Highly dispersed iron phosphate material, preparation method thereof, positive electrode material and lithium ion battery

Abstract

The application provides high-dispersion iron phosphate, wherein the primary particle size of the iron phosphate is 50-100 nm, the secondary particle size of the iron phosphate is small, the secondary particle size distribution of the iron phosphate is narrow, and the specific surface area of the iron phosphate is 10-12 m 2 / g. When the iron phosphate is used to prepare a positive electrode material, the small secondary particle size and the narrow particle size distribution are beneficial to improving the grinding efficiency, and the iron phosphate cannot be broken, which is beneficial to the batch production of iron lithium and reduces the production cost. In addition, the small primary particle size is beneficial to the subsequent preparation of a positive electrode material with a small primary particle size, the positive electrode material can be more fully contacted with an electrolyte, the lithium ion insertion / desorption is facilitated, the electrochemical activity of the positive electrode material is improved, and the battery capacity and the rate performance are improved. The application also provides a preparation method of the high-dispersion iron phosphate, a positive electrode material and a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a high-dispersion iron phosphate material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, lithium iron phosphate has been increasingly concerned as a lithium ion battery cathode material due to its high safety, thermal stability and good cycle stability. However, lithium iron phosphate with an olivine structure has problems such as poor electrical conductivity and slow lithium ion diffusion kinetics, which restrict its development and application. The morphology, particle size and dispersity of iron phosphate as a precursor material of lithium iron phosphate directly affect the properties of lithium iron phosphate.

[0003] At present, the mainstream production method of iron phosphate is the precipitation method, that is, by mixing an iron source and a phosphorus source, precipitating at a suitable pH, and then further crystallizing and calcining to obtain an iron phosphate product. This method is simple and efficient, but the prepared iron phosphate has problems such as irregular morphology, large particle size and poor dispersity, which results in low lithium iron capacity and poor electrochemical performance.

[0004] The prior art such as CN105118995A discloses a means of introducing ultrasonic waves in the synthesis / oxidation process to reduce the primary particle size of iron phosphate and reduce the particle size distribution width, thereby improving the electrochemical performance of lithium iron, but the improvement effect is limited. SUMMARY

[0005] To solve the above technical problems, the application provides a high-dispersion iron phosphate material, a preparation method thereof, a cathode material and a lithium ion battery.

[0006] To achieve the above purpose, the application provides the following technical solutions:

[0007] In a first aspect, a high-dispersion iron phosphate is provided, wherein the primary particle size of the iron phosphate is 50-100 nm; the secondary particle size D50 of the iron phosphate is 3.0-4.0 μm, the secondary particle size D90 is 7.0-8.5 μm, the secondary particle size D10 is 1.0-1.2 μm, and the value of the secondary particle size range (D90-D10) / D50 is 1.8-2.0; and the specific surface area of the iron phosphate is 10-12 m 2 / g.

[0008] In a second aspect, a preparation method of the high-dispersion iron phosphate is provided, comprising:

[0009] S1, preparing solution A with iron source as raw material, and preparing mixed solution B with phosphorus source, oxidizing agent and ammonia water as raw material; taking solution A as bottom liquid, introducing mixed solution B into the bottom liquid, carrying out precipitation reaction to obtain first slurry, and carrying out solid-liquid separation to obtain first solid;

[0010] S2, preparing second slurry by adding water to the first solid; adding phosphoric acid into the second slurry, heating to 80-100℃ and carrying out first heat preservation until the second slurry changes from light yellow to white, and carrying out second heat preservation to obtain third slurry; the first heat preservation process is carried out under ultrasonic treatment;

[0011] S3, carrying out washing and solid-liquid separation on the third slurry to obtain second solid, and drying the second solid to obtain iron phosphate powder with two waters;

[0012] S4, calcining the iron phosphate powder with two waters to obtain anhydrous high-dispersed iron phosphate.

[0013] Further, in step S2, the frequency of the ultrasonic treatment in the first heat preservation process is 10-40 kHz.

[0014] Further, in step S2, the duration of the second heat preservation is 1-2 h.

[0015] Further, in step S2, the addition amount of the phosphoric acid is determined according to the pH of 1.6-2.0 of the slurry; the phosphoric acid is concentrated phosphoric acid.

[0016] Further, in step S2, the second heat preservation process is carried out under ultrasonic treatment; the frequency of the ultrasonic treatment is 10-40 kHz.

[0017] Further, in step S2, the solid content of the second slurry is 5-15%, preferably 7.5-15%.

[0018] Further, in step S2, the preparation of the second slurry includes: preparing by adding water to the first solid; the beating is carried out under stirring.

[0019] Further, in step S1, the temperature of the precipitation reaction is 40-55℃.

[0020] Further, in step S1, the addition duration of the mixed solution B is 60-150 min.

[0021] Further, in step S1, the precipitation reaction is carried out under stirring.

[0022] Further, in step S1, during the precipitation reaction, after the introduction of the mixed solution B is completed, the pH value of the reaction system is adjusted to 1.8-2.0, and the reaction is continued.

[0023] Further, in step S1, the mass concentration of iron in the solution A is 5-10%.

[0024] Further, in step S1, the mass concentration of phosphorus in the mixed solution B is 3-10%.

[0025] Further, in step S1, the molar ratio of iron in the iron source solution to ammonia in the mixed solution is 1:1-1.1.

[0026] Further, in step S1, the oxidizing agent is hydrogen peroxide.

[0027] Further, in step S4, the calcination temperature is 530-600℃, and the calcination time is 2-4h.

[0028] In a third aspect, a positive electrode material is provided, which is prepared using the aforementioned iron phosphate or the aforementioned method.

[0029] In a fourth aspect, a lithium ion battery is provided, which comprises the aforementioned positive electrode material.

[0030] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0031] The present application provides high-dispersion iron phosphate, wherein the primary particle size of the iron phosphate is 50-100nm, the secondary particle size D50 of the iron phosphate is 3.0-4.0μm, the secondary particle size D90 is 7.0-8.5μm, the secondary particle size D10 is 1.0-1.2μm, and the value of the secondary particle size range (D90-D10) / D50 is 1.8-2.0, and the specific surface area of the iron phosphate is 10-12m 2 / g. The primary particle size of the iron phosphate is small, the dispersion is good, and the secondary particle size is small, the secondary particle size distribution is narrow, and the specific surface area is high. When the iron phosphate is used to prepare the positive electrode material lithium iron phosphate or lithium manganese iron phosphate, the small secondary particle size and narrow particle size distribution are beneficial to improve the grinding efficiency and prevent the iron lithium from being difficult to break, which is beneficial to the batch production of iron lithium and reduces the production cost. In addition, the small primary particle size of the iron phosphate is beneficial to the subsequent preparation of the positive electrode material with small primary particle size, which enables the contact with the electrolyte to be more sufficient, is beneficial to the lithium ion insertion / extraction, and improves the electrochemical activity of the positive electrode material, thereby achieving the effects of improving the battery capacity and rate performance.

[0032] The preparation method provided by the present application can prepare iron phosphate with small primary particle size, good dispersion, small agglomeration, and high specific surface area by first preparing amorphous iron phosphate, then crystallizing the amorphous iron phosphate, and performing ultrasonic treatment during the crystallization process, and then calcining the obtained dihydrate iron phosphate. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The images show SEM images of ferric phosphate dihydrate prepared in Example 1 and Comparative Example 1, where (a) corresponds to Comparative Example 1 and (b) corresponds to Example 1.

[0035] Figure 2 The anhydrous ferric phosphates prepared in Example 1 and Comparative Example 1 are shown, where (a) corresponds to Comparative Example 1 and (b) corresponds to Example 1.

[0036] Figure 3 The image shows the XRD pattern of anhydrous ferric phosphate prepared in Example 1.

[0037] Figure 4 Charge-discharge curves of batteries assembled with the cathode materials prepared in Example 1 and Comparative Example 1 at 0.1C.

[0038] Figure 5 The charge-discharge curves of batteries assembled with the cathode materials prepared in Example 1 and Comparative Example 1 at 1C. Detailed Implementation

[0039] The iron phosphate particles prepared by the precipitation method have large particle size and poor dispersibility; in view of this phenomenon, the ultrasonic treatment is performed in the process of coprecipitation for preparing the iron phosphate, which is beneficial to reducing the particle size and agglomeration of the iron phosphate and improving the dispersibility, however, the modification effect is limited; based on this, the applicant finds through research that the iron phosphate with small primary particle size, good dispersibility, small agglomeration (small secondary particle size, narrow distribution, good dispersibility) and high specific surface area can be prepared by first preparing amorphous iron phosphate, then crystallizing the amorphous iron phosphate, performing ultrasonic treatment in the crystallization process, and then calcining the iron phosphate dihydrate obtained by crystallization; the applicant finds through research and analysis that this may be because in the crystallization process, the amorphous iron phosphate is dissolved and recrystallized, the nucleation speed of the tiny crystal nucleus is fast and the number of the crystal nucleus is large in the initial stage of the reaction, so that the viscosity of the reaction system rapidly rises, the collision probability between the particles increases, which is not conducive to the formation and dispersion of the product particles, the ultrasonic treatment in the crystallization process can continuously break the large particles, reduce the surface tension of the liquid, prevent the agglomeration of the tiny crystal nucleus, make the tiny crystal nucleus uniformly dispersed in the solution or adsorbed on the undissolved amorphous iron phosphate, and make the crystal grains of the iron phosphate dihydrate stably and uniformly grow, so that the particle size of the iron phosphate is significantly reduced, the dispersibility of the particles is improved, and the specific surface area is increased.

[0040] The application provides nano high-dispersity iron phosphate, wherein the primary particle size of the iron phosphate is 50-100 nm; the secondary particle size D50 of the iron phosphate is 3.0-4.0 μm, the secondary particle size D90 is 7.0-8.5 μm, the secondary particle size D10 is 1.0-1.2 μm, and the value of (D90-D10) / D50 is 1.8-2.0; and the specific surface area of the iron phosphate is 10-12 m 2 / g.

[0041] In the application, when the particle size distribution width of the iron phosphate increases, the number of large particles also increases, and in the preparation of lithium iron, the material is not easy to grind, which affects the grinding efficiency; in addition, the limit of grinding is several hundred nanometers, and the particles below the grinding limit size are difficult to continue to break, therefore, the more the initial small-size primary particles, the smaller the primary particles of the prepared positive electrode material, the smaller particles contact the electrolyte more fully, which is beneficial to the embedding and de-embedding of lithium ions, improves the electrochemical activity of the positive electrode material, and thus the effects of improving the battery capacity and rate performance are achieved.

[0042] The application provides a preparation method of nano high-dispersity iron phosphate, which comprises the following steps:

[0043] S1, a solution A is prepared by taking an iron source as a raw material, a mixed solution B is prepared by taking a phosphorus source, an oxidizing agent and ammonia water as raw materials; the mixed solution B is introduced into the solution A as a bottom liquid, a precipitation reaction is performed to obtain a first slurry, and the first slurry is subjected to solid-liquid separation to obtain a first solid;

[0044] S2, the first solid is prepared into a second slurry by adding water; phosphoric acid is added into the second slurry, the temperature is raised to 80-100℃ and the first holding is carried out until the second slurry changes from light yellow to white, the second holding is continued to obtain a third slurry; the first holding process is carried out by ultrasonic treatment;

[0045] S3, the third slurry is washed and solid-liquid separated to obtain a second solid, and the second solid is dried to obtain iron phosphate dihydrate powder;

[0046] S4, the iron phosphate dihydrate powder is calcined to obtain anhydrous high-dispersed iron phosphate.

[0047] In some preferred embodiments, in step S2, the frequency of the ultrasonic treatment in the first holding process is 10-40 kHz, for example, 10 kHz, 15 kHz, 20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, etc.

[0048] In some preferred embodiments, in step S2, the length of the second holding is 1-2 h, for example, 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, etc.

[0049] In some preferred embodiments, in step S2, the amount of the phosphoric acid is determined according to the pH of the slurry, which is 1.6-2.0, for example, 1.6, 1.7, 1.8, 1.9, 2.0, etc.; the phosphoric acid is preferably concentrated phosphoric acid, which can have a conventional concentration in the art, for example, 70-90%.

[0050] In some preferred embodiments, in step S2, the second holding process is carried out by ultrasonic treatment, which is beneficial to more complete crystallization; preferably, the frequency of the ultrasonic treatment in the second holding process is 10-40 kHz, for example, 10 kHz, 15 kHz, 20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, etc.

[0051] In some preferred embodiments, in step S2, the solid content of the second slurry is 5-15%. A lower solid content can reduce the viscosity of the crystallization system and the collision probability between the crystals, thereby reducing the particle size of the white material after crystallization, reducing the particle size of the iron phosphate prepared by sintering and increasing its specific surface area. However, a lower solid content can reduce the production efficiency, and in the case of constant addition of phosphoric acid, it often leads to an extension of the crystallization time, further reducing the production efficiency. Therefore, the solid content is further preferably 7.5-15%, and more preferably 10-15%.

[0052] The preparation of the second slurry comprises: preparing by adding water to the first solid; the slurry is prepared under stirring; the stirring speed can be controlled conventionally, as long as the solid can be dispersed well in water, for example, it can be 300-500 rpm. Further preferably, the slurry is prepared under stirring and ultrasonic treatment; the frequency of ultrasonic treatment is 10-40 kHz, and the ultrasonic treatment can further improve the dispersion of particles in the slurry. However, it is worth noting that the ultrasonic treatment in the slurry preparation process is not a necessary operation, but an optional operation.

[0053] In some preferred embodiments, in step S1, the temperature of the precipitation reaction is 40-55°C, for example, 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, etc.

[0054] In some preferred embodiments, in step S1, the mixing solution is added for 60-150 min, for example, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, etc.

[0055] In some preferred embodiments, in step S1, the precipitation reaction is carried out under stirring; the stirring speed can be the conventional stirring speed for preparing iron phosphate by precipitation method in the art, for example, it can be 300-500 rpm.

[0056] In some preferred embodiments, in step S1, during the precipitation reaction, after the mixing solution is finished, the pH value of the reaction system is adjusted to 1.8-2.0 (for example, 1.8, 1.9, 2.0, etc.), and the reaction is continued. The pH adjustment can be achieved by conventional control, for example, ammonia can be used as a pH adjuster for adjustment and control.

[0057] In step S1, the iron source can be a conventional iron source for preparing iron phosphate, specifically, it can be at least one of titanium dioxide by-product ferrous sulfate, industrial-grade ferrous sulfate, ferric nitrate, ferrous chloride, ferrous oxalate, ferrous acetate, ferrous carbonate, and iron carbonate. It is worth noting that when the iron source is used as the raw material to prepare solution A, if the iron source is an insoluble iron source, the iron source can be prepared into solution A by adding an acidic solution. Of course, even if the raw material is a soluble iron source, an acidic solution can also be added as needed. Both the process step and the raw material can be conventional in the art for preparing iron phosphate.

[0058] In some preferred embodiments, in step S1, the phosphorus source is at least one of ammonium dihydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium phosphate.

[0059] In step S1, the oxidizing agent can be a liquid oxidizing agent (hydrogen peroxide), a solid oxidizing agent (sodium persulfate, sodium chlorate, sodium thiosulfate, etc.), and a gaseous oxidizing agent (ozone), however, the solid oxidizing agent is usually easy to introduce impurities affecting the purity of the product, and the safety of ozone is relatively poor; in some preferred embodiments, in step S1, the oxidizing agent is hydrogen peroxide.

[0060] In step S1, the iron source and the oxidizing agent can be in the conventional ratio for preparing iron phosphate in the art, for example, the molar ratio of iron in the iron source to the oxidizing agent is 1:0.7~1, for example, 1:0.7, 1:0.8, 1:0.9, 1:1, etc.

[0061] In some preferred embodiments, in step S1, the mass concentration of iron in the iron source solution is 5~10%, for example, 5%, 6%, 7%, 8%, 9%, 10%, etc. When the concentration is too high, it will cause the viscosity of the synthesis solution system to be too large, which is not conducive to the synthesis and dispersion of the yellow material, and the crystals in the solution are easy to precipitate at low temperature. When the concentration is too low, too much ammonia water is needed to control the pH value of the system after the subsequent feeding is completed, the existence of too much ammonium ion will affect the product particle size and specific surface area, etc. and too low concentration will also reduce the production efficiency.

[0062] In some preferred embodiments, in step S1, the mass concentration of phosphorus in the mixed solution is 3~10%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0063] In some preferred embodiments, in step S1, the molar ratio of iron in the iron source solution to ammonia water is 1:1~1.1, for example, 1:1, 1:1.01, 1:1.02, 1:1.03, 1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.10, etc.

[0064] In step S1, the iron source and the phosphorus source can be in the conventional ratio for preparing iron phosphate in the art, for example, the molar ratio of the iron source in the phosphorus source to the phosphorus source is 1:1~1.2, for example, 1:1, 1:1.02, 1:1.05, 1:1.08, 1:1.1, 1:1.12, 1:1.15, 1:1.18, 1:1.2, etc.

[0065] In some preferred embodiments, in step S4, the calcination temperature is 530-600℃, such as 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, etc. If the sintering temperature is too high, the iron phosphate particles will be adhered to each other, resulting in increased particle size and reduced specific surface area. If the sintering temperature is too low, the crystal transformation will not be complete. Preferably, the calcination is performed at 530-600℃ to prevent particle adhesion and ensure complete crystal transformation. The calcination time is 2-4h, such as 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0066] The present application provides a positive electrode material, which is prepared by using the aforementioned iron phosphate or the aforementioned method.

[0067] The present application provides a lithium ion battery comprising the aforementioned positive electrode material.

[0068] In order to facilitate the understanding of the present application, the present application will be described in more detail below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0069] Example 1

[0070] (1) The impurity-removed titanium dioxide ferrous sulfate and ammonium dihydrogen phosphate were weighed according to a molar ratio of Fe to P of 1:1 to prepare a 7% ferrous sulfate solution and an ammonium dihydrogen phosphate solution, respectively, for standby use. An excess amount of hydrogen peroxide solution (molar ratio of Fe in the Fe source to H2O2 in the hydrogen peroxide solution was 1:0.8) was prepared for standby use. An amount of ammonia solution (molar ratio of the Fe source to ammonia in terms of ammonium ion was 1:1.05) was prepared for standby use.

[0071] (2) The ammonium dihydrogen phosphate solution was mixed with the ammonia and hydrogen peroxide solutions to obtain a first mixed system, and the mass concentration of phosphorus in the first mixed system was 3%.

[0072] (3) The ferrous sulfate solution was placed in a reaction kettle and heated to 45℃, and the stirring speed was controlled at 500 rpm. Then, the solution of the first mixed system was pumped into the reaction kettle through a peristaltic pump, and the feeding time was controlled at 60 min. After the feeding was completed, the pH of the reaction system was controlled at 1.9 with ammonia, and the stirring speed was controlled at 500 rpm. After 30 min of incubation, the precipitate was washed and suction-filtered to obtain a first filter cake.

[0073] (4) The first filter cake was put into a reaction kettle, and water was added for slurry making, with the solid content being controlled at 10% and the slurry making speed being controlled at 500 rpm. An industrial ultrasonic vibration rod was put into the reaction kettle, and the ultrasonic frequency was controlled at 40 kHz.

[0074] (5) A certain amount of concentrated phosphoric acid was put into the reactor, the pH of the solution was controlled to be 1.8, and the temperature was increased to 95°C. After 1 h of incubation, the slurry became white, and the slurry was continuously incubated for 2 h. The precipitate was washed and filtered to obtain a second filter cake. The temperature increase and the two incubation steps were both carried out under ultrasonic and mechanical stirring conditions, the ultrasonic frequency was 40 kHz, and the stirring speed was 500 rpm.

[0075] (6) After drying the second filter cake, white iron phosphate dihydrate powder was obtained, and the SEM image thereof is shown in Fig. (b). Figure 1

[0076] (7) The iron phosphate dihydrate powder was calcined at a temperature of 550°C for 120 min to obtain yellowish FePO4. The SEM image of the product is shown in Fig. (b), and it can be seen from the figure that the particle size of the anhydrous iron phosphate is 50-100 nm. The XRD pattern of the product is shown in Fig. (c), and it can be seen from the figure that pure-phase anhydrous iron phosphate is synthesized. Figure 2 Figure 3 Figure 3

[0077] Example 2

[0078] The difference between this example and Example 1 is that in step (5), the temperature increase and the first incubation step are both carried out under ultrasonic and mechanical stirring conditions, the ultrasonic frequency is 40 kHz, and the stirring speed is 500 rpm; and the second incubation step is only carried out under mechanical stirring, and the stirring speed is 500 rpm.

[0079] Example 3

[0080] The difference between this example and Example 1 is that in step (5), the ultrasonic frequency of the temperature increase and the two incubation steps is 30 kHz.

[0081] Example 4

[0082] The difference between this example and Example 1 is that in step (5), the ultrasonic frequency of the temperature increase and the two incubation steps is 20 kHz.

[0083] Example 5

[0084] The difference between this example and Example 1 is that in step (5), the ultrasonic frequency of the temperature increase and the two incubation steps is 10 kHz.

[0085] Example 6

[0086] The difference between this example and Example 1 is that in step (3), ultrasonic treatment is also carried out during the entire reaction process, and the ultrasonic frequency is controlled to be 40 kHz.

[0087] Comparative Example 1

[0088] ​​​​The difference between the present comparative example and example 1 is only that in step (5), the temperature rising and the two-stage temperature keeping are only carried out under mechanical stirring without ultrasonic treatment.

[0089] The SEM image of the obtained iron phosphate dihydrate powder is shown in Fig. 1 (a). Figure 1 The SEM image of the obtained light yellow iron phosphate anhydrous is shown in Fig. 1 (a), from which it can be seen that the primary particle size of the iron phosphate anhydrous is 70-320 nm. Figure 2

[0090] It can be found from the iron phosphate dihydrate powder and the iron phosphate anhydrous obtained in comparative example 1 and comparative example 2 that the primary particle size and the secondary particle size of the iron phosphate dihydrate prepared in example 1 are both smaller, and the particle size distribution of the primary particles and the secondary particles is also narrower; the primary particle size and the secondary particle size of the iron phosphate anhydrous obtained after calcination are also smaller, and the dispersibility of the primary particles and the secondary particles is obviously better than that of the iron phosphate anhydrous obtained in comparative example 1.

[0091] Comparative example 2

[0092] The difference between the present comparative example and example 1 is only that in step (5), the temperature rising and the first-stage temperature keeping are only carried out under mechanical stirring without ultrasonic treatment, and the second-stage temperature keeping is carried out under mechanical stirring and ultrasonic treatment; the stirring speed is 500 r / min, and the ultrasonic power is 40 kHz.

[0093] Comparative example 3

[0094] (1) The impurity-removed titanium dioxide ferrous sulfate and ammonium dihydrogen phosphate were weighed according to the molar ratio of Fe to P of 1:1 to prepare a ferrous sulfate solution and an ammonium dihydrogen phosphate solution with a mass concentration of 7% respectively for standby use; an excess amount of hydrogen peroxide solution (the molar ratio of Fe source to H2O2 was 1:0.8) was prepared for standby use; and a certain amount of ammonia solution (the molar ratio of Fe source to ammonia water in terms of ammonium ion was 1:1.05) was prepared for standby use.

[0095] (2) The ammonium dihydrogen phosphate solution was mixed with the ammonia water and the hydrogen peroxide solution to obtain a first mixed system, and in the first mixed system, the mass concentration of the ammonium dihydrogen phosphate was 3%.

[0096] (3) The titanium dioxide ferrous sulfate solution was placed in a reaction kettle and heated to 45°C, and the stirring speed was controlled at 500 r / min, and then the solution of the first mixed system was pumped into the reaction kettle through a peristaltic pump, and the feeding time was controlled at 60 min, and the reaction was carried out, and after the feeding was completed, the pH of the reaction system was controlled at 1.9 by using ammonia water, and the stirring speed was controlled at 500 r / min, and after temperature keeping for 30 min, the precipitate was washed and suction-filtered to obtain a first filter cake; the ultrasonic treatment was carried out during the whole reaction process, and the ultrasonic frequency was controlled at 40 kHz.

[0097] ​(4) The first filter cake is put into a reaction kettle, water is added for beating, and the solid content is controlled to be 15%, and the beating speed is 500 rpm. An industrial ultrasonic vibration rod is put into the reaction kettle, and the ultrasonic frequency is controlled to be 40 kHz;

[0098] (5) A proper amount of concentrated phosphoric acid is put into the reaction kettle, the solution pH is controlled to be 1.8, and the temperature is increased to 95°C, and after 1 h of incubation, the slurry becomes white, and after the slurry becomes white, the incubation is continued for 2 h, the precipitate is washed and filtered, and the second filter cake is obtained, and the temperature increase and the two incubations are both carried out under mechanical stirring, and the stirring speed is 500 rpm.

[0099] (6) After the second filter cake is dried, white iron phosphate dihydrate powder is obtained.

[0100] (7) The iron phosphate dihydrate powder is calcined at a temperature of 550°C for 120 min to obtain yellowish FePO4.

[0101] Example 7

[0102] The difference between this example and Example 1 is only that the solid content is controlled to be 12.5% when water is added for beating in step (4).

[0103] Example 8

[0104] The difference between this example and Example 1 is only that the solid content is controlled to be 15% when water is added for beating in step (4).

[0105] Example 9

[0106] The difference between this example and Example 1 is only that the solid content is controlled to be 7.5% when water is added for beating in step (4), and in step (5), the temperature is increased to 95°C, and after 3 h of incubation, the slurry becomes white.

[0107] Comparative Example 4

[0108] The difference between this example and Example 1 is only that the solid content is controlled to be 17.5% when water is added for beating in step (4).

[0109] Example 10

[0110] The difference between this example and Example 1 is only that the stirring speed is 400 rpm in step (5).

[0111] Example 11

[0112] The difference between this example and Example 1 is only that the stirring speed is 300 rpm in step (5).

[0113] Comparative Example 5

[0114] The difference between the present comparative example and Example 1 is only that in step (5), the stirring speed is 200 rpm.

[0115] Comparative Example 6

[0116] The difference between the present comparative example and Example 1 is only that in step (5), the stirring speed is 100 rpm.

[0117] Comparative Example 7

[0118] The difference between the present comparative example and Example 1 is only that in step (5), no stirring is performed.

[0119] The physicochemical characteristics of the anhydrous FePO4 prepared in each example and comparative example are tested by the following method:

[0120] Specific surface area: GB / T 13390-2008 Metal powders-determination of specific surface area-nitrogen adsorption method is cited, and a specific surface area instrument is used to test the specific surface area.

[0121] Particle size distribution: HG / T 4701 Iron phosphate for batteries 5.11 Particle size determination method is cited; the sample is mixed uniformly, 0.1 g of the sample is weighed, placed in a 100 mL clean beaker containing 50 mL of water, and then detected by a Bettersize 2600 laser particle size distribution instrument wet system after ultrasonic treatment for 15 min.

[0122] The characterization parameters of the anhydrous FePO4 prepared in each example and comparative example are shown in Table 1. It can be seen from the comparison of the parameters in Table 1 that the anhydrous iron phosphate prepared in each example has a higher surface area, and the secondary particle size distribution is narrower (i.e., the secondary particles are consistent and also reflect good dispersion of the secondary particles), the primary particle size of the prepared anhydrous iron phosphate is 50-100 nm, the secondary particle size D50 is 3.0-4.0 μm, the secondary particle size D90 is 7.0-8.5 μm, and the secondary particle size D10 is 1.0-1.2 μm; the value of (D90-D10) / D50 is 1.8-2.0, and the specific surface area of the iron phosphate is 10-12 m 2 / g.

[0123] It can be seen from the characterization parameters of the products of Comparative Example 1, Example 2, Comparative Example 1 and Comparative Example 2 that the ultrasonic treatment in the first holding process in step (5) can significantly improve the specific surface area of the anhydrous FePO4 and the particle size distribution is narrower. Although the ultrasonic treatment in the second holding process in step (5) can improve the specific surface area of the anhydrous FePO4 and the particle size distribution is narrower, the improvement effect is not obvious and does not achieve the expected purpose.

[0124] As can be seen from the product characterization parameters of Comparative Example 1 and Comparative Example 3, the characterization parameters of anhydrous iron phosphate can be improved by ultrasonic treatment during the preparation of amorphous iron phosphate in step (3), but the improvement is not good. As can be seen from the product characterization parameters of Comparative Example 1 and Example 6, the introduction of ultrasonic treatment during the preparation of amorphous iron phosphate in step (3) does not have a significant effect on the characterization parameters of anhydrous iron phosphate, while the introduction of ultrasonic treatment during the heat preservation process in step (5) significantly optimizes the characterization parameters of the product.

[0125] Table 1

[0126]

[0127] Application Example

[0128] Preparation of lithium iron phosphate, comprising:

[0129] (1) A certain amount of iron phosphate, lithium carbonate, glucose and PEG-2000 powder are weighed and added to a ball mill tank, the molar ratio of iron phosphate to lithium carbonate is 1:1.03, and the mass of glucose and PEG-2000 is 6% and 4% of the mass of iron phosphate, respectively.

[0130] (2) Add an appropriate amount of deionized water and control the solid content to 30% for ball milling, and the ball milling parameters are 500 revolutions / min for 6 hours.

[0131] (3) The slurry after ball milling is spray dried, and the powder after spray drying is placed in a tube furnace and sintered at 760°C for 8 hours under a nitrogen atmosphere to obtain carbon-coated lithium iron phosphate powder.

[0132] Battery assembly:

[0133] The lithium iron phosphate powder prepared in Example 1 and Comparative Example 1 is added to a homogenizer in a mass ratio of 8:1:1 with PVDF and conductive carbon, and an appropriate amount of polyvinylpyrrolidone is added for homogenization.

[0134] The homogenized slurry is evenly coated on an aluminum foil by a doctor blade and dried in a vacuum oven overnight.

[0135] The dried material is sliced into positive electrode sheets using a slicer, and the active material loading is calculated by weighing. The positive electrode shell, positive electrode sheet, separator, lithium sheet, gasket, spring and negative electrode shell are assembled in order, and an appropriate amount of electrolyte is added, and the tablet is pressed and packaged in a tablet press to obtain the required test button.

[0136] The button batteries assembled from the lithium iron phosphate prepared in Example 1 and Comparative Example 1 are placed in a new battery test system for battery performance testing, and the test voltage range is 2.5V~4.3V and the test temperature is room temperature.

[0137] Figure 4 The charge-discharge curves of the batteries assembled with the positive electrode materials prepared in Example 1 and Comparative Example 1 at 0.1C show that the charge-discharge specific capacity of the battery assembled with the lithium iron phosphate prepared in Example 1 is obviously improved compared with the battery assembled with the lithium iron phosphate prepared in Comparative Example 1.

[0138] Figure 5 The charge-discharge curves of the batteries assembled with the positive electrode materials prepared in Example 1 and Comparative Example 1 at 1C show that the charge-discharge specific capacity of the battery assembled with the lithium iron phosphate prepared in Example 1 is obviously improved compared with the battery assembled with the lithium iron phosphate prepared in Comparative Example 1, and the improvement is obviously higher than that at low rate (0.1C), which indicates that the charge-discharge specific capacity and rate performance of the battery assembled with the lithium iron phosphate prepared in Example 1 are obviously improved. After analysis, this may be because the primary particle size of the anhydrous iron phosphate prepared is small (50-100 nm) and the secondary particle has good dispersibility, so the secondary particle is easy to be dissociated by grinding, the primary particle size of the lithium iron phosphate prepared is small and the dispersibility is good, so the contact with the electrolyte is more sufficient, which is beneficial to the embedding / extraction of lithium ions and improves the electrochemical activity of the positive electrode material, thereby achieving the effect of improving the battery capacity and rate performance. The primary particle size of the anhydrous iron phosphate prepared in Comparative Example 1 is large and the dispersibility is poor, and the dispersibility of the secondary particle is also poor, so the secondary particle is difficult to be dissociated by grinding, the primary particle size of the lithium iron phosphate prepared is large and the dispersibility is poor, so the contact with the electrolyte is relatively poor, which is not conducive to the embedding / extraction of lithium ions, and thus the battery capacity and rate performance of the battery assembled are relatively poor.

[0139] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A highly dispersed iron phosphate characterized in that, The primary particle size of the iron phosphate is 50-100 nm; the secondary particle size D50 of the iron phosphate is 3.0-4.0 μm, the secondary particle size D90 is 7.0-8.5 μm, the secondary particle size D10 is 1.0-1.2 μm, and the value of (D90-D10) / D50 is 1.8-2.0; and the specific surface area of the iron phosphate is 10-12 m 2 / g.

2. The method of claim 1, wherein the high dispersion iron phosphate is prepared by the steps of: The method comprises the following steps: ​ S1, preparing a solution A by using an iron source as a raw material, and preparing a mixed solution B by using a phosphorus source, an oxidizing agent and ammonia water as raw materials; using the solution A as a base solution, introducing the mixed solution B into the base solution to perform a precipitation reaction to obtain a first slurry, and performing solid-liquid separation to obtain a first solid; S2, preparing a second slurry by adding water to the first solid, adding phosphoric acid into the second slurry, heating to 80-100 ℃ and performing a first heat preservation until the second slurry changes from light yellow to white, and then performing a second heat preservation to obtain a third slurry; the first heat preservation process is performed by ultrasonic treatment; the frequency of the ultrasonic treatment in the first heat preservation process is 10-40 kHz; and the solid content of the second slurry is 5-15%; S3, performing washing and solid-liquid separation on the third slurry to obtain a second solid, and drying the second solid to obtain a dihydrate iron phosphate powder; S4, calcining the dihydrate iron phosphate powder to obtain anhydrous high-dispersed iron phosphate.

3. The method for preparing highly dispersed ferric phosphate as described in claim 2, characterized in that, In step S2, the duration of the second heat preservation is 1-2 h; In step S2, the amount of the phosphoric acid is determined according to the pH of 1.6-2.0 of the slurry; and the phosphoric acid is concentrated phosphoric acid; In step S2, the second heat preservation process is performed by ultrasonic treatment; The frequency of the ultrasonic treatment is 10-40 kHz.

4. The method for preparing highly dispersed ferric phosphate as described in claim 2, characterized in that, In step S2, the solid content of the second slurry is 7.5-15%; In step S2, the preparation of the second slurry comprises: beating the first solid with water to obtain the second slurry; and the beating is performed under stirring.

5. The method for preparing highly dispersed ferric phosphate as described in claim 2, characterized in that, In step S1, the temperature of the precipitation reaction is 40-55 ℃; In step S1, the duration of the introduction of the mixed solution B is 60-150 min; In step S1, the precipitation reaction is performed under stirring; In step S1, during the precipitation reaction, after the introduction of the mixed solution B is completed, the pH value of the reaction system is adjusted to 1.8-2.0, and the reaction is continued.

6. The method of producing highly dispersible iron phosphate according to any one of claims 2 to 5, characterized in that, In step S1, the mass concentration of iron in the solution A is 5-10%; In step S1, the mass concentration of phosphorus in the mixed solution B is 3-10%; In step S1, the molar ratio of iron in the iron source solution to ammonia water in the mixed solution is 1:1-1.1; In step S1, the oxidizing agent is hydrogen peroxide.

7. The method for preparing highly dispersed ferric phosphate as described in claim 2, characterized in that, In step S4, the calcination temperature is 530-600 ℃; and the calcination time is 2-4 h.

8. A positive electrode material, characterized by The iron phosphate is prepared by using the iron phosphate as claimed in claim 1 or the method as claimed in any one of claims 2-7 as a raw material; and the positive electrode material is lithium iron phosphate or lithium manganese iron phosphate.

9. A lithium-ion battery, characterized by The positive electrode material as claimed in claim 8 is included.

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