferred technical solution of the lithium-sodium dual-ion cathode material of the present invention, in the lithium-sodium dual-ion cathode material, Li + and Na + It exhibits a gradient distribution within the alkali metal layer, wherein Li + The concentration of Na gradually decreases from the inside out. + The concentration gradually increases from the inside out. The presence of sodium ions in the alkali metal layer, especially on the surface, can significantly improve the solvation ability of the ions, thereby improving the rate performance and cycle performance of the material. The presence of lithium ions in the alkali metal layer, especially inside, can ensure that the material has a high energy density and good cycle stability, while the operating voltage is also higher than that of a pure sodium-ion battery.

[0017] Preferably, the lithium-sodium dual-ion cathode material is a polycrystalline material with a secondary spherical morphology, or the lithium-sodium dual-ion cathode material is a single-crystal material.

[0018] This invention also provides two methods for preparing the above-mentioned lithium-sodium dual-ion cathode material.

[0019] Secondly, the present invention provides a method for preparing a lithium-sodium dual-ion cathode material, the method comprising the following steps:

[0020] (1) Ni, the precursor of the cathode material a Co b M 1-a-b (OH)2 is mixed with lithium source and sodium source in a certain chemical ratio, wherein 0≤a≤1, 0.1<b≤1, and M is a doping element;

[0021] (2) The mixture from step (1) is sintered at a gradient temperature. The gradient temperature sintering includes sintering at a first temperature and then sintering at a second temperature to obtain a lithium-sodium dual-ion cathode material.

[0022] The lithium-sodium dual-ion cathode material is a polycrystalline material with a secondary spherical morphology.

[0023] This method can be used to prepare the lithium-sodium dual-ion cathode material described in the first aspect. This method allows for precise control of the lithium-ion and sodium-ion insertion sequence and the formation of a gradient distribution within the particles, thus better leveraging the advantages of both. Furthermore, the method is simple, highly compatible with current industrial equipment, and facilitates large-scale production.

[0024] Preferably, the lithium-sodium dual-ion cathode material precursor Ni in step (1) a Co b M 1-a-b (OH)2 was prepared by co-precipitation.

[0025] Preferably, the lithium-sodium dual-ion cathode material precursor Ni in step (1) a Co b M 1-a-b In (OH)2, M is selected from at least one of Mn, Al, Ti, Zr, Mg, W, Sr or Y.

[0026] Preferably, the lithium-sodium dual-ion cathode material precursor Ni in step (1) a Co b M 1-a-b The particle size D50 of (OH)2 is 6 to 16 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm.

[0027] Preferably, the lithium source in step (1) includes at least one of hydrated LiOH or Li2CO3.

[0028] Preferably, the sodium source in step (1) includes at least one of NaOH or Na2CO3.

[0029] Preferably, the chemical ratio in step (1) is a molar ratio of Li∶Na∶(Ni+Co+M)=x∶y∶1.

[0030] Preferably, in step (2), the first temperature is 600 to 800°C, for example, 600°C, 650°C, 700°C, 750°C or 800°C; and the sintering time at the first temperature is 3 to 9 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or 9 hours.

[0031] Preferably, the second temperature is 800-1200℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃, and more preferably 850-1200℃; the sintering time at the second temperature is 5-12h, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0032] Thirdly, the present invention provides a method for preparing a lithium-sodium dual-ion cathode material, the method comprising the following steps:

[0033] (A) Ni, the precursor for cathode materials a Co b M 1-a-b (OH)2 is mixed with sodium source in a certain chemical ratio, wherein 0≤a≤1, 0.1<b≤1, and M is a dopant element;

[0034] (B) The mixture from step (A) is sintered at a first temperature and then crushed to obtain a sodium-containing oxide material.

[0035] (C) The sodium-containing oxide material obtained in step (B) is mixed with the lithium source in a certain chemical ratio, and then sintered at a second temperature to obtain a lithium sodium dual-ion cathode material.

[0036] The lithium-sodium dual-ion cathode material is a single-crystal material.

[0037] The above method is a phase transition method, which can be used to prepare the lithium-sodium dual-ion cathode material described in the first aspect. It can effectively solve the problem of lithium, sodium, and oxygen precipitation on the surface of single-crystal materials under high-temperature calcination and prevent the formation of rock salt phase structure; moreover, the method is simple, highly compatible with current industrial equipment, and convenient for large-scale production.

[0038] Preferably, the lithium-sodium dual-ion cathode material precursor Ni in step (A) a Co b M 1-a-b (OH)2 was prepared by co-precipitation.

[0039] Preferably, the lithium-sodium dual-ion cathode material precursor Ni in step (A) a Co b M 1-a-b In (OH)2, M is selected from at least one of Mn, Al, Ti, Zr, Mg, W, Sr or Y.

[0040] Preferably, the lithium-sodium dual-ion cathode material precursor Ni in step (A) a Cob M 1-a-b The particle size D50 of (OH)2 is 3 to 6 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm.

[0041] Preferably, the sodium source in step (A) includes at least one of NaOH or Na2CO3.

[0042] Preferably, the chemical ratio in step (A) is a molar ratio Na:(Ni+Co+M)=y:1.

[0043] Preferably, in step (B), the first temperature is 900 to 1200°C, such as 900°C, 950°C, 975°C, 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C; and the sintering time at the first temperature is 8 to 12 hours, such as 8 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, or 12 hours.

[0044] Preferably, the sodium-containing oxide material in step (B) has a spinel structure.

[0045] Preferably, the lithium source in step (C) is at least one of hydrated LiOH or Li2CO3.

[0046] Preferably, the chemical ratio in step (C) is a molar ratio of Li:(Ni+Co+M)=x:1.

[0047] Preferably, the second temperature in step (C) is 400-600°C, such as 400°C, 425°C, 450°C, 500°C, 550°C, 575°C, or 600°C; and the sintering time at the second temperature is 6-10 hours, such as 6 hours, 7 hours, 7.5 hours, 8 hours, 9 hours, or 10 hours.

[0048] Fourthly, the present invention provides a secondary battery, wherein the positive electrode of the secondary battery comprises the lithium-sodium dual-ion positive electrode material described in the first aspect. In this secondary battery, lithium ions and sodium ions simultaneously act as active ions, participating in energy storage and release.

[0049] Compared with existing technologies, the present invention has the following beneficial effects:

[0050] 1. This invention provides a lithium-sodium dual-ion cathode material, which exhibits high rate performance, low-temperature performance, and safety performance, while also possessing high energy density, good cycle performance, and a high operating voltage. This reduces the dependence of lithium-ion batteries on lithium resources and significantly lowers the cost of both materials and the battery. Furthermore, this invention can create a gradient distribution within the particles, better leveraging the advantages of both materials.

[0051] 2. Since the lithium-sodium dual-ion cathode material provided by this invention can be in the O3 phase, it is no different from the current mainstream layered cathode materials for lithium-ion batteries, and is suitable for large-scale industrial production.

[0052] 3. The method for preparing polycrystalline lithium-sodium dual-ion cathode material provided by the present invention has the following advantages: it can effectively control the insertion order of lithium ions and sodium ions and form a gradient distribution inside the particles, so as to better leverage the advantages of both. Moreover, the method is simple, highly compatible with current industrial equipment, and easy to mass-produce.

[0053] 4. The method for preparing single-crystal lithium-sodium dual-ion cathode material provided by the present invention has the following advantages: it can effectively solve the problem of lithium, sodium and oxygen precipitation on the surface of single-crystal materials under high-temperature calcination and prevent the formation of rock salt phase structure; moreover, the method is simple, highly compatible with current industrial equipment, and easy to mass-produce. Attached Figure Description

[0054] Figure 1 The image shows the XRD pattern of the lithium-sodium dual-ion cathode material in Example 1 of this invention.

[0055] Figure 2 This is a SEM image of the lithium-sodium dual-ion cathode material in Example 1 of the present invention.

[0056] Figure 3 This is a cross-sectional elemental content line scan of Embodiment 1 of the present invention.

[0057] Figure 4 The image shows the XRD pattern of the lithium-sodium dual-ion cathode material in Example 2 of this invention.

[0058] Figure 5 This is a SEM image of the lithium-sodium dual-ion cathode material in Example 2 of the present invention.

[0059] Figure 6 This is a schematic diagram of the structure of the lithium-sodium dual-ion cathode material in this invention. Detailed Implementation

[0060] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0061] Example 1

[0062] This embodiment provides a polycrystalline lithium-sodium dual-ion cathode material, the preparation of which includes the following steps:

[0063] 1. Take 1 mol of D 50 Ni is a precursor with a diameter of 10 μm. 0.5 Co 0.2 Mn 0.3(OH)2 is mixed with 0.6 mol of LiOH monohydrate and 0.2 mol of Na2CO3;

[0064] 2. The mixture obtained in step 1 is sintered. The sintering regime is as follows: sinter at the first temperature point of 750℃ for 6 hours, and then sinter at the second temperature point of 950℃ for 8 hours.

[0065] 3. After the sintered material in step 2 is allowed to cool naturally, polycrystalline lithium-sodium dual-ion battery cathode material Li can be obtained. 0.6 Na 0.4 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0066] Figure 1 The image shows the XRD pattern of the lithium-sodium dual-ion battery cathode material in Example 1 of this invention. As can be seen from the image, the material has a typical layered O3 phase structure with space group R-3m.

[0067] Figure 2 The image shows a SEM image of the lithium-sodium dual-ion battery cathode material in Example 1 of this invention. As can be seen from the image, its morphology is polycrystalline secondary spherical particles.

[0068] Figure 3 This is a cross-sectional elemental content line scan of Embodiment 1 of the present invention. As can be seen from the figure, Li and Na exhibit a gradient distribution along the radial direction of the spherical particles, with Li gradually decreasing from the inside to the outside and Na gradually increasing from the inside to the outside.

[0069] Example 2

[0070] This embodiment provides a polycrystalline lithium-sodium dual-ion battery cathode material, the preparation of which includes the following steps:

[0071] 1. Take 1 mol of D 50 Ni is a 4μm precursor 0.5 Co 0.2 Mn 0.3 (OH)2 is mixed with 0.2 mol of Na2CO3;

[0072] 2. The mixture obtained in step 1 is sintered. The sintering process is as follows: sinter at 1000℃ for 8 hours at the first temperature point, and then pulverize after natural cooling to room temperature.

[0073] 3. The sodium oxide material from step 2 is mixed with 0.6 mol of LiOH monohydrate, and then sintered at 600℃ for 9 hours at the second temperature point. After natural cooling to room temperature, a single-crystal lithium-sodium dual-ion battery cathode material, Li, is obtained. 0.6 Na 0.4 Ni0.5 Co 0.2 Mn 0.3 O2.

[0074] Figure 4 The image shows the XRD pattern of the lithium-sodium dual-ion battery cathode material in Example 2 of this invention. As can be seen from the image, the material has a typical layered O3 phase structure with space group R-3m.

[0075] Table 1 shows the refined XRD pattern of the positive electrode material of the lithium-sodium dual-ion battery in Example 2 of the present invention. It can be seen that lithium and sodium ions are located at position 3a, transition metal is located at position 3b, and O is located at position 6c.

[0076]

[0077] Bragg R-factor: 1.52%, Rf-factor: 0.78%, χ 2 =6.5

[0078] Figure 5 The image shows a SEM image of the lithium-sodium dual-ion battery cathode material in Example 2 of this invention. As can be seen from the image, its morphology is that of single-crystal particles.

[0079] Example 3

[0080] This embodiment provides a polycrystalline lithium-sodium dual-ion cathode material, the preparation of which includes the following steps:

[0081] 1. Take 1 mol of D 50 Ni is a precursor with a diameter of 10 μm. 0.85 Co 0.12 Al 0.03 (OH)2 is mixed with 0.6 mol of LiOH monohydrate and 0.2 mol of Na2CO3;

[0082] 2. The mixture obtained in step 1 is sintered. The sintering regime is as follows: sinter at the first temperature point of 650℃ for 6 hours, and then sinter at the second temperature point of 850℃ for 8 hours.

[0083] 3. After the sintered material in step 2 is allowed to cool naturally, polycrystalline lithium-sodium dual-ion battery cathode material Li can be obtained. 0.6 Na 0.4 Ni 0.85 Co 0.12 Al 0.03 O2.

[0084] Example 4

[0085] The difference between this embodiment and Embodiment 1 is that the sintering process is sintering at 800°C for 14 hours.

[0086] Example 5

[0087] The difference between this embodiment and Embodiment 1 is that the sintering process is sintering at 950°C for 14 hours.

[0088] Comparative Example 1

[0089] This comparative example provides a polycrystalline lithium-ion battery cathode material, which is prepared by the following steps:

[0090] 1. Take 1 mol of D 50 Ni is a precursor with a diameter of 10 μm. 0.5 Co 0.2 Mn 0.3 (OH)₂ was mixed with 1 mol of LiOH monohydrate;

[0091] 2. The mixture obtained in step 1 is sintered at 890℃ for 10 hours.

[0092] 3. After the sintered material in step 2 is allowed to cool naturally, the polycrystalline lithium-ion battery cathode material LiNi can be obtained. 0.5 Co 0.2 Mn 0.3 O2.

[0093] Comparative Example 2

[0094] This comparative example provides a polycrystalline sodium-ion battery cathode material, which is prepared by the following steps:

[0095] 1. Take 1 mol of D 50 Ni is a precursor with a diameter of 10 μm. 0.5 Co 0.2 Mn 0.3 (OH)2 is mixed with 0.5 mol of Na2CO3;

[0096] 2. The mixture obtained in step 1 is sintered at 950℃ for 10 hours.

[0097] 3. After the sintered material in step 2 is allowed to cool naturally, the polycrystalline sodium-ion battery cathode material NaNi can be obtained. 0.5 Co 0.2 Mn 0.3 O2.

[0098] Comparative Example 3

[0099] This comparative example provides a single-crystal lithium-ion battery cathode material, which is prepared by the following steps:

[0100] 1. Take 1 mol of D 50 Ni is a 4μm precursor 0.5 Co 0.2 Mn0.3 (OH)₂ was mixed with 1 mol of LiOH monohydrate;

[0101] 2. The mixture obtained in step 1 is sintered at 920℃ for 10 hours.

[0102] 3. After the sintered material in step 2 is allowed to cool naturally, the single-crystal lithium-ion battery cathode material LiNi can be obtained. 0.5 Co 0.2 Mn 0.3 O2.

[0103] Comparative Example 4

[0104] This comparative example provides a single-crystal sodium-ion battery cathode material, which is prepared by the following steps:

[0105] 1. Take 1 mol of D 50 Ni is a 4μm precursor 0.5 Co 0.2 Mn 0.3 (OH)2 is mixed with 0.5 mol of Na2CO3;

[0106] 2. The mixture obtained in step 1 is sintered at 990℃ for 10 hours.

[0107] 3. After the sintered material in step 2 is allowed to cool naturally, the monocrystalline sodium-ion battery cathode material NaNi can be obtained. 0.5 Co 0.2 Mn 0.3 O2.

[0108] Comparative Example 5

[0109] The difference between this comparative example and Example 2 is that Na2CO3 in step 1 is replaced with 0.6 mol of LiOH monohydrate, and the sintering regime in step 2 is adjusted to: sintering at 600℃ for 9 h; LiOH monohydrate in step 3 is replaced with 0.2 mol of Na2CO3, and the sintering regime in step 3 is adjusted to: sintering at 1000℃ for 8 h.

[0110] Assemble the battery and test it:

[0111] The positive electrode was prepared using the positive electrode materials prepared in the above embodiments and comparative examples. Specifically, a half-cell was prepared using a 2032 button cell casing. The negative electrode was nickel foam. The ratio of active material to binder and conductive agent in the positive electrode was 95:3:2. The current collector was aluminum foil. Conventional lithium-ion battery electrolytes and separators were used. The cells were then assembled into a half-cell.

[0112] Discharge capacity test: The test temperatures were 25℃ and 0℃, the nominal capacity at 1C was 170mA / g, and the voltage range was 2.75~4.3V. The results are shown in Tables 1 and 2.

[0113] Cyclic performance test: The test temperature was 25℃, the nominal capacity at 1C was 170mA / g, and the voltage range was 2.75~4.3V. The results are shown in Tables 1 and 2.

[0114] Table 2

[0115] 0.2C discharge capacity (mAh / g, 25℃) 158.48 154.23 144.12 172.34 124.61 5C discharge capacity (mAh / g, 25℃) 109.26 100.60 92.73 103.77 92.20 5C / 0.2C retention rate (%, 25℃) 68.94％ 65.23％ 64.34％ 60.21％ 73.99％ Retention rate (%) after 50 cycles, at 25°C and 0.2°C 89.34％ 85.31％ 82.11％ 92.45％ 80.13％ 0.2C discharge capacity (mAh / g, 0℃) 111.30 101.42 89.97 86.58 92.23 Low-temperature capacity retention (%, 25℃ / 0℃) 70.23％ 65.76％ 62.43％ 50.24％ 74.01％

[0116] Table 3

[0117] 0.2C discharge capacity (mAh / g, 25℃) 154.28 184.34 166.11 116.86 142.06 5C discharge capacity (mAh / g, 25℃) 106.81 132.43 95.03 86.92 87.22 5C / 0.2C retention rate (%C at 25℃) 69.23％ 71.84％ 57.21％ 74.38％ 61.40％ Retention rate (%) after 50 cycles, at 25°C and 0.2°C 93.40％ 92.12％ 96.89％ 82.65％ 86.54％ 0.2C discharge capacity (mAh / g, 0℃) 107.15 131.54 77.59 87.88 82.81 Low-temperature capacity retention (%, 25℃ / 0℃) 69.45％ 71.36％ 46.71％ 75.20％ 58.29％

[0118] By comparing the electrochemical performance of the polycrystalline lithium-sodium dual-ion cathode material in Example 1 with the polycrystalline lithium-ion battery cathode material in Comparative Example 1 and the polycrystalline sodium-ion battery cathode material in Comparative Example 2, it can be seen that although the discharge capacity of Example 1 is slightly lower than that of Comparative Example 1, its low-temperature and rate performance is significantly improved. The discharge capacity of Example 1 is higher than that of Comparative Example 2, and its cycle performance is significantly improved. This shows that the lithium-sodium dual-ion battery cathode material has the advantages of both lithium-ion and sodium-ion battery cathode materials, and solves the problems of low temperature, rate, cycle and energy density.

[0119] By comparing the electrochemical performance of the single-crystal lithium-sodium dual-ion battery cathode material in Example 2 with the single-crystal lithium-ion battery cathode material in Comparative Example 3 and the single-crystal sodium-ion battery cathode material in Comparative Example 4, it can be seen that although the discharge capacity of the material in Example 2 is slightly lower than that in Comparative Example 3, its low-temperature and rate performance is significantly improved. The discharge capacity of the material in Example 2 is higher than that in Comparative Example 4, and its cycle performance is significantly improved. This also shows that the lithium-sodium dual-ion battery cathode material has the advantages of both lithium-ion and sodium-ion battery cathode materials, and solves problems such as low temperature, rate, cycle and energy density.

[0120] A comparison of Examples 1 and 4-5 shows that by adjusting the preferred sintering process, the electrochemical performance of the lithium-sodium dual-ion battery cathode material can be improved more effectively.

[0121] The comparison between Example 2 and Comparative Example 5 shows that the electrochemical performance of the lithium-sodium dual-ion battery cathode material can be effectively improved by reasonably controlling the ion insertion sequence.

[0122] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium-sodium dual-ion cathode material, characterized in that, The chemical formula of the lithium-sodium dual-ion cathode material is: , where 0.55≤ x ≤0.7, 0.3≤ y ≤0.45, x + y =1, 0≤ a ≤1, 0.1< b ≤1, M is a doping element, in the lithium-sodium dual-ion cathode material, Li + Mainly distributed inside, Na + Mainly distributed in the external area; Li + and Na + are gradiently distributed in the alkali metal layer, wherein Li + gradually decreases from inside to outside, and Na + gradually increases from inside to outside; with the total mole amount of the Li + as the basis, the mole proportion of the internal Li + is greater than 50% and less than 100%; with the total mole amount of the Na + as the basis, the mole proportion of the external Na + is greater than 50% and less than 100%.

2. The lithium-sodium dual-ion cathode material according to claim 1, characterized in that, M is selected from at least one of Mn, Al, Ti, Zr, Mg, W, Sr, or Y.

3. The lithium-sodium dual-ion cathode material according to claim 1, characterized in that, The lithium-sodium dual-ion cathode material is a layered O3 phase with space group R-3m; Li in the lithium-sodium dual-ion positive electrode material + and Na + are located at 3a positions; Ni, Co and M elements are located at 3b positions and are distributed in the transition metal layer in a disordered distribution form; O elements are located at 6c positions.

4. The lithium-sodium dual-ion cathode material according to claim 1, characterized in that, The lithium-sodium dual-ion cathode material is a polycrystalline material with a secondary spherical morphology, or the lithium-sodium dual-ion cathode material is a single-crystal material.

5. A method for preparing a lithium-sodium dual-ion cathode material according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) Mixing the positive electrode material precursor with a lithium source and a sodium source according to a certain chemical ratio, wherein 0≤a≤1, 0.1<b≤1, and M is a doping element; (2) The mixture from step (1) is sintered at a gradient temperature. The gradient temperature sintering includes sintering at a first temperature and then sintering at a second temperature to obtain a lithium-sodium dual-ion cathode material. The lithium-sodium dual-ion cathode material is a polycrystalline material with a secondary spherical morphology.

6. The preparation method according to claim 5, characterized in that, The lithium-sodium dual-ion cathode material precursor described in step (1) It was prepared by co-precipitation method.

7. The preparation method according to claim 5, characterized in that, The lithium-sodium dual-ion cathode material precursor described in step (1) In this context, M is selected from at least one of Mn, Al, Ti, Zr, Mg, W, Sr, or Y.

8. The preparation method according to claim 5, characterized in that, The lithium-sodium dual-ion cathode material precursor described in step (1) The particle size D50 is 6~16μm.

9. The preparation method according to claim 5, characterized in that, The lithium source in step (1) includes at least one of hydrated LiOH or Li2CO3.

10. The preparation method according to claim 5, characterized in that, The sodium source in step (1) includes at least one of NaOH or Na2CO3.

11. The preparation method according to claim 5, characterized in that, The chemical ratio mentioned in step (1) is the molar ratio Li:Na:(Ni+Co+M)=x:y:

1.

12. The preparation method according to claim 5, characterized in that, Step (2) The first temperature is 600~800℃, and the sintering time at the first temperature is 3~9h.

13. The preparation method according to claim 5, characterized in that, The second temperature is 800~1200℃.

14. The preparation method according to claim 13, characterized in that, The second temperature is 850~1200℃, and the sintering time at the second temperature is 5~12h.

15. A method for preparing a lithium-sodium dual-ion cathode material according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: (A) Cathode material precursor is mixed with a sodium source according to a certain chemical ratio, wherein 0≤a≤1, 0.1<b≤1, and M is a doping element; (B) The mixture from step (A) is sintered at a first temperature and then crushed to obtain a sodium-containing oxide material; (C) The sodium-containing oxide material obtained in step (B) is mixed with the lithium source in a certain chemical ratio, and then sintered at a second temperature to obtain a lithium sodium dual-ion cathode material. The lithium-sodium dual-ion cathode material is a single-crystal material.

16. The preparation method according to claim 15, characterized in that, The lithium-sodium dual-ion cathode material precursor described in step (A) It was prepared by co-precipitation method.

17. The preparation method according to claim 15, characterized in that, The lithium-sodium dual-ion cathode material precursor described in step (A) In this context, M is selected from at least one of Mn, Al, Ti, Zr, Mg, W, Sr, or Y.

18. The preparation method according to claim 15, characterized in that, The lithium-sodium dual-ion cathode material precursor described in step (A) The particle size D50 is 3~6μm.

19. The preparation method according to claim 15, characterized in that, The sodium source in step (A) includes at least one of NaOH or Na2CO3.

20. The preparation method according to claim 15, characterized in that, The chemical ratio mentioned in step (A) is a molar ratio Na:(Ni+Co+M)=y:

1.

21. The preparation method according to claim 15, characterized in that, In step (B), the first temperature is 900~1200℃, and the sintering time at the first temperature is 8~12h.

22. The preparation method according to claim 15, characterized in that, The sodium-containing oxide material in step (B) has a spinel structure.

23. The preparation method according to claim 15, characterized in that, The lithium source in step (C) is at least one of hydrated LiOH or Li2CO3.

24. The preparation method according to claim 15, characterized in that, The chemical ratio in step (C) is a molar ratio of Li:(Ni+Co+M)=x:

1.

25. The preparation method according to claim 15, characterized in that, In step (C), the second temperature is 400~600℃, and the sintering time at the second temperature is 6~10h.

26. A secondary battery, characterized in that, The positive electrode of the secondary battery includes the lithium-sodium dual-ion positive electrode material as described in any one of claims 1-4.

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