Preparation method of a cathode material with a coating layer, a lithium battery and an electric vehicle

Abstract

The present application discloses a preparation method of a cathode material with a coating layer, a lithium battery and an electric vehicle. The method includes: under the condition of the presence of a complexing agent, causing a soluble metal salt and an alkaline substance to undergo a coprecipitation reaction in a solvent; under the condition that the pH value is 9-13, causing the precipitate on the surface layer of the precursor precipitate to be in-situ converted into a phosphate precipitate, obtaining a precursor with a phosphate precipitate coating layer on the surface, and obtaining a second solid-liquid mixture; aging the second solid-liquid mixture to enable nickel phosphate, cobalt phosphate and manganese phosphate to be adsorbed on the outer layer of the precursor with a phosphate precipitate coating layer; mixing the precursor with a lithium source and performing a high-temperature sintering treatment to obtain a cathode material with a coating layer. In the embodiment of the application, a precursor with a coating layer is obtained through the conversion of a phosphate precipitate; and through aging, free metal salt ions are adsorbed on the outer layer of the precursor as a coating layer, achieving the purpose of improving the utilization rate of raw materials.

Description

Technical Field

[0001] The present application relates to the technical field of cathode material preparation, and particularly relates to a preparation method of a cathode material with a coating layer, a lithium battery, and an electric vehicle. Background Art

[0002] At present, lithium-ion batteries have been widely used in power batteries, household appliances, aerospace and other fields. Among them, ternary cathode materials (such as lithium-rich manganese-based materials and high-nickel ternary cathode materials) as the cathode materials of lithium-ion batteries have become the focus of attention due to their excellent specific capacity and theoretical energy density. For ternary cathode materials, the problems that need to be overcome currently include: the first is the problem of low initial Coulomb efficiency, that is, the problem of irreversible lithium removal in the form of Li2O during the first activation process needs to be overcome. The second is that the total alkali content and pH value on the surface of the ternary cathode material are high, resulting in the difficulty of coating the ternary cathode material (on the electrode sheet) during the battery preparation process. Among them, the second problem is to avoid the volatilization of the lithium source during the high-temperature preparation process, resulting in the lithium content in the ternary cathode material being lower than the lithium source addition amount, and the lithium source addition amount is higher than the lithium source content corresponding to the stoichiometric number of lithium elements in the ternary cathode material.

[0003] To solve the problems of ternary cathode materials such as lithium-rich manganese-based materials and high-nickel ternary cathode materials as described above, surface coating is an effective method. Generally, a fast ion conductor is selected as the coating agent. For example, dopamine is used as the coating agent to coat the ternary cathode material, thereby inhibiting the interfacial activation reaction between the electrode material and the electrolyte, and effectively improving the rate performance and stability of the coated material. However, in the prior art, when coating the ternary cathode material, there are problems such as uneven coating due to the performance of the coating agent, the coating matrix, etc., and the preparation process is complex, resulting in low preparation efficiency. Summary of the Invention

[0004] The present application provides a preparation method of a cathode material with a coating layer, a lithium battery, and an electric vehicle to improve the raw material utilization rate.

[0005] In a first aspect, the present application provides a preparation method of a cathode material with a coating layer, including:

[0006] In the presence of a complexing agent, a soluble metal salt and an alkaline substance undergo a coprecipitation reaction in a solvent to form a precursor precipitate, thereby obtaining a first solid-liquid mixture containing the precursor precipitate; wherein, the soluble metal salt includes a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt, and the first solid-liquid mixture further includes complexed nickel ions, cobalt ions, and manganese ions that do not participate in the coprecipitation reaction;

[0007] Under the condition that the pH value is 9 - 13, the first solid-liquid mixture is mixed with a solution containing phosphate ions, so that the precipitate on the surface layer of the precursor precipitate is in-situ converted into a phosphate precipitate, and a precursor with a phosphate precipitate coating layer on the surface is obtained, thereby obtaining a second solid-liquid mixture. The second solid-liquid mixture also contains nickel ions, cobalt ions, and manganese ions in complex state that did not participate in the coprecipitation reaction in the first solid-liquid mixture, and nickel phosphate, cobalt phosphate, and manganese phosphate generated by the reaction with the soluble phosphate;

[0008] The second solid-liquid mixture is aged, so that nickel phosphate, cobalt phosphate, and manganese phosphate are adsorbed on the outer layer of the precursor with a phosphate precipitate coating layer, and a third solid-liquid mixture is obtained;

[0009] After the third solid-liquid mixture is filtered, washed with water, and dried, the precursor in the third solid-liquid mixture is obtained, and the precursor is mixed with a lithium source for high-temperature sintering treatment to obtain a cathode material with a coating layer.

[0010] In the embodiment of the present application, after the precursor precipitate is obtained, by mixing the first solid-liquid mixture with a solution containing phosphate ions, the surface layer substance of the precursor precipitate undergoes precipitation conversion to generate a precursor with a phosphate precipitate coating layer. On this basis, aging is carried out, so that nickel phosphate, cobalt phosphate, and manganese phosphate in the solution are adsorbed on the surface layer of the precursor with a coating layer, and then filtration, washing with water, and drying are carried out to obtain the precursor, thereby avoiding the complexity of the preparation method caused by multiple filtrations, washings with water, and dryings during the preparation of the precursor; and by aging, nickel phosphate, cobalt phosphate, and manganese phosphate in the second solid-liquid mixture are adsorbed on the surface layer of the precursor with a coating layer to achieve the purpose of improving the utilization rate of raw materials.

[0011] A possible implementation manner is that the reaction temperature of the coprecipitation reaction is 50°C - 70°C.

[0012] A possible implementation manner is that the aging time is 1 - 3 hours.

[0013] A possible implementation manner is that the complexing agent includes at least one of ammonia water, ammonium sulfate, ammonium nitrate, ammonium chloride, glycine, triethanolamine, ethylenediaminetetraacetic acid, polyacrylic acid, aminotrimethylene phosphonic acid, sodium pyrophosphate, tartaric acid, or citric acid.

[0014] A possible implementation manner is that the phosphate ions in the solution containing phosphate ions are derived from at least one of sodium phosphate, potassium phosphate, ammonium phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, or diluted phosphoric acid.

[0015] A possible implementation manner is that the alkaline substance is sodium carbonate, sodium bicarbonate, or sodium hydroxide.

[0016] In a possible implementation, when the alkaline substance is sodium carbonate or sodium bicarbonate, a coprecipitation reaction occurs between the soluble metal salt and the alkaline substance in a solvent in the presence of a complexing agent to form a precursor precipitate, thereby obtaining a first solid-liquid mixture containing the precursor precipitate, including:

[0017] Control the pH of the reaction system to be between 7.0 and 8.5, and the reaction temperature to be 50 - 70 °C until the median particle size of the precursor precipitate increases to a first preset value to obtain the first solid-liquid mixture.

[0018] In a possible implementation, the first preset value is any value between 3 and 10 microns.

[0019] In a possible implementation, when the alkaline substance is sodium hydroxide, a coprecipitation reaction occurs between the soluble metal salt and the alkaline substance in a solvent in the presence of a complexing agent to form a precursor precipitate, thereby obtaining a first solid-liquid mixture containing the precursor precipitate, including:

[0020] Control the pH of the reaction system to be between 9.0 and 12.0, and the reaction temperature to be 50 - 70 °C until the median particle size of the precursor precipitate increases to a second preset value to obtain the first solid-liquid mixture.

[0021] In a possible implementation, the second preset value is any value between 3 and 10 microns.

[0022] In a possible implementation, both the first solid-liquid mixture and the second solid-liquid mixture are obtained in a reaction kettle, and the state of the reaction kettle is in a turbulent stirring state.

[0023] In a possible implementation, the addition amount of the phosphate is determined according to the following conditions:

[0024] t×c×x = θ×λ×V / M;

[0025] Where θ is a preset coefficient and 0 < θ ≤ 5%, c is the concentration of the phosphate solution (mol / L), x is the flow rate of the phosphate solution into the reaction kettle (L / min), t is the time for the phosphate solution to flow into the reaction kettle (min), V is the volume of the reaction kettle (L), λ is the solid content g / L, and M is the standard molar mass of the nickel cobalt manganese carbonate precursor or the nickel cobalt manganese hydroxide precursor (g / mol).

[0026] In a possible implementation, the coating layer of the cathode material with a coating layer is a mixture of lithium phosphate and lithium phosphate salt.

[0027] A possible implementation manner, the average thickness of the coating layer of the cathode material with the coating layer is 1 nm - 2 μm.

[0028] In a second aspect, the present application provides a lithium battery, including the cathode material prepared by the method according to the first aspect and any possible implementation manner.

[0029] In a third aspect, the present application provides an electric vehicle, including the lithium battery according to the first aspect and any possible implementation manner. Description of the Drawings

[0030] Figure 1 It is a schematic flow chart of a preparation method of a cathode material with a coating layer provided by an embodiment of the present application;

[0031] Figure 2 It is a schematic diagram of the structural change of the cathode material with a coating layer prepared by an embodiment of the present application. Detailed Embodiments

[0032] Aiming at the problem of the complex preparation process of the cathode material with a coating structure in the prior art: the present application proposes a preparation method of a cathode material with a coating layer: after preparing a first solid-liquid mixture including a precursor precipitate by a co-precipitation method, directly mixing the first solid-liquid mixture with a solution containing phosphate ions and aging, so that the surface precipitate of the precursor precipitate is in-situ transformed into a phosphate precipitate, and nickel ions, cobalt ions, and manganese ions in the complex state in the solution are adsorbed through molecular van der Waals forces, obtaining a precursor with a phosphate precipitate coating layer, and further performing filtration, washing with water, and drying to obtain a precursor with a phosphate precipitate coating layer, and mixing and sintering the precursor with a lithium source to obtain a cathode material with a coating layer.

[0033] In the above preparation method provided by the embodiment of the present application, after preparing the first solid-liquid mixture, directly mixing and reacting with a solution containing phosphate ions, a precipitation transformation reaction can occur on the surface of the precursor, obtaining a precursor coated with a phosphate precipitate, and then aging to adsorb the complex nickel ions, cobalt ions, and manganese ions in the first solid-liquid mixture (in the supernatant) on the outer layer of the precursor coated with a phosphate precipitate. Therefore, not only the process is effectively simplified, but also the raw material utilization rate can be effectively improved.

[0034] In a first aspect, the present application provides a preparation method of a cathode material with a coating layer, which is specifically described below. Please refer to Figure 1 .

[0035] Step 101, in the presence of a complexing agent, make a soluble metal salt and an alkaline substance undergo a co-precipitation reaction in a solvent (such as water) to generate a precursor precipitate, thereby obtaining a first solid-liquid mixture including the precursor precipitate.

[0036] Among them, the soluble metal salt at least includes soluble nickel salt, soluble cobalt salt and soluble manganese salt.

[0037] Actually, the above-mentioned soluble metal salts can be the soluble metal salts corresponding to the remaining metal elements except lithium in the cathode material. For example, sulfates. And the above-mentioned soluble metal salts can also include soluble aluminum salts. For example, aluminum sulfate.

[0038] The soluble metal salt and the alkaline substance carry out a coprecipitation reaction in a solvent. Actually, a soluble metal salt solution and an alkali solution corresponding to the alkaline substance are obtained, and the solutes between the two solutions carry out a coprecipitation reaction.

[0039] The above-mentioned alkaline substance can be any one of sodium carbonate, sodium bicarbonate or sodium hydroxide.

[0040] The complexing agent includes at least one of ammonia water, ammonium sulfate, ammonium nitrate, ammonium chloride, glycine, triethanolamine, ethylenediaminetetraacetic acid, polyacrylic acid, aminotrimethylenephosphonic acid, sodium pyrophosphate, tartaric acid, or citric acid.

[0041] The first solid-liquid mixture also includes complexed nickel ions, cobalt ions, and manganese ions that did not participate in the coprecipitation reaction. The complexed nickel ions, cobalt ions, and manganese ions are obtained by the complexation reaction of the soluble metal salt and the complexing agent.

[0042] The first solid-liquid mixture can be obtained in a reaction kettle. The reaction kettle can be in a turbulent state through continuous stirring, so that the reactants can be evenly dispersed in the solvent to fully react. The stirring speed can be 300-900 r / min. Therefore, in an embodiment of the present application, after mixing the soluble metal salt in water (i.e., the solvent), sodium carbonate, sodium bicarbonate, or sodium hydroxide in water, and the complexing agent in water, they are respectively introduced into the reaction kettle.

[0043] Specifically, the molar ratio of the soluble metal salt to the molar amount of sodium carbonate, sodium bicarbonate, or sodium hydroxide is 1:2. Among them, the flow rate of the soluble metal salt solution introduced into the reaction kettle is 5 ml / min, and the flow rate of the sodium carbonate solution, sodium bicarbonate solution, or sodium hydroxide solution introduced into the reaction kettle is 1 ml / min - 5 ml / min. The flow rate of the complexing agent solution is 0.1 ml / min - 5 ml / min.

[0044] Furthermore, the reaction temperature of the coprecipitation can be 50-70 °C, and the reaction time can be 8-24 hours; and during the coprecipitation reaction, the stirring rate of the reaction kettle can be controlled at 300-900 r / min.

[0045] During the coprecipitation reaction process, control the pH to gradually decrease to avoid the influence of too high pH on the growth of the precursor. When the alkaline substance is sodium carbonate or sodium bicarbonate, the pH of the reaction system can be controlled to be between 7.0 and 8.5, and the reaction temperature is 50 - 70 °C until the median particle size of the precursor precipitate increases to the first preset value to obtain the first solid-liquid mixture.

[0046] Among them, the first preset value can be any value from 3 to 10 microns.

[0047] When the alkaline substance is sodium hydroxide, control the pH of the reaction system to be between 9.0 and 12.0, and the reaction temperature is 50 - 70 °C until the median particle size of the precursor precipitate increases to the second preset value to obtain the first solid-liquid mixture. Among them, the second preset value can be any value from 3 to 10 microns.

[0048] Step 102: Under the condition of pH 9 - 13, mix the first solid-liquid mixture with the solution containing phosphate ions to in-situ convert the precipitate on the surface layer of the precursor precipitate into phosphate precipitate, obtaining a precursor with a phosphate precipitate coating layer on the surface, thereby obtaining the second solid-liquid mixture.

[0049] The phosphate ions in the solution containing phosphate ions are derived from at least one of sodium phosphate, potassium phosphate, ammonium phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, or diluted phosphoric acid.

[0050] Due to the presence of the complexing agent, in the first solid-liquid mixture, the soluble metal salts independently react with the complexing agent to obtain complex nickel ions, cobalt ions, and manganese ions; the complex containing the above complex nickel ions, cobalt ions, and manganese ions does not participate in the coprecipitation reaction and reacts with the newly added solution containing phosphate ions in the second solid-liquid mixture to generate nickel phosphate, cobalt phosphate, and manganese phosphate.

[0051] Specifically, the following chemical reaction formula can be referred to:

[0052] 3M(NH3) x 2+ +2PO4 3- +3xH2O=M3(PO4)2+3xNH3·H2O;

[0053] Among them, M can be nickel ions, cobalt ions, or manganese ions.

[0054] In the embodiment of the present application, the second solid-liquid mixture can also be obtained in a reaction kettle to evenly disperse the reactants in the solvent for sufficient reaction. That is, a solution containing phosphate ions with a concentration of 0.01-5 mol / L can be prepared and introduced into the reaction kettle containing the first solid-liquid mixture. Among them, the stirring speed is 300-1000 r / min, and the reaction temperature can be 40-70 °C. The reaction time can be 1 min-12 hours; preferably 0.25-1 hour.

[0055] Further, the addition amount of the phosphate is determined according to the following conditions: t×c×x = θ×λ×V / M. Where θ is a preset coefficient, 0 < θ ≤ 5%, c is the concentration of the phosphate solution (mol / L), x is the flow rate of the phosphate solution introduced into the reaction kettle (L / min), t is the time for the phosphate solution to be introduced into the reaction kettle (min), V is the volume of the reaction kettle (L), λ is the solid content g / L, and M is the standard molar mass (g / mol) of the nickel cobalt manganese carbonate precursor or the nickel cobalt manganese hydroxide precursor.

[0056] After the first solid-liquid mixture is prepared by the coprecipitation method and mixed with the phosphate solution, the nickel cobalt manganese carbonate precursor or the nickel cobalt manganese hydroxide precursor in the first solid-liquid mixture can undergo in-situ precipitation transformation with phosphate ions, and then a second solid-liquid mixture including a precursor coated with phosphate is obtained. The following specifically describes the in-situ precipitation transformation.

[0057] In-situ precipitation transformation refers to the precipitation transformation occurring at the target site.

[0058] The precipitation and dissolution of substances are a pair of equilibrium processes, and the solubility product constant Ksp is usually used to represent the precipitation or dissolution state of a sparingly soluble salt in a solution. In the embodiment of the present application, by obtaining the ion concentrations in phosphoric acid systems / phosphate systems in solutions with different pH values, as well as Ksp1 of nickel cobalt manganese phosphate, Ksp2 of carbonate precipitation, and Ksp3 of hydroxide precipitation, it is obtained that the solubility product constant of nickel cobalt manganese phosphate is less than the solubility product constant of carbonate precipitation, and the solubility product constant of nickel cobalt manganese phosphate is less than the solubility product constant of hydroxide precipitation, that is:

[0059] Ksp1 < Ksp2, and Ksp1 is less than Ksp3;

[0060] Therefore, the precursor precipitate in the first solid-liquid mixture, i.e., the surface layer (precipitate) of nickel-cobalt-manganese carbonate precursor / phosphate precursor, will undergo precipitation transformation under the action of phosphate ions. Meanwhile, the free nickel / cobalt / manganese ions in the first solid-liquid mixture will also undergo precipitation reactions under the action of phosphate ions and be adsorbed onto the precursor shell that has undergone precipitation transformation during the aging stage. Therefore, the outer shell of the precursor coated with phosphate described in the embodiments of the present application, i.e., the phosphate outer shell, is actually generated from the above two aspects.

[0061] Further, the reactions that occur after the mixing of the first solid-liquid mixture and the phosphate solution in the embodiments of the present application are described below:

[0062]

[0063]

[0064]

[0065] 3TMCO3 + 2PO4 3- = TM3(PO4)2 + 3CO3 2- (4)

[0066] 3TM(OH)2 + 2PO4 3- = TM3(PO4)2 + 6OH - (5)

[0067] 3TM 2+ + 2PO4 3- = TM3(PO4)2 (6)

[0068] In the above reaction formulas (1)-(6), (1)-(3) are the chemical reaction formulas for the ionization of phosphoric acid (H3PO4) in the phosphate solution to obtain phosphate ions (PO4 3- ). (4) is the chemical reaction formula for the precipitation reaction between the nickel-cobalt-manganese carbonate precursor and phosphate ions, (5) is the chemical reaction formula for the precipitation reaction between the nickel-cobalt-manganese hydroxide precursor and phosphate ions; (6) is the precipitation reaction between phosphate ions and any free transition metal ions in the first solid-liquid mixture.

[0069] Further, Table 1 shows the ion concentrations in the phosphoric acid system / phosphate system in different pH environments. Table 2 shows the minimum concentration of phosphate ions in the second solid-liquid mixture determined based on the precipitation transformation constant K of the precipitation transformation from hydroxide to nickel-cobalt-manganese phosphate in reaction formula (4).

[0070] Table 1

[0071] PH <![CDATA[H3PO4]]> <![CDATA[H2PO4 - > <![CDATA[HPO4 2- > <![CDATA[PO4 3- > 8 <![CDATA[1.8×10 -7 > 0.14 0.86 <![CDATA[3.8×10 -5 > 9 <![CDATA[2.06×10 -9 > <![CDATA[1.56×10 -2 > 0.98 4.3×10-4 10 <![CDATA[2.08×10 -11 > <![CDATA[1.58×10 -3 > 0.99 <![CDATA[4.37×10 -3 > 11 <![CDATA[2×10 -13 > <![CDATA[1.52×10 -4 > 0.96 <![CDATA[4.21×10 -2 > 12 <![CDATA[1.3×10 -15 > <![CDATA[1.1×10 -5 > 0.69 0.31

[0072] Table 2

[0073] PH = 10

[0074]

[0075]

[0076] As can be seen from Table 1, as the PH value increases, the concentration of phosphate ions in the system increases accordingly. Therefore, the higher the PH, the more conducive it is to the transformation of phosphate precipitation.

[0077] Continuing to refer to Table 1, when PH = 10, the minimum concentration of phosphate ions is 4.37×10 -3 . Comparing the minimum concentration of phosphate calculated in Table 2, they are all much less than 4.37×10 -3 . It can be seen that when PH = 10, when the first solid-liquid mixture and the phosphate solution are mixed, a second solid-liquid mixture containing a precursor with a phosphate-coated hydroxide can be obtained through a precipitation transformation reaction. Further referring to the concentration of phosphate ions in the corresponding PH environment in Table 1, it can be known that the phosphate concentration corresponding to Table 1 is much greater than the minimum concentration in the second solid-liquid mixture. Therefore, there is basically no free phosphate ion in the system corresponding to Table 2, and they are all converted into phosphate precipitates. Similarly, when any value of PH is between 9 and 13, the minimum concentration of phosphate ions in the second solid-liquid mixture can be determined, and they are all less than the phosphate ion concentration in the corresponding PH environment in Table 1. Therefore, phosphate precipitates can be obtained when PH is between 9 and 13. Therefore, precursor particles with a phosphate (precipitate) coating layer can be formed in the second solid-liquid mixture. Similarly, the surface layer of the carbonate precursor also undergoes a precipitation reaction based on the above principle, converting the surface layer of the carbonate precipitate into phosphate (precipitate), and precursor particles with a phosphate (precipitate) coating can be obtained, which will not be elaborated here.

[0078] Step 103: Aging the second solid-liquid mixture. The aging time can be 1-3 hours.

[0079] Since the outer layer of the precursor coated with phosphate precipitate in the second solid-liquid mixture is a phosphate precipitate, and nickel phosphate, cobalt phosphate, and manganese phosphate in the second solid-liquid mixture are all phosphates, nickel phosphate, manganese phosphate, and cobalt phosphate can be adsorbed on the outer layer of the precursor with a phosphate precipitate coating during the aging process according to the van der Waals force between molecules, thereby obtaining a third solid-liquid mixture.

[0080] Please continue to refer to Figure 1 , and in combination with Figure 2It can be seen that the coating layer of the precursor after aging includes not only the phosphate precipitate generated by the precipitation conversion reaction, but also nickel phosphate, cobalt phosphate, and cobalt phosphate particles adsorbed due to intermolecular van der Waals forces during the aging process. Among them, nickel phosphate, cobalt phosphate, and cobalt phosphate come from the supernatant of the second solid-liquid mixture.

[0081] Step 104: Filter, wash with water, and dry the third solid-liquid mixture to obtain the precursor in the third solid-liquid mixture, and mix the precursor with a lithium source, followed by high-temperature sintering treatment to obtain a cathode material with a coating layer.

[0082] In the embodiment of the present application, the cathode material described is not limited to the lithium-rich manganese-based material. Therefore, the molar ratio between the precursor and the lithium source can be 1:1.1 - 1:1.5.

[0083] The following describes the process of filtering, washing with water, and drying to obtain the precursor: First, filter the third solid-liquid mixture to obtain the precursor attached with water molecules and impurities. Then, wash the precursor attached with water molecules and impurities with water to remove the impurities on the surface of the precursor. Finally, dry it to obtain the precursor as described above. The coating layer of this precursor is phosphate.

[0084] Further, mix the precursor coated with phosphate with a lithium source and then perform high-temperature sintering treatment to obtain a cathode material with a coating layer. Please continue to refer to Figure 2 The coating layer of this cathode material is a mixture of lithium phosphate Li3PO4 and lithium phosphate salt LiTMPO4, and the inner layer material is a metal oxide. Among them, TM corresponds to the metal ions in the soluble metal salt described in step 101; TM includes at least Ni, Co, and Mn.

[0085] This cathode material can be represented by the following chemical formula:

[0086] (1-k)Li v Ni x Co y Mn z M w O2@k[(u)Li3PO4,(1-u)LiTMPO4];

[0087] Among them, v≥1, 0<x<1, 0≤y<0.3, 0<z<1, 0<w<0.05; 0.5%<k≤5%, 0<u<1, M is a doping element, and TM represents at least one of Ni, Co, and Mn.

[0088] Due to continuous stirring and turbulence in the reaction kettle, a cathode material with a relatively uniform coating layer thickness can be obtained. The average thickness of this coating layer can be 1 nm - 2 μm.

[0089] The high-temperature sintering treatment described in this step can be a one-stage sintering treatment or a multi-stage sintering treatment. If it is a one-stage sintering treatment, the sintering temperature is controlled at 500-900 °C and the heat preservation time is 6-24 hours. If it is a two-stage sintering treatment, the sintering temperature of the first stage is 300-600 °C, the heat preservation time is 2-6 hours, the sintering temperature of the second stage is 650-900 °C, and the heat preservation time is 6-12 hours.

[0090] During the high-temperature sintering treatment, the phosphate on the coating layer of the precursor is in-situ converted into lithium phosphate salts (Li3PO4 and LiTMPO4, where TM includes at least Ni, Co, and Mn). The lithium phosphate salts on the coating layer do not decompose at high temperatures and have relatively large ionic radii and cannot diffuse inward. Therefore, the coating layer of the precursor has inheritability and still has a coating layer structure in the cathode material after high-temperature sintering treatment.

[0091] In a second aspect, the present application provides a lithium battery, which includes a cathode material prepared by the preparation method described in the first aspect.

[0092] The ionic conductivity of lithium phosphate and lithium phosphate salts (10 -4 S / m) is good. Therefore, the cathode material coated with lithium phosphate and lithium phosphate salts prepared in the embodiments of the present application can increase the rate of Li + insertion or extraction, thereby improving the cycle rate performance of the cathode material. At the same time, since the cathode material prepared in the embodiments of the present application has a coating layer structure and the coating layer material is stable lithium phosphate and lithium phosphate salts, the following two aspects can be used to improve the problem in the prior art that Li + irreversibly extracts in the form of Li2O, resulting in a low initial Coulomb efficiency of the lithium battery:

[0093] First aspect: The surface layer of the cathode material is a coating layer composed of lithium phosphate and lithium phosphate salts, and lithium phosphate and lithium phosphate salts have good lithium ion (Li + ) deintercalation and intercalation performance, so it can effectively alleviate the problem of irreversible lithium ion extraction from the cathode material. Second aspect: Since the cathode material has a coating layer, the coating layer can effectively stabilize the overall structure of the cathode material. Thus, during the operation of the lithium battery, the stress change caused by the internal phase change of the cathode material can be effectively suppressed, making the sites where lithium ions are located in the cathode material more stable, thereby suppressing the irreversible extraction of lithium ions.

[0094] Furthermore, the positive electrode material obtained by the method for preparing a positive electrode material provided in the embodiments of the present application has a coating layer. During the charging and discharging processes of the prepared ion battery, the coating layer can form a stable "separator" with the electrolyte (for example, LiPF4) to avoid the corrosion of the electrode material by hydrogen fluoride (HF) and water (H2O) generated by the decomposition of the electrolyte. Therefore, the interfacial stability can be effectively improved, thereby enhancing the cycle stability and safety of the lithium battery.

[0095] Furthermore, due to the stable crystal phase structures of lithium phosphate and lithium phosphate salts, during the charging and discharging processes of the lithium battery, the coating layer of the positive electrode material can effectively inhibit the phase transformation of the crystal phase structure of the inner layer, thereby effectively improving the stability of the positive electrode material and the cycle life of the positive electrode material and the lithium battery.

[0096] In a third aspect, the present application provides a power battery including the lithium battery as described in the second aspect.

[0097] The following will further explain and illustrate the method for preparing a positive electrode material with a coating layer and the prepared positive electrode material provided in the present application in combination with specific examples and comparative examples.

[0098] Synthesis Example 1

[0099] Step S1: Introduce a small amount of sodium hydroxide solution (4.5 mol / L) into the reaction kettle under preset conditions until the pH in the reaction kettle reaches 11.3.

[0100] The reaction kettle under preset conditions refers to a reaction kettle (2 L) with a stirring rate of 700 r / min, a temperature of 55 °C, and deionized water already introduced.

[0101] Step S2: Introduce sodium hydroxide solution (4.5 mol / L) into the reaction kettle at a flow rate of 3.3 ml / min; sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with a molar ratio of nickel, cobalt, and manganese of 8:1:1; complexing agent solution - ammonia water (0.3 mol / L) at a flow rate of 1 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.5. Continue feeding until the median particle size of the generated precursor precipitate is 10 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reaction kettle to obtain a first solid-liquid mixture.

[0102] Step S3: After controlling the pH value in the reaction kettle to 11 by adjusting the flow rate of the sodium hydroxide solution, introduce diammonium hydrogen phosphate solution (2 mol / L) at a flow rate of 4 ml / min, and react for 30 minutes. Then stop introducing the diammonium hydrogen phosphate solution into the reaction kettle to obtain a second solid-liquid mixture.

[0103] Step S4: Feed the second solid-liquid mixture into an aging kettle, age for 4 hours, then filter, wash with water, and dry to obtain a precursor with a phosphate coating layer.

[0104] Step S5: Mix the precursor with a phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.1 and sinter: Heat at a heating rate of 2 °C / min to 600 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 750 °C, hold for 8 hours and then cool to obtain a cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salts, and this cathode material is a high-nickel ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0105] Synthesis Example 2

[0106] Step S1: Introduce a small amount of sodium hydroxide solution (4.5 mol / L) into a reaction kettle under preset conditions until the pH in the reaction kettle reaches 11.3.

[0107] The reaction kettle under preset conditions refers to: a reaction kettle (2 L) with a stirring rate of 700 r / min, a temperature of 50 °C, and deionized water already introduced.

[0108] Step S2: Introduce sodium hydroxide solution (4.5 mol / L) into the reaction kettle at a flow rate of 3.3 ml / min; sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with a molar ratio of nickel, cobalt, and manganese of 8:1:1; complexing agent solution - ethylenediaminetetraacetic acid (0.1 mol / L) at a flow rate of 3 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.5. Continue feeding until the median particle size of the generated precursor precipitate is 10 microns, and stop introducing the sulfate solution and the complexing agent solution into the reaction kettle to obtain the first solid-liquid mixture.

[0109] Step S3: After controlling the pH value in the reaction kettle to 11 by adjusting the flow rate of the sodium hydroxide solution, introduce disodium hydrogen phosphate solution (3 mol / L) at a flow rate of 5 ml / min, with a reaction time of 60 minutes, and stop introducing the disodium hydrogen phosphate solution into the reaction kettle to obtain the second solid-liquid mixture.

[0110] Step S4: Feed the second solid-liquid mixture into an aging kettle, age for 4 hours, then filter, wash with water, and dry to obtain a precursor with a phosphate coating layer.

[0111] Step S5: Mix the precursor with lithium hydroxide in a molar ratio of 1:1.45 and sinter them: Heat at a rate of 2 °C / min to 600 °C and hold for 5 hours; then continue to heat at a rate of 2 °C / min to 800 °C, hold for 8 hours and then cool to obtain the cathode material with a coating layer. The coating layer is a mixture of lithium phosphate and lithium phosphate salts, and the cathode material is a high-nickel ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0112] Synthesis Example 3

[0113] Step S1: Introduce a small amount of sodium hydroxide solution (5 mol / L) into the reaction kettle under preset conditions until the pH in the reaction kettle reaches 11.5.

[0114] The reaction kettle under preset conditions refers to: a reaction kettle (2 L) with a stirring rate of 700 r / min, a temperature of 55 °C, and deionized water already introduced.

[0115] Step S2: Introduce sodium hydroxide solution (5 mol / L) into the reaction kettle at a flow rate of 4 ml / min; introduce sulfate solution (2 mol / L) at a flow rate of 5 ml / min, and the molar ratio of nickel, cobalt, and manganese is 1:1:1; introduce complexing agent solution - ammonia water (0.3 mol / L) at a flow rate of 1.3 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.2. Keep feeding until the median particle size of the generated precursor precipitate is 8 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reaction kettle to obtain the first solid-liquid mixture.

[0116] Step S3: After adjusting the flow rate of the sodium hydroxide solution to control the pH value in the reaction kettle to 12, introduce disodium hydrogen phosphate solution (3 mol / L) at a flow rate of 10 ml / min and react for 20 minutes, then stop introducing the disodium hydrogen phosphate solution into the reaction kettle to obtain the second solid-liquid mixture.

[0117] Step S4: Transfer the second solid-liquid mixture to an aging kettle, age for 3 hours, then filter, wash with water, and dry to obtain the precursor with a phosphate coating layer.

[0118] Step S5: Mix the precursor with lithium carbonate in a molar ratio of 1:1.05 and sinter them: Heat at a rate of 2 °C / min to 600 °C and hold for 8 hours; then continue to heat at a rate of 2 °C / min to 850 °C, hold for 8 hours and then cool to obtain the cathode material with a coating layer. The coating layer is a mixture of lithium phosphate and lithium phosphate salts, and the cathode material is a ternary material LiNi 0.33 Co 0.33Mn 0.33 O2。

[0119] Synthesis Example 4

[0120] Step S1: Introduce a small amount of sodium hydroxide solution (5 mol / L) into the reaction kettle under preset conditions until the pH in the reaction kettle reaches 11.5.

[0121] The reaction kettle under preset conditions refers to: a reaction kettle (2 L) with a stirring rate of 700 r / min, a temperature of 55 °C, and deionized water already introduced.

[0122] Step S2: Introduce sodium hydroxide solution (5 mol / L) into the reaction kettle at a flow rate of 3 ml / min; sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with a molar ratio of nickel, cobalt, and manganese of 8:1:1; complexing agent solution - ammonia water (0.33 mol / L) at a flow rate of 1 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.0. Continue feeding until the median particle size of the generated precursor precipitate is 10 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reaction kettle to obtain the first solid-liquid mixture.

[0123] Step S3: After controlling the pH value in the reaction kettle to 11 by adjusting the flow rate of the sodium hydroxide solution, introduce phosphoric acid solution (1.5 mol / L) at a flow rate of 10 ml / min, and the reaction time is 150 minutes. Then stop introducing the phosphoric acid solution into the reaction kettle to obtain the second solid-liquid mixture.

[0124] Step S4: Transfer the second solid-liquid mixture to the aging kettle for aging for 3 hours, then filter, wash with water, and dry to obtain a precursor with a phosphate coating layer.

[0125] Step S5: Mix the precursor with phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.05 for sintering: heat at a heating rate of 2 °C / min to 450 °C and hold for 4 hours; continue to heat at a heating rate of 2 °C / min to 700 °C, hold for 10 hours and then cool to obtain a cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salt, and this cathode material is a high-nickel ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2。

[0126] Synthesis Example 5

[0127] Step S1: Introduce a small amount of sodium hydroxide solution (5 mol / L) into the reaction kettle under preset conditions until the pH in the reaction kettle reaches 11.5.

[0128] The reactor under preset conditions refers to: a reactor (2L) with a stirring rate of 700 r / min, a temperature of 55 °C, and deionized water already introduced into it.

[0129] Step S2: Introduce sodium hydroxide solution (5 mol / L) into the reactor at a flow rate of 3 ml / min; introduce sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of nickel, cobalt, and manganese being 8:1:1; introduce complexing agent solution - ammonia water (0.33 mol / L) at a flow rate of 1 ml / min to carry out a coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.0. Keep feeding until the median particle size of the generated precursor precipitate is 10 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reactor to obtain a first solid-liquid mixture.

[0130] Step S3: After controlling the pH value in the reactor to 11 by adjusting the flow rate of the sodium hydroxide solution, introduce phosphoric acid solution (1.5 mol / L) at a flow rate of 10 ml / min, and the reaction time is 120 minutes. Then stop introducing the phosphoric acid solution into the reactor to obtain a second solid-liquid mixture.

[0131] Step S4: Transfer the second solid-liquid mixture to an aging kettle, age for 3 hours, then filter, wash with water, and dry to obtain a precursor with a phosphate coating layer.

[0132] Step S5: Mix the precursor with phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.05 for sintering: heat at a heating rate of 2 °C / min to 450 °C and hold for 4 hours; continue to heat at a heating rate of 2 °C / min to 700 °C, hold for 10 hours and then cool to obtain a cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salt, and this cathode material is a high-nickel ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0133] Synthesis Example 6

[0134] Step S1: Introduce a small amount of sodium carbonate solution (1 mol / L) into the reactor under preset conditions until the pH in the reactor is 8.0.

[0135] The reactor under preset conditions refers to: a reactor (2L) with a stirring rate of 700 r / min, a temperature of 50 °C, and deionized water already introduced into it.

[0136] Step S2: Feed sodium carbonate solution (1 mol / L) into the reactor at a flow rate of 10 ml / min; feed sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of manganese, nickel, and cobalt being 54:13:13; feed complexing agent solution - ammonia water (2.5 mol / L) at a flow rate of 8 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 7.2. Continuously feed until the median particle size of the generated precursor precipitate is 10 microns, then stop feeding the sulfate solution and the complexing agent solution into the reactor to obtain the first solid-liquid mixture.

[0137] Step S3: After controlling the pH value in the reactor to 12 by adjusting the flow rate of the sodium carbonate solution, feed sodium dihydrogen phosphate solution (2 mol / L) at a flow rate of 10 ml / min for 150 minutes, then stop feeding the sodium dihydrogen phosphate solution into the reactor to obtain the second solid-liquid mixture.

[0138] Step S4: Transfer the second solid-liquid mixture to an aging kettle, age for 3 hours, then filter, wash with water, and dry to obtain a precursor with a phosphate coating layer.

[0139] Step S5: Mix the precursor with phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.5 for sintering: Heat at a heating rate of 2 °C / min to 500 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 800 °C, hold for 12 hours and then cool to obtain a cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salts, and this cathode material is a lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0140] Synthesis Example 7

[0141] Step S1: Feed a small amount of sodium carbonate solution (1 mol / L) into the reactor under preset conditions until the pH in the reactor reaches 8.0.

[0142] The reactor under preset conditions refers to a reactor (2 L) with a stirring rate of 700 r / min, a temperature of 50 °C, and deionized water already fed into it.

[0143] Step S2: Feed sodium carbonate solution (1 mol / L) into the reactor at a flow rate of 10 ml / min; feed sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of manganese, nickel, and cobalt being 54:13:13; feed complexing agent solution - ammonia water (2.5 mol / L) at a flow rate of 8 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 7.2. Continuously feed until the median particle size of the generated precursor precipitate is 10 microns, then stop feeding the sulfate solution and the complexing agent solution into the reactor to obtain the first solid-liquid mixture.

[0144] Step S3: After controlling the pH value in the reactor to 12 by adjusting the flow rate of the sodium carbonate solution, feed diammonium hydrogen phosphate solution (2 mol / L) at a flow rate of 10 ml / min, and the reaction time is 180 minutes. Then stop feeding the diammonium hydrogen phosphate solution into the reactor to obtain the second solid-liquid mixture.

[0145] Step S4: Transfer the second solid-liquid mixture to an aging tank, age for 3 hours, then filter, wash with water, and dry to obtain the precursor with a phosphate coating layer.

[0146] Step S5: Mix the precursor with a phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.5 for sintering: heat at a heating rate of 2 °C / min to 500 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 800 °C, hold for 12 hours and then cool to obtain the cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salt, and this cathode material is a lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0147] Synthesis Example 8

[0148] Step S1: Feed a small amount of sodium carbonate solution (1 mol / L) into the reactor under preset conditions until the pH in the reactor reaches 8.0.

[0149] The reactor under preset conditions refers to a reactor (2 L) with a stirring rate of 700 r / min, a temperature of 50 °C, and deionized water already fed into it.

[0150] Step S2: Introduce sodium carbonate solution (1 mol / L) into the reactor at a flow rate of 10 ml / min; introduce sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of nickel, cobalt, and manganese being 12:03:25; introduce complexing agent solution - ammonia water (2.5 mol / L) at a flow rate of 8 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 7.2. Continuously feed until the median particle size of the generated precursor precipitate is 8 microns, then stop introducing sulfate solution and complexing agent solution into the reactor to obtain the first solid-liquid mixture.

[0151] Step S3: After controlling the pH value in the reactor to be 11 by adjusting the flow rate of sodium carbonate solution, introduce dipotassium hydrogen phosphate solution (2 mol / L) at a flow rate of 10 ml / min, and the reaction time is 180 minutes. Then stop introducing dipotassium hydrogen phosphate solution into the reactor to obtain the second solid-liquid mixture.

[0152] Step S4: Transfer the second solid-liquid mixture to the aging kettle, age for 3 hours, then filter, wash with water, and dry to obtain the precursor with a phosphate coating layer.

[0153] Step S5: Mix the precursor with phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.5 for sintering: heat at a heating rate of 2 °C / min to 500 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 800 °C, hold for 12 hours and then cool to obtain the cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salt, and this cathode material is a lithium-rich manganese-based material Li 1.2 Ni 0.24 Co 0.06 Mn 0.50 O2.

[0154] Synthesis Example 9

[0155] Step S1: Introduce a small amount of sodium carbonate solution (1 mol / L) into the reactor under preset conditions until the pH in the reactor is 8.0.

[0156] The reactor under preset conditions refers to: the reactor with a stirring rate of 700 r / min, a temperature of 50 °C, and deionized water already introduced.

[0157] Step S2: Feed sodium carbonate solution (1 mol / L) into the reactor at a flow rate of 10 ml / min; feed sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of manganese, cobalt, and nickel being 5:1:1; feed complexing agent solution - ammonia water (2.5 mol / L) at a flow rate of 8 ml / min for coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 7.2. Keep feeding until the median particle size of the generated precursor precipitate is 10 microns, then stop feeding the sulfate solution and the complexing agent solution into the reactor to obtain the first solid-liquid mixture.

[0158] Step S3: After controlling the pH value in the reactor to be 11 by adjusting the flow rate of the sodium carbonate solution, feed sodium phosphate solution (2 mol / L) at a flow rate of 10 ml / min for 180 minutes, then stop feeding the sodium phosphate solution into the reactor to obtain the second solid-liquid mixture.

[0159] Step S4: Transfer the second solid-liquid mixture to an aging tank, age for 3 hours, then filter, wash with water, and dry to obtain a precursor with a phosphate coating layer.

[0160] Step S5: Mix the precursor with a phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.3 for sintering: heat at a heating rate of 2 °C / min to 500 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 780 °C, hold for 12 hours and then cool to obtain a cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salt, and this cathode material is a lithium-rich manganese-based cathode material Li 1.16 Ni 0.12 Co 0.12 Mn 0.6 O2.

[0161] Synthesis Example 10

[0162] Step S1: Feed a small amount of sodium hydroxide solution (4.5 mol / L) into the reactor under preset conditions until the pH in the reactor is 11.5.

[0163] The reactor under preset conditions refers to: a reactor with a stirring rate of 700 r / min, a temperature of 55 °C, and deionized water already fed.

[0164] Step S2: Introduce sodium hydroxide solution (4.5 mol / L) into the reaction kettle at a flow rate of 3.3 ml / min; introduce sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of nickel, cobalt, and manganese being 8:1:0.5; introduce sodium aluminate solution (0.47 mol / L) at a flow rate of 1 ml / min; introduce complexing agent solution - ammonia water (0.3 mol / L) at a flow rate of 1 ml / min, and conduct a coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.3. Continuously feed until the median particle size of the generated precursor precipitate is 10 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reaction kettle, thereby obtaining the first solid-liquid mixture.

[0165] Step S3: After controlling the pH value in the reaction kettle to 10.3 by adjusting the flow rate of the sodium hydroxide solution, introduce diammonium hydrogen phosphate solution (2 mol / L) at a flow rate of 5 ml / min, and the reaction time is 30 minutes. Then stop introducing the diammonium hydrogen phosphate solution into the reaction kettle, thereby obtaining the second solid-liquid mixture.

[0166] Step S4: Send the second solid-liquid mixture to the aging kettle for aging for 3 hours, then filter, wash with water, and dry to obtain the precursor with a phosphate coating layer.

[0167] Step S5: Mix the precursor with a phosphate coating layer and lithium hydroxide in a molar ratio of 1:1.05 for sintering: heat at a heating rate of 2 °C / min to 650 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 800 °C, cool after holding for 8 hours, and obtain the cathode material with a coating layer. This coating layer is a mixture of lithium phosphate and lithium phosphate salt, and this cathode material is a high-nickel cathode material LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2.

[0168] Synthesis comparative example 1

[0169] Step S1: Introduce a small amount of sodium hydroxide solution (4.5 mol / L) into the reaction kettle under preset conditions until the pH in the reaction kettle is 11.3.

[0170] The reaction kettle under preset conditions refers to: the reaction kettle with a stirring rate of 700 r / min, a temperature of 55 °C, and deionized water already introduced.

[0171] Step S2: Introduce sodium hydroxide solution (4.5 mol / L) into the reaction kettle at a flow rate of 3.3 ml / min; introduce sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of nickel, cobalt, and manganese being 8:1:1; introduce complexing agent solution - ammonia water (0.3 mol / L) at a flow rate of 1 ml / min to conduct a coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 10.5. Continuously feed until the median particle size of the generated precursor precipitate is 10 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reaction kettle to obtain a first solid-liquid mixture.

[0172] Step S3: Transfer the first solid-liquid mixture to an aging kettle, age for 4 hours, then filter, wash with water, and dry to obtain the precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2.

[0173] Step S4: Mix the precursor and lithium hydroxide in a molar ratio of 1:1.05 for sintering: heat at a heating rate of 2 °C / min to 600 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 750 °C, hold for 8 hours and then cool to obtain the high-nickel ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0174] Synthesis Comparative Example 2

[0175] Step S1: Introduce a small amount of sodium carbonate solution (1 mol / L) into the reaction kettle under preset conditions until the pH in the reaction kettle reaches 8.0.

[0176] The reaction kettle under preset conditions refers to a reaction kettle with a stirring rate of 700 r / min, a temperature of 50 °C, and deionized water already introduced.

[0177] Step S2: Introduce sodium carbonate solution (1 mol / L) into the reaction kettle at a flow rate of 10 ml / min; introduce sulfate solution (1.5 mol / L) at a flow rate of 5 ml / min, with the molar ratio of manganese, nickel, and cobalt being 54:13:13; introduce complexing agent solution - ammonia water (0.25 mol / L) at a flow rate of 8 ml / min to conduct a coprecipitation reaction. During the reaction process, control the pH to gradually decrease to 7.2. Continuously feed until the median particle size of the generated precursor precipitate is 10 microns, and then stop introducing the sulfate solution and the complexing agent solution into the reaction kettle to obtain a first solid-liquid mixture.

[0178] Step S3: Transfer the first solid-liquid mixture to an aging kettle, age for 3 hours, then filter, wash with water, and dry to obtain the precursor.

[0179] Step S4: Mix the precursor with lithium hydroxide in a molar ratio of 1:1.5 and sinter: Heat at a heating rate of 2 °C / min to 500 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 800 °C, hold for 12 hours and then cool to obtain the lithium-rich manganese-based cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0180] Synthesis Comparative Example 3

[0181] Steps S1 - S3 are the same as those in Synthesis Comparative Example 1 to obtain a precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 that is the same as the precursor in Step S3 of Synthesis Comparative Example 1:

[0182] Step S4: Mix the precursor with lithium hydroxide in a molar ratio of 1:1.05 and sinter: Heat at a heating rate of 2 °C / min to 600 °C and hold for 5 hours; continue to heat at a heating rate of 2 °C / min to 750 °C, hold for 8 hours and then cool to obtain the high-nickel cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0183] Step S5: Disperse the high-nickel cathode material in the first solution, heat and stir under an 80 °C oil bath condition until dried to obtain an intermediate.

[0184] Among them, the solvent of the first solution is ethanol and the solute is sodium hydrogen phosphate (accounting for 1% of the total molar amount of the solution, with a concentration of 0.1 mol / L).

[0185] Step S6: Sinter the intermediate in air at a sintering temperature of 480 °C and a holding time of 5 hours to obtain the high-nickel cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@Li3PO4.

[0186] Synthesis Comparative Example 4

[0187] Steps S1 - S3 are the same as those in Step S1 - S3 of Synthesis Comparative Example 1 to obtain a precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2.

[0188] Step S4: Take 100 g of the precursor Ni 0.8 Co 0.1 Mn0.1 (OH)2 was dissolved in 2L of diammonium hydrogen phosphate (0.1mol / L), stirred evenly, and heated to 55°C to control the pH to 11. The reaction time was 30 minutes to obtain a precursor with a coating layer.

[0189] Step S5, the precursor is mixed with lithium hydroxide (molar ratio of 1:1.1), and sintered: the temperature is raised to 600 ° C at a heating rate of 2 ° C / min, and kept warm for 5 hours; the temperature is further raised to 750 ° C at a heating rate of 2 ° C / min, kept warm for 8 hours, and then cooled to obtain a positive electrode material with a coating layer. The coating layer is a mixture of lithium phosphate and lithium phosphate salt. The positive electrode material is a high nickel ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0190] The pH value in the above reactor was determined by a Raman pH meter, and the median particle size was determined by a Malvern 3000 particle size tester.

[0191] Comparative Synthesis Example 5

[0192] There is no aging step in the preparation steps of Synthesis Example 5, and the other steps are consistent with those of Synthesis Example.

[0193] Table 3 shows the element yields of the positive electrode materials obtained in Synthesis Example 1 and Synthesis Comparative Example 5 based on the material balance principle.

[0194] Table 3

[0195]

[0196] As can be seen from Table 3, the element recovery rates of nickel, cobalt and manganese in Synthesis Example 1 are all higher than the recovery rates of the corresponding elements in Synthesis Comparative Example 5. It can be seen that the raw material utilization rate of Synthesis Example 1 is effectively improved.

[0197] Device Examples 1-10, Device Comparative Examples 1-5

[0198] Device Examples 1-10 and Comparative Examples 1-5 correspond to Synthesis Examples 1-10 and Comparative Examples 1-5, respectively. That is, the positive electrode materials of Device Examples 1-10 and Comparative Examples 1-5 are the positive electrode materials prepared in Synthesis Examples 1-10 and Comparative Examples 1-5, respectively. The preparation methods are described below:

[0199] Step S1: Dissolve the cathode material, acetylene black (conductive agent), and polyethylene glycol (binder) in a mass ratio of 96.5:1.5:2 in 2-methylpyrrolidone (NMP) to prepare a viscous slurry. Coat the slurry evenly on the surface of the aluminum foil and then dry it. The drying environment can be a vacuum oven at 120°C, and the drying time is 2 hours.

[0200] Step S2: Use a punching machine to cut the dried aluminum foil into circular electrode sheets (the diameter can be 10 nanometers). The surface loading of the cathode material on each electrode sheet is 15 mg / cm 2 , and then put it back into the vacuum oven (120°C) to dry for 12 hours (to remove moisture), and finally store it in a glove box under an argon atmosphere.

[0201] Step S3: Use the electrode sheets stored in the glove box as the positive electrode sheets, use lithium sheets as the negative electrode, separate the positive and negative electrodes through a separator, and add 30 μL of ternary commercial electrolyte (LiPF6 / EC-DEC-EMC, volume ratio 1:1:1). Assemble them in the order of negative electrode shell, elastic sheet, gasket, lithium sheet, separator, positive electrode, and positive electrode shell, and finally complete the encapsulation with a sealing machine to obtain a button cell.

[0202] Perform charge and discharge tests on the button cell within a voltage window of 3 - 4.3V; perform capacity tests under the conditions of 0.2C charge / 0.2C discharge, perform high-rate performance tests under the conditions of 0.5C charge / 5C discharge, and perform cycle stability tests under the conditions of 0.2C charge / 0.2C discharge for 100 cycles to obtain the data shown in Table 4.

[0203] Table 4

[0204]

[0205]

[0206] Based on the data in Table 4, especially between Device Examples 1 - 2, 4 - 5 and Device Comparative Example 1, and between Device Examples 6 - 7 and Comparative Example 3, it can be seen that in the embodiments of the present application, by performing coating in the precursor synthesis stage to prepare a precursor with a phosphate precipitation coating layer, a cathode material with a coating layer (i.e., composed of a mixture of lithium phosphate and lithium phosphate salt) is obtained, which can effectively improve the initial Coulombic efficiency and cycle stability of the corresponding lithium battery.

[0207] Furthermore, from the performance data of Device Example 1 and Device Comparative Example 5, it can be obtained that in the embodiments of the present application, the aging step can not only effectively improve the raw material utilization rate, but also effectively improve the initial Coulombic efficiency and cycle stability of the cathode material and the lithium battery.

[0208] Furthermore, from Device Example 1 and Device Comparative Example 3, it can be seen that although a cathode material with a coating layer was also prepared in Device Comparative Example 3, the discharge capacity, initial Coulombic efficiency, and cycle stability of the cathode material obtained by coating the precursor in the examples of the present application are all superior to those of the cathode material with a coating layer obtained by secondary lithium coating in Device Comparative Example 3.

[0209] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a cathode material with a coating layer, characterized in that, Comprising: In the presence of a complexing agent, a soluble metal salt and an alkaline substance undergo a coprecipitation reaction in a solvent to form a precursor precipitate, thereby obtaining a first solid-liquid mixture containing the precursor precipitate; wherein, the soluble metal salt includes a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt, and the first solid-liquid mixture further includes complexed nickel ions, cobalt ions, and manganese ions that did not participate in the coprecipitation reaction; the precursor precipitate is a nickel cobalt manganese carbonate precursor or a nickel cobalt manganese hydroxide precursor; Under the condition that the pH value is 9 - 13, the first solid-liquid mixture is mixed with a solution containing phosphate ions, so that the precipitate on the surface layer of the precursor precipitate is in-situ converted into a phosphate precipitate, obtaining a precursor with a phosphate precipitate coating layer on the surface, thereby obtaining a second solid-liquid mixture, and the second solid-liquid mixture further contains nickel phosphate, cobalt phosphate, and manganese phosphate formed by the reaction of the complexed nickel ions, cobalt ions, and manganese ions that did not participate in the coprecipitation reaction in the first solid-liquid mixture with the soluble phosphate; The second solid-liquid mixture is aged to adsorb nickel phosphate, cobalt phosphate, and manganese phosphate on the outer layer of the precursor with a phosphate precipitate coating layer, obtaining a third solid-liquid mixture; The third solid-liquid mixture is filtered, washed with water, and dried to obtain the precursor in the third solid-liquid mixture, and the precursor is mixed with a lithium source and subjected to a high-temperature sintering treatment to obtain a cathode material with a coating layer.

2. The method according to claim 1, characterized in that, The reaction temperature of the coprecipitation reaction is 50°C - 70°C.

3. The method according to claim 1, wherein The aging time is 1 - 3 hours.

4. The method according to claim 1, wherein The complexing agent includes at least one of ammonia water, ammonium sulfate, ammonium nitrate, ammonium chloride, glycine, triethanolamine, ethylenediaminetetraacetic acid, polyacrylic acid, aminotrimethylenephosphonic acid, sodium pyrophosphate, tartaric acid, or citric acid.

5. The method according to claim 1, characterized in that, The phosphate ions in the solution containing phosphate ions are derived from at least one of sodium phosphate, potassium phosphate, ammonium phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, or diluted phosphoric acid.

6. The method according to claim 1, characterized in that, The alkaline substance is sodium carbonate, sodium bicarbonate, or sodium hydroxide.

7. The method according to any one of claims 1-6, characterized in that, If the alkaline substance is sodium carbonate or sodium bicarbonate, then in the presence of a complexing agent, a soluble metal salt and an alkaline substance undergo a coprecipitation reaction in a solvent to form a precursor precipitate, thereby obtaining a first solid-liquid mixture containing the precursor precipitate, including: Controlling the pH of the reaction system to be 7.0 - 8.5 and the reaction temperature to be 50 - 70°C until the median particle size of the precursor precipitate increases to a first preset value, obtaining the first solid-liquid mixture.

8. The method according to any one of claims 1 to 6, characterized in that If the alkaline substance is sodium hydroxide, then in the presence of a complexing agent, a soluble metal salt and an alkaline substance undergo a coprecipitation reaction in a solvent to form a precursor precipitate, thereby obtaining a first solid-liquid mixture containing the precursor precipitate, including: Controlling the pH of the reaction system to be 9.0 - 12.0 and the reaction temperature to be 50 - 70°C until the median particle size of the precursor precipitate increases to a second preset value, obtaining the first solid-liquid mixture.

9. The method according to claim 1, characterized in that, Both the first solid-liquid mixture and the second solid-liquid mixture are obtained in a reaction kettle, and the state of the reaction kettle is a turbulent stirring state.

10. The method according to claim 9, wherein The addition amount of the phosphate is determined according to the following conditions: t×c×x = θ×λ×V / M; wherein, θ is a preset coefficient, and 0 < θ ≤ 5%, c is the concentration of the phosphate solution in mol / L, x is the flow rate of the phosphate solution introduced into the reaction kettle in L / min, t is the time of the phosphate solution introduced into the reaction kettle in min, V is the volume of the reaction kettle in L, λ is the solid content in g / L, and M is the standard molar mass of the nickel cobalt manganese carbonate precursor or nickel cobalt manganese hydroxide precursor in g / mol.

11. The method according to claim 1, characterized in that, The coating layer of the cathode material with a coating layer is a mixture of lithium phosphate and lithium phosphate salt.

12. The method according to claim 11, wherein The average thickness of the coating layer of the cathode material with a coating layer is 1 nm - 2 μm.

13. A lithium battery, characterized in that, It includes the cathode material prepared by the method according to any one of claims 1-12.

14. An electric vehicle, characterized in that, It includes the lithium battery according to claim 13.

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