Preparation method and application of self-assembled rare earth doped high-nickel cobalt-free positive electrode material

Abstract

The application relates to a preparation method and application of a self-assembled rare earth doped high-nickel cobalt-free positive electrode material, and belongs to the field of lithium ion batteries. The preparation method of the self-assembled rare earth doped high-nickel cobalt-free positive electrode material comprises the following steps: (1) mixing a lithium salt, a nickel salt, a manganese salt, an aqueous solution of a single-layer MXene, a surfactant and water to obtain a dispersion liquid; (2) adding the dispersion liquid into a solution containing a metal ion chelating agent, adjusting the pH value and heating to form a gel; and (3) calcining and annealing under a pure oxygen atmosphere to obtain a rare earth doped LiNi x Mn 1‑x O2 powder. The method improves the problems of cobalt-free positive electrode cation disordering and poor cycle stability in the prior art.

Description

Technical Field

[0001] This application relates to a method for preparing and applying a self-assembled rare-earth-doped high-nickel cobalt-free cathode material, which belongs to the field of lithium-ion batteries. Background Technology

[0002] The cost of cathode materials in lithium-ion batteries accounts for 40% of the total battery cost, posing a major obstacle to their widespread application in new energy vehicles. Against this backdrop, low-cost, high-nickel, cobalt-free cathodes have attracted the attention of companies and researchers. However, current cobalt-free cathodes exhibit lithium oxide residues during charge and discharge processes. + / Ni 2+ The lithium nickel cobalt manganese oxide cathode suffers from severe mixing, poor thermal stability, poor rate performance, susceptibility to multiple phase transitions at high voltages, and poor cycle stability. Studies have shown that ion doping can improve these problems to some extent. However, in traditional solid-state mixing and sintering methods, doped ions tend to form oxides on the surface, resulting in incomplete doping. Therefore, there is an urgent need to develop more reasonable doping methods to achieve cobalt-free lithium nickel cobalt manganese oxide cathodes. Summary of the Invention

[0003] According to one aspect of this application, a method for preparing a self-assembled rare-earth-doped high-nickel cobalt-free cathode material is provided. During the synthesis process, rare-earth-doped MXene two-dimensional material is added as a dopant source. Through the linkage effect of chelating agents and surfactants, the wettability of the two-phase interface is improved, allowing MXene to stably complex the high-nickel cobalt-free precursor. After sintering, ions are better doped into the crystal lattice, improving problems such as cation mixing and poor cycle stability in existing cobalt-free cathode materials.

[0004] The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material includes the following steps:

[0005] (1) A dispersion was obtained by mixing an aqueous solution of lithium salt, nickel salt, manganese salt, monolayer MXene, surfactant, and water;

[0006] (2) Add the dispersion to the solution containing the metal ion chelating agent, adjust the pH, and heat to form a gel;

[0007] (3) Under a pure oxygen atmosphere, calcination and annealing were performed to obtain rare earth-doped LiNi. x Mn 1-x O2 powder;

[0008] The monolayer MXene is doped with rare earth elements.

[0009] Optionally, the rare earth elements are selected from one or more of Y, Sc, Yb, Ce, Pr and Gd.

[0010] Optionally, LiNi x Mn1-x In O2, x ≥ 0.8.

[0011] Optionally, LiNi x Mn 1-x O2 is LiNi 0.9 Mn 0.1 O2.

[0012] Optionally, the monolayer MXene is rare earth element-doped Ti3C2.

[0013] Optionally, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, stearic acid, and sodium hexadecyl sulfate.

[0014] Optionally, the amount of surfactant added is 0.5%-5% of the total mass of the metal salt; the metal salt includes lithium salt, nickel salt and manganese salt.

[0015] Preferably, the amount of surfactant added is 0.5%-2% of the total mass of the metal salt; the metal salt includes lithium salt, nickel salt and manganese salt.

[0016] Optionally, the amount of surfactant added is any one of 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, or 5% of the total mass of the metal salt, or a range between any two of the above; the metal salt includes lithium salt, nickel salt, and manganese salt.

[0017] Optionally, the metal ion chelating agent is ethylenediaminetetraacetic acid and / or citric acid.

[0018] Optionally, the amount of metal ion chelating agent added is 80%-120% of the total mass of the metal salt; preferably, the amount of metal ion chelating agent added is 95%-110% of the total mass of the metal salt; the metal salt includes lithium salt, nickel salt and manganese salt.

[0019] Optionally, the amount of metal ion chelating agent added is any one of 80%, 90%, 95%, 100%, 105%, 110%, or 120% of the total mass of the metal salt, or any value between the two; the metal salt includes lithium salt, nickel salt, and manganese salt.

[0020] Optionally, the amount of monolayer MXene added is 0.5%-5% of the total mass of the metal salt; preferably, the amount of monolayer MXene added is 1%-4% of the total mass of the metal salt; the metal salt includes lithium salt, nickel salt and manganese salt.

[0021] Optionally, the amount of monolayer MXene added is any one of 0.5%, 1%, 2%, 3%, 3.5%, 4%, or 5% of the total mass of the metal salt, or a range between any two of the above; the metal salt includes lithium salt, nickel salt, and manganese salt.

[0022] Optionally, the mass ratio of lithium salt, nickel salt, and manganese salt is (5-10):(10-20):1; preferably, the mass ratio of lithium salt, nickel salt, and manganese salt is (7.5-8.5):(13-16):1.

[0023] Optionally, the calcination is carried out in two stages; the first stage calcination temperature is 400-600℃; and the second stage calcination temperature is 650-850℃.

[0024] Preferably, the first calcination temperature is 450-550℃; the second calcination temperature is 650-780℃.

[0025] Optionally, the calcination time for the first stage is 10-14 hours, and the calcination temperature for the second stage is 10-14 hours.

[0026] Optionally, during calcination, the temperature is first increased to 400-600℃ at a rate of 0.3-1.5℃ / min and calcined for 10-14 hours, and then increased to 650-850℃ at a rate of 0.3-1.5℃ / min and calcined for 10-14 hours.

[0027] Preferably, during calcination, the temperature is first increased to 450-550℃ at a rate of 0.8-1.2℃ / min and calcined for 11-13 hours, and then increased to 650-780℃ at a rate of 0.8-1.2℃ / min and calcined for 11-13 hours.

[0028] Optionally, the concentration of the aqueous solution of monolayer MXene is 10-20 mg / mL.

[0029] Optionally, the preparation method of monolayer MXene includes: etching the MAX phase material with an etching solution to obtain monolayer MXene; wherein the MAX phase material is doped with rare earth elements.

[0030] Optionally, the MAX phase material is rare earth element-doped Ti3AlC2.

[0031] Optionally, the etching solution is hydrofluoric acid or a solution containing LiF or HCl.

[0032] Optionally, the etching temperature is 20℃-50℃, and the etching time is 24h-48h.

[0033] Preferably, the etching temperature is 30℃-40℃ and the etching time is 38h-40h.

[0034] Optionally, the etching process can be followed by cleaning until the pH is greater than 6.

[0035] Optionally, the MAX phase material is ground into powder, and then etched with an etching solution.

[0036] Optionally, the preparation method of MAX phase material includes: mixing metal powder, rare earth metal powder, aluminum powder and carbon powder, pressing into tablets, and sintering to obtain MAX phase material;

[0037] The metal powder is selected from one or more of titanium powder, molybdenum powder, and vanadium powder.

[0038] Optionally, when the metal powder is titanium powder, the molar ratio of metal powder:aluminum powder:carbon powder is 3:1:2 or 2:1:1.

[0039] Optionally, when the metal powder is molybdenum powder, the molar ratio of metal powder:aluminum powder:carbon powder is 2:1:1.

[0040] Optionally, when the metal powder is vanadium powder, the molar ratio of metal powder: aluminum powder: carbon powder is 2:1:1.

[0041] Optionally, the molar ratio of rare earth metal powder to metal powder is 1:(1-10); preferably, the molar ratio of rare earth metal powder to metal powder is 1:(1-5).

[0042] Optionally, the molar ratio of rare earth metal powder to metal powder is selected from any one of 1:1, 1:2, 1:3, 1:5, 1:8, 1:10 or any range between the two.

[0043] Optionally, the metal powder, rare earth metal powder, aluminum powder, and carbon powder can be mixed by ball milling in a high-speed ball mill. There are no restrictions on the ball-to-material ratio or the ball milling time; the mixture can be mixed until it is uniform.

[0044] Optionally, the pressure during tablet compression is 0.5MPa-2MPa, preferably 0.5MPa-1.5MPa.

[0045] Optionally, the tableting time is 0.5 to 2 minutes.

[0046] Optionally, the sintering temperature is 1300℃~1500℃, the heating rate is 35-45℃ / min, and the sintering time is 0.5-1.5h.

[0047] Preferably, the sintering temperature is 1300℃-1500℃, the heating rate is 40℃ / min, and the sintering time is 1h.

[0048] In one embodiment, the method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material includes the following steps:

[0049] (1) Mix metal powder, rare earth metal powder, aluminum powder and carbon powder, press into tablets, and sinter by discharge plasma to obtain rare earth doped MAX phase material, and grind into powder.

[0050] (2) Under water bath heating, the MAX phase material is etched with etching solution, centrifuged and washed until the pH is greater than 6, and a rare earth-doped monolayer MXene aqueous solution is prepared.

[0051] (3) Weigh lithium salt, nickel salt and manganese salt in a certain stoichiometric ratio, prepare a clear aqueous solution, and add monolayer MXene aqueous solution and surfactant to prepare a uniform dispersion.

[0052] (4) Weigh out the chelating agent and prepare a clear solution of a certain volume.

[0053] (5) Add the solution from step (3) dropwise to the chelating agent solution from step (4) while stirring continuously. Adjust the pH to neutral with an alkaline solution, and stir under 80°C water bath heating until a gel is formed. After the gel is thoroughly vacuum dried, grind it into powder, calcine it in a pure oxygen atmosphere, and anneal it to obtain modified LiNi. x Mn 1-x O2 powder.

[0054] This application utilizes rare-earth-doped two-dimensional MXene as a self-assembly site. The negatively charged MXene itself attracts metal ions, and with the aid of the affinity of surfactants and the adhesive effect of metal ion chelators, the interphase stability between MXene and the high-nickel cobalt-free gel is improved, allowing the precursor to stably complex on the two-dimensional MXene. After sintering, carbon is oxidized, while the Ti, Mo, or V of the MXene itself, as well as the target doped rare-earth ions, are simultaneously incorporated into the material to improve the electronic structure of the cobalt-free cathode and suppress problems such as cation mixing, multiple phase transitions, and poor cycle performance. Compared with traditional solid-state sintering methods, this application incorporates doping in situ during material growth, resulting in better doping effects and enabling simultaneous multi-ion doping. Furthermore, the small amount of fluorine ions contained in MXene and the pores formed during subsequent sintering also improve the interphase stability between the material and the electrolyte. The cobalt-free cathode prepared by the novel doping method reported in this application exhibits high specific capacity and good cycle stability.

[0055] This application also provides a self-assembled rare-earth-doped high-nickel cobalt-free cathode material prepared by the preparation method of the self-assembled rare-earth-doped high-nickel cobalt-free cathode material.

[0056] This application also provides a lithium-ion battery obtained from the self-assembled rare-earth-doped high-nickel cobalt-free cathode.

[0057] The beneficial effects that this application can produce include:

[0058] 1) The method for preparing self-assembled rare earth-doped high-nickel cobalt-free cathode material provided in this application allows MXene to stably complex high-nickel cobalt-free precursors, improving the problems of cation mixing and poor cycle stability in cobalt-free cathodes in the prior art.

[0059] 2) The method for preparing self-assembled rare earth-doped high-nickel cobalt-free cathode material provided in this application involves in-situ doping, resulting in better doping effect and the ability to achieve multi-ion doping simultaneously.

[0060] 3) The preparation method of the self-assembled rare earth-doped high-nickel cobalt-free cathode material provided in this application can improve the interfacial stability between the material and the electrolyte.

[0061] 4) The method for preparing self-assembled rare earth-doped high-nickel cobalt-free cathode material provided in this application yields cathode materials with high specific capacity and good cycle stability. Attached Figure Description

[0062] Figure 1 This is a SEM image of Y-Ti3C2 in Example 1 of this application, with a size of 1 μm;

[0063] Figure 2 The images shown are of the D-LNM91 precursor powder sample (top) and SEM image (bottom) in Example 1 of this application, with a size of 10 μm.

[0064] Figure 3 The images shown are a sample image (top) and a SEM image (bottom) of the LNM91 precursor powder in Comparative Example 1 of this application, with a size of 5 μm.

[0065] Figure 4 This is a comparison chart showing the electrochemical performance of button batteries assembled in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0066] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0067] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0068] The morphology of the samples was measured using a Thermo Fisher Apreo S LoVac microscope at a voltage of 15.00 kV.

[0069] The electrochemical performance test was conducted using the Landon CT2001A battery testing system, with voltage and current test ranges of 5V and 5mA.

[0070] Example 1

[0071] (1) Weigh 3.59g of titanium powder, 2.6g of yttrium powder, 0.68g of aluminum powder and 0.6g of carbon powder, and mix them evenly by ball milling in a planetary ball mill. Press the mixture into tablets at a pressure of 1MPa for 1min, heat it to 1400℃ at a rate of 40℃ / min, and sinter for 1h to obtain Y-doped Ti3AlC2. Grind it into powder and denot it as Y-Ti3AlC2.

[0072] (2) 1 g of Y-Ti3AlC2 was weighed and etched for 36 h using a LiF+HCl etching solution (where the mass of LiF was 1 g and the mass of HCl was 20 mL of 9 mol / L hydrochloric acid solution). The solution was centrifuged and washed multiple times until the pH was greater than 6. After thorough ultrasonic dispersion, a 15 mg / mL monolayer Y-Ti3C2 solution was prepared. The SEM morphology of the filtered solution is shown below. Figure 1 As shown, this is a nanosheet structure.

[0073] (3) Weigh 2.76g lithium sulfate monohydrate, 4.73g nickel sulfate hexahydrate, and 0.338g manganese sulfate monohydrate, add 10mL deionized water, 20mL of the above Y-Ti3C2 solution and 0.1g sodium dodecylbenzenesulfonate, stir and disperse for later use.

[0074] (4) Weigh 8g of citric acid powder, dissolve it in 20ml of deionized water, and prepare a second aqueous solution.

[0075] (5) Slowly add the metal ion solution from step (3) dropwise to the citric acid solution, stir until homogeneous, and then adjust the pH to neutral with ammonia. Heat and stir in an 85°C water bath to evaporate the solvent until a viscous gel is formed. Dry thoroughly under vacuum and grind into a paste. Figure 2 The gray precursor powder shown (denoted as D-LNM91 precursor powder) was calcined at 500℃ for 12 h under a pure oxygen atmosphere by heating at a rate of 1℃ / min, and then sintered at 720℃ for 12 h by heating at the same rate to obtain Ti. 4+ Y 3+ Co-doped LiNi 09 Mn 01 The O2 cathode material is designated as D-LNM91.

[0076] Comparative Example 1

[0077] (1) Weigh 2.76g lithium sulfate monohydrate, 4.73g nickel sulfate hexahydrate, and 0.338g manganese sulfate monohydrate, add 30mL of deionized water, stir and disperse, and set aside for later use.

[0078] (2) Weigh 8g of citric acid powder, dissolve it in 20ml of deionized water, and prepare a second aqueous solution.

[0079] (3) Slowly add the metal ion solution from step (1) dropwise to the citric acid solution, stir until homogeneous, and then adjust the pH to neutral with ammonia. Heat in a water bath at 85°C, stirring to evaporate the solvent until a viscous gel is formed. Dry thoroughly under vacuum and grind into a paste. Figure 3 The pale green precursor powder shown (denoted as LNM91 precursor powder) was calcined at 500℃ for 12 h at a rate of 1℃ / min under a pure oxygen atmosphere, and then sintered at 720℃ for 12 h at the same rate to obtain LiNi. 0.9 Mn 0.1 The O2 cathode material, denoted as LNM91, is used as a control sample.

[0080] contrast Figure 2 and Figure 3 The electron microscopy image shows that after the addition of Y-Ti3C2, the precursor tightly complexes with the Y-Ti3C2 nanosheets through the electrostatic interaction of the anions and cations and the wetting effect of the surfactant, resulting in in-situ growth on the sheets. Figure 2 After calcination, the metal ions on the nanosheets can be better incorporated into LNM91. In contrast, those without nanosheets agglomerate randomly into particles.

[0081] The cells of Example 1 and Comparative Example 1 were assembled into button batteries and subjected to charge-discharge tests and cycle tests, respectively. Figure 4 At 1C rate, within a cutoff voltage range of 2.8V-4.3V, the capacity of D-LNM91 is 176.9 mAh / g, while the capacity of LNM91 is 173.4 mAh / g. After 200 cycles, the capacity retention of D-LNM91 is 74.7%, while the capacity retention of undoped LNM91 drops to 62.6% after only 100 cycles. This indicates that the novel doping method of this application can effectively improve the cycle stability of high-nickel cobalt-free cathodes, and holds promise for achieving cobalt-free lithium-ion battery cathodes.

[0082] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a self-assembled rare-earth-doped high-nickel cobalt-free cathode material, characterized in that, Includes the following steps: (1) A dispersion was obtained by mixing an aqueous solution of lithium salt, nickel salt, manganese salt, monolayer MXene, surfactant, and water; (2) Add the dispersion to a solution containing a metal ion chelating agent, adjust the pH, and heat to form a gel; (3) Under a pure oxygen atmosphere, calcination and annealing were performed to obtain rare earth-doped LiNi. x Mn 1-x O2 powder; The monolayer MXene is doped with rare earth elements; The rare earth elements are selected from one or more of Y, Sc, Yb, Ce, Pr and Gd; The amount of monolayer MXene added is 0.5%-5% of the total mass of the metal salt; The metal salts include lithium salts, nickel salts, and manganese salts; The method for preparing the monolayer MXene includes: etching the MAX phase material with an etching solution to obtain a monolayer MXene; The MAX phase material is doped with rare earth elements; The preparation method of the MAX phase material includes: mixing metal powder, rare earth metal powder, aluminum powder and carbon powder, pressing into tablets, and sintering to obtain the MAX phase material; The metal powder is selected from one or more of titanium powder, molybdenum powder, and vanadium powder; When the metal powder is titanium powder, the molar ratio of metal powder: aluminum powder: carbon powder is 3:1:2 or 2:1:1; When the metal powder is molybdenum powder, the molar ratio of metal powder: aluminum powder: carbon powder is 2:1:1; When the metal powder is vanadium powder, the molar ratio of metal powder: aluminum powder: carbon powder is 2:1:

1.

2. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The monolayer MXene is rare earth element-doped Ti3C2.

3. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The surfactant is selected from one or more of sodium dodecylbenzene sulfonate, stearic acid, and sodium hexadecyl sulfate. The amount of surfactant added is 0.5%-5% of the total mass of the metal salt; The metal salts include lithium salts, nickel salts, and manganese salts.

4. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The amount of surfactant added is 0.5%-2% of the total mass of the metal salt; The metal salts include lithium salts, nickel salts, and manganese salts.

5. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The metal ion chelating agents are ethylenediaminetetraacetic acid and / or citric acid; The amount of the metal ion chelating agent added is 80%-120% of the total mass of the metal salt; The metal salts include lithium salts, nickel salts, and manganese salts.

6. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The amount of the metal ion chelating agent added is 95%-110% of the total mass of the metal salt; The metal salts include lithium salts, nickel salts, and manganese salts.

7. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The amount of monolayer MXene added is 1%-4% of the total mass of the metal salt; The metal salts include lithium salts, nickel salts, and manganese salts.

8. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The mass ratio of lithium salt, nickel salt, and manganese salt is (5-10):(10-20):

1.

9. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, LiNi x Mn 1-x In O2, x ≥ 0.8; LiNi x Mn 1-x O2 is LiNi 0.9 Mn 0.1 O2.

10. The method for preparing the self-assembled rare-earth-doped high-nickel cobalt-free cathode material according to claim 1, characterized in that, The MAX phase material is Ti3AlC2 doped with rare earth elements.

11. A self-assembled rare-earth-doped high-nickel cobalt-free cathode material, characterized in that, It is prepared by the method for preparing self-assembled rare earth-doped high-nickel cobalt-free cathode material according to any one of claims 1-10.

12. A lithium-ion battery, characterized in that, It is prepared from the self-assembled rare earth-doped high-nickel cobalt-free cathode material as described in claim 11.

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