A high-nickel ternary cathode material, its preparation method and application

Abstract

This invention relates to the field of electrode materials, specifically to a high-nickel ternary cathode material, its preparation method, and its applications. The high-nickel ternary cathode material comprises a high-nickel ternary material matrix; the surface layer of the high-nickel ternary material matrix includes a spinel structure; the surface layer of the high-nickel ternary material matrix is ​​doped with anions; the anions contain fluorine and / or phosphorus elements. The high-nickel ternary cathode material exhibits good high-temperature cycling performance and high-voltage electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of electrode materials, and more specifically, to a high-nickel ternary cathode material, its preparation method, and its application. Background Technology

[0002] In recent years, increasing the charging cut-off voltage of ternary cathodes (NCMs) to achieve higher capacity utilization has been a major method for improving the energy density of battery cells. Surface optimization is considered the most effective strategy for improving the cycle stability of NCMs under high voltage. However, current research mainly focuses on improving the cycle stability of high-voltage NCMs at room temperature (25°C), with less attention paid to cycle life under high-temperature conditions. Considering practical applications and safety, researchers and industry should pay more attention to improving the high-temperature performance of batteries, including cycle stability, float charging durability, and high-temperature energy storage. The significantly reduced cycle stability of NCM electrodes under high-temperature (≥45°C) conditions is generally attributed to particle breakage and intensified side reactions. However, the mechanism of intensified side reactions at high temperatures remains unclear, limiting the development of more advanced and durable NCM materials.

[0003] Layered oxide cathode materials, such as ternary materials and lithium-rich materials, have been widely used in lithium-ion batteries due to their excellent lithium-ion transport characteristics, high energy density, and relatively low cost. Currently, the mainstream synthesis method involves mixing precursors with lithium salts and doping additives, followed by high-temperature sintering. However, layered cathode materials synthesized through high-temperature sintering face several inherent problems: 1) low structural stability, leading to structural collapse during cycling; 2) irreversible migration of transition metal (TM) ions into the lithium layer, causing cation mixing; 3) reconstruction of inactive surface phases, resulting in increased impedance; and 4) irreversible redox reactions of anionic oxygen under high voltage, leading to the collapse of the anionic framework. In short, these problems significantly reduce the electrochemical performance of the material.

[0004] In summary, although the mainstream cathode material preparation process is simple, it has some defects that limit further improvement of the materials and have contributed to the shrinking of the current ternary material market.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a high-nickel ternary cathode material with a stable structure, good electrochemical performance, and minimal increase in state of charge (SOC) under high-temperature charging conditions.

[0007] The second objective of this invention is to provide a method for preparing the high-nickel ternary cathode material, wherein the preparation conditions are mild, and the prepared high-nickel ternary cathode material has a stable structure at high temperatures and is not prone to side reactions.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] One aspect of the present invention relates to a high-nickel ternary cathode material, comprising a high-nickel ternary material matrix;

[0010] The surface layer of the high-nickel ternary material matrix includes a spinel structure; the surface layer of the high-nickel ternary material matrix is ​​doped with anions;

[0011] The anion contains fluorine and / or phosphorus.

[0012] The high-nickel ternary cathode material described above exhibits good high-temperature cycling performance and high-voltage electrochemical performance.

[0013] Another aspect of the present invention relates to a method for preparing the aforementioned high-nickel ternary cathode material, comprising the following steps:

[0014] (a) Disperse the high-nickel ternary material in a cation exchange solution to carry out ion exchange reaction and solid-liquid separation, and collect the powder;

[0015] The cations in the cation exchange solution have a higher valence state than lithium ions;

[0016] (b) The heat-treated powder and the anion-doped material are mixed and then anion-doped.

[0017] The method described above has mild preparation conditions, simple process, and is easy to implement. The high-nickel ternary cathode material prepared by this method has a stable structure at high temperature and is not prone to side reactions.

[0018] Another aspect of the present invention relates to a positive electrode sheet, mainly made of a high-nickel ternary positive electrode material prepared by the aforementioned method for preparing high-nickel ternary positive electrode material or the aforementioned high-nickel ternary positive electrode material.

[0019] Another aspect of the present invention relates to a lithium-ion battery, including the aforementioned positive electrode.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The high-nickel ternary cathode material provided by the present invention has good high-temperature cycling performance and high-voltage electrochemical performance. The surface layer of the high-nickel ternary material matrix is ​​subjected to cation exchange and heat treatment to form a spinel structure on the surface layer. Anions are doped into the holes formed on the surface layer, so that the high-nickel ternary cathode material has a relatively stable surface structure.

[0022] (2) The preparation method of high-nickel ternary cathode material provided by the present invention involves dispersing the high-nickel ternary material in a cation exchange solution for ion exchange. Due to the concentration difference between the bulk phase and the solution, lithium ions on the surface (including lithium ions at Ni sites) diffuse into the solution, and metal cations in the solution diffuse into the bulk phase (including lithium layers and transition metal layers). After filtering the solution, the surface is reconstructed by low-temperature heat treatment to form a spinel / layered mixed phase. Since the valence state of the metal ions entering the bulk phase is higher than that of lithium ions, local vacancies are formed. After the anions are mixed evenly with the material, heat treatment is performed. The anions diffuse into the bulk phase to fill the vacancies and stabilize the surface structure, which improves a series of problems caused by high-temperature sintering. At the same time, it effectively suppresses the increase of SOC under high-temperature charging conditions, improves crack generation, and reduces the degree of side reactions. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0024] One aspect of the present invention relates to a high-nickel ternary cathode material, comprising a high-nickel ternary material matrix;

[0025] The surface layer of the high-nickel ternary material matrix includes a spinel structure; the surface layer of the high-nickel ternary material matrix is ​​doped with anions;

[0026] The anion contains fluorine and / or phosphorus.

[0027] The high-nickel ternary cathode material has a stable structure and good high-temperature cycling performance and high-voltage electrochemical performance. The surface layer of the high-nickel ternary material matrix undergoes cation exchange and heat treatment to form a spinel structure. Anions are doped into the holes formed on the surface, giving the high-nickel ternary cathode material a relatively stable surface structure.

[0028] Furthermore, the spinel structure is mainly formed by cations with a valence state greater than that of lithium ions.

[0029] Further, the cation includes: Zr 4+ Ti 4+ Al 3+ Mg 2+ W6+ Or La 3+ At least one of them.

[0030] Furthermore, the contents of Co, Ni, and Mn in the high-nickel ternary material matrix satisfy the following conditions:

[0031] 50% ≤ Nimol% ≤ 98%;

[0032] 0% ≤ Comol% ≤ 20%;

[0033] Mnmol%=1-Nimol%-Comol%.

[0034] Another aspect of the present invention relates to a method for preparing a high-nickel ternary cathode material, comprising the following steps:

[0035] (a) Disperse the high-nickel ternary material in a cation exchange solution to carry out ion exchange reaction and solid-liquid separation, and collect the powder;

[0036] The cations in the cation exchange solution have a higher valence state than lithium ions;

[0037] (b) The heat-treated powder and the anion-doped material are mixed and then anion-doped.

[0038] The aforementioned method for preparing high-nickel ternary cathode materials combines a high-nickel ternary material washing process with a conventional method. Washing reduces residual alkali while simultaneously enabling surface ion exchange. The heat treatment process reconstructs the surface layer of the high-nickel ternary cathode material, and the coating and surface treatment processes are combined to stabilize the anion layer structure. This method improves the high-temperature cycling performance and high-pressure structural stability of the material without requiring new equipment or major production line adjustments, thereby enhancing product competitiveness.

[0039] Studies have shown that the deterioration of structural stability and the exacerbation of side reactions at high temperatures are mainly due to two reasons: 1. The bulk Li phase is promoted at high temperatures. + Diffusion kinetics lead to a higher state of charge (SOC) of the charged cathode material compared to the room-temperature state, thus triggering more side reactions; 2. More significant surface structure collapse at high temperatures blocks Li + The transmission channel.

[0040] This invention uses an ion exchange method to synthesize (F – PO4 3- (etc.) and cations (Zr) 4+ Al 3+ Ti 4+ Mg 2+ W 6+The surface modification combined with the subsurface spinel structure to enhance the high temperature and high pressure ternary cathode material improves a series of problems caused by high temperature sintering, and also effectively suppresses the increase of SOC under high temperature charging conditions, improves crack generation, and reduces the degree of side reaction.

[0041] In ion exchange reactions, substituted ions diffuse from the host material's main lattice into the solution, while ions of the same charge in the solution diffuse into the host lattice. The chemical potential difference between the two types of ions provides the driving force for ion exchange, resulting in stable products with higher lattice energies. Whether an ion exchange reaction proceeds is controlled by thermodynamic conditions, while kinetics determine the reaction rate. In the synthesis of cathode materials using ion exchange, the exchange of cations is mainly involved. Although increasing the reaction temperature can promote the kinetics of cation exchange, excessively high temperatures not only favor cation diffusion but also accelerate anion diffusion, leading to instability in the anion-based structural framework. Since cations have smaller radii than anions and diffuse faster, low-temperature ion exchange satisfies both thermodynamic requirements and kinetic equilibrium, allowing ion exchange to proceed smoothly while preserving the original structure. During ion exchange, the kinetics are quite rapid, and an intermediate phase is generated, in which exchanged ions are randomly distributed within the alkali metal layer. Towards the later stages of exchange, the phase transition slows down until the crystal structure of the target material is formed.

[0042] By employing the ion exchange method, elemental doping of the surface layer of ternary cathode materials is carried out under relatively mild conditions. This method not only avoids increasing the lithium-nickel mixture but also utilizes the lithium-nickel mixture that occurs during the first sintering process for elemental exchange, achieving the goal of co-doping of lithium sites and transition metal sites.

[0043] High-valence metal ion doping leads to local potential imbalance, forming local spinel phases and vacancies. These vacancies reduce the difficulty of anion doping.

[0044] The spinel / layered structure mixed phase on the surface can effectively improve the high-voltage performance of the material, and anion doping can effectively suppress oxygen release from the bulk phase structure under high voltage, thereby improving the cycling performance of the material to a certain extent.

[0045] Further, in step (a), the high-nickel ternary material is dispersed in the cation exchange solution according to the following mass relationship: 0.40≤m1 / (m1+m2)≤0.75;

[0046] Where m1 is the mass of the high-nickel ternary material and m2 is the mass of the cation exchange liquid.

[0047] Furthermore, the concentration of cations in the cation exchange solution is 1–5 mol / L (e.g., 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, or 5 mol / L).

[0048] Furthermore, the cations in the cation exchange solution include: Zr 4+ Ti 4+ Al 3+ Mg 2+ W 6+ Or La 3+ At least one of them.

[0049] Furthermore, the cations in the cation exchange solution are selected from metal salts containing the corresponding cations.

[0050] Furthermore, the solvent of the cation exchange solution can be water or ethanol.

[0051] Furthermore, the ion exchange reaction takes place over a period of 5 to 60 minutes (e.g., 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes). The ion exchange reaction is carried out at room temperature.

[0052] Furthermore, the heat treatment temperature is 200–500℃ (e.g., 200℃, 230℃, 250℃, 270℃, 290℃, 310℃, 330℃, 350℃, 370℃, 390℃, 410℃, 430℃, 450℃, 470℃, 490℃, or 500℃). Different heat treatment temperatures can adjust the thickness of the material for ion exchange. Below 200℃, the ion diffusion rate is slow, the exchange thickness is too thin, the proportion of spinel phase in the surface spinel phase / layered mixed phase layer is too high, or even the entire layer becomes spinel phase, leading to a difference in expansion stress between the surface and inner layers, resulting in accelerated pulverization failure during cycling; above 500℃, the ion diffusion rate is fast, the exchange depth is too high, the concentration of spinel phase in the surface layer is too low, and the high pressure improvement effect is poor.

[0053] Furthermore, the heat treatment time is 3 to 8 hours (e.g., 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours).

[0054] Furthermore, the heat treatment is carried out under aerobic conditions with an oxygen concentration of 35% to 99% (e.g., 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99%).

[0055] Furthermore, the anion doping temperature is 250–600°C (e.g., 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C). If the anion doping temperature is too low, the anion doping amount is too small, resulting in more holes and poor cycle stability; if the temperature is too high, the anion doping amount is too large, resulting in fewer holes, fewer lithium-ion diffusion channels, and higher impedance.

[0056] Furthermore, the anion doping time is 3 to 7 hours (e.g., 3 hours, 4 hours, 5 hours, 6 hours, or 7 hours).

[0057] Furthermore, the anion-doped material includes: fluoride salts and / or phosphates.

[0058] Furthermore, the fluoride salt includes, but is not limited to, ammonium fluoride. Other fluoride salts that can provide fluoride ions are also acceptable.

[0059] Furthermore, the phosphates include, but are not limited to, ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate. Other phosphates that provide phosphate groups are also acceptable.

[0060] Further, the mass ratio of the phosphate to the fluoride is (0-2):(0-2) (e.g., 0:1, 1:2, 1:1, 2:1 or 1:0).

[0061] Using PO4 3- and F - Co-doping can synergistically improve the stability of the surface structure, suppress the release of bulk oxygen under high voltage, and enhance cycle performance.

[0062] Furthermore, the mass sum of P and F in the anion-doped material is 500 to 8000 ppm (e.g., 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm or 8000 ppm) of the mass of the high-nickel ternary material.

[0063] Another aspect of the present invention relates to a positive electrode sheet, mainly made of a high-nickel ternary positive electrode material prepared by the aforementioned method for preparing high-nickel ternary positive electrode material or the aforementioned high-nickel ternary positive electrode material.

[0064] Another aspect of the present invention relates to a lithium-ion battery, including the aforementioned positive electrode.

[0065] The embodiments of the present invention will now be described in detail with reference to specific examples and comparative examples.

[0066] Example 1

[0067] The preparation method of the high-nickel ternary cathode material provided in this embodiment includes the following steps:

[0068] S1. Ion Exchange: High-nickel ternary single-crystal cathode material with a molar ratio of Ni:Co:Mn = 8:1:1 was added to a cation exchange solution with a cation concentration of 3 mol / L. The mass ratio of the high-nickel ternary single-crystal cathode material to the cation exchange solution was 60:40. The Zr content in the cation exchange solution was... 4+ W 6+ and La 3+ The molar ratio was 3:4:3. After stirring for 40 minutes, the mixture was filtered to obtain powder M1.

[0069] S2. Heat treatment: M1 is placed in a crucible and treated at 300°C in an atmosphere of 85% oxygen concentration for 5 hours. After that, it is crushed and sieved to obtain powder M2.

[0070] S3. Surface treatment: Powder M2 and anion doping material are mixed evenly using a high-speed mixer. The total mass of P and F in the anion doping material is 4000 ppm of the mass of the high-nickel ternary single crystal cathode material. The anion doping material includes ammonium dihydrogen phosphate and ammonium fluoride, with a mass ratio of ammonium dihydrogen phosphate to ammonium fluoride of 1:2. After treatment at 450℃ for 5 hours, the material is sieved to obtain the target material.

[0071] Examples 2 to 4

[0072] The difference between Examples 2 to 4 and Example 1 lies in the stirring time in step S1, as detailed below:

[0073] Example 2: The stirring time in step S1 of Example 1 was adjusted to 10 min;

[0074] Example 3: The stirring time in step S1 of Example 1 was adjusted to 20 min;

[0075] Example 4: The stirring time in step S1 of Example 1 was adjusted to 60 min.

[0076] Examples 5 to 6

[0077] The difference between Examples 5-6 and Example 1 lies in the heat treatment temperature of step S2, as detailed below:

[0078] Example 5: The heat treatment temperature in step S2 of Example 1 is adjusted to 200℃;

[0079] Example 6: The heat treatment temperature in step S2 of Example 1 is adjusted to 500℃.

[0080] Examples 7 to 8

[0081] The difference between Examples 7-8 and Example 1 lies in the heat treatment time in step S2, as detailed below:

[0082] Example 7: The heat treatment time in step S2 of Example 1 is adjusted to 3 hours;

[0083] Example 8: The heat treatment time in step S2 of Example 1 is adjusted to 8 hours.

[0084] Examples 9 to 10

[0085] The difference between Examples 9-10 and Example 1 lies in the different masses of P and F elements in the anion-doped material of step S3, as detailed below:

[0086] Example 9: In step S3 of Example 1, the total mass of P and F in the anion-doped material is 500 ppm of the mass of the high-nickel ternary single-crystal cathode material;

[0087] Example 10: In step S3 of Example 1, the total mass of P and F in the anion-doped material is 8000 ppm of the mass of the high-nickel ternary single-crystal cathode material.

[0088] Comparative Example 1

[0089] The cathode material is a ternary single-crystal cathode material with a molar ratio of Ni:Co:Mn = 8:1:1. It is a cathode material that has undergone conventional one-time sintering doping, deionized water washing, vacuum drying and high-mix coating treatment.

[0090] Comparative Example 2

[0091] The only difference from Example 1 is that step 3 is omitted.

[0092] Comparative Example 3

[0093] The only difference between this comparative example and Example 1 is that the heat treatment temperature is 150°C.

[0094] Comparative Example 4

[0095] The only difference between this comparative example and Example 1 is that the anion doping temperature is 200°C.

[0096] Experimental Example

[0097] The high-nickel ternary cathode materials provided in the various embodiments and comparative examples were used to test their electrochemical performance in coin cell half-cells. Specifically, the cathode material, conductive agent Super-P, and binder PVDF were mixed and dispersed in NMP solvent at a mass ratio of 94:3:3, with the solid content controlled at approximately 50%. This mixture was then uniformly coated onto aluminum foil, vacuum dried at 120°C for 10 hours, and finally rolled at 10 MPa to obtain the electrode sheet. CR2032 coin cells were assembled using lithium metal sheets as the negative electrode, a commercially available separator, and an electrolyte matching the ternary high-nickel / lithium-rich cathode material. The cells were tested on a Blue Electric testing system according to the 25°C high-voltage test procedure for ternary high-nickel cathode materials. The test results are shown in Table 1.

[0098] Table 1 Performance Test Table

[0099]

[0100]

[0101] As can be seen from the data in Table 1, the initial discharge efficiency of all examples and comparative examples is at the same level, indicating that this method does not lead to excessive consumption of structural lithium, and the capacities of the examples and comparative examples are at the same level.

[0102] Comparing Example 1 with Comparative Example 1 demonstrates that the ternary high-nickel material prepared using the method of the present invention exhibits significantly improved high-temperature and high-pressure cycling performance.

[0103] Comparing Example 1 with Comparative Example 2 demonstrates that both cation exchange and anion doping are indispensable in the method of the present invention.

[0104] Comparing Example 1 with Examples 2-4, Examples 5-6, and Examples 7-8, it is evident that the cycling performance initially increases and then decreases with increasing ion exchange time, heat treatment temperature, or time. Under otherwise constant processing conditions, the ion exchange time and the duration of heat treatment temperature / time reflect the depth of surface treatment; longer times and higher temperatures result in greater treatment depth and a thicker surface spinel / layered composite phase. When the composite phase is thin, the time it can withstand high temperature and high voltage is short, limiting the performance improvement; conversely, when the composite phase is too thick, it leads to a significant increase in impedance during cycling and rapid cycle decay.

[0105] Comparing Example 1 with Examples 9-10 shows that as the amount of anion doping increases, the number of holes in the composite phase decreases. Too many holes result in insufficient structural stability, making the structure more prone to collapse at high temperatures and high voltages. Conversely, too few holes lead to weaker lithium-ion diffusion dynamics and higher impedance at low SOCs.

[0106] Based on the above embodiments and comparative examples, it can be seen that the solution of the present invention can achieve a higher level than conventional methods or single-cation doping methods.

[0107] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A high-nickel ternary cathode material, characterized in that, Including high-nickel ternary material matrix; The surface layer of the high-nickel ternary material matrix includes a spinel structure; the surface layer of the high-nickel ternary material matrix is ​​doped with anions; The anion contains: fluorine and / or phosphorus; The spinel structure is mainly formed by cations with a valence state greater than that of lithium ions; The cation includes: Zr 4+ Ti 4+ Al 3+ Mg 2+ W 6+ Or La 3+ At least one of them; The preparation method of the high-nickel ternary cathode material includes the following steps: (a) Disperse the high-nickel ternary material in a cation exchange solution to carry out ion exchange reaction and solid-liquid separation, and collect the powder; The cations in the cation exchange solution have a higher valence state than lithium ions; (b) The heat-treated powder and the anion-doped material are mixed and then anion-doped. The heat treatment temperature is 200~500℃; The heat treatment time is 5-8 hours; The anion doping temperature is 250~600℃; The ion exchange reaction takes 20 to 60 minutes.

2. The high-nickel ternary cathode material according to claim 1, characterized in that, The contents of Co, Ni, and Mn in the high-nickel ternary material matrix meet the following conditions: 50%≤Ni mol%≤98%; 0%≤Co mol%≤20%; Mn mol% = 1 - Ni mol% - Co mol%.

3. The high-nickel ternary cathode material according to claim 1, characterized in that, In step a, the high-nickel ternary material is dispersed in the cation exchange solution according to the following mass relationship: 0.40≤m1 / (m1+m2)≤0.75; Where m1 is the mass of the high-nickel ternary material and m2 is the mass of the cation exchange liquid.

4. The high-nickel ternary cathode material according to claim 1, characterized in that, The concentration of cations in the cation exchange solution is 1~5 mol / L; The cation exchange solution contains cations including: Zr 4+ Ti 4+ Al 3+ Mg 2+ W 6+ Or La 3+ At least one of them.

5. The high-nickel ternary cathode material according to claim 1, characterized in that, The heat treatment is carried out under aerobic conditions, with an oxygen concentration of 35% to 99%.

6. The high-nickel ternary cathode material according to claim 1, characterized in that, Includes at least one of the following technical features (1) to (3): (1) The anion doping time is 3~7h; (2) The anion-doped material includes: fluoride salts and / or phosphates; (3) The sum of the mass of P and F in the anion-doped material is 500~8000 ppm of the mass of the high-nickel ternary material.

7. A positive electrode sheet, characterized in that, It is made of the high-nickel ternary cathode material as described in any one of claims 1 to 6.

8. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 7.

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