A coated multi-element positive electrode material, a preparation method thereof, and a lithium-ion battery

Abstract

The present invention discloses a coated multi-element positive electrode material, a preparation method thereof, and a lithium-ion battery. The coated multi-element positive electrode material provided by the present invention comprises a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material, wherein the component material of the coating layer comprises polyaniline with a doping element. The preparation method comprises: coating the multi-element positive electrode material with a coating to obtain the coated multi-element positive electrode material, wherein the coating comprises polyaniline with a doping element. The present invention can improve the conductivity of the positive electrode material by coating with polyaniline, and at the same time, the conductive properties of the polyaniline will not be reduced after the modification of the polyaniline, and the high-temperature cycle stability of the material can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a positive electrode material, a preparation method thereof, and a lithium ion battery, and in particular to a coated multi-element positive electrode material, a preparation method thereof, and a lithium ion battery. Background Art

[0002] With the development of lithium-ion batteries, multi-element cathode materials have become a focus of attention. Low-cobalt, high-nickel materials are attracting significant attention due to their high specific capacity and low cost. However, due to adjustments in the nickel, cobalt, and manganese ratios, high-nickel materials like NCM811, while increasing the nickel content and significantly improving battery energy density, also lead to a continuous decline in thermal stability, thus affecting battery safety. Nickel also affects the battery's reversible specific capacity and cycle performance during the reaction process, resulting in reduced cycle performance and charging efficiency, hindering large-scale application.

[0003] Batteries with high consistency, high safety, and high energy density are more competitive in the market. Although multi-element positive electrode materials have advantages such as high capacity and high energy density, their cycle stability, thermal stability, and rate performance are relatively poor, especially the high-temperature cycle performance is difficult to improve. In order to address the safety performance of multi-element materials, the current conventional improvement method is to coat the surface with a single chemical compound to act as a physical protective layer to inhibit electrolyte corrosion, but the improvement effect is not obvious; there are also conductive polymers such as polythiophene, polypyrrole, polyacetylene, and polyaniline to coat the multi-element materials, but the single conductive polymer coating is limited to improving the conductivity of the material.

[0004] For example, CN108183209A discloses a method for coating a LiNixCoyMnzO2 cathode material with polyaniline. Due to the high electrical conductivity of polyaniline, the coated material forms a conductive network, providing good electrical contact between particles and improving the diffusion rate of lithium ions. Furthermore, polyaniline can participate in the electrode reaction, increasing the initial discharge specific capacity. CN108807879A primarily coats polyaniline on the surface of cerium-doped lithium nickel cobalt aluminum oxide. The polyaniline acts synergistically with the doped cerium to reduce the reaction between the cathode material and the electrolyte during the charge and discharge process. The coated polyaniline improves conductivity and reduces impedance.

[0005] However, existing technologies still cannot meet the demand for improving the high-temperature cycling stability of multi-element cathode materials, especially high-nickel cathode materials. Therefore, solving the problem of poor cycling stability of high-nickel materials, especially poor high-temperature cycling stability, is of great significance and will facilitate the large-scale application of high-nickel cathode materials. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a coated multi-element positive electrode material, a preparation method thereof, and a lithium-ion battery. The polyaniline coating can not only improve the conductivity of the positive electrode material, but also improve the high-temperature cycle stability of the material without reducing the conductive properties of the polyaniline after modification.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a coated multi-element positive electrode material, comprising a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material, wherein the coating layer comprises polyaniline with a doping element.

[0009] The coating layer of the present invention is a conductive polymer compound of a specific composition, which is used to coat the multi-element material; this functionalized polyaniline is doped at the molecular level, and the doping element exists in the polyaniline molecular chain, replacing the position of some nitrogen elements in the polyaniline main chain, which not only retains high conductivity but also facilitates the flame retardant properties of P and B. Moreover, this type of doping compound can be dehydrated under high temperature conditions to generate corresponding partial acids or oxides, which adhere to the material surface and promote carbonization, thereby achieving good flame retardancy. At the same time, the doped polyaniline has better compatibility with organic solvents in the electrolyte, significantly improving the thermal stability of the material.

[0010] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0011] As a preferred technical solution of the present invention, the doping element exists in the polyaniline molecular chain.

[0012] Preferably, the doping element includes element B and / or element P. The element B and / or element P in the present invention can be element B, element P, or a combination of elements B and P.

[0013] Preferably, in the coating layer, the mass percentage of the doping element is 0.5% to 20%, for example, 0.5%, 1.0%, 2.0%, 5.0%, 8.0%, 10.0%, 16.0%, 20.0%, etc., based on the total mass of the doping element and polyaniline as 100%.

[0014] When the doping element is B element and / or P element and the mass percentage of the doping element is 0.5% to 20%, better electrochemical performance can be obtained.

[0015] Preferably, the chemical composition of the multi-element positive electrode material is Li a Nix Co y M 1-x-y O2, where M is any one or a combination of at least two of Mn, Al, V, Mg, Mo, Nb or Ti, 0.90 < a < 1.10, such as 0.90, 0.95, 0.98, 1.00, 1.05 or 1.10, etc.; 0.30 ≤ x < 1.0, such as 0.30, 0.35, 0.40, 0.50, 0.60, 0.70, 0.80 or 0.90, etc.; 0 < y ≤ 0.3, such as 0.05, 0.08, 0.10, 0.15, 0.18, 0.20, 0.25 or 0.30, etc.

[0016] Preferably, M is Al or Mn.

[0017] Preferably, 0.6 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.4.

[0018] Preferably, 0.80 ≤ x < 0.95, 0.05 < y ≤ 0.2.

[0019] In the present invention, the multi-component cathode material may be a ternary cathode material or a quaternary cathode material. The ternary cathode material may be a high-nickel ternary cathode material. The "high-nickel ternary cathode material" in the present invention means that the molar percentage of nickel in the ternary cathode material is above 60%. <00​​​​​​​​​​​​Preferably, based on the mass of the multi-element positive electrode material being 100%, the mass percentage of the coating layer is 0.1% to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%. If the mass percentage is less than 0.1%, the coating amount is too small, which may lead to uneven coating, a larger area between the electrolyte and the material, and significant secondary reactions, affecting electrochemical performance. If the mass percentage is greater than 0.5%, the coating amount is too large, resulting in increased coating thickness, obstructing the diffusion path of lithium ions, increasing impedance, and also affecting electrochemical performance.

[0025] In a second aspect, the present invention provides a method for preparing the coated multi-element positive electrode material according to the first aspect, the method comprising the following steps:

[0026] The multi-element positive electrode material is coated with a coating to obtain the coated multi-element positive electrode material, wherein the coating comprises polyaniline with doping elements.

[0027] In the preparation method provided by the present invention, the doping element is preferably B element and / or P element.

[0028] As a preferred technical solution of the present invention, the particle size of the coating is 50nm~2μm, for example 50nm, 75nm, 85nm, 100nm, 120nm, 140nm, 150nm, 160nm, 180nm, 200nm, 220nm, 260nm, 280nm, 300nm, 325nm, 350nm, 370nm, 400nm, 430nm, 450nm, 460nm, 480nm or 500nm, etc., preferably 50nm~500nm, more preferably 50nm~200nm. If the particle size is less than 50nm, the coating material with too small a particle size is difficult to prepare and the cost is high; if the particle size is greater than 500nm, the particle size is too large, which will lead to an increase in coating thickness, hindering the diffusion channel of lithium ions, increasing impedance, and affecting electrochemical performance.

[0029] Preferably, the chemical composition of the multi-element positive electrode material is Li a Ni x Co y M 1-x-y O2, wherein M is any one of Mn, Al, V, Mg, Mo, Nb or Ti or a combination of at least two thereof, 0.90 <a<1.10,0.30≤x<1.0,0<y≤0.3。

[0030] Preferably, M is Al or Mn.

[0031] Preferably, 0.6 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.4.

[0032] Preferably, 0.80≤x<0.95, 0.05 <y≤0.2。

[0033] Preferably, in the multi-element positive electrode material, when the molar percentage of Ni in the metal elements other than Li is greater than 80%, for example, when the molar percentage of Ni is 80%, 82%, 85%, 88%, 90%, 92.5%, 95%, or 96%, the material is post-treated before coating. Water washing can reduce residual alkali on the surface of the material, and coating with doped polyaniline can improve the electrochemical performance of the material.

[0034] If the molar percentage of Ni in the multi-element positive electrode material is less than 80%, the doped polyaniline coating process does not require a water washing process after the substrate is sintered.

[0035] Preferably, the post-treatment is water washing and drying.

[0036] Preferably, the water washing method is: mixing the multi-element positive electrode material and water at a water-to-material mass ratio of (1-2):1, and stirring for 10-60 minutes.

[0037] As a preferred technical solution of the present invention, the method of coating the multi-element positive electrode material with a coating comprises: mixing the multi-element positive electrode material with the coating, and sintering them in an oxidizing atmosphere to obtain the coated multi-element positive electrode material.

[0038] In the method, the mass ratio of the multi-element positive electrode material to the coating can be configured according to the ratio required in the product. For example, based on the mass of the multi-element positive electrode material being 100%, the mass percentage of the coating layer is 0.1%-0.5%.

[0039] Preferably, the oxidizing atmosphere includes an oxygen atmosphere or an air atmosphere.

[0040] Preferably, the oxygen volume concentration of the oxygen atmosphere is ≥90%.

[0041] Preferably, the sintering temperature is 200°C to 800°C, for example, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C or 800°C.

[0042] Preferably, the sintering time is 0.5 h to 10 h, for example, 0.5 h, 1 h, 2 h, 2.5 h, 3.5 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0043] As a preferred technical solution of the present invention, the method for preparing the multi-element positive electrode material includes: mixing a multi-element positive electrode material precursor and a lithium source, and calcining to obtain the multi-element positive electrode material.

[0044] In this method, the mass ratio of the multi-component cathode material precursor to the lithium source can be selected to be the same as the stoichiometric ratio of the desired multi-component cathode material.

[0045] Preferably, the chemical composition of the multi-component cathode material precursor is Ni x Co y M 1-x-y (OH)2, where M is any one or a combination of at least two of Mn, Al, V, Mg, Mo, Nb or Ti, 0.30 ≤ x < 1.0, such as 0.30, 0.40, 0.50, 0.70 or 0.90, etc.; 0 < y ≤ 0.3, such as 0.1, 0.15, 0.2, 0.25 or 0.3, etc.

[0046] Preferably, the multi-component cathode material precursor is pretreated before use, and the pretreatment includes any one or a combination of at least two of washing, drying or heat treatment.

[0047] Preferably, the multi-component cathode material precursor is a ternary cathode material precursor.

[0048] Preferably, the amounts of the multi-component cathode material precursor and the lithium source are such that the molar ratio of the lithium element in the lithium source to the total molar number of the metal elements in the multi-component cathode material precursor is 1.01 - 1.06, such as 1.01, 1.02, 1.03, 1.04, 1.05 or 1.06, etc.

[0049] Preferably, the calcination temperature is 700°C - 1000°C, such as 700°C, 750°C, 800°C, 850°C, 900°C, 930°C, 960°C or 1000°C, etc., and preferably 700°C - 800°C.

[0050] Preferably, the heating rate of the calcination is 1°C / min - 10°C / min, such as 1°C / min, 2°C / min, 3°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, etc.

[0051] Preferably, the calcination time is 5h - 20h, such as 5h, 6h, 8h, 10h, 12h, 15h, 16h, 18h or 20h, etc., and preferably 5h - 10h.

[0052] Preferably, the calcination atmosphere includes an air atmosphere and / or an oxygen atmosphere.

[0053] Preferably, the volume concentration of oxygen in the oxygen atmosphere ≥ 90%.

[0054] As a preferred technical solution of the present invention, the preparation method of polyaniline with doping elements includes: oxidative polymerization of aniline monomer with an oxidant under acidic conditions to obtain polyaniline, and adding a dopant during the polymerization to obtain the polyaniline with doping elements.

[0055] This method is chemical oxidative polymerization.

[0056] Preferably, the aniline monomer includes any one or a combination of at least two of aniline, diphenylamine, 2-methylaniline, 2-ethylaniline or 2-propylaniline, preferably aniline and / or diphenylamine.

[0057] Preferably, the acidic conditions are provided by a protic acid.

[0058] Preferably, the protonic acid includes any one of alkylsulfonic acid, benzenesulfonic acid, hydrochloric acid, sulfuric acid, nitric acid or perchloric acid, or a combination of at least two thereof, preferably hydrochloric acid and / or sulfuric acid.

[0059] Preferably, the oxidant comprises any one of hydrogen peroxide, persulfate, iron salt of inorganic acid, copper salt of inorganic acid, bromine, iodine or ozone, or a combination of at least two thereof, preferably hydrogen peroxide and / or persulfate.

[0060] Preferably, the molar ratio of the oxidant to the aniline monomer is 0.1-10, such as 0.1, 0.5, 1, 2, 4, 5, 6, 8 or 10, etc., preferably 0.2-5, and more preferably 0.5-2.

[0061] Preferably, the dopant includes a P-containing dopant and / or a B-containing dopant.

[0062] Preferably, the P-containing dopant includes a phosphorus-containing acid and / or a phosphorus-containing salt, preferably any one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate or sodium dihydrogen phosphate, or a combination of at least two thereof.

[0063] Preferably, the B-containing dopant includes any one or a combination of at least two of a boron-containing acid, a boron-containing salt or a boron-containing organic matter, preferably includes any one or a combination of at least two of boric acid, boron oxide, boron fluoride or borane.

[0064] Preferably, the reaction time of the oxidative polymerization is 0.5 h to 40 h, for example, 0.5 h, 2 h, 4 h, 5 h, 8 h, 12 h, 20 h, etc., preferably 0.5 h to 20 h.

[0065] As a further preferred technical solution of the preparation method of the present invention, the method comprises the following steps:

[0066] (1) Mixing the multi-element cathode material precursor and the lithium source, heating the mixture to 700°C~800°C at a heating rate of 1°C / min~10°C / min, and calcining the mixture for 5h~10h to obtain the multi-element cathode material, washing the mixture with water, and drying the mixture to obtain the post-treated multi-element cathode material;

[0067] (2) oxidatively polymerizing aniline monomer with an oxidant under acidic conditions for 0.5 h to 40 h to obtain polyaniline, while adding a P-containing dopant and / or a B-containing dopant to obtain the polyaniline with the doping element as a coating; the particle size of the coating is 50 nm to 200 nm; wherein the molar ratio of the oxidant to the aniline monomer is 0.5 to 2;

[0068] (3) The post-treated multi-element positive electrode material of step (1) and the coating of step (2) are mixed, and sintered at a constant temperature of 200° C. to 800° C. for 0.5 h to 10 h in an air atmosphere or an oxygen atmosphere to obtain the coated multi-element positive electrode material.

[0069] In a third aspect, the present invention provides a lithium-ion battery, comprising the coated multi-element positive electrode material as described in the first aspect.

[0070] Preferably, the positive electrode active material of the lithium-ion battery adopts the coated multi-element positive electrode material described in the first aspect.

[0071] Exemplarily, the positive electrode sheet of the lithium-ion battery can be prepared according to the following method: the positive electrode active material, conductive carbon black and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, N-methylpyrrolidone (NMP) is added to form a uniform slurry, which is coated on aluminum foil, dried in an oven at 120°C for 12 hours, and then rolled and cut into circular sheets with a diameter of 14 mm under a pressure of 10 MPa.

[0072] For example, the lithium-ion battery can be assembled as follows: the lithium-ion battery is assembled according to the industrial CR2025 button cell model, the separator is a Cellgard separator, the electrolyte is a 1 mol / L LiPF6 solution with an EC:EMC (v / v) ratio of 1:2, and the negative electrode is a pure lithium sheet. The entire assembly process is carried out in an argon-filled glove box, and the oxygen and moisture contents in the glove box are both controlled below 0.5 ppm. The battery's conventional electrochemical performance test temperature is 25°C ± 1°C, and the high-temperature cycle performance test temperature is 45 ± 1°C. The charge and discharge cycle voltage range is 3.0V to 4.3V, and the current size is 1C = 200mAh / g.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] (1) The coating layer of the present invention is a conductive polymer compound of a specific composition, which is used to coat the multi-element material; this functionalized polyaniline is doped at the molecular level, which not only retains high conductivity but also helps to exert the flame retardant properties of P and B. Moreover, this type of doped compound can be dehydrated under high temperature conditions to generate corresponding partial acids or oxides and adhere to the surface of the material, promoting carbonization and achieving good flame retardancy. At the same time, the doped polyaniline has better compatibility with the organic solvent in the electrolyte, significantly improving the thermal stability of the material. After the conductive polymer is doped and modified and then coated with the ternary material, the powder conductivity is increased by one order of magnitude compared with the unmodified product; the rate performance is also improved, and the 2C / 0.5C capacity retention rate is increased from 93% to 97%. The thermal stability of the ternary material coated with the conductive polymer after doping and modification is significantly improved, and the retention rate at 45°C for 50 weeks reaches 98%, which is 5% higher than that of the unmodified product. After the undoped and modified polyaniline is coated with the ternary material, its retention rate at 45°C for 50 weeks is only about 93%.

[0075] (2) The preparation method provided by the present invention is simple to operate, has a short process, and is easy to carry out industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 This is an electron microscope image of the ternary cathode material after coating and modification in Example 1;

[0077] Figure 2 This is the XRD pattern of the ternary cathode material after coating and modification in Example 1;

[0078] Figure 3 The first charge and discharge curves obtained by testing a lithium-ion battery made of the modified ternary cathode material coated in Example 1;

[0079] Figure 4 A lithium-ion battery was made using the modified ternary cathode material coated in Example 1, and the high-temperature cycle performance curve obtained by testing was obtained. DETAILED DESCRIPTION

[0080] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0081] The following are typical but non-limiting examples of the present invention:

[0082] Example 1

[0083] This embodiment prepares the coated multi-element positive electrode material according to the following method:

[0084] (1) Synthesis of high nickel precursor Ni by co-precipitation technology 0.8 Co 0.1 Mn 0.1 (OH)2, after washing and drying process, Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor product.

[0085] (2) Ni precursor 0.8 Co 0.1 Mn 0.1 The (OH)2 product and the lithium source are fully mixed, wherein the molar ratio of lithium to transition metal (Ni+Co+Mn) is 1.05. The fully mixed precursors are heated to 800℃ at 1.5℃ / min in an oxygen atmosphere and kept at this temperature for 15h to obtain the untreated matrix high nickel cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0086] (3) The obtained untreated matrix high nickel cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 was added into deionized water with a water-to-material ratio of 2:1, and after stirring for 30 minutes, the washed matrix material was obtained by separation and drying.

[0087] (4) Preparation of doped polyaniline by chemical oxidation polymerization: Take 500 ml of deionized water, add 50 ml of 1 mol / L hydrochloric acid, adjust the pH to 3, and stir evenly to obtain solution A; then slowly add 4 g of aniline, stir for 10 min, add 0.08 g of boric acid, and continue stirring for 10 min; continue to add 50 ml of 1 mol / L ammonium persulfate solution, keep stirring in an ice water bath at 0°C for 10 h, filter to obtain a solid, and wash it with deionized water and ethanol, and dry it at 80°C for 12 h to obtain B-doped polyaniline (particle size range 100 nm-2 μm) as a coating.

[0088] (5) The washed base material and the coating are mixed evenly, wherein the coating amount (the amount of the coating used is calculated based on the amount of the washed base material as 100%) is 0.2%. The mixture is sintered for a second time at 300°C for 5 hours and cooled to room temperature to obtain the coated and modified ternary positive electrode material, i.e., the coated ternary positive electrode material.

[0089] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.8 Co 0.1 Mn 0.1O2 (hexagonal layered structure, R3m space group), the coating layer is a B-doped polyaniline layer. In the coating layer, the mass percentage of the doping element B is 0.2%, based on the total mass of the doping element and polyaniline as 100%. The coating layer has a thickness of 200-500 nm and a mass percentage of 0.2%, based on the mass of the multi-element positive electrode material as 100%.

[0090] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0091] Figure 1 This is an electron microscope picture of the ternary positive electrode material after coating and modification in this embodiment. It can be seen from the figure that the coated material is still composed of primary particles of about 200~400nm and secondary spherical particles with a diameter of about 10 microns. Due to the coating, the surface of the particles is relatively rough.

[0092] Figure 2 The XRD pattern of the modified ternary cathode material after coating in this example shows that the coated material still has an α-NaFeO2 layered structure without any impurity peaks, which may be due to the small amount of coating. The obvious peak separation between (006) / (102) and (108) / (110) indicates the formation of a good layered structure and a small Li / Ni mixing.

[0093] Figure 3 In order to use the coated and modified ternary positive electrode material in this embodiment to make a lithium-ion battery (the specific method for preparing the lithium-ion battery is shown in the test method section), the first charge and discharge curve obtained by the test is specifically the first charge and discharge curve of the coated material at 3.0~4.3V and 0.1C (1C=200mAh / g) current density. As can be seen from the figure, the charging capacity is 230mAh / g, the discharge capacity is 207mAh / g, and the first efficiency reaches 90%.

[0094] Figure 4 The modified ternary cathode material in this embodiment is used to make a lithium-ion battery (the specific method for preparing the lithium-ion battery is shown in the test method section), and the high-temperature cycle performance curve obtained by testing is shown in the figure. Figure 4 The coated material exhibits excellent high-temperature cycling performance, with a 97.2% retention rate after 50 cycles at 0.5C / 1C charge and discharge. This excellent high-temperature cycling performance stems from the heat resistance of the specific coating layer of the present invention, as well as its improved compatibility with organic solvents, which inhibits electrolyte corrosion.

[0095] Example 2

[0096] Other conditions are the same as those in Example 1, except that the doping amount of polyaniline is changed. The doping amount of boric acid in Example 1 is 0.2%, while that in Example 2 is 0.5%. The coating amount remains unchanged at 0.2%.

[0097] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.8 Co 0.1 Mn 0.1 O2 (hexagonal layered structure, R3m space group), the coating layer is a B-doped polyaniline layer. In the coating layer, the mass percentage of the doping element B is 0.5%, based on the total mass of the doping element and polyaniline as 100%. The coating layer has a thickness of 200-500 nm and a mass percentage of 0.2%, based on the mass of the multi-element positive electrode material as 100%.

[0098] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0099] Example 3

[0100] Other conditions were the same as those in Example 2, with the boric acid doping amount being 0.5%, but the coating amount was changed to 0.5%.

[0101] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.8 Co 0.1 Mn 0.1 O2 (hexagonal layered structure, R3m space group), the coating layer is a B-doped polyaniline layer. In the coating layer, the mass percentage of the doping element B is 0.5%, based on the total mass of the doping element and polyaniline as 100%. The coating layer has a thickness of 500-800 nm and a mass percentage of 0.5%, based on the mass of the multi-element positive electrode material as 100%.

[0102] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0103] Example 4

[0104] Other conditions are the same as those in Example 3, except that the polyaniline doping element is adjusted to P element, phosphoric acid is selected as the dopant, the doping amount is 0.5%, and the coating amount is 0.5%.

[0105] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.8 Co 0.1 Mn 0.1 O2 (hexagonal layered structure, R3m space group), the coating layer is a P-doped polyaniline layer. In the coating layer, the weight percentage of the doping element B is 0.5%, based on the total weight of the doping element and polyaniline as 100%. The coating layer has a thickness of 500-800 nm and a weight percentage of 0.5%, based on the weight of the multi-element positive electrode material as 100%.

[0106] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0107] Example 5

[0108] This embodiment prepares the coated multi-element positive electrode material according to the following method:

[0109] (1) Ni precursor 0.815 Co 0.15 Al 0.035 The (OH)2 product and the lithium source are fully mixed, wherein the molar ratio of lithium to transition metal (Ni+Co+Al) is 1.05. The fully mixed precursors are heated to 800℃ at 1.5℃ / min in an oxygen atmosphere and kept at this temperature for 15h to obtain the untreated matrix high nickel cathode material LiNi 0.815 Co 0.15 Al 0.035 O2.

[0110] (2) The obtained untreated matrix high nickel cathode material LiNi 0.815 Co 0.15 Al 0.035 O2 was added into deionized water with a water-to-material ratio of 2:1, and after stirring for 40 minutes, the washed matrix material was obtained by separation and drying.

[0111] (3) Preparation of doped polyaniline by chemical oxidation polymerization: Take 500 ml of deionized water, add 50 ml of 1 mol / L hydrochloric acid, adjust the pH to 4, and stir evenly to obtain solution A; then slowly add 4 g of aniline, stir for 10 min, add 0.2 g of boric acid, and continue stirring for 10 min; continue to add 50 ml of 1 mol / L ammonium persulfate solution, keep stirring in an ice water bath at 0 ° C for 10 h, filter to obtain a solid, and wash it with deionized water and ethanol, and dry it at 80 ° C for 12 h to obtain B-doped polyaniline (particle size range of 100 nm~2 μm) as a coating.

[0112] (4) The washed base material and the coating are mixed evenly, wherein the coating amount (the amount of the coating used is calculated based on the amount of the washed base material as 100%) is 0.5%, and secondary sintering is performed at 300°C for 5 hours. After cooling to room temperature, the coated modified ternary positive electrode material is obtained, that is, the coated ternary positive electrode material.

[0113] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.815 Co 0.15 Al 0.035 O2 (hexagonal layered structure, R3m space group), the coating layer is a B-doped polyaniline layer. In the coating layer, the mass percentage of the doping element B is 0.5%, based on the total mass of the doping element and polyaniline as 100%. The coating layer has a thickness of 500-800 nm and a mass percentage of 0.5%, based on the mass of the multi-element positive electrode material as 100%.

[0114] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0115] Example 6

[0116] This embodiment prepares the coated multi-element positive electrode material according to the following method:

[0117] (1) Ni precursor 0.85 Co 0.05 Mn 0.1 The (OH)2 product and the lithium source are fully mixed, wherein the molar ratio of lithium to transition metal (Ni+Co+Mn) is 1.01. The fully mixed precursors are heated to 700℃ at 1℃ / min in an oxygen atmosphere and kept at this temperature for 20h to obtain the untreated matrix high nickel cathode material LiNi 0.85 Co 0.05 Mn 0.1 O2.

[0118] (2) The obtained untreated matrix high nickel cathode material LiNi 0.85 Co 0.05 Mn 0.1 O2 was added into deionized water with a water-to-material ratio of 1.5:1, and after stirring for 10 minutes, the washed matrix material was obtained by separation and drying.

[0119] (3) Preparation of doped polyaniline by chemical oxidation polymerization: 500 ml of deionized water was added with 1 mol / L hydrochloric acid, the pH was adjusted to 1, and the mixture was stirred to obtain solution A. 4 g of aniline was then slowly added and stirred for 10 min. Ammonium dihydrogen phosphate was added (added at a P doping amount of 10%) and the mixture was stirred for 10 min. 1 mol / L hydrogen peroxide solution was added (added at a molar ratio of hydrogen peroxide to aniline of 0.1:1) and the mixture was stirred in an ice-water bath at 0 °C for 40 h. The solid was filtered and washed with deionized water and ethanol. The solid was dried at 80 °C for 12 h to obtain P-doped polyaniline (particle size range of 50 nm~1 μm) as a coating.

[0120] (4) The washed base material and the coating are mixed evenly, wherein the coating amount (the amount of the coating used is calculated based on the amount of the washed base material as 100%) is 0.1%, and secondary sintering is performed at 200°C for 10 hours. After cooling to room temperature, the coated modified ternary positive electrode material is obtained, that is, the coated ternary positive electrode material.

[0121] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.85 Co 0.05 Mn 0.1 (OH)2 (hexagonal layered structure, R3m space group), the coating layer is a P-doped polyaniline layer. In the coating layer, the weight percentage of the doping element B is 10%, based on the total weight of the doping element and polyaniline as 100%. The coating layer has a thickness of 100-200 nm and a weight percentage of 0.1%, based on the weight of the multi-element positive electrode material as 100%.

[0122] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0123] Example 7

[0124] This embodiment prepares the coated multi-element positive electrode material according to the following method:

[0125] (1) Ni precursor 0.815 Co 0.15 Al 0.035 The (OH)2 product and the lithium source are fully mixed, wherein the molar ratio of lithium to transition metal (Ni+Co+Al) is 1.06. The fully mixed precursors are heated to 1000°C at 10°C / min in an oxygen atmosphere and kept at this temperature for 5 hours to obtain the untreated matrix high nickel cathode material LiNi 0.815 Co 0.15 Al 0.035 O2.

[0126] (2) The obtained untreated matrix high nickel cathode material LiNi 0.815 Co 0.15 Al 0.035 O2 was added into deionized water with a water-to-material ratio of 1:1, and after stirring for 60 minutes, the washed matrix material was obtained by separation and drying.

[0127] (3) Preparation of doped polyaniline by chemical oxidation polymerization: 500 ml of deionized water was added with 1 mol / L sulfuric acid, the pH was adjusted to 5, and the mixture was stirred to obtain solution A; then 4 g of diphenylamine was slowly added, stirred for 10 min, and boron oxide and ammonium dihydrogen phosphate were added (according to the molar ratio of B and P of 1:1, and the total doping amount of B and P was 20%), and the stirring was continued for 10 min; 1 mol / L ammonium persulfate solution was added (according to the molar ratio of ammonium persulfate to diphenylamine of 10:1), and the mixture was stirred in an ice-water bath at 0°C for 0.5 h. The solid was filtered and washed with deionized water and ethanol, and dried at 80°C for 12 h to obtain polyaniline doped with B and P as a coating (particle size range of 80 nm~1.5 μm).

[0128] (4) The washed base material and the coating are mixed evenly, wherein the coating amount (the amount of the coating used is calculated based on the amount of the washed base material as 100%) is 0.5%, and secondary sintering is performed at 800°C for 0.5h. After cooling to room temperature, the coated modified ternary positive electrode material is obtained, that is, the coated ternary positive electrode material.

[0129] The coated multi-element positive electrode material obtained in this embodiment includes a multi-element positive electrode material and a coating layer coated on the surface of the multi-element positive electrode material. The multi-element positive electrode material is a high nickel ternary positive electrode material. 0.815 Co 0.15 Al 0.035 O2 (hexagonal layered structure, R3m space group), the coating layer is a polyaniline layer doped with boron and phosphorus (the molar ratio of boron to phosphorus is 1:1). In the coating layer, the combined mass percentage of the doping elements B and phosphorus is 20%, based on the total mass of the doping elements and polyaniline as 100%. The coating layer has a thickness of 500-800 nm and a mass percentage of 0.5%, based on the mass of the multi-element positive electrode material as 100%.

[0130] The performance test results of the coated ternary cathode material prepared in this example are shown in Table 1.

[0131] Comparative Example 1

[0132] This comparative example is the same as Example 1 except that the coating modification and secondary sintering are not performed, that is, the operations of step (4) and step (5) are not performed.

[0133] The performance test results of the ternary cathode material prepared in this comparative example are shown in Table 1.

[0134] Comparative Example 2

[0135] This comparative example is the same as Example 1 except that step (4) is not performed and step (5) is performed directly using Al2O3 powder as the coating.

[0136] The performance test results of the coated ternary positive electrode material prepared in this comparative example are shown in Table 1.

[0137] Comparative Example 3

[0138] This comparative example is the same as Example 1 except that boric acid is not added in step (4), that is, no doping is performed.

[0139] The performance test results of the coated ternary positive electrode material prepared in this comparative example are shown in Table 1.

[0140] Test method:

[0141] The products provided in the examples or comparative examples were prepared into batteries according to the following method and subjected to electrochemical testing:

[0142] First, prepare the positive electrode sheet: mix the coated modified ternary positive electrode material, conductive carbon black and binder polyvinylidene fluoride (PVDF) in a mass ratio of 96:2:2, add N-methylpyrrolidone (NMP) to make a uniform slurry, apply it on aluminum foil, dry it in an oven at 120°C for 12 hours, and then roll it under a pressure of 10 MPa to cut it into a circular positive electrode sheet with a diameter of 14 mm.

[0143] The above-mentioned positive electrode sheet was then used to assemble a lithium-ion battery similar to an industrial CR2016 button cell. The separator was a Cellgard membrane, the electrolyte was a 1 mol / L LiPF6 solution with an EC:EMC (v / v) ratio of 1:2, and the negative electrode was a pure lithium sheet. The entire assembly process took place in an argon-filled glove box, where oxygen and moisture levels were controlled below 0.5 ppm. The lithium-ion battery was tested at a temperature of 25°C ± 2°C, and high-temperature cycling performance was tested at a temperature of 45°C ± 1°C. The charge-discharge cycle voltage range was 3.0 V to 4.3 V, and the current was 1C = 200 mAh / g. The test results are shown in Table 1.

[0144] Figure 1

[0145]

[0146] Comparing Examples 1-7 with Comparative Examples 1-3 shows that the coated multi-element cathode materials of the present invention, using a specifically doped polyaniline coating layer, exhibit excellent initial charge-discharge efficiency and cycle performance, particularly high-temperature cycling performance. In contrast, the uncoated materials (Comparative Example 1) or materials with an oxide coating layer (Comparative Example 2) exhibit slightly lower initial efficiency and high-temperature cycling stability, particularly for the uncoated materials. The improved performance of the coated materials is attributed to the excellent conductivity and heat resistance of the coating layer.

[0147] By comparing Example 1 and Example 2, after increasing the doping amount of polyaniline, the first efficiency and high-temperature cycle stability are improved, indicating that the conductivity of polyaniline is more significantly improved after the doping amount is increased. This is because the doping elements enter the main chain, combine with N atoms to form poles that are dispersed in the P bonds of the entire molecular chain, thereby making polyaniline exhibit higher conductivity. The greater the doping amount, the higher the conductivity.

[0148] By comparing Example 2 and Example 3, it can be seen that after the coating amount is increased, the high-temperature cycle performance is slightly improved. This is because the coating is denser and more uniform, which reduces side reactions.

[0149] By comparing Example 3 and Example 4, it can be seen that the effects of B- and P-doped polyaniline on improving the ternary material are very similar. This is because the doping compounds containing B or P can be dehydrated under high temperature conditions to generate corresponding partial acids or oxides and adhere to the material surface.

[0150] By comparing Example 1 and Comparative Example 3, it can be found that the high-temperature cycle stability of the ternary material coated with polyaniline without B or P doping is very poor, and the 50-cycle retention rate is only 88%. On the one hand, it is due to the heat resistance of the doping elements. On the other hand, the doping elements delay the cross-linking reaction of the polyaniline heat treatment process, thereby stabilizing the coating layer and improving the high-temperature stability.

[0151] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed process equipment and process flow of the present invention. However, the present invention is not limited to the above-described detailed process equipment and process flow, and does not necessarily rely on the above-described detailed process equipment and process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for the raw materials of the present invention's products, additions of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a coated multi-element positive electrode material, characterized in that: The following steps are involved: Mixing the multi-element positive electrode material with a coating, and sintering the mixture in an oxidizing atmosphere to obtain the coated multi-element positive electrode material, wherein the coating comprises polyaniline with a doping element; The doping element includes B element and / or P element; The preparation method of the polyaniline with doping elements comprises: oxidatively polymerizing aniline monomer with an oxidant under acidic conditions to obtain polyaniline, and adding a dopant during the polymerization to obtain the polyaniline with doping elements; The dopant includes a P-containing dopant and / or a B-containing dopant; The P-containing dopant includes a phosphorus-containing salt; The B-containing dopant includes a boron-containing salt.

2. The preparation method according to claim 1, characterized in that The doping element exists in the polyaniline molecular chain.

3. The preparation method according to claim 1, characterized in that The coating layer coated on the surface of the coated multi-element positive electrode material has a mass percentage of the doping element of 0.5% to 20% based on the total mass of the doping element and the polyaniline as 100%.

4. The preparation method according to claim 1, characterized in that The chemical composition of the multi-element positive electrode material is Li a Ni x Co y M 1-x-y O2, wherein M is any one of Mn, Al, V, Mg, Mo, Nb or Ti or a combination of at least two thereof, 0.90 <a<1.10,0.30≤x<1.0,0<y≤0.3。 5. The preparation method according to claim 4, characterized in that The M is Al or Mn.

6. The preparation method according to claim 4, characterized in that The chemical composition of the multi-element positive electrode material is Li a Ni x Co y M 1-x-y O2, where 0.6 ≤x≤1.0, 0≤y≤0.

4.

7. The preparation method according to claim 6, characterized in that The chemical composition of the multi-element positive electrode material is Li a Ni x Co y M 1-x-y O2, where 0.80≤x<0.95, 0.05 <y≤0.2。 8. The preparation method according to claim 1, characterized in that The multi-element positive electrode material is a ternary positive electrode material.

9. The preparation method according to claim 8, characterized in that The ternary positive electrode material is a hexagonal layered structure with an R3m space group.

10. The preparation method according to claim 1, characterized in that The thickness of the coating layer coated on the surface of the coated multi-element positive electrode material is 50 nm~500 nm.

11. The preparation method according to claim 1, characterized in that Based on the mass of the multi-element positive electrode material being 100%, the mass percentage of the coating layer coated on the surface of the coated multi-element positive electrode material is 0.1% to 0.5%.

12. The preparation method according to claim 1, characterized in that The particle size of the coating is 50nm~2μm.

13. The preparation method according to claim 12, characterized in that The particle size of the coating is 50nm~500nm.

14. The preparation method according to claim 13, characterized in that The particle size of the coating is 50nm~200nm.

15. The preparation method according to claim 1, characterized in that The chemical composition of the multi-element positive electrode material is Li a Ni x Co y M 1-x-y O2, wherein M is any one of Mn, Al, V, Mg, Mo, Nb or Ti or a combination of at least two thereof, 0.90 <a<1.10,0.30≤x<1.0,0<y≤0.3。 16. The preparation method according to claim 15, characterized in that In the multi-element positive electrode material, when the molar percentage of Ni in other metal elements except Li is above 80%, post-treatment is performed before coating.

17. The preparation method according to claim 16, characterized in that The post-treatment is water washing and drying.

18. The preparation method according to claim 17, characterized in that The water washing method comprises: mixing the multi-element positive electrode material and water at a water-to-material mass ratio of (1-2):1, and stirring for 10-60 minutes.

19. The preparation method according to claim 1, characterized in that The oxidizing atmosphere includes an oxygen atmosphere or an air atmosphere.

20. The preparation method according to claim 19, characterized in that The oxygen volume concentration of the oxygen atmosphere is ≥90%.

21. The preparation method according to claim 1, characterized in that The sintering temperature is 200°C to 800°C.

22. The preparation method according to claim 1, characterized in that The sintering time is 0.5h~10h.

23. The preparation method according to claim 1, characterized in that The preparation method of the multi-element positive electrode material comprises: mixing a multi-element positive electrode material precursor and a lithium source, and calcining to obtain the multi-element positive electrode material.

24. The preparation method according to claim 23, characterized in that The chemical composition of the multi-element positive electrode material precursor is Ni x Co y M 1-x-y (OH)2, M is any one of Mn, Al, V, Mg, Mo, Nb or Ti or a combination of at least two, 0.30≤x<1.0, 0 <y≤0.3。 25. The preparation method according to claim 23, characterized in that The multi-element positive electrode material precursor is pretreated before use, and the pretreatment includes any one of washing and heat treatment or a combination of the two.

26. The preparation method according to claim 23, characterized in that The multi-element cathode material precursor is a ternary cathode material precursor.

27. The preparation method according to claim 23, characterized in that The amounts of the multi-element positive electrode material precursor and the lithium source are such that the molar ratio of the molar number of the lithium element in the lithium source to the total molar number of the metal elements in the multi-element positive electrode material precursor is 1.01-1.

06.

28. The preparation method according to claim 23, characterized in that The calcination temperature is 700°C to 1000°C.

29. The preparation method according to claim 28, characterized in that The calcination temperature is 700°C to 800°C.

30. The preparation method according to claim 23, characterized in that The heating rate of the calcination is 1°C / min to 10°C / min.

31. The preparation method according to claim 23, characterized in that The calcination time is 5h~20h.

32. The preparation method according to claim 31, characterized in that The calcination time is 5h~10h.

33. The preparation method according to claim 23, characterized in that The calcination atmosphere includes air atmosphere and / or oxygen atmosphere.

34. The preparation method according to claim 33, characterized in that The oxygen volume concentration of the oxygen atmosphere is ≥90%.

35. The preparation method according to claim 1, characterized in that The aniline monomer includes any one of aniline, diphenylamine, 2-methylaniline, 2-ethylaniline or 2-propylaniline, or a combination of at least two thereof.

36. The preparation method according to claim 35, characterized in that The aniline monomer is aniline and / or diphenylamine.

37. The preparation method according to claim 1, characterized in that The acidic conditions are provided by protic acids.

38. The preparation method according to claim 37, characterized in that The protonic acid includes any one of alkylsulfonic acid, benzenesulfonic acid, hydrochloric acid, sulfuric acid, nitric acid or perchloric acid, or a combination of at least two thereof.

39. The preparation method according to claim 38, characterized in that The protonic acid is hydrochloric acid and / or sulfuric acid.

40. The preparation method according to claim 1, characterized in that The oxidant includes any one of hydrogen peroxide, persulfate, iron salt of inorganic acid, copper salt of inorganic acid, bromine, iodine or ozone, or a combination of at least two thereof.

41. The preparation method according to claim 40, characterized in that The oxidizing agent is hydrogen peroxide and / or persulfate.

42. The preparation method according to claim 1, characterized in that The molar ratio of the oxidant to the aniline monomer is 0.1-10.

43. The preparation method according to claim 39, characterized in that The molar ratio of the oxidant to the aniline monomer is 0.2-5.

44. The preparation method according to claim 43, characterized in that The molar ratio of the oxidant to the aniline monomer is 0.5-2.

45. The preparation method according to claim 1, characterized in that The phosphorus-containing salt includes any one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate or sodium dihydrogen phosphate, or a combination of at least two thereof.

46. The preparation method according to claim 1, characterized in that The boron-containing salt includes any one of boron oxide, boron fluoride or borane, or a combination of at least two thereof.

47. The preparation method according to claim 1, characterized in that The reaction time of the oxidative polymerization is 0.5h~40h.

48. The preparation method according to claim 1, characterized in that The following steps are involved: (1) Mixing the multi-element cathode material precursor and the lithium source, heating the mixture to 700°C~800°C at a heating rate of 1°C / min~10°C / min, and calcining the mixture for 5h~10h to obtain the multi-element cathode material, washing the mixture with water, and drying the mixture to obtain the post-treated multi-element cathode material; (2) oxidatively polymerizing aniline monomer with an oxidant under acidic conditions for 0.5 h to 40 h to obtain polyaniline, while adding a P-containing dopant and / or a B-containing dopant to obtain the polyaniline with the doping element as a coating; the particle size of the coating is 50 nm to 200 nm; wherein the molar ratio of the oxidant to the aniline monomer is 0.5 to 2; (3) The post-treated multi-element positive electrode material of step (1) and the coating of step (2) are mixed, and sintered at a constant temperature of 200° C. to 800° C. for 0.5 h to 10 h in an air atmosphere or an oxygen atmosphere to obtain the coated multi-element positive electrode material.

49. A coated multi-element positive electrode material, characterized in that The coated multi-element positive electrode material is prepared according to the preparation method according to any one of claims 1-48.

50. A lithium ion battery, characterized in that The lithium-ion battery comprises the coated multi-element positive electrode material as claimed in claim 49.

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