Single-crystal ternary positive electrode material and preparation method therefor

Abstract

A single-crystal ternary positive electrode material and a preparation method therefor. The preparation method comprises: firstly, mixing a first-stage lithium source with a single-crystal ternary precursor until uniform, and conducting first-stage low-temperature sintering, so as to obtain a first sintered material; then, mixing a second-stage lithium source with the first sintered material until uniform, and conducting second-stage low-temperature sintering, so as to obtain a second sintered material; and sintering the second sintered material at a high temperature, so as to obtain a single-crystal ternary positive electrode material, wherein the first-stage lithium source is lithium carbonate, the sintering temperature of the first-stage low-temperature sintering is 600-800ºC, the sintering temperature of the second-stage low-temperature sintering is 600-800ºC, and the sintering temperature of the high-temperature sintering is 900-1000ºC. In the present application, lithium carbonate is used as the first-stage lithium source, and the sintering process is divided into three stages, thereby allowing for a more sufficient reaction of lithium carbonate with the single-crystal ternary precursor; therefore, the defect of low activity of lithium carbonate is favorably avoided, and a ternary positive electrode material with a lower alkali content is obtained.

Description

A single crystal ternary cathode material and its preparation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent filed with the Patent Office of China on December 22, 2023, with application number 202311783406.7 and application name “A single-crystal ternary positive electrode material and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of lithium battery positive electrode materials, and in particular to a single crystal ternary positive electrode material and a preparation method thereof. Background Art

[0004] The commonly used preparation method for lithium battery positive electrode materials is to sinter the precursor with a lithium source at high temperature. The main lithium sources are lithium hydroxide and lithium carbonate. Lithium carbonate is cheaper than lithium hydroxide, which can further reduce the cost of positive electrode materials. However, the current preparation of ternary positive electrode materials still mainly uses lithium hydroxide as the lithium source. The main reason is that lithium hydroxide is highly active and reacts more easily with the precursor, resulting in higher production capacity and better particle uniformity of the positive electrode material. Lithium carbonate, however, has low activity and reacts unevenly with the precursor, resulting in a high alkaline content and poor particle uniformity in the prepared positive electrode material.

[0005] Summary of the Invention

[0006] The main technical problem solved by the present application is to provide a single crystal ternary positive electrode material and a preparation method thereof, which can reduce the alkali content of the ternary positive electrode material using lithium carbonate as the lithium source.

[0007] To solve the above technical problems, a technical solution adopted in this application is to provide a single crystal ternary cathode material and a preparation method thereof, comprising:

[0008] The first stage lithium source is mixed evenly with the single crystal ternary precursor, and a first stage low temperature sintering is performed to obtain a first sintered material; the first stage lithium source is lithium carbonate, and the sintering temperature of the first stage low temperature sintering is 600° C. to 800° C.;

[0009] The second stage lithium source is mixed evenly with the first sintering material, and a second stage low-temperature sintering is performed to obtain a second sintered material; the sintering temperature of the second stage low-temperature sintering is 600° C. to 800° C.;

[0010] The second sintered material is sintered at a high temperature to obtain the single crystal ternary positive electrode material; the sintering temperature of the high temperature sintering is 900°C to 1000°C.

[0011] The molar ratio of the first lithium source to the single crystal ternary precursor is (0.6-1):1.

[0012] The sintering time of the first low-temperature sintering stage is 5 hours to 15 hours.

[0013] The molar ratio of the second stage lithium source to the first sintering material is (0.03-0.5):1.

[0014] The second stage of low-temperature sintering has a sintering time of 5 to 15 hours.

[0015] Wherein, the second stage lithium source is lithium carbonate or lithium hydroxide.

[0016] Wherein, the sintering time of the high-temperature sintering is 5h to 25h.

[0017] The chemical formula of the single crystal ternary precursor is Ni x Co y Mn 1-x-y (OH)2, wherein 0.5≤x<1, 0<y<0.5, x+y<1.

[0018] Wherein, the parameter D50 characterizing the particle size of the single-crystal ternary precursor is 2 μm to 20 μm.

[0019] In order to solve the above technical problems, another technical solution adopted in this application is to provide a single crystal ternary positive electrode material prepared according to the preparation method described in the above technical solution.

[0020] The beneficial effects of the present application are as follows: the preparation method provided by the present application first mixes the first lithium source with the single crystal ternary precursor evenly, and performs the first low-temperature sintering to obtain a first sintered material; then mixes the second lithium source with the first sintered material evenly, and performs the second low-temperature sintering to obtain a second sintered material; and then performs high-temperature sintering on the second sintered material to obtain a single crystal ternary positive electrode material; wherein the first lithium source is lithium carbonate, the sintering temperature of the first low-temperature sintering is 600℃~800℃, the sintering temperature of the second low-temperature sintering is 600℃~800℃, and the sintering temperature of the high-temperature sintering is 900℃~1000℃. It can be seen that the present application uses lithium carbonate as the first lithium source and divides the sintering process of preparing the positive electrode material into three stages, which is equivalent to improving the activity of lithium carbonate, making its reaction with the single crystal ternary precursor more sufficient, which is beneficial to circumventing the disadvantages of the low activity of lithium carbonate, thereby obtaining a ternary positive electrode material with a lower alkali content, and can be implemented in continuous production, which is beneficial to improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without inventive efforts. Among them:

[0022] FIG1 is a schematic flow chart of an embodiment of a method for preparing a single-crystal ternary cathode material according to the present application;

[0023] FIG2 is a SEM photograph of each comparative example and each embodiment;

[0024] FIG3 is a comparison of alkali content between comparative examples and examples;

[0025] FIG4 is a comparison of rate performance between comparative examples and embodiments;

[0026] FIG5 is a graph showing the 45° C. cycle capacity retention rate of each comparative example and each embodiment;

[0027] FIG6 is a graph showing DCR data at 20% SOC for each comparative example and each embodiment. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] Please refer to FIG1 , which is a schematic flow chart of an embodiment of a method for preparing a single-crystal ternary cathode material of the present application. The method includes the following steps S11 - S13 .

[0030] Step S11, uniformly mix the first stage lithium source and the single crystal ternary precursor, and perform the first stage low temperature sintering to obtain a first sintered material; the first stage lithium source is lithium carbonate, and the sintering temperature of the first stage low temperature sintering is 600°C to 800°C.

[0031] The single crystal ternary precursor can be obtained using the preparation method in the prior art. In this embodiment, the chemical formula of the single crystal ternary precursor is Ni x Co y Mn 1-x-y (OH)2, wherein 0.5≤x<1, 0<y<0.5, x+y<1, and the parameter D50 characterizing the particle size of the preferred single crystal ternary precursor is 2μm~20μm.

[0032] For example, a single-crystalline ternary precursor can be prepared by the following steps ad.

[0033] Step a, solution preparation: Prepare a mixed salt solution L1 with a molar ratio of Ni:Co:Mn=x:y:1-xy, so that the metal ion concentration in the salt solution is 0.5-3 mol / L; prepare an alkaline solution with a concentration of 1.5-12 mol / L, and prepare a complexing agent solution with a concentration of 0.5-5 mol / L. The nickel salt and cobalt salt solutions are mixed solutions of one or more of sulfate, nitrate, and chloride. The alkaline solution is a mixed solution of one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide; and the complexing agent is a mixed solution of one or more of ammonia water, ammonium bicarbonate, ammonium sulfate, ammonium carbonate, citric acid, and disodium ethylenediaminetetracarboxylate.

[0034] Step b, preparation of the initial solution: pure water is injected into the reaction vessel, and the pH value of the solution is adjusted to 8.5-13.5 with an alkaline solution, and the temperature in the reaction vessel is maintained at 40-80° C., while an inert gas is introduced throughout the entire reaction process.

[0035] Step c, reaction of the precursor: add L1 solution to the reaction vessel at a flow rate of 5 to 30 L / min, and slowly add an appropriate amount of complexing agent and alkaline solution, maintain the temperature in the reaction vessel at 40 to 80°C, and adjust the stirring speed to 120 to 950 r / min;

[0036] Step d, solid-liquid separation: The material in step c is surface treated, and the synthesized ternary cathode material precursor is transferred to a aging tank for solid-liquid separation, washed with deionized water for solid-liquid separation, and dried to obtain the desired single crystal ternary precursor Ni x Co y Mn 1-x-y (OH)2.

[0037] These metals can also be doped into the precursor through oxides, halides, hydroxides, metal organics, nitrates, sulfates, carbonates, phosphates, oxalates of metal elements such as Mg, Al, Zr, Ti, Er, Sr, Nd, Y, W, or composite oxides or metal fluorides with other metal elements to improve the stability of the structure.

[0038] In this embodiment, the molar ratio of the lithium source to the single crystal ternary precursor in the first stage is (0.6-1):1, for example, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, etc. Most of the required lithium is added during the first low-temperature sintering. In this embodiment, the sintering temperature of the first low-temperature sintering is 600°C to 800°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, etc., and the sintering time is 5h to 15h, for example, 5h, 8h, 10h, 12h, 14h, etc., and cooling is performed after sintering.

[0039] Step S12: uniformly mix the second stage lithium source and the first sintering material, and perform a second stage low-temperature sintering to obtain a second sintering material; the sintering temperature of the second stage low-temperature sintering is 600° C. to 800° C.

[0040] The molar ratio of the second-stage lithium source to the first sintering material is (0.03-0.5):1, for example, 0.03:1, 0.06:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, etc. In this embodiment, the sintering temperature of the second-stage low-temperature sintering is 600°C to 800°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, etc., and the sintering time is 5h to 15h, for example, 5h, 8h, 10h, 12h, 14h, etc., followed by cooling. The second-stage lithium source is lithium carbonate or lithium hydroxide, or a mixture of the two.

[0041] Step S13, sintering the second sintering material at a high temperature to obtain a single crystal ternary positive electrode material; the sintering temperature of the high temperature sintering is 900°C to 1000°C.

[0042] After performing relatively low-temperature sintering in two stages, the second sintered material is subjected to high-temperature sintering at 900°C to 1000°C, such as 900°C, 920°C, 940°C, 960°C, 980°C, etc. The sintering time of the high-temperature sintering is 5 hours to 25 hours, such as 5 hours, 8 hours, 10 hours, 15 hours, 20 hours, 25 hours, etc. After sintering, conventional post-processing such as cooling, crushing, and screening for iron removal is performed to obtain a single-crystal ternary cathode material.

[0043] This embodiment uses lower-cost lithium carbonate as the majority of the lithium source, and adopts a combination of staged lithium replenishment and two-stage low-temperature sintering to prepare a ternary positive electrode material. This not only reduces the alkali content of the material and improves the uniformity of the particles, but also improves its electrochemical performance and high-temperature performance, bringing it to the same level as the performance of a ternary positive electrode material using lithium hydroxide as the lithium source.

[0044] Based on the same inventive concept, the present application also provides a single-crystal ternary positive electrode material, which is prepared by the preparation method in the above embodiment. This embodiment has the same beneficial effects as the above embodiment, which will not be repeated here.

[0045] Based on the same inventive concept, the present application also provides a lithium-ion battery, which includes the single-crystal ternary positive electrode material in the above-mentioned embodiment, and of course also includes the negative electrode material, diaphragm, electrolyte, etc. that can be obtained from the scheme disclosed in the prior art. The lithium-ion battery also has the same beneficial effects as the above-mentioned embodiment, which will not be repeated here.

[0046] The performance improvement brought about by the technical solution provided in this application is illustrated below with reference to specific embodiments and comparative examples.

[0047] The positive electrode material was prepared according to the following steps, which is recorded as Comparative Example 1:

[0048] Step 1, prepare a single crystal ternary precursor: Ni:Co:Mn=0.70:0.10:0.20 to prepare a 1.5 mol / L mixed solution L1, prepare 1.5 mol / L sodium hydroxide solution and 0.5 mol / L ammonium sulfate solution; inject pure water into the reaction vessel, and adjust the pH value of the initial solution to 11.5 with 1.5 mol / L sodium hydroxide solution, adjust the temperature in the reaction vessel to 40°C, the rotation speed to 200 r / min, and introduce nitrogen; adjust the flow rate of L1 solution to 5 L / min, and slowly add sodium hydroxide and ammonium sulfate at the same time. When the particle size reaches the requirement, perform solid-liquid separation and dry to obtain the required single crystal ternary precursor S1.

[0049] Step 2, prepare the ternary positive electrode material: lithium hydroxide, single crystal ternary precursor S1 and aluminum hydroxide are mixed in proportion, the precursor and lithium hydroxide are in a molar ratio of n(Li) / n(Me)=1.05, and then sintered at a sintering temperature of 910°C and a sintering time of 8 hours. Oxygen is introduced during the sintering process, and the sintered material is crushed, classified, iron removed and other processes to obtain the ternary positive electrode material of Comparative Example 1.

[0050] The positive electrode material was prepared according to the following steps, which is recorded as Comparative Example 2:

[0051] Step 1: Obtain the above-mentioned single-crystal ternary precursor S1.

[0052] Step 2, prepare the ternary positive electrode material: lithium carbonate, single crystal ternary precursor S1 and aluminum hydroxide are mixed in proportion, the precursor and lithium carbonate are in a molar ratio of n(Li) / n(Me) = 1.05, and then sintered at a sintering temperature of 910°C and a sintering time of 8 hours. Oxygen is introduced during the sintering process, and the sintered material is crushed, classified, iron removed and other processes to obtain the ternary positive electrode material of Comparative Example 2.

[0053] The positive electrode material was prepared according to the following steps, which is recorded as Example 1:

[0054] Step 1: Obtain the above-mentioned single-crystal ternary precursor S1.

[0055] Step 2, preparing a ternary positive electrode material: lithium carbonate, a single crystal ternary precursor S1 and aluminum hydroxide are mixed in proportion for the first stage, and the precursor and lithium carbonate are mixed in a molar ratio of n(Li) / n(Me)=0.8 in the first stage; a first low-temperature sintering is performed with a sintering temperature of 750°C, a sintering time of 10h, and air is passed through the sintering process to obtain a first-stage low-temperature sintered material; in the second stage, the first-stage low-temperature sintered material is mixed with lithium carbonate in a molar ratio of n(Li) / n(Me)=0.25, and a second low-temperature sintering is performed with a sintering temperature of 700°C, a sintering time of 10h, and air is passed through the sintering process to obtain a second-stage low-temperature sintered material; a high-temperature sintering is performed with a sintering temperature of 910°C, a sintering time of 8h, and oxygen is passed through the sintering process, and the sintered material is subjected to crushing, grading, iron removal and other process treatments to obtain the ternary positive electrode material of Example 1.

[0056] The positive electrode material was prepared according to the following steps, which is recorded as Example 2:

[0057] Step 1: Obtain the above-mentioned single-crystal ternary precursor S1.

[0058] Step 2, prepare a ternary positive electrode material: lithium carbonate, a single crystal ternary precursor S1 and aluminum hydroxide are mixed in proportion for the first stage, and the precursor and lithium carbonate are mixed in a molar ratio of n(Li) / n(Me)=0.8 in the first stage; a first low-temperature sintering is performed with a sintering temperature of 750°C, a sintering time of 10h, and air is passed through the sintering process to obtain a first-stage low-temperature sintered material; in the second stage, the first-stage low-temperature sintered material is mixed with lithium hydroxide in a molar ratio of n(Li) / n(Me)=0.25, and a second low-temperature sintering is performed with a sintering temperature of 700°C, a sintering time of 10h, and air is passed through the sintering process to obtain a second-stage low-temperature sintered material; a high-temperature sintering is performed with a sintering temperature of 910°C, a sintering time of 8h, and oxygen is passed through the sintering process, and the sintered material is subjected to crushing, grading, iron removal and other process treatments to obtain the ternary positive electrode material of Example 1.

[0059] The difference between Example 1 and Example 2 is that the lithium source for the second stage of low-temperature sintering is different, that is, lithium carbonate in Example 1 and lithium hydroxide in Example 2.

[0060] The SEM photos of each comparative example and each embodiment are shown in Figure 2. It can be seen that the comparative example 2 is directly sintered once after mixing the precursor and lithium carbonate, and cannot be sintered into a single crystal material, and the particle morphology is poor. Example 1 and Example 2 can reach the morphology of the process of comparative example 1 using lithium hydroxide as the lithium source, forming a single crystal with good morphology.

[0061] The comparison of the alkali content of each comparative example and each embodiment is shown in FIG3 . It can be seen that the alkali content of comparative example 2 is significantly higher, and it can be inferred that its material properties will be significantly worse. The alkali content of embodiments 1 and 2 is at the same level as that of comparative example 1.

[0062] The rate performance comparison of each comparative example and each embodiment is shown in FIG4 . It can be seen that the capacity and rate of comparative example 2 are significantly worse, while the levels of embodiments 1 and 2 are comparable to those of comparative example 1.

[0063] The 45°C cycle capacity retention curves of the comparative examples and the examples are shown in FIG5 . It can be seen that the cycle performance of the comparative example 2 is significantly poor, while the levels of the examples 1 and 2 are comparable to those of the comparative example 1.

[0064] The DCR data of each comparative example and each embodiment at 20% SOC are shown in FIG6 . It can be seen that the low-temperature DCR performance of comparative example 2 is significantly poor, while the performance of embodiments 1 and 2 is comparable to that of comparative example 1.

[0065] The above description is only an implementation method of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a single crystal ternary cathode material, characterized in that: include: The first stage lithium source is mixed evenly with the single crystal ternary precursor, and a first stage low temperature sintering is performed to obtain a first sintered material; the first stage lithium source is lithium carbonate, and the sintering temperature of the first stage low temperature sintering is 600° C. to 800° C.; The second stage lithium source is mixed evenly with the first sintering material, and a second stage low temperature sintering is performed to obtain a second sintering material; the sintering temperature of the second stage low temperature sintering is 600° C. to 800° C.; The second sintering material is subjected to high-temperature sintering to obtain the single-crystal ternary positive electrode material; the sintering temperature of the high-temperature sintering is 900°C to 1000°C.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the first lithium source to the single crystal ternary precursor is (0.6-1):

1.

3. The preparation method according to claim 2, characterized in that: The sintering time of the first stage of low-temperature sintering is 5 hours to 15 hours.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the second stage lithium source to the first sintering material is (0.03-0.5):

1.

5. The preparation method according to claim 4, characterized in that: The sintering time of the second low-temperature sintering is 5 hours to 15 hours.

6. The preparation method according to claim 1, characterized in that: The second stage lithium source is lithium carbonate or lithium hydroxide.

7. The preparation method according to claim 1, characterized in that: The sintering time of the high temperature sintering is 5h to 25h.

8. The preparation method according to claim 1, characterized in that: The chemical formula of the single crystal ternary precursor is Ni x Co y Mn 1-x-y (OH)2, wherein 0.5≤x<1, 0<y<0.5, x+y<1.

9. The preparation method according to claim 8, characterized in that: The parameter D50 characterizing the particle size of the single-crystal ternary precursor is 2 μm to 20 μm.

10. A single crystal ternary positive electrode material prepared according to the preparation method according to any one of claims 1 to 9.

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