A positive electrode material, a preparation method thereof and a lithium ion battery

Abstract

The application discloses a positive electrode material, a preparation method thereof and a lithium ion battery. The positive electrode material comprises LiNi x Co y Mn z A a M m N n O2 and a fast-ion conductor passivation layer located at a grain boundary of the positive electrode material, wherein 0.6≤x<1, 0

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the increasing global demand for clean energy and sustainable transportation, lithium-ion batteries, as the core energy storage and conversion device, have become key technological bottlenecks restricting the driving range and market penetration of electric vehicles due to their energy density, cycle life, and safety.

[0003] Cathode materials are key materials for lithium-ion batteries, representing a bottleneck in energy density and a major contributor to cost. Among numerous cathode materials, high-nickel layered oxide materials are considered promising for achieving high-energy-density battery systems due to their high reversible specific capacity and high operating voltage.

[0004] However, with increasing nickel content, a series of inherent materials science challenges are exacerbated, severely restricting its large-scale commercial application. High-nickel materials exhibit poor intrinsic structural stability; in a highly delithiated state, the Ni content in the material... 4+ The strong oxidizing properties of lithium lead to a significant decrease in thermodynamic stability, causing decomposition reactions at relatively low temperatures, releasing oxygen and accompanied by a severe thermal effect, posing a safety hazard of battery thermal runaway. Simultaneously, the lithium-nickel mixing phenomenon and the irreversible phase transition from a layered structure to a spinel phase and even a rock salt phase during cycling result in rapid capacity decay and a continuous increase in internal resistance.

[0005] Secondly, the interfacial stability of polycrystalline secondary spherical particles in high-nickel materials is particularly prominent. During long-term cycling, anisotropic volume changes within the particles generate internal stress, leading to the initiation of microcracks at grain boundaries. These microcracks provide channels for electrolyte penetration, constantly exposing new active surfaces and triggering continuous interfacial side reactions. This consumes active lithium and electrolyte, generates gas, and accelerates performance degradation. More seriously, transition metal ions dissolved from the cathode material migrate to the anode, catalyzing the decomposition of the solid electrolyte interfacial film, triggering severe cross-reactions, and further deteriorating battery life and safety.

[0006] To address these challenges, the industry generally employs modification strategies involving elemental doping and surface coating. Bulk doping can stabilize the crystal structure and suppress phase transitions to some extent. However, traditional uniform doping strategies are insufficient to effectively strengthen fragile grain boundary regions. Traditional dry or wet coating methods often suffer from problems such as uneven coating layers, weak adhesion to the substrate, and potential obstruction of lithium-ion transport. Furthermore, existing coating technologies primarily act on the outermost layer of the particles, failing to effectively modify the grain boundaries within the secondary spherical structure.

[0007] Therefore, the prior art lacks a solution that can essentially and uniformly strengthen grain boundaries from the inside of the material, without sacrificing ionic conductivity, and is compatible with industrial production. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a cathode material, a preparation method thereof, and a lithium-ion battery.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a cathode material, which includes LiNi x Co y Mn z A a M m N n O2 and a fast ion conductor passivation layer, and the fast ion conductor passivation layer is located at the grain boundaries of the cathode material, where 0.6 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0 < a ≤ 0.01, 0 < m ≤ 0.01, 0 < n ≤ 0.01, A is at least one of Mg and Al, M is at least one of Zr, Ta, and Ti, and N is at least one of B, P, W, Mo, S, and F.

[0011] In the cathode material of the present invention, 0.6 ≤ x < 1, for example, it can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 0.98, etc.; 0 < y ≤ 0.2, for example, it can be 0.01, 0.03, 0.05, 0.07, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, or 0.2, etc.; 0 < z ≤ 0.2, for example, it can be 0.01, 0.03, 0.05, 0.07, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, or 0.2, etc.; 0 < a ≤ 0.01, for example, it can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc.; 0 < m ≤ 0.01, for example, it can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc.; 0 < n ≤ 0.01, for example, it can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc.

[0012] The cathode material of this invention, through multi-element synergistic doping, can suppress lithium-nickel mixing and stabilize the layered structure. A is at least one of Mg and Al, and M is at least one of Zr, Ta, and Ti. A and M can achieve a "bulk doping stable framework," improving intrinsic stability from the bulk phase. For example, M forms strong MO bonds, acting as a bulk phase "pillar" to effectively suppress lattice oxygen precipitation and layered structure collapse. N is at least one of B, P, W, Mo, S, and F, which can be used to form a fast ion conductor passivation layer at grain boundaries, repairing internal grain boundaries, and strengthening crystallization without sacrificing ionic conductivity. Therefore, the high-nickel cathode material of this invention stabilizes its structure through a dual mechanism of "bulk doping stable framework" and "grain boundary segregation passivation defect," forming comprehensive protection. This allows the high-nickel cathode material to possess high reversible specific capacity while also exhibiting good rate performance, high safety, and long lifespan. Moreover, due to its more robust structure and effective suppression of interfacial side reactions, the thermal stability of the battery is significantly improved, reducing the risk of thermal runaway.

[0013] Preferably, the fast ion conductor passivation layer is formed by the segregation and reaction of nitrogen at the grain boundaries of the positive electrode material.

[0014] Preferably, the fast ion conductor passivation layer has an amorphous structure. In this invention, the passivation layer formed at the crystallization point has an amorphous structure, thereby enabling the cathode material to possess excellent ionic conductivity.

[0015] Preferably, the fast ion conductor passivation layer includes a compound formed from N, wherein the compound formed from N is at least one selected from Li3BO3, Li3PO4, Li2WO4, Li3MoO4, Li2SO4, and LiF.

[0016] Preferably, N is at least two of B, P, W, Mo, S, and F. Under these conditions, the fast ion conductor passivation layer includes at least two fast ion conductors to form a composite passivation layer, which can better improve the electrochemical performance of the material.

[0017] Preferably, N is element B, and the fast ion conductor passivation layer is Li3BO3. Alternatively, N is a combination of elements B and F, and the fast ion conductor passivation layer includes Li3BO3 and LiF. When N is element B, LiNi... x Co y Mn z A a M m N n The boron element in O2 will segregate to form amorphous Li3BO3, a fast ion conductor; when N is a combination of boron and ferrite, LiNi... x Co y Mn z Aa M m N n In O2, elements B and F can work together to form a composite passivation layer containing lithium borate and lithium fluoride, which has both high ionic conductivity and excellent chemical stability.

[0018] Preferably, M is a combination of Zr and Ti.

[0019] In a second aspect, the present invention provides a method for preparing a cathode material as described in the first aspect, the method comprising the following steps:

[0020] (1) According to LiNi x Co y Mn z A a M m N n By mixing and reacting nickel, cobalt, manganese, A, M, and N sources in the stoichiometric ratio of O2, a precursor is obtained.

[0021] (2) The precursor is mixed with lithium salt and then sintered to obtain LiNi x Co y Mn z A a M m N n O2 materials;

[0022] (3) The chemical formula is LiNi x Co y Mn z A a M m N n The O2 material is subjected to heat treatment at 400℃~600℃ in a humid oxygen atmosphere to promote the segregation of N to the grain boundaries and react with lithium elements, thereby generating a fast ion conductor passivation layer in situ, and obtaining the positive electrode material.

[0023] In the preparation method of the present invention, in step (3), a heat preservation treatment is performed at 400℃~600℃. For example, the temperature can be 400℃, 425℃, 450℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃ or 600℃, etc.

[0024] In the method of this invention, step (3) utilizes elemental segregation and in-situ reaction to self-grow a fast ion conductor passivation layer with strong adhesion to the substrate and uniform distribution at the grain boundary. This passivation layer can prevent the initiation and propagation of microcracks and inhibit electrolyte penetration along the grain boundary, fundamentally solving the grain boundary failure problem of polycrystalline high-nickel materials. It should be noted that step (3) should be carried out in a humid oxygen atmosphere, which is a key control factor for triggering the activation of lithium species and interfacial reactions at the grain boundary. Here, a humid oxygen atmosphere refers to oxygen gas containing water.

[0025] The preparation method of the present invention is simple, requires no complicated post-processing coating equipment, is well compatible with existing cathode material production lines, and is easy to achieve large-scale stable production.

[0026] Preferably, the humidified oxygen atmosphere in step (3) is a water-oxygen mixture atmosphere with a water content of 0.5 vol% to 5 vol%. For example, the water content in the water-oxygen mixture atmosphere is 0.5 vol% to 5 vol%, such as 0.5 vol%, 0.6 vol%, 0.7 vol%, 0.8 vol%, 0.9 vol%, 1.0 vol%, 1.2 vol%, 1.4 vol%, 1.5 vol%, 1.7 vol%, 1.8 vol%, 2.0 vol%, 2.2 vol%, 2.5 vol%, 2.7 vol%, 3.0 vol%, 3.3 vol%, 3.6 vol%, 3.8 vol%, 4.0 vol%, 4.2 vol%, 4.4 vol%, 4.6 vol%, 4.8 vol%, or 5.0 vol%, etc., preferably 1 vol% to 3 vol%.

[0027] Preferably, the heat preservation treatment time in step (3) is 2h to 10h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, preferably 3h to 9h.

[0028] Preferably, the temperature of the heat preservation treatment in step (3) is 400℃~600℃, for example, it can be 400℃, 425℃, 450℃, 465℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃ or 600℃, etc., preferably 480℃~580℃.

[0029] Preferably, the precursor in step (1) is prepared by a coprecipitation method, which includes: mixing a nickel source, a cobalt source, a manganese source, an A source, an M source and an N source in a solvent to obtain a mixed salt solution, and adding the mixed salt solution, the precipitant solution and the complexing agent solution in parallel into a reaction vessel to carry out a coprecipitation reaction.

[0030] Preferably, the sintering in step (2) includes: pre-firing at 400℃~550℃ (e.g., 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 515℃, 530℃ or 550℃, etc.) for 3h~5h (e.g., 3h, 3.5h, 4h, 4.5h or 5h, etc.), and then heating up to 750℃~900℃ (e.g., 750℃, 800℃, 850℃ or 900℃, etc.) for final firing for 9h~11h (e.g., 9h, 9.5h, 10h, 10.5h or 11h, etc.).

[0031] As a preferred embodiment of the method for preparing the cathode material of the present invention, the method includes the following steps:

[0032] (1) Precursor synthesis and mixing: according to LiNi x Co y Mn z A a M m N n By mixing nickel, cobalt, manganese, a, m, and n elements in the stoichiometric ratio of O2 and carrying out a co-precipitation reaction, a precursor is obtained.

[0033] (2) Mixing and high-temperature sintering: The precursor is mixed with the lithium source to obtain a precursor mixture. The precursor mixture is pre-fired at 400℃~550℃ in an oxygen atmosphere for 3h~5h, and then final-fired at 750℃~900℃ for 9h~11h to form a layered structure.

[0034] (3) Programmed cooling and grain boundary self-passivation: After high-temperature sintering, the system is kept at 400℃~600℃ in a humid oxygen atmosphere for 2h~10h to promote N segregation to high-energy defects such as grain boundaries and react with lithium species to generate a fast ion conductor passivation layer in situ.

[0035] (4) Post-processing: After the heat preservation is completed, the material is cooled to room temperature, crushed, sieved and demagnetized to obtain the high-nickel cathode material.

[0036] Thirdly, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the positive electrode material described in the first aspect, or the positive electrode material prepared by the method described in the second aspect.

[0037] Compared with existing technologies, the present invention has the following beneficial effects:

[0038] (1) The cathode material of the present invention can suppress lithium-nickel mixing and stabilize the layered structure through multi-element synergistic doping. A is at least one of Mg and Al, and M is at least one of Zr, Ta and Ti. A and M can achieve "bulk doping stable framework" to improve intrinsic stability from the bulk phase. For example, M forms strong MO bonds as a bulk phase "pillar" to effectively suppress lattice oxygen precipitation and layered structure collapse. N is at least one of B, P, W, Mo, S and F, which can be used to form a fast ion conductor passivation layer at the grain boundary to repair the internal grain boundary, and strengthen crystallization without sacrificing ionic conductivity. Therefore, the high-nickel cathode material of the present invention stabilizes the structure through the dual mechanism of "bulk doping stable framework" and "grain boundary segregation passivation defect", forming all-round protection. This allows the high-nickel cathode material to have high reversible specific capacity while also having good rate performance, high safety and long life. Moreover, due to its more stable structure and effective suppression of interfacial side reactions, the thermal stability of the battery is greatly improved, reducing the risk of thermal runaway.

[0039] (2) The cathode material of the present invention is applied to lithium-ion batteries, and the initial discharge capacity at 0.1C is above 205.7mAh / g; the capacity retention rate after 200 cycles at 1C rate is above 88.1%, preferably above 89.8%; and the thermal runaway initiation temperature is above 205℃, preferably above 210℃.

[0040] (3) The preparation method of the present invention is simple, does not require complicated post-processing coating equipment, is compatible with existing cathode material production lines, and is easy to achieve large-scale stable production. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0042] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0043] Example 1

[0044] This embodiment provides a cathode material, including LiNi. 0.88 Co 0.05 Mn 0.05 Mg 0.01 Zr 0.005 B 0.005 O2 and a fast ion conductor passivation layer, wherein the fast ion conductor passivation layer is located at the grain boundary of the positive electrode material, and the fast ion conductor passivation layer includes Li3BO3.

[0045] This embodiment also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0046] (1) Coprecipitation synthesis of precursor: Nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate, zirconium oxychloride, and boric acid were prepared into a mixed salt solution with a total metal ion concentration of 2.0 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate, zirconium oxychloride, and boric acid in a molar ratio of 0.88:0.05:0.05:0.01:0.005:0.005. This mixed salt solution was then fed into a reaction vessel in a parallel flow with 4.0 mol / L NaOH solution and 2 mol / L NH3·H2O solution. The reaction was controlled at pH=11.2, temperature 55℃, and reaction time 12 h with stirring speed 500 rpm until the desired particle size (D50=10±0.5μm) was reached. The mixture was then filtered, washed, and vacuum dried at 110℃ to obtain the hydroxide precursor.

[0047] (2) Mixing and sintering: The dried precursor and lithium hydroxide were mixed at a molar ratio of Li / M=1.05 (where M=Ni+Co+Mn) to obtain a mixture. The mixture was placed in an oxygen atmosphere and pre-calcined at 500℃ for 4h at a rate of 3℃ / min, and then sintered at 800℃ for 10h at a rate of 5℃ / min.

[0048] (3) Programmed cooling and grain boundary passivation: After sintering, the furnace is cooled to 550°C, switched to humid oxygen with a water volume content of 2%, and kept warm for 5 hours.

[0049] (4) Post-processing: After the process is completed, the product is naturally cooled to room temperature, and the sintered product is crushed, sieved, and demagnetized to obtain the final cathode material powder.

[0050] Example 2

[0051] This embodiment provides a cathode material, including LiNi. 0.83 Co 0.095 Mn 0.05 Al 0.01 Ta 0.005 B 0.005 F 0.005 O2 and a fast ion conductor passivation layer, the fast ion conductor passivation layer being located at the grain boundaries of the positive electrode material, the fast ion conductor passivation layer comprising Li3BO3 and LiF.

[0052] This embodiment also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0053] (1) Coprecipitation synthesis of precursor: Nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, ammonium tantalate, boric acid and ammonium fluoride were prepared into a mixed salt solution with a total metal ion concentration of 2.0 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, ammonium tantalate, boric acid and ammonium fluoride in a molar ratio of 0.83:0.1:0.05:0.01:0.005:0.005. The mixed salt solution was then fed into a reaction vessel in a parallel flow with 4.0 mol / L NaOH solution and 2 mol / L NH3·H2O solution. The reaction was controlled at pH=11.2, temperature 55℃ for 12 h, stirring speed 500 rpm, until the desired particle size (D50=10±0.5μm) was reached. The mixture was then filtered, washed and dried under vacuum at 110℃ to obtain the hydroxide precursor.

[0054] (2) Mixing and sintering: The dried precursor and lithium hydroxide were mixed at a molar ratio of Li / M=1.05 (where M=Ni+Co+Mn) to obtain a mixture. The mixture was placed in an oxygen atmosphere and pre-calcined at 500℃ for 4h at a rate of 3℃ / min, and then sintered at 800℃ for 10h at a rate of 5℃ / min.

[0055] (3) Programmed cooling and grain boundary passivation: After sintering, the furnace is cooled to 500°C, then switched to humid oxygen with a water volume content of 2%, and kept warm for 8 hours.

[0056] (4) Post-processing: After the process is completed, the product is naturally cooled to room temperature, and the sintered product is crushed, sieved, and demagnetized to obtain the final cathode material powder.

[0057] Example 3

[0058] This embodiment provides a cathode material, including LiNi. 0.8 Co 0.1 Mn 0.08 Al 0.01 Zr 0.005 P 0.005 O2 and a fast ion conductor passivation layer, the fast ion conductor passivation layer being located at the grain boundaries of the positive electrode material, the fast ion conductor passivation layer comprising Li3PO4.

[0059] This embodiment also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0060] (1) Coprecipitation synthesis of precursor: Nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, zirconium oxychloride, and ammonium dihydrogen phosphate were prepared into a mixed salt solution with a total metal ion concentration of 2.0 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, zirconium oxychloride, and ammonium dihydrogen phosphate in a molar ratio of 0.8:0.1:0.08:0.01:0.005:0.005. This mixed salt solution was then co-flushed into a reaction vessel with 4.0 mol / L NaOH solution and 2 mol / L NH3·H2O solution. The reaction was controlled at pH=11.2, temperature 55℃ for 12 h, and stirring speed 500 rpm until the desired particle size (D50=10±0.5μm) was reached to obtain the hydroxide precursor. The precursor was filtered, washed, and vacuum dried at 110℃.

[0061] (2) Mixing and sintering: The dried precursor was mixed with lithium hydroxide at a molar ratio of Li / M=1.05. The mixture was placed in an oxygen atmosphere and pre-calcined at 500℃ for 4h by heating at 3℃ / min, and then sintered at 800℃ for 10h by heating at a rate of 5℃ / min.

[0062] (3) Programmed cooling and grain boundary passivation: After sintering, the furnace is cooled to 580°C, switched to humid oxygen with a water volume content of 2%, and kept warm for 3 hours.

[0063] (4) Post-processing: After the process is completed, the product is naturally cooled to room temperature, and the sintered product is crushed, sieved, and demagnetized to obtain the final cathode material powder.

[0064] Example 4

[0065] This embodiment provides a cathode material, including LiNi. 0.85 Co 0.1 Mn 0.04 Mg 0.005 Zr 0.005 W 0.005 F 0.005 O2 and a fast ion conductor passivation layer, the fast ion conductor passivation layer being located at the grain boundaries of the positive electrode material, the fast ion conductor passivation layer comprising Li2WO4 and LiF.

[0066] This embodiment also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0067] (1) Coprecipitation synthesis of precursor: Nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate, zirconium oxychloride, ammonium tungstate, and ammonium fluoride were prepared into a mixed salt solution with a total metal ion concentration of 2.0 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate, zirconium oxychloride, ammonium tungstate, and ammonium fluoride in a molar ratio of 0.85:0.1:0.04:0.01:0.005:0.005. The mixed salt solution was then fed into a reaction vessel in a parallel flow with 4.0 mol / L NaOH solution and 2 mol / L NH3·H2O solution. The reaction was controlled at pH=11.2, temperature 55℃ for 12 h, and stirring speed 500 rpm until the desired particle size (D50=10±0.5μm) was reached. The mixture was then filtered, washed, and vacuum dried at 110℃ to obtain the hydroxide precursor.

[0068] (2) Mixing and sintering: The dried precursor and lithium hydroxide were mixed at a molar ratio of Li / M=1.05 (where M=Ni+Co+Mn) to obtain a mixture. The mixture was placed in an oxygen atmosphere and pre-calcined at 500℃ for 4h at a rate of 3℃ / min, and then sintered at 800℃ for 10h at a rate of 5℃ / min.

[0069] (3) Programmed cooling and grain boundary passivation: After sintering, the furnace is cooled to 520°C, switched to humid oxygen with a water volume content of 2%, and kept warm for 6 hours.

[0070] (4) Post-processing: After the process is completed, the product is naturally cooled to room temperature, and the sintered product is crushed, sieved, and demagnetized to obtain the final cathode material powder.

[0071] Example 5

[0072] This embodiment provides a cathode material, including LiNi. 0.9 Co 0.05 Mn 0.03 Al 0.01 Ti 0.005 B 0.01 O2 and a fast ion conductor passivation layer, wherein the fast ion conductor passivation layer is located at the grain boundary of the positive electrode material, and the fast ion conductor passivation layer includes Li3BO3.

[0073] This embodiment also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0074] (1) Coprecipitation synthesis of precursor: Nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, titanium oxalate and boric acid were prepared into a mixed salt solution with a total metal ion concentration of 2.0 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, titanium oxalate and boric acid in a molar ratio of 0.9:0.05:0.03:0.01:0.005:0.01. The mixed salt solution was then fed into a reaction vessel in a parallel flow with 4.0 mol / L NaOH solution and 2 mol / L NH3·H2O solution. The reaction was controlled at pH=11.2, temperature 55℃ for 12 h, stirring speed 500 rpm, until the desired particle size (D50=10±0.5μm) was reached. The mixture was then filtered, washed and dried under vacuum at 110℃ to obtain the hydroxide precursor.

[0075] (2) Mixing and sintering: The dried precursor and lithium hydroxide were mixed at a molar ratio of Li / M=1.05 (where M=Ni+Co+Mn) to obtain a mixture. The mixture was placed in an oxygen atmosphere and pre-calcined at 500℃ for 4h at a rate of 3℃ / min, and then sintered at 800℃ for 10h at a rate of 5℃ / min.

[0076] (3) Programmed cooling and grain boundary passivation: After sintering, the furnace is cooled to 550°C, switched to humid oxygen with a water volume content of 2%, and kept warm for 5 hours.

[0077] (4) Post-processing: After the process is completed, the product is naturally cooled to room temperature, and the sintered product is crushed, sieved, and demagnetized to obtain the final cathode material powder.

[0078] Example 6

[0079] This embodiment provides a cathode material, including LiNi. 0.82 Co 0.12 Mn 0.04 Al 0.01 Zr 0.005 Mo 0.005 O2 and a fast ion conductor passivation layer, wherein the fast ion conductor passivation layer is located at the grain boundary of the positive electrode material, and the fast ion conductor passivation layer includes Li3MoO4.

[0080] This embodiment also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0081] (1) Coprecipitation synthesis of precursor: Nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, zirconium oxychloride, and ammonium molybdate were prepared into a mixed salt solution with a total metal ion concentration of 2.0 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate, aluminum sulfate, zirconium oxychloride, and ammonium molybdate in a molar ratio of 0.82:0.12:0.04:0.01:0.005:0.005. This mixed salt solution was then fed into a reaction vessel in a parallel flow with 4.0 mol / L NaOH solution and 2 mol / L NH3·H2O solution. The reaction was controlled at pH=11.2, temperature 55℃ for 12 h, and stirring speed 500 rpm until the desired particle size (D50=10±0.5μm) was reached. The mixture was then filtered, washed, and vacuum dried at 110℃ to obtain the hydroxide precursor.

[0082] (2) Mixing and sintering: The dried precursor and lithium hydroxide were mixed at a molar ratio of Li / M=1.05 (where M=Ni+Co+Mn) to obtain a mixture. The mixture was placed in an oxygen atmosphere and pre-calcined at 500℃ for 4h at a rate of 3℃ / min, and then sintered at 800℃ for 10h at a rate of 5℃ / min.

[0083] (3) Programmed cooling and grain boundary passivation: After sintering, the furnace is cooled to 530°C, switched to humid oxygen with a water volume content of 2%, and kept warm for 5 hours.

[0084] (4) Post-processing: After the process is completed, the product is naturally cooled to room temperature, and the sintered product is crushed, sieved, and demagnetized to obtain the final cathode material powder.

[0085] Example 7

[0086] This embodiment provides a cathode material, the preparation method of which is the same as in Embodiment 1, except that the programmed cooling temperature is 450°C and the material is kept warm in humid oxygen with a water volume content of 2% for 10 hours.

[0087] Example 8

[0088] This embodiment provides a cathode material, the preparation method of which is the same as in Embodiment 1, except that the programmed cooling temperature is 620°C and the material is kept warm in humid oxygen with a water volume content of 2% for 2 hours.

[0089] Example 9

[0090] This embodiment provides a positive electrode material, the preparation method of which is the same as in Embodiment 1, except that in step (3), the volume content of water that wets oxygen is 0.5%.

[0091] Example 10

[0092] This embodiment provides a positive electrode material, the preparation method of which is the same as in Embodiment 1, except that in step (3), the volume content of water that wets oxygen is 5%.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is that the cathode material preparation method does not involve programmed cooling and grain boundary passivation. After sintering at 800°C, it is directly cooled naturally to room temperature in a pure oxygen atmosphere. The chemical formula of the cathode material in this comparative example is LiNi. 0.88 Co 0.05 Mn 0.05 Mg 0.01 Zr 0.005 B 0.005 O2, the grain boundaries of this cathode material are not modified.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that zirconium oxychloride was not added in step (1) of the cathode material preparation method, and the boric acid content was adjusted. The cathode material in this comparative example is not doped with Zr, and includes LiNi. 0.88 Co 0.05 Mn 0.05 Mg 0.01 B 0.01 O2 and a fast ion conductor passivation layer, wherein the fast ion conductor passivation layer is located at the grain boundary of the positive electrode material, and the fast ion conductor passivation layer includes Li3BO3.

[0097] Comparative Example 3

[0098] This comparative example provides a cathode material, including LiNi. 0.88 Co 0.05 Mn 0.05 Mg 0.01 Zr 0.01 O2 and an Al2O3 coating layer on the surface, the Al2O3 coating layer relative to LiNi 0.88 Co 0.05 Mn 0.05 Mg 0.01 Zr 0.01 The O2 coating amount is 1 wt%.

[0099] The preparation method of the cathode material in this comparative example includes the following steps:

[0100] (1) Coprecipitation synthesis of precursor: Same as in Example 1.

[0101] (2) Mixing and sintering: Same as in Example 1, to obtain matrix material powder.

[0102] (3) Traditional wet coating: The above matrix material powder is added to aluminum nitrate ethanol solution, and the mass fraction of Al2O3 is controlled to be 1.0% of the mass of matrix material. After mechanical stirring at room temperature for 4 hours, the ethanol is stirred and heated at 80°C to evaporate until a completely dry powder is obtained.

[0103] (4) Heat treatment to form a coating layer: The dried powder is collected in a crucible, placed in a tube furnace, and heated to 500°C at a heating rate of 2°C / min under an oxygen atmosphere, and held for 4 hours.

[0104] (5) Post-treatment: After the heat treatment is completed, the sample is naturally cooled to room temperature and then sieved to remove any agglomerates that may have been generated during the treatment, thus obtaining the final sample.

[0105] Comparative Example 4

[0106] The cathode material provided in this comparative example is commercially available LiNi without special grain boundary modification, purchased from the market. 0.88 Co 0.05 Mn 0.05 Mg 0.01 Zr 0.01 O2.

[0107] Electrical performance testing:

[0108] The materials obtained in Examples 1-10 and Comparative Examples 1-4 were used as positive electrode materials and assembled into 2032 coin cells. The ratio of positive electrode material to PVDF to SP was 89.5:5:5 by mass. The positive electrode material, PVDF and SP were added to NMP and degassed to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil, dried and rolled to obtain a positive electrode sheet. A lithium metal sheet was used as the counter electrode to obtain a coin cell.

[0109] Charge and discharge tests were performed on it: the voltage window was 2.8-4.3V, and the initial discharge capacity at 0.1C, the initial discharge capacity at 1C (denoted as C1), and the capacity after 200 cycles at 1C (denoted as C) were tested. 200 Based on this, the capacity retention rate after 200 cycles at a 1C rate is calculated: Capacity retention rate after 200 cycles at a 1C rate = C 200 / C1×100%.

[0110] Thermal runaway temperature test: At room temperature, the battery was charged at a constant current rate of 0.1C to 4.3V, and then charged at a constant voltage until the current dropped below 0.05C, so that the positive electrode material was in a fully charged state. After disassembly in a glove box, 3mg of active material powder was scraped off and heated to 400℃ at a heating rate of 10℃ / min using differential scanning calorimetry to simulate the actual temperature rise inside the battery and determine the onset temperature of its exothermic reaction.

[0111] The results are shown in Table 1.

[0112]

[0113] As shown in Table 1, the capacity retention and thermal runaway initiation temperature of Examples 1-10 after 200 cycles at 1C rate are higher than those of Comparative Examples 1-4. The performance of the cathode materials obtained without a passivation layer or with a passivation layer (Al2O3 coating layer) prepared by conventional wet coating is far inferior to that of the embodiments of the present invention. This proves that the method of the present invention can effectively suppress structural degradation and interfacial side reactions during cycling and improve the thermal stability of the material by stabilizing the bulk phase structure and forming a self-passivating layer at grain boundaries in the cathode material.

[0114] Furthermore, the fast ion conductor passivation layers in Examples 4 and 2 include two fast ion conductor materials, and this composite passivation layer performs even better.

[0115] Meanwhile, Comparative Example 2 had the lowest thermal runaway initiation temperature, indicating that it had the worst safety and proved that the lack of bulk stability meant that interface modification alone was insufficient to cope with severe thermal abuse.

[0116] As can be seen from Examples 1 to 12, the nickel content in Example 5 is the highest. The higher the nickel content, the better it is to obtain a high discharge capacity. At the same time, a high nickel content will reduce the cycle stability. There is a balance between high discharge specific capacity and stability.

[0117] A comparison of Example 1 with Examples 7-8 shows that the process window for programmed cooling needs to be optimized, as temperatures that are too low or too high will affect material properties.

[0118] A comparison of Examples 1 and 9-10 shows that the water volume content for wetting oxygen is preferably within the range of 1% to 3%, which is more conducive to improving the performance of the material.

[0119] In summary, this invention utilizes multi-element synergistic doping combined with a special programmed cooling process to selectively segregate elements, enabling them to self-assemble with lithium oxide to form a fast-ion conductor passivation layer. This achieves multiple benefits, including strengthening the bulk structure, stabilizing grain boundaries, and suppressing interfacial side reactions, thereby improving its cycle stability, rate performance, and thermal safety. The process is simple and suitable for industrial production.

[0120] This invention successfully prepared a high-nickel cathode material that combines high capacity, long lifespan, and high safety, and its overall performance is significantly better than that of existing technologies.

[0121] Finally, it should be noted that while the above embodiments illustrate the detailed method of the present invention, the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0122] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that, The preparation method includes the following steps: (1) According to LiNi x Co y Mn z A a M m N n The stoichiometric ratio of O2 is used to mix nickel, cobalt, manganese, A, M and N sources in a solvent to obtain a mixed salt solution. The mixed salt solution, precipitant solution and complexing agent solution are added to the reactor in parallel to carry out a co-precipitation reaction to obtain the precursor. (2) The precursor is mixed with lithium salt and then sintered to obtain LiNi x Co y Mn z A a M m N n O2 materials; (3) The chemical formula is LiNi x Co y Mn z A a M m N n The O2 material is subjected to heat treatment at 400℃~600℃ in a humid oxygen atmosphere for 2h~10h, which promotes N segregation to the grain boundary and reacts with lithium to generate a fast ion conductor passivation layer in situ, thus obtaining the positive electrode material. The humid oxygen atmosphere is a water-oxygen mixture with a water content of 1 vol% to 3 vol%. The positive electrode material includes LiNi x Co y Mn z A a M m N n O2 and a fast ion conductor passivation layer, the fast ion conductor passivation layer is located at the grain boundaries of the positive electrode material, where 0.6 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0 < a ≤ 0.01, 0 < m ≤ 0.01, 0 < n ≤ 0.01, A is at least one of Mg and Al, M is at least one of Zr, Ta and Ti, and N is at least two of B, P, W, Mo and F.

2. The method for preparing the cathode material according to claim 1, characterized in that, The fast ion conductor passivation layer has an amorphous structure; And / or, the fast ion conductor passivation layer includes a compound formed from N, wherein the compound formed from N is at least one of Li3BO3, Li3PO4, Li2WO4, Li3MoO4 and LiF.

3. The method for preparing the cathode material according to claim 1, characterized in that, N is element B, and the fast ion conductor passivation layer is Li3BO3; or... N is a combination of elements B and F, and the fast ion conductor passivation layer includes Li3BO3 and LiF.

4. The method for preparing the cathode material according to claim 1, characterized in that, M is a combination of Zr and Ti.

5. The method for preparing the cathode material according to claim 1, characterized in that, The sintering in step (2) includes: pre-firing at 400℃~550℃ for 3h~5h, and then heating to 750℃~900℃ for final firing for 9h~11h.

6. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes a positive electrode material prepared by any one of claims 1-5.

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