Sodium-lithium dual-ion positive electrode material, positive electrode plate and sodium-ion battery

Abstract

The application discloses a sodium-lithium dual-ion positive electrode material, which has a three-layer heterostructure; a core layer is in a spinel structure; a middle layer is in a two-dimensional layered structure; and a surface layer is in a three-dimensional tunnel structure; wherein the two-dimensional layered structure of the middle layer comprises [Na x Li 1‑x ]MnO2, and 0.6<=x<=0.9. The application further discloses a preparation method of the sodium-lithium dual-ion positive electrode material, a positive electrode sheet and a sodium-ion battery. The sodium-lithium dual-ion positive electrode material has ion exchange between the core layer material LiMn2O4 and the middle layer material [Na x Li 1‑x ]MnO2, and the two materials have a synergistic effect to stabilize the structures of the two materials; the surface layer Na 0.44 MnO2 is grown on the surface of the middle layer, so that the overall structure of the positive electrode material is more stable; compared with a traditional sodium-based layered transition metal oxide positive electrode material, the sodium-ion battery adopting the sodium-lithium dual-ion positive electrode material has higher capacity and better cycle stability.

Description

Technical Field

[0001] This invention relates to the field of new energy battery technology, and in particular to a sodium-lithium dual-ion cathode material, cathode sheet, and sodium-ion battery. Background Technology

[0002] In sodium-ion batteries, developing suitable electrode materials to achieve high performance is becoming increasingly important. Although electrochemical performance can be improved to some extent by adjusting the morphology and structure of single-phase materials, simultaneously achieving high specific capacity, cycle stability, and superior rate performance of single-phase electrode materials remains a challenging task.

[0003] Heterogeneous structures refer to structures formed by two or more different materials through layering, lattice, or other arrangements. They are the integration of two or more different phases sharing a common interface, resulting in unique chemical and physical properties at the interface. Local distortion of the electronic structure generates an electric field, which can activate new sodium ion storage sites and accelerate ion and electron transport. Microstrain generated by chemical-mechanical coupling and interfacial bonding can enhance the mechanical integrity of fragile electrode materials.

[0004] In current sodium-ion battery technology, various cathode materials generally employ layered transition metal oxides, which possess higher energy density and abundant transition metal elements. Layered heterostructures overcome the shortcomings of single-phase structures by utilizing the synergistic effect of P-type and O-type (P2, P3, O3) structures, combined with a three-dimensional spinel-like surface layer with high ionic conductivity. Here, P2 refers to the P2 phase, where P stands for prism, and 2 indicates that the minimum repeating period of the close-packed oxygen atoms is 2. P-phase Na x Na in MO2 + It occupies the triangular prism interstitial positions between the MO6 layers. O3 refers to the O3 phase, where O stands for octahedral and 3 indicates that the minimum repeating period of the close-packed oxygen atoms is 3. O phase Na x Na in MO2 + It occupies the octahedral gap position between the MO6 interlayers.

[0005] For cathode materials in sodium-ion batteries, doping a small amount of lithium into sodium-based transition metal oxides is a cost-effective modification strategy. However, technologies that use heterostructures combining lithium-based and sodium-based transition metal oxides as cathode materials for sodium-ion batteries are currently rare.

[0006] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the Invention

[0007] The present application aims at the deficiencies of the prior art, and provides a sodium-lithium dual-ion positive electrode material to improve the capacity and cycle stability of a sodium-ion battery.

[0008] To achieve the above-mentioned object, the present application adopts the following technical solutions.

[0009] A sodium-lithium dual-ion positive electrode material, the structure of the sodium-lithium dual-ion positive electrode material is a three-layer heterostructure; the core layer is a spinel structure; the middle layer is a two-dimensional layered structure; and the surface layer is a three-dimensional tunnel structure; the middle layer of the two-dimensional layered structure comprises active material with a chemical formula of [Na x Li 1-x ]MnO2, wherein 0.6<=x<=0.9.

[0010] The heterostructure refers to a structure composed of two or more different materials through a layered, lattice or other arrangement.

[0011] In some embodiments, the core layer of the spinel structure in the sodium-lithium dual-ion positive electrode material comprises active material with a chemical formula of LiMn2O4; and the surface layer of the three-dimensional tunnel structure comprises active material with a chemical formula of Na 0.44 MnO2.

[0012] In some embodiments, the thickness ratio H1:H2:H3 of the core layer thickness H1, the middle layer thickness H2 and the surface layer thickness H3 of the sodium-lithium dual-ion positive electrode material is 1-4:5-6:1-2.

[0013] In some embodiments, the thickness ratio H1:H2:H3 of the sodium-lithium dual-ion positive electrode material is 3:5:2.

[0014] In the sodium-lithium dual-ion positive electrode material provided by the present application, the middle layer is a sodium ion storage layer and also the main site of ion exchange, and thus needs the most active material, so the middle layer thickness H2 is the thickest. The outer layer is the thinnest because the surface layer is a three-dimensional tunnel structure that can provide more ion channels, but the sodium ion intercalation and deintercalation is less and the capacity provided is extremely small, so the surface layer is the thinnest. The thin surface layer can avoid the loss of capacity per unit mass.

[0015] In some embodiments, the particle size D1 of the sodium-lithium dual-ion positive electrode material ranges from 5 to 25 microns.

[0016] The particle size of the sodium-lithium dual-ion positive electrode material provided by the present application needs to be controlled within the range of 5-25 microns. If the particle size exceeds 25 microns, the wettability of the electrolyte will deteriorate; and if the particle size is less than 5 microns, the particle processing difficulty of the sodium-lithium dual-ion positive electrode material will increase, the particle processing cost will increase, and the compaction density and capacity will also decrease.

[0017] In some embodiments, the space group of the core layer spinel structure of the sodium-lithium dual-ion positive electrode material is Fd-3m, PDF # 35-0782. The space group of the two-dimensional layered structure of the intermediate layer is P63 / mmc, PDF # 54-0894. The space group of the three-dimensional tunnel structure of the surface layer is Pbam, PDF # 27-0750.

[0018] The purpose of the present application is also to provide a preparation method of a sodium-lithium dual-ion positive electrode material, comprising the following steps:

[0019] Step S1: mixing and reacting the first manganese source solution and the first lithium source solution to obtain a precipitate; the precipitate is subjected to secondary high-temperature sintering to obtain a first intermediate product: a core layer material LiMn2O4;

[0020] Step S2: dispersing the first intermediate product in ammonia water to obtain a first mixture; adding a second lithium source solution, a second manganese source solution, and a first sodium source solution to the first mixture to form a second mixture; the second mixture is reacted under stirring conditions to obtain a second intermediate product: the core layer grows a layer of intermediate layer material [Na x Li 1-x ]MnO2, wherein, 0.6≤x≤0.9.

[0021] Step S3: dispersing the second intermediate product in deionized water to obtain a third mixture; adding a third manganese source solution and a second sodium source solution to the third mixture to form a fourth mixture, and the fourth mixture is reacted under stirring conditions to obtain a third intermediate product: the intermediate layer grows a layer of surface layer material Na 0.44 MnO2;

[0022] Step S4: the third intermediate product is subjected to secondary high-temperature sintering to obtain a sodium-lithium dual-ion positive electrode material with a three-layer heterostructure.

[0023] In some embodiments, the first manganese source solution is Mn(CH3COO)2 solution A; the first lithium source solution is LiOH solution B1;

[0024] The second lithium source solution is LiOH solution B2; the second manganese source solution is Mn(NO3)2 solution C1; the first sodium source solution is NaOH solution D1;

[0025] The third manganese source solution is Mn(NO3)2 solution C2; the second sodium source solution is NaOH solution D2.

[0026] In some embodiments, the concentration ratio of the Mn(CH3COO)2 solution A and the LiOH solution B1 in step S1 is 2-3:1; the concentration ratio of the LiOH solution B2, the Mn(NO3)2 solution C1, and the NaOH solution D1 in step S2 is 0.1-0.4:1:0.6-0.9; and the concentration ratio of the Mn(NO3)2 solution C2 and the NaOH solution D2 in step S3 is 2-3:1.

[0027] In some embodiments, the Mn(CH3COO)2 solution A and the LiOH solution B1 in step S1 are reacted at a stirring speed of 600-1200 rpm for 5-20 hours to obtain the precipitate.

[0028] The secondary high-temperature sintering of the precipitate is specifically sintering the precipitate in an environment at 350-450℃ for 1-3 hours and then sintering the precipitate in an environment at 750-950℃ for 8-12 hours.

[0029] In some embodiments, the LiOH solution B2, the Mn(NO3)2 solution C1, and the NaOH solution D1 in step S2 are added at a constant flow rate by a peristaltic pump.

[0030] The second mixture in step S2 is reacted at a stirring speed of 1200-1500 rpm for 10-18 hours to obtain the second intermediate product.

[0031] In some embodiments, step S2 further comprises controlling the pH value of the second mixture to be between 10 and 13.

[0032] In some embodiments, the fourth mixture in step S3 is reacted at a stirring speed of 300-600 rpm for 1-4 hours to obtain the third intermediate product.

[0033] The secondary high-temperature sintering of the third intermediate product in step S4 is specifically sintering the third intermediate product in an environment at 400-500℃ for 4-8 hours and then sintering the third intermediate product in an environment at 850-1200℃ for 2-14 hours.

[0034] In the preparation method of the sodium-lithium dual-ion positive electrode material, the thickness of each layer of material is controlled by controlling the precipitation reaction time when each layer of material is formed.

[0035] In the preparation method of the sodium-lithium dual-ion positive electrode material, the particle size of the sodium-lithium dual-ion positive electrode material is controlled by controlling the sintering temperature and sintering time of the third intermediate product in the secondary high-temperature sintering process. Increasing the sintering temperature is beneficial to mass transfer such as solid-phase diffusion, but too high a temperature will promote the secondary crystallization of the positive electrode material, which will deteriorate the performance of the positive electrode material. The low-temperature stage of sintering is mainly surface diffusion, and the high-temperature stage is mainly volume diffusion. Too long sintering time at the low-temperature stage is not conducive to the densification of the positive electrode material, which will deteriorate the performance of the positive electrode material, so the high-temperature short-time sintering method is usually used at the low-temperature stage to improve the density of the positive electrode material.

[0036] The application also aims to provide a positive electrode sheet, which comprises a current collector and a positive electrode paste coated on the current collector; the positive electrode paste comprises the sodium-lithium dual-ion positive electrode material described above.

[0037] The application also aims to provide a sodium-ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator interposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the positive electrode sheet is the positive electrode sheet described above.

[0038] Compared with the prior art, the application has the following beneficial effects:

[0039] The sodium-lithium dual-ion positive electrode material provided by the application has a three-layer heterostructure, and sodium-lithium dual ions can exchange between the core layer material LiMn2O4 and the intermediate layer material [Na x Li 1-x ]MnO2, and the two materials have a synergistic effect and can stabilize the structure of the two materials; the surface layer Na 0.44 MnO2 grows on the surface of the intermediate layer, so that the overall structure of the sodium-lithium dual-ion positive electrode material is more stable. Compared with the positive electrode material with a heterostructure of a traditional sodium-based layered transition metal oxide, the sodium-ion battery provided by the application has a three-layer heterostructure and has higher capacity and better cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The XRD pattern of the sodium-lithium dual-ion positive electrode material of Example 5.

[0041] The implementation, functional features and advantages of the application will be further described with reference to the embodiments and the accompanying drawings.

[0042] Reference Figure 1 , Figure 1 The XRD pattern of the sodium-lithium dual-ion positive electrode material prepared in Example 5, Figure 1The 002 main peak between 15-17° indicates that the sodium lithium dual-ion positive electrode material prepared in Example 5 takes the P2 phase interlayer as the main phase. The out peak position of the XRD diagram indicates that the structure of the sodium lithium dual-ion positive electrode material prepared in Example 5 is a three-layer heterostructure. Among them, the space group of the core layer spinel structure is Fd-3m, PDF # 35-0782. The space group of the two-dimensional layered structure of the intermediate layer is P63 / mmc, PDF # 54-0894. The space group of the three-dimensional tunnel structure of the surface layer is Pbam, PDF # 27-0750. DETAILED DESCRIPTION

[0043] In order to make the technical solutions and advantages of the present application clearer, the following will combine specific embodiments to further describe the present application and its beneficial effects, but the embodiments of the present application are not limited thereto.

[0044] The specific preparation method of the sodium lithium dual-ion positive electrode material provided by the present application is as follows:

[0045] Step S1: The first manganese source solution and the first lithium source solution are mixed according to a concentration ratio of 2-3:1, and after mixing, the stirring speed v1 is 600-1200 rpm and the reaction time t1 is 5-20 hours to obtain the precipitate; the precipitate is sintered in a T1 of 350-450℃ environment for t2 of 1-3 hours, and then sintered in a T2 of 750-950℃ environment for t3 of 7-12 hours to obtain the first intermediate product: the core layer material LiMn2O4.

[0046] Step S2: The first intermediate product is dispersed in ammonia water to obtain a first mixture; the second lithium source solution, the second manganese source solution and the first sodium source solution are added to the first mixture at a constant flow rate by a peristaltic pump according to a concentration ratio of 0.1-0.4:1:0.6-0.9 to form a second mixture; the second mixture is reacted for t4 of 10-18 hours under the condition of a stirring speed v2 of 1200-1500 rpm and a pH value of 10-13 to obtain the second intermediate product: the core layer grows a layer of intermediate layer material [Na x Li 1-x ]MnO2.

[0047] Step S3: The second intermediate product is dispersed in deionized water to obtain a third mixture; the third manganese source solution and the second sodium source solution are added to the third mixture according to a concentration ratio of 2-3:1 to form a fourth mixture, and the fourth mixture is reacted for t5 of 1-4 hours under a stirring speed v3 of 300-600 rpm to obtain the third intermediate product: the intermediate layer grows a layer of surface layer material Na 0.44 MnO2;

[0048] Step S4: sintering the third intermediate product in a T3 of 400-500 DEG C for t6 of 4-8 hours, and then sintering in a T4 of 850-1200 DEG C for t7 of 2-14 hours, to obtain a sodium-lithium dual-ion positive electrode material with a three-layer heterostructure.

[0049] The first manganese source solution can be a Mn(CH3COO)2 solution A; the first lithium source solution can be a LiOH solution B1.

[0050] The second lithium source solution can be a LiOH solution B2; the second manganese source solution can be a Mn(NO3)2 solution C1; and the first sodium source solution can be a NaOH solution D1.

[0051] The third manganese source solution can be a Mn(NO3)2 solution C2; and the second sodium source solution can be a NaOH solution D2.

[0052] Example 1:

[0053] Preparation of a sodium-lithium dual-ion positive electrode material

[0054] I. Preparation of reactant solutions

[0055] Manganese acetate Mn(CH3COO)2 was dissolved in deionized water to obtain a Mn(CH3COO)2 solution A.

[0056] Lithium hydroxide LiOH was dissolved in deionized water to obtain a LiOH solution, which was divided into two parts: a LiOH solution B1 and a LiOH solution B2.

[0057] Manganese nitrate Mn(NO3)2 was dissolved in deionized water to obtain a Mn(NO3)2 solution, which was divided into two parts: a Mn(NO3)2 solution C1 and a Mn(NO3)2 solution C2.

[0058] Sodium hydroxide NaOH was dissolved in deionized water to obtain a NaOH solution, which was divided into two parts: a NaOH solution D1 and a NaOH solution D2.

[0059] The concentration ratio of the Mn(CH3COO)2 solution A to the LiOH solution B1 was 2:1.

[0060] The concentration ratio of the LiOH solution B2, the Mn(NO3)2 solution C1, and the NaOH solution D1 was 0.1:1:0.9.

[0061] The concentration ratio of the Mn(NO3)2 solution C2 and the NaOH solution D2 was 2:1.

[0062] II. Preparation of a first intermediate product

[0063] Under the condition of continuous stirring at stirring speed v1 of 800 rpm, the precipitation reaction t1 of 8 hours was carried out by adding the LiOH solution B1 into the Mn(CH3COO)2 solution A, and the precipitate was obtained after the reaction product was centrifuged and dried; the first intermediate product: the core layer material LiMn2O4 was obtained after the precipitate was sintered at T1 of 400 ℃ for t2 of 2 hours and then sintered at T2 of 800 ℃ for t3 of 10 hours.

[0064] III. Preparation of the second intermediate product

[0065] The first intermediate product was uniformly dispersed in ammonia water, and the co-precipitation reaction t4 of 14 hours was carried out by adding the LiOH solution B2, the Mn(NO3)2 solution C1 and the NaOH solution D1 at a constant flow rate through a peristaltic pump under the condition of continuous stirring at stirring speed v2 of 1200 rpm; the pH value of the solution was controlled to be 12±0.1 during the reaction, and the second intermediate product: the intermediate layer material [Na 0.9 Li 0.1 ]MnO2 was obtained after the reaction product was centrifuged.

[0066] IV. Preparation of the sodium-lithium dual-ion positive electrode material

[0067] The second intermediate product was dispersed in deionized water, and the precipitation reaction t5 of 3 hours was carried out by adding the Mn(NO3)2 solution C2 and the NaOH solution D2 under the condition of continuous stirring at stirring speed v3 of 500 rpm; the third intermediate product: the surface layer material Na 0.44 MnO2 was obtained after the intermediate layer material grew a layer of the surface layer material on the surface; the third intermediate product was sintered at T3 of 450 ℃ for t6 of 6 hours and then sintered at T4 of 900 ℃ for t7 of 12 hours, and the sodium-lithium dual-ion positive electrode material with a three-layer heterostructure was obtained.

[0068] V. Preparation of the positive electrode sheet

[0069] After the sodium-lithium dual-ion positive electrode material, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) were fully stirred and uniformly mixed in the N-methyl pyrrolidone solvent system at a mass ratio of 8:1:1, the positive electrode sheet was obtained by coating on the positive electrode current collector Al foil, drying under vacuum at 80 ℃ and cutting.

[0070] VI. Preparation of the electrolyte

[0071] In the glove box, the sodium-ion battery electrolyte was prepared by using NaPF6 as the sodium salt, adding 5% mass percentage of fluoroethylene carbonate (FEC) as the electrolyte solvent at a volume ratio of (EC:PC) of 1:1 and preparing at a concentration of 1 mol / L.

[0072] VII. Preparation of the sodium-ion button cell

[0073] The positive electrode sheet (surface density ~ 2.5 mg / cm 2 ) was used as the positive electrode, sodium metal as the negative electrode, and a PE separator. A 2032 type layered oxide button cell was assembled from bottom to top in the following order: negative electrode shell, spring, stainless steel gasket, sodium sheet, electrolyte, PE separator, electrolyte, positive electrode sheet, and positive electrode shell.

[0074] Examples 2 to 6

[0075] The steps of Example 1 were repeated according to the parameters specified in Table 1 for Examples 2 to 6.

[0076] Table 1 shows some of the process parameters for preparing the sodium-lithium dual-ion positive electrode material in Examples 1 to 6.

[0077]

[0078] The preparation method of the sodium-lithium dual-ion positive electrode material provided by the present application can be used in specific embodiments, and each process condition such as stirring speed, reaction time, sintering temperature, and sintering time can be within the corresponding value range. For example, v1 is within the range of 600-1200 rpm; v2 is within the range of 1200-1500 rpm; v3 is within the range of 300-600 rpm; t1 is within the range of 5-20 hours; t2 is within the range of 1-3 hours; t3 is within the range of 7-12 hours; t4 is within the range of 10-18 hours; t6 is within the range of 4-8 hours; t7 is within the range of 2-14 hours; T1 is within the range of 350℃-450℃; T2 is within the range of 750℃-950℃; T3 is within the range of 400℃-500℃; and T4 is within the range of 850℃-1200℃.

[0079] Comparative Example 1

[0080] The preparation method of Comparative Example 1 was consistent with that of Example 1, except that Comparative Example 1 did not have Step 4 in Example 1, but instead the second intermediate product: the core layer was grown with an intermediate layer of material [Na x Li 1-x ]MnO2 was placed in a high-temperature environment of 450℃ for sintering for 6H, and then placed in a high-temperature environment of 900℃ for sintering for 12H, thereby obtaining the sodium-lithium dual-ion positive electrode material of Comparative Example 1.

[0081] Comparative Example 2

[0082] The preparation method of Example 1 is consistent, except that Comparative Example 2 divides the obtained NaOH solution into three NaOH solutions D1, NaOH solution D2, and NaOH solution D3, wherein the LiOH solution B1 in step two is replaced with NaOH solution D3 to perform the precipitation reaction, the concentration ratio of the Mn(CH3COO)2 solution A to the NaOH solution D3 is 2:1, and finally the core layer material is Na 0.7 MnO2.

[0083] Comparative Example 3

[0084] The preparation method of Comparative Example 2 is consistent, except that Comparative Example 3 adjusts the concentration ratio of the LiOH solution B2, the Mn(NO3)2 solution C1, and the NaOH solution D1 to 0:2:1, and finally the core layer material is Na 0.7 MnO2, the intermediate layer material and the surface layer material are both Na 0.44 MnO2.

[0085] Comparative Example 4

[0086] The difference between Example 1 and Comparative Example 4 is that a traditional single-phase sodium NaCoO2 is sintered into a positive electrode material.

[0087] Experimental method for performance testing:

[0088] (1) XRD test

[0089] The sodium lithium bi-ion positive electrode material prepared in Example 5 is subjected to X-ray diffraction (XRD) test. X-ray diffraction (XRD) is mainly used to study the crystal structure inside the material. Because X-rays have a wavelength similar to the interplanar spacing, and have a certain penetration ability, a beam of X-rays is diffracted when it passes through the crystal, and then the diffraction pattern is analyzed, so that the phase identification and structure analysis can be performed.

[0090] Test working conditions: Cu Kα radiation, working current 250 mA, continuous scanning is adopted, working voltage is 40 kV, scanning range 2θ is 10-80°, scanning speed is 2°·min -1 .

[0091] (2) Gravimetric capacity test

[0092] Five sodium ion button cells in the examples and comparative examples are each charged at a constant current of 0.1C rate to a voltage of 4.5V at room temperature, and then further charged at a constant voltage of 4.5V until the current is less than 0.05C, so that they are in a full charge state of 4.5V. Subsequently, constant current discharge is performed at a rate of 0.1C until the voltage is 2.0V.

[0093] (3) Cycle performance test

[0094] Take 5 of each of the sodium-ion button cells prepared in the examples and comparative examples, and repeat the charging and discharging of the sodium-ion button cells by the following steps, and calculate the cycle capacity retention rate.

[0095] First, in an environment of 25℃, the first charging and discharging is carried out, constant current and constant voltage charging is carried out at a charging current of 1C (i.e. the current value of fully discharging the theoretical capacity within 1h), until the upper limit voltage is 4.5V, then constant current discharging is carried out at a discharging current of 1C, until the final voltage is 2V, and the discharge capacity of the first cycle is recorded; and then 100 cycles of charging and discharging are carried out, and the discharge capacity of the 100th cycle is recorded.

[0096] Cycle capacity retention rate = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) x 100%.

[0097] Performance test data:

[0098] Table 2 is the material composition and performance test results of each layer of the positive electrode material of examples 1-6 and comparative examples 1-3.

[0099]

[0100] Result analysis:

[0101] By comparing examples 1 and comparative examples 1-3, it can be seen that the surface layer material Na 0.44 MnO2 has high stability due to the three-dimensional tunnel phase structure, improves ion migration rate, and at the same time improves the cycle life of the positive electrode material. The intermediate layer material [Na x Li 1-x ]MnO2 (0.6≤x≤0.9) provides capacity as the main structure, and the Li + in the core layer material LiMn2O4 can migrate to the intermediate layer material, and the two have a synergistic effect to stabilize the structure of the two, increase the retention of sodium and lithium ions in the cathode during deep charging, and improve the specific capacity and cycle life of the positive electrode material.

[0102] By comparing examples 1-6, it can be seen that: by controlling the concentration of lithium source, manganese source and sodium source, and controlling the pH of the mixing process, the intermediate layer [Na x Li 1-x ]MnO2 (0.6≤x≤0.9) with different sodium and lithium ratios can be synthesized, so as to select the best concentration ratio and pH. When the concentration ratio of B2:C1:D1 is controlled to be 0.2:1:0.8, and the pH value is controlled to be 12±0.1, the sodium-ion battery can achieve the highest specific capacity and cycle stability.

[0103] In summary, the sodium and lithium ion positive electrode material provided by the present application has a three-layer heterostructure, and the Li+ The intermediate layer material [Na x Li 1-x ]MnO2(0.6≤x≤0.9) migrates, so that the two-dimensional structure of the intermediate layer material [Na x Li 1-x ]MnO2 can be achieved; at the same time, the Na x Li 1-x ion radius of the intermediate layer material [Na + Li + The embedded core layer can effectively avoid the collapse of the structure of the core layer material LiMn2O4. The sodium-lithium double ions exchange in the core layer material LiMn2O4 and the intermediate layer material [Na x Li 1-x ]MnO2, and the two have a synergistic effect, which can stabilize the structure of the two, increase the retention of sodium-lithium double ions in the cathode during deep charging, and thus improve the long cycle life of the positive electrode material. At the same time, the surface layer material Na 0.44 MnO2 with a three-dimensional tunnel structure provides more migration channels for sodium-lithium double ions, thereby improving the migration rate of sodium-lithium double ions; the surface layer Na 0.44 MnO2 grows on the surface of the intermediate layer, making the overall structure of the sodium-lithium double ion positive electrode material more stable, acting as a surface barrier to reduce direct contact between the electrolyte and the intermediate layer, improve the cycle life of the positive electrode material, and improve the electrochemical performance of the sodium-lithium double ion positive electrode material at high voltage. Compared with the positive electrode material with a heterostructure of a sodium-based layered transition metal oxide in Comparative Example 3 and the traditional single-phase sodium electrode material in Comparative Example 4, the sodium ion battery provided by the present application uses a sodium-lithium double ion positive electrode material with a three-layer heterostructure, which has higher capacity and better cycle stability.

[0104] In the case of no contradiction, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples.

[0105] The above only describes some or preferred embodiments of the present application, and the text cannot limit the scope of protection of the present application. Any equivalent structural transformation made by using the content of the present application specification, or direct / indirect application in other related technical fields is included in the scope of protection of the present application.

Claims

1. A sodium-lithium dual-ion positive electrode material, characterized in that, The sodium-lithium dual-ion positive electrode material is a three-layer heterostructure; the core layer is a spinel structure; the intermediate layer is a two-dimensional layered structure; the surface layer is a three-dimensional tunnel structure; the two-dimensional layered structure intermediate layer comprises an active material with a chemical formula of [NaxLi1-x]MnO2, wherein 0.6≤x≤0.9; the spinel structure core layer comprises an active material with a chemical formula of LiMn2O4; the three-dimensional tunnel structure surface layer comprises an active material with a chemical formula of Na0.44MnO2; the space group of the core layer spinel structure is Fd-3m, PDF # 35-0782, the space group of the two-dimensional layered structure of the intermediate layer is P63 / mmc, PDF # 54-0894, and the space group of the three-dimensional tunnel structure of the surface layer is Pbam, PDF # 27-0750.

2. The sodium-lithium-bifluid cathode material of claim 1, wherein, The thickness ratio H1:H2:H3 of the core layer thickness H1, the intermediate layer thickness H2, and the surface layer thickness H3 is 1-4:5-6:1-2.

3. The sodium-lithium-bifluid cathode material of claim 2, wherein, The thickness ratio H1:H2:H3 is 3:5:

2.

4. The sodium-lithium-bifluid cathode material of claim 2, wherein, The particle size D1 of the sodium-lithium dual-ion positive electrode material ranges from 5 μm to 25 μm.

5. A method of preparing a sodium lithium bionic positive electrode material as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: Step S1: mixing a first manganese source solution and a first lithium source solution to obtain a precipitate; and performing secondary high-temperature sintering on the precipitate to obtain a first intermediate product, i.e., a core layer material LiMn2O4; Step S2: dispersing the first intermediate product in ammonia water to obtain a first mixture; adding a second lithium source solution, a second manganese source solution, and a first sodium source solution to the first mixture to form a second mixture; and reacting the second mixture under stirring to obtain a second intermediate product, i.e., the core layer grows a layer of intermediate layer material [NaxLi1-x]MnO2, wherein 0.6≤x≤0.9; Step S3: dispersing the second intermediate product in deionized water to obtain a third mixture; adding a third manganese source solution and a second sodium source solution to the third mixture to form a fourth mixture; and reacting the fourth mixture under stirring to obtain a third intermediate product, i.e., the intermediate layer grows a layer of surface layer material Na0.44MnO2; Step S4: performing secondary high-temperature sintering on the third intermediate product to obtain a three-layer heterostructure sodium-lithium dual-ion positive electrode material.

6. The method for preparing the sodium-lithium dual-ion positive electrode material according to claim 5, wherein the first manganese source solution is a Mn(CH3COO)2 solution A; and the first lithium source solution is a LiOH solution B1. The second lithium source solution is a LiOH solution B2; the second manganese source solution is a Mn(NO3)2 solution C1; and the first sodium source solution is a NaOH solution D1. The third manganese source solution is a Mn(NO3)2 solution C2. The second sodium source solution is a NaOH solution D2.

7. The method for preparing the sodium-lithium dual-ion positive electrode material according to claim 6, wherein the concentration ratio of the Mn(CH3COO)2 solution A and the LiOH solution B1 in step S1 is 2-3:

1. ​ ​ The concentration ratio of the LiOH solution B2, the Mn(NO3)2 solution C1 and the NaOH solution D1 in the step S2 is 0.1-0.4:1:0.6-0.9; The concentration ratio of the Mn(NO3)2 solution C2 and the NaOH solution D2 in the step S3 is 2-3:

1. 8.The preparation method of the sodium-lithium dual-ion positive electrode material according to claim 6, characterized in that, The Mn(CH3COO)2 solution A and the LiOH solution B1 in the step S1 are reacted at a stirring speed of 600-1200 rpm for 5-20 hours to obtain the precipitate; The secondary high-temperature sintering of the precipitate is specifically: sintering the precipitate in an environment of 350-450 ℃ for 1-3 hours, and then sintering the precipitate in an environment of 750-950 ℃ for 7-12 hours. 9.The preparation method of the sodium-lithium dual-ion positive electrode material according to claim 6, characterized in that, The LiOH solution B2, the Mn(NO3)2 solution C1 and the NaOH solution D1 are added by a constant flow rate of a peristaltic pump in the step S2; The second mixture in the step S2 is reacted at a stirring speed of 1200-1500 rpm for 10-18 hours to obtain the second intermediate product.

10. The method for preparing the sodium-lithium dual-ion cathode material according to claim 5, characterized in that, The step S2 further comprises: The pH value of the second mixture is controlled to be between 10 and 13. 11.The preparation method of the sodium-lithium dual-ion positive electrode material according to any one of claims 5 to 10, characterized in that, The fourth mixture in the step S3 is reacted at a stirring speed of 300-600 rpm for 1-4 hours to obtain the third intermediate product; The secondary high-temperature sintering of the third intermediate product in the step S4 is specifically: sintering the third intermediate product in an environment of 400-500 ℃ for 4-8 hours, and then sintering the third intermediate product in an environment of 850-1200 ℃ for 2-14 hours.

12. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises a current collector and a positive electrode slurry coated on the current collector; and the positive electrode slurry comprises the sodium-lithium dual-ion positive electrode material according to any one of claims 1 to 4.

13. A sodium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator interposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, characterized by, The positive electrode sheet is the positive electrode sheet according to claim 12.

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