A battery cell, a battery, an electric device, a lithium iron phosphate material and a preparation method

Abstract

The application provides a battery monomer, a battery, an electric device, a lithium iron phosphate material and a preparation method, relates to the technical field of lithium batteries, and the preparation method of the lithium iron phosphate material comprises the following steps: lithium sources, iron sources, phosphorus sources, carbon sources, dopants and solvents for preparing first lithium iron phosphate materials and second lithium iron phosphate materials are selected respectively, the lithium sources, the iron sources and the phosphorus sources are proportioned according to certain proportions, the carbon sources and the dopants are proportioned according to certain adding amounts, and grinding, granulation, sintering and crushing are sequentially performed to obtain the first lithium iron phosphate material with a Dv50 of 0.3-0.5 mu m and the second lithium iron phosphate material with a Dv50 of 1.8-2.4 mu m; and the first lithium iron phosphate material and the second lithium iron phosphate material are proportioned and mixed according to a weight ratio of (0.8-1.2) to 6. The battery monomer, the battery, the electric device, the lithium iron phosphate material and the preparation method have high energy density, and have high specific capacity and capacity retention rate.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a battery cell, a battery, an electrical device, lithium iron phosphate material, and a preparation method thereof. Background Technology

[0002] Lithium iron phosphate (LFP) is widely used in the new energy vehicle field as a cathode material for lithium-ion batteries due to its advantages such as high energy density, long lifespan, and good charge-discharge performance. However, compared with other lithium-ion battery cathode materials, LFP has a relatively low energy density. Therefore, how to improve the energy density of LFP materials has become an important issue for the LFP industry.

[0003] In existing technologies, finished lithium iron phosphate powder is typically classified by particle size and then mixed to obtain graded lithium iron phosphate materials. Energy density is increased by improving the compaction density of the material. However, the specific capacity and capacity retention of this type of lithium iron phosphate material need further improvement. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell, battery, power device, lithium iron phosphate material and preparation method, which have high energy density and high specific capacity and capacity retention.

[0005] To achieve the above objectives, the first aspect of this application provides a method for preparing lithium iron phosphate material, comprising the following steps:

[0006] A lithium source, iron source, phosphorus source, carbon source, dopant, and solvent for preparing the first lithium iron phosphate material are selected. The lithium source, iron source, and phosphorus source are prepared in a lithium-iron-phosphorus molar ratio of (1-1.2):1:(0.95-0.96). The amount of carbon source added is 8%-15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material. The amount of dopant added is 3000-5000 ppm of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, to obtain a first precursor slurry. The first precursor slurry is then subjected to grinding, granulation, sintering, and pulverization to obtain a first lithium iron phosphate material with a Dv50 of 0.3-0.5 μm.

[0007] A lithium source, iron source, phosphorus source, carbon source, dopant, and solvent for preparing the second lithium iron phosphate material are selected. The lithium source, iron source, and phosphorus source are mixed in a lithium-iron-phosphorus molar ratio of (1.2-1.5):1:(0.96-0.97). The amount of carbon source added is 8%-11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material. The amount of dopant added is 1000-2000 ppm of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, to obtain a second precursor slurry. The second precursor slurry is then subjected to grinding, granulation, sintering, and pulverization to obtain a second lithium iron phosphate material with a Dv50 of 1.8-2.4 μm.

[0008] The first lithium iron phosphate material and the second lithium iron phosphate material are mixed in a weight ratio of (0.8~1.2):6.

[0009] Therefore, this application prepares two lithium iron phosphate materials with different particle sizes and high performance by separately controlling the lithium iron phosphate ratio, carbon coating amount, doping ratio, etc. during the batching process. Then, these two materials are mixed in a certain proportion to obtain a high-compact, high-performance graded lithium iron phosphate material, so that the resulting product not only has high energy density, but also has high specific capacity and capacity retention.

[0010] In any embodiment, the molar ratio of lithium iron phosphate to phosphorus in the preparation of the first lithium iron phosphate material is (1-1.1):1:(0.955-0.96), and the molar ratio of lithium iron phosphate to phosphorus in the preparation of the second lithium iron phosphate material is (1.2-1.3):1:(0.965-0.97).

[0011] And / or, the amount of carbon source added when preparing the first lithium iron phosphate material is 12% to 15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, and the amount of carbon source added when preparing the second lithium iron phosphate material is 8% to 11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material.

[0012] In any embodiment, the solid content of the first precursor slurry is 45% to 55%, and it is ground to a Dv50 of 0.15 to 0.25 μm;

[0013] The second precursor slurry has a solid content of 30%–40% and is ground to a Dv50 of 0.45–0.65 μm. By controlling the grinding particle size of the first precursor slurry and using a higher proportion of carbon source, lithium iron phosphate material with smaller particles and high rate performance is generated. By controlling the grinding particle size of the second precursor slurry and using a lower proportion of carbon source, lithium iron phosphate material with larger particles and high capacity is generated.

[0014] In any embodiment, the granulation method of the first precursor slurry includes spray drying, granulation to a Dv50 of 8-15 μm;

[0015] The granulation method of the second precursor slurry includes spray drying, granulation to a Dv50 of 15–30 μm. By controlling the granulation particle size of the first precursor slurry, small particles of a specific particle size can be obtained stepwise. By controlling the granulation particle size of the second precursor slurry, large particles of a specific particle size can be obtained stepwise.

[0016] In any embodiment, the sintering temperature of the first precursor slurry is 710–760°C, and the holding time is 6–12 hours.

[0017] The sintering temperature of the second precursor slurry is 760–820°C, and the holding time is approximately 8–16 hours.

[0018] In any embodiment, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium sulfate, lithium nitrate, and lithium chloride.

[0019] And / or, the carbon source includes one or any combination of cyclodextrin, urea, glucose, sucrose, glycine, citric acid, oxalic acid, vinyl alcohol, and polyethylene glycol;

[0020] And / or, the dopant includes one or more of titanium dioxide, titanium hydroxide, tetrabutyl titanate, ammonium metavanadate, vanadium pentoxide, magnesium oxide, magnesium acetate, boric acid, and nano-yttrium oxide.

[0021] The second aspect of this application also provides a lithium iron phosphate material, including the lithium iron phosphate material prepared by the preparation method of the first aspect.

[0022] A third aspect of this application also provides a battery cell, including a positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material, the positive electrode active material comprising the lithium iron phosphate material of the second aspect.

[0023] A fourth aspect of this application also provides a battery, including the battery cell of the third aspect.

[0024] The fifth aspect of this application also provides an electrical device, including the battery of the fourth aspect, said battery being used to provide electrical energy. Attached Figure Description

[0025] Figure 1 This is a SEM image of the lithium iron phosphate material product prepared in Example 1.

[0026] Figure 2 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0027] Figure 3 yes Figure 2 An exploded view of a battery cell according to one embodiment of this application is shown.

[0028] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0029] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0030] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0031] Figure 7 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0034] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, battery, power device, lithium iron phosphate material, and preparation method of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0035] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0038] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0039] Lithium iron phosphate (LFP) is widely used in the new energy vehicle field as a cathode material for lithium batteries due to its advantages such as high energy density, long lifespan, and good charge-discharge performance. However, compared with other lithium battery cathode materials, LFP has a relatively low energy density. Therefore, how to improve the energy density of LFP materials has become an important issue for the LFP industry.

[0040] Generally, there is a strong correlation between the compaction density of powder and the particle size. Powder composed of large particles has a higher compaction density than powder composed of small particles. Therefore, the main way to improve the compaction density of lithium iron phosphate materials is to use particle size gradation, filling the gaps between large particles with small particles, thereby increasing the energy density by improving the compaction density of the powder. Moreover, the superior electrical performance brought about by the larger specific surface area of ​​small particles can compensate for the electrical performance loss caused by large particles.

[0041] In existing technologies, finished lithium iron phosphate powder is typically classified by particle size. For example, finished lithium iron phosphate powder is subjected to air jet milling to obtain powders of different particle sizes, which are then mixed to obtain graded lithium iron phosphate material in order to improve the compaction density of the material.

[0042] In the synthesis of lithium iron phosphate, lithium, iron, and phosphorus sources form a lithium iron phosphate lattice through solid-state melting. Different ratios of lithium, iron, and phosphorus affect the lattice production rate, thus affecting the final lattice size. At the same time, the incorporation of doping elements into the lithium iron phosphate lattice broadens the migration channels of lithium ions, and the outer carbon coating also affects the crystal production rate and crystal size. Therefore, differences in the lithium-iron-phosphorus ratio, doping amount, and carbon coating amount will greatly affect the particle size and overall performance of the finished lithium iron phosphate.

[0043] In existing graded lithium iron phosphate materials, powders of different particle sizes are prepared and graded simultaneously. This means that lithium iron phosphate materials of different particle sizes are produced using the same process. As a result, lithium iron phosphate materials of different particle sizes cannot all have good overall performance, and the graded lithium iron phosphate materials obtained by mixing cannot have excellent overall performance.

[0044] As the synthesis route of lithium iron phosphate in industrial production becomes more mature, controlling the electrical properties of lithium iron phosphate materials with different particle sizes by adjusting parameters such as lithium-iron-phosphorus ratio, doping amount, and carbon coating amount will become an important method for preparing lithium iron phosphate materials with high compaction density, high specific capacity, and high capacity retention.

[0045] Based on this, the first aspect of the present application provides a method for preparing lithium iron phosphate material, comprising the following steps:

[0046] Lithium source, iron source, phosphorus source, carbon source, dopant, and solvent for preparing the first lithium iron phosphate material were selected. The lithium source, iron source, and phosphorus source were prepared according to a lithium iron phosphorus molar ratio of (1-1.2):1:(0.95-0.96). The amount of carbon source added was 8%-15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material. The amount of dopant added was 3000-5000 ppm of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, and a first precursor slurry was prepared. The first precursor slurry was then subjected to grinding, granulation, sintering, and pulverization to obtain the first lithium iron phosphate material with a Dv50 of 0.3-0.5 μm.

[0047] Lithium source, iron source, phosphorus source, carbon source, dopant, and solvent for preparing the second lithium iron phosphate material were selected. The lithium source, iron source, and phosphorus source were mixed in a lithium-iron-phosphorus molar ratio of (1.2-1.5):1:(0.96-0.97). The amount of carbon source added was 8%-11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, and the amount of dopant added was 1000-2000 ppm of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, to obtain a second precursor slurry. The second precursor slurry was then subjected to grinding, granulation, sintering, and pulverization to obtain a second lithium iron phosphate material with a Dv50 of 1.8-2.4 μm.

[0048] The first lithium iron phosphate material and the second lithium iron phosphate material are mixed in a weight ratio of (0.8~1.2):6.

[0049] Lithium iron phosphate material refers to a material whose main body is lithium iron phosphate (LixFeyPzO4). In some embodiments of this application, doping elements are also introduced into the main body, and a carbon coating layer is also applied to the outside.

[0050] In the embodiments of this application, the lithium iron phosphate mass corresponding to the first lithium iron phosphate material and the lithium iron phosphate mass corresponding to the second lithium iron phosphate material refer to the mass of lithium iron phosphate generated based on their respective lithium source, iron source, and phosphorus source, and the amount of carbon source and dopant is then calculated based on this mass.

[0051] The mass of lithium iron phosphate = (mass of lithium source + mass of iron source + mass of phosphorus source) * 89%, which is the theoretical empirical value during verification.

[0052] A carbon source is a compound that provides carbon to form a carbon coating layer, while a dopant is a compound that provides doping elements.

[0053] 1ppm = 0.0001%, meaning that when preparing the first lithium iron phosphate material, the amount of dopant added is 0.3% to 0.5% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, and when preparing the second lithium iron phosphate material, the amount of dopant added is 0.1% to 0.2% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material.

[0054] Dv50, also known as median particle size, refers to the particle size corresponding to 50% of the cumulative volumetric particle size distribution. The cumulative volumetric particle size distribution, also called the differential particle size distribution, is a curve plotted with particle size on the x-axis and the differential distribution of particle size at different dimensions on the y-axis. It can accurately reflect the particle size distribution characteristics of a material. A laser particle size analyzer can be used to determine the volumetric particle size distribution of a material and plot the interval particle size distribution curves.

[0055] For example, the molar ratio of lithium iron phosphate to phosphorus in the preparation of the first lithium iron phosphate material is 1:1:0.95, 1:1:0.96, 1.1:1:0.95, 1.1:1:0.96, 1.2:1:0.95, 1.2:1:0.96, or any value within the range of (1 to 1.2):1:(0.95 to 0.96); the molar ratio of lithium iron phosphate to phosphorus in the preparation of the second lithium iron phosphate material is 1.2:1:0.97, 1.3:1:0.96, 1.3:1:0.97, 1.5:1:0.96, 1.5:1:0.97, or any value within the range of (1.2 to 1.5):1:(0.96 to 0.97).

[0056] For example, the amount of carbon source added to prepare the first lithium iron phosphate material is 8%, 10%, 12%, 13%, 14%, or 15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, or any value within the range of 8% to 15%. The amount of dopant added is 3000 ppm, 4000 ppm, or 5000 ppm of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, or any value within the range of 3000 to 5000 ppm. The amount of carbon source added to prepare the second lithium iron phosphate material is 8%, 9%, 10%, or 11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, or any value within the range of 8% to 11%. The amount of dopant added is 1000 ppm, 1500 ppm, or 2000 ppm of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, or any value within the range of 1000 to 2000 ppm.

[0057] For example, the Dv50 of the first lithium iron phosphate material is 0.3μm, 0.4μm, or 0.5μm, or any value in the range of 0.3 to 0.5μm; the Dv50 of the second lithium iron phosphate material is 1.8μm, 2μm, 2.2μm, or 2.4μm, or any value in the range of 1.8 to 2.4μm.

[0058] For example, the weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material is 0.8:6, 1:6, 1.2:6, or any value within the range of (0.8 to 1.2):6.

[0059] This application involves mixing lithium, iron, phosphorus, carbon sources, and dopants with different lithium-iron-phosphorus ratios, carbon source ratios, and doping ratios to obtain two precursor mixtures with varying lithium-iron-phosphorus ratios, carbon source ratios, and doping ratios. During the sintering process, the influence of these ratios on the precursor mixtures leads to differences in crystal growth and solid-state melt doping during the preparation of the two lithium iron phosphate materials, resulting in two lithium iron phosphate materials with different electrical properties and particle sizes. These two lithium iron phosphate materials with different particle sizes are then mixed in a specific weight ratio. Smaller particles easily fill the gaps between larger particles, achieving particle gradation, increasing the material's compaction density, and thus improving energy density. Furthermore, the differences in lithium-iron-phosphorus ratios, carbon source ratios, and doping ratios allow each lithium iron phosphate material to possess excellent electrical properties and low polarization, achieving a graded material that balances high specific capacity and capacity retention.

[0060] Phosphorus-oxygen bonds constitute the basic common framework of the olivine cell structure of lithium iron phosphate (LFP). Differentiated selection of the lithium-iron-phosphorus ratio and doping ratio affects the formation of crystals of different sizes. Specifically, in the preparation of the second type of LFP material, the growth and melting of LFP crystals are active in a sintering atmosphere with high phosphorus content, resulting in larger primary LFP particles. Simultaneously, more doping elements can be used to achieve iron site doping, improving the conductivity and lithium-ion diffusion performance of the large particles. In the preparation of the first type of LFP material, in a sintering atmosphere with high iron content, the growth of LFP crystals is limited due to the decreased phosphorus enrichment and the Li / Fe antisite defects generated by excessive iron during synthesis. The resulting primary LFP particles are smaller, and the higher proportion of doping elements also leads to more ion inclusion defects in the lattice, further inhibiting the growth of primary particles.

[0061] The differentiated selection of carbon source ratios ensures good protection of the carbon coating layer on the surface of both materials, precise particle size control of both lithium iron phosphate particles, and a high degree of gradation in the finished product. Furthermore, the smooth transition in volume density between these two particle groups with different particle size ranges results in superior electrical performance and lower polarization at high rates compared to conventionally graded lithium iron phosphate materials with the same compaction.

[0062] In some embodiments, the molar ratio of lithium iron phosphate to phosphorus in the preparation of the first lithium iron phosphate material is (1-1.1):1:(0.955-0.96), and the molar ratio of lithium iron phosphate to phosphorus in the preparation of the second lithium iron phosphate material is (1.2-1.3):1:(0.965-0.97).

[0063] And / or, the amount of carbon source added when preparing the first lithium iron phosphate material is 12% to 15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, and the amount of carbon source added when preparing the second lithium iron phosphate material is 8% to 11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material.

[0064] For example, the molar ratio of lithium iron phosphate to phosphorus in the preparation of the first lithium iron phosphate material is 1:1:0.955, 1:1:0.96, 1.1:1:0.955, 1.1:1:0.96, or any value in the range of (1 to 1.1):1:(0.955 to 0.96). The molar ratio of lithium iron phosphate to phosphorus in the preparation of the second lithium iron phosphate material is 1.2:1:0.965, 1.2:1:0.97, 1.3:1:0.965, 1.3:1:0.97, or any value in the range of (1.2 to 1.3):1:(0.965 to 0.97).

[0065] For example, the amount of carbon source added when preparing the first lithium iron phosphate material is 12%, 13%, 14%, or 15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, or any value within the range of 12% to 15%. The amount of carbon source added when preparing the second lithium iron phosphate material is 8%, 9%, 10%, or 11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, or any value within the range of 8% to 11%.

[0066] In some embodiments, the first precursor slurry has a solid content of 45% to 55% and is ground to a Dv50 of 0.15 to 0.25 μm;

[0067] The solid content of the second precursor slurry is 30% to 40%, and it is ground to a Dv50 of 0.45 to 0.65 μm.

[0068] For example, the solid content of the first precursor slurry is 45%, 50%, or 55%, or any value within the range of 45% to 55%, and it is ground to a Dv50 of 0.15μm, 0.2μm, or 0.25μm, or any value within the range of 0.15 to 0.25μm; the solid content of the second precursor slurry is 30%, 35%, or 40%, or any value within the range of 30% to 40%, and it is ground to a Dv50 of 0.45μm, 0.55μm, or 0.65μm, or any value within the range of 0.45 to 0.65μm.

[0069] In the process of synthesizing the first lithium iron phosphate material, this application uses a small grinding particle size for the precursor slurry and a higher proportion of carbon source. Due to the larger specific surface energy, the carbon source is more fully coated, and the reaction between the center and outer surface of the small particles is more complete and consistent. Due to the isolation of the carbon coating layer, the particles are difficult to melt, thus promoting the formation of small-particle lithium iron phosphate material with high rate performance.

[0070] In the process of synthesizing the second lithium iron phosphate material, this application uses a large grinding particle size for the precursor slurry and a low proportion of carbon source, resulting in a large contact surface between particles and easy melting between them, thereby forming a large-particle lithium iron phosphate material with high capacity.

[0071] In some embodiments, the granulation of the first precursor slurry includes spray drying, granulation to a Dv50 of 8–15 μm, optionally 10–15 μm;

[0072] The granulation method for the second precursor slurry includes spray drying, granulation to a Dv50 of 15-30 μm, or optionally 20-30 μm.

[0073] In some embodiments, the sintering temperature of the first precursor slurry is 710–760°C, and the holding time is 6–12 hours.

[0074] The sintering temperature of the second precursor slurry is 760–820℃, and the holding time is approximately 8–16 hours.

[0075] In some embodiments of this application, a first lithium iron phosphate material with a Dv50 of 0.3 to 0.5 μm can be obtained by air jet milling; a second lithium iron phosphate material with a Dv50 of 1.8 to 2.4 μm can be obtained by air jet milling.

[0076] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium sulfate, lithium nitrate, and lithium chloride. Among them, lithium dihydrogen phosphate and lithium phosphate can also provide phosphate ions during the preparation process and can also be used as phosphorus sources.

[0077] And / or, an iron source refers to a substance that can provide iron during the preparation process. It can usually be an iron salt, such as one or more of iron phosphate and iron sulfate. Iron phosphate can also provide phosphate ions during the preparation process and can also be used as a phosphorus source.

[0078] And / or, the phosphorus source includes one or more of the phosphorus sources listed above and hydrogen phosphate;

[0079] And / or, the carbon source includes one or any combination of cyclodextrin, urea, glucose, sucrose, glycine, citric acid, oxalic acid, vinyl alcohol, and polyethylene glycol;

[0080] And / or, the dopants include one or more of titanium dioxide, titanium hydroxide, tetrabutyl titanate, ammonium metavanadate, vanadium pentoxide, magnesium oxide, magnesium acetate, boric acid, and nano-yttrium oxide.

[0081] The second aspect of this application also provides a lithium iron phosphate material, including the lithium iron phosphate material prepared by the preparation method of the first aspect; the lithium iron phosphate material includes a mixture of a first lithium iron phosphate material and a second lithium iron phosphate material, wherein the Dv50 of the first lithium iron phosphate material is 0.3 to 0.5 μm, the Dv50 of the second lithium iron phosphate material is 1.8 to 2.4 μm, and the weight ratio of the first lithium iron phosphate material to the second lithium iron phosphate material is (0.8 to 1.2):6.

[0082] A third aspect of this application also provides a battery cell, including a positive electrode sheet, the positive electrode sheet including a positive active material layer, the positive active material layer including a positive active material, and the positive active material including the lithium iron phosphate material of the second aspect.

[0083] A fourth aspect of this application also provides a battery, including the battery cell of the third aspect.

[0084] The fifth aspect of this application also provides an electrical device, including the battery of the fourth aspect, the battery being used to provide electrical energy.

[0085] In addition, the battery cell and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0086] [Battery cell]

[0087] The third aspect of this application provides a battery cell. This application does not particularly limit the type of battery cell; for example, the battery cell can be a lithium-ion battery, etc.

[0088] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0089] This application does not impose any particular restrictions on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This includes battery cells using electrolyte solutions and some battery cells using solid electrolytes.

[0090] [Positive electrode plate]

[0091] The positive electrode sheet, also known as the cathode electrode sheet, includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate material according to the second aspect of this application.

[0092] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0093] In some embodiments, the positive current collector 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0094] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may also simultaneously employ positive electrode active materials known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622)、LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of olivine-structured lithium phosphate may include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), 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 manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0095] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material for a lithium-ion battery may include a lithium transition metal oxide with the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0096] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4, and one or more of them.

[0097] In some embodiments, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0098] As an optional technical approach in this application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4; where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0099] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0100] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0101] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0102] As an optional technical approach in this application, the polyanionic compound can be Na...4+x R 3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0103] As an optional technical solution of the present application, the polyanionic compound may be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , wherein the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0104] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0105] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an 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.

[0106] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0107] [Negative electrode plate]

[0108] The negative electrode sheet, also known as the anode sheet, in some embodiments includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0109] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0110] 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 material substrate and a metal layer formed on at least one surface of the polymer material substrate. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0112] In some embodiments, the negative electrode film layer may optionally 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).

[0113] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0115] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0116] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, and may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0117] In some embodiments, the membrane layer may also include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0118] [Electrolytes]

[0119] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0120] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0121] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0122] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0123] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0124] [Isolation membrane]

[0125] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0126] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0127] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0128] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0129] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0130] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 The example shown is a square-structured battery cell 5.

[0131] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0132] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0133] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0134] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0135] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0136] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0137] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0138] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0139] Figure 7This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0140] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0141] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0142] Example 1

[0143] Preparation of the first lithium iron phosphate material: The lithium source (lithium carbonate), iron source (iron phosphate + iron sulfate, molar ratio 1:1), and phosphorus source (iron phosphate + ammonium hydrogen phosphate, molar ratio 1:1) are mixed at a lithium-iron-phosphorus molar ratio of 1.1:1:0.96. Then, 13.5% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material product is added as a carbon source (2% glucose + 10% polyethylene glycol + 1% cyclodextrin + 0.5% citric acid). 3000ppm of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material product is added as a dopant (2000ppm titanium dioxide + 1000ppm magnesium oxide).

[0144] The powder material obtained from the above-mentioned ingredients was dissolved in deionized water, and the solid content was adjusted to 45%. Then, it was wet-milled to make the particle size Dv50 of the slurry product 0.2μm. The slurry was then pumped into a spray drying device through a diaphragm pump for drying and granulation. The particle size of the dried material was required to be approximately Dv50 of 12μm. The dried material was then sintered in a kiln at a temperature of 730℃ for a holding time of approximately 10 hours. Finally, the sintered material was subjected to air jet milling, and the Dv50 of the pulverized material was controlled at 0.4μm to obtain the first lithium iron phosphate material.

[0145] Preparation of the second lithium iron phosphate material: The lithium source (lithium carbonate), iron source (iron phosphate + iron sulfate, molar ratio 1:1), and phosphorus source (iron phosphate + ammonium hydrogen phosphate, molar ratio 1:1) are mixed according to a lithium iron phosphorus molar ratio of 1.2:1:0.97. Then, 8% carbon source (7% sucrose + 1% polyethylene glycol) corresponding to the mass of lithium iron phosphate in the second lithium iron phosphate material product is added, and 2000ppm dopant (1000ppm titanium dioxide + 1000ppm magnesium oxide) corresponding to the mass of lithium iron phosphate in the second lithium iron phosphate material product is added.

[0146] The powder material obtained from the above-mentioned ingredients is dissolved in deionized water, and the solid content is adjusted to 35%. Then, it is wet-milled to make the particle size Dv50 of the slurry product 0.5μm. The slurry is then pumped into a spray drying device through a diaphragm pump for drying and granulation. The particle size of the dried material is required to be approximately 20μm. The dried material is then sintered in a kiln at a temperature of 790℃ for a holding time of approximately 12 hours. Finally, the sintered material is subjected to air jet milling, and the particle size Dv50 of the milled material is controlled at 2.0μm to obtain the second lithium iron phosphate material.

[0147] The first lithium iron phosphate material and the second lithium iron phosphate material were mixed at a weight ratio of 1.1:6 to obtain the finished lithium iron phosphate material.

[0148] Examples 2-4

[0149] The preparation process is roughly the same as in Example 1, except that the amount of carbon source added is changed by changing the amount of polyethylene glycol, and the amount of dopant added is changed by changing the amount of titanium dioxide, thereby obtaining different finished lithium iron phosphate materials.

[0150] Comparative Examples 1-6

[0151] The preparation process is largely the same as in Example 1, except that:

[0152] The finished lithium iron phosphate material of Comparative Example 1 uses only the first lithium iron phosphate material;

[0153] The finished lithium iron phosphate material in Comparative Example 2 only uses the second lithium iron phosphate material;

[0154] The finished lithium iron phosphate material of Comparative Example 3 was made by mixing the first lithium iron phosphate material and the second lithium iron phosphate material at a weight ratio of 2:3.

[0155] The finished lithium iron phosphate material of Comparative Example 4 was made by mixing first lithium iron phosphate material and second lithium iron phosphate material with different particle sizes.

[0156] The finished lithium iron phosphate material of Comparative Example 5 was prepared by using the same method as the first lithium iron phosphate material preparation method to obtain sintered material, which was then crushed and sieved to obtain powders of different particle sizes, and then mixed.

[0157] The finished lithium iron phosphate material of Comparative Example 6 was prepared by using the second lithium iron phosphate material preparation method to obtain sintered material, which was then crushed and sieved to obtain powders of different particle sizes, and then mixed.

[0158] The relevant parameters of the finished lithium iron phosphate materials of Examples 1-4 and Comparative Examples 1-6 are shown in Table 1 below.

[0159] Table 1: Parameter results of Examples 1-4 and Comparative Examples 1-6

[0160]

[0161]

[0162] The finished lithium iron phosphate materials provided in each embodiment and comparative example were used as positive electrode active materials to prepare secondary batteries. The specific preparation process is as follows:

[0163] Preparation of the positive electrode sheet

[0164] The finished lithium iron phosphate material (positive electrode active material), conductive carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) prepared in each embodiment and comparative example were added to N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 and stirred to obtain a coating slurry. The slurry was then uniformly coated onto the positive electrode current collector aluminum foil, dried, rolled, and then die-cut to obtain the positive electrode sheet.

[0165] Preparation of the negative electrode sheet

[0166] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 96.5:0.7:1.8:1 and mixed evenly to prepare a slurry. The slurry is coated evenly on the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0167] Preparation of Electrolyte

[0168] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvents ethylene carbonate, diethyl carbonate, and dimethyl carbonate are mixed evenly in a volume ratio of 1:1:1, and 1 mol / L LiPF6 lithium salt is added and dispersed evenly to obtain the electrolyte.

[0169]

Isolation Film

[0170] A polyethylene film with a thickness of 12 μm was used as the separator.

[0171] [Preparation of Lithium-ion Batteries]

[0172] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0173] In addition, the finished lithium iron phosphate materials and corresponding secondary batteries obtained in Examples 1-4 and Comparative Examples 1-6 were subjected to performance tests.

[0174] The finished lithium iron phosphate materials of each embodiment and comparative example were tested, including:

[0175] The secondary batteries of each embodiment and comparative example were tested, including:

[0176] Test of 0.1C rate performance: Under normal temperature (25℃) conditions, the battery is charged to 3.75V at a constant current of 0.1C, then charged to 0.05C at a constant voltage of 3.75V, and left to rest for 5 minutes; then discharged to 2.0V at 0.1C, and the cycle is repeated twice; the average discharge capacity obtained from the two cycles is recorded.

[0177] 1C rate performance test: Under normal temperature (25℃) conditions, the battery is charged at a constant current of 0.1C to 3.75V, then charged at a constant voltage of 3.75V to a current of 0.05C, and left to rest for 5 minutes; then discharged at 0.1C to 2.0V, and the cycle is repeated twice; then the battery is charged at a constant current of 1C to 3.75V, then charged at a constant voltage of 3.75V to a current of 0.05C, and left to rest for 5 minutes; then discharged at 1C, and the average 1C capacity obtained from the two cycles is recorded.

[0178] The test results are shown in Table 2 below.

[0179] Table 2: Performance test results of Examples 1-4 and Comparative Examples 1-6

[0180]

[0181] Based on the above results, it can be seen that the compaction density of the finished lithium iron phosphate material in the secondary batteries of Examples 1-4 is relatively high, corresponding to high energy density of the secondary batteries, while also maintaining high specific capacity and capacity retention. However, the secondary batteries of Comparative Examples 1-6 cannot simultaneously achieve both high energy density (reflected in the compaction density of the finished lithium iron phosphate material) and high specific capacity and capacity retention.

[0182] In addition, the morphology and structure of the finished lithium iron phosphate material of Example 1 were observed using a scanning electron microscope, such as... Figure 1 As shown, the microstructure of the finished powder exhibits a very obvious gradation phenomenon, with nano and small-sized particles uniformly filling the gaps between large-sized particles.

[0183] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing lithium iron phosphate material, characterized in that, Includes the following steps: A lithium source, iron source, phosphorus source, carbon source, dopant, and solvent for preparing the first lithium iron phosphate material are selected. The lithium source, iron source, and phosphorus source are prepared in a lithium-iron-phosphorus molar ratio of (1-1.2):1:(0.95-0.96). The amount of carbon source added is 8%-15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material. The amount of dopant added is 3000-5000 ppm of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, to obtain a first precursor slurry. The first precursor slurry is then subjected to grinding, granulation, sintering, and pulverization to obtain a first lithium iron phosphate material with a Dv50 of 0.3-0.5 μm. A lithium source, iron source, phosphorus source, carbon source, dopant, and solvent for preparing the second lithium iron phosphate material are selected. The lithium source, iron source, and phosphorus source are mixed in a lithium-iron-phosphorus molar ratio of (1.2-1.5):1:(0.96-0.97). The amount of carbon source added is 8%-11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material. The amount of dopant added is 1000-2000 ppm of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material, to obtain a second precursor slurry. The second precursor slurry is then subjected to grinding, granulation, sintering, and pulverization to obtain a second lithium iron phosphate material with a Dv50 of 1.8-2.4 μm. The first lithium iron phosphate material and the second lithium iron phosphate material are mixed in a weight ratio of (0.8~1.2):

6.

2. The method for preparing lithium iron phosphate material as described in claim 1, characterized in that, The molar ratio of lithium iron phosphate to phosphorus in the preparation of the first lithium iron phosphate material is (1-1.1):1:(0.955-0.96), and the molar ratio of lithium iron phosphate to phosphorus in the preparation of the second lithium iron phosphate material is (1.2-1.3):1:(0.965-0.97). And / or, the amount of carbon source added when preparing the first lithium iron phosphate material is 12% to 15% of the mass of lithium iron phosphate corresponding to the first lithium iron phosphate material, and the amount of carbon source added when preparing the second lithium iron phosphate material is 8% to 11% of the mass of lithium iron phosphate corresponding to the second lithium iron phosphate material.

3. The method for preparing lithium iron phosphate material as described in claim 1, characterized in that, The first precursor slurry has a solid content of 45% to 55% and is ground to a Dv50 of 0.15 to 0.25 μm; The second precursor slurry has a solid content of 30% to 40% and is ground to a Dv50 of 0.45 to 0.65 μm.

4. The method for preparing lithium iron phosphate material as described in claim 1 or 3, characterized in that, The granulation method of the first precursor slurry includes spray drying, granulation to a Dv50 of 8-15 μm; The granulation method of the second precursor slurry includes spray drying and granulation to a Dv50 of 15-30 μm.

5. The method for preparing lithium iron phosphate material as described in claim 1 or 3, characterized in that, The sintering temperature of the first precursor slurry is 710–760°C, and the holding time is 6–12 hours. The sintering temperature of the second precursor slurry is 760–820°C, and the holding time is approximately 8–16 hours.

6. The method for preparing lithium iron phosphate material as described in claim 1, characterized in that, The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium sulfate, lithium nitrate, and lithium chloride. And / or, the carbon source includes one or any combination of cyclodextrin, urea, glucose, sucrose, glycine, citric acid, oxalic acid, vinyl alcohol, and polyethylene glycol; And / or, the dopant includes one or more of titanium dioxide, titanium hydroxide, tetrabutyl titanate, ammonium metavanadate, vanadium pentoxide, magnesium oxide, magnesium acetate, boric acid, and nano-yttrium oxide.

7. A lithium iron phosphate material, characterized in that, The lithium iron phosphate material prepared by any one of claims 1 to 6.

8. A single battery cell, characterized in that, It includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material layer, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including the lithium iron phosphate material as described in claim 7.

9. A battery, characterized in that, Includes the battery cell as described in claim 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 9, wherein the battery is used to provide electrical energy.

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