Medium-low nickel positive electrode precursor as well as preparation method and application thereof

Abstract

The invention provides a medium-low nickel positive electrode precursor and a preparation method and application thereof. The preparation method comprises the following steps: (1) performing seed crystal stage coprecipitation reaction on a first medium-low nickel-based mixed salt solution, a doped salt solution, a first precipitator solution and a first complexing agent solution in a first mixed gas atmosphere containing oxygen; and (2) adding the second medium-low nickel-based mixed salt solution, the second precipitant solution and the second complexing agent solution into the solution with the seed crystal in a parallel flow manner, and carrying out a growth-stage coprecipitation reaction in a second mixed gas atmosphere containing oxygen to obtain the medium-low nickel positive electrode precursor. According to the invention, the medium-low nickel positive electrode precursor particles with needle-shaped primary particles and high sphericity degree are obtained; therefore, the medium-low nickel polycrystalline positive electrode material is suitable for a high-voltage system, the concentration gradient distribution of doped elements is presented from inside to outside, and the cycle performance, the rate capability and the safety performance of the material can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a low-nickel cathode precursor, its preparation method, and its application. Background Technology

[0002] High-nickel ternary materials are widely used in high-end electric vehicles due to their high capacity. However, the increase in Ni content also brings many problems. The poor stability and safety of high-nickel materials during cycling due to Li / Ni mixing, microcracks, and surface side reactions have always been a challenge for the industry. Furthermore, the relatively complex production process and high cost of high-nickel materials are barriers to their development. Ni6 series materials, at 4.40V, have an energy density close to that of Ni8 series materials, but with a lower Ni content, their cathode preparation process is simpler (lithium carbonate sintering, eliminating the need for complex processes like water washing), and they have a cost advantage. These advantages make low- to medium-nickel high-voltage products (nickel molar percentage ≤70%) currently the best-selling ternary cathode materials. Low- to medium-nickel single crystals are a commonly used high-voltage route, but single crystals experience rapid capacity decay and poor rate performance during cycling. The grain boundaries of polycrystalline particles can hinder the contact between the electrolyte and the material's interior. Even if side reactions occur on the surface due to high voltage (such as the formation of an unstable SEI film), the grain boundaries can delay the diffusion of these side reactions to the particle core. In contrast, once the surface of monocrystalline particles is eroded, the damage is directly and rapidly transmitted to the interior along a single grain, which can improve the cycling performance of high-voltage materials. Furthermore, polycrystalline materials have shorter diffusion paths, resulting in superior rate performance. Additionally, polycrystalline materials have a higher compaction density compared to monocrystalline materials.

[0003] Low- and medium-nickel polycrystalline cathode materials are often prepared by co-precipitation reaction to obtain low- and medium-nickel cathode precursor materials, followed by lithium-ion sintering. However, in the existing co-precipitation reaction preparation process of low- and medium-nickel cathode precursors, blocky primary particles and twinned particles are prone to occur, especially for large-particle systems of low- and medium-nickel cathode precursors. During cathode sintering, the blocky primary particles require a high sintering temperature to react with Li salt, and the sintered primary particles also inherit the blocky morphology, which is detrimental to the Li-ion exchange process. + The insertion and extraction of nickel can affect the performance of subsequent low- and medium-nickel polycrystalline cathode materials.

[0004] Therefore, how to solve the twinning problem of low- and medium-nickel cathode precursors and improve the electrochemical performance of low- and medium-nickel polycrystalline cathode materials in high-voltage systems are urgent technical problems to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a low- to medium-nickel cathode precursor, its preparation method, and its applications. In the preparation process, the present invention obtains low- to medium-nickel cathode precursor particles with a needle-like structure and high sphericity by introducing doping salts during the seed crystal stage and controlling the micro-oxidation process during the growth stage. The subsequent lithium-based sintering yields a low- to medium-nickel polycrystalline cathode material suitable for high-voltage systems, maintaining a concentration gradient distribution of doped elements from the inside out, which is beneficial for improving the material's cycle performance, rate performance, and safety performance.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a low-to-medium nickel cathode precursor, the method comprising the following steps:

[0008] (1) The first low-nickel-based mixed salt solution, the doped salt solution, the first precipitant solution and the first complexing agent solution are added in parallel streams and a seed stage co-precipitation reaction is carried out in a first mixed gas atmosphere containing oxygen to obtain seed crystals;

[0009] (2) The second low-nickel mixed salt solution, the second precipitant solution, and the second complexing agent solution are added in parallel to the solution containing seed crystals, and a growth stage co-precipitation reaction is carried out in a second mixed gas atmosphere containing oxygen to obtain the low-nickel cathode precursor.

[0010] It should be noted that in this invention, medium and low nickel refers to materials in which nickel is one of the main elements, such as nickel-cobalt-manganese systems, where nickel accounts for 50% to 70% of the total molar amount of nickel, cobalt, and manganese, and those with a molar amount of less than 50% are considered low nickel materials.

[0011] This invention effectively solves the sphericity problem of low- and medium-nickel cathode precursors by using a stepwise co-precipitation reaction in the seeding and growth stages, and avoids the twinning phenomenon that easily occurs in large-particle low- and medium-nickel cathode precursors. Simultaneously, the micro-oxidation process during growth ensures that the primary particles have a needle-like structure, solving the problem of the primary particles of low- and medium-nickel cathode polycrystalline precursors easily becoming blocky. Furthermore, the addition of doping elements during the seeding stage co-precipitation in the first mixed gas atmosphere of micro-oxidation, without doping during the growth stage, ensures that the doping elements in the low- and medium-nickel cathode precursors can be distributed in a gradient from the inside to the outside during lithium-ion sintering. This makes the resulting low- and medium-nickel polycrystalline cathode material suitable for high-voltage systems (≥4.4V) and can be blended with low- and medium-nickel single-crystal materials, which is beneficial for improving subsequent cycle performance, rate performance, and safety performance.

[0012] Preferably, in step (1), the total molar amount of all metal elements in the first low-nickel mixed salt solution is 100%, and the molar amount of nickel is ≤70%, for example, 30%, 33%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68% or 70%, etc.

[0013] Preferably, in step (1), the first low-nickel-based mixed salt solution includes transition metal elements in addition to nickel, and the transition metal elements include manganese and / or cobalt.

[0014] Preferably, the first low-nickel mixed salt solution in step (1) is consistent with the second low-nickel mixed salt solution in step (2).

[0015] This invention uses the same nickel-based raw material in both the seeding and growth stages, thus avoiding the problem of poor particle transition caused by abrupt changes in element content during the seeding to particle growth process.

[0016] Preferably, in step (1), the total concentration of metal ions in the first low-nickel mixed salt solution is 1 mol / L to 4 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L.

[0017] Preferably, the concentration of the doped salt solution in step (1) is 1 mol / L to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0018] It is understood that the types of doped salt solutions used in this invention are all conventionally selected. Without departing from the technical concept of this invention, any type of doping element that can be obtained within a reasonable range by those skilled in the art is applicable to this invention. For example, the doping element in the doped salt includes, but is not limited to, at least one of tungsten, aluminum, zirconium, titanium, boron, or magnesium. The specific type of doped salt can be a water-soluble salt.

[0019] Preferably, in step (1), the concentration of the first precipitant solution is 1 mol / L to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0020] Preferably, in step (1), the concentration of the first complexing agent solution is 1 mol / L to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0021] Preferably, the reaction temperature of the co-precipitation reaction in the seed stage of step (1) is 45℃~75℃, for example, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃ or 75℃.

[0022] Preferably, the pH value of the coprecipitation reaction in the seed stage of step (1) is 10.5~12.5, such as 10.5, 10.8, 11, 11.3, 11.5, 11.8, 12, 12.3 or 12.5.

[0023] Preferably, the initial stirring speed of the seed crystal stage co-precipitation reaction in step (1) is 300 r / min to 380 r / min, for example, 300 r / min, 310 r / min, 320 r / min, 330 r / min, 340 r / min, 350 r / min, 360 r / min, 370 r / min or 380 r / min, etc.

[0024] Preferably, the median particle size D50 of the seed crystal in step (1) is 2μm to 5μm, such as 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, 3.3μm, 3.5μm, 3.8μm, 4μm, 4.3μm, 4.5μm, 4.8μm or 5μm.

[0025] In this invention, the median particle size D50 of the seed crystal is 2μm~5μm. On the one hand, it affects the final particle size of the subsequent particles, which helps to obtain larger particles. On the other hand, the doping of doping elements within this particle size range, followed by the formation of the undoped particle growth shell from the seed crystal surface, better realizes the regional controllability of doping elements inside the particles.

[0026] Preferably, in step (2), the total concentration of metal ions in the second low-nickel mixed salt solution is 1 mol / L to 4 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L.

[0027] Preferably, in step (2), the concentration of the second precipitant solution is 1 mol / L to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0028] Preferably, in step (2), the concentration of the second complexing agent solution is 1 mol / L to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0029] Preferably, the volume ratio of oxygen in the first mixed gas in step (1) is greater than the volume ratio of oxygen in the second mixed gas in step (2).

[0030] Preferably, in step (1), the first mixed gas includes a protective gas and oxygen.

[0031] Preferably, in step (2), the second mixed gas includes a protective gas and oxygen, and the volume ratio of the protective gas to oxygen is 1:(0.01~2), for example, 1:0.01, 1:0.03, 1:0.05, 1:0.08, 1:1, 1:1.13, 1:1.15, 1:1.18 or 1:2, etc.

[0032] In the preparation method provided by this invention, the oxygen volume ratio is higher in the seed crystal stage than in the growth stage, and / or the volume ratio of protective gas to oxygen in the second mixed gas is 1:(0.01~2), which achieves consistent growth rate between the initial and growth stages of the particles, resulting in particles with higher sphericity. Furthermore, it regulates the morphology of primary particles in the low-nickel cathode precursor, resulting in a uniform needle-like structure, which is beneficial for the formation of a dense structure.

[0033] Preferably, the reaction temperature of the coprecipitation reaction in the growth stage of step (2) is 45℃~75℃, for example, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃ or 75℃.

[0034] Preferably, the pH value of the coprecipitation reaction in the growth stage of step (2) is 9.5~11, such as 9.5, 9.8, 10, 10.3, 10.5, 10.8 or 11.

[0035] Preferably, the initial stirring speed of the coprecipitation reaction in the growth stage of step (2) is 100r / min to 300r / min, for example, 100r / min, 130r / min, 150r / min, 180r / min, 200r / min, 230r / min, 250r / min, 280r / min or 300r / min.

[0036] Preferably, during the co-precipitation reaction in the growth stage described in step (2), as the reaction proceeds, the feed flow rate of all reaction raw materials is increased by 0.5 times to 1.5 times at each fixed reaction time, for example, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 time, 1.1 times, 1.2 times, 1.3 times, 1.4 times or 1.5 times; the fixed reaction time is 2h to 15h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h.

[0037] It should be noted that the increase in the feed flow rate of all raw materials remained consistent each time.

[0038] In the growth stage co-precipitation reaction process of step (2) of the present invention, as the particle size of the reaction particles increases, the feed flow rate of the raw materials is increased in stages to maintain a consistent growth rate, further ensuring that the internal packing looseness of the particles remains consistent, which is conducive to forming a radially arranged structure and improving the rate and cycle performance of the cathode material.

[0039] Preferably, the median particle size D50 of the low-nickel cathode precursor is ≥7μm, such as 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 21μm, 22μm, 23μm, 24μm or 25μm, etc.

[0040] When the low-nickel cathode precursor of the present invention is a large particle material (≥7μm), the morphology of the primary particles is very likely to form a blocky structure during the later growth process of the particles, resulting in loose particle accumulation and poor sphericity. Therefore, the present invention solves the above problems better through a specific step-by-step preparation process.

[0041] It should be noted that, in the preparation process of the low-nickel cathode precursor of the present invention, apart from the above-mentioned feature limitations, other preparation details can be adapted and adjusted by those skilled in the art without violating the technical concept of the present invention.

[0042] Optionally, the type of salt in the nickel-based mixed salt solution includes, but is not limited to, at least one of soluble sulfates, soluble chlorides, soluble nitrates, or soluble acetates.

[0043] Optionally, the first precipitant and the second precipitant include, but are not limited to, sodium hydroxide and / or potassium hydroxide.

[0044] Optionally, the first complexing agent and the second complexing agent include, but are not limited to, ammonia.

[0045] Optionally, in the initial stage of step (1), a base liquid can be added to the reaction vessel. The base liquid includes water, a precipitant and a complexing agent. The concentration of the complexing agent in the base liquid is 4 g / L to 6 g / L, for example, 4 g / L, 5 g / L or 6 g / L.

[0046] Optionally, the protective gas includes nitrogen, argon, or helium.

[0047] Optionally, after the co-precipitation reaction of the seed crystal stage in step (1) is completed, the solution after the reaction is centrifuged to obtain the seed crystal.

[0048] Optionally, the seed solution in step (2) can be a seeded solution, which also includes water, a precipitant and a complexing agent. The concentration of the complexing agent in the seed solution is 4 g / L to 6 g / L, for example, 4 g / L, 5 g / L or 6 g / L.

[0049] Optionally, the present invention does not limit the feed flow rate of each raw material in the co-precipitation reaction process of steps (1) and (2). It can be adaptively controlled according to the target doping amount and target reaction conditions. The raw materials are added continuously until the reaction is completed.

[0050] Optionally, after the coprecipitation reaction of the growth stage in step (2) is completed, conventional treatment processes such as aging, washing and drying can be carried out as appropriate.

[0051] In a second aspect, the present invention provides a low-nickel cathode precursor, which is prepared by the preparation method described in the first aspect.

[0052] The low-nickel cathode precursor has a spherical or near-spherical shape, and the particles of the low-nickel cathode precursor have a needle-like structure from the innermost to the outermost primary particles; and the low-nickel cathode precursor includes a core and a shell covering the surface of the core, and the core is doped with doping elements.

[0053] The low-nickel cathode precursor in this invention is a spherical secondary type obtained from a primary particle stacking reaction, i.e., a "polycrystalline" morphology.

[0054] Thirdly, the present invention provides a low-nickel polycrystalline cathode material, which is obtained by mixing and sintering a low-nickel cathode precursor as described in the second aspect with a substance including at least a lithium source.

[0055] Preferably, the sintering atmosphere includes an oxygen-containing atmosphere.

[0056] The oxygen-containing atmosphere is a gaseous atmosphere containing at least oxygen, such as a pure oxygen atmosphere or an air atmosphere.

[0057] Preferably, the lithium source includes, but is not limited to, at least one of lithium hydroxide, lithium nitrate, lithium carbonate, or lithium acetate.

[0058] Preferably, the molar ratio of the low-nickel cathode precursor to lithium in the lithium source is (1~1.2):1, for example, 1:1, 1.03:1, 1.05:1, 1.08:1, 1.1:1, 1.13:1, 1.15:1, 1.18:1 or 1.2:1, etc.

[0059] Preferably, the sintering temperature is 500℃~900℃, such as 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃.

[0060] Preferably, the sintering time is 6h to 20h, such as 6h, 8h, 10h, 12h, 15h, 18h or 20h.

[0061] Fourthly, the present invention also provides a lithium-ion battery comprising the low-nickel polycrystalline cathode material as described in the third aspect.

[0062] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] This invention effectively solves the sphericity problem of low- and medium-nickel cathode precursors by using a stepwise co-precipitation reaction in the seeding and growth stages, and avoids the twinning phenomenon that easily occurs in large-particle low- and medium-nickel cathode precursors. Simultaneously, the micro-oxidation process during growth ensures that the primary particles have a needle-like structure, solving the problem of the primary particles of low- and medium-nickel cathode polycrystalline precursors easily becoming blocky. Furthermore, the addition of doping elements during the seeding stage co-precipitation in the first mixed gas atmosphere of micro-oxidation, without doping during the growth stage, ensures that the doping elements in the low- and medium-nickel cathode precursors can be distributed in a gradient from the inside to the outside during lithium-ion sintering. This makes the resulting low- and medium-nickel polycrystalline cathode material suitable for high-voltage systems (≥4.4V) and can be blended with low- and medium-nickel single-crystal materials, which is beneficial for improving subsequent cycle performance, rate performance, and safety performance. Attached Figure Description

[0065] Figure 1 The image shows a SEM image of the positive electrode precursor prepared in the example. Detailed Implementation

[0066] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0067] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0068] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0069] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0070] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0071] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0072] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0073] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0074] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0075] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0076] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0077] Example 1

[0078] This embodiment provides a method for preparing a medium-nickel cathode precursor material, the preparation method being as follows:

[0079] Step 1: Prepare a nickel-cobalt-manganese metal salt solution A with a total metal ion concentration of 2 mol / L by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.70:0.05:0.25; prepare a 1 mol / L ammonia complexing agent solution; prepare a 2 mol / L liquid alkali solution; and prepare a 2 mol / L sodium tungstate solution.

[0080] Step 2: Add 400L of pure water, ammonia, and alkaline solution to a 1000L reactor as a base solution to maintain system stability. The concentration of ammonia in the base solution is 4g / L. Add mixed solution A, ammonia complexing agent, liquid alkaline solution, and sodium tungstate solution to the reactor at flow rates of 30kg / h, 10kg / h, 5kg / h, and 6kg / L, respectively. During the reaction, a mixed gas with a nitrogen and oxygen volume ratio of 1:2 is continuously introduced. The seed crystal stage co-precipitation reaction is carried out at 55℃. The pH of the reaction is maintained at 11.5, the ammonia concentration is 4g / L, and the stirring speed is 380r / min. When the median particle size of the precursor reaches 3.5μm, the first stage reaction is stopped to obtain seed crystals.

[0081] Step 3: Add 400L of pure water and ammonia water as the base solution to a 1000L reactor. Weigh 25kg of the first-stage material as seed crystals and add it to the reactor. The ammonia concentration of the system is 4g / L. Continue to add mixed solution A, ammonia water complexing agent, and sodium hydroxide precipitant to the reactor at a certain flow rate. Carry out the growth stage co-precipitation reaction at 55℃. During the reaction, a nitrogen and oxygen mixed gas with a volume ratio of 1:1 is continuously introduced to maintain the pH of the reaction at 10.7 and the stirring speed at 300r / min. During the reaction, the feed flow rate of each raw material is increased by 100% every 8 hours. Sodium tungstate solution is not introduced during this stage until the median particle size of the precursor reaches 15μm. Stop the reaction to obtain the desired product. Figure 1 The medium-nickel cathode precursor material shown has a precursor structure in which the primary particles are needle-shaped from the inside out, dense inside and out, and have excellent sphericity.

[0082] Example 2

[0083] This embodiment provides a method for preparing a medium-nickel cathode precursor material, the preparation method being as follows:

[0084] Step 1: Prepare a nickel-cobalt-manganese metal salt solution A with a total metal ion concentration of 4 mol / L by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.70:0.05:0.25; prepare a 1 mol / L ammonia complexing agent solution; prepare a 2 mol / L liquid alkali solution; and prepare a 3 mol / L sodium tungstate solution.

[0085] Step 2: Add 400L of pure water, ammonia, and alkaline solution to a 1000L reactor as a base solution to maintain system stability. The concentration of ammonia in the base solution is 4g / L. Add mixed solution A, ammonia complexing agent, liquid alkaline solution, and sodium tungstate solution to the reactor in parallel flow. During the reaction, a mixed gas with a nitrogen and oxygen volume ratio of 1:3 is continuously introduced. The seed crystal stage co-precipitation reaction is carried out at 55℃. The feed flow rates of each original feed stage are adjusted to maintain the reaction pH at 11.5, the ammonia concentration at 4g / L, and the stirring speed at 380r / min. When the median particle size of the precursor reaches 5μm, the first stage reaction is stopped to obtain seed crystals.

[0086] Step 3: Add 400L of pure water and ammonia water as the base liquid to a 1000L reactor. Weigh 25kg of the first-stage material as seed crystals and add it to the reactor. The ammonia concentration of the system is 4g / L. Continue to add mixed solution A, ammonia water complexing agent, and sodium hydroxide precipitant to the reactor at a certain flow rate. Carry out the growth stage co-precipitation reaction at 55℃. During the reaction, a mixed gas with a nitrogen and oxygen volume ratio of 1:2 is continuously introduced to maintain the pH of the reaction at 10.7. The stirring speed is 300r / min. During the reaction, the feed flow rate of each raw material is increased by 0.5 times every 8 hours. Sodium tungstate solution is not introduced during this stage until the median particle size of the precursor reaches 7μm. Stop the reaction to obtain the medium nickel cathode precursor material. The obtained precursor structure has needle-like primary particles from the inside to the outside, dense inside and out and loose outside, with excellent sphericity.

[0087] Example 3

[0088] This embodiment provides a method for preparing a medium-nickel cathode precursor material, the preparation method being as follows:

[0089] Step 1: Prepare a nickel-cobalt-manganese metal salt solution A with a total metal ion concentration of 1.5 mol / L by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.70:0.05:0.25; prepare a 2 mol / L ammonia complexing agent solution; prepare a 3 mol / L OH- liquid alkali solution; and prepare a 1 mol / L sodium tungstate solution.

[0090] Step 2: Add 400L of pure water, ammonia, and alkaline solution to a 1000L reactor as a base solution to maintain system stability. The concentration of ammonia in the base solution is 4g / L. Add mixed solution A, ammonia complexing agent, liquid alkaline solution, and sodium tungstate solution to the reactor in parallel flow. During the reaction, a mixed gas with a nitrogen and oxygen volume ratio of 1:1 is continuously introduced. The seed stage co-precipitation reaction is carried out at 45℃. The pH of the reaction is maintained at 12, the ammonia concentration is 4g / L, and the stirring speed is 380r / min. When the median particle size of the precursor reaches 2μm, the first stage reaction is stopped to obtain seed crystals.

[0091] Step 3: Add 400L of pure water and ammonia water as the base liquid to a 1000L reactor. Weigh 25kg of the first-stage material as seed crystals and add it to the reactor. The ammonia concentration of the system is 4g / L. Continue to add mixed solution A, ammonia water complexing agent, and sodium hydroxide precipitant to the reactor at a certain flow rate. Carry out the growth stage co-precipitation reaction at 45℃. During the reaction, a mixed gas with a nitrogen and oxygen volume ratio of 1:0.01 is continuously introduced to maintain the pH of the reaction at 10.5 and the stirring speed at 300r / min. During the reaction, the feed flow rate of each raw material is increased by 1.5 times every 8 hours. Sodium tungstate solution is not introduced during this stage until the median particle size of the precursor reaches 15μm. Stop the reaction to obtain the medium nickel cathode precursor material. The obtained precursor structure has needle-like primary particles from the inside to the outside, dense inside and out and loose outside, with excellent sphericity.

[0092] Example 4

[0093] The difference between this embodiment and Embodiment 1 is that in step 1 of this embodiment, nickel sulfate, cobalt sulfate, and manganese sulfate are mixed in a molar ratio of 1:1:1 to prepare a nickel-cobalt-manganese metal salt solution A with a total metal ion concentration of 2 mol / L.

[0094] All other conditions remain the same as in Example 1.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, the feed flow rate of each raw material is increased by 1 time every 2 hours.

[0097] All other conditions remain the same as in Example 1.

[0098] Example 6

[0099] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, the feed flow rate of each raw material is increased by 1 time every 15 hours.

[0100] All other conditions remain the same as in Example 1.

[0101] Example 7

[0102] The difference between this embodiment and embodiment 1 is that the volume ratio of nitrogen to oxygen in step 3 of this embodiment is 1:0.005.

[0103] All other conditions remain the same as in Example 1.

[0104] Example 8

[0105] The difference between this embodiment and embodiment 1 is that the volume ratio of nitrogen to oxygen in step 3 of this embodiment is 1:2.5.

[0106] All other conditions remain the same as in Example 1.

[0107] Example 9

[0108] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, the feed flow rate of each raw material is doubled every 20 hours.

[0109] All other conditions remain the same as in Example 1.

[0110] Example 10

[0111] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, the feed flow rate of each raw material is increased by 100% every hour.

[0112] All other conditions remain the same as in Example 1.

[0113] Example 11

[0114] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, the feed flow rate of each raw material is increased by 2 times every 8 hours.

[0115] All other conditions remain the same as in Example 1.

[0116] Example 12

[0117] The difference between this embodiment and embodiment 1 is that in step 3 of this embodiment, the feed flow rate of each raw material is increased by 0.1 times every 8 hours.

[0118] All other conditions remain the same as in Example 1.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 1 is that this comparative example does not involve the preparation of sodium tungstate solution in step 1, that is, sodium tungstate is not added during the seed crystal growth reaction stage.

[0121] All other conditions remain the same as in Example 1.

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 1 is that the sodium tungstate prepared in step 1 is added during the co-precipitation reaction in the growth stage, instead of during the seed co-precipitation reaction stage.

[0124] All other conditions remain the same as in Example 1.

[0125] Comparative Example 3

[0126] The difference between this comparative example and Example 1 is that in the coprecipitation reaction of the seed stage in step 2 of this comparative example, the gas introduced is nitrogen gas, just like the gas introduced in the coprecipitation reaction of the growth stage.

[0127] All other conditions remain the same as in Example 1.

[0128] Comparative Example 4

[0129] The difference between this comparative example and Example 1 is that the gas introduced during the coprecipitation reaction in the growth stage of step 3 of this comparative example is pure nitrogen.

[0130] All other conditions remain the same as in Example 1.

[0131] The cathode precursor materials provided in Examples 1-12 and Comparative Examples 1-4 were subjected to SEM morphology detection, including sphericity testing and primary particle morphology (profile) testing. The porosity of the cathode precursors was tested using the physical adsorption method. The relevant test results are shown in Table 1.

[0132] Table 1

[0133]

[0134] Battery fabrication and performance testing

[0135] (I) Preparation of cathode material: The cathode precursor material and lithium carbonate powder provided in the examples and comparative examples were weighed and mixed evenly according to the molar ratio of Li / Me=1:1.2. The mixture was sintered in an air atmosphere using a box furnace at a sintering temperature of 700℃ for 8 hours to obtain the corresponding polycrystalline cathode material.

[0136] (II) Battery fabrication, providing positive electrode, negative electrode, separator, and electrolyte for battery fabrication:

[0137] Preparation of the positive electrode sheet: A positive electrode slurry was prepared according to the ratio of positive electrode material:SP:PVDF=90:5:5, and the solid content of the slurry was 60%. The aluminum foil was placed on a coating machine, and a 150μm coating tool was placed on the aluminum foil. The single crystal slurry was poured in, and the equipment was turned on for coating. After coating, the electrode sheet was obtained. The electrode sheet was placed in an oven at 110℃ to dry and then rolled to obtain the positive electrode sheet.

[0138] The positive electrode sheets provided in the examples and comparative examples were cut into circular pieces with a diameter of 15 mm using a stamping machine in a dry environment. In a glove box, a lithium metal sheet was used as the counter electrode, and a Ceglard composite membrane was selected as the separator. Electrolyte was added to assemble a CR2032 coin-shaped half-cell. The electrolyte was an organic solution obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7. The concentration of lithium salt (lithium hexafluorophosphate) in the electrolyte was 1 mol / L.

[0139] (III) Performance Testing:

[0140] The performance of the CR2032 coin-type half-cells provided in the examples and comparative examples was tested using the Wuhan Landian CT2001A system.

[0141] In an environment of 25℃, under 1C, charge and discharge cycles were performed with a voltage range of 3.0-4.5V to test the initial discharge capacity and initial efficiency, and the capacity retention rate after 100 cycles was obtained. The test results are shown in Table 2.

[0142] In an environment of 25℃, the rate performance test was conducted by charging at 1C and discharging at 5C within a voltage range of 3.0-4.5V, repeating the charge and discharge cycle to obtain the capacity retention rate after 100 cycles. The test results are shown in Table 2.

[0143] Table 2

[0144]

[0145] Combining Tables 1 and 2, we can conclude that:

[0146] This invention addresses the sphericity problem of low- and medium-nickel cathode precursor materials by employing a phased preparation process and controlling different oxidation conditions during the seeding and growth stages, along with synergistic doping during the seeding stage. This approach avoids the twinning phenomenon common in large-particle low- and medium-nickel cathode precursors, ensuring that doping elements in the low- and medium-nickel cathode precursors exhibit a gradient distribution from the inside out during lithium-ion sintering. This results in polycrystalline cathode materials that are more suitable for high-voltage systems, improving the material's cycle and rate performance.

[0147] Data from Examples 1-3 and Examples 7-8 show that controlling the degree of oxidation by adjusting the volume ratio of nitrogen and oxygen during the growth stage achieves primary particle refinement while ensuring particle sphericity, which is more beneficial to the cycle performance of the cathode material.

[0148] Data from Examples 1, 5-6, and 9-12 show that the flow rate during the growth stage, as controlled by the reaction time, affects the growth rate of the precursor, thereby influencing the coarseness of the primary particles and the looseness of their packing. As the reaction proceeds, for every fixed reaction time of 2 to 15 hours, the feed flow rate of all reaction raw materials is increased by 0.5 to 1.5 times, further ensuring that the morphology of the primary particles is needle-like, thus guaranteeing the material's recyclability.

[0149] Data from Examples 1 and Comparative Examples 1-4 show that in the preparation method of the present invention, the corresponding preparation sequence and preparation conditions must be coordinated to solve the problem of the primary particle blockiness of low- and medium-nickel materials leading to the preparation and performance degradation of polycrystalline cathode materials.

[0150] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A preparation method of a medium-low nickel positive electrode precursor, characterized in that, The preparation method comprises the following steps: (1) adding a first middle-low nickel-based mixed salt solution, a doping salt solution, a first precipitant solution and a first complexing agent solution in parallel flow, performing a seed stage co-precipitation reaction in a first mixed gas atmosphere containing oxygen, and obtaining a seed; (2) adding a second middle-low nickel-based mixed salt solution, a second precipitant solution and a second complexing agent solution into the solution with the seed, performing a growth stage co-precipitation reaction in a second mixed gas atmosphere containing oxygen, and obtaining the middle-low nickel positive electrode precursor.

2. The production method according to claim 1, characterized by, In step (1), the molar percentage of nickel in the total molar amount of all metal elements in the first middle-low nickel-based mixed salt solution is ≤70%; Preferably, in step (1), the first middle-low nickel-based mixed salt solution further comprises a transition metal element in addition to the nickel metal element, and the transition metal element comprises manganese and / or cobalt; Preferably, the first middle-low nickel-based mixed salt solution in step (1) is consistent with the second middle-low nickel-based mixed salt solution in step (2).

3. The preparation method according to claim 1, characterized in that, The concentration of total metal ions in the first middle-low nickel-based mixed salt solution in step (1) is 1 mol / L to 4 mol / L; Preferably, the concentration of the doping salt solution in step (1) is 1 mol / L to 3 mol / L; Preferably, the concentration of the first precipitant solution in step (1) is 1 mol / L to 3 mol / L; Preferably, the concentration of the first complexing agent solution in step (1) is 1 mol / L to 3 mol / L.

4. The method of claim 1, wherein, The reaction temperature of the seed stage co-precipitation reaction in step (1) is 45°C to 75°C, and the pH value of the seed stage co-precipitation reaction is 10.5 to 12.5; Preferably, the initial stirring speed of the seed stage co-precipitation reaction in step (1) is 300 r / min to 380 r / min; Preferably, the median particle size D50 of the seed in step (1) is 2 μm to 5 μm.

5. The preparation method according to claim 1, characterized in that, The concentration of total metal ions in the second middle-low nickel-based mixed salt solution in step (2) is 1 mol / L to 4 mol / L; Preferably, the concentration of the second precipitant solution in step (2) is 1 mol / L to 3 mol / L; Preferably, the concentration of the second complexing agent solution in step (2) is 1 mol / L to 3 mol / L.

6. The method of claim 1, wherein, The volume percentage of oxygen in the first mixed gas in step (1) is greater than the volume percentage of oxygen in the second mixed gas in step (2); Preferably, the first mixed gas in step (1) comprises a protective gas and oxygen; Preferably, the second mixed gas in step (2) comprises a protective gas and oxygen, and the volume ratio of the protective gas to oxygen is 1:(0.01 to 2); Preferably, the reaction temperature of the growth stage co-precipitation reaction in step (2) is 45°C to 75°C, and the pH value of the growth stage co-precipitation reaction is 9.5 to 11; Preferably, the initial stirring speed of the growth stage co-precipitation reaction in step (2) is 100 r / min to 300 r / min; Preferably, in the growth stage of step (2), the feeding flow of all raw materials is simultaneously increased by 0.5 times to 1.5 times every fixed reaction time during the co-precipitation reaction process; the fixed reaction time is 2 hours to 15 hours. Preferably, the median particle size D50 of the medium-low nickel positive electrode precursor is greater than or equal to 7 microns.

7. A medium-low nickel positive electrode precursor, characterized in that, The medium-low nickel positive electrode precursor is prepared by the preparation method of any one of claims 1-6. The medium-low nickel positive electrode precursor has a spherical or spherical-like shape, the primary particles of the medium-low nickel positive electrode precursor from inside to outside are needle-like structures, and the medium-low nickel positive electrode precursor comprises a core and a shell layer coated on the surface of the core, and the core is doped with a doping element.

8. A medium-low nickel polycrystalline positive electrode material, characterized in that, The medium-low nickel polycrystalline positive electrode material is obtained by mixing and sintering the medium-low nickel positive electrode precursor of claim 7 and at least a substance comprising a lithium source.

9. The medium-low nickel polycrystalline positive electrode material according to claim 8, characterized in that, The sintering atmosphere comprises an oxygen-containing atmosphere, the sintering temperature is 500 DEG C to 900 DEG C, and the sintering time is 6 hours to 20 hours.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the medium-low nickel polycrystalline positive electrode material of claim 8 or 9.

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