Modified high-nickel ternary positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and provides a modified high-nickel ternary positive electrode material and a preparation method and application thereof, the modified high-nickel ternary positive electrode material comprises an inner core and a coating layer coating the inner core; the inner core comprises a gradient-doped high-nickel ternary material, a doped element comprises a samarium element, and the doping concentration of the samarium element is gradually increased from the center of the inner core to the surface of the inner core; the coating layer comprises a carbon layer, and samarium oxide particles are dispersed in the carbon layer. By forming gradient doping of the metal element samarium and utilizing 4f orbital electrons of Sm < 3 + >, H2-H3 phase change of the high-nickel ternary material can be inhibited, the layered structure of the material can be stabilized, lattice defects can be introduced, Li < + > transmission can be promoted, and diffusion energy barriers can be reduced. Meanwhile, the carbon layer doped with the samarium oxide particles is adopted for coating, on one hand, electrolyte corrosion is effectively inhibited, and on the other hand, the samarium oxide particles can further stabilize lattice oxygen and enhance electron conduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to a modified high-nickel ternary positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, with the transformation of the global energy structure and the continuous advancement of the carbon peak and carbon neutrality goals, lithium-ion batteries, as the core energy carrier supporting electric vehicles and large-scale energy storage systems, are facing increasingly severe challenges in their technical performance. Especially for power batteries, high energy density, long cycle life and good safety have become key indicators to measure their comprehensive performance. In this context, the ternary layered oxide positive electrode material LiNi 1-x-y Co x Mn y O2(NCM) is widely considered to be one of the key materials for achieving 300Wh / kg high energy density lithium-ion battery system due to its excellent specific capacity (usually exceeding 200mAh / g), high operating voltage range (about 3.6~4.3V), and relatively controllable cost advantage.

[0003] However, in actual application, the interfacial stability problem of NCM materials with high nickel content during electrochemical cycling is prominent. Due to the strong surface activity of nickel, transition metal ions are easily dissolved during the charge and discharge process, especially under high voltage (>4.5V) and high temperature (>45°C) conditions. This dissolution not only damages the crystal structure of the positive electrode material itself, but also triggers continuous side reactions in the electrolyte, thereby destroying the stability of the solid electrolyte interface film (CEI film), resulting in increased interface impedance and decreased coulombic efficiency, ultimately affecting the overall cycle performance of the battery. In addition, with the increase of nickel content, the structural distortion of the material in the deep delithiation state becomes more and more significant, especially in the H2-H3 phase transition region, where the lattice parameters change dramatically, which can easily cause the formation and expansion of microcracks. These microcracks not only aggravate the accumulation of stress inside the material, but also expose more fresh surfaces inside the secondary particles, thereby further aggravating the occurrence of interfacial side reactions.

[0004] To alleviate these issues, concentration gradient construction is considered an effective solution. Concentration-gradient ternary cathode materials can optimize interfacial effects through a gradient design of composition, structure, and performance, but this is complex to process and is subject to conductivity limitations. Doping with a single metal or anion element, on the other hand, makes it difficult to optimize multiple issues simultaneously.

[0005] Overall, with electric vehicles and energy storage systems placing increasing demands on battery performance, how to achieve stable operation of high-nickel ternary cathode materials under high-voltage and high-temperature environments without sacrificing energy density remains a technical problem that needs to be solved urgently and has practical significance. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a modified high-nickel ternary positive electrode material and its preparation method and use, wherein the modified high-nickel ternary positive electrode material comprises a core and a coating layer covering the core; the core comprises a high-nickel ternary material that is gradient-doped, the doping element comprises samarium, and the doping concentration of the samarium element gradually decreases from the surface to the center of the core; the coating layer comprises a carbon layer, and samarium oxide particles are dispersed in the carbon layer. By introducing a specific metal element samarium, the use of its Sm 3+ The 4f orbital electrons can inhibit the H2-H3 phase transition of high nickel ternary materials, stabilize the layered structure of the material, and introduce lattice defects to promote Li + At the same time, the carbon layer doped with samarium oxide particles is used to effectively inhibit electrolyte corrosion. On the other hand, the samarium oxide particles can further stabilize the lattice oxygen and enhance electronic conduction.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a modified high-nickel ternary positive electrode material, comprising a core and a coating layer coating the core; the core comprises a gradient-doped high-nickel ternary material, the doping element comprises samarium, and the doping concentration of the samarium element gradually increases from the center to the surface of the core; the coating layer comprises a carbon layer, and samarium oxide particles are dispersed in the carbon layer.

[0009] The present invention realizes the coordinated optimization of material properties by constructing a multi-level structure of "core-transition layer-shell" through gradient doping of samarium elements, which can inhibit the H2-H3 phase transition of high-nickel ternary materials, improve the stability of large-particle high-nickel ternary positive electrode materials during the cycle, and at the same time introduce lattice defects to promote Li + The present invention also reduces the diffusion energy barrier by doping samarium oxide particles in the carbon layer to form a specific coating layer, which can inhibit surface nickel dissolution, enhance lithium ion transport, and reduce interfacial impedance. Through the synergistic effect of the gradient doping of samarium and the specific coating layer, the high energy density and high stability of the high-nickel ternary cathode material are effectively achieved.

[0010] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0011] As a preferred technical solution of the present invention, the chemical formula of the high nickel ternary material includes Ni x Co y Mn 1-x-y O2, 0.8≤x≤0.99, for example, x can be 0.8, 0.83, 0.85, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98 or 0.9, etc.; 0.05≤y≤0.1, for example, y can be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, etc.

[0012] Preferably, the average particle size of the core is 10-15 μm, for example, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm or 15 μm.

[0013] Preferably, in the core, the doping amount of the samarium element accounts for 0.3% to 0.5% of the molar amount of the high-nickel ternary material, for example, 0.3%, 0.33%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48% or 0.5%, etc.

[0014] Preferably, in the coating layer, the molar amount of samarium element in the samarium oxide particles accounts for 1% to 1.5% of the molar amount of carbon element in the carbon layer, for example, 1%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45% or 1.5%, etc.

[0015] Preferably, in the coating layer, the average particle size of the samarium oxide particles is 4 to 6 nm.

[0016] Preferably, the samarium oxide particles include Sm2O3.

[0017] Preferably, the coating layer has a thickness of 10 to 30 nm, for example, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm or 30 nm.

[0018] In a second aspect, the present invention provides a method for preparing the modified high-nickel ternary positive electrode material according to the first aspect, the preparation method comprising the following steps:

[0019] S1. A samarium source, a ternary metal salt, a precipitant and a complexing agent are mixed in a first liquid phase and subjected to a coprecipitation reaction. During the coprecipitation reaction, the feeding frequency of the samarium source is gradually increased to obtain a samarium gradient-doped precursor;

[0020] S2. The samarium source, reducing agent, dopamine and buffer solution are mixed in the second liquid phase and subjected to a self-polymerization reaction to generate samarium nanoparticles doped with polydopamine to obtain a coating solution;

[0021] S3. The samarium gradient-doped precursor is mixed with the coating solution in a third liquid phase to obtain a coating precursor;

[0022] S4. After mixing the coated precursor with a lithium source, calcining to obtain a modified high-nickel ternary cathode material;

[0023] There is no particular order for step S1 and step S2.

[0024] The preparation method of the present invention achieves gradient doping of samarium elements in the core through coprecipitation, while also introducing lattice defects, thereby promoting lithium ion transport and reducing the diffusion energy barrier. By first preparing polydopamine doped with samarium nanoparticles, fixing the samarium nanoparticles within the polydopamine network, and then forming a coating layer on the surface of the samarium gradient-doped precursor, followed by a calcination treatment, the polydopamine simultaneously forms a carbon layer while the samarium nanoparticles are converted into samarium oxide particles that are uniformly dispersed within the carbon layer, forming a coating layer.

[0025] As a preferred technical solution of the present invention, in step S1 and step S2, the samarium source includes samarium nitrate.

[0026] As a preferred technical solution of the present invention, in step S1, the ternary metal salt includes a nickel salt, a cobalt salt and a manganese salt; the nickel salt includes at least one of nickel chloride, nickel sulfate or nickel nitrate; the cobalt salt includes at least one of cobalt chloride, cobalt sulfate or cobalt nitrate; and the manganese salt includes at least one of manganese chloride, manganese sulfate or manganese nitrate.

[0027] Preferably, the precipitant comprises liquid alkali.

[0028] Preferably, the complexing agent comprises an ammonia solution.

[0029] As a preferred technical solution of the present invention, in step S1, the preparation method includes: first preparing the samarium source into a samarium source solution, preparing the ternary metal salt into a ternary metal salt solution, preparing the precipitant into a precipitant solution, and preparing the complexing agent into a complexing agent solution, and then adding the samarium source solution, the ternary metal salt solution, the precipitant solution and the complexing agent solution to a first bottom liquid and mixing them in parallel to perform a first co-precipitation reaction. During the first co-precipitation reaction, the feeding frequency of the samarium source solution is controlled to gradually increase to obtain samarium-doped seed crystals; then mixing the samarium-doped seed crystals into a second bottom liquid, and then again adding the samarium source solution, the ternary metal salt solution, the precipitant solution and the complexing agent solution to the second bottom liquid and mixing them in parallel to perform a second co-precipitation reaction. During the second co-precipitation reaction, the feeding frequency of the samarium source solution is controlled to gradually increase to obtain the samarium gradient-doped precursor.

[0030] Preferably, the concentration of samarium ions in the samarium source solution is 5 to 20 mmol / L, for example, 5 mmol / L, 8 mmol / L, 10 mmol / L, 12 mmol / L, 14 mmol / L, 16 mmol / L, 18 mmol / L or 20 mmol / L.

[0031] Preferably, the total concentration of the ternary metal ions in the ternary metal salt solution is 1 to 2 mol / L, for example, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L, etc.

[0032] Preferably, the first base solution contains the precipitant and the complexing agent, and the pH of the first base solution is 10.5-11.5, for example, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4 or 11.5.

[0033] Preferably, the temperature of the first coprecipitation reaction is 40-60°C, for example, 40°C, 43°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C or 60°C, etc., the pH is 11-11.5, for example, 11, 11.1, 11.2, 11.3, 11.4 or 11.5, etc., the ammonia concentration is 0.2-0.3 mol / L, for example, 0.2mol / L, 0.21mol / L, 0.22mol / L, 0.23mol / L, 0.24mol / L, 0.25mol / L, 0.26mol / L, 0.27mol / L, 0.28mol / L, 0.29mol / L or 0.3mol / L, etc., and the stirring speed is 380-400rpm, for example, 380rpm, 385rpm, 390rpm, 395rpm or 400rpm, etc.

[0034] Preferably, the average particle size of the samarium-doped seed crystals is 2 to 4 μm, for example, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm.

[0035] Preferably, the samarium-doped seed crystals are pre-centrifuged, washed and dehydrated before being mixed into the second base liquid.

[0036] Preferably, the second base liquid contains the complexing agent.

[0037] Preferably, the temperature of the second coprecipitation reaction is 40-60°C, for example, 40°C, 43°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C or 60°C, etc., the pH is 10-10.5, for example, 10, 10.1, 10.2, 10.3, 10.4 or 10.5, etc., the ammonia concentration is 0.15-0.25 mol / L, for example, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, 0.2 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L or 0.25 mol / L, etc., and the stirring speed is 380-400 rpm, for example, 380 rpm, 385 rpm, 390 rpm, 395 rpm or 400 rpm, etc.

[0038] As a preferred technical solution of the present invention, in step S2, the reducing agent includes ascorbic acid.

[0039] Preferably, the dopamine comprises dopamine hydrochloride.

[0040] Preferably, the buffer solution comprises a Tris buffer solution.

[0041] Preferably, the molar ratio of the samarium element in the samarium source to the dopamine is (0.03-0.1):1, for example, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1 or 0.1:1, etc.

[0042] Preferably, the preparation method comprises: first mixing the dopamine with the buffer solution, then adding the samarium source and mixing, and finally adding the reducing agent and mixing.

[0043] Preferably, the temperature of the self-polymerization reaction is 30-50°C, for example, 30°C, 35°C, 40°C, 45°C or 50°C, and the time is 4-8h, for example, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h.

[0044] As a preferred technical solution of the present invention, in step S3, the samarium gradient-doped precursor is pre-washed and dried, and then mixed with the coating solution in a third liquid phase.

[0045] Preferably, the solid-liquid ratio of the samarium gradient-doped precursor to the coating solution is 1g:(15-25)mL, for example, 1g:15mL, 1g:16mL, 1g:17mL, 1g:18mL, 1g:19mL, 1g:20mL, 1g:21mL, 1g:22mL, 1g:23mL, 1g:24mL or 1g:25mL, etc.

[0046] As a preferred technical solution of the present invention, in step S1, the lithium source includes lithium carbonate and / or lithium hydroxide.

[0047] Preferably, the calcination process includes: firstly performing low-temperature calcination at 300-400°C for 3-4 hours, for example, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, and then performing high-temperature calcination at 750-850°C for 4-5 hours, for example, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C or 850°C.

[0048] In the present invention, the low-temperature calcination serves as a pre-burning to fully remove the residual organic matter in the coating precursor and preliminarily fix the distribution of the samarium element, and then high-temperature calcination is performed to form a layered structure of the high-nickel ternary material. At the same time, samarium oxide particles are generated to promote the formation of strong chemical bonds with the surface of the high-nickel ternary material in the core through Sm-OM bonds, and to help the samarium element in the coating layer diffuse into the core, thereby enhancing gradient doping.

[0049] In a third aspect, the present invention provides a battery comprising the modified high-nickel ternary positive electrode material described in the first aspect.

[0050] It should be noted that due to space limitations and to avoid redundancy, the present invention does not exhaustively list all point values ​​within the above numerical range, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0051] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0052] In the modified high nickel ternary cathode material of the present invention, the gradient doping of samarium element in the core can inhibit the H2-H3 phase transition of the high nickel ternary material, improve the stability of the large particle size high nickel ternary cathode material during the cycle, and at the same time introduce lattice defects to promote Li + The present invention also reduces the diffusion energy barrier by doping samarium oxide particles in the carbon layer to form a specific coating on the surface of the core, which can inhibit nickel dissolution from the core surface, enhance lithium ion transport, and reduce interfacial impedance. Through the synergistic effect of the gradient doping of samarium and the specific coating, the high energy density and high stability of the high-nickel ternary cathode material are effectively achieved. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0054] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0055] Example 1

[0056] This embodiment provides a modified high-nickel ternary positive electrode material, comprising a core and a coating layer covering the core; the core is a high-nickel ternary material that is gradient-doped, the doping element is samarium, and the doping concentration of the samarium element gradually increases from the center to the surface of the core; the coating layer is a carbon layer, and samarium oxide particles are dispersed in the carbon layer; the chemical formula of the high-nickel ternary material includes Ni 0.92 Co 0.05 Mn 0.03 O2; the average particle size of the inner core is 12.3 μm; in the inner core, the doping amount of the samarium element accounts for 0.4% of the molar amount of the high-nickel ternary material; in the coating layer, the molar amount of the samarium element in the samarium oxide particles accounts for 1.28% of the molar amount of the carbon element in the carbon layer; in the coating layer, the average particle size of the samarium oxide particles is 4.2 nm; the thickness of the coating layer is 22 nm.

[0057] The preparation method of the modified high-nickel ternary positive electrode material comprises:

[0058] S1. First, a samarium source samarium nitrate is prepared as a samarium source solution, wherein the concentration of samarium ions in the samarium source solution is 13 mmol / L; a ternary metal salt comprising a nickel salt of nickel nitrate, a cobalt salt of cobalt nitrate and a manganese salt of manganese nitrate is prepared as a ternary metal salt solution, wherein the total concentration of ternary metal ions in the ternary metal salt solution is 1.5 mol / L; providing liquid alkali as a precipitant solution, providing an ammonia solution as a complexing agent solution;

[0059] Inject water into the reactor to half of its volume, start the stirring speed at 400 rpm, control the temperature at 50°C, and then add the ammonia solution and the liquid alkali to prepare a first bottom liquid, so that the pH of the first bottom liquid is 11; after stirring and mixing for 30 minutes, turn on the metering pumps of the ternary metal salt solution, ammonia solution, and liquid alkali, and turn on the peristaltic pump of the samarium source solution to mix them in parallel in the first bottom liquid to carry out a first coprecipitation reaction, control the temperature of the first coprecipitation reaction to 50°C, the pH to 11-11.5, the ammonia concentration to 0.25 mol / L, the stirring speed to 380-400 rpm, and during the first coprecipitation reaction, control the feeding frequency of the samarium source solution to gradually increase to generate samarium-doped seed crystals, and stop the first coprecipitation reaction when the average particle size of the samarium-doped seed crystals reaches 3 μm;

[0060] The samarium-doped seed crystals are centrifuged, washed, and dehydrated, and then mixed into a reactor containing a second bottom liquid, wherein the second bottom liquid is a portion of the complexing agent solution. The samarium source solution, the ternary metal salt solution, the precipitant solution, and the complexing agent solution are then added to the second bottom liquid and mixed in parallel to perform a second coprecipitation reaction. The temperature of the second coprecipitation reaction is controlled to be 50° C., the pH is 10 to 10.5, the ammonia concentration is 0.2 mol / L, and the stirring speed is 380 to 400 rpm. During the second coprecipitation reaction, the feeding frequency of the samarium source solution is controlled to gradually increase to generate the samarium gradient-doped precursor. When the average particle size of the samarium gradient-doped precursor reaches 11 μm, the second coprecipitation reaction is stopped.

[0061] S2. dopamine hydrochloride was mixed with the Tris buffer solution, and then a samarium source samarium nitrate was added, wherein the molar ratio of samarium element in the samarium source to dopamine was 0.06:1. Finally, ascorbic acid, a reducing agent, was added and mixed, and a self-polymerization reaction was carried out at 40 ° C under stirring for 6 h to generate samarium nanoparticles doped with polydopamine to obtain a coating solution;

[0062] S3. The samarium gradient-doped precursor was washed and dried, and then mixed with the coating solution in a third liquid phase, controlling the solid-liquid ratio of the samarium gradient-doped precursor to the coating solution to be 1:20 g / mL to obtain a coated precursor;

[0063] S4. After mixing the coated precursor with lithium carbonate as a lithium source, the mixture was first calcined at 350°C and then calcined at 750°C to obtain a modified high-nickel ternary cathode material;

[0064] There is no particular order for step S1 and step S2.

[0065] Example 2

[0066] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source solution in step S1 of the preparation method, the doping amount of the samarium element in the core of the modified high-nickel ternary positive electrode material is changed from 0.4% of the molar amount of the high-nickel ternary material to 0.2%. Except for the above, other conditions are exactly the same as those in Example 1.

[0067] Example 3

[0068] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source solution in step S1 of the preparation method, the doping amount of the samarium element in the core of the modified high-nickel ternary positive electrode material is changed from 0.4% of the molar amount of the high-nickel ternary material to 0.3%. Except for the above, other conditions are exactly the same as those in Example 1.

[0069] Example 4

[0070] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source solution in step S1 of the preparation method, the doping amount of the samarium element in the core of the modified high-nickel ternary positive electrode material is changed from 0.4% of the molar amount of the high-nickel ternary material to 0.5%. Except for the above, other conditions are exactly the same as those in Example 1.

[0071] Example 5

[0072] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source solution in step S1 of the preparation method, the doping amount of the samarium element in the core of the modified high-nickel ternary positive electrode material is changed from 0.4% of the molar amount of the high-nickel ternary material to 0.5%. Except for the above, other conditions are exactly the same as those in Example 1.

[0073] Example 6

[0074] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source in step S2 of the preparation method, the molar ratio of the samarium element in the coating layer of the modified high-nickel ternary positive electrode material is changed from 1.28% to 0.5% of the molar ratio of the carbon element in the carbon layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0075] Example 7

[0076] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source in step S2 of the preparation method, the molar ratio of the samarium element in the coating layer of the modified high-nickel ternary positive electrode material is changed from 1.28% of the molar ratio of the carbon element in the carbon layer to 1%. Except for the above, other conditions are exactly the same as those in Example 1.

[0077] Example 8

[0078] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source in step S2 of the preparation method, the molar ratio of the samarium element in the coating layer of the modified high-nickel ternary positive electrode material is changed, so that the molar ratio of the samarium element in the carbon layer is adjusted from 1.28% to 1.5%. Except for the above, other conditions are exactly the same as those in Example 1.

[0079] Example 9

[0080] This embodiment provides a modified high-nickel ternary positive electrode material. By adjusting the feeding frequency of the samarium source in step S2 of the preparation method, the molar ratio of the samarium element in the coating layer of the modified high-nickel ternary positive electrode material is changed from 1.28% to 2% of the molar ratio of the carbon element in the carbon layer. Except for the above, other conditions are exactly the same as those in Example 1.

[0081] Example 10

[0082] This embodiment provides a modified high-nickel ternary positive electrode material, and steps S2 and S3 of the preparation method are combined, that is, the samarium gradient-doped precursor obtained in step S1 is directly mixed with the dopamine hydrochloride and the Tris buffer solution in step S2, and then the samarium source and the reducing agent are added and mixed, and the self-polymerization reaction is carried out to obtain a coating solution. After filtering, washing and drying, a coating precursor is obtained. Except for the above, other conditions are exactly the same as those in Example 1.

[0083] Comparative Example 1

[0084] This comparative example provides a modified high-nickel ternary positive electrode material, in which the feeding frequency of the samarium source solution in the first coprecipitation reaction and the second coprecipitation reaction in step S1 of the preparation method is adjusted to be constant over time, so that the doping amount of the samarium element in the precursor obtained by the second coprecipitation reaction remains unchanged, but is a uniform bulk doping. Except for the above, other conditions are exactly the same as those in Example 1.

[0085] Comparative Example 2

[0086] This comparative example provides a modified high-nickel ternary positive electrode material. In the preparation method step S1, the samarium source and samarium source solution are not used, so that the core of the modified high-nickel ternary positive electrode material is not doped. Except for the above, other conditions are exactly the same as those in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a modified high-nickel ternary positive electrode material. In step S2 of the preparation method, no samarium source is used, so that the coating layer of the modified high-nickel ternary positive electrode material does not contain samarium oxide particles. Except for the above, other conditions are exactly the same as those in Example 1.

[0089] Characterization and testing:

[0090] The coated positive electrode materials obtained in the examples and comparative examples were prepared into positive electrode sheets and assembled into batteries. A lithium sheet was used as the negative electrode, the separator was a φ19 PP microporous membrane (Celgard2400), and the electrolyte was 1 mol / L LiPF6 dissolved in EC and DMC in a volume ratio of 1:1. The tests were carried out under the electrochemical window of 2.8V to 4.3V, including the cycle capacity retention rate after 2000 cycles at 0.5C, the capacity at 10C, and the interface impedance after cycling (2000 cycles at 0.5C). The results are shown in Table 1.

[0091] Table 1

[0092]

[0093] As can be seen from Table 1: This scheme uses the synergistic mechanism of gradient doping and coating, in which gradient doping constructs a stress buffer layer, and Sm2O3 coating realizes interface self-purification, synergistically reducing mechanical degradation and chemical corrosion; the Sm gradient doping concentration is regulated, in which the surface Sm concentration needs to reach a critical value of 0.6% to 0.7% to completely passivate the highly active Ni 3+ , but the average bulk concentration is ≤0.4% to avoid blocking the Li channel; the Sm2O3 coating layer content was investigated and it was found that if the conductive network is too low, the discontinuous carbon layer does not form an effective electron channel, and the local current density is uneven, while if the content is too high, the hard Sm2O3 agglomerates will induce local stress, and the cracks in the electrode will increase by 50% after cycling; the one-step coating process is compared, and the one-step comparison method may cause dopamine to be deposited in the Sm 3+ The polymerization rate under catalysis is uneven, and the thickness is uneven, so that the surface energy difference of the Sm gradient-doped precursor triggers local enrichment of the capping agent.

[0094] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0095] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0096] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A modified high-nickel ternary cathode material, characterized in that: It includes a core and a coating layer covering the core; the core includes a high-nickel ternary material that is gradient-doped, the doping element includes samarium, and the doping concentration of the samarium element gradually increases from the center to the surface of the core; the coating layer includes a carbon layer, and samarium oxide particles are dispersed in the carbon layer.

2. The modified high-nickel ternary cathode material according to claim 1, characterized in that The chemical formula of the high nickel ternary material includes Ni x Co y Mn 1-x-y O2, 0.8≤x≤0.99, 0.05≤y≤0.1; Preferably, the average particle size of the core is 10 to 15 μm; Preferably, in the core, the doping amount of the samarium element accounts for 0.3% to 0.5% of the molar amount of the high-nickel ternary material; Preferably, in the coating layer, the molar amount of samarium in the samarium oxide particles accounts for 1% to 1.5% of the molar amount of carbon in the carbon layer; Preferably, in the coating layer, the average particle size of the samarium oxide particles is 4 to 6 nm; Preferably, the samarium oxide particles include Sm2O3; Preferably, the coating layer has a thickness of 10 to 30 nm.

3. A method for preparing a modified high-nickel ternary positive electrode material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: S1. A samarium source, a ternary metal salt, a precipitant and a complexing agent are mixed in a first liquid phase to perform a coprecipitation reaction, wherein the feeding frequency of the samarium source is gradually increased during the coprecipitation reaction to obtain a samarium gradient-doped precursor; S2. The samarium source, reducing agent, dopamine and buffer solution are mixed in the second liquid phase and subjected to a self-polymerization reaction to generate samarium nanoparticles doped with polydopamine to obtain a coating solution; S3. The samarium gradient-doped precursor is mixed with the coating solution in a third liquid phase to obtain a coating precursor; S4. After mixing the coated precursor with a lithium source, calcining to obtain a modified high-nickel ternary cathode material; There is no particular order for step S1 and step S2.

4. The method for preparing the modified high-nickel ternary cathode material according to claim 3, characterized in that: In step S1 and step S2, the samarium source includes samarium nitrate.

5. The method for preparing the modified high-nickel ternary cathode material according to claim 3 or 4, characterized in that: In step S1, the ternary metal salt includes a nickel salt, a cobalt salt and a manganese salt; the nickel salt includes at least one of nickel chloride, nickel sulfate or nickel nitrate; the cobalt salt includes at least one of cobalt chloride, cobalt sulfate or cobalt nitrate; the manganese salt includes at least one of manganese chloride, manganese sulfate or manganese nitrate; Preferably, the precipitant comprises liquid alkali; Preferably, the complexing agent comprises an ammonia solution.

6. The method for preparing the modified high-nickel ternary cathode material according to any one of claims 3 to 5, characterized in that: In step S1, the preparation method includes: first preparing the samarium source as a samarium source solution, preparing the ternary metal salt as a ternary metal salt solution, preparing the precipitant as a precipitant solution, and preparing the complexing agent as a complexing agent solution, then adding the samarium source solution, the ternary metal salt solution, the precipitant solution and the complexing agent solution to a first bottom liquid and mixing them in parallel to perform a first coprecipitation reaction, during the first coprecipitation reaction, controlling the feeding frequency of the samarium source solution to gradually increase to obtain samarium-doped seed crystals; then mixing the samarium-doped seed crystals into a second bottom liquid, and then again adding the samarium source solution, the ternary metal salt solution, the precipitant solution and the complexing agent solution to the second bottom liquid and mixing them in parallel to perform a second coprecipitation reaction, during the second coprecipitation reaction, controlling the feeding frequency of the samarium source solution to gradually increase to obtain the samarium gradient-doped precursor; Preferably, the concentration of samarium ions in the samarium source solution is 5 to 20 mmol / L; Preferably, the total concentration of ternary metal ions in the ternary metal salt solution is 1 to 2 mol / L; Preferably, the first base liquid contains the precipitant and the complexing agent, and the pH of the first base liquid is 10.5 to 11.5; Preferably, the temperature of the first coprecipitation reaction is 40-60°C, the pH is 11-11.5, the ammonia concentration is 0.2-0.3 mol / L, and the stirring speed is 380-400 rpm; Preferably, the average particle size of the samarium-doped seed crystals is 2 to 4 μm; Preferably, the samarium-doped seed crystals are pre-centrifuged, washed and dehydrated before being mixed into the second base liquid; Preferably, the second base liquid contains the complexing agent; Preferably, the temperature of the second coprecipitation reaction is 40-60° C., the pH is 10-10.5, the ammonia concentration is 0.15-0.25 mol / L, and the stirring speed is 380-400 rpm.

7. The method for preparing the modified high-nickel ternary cathode material according to any one of claims 3 to 6, characterized in that: In step S2, the reducing agent includes ascorbic acid; Preferably, the dopamine comprises dopamine hydrochloride; Preferably, the buffer solution comprises a Tris buffer solution; Preferably, the molar ratio of the samarium element in the samarium source to the dopamine is (0.03-0.1):1; Preferably, the preparation method comprises: first mixing the dopamine with the buffer solution, then adding the samarium source and mixing, and finally adding the reducing agent and mixing; Preferably, the temperature of the self-polymerization reaction is 30-50° C., and the time is 4-8 hours.

8. The method for preparing the modified high-nickel ternary cathode material according to any one of claims 3 to 7, characterized in that: In step S3, the samarium gradient-doped precursor is pre-washed and dried, and then mixed with the coating solution in a third liquid phase; Preferably, the solid-to-liquid ratio of the samarium gradient-doped precursor to the coating solution is 1 g:(15-25) mL.

9. The method for preparing the modified high-nickel ternary cathode material according to any one of claims 3 to 8, characterized in that: In step S1, the lithium source includes lithium carbonate and / or lithium hydroxide; Preferably, the calcination process comprises: firstly performing low-temperature calcination at 300-400° C. for 3-4 hours, and then performing high-temperature calcination at 750-850° C. for 4-5 hours.

10. A battery, characterized in that: Contains the modified high-nickel ternary positive electrode material according to claim 1 or 2.

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