Doped modified lithium manganese iron phosphate positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and discloses a doped modified lithium manganese iron phosphate positive electrode material and a preparation method and application thereof.The preparation method comprises the steps that a manganese source, an iron source, a phosphorus source and a titanium source are subjected to a co-precipitation reaction, and titanium-doped manganese iron phosphate is obtained; mixing the titanium-doped ferromanganese phosphate, a lithium source, a magnesium source, a vanadium source and water, and performing first ball milling to obtain a first mixture; and mixing the first mixture with a carbon source, and performing first sintering to obtain the doped modified lithium manganese iron phosphate positive electrode material. According to the preparation method, the doped particles can be uniformly doped in the lithium manganese iron phosphate, and the doped and modified lithium manganese iron phosphate positive electrode material with relatively high uniformity is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, in particular, relates to a doped modified lithium manganese iron phosphate positive electrode material and a preparation method and application thereof, more particularly, relates to a doped modified lithium manganese iron phosphate positive electrode material and a preparation method, a positive electrode sheet, a battery and an electric device. BACKGROUND

[0002] With the rapid development of the markets of electronic equipment, electric vehicles, smart home, electric tools, intelligent transportation and the like, the demand for batteries is also increasing. Lithium ion batteries gradually become the most mainstream power battery due to their excellent energy density, high safety performance, low cost and long service life and the like.

[0003] However, as a positive electrode material, lithium manganese iron phosphate also faces inherent low conductivity and ion diffusion limitations, thereby affecting the charge and discharge rate, capacity and the like of the battery. Particle doping of lithium manganese iron phosphate can effectively improve the above-mentioned drawbacks. Therefore, developing a preparation method of a doped modified lithium manganese iron phosphate positive electrode material is one of the current challenges. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the related art to some extent. To this end, the present application provides a doped modified lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. The preparation method of the doped modified lithium manganese iron phosphate positive electrode material can uniformly dope different doping particles in lithium manganese iron phosphate, so as to obtain a doped modified lithium manganese iron phosphate positive electrode material with high uniformity. The battery using the doped modified lithium manganese iron phosphate positive electrode material has excellent electrochemical performance and the like.

[0005] In a first aspect, the present application provides a preparation method of a doped modified lithium manganese iron phosphate positive electrode material, comprising: causing a co-precipitation reaction of a manganese source, an iron source, a phosphorus source and a titanium source to obtain titanium-doped manganese iron phosphate; mixing the titanium-doped manganese iron phosphate, a lithium source, a magnesium source, a vanadium source and water and performing first ball milling to obtain a first mixture; After mixing the first mixture and the carbon source, first sintering is performed to obtain the doped modified lithium manganese iron phosphate positive electrode material. In the preparation method, the titanium source reacts with the manganese source, the iron source and the phosphorus source first, liquid-phase mixing enables titanium to coexist with manganese, iron and phosphorus at close range, and then through calcination, titanium atoms only need to migrate a short distance to successfully enter the crystal structure of manganese iron phosphate, and finally realize the uniform doping of titanium in the entire manganese iron phosphate. After the titanium source is doped into the manganese iron phosphate, the vanadium source and the magnesium source are added for subsequent mixing, which helps the multi-valence characteristics of vanadium to form an electronic hopping channel in the crystal lattice of the manganese iron phosphate, thereby improving the intrinsic electronic conductivity of the material, and the magnesium can enter the interstitial gap of the crystal lattice of the manganese iron phosphate to stabilize the crystal lattice structure. In the later doping of magnesium, the fine-tuning effect of magnesium on the crystal lattice structure of the manganese iron phosphate can be better utilized to optimize the lattice parameters, In some embodiments, the co-precipitation reaction of the manganese source, the iron source, the phosphorus source and the titanium source comprises: Mixing the manganese source, the iron source, the phosphorus source and the titanium source to obtain a raw material mixture; Co-precipitation reaction of the raw material mixture under the condition of pH 4.0-4.5 to obtain a second mixture; Second sintering of the second mixture; Wherein, the second sintering comprises: sintering at 400-450℃ for 2-4h, and then sintering at 600-650℃ for 4-8h. Through the above liquid-phase mixing, it is helpful to form an atomically uniformly dispersed titanium-doped manganese iron phosphate, which can to some extent reduce the solid-state diffusion resistance and help to improve the structural stability of the titanium-doped manganese iron phosphate.

[0006] In some embodiments, at least one of the following conditions is met: The mass ratio of the manganese source, the iron source, the phosphorus source and the lithium source is 3-3.09:2-2.09:5-5.09; Based on the theoretical mass of the titanium-doped manganese iron phosphate, the addition amount of the titanium source is 0.1wt%-0.6wt%; Based on the theoretical mass of the titanium-doped manganese iron phosphate, the addition amount of the lithium source is 102wt%-108wt%; Based on the theoretical mass of the doped modified lithium manganese iron phosphate positive electrode material, the addition amount of the magnesium source is 0.1wt%-0.8wt%; Based on the theoretical mass of the doped modified lithium manganese iron phosphate positive electrode material, the addition amount of the vanadium source is 0.1wt%-0.5wt%; Based on the theoretical mass of the doped modified lithium manganese iron phosphate positive electrode material, the addition amount of the carbon source is 1wt%-2wt%. Thus, it is helpful to obtain a doped modified lithium manganese iron phosphate positive electrode material with excellent performance and stable structure.

[0007] In some embodiments, at least one of the following conditions is met: The first ball milling time is 5-10 minutes; The manganese source includes at least one of manganese carbonate, manganese sulfate, manganese dioxide, manganese oxide; The iron source includes at least one of ferrous sulfate, iron carbonate, ferrous oxide; The phosphorus source includes at least one of sodium dihydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, phosphoric acid; The titanium source includes at least one of titanium dioxide, titanyl sulfate, titanium tetrachloride, tetrabutyl titanate; The lithium source includes at least one of lithium carbonate, lithium sulfate, lithium monohydrogen carbonate, lithium dihydrogen carbonate; The magnesium source includes at least one of magnesium carbonate, magnesium oxide, magnesium hydroxide; The vanadium source includes at least one of ammonium metavanadate, ammonium vanadate, di vanadium pentoxide, vanadyl acetylacetonate; The carbon source includes at least one of sucrose, polyethylene, polypropylene, polyethylene glycol, cellulose. Thus, it helps the reaction to proceed smoothly, and the doped modified manganese iron lithium phosphate positive electrode material with excellent performance and stable structure is obtained.

[0008] In some embodiments, the sintering after mixing the first mixture and the carbon source includes: The first mixture and the carbon source are second ball milled to obtain a third mixture; The third mixture is sand milled, spray dried, and sintered. Thus, it helps to obtain a doped modified manganese iron lithium phosphate positive electrode material with stable structure.

[0009] In some embodiments, at least one of the following conditions is met: The second ball milling time is 30-60 minutes; The solid content of the third mixture is 15%-65%; The particle size of the sand milled product is 0.35-0.45 microns. Thus, it helps to prepare a doped modified manganese iron lithium phosphate positive electrode material with excellent performance and stable structure.

[0010] In some embodiments, the first sintering includes: Raising the temperature to 400-450°C at a rate of 3-6°C and sintering for 3-6 hours; Then, the temperature is increased to 650℃-750℃ at a rate of 3℃-6℃, and sintering is performed for 6h-12h. The gradient temperature increase process can precisely control the formation of the carbon coating layer and the formation of the lithium manganese iron phosphate crystal phase, so that the carbon coating layer closely adheres to the surface of the lithium manganese iron phosphate particles with an olivine structure, thereby enhancing the electrical conductivity and protecting the material structure, and thus improving the electrochemical performance of the positive electrode material.

[0011] In a second aspect of the present application, a doped modified lithium manganese iron phosphate positive electrode material is provided, which is prepared by the above preparation method. Thus, the doped modified lithium manganese iron phosphate positive electrode material has high electrical conductivity and ion diffusion rate.

[0012] In some embodiments, the doped modified lithium manganese iron phosphate positive electrode material comprises: a doped lithium manganese iron phosphate and a carbon coating layer; the carbon coating layer is coated on the surface of the doped lithium manganese iron phosphate; the chemical formula of the doped lithium manganese iron phosphate is Li a Fe b Mn c Ti x V y Mg z PO4; wherein 0.01≤x≤0.1, 0.01≤y≤0.1, 0.01≤z≤0.1, 0.4≤b≤0.5, 0.5≤c≤0.6, and 0.9≤a≤1.2. The carbon coating layer and the lithium manganese iron phosphate can form a conductive network and a conductive channel, thereby increasing the diffusion rate of lithium ions and improving the electrical conductivity of electrons. Meanwhile, the doping of titanium can inhibit the structural reconstruction caused by the migration of oxygen atoms and inhibit the lattice distortion; the doping of vanadium can improve the electronic conductivity of the material, and the doping of magnesium can optimize the lattice structure and reduce the ion migration energy barrier. Thus, the doped modified lithium manganese iron phosphate positive electrode material has excellent electrochemical performance.

[0013] In some embodiments, at least one of the following conditions is satisfied: The particle size of the doped modified lithium manganese iron phosphate positive electrode material is 0.35μm-0.55μm; The tap density of the doped modified lithium manganese iron phosphate positive electrode material is 2.25g / cm 3 ~2.35g / cm 3 . Thus, the doped modified lithium manganese iron phosphate positive electrode material has excellent electrochemical performance.

[0014] In a third aspect of the present application, a positive electrode sheet is provided, which comprises the above doped modified lithium manganese iron phosphate positive electrode material. Thus, the positive electrode sheet has excellent electrical conductivity.

[0015] In a fourth aspect of the present application, a battery is provided, comprising the doped modified lithium manganese iron phosphate positive electrode material or the positive electrode plate as described above. The battery has a high charge and discharge rate, excellent energy density, and capacity, etc.

[0016] In a fifth aspect of the present application, a power consuming device is provided, comprising the doped modified lithium manganese iron phosphate positive electrode material or the positive electrode plate or the battery as described above. Thus, the power consuming device has a high capacity and energy density. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is an SEM image of the doped modified lithium manganese iron phosphate positive electrode material of Example 1 in the application.

[0018] Figure 2 is an EDS detection image of the magnesium element in the doped modified lithium manganese iron phosphate positive electrode material of Example 1 in the application.

[0019] Figure 3 is an EDS detection image of the titanium element in the doped modified lithium manganese iron phosphate positive electrode material of Example 1 in the application.

[0020] Figure 4 is an EDS detection image of the vanadium element in the doped modified lithium manganese iron phosphate positive electrode material of Example 1 in the application. DETAILED DESCRIPTION

[0021] Embodiments of the present application are described in detail below. The embodiments described below are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0022] As described above, lithium manganese iron phosphate as a positive electrode material has some drawbacks, specifically, for example: the lithium manganese iron phosphate has an electrical conductivity of only 10 -11 S / cm, and a lithium ion diffusion rate of 10 -9 cm 2 / s, which is 1 2 orders of magnitude lower than that of lithium iron phosphate, resulting in low electronic conductivity and low lithium ion diffusion rate, thereby affecting the charge and discharge rate, capacity, and other properties of the battery. In the related art, by doping different particles into lithium manganese iron phosphate, the above drawbacks can be solved to some extent, such as doping titanium, vanadium, magnesium, etc., to obtain doped modified lithium manganese iron phosphate. On the one hand, the size of the doped modified lithium manganese iron phosphate is nanoscale, which can reduce the diffusion path of lithium ions inside the doped modified lithium manganese iron phosphate particles, achieve efficient de-intercalation, and improve the lithium ion diffusion coefficient. On the other hand, the doped particles can improve the conductivity and lithium ion diffusion performance of lithium manganese iron phosphate from the inside of the crystal lattice. After doping different particles, defects will be caused in the crystal lattice structure, and the diffusion channel of lithium ions will be widened, thereby improving the electrical conductivity of the material.

[0023] However, most of the current preparation methods of the doped modified lithium manganese iron phosphate are to mix the doped particles and the phosphoric acid source, the manganese source, the iron source, the lithium source and the like at the same time, and to sinter, which is easy to cause uneven particle doping in the doped modified lithium manganese iron phosphate prepared, especially the titanium doping, which is more difficult to enter the lithium manganese iron phosphate crystal lattice compared with other particles, and the uneven particle doping will greatly affect the performance of the positive electrode material. Therefore, the inventors consider developing a new particle doping method, so that different doped particles can effectively enter the crystal lattice of the lithium manganese iron phosphate, and the particle doping is uniform; meanwhile, the inventors also consider that titanium can inhibit the structural reconstruction caused by the migration of oxygen atoms and inhibit the lattice distortion; vanadium can improve the electronic conductivity of the material, and magnesium can optimize the lattice structure and reduce the ion migration energy barrier. Therefore, the titanium source, the vanadium source and the magnesium source are all doped into the lithium manganese iron phosphate, and the doped modified lithium manganese iron phosphate with excellent performance is obtained, so as to improve the capacity of the positive electrode material.

[0024] In view of this, in a first aspect of the present application, a preparation method of a doped modified lithium manganese iron phosphate positive electrode material is provided, which comprises: S10: causing the manganese source, the iron source, the phosphorus source and the titanium source to undergo a coprecipitation reaction to obtain titanium-doped manganese iron phosphate.

[0025] In this step, for example, the manganese source, the iron source, the phosphorus source and the titanium source are placed in a liquid phase mixing reactor for mixing and grinding to obtain a raw material mixture, ammonia water is added to the raw material mixture to adjust the pH of the raw material mixture to 4.0-4.5, the manganese source, the iron source, the phosphorus source and the titanium source undergo a coprecipitation reaction to obtain a second mixture containing titanium-doped manganese iron phosphate, and the second mixture is subjected to a second sintering to obtain titanium-doped manganese iron phosphate.

[0026] In some embodiments, the titanium source is first reacted with the manganese source, the iron source and the phosphorus source, the titanium and the manganese, the iron and the phosphorus are in close proximity by liquid phase mixing, and then the titanium atoms only need to migrate a short distance to smoothly enter the crystal structure of the manganese iron phosphate by calcination, so as to finally realize the uniform doping of titanium in the manganese iron phosphate; at the same time, the titanium-doped manganese iron phosphate formed by the liquid phase reaction is atomically uniformly dispersed, which can reduce the solid state diffusion resistance to a certain extent, and is helpful to improve the structure stability of the titanium-doped manganese iron phosphate, so as to improve the performance of the positive electrode material. If the titanium is added in the later stage of the reaction (after the formation of the manganese iron phosphate precipitate), it needs to replace the lattice sites of manganese / iron by long-distance diffusion in the solid state at high temperature, which is easy to form a local titanium enrichment area due to insufficient diffusion, thereby causing uneven titanium doping.

[0027] Furthermore, titanium's precipitation equilibrium constant is much smaller than that of elements such as iron and manganese. In co-precipitation reactions, it preferentially precipitates. Doping titanium first allows it to be uniformly dispersed with manganese, iron, phosphorus, and other elements in the form of extremely fine particles or molecules, laying the foundation for the subsequent formation of a uniform crystal structure. This essentially avoids the situation where titanium, when added later in the reaction, mixes with other elements and agglomerates into small particles that are difficult to disperse uniformly in ferric manganese phosphate.

[0028] In some embodiments, the pH for co-precipitation of manganese, iron, phosphorus, and titanium sources is 4.0–4.5, specifically 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, etc. When the acidity is strong, the phosphorus source is mainly H3PO4 or H2PO4. - H2PO4 exists in various forms, and as pH increases, H2PO4... - It will gradually transform into HPO4 2- Only when the pH rises further will it be converted into PO4 in large quantities. 3- Therefore, only when the pH is between 4.0 and 4.5 can the phosphate ions in the solution combine with manganese, iron, and titanium ions to form manganese iron titanium phosphate precipitates. At the same time, within the above pH range, the concentration product of hydroxides or related complexes produced by the hydrolysis of iron and manganese ions reaches the solubility product constant, thus initiating precipitation.

[0029] In some embodiments, the mass ratio of the manganese source, the iron source, and the phosphorus source is 3~3.09:2~2.09:5~5.09. Specifically, it can be 3:2:5, 3.05:2:5, 3.05:2:5.05, 3.09:2:5, 3.09:2.09:5.09, etc. The mass ratio of the manganese source, the iron source, and the phosphorus source within the above range can basically ensure the stability of the titanium-doped manganese iron phosphate structure prepared, which is beneficial to obtaining a high-performance cathode material in subsequent steps.

[0030] In some embodiments, based on the theoretical mass of the titanium-doped manganese ferrophosphate, the amount of titanium source added is 0.1wt% to 0.6wt%, specifically, it can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, etc. The amount of titanium source added within the above range can basically ensure that defects are introduced or solid solutions are formed in the crystal structure of manganese ferrophosphate, thereby helping to improve the electron transport path of the cathode material, reduce the electron transport resistance, and improve the electronic conductivity of the cathode material.

[0031] For example, if the target titanium-doped manganese iron phosphate has the chemical formula Fe 0.5 Mn 0.5 Ti 0.1In the reaction of PO4, 0.5 mol of iron source (based on iron atoms) and 0.5 mol and 1 mol of manganese source (based on manganese atoms) and phosphorus source (based on phosphorus atoms) were actually added, respectively. Then, an appropriate amount of titanium source was added to produce 1 mol of Fe. 0.5 Mn 0.5 Ti 0.1 The theoretical mass of PO4 is m = 0.5 × (M Fe +M Mn )+0.1×M Ti +M P +4×M o Where M is the relative atomic mass, the amount of titanium source added can be calculated based on the theoretical weight mentioned above.

[0032] In some embodiments, the second sintering includes sintering at 400°C to 450°C for 2 to 4 hours, followed by sintering at 600°C to 650°C for 4 to 8 hours. This helps to obtain structurally stable titanium-doped ferromanganese phosphate.

[0033] In some embodiments, the manganese source includes at least one selected from manganese carbonate, manganese sulfate, manganese dioxide, and manganese oxide; the iron source includes at least one selected from ferrous sulfate, ferric carbonate, and ferrous oxide; and the phosphorus source includes at least one selected from sodium dihydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, and phosphoric acid. Different manganese, iron, and phosphorus sources can be selected according to actual needs.

[0034] In some embodiments, the titanium source can be at least one of titanium dioxide, titanium oxysulfate, titanium tetrachloride, and tetrabutyl titanate. The above-mentioned titanium sources are chemically stable and do not readily undergo side reactions with other common substances, which facilitates storage and use, ensuring the stability and reliability of the raw materials. Simultaneously, through appropriate grinding or dispersion processes, the above-mentioned titanium sources can be uniformly dispersed in raw material systems such as manganese, iron, and phosphorus sources, which is beneficial for the uniform doping of titanium elements into the manganese-iron phosphate lattice during subsequent co-precipitation reactions, thereby obtaining products with uniform properties.

[0035] S20: The titanium-doped manganese iron phosphate, lithium source, magnesium source, vanadium source and water are subjected to a first ball milling to obtain a first mixture.

[0036] In this step, for example, the aforementioned titanium-doped ferromanganese phosphate, lithium source, magnesium source, vanadium source, and an appropriate amount of water are placed in a ball mill for a first ball milling and mixing to obtain a first mixture. Specifically, the first ball milling time is 1 min to 5 min, for example, it can be 1 min, 2 min, 3 min, 4 min, 5 min, etc. The first ball milling time within the above range can basically ensure that the titanium-doped ferromanganese phosphate, lithium source, magnesium source, and vanadium source are uniformly dispersed in water to obtain a uniform first mixture.

[0037] In some embodiments, after the titanium source is doped into manganese iron phosphate, a vanadium source is added for subsequent mixing because of the multivalent state characteristics of vanadium (such as V). 3＋ / V 4+ / V 5+ Vanadium sources can form electron hopping channels in the crystal lattice of ferromanganese phosphate, thereby improving the intrinsic electronic conductivity of the material. If vanadium sources are mixed simultaneously with phosphorus, manganese, and iron sources in the early mixing stage, vanadium will undergo valence state changes due to redox reactions during high-temperature sintering, affecting its distribution in the crystal lattice and thus impacting the improvement in the conductivity of the cathode material.

[0038] Furthermore, the magnesium source is mixed with the vanadium source and titanium-doped ferromanganese phosphate in the later stages because magnesium ions have a smaller radius and can enter the interstitial spaces of the ferromanganese phosphate lattice, stabilizing the lattice structure. Later doping with magnesium allows for better utilization of its fine-tuning effect on the ferromanganese phosphate lattice structure, optimizing lattice parameters, reducing ion migration barriers, and further improving the electrochemical performance of the cathode material. If the doping order is reversed, and the vanadium, magnesium, phosphorus, iron, and manganese sources are mixed first to form doped ferromanganese phosphate, titanium may not be able to uniformly enter the lattice, affecting the final doping effect and failing to fully utilize titanium's role in improving structural stability. Simultaneously, the distribution of vanadium and magnesium may change due to the subsequent titanium doping process, affecting their respective functions.

[0039] In some embodiments, the amount of lithium source added is related to the amount of titanium-doped manganese iron phosphate used; specifically, Based on the theoretical mass of the titanium-doped manganese iron phosphate, the amount of lithium source added is 102 wt% to 108 wt%. For example, the amount of lithium source added can be 102 wt%, 103 wt%, 104 wt%, 105 wt%, 106 wt%, 107 wt%, 108 wt%, etc. This ensures that the prepared doped and modified lithium manganese iron phosphate cathode material has an accurate chemical composition and stable structure, thus giving the cathode material excellent electrochemical performance.

[0040] In some embodiments, based on the theoretical mass of the doped modified lithium manganese iron phosphate cathode material, the amount of magnesium source added is 0.1wt%~0.8wt%. Specifically, the amount of magnesium source added can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, etc. The amount of magnesium source added within the above range can basically ensure that the interstitial spaces of the manganese iron phosphate are filled, thus better stabilizing the lattice structure.

[0041] In some embodiments, based on the theoretical mass of the doped modified lithium manganese iron phosphate cathode material, the amount of vanadium source added is 0.1wt%~0.5wt%. Specifically, the amount of vanadium source added can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, etc. Within the above range, it can be basically ensured that vanadium forms an appropriate amount of electron jumping channels in the lattice of manganese iron phosphate, thereby improving the intrinsic electronic conductivity of the material.

[0042] For example, if the target doped modified lithium manganese iron phosphate cathode material has the chemical formula Li 0.9 Fe 0.5 Mn 0.5 Ti 0. 1V 0.1 Mg 0.1 PO4, 1 mol Fe is added during the reaction 0.5 Mn 0.5 Ti 0.1 Using PO4 and 0.9 mol of lithium source (based on lithium atoms), and then adding 0.1 mol of vanadium source and 0.1 mol of magnesium source during the subsequent doping process, 1 mol of Li is generated. 0.9 Fe 0.5 Mn 0.5 Ti 0.1 V 0.1 Mg 0.1 The theoretical mass of PO4 is m = 0.5 × (M Fe +M Mn ) + 0.1 × (M Ti +M V +M Mg )+M P +4×M o +0.9×M Li Where M is the relative atomic mass, the amount of titanium source added can be calculated based on the theoretical weight mentioned above.

[0043] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium sulfate, lithium monohydrogen carbonate, and lithium dihydrogen carbonate. All of the above lithium sources have high solubility, which helps to uniformly disperse in different solutions to obtain a uniform first mixture. Furthermore, the above lithium sources have high chemical stability at room temperature, which facilitates storage and transportation.

[0044] In some embodiments, the magnesium source includes at least one of magnesium carbonate, magnesium oxide, and magnesium hydroxide, and the vanadium source includes at least one of ammonium metavanadate, ammonium vanadate, vanadium pentoxide, and vanadium acetylacetonate. Different raw materials can be selected according to actual conditions.

[0045] S30: The first mixture and the carbon source are mixed and sintered to obtain a doped and modified lithium manganese iron phosphate cathode material.

[0046] In this step, for example, the first mixture and the carbon source are placed in a ball mill for a second ball milling to obtain a third mixture. The third mixture is then subjected to sand milling, spray drying, sintering, and pulverization in sequence to finally obtain the doped modified lithium manganese iron phosphate cathode material of this application.

[0047] In some embodiments, the solid content of the third mixture is 15% to 65%, specifically, it can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc. The solid content within the above range helps to balance the flowability of the third mixture with the particle dispersibility therein, thereby further improving the uniformity of the cathode material. It can basically avoid particle agglomeration caused by excessively high solid content of the third mixture, as well as the reduction in subsequent drying and sintering efficiency caused by excessively low solid content.

[0048] In some embodiments, the second ball milling time is 30 min to 60 min, specifically, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc. The second ball milling time within the above range can basically ensure that the carbon source and the first mixture are mixed evenly, which helps to form a carbon coating layer on the surface of the doped lithium manganese iron phosphate through subsequent sintering, while ensuring the structural stability of the doped lithium manganese iron phosphate obtained after sintering. In some embodiments, the particle size of the product after sand milling is controlled to be 0.35 micrometers to 0.45 micrometers, specifically, it can be 0.35 micrometers, 0.37 micrometers, 0.39 micrometers, 0.40 micrometers, 0.42 micrometers, 0.44 micrometers, 0.45 micrometers, etc. The particle size of the product after sand milling within the above range can basically ensure that the specific surface area of ​​the product is suitable, which helps to accelerate the evaporation of moisture and improve the drying efficiency during subsequent drying, while also making the drying more uniform and helping to make the subsequent sintering more complete.

[0049] Specifically, the particle size mentioned above is the D50 particle size, meaning that 50% of the particles are smaller than this size. This can be tested using a Malvern particle size analyzer. During testing, the instrument's opacity should be set to 5%~12%. A suitable dispersant should be selected based on the particle size being tested, and samples should be taken gradually for analysis.

[0050] In some embodiments, the temperature of the spray drying inlet is 100℃~105℃, specifically 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, etc. This temperature range provides sufficient heat to rapidly evaporate the moisture in the mixture, achieving efficient drying. Effective removal of moisture ensures the stability of the material composition during subsequent high-temperature sintering, preventing material agglomeration and porosity caused by residual moisture during sintering, which would otherwise affect the quality and structure of the product.

[0051] In some embodiments, sintering includes: heating to 400℃~450℃ at a rate of 3℃ / min~6℃ / min and sintering for 3h~6h, then heating to 650℃~750℃ at a rate of 3℃ / min~6℃ / min and sintering for 6h~12h. Specifically, the heating rate can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, etc. Heating rates within the above range can basically ensure uniform heating of the mixture, which helps to achieve a uniform structure in the final product. This largely avoids uneven heating of the mixture caused by excessively rapid heating rates, which can easily damage the structural stability of the doped modified lithium manganese iron phosphate cathode material due to localized overheating.

[0052] Furthermore, in the first sintering process, the temperature is first raised to 400℃~450℃, for example, it can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc. Within the above temperature range, the carbon source begins to initially carbonize and form some small carbon particles. Sintering for 3h~6h can basically ensure that the carbon source is completely carbonized into carbon particles. Then the sintering temperature is raised to 650℃~750℃, specifically, it can be 650℃, 700℃, 750℃, etc. Within the above temperature range, the carbon particles further grow and fuse to form a continuous and uniform carbon coating layer. At the same time, the doped particles can also be stably doped into the lattice of lithium manganese iron phosphate within the above temperature range, forming a structurally stable doped modified lithium manganese iron phosphate cathode material.

[0053] The aforementioned gradient heating process can precisely control the formation of the carbon coating layer and the formation of the lithium manganese iron phosphate crystal phase, so that the carbon coating layer is tightly attached to the surface of the lithium manganese iron phosphate particles with olivine structure, which can enhance conductivity, protect the material structure, and thus improve the electrochemical performance of the cathode material.

[0054] In some embodiments, the sintered product is pulverized to obtain a refined doped modified lithium manganese iron phosphate cathode material. Specifically, the pulverization frequency is 1 min / time to 3 min / time, for example, it can be 1 min / time, 2 min / time, 3 min / time, etc., and the number of pulverizations is 2 to 5 times. This helps to ensure that the particle size of the obtained doped modified lithium manganese iron phosphate cathode material is within the target range, thereby further improving the compaction density of the doped modified lithium manganese iron phosphate cathode material and increasing the energy density of the cathode material.

[0055] In some embodiments, based on the theoretical mass of the doped and modified lithium manganese iron phosphate cathode material, the amount of carbon source added is 1wt% to 2wt%. Specifically, the amount of carbon source added can be 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2.0wt%, etc. Within the above range, the amount of carbon source added can basically ensure the formation of a carbon coating layer of the target thickness on the surface of the lithium manganese iron phosphate. Thus, the carbon coating layer and the lithium manganese iron phosphate can form a conductive network and conductive channels, thereby increasing the diffusion rate of lithium ions, improving electron conductivity, and also increasing the compaction density of the cathode material to a certain extent, thereby further improving the energy density of the battery.

[0056] In some embodiments, the carbon source includes at least one of sucrose, polyethylene, polypropylene, polyethylene glycol, and cellulose. These carbon sources are widely available, ensuring a stable supply of raw materials, while also being low in cost, making them suitable for industrial production applications.

[0057] In a second aspect of this application, a doped modified lithium manganese iron phosphate cathode material is proposed, which is obtained by the aforementioned preparation method. As a result, the doped modified lithium manganese iron phosphate cathode material has high electronic conductivity and ion diffusion rate.

[0058] In some embodiments, the doped modified lithium manganese iron phosphate cathode material includes: doped lithium manganese iron phosphate and a carbon coating layer; the carbon coating layer coats the surface of the doped lithium manganese iron phosphate. The carbon coating layer and the doped lithium manganese iron phosphate can form a conductive network and conductive channels, thereby increasing the diffusion rate of lithium ions and improving the electron conductivity. It can also increase the compaction density of the cathode material to a certain extent, thereby further improving the energy density of the battery. The carbon coating layer can also increase the compaction density of the cathode material to a certain extent, thereby further improving the energy density of the battery. In addition, carbon itself can act as a reducing agent and effectively suppress Fe. 2+ Mn 2+ Oxidation can reduce the dissolution of trivalent manganese ions, which can, to some extent, prevent the capacity reduction or migration of trivalent manganese ions to the negative electrode, damage the SEI film, and accelerate the degradation of cycle performance caused by the dissolution of trivalent manganese ions.

[0059] In some embodiments, the doped lithium manganese iron phosphate has the general chemical formula Li. a Fe b Mn c Ti x V y Mg z PO4; where 0.01≤x≤0.1, 0.01≤y≤0.1, 0.01≤z≤0.1, 0.4≤b≤0.5, 0.5≤c≤0.6, and 0.9≤a≤1.2. Doping lithium manganese iron phosphate with titanium can suppress structural reconstruction caused by oxygen atom migration and inhibit lattice distortion; doping with vanadium can improve the electronic conductivity of the material, and doping with magnesium can optimize the lattice structure and reduce the ion migration barrier. Therefore, this doped and modified lithium manganese iron phosphate cathode material exhibits excellent electrochemical performance.

[0060] In some embodiments, the particle size of the doped modified lithium manganese iron phosphate cathode material is 0.35 μm to 0.55 μm, specifically, it can be 0.35 μm, 0.45 μm, 0.55 μm, etc. The particle size of the cathode material within the above range can basically ensure that lithium ions can be inserted and extracted more quickly, thereby helping to improve the charge and discharge rate and rate performance of the battery. At the same time, the particle size of the cathode material within the above range is also conducive to ensuring the contact area between the cathode material and the electrolyte, promoting the electrochemical reaction, and improving the battery capacity.

[0061] Specifically, the particle size mentioned above is the D50 particle size, which means that 50% of the particles in the doped and modified lithium manganese iron phosphate cathode material are smaller than this particle size. It can be measured using a Malvern particle size analyzer.

[0062] In some embodiments, the compaction density of the doped and modified lithium manganese iron phosphate cathode material is 2.25 g / cm³. 3 ~2.35g / cm 3 Specifically, it can be 2.25 g / cm³. 3 2.30 g / cm 3 2.35 g / cm 3 The compaction density within the above range can basically ensure sufficient contact between the cathode material particles, thereby ensuring the electronic conductivity of the electrode, reducing the internal resistance of the electrode, promoting the electrochemical reaction, and improving the power performance of the battery.

[0063] Specifically, compaction density is a physical parameter that measures the mass of a unit volume of a loose solid material (such as the carbon-coated modified lithium manganese iron phosphate cathode material particles mentioned above) after being compacted under external pressure. Essentially, it reflects the degree to which the voids between the material particles are compressed. The compaction density of particles can be calculated using ρ=m / v, where m is the mass of the particle (in grams) and v is the total volume of the compacted particles (in centimeters).3 .

[0064] In a third aspect of this application, a positive electrode sheet is provided, comprising the aforementioned doped and modified lithium manganese iron phosphate positive electrode material. Specifically, the positive electrode sheet comprises a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer comprising the doped and modified lithium manganese iron phosphate positive electrode material.

[0065] In some embodiments, the cathode material layer includes the aforementioned doped and modified lithium manganese iron phosphate cathode material and auxiliary materials, including conductive agents, binders, dispersants, etc., thereby helping to obtain a cathode material layer with superior conductivity.

[0066] In a fourth aspect of this application, a battery is proposed. This battery includes the aforementioned doped and modified lithium manganese iron phosphate cathode material or the aforementioned cathode sheet, thereby exhibiting high charge / discharge rates, excellent energy density, and capacity.

[0067] In some embodiments, the battery can be an all-solid-state battery, including the above-mentioned positive electrode, negative electrode and separator, etc. During the charging and discharging process of the battery, active ions are inserted and extracted back and forth between the positive electrode and the negative electrode. The separator is disposed between the positive electrode and the negative electrode, mainly to prevent short circuit between the positive electrode and the negative electrode, while allowing active ions to pass through.

[0068] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. As an example, the negative electrode active material layer may include a negative electrode material, a thickener, a conductive agent, and a binder.

[0069] Specifically, the negative electrode current collector can be a metal foil, for example, copper foil. The negative electrode material can include carbon-based materials, silicon-based materials, tin-based materials, etc. The binder in the negative electrode material layer can include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS). The conductive agent in the negative electrode material layer can include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the separator may be a separator known in the art that can be used in lithium-ion batteries and is stable to the electrolyte used, such as a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene composite separator, etc.

[0071] In a fifth aspect of this application, an electrical device is provided, comprising the aforementioned positive electrode or the aforementioned battery. Therefore, the electrical device has high capacity and energy density.

[0072] In some embodiments, the specific type of electrical device is not particularly limited and can be any device that uses an all-solid-state battery as a power source or energy storage unit. Examples of electrical devices include, but are not limited to, electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, and so on.

[0073] It is understandable that, in addition to the all-solid-state battery mentioned above, the electrical device also includes other necessary structures and components, all of which can be made with reference to conventional technologies, such as electric vehicles, which may include the body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0074] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0075] Example 1 The doped and modified lithium manganese iron phosphate cathode material was prepared according to the preparation method of this application, as follows: 1. Preparation of titanium-doped ferromanganese phosphate: 917.4 g of ferrous sulfate heptahydrate, 557.7 g of manganese sulfate monohydrate, 759 g of lithium dihydrogen phosphate and 3 g of titanium source were placed in a reaction vessel and mixed to obtain a raw material mixture. 400 g of ammonia water was added to the raw material mixture to adjust the pH of the raw material mixture to 4.2. The reaction was carried out for 4 h to obtain a second mixture of ferromanganese phosphate containing titanium doping. The second mixture was sintered at 400 °C for 2 h and then sintered at 605 °C for 5 h to obtain titanium-doped ferromanganese phosphate.

[0076] 2. The titanium-doped manganese iron phosphate prepared above, along with 280.79g of lithium carbonate, 4.2g of magnesium oxide, 3.2g of ammonium vanadate, and water, were placed in a ball mill and milled for 5 minutes. Then, sucrose carbon source was added, and the mixture was milled for another 30 minutes to obtain the third mixture.

[0077] 3. Place the third mixture in a sand mill and mill for 60 minutes. Spray dry the milled mixture at 100°C for 60 minutes. Then, heat the mixture to 450°C at a rate of 3°C / min and sinter for 3 hours. Then, heat the mixture to 720°C at a rate of 3°C / min and sinter for 8 hours. After sintering, place the mixture in a pulverizer and pulverize it 5 times at a frequency of 1 minute / time to obtain the doped modified lithium manganese iron phosphate cathode material.

[0078] Preparation of the positive electrode sheet: The positive electrode material, conductive agent, binder, and dispersant were mixed in a mass ratio of 96.8:1.5:1.5:0.2. The mixture was first dry-mixed, then wet-mixed with an appropriate amount of solvent to obtain a positive electrode slurry. The solid content of the positive electrode slurry was controlled to be 65%. Further, the positive electrode slurry was coated onto a 14μm thick carbon-coated aluminum foil (where the aluminum foil thickness was 12 micrometers, and each side of the aluminum foil was coated with a 1-micrometer thick carbon layer), resulting in a double-sided areal density of 40 mg / cm³ for the positive electrode sheet. 2 After drying at 100℃~120℃, the dried positive electrode sheet is obtained. Finally, the dried positive electrode sheet is rolled to achieve a compaction density of 2.30 g / cm³. 3 The prepared positive electrode sheet is die-cut according to the cell size and placed in a nitrogen oven at 100℃ for later use. Preparation of the negative electrode sheet: A slurry was prepared by mixing hard carbon, conductive agent, and binder in a mass ratio of 96.5:1.0:2.5. The mixture was first dry-mixed, and then wet-mixed with an appropriate amount of solvent to obtain the negative electrode slurry. The solid content of the negative electrode slurry was controlled to be 55%. Then, the negative electrode slurry was coated onto a 6μm thick copper foil to achieve a double-sided areal density of 13mg / cm². 2 The negative electrode sheet is dried at 80℃. Finally, the dried negative electrode sheet is rolled to achieve a compaction density of 1.50 g / cm³. 3 Then, the rolled negative electrode sheet is die-cut according to the cell size and placed in a nitrogen oven at 90℃ for later use. Lithium-ion battery assembly: A stacking process is used, requiring one more negative electrode than positive electrode. The number of electrodes is calculated based on a design capacity of 1Ah. The electrodes are stacked in the order of separator, negative electrode, separator, positive electrode, separator, and negative electrode. After hot pressing, tab welding, and encapsulation, the moisture content is controlled below 400ppm. Electrolyte is injected according to the design capacity, with an injection coefficient of 4.0g / Ah.

[0079] Examples 2-11 Same as Example 1, the main differences are shown in Table 1.

[0080] Comparative Example 1 Same as Example 1, the main difference is: 1. Preparation of ferromanganese phosphate: 917.4 g of ferrous sulfate heptahydrate, 557.7 g of manganese sulfate monohydrate and 759 g of lithium dihydrogen phosphate were placed in a reaction vessel and mixed to obtain a second mixture. The second mixture was then subjected to a second sintering to obtain ferromanganese phosphate. 2. Place the prepared manganese iron phosphate, 280.79g lithium carbonate, 4.2g magnesium oxide, 3.2g ammonium vanadate and water into a ball mill and ball mill for 5 minutes. Then add sucrose carbon source and ball mill for another 30 minutes to obtain the first mixture.

[0081] Comparative Example 2 Same as Example 1, the main difference is: 1. Preparation of titanium-doped ferromanganese phosphate: 917.4 g of ferrous sulfate heptahydrate, 557.7 g of manganese sulfate monohydrate, 759 g of lithium dihydrogen phosphate and 3 g of titanium source were placed in a reaction vessel and mixed to obtain a raw material mixture. 400 g of ammonia water was added to the raw material mixture to adjust the pH of the raw material mixture to 4.2. The reaction was carried out for 4 h to obtain a second mixture of ferromanganese phosphate containing titanium doping. The second mixture was subjected to a second sintering to obtain titanium-doped ferromanganese phosphate. 2. The titanium-doped manganese iron phosphate prepared above, along with 280.79g of lithium carbonate, 4.2g of magnesium oxide, and water, were placed in a ball mill and milled for 5 minutes. Then, sucrose carbon source was added, and the mixture was milled for another 30 minutes to obtain the first mixture.

[0082] Test results SEM images of the doped and modified lithium manganese iron phosphate cathode material prepared in Example 1 are shown below. Figure 1 It can be seen that the prepared cathode material particles are uniform.

[0083] The EDS spectra of magnesium, titanium, and vanadium in the doped and modified lithium manganese iron phosphate cathode material prepared in Example 1 are shown below. Figures 2-4 It can be seen that the elements in the cathode material are uniformly doped.

[0084] The particle size, compaction density, and electrochemical performance of the doped modified lithium manganese iron phosphate cathode materials obtained in Examples 1-11 were tested, as shown in Table 2.

[0085] Detection methods The dissolution values ​​of Mn and Fe are determined by mixing the prepared cathode material particles with the electrolyte and allowing them to stand or stir at a specific temperature for a period of time (usually 24 hours) to simulate the storage or cycling conditions of the battery at high temperatures. The mixed electrolyte is then separated from the solid powder by centrifugation or filtration to obtain a clear electrolyte containing dissolved metal ions. The separated electrolyte is then diluted to a suitable concentration range with reagents such as nitric acid. Finally, the elements Mn and Fe are tested using the ICP-MS method.

[0086] Powder resistivity: The positive electrode material sample is loaded into a mold and pressed into a disc under a fixed pressure; four equally spaced probes are pressed vertically onto the sample surface; current is passed through the two outer probes and the voltage drop between the two inner probes is measured; the volume resistivity or surface resistivity of the sample is calculated according to the formula. The test results are affected by pressure, so they need to be performed under standard pressure, usually 20 MPa.

[0087] Specific surface area: At liquid nitrogen temperature, an inert gas (such as nitrogen) is physically adsorbed on the sample surface; the adsorption amount is measured under different pressures by changing the gas pressure; the adsorption data is processed according to the BET formula to calculate the monolayer saturated adsorption amount; combined with the cross-sectional area of ​​the adsorbed molecules, the total specific surface area of ​​the sample is calculated.

[0088] 0.1C initial efficiency / 0.1C charging capacity / 0.1C discharging capacity: For coin cells, the prepared doped and modified lithium manganese iron phosphate material was mixed with acetylene black and polytetrafluoroethylene at a mass ratio of 97.9:0.9:1.2 in a vacuum mixer. Then, NMP solvent was added to the mixture, and the mixture was stirred until homogeneous under vacuum to obtain the positive electrode slurry of this embodiment. The above positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After drying in the oven, a semi-finished positive electrode sheet was obtained. The semi-finished positive electrode sheet was then cold-pressed and cut to obtain the positive electrode sheet to be assembled. A button cell was then assembled using an R2032 coin cell casing, with a lithium sheet as the negative electrode and a PE separator. 80 mL of electrolyte (using Xinzhoubang lithium-ion battery electrolyte, model LBC3401A60) was added.

[0089]

[0090]

[0091] Conclusion: As can be seen from Examples 1-11 and Comparative Examples 1-2, the batteries prepared using the cathode material of this application have excellent capacity performance.

[0092] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0093] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0094] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0095] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0096] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a doped and modified lithium iron phosphate cathode material, characterized in that, include: A co-precipitation reaction is carried out using manganese, iron, phosphorus, and titanium sources to obtain titanium-doped manganese iron phosphate; The titanium-doped manganese iron phosphate, lithium source, magnesium source, vanadium source and water are mixed and subjected to a first ball milling to obtain a first mixture; The first mixture and carbon source are mixed and then subjected to a first sintering to obtain a doped and modified lithium manganese iron phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, The co-precipitation reaction involving manganese, iron, phosphorus, and titanium sources includes: The manganese source, the iron source, the phosphorus source and the titanium source are mixed to obtain a raw material mixture; The raw material mixture is subjected to a co-precipitation reaction at a pH of 4.0 to 4.5 to obtain a second mixture; The second mixture is subjected to a second sintering; The second sintering process includes sintering at 400℃~450℃ for 2h~4h, and then sintering at 600℃~650℃ for 4h~8h.

3. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: The mass ratio of the manganese source, the iron source, and the phosphorus source is 3~3.09:2~2.09:5~5.09; Based on the theoretical mass of the titanium-doped manganese iron phosphate, the amount of titanium source added is 0.1wt%~0.6wt%; Based on the theoretical mass of the titanium-doped manganese iron phosphate, the amount of lithium source added is 102 wt%~108 wt%; Based on the theoretical mass of the doped and modified lithium manganese iron phosphate cathode material, the amount of magnesium source added is 0.1wt%~0.8wt%; Based on the theoretical mass of the doped and modified lithium manganese iron phosphate cathode material, the amount of vanadium source added is 0.1wt%~0.5wt%; Based on the theoretical mass of the doped and modified lithium manganese iron phosphate cathode material, the amount of carbon source added is 1wt%~2wt%.

4. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: The first ball milling time is 5 min to 10 min; The manganese source includes at least one of manganese carbonate, manganese sulfate, manganese dioxide, and manganese oxide; The iron source includes at least one of ferrous sulfate, ferric carbonate, and ferrous oxide. The phosphorus source includes at least one of sodium dihydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, and phosphoric acid. The titanium source includes at least one of titanium dioxide, titanium oxysulfate, titanium tetrachloride, and tetrabutyl titanate. The lithium source includes at least one of lithium carbonate, lithium sulfate, lithium monohydrogen carbonate, and lithium dihydrogen carbonate. The magnesium source includes at least one of magnesium carbonate, magnesium oxide, and magnesium hydroxide; The vanadium source includes at least one of ammonium metavanadate, ammonium vanadate, vanadium pentoxide, and vanadium acetylacetonate. The carbon source includes at least one of sucrose, polyethylene, polypropylene, polyethylene glycol, and cellulose.

5. The preparation method according to claim 1, characterized in that, The first sintering process after mixing the first mixture and the carbon source includes: The first mixture and the carbon source are subjected to a second ball milling to obtain a third mixture; The third mixture is subjected to sand milling, spray drying, and first sintering.

6. The preparation method according to claim 5, characterized in that, At least one of the following conditions must be met: The second ball milling time is 30 min to 60 min; The solid content of the third mixture is 15% to 65%; The particle size of the product from the sand mill is 0.35 micrometers to 0.45 micrometers.

7. The preparation method according to claim 5, characterized in that, The first sintering includes: Sinter at 400℃~450℃ for 3h~6h by heating at a rate of 3℃ / min~6℃ / min. Then, increase the temperature to 650℃~750℃ at a rate of 3℃ / min ~ 6℃ / min and sinter for 6h~12h.

8. A doped and modified lithium iron phosphate cathode material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

9. The doped and modified lithium iron phosphate cathode material according to claim 8, characterized in that, include: Doped lithium manganese iron phosphate and carbon coating; The carbon coating layer covers the surface of the doped lithium manganese iron phosphate; The chemical formula of the doped lithium manganese iron phosphate is Li. a Fe b Mn c Ti x V y Mg z PO4; Wherein, 0.01≤x≤0.1, 0.01≤y≤0.1, 0.01≤z≤0.1, 0.4≤b≤0.5, 0.5≤c≤0.6, and 0.9≤a≤1.

2.

10. The doped and modified lithium iron phosphate cathode material according to claim 8, characterized in that, At least one of the following conditions must be met: The particle size of the doped and modified lithium manganese iron phosphate cathode material is 0.35 μm to 0.55 μm; The compaction density of the doped and modified lithium manganese iron phosphate cathode material is 2.25 g / cm³. 3 ~2.35g / cm 3 .

11. A positive electrode plate, characterized in that, Including the doped and modified lithium iron phosphate cathode material according to any one of claims 8 to 10.

12. A battery, characterized in that, It includes the doped and modified lithium manganese iron phosphate cathode material according to any one of claims 8 to 10 or the cathode sheet according to claim 11.

13. An electrical appliance, characterized in that, This includes the doped and modified lithium manganese iron phosphate cathode material according to any one of claims 8 to 10, the cathode sheet according to claim 11, or the battery according to claim 12.

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