Positive electrode material, preparation method thereof and lithium ion battery

Abstract

The present invention relates to the technical field of lithium-ion battery materials, and in particular to a cathode material, a preparation method thereof, and a lithium-ion battery. The preparation method of the cathode material comprises the following steps: (a) taking a lithium source, an iron source, a phosphorus source, a manganese source, a carbon source, a doping element source, and a solvent, mixing them to form a mixed solution, and performing a drying treatment to obtain a dried sample; (b) performing a first sintering treatment on the dried sample to obtain a first sintered product; (c) adding a lithium source and a carbon source to the first sintered product and performing a second sintering treatment; (d) crushing to obtain the cathode material; the dosage of the lithium source in step (a) is 50% to 80% of the total amount of the lithium source. Through two specific lithium addition methods, in cooperation with doping elements, it can directionally induce the incorporated metal elements to occupy lithium sites, which can not only broaden the lithium-ion transmission channels, affect the particle morphology, but also partially replace the lithium that does not participate in the charge-discharge insertion and extraction, significantly improving the cycle performance and rate performance while reducing the production cost.

Description

Technical Field

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

[0002] In recent years, with the development of consumer electronic products and energy-powered products such as battery vehicles, power tools, and energy storage devices, the market space for lithium-ion batteries has become larger and larger. As one of the most important parts of lithium-ion batteries, the usage amount of lithium-ion battery cathode materials has increased explosively. Among them, lithium iron phosphate materials are widely used in the fields of power and energy storage batteries due to their advantages such as high safety and high cycle life.

[0003] However, lithium iron phosphate has poor conductivity and slow lithium ion diffusion rate, which limits its application. Commonly used modification methods in the prior art include carbon coating, particle refinement, metal element doping, etc. Metal element doping is an effective method to improve the intrinsic conductivity of materials, but currently the occupation of lattice sites by metal elements has randomness, and situations where metal elements cannot be incorporated or the incorporated metal elements block the Li + migration channels will occur. Summary of the Invention

[0004] An object of the present invention is to provide a preparation method of a cathode material, which can directionally induce the incorporated metal elements to occupy the Li + sites, improve the doping efficiency, and enhance the cycle performance and rate performance.

[0005] In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0006] A preparation method of a cathode material includes the following steps:

[0007] (a) Take a lithium source, an iron source, a phosphorus source, a manganese source, a carbon source, a doping element source, and a solvent and mix them to form a mixed solution, and perform a drying treatment on the mixed solution to obtain a dried sample;

[0008] (b) Perform a first sintering treatment on the dried sample under a protective atmosphere to obtain a first sintered product;

[0009] (c) Add a lithium source and a carbon source to the first sintered product, crush and mix them evenly, and perform a second sintering treatment under a protective atmosphere to obtain a second sintered product;

[0010] (d) Crush the second sintered product to obtain a cathode material;

[0011] Wherein, in step (a), the dosage of the lithium source is 50% - 80% of the total amount of the lithium source.

[0012] Further, the chemical composition of the positive electrode material is Li x A 1-x Mn y Fe 1-y PO 4 ; A is a doping element, 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 1.

[0013] Further, the molar ratio of the total amount of the lithium source, the iron source, the phosphorus source, the manganese source, and the doping element source in terms of Li, Fe, P, Mn, and the doping element is x﹕(1 - y)﹕1﹕y﹕(1 - x).

[0014] Further, the doping element is a metal element. Further, the doping element includes at least one of Na, K, Sr, Mg, Ce, and Ti.

[0015] Further, the total mass of the carbon source is 2% - 8% of the mass of the positive electrode material; the mass ratio of the carbon source in step (a) to the carbon source in step (c) is (1 - 2)﹕1.

[0016] Further, in step (a), the mass of the solvent is 1.2 - 1.8 times the total mass of the lithium source, the iron source, the phosphorus source, the manganese source, the carbon source, and the doping element source.

[0017] Further, the lithium source includes Li 2 O, Li 2 CO 3 , LiH 2 PO 4 , LiOH·H 2 O, CH 3 COOLi, and LiNO 3 ;

[0018] The iron source includes FeCl 3 , Fe(NO 3 ) 3 , Fe 2 O 3 , and FeSO 4 ·7H 2 O;

[0019] The phosphorus source includes (NH 4 ) 3 PO 4 , LiH 2 PO 4 , and H 3 PO 4 ;

[0020] The manganese source includes MnO2 , Mn(NO 3 ) 2 , MnSO 4 and Mn 3 (PO 4 ) 2 ·3H 2 O or at least one of them;

[0021] The doping element source includes at least one of carbonates, hydrochlorides and sulfates of doping elements;

[0022] The carbon source includes at least one of sucrose, glucose, PVDF, carbon black, PEG, paraffin, graphite, graphene and starch.

[0023] Furthermore, the doping element source includes at least one of sodium carbonate, potassium carbonate, strontium chloride, magnesium chloride, cerium sulfate and titanium tetrachloride.

[0024] Furthermore, in step (b), the temperature of the first sintering treatment is 400 - 600 °C, and the time of the first sintering treatment is 6 - 12 h.

[0025] Furthermore, in step (b), the temperature is raised to 400 - 600 °C at a heating rate of 4 - 6 °C / min.

[0026] Furthermore, in step (c), the temperature of the second sintering treatment is 600 - 800 °C, and the time of the second sintering treatment is 4 - 8 h.

[0027] Furthermore, in step (c), the temperature is raised to 600 - 800 °C at a heating rate of 4 - 6 °C / min.

[0028] The present invention also provides a cathode material prepared by using the preparation method of any one of the above-mentioned cathode materials.

[0029] The present invention also provides a lithium-ion battery including any one of the above-mentioned cathode materials.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) In the preparation method of the cathode material of the present invention, the doping element is first mixed with part of lithium and other raw material components to obtain a lithium-deficient crystal structure. The doping element can preferentially occupy the lithium site and be arranged with lithium in a way that is most stable to the crystal structure, improving the doping efficiency. At the same time, only adding part of lithium initially can also eliminate the impurity phases that may be generated by a high doping amount; by adding a lithium source again, on the one hand, the lithium deficiency is filled, and on the other hand, the sphericity of the particles is improved;

[0032] (2) The cathode material prepared by the preparation method of the present invention can, through two specific lithium addition methods and in combination with doping elements, directionally induce the incorporated metal elements to occupy lithium sites. This can not only broaden the lithium ion transport channels, affect the particle morphology, but also partially replace the lithium that does not participate in the charge-discharge insertion and extraction, significantly improving the cycle performance and rate performance while reducing the production cost of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 SEM image of the cathode material provided in Example 1 of the present invention;

[0035] Figure 2 SEM image of the cathode material provided in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments not specified by the manufacturer can be obtained through commercially available conventional products.

[0037] A preparation method of a cathode material includes the following steps:

[0038] (a) Take a lithium source, an iron source, a phosphorus source, a manganese source, a carbon source, a doping element source and a solvent and mix them to form a mixed solution, and dry the mixed solution to obtain a dried sample;

[0039] (b) Subject the dried sample to a first sintering treatment under a protective atmosphere to obtain a first sintered product;

[0040] (c) Add a lithium source and a carbon source to the first sintered product, crush and mix them evenly, and perform a second sintering treatment under a protective atmosphere to obtain a second sintered product;

[0041] (d) Crush the secondary sintered product to obtain the cathode material;

[0042] Among them, in step (a), the dosage of the lithium source is 50% - 80% of the total amount of the lithium source.

[0043] The "total amount of the lithium source" in the present invention refers to the sum of the dosage of the lithium source used in step (a) and the dosage of the lithium source added in step (c). The dosages of the total amount of the lithium source, the iron source, the phosphorus source, the manganese source, and the doping element source are proportioned according to the chemical composition of the target cathode material.

[0044] For example, in different embodiments, in step (a), the dosage of the lithium source can be, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80% of the total amount of the lithium salt, or the range composed of any two of them.

[0045] In the present invention, the doping element is first mixed with part of the lithium and other raw material components to obtain a lithium-deficient crystal structure. The doping element can preferentially occupy the lithium site and arrange with lithium in a manner that is most suitable for crystal structure stability, improving the doping efficiency. At the same time, only adding part of the lithium initially can also eliminate the impurity phases that may be generated by a high doping amount; by the way of adding the lithium source again, on the one hand, the lithium vacancies are filled, and on the other hand, the sphericity of the particles is improved.

[0046] When the dosage of the lithium source in step (a) is lower than the above range, it will cause a regional concentrated distribution when the doping element is incorporated into the crystal lattice; when the dosage of the lithium source in step (a) is higher than the above range, it will cause a reduction in the doping efficiency, a smaller lithium site available for the doping element to choose, and a smaller number of lithium sites in the "dead lithium" inside the particles occupied.

[0047] In some specific embodiments of the present invention, in step (a), the drying treatment methods include spray drying, oven heating drying, vacuum drying, etc. Among them, the drying method and conditions are not limited as long as the mixed solution can be dried. Further, the drying temperature ≤ 150 °C.

[0048] After the drying treatment, crushing can be optionally carried out so that the particle size D50 of the dried sample < 10 μm.

[0049] In actual operation, the lithium source, the iron source, the phosphorus source, the manganese source, the carbon source, the doping element source, and the solvent are mixed in proportion, and are mixed evenly by mechanical stirring and other means to form a mixed solution.

[0050] In some specific embodiments of the present invention, the chemical composition of the cathode material is Li x A 1-x Mn y Fe 1-y PO 4 ; A is a doping element, 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 1.

[0051] In some specific embodiments of the present invention, the molar ratio of the total amount of the lithium source, the iron source, the phosphorus source, the manganese source, and the doping element source, calculated as Li, Fe, P, Mn, and the doping element respectively, is x﹕(1 - y)﹕1﹕y﹕(1 - x).

[0052] In some specific embodiments of the present invention, the doping element is a metal element. Further, the doping element includes at least one of Na, K, Sr, Mg, Ce, and Ti.

[0053] In different embodiments, the doping element may include one, two, three, four, five, or six of Na, K, Sr, Mg, Ce, and Ti.

[0054] In some specific embodiments of the present invention, the doping element includes at least three of Na, K, Sr, Mg, Ce, and Ti. Further, the doping element includes K, Ce, and Ti; or, the doping element includes Na, Sr, and Mg.

[0055] In some specific embodiments of the present invention, when the doping element includes at least two elements, the molar ratio between every two elements is between 0.8 and 1.2; for example, it can be 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, etc.

[0056] In some specific embodiments of the present invention, the total mass of the carbon source is 2% - 8% of the mass of the cathode material; the mass ratio of the carbon source in step (a) to the carbon source in step (c) is (1 - 2)﹕1.

[0057] In different embodiments, the total mass of the carbon source can be 2%, 3%, 4%, 5%, 6%, 7%, 8% of the mass of the cathode material, or the range composed of any two of them; the mass ratio of the carbon source in step (a) to the carbon source in step (c) can be 1﹕1, 1.2﹕1, 1.5﹕1, 1.8﹕1, 2﹕1, or the range composed of any two of them.

[0058] In some specific embodiments of the present invention, in step (a), the mass of the solvent is 1.2 - 1.8 times the total mass of the lithium source, the iron source, the phosphorus source, the manganese source, the carbon source, and the doping element source.

[0059] In different embodiments, in step (a), the mass of the solvent can be 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times the total mass of the lithium source, the iron source, the phosphorus source, the manganese source, the carbon source and the doping element source, or within the range formed by any two of them.

[0060] In some specific embodiments of the present invention, the lithium source includes Li 2 O, Li 2 CO 3 , LiH 2 PO 4 , LiOH·H 2 O, CH 3 COOLi and LiNO 3 ; at least one of them;

[0061] The iron source includes FeCl 3 , Fe(NO 3 ) 3 , Fe 2 O 3 and FeSO 4 ·7H 2 O; at least one of them;

[0062] The phosphorus source includes (NH 4 ) 3 PO 4 , LiH 2 PO 4 and H 3 PO 4 ; at least one of them;

[0063] The manganese source includes MnO 2 , Mn(NO 3 ) 2 , MnSO 4 and Mn 3 (PO 4 ) 2 ·3H 2 O; at least one of them;

[0064] The doping element source includes at least one of carbonates, hydrochlorides and sulfates of the doping element;

[0065] The carbon source includes at least one of sucrose, glucose and citric acid.

[0066] In some specific embodiments of the present invention, the doping element source includes at least one of sodium carbonate, potassium carbonate, strontium chloride, magnesium chloride, cerium sulfate and titanium tetrachloride.

[0067] In some specific embodiments of the present invention, in step (b), the temperature of the first sintering treatment is 400 - 600°C, and the time of the first sintering treatment is 6 - 12 h.

[0068] In different embodiments, in step (b), the temperature of the first sintering treatment can be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C or the range composed of any two of them; the time of the first sintering treatment can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or the range composed of any two of them.

[0069] When the temperature of the first sintering treatment is lower than 400°C, it is likely to cause insufficient roasting during the second sintering treatment; when the temperature of the first sintering treatment is higher than 600°C, the particles of the first sintered product sample obtained are larger, and the particles are too large after the second sintering treatment.

[0070] In some specific embodiments of the present invention, in step (b), the temperature is raised to 400 - 600°C at a heating rate of 4 - 6°C / min.

[0071] In different embodiments, in step (b), the heating rate for raising the temperature to 400 - 600°C can be 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min or the range composed of any two of them.

[0072] In step (b), within the above range of the heating rate, it can balance ensuring efficiency and product performance, and avoid too fast heating rate, where the amount of volatile components removed in the low - temperature section is small, affecting the product performance.

[0073] In some specific embodiments of the present invention, in step (c), the temperature of the second sintering treatment is 600 - 800°C, and the time of the second sintering treatment is 4 - 8 h.

[0074] In different embodiments, in step (c), the temperature of the second sintering treatment can be 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C or the range composed of any two of them; the time of the second sintering treatment can be 4 h, 5 h, 6 h, 7 h, 8 h or the range composed of any two of them.

[0075] By controlling the temperature of the second sintering treatment within the above range, it can balance ensuring the degree of crystallization and avoiding too large finished product particles. When the temperature of the second sintering treatment is lower than 600°C, there are likely to be uncrystallized components or incomplete crystallization; when the temperature of the second sintering treatment is higher than 800°C, it is likely to cause too large finished product particles.

[0076] In some specific embodiments of the present invention, in step (c), the temperature is raised to the 600 - 800 °C at a heating rate of 4 - 6 °C / min.

[0077] In different embodiments, in step (c), the heating rate for raising the temperature to 600 - 800 °C can be 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min, 6 °C / min or a range composed of any two of them.

[0078] In step (c), the heating rate within the above range can balance ensuring efficiency and product performance.

[0079] In some specific embodiments of the present invention, the sintering temperature in step (c) is higher than the sintering temperature in step (b).

[0080] In actual operation, the sintering treatment can be carried out in a tube furnace, and the protective atmosphere can include atmospheres such as nitrogen or argon.

[0081] In some specific embodiments of the present invention, in step (c), the pulverization includes: pulverizing to D50 < 1.0 μm.

[0082] In some specific embodiments of the present invention, the solvent includes but is not limited to water.

[0083] The present invention also provides a positive electrode material prepared by using the preparation method of any one of the above positive electrode materials.

[0084] The present invention also provides a lithium - ion battery including any one of the above positive electrode materials.

[0085] In some specific embodiments of the present invention, the lithium - ion battery includes a positive electrode sheet; the positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on the positive electrode current collector; the positive electrode film includes any one of the above positive electrode materials.

[0086] In some specific embodiments of the present invention, the positive electrode film further includes a conductive agent and a binder. Among them, the conductive agent can be selected from any one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes (CNT), vapor - grown carbon fiber (VGCF); the binder can be selected from any one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), ethylene - propylene - non - conjugated diene terpolymer (ethylene - propylene - diene monomer, EPDM), and styrene - butadiene rubber.

[0087] In some specific embodiments of the present invention, the lithium-ion battery further includes a negative electrode sheet, a separator, and an electrolyte; the separator is disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the separator, and the negative electrode sheet can form an electrode core by winding or stacking.

[0088] In some specific embodiments of the present invention, the negative electrode sheet includes a metallic lithium sheet.

[0089] In some specific embodiments of the present invention, the separator includes any one of polypropylene (PP), polyethylene (PE), and PP / PE composite separator, and is not limited thereto. The electrolyte may include non-aqueous liquid electrolyte or solid electrolyte, etc.

[0090] Example 1

[0091] This example provides a preparation method of a positive electrode material, including the following steps:

[0092] (1) Weigh 1321.70 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ) 2 , 5.68 g of K 2 CO 3 , 23.35 g of Ce 2 (SO 4 ) 3 , 15.58 g of TiCl 4 , 215.26 g of sucrose, and 15071.09 g of water, mix them evenly to form a solution, and perform spray drying (drying temperature ≤ 150 °C) in a spray dryer to obtain a dried sample.

[0093] (2) Place the dried sample obtained in step (1) in a tubular furnace, under a nitrogen atmosphere, heat it to 600 °C at a rate of 5 °C / min, and keep it at a constant temperature for 10 h to obtain a primary sintered product.

[0094] (3) Add 460.34 g of LiNO 3 , 129.16 g of sucrose to the primary sintered product obtained in step (2), crush (crush to D50 < 1.0 μm) and mix them evenly, place them in a tubular furnace, under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min, and keep it at a constant temperature for 5 h to obtain a secondary sintered product; crush the secondary sintered product to obtain the positive electrode material Li 0.991 K 0.003 Ce 0.003 Ti0.003 Mn 0.7 Fe 0.3 PO 4 。

[0095] Example 2

[0096] This example provides a method for preparing a cathode material, which includes the following steps:

[0097] (1) Weigh 1321.70 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ) 2 , 4.35 g of Na 2 CO 3 , 13.02 g of SrCl 2 , 7.82 g of MgCl 2 , 215.26 g of sucrose, and 15071.09 g of water, mix them evenly to form a solution, and perform spray drying (drying temperature ≤ 150 °C) in a spray dryer to obtain a dried sample.

[0098] (2) Place the dried sample obtained in step (1) in a tube furnace, under a nitrogen atmosphere, heat it to 600 °C at a rate of 5 °C / min, and keep it at a constant temperature for 10 h to obtain a sintered product.

[0099] (3) Add 460.34 g of LiNO 3 , 129.16 g of sucrose, crush them (crush to D50 < 1.0 μm) and mix them evenly, place them in a tube furnace, under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min, and keep it at a constant temperature for 5 h, then crush the sintered material to obtain the cathode material Li 0.991 Na 0.003 Sr 0.003 Mg 0.003 Mn 0.7 Fe 0.3 PO 4 。

[0100] Example 3

[0101] This example provides a method for preparing a cathode material, which includes the following steps:

[0102] (1) Weigh 891.02 g of LiNO 3 , 1892.32 g of Fe(NO 3 )3 , 3000 g NH 4 H 2 PO 4 , 3266.93 g Mn(NO 3 ) 2 , 5.68 g K 2 CO 3 , 23.35 g Ce 2 (SO 4 ) 3 , 15.58 g TiCl 4 , 215.26 g sucrose, 15071.09 g water are mixed evenly to form a solution, and spray drying is carried out in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0103] (2) The dried sample obtained in step (1) is placed in a tube furnace. Under a nitrogen atmosphere, it is heated to 600 °C at a rate of 5 °C / min and kept at a constant temperature for 10 h to obtain a primary sintered product.

[0104] (3) 891.02 g LiNO 3 and 129.16 g sucrose are added to the primary sintered product obtained in step (2), crushed (crushed to D50 < 1.0 μm) and mixed evenly, placed in a tube furnace, and heated to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere and kept at a constant temperature for 5 h to obtain a secondary sintered product; the secondary sintered product is crushed to obtain the cathode material Li 0.991 K 0.003 Ce 0.003 Ti 0.003 Mn 0.7 Fe 0.3 PO 4 .

[0105] Example 4

[0106] This example provides a method for preparing a cathode material, including the following steps:

[0107] (1) Weigh 1425.63 g LiNO 3 , 1892.32 g Fe(NO 3 ) 3 , 3000 g NH 4 H 2 PO 4 , 3266.93 g Mn(NO 3 ) 2 , 5.68 g K 2 CO 3 , 23.35 g Ce 2 (SO 4 ) 3, 15.58 g of TiCl 4 , 215.26 g of sucrose, and 15071.09 g of water are mixed evenly to form a solution, which is spray-dried in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0108] (2) The dried sample obtained in step (1) is placed in a tubular furnace. Under a nitrogen atmosphere, it is heated to 600 °C at a rate of 5 °C / min and kept at a constant temperature for 10 h to obtain a primary sintered product.

[0109] (3) 356.41 g of LiNO is added to the primary sintered product obtained in step (2). 3 , 129.16 g of sucrose are pulverized (pulverized to D50 < 1.0 μm) and mixed evenly, placed in a tubular furnace, and heated to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere and kept at a constant temperature for 5 h to obtain a secondary sintered product; the secondary sintered product is pulverized to obtain the cathode material Li 0.991 K 0.003 Ce 0.003 Ti 0.003 Mn 0.7 Fe 0.3 PO 4 .

[0110] Example 5

[0111] This example provides a method for preparing a cathode material, which includes the following steps:

[0112] (1) Weigh 1321.70 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ) 2 , 17.04 g of K 2 CO 3 , 215.26 g of sucrose, and 15071.09 g of water are mixed evenly to form a solution, which is spray-dried in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0113] (2) The dried sample obtained in step (1) is placed in a tubular furnace. Under a nitrogen atmosphere, it is heated to 600 °C at a rate of 5 °C / min and kept at a constant temperature for 10 h to obtain a primary sintered product.

[0114] (3) 460.34 g of LiNO is added to the primary sintered product obtained in step (2). 3, 129.16 g of sucrose is pulverized (pulverized to D50 < 1.0 μm) and mixed evenly, placed in a tube furnace, under a nitrogen atmosphere, heated to 700 °C at a rate of 5 °C / min, and kept at a constant temperature for 5 h to obtain a secondary sintered product; the secondary sintered product is pulverized to obtain the cathode material Li 0.991 K 0.009 Mn 0.7 Fe 0.3 PO 4 。

[0115] Example 6

[0116] This example provides a method for preparing a cathode material, including the following steps:

[0117] (1) Weigh 1321.70 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ) 2 , 8.52 g of K 2 CO 3 , 23.37 g of TiCl 4 , 215.26 g of sucrose, and 15071.09 g of water are mixed evenly to form a solution, and spray-dried in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0118] (2) The dried sample obtained in step (1) is placed in a tube furnace, under a nitrogen atmosphere, heated to 600 °C at a rate of 5 °C / min, and kept at a constant temperature for 10 h to obtain a primary sintered product.

[0119] (3) Add 460.34 g of LiNO 3 and 129.16 g of sucrose pulverized (pulverized to D50 < 1.0 μm) and mixed evenly to the primary sintered product obtained in step (2), place it in a tube furnace, under a nitrogen atmosphere, heat to 700 °C at a rate of 5 °C / min, and keep at a constant temperature for 5 h to obtain a secondary sintered product; the secondary sintered product is pulverized to obtain the cathode material Li 0.991 K 0.0045 Ti 0.0045 Mn 0.7 Fe 0.3 PO 4 。

[0120] Comparative Example 1

[0121] Comparative Example 1 provides a method for preparing a cathode material, including the following steps:

[0122] (1) Weigh 1798.23 g of LiNO 3 , 1892.32 g of Fe(NO 3 ), 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ), 2 , 215.26 g of sucrose, and 15071.09 g of water, mix them evenly to form a solution, and carry out spray drying in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0123] (2) Place the dried sample obtained in step (1) in a tubular furnace. Under a nitrogen atmosphere, heat it to 600 °C at a rate of 5 °C / min and keep it at a constant temperature for 10 h to obtain a primary sintered product.

[0124] (3) Add 129.16 g of sucrose to the primary sintered product obtained in step (2), crush it (crush it to D50 < 1.0 μm) and mix it evenly, place it in a tubular furnace, under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min and keep it at a constant temperature for 5 h to obtain a secondary sintered product; crush the secondary sintered product to obtain the cathode material LiMn 0.7 Fe 0.3 PO 4 .

[0125] Comparative Example 2

[0126] Comparative Example 2 provides a method for preparing a cathode material, including the following steps:

[0127] (1) Weigh 1782.04 g of LiNO 3 , 1892.32 g of Fe(NO 3 ), 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ), 2 , 5.68 g of K 2 CO 3 , 23.35 g of Ce 2 (SO 4 ), 3 , 15.58 g of TiCl 4 , 215.26 g of sucrose, and 15071.09 g of water, mix them evenly to form a solution, and carry out spray drying in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0128] (2) Place the dried sample obtained in step (1) in a tube furnace. Under a nitrogen atmosphere, heat it to 600 °C at a rate of 5 °C / min and keep it at a constant temperature for 10 h to obtain a primary sintered product.

[0129] (3) Add 129.16 g of sucrose to the primary sintered product obtained in step (2), crush it (to a D50 < 1.0 μm), mix it evenly, place it in a tube furnace, under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min, and keep it at a constant temperature for 5 h to obtain a secondary sintered product; crush the secondary sintered product to obtain the cathode material Li 0.991 K 0.003 Ce 0.003 Ti 0.003 Mn 0.7 Fe 0.3 PO 4 。

[0130] Comparative Example 3

[0131] Comparative Example 3 provides a method for preparing a cathode material, including the following steps:

[0132] (1) Weigh 1321.70 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ) 2 , 215.26 g of sucrose, and 15071.09 g of water, mix them evenly to form a solution, and perform spray drying (drying temperature ≤ 150 °C) in a spray dryer to obtain a dried sample.

[0133] (2) Place the dried sample obtained in step (1) in a tube furnace. Under a nitrogen atmosphere, heat it to 600 °C at a rate of 5 °C / min and keep it at a constant temperature for 10 h to obtain a primary sintered product.

[0134] (3) Add 476.53 g of LiNO 3 , 129.16 g of sucrose to the primary sintered product obtained in step (2), crush it (to a D50 < 1.0 μm), mix it evenly, place it in a tube furnace, under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min, and keep it at a constant temperature for 5 h to obtain a secondary sintered product; crush the secondary sintered product to obtain the cathode material LiMn 0.7 Fe 0.3 PO 4 。

[0135] Comparative Example 4

[0136] Comparative Example 4 provides a method for preparing a cathode material, comprising the following steps:

[0137] (1) Weigh 377.63 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO 3 ) 2 , 5.68 g of K 2 CO 3 , 23.35 g of Ce 2 (SO 4 ) 3 , 15.58 g of TiCl 4 , 215.26 g of sucrose, and 15071.09 g of water, mix them evenly to form a solution, and perform spray drying in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0138] (2) Place the dried sample obtained in step (1) in a tube furnace, under a nitrogen atmosphere, heat it to 600 °C at a rate of 5 °C / min, and keep it at a constant temperature for 10 h to obtain a primary sintered product.

[0139] (3) Add 1404.41 g of LiNO 3 , 129.16 g of sucrose, crush them (crush to D50 < 1.0 μm) and mix them evenly, place them in a tube furnace, under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min, and keep it at a constant temperature for 5 h to obtain a secondary sintered product; crush the secondary sintered product to obtain the cathode material Li 0.991 K 0.003 Ce 0.003 Ti 0.003 Mn 0.7 Fe 0.3 PO 4 .

[0140] Comparative Example 5

[0141] Comparative Example 5 provides a method for preparing a cathode material, comprising the following steps:

[0142] (1) Weigh 1699.30 g of LiNO 3 , 1892.32 g of Fe(NO 3 ) 3 , 3000 g of NH 4 H 2 PO 4 , 3266.93 g of Mn(NO3 ) 2 、5.68 g of K 2 CO 3 、23.35 g of Ce 2 (SO 4 ) 3 、15.58 g of TiCl 4 、215.26 g of sucrose and 15071.09 g of water are mixed evenly to form a solution, which is spray-dried in a spray dryer (drying temperature ≤ 150 °C) to obtain a dried sample.

[0143] (2) The dried sample obtained in step (1) is placed in a tubular furnace. Under a nitrogen atmosphere, it is heated to 600 °C at a rate of 5 °C / min and kept at a constant temperature for 10 h to obtain a primary sintered product.

[0144] (3) 82.74 g of LiNO 3 、129.16 g of sucrose are crushed (crushed to D50 < 1.0 μm) and mixed evenly, placed in a tubular furnace, and heated to 700 °C at a rate of 5 °C / min under a nitrogen atmosphere and kept at a constant temperature for 5 h to obtain a secondary sintered product; the secondary sintered product is crushed to obtain the cathode material Li 0.991 K 0.003 Ce 0.003 Ti 0.003 Mn 0.7 Fe 0.3 PO 4 。

[0145] Experimental Example 1

[0146] To compare and illustrate the performance differences of the cathode materials prepared in different examples and comparative examples, the cathode materials prepared in each example and comparative example are made into batteries respectively, and the battery performance is tested. The specific battery manufacturing method and performance testing method are as follows.

[0147] Battery manufacturing method:

[0148] (1) 800 g of the cathode materials Li x A 1-x Mn y Fe 1-y PO 4 of Examples 1-6 and Comparative Examples 1-5, 100 g of conductive agent acetylene black, and 100 g of binder polyvinylidene fluoride (PVDF) are added to 800 g of N-methylpyrrolidone solution (NMP solution), stirred in a vacuum mixer for 2 h to prepare a cathode slurry; the slurry is evenly coated on aluminum foil, then placed in a vacuum drying oven at 120 °C for 12 h, and after rolling, it is punched into a 14 mm diameter circular sheet as the cathode plate.

[0149] (2) Assemble the positive electrode sheet, negative electrode sheet (lithium metal sheet with a diameter of 14.5 mm), separator (Celgard 2400 microporous polypropylene membrane), and electrolyte (1 mo1 / L LiPF 6 / EC + DMC (volume ratio 1:1)) into a CR2025 type button lithium-ion battery in a glove box filled with an inert atmosphere.

[0150] Battery performance test method: For the test batteries corresponding to Examples 1 to 6 and Comparative Examples 1 to 5 prepared, conduct charge and discharge tests using a lithium-ion battery charge and discharge test system under the condition of 25 ± 0.5 °C. Charge and discharge conditions: Charge termination voltage 4.3 V; discharge termination voltage 2 V; charge and discharge current density: 0.1C, 1C, 3C, 5C, for charge and discharge tests at different rates; charge and discharge current density: 1C, the capacity retention rate obtained after 2000 cycles is shown in Table 1 below.

[0151] Table 1 Performance test results of different batteries

[0152]

[0153]

[0154] From the above test results, it can be seen that the method of the present invention can directionally induce the incorporated metal elements to occupy the Li + site by adding lithium step by step in combination with the addition of doping elements, improving the doping efficiency and the arrangement mode of the crystal structure, etc., so that the cycle performance and rate performance of the battery are significantly improved.

[0155] Experimental Example 2

[0156] Figure 1 and Figure 2 are SEM images of the positive electrode materials provided in Example 1 of the present invention and Comparative Example 1 respectively. It can be seen from the figure that the particles of the positive electrode material prepared in Example 1 of the present invention are dispersed and the average sphericity is significantly increased to 0.82, while the average sphericity of the particles of the positive electrode material in Comparative Example 1 is 0.75. Among them, the sphericity refers to the ratio of the shortest diameter to the longest diameter of the particle, and the sphericity of a sphere is 1. The average value is determined as the average sphericity measurement result by randomly statistically analyzing 600 particles.

[0157] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a cathode material, characterized in that, it comprises the following steps: (a) Take a lithium source, an iron source, a phosphorus source, a manganese source, a carbon source, a doping element source and a solvent and mix them to form a mixed solution, and dry the mixed solution to obtain a dried sample; (b) Subject the dried sample to a first sintering treatment under a protective atmosphere to obtain a first sintered product; (c) Add a lithium source and a carbon source to the first sintered product, crush and mix them evenly, and subject them to a second sintering treatment under a protective atmosphere to obtain a second sintered product; (d) Crush the second sintered product to obtain the cathode material; wherein, in step (a), the dosage of the lithium source is 50% to 80% of the total amount of the lithium source; The chemical composition of the positive electrode material is Li x A 1-x Mn y Fe 1-y PO 4 ; A is a doping element, 0.9 ≤ x < 1, 0 ≤ y ≤ 1.

2. The method for preparing a cathode material according to claim 1, characterized in that, the molar ratio of the total amount of the lithium source, the iron source, the phosphorus source, the manganese source and the doping element source in terms of Li, Fe, P, Mn and the doping element is x﹕(1-y)﹕1﹕y﹕(1-x).

3. The method for preparing a cathode material according to claim 1 or 2, characterized in that, the doping element is a metal element.

4. The method for preparing a cathode material according to claim 1, characterized in that, the doping element includes at least one of Na, K, Sr, Mg, Ce and Ti.

5. The method for preparing a cathode material according to claim 1, characterized in that, the total mass of the carbon source is 2% to 8% of the mass of the cathode material.

6. The method for preparing a cathode material according to claim 1, characterized in that, the mass ratio of the carbon source in step (a) to the carbon source in step (c) is (1 to 2)﹕1.

7. The method for preparing a cathode material according to claim 1, characterized in that, the doping element source includes at least one of a carbonate, a hydrochloride and a sulfate of the doping element.

8. The method for preparing a cathode material according to claim 1, characterized in that, the doping element source includes at least one of sodium carbonate, potassium carbonate, strontium chloride, magnesium chloride, cerium sulfate and titanium tetrachloride.

9. The method for preparing a cathode material according to claim 1, characterized in that, in step (b), the temperature of the first sintering treatment is 400 to 600 °C, and the time of the first sintering treatment is 6 to 12 h.

10. The method for preparing a cathode material according to claim 9, characterized in that, in step (b), the temperature is raised to 400 to 600 °C at a heating rate of 4 to 6 °C / min.

11. The method for preparing a cathode material according to claim 1, characterized in that, in step (c), the temperature of the second sintering treatment is 600 to 800 °C, and the time of the second sintering treatment is 4 to 8 h.

12. The method for preparing a cathode material according to claim 11, characterized in that, in step (c), the temperature is raised to 600 to 800 °C at a heating rate of 4 to 6 °C / min.

13. A battery material prepared by using the method for preparing a cathode material according to any one of claims 1 to 12.

14. A lithium ion battery, It is characterized in that it includes the positive electrode material described in claim 13

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