Preparation method for lithium iron phosphate, positive electrode active material, positive electrode plate, battery, and power-consuming device

Abstract

Provided are a preparation method for lithium iron phosphate, a positive electrode active material, a positive electrode plate, a battery, and a power-consuming device. The preparation method for lithium iron phosphate comprises: dissolving a first iron source, a second iron source, a lithium source and a phosphorus source in a solvent to obtain a mixed slurry; and sintering the mixed slurry to obtain lithium iron phosphate, wherein the first iron source comprises at least one of iron oxide or first iron phosphate, and the second iron source comprises at least one of second iron phosphate or ferrous oxalate, the first iron phosphate has an iron to phosphorus ratio of 0.97-0.985, and the second iron phosphate has an iron to phosphorus ratio of 0.93-0.96. The primary particles of lithium iron phosphate, which have different particle sizes, can be mixed and matched, thus improving the compact density of lithium iron phosphate and the energy density of the battery.

Description

Preparation method of lithium iron phosphate, positive electrode active material, positive electrode sheet, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311365889.9, filed on October 20, 2023, entitled “Method for preparing lithium iron phosphate, positive electrode active material, positive electrode sheet, battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and more specifically, to a preparation method of lithium iron phosphate, a positive electrode active material, a positive electrode sheet, a battery, and an electrical device. Background Art

[0004] In recent years, the application of lithium-ion batteries has become increasingly extensive, such as energy storage power supply fields such as wind power, hydropower, thermal power generation and solar power stations, as well as electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. While lithium-ion batteries have made great progress, higher requirements have been put forward for various aspects of performance.

[0005] Therefore, how to improve the energy density of lithium-ion batteries is an urgent problem that needs to be solved.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a preparation method of lithium iron phosphate, a positive electrode active material, a positive electrode sheet, a battery and an electrical device, thereby improving the energy density of the battery.

[0008] In a first aspect, a method for preparing lithium iron phosphate is provided, comprising: dissolving a first iron source, a second iron source, a lithium source, a phosphorus source, and a carbon source in a solvent to obtain a mixed slurry; and sintering the mixed slurry to obtain lithium iron phosphate; wherein the first iron source comprises at least one of iron oxide or a first iron phosphate, and the second iron source comprises at least one of a second iron phosphate or ferrous oxalate; the iron-to-phosphorus ratio of the first iron phosphate is 0.97-0.985, and the iron-to-phosphorus ratio of the second iron phosphate is 0.93-0.96.

[0009] In an embodiment of the present application, the iron source for preparing lithium iron phosphate includes a first iron source and a second iron source, wherein the first iron source includes at least one of iron oxide or a first iron phosphate, and the second iron source includes at least one of a second iron phosphate or ferrous oxalate, and the iron-phosphorus ratio of the first iron phosphate is 0.97-0.985, and the iron-phosphorus ratio of the second iron phosphate is 0.93-0.96. By using the above-mentioned first iron source and second iron source as the iron source for preparing lithium iron phosphate, the prepared lithium iron phosphate has different primary particle sizes, which can achieve a mix of large and small particle sizes of lithium iron phosphate, thereby increasing the compaction density of the lithium iron phosphate and increasing the energy density of the battery.

[0010] In one possible implementation, the iron-to-phosphorus ratio of the second ferric phosphate is 0.94-0.96.

[0011] In the embodiment of the present application, by setting the iron-phosphorus ratio in the second iron phosphate to 0.94-0.96, the compaction density and battery performance of the lithium iron phosphate can be further improved.

[0012] In a possible implementation manner, the molar ratio of the iron element in the first iron source to the iron element in the second iron source is 0.5-4.

[0013] In the embodiments of the present application, the use of a first iron source and a second iron source can respectively produce lithium iron phosphate with smaller and larger particle sizes, thereby achieving a mixture of large and small particle sizes of lithium iron phosphate. By setting the molar ratio of the iron element of the first iron source and the second iron source to 0.5-4, a reasonable mixture of large and small primary particle sizes can be achieved, thereby effectively improving the compaction density of the lithium iron phosphate and the energy density of the battery.

[0014] In one possible embodiment, the volume average particle size Dv50 of the mixed slurry is 0.3 μm-0.8 μm.

[0015] In the embodiment of the present application, the particle size of the lithium iron phosphate particles can be maintained within a reasonable range by setting the volume average particle size Dv50 of the mixed slurry to 0.3 μm-0.8 μm.

[0016] In one possible embodiment, the molar ratio of the iron in the first iron source and the second iron source, the lithium in the lithium source, and the phosphorus in the phosphorus source is (0.9-1):(0.96-1.06):(0.95-1.05). Optionally, the molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is (1.003-1.01):1.

[0017] In the embodiment of the present application, by making the molar ratio of iron in the iron source, lithium in the lithium source and lithium in the phosphorus source (0.9-1): (0.96-1.06): (0.95-1.05), that is, making the molar ratio of iron element, lithium element and phosphorus element the above value, the loss of lithium element and phosphorus element in the preparation process can be compensated to obtain lithium iron phosphate with better performance.

[0018] In the embodiment of the present application, by controlling the molar ratio of the lithium element in the lithium source and the phosphorus element in the phosphorus source to (1.003-1.01):1, the ionic order of the Li element and the Fe element of the formed lithium iron phosphate is improved, the dislocation of Li and Fe in the lithium iron phosphate is effectively reduced, the length of the lithium ion transmission path is controlled, and the reversible capacity of the lithium iron phosphate is thereby increased.

[0019] In one possible implementation, the first iron source includes iron oxide, and the second iron source includes second iron phosphate.

[0020] In the above scheme, by making the first iron source include iron oxide and the second iron source include a second iron phosphate with an iron-phosphorus ratio of 0.93-0.96, the iron oxide and the second iron phosphate are easy to obtain and widely used. They can not only prepare lithium iron phosphate with a mix of large and small particles, thereby increasing the compaction density of lithium iron phosphate and the energy density of the battery, but also can be widely used in industry.

[0021] In a possible implementation, the primary particle size of the iron oxide is 0.05 μm-0.6 μm.

[0022] In the embodiment of the present application, by using iron oxide with a primary particle size of 0.05 μm-0.6 μm, the iron oxide is easy to react during the reaction process, which is conducive to forming better lithium iron phosphate.

[0023] In a possible implementation, the primary particle size of the iron oxide is 0.05 μm-0.4 μm.

[0024] In the embodiment of the present application, by using iron oxide with a primary particle size of 0.05 μm-0.4 μm, lithium iron phosphate with better performance can be obtained.

[0025] In a possible embodiment, the sintering includes: in an inert gas, heating the mixed slurry to 450° C.-600° C. and keeping the temperature for 2 h-5 h, and then heating the mixed slurry to 700° C.-850° C. and keeping the temperature for 6 h-15 h.

[0026] In the embodiment of the present application, by adopting two reaction intervals of 450℃-600℃ and 700℃-850℃, the first iron source and the second iron source react with the phosphorus source and the lithium source respectively to form larger and smaller lithium iron phosphate particle sizes, thereby achieving a mix of large and small particle sizes of lithium iron phosphate.

[0027] In a possible embodiment, the method further includes: dissolving a carbon source in the solvent to form the mixed slurry; the carbon source includes at least one of sucrose, glucose, dextrin, citric acid, fructose or starch.

[0028] In the embodiments of the present application, the addition of carbon material not only increases the conductivity of the lithium iron phosphate, but also reacts with metallic iron powder at high temperatures to form Fe-C compounds. This reduction reaction helps lower the reaction temperature, promotes the reaction, and effectively controls the crystal structure and particle morphology of the lithium iron phosphate product.

[0029] In a possible implementation, the mass ratio of the carbon source to the lithium iron phosphate is 0.01-0.1.

[0030] In the embodiment of the present application, by setting the mass ratio of the carbon source to the lithium iron phosphate to 0.01-0.1, the carbon source can be made to function without affecting the energy density of the battery.

[0031] In a possible embodiment, the method further includes: dissolving a dispersant in the solvent to form the mixed slurry; the dispersant includes at least one of polyethylene glycol, polyvinyl alcohol, or polyvinyl pyrrolidone.

[0032] In the embodiment of the present application, by including a dispersant in the mixed slurry, the viscosity of the mixed slurry can be reduced, thereby facilitating subsequent operations.

[0033] In some embodiments, the mass ratio of the dispersant to the lithium iron phosphate is 0.005-0.08.

[0034] In the embodiment of the present application, by setting the mass ratio of the dispersant to the lithium iron phosphate to 0.005-0.08, the dispersant can be effective without affecting the energy density of the battery.

[0035] In some embodiments, the method further includes: dissolving an additive in the solvent to form the mixed slurry together; the additive includes a compound containing at least one element of Ti, Ga, Sr, W, Mg, Si, Y, Zr, B, Mo or La, or the additive includes a substance containing at least one element of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, V, B, S, Si, N, F, Cl or Br.

[0036] In the embodiment of the present application, by including additives in the mixed slurry, the additives enter the crystal lattice, which can increase the diffusion rate of lithium ions and thereby improve the ionic conductivity and rate performance.

[0037] In some embodiments, the mass ratio of the additive to the lithium iron phosphate is 0.0001-0.0005.

[0038] In the embodiment of the present application, by setting the mass ratio of the additive to lithium iron phosphate to 0.0001-0.0005, the additive can be effective without affecting the energy density of the battery.

[0039] In a possible embodiment, the lithium source includes at least one of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium acetate or lithium oxalate.

[0040] In a possible embodiment, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or lithium dihydrogen phosphate.

[0041] A second aspect of the present application provides a positive electrode active material, which includes lithium iron phosphate prepared by the preparation method described in any embodiment of the first aspect of the present application.

[0042] In one possible embodiment, the compaction density of the lithium iron phosphate at 3T is greater than or equal to 2.5 g / cm 3 Alternatively, in the FTIR spectrum of lithium iron phosphate, PO4 3- Characteristic absorption peak position ≤995cm -1 Alternatively, the powder compaction density of lithium iron phosphate at 3 tons is 2.5g / cm 3 -2.65g / cm 3 Between, further optional at 2.55g / cm 3 -2.65g / cm 3 Optionally, in the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤984cm -1 , optionally PO4 3- Characteristic absorption peak position ≤982.5cm -1 .

[0043] In the embodiment of the present application, the lithium iron phosphate prepared by the preparation method of the present application has a particle size of not less than 2.5g / cm 3 The compaction density helps to improve the capacity of the battery.

[0044] PO4 in the FTIR spectrum of lithium iron phosphate 3- Characteristic absorption peak position ≤984cm -1 , indicating that lithium iron phosphate has lower Li-Fe dislocation and a more regular lattice, so the material has a higher reversible capacity

[0045] In the third aspect of the present application, a phosphate-based cathode material is provided. In the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤995cm -1 The powder compaction density of phosphate cathode materials at 226.0738 MPa is 2.5 g / cm 3 Above. In the FTIR spectrum of lithium iron phosphate, PO4 3- Characteristic absorption peak position ≤995cm -1 , which shows that lithium iron phosphate has lower Li-Fe dislocation and a more regular lattice, so the material has a higher reversible capacity.

[0046] In some embodiments, the powder compaction density of the phosphate-based cathode material at 226.0738 MPa is 2.5 g / cm 3 -2.65g / cm 3 Between, optional 2.55g / cm 3 -2.65g / cm 3 between.

[0047] In some embodiments, in the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤984cm -1 , PO4 3- Characteristic absorption peak position ≤982.5cm -1 .

[0048] In some embodiments, the phosphate-based cathode material includes lithium iron phosphate, and at least one of a doping-modified substance and / or a coating-modified substance thereof; optionally, the phosphate-based cathode material includes a lithium iron phosphate having a molecular formula of Li m A a Fe x D d P y E e O zIn the Gg material, A comprises at least one element selected from Al, Na, K, or Mg; D comprises at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V; E comprises at least one element selected from B, S, Si, or N; and G comprises at least one element selected from S, F, Cl, or Br. m is selected from the range of 0.5 to 1.15; a is selected from the range of 0 to 0.1; x is selected from the range of 0.5 to 1; d is selected from the range of 0 to 0.5; y is selected from the range of 0.5 to 1; e is selected from the range of 0 to 0.5; z is selected from the range of 3.5 to 4; and g is selected from the range of 0 to 0.5. Phosphate-based cathode materials formed by element doping, where the doped elements are incorporated into the crystal lattice, can increase the diffusion rate of lithium ions, thereby improving ionic conductivity and rate performance.

[0049] In some embodiments, the phosphate-based positive electrode material also includes carbon; optionally, the mass content of carbon in the phosphate-based positive electrode material is 1.00%≤Wc≤1.90%, and / or optionally, the powder resistivity S of the phosphate-based positive electrode material at 8MPa is 90Ω.cm, further optionally, further optionally, the mass content of carbon in the phosphate-based positive electrode material is 1.20%≤Wc≤1.80%, and / or the powder resistivity S of the phosphate-based positive electrode material at 8MPa is 60Ω.cm.

[0050] The fourth aspect of the present application provides a positive electrode plate, comprising: a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising lithium iron phosphate prepared by the preparation method described in any one of the embodiments of the first aspect, or the positive electrode active material described in the second aspect, or the phosphate-based positive electrode material described in the third aspect.

[0051] In some embodiments, the positive electrode film layer satisfies any one or more of the following conditions:

[0052] 1) The amount of phosphate-based cathode material with a particle size of 50nm-200nm is 40%-80%;

[0053] 2) The cross-sectional area percentage of the phosphate-based positive electrode material with a particle size of not less than 1500 nm is 30%-80%.

[0054] The fifth aspect of the present application provides a battery cell comprising the positive electrode sheet described in any one of the embodiments of the fourth aspect.

[0055] The sixth aspect of the present application provides a battery, comprising the battery cell described in the fifth aspect of the present application.

[0056] The seventh aspect of the present application provides an electrical device comprising the battery described in the sixth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0058] FIG1 is a flow chart of a method for preparing lithium iron phosphate according to an embodiment of the present application.

[0059] FIG2 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

[0060] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0061] FIG4 is a schematic structural diagram of a battery cell according to an embodiment of the present application;

[0062] FIG5 is a schematic diagram of a battery according to an embodiment of the present application;

[0063] FIG6 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0064] FIG7 is a schematic structural diagram of an electric device according to an embodiment of the present application;

[0065] FIG8 is a SEM image of lithium iron phosphate according to one embodiment of the present application;

[0066] FIG. 9 is a SEM image of lithium iron phosphate according to an embodiment of the related art.

[0067] Figure 1: 1-electrical device; 11-housing, 12-electrode assembly, 13-cover plate; 100-battery cell, 121-positive electrode sheet, 122-positive electrode current collector, 123-positive electrode film layer, 400-battery, 401-upper case, 402-lower case, 500-motor, 600-controller. DETAILED DESCRIPTION

[0068] The following describes in detail the preparation method of the lithium iron phosphate, positive electrode active material, positive electrode sheet, battery cell, battery and electric device of the present application with appropriate reference to the drawings, but there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0069] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of specific range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0071] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0072] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0073] The terms "above", "below", "greater than" or "less than" as used in this application are inclusive of the number, for example, "at least one" means one or more, and "at least one of A and B" means "A", "B" or "A and B".

[0074] In the 21st century, humanity faces two critical challenges: energy crisis and environmental pollution. Therefore, the development and research of clean, renewable energy sources is of far-reaching significance. Automobiles account for approximately 40% of oil consumption, and 42% of global air pollution comes from vehicle emissions. Countries around the world attach great importance to electric vehicles, and my country's 863 Plan also lists their development as a key direction. Research on power batteries, which serve as on-board power sources, has become a major bottleneck in the development of electric vehicles. Currently, the main candidates for power batteries include nickel-metal hydride batteries, lithium-ion batteries, and fuel cells. Lithium-ion batteries offer significant advantages in terms of cost-effectiveness. As energy storage materials, lithium-ion batteries offer advantages over traditional materials, such as high voltage, high specific capacity, long cycle life, and excellent safety. They are widely used in portable electronic devices, electric vehicles, aerospace, and military engineering, offering a wide range of applications and significant economic benefits.

[0075] The performance of the cathode material largely determines the overall performance of the entire lithium-ion battery. Lithium iron phosphate (LiFeO4), with its olivine-type crystal structure, offers outstanding advantages such as high discharge capacity, long cycle life, excellent safety, low cost, and non-toxicity, making it suitable for a wide range of applications. However, its low compaction density is a significant obstacle to its development in the commercial battery industry. Compaction density significantly impacts battery performance, being closely related to specific capacity, efficiency, internal resistance, and battery cycle performance. Generally speaking, a higher compaction density leads to a higher battery capacity, so compaction density is also considered a reference indicator of material energy density. Under certain process conditions, a higher compaction density leads to a higher battery capacity. Especially in today's booming new energy vehicle market, improving the compaction density of lithium iron phosphate is a crucial prerequisite for its widespread application in new energy electric vehicles and hybrid electric vehicles.

[0076] At present, the market mainly increases the compaction density of lithium iron phosphate by increasing the primary particles of lithium iron phosphate or mixing large and small primary particles. However, increasing the primary particles will lengthen the lithium ion deintercalation path, affecting the material dynamics, and thus leading to performance degradation. The mixing of large and small primary particles is generally achieved by sand-milling large and small particles or directly mixing lithium iron phosphate of different particle sizes to increase the compaction density. This increases the production process control points during the production process, resulting in large batch fluctuations, which affects the widespread application of lithium iron phosphate.

[0077] In view of this, the present application provides a method for preparing lithium iron phosphate. The method for preparing lithium iron phosphate comprises: dissolving and mixing a first iron source, a second iron source, a lithium source, and a phosphorus source in a solvent to obtain a mixed slurry, and then sintering the mixed slurry to obtain lithium iron phosphate; wherein the first iron source comprises at least one of iron oxide or a first iron phosphate, and the second iron source comprises at least one of a second iron phosphate or ferrous oxalate. By using the first iron source and the second iron source to prepare lithium iron phosphate, not only can a mix of large and small particle sizes of lithium iron phosphate be achieved, thereby improving the compaction density of lithium iron phosphate and the energy density of the battery, but the preparation method is simple, low-cost, and easy to industrialize.

[0078] The preparation method of lithium iron phosphate, positive electrode active material, positive electrode plate, battery cell, battery and electrical device of the present application are described below with reference to the accompanying drawings.

[0079] In addition, the technical solution of the present application is applicable to various types of batteries such as lithium-ion batteries, and the present application does not limit this; for the convenience of description, the following description will take lithium-ion batteries as an example.

[0080] [Preparation method of lithium iron phosphate]

[0081] The first aspect of the present application provides a method for preparing lithium iron phosphate. FIG1 is a flow chart of the method for preparing lithium iron phosphate according to one embodiment of the present application. As shown in FIG1 , the preparation method includes:

[0082] 110: dissolving the first iron source, the second iron source, the lithium source, and the phosphorus source in a solvent to obtain a mixed slurry;

[0083] 120: sintering the mixed slurry to obtain lithium iron phosphate;

[0084] The first iron source includes at least one of iron oxide or a first iron phosphate, and the second iron source includes at least one of a second iron phosphate or ferrous oxalate; the iron-to-phosphorus ratio of the first iron phosphate is 0.97-0.985, and the iron-to-phosphorus ratio of the second iron phosphate is 0.93-0.96.

[0085] The lithium iron phosphate prepared by using the first iron source and the second iron source has particle sizes of different sizes, which can achieve a high compaction density of the lithium iron phosphate, thereby improving the energy density of the battery.

[0086] The mechanism and synthesis temperature required for the reaction of different iron sources with lithium and phosphorus sources to form lithium iron phosphate are different. The temperature for the reaction of iron oxide with lithium and phosphorus sources to form lithium iron phosphate must be above 600°C, the temperature for the reaction of iron phosphate with lithium and phosphorus sources to form lithium iron phosphate must be above 500°C, and the temperature for the reaction of ferrous oxalate with lithium and phosphorus sources to form lithium iron phosphate must be above 400°C. Therefore, compared with iron phosphate and iron oxide, during the sintering process, when the mixed slurry is heated to above 400°C, ferrous oxalate can preferentially react with the lithium source and the phosphorus source to form ferrous phosphate crystal nuclei; as the sintering temperature continues to increase, after the temperature is raised to above 500°C, iron phosphate can preferentially react with the lithium source and the phosphorus source to form lithium iron phosphate crystal nuclei compared to iron oxide; and iron oxide finally forms lithium iron phosphate crystal nuclei compared to ferrous oxalate and iron phosphate; the preferentially formed lithium iron phosphate crystal nuclei will grow further as the temperature continues to rise, and eventually form lithium iron phosphate with a larger primary particle size; and the lithium iron phosphate crystal nuclei formed later will eventually form lithium iron phosphate with a smaller primary particle size due to their slow growth rate.

[0087] The second iron phosphate with an iron-phosphorus ratio of 0.93-0.96 can be called low iron-phosphorus ratio iron phosphate, and the first iron phosphate with an iron-phosphorus ratio of 0.97-0.985 can be called high iron-phosphorus ratio iron phosphate. When using iron phosphate with a low iron-phosphorus ratio, the P element helps the growth of lithium iron phosphate crystal nuclei, so that the low iron-phosphorus ratio iron phosphate as an iron source, compared with iron oxide or the iron source of the first iron phosphate, makes the lithium iron phosphate crystal nuclei form larger primary particle size lithium iron phosphate as the temperature rises further; in addition, when there is a small amount of iron, iron vacancies can be formed, which can reduce the Li + The diffusion energy barrier increases the possibility of lithium ion transmission in adjacent channels, improves the diffusion rate, and improves the rate performance of the material; at the same time, controlling the amount of iron phosphate with a low iron-phosphorus ratio can control the generation of a small amount of Li3PO4. The inherent ionic conductivity of Li3PO4 will also improve the Li + The diffusion rate and high rate performance of the material are improved, and at the same time, the capacity of the lithium iron phosphate material will not be reduced. When iron phosphate with a high iron-phosphorus ratio is used, it can form lithium iron phosphate with a smaller primary particle size with the lithium source and the phosphorus source compared to ferrous oxalate or the second iron phosphate. In summary, the first iron source uses iron oxide and / or the first iron phosphate, and the second iron source uses ferrous oxalate and / or the second iron phosphate, which can obtain lithium iron phosphate with a larger primary particle size and lithium iron phosphate with a smaller primary particle size, thereby forming a gradation of large and small primary particle sizes of lithium iron phosphate, thereby making the prepared lithium iron phosphate material have a high compaction density, thereby improving the energy density of the battery.

[0088] It should be noted here that the larger particles of lithium iron phosphate and smaller particles of lithium iron phosphate mentioned here refer to the primary particle size of lithium iron phosphate. The primary particle size refers to the grain size of the material, also called the original particle size, that is, the grain size of a single lithium iron phosphate.

[0089] In addition, the embodiment of the present application states that the compaction density is improved by mixing large and small lithium iron phosphate particles because there are large lithium iron phosphate particles and small lithium iron phosphate particles in the lithium iron phosphate. The small lithium iron phosphate particles can be located in the gaps between the larger lithium iron phosphate particles, thereby improving the compaction density of the lithium iron phosphate.

[0090] The iron-phosphorus ratio, M, refers to the molar ratio of iron (Fe) to phosphorus (P) in a compound. According to the national standard HG / T 4701-2021, the iron-phosphorus ratio, M, can be calculated using the following formula: M = (w1 / w2) × 0.5545, where w1 represents the mass content of Fe and w2 represents the mass content of P.

[0091] In the above scheme, the iron source for preparing lithium iron phosphate includes a first iron source and a second iron source, wherein the first iron source includes at least one of iron oxide or a first iron phosphate, and the second iron source includes at least one of a second iron phosphate or ferrous oxalate, and the iron-phosphorus ratio of the first iron phosphate is 0.97-0.985, and the iron-phosphorus ratio of the second iron phosphate is 0.93-0.96. By using the above-mentioned first and second iron sources as the iron sources for preparing the positive electrode material, the prepared lithium iron phosphate has different primary particle sizes, which can achieve a mix of large and small particle sizes of lithium iron phosphate, thereby increasing the compaction density of the lithium iron phosphate and the energy density of the battery.

[0092] In some embodiments, the iron-to-phosphorus ratio of the second iron phosphate is 0.94-0.96. In the above solution, by making the iron-to-phosphorus ratio of the second iron phosphate 0.94-0.96, the compaction density and battery performance of the lithium iron phosphate can be further improved.

[0093] In some embodiments, the molar ratio of the iron element in the first iron source to the iron element in the second iron source is 0.5-4.

[0094] In the above scheme, using the first and second iron sources can produce lithium iron phosphate with smaller and larger particle sizes, respectively, achieving a mix of large and small particle sizes. By setting the molar ratio of the iron element in the first and second iron sources to 0.5-4, a reasonable mix of large and small particle sizes can be achieved, thereby effectively improving the compaction density of the lithium iron phosphate and the energy density of the battery.

[0095] Specifically, the molar ratio of the iron element in the first iron source to the iron element in the second iron source can be 0.5, 1, 1.5, 2.5, 3, 3.5, 4 or any value within the above range.

[0096] In some embodiments, the volume average particle size Dv50 of the mixed slurry is 0.3 μm-0.8 μm.

[0097] In the above solution, by setting the volume average particle size Dv50 of the mixed slurry to 0.3 μm-0.8 μm, the particle size of the lithium iron phosphate particles can be maintained within a reasonable range.

[0098] Specifically, the volume average particle size Dv50 of the mixed slurry can be 0.3 μm, 0.4 μm, 0.5 μm, 0.8 or any value within the above range.

[0099] In some embodiments, the molar ratio of the sum of the iron elements in the first iron source and the second iron source, the lithium element in the lithium source, and the phosphorus element in the phosphorus source is (0.9-1): (0.96-1.06): (0.95-1.05).

[0100] In the above solution, the iron source includes a first iron source and a second iron source. By setting the molar ratio of the iron element in the iron source, the lithium element in the lithium source, and the phosphorus element in the phosphorus source to (0.9-1): (0.96-1.06): (0.95-1.05), that is, setting the molar ratio of the iron element, the lithium element, and the phosphorus element to the above values, the loss of lithium and phosphorus during the preparation process can be compensated, thereby obtaining lithium iron phosphate with better performance.

[0101] The molar ratio of the iron in the first iron source and the second iron source, the lithium in the lithium source, and the phosphorus in the phosphorus source can be 0.9:0.96:0.95, 0.95:0.98:0.98, 1:1:1, or any value within the above ranges.

[0102] In some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is (1.003-1.01):1. By further controlling the ratio of lithium to phosphorus, the ionic order of the Li and Fe elements in the formed lithium iron phosphate is improved, effectively reducing the dislocation of Li and Fe in the lithium iron phosphate, controlling the length of the lithium ion transport path, and thereby increasing the reversible capacity of the lithium iron phosphate.

[0103] In some embodiments, the first iron source comprises iron oxide and the second iron source comprises a second iron phosphate.

[0104] The present application does not limit the combination of the first iron source and the second iron source. For example, the first iron source and the second iron source can be iron oxide and the second iron phosphate, iron oxide and ferrous oxalate, the first iron phosphate and the second iron phosphate, and the first iron phosphate and ferrous oxalate, respectively. In terms of the final effect of the experiment, the lithium iron phosphate obtained by using iron oxide and the second iron phosphate, iron oxide and ferrous oxalate, and the first iron phosphate and ferrous oxalate as the first iron source and the second iron source respectively has particles of significantly different particle sizes.

[0105] In the above scheme, by making the first iron source include iron oxide and the second iron source include a second iron phosphate with an iron-phosphorus ratio of 0.93-0.96, the iron oxide and the second iron phosphate are easy to obtain and widely used. They can not only prepare lithium iron phosphate with a mix of large and small primary particles, thereby increasing the compaction density of lithium iron phosphate and the energy density of the battery, but also can be widely used in industry.

[0106] In some embodiments, the primary particle size of the iron oxide is 0.05 μm to 0.6 μm.

[0107] Iron oxide with a primary particle size of less than 0.6 μm is called small-particle iron oxide. Small-particle iron oxide is easy to react during the sintering process, and lithium iron phosphate with complete primary particles can be obtained, without the occurrence of Li+ caused by particle agglomeration and abnormal growth. + The transmission path increases.

[0108] In the above scheme, by using iron oxide with a primary particle size of 0.05 μm-0.6 μm, the iron oxide is easy to react during the reaction process, which is conducive to forming better lithium iron phosphate.

[0109] Specifically, the primary particle size of the iron oxide may be 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.6 μm, or any value within the above range.

[0110] In some embodiments, the primary particle size of the iron oxide is 0.05 μm to 0.4 μm.

[0111] In the above scheme, by using iron oxide with a primary particle size of 0.05 μm-0.4 μm, lithium iron phosphate particles with better performance can be further obtained.

[0112] In some embodiments, in one possible implementation, the ratio of the number of iron oxide particles having a primary particle size of 0.05 μm to 0.6 μm to the total number of iron oxide particles is greater than or equal to 0.9.

[0113] In the above solution, by making the ratio of the number of iron oxide particles with a primary particle size of 0.05 μm to 0.6 μm to the total number of particles not less than 90%, the production difficulty can be reduced, so as to be widely used in industry.

[0114] In some embodiments, in an inert gas, the mixed slurry is heated to 450° C.-600° C. and kept warm for 2 h-5 h, and then heated to 700° C.-850° C. and kept warm for 6 h-15 h.

[0115] As described above, when the first iron source is iron oxide and the second iron source is ferrous oxalate and / or the second iron phosphate, the ferrous oxalate and / or the second iron phosphate can nucleate at 450°C-600°C and continue to grow at 700°C-850°C to form larger lithium iron phosphate particles, and the iron oxide can nucleate and grow at 700°C-850°C to form smaller lithium iron phosphate particles, thereby forming a lithium iron phosphate particle size with a mix of large and small particle sizes. Specifically, ferrous oxalate and / or the second iron phosphate can nucleate successively at 450°C-600°C and continue to grow at 700°C-850°C to form larger lithium iron phosphate particles. The iron oxide begins to nucleate later than the ferrous oxalate and / or the second iron phosphate during the 450°C-600°C insulation stage, but the nucleation is less, and the nucleation increases and grows at 700°C-850°C to form smaller lithium iron phosphate particles, thereby forming a lithium iron phosphate particle size with a mix of large and small particle sizes.

[0116] When the first iron source is the first iron phosphate and the second iron source is ferrous oxalate and / or the second iron phosphate, the first iron phosphate, ferrous oxalate and the second iron phosphate can all nucleate at 450°C-600°C. Since the nucleation temperature of ferrous phosphate formed by ferrous oxalate, lithium source and phosphorus source is low, it nucleates preferentially compared to the first iron phosphate and continues to grow within 700°C-850°C, thereby forming a lithium iron phosphate material with a larger primary particle size. Since the second iron phosphate has a higher P element content than the first iron phosphate, it is conducive to the growth of the crystal nucleus, so that at 700-850°C, the lithium iron phosphate crystal nucleus formed by the second iron phosphate, lithium source and phosphorus source grows preferentially over the lithium iron phosphate crystal nucleus formed by the first iron phosphate, lithium source and phosphorus source, thereby forming a lithium iron phosphate material with a larger primary particle size. It can be seen that by selecting the types of the first iron source and the second iron source, a lithium iron phosphate material with a mix of large and small primary particle sizes can be formed.

[0117] In the above scheme, by adopting two reaction ranges of 450℃-600℃ and 700℃-850℃, the first iron source and the second iron source react with the phosphorus source and the iron source respectively to form larger and smaller lithium iron phosphate primary particle sizes, thereby achieving a mix of large and small particle sizes of lithium iron phosphate.

[0118] In some embodiments, the method further comprises: dissolving a carbon source in a solvent to form a mixed slurry; the carbon source comprises at least one of sucrose, glucose, dextrin, citric acid, fructose or starch.

[0119] In this solution, the addition of carbon material not only increases the conductivity of lithium iron phosphate, but also reacts with iron at high temperatures to form Fe-C compounds. This reduction reaction helps lower the reaction temperature, accelerates the reaction, and effectively controls the crystal structure and particle morphology of the lithium iron phosphate product.

[0120] In a possible embodiment, the mass ratio of the carbon source to the lithium iron phosphate is 0.01-0.1.

[0121] In the above scheme, by setting the mass ratio of the carbon source to the lithium iron phosphate to 0.01-0.1, the carbon source can be used without affecting the energy density of the battery.

[0122] Specifically, the mass ratio of the carbon source to the lithium iron phosphate can be 0.01, 0.05, 0.1 or any value within the above range.

[0123] The carbon source used in the preparation method of the present application can be selected from the carbon sources used when conventional lithium positive electrode materials are doped or coated with carbon materials. In some embodiments, the above-mentioned carbon sources include small molecule carbon sources and polymer carbon sources; alternatively, the small molecule carbon source includes glucose and / or sucrose; alternatively, the polymer carbon source includes one or more of polyethylene glycol, polyacrylonitrile or polyvinyl alcohol; the cost of the small molecule carbon source is low, and the carbonization rate of the polymer carbon source is high. In some embodiments, optionally, the mass ratio of the small molecule carbon source to the polymer carbon source is 1:1-5:1, so as to achieve the simultaneous optimization of the carbon source cost advantage and the carbonization rate advantage as much as possible.

[0124] In a possible embodiment, the method further includes: dissolving a dispersant in a solvent to form a mixed slurry; the dispersant includes at least one of polyethylene glycol, polyvinyl alcohol, or polyvinyl pyrrolidone.

[0125] In the above solution, by including a dispersant in the mixed slurry, the viscosity of the mixed slurry can be reduced, thereby facilitating subsequent operations.

[0126] In a possible implementation, the mass ratio of the dispersant to the lithium iron phosphate is 0.005-0.08.

[0127] In the above solution, by setting the mass ratio of the dispersant to the lithium iron phosphate to 0.005-0.08, the dispersant can be effective without affecting the energy density of the battery.

[0128] Specifically, the mass ratio of the dispersant to the lithium iron phosphate can be 0.005, 0.01, 0.05 or any value within the above range.

[0129] In some embodiments, the method further comprises: dissolving an additive in a solvent to form a mixed slurry; the additive comprises a compound containing at least one element of Ti, Ga, Sr, W, Mg, Si, Y, Zr, B, Mo or La.

[0130] In the above solution, by including additives in the mixed slurry, the additives enter the crystal lattice, thereby increasing the diffusion rate of lithium ions and thereby improving the ionic conductivity and rate performance.

[0131] In some embodiments, the mass ratio of the additive to the lithium iron phosphate is 0.0001-0.0005.

[0132] In the above solution, by setting the mass ratio of the additive to the lithium iron phosphate to 0.0001-0.0005, the additive can be made to function without affecting the energy density of the battery.

[0133] Specifically, the mass ratio of the additive to the lithium iron phosphate can be 0.0001, 0.0002, 0.0005 or any value within the above range.

[0134] In some embodiments, the additives include substances containing at least one element selected from the group consisting of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, V, B, S, Si, N, F, Cl, and Br. The additives are doped into the lithium, iron, phosphorus, and oxygen sites of lithium iron phosphate to form doped lithium iron phosphate, which can be referred to as a phosphate-based positive electrode material. The phosphate-based positive electrode material includes a phosphate-based positive electrode material having a molecular formula of Li m A a Fe x D d P y E e O z G gFor example, A is a lithium-doping element, and element A includes at least one of Al, Na, K, or Mg provided by the above additives; D is an iron-doping element, and element D includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V provided by the above additives; E is a phosphorus-doping element, and element E includes at least one of B, S, Si, or N provided by the above additives; G is an oxygen-doping element, and element G includes at least one of S, F, Cl, or Br provided by the above additives. Each additive may be a salt or hydroxide containing the element, such as a carbonate, sulfate, or nitrate. In some embodiments, m is selected from the range of 0.5 to 1.15 (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or 1.1); a is selected from the range of 0 to 0.1 (e.g., 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1); x is selected from the range of 0.5 to 1 (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, or 1); d is selected from the range of 0 to 0.5 (e.g., 0, 0.1, 0.2, 0.3, 0.4 or 0.5); y is selected from the range of 0.5 to 1 (such as 0.5, 0.6, 0.7, 0.8, 0.9 or 1); e is selected from the range of 0 to 0.5 (such as 0, 0.1, 0.2, 0.3, 0.4 or 0.5); z is selected from the range of 3.5 to 4 (such as 3.5, 3.6, 3.7, 3.8, 3.9 or 4.0); g is selected from the range of 0 to 0.5 (such as 0, 0.1, 0.2, 0.3, 0.4 or 0.5).

[0135] In some embodiments, the lithium source includes at least one of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium acetate, or lithium oxalate.

[0136] In some embodiments, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or lithium dihydrogen phosphate.

[0137] [Positive electrode active material]

[0138] A second aspect of the present application provides a positive electrode active material, which includes lithium iron phosphate prepared by the method for preparing lithium iron phosphate according to any embodiment of the first aspect of the present application.

[0139] In some embodiments, the compaction density of lithium iron phosphate at 3T is greater than or equal to 2.5 g / cm 3 , optional at 2.5g / cm 3 -2.65g / cm 3 Between, further optional at 2.55g / cm 3 -2.65g / cm3 The above description of 3T is a popular description in this field, which is converted into 226.0738 MPa when converted into standard pressure.

[0140] In the above scheme, the lithium iron phosphate prepared by the preparation method of the present application has a particle size of not less than 2.5g / cm 3 The compaction density helps to improve the capacity of the battery.

[0141] Specifically, the compaction density of lithium iron phosphate can be 2.5g / cm 3 , 2.52g / cm 3 , 2.55g / cm 3 , 2.58g / cm 3 , 2.60g / cm 3 , 2.65g / cm 3 Or any value within the above range.

[0142] Unless otherwise specified, the compaction density in this application refers to the compaction density of lithium iron phosphate under a pressure of 3T.

[0143] In some embodiments, the volume average particle size Dv50 of the lithium iron phosphate is 0.6 μm-2 μm.

[0144] Specifically, the volume average particle size Dv50 of the lithium iron phosphate can be 0.6 μm, 0.8 μm, 1 μm, 1.5 μm, or any value within the above range.

[0145] In some embodiments, the volume average particle size Dv50 of the lithium iron phosphate is 0.6 μm to 1.8 μm.

[0146] In some embodiments, the lithium iron phosphate has a carbon coating.

[0147] In some embodiments, in the FTIR spectrum of lithium iron phosphate, PO4 3- Characteristic absorption peak position ≤995cm -1 , optionally PO4 3- Characteristic absorption peak position ≤984cm -1 , with the above PO4 3- The lithium iron phosphate with the characteristic absorption peak has a lower Li-Fe dislocation and a more regular lattice, so the material has a higher reversible capacity. 3- Characteristic absorption peak position ≤982.5cm -1 .

[0148] The present application also provides a phosphate-based cathode material, wherein in the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤995cm-1 The powder compaction density of phosphate cathode materials at 226.0738 MPa is 2.5 g / cm 3 The phosphate-based cathode material has a relatively regular lattice, thereby enhancing the reversible capacity of the battery cell and having a higher powder compaction density, thereby enabling the battery cell to have a higher reversible capacity and kinetic performance.

[0149] In some embodiments, the powder compaction density of the phosphate-based cathode material at 226.0738 MPa is 2.5 g / cm 3 -2.65g / cm 3 Between, optional 2.55g / cm 3 -2.65g / cm 3 between.

[0150] In some embodiments, in the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤984cm - 1 , optionally PO4 3- Characteristic absorption peak position ≤982.5cm -1 PO4 3- The smaller the characteristic absorption peak, the closer it is to the PO4 in the defect-free LiFePO4 3- The characteristic absorption peak indicates that the lattice structure of the phosphate positive electrode material is more regular.

[0151] In some embodiments, the phosphate-based cathode material includes lithium iron phosphate, and at least one of a doping-modified substance and / or a coating-modified substance thereof; optionally, the phosphate-based cathode material includes a molecular formula of Li m A a Fe x D d P y E e O zIn the Gg material, A includes at least one element selected from Al, Na, K, or Mg; D includes at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V; E includes at least one element selected from B, S, Si, or N; G includes at least one element selected from S, F, Cl, or Br; m is selected from the range of 0.5 to 1.15; a is selected from the range of 0 to 0.1; x is selected from the range of 0.5 to 1; d is selected from the range of 0 to 0.5; y is selected from the range of 0.5 to 1; e is selected from the range of 0 to 0.5; z is selected from the range of 3.5 to 4; and g is selected from the range of 0 to 0.5. The phosphate-based positive electrode material formed by doping with the above elements, in which the doped elements enter the crystal lattice, can increase the diffusion rate of lithium ions, thereby improving ionic conductivity and rate performance.

[0152] In some embodiments, the phosphate-based cathode material further comprises carbon; optionally, the carbon content by mass of the phosphate-based cathode material is 1.00% ≤ Wc ≤ 1.90%, and / or optionally, the powder resistivity S of the phosphate-based cathode material at 8 MPa is ≤ 90 Ω.cm. Further optionally, the carbon content by mass of the phosphate-based cathode material is 1.20% ≤ Wc ≤ 1.80%, and / or the powder resistivity S of the phosphate-based cathode material at 8 MPa is ≤ 60 Ω.cm, thereby improving the conductivity of the phosphate-based cathode material.

[0153] In some embodiments, the positive electrode active material may also include Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y , wherein M includes at least one of Zr, Al, B, Ta, Mo, W, Nb, Sb or La, A includes at least one of S, N, P, F, Cl, Br or I, 0.2<x≤1.2, 0.5≤a<1.0, 0≤b<0.5, 0≤c<1, 0≤d<1, 0≤y<0.02.

[0154] It should be noted that the positive electrode active materials include but are not limited to the following substances: Li 0.5 Ni 0.5 Co 0.1 Mn 0.4 O2、Li 0.5 (Ni 0.5 Co 0.1 Mn 0.4 ) 0.5 Zr 0.5 O 1.9 S0.1 、LiNi 0.4 Co 0.3 Mn 0.3 O2.

[0155] It should be noted that in the positive electrode sheet, battery, or electrical device, lithium ions are consumed during the battery formation and cycling processes, so the measured lithium content in the positive electrode active material may be less than 1. At the same time, if the positive electrode sheet is replenished with lithium, the measured lithium content in the positive electrode material may be greater than 1 after the battery formation and cycling processes.

[0156] Similarly, in the enumeration of positive electrode active materials in this application, in some embodiments, the positive electrode active material may also include positive electrode active materials for batteries that are well known in the art. As an example, the positive electrode active material may also include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and may also include other traditional materials that can be used as battery active positive electrode materials. These positive electrode active materials may be used in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0157] [Positive electrode]

[0158] The third aspect of the present application provides a positive electrode sheet. Figure 2 is a schematic structural diagram of a positive electrode sheet according to one embodiment of the present application. As shown in Figure 2, the positive electrode sheet 121 includes a positive electrode current collector 122 and a positive electrode film layer 123 disposed on at least one side of the positive electrode current collector 122. The positive electrode film layer 123 includes lithium iron phosphate prepared according to the method for preparing lithium iron phosphate according to any embodiment of the first aspect, or the positive electrode active material described in the second aspect, or the phosphate-based positive electrode material described in the third aspect.

[0159] Typically, a battery cell consists of a positive electrode sheet 121, a separator, a negative electrode sheet, and an electrolyte. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte transfers ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0160] It should be noted here that the “positive electrode sheet” and “negative electrode sheet” mentioned in the embodiments of the present application refer to the positive electrode sheet and the negative electrode sheet as a whole including active materials, current collectors or other additives.

[0161] The positive electrode sheet 121 includes a positive electrode current collector 122 and a positive electrode film layer 123 disposed on at least one surface of the positive electrode current collector 122 . The positive electrode film layer 123 includes lithium iron phosphate.

[0162] As an example, the positive electrode current collector 122 has two opposite surfaces in its thickness direction, and the positive electrode film layer 123 is disposed on either or both of the two opposite surfaces of the positive electrode current collector 122 .

[0163] In some embodiments, the positive electrode film layer satisfies any one or more of the following conditions: 1) the content of phosphate-based positive electrode material with a particle size between 50 nm and 200 nm is 40% to 80%, optionally 50% to 70%, and further optionally 45% to 57%; 2) the cross-sectional area percentage of phosphate-based positive electrode material with a particle size of not less than 1500 nm is 30% to 80%, optionally 40% to 75%, and further optionally 40% to 70%. The small-particle phosphate-based positive electrode material in the positive electrode film layer has an appropriate quantitative proportion, while the large-particle phosphate-based positive electrode material has an appropriate cross-sectional area proportion. The large and small particles meet a specific gradation, thereby increasing the compaction density of the positive electrode sheet and further improving the energy density of the battery.

[0164] The relevant characteristics of the above particle sizes are tested using the following methods:

[0165] The positive electrode sheet is cut open perpendicularly to the surface of the positive electrode film layer using an argon ion beam to expose the cross section, which is photographed using a scanning electron microscope and the particle size of the active material is statistically analyzed using a length diameter statistical method.

[0166] Among them, the average particle size It is the total particle size value divided by the total number of particles;

[0167] Since 0<x i Particles ≤50nm are prone to adhesion, and there are large errors in statistics, making it difficult to clearly identify them individually. Therefore, in the particle size statistics process, the particle size 0<x i Particles ≤50nm are not included in the statistics.

[0168] The quantitative content of the phosphate-based positive electrode material with a particle size of 50nm-200nm is calculated by dividing the quantity of the phosphate-based positive electrode material with a particle size of 50nm-200nm in the cross section by the total quantity of the phosphate-based positive electrode material.

[0169] The cross-sectional area percentage of the phosphate-based positive electrode material with a particle size of not less than 1500 nm is calculated by dividing the cross-sectional area of ​​the phosphate-based positive electrode material with a particle size of not less than 1500 nm in the cross section by the total area of ​​the phosphate-based positive electrode material.

[0170] The area of ​​the active material was obtained by statistical analysis of the scanning electron microscopy images of the positive electrode cross-section obtained using Avizo 3D software.

[0171] In some embodiments, the positive electrode current collector 122 may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0172] In some embodiments, the positive electrode film layer 123 may further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0173] In some embodiments, the positive electrode film layer 123 may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0174] In some embodiments, the positive electrode sheet 121 can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector 122. After drying, cold pressing and other processes, the positive electrode sheet 121 can be obtained.

[0175] [Negative electrode]

[0176] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0177] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0178] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0179] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0180] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0181] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0183] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0184] [Electrolytes]

[0185] The electrolyte acts as a conductive medium between the positive electrode 121 and the negative electrode. The present application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0186] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0187] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0188] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0189] In some embodiments, the electrolyte may further include electrolyte additives. For example, the electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0190] [Isolation film]

[0191] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0192] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0193] In some embodiments, the positive electrode sheet 121 , the negative electrode sheet, and the separator may be formed into an electrode assembly through a winding process or a lamination process.

[0194] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0195] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0196] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0197] Figure 4 is a schematic structural diagram of a battery cell according to an embodiment of the present application. As shown in Figure 4, the outer packaging of the battery cell 100 includes a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet 121 and the negative electrode sheet can be formed into an electrode assembly 12 by a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 100 can be one or more, and those skilled in the art can select according to specific actual needs.

[0198] In some embodiments, the battery cells 100 may be assembled into a battery module. The battery module may contain one or more battery cells 100. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0199] Figure 5 is a schematic diagram of a battery according to one embodiment of the present application, and Figure 6 is a schematic diagram of the structure of a battery according to one embodiment of the present application. Referring to Figures 5 and 6, a battery 400 may include a battery box and a plurality of battery cells 100 disposed within the battery box. The battery box includes an upper box body 401 and a lower box body 402. The upper box body 401 can be placed over the lower box body 402 to form an enclosed space for accommodating the battery cells 100. The plurality of battery cells 100 can be arranged in any manner within the battery box.

[0200] In addition, the present application also provides an electrical device, which includes at least one of the positive electrode sheet 121, battery cell 100, or battery 400 provided in the present application. The positive electrode sheet 121, battery cell 100, or battery 400 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0201] For example, FIG7 is a schematic structural diagram of an electric device according to an embodiment of the present application. As shown in FIG7 , the electric device 1 is a vehicle 1. The vehicle 1 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 500, a controller 600 and a battery 400 may be provided inside the vehicle 1. The controller 600 is used to control the battery 400 to supply power to the motor 500. For example, a battery 400 may be provided at the bottom, front or rear of the vehicle 1. The battery 400 may be used to power the vehicle 1. For example, the battery 400 may be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 400 may not only be used as an operating power source for the vehicle 1, but also as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0202] As the electrical device, the positive electrode sheet 121 , the battery cell 100 or the battery 400 can be selected according to its usage requirements.

[0203] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirement for a high capacity battery, a battery cell 100 or a battery 400 may be used.

[0204] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use the battery cell 100 as a power source.

[0205] [Example]

[0206] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0207] [Example 1]

[0208] 1). Preparation of lithium-ion batteries

[0209] 1.11) Preparation of lithium iron phosphate: Iron oxide, secondary iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol were mixed in 10 kg of pure water at a mass ratio of 1.00 kg: 1.26 kg: 1.34 kg: 0.319 kg: 0.0049 kg: 0.28 kg: 0.07 kg. The mixture was ground with a sander to obtain a mixed slurry with a volume average particle size Dv50 of 0.45 μm. The mixed slurry was spray-dried (the specific process of the spray process is: maintain the inlet temperature at 26 0°C, an outlet temperature of 90°C, and a feed rate of 15 Hz), then heating to 550°C at a rate of 3°C / min and holding for 3 hours, then heating to 780°C at a rate of 4°C / min and holding for 10 hours, cooling with the furnace, and performing air flow crushing to obtain lithium iron phosphate powder; wherein the primary particle size of the first iron source iron oxide is 0.2 μm, the iron-phosphorus ratio of the second iron phosphate in the second iron source is 0.95, the volume average particle size Dv50 of the mixed slurry is 0.45 μm, and the molar ratio of the iron element in the first iron source to the iron element in the second iron source is 1.5.

[0210] 1.12) Preparation of positive electrode sheets: The lithium iron phosphate powder prepared in Example 1, the conductive agent carbon nanotubes (CNT), and the positive electrode binder polyvinylidene fluoride (PVDF) were dissolved in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 96%:2%:2%, and the mixture was thoroughly stirred and mixed to prepare a positive electrode slurry. The positive electrode slurry was coated on Al foil, and then dried, cold pressed, and slit to obtain positive electrode sheets.

[0211] 1.2) Preparation of negative electrode sheets: artificial graphite, a conductive agent, acetylene black, a negative electrode binder, styrene-butadiene rubber (SBR), and a thickener, sodium carboxymethyl cellulose (CMC-Na), are mixed thoroughly in a suitable amount of deionized water solvent system at a weight ratio of 96.5%:0.7%:1.8%:1% to obtain a negative electrode slurry. The negative electrode slurry is coated on a Cu foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0212] 1.3) Preparation of diaphragm: PE porous polymer film is used as the isolation membrane.

[0213] 1.4) Electrolyte: Dissolve EC / EMC / DMC in 1M LiPF6 at a volume ratio of 1:1:1 and stir evenly to obtain 1 mol / L LiPF6 electrolyte.

[0214] 1.5) Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to form an electrode assembly, and electrolyte is added. The lithium-ion battery is then produced through formation and resting processes.

[0215] [Example 2]

[0216] The preparation process of the lithium ion battery of Example 2 is basically the same as that of Example 1, except that the second iron source in Example 2 is ferrous oxalate, and the mass ratio of iron oxide, ferrous oxalate, lithium dihydrogen phosphate, titanium dioxide, glucose, and polyethylene glycol is 1.11Kg:1.00Kg:3.01Kg:0.0049Kg:0.28Kg:0.07Kg mixed in 12kg of pure water, and the molar ratio of the iron element in the first iron source to the iron element in the second iron source is 2.

[0217] [Example 3]

[0218] The preparation process of the lithium-ion battery of Example 3 is basically the same as that of Example 1, except that the first iron source in Example 3 is a first iron phosphate, the iron-phosphorus ratio of the first iron phosphate is 0.975, the mass ratio of the first iron phosphate, the second iron phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 1.89Kg:1.26Kg:0.798Kg:0.0049Kg:0.28Kg:0.07Kg, and the molar ratio of the iron element in the first iron source to the iron element in the second iron source is 1.5.

[0219] [Example 4]

[0220] The preparation process of the lithium-ion battery of Example 4 is basically the same as that of Example 3, except that the second iron source in Example 4 is ferrous oxalate, and the mass ratio of the first ferric phosphate, ferrous oxalate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 1.89Kg:1.20Kg:0.895Kg:0.479Kg:0.0049Kg:0.28Kg:0.07Kg mixed in 11Kg of pure water, and the molar ratio of the iron element in the first iron source to the iron element in the second iron source is 1.5.

[0221] [Example 5]

[0222] The preparation process of the lithium-ion battery of Example 5 is substantially the same as that of Example 1, except that in Example 5, the iron-to-phosphorus ratio of the second iron phosphate serving as the second iron source is 0.93.

[0223] [Example 6]

[0224] The preparation process of the lithium-ion battery of Example 6 is substantially the same as that of Example 1, except that in Example 6, the iron-to-phosphorus ratio of the second iron phosphate serving as the second iron source is 0.94.

[0225] [Example 7]

[0226] The preparation process of the lithium-ion battery of Example 7 is substantially the same as that of Example 1, except that in Example 7, the iron-to-phosphorus ratio of the second iron phosphate serving as the second iron source is 0.96.

[0227] [Example 8]

[0228] The preparation process of the lithium-ion battery of Example 8 is substantially the same as that of Example 1, except that the primary particle size of the first iron source iron oxide in Example 8 is 0.4 μm.

[0229] [Example 9]

[0230] The preparation process of the lithium-ion battery of Example 9 is substantially the same as that of Example 1, except that the primary particle size of the first iron source iron oxide in Example 9 is 0.6 μm.

[0231] [Example 10]

[0232] The preparation process of the lithium-ion battery of Example 10 is substantially the same as that of Example 1, except that the primary particle size of the first iron source iron oxide in Example 10 is 1 μm.

[0233] [Example 11]

[0234] The preparation process of the lithium-ion battery of Example 11 is basically the same as that of Example 1, except that, in Example 11, the mass ratio of iron oxide, the second iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 1.33Kg: 0.629Kg: 1.79Kg: 0.160Kg: 0.0049Kg: 0.28Kg: 0.07Kg, and the mass ratio of the iron element in the first iron source to the iron element in the second iron source is 4.

[0235] [Example 12]

[0236] The preparation process of the lithium-ion battery of Example 12 is basically the same as that of Example 1, except that, in Example 12, the mass ratio of iron oxide, the second iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 0.556Kg:2.10Kg:0.746Kg:0.533Kg:0.0049Kg:0.28Kg:0.07Kg, and the mass ratio of the iron element in the first iron source to the iron element in the second iron source is 0.5.

[0237] [Example 13]

[0238] The preparation process of the lithium-ion battery of Example 13 is basically the same as that of Example 1, except that, in Example 13, the mass ratio of iron oxide, the second iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 0.741Kg:1.75Kg:0.994Kg:0.444Kg:0.0049Kg:0.28Kg:0.07Kg, and the molar ratio of iron element in the first iron source to iron element in the second iron source is 0.8.

[0239] [Example 14]

[0240] The preparation process of the lithium-ion battery of Example 14 is basically the same as that of Example 1, except that, in Example 14, the mass ratio of iron oxide, the second iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 1.19Kg:0.899Kg:1.60Kg:0.228Kg:0.0049Kg:0.28Kg:0.07Kg, and the molar ratio of iron in the first iron source to iron in the second iron source is 2.5.

[0241] [Example 15]

[0242] The preparation process of the lithium ion battery of Example 15 is basically the same as that of Example 1, except that, in Example 15, the mass ratio of iron oxide, the second iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 0.334Kg:2.52Kg:0.448Kg:0.639Kg:0.0049Kg:0.28Kg:0.07Kg, and the molar ratio of iron in the first iron source to iron in the second iron source is 0.26.

[0243] [Example 16]

[0244] The preparation process of the lithium-ion battery of Example 16 is basically the same as that of Example 1, except that, in Example 16, the mass ratio of iron oxide, the second iron phosphate, lithium dihydrogen phosphate, lithium carbonate, titanium dioxide, glucose, and polyethylene glycol is 1.48Kg:0.350Kg:1.99Kg:0.089Kg:0.0049Kg:0.28Kg:0.07Kg, and the molar ratio of iron in the first iron source to iron in the second iron source is 8.

[0245] [Example 17]

[0246] The preparation process of the lithium-ion battery of Example 17 is basically the same as that of Example 1, except that in Example 17, the volume average particle size Dv50 of the mixed slurry is 0.3 μm.

[0247] [Example 18]

[0248] The preparation process of the lithium-ion battery of Example 18 is basically the same as that of Example 1, except that in Example 18, the volume average particle size Dv50 of the mixed slurry is 0.8 μm.

[0249] [Example 19]

[0250] The preparation process of the lithium-ion battery of Example 19 is basically the same as that of Example 1, except that in Example 19, the volume average particle size Dv50 of the mixed slurry is 0.2 μm.

[0251] [Example 20]

[0252] The preparation process of the lithium-ion battery of Example 20 is basically the same as that of Example 1, except that in Example 20, the volume average particle size Dv50 of the mixed slurry is 1 μm.

[0253] [Example 21]

[0254] The preparation process of the lithium-ion battery of Example 21 is basically the same as that of Example 1, except that in Example 21, the iron-to-phosphorus ratio of the first iron phosphate serving as the first iron source is 0.985.

[0255] [Example 22]

[0256] The preparation process of the lithium-ion battery of Example 22 is basically the same as that of Example 1, except that in Example 22, the iron-to-phosphorus ratio of the first iron phosphate serving as the first iron source is 0.97.

[0257] [Example 23]

[0258] The preparation process of the lithium-ion battery of Example 23 is basically the same as that of Example 1, except that the primary particle size of the first iron source iron oxide in Example 23 is 0.05 μm.

[0259] [Example 24]

[0260] The preparation process of the lithium-ion battery of Example 24 is basically the same as that of Example 1, except that the primary particle size of the first iron source iron oxide in Example 24 is 0.1 μm.

[0261] [Example 25]

[0262] The preparation process of the lithium-ion battery of Example 25 is basically the same as that of Example 1, except that the first iron source in Example 25 is a first iron phosphate, the iron-phosphorus ratio of the first iron phosphate is 0.97, the second iron source is a second iron phosphate, the iron-phosphorus ratio of the second iron phosphate is 0.955, and the molar ratio of lithium, iron and phosphorus in the first iron phosphate, the second iron phosphate and lithium carbonate is 1.004:0.959:1.

[0263] [Example 26]

[0264] The preparation process of the lithium-ion battery of Example 26 is basically the same as that of Example 1, except that the first iron source in Example 26 is a first iron phosphate, the iron-phosphorus ratio of the first iron phosphate is 0.98, the second iron source is a second iron phosphate, the iron-phosphorus ratio of the second iron phosphate is 0.955, and the molar ratio of lithium, iron and phosphorus in the first iron phosphate, the second iron phosphate and lithium carbonate is 1.005:0.963:1.

[0265] [Example 27]

[0266] The preparation process of the lithium-ion battery of Example 27 is basically the same as that of Example 1, except that the first iron source in Example 27 is a first iron phosphate, the iron-phosphorus ratio of the first iron phosphate is 0.975, the second iron source is a second iron phosphate, the iron-phosphorus ratio of the second iron phosphate is 0.945, and the molar ratio of lithium, iron and phosphorus in the first iron phosphate, the second iron phosphate and lithium carbonate is 1.003:0.954:1.

[0267] [Example 28]

[0268] The preparation process of the lithium-ion battery of Example 28 is basically the same as that of Example 1, except that the first iron source in Example 28 is a first iron phosphate, the iron-phosphorus ratio of the first iron phosphate is 0.975, the second iron source is a second iron phosphate, the iron-phosphorus ratio of the second iron phosphate is 0.945, and the molar ratio of lithium, iron and phosphorus in the first iron phosphate, the second iron phosphate and lithium carbonate is 1.01:0.965:1.

[0269] [Example 29]

[0270] The preparation process of the lithium-ion battery of Example 29 is basically the same as that of Example 1, except that, after spray drying, Example 29 is heated to 450°C at 3°C / min and kept warm for 5 hours, then heated to 850°C at 4°C / min and kept warm for 6 hours, cooled in the furnace, and subjected to air flow crushing to obtain lithium iron phosphate powder.

[0271] [Example 30]

[0272] The preparation process of the lithium-ion battery of Example 30 is basically the same as that of Example 1. The difference is that after spray drying, Example 30 is heated to 600°C at 3°C / min and kept warm for 2 hours, then heated to 700°C at 4°C / min and kept warm for 15 hours, cooled in the furnace, and air flow crushed to obtain lithium iron phosphate powder.

[0273] [Example 31]

[0274] The preparation process of the lithium-ion battery of Example 31 is basically the same as that of Example 1. The difference is that after spray drying, Example 31 is heated to 650°C at 3°C / min and kept warm for 2 hours, then heated to 750°C at 4°C / min and kept warm for 10 hours, cooled in the furnace, and subjected to air flow crushing to obtain lithium iron phosphate powder.

[0275] [Comparative Example 1]

[0276] The preparation process of the lithium ion battery of Comparative Example 1 is basically the same as that of Example 1, except that, in Comparative Example 1, there is no second iron source, and iron oxide, lithium dihydrogen phosphate, titanium dioxide, glucose, and polyethylene glycol are mixed in 10 kg of pure water at a mass ratio of 1.67 kg: 2.24 kg: 0.0049 kg: 0.28 kg: 0.07 kg.

[0277] [Comparative Example 2]

[0278] The preparation process of the lithium ion battery of Comparative Example 2 is substantially the same as that of Example 1, except that, in Comparative Example 2, the first iron phosphate having an iron-to-phosphorus ratio of 0.985 is used as the second iron source.

[0279] [Comparative Example 3]

[0280] The preparation process of the lithium ion battery of Comparative Example 3 is basically the same as that of Example 2, except that, in Comparative Example 3, there is no first iron source, and the mass ratio of ferrous oxalate, lithium dihydrogen phosphate, titanium dioxide, glucose, and polyethylene glycol is 3.00Kg:2.24Kg:0.0049Kg:0.28Kg:0.07Kg mixed in 12kg of pure water.

[0281] [Comparative Example 4]

[0282] The preparation process of the lithium ion battery of Comparative Example 4 is substantially the same as that of Example 1, except that, in Comparative Example 4, the iron-to-phosphorus ratio of the first iron phosphate serving as the second iron source is 0.92.

[0283] 2). Physical characterization

[0284] 2.1) Measurement of primary particle size: A ZEISS Sigma 300 scanning electron microscope was used to capture 10kx electron micrographs. The short sides of 80-120 primary iron oxide particles were measured using Nano Measurer 1.2 software to obtain the average primary particle size.

[0285] 2.2) Measurement of Iron-Phosphorus Ratio: The Fe and P contents are measured using potassium dichromate titration and quinolyl molybdate gravimetric methods, respectively. The iron-phosphorus ratio is then calculated using the formula: Fe content × 0.5546 / P content. For specific operations, refer to the standard: HG / T4701-2021.

[0286] 2.3) Measurement of the volume average particle size Dv50 of the mixed slurry: Take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8-12% opacity), add 20 ml of deionized water, and simultaneously ultraviolet (53 kHz / 120 W) for 5 minutes to ensure that the sample is completely dispersed. Then, the sample is measured using a Malvern 3000 (MasterSizer 3000) laser particle size analyzer in accordance with GB / T19077-2016 / ISO 13320:2009 standard.

[0287] Table 1 Experimental parameters of Examples 1-31 and Comparative Examples 1-4

[0288] 3) Performance testing

[0289] 3.1) Lithium Iron Phosphate Powder Compaction Density Measurement: A certain amount of powder is placed in a compaction mold of known diameter (for example, the Sansi Zongheng UTM7305). A metal sheet is placed above and below the mold, with the powder placed in the middle. A pressure of 3T is applied while measuring the corresponding powder thickness. The compaction density is calculated using the formula ρ = m / v. Specific procedures are based on the standard GB / T24533-2009. See Table 2 for test results.

[0290] 3.2) 0.1C rate performance test: At room temperature (25°C), charge the battery at a constant current of 0.1C to 3.75V, then charge at a constant voltage of 3.75V to a current of 0.05C, and hold for 5 minutes. Discharge at 0.1C to 2.0V, repeating the cycle twice. Record the average discharge capacity obtained after two cycles. See Table 2 for the test results.

[0291] 3.3) 1C rate performance test: At room temperature (25°C), charge the battery at a constant current of 0.1C to 3.75V, then charge at a constant voltage of 3.75V to a current of 0.05C, and let it rest for 5 minutes; then discharge at 0.1C to 2.0V, and cycle twice; then charge the battery at a constant current of 1C to 3.75V, then charge at a constant voltage of 3.75V to a current of 0.05C, and let it rest for 5 minutes; then discharge at 1C, and record the average 1C capacity obtained from the two cycles. The test results are shown in Table 2.

[0292] 3.4) FTIR spectra of the cathode materials of each embodiment and comparative example were measured by Fourier transform infrared spectrometer, and the PO4 values ​​were recorded in Table 2. 3- Characteristic absorption peak position.

[0293] 3.5) Use an argon ion beam to cut the positive electrode sheet perpendicular to the surface with the positive electrode film layer, expose the cross section, take a picture of the cross section using a scanning electron microscope, and use the length diameter statistical method to perform statistical analysis on the particle size of the active material. The average particle size is the total particle size value divided by the total number of particles; because particles with a size of 0 < x 1 < 50 nm are prone to adhesion, there is a large error in the statistics, making it difficult to clearly identify them individually. Therefore, in the particle size statistics process, the particle size 0 < x 1 < 50 nm is used. i Particles ≤50 nm were not included in the statistical range. The area of ​​the positive electrode material was obtained by statistical analysis of the scanning electron micrographs of the positive electrode sections using Avizo 3D software.

[0294] 3.6) Carbon Content: Carbon content is the mass fraction of carbon in the lithium iron phosphate material (unit: %). Determined using a Dekai HCS infrared carbon and sulfur analyzer, in accordance with GB / T21023-2006, "Determination of total carbon and sulfur content of steel - Infrared absorption method after high-frequency induction furnace combustion."

[0295] 3.7) Powder Resistivity Test: Powder resistivity characterizes the electronic conductivity of lithium iron phosphate materials (unit: Ω.cm). This was determined using an ST-2722 powder resistivity analyzer from Suzhou Jingge Electronics Co., Ltd., in accordance with GB / T 30835-2014, "Carbon-composite lithium iron phosphate cathode materials for lithium-ion batteries."

[0296] Table 2 Performance parameters of Examples 1-31 and Comparative Examples 1-4

[0297] According to Examples 1-31 and Comparative Examples 1-4, when two different iron sources are used as raw materials for preparing lithium iron phosphate, the powder compaction density of lithium iron phosphate can be greater than 2.5 g / cm 3 , the battery capacity is improved.

[0298] According to Examples 1-4 and 21-22 and Comparative Examples 1-4, the first iron source is selected from any one of iron oxide or the first iron phosphate with an iron-phosphorus ratio of 0.97-0.985, and the second iron source is selected from any one of the second iron phosphate or ferrous oxalate with an iron-phosphorus ratio of 0.93-0.96, both of which can play a role in increasing the compaction density of lithium iron phosphate and improving the battery capacity.

[0299] According to Examples 1, 5-7, it can be seen that when the iron-phosphorus ratio of the second iron phosphate serving as the second iron source is set to 0.93-0.96, particularly 0.94-0.96, the battery has better performance.

[0300] According to Examples 1, 8-10, and 23-24, by making the primary particle size of iron oxide 0.05 μm-0.6 μm, the battery has a higher capacity; further, by making the primary particle size of iron oxide no greater than 0.4 μm, the compaction density of lithium iron phosphate can be further increased, thereby further increasing the capacity of the battery.

[0301] According to Examples 1 and 11-16, by setting the molar ratio of the iron element in the first iron source to the iron element in the second iron source to 0.5-4, the lithium iron phosphate has a higher compaction density and the battery also has a higher capacity.

[0302] According to Examples 1 and 17-20, by setting the volume average particle size Dv50 of the mixed slurry to 0.3 μm-0.8 μm, the lithium iron phosphate has a higher compaction density and the battery also has a higher capacity.

[0303] According to Examples 1, 21 and 22, when the iron-phosphorus ratio of the first iron phosphate serving as the first iron source is set to 0.97-0.985, the battery has better performance.

[0304] In Examples 25 to 28, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is between (1.003-1.01):1, so that PO4 3- The characteristic absorption peak position decreases, and the surface lithium iron phosphate has a lower Li-Fe dislocation, so the corresponding battery's 0.1C discharge capacity is higher, indicating that the battery has a higher reversible capacity.

[0305] Figure 8 is a SEM image of lithium iron phosphate according to an embodiment of the present application, which is prepared by the method described in Example 1. As can be seen from the SEM image of Figure 8, the prepared lithium iron phosphate has a larger primary particle size and a smaller primary particle size. Figure 9 is a SEM image of lithium iron phosphate according to an embodiment of the related art, which is prepared by the method described in Comparative Example 1. As can be seen from Figure 9, the prepared lithium iron phosphate has a uniform primary particle size.

[0306] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing lithium iron phosphate, characterized in that: include: Dissolving the first iron source, the second iron source, the lithium source, and the phosphorus source in a solvent to obtain a mixed slurry; The mixed slurry is sintered to obtain lithium iron phosphate; Wherein, the first iron source comprises at least one of iron oxide or a first iron phosphate, and the second iron source comprises at least one of a second iron phosphate or ferrous oxalate; The iron-to-phosphorus ratio of the first iron phosphate is 0.97-0.985, and the iron-to-phosphorus ratio of the second iron phosphate is 0.93-0.

96.

2. The method according to claim 1, characterized in that The iron-to-phosphorus ratio of the second ferric phosphate is 0.94-0.

96.

3. The method according to claim 1 or 2, characterized in that: The molar ratio of the iron element in the first iron source to the iron element in the second iron source is 0.5-4.

4. The method according to any one of claims 1 to 3, characterized in that The volume average particle size Dv50 of the mixed slurry is 0.3 μm-0.8 μm.

5. The method according to any one of claims 1 to 4, characterized in that The molar ratio of the sum of the iron element in the first iron source and the iron element in the second iron source, the lithium element in the lithium source, and the phosphorus element in the phosphorus source is (0.9-1): (0.96-1.06): (0.95-1.05).

6. The method according to claim 5, characterized in that The molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is (1.003-1.01):

1.

7. The method according to any one of claims 1 to 6, characterized in that The first iron source includes iron oxide and the second iron source includes a second iron phosphate.

8. The method according to claim 7, characterized in that The primary particle size of the iron oxide is 0.05 μm-0.6 μm.

9. The method according to claim 8, characterized in that The primary particle size of the iron oxide is 0.05 μm-0.4 μm.

10. The method according to any one of claims 1 to 9, characterized in that The sintering process comprises: In an inert gas, the mixed slurry is heated to 450°C-600°C and kept at this temperature for 2h-5h, and then heated to 700°C-850°C and kept at this temperature for 6h-15h.

11. The method according to any one of claims 1 to 10, characterized in that The method further comprises: dissolving the carbon source in the solvent to form the mixed slurry; The carbon source includes at least one of sucrose, glucose, dextrin, citric acid, fructose or starch; Wherein, the mass ratio of the carbon source to the lithium iron phosphate is 0.01-0.

1.

12. The method according to any one of claims 1 to 11, characterized in that The method further comprises: dissolving a dispersant in the solvent to form the mixed slurry; The dispersant includes at least one of polyethylene glycol, polyvinyl alcohol or polyvinyl pyrrolidone; Wherein, the mass ratio of the dispersant to the lithium iron phosphate is 0.005-0.

08.

13. The method according to any one of claims 1 to 12, characterized in that The method further comprises: dissolving the additive in the solvent to form the mixed slurry; The additive includes a compound containing at least one element of Ti, Ga, Sr, W, Mg, Si, Y, Zr, B, Mo or La; Wherein, the mass ratio of the additive to the lithium iron phosphate is 0.0001-0.0005; Alternatively, the additive includes a substance containing at least one element of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, V, B, S, Si, N, F, Cl or Br.

14. The method according to any one of claims 1 to 13, characterized in that The lithium source includes at least one of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium acetate or lithium oxalate.

15. The method according to any one of claims 1 to 14, characterized in that The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate or lithium dihydrogen phosphate.

16. A positive electrode active material, characterized in that: The positive electrode active material comprises lithium iron phosphate prepared by the preparation method according to any one of claims 1 to 15.

17. The positive electrode active material according to claim 16, characterized in that The compaction density of the lithium iron phosphate at 3T is greater than or equal to 2.5 g / cm 3 .

18. The positive electrode active material according to claim 16 or 17, characterized in that: In the FTIR spectrum of lithium iron phosphate, PO4 3- Characteristic absorption peak position ≤995cm -1 .

19. The positive electrode active material according to any one of claims 16 to 18, characterized in that The powder compaction density of the lithium iron phosphate under 3 tons is 2.5g / cm 3 -2.65g / cm 3 between.

20. The positive electrode active material according to any one of claims 16 to 19, characterized in that The powder compaction density of the lithium iron phosphate at 3 tons is 2.55 g / cm 3 -2.65g / cm 3 between.

21. The positive electrode active material according to any one of claims 16 to 20, characterized in that In the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak ≤984cm -1 , optionally PO4 3- Characteristic absorption peak position ≤982.5cm -1 .

22. A phosphate-based positive electrode material, wherein: In the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤995cm -1 The powder compaction density of the phosphate-based cathode material at 226.0738 MPa is 2.50 g / cm 3 above.

23. The phosphate-based positive electrode material according to claim 22, wherein: The powder compaction density of the phosphate-based positive electrode material at 226.0738 MPa is 2.55 g / cm 3 -2.65g / cm 3 between.

24. The phosphate-based positive electrode material according to claim 22 or 23, wherein: In the FTIR spectrum of the phosphate-based cathode material, PO4 3- Characteristic absorption peak position ≤982.5cm -1 .

25. The phosphate-based positive electrode material according to any one of claims 22 to 24, wherein The phosphate-based positive electrode material includes lithium iron phosphate and at least one of a doped modified substance and / or a coated modified substance thereof; optionally, the phosphate-based positive electrode material includes a lithium iron phosphate having a molecular formula of Li m A a Fe x D d P y E e O z Gg material, A includes at least one element selected from Al, Na, K or Mg; D includes at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V; E includes at least one element selected from B, S, Si or N; G includes at least one element selected from S, F, Cl or Br; m is selected from the range of 0.5 to 1.15; a is selected from the range of 0 to 0.1; x is selected from the range of 0.5 to 1; d is selected from the range of 0 to 0.5; y is selected from the range of 0.5 to 1; e is selected from the range of 0 to 0.5; z is selected from the range of 3.5 to 4; g is selected from the range of 0 to 0.

5.

26. The phosphate-based positive electrode material according to any one of claims 22 to 25, wherein The phosphate-based positive electrode material further includes carbon, the mass content of carbon in the phosphate-based positive electrode material is 1.00%≤Wc≤1.90%, and / or the powder resistivity S of the phosphate-based positive electrode material at 8MPa is ≤90Ω.cm.

27. A positive electrode plate, characterized in that: include: A positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, The positive electrode film layer comprises lithium iron phosphate prepared by the preparation method according to any one of claims 1 to 15, or the positive electrode active material according to any one of claims 16 to 21, or the phosphate-based positive electrode material according to any one of claims 22 to 26.

28. The positive electrode sheet according to claim 27, wherein: The positive electrode film layer satisfies any one or more of the following conditions: 1) The quantity content of phosphate-based positive electrode materials with a particle size of 50nm-200nm is 40%-80%; 2) The cross-sectional area percentage of the phosphate-based positive electrode material with a particle size of not less than 1500 nm is 30%-80%.

29. A battery, characterized in that: Including the positive electrode sheet as described in claim 27 or 28.

30. An electrical device, characterized in that: Comprising the battery of claim 29.

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