Ternary single-crystal positive electrode material and preparation method thereof

Abstract

The invention discloses a preparation method of a single-crystal ternary positive electrode material. A mixed lithium source composed of a low-temperature eutectic lithium salt and a high-temperature non-eutectic lithium salt is adopted, the characteristics of rapid fusion in a low-temperature section and slow repair in a high-temperature section in the sintering process of the positive electrode material are realized, and the prepared single-crystal positive electrode material has the characteristics of complete crystallinity, large particle size, good dispersity and excellent electrical property and stability. The preparation method is simple, easy to control in operation and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials, and particularly relates to a single-crystal ternary cathode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life, low self-discharge rate, good environmental friendliness, etc. In recent years, they have been widely applied to fields such as intelligent tools, energy storage, power tools, and power products. Accordingly, as one of the key materials in lithium-ion batteries, cathode materials also have a large market development space.

[0003] Layered cathode materials include materials such as lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium nickel manganese oxide, all of which have the structure of α-NaFeO2 and have a very high specific capacity advantage compared to other cathode materials. However, the material stability is poor. Especially in secondary spherical polycrystalline materials, during charge and discharge, the layered structure is prone to irreversible phase transformation of H2-H3, and the lattice c-axis undergoes a severe shrinkage and expansion effect. Macroscopically, it is manifested as a severe volume change of primary particles. Due to stress concentration problems, the secondary spheres crack, and the formed microcracks will further expose the fresh inner surface of the secondary spheres. When the electrolyte infiltrates and reacts with the material, it will further accelerate the aging of the material, form more rock salt phase structures, cause higher DCR and more gas generation, and release a large amount of heat, resulting in material failure and even inducing safety problems.

[0004] Preparing single-crystal materials by eliminating grain boundaries is a generally recognized solution in the academic and industrial fields. However, the sintering temperature of single-crystal materials is much higher than that of polycrystalline materials, which will lead to an increase in lithium-nickel mixing on the material surface, forming rock salt phase and spinel phase, resulting in effects such as capacity decline and DCR increase. Therefore, how to obtain large single crystals with good dispersibility and high crystallinity while reducing surface degradation is an important issue in the current development of single-crystal materials.

[0005] To solve such problems, Chinese invention patent CN111200129A introduced two or more molten inorganic salts during the sintering process of single-crystal cathodes, effectively reducing the melting temperature of the molten salt, enabling the formation of single-crystal high-nickel ternary cathode materials in the molten salt, and at the same time inhibiting the phenomenon of lithium-nickel mixing. However, the additives additionally added during the sintering process of the molten salt will increase production costs and introduce other elements, which is not conducive to the sintering of pure ternary materials; CN110581259B disclosed a method of introducing Ir 3+ 、Y 3+ 、Te 4+ 、In 3+ 、Ga 3+The preparation method of single crystal materials of cation additives, by reducing the surface energy, the cations occupying the 3b position can reduce the degree of lithium-nickel mixing, but there is a risk of increased cost of cation additives and reduced capacity.

[0006] Therefore, how to improve the sintering process of single crystal materials, while maintaining the advantages of single crystal materials, reduce the damage to the material body and surface in the high-temperature long-time sintering environment, and at the same time take into account economic benefits, has become an important improvement direction for preparing high-nickel single crystal ternary cathode materials. Summary of the Invention

[0007] The present invention provides a ternary single crystal cathode material and a preparation method thereof. By adopting a mixed lithium source composed of a low-temperature eutectic lithium salt and a high-temperature non-eutectic lithium salt, the functions of rapid fusion in the low-temperature section and phase repair in the high-temperature section during the sintering process of the cathode material are realized.

[0008] Among them, the low-temperature eutectic lithium salt adopts a mixed salt of LiOH and LiNO3, and the melting temperature of the eutectic mixed salt can be reduced to below 200 °C. The reaction entropy of liquid sintering increases, which can promote the rapid embedding of lithium and crystal fusion; the high-temperature non-eutectic lithium salt selects lithium sources with different melting temperatures according to the differences in nickel content and sintering temperature, which can promote the repair of lithium-nickel mixing caused by the end stage of high-temperature sintering and promote the transformation of the rock salt phase.

[0009] On the one hand, the present invention provides a preparation method of a single crystal cathode active material, which comprises the following steps:

[0010] 1) Select nickel cobalt manganese hydroxide as the reaction precursor; select a low-temperature eutectic lithium salt and a high-temperature non-eutectic lithium salt as the mixed lithium source;

[0011] 2) Mix the reaction precursor and the mixed lithium source evenly to obtain a mixed material A;

[0012] 3) Perform a first sintering on the mixed material A in an air or oxygen atmosphere, naturally cool to room temperature, and crush to obtain a single crystal ternary cathode material;

[0013] Further, in the step 1), the chemical formula of the nickel cobalt manganese hydroxide precursor is Ni x Co y Mn (1-x-y) (OH)2, where 0.5 ≤ x < 0.95 and 0 ≤ y ≤ 0.5.

[0014] Further, in the step 1), the particle size D50 of the nickel cobalt manganese hydroxide precursor material is 2-5 μm.

[0015] Further, in the step 1), the low-temperature eutectic lithium salt is selected from LiNO3 and LiOH, and the high-temperature non-eutectic salt is selected from Li2CO3 or Li2SO4.

[0016] Further, in the mixed lithium source in step 1), the lithium molar ratio of the low-temperature eutectic lithium salt is m = 2x - 0.9, and the lithium molar ratio of the high-temperature eutectic lithium salt is n = 1.9 - 2x, where x is the nickel content in the nickel cobalt manganese hydroxide precursor.

[0017] Further, the molar composition ratio of the low-temperature eutectic lithium salt in step 1) is LiNO3:LiOH = 1:(0.8 - 1.2).

[0018] Further, the type of the high-temperature non-eutectic lithium salt in step 1) is related to the nickel content x. When x < 0.7, Li2SO4 is preferably used; when x ≥ 0.7, Li2CO3 is preferably used.

[0019] Specifically, since the sintering temperature of the single crystal material is closely related to the nickel content x, it is necessary to select and design the ratio of the low-temperature eutectic salt and the high-temperature non-eutectic salt to adapt to the sintering system of single crystal materials with different nickel contents:

[0020] For medium and low nickel materials (x < 0.7), the sintering temperature is high (≥900 °C), and the mixed lithium is mainly composed of high-temperature non-eutectic salts, and the high-temperature non-eutectic salt selected is Li2SO4 with a higher melting temperature (melting point

[0021] ~845 °C), which can not only ensure the single crystal fusion but also repair the problem of increased lithium-nickel mixing at high temperatures;

[0022] For high nickel materials (x ≥ 0.7), the sintering temperature is low (<900 °C), and the mixed lithium is mainly composed of low-temperature eutectic salts, and the high-temperature non-eutectic salt selected is Li2CO3 with a lower melting temperature (melting point

[0023] ~618 °C), which ensures that most of the liquid lithium is embedded in the low-temperature section, and only a small amount of non-eutectic salt lithium needs to be embedded in the high-temperature section to repair the surface degradation;

[0024] Further, the molar ratio of the mixed lithium source (calculated as Li) to the precursor in step 2) is 0.95 - 1.1;

[0025] Further, the primary sintering temperature in step 3) is 800 - 1000 °C, the heating rate is 1 - 5 °C / min, the sintering cycle is 8 - 15 h, and the sintering atmosphere is air or oxygen atmosphere, where the oxygen concentration in the oxygen atmosphere is 88 - 95%.

[0026] On the other hand, the present invention provides a ternary single crystal cathode material prepared by the above method.

[0027] Compared with the prior art, the preparation method of the single crystal ternary cathode material provided by the present invention has the following main advantages:

[0028] 1) By adjusting the type and proportion of lithium salts, the present invention can adapt to the sintering system of single crystals with different nickel contents. The prepared cathode material has the characteristics of complete crystallinity, large particle size, good dispersibility, excellent electrical properties and stability.

[0029] Specifically, the eutectic lithium salt at low temperature adopts a mixed salt of LiOH and LiNO3. The melting temperature of the eutectic mixed salt with a specific proportion can be reduced, and the reaction entropy of liquid sintering increases, which can promote the rapid embedding of lithium and crystal fusion; the non-eutectic lithium salt at high temperature selects lithium sources with different melting temperatures according to the differences in nickel content and sintering temperature, which can promote the repair of lithium-nickel mixing caused by the end stage of high-temperature sintering, and promote surface repair and rock salt phase transformation.

[0030] 2) The preparation method involved in the present invention is simple, easy to control, and suitable for large-scale production. Description of the Drawings

[0031] Figure 1 SEM image of the ternary single-crystal cathode material prepared in Example 1;

[0032] Figure 2 SEM image of the ternary single-crystal cathode material prepared in Example 2;

[0033] Figure 3 SEM image of the ternary single-crystal cathode material prepared in Example 3;

[0034] Figure 4 SEM image of the ternary single-crystal cathode material prepared in Example 4;

[0035] Figure 5 SEM image of the ternary single-crystal cathode material prepared in Example 5;

[0036] Figure 6 SEM image of the ternary single-crystal cathode material prepared in Example 6;

[0037] Figure 7 SEM image of the ternary single-crystal cathode material prepared in Comparative Example 1;

[0038] Figure 8 SEM image of the ternary single-crystal cathode material prepared in Comparative Example 2;

[0039] Figure 9 SEM image of the ternary single-crystal cathode material prepared in Comparative Example 3;

[0040] Figure 10 SEM image of the ternary single-crystal cathode material prepared in Comparative Example 4;

[0041] Figure 11 SEM image of the ternary single-crystal cathode material prepared in Comparative Example 5; Detailed Embodiments

[0042] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0043] Raw materials and sources:

[0044] The ternary precursors (Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.6 Co 0.1 Mn 0.3 (OH)2, Ni 0.83 Co 0.12 Mn 0.05 (OH)2, Ni 0.94 Co 0.03 Mn 0.03 (OH)2) are all from Zhongwei New Materials Co., Ltd.; lithium hydroxide, lithium carbonate, lithium nitrate, and lithium sulfate are all from Ganfeng Lithium Co., Ltd.

[0045] Testing methods:

[0046] SEM images were taken on the Phenom pro device; XRD data of the materials were tested by the Malvern Aeris benchtop XRD tester, and the data were calculated using the Highscore Plus software; DSC tests were performed using a Mettler Toledo DSC3 differential scanning calorimeter. The program was to heat from room temperature to 400 °C at a rate of 5 °C / min, and the tests were carried out in an air atmosphere.

[0047] Electrochemical performance tests were carried out using coin-type half-cells. The reference standard was GB / T 37201-2018. The test voltage range was 2.8 - 4.3 V. The conditions for the first charge-discharge capacity test were: controlling the test temperature at 25 °C, the charge-discharge cut-off voltage at 2.8 - 4.3 V, and the discharge current density at 0.1 C. The conditions for the coin cell cycling test were: after activation with 0.1 C charge-discharge for two cycles, 0.33 C charge and 1 C discharge cycling for 50 cycles.

[0048] Example 1:

[0049] The preparation method of the single-crystal ternary cathode material in this example includes the following steps:

[0050] 1) Take 1 mol of Ni 0.5 Co 0.2 Mn 0.3 (OH)2 precursor (D50 is 4.2 um) and mix it evenly with 0.47 mol of lithium sulfate, 0.05 mol of lithium nitrate, and 0.05 mol of lithium hydroxide to obtain a mixed material A;

[0051] 2) Put the mixture A obtained in 1) into a box furnace and sinter it in an air atmosphere. The sintering process is set as follows: heat it to 980 °C at a heating rate of 5 °C / min, sinter for 8 h, cool naturally, and then crush and screen to obtain the single-crystal ternary cathode material.

[0052] Example 2:

[0053] The preparation method of the single-crystal ternary cathode material in this example includes the following steps:

[0054] 1) Take 10 mol of Ni 0.6 Co 0.1 Mn 0.3 (OH)2 precursor (D50 is 3.6 um) and mix it evenly with 3.85 mol of lithium sulfate, 1.8 mol of lithium nitrate, and 1.5 mol of lithium hydroxide to obtain mixture A;

[0055] 2) Put the mixture A obtained in 1) into a box furnace and sinter it in an air atmosphere. The sintering process is set as follows: heat it to 950 °C at a heating rate of 3 °C / min, sinter for 10 h, cool naturally, and then crush and screen to obtain the single-crystal ternary cathode material.

[0056] Example 3:

[0057] The preparation method of the single-crystal ternary cathode material in this example includes the following steps:

[0058] 1) Take 10 mol of Ni 0.7 Mn 0.3 (OH)2 precursor (D50 is 5.0 um) and mix it evenly with 2.38 mol of lithium sulfate, 2.38 mol of lithium nitrate, and 2.38 mol of lithium hydroxide to obtain mixture A;

[0059] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 88%, and set the sintering process as follows: heat it to 910 °C at a heating rate of 3 °C / min, sinter for 10 h, cool naturally, and then crush and screen to obtain the single-crystal ternary cathode material.

[0060] Example 4:

[0061] The preparation method of the single-crystal ternary cathode material in this example includes the following steps:

[0062] 1) Take 10 mol of Ni 0.83 Co 0.12 Mn 0.05 (OH)2 precursor (D50 is 3.0 um) and mix it evenly with 1.2 mol of lithium carbonate, 3.55 mol of lithium nitrate, and 4.25 mol of lithium hydroxide to obtain mixture A;

[0063] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 92%, and set the sintering process as follows: heat up to 880 °C at a heating rate of 3 °C / min, sinter for 12 h, cool naturally, and then crush and screen to obtain the single-crystal ternary cathode material.

[0064] Example 5:

[0065] The preparation method of the single-crystal ternary cathode material in this example includes the following steps:

[0066] 1) Take 100 mol of Ni 0.94 Co 0.03 Mn 0.03 (OH)2 precursor (D50 is 2.0 um) and mix it evenly with 1 mol of lithium carbonate, 51 mol of lithium nitrate, and 51 mol of lithium hydroxide to obtain mixture A;

[0067] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 95%, and set the sintering process as follows: heat up to 800 °C at a heating rate of 1 °C / min, sinter for 15 h, cool naturally, and then crush and screen to obtain the single-crystal ternary cathode material.

[0068] Example 6:

[0069] The preparation method of the single-crystal ternary cathode material in this example includes the following steps:

[0070] 1) Take 10 mol of Ni 0.7 Mn 0.3 (OH)2 precursor (D50 is 5.0 um) and mix it evenly with 2.38 mol of lithium carbonate, 2.38 mol of lithium nitrate, and 2.38 mol of lithium hydroxide to obtain mixture A;

[0071] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 88%, and set the sintering process as follows: heat up to 910 °C at a heating rate of 3 °C / min, sinter for 10 h, cool naturally, and then crush and screen to obtain the single-crystal ternary cathode material.

[0072] Comparative Example 1:

[0073] The preparation method of the single-crystal ternary cathode material in this comparative example includes the following steps:

[0074] 1) Take 1 mol of Ni 0.5 Co 0.2 Mn 0.3 (OH)2 precursor (D50 is 4.2 um) and mix it evenly with 0.57 mol of lithium sulfate to obtain mixture A;

[0075] 2) Put the mixture A obtained in 1) into a box furnace and sinter it in an air atmosphere. The sintering process is set as follows: heat it to 980 °C at a heating rate of 5 °C / min, with a sintering time of 8 h, and then cool it naturally and crush and screen it to obtain a single-crystalline ternary cathode material.

[0076] Comparative Example 2:

[0077] The preparation method of the single-crystalline ternary cathode material in this comparative example includes the following steps:

[0078] 1) Take 1 mol of Ni 0.5 Co 0.2 Mn 0.3 (OH)2 precursor (D50 is 4.2 um) and mix it evenly with 0.47 mol of lithium carbonate, 0.05 mol of lithium nitrate, and 0.05 mol of lithium hydroxide to obtain mixture A;

[0079] 2) Put the mixture A obtained in 1) into a box furnace and sinter it in an air atmosphere. The sintering process is set as follows: heat it to 980 °C at a heating rate of 5 °C / min, with a sintering time of 8 h, and then cool it naturally and crush and screen it to obtain a single-crystalline ternary cathode material.

[0080] Comparative Example 3:

[0081] The preparation method of the single-crystalline ternary cathode material in this comparative example includes the following steps:

[0082] 1) Take 100 mol of Ni 0.94 Co 0.03 Mn 0.03 (OH)2 precursor (D50 is 2.0 um) and mix it evenly with 104 mol of lithium hydroxide to obtain mixture A;

[0083] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 95%, and set the sintering process as follows: heat it to 800 °C at a heating rate of 1 °C / min, with a sintering time of 15 h, and then cool it naturally and crush and screen it to obtain a single-crystalline ternary cathode material.

[0084] Comparative Example 4:

[0085] The preparation method of the single-crystalline ternary cathode material in this comparative example includes the following steps:

[0086] 1) Take 100 mol of Ni 0.94 Co 0.03 Mn 0.03 (OH)2 precursor (D50 is 2.0 um) and mix it evenly with 52 mol of lithium nitrate and 52 mol of lithium hydroxide to obtain mixture A;

[0087] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 95%, and set the sintering process as follows: heat up to 800 °C at a heating rate of 1 °C / min, sinter for 15 h, cool naturally, and then crush and screen to obtain a single-crystal ternary cathode material.

[0088] Comparative Example 5:

[0089] The preparation method of the single-crystal ternary cathode material in this comparative example includes the following steps:

[0090] 1) Take 100 mol of Ni 0.94 Co 0.03 Mn 0.03 (OH)2 precursor (D50 is 2.0 um) and 1 mol of lithium carbonate and 102 mol of lithium hydroxide are mixed evenly to obtain a mixed material A;

[0091] 2) Put the mixture A obtained in 1) into a box furnace, control the oxygen concentration in the furnace to 95%, and set the sintering process as follows: heat up to 800 °C at a heating rate of 1 °C / min, sinter for 15 h, cool naturally, and then crush and screen to obtain a single-crystal ternary cathode material.

[0092] From Figure 1 and Figure 7 It can be seen that in the sintering of medium and low nickel single crystals, only the single crystals of the high-temperature non-eutectic salt (Comparative Example 1) have small sizes and there are some small polycrystalline particles, indicating that the time for the molten lithium salt to participate in the reaction is too late; when the low-temperature eutectic salt (Example 1) is introduced, the process of lithium melting and embedding can be advanced, and the sintered single-crystal morphology has larger sizes, smoother edges, and more distinct particles;

[0093] From Figure 5 and Figure 11 It can be seen that during the sintering process of high nickel single crystals, from only lithium hydroxide (Comparative Example 5) to the introduction of the low-temperature eutectic salt lithium nitrate (Example 5), the growth of single crystals can also be promoted, and the sintered single-crystal morphology has larger sizes, smoother edges, and more distinct particles;

[0094] Table 1 shows the physical and electrical property data of the single-crystal cathode materials obtained in each example and comparative example.

[0095] From the data comparison of Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that for low-nickel materials, using a eutectic lithium salt at low temperature can significantly promote the growth of primary particles, and the grain size of the material increases significantly; since the single-crystal sintering temperature is much higher than 900 °C, compared with the traditional lithium carbonate sintering process, using lithium sulfate with a higher melting point can delay the melting of the lithium salt, promote surface repair during high-temperature sintering in the final stage, and reduce the lithium-nickel mixing rate of the material; when sintering medium- and low-nickel materials in the present invention, by combining a eutectic salt at low temperature and a non-eutectic salt at high temperature, a single-crystal cathode material with larger particle size and low lithium-nickel mixing rate is obtained. Therefore, while ensuring the capacity, the thermal stability and cycle stability of the material can be improved.

[0096] From the data comparison of Example 3 and Example 6, it can be seen that for medium-nickel materials (nickel content around 70%), using a combination process of a eutectic salt at low temperature and a non-eutectic salt at high temperature, where the non-eutectic salt at high temperature uses a lithium source of lithium sulfate or lithium carbonate, has no effect on aspects such as lithium-nickel mixing, discharge capacity, cycle stability, and thermal stability of the single-crystal material.

[0097] From the data comparison of Example 5 and Comparative Example 3, it can be seen that in ultra-high-nickel materials, compared with the traditional sintering process using only lithium hydroxide, the preparation method of the eutectic lithium salt at low temperature adopted in the present invention significantly promotes the growth process of primary particles and solves the problem of difficult dispersion of high-nickel single-crystal materials; from the comparison of Example 5 and Comparative Example 4, compared with the process using only the eutectic salt at low temperature, the sintering process introducing a small amount of non-crystalline lithium carbonate at high temperature can delay the melting of the lithium salt, promote the intercalation of lithium during high-temperature sintering in the final stage, thereby repairing the material surface and reducing the lithium-nickel mixing rate of the material; from the comparison of Example 5 and Comparative Example 5, compared with the mixed salt method using lithium hydroxide and lithium carbonate mentioned in Patent CN 106654250, using the eutectic salt process for the low-temperature salt can further promote crystal growth and improve the dispersion degree of the single-crystal material; through the adaptation of the types and proportions of the eutectic salt at low temperature and the non-eutectic salt at high temperature in the present invention, a high-nickel single-crystal cathode material with good dispersion, large particle size, and low lithium-nickel mixing rate is obtained, which has advantages in capacity, cycle, and thermal stability.

[0098] Performance comparison of the prepared ternary cathode materials in Table 1

[0099]

Claims

1. A method for preparing a single-crystal cathode active material, comprising the following steps: 1) Select nickel cobalt manganese hydroxide as a reaction precursor; select a low-temperature eutectic lithium salt and a high-temperature non-eutectic lithium salt as a mixed lithium source; 2) Mix the reaction precursor and the mixed lithium source evenly to obtain a mixed material A; 3) Subject the mixed material A to a first sintering in an air or oxygen atmosphere, naturally cool to room temperature, and crush to obtain a single-crystal ternary cathode material; In the step 1), the low-temperature eutectic lithium salt is selected from LiNO3 and LiOH, and the high-temperature non-eutectic salt is selected from Li2CO3 or Li2SO4.

2. The preparation method according to claim 1, wherein, The chemical formula of the nickel-cobalt-manganese hydroxide precursor in step 1) is Ni x Co y Mn (1-x-y) (OH)2, where 0.5 ≤ x < 0.95, 0 ≤ y ≤ 0.5; and / or, the particle size D50 of the nickel cobalt manganese hydroxide precursor material is 2 - 5 μm.

3. The preparation method according to claim 1 or 2, characterized in that, The said step 1) In the mixed lithium source, the lithium molar ratio of the low-temperature eutectic lithium salt is m = 2x - 0.9, and the lithium molar ratio of the high-temperature eutectic lithium salt is n = 1.9 - 2x, where x is the nickel content in the nickel cobalt manganese hydroxide precursor.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The molar composition ratio of the low-temperature eutectic lithium salt in the step 1) is LiNO3:LiOH = 1: (0.8-1.2)。 5. The preparation method according to any one of claims 1-4, characterized in that, In the high-temperature non-eutectic lithium salt of the step 1), when x < 0.7, Li2SO4 is preferably used; when x ≥ 0.7, Li2CO3 is preferably used.

6. The preparation method according to any one of claims 1-5, characterized in that, The molar ratio of the mixed lithium source (calculated as Li) to the precursor in the step 2) is 0.95 - 1.

1.

7. The preparation method according to any one of claims 1-6, characterized in that, The first sintering temperature in the step 3) is 800 - 1000 °C. Preferably, when x < 0.7 the sintering temperature is 900 - 1000 °C; when x ≥ 0.7, the sintering temperature is 800 - 900 °C.

8. The preparation method according to claim 7, characterized in that, The heating rate is 1 - 5 °C / min, the sintering period is 8 - 15 h, and the sintering atmosphere is air or oxygen atmosphere.

9. A ternary single-crystal cathode material prepared by the preparation method according to any one of claims 1 - 8.

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