Preparation method of lithium phosphate in-situ coated high-nickel ternary positive electrode material

Abstract

The application discloses a preparation method of lithium phosphate in-situ coated high-nickel ternary positive electrode material, which comprises the following steps: (1) adding high-nickel ternary precursor into a lithium hexametaphosphate hexahydrate solution, and drying to obtain high-nickel ternary precursor coated with lithium hexametaphosphate hexahydrate; (2) mixing the high-nickel ternary precursor coated with lithium hexametaphosphate hexahydrate obtained in the step (1) with lithium salt, and performing oxidation sintering treatment to obtain lithium phosphate in-situ coated high-nickel ternary positive electrode material. The preparation method of the lithium phosphate in-situ coated high-nickel ternary positive electrode material solves the technical problem that lithium phosphate is difficult to be uniformly coated on the surface of the positive electrode material by uniformly synthesizing lithium phosphate on the surface of the primary particles of the ternary positive electrode material through the use of lithium hexametaphosphate hexahydrate. The in-situ coating of lithium phosphate can effectively improve the interface stability of the high-nickel ternary positive electrode material, inhibit the occurrence of interface side reactions, and improve the cycle stability of the material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a method for preparing a high-nickel ternary cathode material with a coating layer. Background Technology

[0002] Lithium-ion batteries are widely used due to their advantages such as high energy density, long lifespan, and low self-discharge rate. In lithium-ion batteries, the cathode material accounts for approximately 40% of the production cost and is the key material determining the battery's performance. Compared to the widely used low-nickel ternary cathode materials (Ni < 80%), high-nickel ternary cathode materials (Ni ≥ 80%) are gradually becoming one of the preferred cathode materials for next-generation high-energy lithium-ion batteries due to their high capacity and low cost. Despite these advantages, high-nickel ternary cathode materials still need to address issues such as low initial efficiency, poor storage performance, poor cycle stability, and poor safety before further practical application. These problems mainly stem from the unstable crystal structure of the high-nickel ternary cathode material itself and interfacial side reactions between the cathode material and the electrolyte.

[0003] To address the aforementioned issues, existing technologies generally employ surface coating methods to modify cathode materials. This is primarily because the coating layer can effectively regulate side reactions at the material / electrolyte interface, thereby improving the material's cycle stability. For example, existing technologies mention using lithium dihydrogen phosphate or ammonium dihydrogen phosphate to coat precursors to prepare lithium phosphate-coated cathode materials, thus improving the material's cycle performance. However, the lithium phosphate coating produced by these methods is uneven. Existing technologies also mention using atomic deposition to coat lithium phosphate to improve the cycle stability of cathode materials, but this method is costly and has stringent process requirements. Overall, the lithium phosphate coating layers produced by existing coating methods suffer from uneven coating or high production costs, making industrial application difficult.

[0004] Therefore, it is necessary to design a new method for preparing lithium phosphate-coated high-nickel ternary cathode materials to solve the above problems. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a method for preparing a high-nickel ternary cathode material with in-situ lithium phosphate coating that exhibits uniform coating, simple operation, and excellent cycle stability. To solve the above technical problem, the technical solution proposed by this invention is as follows:

[0006] A method for preparing a high-nickel ternary cathode material with in-situ lithium phosphate coating includes the following steps:

[0007] (1) The high-nickel ternary precursor was added to a solution of lithium hexahydrate cyclic hexametaphosphate ((LiPO3)6·6H2O) and dried to obtain a high-nickel ternary precursor coated with lithium hexahydrate cyclic hexametaphosphate.

[0008] (2) After thoroughly mixing the high-nickel ternary precursor coated with lithium hexahydrate ring hexametaphosphate obtained in step (1) with lithium salt, the high-nickel ternary cathode material coated with lithium phosphate in situ is obtained by oxidation sintering treatment.

[0009] In the above preparation method, the preferred method for preparing the hexahydrate cyclic lithium hexametaphosphate solution includes the following steps: thoroughly mixing phosphoric acid with a lithium source and heating, grinding the heated product and dissolving it in water, separating the insoluble matter, and obtaining the filtrate as the hexahydrate cyclic lithium hexametaphosphate solution.

[0010] In the above preparation method, preferably, the lithium-phosphorus molar ratio is controlled at (1-2):1 when phosphoric acid and lithium source are mixed. After mixing, phosphoric acid and lithium source undergo a chemical reaction to generate intermediate lithium metaphosphate (lithium-phosphorus molar ratio of 1:1) and the final product lithium phosphate (lithium-phosphorus molar ratio of 3:1). When the lithium-phosphorus molar ratio is less than 1:1, a large amount of unreacted lithium salt exists in the product, and the product yield is low; when the lithium-phosphorus molar ratio is greater than 2:1, the main product is lithium phosphate, not cyclopyrophosphate, which also leads to a decrease in the yield of the target product.

[0011] In the above preparation method, preferably, the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate.

[0012] In the above preparation method, preferably, the heating is first performed at 180-230℃ for 0.5-2 hours, then at 280-330℃ for 1-5 hours, and finally at 420-470℃ for 0.25-1 hour. The main basis for controlling these heating conditions is the reaction mechanism of phosphoric acid and lithium source; that is, under these conditions, phosphoric acid and lithium source can generate lithium metaphosphate and lithium phosphate. However, lithium metaphosphate is unstable at high temperatures and easily reacts further with lithium salt to generate lithium phosphate. Therefore, it is necessary to control these reaction conditions to obtain the maximum yield. This invention employs the above multi-stage heating method, resulting in a relatively higher yield of lithium metaphosphate.

[0013] In the above preparation method, preferably, the method for separating insoluble matter is filtration or centrifugation, and the drying method is stirring evaporation drying or spray drying.

[0014] In the above preparation method, preferably, the molar ratio of the hexahydrate cyclic hexametaphosphate lithium to the high-nickel ternary precursor is controlled to be (0.001-0.01):1.

[0015] In the above preparation method, preferably, the molar percentage of nickel in the transition metal ions in the high-nickel ternary precursor is greater than or equal to 80%.

[0016] In the above preparation method, preferably, the molar ratio of the high-nickel ternary precursor coated with lithium hexahydrate hexametaphosphate to the lithium salt is controlled to be 1:(1-1.1).

[0017] In the above preparation method, preferably, the lithium salt includes lithium hydroxide and / or lithium hydroxide monohydrate.

[0018] In the above preparation method, preferably, during the oxidation sintering treatment, the temperature is first heated at 470-500℃ for 4-6 hours, and then heated at 700-800℃ for 10-20 hours. Since the melting point of lithium hydroxide is around 470℃, to ensure that the lithium hydroxide remains in a molten state and reacts more uniformly with the coating on the precursor surface, the initial heating temperature should preferably be between 470-500℃. Higher temperatures will cause the molten lithium hydroxide to decompose into solid lithium oxide, which is detrimental to the contact reaction with the precursor.

[0019] In existing technologies, lithium dihydrogen phosphate (LDH) or ammonium dihydrogen phosphate (MDH) are often used to coat precursors before reacting with lithium hydroxide. Although LDH and MDH can also react with lithium hydroxide at high temperatures to form lithium phosphate, their melting points are lower than those of lithium hydroxide. Therefore, during heating, LDH and MDH melt first and then agglomerate and shrink under surface tension. The resulting lithium phosphate residue remains on the surface of the secondary particles of the cathode material, leading to severe particle agglomeration, poor coating effect, and uneven coating, which is detrimental to improving the electrochemical performance of the material. In contrast, the lithium hexahydrate hexametaphosphate used in this invention is a self-made, uncommon chemical. The melting point of lithium hexahydrate hexametaphosphate is higher than that of lithium hydroxide. Therefore, before the lithium hydroxide melts, the reaction process with lithium hydroxide remains a solid-solid reaction, resulting in more uniform coating. The lithium phosphate formed by the reaction of lithium hexahydrate hexametaphosphate with lithium hydroxide at high temperatures is a fast lithium-ion conductor, which not only reduces interfacial side reactions but also does not hinder lithium-ion transport. Through this specific coating process, a cathode material with excellent cycle stability and good electrochemical performance can be obtained.

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

[0021] 1. The method for preparing high-nickel ternary cathode material with in-situ lithium phosphate coating of the present invention first achieves soluble raw material coating on the surface of high-nickel ternary precursor by using lithium hexahydrate hexametaphosphate. Then, the high-nickel ternary precursor coated with raw material is uniformly mixed with lithium salt and further oxidative sintering reaction is carried out. In this way, lithium phosphate is uniformly synthesized in-situ on the surface of primary particles of ternary cathode material, thereby solving the technical problem that it is difficult to uniformly coat lithium phosphate on the surface of cathode material. The modification method is relatively simple to operate and suitable for industrial application.

[0022] 2. The method for preparing high-nickel ternary cathode material with in-situ lithium phosphate coating of the present invention can effectively improve the interfacial stability of high-nickel ternary cathode material, suppress the occurrence of interfacial side reactions, and improve the cycle stability of the material by in-situ coating of lithium phosphate.

[0023] 3. The method for preparing high-nickel ternary cathode material with in-situ lithium phosphate coating of the present invention uses lithium phosphate as a lithium salt, which is a fast lithium-ion conductor. Through in-situ coating, a stable interface modification layer is formed on the surface of the high-nickel ternary cathode material, which can significantly optimize interface problems.

[0024] 4. The performance parameters of the high-nickel ternary cathode material with in-situ lithium phosphate coating of the present invention in coin lithium batteries are as follows: the interface impedance can be as low as 100Ω or below, the 1C cycle number and capacity retention rate can reach 340 cycles and 80% or above, respectively, and the initial coulombic efficiency can reach 88% or above. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The image shows the SEM / EDS image of the in-situ lithium phosphate coated cathode material of Example 1.

[0027] Figure 2 The image shows the SEM / EDS images of the lithium phosphate-coated cathode material in Comparative Example 2 (Figure (a) corresponds to the coating material with lithium dihydrogen phosphate as the precursor in Comparative Example 2, and Figure (b) corresponds to the cathode material prepared from the precursor coated with lithium dihydrogen phosphate).

[0028] Figure 3 The image shows the SEM / EDS images of the lithium phosphate-coated cathode material of Comparative Example 3 (Figure (a) corresponds to the coating material of Comparative Example 3 using ammonium dihydrogen phosphate as a precursor, and Figure (b) corresponds to the cathode material prepared using the ammonium dihydrogen phosphate-coated precursor). Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0032] Example 1:

[0033] A method for preparing a high-nickel ternary cathode material with in-situ lithium phosphate coating includes the following steps:

[0034] S1: Phosphoric acid and lithium carbonate were thoroughly mixed at a lithium-phosphorus molar ratio of 1.4:1, followed by three combined calcinations at three different temperature settings: 200℃ for 1 hour, 300℃ for 3 hours, and 450℃ for 30 minutes. The heated product was ground and dissolved in water. After filtering out the insoluble matter, Ni was added to the filtrate at a molar ratio of lithium hexahydrate hexametaphosphate ((LiPO3)6·6H2O) to the ternary precursor of 0.005:1. 0.9 Co 0.05 Mn 0.05 After stirring and drying, Ni alloy coated with lithium hexahydrate hexametaphosphate ((LiPO3)6·6H2O) is obtained by (OH)2. 0.9 Co 0.05 Mn 0.05 (OH)2.

[0035] S2: The coated precursor is thoroughly mixed with lithium hydroxide monohydrate at a molar ratio of lithium to high-nickel ternary precursor of 1.05:1 and then subjected to high-temperature oxidation sintering treatment, specifically heating at 480°C for 5 hours and heating at 730°C for 15 hours.

[0036] S3: The prepared lithium phosphate in-situ coated ternary cathode material is coated, rolled, cut into pieces, assembled into batteries, and tested.

[0037] Figure 1 The image shows the SEM / EDS image of the in-situ coated lithium phosphate cathode material prepared in this embodiment. Figure 1 It can be seen that lithium phosphate is uniformly coated on the surface of the ternary cathode material.

[0038] Comparative Example 1:

[0039] This comparative example uses only high-nickel ternary cathode material as a blank control for performance testing. The specific preparation process includes the following steps:

[0040] S1: Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor and lithium hydroxide monohydrate were thoroughly mixed at a molar ratio of 1.05:1 and then subjected to high-temperature oxidation and sintering treatment, specifically heating at 480℃ for 5 hours and heating at 730℃ for 15 hours.

[0041] S2: The prepared ternary cathode material is coated, rolled, cut into sheets, assembled into batteries, and tested.

[0042] Comparative Example 2:

[0043] A method for preparing a lithium phosphate-coated high-nickel ternary cathode material includes the following steps:

[0044] S1: Dissolve lithium dihydrogen phosphate (LiH2PO4) in water, and add Ni to the above solution at a molar ratio of lithium dihydrogen phosphate (LiH2PO4) to ternary precursor of 0.005:1. 0.9 Co 0.05 Mn 0.05 (OH)2, after stirring and drying, yields lithium dihydrogen phosphate (LiH2PO4) coated Ni. 0.9 Co 0.05 Mn 0.05 (OH)2.

[0045] S2: The coated precursor is thoroughly mixed with lithium hydroxide monohydrate at a molar ratio of lithium to high-nickel ternary precursor of 1.05:1 and then subjected to high-temperature oxidation sintering treatment, specifically heating at 480°C for 5 hours and heating at 730°C for 15 hours.

[0046] S3: The prepared lithium phosphate in-situ coated ternary cathode material is coated, rolled, cut into pieces, assembled into batteries, and tested.

[0047] Comparative Example 3:

[0048] A method for preparing a lithium phosphate-coated high-nickel ternary cathode material includes the following steps:

[0049] S1: Dissolve ammonium dihydrogen phosphate (NH4H2PO4) in water, and add Ni to the above solution at a molar ratio of ammonium dihydrogen phosphate (NH4H2PO4) to the ternary precursor of 0.005:1. 0.9 Co 0.05 Mn 0.05 (OH)2, after stirring and drying, yields Ni coated with ammonium dihydrogen phosphate (NH4H2PO4). 0.9 Co 0.05 Mn 0.05 (OH)2.

[0050] S2: The coated precursor is thoroughly mixed with lithium hydroxide monohydrate at a molar ratio of lithium to high-nickel ternary precursor of 1.05:1 and then subjected to high-temperature oxidation sintering treatment, specifically heating at 480°C for 5 hours and heating at 730°C for 15 hours.

[0051] S3: The prepared lithium phosphate in-situ coated ternary cathode material is coated, rolled, cut into pieces, assembled into batteries, and tested.

[0052] The SEM / EDS images of the lithium phosphate-coated high-nickel ternary cathode materials in Comparative Examples 2-3 are shown below. Figure 2 , Figure 3 As shown in the figure, the coating uniformity of lithium phosphate is not good.

[0053] After performance testing, the performance test results of the ternary cathode materials of Example 1 and Comparative Examples 1-3 are shown in Table 1.

[0054] Table 1: Performance test results of Example 1 and Comparative Examples 1-3

[0055] Example 1 89Ω 341 laps, 80% 88.1％ Comparative Example 1 118Ω 200 laps, 80% 87.6％ Comparative Example 2 142Ω 253 laps, 80% 88.0％ Comparative Example 3 179Ω 174 laps, 80% 87.5％

[0056] As can be seen from Table 1, the performance of the lithium phosphate in-situ coated high-nickel ternary cathode material prepared in Example 1 is significantly better than that of Comparative Examples 1-3. This indicates that the lithium phosphate coated high-nickel ternary cathode material prepared by the present invention through wet in-situ coating of precursor lithium hexametaphosphate ((LiPO3)6·6H2O), followed by thorough mixing with lithium salt and high-temperature oxidation sintering, results in uniform coating, which can effectively improve the interface stability and electrochemical performance of the high-nickel ternary cathode material, and solves the technical problem of not being able to uniformly coat the high-nickel ternary cathode material in Comparative Examples 2 and 3.

[0057] Examples 2-7:

[0058] The differences from Example 1 are: the proportion of transition metal ions in the precursor is different, the calcination and sintering settings are different, and the proportion of raw materials is different. Everything else is the same as Example 1. The specific raw material proportions, process parameters and performance test results are shown in Tables 2 and 3 below.

[0059] Table 2: Raw material ratios and process parameter settings for Examples 2-7

[0060]

[0061]

[0062] As shown in Table 2, in the mixture of phosphoric acid and lithium source, the higher the lithium-phosphorus molar ratio, the shorter the low-temperature sintering time and the longer the high-temperature sintering time required for lithium hexahydrate hexametaphosphate ((LiPO3)6·6H2O), thus ensuring a higher product yield. The molar ratio of lithium hexahydrate hexametaphosphate to the ternary precursor is controlled at 0.1-1%, mainly because lithium metaphosphate reacts with molten lithium hydroxide during the subsequent high-temperature sintering process to generate lithium phosphate, which then penetrates into the voids inside the secondary particles of the high-nickel ternary cathode material. Excessive lithium metaphosphate will cause it to remain on the surface of the secondary particles and lead to agglomeration between particles, thereby affecting the electrochemical performance of the material. If the coating amount is too small, the lithium phosphate generated at high temperature cannot effectively achieve complete coating of the interface. With the improvement of interface stability, there is still room for improvement. The effect of nickel content in the precursor on the sintering of ternary cathode materials is as follows: the higher the nickel content, the lower the amount of lithium required during sintering, the lower the sintering temperature, and the shorter the sintering time. This is because divalent nickel ions are prone to cation mixing with lithium ions under high temperature conditions. Therefore, to increase the nickel content in the precursor, the sintering temperature and time should be appropriately reduced to ensure the electrochemical performance of the material. At the same time, the reduction in sintering temperature leads to a reduction in the amount of lithium salt volatilization loss. Therefore, the molar ratio of lithium to high-nickel ternary precursor should also be appropriately reduced.

[0063] After performance testing, the performance test results of the ternary cathode materials in Examples 2-7 are shown in Table 3 below.

[0064] Table 3: Performance test results of Examples 2-7

[0065]

[0066]

Claims

1. A method for preparing a high-nickel ternary cathode material with in-situ lithium phosphate coating, characterized in that, Includes the following steps: (1) The high-nickel ternary precursor was added to a solution of lithium hexahydrate cyclohexametaphosphate and dried to obtain a high-nickel ternary precursor coated with lithium hexahydrate cyclohexametaphosphate. (2) After thoroughly mixing the high-nickel ternary precursor coated with lithium hexahydrate ring hexametaphosphate obtained in step (1) with the lithium-containing material, the high-nickel ternary cathode material coated with lithium phosphate in situ is obtained by oxidation sintering treatment; the lithium-containing material is lithium hydroxide. The molar ratio of the hexahydrated cyclic lithium hexametaphosphate to the high-nickel ternary precursor is controlled to be (0.001-0.01):1; during the oxidation sintering treatment, it is first heated at 470-500℃ for 4-6 hours, and then heated at 700-800℃ for 10-20 hours.

2. The preparation method according to claim 1, characterized in that, The preparation method of lithium hexahydrate hexamethonium phosphate solution includes the following steps: thoroughly mixing phosphoric acid and lithium source and heating, grinding the heated product and dissolving it in water, separating the insoluble matter, and obtaining the filtrate as lithium hexahydrate hexamethonium phosphate solution.

3. The preparation method according to claim 2, characterized in that, When phosphoric acid and lithium source are mixed, the lithium-phosphorus molar ratio is controlled to be (1-2):

1.

4. The preparation method according to claim 2, characterized in that, The lithium source includes one or both of lithium carbonate and lithium hydroxide.

5. The preparation method according to claim 2, characterized in that, When heating, first heat at 180-230℃ for 0.5-2 hours, then heat at 280-330℃ for 1-5 hours, and then heat at 420-470℃ for 0.25-1 hour.

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