Phosphate positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion positive electrode materials, in particular to a phosphate positive electrode material and a preparation method and application thereof. According to the present invention, the phosphate-based positive electrode material is provided, the phosphate-based positive electrode material comprises a phosphate core and a carbon coating layer coating the surface of the phosphate core, and the carbon coating layer is doped with a nitrogen element formed by sintering pyrolysis of an amino carbon source; the nitrogen element can interact with the surface of the phosphate positive electrode material, so that the agglomeration tendency among particles can be enhanced; micropores and defects on the surface of the material can be filled to a certain extent, and the specific surface area of the material is reduced, so that active sites on the surface of the phosphate positive electrode material are reduced, aggregates among particles become tighter, and the agglomeration is improved; meanwhile, the overall pH value is reduced, agglomeration and close packing of particles are facilitated, and wide application is more facilitated.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium-ion positive electrode materials, and in particular relates to a phosphate-based positive electrode material and a preparation method and application thereof. Background Art

[0002] Developing new energy sources is essential for addressing the increasingly pressing energy crisis and environmental pollution, and for achieving sustainable social development. As a new generation of green energy storage devices, lithium-ion batteries offer advantages such as high operating voltage, high energy density, a wide operating temperature range, no memory effect, long cycle life, and a clean, environmentally friendly design. They are an indispensable component of the new energy sector and have been widely used in energy storage, communications, national defense, and especially in new energy vehicles.

[0003] However, the automotive lithium-ion batteries currently produced in China still have problems such as poor endurance and difficulty in starting. The essence of this is that the energy density and power density of lithium-ion batteries cannot meet actual needs. At present, lithium iron phosphate with an olivine structure is still one of the mainstream positive electrode materials for energy storage and power lithium-ion batteries due to its advantages such as a wide range of raw material sources, low price, environmental friendliness, and good safety performance. Solid content is one of the important factors in evaluating electrode materials and needs to be paid attention to. Generally speaking, the higher the solid content of the slurry, the better, because the solid content is positively correlated with the active material density and surface density of the electrode. In addition, the inter-particle fluidity of high-solid content slurry is lower, the slurry stability will be better, and the efficiency during coating will be high. However, too high a solid content will cause other problems. First, it will cause greater wear on the stirring equipment. Second, the viscosity of high-solid content slurry is high, the fluidity is low, and the coating will be very difficult.

[0004] Therefore, there is an urgent need to provide a phosphate-based positive electrode material to ensure that after the positive electrode slurry is prepared, the slurry is within the coating viscosity range and the solid content of the positive electrode slurry can be increased at the same time. Summary of the Invention

[0005] The purpose of this application is to provide a phosphate-based positive electrode material and its preparation method and application, aiming to solve the problem in the prior art that the positive electrode slurry obtained from the phosphate-based positive electrode material cannot have normal viscosity and high solid content at the same time.

[0006] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0007] In a first aspect, the present application provides a phosphate-based positive electrode material, which includes a phosphate core and a carbon coating layer coated on the surface of the phosphate core, wherein the carbon coating layer is doped with nitrogen elements formed by sintering and pyrolysis of an amino carbon source.

[0008] In some embodiments, taking the total mass of the phosphate-based positive electrode material as 100%, the carbon content is 1.00 wt% to 1.02 wt%, and the nitrogen content is 2000 ppm to 8000 ppm.

[0009] In some embodiments, the phosphate-based cathode material has the following characteristics:

[0010] (a) Particle size D 50 2.30~3.60μm;

[0011] (b) The ratio of disorder to graphitization degree of carbon coating in Raman spectrum, ID / IG, is 0.842-0.845;

[0012] (c) Specific surface area is 3.43 to 5.42 m 2 / g;

[0013] (d) pH value is less than 10.0.

[0014] In a second aspect, the present application provides a method for preparing a phosphate-based positive electrode material, comprising the following steps:

[0015] A phosphate precursor is provided, the phosphate precursor is ground, and an amine carbon source is added in batches during the grinding process; wherein the amine carbon source is added in an amount of 0.2% to 20% of the total weight of the amine carbon source each time, and is added in 5 to 20 batches;

[0016] The ground phosphate precursor is sintered to obtain a phosphate positive electrode material with a carbon coating layer doped with nitrogen.

[0017] In some embodiments, the amine carbon source includes one or more of menthylamine, formanilide, dimethylamide, nicotinamide, cyclopropanamide, erucamide, iodoacetamide, caprolactam, and N-tert-butylpropionamide.

[0018] In some embodiments, based on the total mass of the phosphate-based precursor being 100%, the amount of the amino carbon source added is 0.5% to 10%.

[0019] In some embodiments, the specific sintering method is: two-stage high and low temperature sintering in an inert atmosphere; wherein the first stage low temperature sintering temperature is 380-460°C, the time is 6-12 hours, and the second stage high temperature sintering temperature is 720-800°C, the time is 8-12 hours.

[0020] In some embodiments, the preparation method of the phosphate precursor includes the following steps: mixing at least an iron source, a lithium source, a phosphorus source, and a carbon source, adding acid to dissolve and diluting with water, heating and stirring until the solution evaporates to obtain a phosphate precursor.

[0021] In some embodiments, the lithium source is selected from at least one of lithium hydroxide, lithium phosphate, lithium acetate, lithium oxide, lithium carbonate, lithium nitrate, and lithium sulfate.

[0022] In some embodiments, the phosphorus source is selected from at least one of phosphoric acid, ammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, sodium hydrogen phosphate, and diammonium hydrogen phosphate.

[0023] In some embodiments, the iron source is selected from at least one of ferric nitrate nonahydrate, ferrous oxalate, ferrous sulfate, and ferrous acetate.

[0024] In some embodiments, the carbon source is selected from at least one of dopamine, glucose, sucrose, starch, carbon nanotubes, and graphene.

[0025] In some embodiments, the acid is selected from at least one of concentrated nitric acid, concentrated hydrochloric acid, phosphoric acid, a mixed acid solution of concentrated nitric acid and phosphoric acid, and a mixed acid solution of phosphoric acid and hydrochloric acid.

[0026] In some embodiments, based on the mass of the phosphate precursor being 100%, the element contents of the lithium source, the iron source, and the phosphorus source are in the order of 4.6% to 6.5%, 33.7% to 35%, and 18.7% to 19.8%.

[0027] In some embodiments, based on the mass of the phosphate precursor being 100%, the amount of the added carbon source is 20% to 50%.

[0028] In a third aspect, the present application provides a phosphate-based positive electrode slurry, which includes a phosphate-based positive electrode material, a conductive agent, and a binder. The phosphate-based positive electrode slurry has a solid content of 54% to 70% and a discharge viscosity of 8000 to 12000 mPa·s.

[0029] The phosphate-based positive electrode material is the above-mentioned phosphate-based positive electrode material or is prepared by the above-mentioned method for preparing the phosphate-based positive electrode material.

[0030] In a fourth aspect, the present application discloses a lithium-ion battery comprising the above-mentioned phosphate-based positive electrode slurry.

[0031] The first aspect of the present application provides a phosphate-based cathode material, which includes a phosphate core and a carbon coating layer coated on the surface of the phosphate core, wherein the carbon coating layer is doped with nitrogen formed by sintering and pyrolysis of an amino carbon source. The provided amino carbon source has an amino functional group in its molecular structure, which forms nitrogen after sintering and pyrolysis; it can interact with the surface of the phosphate-based cathode material. On the one hand, it can change the charge distribution on the surface of the phosphate-based cathode material, thereby enhancing the tendency of particles to agglomerate; on the other hand, the introduction of nitrogen can effectively fill the microporous structure on the surface of the phosphate cathode material and repair crystal defects, thereby reducing the exposure of surface active sites by reducing the specific surface area of the material, thereby promoting close agglomeration between particles and improving the overall density of the material. Further research has found that the basic groups released by the amino carbon source during pyrolysis can react in situ with the acidic sites on the surface of the material to reduce the overall pH value, ultimately achieving orderly stacking of particles and densified structure construction. At the same time, the interaction between the phosphate-based cathode material and other components, such as the binder, can be improved, allowing them to better combine and form a stable structure, thereby increasing the stability and solid content of the prepared phosphate-based cathode material slurry, which is conducive to wide application. Therefore, by adding an amino carbon source, the specific surface area and pH value of the phosphate-based cathode material can be reduced, thereby achieving the purpose of increasing the solid content of the phosphate-based cathode material.

[0032] The second aspect of the present application provides a method for preparing a phosphate-based positive electrode material. The preparation method provides a phosphate-based precursor, and then prepares a coating layer by adding an amino carbon source in small amounts and multiple times to ensure that the obtained coating layer has a uniform distribution of nitrogen elements. The preparation method is simple, does not require large instruments and equipment, and is conducive to industrial production.

[0033] The third aspect of the present application provides a phosphate-based positive electrode slurry, which includes the above-mentioned phosphate-based positive electrode material. The obtained phosphate-based positive electrode slurry has a solid content of 54% to 70%, and a discharge viscosity of 8000 to 12000 mPa·s. It can be seen that the obtained phosphate-based positive electrode slurry has high stability and solid content, and has a suitable viscosity at room temperature, which is beneficial to improving the electrochemical performance of the positive electrode during application.

[0034] A fourth aspect of the present application provides a lithium-ion battery, comprising the above-mentioned phosphate-based positive electrode slurry. Since the provided phosphate-based positive electrode slurry has high stability and solid content, and has a suitable viscosity at room temperature, the electrode sheet prepared using the phosphate-based positive electrode material is used in the lithium-ion battery, so the obtained lithium-ion battery has excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1 These are SEM images of samples of phosphate-based positive electrode materials obtained in Examples A1 to A3 and Comparative Example A1.

[0037] Figure 2 1C current density, the charge and discharge curves of the secondary batteries assembled in Examples B1 to B3 and Comparative Example B1. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0039] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0040] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0041] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0042] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0043] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass in the examples of this application may be μg, mg, g, kg, etc., which are mass units known in the chemical industry.

[0044] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being referred to. For example, a first XX could also be referred to as a second XX, and similarly, a second XX could also be referred to as a first XX, without departing from the scope of the embodiments of this application. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0045] A first aspect of an embodiment of the present application provides a phosphate-based positive electrode material, which includes a phosphate core and a carbon coating layer coated on the surface of the phosphate core, wherein the carbon coating layer is doped with nitrogen elements formed by sintering and pyrolysis of an amino carbon source.

[0046] The first aspect of the embodiment of the present application provides a phosphate-based positive electrode material, which includes a phosphate core and a carbon coating layer coated on the surface of the phosphate core, wherein the carbon coating layer is doped with nitrogen formed by sintering and pyrolysis of an amino carbon source. The provided amino carbon source has an amino functional group in its molecular structure, which forms nitrogen after sintering and pyrolysis; it can interact with the surface of the phosphate-based positive electrode material. On the one hand, it can change the charge distribution on the surface of the phosphate-based positive electrode material, thereby enhancing the tendency of agglomeration between particles; on the other hand, the introduction of nitrogen can effectively fill the microporous structure on the surface of the phosphate positive electrode material and repair crystal defects, thereby reducing the exposure of surface active sites by reducing the specific surface area of the material, thereby promoting close agglomeration between particles and improving the overall density of the material. Further research found that the basic groups released by the amino carbon source during the pyrolysis process can undergo in-situ neutralization reaction with the acidic sites on the surface of the material, reducing the overall pH value, and ultimately achieving orderly stacking of particles and densified structure construction. At the same time, the interaction between the phosphate-based cathode material and other components, such as the binder, can be improved, allowing them to better combine and form a stable structure, thereby increasing the stability and solid content of the prepared phosphate-based cathode material slurry, which is conducive to wide application. Therefore, by adding an amino carbon source, the specific surface area and pH value of the phosphate-based cathode material can be reduced, thereby achieving the purpose of increasing the solid content of the phosphate-based cathode material.

[0047] In some embodiments, taking the total mass of the phosphate-based positive electrode material as 100%, the carbon content is 1.00 wt% to 1.02 wt%, and the nitrogen content is 2000 ppm to 8000 ppm.

[0048] In some specific embodiments, the carbon content includes, but is not limited to, typical but non-limiting values such as 1.00 wt%, 1.01 wt%, and 1.02 wt%, based on the total mass of the phosphate-based positive electrode material as 100%. If the carbon content is too high, the coating layer will be too thick, affecting the function of the positive electrode material. If the carbon content is too low, the coating layer will be too thin, and a dense coating layer will not be formed.

[0049] In some specific embodiments, the nitrogen content includes, but is not limited to, typical but non-limiting values such as 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, and 8000 ppm, based on the total mass of the phosphate-based positive electrode material as 100%. If the nitrogen content is too low, it is not conducive to reducing the specific surface area and pH value of the phosphate-based positive electrode material, and thus, it is not conducive to improving the solid content and viscosity of the phosphate-based positive electrode slurry.

[0050] In some embodiments, the phosphate-based cathode material has the following characteristics:

[0051] (a) Particle size D 50 2.30~3.60μm;

[0052] (b) The ratio of disorder to graphitization degree of carbon coating in Raman spectrum, ID / IG, is 0.842-0.845;

[0053] (c) Specific surface area is 3.43 to 5.42 m 2 / g;

[0054] (d) pH value is less than 10.0.

[0055] In some specific embodiments, the particle size D of the phosphate-based cathode material is 50 Typical but non-limiting values include but are not limited to 2.30 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, etc.

[0056] In some specific embodiments, the ratio of the degree of disorder to the degree of graphitization of the carbon coating layer in the Raman spectrum of the phosphate-based positive electrode material, ID / IG, includes, but is not limited to, typical but non-limiting values such as 0.842, 0.843, 0.844, and 0.845. Controlling the ratio of the degree of disorder to the degree of graphitization of the carbon coating layer in the Raman spectrum of the phosphate-based positive electrode material, ID / IG, to be within the range of 0.84 to 0.9 primarily indicates that the carbon coating layer of the phosphate-based positive electrode material has good density and good degree of graphitization.

[0057] In some specific embodiments, the specific surface area of the phosphate-based cathode material includes but is not limited to 3.43 m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 / g, 5.42m 2 Within this specific surface area range, phosphate-based cathode materials have the characteristics of good primary particle dispersion and large single particle size.

[0058] In some specific embodiments, the pH value of the phosphate-based positive electrode material is less than 10.0. The processing performance of the phosphate-based positive electrode material within this range is better. If the pH is greater than 10, during the preparation of the slurry, the alkaline groups will cause the long chains of PVDF to break, destroying the adhesion of PVDF and causing the processing performance of the LFP material to deteriorate.

[0059] A second aspect of the present invention provides a method for preparing a phosphate-based positive electrode material, comprising the following steps:

[0060] S01 provides a phosphate precursor, the phosphate precursor is dried and ground into a powder, and an amine carbon source is added during the grinding process; wherein the amine carbon source is added in an amount of 0.2% to 20% of the total mass of the amine carbon source each time, in 5 to 20 steps;

[0061] S02. Sintering the ground phosphate precursor to obtain a phosphate positive electrode material with a carbon coating layer doped with nitrogen.

[0062] The second aspect of the embodiment of the present application provides a method for preparing a phosphate-based positive electrode material. The preparation method provides a phosphate-based precursor, and then prepares a coating layer by adding an amino carbon source in small amounts and multiple times to ensure that the obtained coating layer is uniformly distributed with nitrogen elements. The preparation method is simple, does not require large instruments and equipment, and is conducive to industrial production.

[0063] In step S01, a phosphate precursor is provided, the phosphate precursor is ground, and an amino carbon source is added in batches during the grinding process; wherein the amino carbon source is added in an amount of 0.2% to 20% of the total mass of the amino carbon source each time, and is completed in 5 to 20 times.

[0064] In some embodiments, the phosphate precursor can be prepared using a liquid-phase method or a solid-phase method. Liquid-phase methods include, but are not limited to, sol-gel methods, coprecipitation methods, hydrothermal / solvothermal methods, and solvent evaporation methods; solid-phase methods include, but are not limited to, mechanical ball milling methods and high-temperature solid-phase reaction methods.

[0065] In some embodiments, a method for preparing a phosphate precursor comprises the following steps: mixing at least an iron source, a lithium source, a phosphorus source, and a carbon source, adding an acid to dissolve the mixture, diluting the mixture with water, and heating and stirring the mixture until the solution evaporates, thereby obtaining a phosphate precursor. The heating temperature for the precursor preparation is 100-130°C, and the stirring reaction time is 12-24 hours.

[0066] In some embodiments, the lithium source is selected from at least one of lithium hydroxide, lithium phosphate, lithium acetate, lithium oxide, lithium carbonate, lithium nitrate, and lithium sulfate.

[0067] In some embodiments, the phosphorus source is selected from at least one of phosphoric acid, ammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, sodium hydrogen phosphate, and diammonium hydrogen phosphate.

[0068] In some embodiments, the iron source is selected from at least one of ferric nitrate nonahydrate, ferrous oxalate, ferrous sulfate, and ferrous acetate.

[0069] In some embodiments, the carbon source is selected from at least one of dopamine, glucose, sucrose, starch, carbon nanotubes, and graphene.

[0070] In some embodiments, the acid is selected from at least one of concentrated nitric acid, concentrated hydrochloric acid, phosphoric acid, a mixed acid solution of concentrated nitric acid and phosphoric acid, and a mixed acid solution of phosphoric acid and hydrochloric acid.

[0071] In some embodiments, the raw materials for preparing the phosphate-based precursor also include a manganese source, and the manganese source includes at least one of manganese dioxide, manganese trioxide, manganese tetraoxide, manganese sulfate, manganese nitrate, manganese chloride, manganese dihydrogen phosphate, manganese oxalate, manganese acetate, manganese citrate, manganese glycinate, and manganese gluconate.

[0072] In some embodiments, the raw materials for preparing the phosphate precursor also include a doping source, and the doping elements in the doping source include at least one element selected from titanium, vanadium, chromium, copper, magnesium, aluminum, zinc, cobalt, nickel, tin, niobium, tungsten, zirconium, tantalum, cerium, europium and fluorine.

[0073] In some embodiments, based on the mass of the phosphate precursor being 100%, the element contents of the lithium source, the iron source, and the phosphorus source are in the order of 4.6% to 6.5%, 33.7% to 35%, and 18.7% to 19.8%.

[0074] In some embodiments, based on the mass of the phosphate precursor being 100%, the amount of the added carbon source is 20% to 50%.

[0075] In some embodiments, the phosphate precursor is ground. In some embodiments, the grinding step further includes a drying step, wherein the drying step includes, but is not limited to, one or more of spray drying, vacuum drying, and freeze drying, and the drying time is 8 to 18 hours.

[0076] Furthermore, an amino carbon source is added during the grinding process.

[0077] In some embodiments, the amine carbon source includes one or more of menthylamine, formanilide, dimethylamide, nicotinamide, cyclopropanamide, erucamide, iodoacetamide, caprolactam, and N-tert-butylpropionamide. These amine carbon sources are preferred because, firstly, they have an amino structure, which can lower the pH value of the finished phosphate-based cathode material; and, secondly, they are all small molecule carbon sources, which can inhibit the excessive growth and agglomeration of phosphate-based cathode material particles, forming nano- or submicron-sized particles, thereby shortening the lithium ion diffusion path.

[0078] In some embodiments, the amount of the amino carbon source added is 0.5% to 10%, based on the total mass of the phosphate precursor being 100%. If the amount of the amino carbon source added is too much, the carbon content will be too high and the residual carbon content will increase, thereby increasing the specific surface area and the solid content of the slurry. If the amount of the amino carbon source added is too little, the effect of modifying the carbon layer will not be achieved, and the improvement in processing performance will not be obvious. In some specific embodiments, based on the total mass of the phosphate precursor being 100%, the amount of the amino carbon source added includes but is not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%.

[0079] Furthermore, the amino carbon source is added in 5 to 20 portions at a rate of 0.2% to 20% of the total weight of the amino carbon source. The amino carbon source is added in small, multiple additions to ensure full and uniform contact between the amino carbon source and the phosphate precursor, preventing segregation.

[0080] In step S02 , the ground phosphate precursor is sintered to obtain a phosphate positive electrode material with a carbon coating layer doped with nitrogen.

[0081] In some embodiments, the sintering method comprises a two-stage high-low temperature sintering process under an inert atmosphere; wherein the first stage is a low-temperature sintering process at a temperature of 380-460°C for 6-12 hours, and the second stage is a high-temperature sintering process at a temperature of 720-800°C for 8-12 hours. The purpose of the first stage being a low-temperature sintering process and the second stage being a high-temperature sintering process is to prevent the phosphate-based cathode material particles from becoming too large, for example, with most particles exceeding 800 nm, which would affect electrical performance.

[0082] A third aspect of the present application provides a phosphate-based positive electrode slurry, comprising a phosphate-based positive electrode material, a conductive agent, and a binder. The phosphate-based positive electrode slurry has a solid content of 54% to 70% and a discharge viscosity of 8000 to 12000 mPa·s.

[0083] The phosphate-based positive electrode material is the aforementioned phosphate-based positive electrode material or is prepared by the aforementioned method for preparing the phosphate-based positive electrode material. A third aspect of the present application provides a phosphate-based positive electrode slurry, comprising the aforementioned phosphate-based positive electrode material. The obtained phosphate-based positive electrode slurry has a solids content of 54% to 70% and a discharge viscosity of 8,000 to 12,000 mPa·s. It can be seen that the obtained phosphate-based positive electrode slurry has high stability and solids content, and has a suitable viscosity at room temperature, which is beneficial for improving the electrochemical performance of the positive electrode during application.

[0084] In some specific embodiments, the phosphate-based cathode slurry of the present application has a high solid content characteristic. For example, under the premise of adding an amino carbon source, the solid content of the phosphate-based cathode material prepared by the liquid phase method can be above 60%, and the solid content of the phosphate-based cathode material prepared by other methods (such as the solid phase method) can be increased by 2 to 4 percentage points. Specifically, the phosphate-based cathode material prepared by adding an amino carbon source can increase the original 54% solid content to 56% to 58%, and the original 56% solid content can be increased to 58% to 60%. If the original solid content is 60%, it can be increased to about 64%.

[0085] In some specific embodiments, the phosphate-based positive electrode slurry consists of the following components in percentage by mass:

[0086] Phosphate-based cathode materials 80% to 95%;

[0087] Conductive agent 2% to 10%;

[0088] Binder 1% to 5%;

[0089] The solvent was replenished to 100%;

[0090] In some embodiments, the weight percentage of the phosphate-based positive electrode material is 80% to 95%, based on the total weight of the phosphate-based positive electrode slurry being 100%. In some specific embodiments, the weight percentage of the phosphate-based positive electrode material includes, but is not limited to, typical but non-limiting values such as 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, and 95%, based on the total weight of the phosphate-based positive electrode slurry being 100%. The phosphate-based positive electrode material is the above-mentioned phosphate-based positive electrode material or is prepared by the above-mentioned method for preparing the phosphate-based positive electrode material.

[0091] In some embodiments, the weight percentage of the conductive agent is 2% to 10% based on the total weight of the phosphate-based positive electrode slurry being 100%. In some specific embodiments, the weight percentage of the conductive agent includes, but is not limited to, typical but non-limiting values such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10% based on the total weight of the phosphate-based positive electrode slurry being 100%.

[0092] In some embodiments, the binder content is 1% to 5% by weight, based on the total mass of the phosphate-based positive electrode slurry being 100%. In some specific embodiments, the binder content includes, but is not limited to, 1%, 2%, 3%, 4%, and 5% by weight, based on the total mass of the phosphate-based positive electrode slurry being 100%.

[0093] In some embodiments, solvent replenishment is provided to 100%.

[0094] A fourth aspect of the embodiments of the present application discloses a lithium-ion battery, comprising the above-mentioned phosphate-based positive electrode slurry.

[0095] A lithium-ion battery provided in the fourth aspect of an embodiment of the present application includes the above-mentioned phosphate-based positive electrode slurry. Since the provided phosphate-based positive electrode slurry has high stability and solid content, and has a suitable viscosity at room temperature, the electrode sheet prepared using the phosphate-based positive electrode material is used in the lithium-ion battery, so the obtained lithium-ion battery has excellent electrochemical properties.

[0096] The following describes the details in conjunction with specific embodiments.

[0097] Example A1

[0098] Phosphate-based positive electrode material and preparation method thereof

[0099] (1) 75.75 g of ferric nitrate nonahydrate, 21.72 g of phosphoric acid, 10.41 g of lithium carbonate, and 60 g of glucose were added to a beaker, and an appropriate amount of nitric acid was poured into the beaker to dissolve the mixture, and then an appropriate amount of water was added to dilute the mixture. The mixture was placed on a heated stirrer at 85° C. and stirred for 12 hours until the water evaporated to obtain a phosphate-based cathode material precursor.

[0100] (2) The LFP precursor prepared in step (1) was freeze-dried and then ground, and 1.5 g of menthylamine weighed in advance was added to the mortar in small amounts and multiple times for grinding; wherein, the amino carbon source was added in 5 times with 0.3 g added each time;

[0101] (3) The ground sample in step (2) is placed in a tubular furnace under an argon atmosphere, and the sintering process is set as follows: the first stage is 380°C, sintering for 6 hours, and the second stage is sintering at 780°C for 8 hours. The heating rate of the two stages is 3°C / min. After the sintering is completed, the phosphate-based positive electrode material can be obtained.

[0102] Example A2

[0103] Phosphate-based positive electrode material and preparation method thereof

[0104] Compared with Example A1, the addition amount of menthyl amide was modified to "3.0 g"; the other steps remained unchanged.

[0105] Example A3

[0106] Phosphate-based positive electrode material and preparation method thereof

[0107] Compared with Example A1, the addition amount of menthyl amide was modified to "6.0 g", and the other steps remained unchanged.

[0108] Example A4

[0109] Phosphate-based positive electrode material and preparation method thereof

[0110] Compared with Example A1, "menthyl amide" was changed to "formanilide"; the other steps remained unchanged.

[0111] Example A5

[0112] Phosphate-based positive electrode material and preparation method thereof

[0113] Compared with Example A1, "menthyl amide" was changed to "dimethylamide"; the other steps remained unchanged.

[0114] Example A6

[0115] Phosphate-based positive electrode material and preparation method thereof

[0116] Compared with Example A1, the amount of glucose added was modified to "70 g"; the other steps remained unchanged.

[0117] Example A7

[0118] Phosphate-based positive electrode material and preparation method thereof

[0119] Compared with Example A1, the amount of glucose added was modified to "50 g"; the other steps remained unchanged.

[0120] Example A8

[0121] Phosphate-based positive electrode material and preparation method thereof

[0122] Compared with Example A1, "nitric acid" is changed to "a mixed acid solution of concentrated nitric acid and phosphoric acid"; the other steps remain unchanged.

[0123] Example A9

[0124] Phosphate-based positive electrode material and preparation method thereof

[0125] Compared with Example A1, "nitric acid" is changed to "a mixed acid solution of phosphoric acid and hydrochloric acid"; the other steps remain unchanged.

[0126] Example A10

[0127] Phosphate-based positive electrode material and preparation method thereof

[0128] Compared with Example A1, the sintering process in step (3) was modified as follows: the first stage was sintered at 460°C for 10 hours, and the second stage was sintered at 800°C for 10 hours. The heating rate in both stages was 3°C / min. After the sintering, the phosphate-based positive electrode material was obtained. The remaining steps remained unchanged.

[0129] Example A11

[0130] Phosphate-based positive electrode material and preparation method thereof

[0131] Compared with Example A1, the sintering process in step (3) was modified as follows: the first stage was sintered at 400°C for 12 hours, and the second stage was sintered at 720°C for 12 hours. The heating rate in both stages was 3°C / min. After the sintering, the phosphate-based positive electrode material was obtained. The remaining steps remained unchanged.

[0132] Comparative Example A1

[0133] Phosphate-based positive electrode material and preparation method thereof

[0134] (1) 75.75 g of ferric nitrate nonahydrate, 21.72 g of phosphoric acid, 10.41 g of lithium carbonate, and 60 g of glucose were added to a beaker, and an appropriate amount of nitric acid was poured into the beaker to dissolve the mixture. An appropriate amount of water was added to dilute the mixture, and the mixture was placed on a heated stirrer at 85°C and stirred for 12 hours until the water evaporated to obtain an LFP precursor.

[0135] (2) freeze-drying the LFP precursor obtained in step (1) and grinding it;

[0136] (3) The ground sample in step (2) is placed in a tubular furnace under an argon atmosphere, and the sintering process is set as follows: the first stage is 380°C, calcined for 6 hours, and the second stage is calcined at 780°C for 8 hours. The heating rate of the two stages is 3°C / min. After the sintering is completed, the phosphate-based positive electrode material can be obtained.

[0137] Comparative Example A2

[0138] Compared with Example A1, the difference is that: (2) the LFP precursor of step (1) is freeze-dried and ground, and 1.5 g of menthylamine weighed in advance is poured into the mortar and ground at once. The other steps remain unchanged.

[0139] Examples B1 to B3

[0140] Positive electrode slurry and positive electrode sheet

[0141] A phosphate-based positive electrode slurry, the phosphate-based positive electrode slurry consisting of the following components in percentage by mass:

[0142] Phosphate-based cathode materials 80%;

[0143] Conductive agent 10%;

[0144] Binder 10%;

[0145] The solvent was replenished to 100%;

[0146] The phosphate-based positive electrode materials are provided in Examples A1 to A3 respectively.

[0147] Positive electrode

[0148] A current collector is provided, and the positive electrode slurry is coated on the surface of the current collector to obtain the positive electrode sheets of Examples B1 to B3.

[0149] Examples B4 to B7

[0150] Positive electrode slurry and positive electrode sheet

[0151] A phosphate-based positive electrode slurry, the phosphate-based positive electrode slurry consisting of the following components in percentage by mass:

[0152] Phosphate-based cathode materials 85%;

[0153] Conductive agent 5%;

[0154] Binder 5%;

[0155] The solvent was replenished to 100%;

[0156] Among them, the phosphate-based positive electrode material is provided by Examples A4 to A7.

[0157] Positive electrode

[0158] A current collector is provided, and the positive electrode slurry is coated on the surface of the current collector to obtain the positive electrode sheets of Examples B4 to B7.

[0159] Examples B8 to B11

[0160] Positive electrode slurry and positive electrode sheet

[0161] A phosphate-based positive electrode slurry, the phosphate-based positive electrode slurry consisting of the following components in percentage by mass:

[0162] Phosphate-based cathode material 95%;

[0163] Conductive agent 2%;

[0164] Binder 3%;

[0165] The solvent was replenished to 100%;

[0166] Among them, the phosphate-based positive electrode material is provided by Examples A8 to A11.

[0167] Positive electrode

[0168] A current collector is provided, and the positive electrode slurry is coated on the surface of the current collector to obtain the positive electrode sheets of Examples B8 to B11.

[0169] Comparative Examples B1-B2

[0170] Positive electrode slurry and positive electrode sheet

[0171] A phosphate-based positive electrode slurry, the phosphate-based positive electrode slurry consisting of the following components in percentage by mass:

[0172] Phosphate-based cathode materials 80%;

[0173] Conductive agent 10%;

[0174] Binder 10%;

[0175] The solvent was replenished to 100%;

[0176] The phosphate-based positive electrode material is provided in Comparative Examples A1 to A2.

[0177] Positive electrode

[0178] A current collector is provided, and the positive electrode slurry is coated on the surface of the current collector to obtain the positive electrode sheets of Comparative Examples B1 and B2.

[0179] secondary batteries

[0180] The positive electrode sheets of Examples B1 to B11 and Comparative Examples B1 to B2 were assembled to obtain a secondary battery.

[0181] Property Test

[0182] (1) The samples of the phosphate-based cathode materials obtained in Examples A1 to A11 and Comparative Examples A1 to A2 were tested and analyzed for carbon content, compacted density, ID / IG, specific surface area, pH, and particle size.

[0183] The instruments and equipment involved in the test are as follows:

[0184] Compaction density: UTM7305 electronic testing press;

[0185] Carbon content: high frequency carbon and sulfur analyzer;

[0186] Specific surface area: Tristar 3020 specific surface area analyzer, nitrogen adsorption method test;

[0187] pH: pHS-3C pH meter, the cathode material sample was mixed with distilled water in a ratio of 1:9, and after standing, the supernatant was taken to test the pH value;

[0188] Particle size: Measured using a Malvern 3000 laser particle size analyzer. Parameters: material refractive index 1.692, dispersion medium water (refractive index 1.33), ultrasound intensity 30%, stirring speed 2000 rpm. After adding the stirred sample to a specified opacity of 8%-12%, internal ultrasound was activated and testing began after 1 minute.

[0189] (2) The solid content and discharge viscosity of the positive electrode slurries obtained in Examples B1 to B11 and Comparative Examples B1 to B2 were tested and analyzed.

[0190] The discharge viscosity analysis step includes: the prepared positive electrode slurry is allowed to stand for 10 minutes before discharging the slurry. The viscosity value is recorded as the discharge viscosity using a Dveslvtjo rotary viscometer (BROOKFIELD). The test conditions are: 25°C, 12 rpm, a 64-spindle when the slurry viscosity is not less than 2000 mPa·s, and a 62-spindle when the slurry viscosity is less than 2000 mPa·s. The measurement is repeated three times and the average value is calculated.

[0191] (3) The obtained secondary battery was subjected to performance testing, and conventional testing (0.1C and 1C) was performed on a blue light test system at 25°C.

[0192] Result Analysis

[0193] (1) The results of the analysis of the samples of the phosphate-based positive electrode materials obtained in Examples A1 to A11 and Comparative Examples A1 to A2 are shown in Table 1 below. It can be seen that the carbon content of the phosphate-based positive electrode materials obtained in Examples A1 to A11 is ≤1.11% compared with the materials in Comparative Examples A1 to A2, and the carbon content of the positive electrode materials in the comparative examples is ≥1.2%. It can be seen that the carbon content of the positive electrode materials in the examples is lower; in terms of specific surface area, the specific surface area of the positive electrode materials in the examples is 3.43–5.78 m 2 / g, and the specific surface area of the positive electrode material of the comparative example is 7.12–7.45m 2 / g, it can be seen that the specific surface area of the positive electrode materials of the examples is significantly lower. Regarding pH, the pH of the positive electrode materials of the examples is 9.35-9.99, while the pH of the positive electrode materials of the comparative examples is 10.13-10.15, indicating that the pH of the positive electrode materials of the examples is significantly lower. Furthermore, particle size analysis shows that the particle size distribution of the positive electrode materials of the examples is more concentrated. Furthermore, the ID / IG values of the positive electrode materials of the examples vary slightly, indicating that the degree of graphitization does not differ significantly between the samples.

[0194] In the embodiment, due to the introduction of an amino carbon source, nitrogen elements are formed by sintering and pyrolysis of the amino carbon source; the nitrogen elements can interact with the surface of the phosphate-based positive electrode material, which can enhance the tendency of particles to agglomerate; and can fill the micropores and defects on the surface of the material to a certain extent, reduce its specific surface area, and thereby reduce the active sites on the surface of the phosphate-based positive electrode material, making the agglomerates between the particles more compact and improving the agglomeration; at the same time, the overall pH value is reduced, which is conducive to the agglomeration and close stacking of the particles.

[0195] Table 1

[0196]

[0197]

[0198] further, Figure 1 These are SEM images of samples of phosphate-based cathode materials obtained in Examples A1 to A3 and Comparative Example A1. It can be seen that the phosphate-based cathode materials of Examples A1 to A3 have better dispersibility and discreteness, and particle adhesion is improved.

[0199] (2) The solid content and discharge viscosity of the positive electrode slurries obtained in Examples B1 to B11 and Comparative Examples B1 to B2 were tested and analyzed. As shown in Table 2, it can be seen that in the positive electrode slurries obtained in Examples B1 to B11, a higher solid content is ensured while the discharge viscosity is also controlled to be lower, ensuring that the obtained positive electrode slurries are more advantageous for use in lithium-ion batteries.

[0200] Table 2

[0201]

[0202]

[0203] (3) Analysis of electrochemical properties of secondary batteries

[0204] like Figure 2 As shown, Figure 2 The charge and discharge curves of the secondary batteries assembled in Examples B1 to B3 and Comparative Example B1 at a current density of 1C show that the carbon coating layers in the positive electrode materials of the secondary batteries of Examples B1 to B3 are doped with N elements obtained by sintering an amino carbon source. Therefore, compared with Comparative Example B1, the charge and discharge platforms of the secondary batteries of Examples B1 to B3 are prolonged, the battery polarization is weakened, and the 1C discharge performance is improved.

[0205] In summary, the phosphate-based cathode material provided in the embodiments of the present application includes a phosphate core and a carbon coating layer coated on the surface of the phosphate core, wherein the carbon coating layer is doped with nitrogen elements formed by sintering and pyrolysis of an amino carbon source; the molecular structure of the amino carbon source provided has an amino functional group, which forms nitrogen elements after sintering and pyrolysis; it can interact with the surface of the phosphate-based cathode material. On the one hand, it can change the charge distribution on the surface of the phosphate-based cathode material, thereby enhancing the tendency of agglomeration between particles; on the other hand, the introduction of nitrogen elements can effectively fill the microporous structure on the surface of the phosphate cathode material and repair crystal defects, thereby reducing the exposure of surface active sites by reducing the specific surface area of the material, thereby promoting close agglomeration between particles and improving the overall density of the material. Further research found that the basic groups released by the amino carbon source during the pyrolysis process can react with the acidic sites on the surface of the material in situ to neutralize, reduce the overall pH value, and ultimately achieve orderly stacking of particles and densified structure construction. At the same time, the interaction between the phosphate-based positive electrode material and other components such as the binder can be improved, so that they can be better combined together to form a stable structure, thereby improving the stability and solid content of the prepared phosphate-based positive electrode material slurry, which is conducive to wide application.

[0206] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A phosphate-based cathode material, characterized in that: The phosphate-based positive electrode material includes a phosphate core and a carbon coating layer coated on the surface of the phosphate core, wherein the carbon coating layer is doped with nitrogen elements formed by sintering and pyrolysis of an amino carbon source.

2. The phosphate-based cathode material according to claim 1, wherein Taking the total mass of the phosphate-based positive electrode material as 100%, the content of carbon element is 1.00 wt% to 1.02 wt%, and the content of nitrogen element is 2000 ppm to 8000 ppm.

3. The phosphate-based cathode material according to claim 1, wherein The phosphate-based positive electrode material has the following characteristics: (a) Particle size D 50 2.30~3.60μm; (b) The ratio of disorder to graphitization degree of carbon coating in Raman spectrum, ID / IG, is 0.842-0.845; (c) Specific surface area is 3.43 to 5.42 m 2 / g; (d) pH value is less than 10.

0.

4. A method for preparing a phosphate-based positive electrode material, characterized in that: The steps include: Providing a phosphate precursor, grinding the phosphate precursor, and adding an amine carbon source in batches during the grinding process; wherein the amine carbon source is added in a manner of 0.2% to 20% of the total mass of the amine carbon source each time, and is completed in 5 to 20 batches; The ground phosphate precursor is sintered to obtain a phosphate positive electrode material with a carbon coating layer doped with nitrogen.

5. The method for preparing a phosphate-based cathode material according to claim 4, wherein: The amino carbon source includes one or more of menthylamine, formylanilide, dimethylamide, nicotinamide, cyclopropanamide, erucamide, iodoacetamide, caprolactam, and N-tert-butylpropionamide; and / or, Based on the total mass of the phosphate-based precursor being 100%, the added amount of the amino carbon source is 0.5% to 10%.

6. The method for preparing a phosphate-based cathode material according to claim 4, wherein: The specific sintering method is: two-stage high and low temperature sintering in an inert atmosphere; wherein the first stage low temperature sintering temperature is 380-460°C, the time is 6-12 hours, and the second stage high temperature sintering temperature is 720-800°C, the time is 8-12 hours.

7. The method for preparing a phosphate-based positive electrode material according to claim 4, wherein: The preparation method of the phosphate precursor comprises the following steps: mixing at least an iron source, a lithium source, a phosphorus source and a carbon source, adding acid to dissolve the mixture and diluting the mixture with water, heating and stirring the mixture until the solution evaporates, thereby obtaining the phosphate precursor.

8. The method for preparing a phosphate-based cathode material according to claim 7, wherein: The carbon source is selected from at least one of dopamine, glucose, sucrose, starch, carbon nanotubes, and graphene; and / or, The acid is selected from at least one of concentrated nitric acid, concentrated hydrochloric acid, phosphoric acid, a mixed acid solution of concentrated nitric acid and phosphoric acid, and a mixed acid solution of phosphoric acid and hydrochloric acid; and / or, Based on the mass of the phosphate precursor being 100%, the element contents of the lithium source, the iron source, and the phosphorus source are 4.6% to 6.5%: 33.7% to 35%: 18.7% to 19.8%; and / or, Based on the mass of the phosphate precursor being 100%, the added amount of the carbon source is 20% to 50%.

9. A phosphate-based positive electrode slurry, characterized in that: The phosphate-based positive electrode slurry comprises a phosphate-based positive electrode material, a conductive agent, and a binder, and the solid content of the phosphate-based positive electrode slurry is 54% to 70%, and the discharge viscosity is 8000 to 12000 mPa·s; Wherein, the phosphate-based positive electrode material is the phosphate-based positive electrode material according to any one of claims 1 to 3 or is prepared by the preparation method of the phosphate-based positive electrode material according to any one of claims 4 to 8.

10. A lithium ion battery, characterized in that: The invention comprises the phosphate-based positive electrode slurry according to claim 9.

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