Ultra-high nickel concentration gradient positive electrode material and coaxial spinning preparation method and application thereof

Abstract

The application provides a super-high nickel concentration gradient positive electrode material and a coaxial spinning preparation method and application thereof, the coaxial spinning preparation method of the super-high nickel concentration gradient positive electrode material comprises the following steps: preparing a core layer spinning liquid and a shell layer spinning liquid, wherein the nickel molar content of the core layer precursor is greater than or equal to 0.90, and the nickel molar content of the shell layer precursor is less than or equal to 0.85; a composite nanofiber membrane is obtained through coaxial electrostatic spinning treatment; and then, segmented heat treatment is carried out, the temperature is first increased to 300 DEG C to 500 DEG C and kept for 1h to 5h, and then the temperature is increased to 700 DEG C to 900 DEG C and kept for 8h to 12h. The coaxial spinning preparation method of the super-high nickel concentration gradient positive electrode material provided by the application constructs a core-shell structure and a nickel concentration gradient through coaxial spinning, effectively inhibits the generation and expansion of micro-cracks in the charging and discharging process, and the obtained positive electrode material has a high cycle retention rate under high-voltage working conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to ultra-high nickel concentration gradient cathode materials and their coaxial spinning preparation methods and applications. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage due to their high energy density and long cycle life. Layered lithium nickel manganese oxide ternary materials, especially ultra-high nickel (Ni content ≥90%) cathode materials, are considered key materials for next-generation high-energy-density lithium-ion batteries due to their high theoretical specific capacity and relatively low cobalt content. However, ultra-high nickel cathode materials suffer from poor structural stability under high voltage (≥4.5V) conditions, manifested as irreversible phase transitions, lattice oxygen precipitation, microcrack initiation and propagation, and intensified interfacial side reactions.

[0003] The initiation and propagation of microcracks allow newly exposed surfaces within the material to directly contact the electrolyte, exacerbating interfacial side reactions and disrupting electrical contacts between particles, leading to rapid capacity decay. Even with optimized material structure, the cycle retention rate still falls short of the requirements for high-voltage, long-life applications. Effectively controlling microcracks during charge and discharge processes to achieve higher cycle retention rates remains a key challenge. Summary of the Invention

[0004] This invention provides an ultra-high nickel concentration gradient cathode material, its coaxial spinning preparation method, and its application, in order to solve the problem of low cycle retention rate of ultra-high nickel cathode materials under high voltage conditions due to microcrack propagation.

[0005] In a first aspect, the present invention provides a method for preparing an ultra-high nickel concentration gradient cathode material by coaxial spinning, comprising: (1) Preparation of core spinning solution: Dissolve the first polymer in the first organic solvent, add a precursor with a nickel molar content ≥0.90 and the first lithium salt and mix to obtain the core spinning solution; (2) Preparation of shell spinning solution: Dissolve the second polymer in the second organic solvent, add the precursor with nickel molar content ≤0.85 and the second lithium salt and mix to obtain the shell spinning solution; (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected into the inner and outer channels of the coaxial needle of the coaxial electrospinning device and coaxial electrospinning treatment is performed to obtain a composite nanofiber membrane. (4) Segmented heat treatment: The composite nanofiber membrane is subjected to segmented heat treatment in an oxygen atmosphere: first, the temperature is raised to 300℃~500℃ and held for 1h~5h, then the temperature is raised to 700℃~900℃ and held for 8h~12h to obtain ultra-high nickel concentration gradient cathode material.

[0006] In this invention, coaxial electrospinning refers to injecting the core spinning solution and the shell spinning solution simultaneously into the inner and outer channels of a coaxial needle via independent propulsion pumps. The solutions converge at the needle outlet to form a Taylor cone with a core-shell structure. This cone is then stretched and refined under a high-voltage electric field, ultimately yielding a composite nanofiber membrane with a core layer encapsulated by a shell layer. The ratio of core spinning solution to shell spinning solution is determined by the ratio of the core propulsion rate to the shell propulsion rate.

[0007] In one optional embodiment, in the segmented heat treatment, the heating rate to 300℃~500℃ is 1℃ / min~3℃ / min; optionally, the heating rate is 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, or within any of the above values.

[0008] The heating rate to 700℃~900℃ is 1℃ / min~3℃ / min; optionally, the heating rate is 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, or within any of the above values.

[0009] And / or, the segmented heat treatment may further include a step of natural cooling to room temperature.

[0010] In one optional embodiment, the nickel molar content in the precursor with a nickel molar content ≥ 0.90 in the core spinning solution is 0.90~0.98; optionally, the nickel molar content is 0.90, 0.92, 0.95, 0.96, 0.98, or within any range of the above values. And / or, in the shell spinning solution, the nickel molar content in the precursor with a nickel molar content ≤ 0.85 is 0.70~0.85; optionally, the nickel molar content is 0.70, 0.75, 0.80, 0.85, or within any of the above values.

[0011] In one optional embodiment, metal oxide additives are further added to the core spinning solution and / or shell spinning solution.

[0012] In one optional embodiment, the metal oxide additive includes at least one of ZrO2, MgO, TiO2, and Y2O3; And / or, the content of the metal oxide additive is 1000~3000ppm; optionally, the content is 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, or within any of the above values.

[0013] In one optional embodiment, the parameters of the coaxial electrospinning treatment are: core layer advance rate of 0.2 mL / h to 2.0 mL / h; optionally, the core layer advance rate is 0.2 mL / h, 0.5 mL / h, 1.0 mL / h, 1.5 mL / h, 2.0 mL / h, or within any range of the above values. The shell propulsion rate is 0.5 mL / h to 3.0 mL / h; optionally, the shell propulsion rate is 0.5 mL / h, 1.0 mL / h, 1.5 mL / h, 2.0 mL / h, 2.5 mL / h, 3.0 mL / h, or within any range of the above values. The voltage is 10kV to 25kV; optionally, the voltage is 10kV, 15kV, 20kV, 25kV, or within any range of the above values. The receiving distance is 10cm to 25cm; optionally, the receiving distance is 10cm, 15cm, 20cm, 25cm, or within any of the above values.

[0014] In one alternative embodiment, the first polymer comprises at least one of polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polymethyl methacrylate (PMMA). And / or, the second polymer comprises at least one of polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polymethyl methacrylate (PMMA).

[0015] In one optional embodiment, the first organic solvent includes at least one of N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP); And / or, the second organic solvent includes at least one of N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP); And / or, the first lithium salt includes at least one of lithium hydroxide and lithium nitrate; And / or, the second lithium salt includes at least one of lithium hydroxide and lithium nitrate.

[0016] In one optional embodiment, the molar ratio of lithium in the first lithium salt to the total transition metals contained in the precursor in the core spinning solution is (1.02–1.08):1; optionally, the molar ratio is 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, or within any range of the above values. And / or, the molar ratio of lithium in the second lithium salt to the total transition metals contained in the precursor in the shell spinning solution is (1.02 to 1.08):1; optionally, the molar ratio is 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, or within any of the above values.

[0017] In one optional embodiment, the mass fraction of the first polymer in the core spinning solution is 5 wt% to 20 wt%; optionally, the mass fraction is 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, or within any of the above values; the amount of the first organic solvent is determined according to the mass fraction of the first polymer. And / or, in the shell spinning solution, the mass fraction of the second polymer is 5wt% to 20wt%; optionally, the mass fraction is 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, or within any of the above values; the amount of the second organic solvent is determined according to the mass fraction of the second polymer. And / or, the mass ratio of the first polymer to the precursor with a nickel molar content ≥0.90 is 1:(1-5); optionally, the mass ratio is 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, 1:5, or within any of the above values. And / or, in the shell spinning solution, the mass ratio of the second polymer to the precursor with a nickel molar content ≤0.80 is 1:(1-5); optionally, the mass ratio is 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, 1:5, or within any of the above values.

[0018] Secondly, the present invention also provides an ultra-high nickel concentration gradient cathode material, which is prepared by the coaxial spinning preparation method of the ultra-high nickel concentration gradient cathode material described in the first aspect.

[0019] Thirdly, the present invention also provides the application of the ultra-high nickel concentration gradient cathode material described in the second aspect in lithium-ion battery cathode materials.

[0020] The beneficial effects of this invention are as follows: 1. The coaxial spinning preparation method for ultra-high nickel concentration gradient cathode materials provided by this invention employs coaxial electrospinning technology. A core spinning solution with a nickel molar content ≥0.90 and a shell spinning solution with a nickel molar content ≤0.80 are injected into the inner and outer channels of a coaxial needle for spinning, respectively, to obtain a composite nanofiber membrane. This membrane is then subjected to segmented heat treatment to create a gradual transition zone at the core-shell interface with a decreasing nickel content. This gradual interface avoids lattice mismatch and stress concentration at traditional clear interfaces, reducing the initiation of microcracks at their source. Simultaneously, the fiber morphology can buffer volume change stress during charge and discharge, thus achieving a higher cycle retention rate under high-voltage conditions.

[0021] 2. In the preparation method provided by this invention, metal oxide additives are also added to the spinning solution. These additives can play a doping modification role after sintering, stabilize the layered structure of the material, inhibit lattice oxygen precipitation, and further improve the structural stability and cycle life of the material under high voltage. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0023] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] Example 1 This embodiment provides a method for preparing ultra-high nickel concentration gradient cathode materials via coaxial spinning, the specific steps of which are as follows: (1) Preparation of core spinning solution: Dissolve 1.2g of polyacrylonitrile in 10mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.92. 0.92 Co 0.05 Mn 0.03 The solution is prepared by mixing (OH)2, lithium hydroxide and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to precursor is 1:1.5.

[0025] (2) Preparation of shell spinning solution: Dissolve 1.0 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.80. 0.80 Co 0.10 Mn0.10 The mixture of (OH)2, lithium hydroxide, and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt, and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to the precursor is 1:1.5, is stirred evenly to obtain the shell spinning solution.

[0026] (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected simultaneously into the inner and outer channels of the coaxial needle through independent propulsion pumps, and converge at the needle outlet to form a Taylor cone with a core-shell structure. Then, it is stretched and refined under the action of a high voltage electric field. The core propulsion rate is 0.5 mL / h, the shell propulsion rate is 1.0 mL / h, the voltage is 15 kV, and the receiving distance is 15 cm, resulting in a composite nanofiber membrane in which the core layer is wrapped by the shell layer.

[0027] (4) Segmented heat treatment: The composite nanofiber membrane was placed in an atmosphere furnace and subjected to segmented heat treatment under an oxygen atmosphere: the temperature was raised to 400℃ at a heating rate of 3℃ / min and held for 2h; then the temperature was raised to 800℃ at a heating rate of 3℃ / min and held for 10h, and then naturally cooled to room temperature to obtain an ultra-high nickel concentration gradient cathode material.

[0028] Example 2 This embodiment provides a method for preparing ultra-high nickel concentration gradient cathode materials via coaxial spinning, the specific steps of which are as follows: (1) Preparation of core spinning solution: Dissolve 1.2g of polyacrylonitrile in 10mL of N,N-dimethylformamide, and add a precursor Ni with a nickel molar content of 0.95. 0.95 Co 0.02 Mn 0.03 The solution is prepared by mixing (OH)2, lithium hydroxide and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to precursor is 1:1.5.

[0029] (2) Preparation of shell spinning solution: Dissolve 1.0 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add a precursor Ni with a nickel molar content of 0.85. 0.85 Co 0.08 Mn 0.07 The mixture of (OH)2, lithium hydroxide, and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt, and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to the precursor is 1:1.5, is stirred evenly to obtain the shell spinning solution.

[0030] (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected simultaneously into the inner and outer channels of the coaxial needle through independent propulsion pumps, and converge at the needle outlet to form a Taylor cone with a core-shell structure. Then, it is stretched and refined under the action of a high voltage electric field. The core propulsion rate is 0.5 mL / h, the shell propulsion rate is 1.0 mL / h, the voltage is 15 kV, and the receiving distance is 15 cm, resulting in a composite nanofiber membrane in which the core layer is wrapped by the shell layer.

[0031] (4) Segmented heat treatment: The composite nanofiber membrane was placed in an atmosphere furnace and subjected to segmented heat treatment under an oxygen atmosphere: the temperature was increased to 400℃ at a heating rate of 3℃ / min and held for 2h; then the temperature was increased to 760℃ at a heating rate of 3℃ / min and held for 10h, and then naturally cooled to room temperature to obtain an ultra-high nickel concentration gradient cathode material.

[0032] Example 3 This embodiment provides a method for preparing ultra-high nickel concentration gradient cathode materials via coaxial spinning, the specific steps of which are as follows: (1) Preparation of core spinning solution: Dissolve 1.2 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.90. 0.90 Co 0.05 Mn 0.05 The solution is prepared by mixing (OH)2, lithium hydroxide and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to precursor is 1:1. The mixture is stirred evenly to obtain the core spinning solution.

[0033] (2) Preparation of shell spinning solution: Dissolve 1.0 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.70. 0.70 Co 0.15 Mn 0.15 The mixture consists of (OH)2, lithium hydroxide, and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt, and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to the precursor is 1:1. The mixture is stirred evenly to obtain the shell spinning solution.

[0034] (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected simultaneously into the inner and outer channels of the coaxial needle through independent propulsion pumps, and converge at the needle outlet to form a Taylor cone with a core-shell structure. Then, it is stretched and refined under the action of a high voltage electric field. The core propulsion rate is 0.5 mL / h, the shell propulsion rate is 1.0 mL / h, the voltage is 15 kV, and the receiving distance is 15 cm, resulting in a composite nanofiber membrane in which the core layer is wrapped by the shell layer.

[0035] (4) Segmented heat treatment: The composite nanofiber membrane was placed in an atmosphere furnace and subjected to segmented heat treatment under an oxygen atmosphere: the temperature was raised to 400℃ at a heating rate of 3℃ / min and held for 2h; then the temperature was raised to 880℃ at a heating rate of 3℃ / min and held for 10h, and then naturally cooled to room temperature to obtain an ultra-high nickel concentration gradient cathode material.

[0036] Example 4 This embodiment provides a method for preparing ultra-high nickel concentration gradient cathode materials via coaxial spinning, the specific steps of which are as follows: (1) Preparation of core spinning solution: Dissolve 1.2 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.98. 0.98 Co 0.01 Mn 0.01 The solution is prepared by mixing (OH)2, lithium hydroxide and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to precursor is 1:4.

[0037] (2) Preparation of shell spinning solution: Dissolve 1.0 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add a precursor Ni with a nickel molar content of 0.85. 0.85 Co 0.10 Mn 0.05 The mixture of (OH)2, lithium hydroxide, and 2000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt, and manganese in the precursor is 1.05:1, and the mass ratio of polyacrylonitrile to the precursor is 1:4, is stirred evenly to obtain the shell spinning solution.

[0038] (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected simultaneously into the inner and outer channels of the coaxial needle through independent propulsion pumps, and converge at the needle outlet to form a Taylor cone with a core-shell structure. Then, it is stretched and refined under the action of a high voltage electric field. The core propulsion rate is 0.5 mL / h, the shell propulsion rate is 1.0 mL / h, the voltage is 15 kV, and the receiving distance is 15 cm, resulting in a composite nanofiber membrane in which the core layer is wrapped by the shell layer.

[0039] (4) Segmented heat treatment: The composite nanofiber membrane was placed in an atmosphere furnace and subjected to segmented heat treatment under an oxygen atmosphere: the temperature was increased to 400℃ at a heating rate of 3℃ / min and held for 2h; then the temperature was increased to 730℃ at a heating rate of 3℃ / min and held for 10h, and then naturally cooled to room temperature to obtain an ultra-high nickel concentration gradient cathode material.

[0040] Example 5 This embodiment provides a method for preparing ultra-high nickel concentration gradient cathode materials via coaxial spinning, the specific steps of which are as follows: (1) Preparation of core spinning solution: Dissolve 1.2 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.90. 0.90 Co 0.05 Mn 0.05 The solution is prepared by mixing (OH)2, lithium hydroxide and 1000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt and manganese in the precursor is 1.02:1, and the mass ratio of polyacrylonitrile to precursor is 1:5.

[0041] (2) Preparation of shell spinning solution: Dissolve 1.2g of polyacrylonitrile in 10mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.70. 0.70 Co 0.15 Mn 0.15 The mixture consists of (OH)2, lithium hydroxide, and 1000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt, and manganese in the precursor is 1.02:1, and the mass ratio of polyacrylonitrile to the precursor is 1:5. The mixture is stirred evenly to obtain the shell spinning solution.

[0042] (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected simultaneously into the inner and outer channels of the coaxial needle through independent propulsion pumps, and converge at the needle outlet to form a Taylor cone with a core-shell structure. Then, it is stretched and refined under the action of a high voltage electric field. The core propulsion rate is 0.2 mL / h, the shell propulsion rate is 0.5 mL / h, the voltage is 10 kV, and the receiving distance is 10 cm, resulting in a composite nanofiber membrane in which the core layer is wrapped by the shell layer.

[0043] (4) Segmented heat treatment: The composite nanofiber membrane was placed in an atmosphere furnace and subjected to segmented heat treatment under an oxygen atmosphere: the temperature was increased to 300℃ at a heating rate of 1℃ / min and held for 5h; then the temperature was increased to 880℃ at a heating rate of 1℃ / min and held for 12h, and then naturally cooled to room temperature to obtain an ultra-high nickel concentration gradient cathode material.

[0044] Example 6 This embodiment provides a method for preparing ultra-high nickel concentration gradient cathode materials via coaxial spinning, the specific steps of which are as follows: (1) Preparation of core spinning solution: Dissolve 2.0 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.96. 0.96 Co 0.02 Mn 0.02The solution is prepared by mixing (OH)2, lithium hydroxide and 3000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt and manganese in the precursor is 1.08:1, and the mass ratio of polyacrylonitrile to precursor is 1:1. The mixture is stirred evenly to obtain the core spinning solution.

[0045] (2) Preparation of shell spinning solution: Dissolve 2.0 g of polyacrylonitrile in 10 mL of N,N-dimethylformamide, and add Ni precursor with a nickel molar content of 0.80. 0.80 Co 0.10 Mn 0.10 The mixture consists of (OH)2, lithium hydroxide, and 3000 ppm ZrO2, wherein the ratio of lithium element in lithium hydroxide to the total molar number of nickel, cobalt, and manganese in the precursor is 1.08:1, and the mass ratio of polyacrylonitrile to the precursor is 1:1. The mixture is stirred evenly to obtain the shell spinning solution.

[0046] (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected simultaneously into the inner and outer channels of the coaxial needle through independent propulsion pumps, and converge at the needle outlet to form a Taylor cone with a core-shell structure. Then, it is stretched and refined under the action of a high voltage electric field. The core propulsion rate is 2.0 mL / h, the shell propulsion rate is 3.0 mL / h, the voltage is 25 kV, and the receiving distance is 25 cm, resulting in a composite nanofiber membrane in which the core layer is wrapped by the shell layer.

[0047] (4) Segmented heat treatment: The composite nanofiber membrane was placed in an atmosphere furnace and subjected to segmented heat treatment under an oxygen atmosphere: the temperature was increased to 500℃ at a heating rate of 3℃ / min and held for 1h; then the temperature was increased to 750℃ at a heating rate of 3℃ / min and held for 8h, and then naturally cooled to room temperature to obtain an ultra-high nickel concentration gradient cathode material.

[0048] Example 7 This embodiment provides a method for preparing an ultra-high nickel concentration gradient cathode material by coaxial spinning. The only difference between this method and Example 1 is that no metal oxide additive (ZrO2) is added in steps (1) and (2), while the other conditions are the same as in Example 1.

[0049] Example 8 This embodiment provides a method for preparing an ultra-high nickel concentration gradient cathode material by coaxial spinning. The only difference between this method and Example 1 is that the lithium salt ratio of the core layer to the shell layer is different in steps (1) and (2). Specifically, the molar ratio of lithium element to the total precursor transition metal in the core layer spinning solution is 1.05:1, and the molar ratio of lithium element to the total precursor transition metal in the shell layer spinning solution is 1.02:1. Other conditions are the same as in Example 1.

[0050] Comparative Example 1 This comparative example provides a method for preparing an ultra-high nickel cathode material. The difference between this method and Example 1 is that in step (3), ordinary electrospinning (non-coaxial) is used instead of coaxial electrospinning. That is, only a single needle is used to electrospin the core spinning solution separately, without preparing the shell spinning solution. Other conditions are the same as in Example 1.

[0051] Comparative Example 2 This comparative example provides a method for preparing an ultra-high nickel cathode material. The difference between this method and Example 1 is that no lithium salt is added to the shell spinning solution in step (2), while the other conditions are the same as in Example 1.

[0052] Comparative Example 3 This comparative example provides a method for preparing an ultra-high nickel cathode material. The difference between this method and Example 1 is that in steps (1) and (2), the core spinning solution and the shell spinning solution use precursors with the same nickel molar content, i.e., the core precursor is Ni. 0.92 Co 0.05 Mn 0.03 (OH)2 (nickel molar content 0.92), the shell precursor is also Ni 0.92 Co 0.05 Mn 0.03 (OH)2 (nickel molar content 0.92), other conditions are the same as in Example 1.

[0053] Comparative Example 4 A comparative example provides a method for preparing an ultra-high nickel cathode material, which differs from Example 1 in that the nickel content of the core layer and shell layer precursors in steps (1) and (2) is reversed, i.e., the core layer precursor is Ni with a nickel molar content of 0.80. 0.80 Co 0.10 Mn 0.10 (OH)2, the shell precursor is Ni with a nickel molar content of 0.92. 0.92 Co 0.05 Mn 0.03 (OH)2, other conditions are the same as in Example 1.

[0054] Comparative Example 5 This comparative example provides a method for preparing an ultra-high nickel cathode material. The difference between this method and Example 1 is that step (4) involves a one-step heat treatment: the composite nanofiber membrane is directly heated to 800°C at a heating rate of 3°C / min under an oxygen atmosphere and kept at that temperature for 12 hours without going through a heat preservation step of 300°C to 500°C. Other conditions are the same as in Example 1.

[0055] Comparative Example 6 This comparative example provides a method for preparing an ultra-high nickel cathode material. The difference between this method and Example 1 is that the heat treatment in step (4) is performed in stages: the temperature is increased to 200°C at a heating rate of 3°C / min and held for 2 hours; then the temperature is increased to 800°C at a heating rate of 3°C / min and held for 10 hours. Other conditions are the same as in Example 1.

[0056] Comparative Example 7 This comparative example provides a method for preparing an ultra-high nickel cathode material. The difference between this method and Example 1 is that the heat treatment in step (4) is performed in stages: the temperature is raised to 400°C at a heating rate of 3°C / min and held for 2 hours; then the temperature is raised to 600°C at a heating rate of 3°C / min and held for 10 hours. Other conditions are the same as in Example 1.

[0057] Test case The performance of the cathode materials prepared in the above embodiments and comparative examples was tested, as follows: Using N-methylpyrrolidone as a dispersant, the positive electrode material, carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5. N-methylpyrrolidone (the mass ratio of N-methylpyrrolidone to the total solid mass was 1:1) was then added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The slurry was then uniformly coated onto carbon-coated aluminum foil, with a coating density of 3 mg / cm³. 2 The positive electrode was dried in an oven at 80℃ for 2 hours to obtain the positive electrode sheet. The positive electrode sheet, solid electrolyte membrane, lithium-indium alloy negative electrode, and current collector were stacked sequentially, placed in a coin cell casing under an argon atmosphere in a glove box, pressurized, and then sealed to obtain a coin cell solid-state battery. The performance of the battery prepared above was tested, as follows: (1) 0.1C charge-discharge specific capacity test: At 25℃, the battery is charged to 4.5V at a constant current of 0.1C and the charging specific capacity is recorded; then it is discharged to 2.5V at a constant current of 0.1C and the discharging specific capacity is recorded. The formula for calculating the first efficiency is: First efficiency = 100% × first discharge specific capacity / first charge specific capacity.

[0058] (2) Cyclic performance test: At 25℃, the battery was activated by charging and discharging at 0.1C, 0.2C, 0.5C and 1C once each (voltage range 2.5~4.5V), and then cycled at 1C for 500 times (voltage range 2.5~4.5V). The cycle retention rate was calculated as follows: Cyclic retention rate = 100% × specific capacity of the 504th discharge / specific capacity of the 4th discharge (where the 4th discharge is the first 1C discharge after activation, and the 504th discharge is the last discharge after 500 1C cycles).

[0059] The test results are shown in Table 1.

[0060] Table 1. Electrochemical performance test results of the cathode materials in the examples and comparative examples.

[0061] Based on the above test results, it can be seen that Examples 1 to 8 of the present invention effectively improve the cycle stability of the ultra-high nickel cathode material under high voltage (4.5V). The capacity retention rate after 500 cycles at 1C is above 82%, while the specific capacity at 0.1C discharge is not less than 218.6mAh / g, and the first-time efficiency is not less than 91.5%. Among them, Example 7 did not add metal oxide additive (ZrO2), and the cycle retention rate was 84.5%, which was lower than that of Example 1 (88.6%), but the first-time efficiency (92.9%) was slightly higher than that of Example 1 (91.9%).

[0062] In contrast, Comparative Examples 1 through 7 failed to achieve excellent cycling stability while maintaining high capacity. Specifically, Comparative Example 1, using ordinary electrospinning (without a core-shell gradient structure), had a cycle retention rate of only 45.2%; Comparative Example 2, without lithium salt added to the shell, saw its initial efficiency drop to 83.1%, with a cycle retention rate of 68.5%; Comparative Example 3, with the same nickel content in both the core and shell (no concentration gradient), achieved a cycle retention rate of 65.7%; Comparative Example 4, with its reversed nickel content in the core and shell (high-nickel shell, low-nickel core), experienced a decrease in both initial efficiency and capacity; Comparative Examples 5 through 7, employing different heat treatment processes (one-step sintering, excessively low pre-sintering temperature, or excessively low final sintering temperature), all resulted in a significant reduction in capacity or initial efficiency.

[0063] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing ultra-high nickel concentration gradient cathode material by coaxial spinning, characterized in that, include: (1) Preparation of core spinning solution: Dissolve the first polymer in the first organic solvent, add a precursor with a nickel molar content ≥0.90 and the first lithium salt and mix to obtain the core spinning solution; (2) Preparation of shell spinning solution: Dissolve the second polymer in the second organic solvent, add the precursor with nickel molar content ≤0.85 and the second lithium salt and mix to obtain the shell spinning solution; (3) Coaxial electrospinning treatment: The core spinning solution and the shell spinning solution are injected into the inner and outer channels of the coaxial needle of the coaxial electrospinning device and coaxial electrospinning treatment is performed to obtain a composite nanofiber membrane. (4) Segmented heat treatment: The composite nanofiber membrane is subjected to segmented heat treatment in an oxygen atmosphere: first, the temperature is raised to 300℃~500℃ and held for 1h~5h, then the temperature is raised to 700℃~900℃ and held for 8h~12h to obtain ultra-high nickel concentration gradient cathode material.

2. The method for preparing coaxial fibers according to claim 1, characterized in that, In the core spinning solution, the nickel molar content in the precursor with a nickel molar content ≥ 0.90 is 0.90~0.98; And / or, in the shell spinning solution, the nickel molar content in the precursor with a nickel molar content ≤ 0.85 is 0.70~0.

85.

3. The method for preparing coaxial fibers according to claim 1 or 2, characterized in that, Metal oxide additives are also added to the core spinning solution and / or shell spinning solution.

4. The method for preparing coaxial fibers according to claim 3, characterized in that, The metal oxide additive includes at least one of ZrO2, MgO, TiO2, and Y2O3; And / or, the content of the metal oxide additive is 1000~3000ppm.

5. The method for preparing coaxial fibers according to claim 1 or 2, characterized in that, The parameters for the coaxial electrospinning process are as follows: core propulsion rate 0.2 mL / h to 2.0 mL / h, shell propulsion rate 0.5 mL / h to 3.0 mL / h, voltage 10 kV to 25 kV, and receiving distance 10 cm to 25 cm.

6. The method for preparing coaxial fibers according to claim 1 or 2, characterized in that, The first polymer comprises at least one of polyacrylonitrile, polyvinylpyrrolidone, polyvinyl alcohol, and polymethyl methacrylate; And / or, the second polymer comprises at least one of polyacrylonitrile, polyvinylpyrrolidone, polyvinyl alcohol, and polymethyl methacrylate.

7. The method for preparing coaxial fibers according to claim 1 or 2, characterized in that, The first organic solvent includes at least one of N,N-dimethylformamide and N-methylpyrrolidone; And / or, the second organic solvent includes at least one of N,N-dimethylformamide and N-methylpyrrolidone; And / or, the first lithium salt includes at least one of lithium hydroxide and lithium nitrate; And / or, the second lithium salt includes at least one of lithium hydroxide and lithium nitrate.

8. The method for preparing coaxial fibers according to claim 1 or 2, characterized in that, The mass ratio of the first polymer to the precursor with a nickel molar content ≥0.90 is 1:(1-5). And / or, in the shell spinning solution, the mass ratio of the second polymer to the precursor with a nickel molar content ≤0.80 is 1:(1-5).

9. A high nickel concentration gradient cathode material, characterized in that, It is prepared by the coaxial spinning method for preparing ultra-high nickel concentration gradient cathode material according to any one of claims 1 to 8.

10. The application of the ultra-high nickel concentration gradient cathode material according to claim 9 in lithium-ion battery cathode materials.

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