Iron phosphate as well as preparation method, device and application thereof

Abstract

The invention provides iron phosphate and a preparation method, device and application thereof, and belongs to the technical field of lithium ion batteries, and the preparation method of the iron phosphate comprises the following steps: providing a ferrous solution and a mixed solution of a phosphorus source and an oxidizing agent; mixing the ferrous solution with the mixed solution of the phosphorus source and the oxidizing agent, and reacting to obtain reaction slurry; carrying out solid-liquid separation on the reaction slurry to obtain a filter cake, and then slurrying the filter cake to obtain slurry; carrying out aging treatment on the slurry to obtain aged slurry, and then carrying out solid-liquid separation and water washing on the aged slurry to obtain iron phosphate dihydrate; and calcining the iron phosphate dihydrate to obtain the iron phosphate.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to iron phosphate and a preparation method, device and application thereof. Background Art

[0002] As a precursor for lithium iron phosphate batteries, iron phosphate offers advantages such as abundant raw material resources, low cost, high capacity, and good safety. Iron phosphate preparation methods primarily include batch and continuous processes. The continuous process offers advantages such as high production efficiency, high product quality stability, and high product consistency. However, traditional continuous iron phosphate preparation methods have difficulty controlling the particle size of the resulting iron phosphate. Summary of the Invention

[0003] In view of the technical problems existing in the background technology, the present application provides a method for preparing iron phosphate, which aims to solve the technical problem of difficulty in controlling the particle size of the prepared iron phosphate in the traditional continuous method for preparing iron phosphate.

[0004] The present invention provides a method for preparing iron phosphate, comprising the following steps:

[0005] providing a ferrous solution and a mixed solution of a phosphorus source and an oxidant;

[0006] Mixing the ferrous solution with the mixed solution of the phosphorus source and the oxidant to obtain a reaction slurry;

[0007] The reaction slurry is subjected to solid-liquid separation to obtain a filter cake, and then the filter cake is subjected to slurry treatment to obtain a slurry;

[0008] The slurry is subjected to aging treatment to obtain an aged slurry, and then the aged slurry is subjected to solid-liquid separation and water washing to obtain ferric phosphate dihydrate;

[0009] calcining the ferric phosphate dihydrate to obtain the ferric phosphate;

[0010] Wherein, the mixing reaction of the ferrous solution and the mixed solution of the phosphorus source and the oxidant is carried out in a reactor, and the reactor includes a reaction chamber, a feed port arranged at the top of the reaction chamber, and a discharge port arranged at the bottom of the reaction chamber, and a discharge pipe connected to the discharge port, the discharge pipe and the reaction chamber are arranged parallel in the vertical direction, the end of the discharge pipe not connected to the discharge port is higher in the vertical direction than the discharge port, and the height of the discharge pipe in the vertical direction is adjusted according to the liquid level in the reaction chamber.

[0011] In the technical solution of the embodiment of the present application, the ferrous solution and the mixed solution of the phosphorus source and the oxidant are added to the reaction chamber respectively through the feed port provided at the top of the reaction chamber for mixed reaction, and at the same time, the mixed reaction liquid flows into the discharge pipe through the discharge port at the bottom of the reaction chamber. By adjusting the height of the end of the discharge pipe that is not connected to the discharge port in the vertical direction, the liquid level in the reaction chamber can be controlled, thereby controlling the time for the ferrous solution and the mixed solution of the phosphorus source and the oxidant to contact in the reaction chamber, and then controlling the particle size of the iron phosphate. Furthermore, since the discharge pipe and the reaction chamber are arranged parallel in the vertical direction, the mixed reaction liquid will rise in the discharge pipe in the vertical direction. During the rising process, the iron phosphate particles generated by the mixed reaction will produce slow sedimentation, so that in the discharge pipe, the particle size of the iron phosphate particles at one end close to the discharge port is larger, and the particle size of the iron phosphate particles at one end away from the discharge port is smaller. Therefore, by adjusting the vertical height of the end of the discharge pipe that is not connected to the discharge port, the growth particle size of the iron phosphate collected from the end of the discharge pipe that is not connected to the discharge port can be controlled.

[0012] In some embodiments of the present application, the molar ratio of the phosphorus element in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution is (1-1.1):1.

[0013] In this embodiment, within the range of the molar ratio of the phosphorus element in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution, it is beneficial for the iron phosphate particles to grow to a suitable size, which is beneficial for the particle size and distribution of the lithium iron phosphate prepared by the iron phosphate to be more suitable, thereby obtaining a higher compaction density and capacity.

[0014] In some embodiments of the present application, the molar ratio of the oxidant in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution is (0.5-0.75):1.

[0015] In this embodiment, the molar ratio of the oxidant to the iron element in the ferrous solution is within the above range, which is conducive to the reaction of the ferrous solution with the mixed solution of the phosphorus source and the oxidant to form ferric phosphate.

[0016] In some embodiments of the present application, the preparation of the mixed solution of the phosphorus source and the oxidant comprises the following steps:

[0017] dissolving a phosphorus source in pure water to obtain a first solution;

[0018] Adjusting the pH value of the first solution to 6.5-7.5 to obtain a second solution;

[0019] The second solution is mixed with an oxidant to obtain a mixed solution of the phosphorus source and the oxidant.

[0020] In this embodiment, within the pH value range of the second solution, the ionization of the phosphorus source is facilitated, thereby increasing the concentration of phosphate ions in the mixed solution, and facilitating the precipitation of Fe elements to form iron phosphate.

[0021] In some embodiments of the present application, the step of aging the slurry to obtain an aged slurry includes:

[0022] Mixing the slurry and phosphoric acid solution to obtain reaction slurry;

[0023] The reaction slurry is subjected to heat preservation treatment to obtain the aged slurry.

[0024] In this embodiment, the aging treatment is beneficial for the unreacted materials to continue to generate iron phosphate, thereby improving the yield of iron phosphate.

[0025] In some embodiments of the present application, the mass percentage concentration of the phosphoric acid solution is 80% to 90%.

[0026] In this embodiment, within the mass percentage concentration range of the phosphoric acid solution, it is beneficial for the unreacted material to continue to generate iron phosphate during the aging treatment of the slurry to obtain the aged slurry, thereby improving the yield of iron phosphate.

[0027] In some embodiments of the present application, the molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution is (0.1-0.2):1.

[0028] In this embodiment, within the range of the molar ratio of the phosphorus element in the above-mentioned phosphoric acid solution to the iron element in the ferrous solution, it is beneficial for the unreacted material to continue to generate iron phosphate during the aging treatment of the slurry to obtain the aged slurry, thereby improving the yield of iron phosphate.

[0029] In some embodiments of the present application, the insulation temperature of the insulation treatment is 95°C~100°C.

[0030] In this embodiment, within the insulation temperature range of the above insulation treatment, it is beneficial for the slurry to be aged during the aging treatment to obtain the aged slurry, and the unreacted material continues to generate iron phosphate, thereby improving the yield of iron phosphate.

[0031] In some embodiments of the present application, the insulation time of the insulation treatment is 1 hour to 2 hours.

[0032] In this embodiment, within the range of the insulation time of the above insulation treatment, it is beneficial for the slurry to be aged during the aging treatment to obtain the aged slurry, and the unreacted material continues to generate iron phosphate, thereby improving the yield of iron phosphate.

[0033] An embodiment of the present application provides a device for preparing ferric phosphate, which is used to prepare ferric phosphate using any of the above-mentioned methods for preparing ferric phosphate, and includes: a reaction kettle;

[0034] The reactor includes a reaction chamber, a feed port arranged at the top of the reaction chamber, a discharge port arranged at the bottom of the reaction chamber, and a discharge pipe connected to the discharge port. The discharge pipe is arranged parallel to the reaction chamber in the vertical direction, and the end of the discharge pipe that is not connected to the discharge port is higher in the vertical direction than the discharge port, and the height of the discharge pipe in the vertical direction is adjusted according to the liquid level in the reaction chamber.

[0035] In the technical solution of the embodiment of the present application, the preparation device of iron phosphate can be used to prepare iron phosphate using any of the above-mentioned preparation methods of iron phosphate, so as to control the particle size of the prepared iron phosphate. By adjusting the height of the end of the discharge pipe that is not connected to the discharge port in the vertical direction, the liquid level in the reaction chamber can be controlled, thereby controlling the time for the ferrous solution and the mixed solution of the phosphorus source and the oxidant to contact in the reaction chamber, and then controlling the particle size of the iron phosphate. Furthermore, since the discharge pipe and the reaction chamber are arranged in parallel in the vertical direction, the mixed reaction liquid will rise in the discharge pipe in the vertical direction. During the rising process, the iron phosphate particles generated by the mixed reaction will produce slow sedimentation, so that in the discharge pipe, the particle size of the iron phosphate particles at one end close to the discharge port is larger, and the particle size of the iron phosphate particles at one end away from the discharge port is smaller. Therefore, by adjusting the vertical height of the end of the discharge pipe that is not connected to the discharge port, the growth particle size of the iron phosphate collected from the end of the discharge pipe that is not connected to the discharge port can be controlled.

[0036] An embodiment of the present application provides an iron phosphate prepared by any of the above-described methods for preparing iron phosphate.

[0037] In the technical solution of the embodiment of the present application, the particle size of the iron phosphate can be adjusted, which is conducive to obtaining iron phosphate with uniform particle size distribution, and further conducive to the prepared positive electrode material having better electrochemical properties.

[0038] An embodiment of the present application provides a lithium iron phosphate material prepared using raw materials including the above-mentioned iron phosphate.

[0039] In the technical solution of the embodiment of the present application, the lithium iron phosphate material has electrochemical properties such as a higher charge specific capacity, a higher discharge specific capacity, and better rate performance.

[0040] An embodiment of the present application provides a positive electrode plate, comprising a current collector and an active layer located on a surface of the current collector, wherein the active layer comprises the above-mentioned lithium iron phosphate material.

[0041] In the technical solution of the embodiment of the present application, the active layer of the positive electrode plate includes the above-mentioned positive electrode material, and thus has good electrochemical performance.

[0042] An embodiment of the present application provides a secondary battery, comprising the above-mentioned positive electrode plate.

[0043] In the technical solution of the embodiment of the present application, the secondary battery includes the above-mentioned positive electrode plate, and thus has comprehensively improved electrochemical performance, so that it can be well applied in multiple usage scenarios.

[0044] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0046] Figure 1 A schematic diagram of the steps of a method for preparing iron phosphate provided in an embodiment of the present application;

[0047] Figure 2 A schematic structural diagram of a device for preparing iron phosphate provided in an embodiment of the present application;

[0048] Figure 3 This is the XRD pattern of the iron phosphate prepared in Example 1 of the present application;

[0049] Figure 4 This is a SEM image of the iron phosphate prepared in Example 1 of the present application;

[0050] Figure 5 This is the SEM image of the iron phosphate prepared in Example 1 of the present application.

[0051] Description of Reference Numerals

[0052] 1-reaction chamber; 2-feed port; 3-discharge port; 4-discharge pipe. DETAILED DESCRIPTION

[0053] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0055] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0056] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0057] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0058] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0059] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0060] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0061] Reference Figure 1 、 Figure 2 As shown, in the first aspect, the embodiments of the present application provide a method for preparing iron phosphate, comprising the following steps:

[0062] S1, providing a ferrous solution and a mixed solution of a phosphorus source and an oxidant;

[0063] S2, mixing the ferrous solution and the mixed solution of the phosphorus source and the oxidant to obtain a reaction slurry;

[0064] S3, separating the reaction slurry into a filter cake by solid-liquid separation, and then slurrying the filter cake to obtain a slurry;

[0065] S4, aging the slurry to obtain an aged slurry, and then subjecting the aged slurry to solid-liquid separation and water washing to obtain ferric phosphate dihydrate;

[0066] S5, calcining ferric phosphate dihydrate to obtain ferric phosphate;

[0067] Among them, the mixed reaction of the ferrous solution and the mixed solution of the phosphorus source and the oxidant is carried out in a reactor, which includes a reaction chamber 1, a feed port 2 arranged at the top of the reaction chamber 1, and a discharge port 3 arranged at the bottom of the reaction chamber 1, and a discharge pipe 4 connected to the discharge port 3. The discharge pipe 4 is arranged parallel to the reaction chamber 1 in the vertical direction, and the end of the discharge pipe 4 that is not connected to the discharge port 3 is higher than the discharge port 3 in the vertical direction, and the height of the discharge pipe 4 in the vertical direction is adjusted according to the liquid level in the reaction chamber 1.

[0068] In the technical solution of the embodiment of the present application, the ferrous solution and the mixed solution of the phosphorus source and the oxidant are added to the reaction chamber 1 respectively through the feed port 2 provided at the top of the reaction chamber 1 for mixed reaction. At the same time, the mixed reaction liquid flows into the discharge pipe 4 through the discharge port 3 at the bottom of the reaction chamber 1. By adjusting the height of the end of the discharge pipe 4 that is not connected to the discharge port 3 in the vertical direction, the liquid level in the reaction chamber 1 can be controlled, thereby controlling the contact time of the ferrous solution and the mixed solution of the phosphorus source and the oxidant in the reaction chamber 1, and then controlling the particle size of the iron phosphate. Furthermore, since the discharge pipe 4 is arranged parallel to the reaction chamber 1 in the vertical direction, the mixed reaction liquid will rise in the discharge pipe 4 in the vertical direction. During the rising process, the iron phosphate particles generated by the mixed reaction will produce slow sedimentation, so that in the discharge pipe 4, the particle size of the iron phosphate particles close to the end of the discharge port 3 is larger, and the particle size of the iron phosphate particles away from the end of the discharge port 3 is smaller. Therefore, by adjusting the vertical height of the end of the discharge pipe 4 not connected to the discharge port 3 , the growth particle size of the iron phosphate collected from the end of the discharge pipe 4 not connected to the discharge port 3 can be controlled.

[0069] In some embodiments of the present application, the solute of the ferrous solution includes at least one of ferrous sulfate, ferrous chloride and ferric sulfate.

[0070] In some embodiments of the present application, the phosphorus source includes at least one of monoammonium dihydrogen phosphate, diammonium monohydrogen phosphate, calcium hydrogen phosphate, and phosphoric acid.

[0071] In some embodiments of the present application, the concentration of Fe element in the ferrous solution is 0.5 mol / L~2 mol / L.

[0072] In this embodiment, when the concentration of Fe element in ferrous solution is too high, the preservation difficulty of ferrous solution easily produces crystallization. When the concentration of ferrous solution is too low, the product amount under the same volume is too few, easily causing manufacturing cost to increase. Alternatively, in ferrous solution, the concentration of Fe element is 0.5mol / L, 0.75mol / L, 1mol / L, 1.25mol / L, 1.5mol / L, 1.75mol / L or 2mol / L, or, in ferrous solution, the concentration of Fe element can also be in the scope between above-mentioned any two concentrations.

[0073] In some embodiments of the present application, the concentration of the P element in the mixed solution of the phosphorus source and the oxidant is 0.5 mol / L to 2.2 mol / L.

[0074] In this embodiment, when the concentration of the element P in the mixed solution of the phosphorus source and the oxidant is too high, the mixed solution of the phosphorus source and the oxidant is difficult to store and is prone to crystallization. When the concentration of the element P in the mixed solution of the phosphorus source and the oxidant is too low, the amount of product per volume is too small, which can easily lead to increased manufacturing costs. Optionally, the concentration of the element P in the mixed solution of the phosphorus source and the oxidant is 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, or 2.2 mol / L. Alternatively, the concentration of the element P in the mixed solution of the phosphorus source and the oxidant can also be within a range between any two of the above concentrations.

[0075] In some embodiments of the present application, in the mixed solution of the phosphorus source and the oxidant, the concentration of the oxidant is 0.25 mol / L to 1.5 mol / L.

[0076] Optionally, the concentration of the oxidant in the mixed solution of the phosphorus source and the oxidant is 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, 1 mol / L, 1.25 mol / L or 1.5 mol / L, or the concentration of the oxidant in the mixed solution of the phosphorus source and the oxidant may also be within the range between any two of the above concentrations.

[0077] In some embodiments of the present application, the molar ratio of phosphorus in the mixed solution of the phosphorus source and the oxidant to iron in the ferrous solution is (1-1.1):1.

[0078] In this embodiment, within the range of the molar ratio of the phosphorus element in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution, the iron phosphate particles are favored to grow to a suitable size, thereby being beneficial for the particle size and distribution of the lithium iron phosphate prepared by the iron phosphate to be more suitable, thereby obtaining a higher compaction density and capacity. Optionally, the molar ratio of the phosphorus element in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution is 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1 or 1.1:1, or the molar ratio of the phosphorus element in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution can also be within the range between any two of the above molar ratios.

[0079] In some embodiments of the present application, the molar ratio of the oxidant in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution is (0.5-0.75):1.

[0080] In this embodiment, the molar ratio of the oxidant to the iron in the ferrous solution is within the range that facilitates the reaction of the ferrous solution with the mixed solution of the phosphorus source and the oxidant to produce ferric phosphate. Alternatively, the molar ratio of the oxidant to the iron in the ferrous solution is 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, or 0.75:1, or the molar ratio of the oxidant to the iron in the ferrous solution may also be within a range between any two of the above molar ratios.

[0081] In some embodiments of the present application, the preparation of a mixed solution of a phosphorus source and an oxidant comprises the following steps:

[0082] dissolving a phosphorus source in pure water to obtain a first solution;

[0083] Adjusting the pH value of the first solution to 6.5-7.5 to obtain a second solution;

[0084] The second solution is mixed with an oxidant to obtain a mixed solution of a phosphorus source and an oxidant.

[0085] In this embodiment, within the pH range of the second solution, the ionization of the phosphorus source is facilitated, thereby increasing the concentration of phosphate ions in the mixed solution, which is conducive to the precipitation of Fe element to form ferric phosphate. Optionally, the pH value of the second solution is 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4 or 7.5, or the pH value of the second solution can also be within the range between any two of the above pH values.

[0086] In some embodiments of the present application, the feed port 2 disposed at the top of the reaction chamber 1 is vertically higher than the end of the discharge pipe 4 that is not connected to the discharge port 3 .

[0087] In this embodiment, the height of the feed port 2 in the vertical direction is higher than the end of the discharge pipe 4 that is not connected to the discharge port 3, so that the ferrous solution and the mixed solution of the phosphorus source and the oxidant can be added into the reaction chamber 1 above the liquid surface in the reaction chamber 1, and the blockage caused by the feed port 2 being located below the liquid surface can be avoided.

[0088] In some embodiments of the present application, the addition rate of the ferrous solution is 0.5 L / min to 2 L / min.

[0089] Optionally, the addition rate of the ferrous solution is 0.5 L / min, 0.75 L / min, 1 L / min, 1.25 L / min, 1.7 L / min, 1.75 L / min or 2 L / min, or, the addition rate of the ferrous solution may be within the range between any two of the above rates.

[0090] In some embodiments of the present application, the addition rate of the mixed solution of the phosphorus source and the oxidant is 0.5 L / min to 2 L / min.

[0091] Optionally, the addition rate of the mixed solution of the phosphorus source and the oxidant is 0.5 L / min, 0.75 L / min, 1 L / min, 1.25 L / min, 1.7 L / min, 1.75 L / min or 2 L / min, or, the addition rate of the mixed solution of the phosphorus source and the oxidant may also be within the range between any two of the above rates.

[0092] In this embodiment, within the range of the addition rates of the ferrous solution and the mixed solution of the phosphorus source and the oxidant, uniform mixing of the materials is facilitated, and continuous preparation of ferric phosphate with controllable particle size is facilitated.

[0093] In some embodiments of the present application, the step of aging the slurry to obtain an aged slurry includes:

[0094] Mixing the slurry and the phosphoric acid solution to obtain a reaction slurry;

[0095] The reaction slurry is subjected to heat preservation treatment to obtain aged slurry.

[0096] In this embodiment, the aging treatment is beneficial for the unreacted materials to continue to generate iron phosphate, thereby improving the yield of iron phosphate.

[0097] In some embodiments of the present application, the mass percentage concentration of the phosphoric acid solution is 80% to 90%.

[0098] In this embodiment, within the above-mentioned mass percentage concentration range of the phosphoric acid solution, it is beneficial for the unreacted material to continue to generate iron phosphate during the aging process of the slurry to obtain the aged slurry, thereby improving the yield of iron phosphate. Optionally, the mass percentage concentration of the phosphoric acid solution is 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89% or 90%, or the mass percentage concentration of the phosphoric acid solution can also be within the range between any two of the above mass percentage concentrations.

[0099] In some embodiments of the present application, the molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution is (0.1-0.2):1.

[0100] In this embodiment, within the range of the molar ratio of the phosphorus element in the phosphoric acid solution to the iron element in the ferrous solution, it is beneficial for the slurry to be aged to obtain an aged slurry, and the unreacted material continues to generate iron phosphate, thereby improving the yield of iron phosphate. Optionally, the molar ratio of the phosphorus element in the phosphoric acid solution to the iron element in the ferrous solution is 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1 or 0.2:1, or the molar ratio of the phosphorus element in the phosphoric acid solution to the iron element in the ferrous solution can also be within the range between any two of the above molar ratios.

[0101] In some embodiments of the present application, the insulation temperature of the insulation treatment is 95°C~100°C.

[0102] In this embodiment, within the above-mentioned holding temperature range for the holding treatment, it is beneficial for the unreacted material to continue to generate iron phosphate during the aging treatment of the slurry to obtain the aged slurry, thereby improving the yield of iron phosphate. Optionally, the holding temperature for the holding treatment is 95°C, 95.5°C, 96°C, 96.5°C, 97°C, 97.5°C, 98°C, 98.5°C, 99°C or 100°C, or the holding temperature for the holding treatment can also be within the range between any two of the above-mentioned temperatures.

[0103] In some embodiments of the present application, the insulation time of the insulation treatment is 1 hour to 2 hours.

[0104] In this embodiment, within the range of the holding time of the above-mentioned insulation treatment, it is beneficial for the unreacted material to continue to generate iron phosphate during the aging treatment of the slurry to obtain the aged slurry, thereby improving the yield of iron phosphate. Optionally, the insulation time of the insulation treatment is 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2 hours, or the insulation time of the insulation treatment can also be within the range between any two of the above-mentioned times.

[0105] In some embodiments of the present application, the calcination temperature of the calcination treatment is 500°C to 800°C.

[0106] In some embodiments of the present application, the calcination time of the calcination treatment is 1 hour to 10 hours.

[0107] In this embodiment, within the above parameter ranges of the calcination treatment, it is beneficial to ensure sufficient dehydration time and uniform heating of the particles, thereby preparing iron phosphate with a more uniform particle size distribution and a more suitable particle size.

[0108] Optionally, the calcination temperature of the calcination treatment is 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, or the calcination temperature of the calcination treatment may also be within the range between any two of the above temperatures.

[0109] Optionally, the calcination time of the calcination treatment is 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, or, the calcination time of the calcination treatment may also be within the range between any two of the above times.

[0110] In a second aspect, an embodiment of the present application provides a device for preparing ferric phosphate, which is used to prepare ferric phosphate using any of the above methods for preparing ferric phosphate, comprising: a reactor;

[0111] The reactor includes a reaction chamber 1, a feed port 2 arranged at the top of the reaction chamber 1, a discharge port 3 arranged at the bottom of the reaction chamber 1, and a discharge pipe 4 connected to the discharge port 3. The discharge pipe 4 is arranged parallel to the reaction chamber 1 in the vertical direction. The end of the discharge pipe 4 not connected to the discharge port 3 is higher in the vertical direction than the discharge port 3, and the height of the discharge pipe 4 in the vertical direction is adjusted according to the liquid level in the reaction chamber 1.

[0112] In the technical solution of the embodiment of the present application, the preparation device of iron phosphate can be used to prepare iron phosphate using any of the above-mentioned preparation methods of iron phosphate to achieve control of the particle size of the prepared iron phosphate. By adjusting the height of the end of the discharge pipe 4 that is not connected to the discharge port 3 in the vertical direction, the liquid level in the reaction chamber 1 can be controlled, thereby controlling the contact time of the ferrous solution and the mixed solution of the phosphorus source and the oxidant in the reaction chamber 1, and then controlling the particle size of the iron phosphate. Furthermore, since the discharge pipe 4 and the reaction chamber 1 are arranged in parallel in the vertical direction, the mixed reaction liquid will rise in the discharge pipe 4 in the vertical direction. During the rising process, the iron phosphate particles generated by the mixed reaction will produce slow sedimentation, so that in the discharge pipe 4, the particle size of the iron phosphate particles close to the end of the discharge port 3 is larger, and the particle size of the iron phosphate particles away from the end of the discharge port 3 is smaller. Therefore, by adjusting the vertical height of the end of the discharge pipe 4 not connected to the discharge port 3 , the growth particle size of the iron phosphate collected from the end of the discharge pipe 4 not connected to the discharge port 3 can be controlled.

[0113] In some embodiments of the present application, the feed port 2 arranged at the top of the reaction chamber 1 includes a first feed port 2 and a second feed port 2, and the first feed port 2 and the second feed port 2 are respectively used to add ferrous solution and a mixed solution of phosphorus source and oxidant into the reaction chamber 1.

[0114] In a third aspect, an embodiment of the present application provides an iron phosphate prepared by any of the above-mentioned methods for preparing iron phosphate.

[0115] In the technical solution of the embodiment of the present application, the particle size of the iron phosphate can be adjusted, which is conducive to obtaining iron phosphate with uniform particle size distribution, and further conducive to the prepared positive electrode material having better electrochemical properties.

[0116] In a fourth aspect, an embodiment of the present application provides a lithium iron phosphate material prepared using raw materials including the above-mentioned iron phosphate.

[0117] In the technical solution of the embodiment of the present application, the lithium iron phosphate material has electrochemical properties such as a higher charge specific capacity, a higher discharge specific capacity, and better rate performance.

[0118] In a fifth aspect, an embodiment of the present application provides a positive electrode plate, comprising a current collector and an active layer located on the surface of the current collector, wherein the active layer comprises the above-mentioned lithium iron phosphate material.

[0119] In a sixth aspect, in the technical solution of the embodiment of the present application, the active layer of the positive electrode plate includes the above-mentioned positive electrode material, and thus has good electrochemical performance.

[0120] In a seventh aspect, an embodiment of the present application provides a secondary battery comprising the above-mentioned positive electrode plate.

[0121] In the technical solution of the embodiment of the present application, the secondary battery includes the above-mentioned positive electrode plate, and thus has comprehensively improved electrochemical performance, so that it can be well applied in multiple usage scenarios.

[0122] In an eighth aspect, an embodiment of the present application provides an electrical device.

[0123] The electrical devices provided in the embodiments of the present application may be, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery-powered vehicles, electric cars, ships, spacecraft, etc. The electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0124] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0125] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0126] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0127] 1. Preparation method

[0128] Example 1

[0129] Preparation method of ferric phosphate:

[0130] (1) Dissolve solid ferrous phosphate in pure water to prepare 10 kg of ferrous sulfate solution with an Fe concentration of 1 mol / L. Dissolve monoammonium dihydrogen phosphate in pure water to obtain a first solution, and then add ammonia water to adjust the pH of the first solution to 7.0 to obtain a second solution. Mix the second solution with hydrogen peroxide to prepare a 10 kg mixed solution of monoammonium dihydrogen phosphate and hydrogen peroxide with a P concentration of 1.05 mol / L and a H2O2 concentration of 0.6 mol / L.

[0131] (2) 500 g of pure water was placed as the base liquid in the reaction chamber 1 of the reactor. Ferrous sulfate solution and a mixture of monoammonium dihydrogen phosphate and hydrogen peroxide were dripped into the reaction chamber 1 through two pipelines at a rate of 0.5 L / min, and the reaction slurry was collected from the end of the discharge pipe 4 that was not connected to the discharge port 3.

[0132] (3) The reaction slurry was filtered and washed with water to obtain a filter cake. 600 g of the filter cake was mixed with 1000 g of water for slurry treatment to obtain a slurry. 20 g of a phosphoric acid solution with a mass percentage concentration of 85% was added to the slurry and continued stirring. The molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution was 0.15. The slurry was kept warm in a 98°C water bath. When the slurry turned pink, it was kept warm for 1.5 hours and then filtered and washed with water to obtain dihydrated iron phosphate. The dihydrated iron phosphate was dried and calcined at 600°C for 2 hours to obtain iron phosphate.

[0133] Preparation method of lithium iron phosphate:

[0134] Iron phosphate, lithium carbonate and glucose were mixed in a molar ratio of 1:1:0.15, mixed evenly and then calcined under nitrogen atmosphere at a temperature of 600°C for 10 hours to obtain lithium iron phosphate positive electrode material.

[0135] Example 2

[0136] Preparation method of ferric phosphate:

[0137] The preparation method of ferric phosphate in Example 2 is the same or similar to that in Example 1, except that in step (1) of this example, the concentration of the Fe element in the ferrous phosphate solution is 0.5 mol / L, the concentration of the P element in the mixed solution of monoammonium dihydrogen phosphate and hydrogen peroxide is 0.5 mol / L, and the concentration of H2O2 is 0.25 mol / L.

[0138] Example 3

[0139] The preparation method of ferric phosphate in Example 3 is the same or similar to that in Example 1, except that in step (1) of this example, the concentration of the Fe element in the ferrous phosphate solution is 2 mol / L, the concentration of the P element in the mixed solution of monoammonium dihydrogen phosphate and hydrogen peroxide is 2.2 mol / L, and the concentration of H2O2 is 1.5 mol / L.

[0140] Example 4

[0141] The preparation method of ferric phosphate in Example 4 is the same as or similar to that in Example 1, except that, in step (1) of this example, aqueous ammonia is added to adjust the pH value of the first solution to 6.5.

[0142] Example 5

[0143] The preparation method of ferric phosphate in Example 5 is the same or similar to that in Example 1, except that, in step (1) of this example, ammonia water is added to adjust the pH value of the first solution to 7.5.

[0144] Example 6

[0145] The preparation method of ferric phosphate in Example 6 is the same or similar to that in Example 1, except that in step (2) of this example, the dripping rate of the ferrous sulfate solution and the mixed solution of monoammonium dihydrogen phosphate and hydrogen peroxide is 2 L / min.

[0146] Example 7

[0147] The preparation method of ferric phosphate in Example 7 is the same as or similar to that in Example 1, except that in step (3) of this example, the molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution is 0.1:1.

[0148] Example 8

[0149] The preparation method of ferric phosphate in Example 8 is the same or similar to that in Example 1, except that in step (3) of this example, the molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution is 0.2:1.

[0150] Example 9

[0151] The preparation method of ferric phosphate in Example 9 is the same or similar to that in Example 1, except that in step (3) of this example, the holding temperature is 95°C, the holding time is 2 hours, the calcination temperature is 400°C, and the calcination time is 10 hours.

[0152] Comparative Example 1

[0153] Preparation method of ferric phosphate:

[0154] (1) Dissolve solid ferrous phosphate in pure water to prepare 10 kg of ferrous sulfate solution with an Fe concentration of 1 mol / L. Dissolve monoammonium dihydrogen phosphate in pure water to obtain a first solution, and then add ammonia water to adjust the pH of the first solution to 7.0 to obtain a second solution. Mix the second solution with hydrogen peroxide to prepare a 10 kg mixed solution of monoammonium dihydrogen phosphate and hydrogen peroxide with a P concentration of 1.05 mol / L and a H2O2 concentration of 0.6 mol / L.

[0155] (2) Place 10 kg of ferrous sulfate solution as the base liquid in a 50 L reactor, and use a peristaltic pump to drip a mixture of monoammonium dihydrogen phosphate and hydrogen peroxide into the reactor at a rate of 0.5 L / min. After the addition is completed, continue stirring for 50 minutes to obtain a reaction slurry.

[0156] (3) The reaction slurry was filtered and washed with water to obtain a filter cake. 600 g of the filter cake was mixed with 1000 g of water for slurry treatment to obtain a slurry. 20 g of a phosphoric acid solution with a mass percentage concentration of 85% was added to the slurry and continued stirring. The molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution was 0.15. The slurry was kept warm in a 98°C water bath. When the slurry turned pink, it was kept warm for 1.5 hours and then filtered and washed with water to obtain dihydrated iron phosphate. The dihydrated iron phosphate was dried and calcined at 600°C for 2 hours to obtain iron phosphate.

[0157] Preparation method of lithium iron phosphate:

[0158] Iron phosphate, lithium carbonate and glucose were mixed in a molar ratio of 1:1:0.15, mixed evenly and then calcined under nitrogen atmosphere at a temperature of 600°C for 10 hours to obtain lithium iron phosphate positive electrode material.

[0159] 2. Test Method

[0160] The ferric phosphate prepared in Examples 1-8 and Comparative Example 1 was tested, wherein the elemental composition was determined by ICP-OES; the specific surface area was determined by the gas adsorption BET method; the particle size was determined by a laser particle size analyzer; the pH value was determined according to GB / T 9724, General Rules for the Determination of pH Value of Chemical Reagents; and the tap density was determined using a tap density meter with 5000 taps. The test results are shown in Table 1 below:

[0161] Table 1

[0162]

[0163] The lithium iron phosphate prepared in Examples 1 to 9 and Comparative Example 1 was mixed with conductive carbon black and PVDF binder in a mass ratio of 90:5:5 and coated on a 12 μm thick aluminum foil. The pole piece was then placed in an oven at 110°C and dried for 10 hours. The dried pole piece was punched into a positive electrode disc with a diameter of 15 mm and rolled to a compact density of 2.5 g / cm3. A 16 mm diameter lithium sheet was used as the counter electrode, and the electrolyte was 1 M LiPF6 dissolved in EC:EMC:DEC with a volume ratio of 1:1:1. The battery was assembled in an LG2400 / 1000TS glove box produced by Weige Gas Purification Technology (Suzhou) Co., Ltd. to obtain a button half-cell, which was then subjected to a rate performance test.

[0164] The battery performance test system (model: CT3002A) from Wuhan Blue Electric Electronic Technology Co., Ltd. was used. The test temperature was 25°C, the voltage range was 2V~3.75V, and the test was performed at 0.1C rate and 1C rate respectively. The test results are shown in Table 2 below:

[0165] Table 2

[0166]

[0167] 3. Analysis of test results of various embodiments and comparative examples

[0168] Reference Figures 3 to 5 As shown, Figure 3 This is the XRD pattern of the iron phosphate prepared in Example 1. Figure 4 、 Figure 5 The SEM image of the iron phosphate prepared in Example 1. Compared with Example 1, the concentrations of the Fe element and the P element in Examples 2 and 3 are different, that is, the supersaturation in the iron-phosphorus precipitation environment is different. In the precipitation synthesis process, supersaturation (the degree to which the solute concentration in the solution exceeds the equilibrium solubility) is a key parameter for controlling particle characteristics and directly affects the competitive relationship between nucleation and growth. Under low supersaturation, the nucleation rate is slow, and the solute tends to grow slowly on the existing crystal nuclei. Since fewer new nuclei are formed, the crystals have ample time to grow by diffusion, eventually forming particles with larger particle size and a narrower particle size distribution. High supersaturation significantly accelerates nucleation, generating a large number of crystal nuclei in a short period of time, solutes are quickly consumed, and the growth time of individual particles is limited, thus forming smaller particles.

[0169] Compared with Example 1, in Examples 4 and 5, the pH value of the first solution is different. The high pH value increases the pH value in the precipitation system, and the utilization rate of Fe increases slightly, but the magnitude is not obvious. When the pH value is relatively low, the Fe element precipitates completely, and there is relatively more residual Fe in the filtrate, which makes the iron-phosphorus ratio in the ferric phosphate relatively low, and has no effect on other indicators.

[0170] Compared to Example 1, in Example 6, the dripping rate of the mixed solution of ferrous sulfate solution and monoammonium dihydrogen phosphate is different from that of hydrogen peroxide, and in serialization precipitation building-up process, the size of flow directly affects the mixing rate of reactant, the residence time and the local supersaturation, and then the particle size distribution, particle size and shape of precipitate are significantly affected. In the case of high flow, iron phosphorus raw material rapidly enters reactor, and local supersaturation sharply increases, and nucleation rate is accelerated, and a large amount of nuclei are generated in a short time, and small-sized particles are easily formed, and final particle size is less.

[0171] Compared to Example 1, Examples 7 and 8 adjusted the proportion of added phosphoric acid. This phosphoric acid consumes the iron hydroxide that was not fully converted to iron phosphate in the initial precipitation, while also providing the pH environment required for the crystallization of iron phosphate. Therefore, increasing or decreasing the amount of this phosphoric acid affects the yield of the Fe element and the efficiency of the crystallization, and the iron-to-phosphorus ratio in the anhydrous iron phosphate will decrease or increase accordingly.

[0172] Compared with Example 1, Example 9 reduces the aging temperature and prolongs the holding time. This operation does not affect the crystallization process of ferric phosphate, and ferric phosphate in the dihydrate phase is also obtained. In the subsequent calcination process, the calcination temperature is 400 ° C and the holding time is 10 hours. At this temperature, ferric phosphate dihydrate can be dehydrated, but crystallization cannot be achieved, and the particles fail to integrate. The obtained material has a high BET, a particle size distribution close to the dihydrate phase, and a low tap density.

[0173] In the process of synthesizing lithium iron phosphate, the particle characteristics of iron phosphate may be partially retained or modified. If the tap density of the precursor iron phosphate is high, its particles are more compact and have good fluidity. After conversion to lithium iron phosphate, the gaps between the particles may be smaller, making it easier to form a high compaction density electrode during compaction. Iron phosphate with a high tap density usually corresponds to lithium iron phosphate with a higher compaction density, thereby also increasing the volume energy density of the battery. The preparation method of iron phosphate in this application can indirectly affect the compaction density of lithium iron phosphate by regulating the particle size of iron phosphate particles.

[0174] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing ferric phosphate, characterized in that: The steps include: providing a ferrous solution and a mixed solution of a phosphorus source and an oxidant; Mixing the ferrous solution with the mixed solution of the phosphorus source and the oxidant to obtain a reaction slurry; The reaction slurry is subjected to solid-liquid separation to obtain a filter cake, and then the filter cake is subjected to slurry treatment to obtain a slurry; The slurry is subjected to aging treatment to obtain an aged slurry, and then the aged slurry is subjected to solid-liquid separation and water washing to obtain ferric phosphate dihydrate; calcining the ferric phosphate dihydrate to obtain the ferric phosphate; Wherein, the mixing reaction of the ferrous solution and the mixed solution of the phosphorus source and the oxidant is carried out in a reactor, and the reactor includes a reaction chamber, a feed port arranged at the top of the reaction chamber, a discharge port arranged at the bottom of the reaction chamber, and a discharge pipe connected to the discharge port, the discharge pipe and the reaction chamber are arranged parallel in the vertical direction, the end of the discharge pipe not connected to the discharge port is higher in the vertical direction than the discharge port, and the height of the discharge pipe in the vertical direction is adjusted according to the liquid level in the reaction chamber.

2. The method for preparing ferric phosphate according to claim 1, wherein The molar ratio of phosphorus in the mixed solution of the phosphorus source and the oxidant to iron in the ferrous solution is (1-1.1):1; and / or, The molar ratio of the oxidant in the mixed solution of the phosphorus source and the oxidant to the iron element in the ferrous solution is (0.5-0.75):

1.

3. The method for preparing ferric phosphate according to claim 1, wherein The preparation of the mixed solution of the phosphorus source and the oxidant comprises the following steps: dissolving a phosphorus source in pure water to obtain a first solution; Adjusting the pH value of the first solution to 6.5-7.5 to obtain a second solution; The second solution is mixed with an oxidant to obtain a mixed solution of the phosphorus source and the oxidant.

4. The method for preparing ferric phosphate according to claim 1, wherein The step of aging the slurry to obtain an aged slurry comprises: Mixing the slurry and phosphoric acid solution to obtain reaction slurry; The reaction slurry is subjected to heat preservation treatment to obtain the aged slurry.

5. The method for preparing ferric phosphate according to claim 4, wherein: The mass percentage concentration of the phosphoric acid solution is 80% to 90%; and / or, The molar ratio of phosphorus in the phosphoric acid solution to iron in the ferrous solution is (0.1-0.2):1; and / or, The heat preservation temperature of the heat preservation treatment is 95°C to 100°C; and / or, The heat preservation time of the heat preservation treatment is 1h~2h.

6. A device for preparing iron phosphate, characterized in that: Used to prepare ferric phosphate using the preparation method of ferric phosphate according to any one of claims 1 to 5, comprising: a reaction kettle; The reactor includes a reaction chamber, a feed port arranged at the top of the reaction chamber, a discharge port arranged at the bottom of the reaction chamber, and a discharge pipe connected to the discharge port. The discharge pipe is arranged parallel to the reaction chamber in the vertical direction, and the end of the discharge pipe that is not connected to the discharge port is higher in the vertical direction than the discharge port, and the height of the discharge pipe in the vertical direction is adjusted according to the liquid level in the reaction chamber.

7. A ferric phosphate, characterized in that: The ferric phosphate is prepared by the method for preparing the ferric phosphate according to any one of claims 1 to 6.

8. A lithium iron phosphate material, characterized in that: The ferric phosphate is prepared from raw materials comprising the ferric phosphate according to claim 7.

9. A positive electrode plate, characterized in that: It comprises a current collector and an active layer located on the surface of the current collector, wherein the active layer comprises the lithium iron phosphate material according to claim 8.

10. A secondary battery, characterized in that: Including the positive electrode sheet according to claim 9.

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