A flaky composite lithium manganese iron phosphate material and a preparation method thereof

Abstract

The application discloses a sheet-shaped composite manganese iron lithium phosphate material and a preparation method thereof. The sheet-shaped composite manganese iron lithium phosphate material takes sheet-shaped manganese iron lithium phosphate as a core, the surface of the core is loaded with nano titanium dioxide and nano silicon dioxide, and the outermost layer of the core is coated with a carbon layer; wherein the carbon layer is formed by carbonization after a polydopamine layer is coated on the surface of the core. The sheet-shaped composite manganese iron lithium phosphate material has excellent structural stability, excellent cycle performance, and can greatly improve the electrochemical performance of a battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium manganese iron phosphate materials, and particularly relates to a sheet-shaped composite lithium manganese iron phosphate material and a preparation method thereof. BACKGROUND

[0002] Although the lithium iron phosphate battery has become the mainstream choice in the new energy vehicle market due to the advantages of high safety and low cost, the low energy density and poor low-temperature performance thereof directly affect the user experience and industrial development. At present, the lithium manganese iron phosphate battery is superior to the lithium iron phosphate battery in terms of cost reduction, energy density and low-temperature performance, and becomes a new research direction of high-energy-density devices.

[0003] Compared with the lithium iron phosphate, the lithium manganese iron phosphate is doped with manganese elements, and the addition of manganese can improve the working voltage of the battery and solve the problem of low energy density. For the same weight of the lithium iron phosphate battery and the lithium manganese iron phosphate battery, the lithium manganese iron phosphate battery can provide a longer cruising range for an electric vehicle.

[0004] However, the current lithium manganese iron phosphate battery still faces challenges in research and development, and the low tap density and rapid capacity attenuation after repeated charge and discharge are problems to be solved. SUMMARY

[0005] The purpose of the present application is to provide a sheet-shaped composite lithium manganese iron phosphate material and a preparation method thereof, which has a high tap density and stable cycle performance.

[0006] To achieve the above purpose, the technical scheme provided by one specific embodiment of the present application is as follows:

[0007] A sheet-shaped composite lithium manganese iron phosphate material, wherein the sheet-shaped composite lithium manganese iron phosphate material has a sheet-shaped lithium manganese iron phosphate as a core, the core surface is loaded with nano-titanium dioxide and nano-silicon dioxide, and the outermost layer of the core is coated with a carbon layer.

[0008] The carbon layer is formed by carbonizing a polydopamine layer coated on the core surface.

[0009] In one or more embodiments of the present application, the loading amount of the nano-titanium dioxide on the core is 0.5wt%-1.3wt%;

[0010] And / or, the loading amount of the nano-silicon dioxide on the core is 0.3wt%-1.0wt%.

[0011] In one or more embodiments of the present application, the loading amount of the nano-titanium dioxide on the core surface is greater than that of the nano-silicon dioxide.

[0012] The technical scheme provided by another specific embodiment of the present application is as follows:

[0013] A preparation method of a flaky composite lithium manganese iron phosphate material, comprising the following steps:

[0014] Taking a lithium source, a manganese source, an iron source and a phosphorus source, dispersing them in a hydrophobic solvent to prepare a mixed solution;

[0015] Preparation of the mixed solution into a colloid;

[0016] Sintering the colloid to obtain flaky lithium manganese iron phosphate;

[0017] Loading nano-titanium dioxide and nano-silicon dioxide on the flaky lithium manganese iron phosphate to obtain flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface;

[0018] Coating a polydopamine layer on the flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface, and then sintering to obtain a flaky composite lithium manganese iron phosphate material.

[0019] In one or more embodiments of the present application, a titanium source and a silicon source are taken, and the titanium source and the silicon source are respectively dissolved in an acidic hydrolysis solution to obtain a titanium source hydrolysis solution and a silicon source hydrolysis solution;

[0020] The flaky lithium manganese iron phosphate is placed in the titanium source hydrolysis solution for reaction, and then taken out and placed in the silicon source hydrolysis solution for reaction to obtain flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface.

[0021] In one or more embodiments of the present application, the reaction conditions of the flaky lithium manganese iron phosphate in the titanium source hydrolysis solution are: temperature 30-70℃, time 3-6h;

[0022] And / or, the reaction conditions of the flaky lithium manganese iron phosphate in the silicon source hydrolysis solution are: temperature 30-70℃, time 3-6h;

[0023] And / or, the silicon source is at least one of tetraethyl silicate and tetrabutyl silicate;

[0024] And / or, the titanium source is at least one of tetraethyl titanate and tetrabutyl titanate.

[0025] In one or more embodiments of the present application, the operation of coating the polydopamine layer is: mixing the flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface with a weak alkaline Tris buffer solution, then adding hydrochloric acid dopamine, centrifuging after reaction to obtain flaky lithium manganese iron phosphate coated with a polydopamine layer;

[0026] Wherein, the amount of hydrochloric acid dopamine is 2-3% of the mass of the flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface.

[0027] In one or more embodiments of the present application, the sintering condition of the sheet-shaped manganese iron lithium phosphate coated with the polydopamine layer is: inert atmosphere, temperature 600-700 DEG C, time 2-3h.

[0028] In one or more embodiments of the present application, the hydrophobic solvent is at least one of oleic acid, oleylamine, trioctylphosphine;

[0029] And / or, the mixed solution is reacted at 40-80 DEG C for 30 minutes-1h to form a colloid;

[0030] And / or, the sintering condition of the colloid is: inert atmosphere, temperature 300-600 DEG C, sintering 8-12h.

[0031] In one or more embodiments of the present application, the lithium source is at least one of lithium hydroxide, lithium phosphate, lithium carbonate, lithium acetate;

[0032] And / or, the manganese source is at least one of manganese carbonate, manganese acetate, manganese chloride;

[0033] And / or, the iron source is at least one of ferrous phosphate, ferrous nitrate, ferrous oxalate;

[0034] And / or, the phosphorus source is at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate.

[0035] Compared with the prior art, the present application loads nanometer titanium dioxide and nanometer silicon dioxide on the sheet-shaped manganese iron lithium phosphate, and is coated with a carbon layer, thereby optimizing the structural stability of the sheet-shaped composite manganese iron lithium phosphate material, inhibiting the dissolution of manganese ions, promoting the transmission of lithium ions, having excellent cycle performance, and greatly improving the electrochemical performance of the battery. DETAILED DESCRIPTION

[0036] In order for those skilled in the art to better understand the technical solutions in the present disclosure, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present disclosure, not all. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative labor should fall within the scope of protection of the present disclosure.

[0037] A sheet-shaped composite manganese iron lithium phosphate material provided by a specific embodiment of the present application has a sheet-shaped manganese iron lithium phosphate as a core, nanometer titanium dioxide and nanometer silicon dioxide are loaded on the surface of the core, and a carbon layer is coated on the outermost layer of the core; wherein the carbon layer is formed by carbonization after coating a polydopamine layer on the surface of the core.

[0038] Specifically, the sheet structure helps to shorten the diffusion path of lithium ions, and the sheet structure stack helps to reduce the porosity, improve the compaction density, and improve the cycle stability of the material. By loading nano-titanium dioxide and nano-silicon dioxide on the surface of the core, on the one hand, the contact between the electrolyte and the manganese ions can be blocked, the manganese ion dissolution can be reduced, and the cycle stability can be maintained; on the other hand, the structural stability of the material can be improved, and the volume expansion of the material during use can be reduced; moreover, the nano-titanium dioxide and the nano-silicon dioxide cooperate with each other, and the transmission efficiency of lithium ions can be improved, and the high capacity retention rate can be maintained.

[0039] Finally, the carbon layer is coated on the surface of the core to further improve the compaction density and improve the conductivity, which makes up for the weak conductivity of nano-titanium dioxide and nano-silicon dioxide, and optimizes the electrochemical performance of the battery. Moreover, the carbon layer can further inhibit the dissolution of manganese ions and maintain the cycle stability.

[0040] Further, the loading amount of nano-titanium dioxide on the core is 0.5wt%-1.3wt%, and the loading amount of nano-silicon dioxide on the core is 0.3wt%-1.0wt%.

[0041] Specifically, by controlling the loading amount of nano-titanium dioxide and nano-silicon dioxide, the dissolution of manganese ions is effectively inhibited, the transmission of lithium ions is not affected, the structural stability is effectively improved, and the cycle performance of the battery is excellent.

[0042] Further, the loading amount of nano-titanium dioxide on the surface of the core is greater than the loading amount of nano-silicon dioxide.

[0043] Specifically, the conductivity of nano-silicon dioxide is weaker than that of nano-titanium dioxide, and the high loading amount of nano-titanium dioxide can ensure that the sheet-shaped composite lithium manganese iron phosphate material has high conductivity, which helps to improve the electrochemical performance of the battery.

[0044] Another specific embodiment of the present application provides a preparation method of a sheet-shaped composite lithium manganese iron phosphate material, comprising the following steps:

[0045] Step 1, preparing sheet-shaped lithium manganese iron phosphate.

[0046] Specifically, the lithium source, the manganese source, the iron source and the phosphorus source are dispersed in a hydrophobic solvent to prepare a mixed solution. The mixed solution is made into a colloid, and the colloid is sintered to obtain sheet-shaped lithium manganese iron phosphate.

[0047] The lithium source is at least one of lithium hydroxide, lithium phosphate, lithium carbonate, and lithium acetate; the manganese source is at least one of manganese carbonate, manganese acetate, and manganese chloride; the iron source is at least one of ferrous phosphate, ferrous nitrate, and ferrous oxalate; the phosphorus source is at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate, and potassium monohydrogen phosphate; and the hydrophobic solvent is at least one of oleic acid, oleylamine, and trioctylphosphine.

[0048] The lithium source, the manganese source, the iron source, and the phosphorus source are selected to form a mixed solution, the mixed solution is reacted at 40-80 DEG C for 30 min-1 h to form a colloid, and then the colloid is sintered at 300-600 DEG C for 8-12 h in an inert atmosphere such as nitrogen or argon, and in the sintering process, the lithium manganese iron phosphate crystals grow into a flaky structure.

[0049] In step 2, the titanium source and the silicon source are respectively dissolved in an acidic hydrolysis solution to obtain a titanium source hydrolysis solution and a silicon source hydrolysis solution.

[0050] Specifically, the silicon source is at least one of tetraethyl silicate and tetrabutyl silicate, and the titanium source is at least one of tetraethyl titanate and tetrabutyl titanate. The silicon source and the titanium source are dissolved in an acidic hydrolysis solution formed by ethanol, acetic acid, and deionized water, and the pH of the acidic hydrolysis solution is 3-5. In the titanium source hydrolysis solution, the mass concentration of the titanium source is 1%-3%. In the silicon source hydrolysis solution, the mass concentration of the silicon source is 1%-3%.

[0051] In step 3, the flaky lithium manganese iron phosphate is placed in the titanium source hydrolysis solution for reaction, and then taken out and placed in the silicon source hydrolysis solution for reaction, to obtain flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface.

[0052] Specifically, the loading amount of nano-titanium dioxide on the core is 0.5wt%-1.3wt%, and the loading amount of nano-silicon dioxide on the core is 0.3wt%-1.0wt%, which can be calculated according to the molar amount of titanium atoms and silicon atoms. The flaky lithium manganese iron phosphate is placed in the titanium source hydrolysis solution and the silicon source hydrolysis solution for reaction, and in the reaction, ultrasonic dispersion can be used for assistance to improve the uniformity of the loading of nano-titanium dioxide and nano-silicon dioxide. The reaction conditions of the flaky lithium manganese iron phosphate in the titanium source hydrolysis solution are a temperature of 30-70 DEG C and a time of 3-6 h, and the reaction conditions of the flaky lithium manganese iron phosphate in the silicon source hydrolysis solution are a temperature of 30-70 DEG C and a time of 3-6 h.

[0053] The nanometer titanium dioxide is first loaded, so that the nanometer titanium dioxide forms a stable attached layer on the surface of the flaky lithium manganese iron phosphate, which is beneficial to enhance the inhibition effect on the dissolution of manganese ions and facilitate the transmission of lithium ions. The nanometer silicon dioxide is then loaded, so that the nanometer silicon dioxide can be filled in the pores between the nanometer titanium dioxide, increase the compactness, and then improve the compaction density, and meanwhile, block the contact between the electrolyte and the manganese ions, and further inhibit the dissolution of manganese ions.

[0054] In step 4, the flaky lithium manganese iron phosphate with the nanometer titanium dioxide and the nanometer silicon dioxide loaded on the surface is coated with a polydopamine layer, and then sintered to obtain a flaky composite lithium manganese iron phosphate material.

[0055] Specifically, after the flaky lithium manganese iron phosphate with the nanometer titanium dioxide and the nanometer silicon dioxide loaded on the surface, the polydopamine layer can be uniformly coated on the surface, and the carbon layer formed after sintering cooperates with the nanometer titanium dioxide to improve the conductivity of the material and improve the electrochemical performance of the battery.

[0056] Further, the operation of coating the polydopamine layer is as follows: the flaky lithium manganese iron phosphate with the nanometer titanium dioxide and the nanometer silicon dioxide loaded on the surface is mixed with a weak alkaline Tris buffer solution, and then hydrochloric acid dopamine is added, centrifuged after reaction to obtain the flaky lithium manganese iron phosphate coated with the polydopamine layer. The amount of hydrochloric acid dopamine is 2-3% of the mass of the flaky lithium manganese iron phosphate with the nanometer titanium dioxide and the nanometer silicon dioxide loaded on the surface.

[0057] Further, the sintering condition in step 4 is as follows: under an inert atmosphere such as nitrogen, the temperature is 600-700℃, and the time is 2-3h.

[0058] The application will be further described in detail in combination with specific examples. Unless otherwise specified, the reagents used in the application can be obtained commercially.

[0059] Preparation Example 1

[0060] The flaky lithium manganese iron phosphate is prepared as follows:

[0061] Take 0.1 mol of lithium carbonate, disperse it in 40 ml of oleylamine to obtain a lithium carbonate dispersion; take 0.04 mol of manganese acetate, disperse it in 20 ml of oleic acid to obtain a manganese acetate dispersion; take 0.16 mol of ferrous oxalate, disperse it in 30 ml of trioctylphosphine to obtain a ferrous oxalate dispersion; take 0.2 mol of ammonium dihydrogen phosphate, disperse it in 40 ml of oleylamine to obtain an ammonium dihydrogen phosphate dispersion.

[0062] Mix the above dispersions, stir and heat to 40℃ for 50 min to prepare a colloid.

[0063] Sinter the colloid under a nitrogen atmosphere at 450℃ for 12h to obtain flaky lithium manganese iron phosphate.

[0064] Example 1

[0065] Deionized water, ethanol and acetic acid were mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution. Tetraethyl titanate was dispersed in the acidic hydrolysis solution to prepare a titanium source hydrolysis solution, and the mass concentration of the tetraethyl titanate was 1%. Another acidic hydrolysis solution was prepared, and tetraethyl silicate was dispersed in the acidic hydrolysis solution to prepare a silicon source hydrolysis solution, and the mass concentration of the tetraethyl silicate was 1%.

[0066] The flaky lithium manganese iron phosphate in Preparation Example 1 was added to the titanium source hydrolysis solution, and ultrasonic dispersion was performed to uniformly disperse the flaky lithium manganese iron phosphate. The reaction was performed at 60°C for 3h. The flaky lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flaky lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of the titanium source hydrolysis solution was calculated based on the loading amount of nano-titanium dioxide on the flaky lithium manganese iron phosphate, and the loading amount of nano-titanium dioxide was 0.5wt%.

[0067] The flaky lithium manganese iron phosphate loaded with nano-titanium dioxide was added to the silicon source hydrolysis solution, and ultrasonic dispersion was performed to uniformly disperse the flaky lithium manganese iron phosphate. The reaction was performed at 60°C for 3h. The flaky lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide. The amount of the silicon source hydrolysis solution was calculated based on the loading amount of nano-silicon dioxide on the flaky lithium manganese iron phosphate, and the loading amount of nano-silicon dioxide was 0.3wt%.

[0068] The flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide was added to a Tris buffer solution with a pH of 8.5, and dopamine hydrochloride was added. The mixture was continuously stirred for 2h, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride was 2% of the mass of the flaky lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide. Finally, sintering was performed at 600°C for 3h under a nitrogen atmosphere to obtain flaky composite lithium manganese iron phosphate material.

[0069] Example 2

[0070] Ethanol, acetic acid and deionized water were mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution. Tetraethyl titanate was dispersed in the acidic hydrolysis solution to prepare a titanium source hydrolysis solution, and the mass concentration of the tetraethyl titanate was 1%. Another acidic hydrolysis solution was prepared, and tetraethyl silicate was dispersed in the acidic hydrolysis solution to prepare a silicon source hydrolysis solution, and the mass concentration of the tetraethyl silicate was 1%.

[0071] The flaky lithium manganese iron phosphate in Preparation Example 1 was added to the titanium source hydrolysis solution, and ultrasonic dispersion was performed to uniformly disperse the flaky lithium manganese iron phosphate. The reaction was performed at 50°C for 4h. The flaky lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flaky lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of the titanium source hydrolysis solution was calculated based on the loading amount of nano-titanium dioxide on the flaky lithium manganese iron phosphate, and the loading amount of nano-titanium dioxide was 0.8wt%.

[0072] The sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica is added into the Tris buffer solution with pH of 8.5, and then dopamine hydrochloride is added, and stirring is continued for 2 h, and the precipitate is collected by centrifugation. The amount of dopamine hydrochloride is 3% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica on the surface. Finally, sintering is performed under nitrogen atmosphere at 700 ℃ for 2 h to obtain the sheet-shaped composite manganese iron phosphate material.

[0073] The sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica is added into the Tris buffer solution with pH of 8.5, and then dopamine hydrochloride is added, and stirring is continued for 2 h, and the precipitate is collected by centrifugation. The amount of dopamine hydrochloride is 3% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica on the surface. Finally, sintering is performed under nitrogen atmosphere at 700 ℃ for 2 h to obtain the sheet-shaped composite manganese iron phosphate material.

[0074] Example 3

[0075] Ethanol, acetic acid and deionized water are mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution. Tetraethyl titanate is dispersed in the acidic hydrolysis solution, and the mass concentration of tetraethyl titanate is 1% to prepare a titanium source hydrolysis solution. Another acidic hydrolysis solution is prepared, and tetraethyl silicate is dispersed in the acidic hydrolysis solution, and the mass concentration of tetraethyl silicate is 1% to prepare a silicon source hydrolysis solution.

[0076] The sheet-shaped manganese iron phosphate in Preparation Example 1 is added into the titanium source hydrolysis solution, and ultrasonic dispersion is performed to uniformly disperse the sheet-shaped manganese iron phosphate, and reaction is performed at 60 ℃ for 3 h, and the sheet-shaped manganese iron phosphate is collected by centrifugation, and washed with deionized water, and dried to obtain the sheet-shaped manganese iron phosphate loaded with nano-titania. The amount of the titanium source hydrolysis solution is calculated based on the loading amount of nano-titania on the sheet-shaped manganese iron phosphate, and the loading amount of nano-titania is 1.0 wt%.

[0077] The sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica is added into the Tris buffer solution with pH of 8.5, and then dopamine hydrochloride is added, and stirring is continued for 2 h, and the precipitate is collected by centrifugation. The amount of dopamine hydrochloride is 3% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica on the surface. Finally, sintering is performed under nitrogen atmosphere at 700 ℃ for 2 h to obtain the sheet-shaped composite manganese iron phosphate material.

[0078] The sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica is added into Tris buffer solution with pH of 8.5, then hydrochloric acid dopamine is added, and stirring is continued for 2 hours, and the precipitate is taken by centrifugation. The amount of hydrochloric acid dopamine is 2% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica. Finally, sintering is performed under nitrogen atmosphere at 600°C for 3 hours to obtain the sheet-shaped composite manganese iron phosphate material.

[0079] Example 4

[0080] Ethanol, acetic acid and deionized water are mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution, and tetraethyl titanate is dispersed in the acidic hydrolysis solution to prepare a titanium source hydrolysis solution, and the mass concentration of the tetraethyl titanate is 1%. Another acidic hydrolysis solution is prepared, and tetraethyl silicate is dispersed in the acidic hydrolysis solution to prepare a silicon source hydrolysis solution, and the mass concentration of the tetraethyl silicate is 1%.

[0081] The sheet-shaped manganese iron phosphate in the preparation example 1 is added into the titanium source hydrolysis solution, and ultrasonic dispersion is performed to uniformly disperse the sheet-shaped manganese iron phosphate, and reaction is performed at 60°C for 3 hours, and the sheet-shaped manganese iron phosphate is collected by centrifugation, and washed with deionized water, and dried to obtain the sheet-shaped manganese iron phosphate loaded with nano-titania. The amount of the titanium source hydrolysis solution is calculated according to the loading amount of nano-titania on the sheet-shaped manganese iron phosphate, and the loading amount of nano-titania is 1.3wt%.

[0082] The sheet-shaped manganese iron phosphate loaded with nano-titania is added into the silicon source hydrolysis solution, and ultrasonic dispersion is performed to uniformly disperse the sheet-shaped manganese iron phosphate, and reaction is performed at 60°C for 3 hours, and the sheet-shaped manganese iron phosphate is collected by centrifugation, and washed with deionized water, and dried to obtain the sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica. The amount of the silicon source hydrolysis solution is calculated according to the loading amount of nano-silica on the sheet-shaped manganese iron phosphate, and the loading amount of nano-silica is 1.0wt%.

[0083] The sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica is added into Tris buffer solution with pH of 8.5, then hydrochloric acid dopamine is added, and stirring is continued for 2 hours, and the precipitate is taken by centrifugation. The amount of hydrochloric acid dopamine is 2% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titania and nano-silica. Finally, sintering is performed under nitrogen atmosphere at 600°C for 3 hours to obtain the sheet-shaped composite manganese iron phosphate material.

[0084] Example 5

[0085] Ethanol, acetic acid and deionized water are mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution, and tetraethyl titanate is dispersed in the acidic hydrolysis solution to prepare a titanium source hydrolysis solution, and the mass concentration of the tetraethyl titanate is 1%. Another acidic hydrolysis solution is prepared, and tetraethyl silicate is dispersed in the acidic hydrolysis solution to prepare a silicon source hydrolysis solution, and the mass concentration of the tetraethyl silicate is 1%.

[0086] The flaky manganese iron lithium phosphate in Preparation Example 1 was added to the titanium source hydrolysis solution, and the flaky manganese iron lithium phosphate was uniformly dispersed by ultrasonic dispersion, and reacted at 60°C for 3h. The flaky manganese iron lithium phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flaky manganese iron lithium phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysis solution was calculated based on the loading amount of nano-titanium dioxide on the flaky manganese iron lithium phosphate being 1.0wt%.

[0087] The flaky manganese iron lithium phosphate loaded with nano-titanium dioxide was added to the silicon source hydrolysis solution, and the flaky manganese iron lithium phosphate was uniformly dispersed by ultrasonic dispersion, and reacted at 60°C for 3h. The flaky manganese iron lithium phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flaky manganese iron lithium phosphate loaded with nano-titanium dioxide and nano-silicon dioxide. The amount of silicon source hydrolysis solution was calculated based on the loading amount of nano-silicon dioxide on the flaky manganese iron lithium phosphate being 1.0wt%.

[0088] The flaky manganese iron lithium phosphate loaded with nano-titanium dioxide and nano-silicon dioxide was added to the Tris buffer solution with a pH of 8.5, and then dopamine hydrochloride was added. The stirring was continued for 2h, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride was 2% of the mass of the flaky manganese iron lithium phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface. Finally, sintering was carried out at 600°C for 3h under a nitrogen atmosphere to obtain a flaky composite manganese iron lithium phosphate material.

[0089] Example 6

[0090] Ethanol, acetic acid and deionized water were mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution. Tetraethyl titanate was dispersed in the acidic hydrolysis solution, and the mass concentration of tetraethyl titanate was 1% to prepare a titanium source hydrolysis solution. Another acidic hydrolysis solution was prepared, and tetraethyl silicate was dispersed in the acidic hydrolysis solution, and the mass concentration of tetraethyl silicate was 1% to prepare a silicon source hydrolysis solution.

[0091] The flaky manganese iron lithium phosphate in Preparation Example 1 was added to the titanium source hydrolysis solution, and the flaky manganese iron lithium phosphate was uniformly dispersed by ultrasonic dispersion, and reacted at 60°C for 3h. The flaky manganese iron lithium phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flaky manganese iron lithium phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysis solution was calculated based on the loading amount of nano-titanium dioxide on the flaky manganese iron lithium phosphate being 0.5wt%.

[0092] The sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide is added into a silicon source hydrolysis solution, and ultrasonic dispersion is performed to uniformly disperse the sheet-shaped manganese iron phosphate, and then the mixture is reacted at 60°C for 3h. The sheet-shaped manganese iron phosphate is collected by centrifugation, washed with deionized water, and dried to obtain the sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide. The amount of the silicon source hydrolysis solution is calculated based on the loading amount of nano-silicon dioxide on the sheet-shaped manganese iron phosphate being 1.0wt%.

[0093] The sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide is added into a Tris buffer solution with a pH of 8.5, and then dopamine hydrochloride is added. The mixture is continuously stirred for 2h, and the precipitate is collected by centrifugation. The amount of dopamine hydrochloride is 2% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface. Finally, sintering is performed at 600°C for 3h under a nitrogen atmosphere to obtain the sheet-shaped composite manganese iron phosphate material.

[0094] Example 7

[0095] Ethanol, acetic acid and deionized water are mixed in a mass ratio of 39:60:1 to prepare an acidic hydrolysis solution. Tetraethyl titanate is dispersed in the acidic hydrolysis solution, and the mass concentration of the tetraethyl titanate is 1% to prepare a titanium source hydrolysis solution. Another acidic hydrolysis solution is prepared, and tetraethyl silicate is dispersed in the acidic hydrolysis solution, and the mass concentration of the tetraethyl silicate is 1% to prepare a silicon source hydrolysis solution.

[0096] The titanium source hydrolysis solution and the silicon source hydrolysis solution are mixed, and then the sheet-shaped manganese iron phosphate in Preparation Example 1 is added. Ultrasonic dispersion is performed to uniformly disperse the sheet-shaped manganese iron phosphate, and then the mixture is reacted at 60°C for 3h. The sheet-shaped manganese iron phosphate is collected by centrifugation, washed with deionized water, and dried to obtain the sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide. The amount of the titanium source hydrolysis solution and the silicon source hydrolysis solution is calculated based on the loading amount of nano-titanium dioxide on the sheet-shaped manganese iron phosphate being 0.5wt% and the loading amount of nano-silicon dioxide on the sheet-shaped manganese iron phosphate being 0.3wt%.

[0097] The sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide is added into a Tris buffer solution with a pH of 8.5, and then dopamine hydrochloride is added. The mixture is continuously stirred for 2h, and the precipitate is collected by centrifugation. The amount of dopamine hydrochloride is 2% of the mass of the sheet-shaped manganese iron phosphate loaded with nano-titanium dioxide and nano-silicon dioxide on the surface. Finally, sintering is performed at 600°C for 3h under a nitrogen atmosphere to obtain the sheet-shaped composite manganese iron phosphate material.

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is that only nano-titanium dioxide is loaded on the surface of the sheet-shaped manganese iron phosphate.

[0100] Comparative Example 2

[0101] The present comparative example differs from Example 1 only in that the surface of the flaky lithium manganese iron phosphate is loaded with only nano-silicon dioxide.

[0102] Comparative Example 3

[0103] The present comparative example differs from Example 1 only in that the surface of the flaky lithium manganese iron phosphate is loaded with nano-titanium dioxide and nano-silicon dioxide, and is not coated with a polydopamine layer.

[0104] Performance test

[0105] The flaky composite lithium manganese iron phosphate materials in each example and each comparative example were respectively assembled into button cells and tested for compaction density and discharge performance.

[0106] The flaky composite lithium manganese iron phosphate material, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5 in N-methylpyrrolidone to form a slurry, which was coated on a 20 μm thick aluminum foil, and then dried, rolled, die-cut, and punched into positive electrode sheets. Lithium sheets were used as the negative electrode, a polypropylene separator was used, and an electrolyte of 1 mol / L LiPF6 (EC:DMC = 1:1) was used to assemble button cells.

[0107] (1) Compaction density: First, the surface density of the positive electrode sheet was calculated, surface density = (sheet mass - aluminum foil mass) / sheet area, then the thickness of the rolled sheet and aluminum foil was measured, and the compaction density = surface density / (sheet thickness - aluminum foil thickness).

[0108] (2) The test voltage was set to 2.0-4.5 V, the test temperature was 25°C, and the capacity retention rate of the test battery after 300 cycles at 1C rate was tested.

[0109] Table 1 Performance test results

[0110]

[0111] Compared with Comparative Examples 1 and 2, the flaky composite lithium manganese iron phosphate material in the present example exhibits high compaction density and high stable cycle performance, indicating that the present application optimizes the compaction density and cycle performance of the flaky composite lithium manganese iron phosphate material by loading nano-titanium dioxide and nano-silicon dioxide on the surface of the flaky lithium manganese iron phosphate and coating a carbon layer, which helps to improve the electrochemical performance of the battery.

[0112] As can be seen from the comparative example and Comparative Example 2, the carbon layer helps to improve the electrical conductivity of the material, and optimizes the negative impact of loading nano-titanium dioxide and nano-silicon dioxide on the electrical conductivity, so that the flaky composite lithium manganese iron phosphate material exhibits excellent cycle stability.

[0113] It can be seen from the combination of Embodiment 1-Embodiment 6 that the loading amount of nano-titanium dioxide on the surface of the flaky lithium manganese iron phosphate is higher than that of nano-silicon dioxide, which is more conducive to improving the electrochemical performance of the battery.

[0114] It can be seen from the combination of Embodiment 1 and Embodiment 7 that the method of loading nano-titanium dioxide first and then loading nano-silicon dioxide in Embodiment 1 is more conducive to improving the electrochemical performance of the battery. It is believed that when nano-titanium dioxide and nano-silicon dioxide are simultaneously loaded on the surface of the flaky lithium manganese iron phosphate, the nano-silicon dioxide may first attach to the surface of the flaky lithium manganese iron phosphate, blocking the attachment of the nano-titanium dioxide on the surface of the flaky lithium manganese iron phosphate, so that the conductivity of the flaky composite lithium manganese iron phosphate material is reduced to a certain extent, and the inhibition effect on the dissolution of manganese ions is reduced. Loading nano-titanium dioxide first ensures that the nano-titanium dioxide is uniformly loaded on the surface of the flaky lithium manganese iron phosphate, ensuring the inhibition effect on the dissolution of manganese ions, and at the same time, cooperating with the carbon layer to ensure that the flaky composite lithium manganese iron phosphate material has excellent conductivity. When loading nano-silicon dioxide second, the nano-silicon dioxide fills the pores between the nano-titanium dioxide, which improves the compactness and inhibits the dissolution of manganese ions, while having little effect on the conductivity, so as to ensure that the flaky composite lithium manganese iron phosphate material has high conductivity, thereby showing that the battery has excellent electrochemical performance.

[0115] It is apparent to those skilled in the art that the present disclosure is not limited to the details of the foregoing exemplary embodiments, and that the present disclosure can be implemented in other particular forms without departing from the spirit or essential characteristics of the present disclosure. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the present disclosure is defined by the appended claims rather than the foregoing description, and it is intended to encompass all changes falling within the meaning and range of equivalents of the elements of the claims.

[0116] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for preparing a sheet-shaped composite lithium iron manganese phosphate material, characterized in that, The method comprises the following steps: dispersing a lithium source, a manganese source, an iron source and a phosphorus source in a hydrophobic solvent to prepare a mixed solution; preparing a colloid from the mixed solution; sintering the colloid to obtain flaky lithium manganese iron phosphate; taking a titanium source and a silicon source, dissolving the titanium source and the silicon source in an acidic hydrolysis solution respectively to obtain a titanium source hydrolysis solution and a silicon source hydrolysis solution; reacting the flaky lithium manganese iron phosphate in the titanium source hydrolysis solution, taking it out and then reacting it in the silicon source hydrolysis solution to obtain flaky lithium manganese iron phosphate loaded with nano titanium dioxide and nano silicon dioxide on the surface; coating a polydopamine layer on the flaky lithium manganese iron phosphate loaded with nano titanium dioxide and nano silicon dioxide on the surface, and then sintering to obtain flaky composite lithium manganese iron phosphate material.

2. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 1, characterized in that, The reaction of the flaky lithium manganese iron phosphate in the titanium source hydrolysis solution is carried out at a temperature of 30-70℃ for 3-6h; and / or, the reaction of the flaky lithium manganese iron phosphate in the silicon source hydrolysis solution is carried out at a temperature of 30-70℃ for 3-6h; and / or, the silicon source is at least one of tetraethyl silicate and tetrabutyl silicate; and / or, the titanium source is at least one of tetraethyl titanate and tetrabutyl titanate.

3. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 1, characterized in that, The operation of coating the polydopamine layer is mixing the flaky lithium manganese iron phosphate loaded with nano titanium dioxide and nano silicon dioxide on the surface with a weak alkaline Tris buffer solution, adding hydrochloric acid dopamine, centrifuging after reaction to obtain flaky lithium manganese iron phosphate coated with a polydopamine layer; wherein the amount of hydrochloric acid dopamine is 2-3% of the mass of the flaky lithium manganese iron phosphate loaded with nano titanium dioxide and nano silicon dioxide on the surface.

4. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 1, characterized in that, The sintering condition of the flaky lithium manganese iron phosphate coated with a polydopamine layer is a temperature of 600-700℃ for 2-3h in an inert atmosphere.

5. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 1, characterized in that, The hydrophobic solvent is at least one of oleic acid, oleylamine and trioctyl phosphine; and / or, the mixed solution is reacted at 40-80℃ for 30min-1h to prepare a colloid; and / or, the sintering condition of the colloid is a temperature of 300-600℃ for 8-12h in an inert atmosphere.

6. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 1, characterized in that, The lithium source is at least one of lithium hydroxide, lithium phosphate, lithium carbonate and lithium acetate; and / or, the manganese source is at least one of manganese carbonate, manganese acetate and manganese chloride; and / or, the iron source is at least one of ferrous phosphate, ferrous nitrate and ferrous oxalate; and / or, the phosphorus source is at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate and potassium monohydrogen phosphate.

7. A flaky composite lithium iron manganese phosphate material, characterized in that, The flaky composite lithium manganese iron phosphate material prepared by the method of claim 1 has a flaky lithium manganese iron phosphate as a core, the core is loaded with nano titanium dioxide and nano silicon dioxide on the surface, and the core is coated with a carbon layer on the outermost layer; wherein the carbon layer is formed by carbonization after coating a polydopamine layer on the surface of the core.

8. The flaky composite lithium iron manganese phosphate material of claim 7, wherein, The loading amount of the nano titanium dioxide on the core is 0.5wt%-1.3wt%; and / or, the loading amount of the nano silicon dioxide on the core is 0.3wt%-1.0wt%.

9. The flaky composite lithium iron manganese phosphate material of claim 7, wherein, The loading amount of the nano titanium dioxide on the surface of the core is greater than the loading amount of the nano silicon dioxide.

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