A fluorine-aluminum doped positive electrode material, a preparation method and application thereof

Abstract

The application belongs to the technical field of lithium battery positive electrode materials, and particularly relates to a fluorine-aluminum doped positive electrode material and a preparation method and application thereof. + The application forms a porous structure on the surface layer of the positive electrode material, and co-dopes fluorine elements and aluminum elements on the surface layer. The application forms a porous structure on the surface layer of the positive electrode material, which can effectively buffer the volume and stress changes of Li + ions generated in the repeated deintercalation process, slows down the generation of cracks, and the porous structure can effectively improve the rate performance of the material. Moreover, the fluorine-aluminum doping improves the electrochemical performance and material stability of the positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery cathode materials, and particularly relates to a fluorine-aluminum doped cathode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have been widely applied in the power supply (HEV) and electric vehicles (EV) of various energy conversion / storage devices such as mobile phones, electric tools, energy storage systems and hybrid electric vehicles, as one of the most important components in the lithium ion battery system, the cathode material determines the energy density, power capability and life of lithium ions, but the serious structural change in the positive electrode particles seriously affects the performance of the battery. The chemical instability of the nickel-rich positive electrode material is mainly due to the weak Ni-O bond, and the material will undergo a serious phase change from H2 to H3 during charging, the crystal structure will appear a high anisotropic shrinkage, and a serious mechanical strain will occur in the crystal, and then microcracks will be formed, these cracks will propagate to the surface of the secondary particles during repeated cycles, and the electrolyte will penetrate into the interior of the positive electrode particles, forming a nano-scale NiO rock-salt interface exposed to the electrolyte, resulting in a decrease in the capacity of the nickel-rich positive electrode. These capacity attenuation phenomena will be further intensified in the case of increasing the nickel content or increasing the cutoff voltage, however, increasing the nickel content in the nickel-rich positive electrode material and increasing the cutoff voltage are important means to further improve the energy density of the battery.

[0003] In order to suppress the crack generation in the positive electrode material during the cycle process and improve the material stability, further improve the energy density of the battery, researchers have tried various methods to improve the material stability, among which, the method of stabilizing the material structure by material structure design is a remarkable method, but the methods are different. SUMMARY

[0004] In order to solve the problems of the prior art, the application provides a fluorine-aluminum doped positive electrode material and a preparation method and application thereof. The porous structure formed on the surface layer of the positive electrode material can effectively buffer the volume and stress changes generated by Li + ions during repeated deintercalation, and slow down the crack generation, and the porous structure can effectively improve the rate performance of the material. Moreover, the fluorine-aluminum doping improves the electrochemical performance and material stability of the positive electrode material.

[0005] The technical scheme provided by the application is as follows:

[0006] A preparation method of a fluorine-aluminum doped positive electrode material, comprising the following steps:

[0007] 1) obtaining an alkaline mixed solution; the mixed solution contains nickel salt, cobalt salt, manganese salt, complexing agent and nickel-cobalt-manganese hydroxide;

[0008] 2) adding fluorine-containing plastic-coated metal aluminum into the mixed solution to perform a co-precipitation reaction in an inert atmosphere to obtain a precursor slurry;

[0009] 3) sequentially subjecting the precursor slurry to aging, filtration, washing and drying to obtain an anode material precursor, and the surface layer of the anode material precursor is mixed with fluorine-containing plastic-coated metal aluminum;

[0010] 4) mixing the anode material precursor obtained in step 3) with lithium hydroxide, and then sintering the mixture in an oxygen-containing atmosphere (oxygen volume fraction is greater than or equal to 95%) to obtain a fluorine-aluminum-doped anode material.

[0011] Based on the above technical solutions:

[0012] In step 1), the fine particles of nickel-cobalt-manganese hydroxide serve as a dense inner layer material, and the mixed solution contains nickel salt, cobalt salt, manganese salt and complexing agent for further co-precipitation synthesis of nickel-cobalt-manganese hydroxide.

[0013] In step 2), fluorine-containing plastic-coated metal aluminum is added for co-precipitation, so that the fluorine-containing plastic-coated metal aluminum powder is co-precipitated with the nickel-cobalt-manganese hydroxide, and the nickel-cobalt-manganese hydroxide inner layer material in step 1) is further grown, thereby forming a larger particle material with a surface layer mixed with fluorine-containing plastic-coated metal aluminum, i.e. obtaining an anode material precursor.

[0014] In step 4), fluorine-containing plastic is removed by sintering, so that lithium meta-aluminate is generated after aluminum reacts with lithium hydroxide, and the reaction gas can be used for pore forming, thereby forming a porous structure surface layer.

[0015] Through the above method, an anode material with a porous structure on the surface layer can be obtained, and co-doping of fluorine and aluminum elements is realized, thereby enhancing the bond energy of the crystal, optimizing the structural stability of the material, improving the electrochemical performance of the material, and further improving the stability of the material.

[0016] Although one-stage high-temperature sintering (600-750°C) can also obtain porous fluorine-aluminum-doped positive electrode material, in order to make aluminum and alkali react more fully in the sintering process and further improve the porosity, the sintering process in step 4) can preferably be carried out in the manner of low-temperature sintering first and then high-temperature sintering. The low-temperature sintering temperature can be 100-300°C (for example, 100°C, 110°C, 130°C, 150°C, 200°C, 250°C, 300°C), the holding time can be 1-3h (for example, 1h, 1.2h, 1.5h, 2h, 2.3h, 2.5h, 3h), and the heating rate is not particularly limited, and exemplarily can be 1-2°C / min. The high-temperature sintering temperature can be 600-750°C (for example, 600°C, 610°C, 630°C, 650°C, 700°C, 730°C, 750°C), the holding time can be 8-20h (for example, 8h, 10h, 13h, 15h, 16h, 18h, 20h), and the heating rate is not particularly limited, and exemplarily can be 3-5°C / min.

[0017] Based on the above technical solution, in the sintering process, the aluminum metal surface layer of the fluorine-containing plastic layer is first melted, the aluminum metal is exposed, and reacts with lithium hydroxide to produce hydrogen, thereby performing pore formation. In the sintering process, the lithium hydroxide and the water generated in the precursor provide a water environment for the reaction of aluminum and lithium hydroxide. When sintering at high temperature, the fluorine ions after the decomposition of the fluorine-containing organic matter are doped into the surface layer of the positive electrode material, and the aluminum ions are also doped into the surface layer of the positive electrode material, forming co-doping of fluorine and aluminum elements.

[0018] Through the above method, a positive electrode material with a porous structure on the surface layer can be obtained, and the co-doping of fluorine and aluminum elements can enhance the bond energy of the crystal, optimize the structural stability of the material, and effectively improve the electrochemical performance of the material, thereby further improving the stability of the material.

[0019] The method of step 1) is a prior art, for example, a metal salt solution and an ammonia solution are flowed into a constant-temperature reaction kettle containing an ammonia water bottom solution for co-precipitation, then an alkali solution is introduced to adjust the pH of the slurry in the reaction kettle, the pH is controlled at 10-12, and inert protective gas is introduced during the reaction.

[0020] Specifically, in step 1), the general formula of the nickel-cobalt-manganese hydroxide is Ni x Co y M z (OH)2, wherein 0.8≤x<1, 0

[0021] Based on the above technical solution, a positive electrode material with ordinary nickel content can also be obtained.

[0022] Specifically, in step 1), the particle size of the nickel-cobalt-manganese hydroxide is 5-6 um.

[0023] Specifically, in step 1), the molar ratio of nickel, cobalt and manganese in the mixed solution is (80-100):(0-20):(0-20).

[0024] Specifically, in step 1), the nickel salt is at least one of carbonate, nitrate, sulfate or acetate; the cobalt salt is at least one of carbonate, nitrate, sulfate or acetate; and the manganese salt is at least one of carbonate, nitrate, sulfate or acetate.

[0025] Specifically, in step 1), the complexing agent is at least one of ammonium bicarbonate, glycine, ammonia or triethanolamine, and the concentration of the complexing agent is 0.1-1 mol / L.

[0026] Specifically, in step 1), the mixed solution further contains at least one of LiOH, NaOH or KOH.

[0027] Specifically, in step 1), the pH of the mixed solution is 10-12.

[0028] Specifically, the fluorine-containing plastic is selected from any one or more of polytetrafluoroethylene, polyfluoroethylene-propylene and polyvinylidene fluoride.

[0029] Specifically, the particle size of the metal aluminum coated with the fluorine-containing plastic is 100-200 nm.

[0030] Specifically, in the metal aluminum coated with the fluorine-containing plastic, the molar ratio of fluorine element to aluminum element is F:Al=(1-2):1.

[0031] Specifically, the thickness of the fluorine-containing plastic coating is 5-20 nm.

[0032] Specifically, in step 4), in the fluorine-aluminum doped positive electrode material prepared, the molar ratio of aluminum to nickel, cobalt and manganese is Al:(Ni+Co+Mn)=0.002-0.01.

[0033] Specifically, in step 3), the particle size of the positive electrode material precursor is 9-11 um.

[0034] Specifically, in step 4), the molar ratio of the amount of lithium to the sum of the amounts of nickel, cobalt, manganese and aluminum in the positive electrode material precursor is Li:(Ni+Co+Mn+Al)=(1.0-1.06):1.

[0035] The application further provides the fluorine-aluminum doped positive electrode material prepared by the preparation method.

[0036] Specifically, the fluorine and aluminum doped positive electrode material particle comprises a core and a coating layer, the coating layer contains pores, and the coating layer is doped with aluminum and fluorine; the core has a molecular formula of NixCoyMzO2, wherein 0.8<=x<1, 0<y<=0.2, 0<=z<0.2, and x+y+z=1.

[0037] In the prepared fluorine and aluminum doped positive electrode material, the molar ratio of fluorine to aluminum is F:Al=(1-2):1, the molar ratio of fluorine, aluminum and nickel, cobalt and manganese is (F+Al):(Ni+Co+Mn)=0.004-0.03, and the molar ratio of lithium to the sum of the amounts of nickel, cobalt, manganese and aluminum is Li:(Ni+Co+Mn+Al)=(1.0-1.06):1.

[0038] In the above technical solution:

[0039] The radius of Al 3+ is similar to that of Co 3+ , and Al 2- is electrochemically inert, can stably bond with O around it even at high voltage, and can play a role in stabilizing the structure, thereby improving the cycle stability of the battery. In addition, the strength of the Al-O bond is stronger than that of the Ni(Co, Mn)-O bond, and is more inclined to improve the thermal stability.

[0040] The fluorine element doping can reduce the interface impedance and charge transfer impedance of the material, increase the interface distance, accelerate the transmission of lithium ions, and the fluorine element has strong electronegativity, which can increase the bonding between the transition metal element and the anion and stabilize the layered structure, thereby significantly improving the electrochemical performance of the material.

[0041] The electrochemical performance and material stability of the fluorine and aluminum doped positive electrode material are improved.

[0042] Based on the above technical solution, too high a fluorine doping amount will lead to the formation of a large number of Li-F bonds, making it difficult for Li+ to be further released and reducing the lithium ion diffusion rate, and too low a fluorine doping amount will not significantly improve the performance of the material. Too high an aluminum doping amount will greatly reduce the initial capacity of the material, and too low an aluminum doping amount will result in fewer Al-O bonds with strong bond energy and a more unstable transition metal layer structure, which will result in poor high-temperature performance.

[0043] The application also provides an application of the fluorine and aluminum doped positive electrode material as a lithium battery positive electrode material.

[0044] The application has the following beneficial effects:

[0045] The present application adds fluorine-containing plastic coated metal aluminum in the precursor preparation process, co-precipitates with nickel-cobalt-manganese hydroxide precipitation, forms a porous structure on the particle surface layer after reacting with lithium hydroxide in the sintering process, and simultaneously carries out aluminum element and fluorine element doping, optimizes the structural stability of the material, and effectively improves the electrochemical performance of the material;

[0046] The present application forms a porous structure on the surface layer of the positive electrode material, effectively buffers the volume and stress changes of Li + Ions in repeated deintercalation process, slows down crack generation, can play a role in stabilizing the structure and improving the cycle performance, and the porous structure shortens the lithium ion diffusion path, which can effectively improve the rate performance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a preparation schematic diagram of the porous positive electrode material of the present application.

[0048] Figure 2 is a cross-sectional electron microscope graph of the positive electrode material prepared in example 1 of the present application.

[0049] Figure 3 is a cross-sectional electron microscope graph of the positive electrode material prepared in example 1 of the present application after 1C cycle for 100 times.

[0050] Figure 4 is a cross-sectional electron microscope graph of the positive electrode material prepared in comparative example 1 of the present application after 1C cycle for 100 times. DETAILED DESCRIPTION

[0051] The principles and characteristics of the present application are described below, and the examples are only used to explain the present application and are not used to limit the scope of the present application.

[0052] Example 1

[0053] Precursor preparation: A metal salt solution (nickel, cobalt, and manganese molar ratio of 92:4:4, salt being nitrate, with a total concentration of nickel, cobalt, and manganese ions of 2 mol / L) and a 0.5 mol / L ammonia solution were fed into a constant-temperature reactor containing a 0.05 mol / L ammonia solution at a flow rate of 5 L / h. Co-precipitation was carried out at a constant temperature of 45°C. During co-precipitation, the pH of the slurry in the reactor was adjusted by introducing a 4 mol / L sodium hydroxide solution to maintain the pH at 12. An inert protective gas was introduced during the reaction. Once the particles grew to 5–6 μm, a certain amount of PVDF-coated aluminum powder (particle size 200 nm, coated with a 10 nm PVDF film, where the molar ratio of F to Al is approximately F:Al = 1:1; the amount of aluminum powder added is in the molar ratio Al:(Ni+Co+Mn) = 0.005) was added for co-precipitation, so that the PVDF-coated aluminum powder and nickel-cobalt-manganese hydroxide co-precipitated on the particle surface. Once the particles grow to about 10 μm, the precursor slurry is aged, filtered, washed, and dried to obtain a precursor of a cathode material with a fluoroplastic coating on the surface.

[0054] Cathode material preparation: The dried precursor was mixed with lithium hydroxide at a molar ratio of lithium to metal elements in the precursor, Li:(Ni+Co+Mn+Al)=1.06:1. The mixture was sintered in an oxygen atmosphere. First, the temperature was raised to 200℃ at a heating rate of 2℃ / min and held for 2h. Then, the temperature was raised to 710℃ at a heating rate of 3℃ / min and held for 10h to obtain a fluorine-aluminum doped high-nickel cathode material.

[0055] The preparation schematic diagram of the above embodiment is shown below. Figure 1 As shown, the obtained material was subjected to cross-sectional electron microscopy analysis, and the results are as follows. Figure 2 As shown, a porous structure can be seen on the surface of the cathode material.

[0056] Example 2

[0057] Compared to Example 1, the amount of aluminum used was: molar ratio Al:(Ni+Co+Mn)=0.01.

[0058] Example 3

[0059] Compared to Example 1, the amount of aluminum used was: molar ratio Al:(Ni+Co+Mn)=0.002.

[0060] Comparative Example 1

[0061] Preparation of the precursor: the metal salt solution (molar ratio of nickel, cobalt and manganese is 92:4:4, the salt is nitrate, the total concentration of nickel ions, cobalt ions and manganese ions in the salt solution is 2 mol / L) and 0.5 mol / L ammonia solution are flowed into a constant-temperature reactor with an ammonia water bottom solution with a concentration of 0.05 mol / L at a flow rate of 5 L / h, and co-precipitation is carried out at a constant temperature of 45 degrees. During the co-precipitation process, the pH of the slurry in the reactor is adjusted by introducing 4 mol / L sodium hydroxide solution, and the pH is controlled at 12. Inert protective gas is introduced during the reaction process. After the particles grow to about 10 um, the precursor slurry is aged, filtered, washed and dried to obtain the precursor of the positive electrode material.

[0062] Preparation of the positive electrode material: the dried precursor is mixed with lithium hydroxide, and the mixing is carried out according to the molar ratio of lithium to the metal element content in the precursor, Li:(Ni+Co+Mn)=1.06. The mixture is sintered in an oxygen atmosphere, first heated to 200℃ at a rate of 2℃ / min, and then heated to 710℃ at a rate of 3℃ / min, and kept for 10h to obtain the high-nickel positive electrode material.

[0063] Comparative Example 2

[0064] Compared with Example 1, the metal aluminum used is not coated with a fluorine-containing plastic layer, and the amount of metal aluminum is: molar ratio Al:(Ni+Co+Mn)=0.005.

[0065] Performance test:

[0066] The positive electrode materials obtained in each example and the comparative example of the application are assembled into batteries:

[0067] The positive electrode materials, conductive carbon black and binder PVDF are mixed in a mass ratio of 80:1:1, and then mixed with NMP as a solvent to form a slurry, which is coated on an aluminum foil, and then vacuum dried at 110℃ for 10h to obtain a positive electrode sheet. Then, the positive electrode sheet, electrolyte (1 mol / L LiPF6, EC:EMC=1:1), separator and metal lithium sheet are assembled into a battery.

[0068] The obtained battery is tested for charge and discharge at 25±2℃ in an environment, using a NEWARE BTS-5V / 10mA type charge-discharge tester produced by Shenzhen Xinweier Electronic Co., Ltd., with a charge-discharge voltage of 2.8-4.3V, a nominal specific capacity of 200mAh / g, and the first week charge specific capacity, first week efficiency and 1C cycle performance for 100 weeks are tested respectively.

[0069] The test results are shown in Table 1:

[0070]

[0071] As shown in Table 1, the positive electrode material obtained in the embodiment has good electrochemical performance, cycle performance and rate capability.

[0072] Anti-crack effect

[0073] By Figure 3 With Figure 4 As can be seen from the comparison of the cross-sectional electron microscope images of the positive electrode material 1C after 100 cycles, the positive electrode material prepared in Example 1 with the porous structure in the surface layer can obviously inhibit the generation of cracks during the cycle process.

[0074] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a fluorine-aluminum doped cathode material, characterized in that, Includes the following steps: 1) Obtain an alkaline mixture; the mixture contains nickel salt, cobalt salt, manganese salt, complexing agent, and nickel-cobalt-manganese hydroxide; 2) Fluoroplastic-coated metallic aluminum is added to the mixture to carry out a co-precipitation reaction to obtain a precursor slurry; 3) The precursor slurry is successively aged, filtered, washed and dried to obtain a cathode material precursor, wherein the surface of the cathode material precursor is intercalated with metallic aluminum coated with fluoroplastic. 4) The cathode material precursor obtained in step 3) is mixed with lithium hydroxide, and then the mixture is sintered in an oxygen-containing atmosphere to obtain fluorine-aluminum doped cathode material. In step 1), the general formula of nickel-cobalt-manganese hydroxide is Ni x Co y Mn z (OH)2, wherein 0.8≤x<1, 0<y≤0.2, 0<z<0.2, and x+y+z=1; in the mixture, the molar ratio of nickel, cobalt and manganese is (80~100):(0~20):(0~20), and the molar amounts of nickel, cobalt and manganese are all non-zero.

2. The method for preparing the fluorine-aluminum doped cathode material according to claim 1, characterized in that, In step 4), the specific steps of sintering are as follows: first, heat to 100℃~300℃ and hold for 1~3 hours, then heat to 600℃~750℃ and hold for 8~20 hours to obtain fluorine-aluminum doped cathode material.

3. The method for preparing the fluorine-aluminum doped cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: A. In step 1), the particle size of the nickel cobalt manganese hydroxide is 5~6µm; the complexing agent is at least one of ammonium bicarbonate, glycine, ammonia or triethanolamine, and the concentration of the complexing agent is 0.1mol / L~1mol / L; B. The mixture also contains at least one of LiOH, NaOH, or KOH; C. The pH of the mixture is 10-12.

4. The method for preparing the fluorine-aluminum doped cathode material according to claim 1, characterized in that, In step 2): The fluoroplastic is selected from any one or more of polytetrafluoroethylene, perfluoroethylene propylene, and polyvinylidene fluoride; The particle size of the fluoroplastic-coated aluminum is 100~200nm; The thickness of the fluoroplastic coating is 5~20nm; The molar ratio of fluorine to aluminum in the fluoroplastic-coated aluminum is F:Al = (1~2):

1.

5. The method for preparing the fluorine-aluminum doped cathode material according to claim 1, characterized in that, In step 4), the molar ratio of aluminum to nickel, cobalt and manganese in the obtained fluorine-aluminum doped cathode material is Al:(Ni+Co+Mn)=0.002~0.

01.

6. The method for preparing the fluorine-aluminum doped cathode material according to claim 1, characterized in that, In step 3), the particle size of the cathode material precursor is 9~11μm.

7. The method for preparing the fluorine-aluminum doped cathode material according to any one of claims 1 to 6, characterized in that, In step 4), at least one of the following conditions must be met: L1, the oxygen volume fraction in the oxygen-containing atmosphere is greater than or equal to 95%; L2. The molar ratio of the amount of lithium added to the sum of the amounts of nickel, cobalt, manganese and aluminum in the cathode material precursor is Li:(Ni+Co+Mn+Al)=(1.0~1.06):

1.

8. A fluorine-aluminum doped cathode material prepared by the preparation method according to any one of claims 1 to 7.

9. The fluorine-aluminum doped cathode material according to claim 8, characterized in that: The fluorine-aluminum doped cathode material particles comprise a core and a coating layer, the coating layer containing pores, and the coating layer being doped with aluminum and fluorine; the core has the molecular formula Ni. x Co y Mn z O2, where 0.8≤x<1, 0<y≤0.2, 0<z<0.2, and x+y+z=1.

10. An application of the fluorine-aluminum doped cathode material according to claim 8 or 9, characterized in that: As a cathode material for lithium batteries.

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