Preparation method of lithium iron phosphate positive electrode material, positive electrode material and battery

Abstract

The present invention provides a method for preparing a lithium iron phosphate positive electrode material, a positive electrode material, and a battery. The preparation method comprises: (I) mixing an iron phosphate precursor, a lithium source, a dopant, a carbon source, and a solvent to obtain a dispersion; (II) wet-grinding the dispersion to obtain an intermediate material; and (III) sequentially calcining and crushing the intermediate material to obtain the lithium iron phosphate positive electrode material. The present invention increases the compaction density of the positive electrode material and improves electrochemical performance by controlling the sanding particle size, sintering temperature, and particle size distribution of the lithium iron phosphate particles.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode material preparation, and relates to a preparation method of a lithium iron phosphate cathode material, the cathode material and a battery. Background Art

[0002] The energy storage market has flourished in recent years. Energy storage batteries using lithium iron phosphate as their cathode material have attracted increasing attention due to their long lifespan, safety, high temperature resistance, high capacity, lack of memory effect, and environmental friendliness. Furthermore, with the growing demand for storage capacity, the energy density requirements for lithium iron phosphate batteries are becoming increasingly higher.

[0003] CN104766973A discloses a lithium iron phosphate for high-performance lithium-ion batteries and a preparation method thereof, comprising the following steps: (1) preparing a lithium iron phosphate precursor solution; (2) preparing an electrospinning solution; (3) preparing a lithium iron phosphate precursor / polymer composite nanofiber; and (4) preparing lithium iron phosphate nanofibers. The prepared lithium iron phosphate cathode material has a smooth surface and presents a nanofiber network distribution, and has high specific capacity and high initial efficiency, and is particularly suitable for the cathode material needs of high-energy density batteries. CN116002652A discloses a lithium iron phosphate prepared using iron phosphate and lithium phosphate and a preparation method thereof. The iron phosphate, phosphoric acid and lithium phosphate are mixed, an ethanol solution is added, and multi-stage mixing and grinding is performed, followed by spray drying to obtain a precursor; the precursor is heat-treated under nitrogen protection to generate the lithium iron phosphate material.

[0004] Under the premise of consistent process conditions, the greater the compaction density of lithium iron phosphate, the higher the energy density of the finished battery. The compaction density of lithium iron phosphate is closely related to its particle size distribution and gradation. When small particles (such as D1 and D 10 ) or the overall particle size is too small, the positive electrode material has a larger contact area with the electrolyte, and the discharge capacity performance is better, but the compaction density is low and there are more side reactions, which will cause the battery cell to produce gas and reduce the cycle performance of the battery cell; when the large particles are too large (such as D 50 and D 99 ) or the overall particles are too large. Although the compaction density is high, it will lead to too high DCR (DC internal resistance) and easily cause the capacity and cycle performance to decay.

[0005] Therefore, reasonable sanding particle size and particle grading can take into account both the compaction density and discharge capacity of the material, thereby improving the energy density and discharge capacity of the positive electrode material. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a platform access control system and method, which increases the compaction density of the positive electrode material and improves the electrochemical performance by controlling the sanding particle size, sintering temperature and particle size distribution of lithium iron phosphate particles.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate positive electrode material, the preparation method comprising:

[0009] (I) mixing an iron phosphate precursor, a lithium source, a dopant, a carbon source, and a solvent to obtain a dispersion;

[0010] (II) wet grinding the dispersion to obtain an intermediate material;

[0011] (III) calcining and crushing the intermediate material in sequence to obtain a lithium iron phosphate positive electrode material;

[0012] The wet grinding particle size is D n The calcination temperature is T, and the volume cumulative distribution percentages of the lithium iron phosphate cathode material reach 1%, 10%, 50% and 99% when the corresponding particle sizes are D1, D 10 、D 50 With D 99 , satisfying the following relationship:

[0013]

[0014] Among them, 11.0≤S≤13.3.

[0015] In the present invention, 11.0≤S≤13.3, and S can be, for example, 11.00, 11.14, 11.20, 11.30, 11.40, 11.50, 11.60, 11.80, 11.93, 12.00, 12.21, 12.33, 12.42, 12.55, 12.60, 12.85, 13.00, 13.15, 13.20, 13.25, 13.28 or 13.30, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] The present invention sequentially wet-grinds, calcines, and crushes a dispersion of an iron phosphate precursor, a lithium source, a dopant, a carbon source, and a solvent. By controlling the grinding particle size, the calcination temperature, and the particle size distribution after the crushing process, the compaction density of the resulting positive electrode material is increased, resulting in a higher volume energy density when prepared into an energy storage battery. Compared with traditional positive electrode materials, the side reactions between the battery cell and the electrolyte in the prepared energy storage battery can be reduced, which is beneficial to reducing gas production and effectively improving the discharge specific capacity and cycle performance.

[0017] As a preferred technical solution of the present invention, the molar ratio of the iron phosphate precursor to the lithium source is 1:(1~1.05), for example, it can be 1:1, 1:1.01, 1:1.015, 1:1.02, 1:1.025, 1:1.03, 1:1.035, 1:1.04, 1:1.045 or 1:1.05, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] It should be noted that the present invention does not specifically limit the lithium source, and any lithium source for preparing lithium iron phosphate batteries known to those skilled in the art can be used. Exemplarily, the lithium source includes but is not limited to any one of Li2CO3, Li3PO4 or LiNO3, or a combination of at least two of them.

[0019] Preferably, the dopant includes any one of TiO2, WO3 and MgO, or a combination of at least two thereof.

[0020] Preferably, based on the total mass of the iron phosphate precursor, lithium source, dopant and carbon source, the added amount of the dopant is 1000-5000 ppm, for example, it can be 1000 ppm, 1200 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 2800 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4300 ppm, 4500 ppm, 4800 ppm or 5000 ppm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0021] Preferably, the carbon source comprises glucose.

[0022] Preferably, the total mass of the iron phosphate precursor, lithium source, dopant and carbon source is taken as 100%, and the added amount of the carbon source is 10 to 15 wt%, for example, it can be 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt% or 15 wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0023] Preferably, the solvent comprises water.

[0024] Preferably, the solid content of the dispersion is 30-50%, for example, it can be 30%, 32%, 35%, 40%, 43%, 45%, 48% or 50%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] As a preferred technical solution of the present invention, the wet grinding includes sand grinding.

[0026] Preferably, the wet grinding particle size D n It is 400-600nm, for example, it can be 400nm, 420nm, 430nm, 450nm, 495nm, 500nm, 510nm, 550nm, 580nm, 598nm or 600nm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0027] In the present invention, when the grinding particle size of wet grinding is too large, it is easy to cause the sintered particles to be unable to grow, increase the proportion of small particles, and thus cause the compaction density of the product to be low, affecting the volume energy density; when the grinding particle size of wet grinding is too small, the proportion of large particles increases, which is easy to cause the subsequent crushing process to be obstructed, and the gradation after crushing is uncontrollable, resulting in poor material consistency.

[0028] It should be noted that the large particles in the present invention refer to the material particles corresponding to the cumulative volume distribution percentage of the lithium iron phosphate positive electrode material being greater than or equal to 50%, and the small particles refer to the material particles corresponding to the cumulative volume distribution percentage of the lithium iron phosphate positive electrode material being less than 50%.

[0029] As a preferred technical solution of the present invention, in step (II), after the wet grinding is completed, the intermediate material is dried.

[0030] Preferably, the drying process comprises spray drying.

[0031] Preferably, the spray drying pressure is 0.1 to 0.5 MPa, for example, 0.1 MPa, 0.15 MPa, 0.18 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.38 MPa, 0.4 MPa, 0.45 MPa, 0.47 MPa or 0.5 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the spray drying temperature is 140-190°C, for example, it can be 140°C, 143°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 172°C, 175°C, 170°C, 180°C, 183°C, 185°C, 186°C, 188°C or 190°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the calcination treatment includes: subjecting the intermediate material to microwave heating.

[0034] Compared to conventional box-type heating equipment that relies on heat conduction, the present invention uses microwave heating to ensure that the temperature of the sintered material at all locations in the graphite container is consistent, preventing the generation of temperature gradients within the material, thereby ensuring the consistency of the lithium iron phosphate sintered product and significantly improving the product's cyclic stability. Furthermore, compared to conventional box-type furnaces, microwave heating heats up quickly, quickly reaching the set temperature and significantly reducing the side reactions generated during the temperature rise process. The present invention does not specifically limit the container used to hold the intermediate material during microwave heating; any container known to those skilled in the art may be used, for example, a graphite crucible.

[0035] Preferably, after the calcination process is completed, the intermediate material is cooled until it reaches room temperature, and then the crushing process is performed.

[0036] As a preferred technical solution of the present invention, the temperature of the calcination treatment is 780-850°C, for example, it can be 780°C, 785°C, 790°C, 800°C, 810°C, 815°C, 820°C, 825°C, 830°C, 835°C, 840°C, 845°C or 850°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0037] The present invention controls the calcination treatment temperature within a reasonable range. On the one hand, it can avoid the sintered particles from not being able to grow due to the calcination temperature being too low, resulting in an increase in the proportion of small particles, and then resulting in a low compaction density of the finished product, affecting the volume energy density. On the other hand, it can avoid the particles from growing continuously due to the calcination temperature being too high. Although the compaction density will increase, the proportion of large particles will increase, which will easily lead to the subsequent crushing process being hindered, and the gradation after crushing cannot be controlled, resulting in poor material consistency.

[0038] Preferably, the calcination treatment time is 8 to 12 hours, for example, it can be 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours or 12 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the calcination of the intermediate material is carried out under the protection of a protective atmosphere.

[0040] Preferably, the protective atmosphere comprises nitrogen.

[0041] Preferably, the concentration of oxygen in the protective atmosphere is less than 50 ppm.

[0042] As a preferred technical solution of the present invention, the crushing process includes air flow grinding.

[0043] Preferably, the pressure of the air flow mill is 0.8-0.9 MPa, for example, it can be 0.8 MPa, 0.81 MPa, 0.82 MPa, 0.83 MPa, 0.84 MPa, 0.85 MPa, 0.86 MPa, 0.87 MPa, 0.88 MPa, 0.89 MPa or 0.9 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the particle size D1 of the lithium iron phosphate positive electrode material is 0.1 to 0.3 μm, and is not 0.3 μm. For example, it can be 0.1 μm, 0.11 μm, 0.13 μm, 0.15 μm, 0.16 μm, 0.18 μm, 0.2 μm, 0.22 μm, 0.23 μm, 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm or 0.29 μm, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0045] Preferably, the particle size D of the lithium iron phosphate positive electrode material is 10 It is 0.3 to 0.5 μm, for example, it can be 0.3 μm, 0.33 μm, 0.35 μm, 0.37 μm, 0.38 μm, 0.39 μm, 0.4 μm, 0.42 μm, 0.45 μm, 0.47 μm, 0.48 μm or 0.5 μm, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the particle size D of the lithium iron phosphate positive electrode material is 50 It is 0.8 to 1.2 μm, for example, it can be 0.8 μm, 0.82 μm, 0.85 μm, 0.87 μm, 0.89 μm, 0.9 μm, 0.92 μm, 0.93 μm, 0.94 μm, 0.95 μm, 0.98 μm, 1 μm, 1.05 μm, 1.08 μm, 1.1 μm, 1.12 μm, 1.15 μm, 1.18 μm, 1.19 μm or 1.2 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] Preferably, the particle size D of the lithium iron phosphate positive electrode material is 99 It is 5 to 10μm, for example, it can be 5μm, 5.2μm, 5.5μm, 5.7μm, 6μm, 6.2μm, 6.5μm, 6.7μm, 7μm, 7.14μm, 7.25μm, 7.26μm, 7.5μm, 7.9μm, 7.99μm, 8μm, 8.5μm, 8.7μm, 9μm, 9.5μm, 9.7μm, 9.85μm, 9.9μm or 10μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In a second aspect, the present invention provides a positive electrode material, which is prepared using the preparation method described in the first aspect.

[0049] As a preferred technical solution of the present invention, the compaction density of the positive electrode material is 2.1 to 2.5 g / cm 3 , for example, it can be 2.1g / cm 3 , 2.12g / cm 3 , 2.15g / cm 3 , 2.2g / cm 3 , 2.22g / cm 3 , 2.25g / cm 3 , 2.28g / cm 3 , 2.3g / cm 3 , 2.35g / cm 3 , 2.38g / cm 3 , 2.4g / cm 3 , 2.42g / cm 3 , 2.45g / cm 3 , 2.48g / cm 3 or 2.5g / cm 3 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] In a third aspect, the present invention provides a battery, wherein the positive electrode of the battery comprises the positive electrode material described in the second aspect.

[0051] The positive electrode of the battery in the present invention typically comprises an aluminum foil, as is well known to those skilled in the art, and a surface active material layer coated on at least one side of the aluminum foil. The active material layer is composed of a conductive agent, a binder, and the aforementioned positive electrode materials mixed in a specific mass ratio. Conductive agents include, but are not limited to, conductive carbon black, carbon nanotubes, and acetylene black; binders include, but are not limited to, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl pyrrolidone, styrene-butadiene rubber, or fluororubber.

[0052] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The present invention provides a preparation method of a lithium iron phosphate positive electrode material, a positive electrode material, and a battery. The method comprises sequentially subjecting a dispersion of an iron phosphate precursor, a lithium source, a dopant, a carbon source, and a solvent to wet grinding, calcination, and crushing. By controlling the grinding particle size, the calcination temperature, and the particle size distribution after the crushing treatment, the compaction density of the obtained positive electrode material is increased. When prepared into an energy storage battery, the material has a higher volume energy density. Compared with traditional positive electrode materials, the method can reduce side reactions between the battery cell and the electrolyte in the prepared energy storage battery, thereby reducing gas production and effectively improving the discharge specific capacity and cycle performance. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0056] In one embodiment, the present invention provides a method for preparing a lithium iron phosphate positive electrode material, the preparation method comprising:

[0057] (1) mixing an iron phosphate precursor, a lithium source, a dopant, a carbon source, and a solvent to obtain a dispersion having a solid content of 30 to 50%;

[0058] (2) wet grinding the dispersion to obtain an intermediate material, wherein the wet grinding particle size D n 400~600nm;

[0059] (3) The intermediate material is dried, calcined and crushed in sequence to obtain a lithium iron phosphate positive electrode material.

[0060] The wet grinding particle size is D n The calcination temperature is T, and the volume cumulative distribution percentages of the lithium iron phosphate cathode material reach 1%, 10%, 50% and 99% when the corresponding particle sizes are D1, D 10 、D 50 With D 99 , satisfying the following relationship:

[0061]

[0062] Among them, 11.0≤S≤13.3.

[0063] In some embodiments, the molar ratio of the iron phosphate precursor to the lithium source is 1:(1 to 1.05). The lithium source includes any one of Li2CO3, Li3PO4 or LiNO3, or a combination of at least two of them. The dopant includes any one of TiO2, WO3 and MgO, or a combination of at least two of them. The carbon source includes glucose. The solvent includes water. The total mass of the iron phosphate precursor, the lithium source, the dopant and the carbon source is taken as 100%, and the amount of the carbon source added is 10 to 15 wt%. The amount of the dopant added is 1000 to 5000 ppm, based on the total mass of the iron phosphate precursor, the lithium source, the dopant and the carbon source.

[0064] In some embodiments, the wet grinding comprises wet sand grinding.

[0065] In some embodiments, the drying process comprises spray drying, the pressure of the spray drying is 0.1-0.5 MPa, and the temperature of the spray drying is 140-190°C.

[0066] In some embodiments, the calcination process comprises: subjecting the intermediate material to microwave heating.

[0067] In some embodiments, the calcination temperature is 780-850° C., and the calcination time is 8-12 hours.

[0068] In some embodiments, after the calcination process is completed, the intermediate material is cooled until it reaches room temperature, and then the crushing process is performed.

[0069] In some embodiments, the calcination of the intermediate material is performed under the protection of a protective atmosphere, wherein the protective atmosphere comprises nitrogen, and the concentration of oxygen in the protective atmosphere is less than 50 ppm.

[0070] In some embodiments, the crushing process includes air flow milling, and the pressure of the air flow milling is 0.8 to 0.9 MPa.

[0071] In some embodiments, the particle size D1 of the lithium iron phosphate positive electrode material is 0.1 to 0.3 μm, and is not 0.3 μm. 10 0.3~0.5μm, particle size D 50 0.8~1.2μm, particle size D 99 5 to 10 μm.

[0072] In another embodiment, the present invention provides a positive electrode material, which is prepared by the preparation method described in a specific embodiment. The compacted density of the positive electrode material is 2.1 to 2.5 g / cm 3 .

[0073] In another embodiment, the present invention provides a battery, wherein the positive electrode of the battery comprises the positive electrode material described in another embodiment. The positive electrode of the battery in the present invention generally comprises aluminum foil, as is well known to those skilled in the art, and a surface active material layer coated on at least one side of the aluminum foil. The active material layer is formed by mixing a conductive agent, a binder, and the positive electrode material described above in a specific mass ratio. Conductive agents include, but are not limited to, conductive carbon black, carbon nanotubes, and acetylene black; binders include, but are not limited to, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl pyrrolidone, styrene-butadiene rubber, or fluororubber.

[0074] In the following examples, the addition amount of each material is based on the total mass of the iron phosphate precursor, lithium source, dopant and carbon source. For example, the total mass of the iron phosphate precursor, lithium source, dopant and carbon source is recorded as 100%, the addition amount of glucose is 10-15wt%, and the addition amount of TiO2 is 1000-5000ppm based on the total mass of the iron phosphate precursor, lithium source, dopant and carbon source.

[0075] Example 1

[0076] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0077] (1) FePO4 precursor and Li2CO3 were mixed in a molar ratio of 1:1.015, and 1500 ppm of TiO2 and 12 wt% of glucose were added in sequence to obtain a dispersion with a solid content of 40%;

[0078] (2) The dispersion is wet-grinded to obtain an intermediate material, wherein the grinding particle size D n =500nm, collect the intermediate material and spray dry it at a pressure of 0.2MPa and a temperature of 180℃;

[0079] (3) The spray-dried intermediate material was placed in a graphite crucible for microwave heating. The microwave frequency was adjusted to control the temperature T to 820°C and calcined for 12 hours in a nitrogen atmosphere (oxygen concentration <50 ppm);

[0080] (4) The temperature is then lowered until it reaches room temperature, and then the mixture is subjected to air flow milling at a pressure of 0.88 MPa to obtain a lithium iron phosphate positive electrode material.

[0081] Example 2

[0082] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0083] (1) FePO4 precursor and Li2CO3 were mixed in a molar ratio of 1:1.015, and 1500 ppm of TiO2 and 12 wt% of glucose were added in sequence to obtain a dispersion with a solid content of 40%;

[0084] (2) The dispersion is wet-grinded to obtain an intermediate material, wherein the grinding particle size D n =600nm, collect the intermediate material and spray dry it at a pressure of 0.15MPa and a temperature of 185℃;

[0085] (3) The spray-dried intermediate material was placed in a graphite crucible for microwave heating. The microwave frequency was adjusted to control the temperature T to 830°C and calcined for 12 hours in a nitrogen atmosphere (oxygen concentration <50 ppm);

[0086] (4) The temperature is then lowered until it reaches room temperature, and then the mixture is subjected to air flow milling at a pressure of 0.85 MPa to obtain a lithium iron phosphate positive electrode material.

[0087] Example 3

[0088] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0089] (1) FePO4 precursor and Li2CO3 were mixed in a molar ratio of 1:1, and 1000 ppm of WO3 and 14 wt% of glucose were added in sequence to obtain a dispersion with a solid content of 30%;

[0090] (2) The dispersion is wet-grinded to obtain an intermediate material, wherein the grinding particle size D n =495nm, collect the intermediate material and spray dry it at a pressure of 0.3MPa and a temperature of 170°C;

[0091] (3) The spray-dried intermediate material was placed in a graphite crucible for microwave heating. The microwave frequency was adjusted to control the temperature T to 825°C and calcined for 11 hours in a nitrogen atmosphere (oxygen concentration <50 ppm);

[0092] (4) The temperature is then lowered until it reaches room temperature, and then the mixture is subjected to air flow milling at a pressure of 0.8 MPa to obtain a lithium iron phosphate positive electrode material.

[0093] Example 4

[0094] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0095] (1) FePO4 precursor and Li2CO3 were mixed in a molar ratio of 1:1.02, and a mixture of 5000 ppm of MgO and 15 wt% of glucose were added in sequence to obtain a dispersion with a solid content of 50%;

[0096] (2) The dispersion is wet-grinded to obtain an intermediate material, wherein the grinding particle size D n =510nm, collect the intermediate material and spray dry it at a pressure of 0.4MPa and a temperature of 145℃;

[0097] (3) The spray-dried intermediate material was placed in a graphite crucible for microwave heating. The microwave frequency was adjusted to control the temperature T to 830°C and calcined for 10 hours in a nitrogen atmosphere (oxygen concentration <50 ppm);

[0098] (4) The temperature is then lowered until it reaches room temperature, and then the mixture is subjected to air flow milling at a pressure of 0.9 MPa to obtain a lithium iron phosphate positive electrode material.

[0099] Example 5

[0100] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0101] (1) FePO4 precursor and Li2CO3 were mixed in a molar ratio of 1:1.04, and a mixture of 3500 ppm of TiO2 and MgO and 13 wt% of glucose were added in sequence to obtain a dispersion with a solid content of 45%;

[0102] (2) The dispersion is wet-grinded to obtain an intermediate material, wherein the grinding particle size D n =598nm, collect the intermediate material and spray dry it at a pressure of 0.5MPa and a temperature of 190°C;

[0103] (3) The spray-dried intermediate material was placed in a graphite crucible for microwave heating. The microwave frequency was adjusted to control the temperature T to 835°C and calcined for 8 hours in a nitrogen atmosphere (oxygen concentration <50 ppm);

[0104] (4) The temperature is then lowered until it reaches room temperature, and then the mixture is subjected to air flow milling at a pressure of 0.9 MPa to obtain a lithium iron phosphate positive electrode material.

[0105] Example 6

[0106] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material, which differs from Example 1 in that the calcination treatment is carried out in a box-type heating furnace without microwave heating, and the remaining process parameters and operating conditions are the same as those in Example 1.

[0107] Comparative Example 1

[0108] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n =400nm, the calcination temperature T is 780℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n =500nm, the calcination temperature T is 790℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0111] Comparative Example 3

[0112] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n =600nm, the calcination temperature T is 800℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0113] Comparative Example 4

[0114] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n =400nm, the calcination temperature T is 810℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0115] Comparative Example 5

[0116] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n =600nm, the calcination temperature T is 840℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0117] Comparative Example 6

[0118] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n =400nm, the calcination temperature T is 850℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0119] Comparative Example 7

[0120] This comparative example provides a preparation method of lithium iron phosphate positive electrode material, which is different from Example 1 in that: the grinding particle size D n=500nm, the calcination temperature T is 860℃, and the other process parameters and operating conditions are the same as those in Example 1.

[0121] The particle sizes corresponding to the volume cumulative distribution percentages of the lithium iron phosphate positive electrode materials obtained in Examples 1 to 6 of the present invention and Comparative Examples 1 to 7 when they reach 1%, 10%, 50% and 99% are D1, D2 and D3, respectively. 10 、D 50 With D 99 , as shown in Table 1.

[0122] The present invention calculates S according to the following formula, wherein D n is the particle size of wet grinding (unit: nm), T is the calcination temperature (unit: °C), D1, D 10 、D 50 With D 99 They are the particle sizes (unit: μm) corresponding to the volume cumulative distribution percentages of the lithium iron phosphate positive electrode material reaching 1%, 10%, 50% and 99%, respectively. The calculation results of S are shown in Table 1.

[0123]

[0124] Table 1

[0125]

[0126] The present invention uses the lithium iron phosphate positive electrode materials obtained in Examples 1 to 6 and Comparative Examples 1 to 7 to make soft-pack batteries, and performs compaction density, gas production and electrical performance tests on the soft-pack batteries.

[0127] The steps of making a soft pack battery using lithium iron phosphate positive electrode material specifically include:

[0128] ① Positive electrode sheet preparation: According to the mass ratio of lithium iron phosphate positive electrode material: conductive agent: binder = 96:2:2, lithium iron phosphate positive electrode material, conductive agent and binder are mixed evenly, and then coated on aluminum foil (width × thickness = 163mm × 0.012mm) by double-sided coating, with a single-sided surface density of 18.05mg / cm 2 (Tolerance is ±0.36mg / cm 2 ), baked at 100℃ for 24h, cut into pieces, and rolled to a compaction density of 2.5g / cm 3 ;

[0129] ② Negative electrode sheet preparation: Graphite, conductive agent and binder were mixed evenly according to the mass ratio of graphite: conductive agent: binder = 96:1:3, deionized water was added as solvent and stirred evenly, and double-sided coating was used to coat the copper foil (width × thickness = 153mm × 0.006mm), with a single-sided density of 9.04mg / cm2 (Tolerance is ±0.18mg / cm 2 ), vacuum dried at 85 °C for 24 h;

[0130] ③ Use purchased electrolyte for injection;

[0131] ④ Assemble the soft pack: 17 positive electrode sheets, 18 negative electrode sheets and diaphragms are stacked, tab welded, shell punched, packaged, liquid injected, pre-charged, aged, formed, aged and degassed to make a soft pack.

[0132] (1) Compaction density test

[0133] Assemble the die and use a digital vernier caliper to measure the original height h0 and the die diameter of the die. Weigh 1.0000g ± 0.0010g of the sample to be tested, m, using weighing paper, and pour it into the compaction mold. After assembling the mold, place it in the center of the compaction density meter table. Adjust the pressure unit of the compaction density meter to tons. Manually apply pressure to 2.00T and maintain it for 60 seconds before releasing the pressure. Remove the mold and measure the mold height h1 after returning it to zero with a digital vernier caliper. Record the data and calculate the compaction density using the following formula. The results are shown in Table 2:

[0134]

[0135] (2) Gas production and electrical performance test

[0136] After recording the initial cell volume using the water displacement method, the cell was placed in a 40°C constant temperature box and cycled 3 times with 1C charge / 1C discharge. The third 1C discharge capacity was recorded as the initial discharge capacity. The cell was cycled from 5% to 97% SOC to 1200 cycles and the cycle was stopped. The discharge capacity at 1200 cycles was recorded. The gas production volume and cycle retention rate were tested. The results are shown in Table 2, where:

[0137] Gas production volume per ampere-hour = (cell volume at 1500th cycle - initial cell volume) / initial 1C discharge capacity;

[0138] Cycle retention rate = discharge capacity at 1500 cycles / initial discharge capacity × 100.

[0139] (3) The cycle retention rate was tested in a 40°C constant temperature box at 1C charge / 1C discharge and 0-100% SOC for 1500 cycles. The results are shown in Table 2.

[0140] Table 2

[0141]

[0142] It is not difficult to see from the contents of Table 1 and Table 2 that Examples 1 to 6 control S within 11≤S≤13.3 by adjusting the sanding particle size, sintering temperature and particle size distribution of lithium iron phosphate particles, thereby effectively improving the compaction density of the positive electrode material and improving the overall electrochemical performance.

[0143] As can be seen from Tables 1 and 2, compared to Example 1, the compaction density and comprehensive electrochemical performance of the battery of Example 6 are both reduced. This is mainly due to the microwave heating treatment used in Example 1, which can ensure that the sintering temperature of each position of the material in the graphite container is consistent, so that the material is heated evenly, which is conducive to improving the cycle stability of the material. At the same time, it reduces the generation of side reactions and can improve the electrochemical performance of the battery. As can be seen from Examples 2 and 4, as the grinding particle size of wet sand milling increases, the particle size of the lithium iron phosphate positive electrode material decreases overall. This is mainly because the size of the grinding particle size affects the growth of the particles. Increasing the size of the grinding particle size will inhibit the growth of the particles, resulting in a decrease in the particle size.

[0144] It is not difficult to see from Example 1, Comparative Example 2, and Comparative Example 7 that the overall particle size of the lithium iron phosphate cathode material increases with increasing calcination temperature. This is mainly because increasing temperature promotes the growth of material particles. Comparing Example 2, Comparative Example 3, and Comparative Example 6, we can also obtain a trend that the overall particle size of the lithium iron phosphate cathode material increases with increasing calcination temperature.

[0145] From Example 1 and Comparative Example 7, it can be seen that when the calcination temperature is too high, the particle size of the lithium iron phosphate positive electrode material increases as a whole, and the particle size distribution S exceeds the range. Although the compaction density is increased, the 0.33C gram capacity is reduced, which cannot meet the battery capacity requirements of the energy storage type lithium iron phosphate. Comparing Example 2 with Comparative Example 5, it can be seen that although the calcination temperature is increased, the D of the lithium iron phosphate positive electrode material is 10 With D 50 When the particle size is significantly reduced, the particle size distribution S will also exceed the range, the product compaction density and cycle retention rate will be significantly reduced, and the battery capacity requirements of energy storage lithium iron phosphate cannot be met.

[0146] Comparing Example 1 with Comparative Example 2, it is not difficult to see that when the calcination temperature is lowered and the overall particle size of the lithium iron phosphate cathode material is smaller, the particle size distribution S exceeds the range. Although the gram capacity increases, the compaction density and cycle retention rate decrease significantly, and the gas production increases, which also cannot meet the requirements. Comparing Example 2 with Comparative Example 3, when the calcination temperature is lowered and the overall particle size of the lithium iron phosphate cathode material is smaller, the particle size distribution S exceeds the range, and the compaction density, cycle retention rate, and gas production of the material cannot meet the requirements.

[0147] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a lithium iron phosphate positive electrode material, characterized in that: The preparation method comprises: (I) mixing an iron phosphate precursor, a lithium source, a dopant, a carbon source, and a solvent to obtain a dispersion; (II) wet grinding the dispersion to obtain an intermediate material; (III) calcining and crushing the intermediate material in sequence to obtain a lithium iron phosphate positive electrode material; The wet grinding particle size is D n The calcination temperature is T, and the particle sizes corresponding to the volume cumulative distribution percentages of the lithium iron phosphate cathode material are D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15, D16, D17, D18, D19, D20, D210, D220, D230, D240, D260, D 10 、D 50 With D 99 , satisfying the following relationship: Among them, 11.0≤S≤13.3; The particle size D1 of the lithium iron phosphate positive electrode material is 0.1-0.3 μm, and is not 0.3 μm; The particle size D of the lithium iron phosphate positive electrode material 10 0.3~0.5μm; The particle size D of the lithium iron phosphate positive electrode material 50 0.8~1.2μm; The particle size D of the lithium iron phosphate positive electrode material 99 5~10μm.

2. The preparation method according to claim 1, characterized in that The molar ratio of the iron phosphate precursor to the lithium source is 1:(1-1.05).

3. The preparation method according to claim 1, characterized in that The dopant includes any one of TiO2, WO3 and MgO, or a combination of at least two of them.

4. The preparation method according to claim 1, characterized in that Based on the total mass of the iron phosphate precursor, the lithium source, the dopant and the carbon source, the added amount of the dopant is 1000-5000 ppm.

5. The preparation method according to claim 1, characterized in that The carbon source includes glucose.

6. The preparation method according to claim 1, characterized in that The total mass of the iron phosphate precursor, the lithium source, the dopant and the carbon source is calculated as 100%, and the added amount of the carbon source is 10-15 wt%.

7. The preparation method according to claim 1, characterized in that The solvent includes water.

8. The preparation method according to claim 1, characterized in that The solid content of the dispersion is 30-50%.

9. The preparation method according to any one of claims 1 to 8, characterized in that The wet grinding includes sand grinding.

10. The preparation method according to any one of claims 1 to 8, characterized in that The grinding particle size D of the wet grinding n 400~600nm.

11. The preparation method according to any one of claims 1 to 10, characterized in that: In step (II), after the wet grinding is completed, the intermediate material is dried; The drying process includes spray drying.

12. The preparation method according to claim 11, characterized in that The spray drying pressure is 0.1~0.5MPa; The spray drying temperature is 140-190°C.

13. The preparation method according to any one of claims 1 to 12, characterized in that: The calcination treatment includes: subjecting the intermediate material to microwave heating.

14. The preparation method according to claim 13, characterized in that After the calcination process is completed, the intermediate material is subjected to a cooling process.

15. The preparation method according to any one of claims 1 to 14, characterized in that: The calcination temperature is 780-850°C.

16. The preparation method according to claim 15, characterized in that The calcination time is 8 to 12 hours.

17. The preparation method according to claim 15, characterized in that calcining the intermediate material under the protection of a protective atmosphere; The protective atmosphere comprises nitrogen; The concentration of oxygen in the protective atmosphere is less than 50 ppm.

18. The preparation method according to any one of claims 1 to 17, characterized in that: The crushing process includes jet mill crushing.

19. The preparation method according to claim 18, characterized in that The pressure of the jet mill is 0.8-0.9 MPa.

20. A positive electrode material, characterized in that The positive electrode material is prepared by the preparation method described in any one of claims 1 to 19.

21. The positive electrode material according to claim 20, characterized in that The compaction density of the positive electrode material is 2.1-2.5 g / cm 3 .

22. A battery, characterized in that: The positive electrode of the battery comprises the positive electrode material according to claim 20 or 21.

Images