A low internal resistance sodium ion battery positive electrode material and preparation method thereof

Abstract

The present invention discloses a low internal resistance sodium ion battery positive electrode material, the chemical expression of which is Na m Ni a Mn b Ti c X n O2, wherein 0.65≤m≤0.75, 0.25≤a≤0.35, 0.30≤b≤0.60, 0.10≤c≤0.35, 0≤n≤0.1, and X is a combination of one or more elements selected from the metal elements Co, Cu, Fe, Mg, Zr, Sr, Hf, Al, Sn, Nb, and Zn. The present invention dilutes Ni and Mn ions with the Jeng-Taylor effect by doping the bulk phase with elements that do not have the Jeng-Taylor effect, making it less likely for them to undergo a dissolution reaction and migrate to the negative electrode side for deposition, thereby reducing the internal resistance of the battery. In terms of preparation process, it is proposed to pre-sinter the precursor so that the additive elements are initially diffused in the host structure, and then sintered after mixing with a sodium source, thereby effectively improving the electrochemical properties of the material.

Description

Technical Field

[0001] The present invention belongs to the field of chemical power sources, and in particular relates to a low internal resistance sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] Sodium battery layered oxide cathode materials have become the fastest technology route for industrialization due to their high specific capacity and high compatibility with lithium battery cathode material process equipment. P2 phase layered cathode materials have become one of the most promising sodium ion battery cathode materials for large-scale application due to their high rate, good cycle and good air stability. The most typical P2 phase structure sodium ion battery cathode material is P2-Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O2, the space group corresponding to the structure is P63 / mmc, which belongs to the hexagonal system. In the transition metal layer, Ni and Mn are arranged in a honeycomb pattern, that is, each Ni 2+ By 6 Mn 4+ However, during the charge and discharge process, the internal structure of the crystal will change, the (101) peak will shift to a low angle, and the (110) peak will shift to a high angle, which means that in Na + During the process of escape, the c-axis is expanding and the a-axis is shrinking. + The continuous removal of Ni and Mn will be accompanied by the occurrence of phase transition. In order to reduce this phase transition, a common method is to dope the bulk phase with elements that do not have the Jahn-Teller effect, such as Ti, Al, Mg, Zn, Sn and other elements. These elements can dilute the Ni and Mn ions with the Jahn-Teller effect, making it less likely for them to dissolve and migrate to the negative electrode side for deposition, thereby avoiding the increase in the thickness of the fixed electrolyte interphase film on the negative electrode side.

[0003] One problem with sodium-ion cathode materials is their high internal resistance, which makes the battery prone to heating during use. Excessive temperature can reduce the battery's discharge operating voltage, affecting battery performance. Lowering the internal resistance of sodium-ion battery cathode materials reduces heat loss, enabling high-current discharge in low-temperature environments. This also extends discharge time, benefiting battery rate and cycle performance.

[0004] There are reports in the prior art on doping sodium ion battery positive electrode materials with Ti and other metal elements, such as patents CN117199324A, CN117133912A, CN117254012A, and CN117117197A. The above patents adopt a traditional doping method, that is, after the sodium source, precursor and additives are evenly mixed, a high-temperature treatment is performed in one step. The doping elements diffuse into the interior of the crystal under the action of high temperature, and then annealing is performed to complete the doping. However, this one-time high-temperature treatment method makes it difficult to evenly dope elements with large ionic radius into the bulk phase of the positive electrode material, making it difficult to achieve the purpose of reducing the internal resistance of the positive electrode material. The high internal resistance of nickel-manganese-based positive electrode materials for sodium ion batteries hinders their use in sodium ion batteries, especially under low temperature conditions. Summary of the Invention

[0005] To address the aforementioned issues with layered oxide cathode materials, the present invention proposes a low-internal-resistance sodium-ion battery cathode material and its preparation method. This method utilizes a two-stage mixing and calcination process: first, the precursor and additives are mixed and sintered at high temperature; then, the sintered material is mixed with a sodium source and sintered a second time. This double mixing and sintering process allows elements with large radii to fully diffuse within the material, allowing the doping elements to fully exert their effects and reduce the battery's internal resistance.

[0006] To achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A low internal resistance sodium ion battery cathode material, the chemical formula is Na m Ni a Mn b Ti c X n O2, wherein 0.65≤m≤0.75, 0.25≤a≤0.35, 0.30≤b≤0.60, 0.10≤c≤0.35, 0≤n≤0.1, and X is a combination of one or more metal elements selected from Co, Cu, Fe, Mg, Zr, Sr, Hf, Al, Sn, Nb, and Zn.

[0008] Preferably, 0.10≤c≤0.20, 0.01≤n≤0.05, and X is at least one of Fe, Cu, Zn, and Mg. For example, X is Mg, or X is a combination of Fe and Cu, or X is a combination of Fe, Cu, Zn, and Mg.

[0009] Among them, Ti element and one or more doping elements X need to be evenly mixed with the precursor first and then subjected to high-temperature sintering so that they can be fully dissolved into the P2 phase structure. The sintered product containing the additive elements is then evenly mixed with sodium carbonate to obtain a P2 phase structure sodium ion battery positive electrode material.

[0010] A second object of the present invention is to provide a method for preparing the low internal resistance sodium ion battery positive electrode material, comprising the following steps:

[0011] (S1) Primary mixing: TiO2, nickel-manganese precursor and oxide of doping element X are weighed and mixed uniformly;

[0012] (S2) Primary sintering: The mixture obtained in step (S1) is sintered in a muffle furnace and cooled to room temperature to obtain a transition metal oxide precursor Ni containing doping elements. a Mn b TicXnO 1.6-1.7 , where 0.25≤a≤0.35, 0.30≤b≤0.60, 0.10≤c≤0.35, 0≤n≤0.1;

[0013] (S3) secondary mixing: uniformly mixing the transition metal oxide precursor containing the doping element in step (S2) with the sodium source;

[0014] (S4) Secondary sintering: The mixture obtained in step (S3) is sintered in a muffle furnace for secondary sintering, kept warm for 10 h to 20 h, and cooled to room temperature to obtain sodium ion layered oxide Na m Ni a Mn b TicXnO2.

[0015] Furthermore, the sodium source material required for the positive electrode is selected from at least one of sodium oxide, sodium peroxide, sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium oxalate; the nickel-manganese precursor is nickel and / or manganese hydroxide, nickel and / or manganese oxide.

[0016] Furthermore, the oxide of the doping element X is an oxide of Co, Cu, Fe, Mg, Zr, Sr, Hf, Al, Sn, Nb, or Zn, such as CuO, Fe2O3, MgO, or ZnO.

[0017] Furthermore, the amounts of TiO2, nickel-manganese precursor, oxide of doping element X, and sodium source satisfy the chemical formula Na m Ni a Mn b TicXnO2.

[0018] Furthermore, the sintering atmosphere is at least one of oxygen and air, the heating rate is 2-8°C / min, and the cooling rate during cooling is 10-20°C / min.

[0019] Furthermore, in step (S2), the primary sintering temperature is 800-900°C, and the sintering time is 6-10 hours; in step (S4), the primary sintering temperature is 900-1000°C, and the sintering time is 10-20 hours; and the secondary sintering temperature is 50-200°C higher than the primary sintering temperature, and the secondary sintering time is 4-10 hours longer than the primary sintering time.

[0020] The principles of the present invention include:

[0021] (1) Ti doping can significantly reduce the internal resistance of sodium ion batteries. This is because Ti doping can inhibit the (101) peak from shifting to a lower angle, and Ti does not have the Jan-Taylor effect, which can reduce the decomposition and dissolution of Ni and Mn elements, thereby reducing the consumption of active materials by the negative electrode. At the same time, the Ti-O bond energy is larger, which can firmly stabilize the oxygen atoms inside the crystal structure, reduce the release of oxygen during the charge and discharge process, and reduce the occurrence of side reactions.

[0022] (2) Ti doping has a positive effect on reducing the internal resistance of the P2 phase cathode material. However, while reducing the internal resistance, we must also ensure the cycling stability of the material, especially the cycling stability under fast charging conditions. Therefore, in addition to Ti doping, we must also construct a high entropy host structure, Na + While diffusing, the additive elements further diffuse in the host structure, constructing more ion migration tunnels. The configurational entropy of the high-entropy nanoparticles increases with the increase in the number of elements and serves as a driving force for single-phase mixing.

[0023] (3) The present invention adopts a two-stage mixing and sintering process, wherein no carbon source is added during the first mixing and sintering, and a carbon source is added during the second mixing and sintering, so that the doping element can be fully doped into the structure of the P2 phase. The sintered product containing the additive element is then uniformly mixed with sodium carbonate and sintered a second time to obtain a P2 phase structured sodium ion battery positive electrode material, which is beneficial to reducing the internal resistance of the positive electrode material.

[0024] The beneficial effects of the present invention are:

[0025] First, the preparation process of this invention is similar to that of lithium-ion battery cathode materials and can be directly converted to production on lithium-ion battery cathode material production lines. Furthermore, the raw materials used in this method are all common battery-grade raw materials on the market, which are low-cost and help leverage the cost advantages of sodium-ion battery cathode materials.

[0026] 2. The preparation process of the present invention is highly controllable, and the special sintering process is conducive to maximizing the effect of the doping elements, which has a promoting effect on reducing the internal resistance of the positive electrode material.

[0027] 3. The additive of the present invention can not only reduce the internal resistance of the positive electrode material, but also effectively improve the capacity and cycle performance of the battery, providing a new development idea for the research of layered oxide sodium ion battery positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the SEM image of the positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0029] The sodium ion layered oxide positive electrode material containing doping elements of the present invention will be further described below in conjunction with specific examples and the specification. However, it should be understood that the protection scope of the present invention is not limited to the following examples.

[0030] Example 1

[0031] Preparation of Mg and Ti co-doped P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Mg 0.01 O2 layered cathode materials:

[0032] (S1) Weigh 0.68 mol Ni 0.5 Mn 0.5 (OH)2, 0.11 mol MnO2, 0.2 mol TiO2, and 0.01 mol MgO are mixed evenly in a mixer.

[0033] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 2°C / min to 800°C and then kept at this temperature for 8 hours, cooled to room temperature, and ground into powder using a mortar to obtain Ni 0.34 Mn 0.45 Ti 0.2 Mg 0.01 O 1.7 Intermediate product.

[0034] (S3) 0.335 mol of Na2CO3 and the intermediate product are uniformly mixed in a mixer to obtain a secondary mixture.

[0035] (S4) The secondary mixture obtained in step (S3) was placed in a muffle furnace and calcined at a heating rate of 5°C / min to 1000°C, then kept warm for 16 hours, and cooled to room temperature to obtain P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Mg 0.01 O2 layered oxide positive electrode material.

[0036] The obtained P2-Na0.67 Ni 0.34 Mn 0.45 Ti 0.2 Mg 0.01 The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0037] Figure 1 This is the SEM image of the positive electrode material prepared in Example 1.

[0038] Example 2

[0039] Preparation of Fe, Cu, and Ti co-doped P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.002 Cu 0.008 O2 layered cathode materials:

[0040] (S1) Weigh 0.68 mol Ni 0.5 Mn 0.5 (OH)2, 0.11 mol MnO2, 0.2 mol TiO2, 0.008 mol CuO and 0.002 mol Fe2O3 were mixed uniformly in a mixer.

[0041] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 2°C / min to 900°C and then kept at this temperature for 6 hours, cooled to room temperature, and ground into powder using a mortar to obtain Fe and Cu co-doped Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.002 Cu 0.00 8O 1.7 Intermediate product.

[0042] (S3) Weigh 0.335 mol of the above intermediate product Na2CO3 and mix it evenly in a mixer to obtain a secondary mixture.

[0043] (S4) The secondary mixture obtained in step (S3) is placed in a muffle furnace and calcined at a heating rate of 2°C / min to 1000°C, then kept at this temperature for 16 hours, and cooled to room temperature to obtain Fe and Cu co-doped P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.002 Cu 0.008O2 layered oxide positive electrode material.

[0044] The obtained P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.002 Cu 0.008 The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0045] Example 3

[0046] Preparation of P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.002 Cu 0.003 Zn 0.003 Mg 0.002 O2 layered cathode materials:

[0047] (S1) Weigh 0.68 mol Ni 0.5 Mn 0.5 (OH)2, 0.11 mol MnO2, 0.2 mol TiO2, 0.003 mol CuO and 0.002 mol Fe2O3, 0.003 mol ZnO, 0.002 mol MgO are mixed uniformly in a mixer.

[0048] (S2) calcining the powder obtained in step (S1) in a muffle furnace at a heating rate of 2°C / min to 890°C and then keeping the temperature for 8 hours, cooling to room temperature, and grinding the powder in a mortar to obtain Fe, Cu, Mg, Zn, and Ti co-doped Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.002 Cu 0.003 Zn 0.003 Mg 0.002 O 1.7 High entropy oxide.

[0049] (S3) Weigh 0.335 mol of the above intermediate product Na2CO3 and mix it evenly in a mixer to obtain a secondary mixture.

[0050] (S4) placing the secondary mixture obtained in step (S3) in a muffle furnace for calcination at a heating rate of 2°C / min, heating to 1000°C and then keeping the temperature for 15 hours, and cooling to room temperature to obtain Fe, Cu, Mg, Zn, and Ti co-doped P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.02 Cu 0.08 O2 layered oxide positive electrode material.

[0051] The obtained P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Fe 0.02 Cu 0.03 Zn 0.03 Mg 0.02 The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0052] Example 4

[0053] Preparation of P2-Na 0.67 Ni 0.33 Mn 0.33 Ti 0.33 O2 layered cathode materials:

[0054] (S1) Weigh 0.66 mol Ni 0.5 Mn 0.5 (OH)2 and 0.33 mol TiO2 are mixed evenly in a mixer.

[0055] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 2°C / min. After heating to 800°C and holding for 10 hours, the powder was cooled to room temperature and ground into powder using a mortar to obtain Ni 0.33 Mn 0.33 Ti 0.33 O 1.7 .

[0056] (S3) Weigh 0.335 mol of the above intermediate product Na2CO3 and mix it evenly in a mixer to obtain a secondary mixture.

[0057] (S4) The secondary mixture obtained in step (S3) was placed in a muffle furnace and calcined at a heating rate of 2°C / min to 900°C, then kept warm for 18 hours, and cooled to room temperature to obtain P2-Na 0.67 Ni0.33 Mn 0.33 Ti 0.33 O2 layered cathode material.

[0058] The obtained P2-Na 0.67 Ni 0.33 Mn 0.33 Ti 0.33 The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0059] Example 5

[0060] Preparation of P2-Na 0.67 Ni 0.33 Mn 0.52 Ti 0.15 O2 layered cathode materials:

[0061] (S1) Weigh 0.66 mol Ni 0.5 Mn 0.5 (OH)2, 0.19 mol MnO2 and 0.15 mol TiO2 were mixed evenly in a mixer.

[0062] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 2°C / min to 850°C and then kept at this temperature for 8 hours, cooled to room temperature, and ground into powder using a mortar to obtain Ni 0.33 Mn 0.52 Ti 0.15 O 1.7 Intermediate product.

[0063] (S3) 0.335 mol of Na2CO3 and the intermediate product are uniformly mixed in a mixer to obtain a secondary mixture.

[0064] (S4) The secondary mixture obtained in step (S3) was placed in a muffle furnace and calcined at a heating rate of 5°C / min to 1000°C, then kept warm for 16 hours, and cooled to room temperature to obtain P2-Na 0.67 Ni 0.33 Mn 0.52 Ti 0.15 O2 layered oxide positive electrode material.

[0065] The obtained P2-Na 0.67 Ni 0.33 Mn 0.52 Ti 0.15The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0066] Example 6

[0067] Preparation of P2-Na 0.67 Ni 0.30 Mn 0.52 Ti 0.15 Cu 0.03 O2 layered cathode materials:

[0068] (S1) Weigh 0.60 mol Ni0.5Mn0.5(OH)2, 0.22 mol MnO2, 0.15 mol TiO2, and 0.03 mol CuO in a mixer and mix them evenly.

[0069] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 5°C / min. After heating to 900°C, the mixture was kept warm for 13 hours, cooled to room temperature, and ground into powder using a mortar to obtain a Ni0.33Mn0.52Ti0.15O1.7 intermediate product.

[0070] (S3) 0.335 mol of Na2CO3 and the intermediate product are uniformly mixed in a mixer to obtain a secondary mixture.

[0071] (S4) The secondary mixture obtained in step (S3) was placed in a muffle furnace and calcined at a heating rate of 5°C / min to 1000°C, then kept warm for 16 hours, and cooled to room temperature to obtain P2-Na 0.67 Ni 0.30 Mn 0.52 Ti 0.15 Cu 0.03 O2 layered oxide positive electrode material.

[0072] The obtained P2-Na 0.67 Ni 0.30 Mn 0.52 Ti 0.15 Cu 0.03 The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0073] Example 7

[0074] Preparation of P2-Na 0.67 Ni0.28 Mn 0.52 Ti 0.15 Cu 0.05 O2-like positive electrode material:

[0075] The operation steps are the same as those in Example 6, except that 0.6 mol Ni 0.5 Mn 0.5 (OH)2, 0.22 mol MnO2, 0.03 mol CuO were changed to 0.56 mol Ni 0.5 Mn 0.5 (OH)2, 0.24mol MnO2, 0.05mol CuO.

[0076] Example 8

[0077] Preparation of P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Zn 0.01 O2 layered cathode materials:

[0078] (S1) Weigh 0.68 mol Ni 0.5 Mn 0.5 (OH)2, 0.11 mol MnO2, 0.2 mol TiO2, and 0.01 mol ZnO are mixed evenly in a mixer.

[0079] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 2°C / min to 800°C, then kept at this temperature for 9 hours and cooled to room temperature to obtain Ni 0.34 Mn 0.45 Ti 0.2 Zn 0.01 O 1.7 Intermediate product.

[0080] (S3) Weigh 0.335 mol of Na2CO3 and the above intermediate product and mix them evenly in a mixer.

[0081] (S4) The powder obtained in step (S3) was placed in a muffle furnace and calcined at a heating rate of 2°C / min to 1000°C, then kept at this temperature for 15 hours and cooled to room temperature to obtain P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Zn 0.01 O2 layered oxide positive electrode material.

[0082] The obtained P2-Na 0.67 Ni 0.34 Mn 0.45 Ti0.2 Zn 0.01 The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0083] Example 9

[0084] Preparation of P2-Na 0.67 Ni 0.34 Mn 0.52 Ti 0.15 Zn 0.005 Mg 0.005 O2 layered cathode materials:

[0085] (S1) Weigh 0.335mol Na2CO3 and 0.68mol Ni 0.5 Mn 0.5 (OH)2, 0.18 mol MnO2, 0.15 mol TiO2, and 0.01 mol ZnO are mixed evenly in a mixer.

[0086] (S2) The powder obtained in step (S1) was placed in a muffle furnace and calcined at a heating rate of 5°C / min to 800°C, then kept at this temperature for 10 hours and cooled to room temperature to obtain Ni 0.34 Mn 0.52 Ti 0.15 Zn 0.005 Mg 0.005 O 1.7 Intermediate product.

[0087] (S3) Weigh 0.335 mol of Na2CO3 and the above intermediate product and mix them evenly in a mixer.

[0088] (S4) The powder obtained in step (S3) was placed in a muffle furnace and calcined at a heating rate of 5°C / min to 1000°C, then kept at this temperature for 15 hours and cooled to room temperature to obtain P2-Na 0.67 Ni 0.34 Mn 0.52 Ti 0.15 Zn 0.005 Mg 0.005 O2 layered oxide positive electrode material.

[0089] The obtained P2-Na 0.67 Ni 0.34 Mn 0.52 Ti 0.15 Zn 0.005 Mg 0.005The O2 layered oxide positive electrode material, the conductive additive SP, and the binder PVDF were mixed and dissolved in NMP in a mass ratio of 90:5:5. After stirring, a uniform slurry was obtained. The slurry was then evenly coated on the surface of the aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the required electrode sheet.

[0090] Comparative Example 1

[0091] Preparation of P2-Na 0.67 Ni 0.34 Mn 0.45 Ti 0.2 Mg 0.01 O2 layered cathode material, weigh 0.335 mol Na2CO3, 0.68 mol Ni 0.5 Mn 0.5 (OH)2, 0.11 mol MnO2, 0.2 mol TiO2, and 0.01 mol MgO were ground and mixed evenly in a mixer, and then placed in a muffle furnace for calcination at a heating rate of 5°C / min. After heating to 1000°C, the mixture was kept warm for 20 hours, cooled to room temperature, and then transferred to a drying cabinet for use.

[0092] The obtained positive electrode material, conductive additive SP, and binder were mixed in a mass ratio of 90:5:5, dissolved in NMP and stirred to obtain a slurry, and then the slurry was evenly coated on the surface of aluminum foil with a 200 μm scraper, dried, and sliced ​​to obtain the desired positive electrode sheet.

[0093] That is, compared with Example 1, the raw materials are the same, and the difference of Comparative Example 1 is that the two-stage mixing and sintering process is replaced by a conventional mixing and calcining process.

[0094] Comparative Example 2

[0095] Preparation of P2-Na 0.67 Ni 0.33 Mn 0.33 Ti 0.33 O2 layered cathode material, weigh 0.335 mol Na2CO3, 0.66 molNi 0.5 Mn 0.5 (OH)2 and 0.33 mol TiO2 were ground and mixed evenly in a mixer, and then placed in a muffle furnace for calcination at a heating rate of 5°C / min. After heating to 1000°C, the mixture was kept warm for 20 hours, cooled to room temperature, and then transferred to a drying cabinet for use.

[0096] The obtained positive electrode material, conductive additive SP, and binder were mixed in a mass ratio of 90:5:5, dissolved in NMP and stirred to obtain a slurry, and then the slurry was evenly coated on the surface of aluminum foil with a 200 μm scraper, dried, and sliced ​​to obtain the desired positive electrode sheet.

[0097] That is, compared with Example 4, the raw materials are the same, and the difference of Comparative Example 2 is that the two-stage mixing and sintering process is replaced by a conventional mixing and calcining process.

[0098] Application example: Electrochemical performance test:

[0099] Electrochemical performance test: The pole pieces obtained in Examples 1-11 and Comparative Example 1 were used as positive electrodes, glass fiber as diaphragm, and graphite as negative electrodes to assemble button batteries. Test voltage range 2.0-4.1V, 0.2C discharge test, 50% SOC-1.0C internal resistance test: The battery cell was discharged at a rate of 1C. The battery cell was then fully charged with constant current and constant voltage, left for 1 hour to restore the electrochemical and thermal equilibrium state, and then discharged at a constant current of 1C to 50% SOC, left for 1 hour, and the internal resistance at 50% SOC was recorded. The following tests were all tested at -10°C. The electrochemical properties of the corresponding soft-pack batteries of the embodiments of the present invention and the comparative example materials were tested, and the results are shown in Table 1:

[0100] Table 1 Electrochemical performance

[0101]

[0102] The test results for the half-cells of various examples in Table 1 show that after doping and process modification of the layered cathode material, the first-cycle discharge capacity of the battery is higher than that of the comparative example, and the direct current internal resistance (DCR) is significantly reduced. However, it is worth noting that the type and amount of doping metal ions must be appropriate. A high Ti doping level increases the DCR, while a low doping level has little effect on the capacity improvement.

[0103] The present invention provides a low internal resistance sodium ion battery positive electrode material and a preparation method thereof. The preparation process is simple and can effectively improve the electrochemical performance of layered oxide positive electrode materials. It is understandable that in each embodiment of the present invention, although the present invention is described in detail in combination with specific electrolytes, separators, current collectors, active materials, binders, conductive additives, etc., the above is only to meet legal requirements and illustrate the composition of sodium ion batteries. The present invention is not limited to the given embodiments. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention using the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the scope of patent protection of the present invention.

Claims

1. A method for preparing a low internal resistance sodium ion battery positive electrode material, characterized in that: The following steps are involved: (S1) Primary mixing: TiO2, nickel-manganese precursor and oxide of doping element X are weighed and mixed uniformly; (S2) Primary sintering: The mixture obtained in step (S1) is sintered in a muffle furnace and cooled to room temperature to obtain a transition metal oxide precursor Ni containing doping elements. a Mn b TicXnO 1.6-1.7 , where 0.25≤a≤0.35, 0.30≤b≤0.60, 0.10≤c≤0.20, 0.01≤n≤0.05; (S3) secondary mixing: uniformly mixing the transition metal oxide precursor containing the doping element in step (S2) with the sodium source; (S4) secondary sintering: the mixture obtained in step (S3) is sintered in a muffle furnace for secondary sintering, kept warm for 10 h to 20 h, and cooled to room temperature to obtain a sodium ion layered oxide with low internal resistance as a positive electrode material for sodium ion batteries; The primary sintering temperature is 800-900°C, and the sintering time is 6-10 hours. In step (S4), the secondary sintering temperature is 1000°C, and the sintering time is 10-20 hours. The secondary sintering time is 4-10 hours longer than the primary sintering time. The chemical expression of the low internal resistance sodium ion battery positive electrode material is Na m Ni a Mn b Ti c X n O2, wherein 0.65≤m≤0.75, 0.25≤a≤0.35, 0.30≤b≤0.60, 0.10≤c≤0.20, 0.01≤n≤0.05, and X is a combination of Fe, Cu, Zn, and Mg.

2. The preparation method according to claim 1, characterized in that The oxide of the doping element X is a combination of CuO, Fe2O3, MgO, and ZnO.

3. The preparation method according to claim 1, characterized in that The amount of TiO2, nickel-manganese precursor, oxide of doping element X, and sodium source satisfies the chemical formula Na m Ni a Mn b Ti c X n O2.

4. The preparation method according to claim 1, characterized in that: The sintering atmosphere is at least one of oxygen and air, the heating rate is 2-8°C / min, and the cooling rate during cooling is 10-20°C / min.

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