Flaky composite lithium manganese iron phosphate material and preparation method thereof

Abstract

The invention discloses a sheet-shaped composite lithium manganese iron phosphate material and a preparation method thereof, the sheet-shaped composite lithium manganese iron phosphate material takes sheet-shaped lithium manganese iron 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 coating the surface of the core with a polydopamine layer and then carbonizing. The sheet-shaped composite lithium manganese iron phosphate material disclosed by the invention has excellent structural stability and excellent cycle performance, and the electrochemical performance of the battery can be greatly improved.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium manganese iron phosphate materials, specifically relating to a sheet-like composite lithium manganese iron phosphate material and its preparation method. Background Technology

[0002] While lithium iron phosphate (LFP) batteries have become the mainstream choice in the new energy vehicle market due to their high safety and low cost, their low energy density and poor low-temperature performance directly impact user experience and industry development. Currently, lithium manganese iron phosphate (MFP) batteries outperform LFP batteries in terms of cost reduction, efficiency improvement, energy density, and low-temperature performance, making them a new research direction for high-energy-density devices.

[0003] Compared to lithium iron phosphate (LFP), lithium manganese iron phosphate (LFP) incorporates manganese, which increases the battery's operating voltage and addresses the issue of low energy density. For the same weight, LFP batteries offer a longer driving range for electric vehicles.

[0004] However, current lithium iron phosphate batteries still face challenges in research and development, among which low compaction density and rapid capacity decay after repeated charge and discharge are problems that urgently need to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a sheet-like composite lithium manganese iron phosphate material and its preparation method. This sheet-like composite lithium manganese iron phosphate material has a high compaction density and stable cycle performance.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution: A sheet-like composite lithium manganese iron phosphate material, wherein the sheet-like composite lithium manganese iron phosphate material has sheet-like lithium manganese iron phosphate as the core, the surface of the core is loaded with nano-titanium dioxide and nano-silica, and the outermost layer of the core is coated with a carbon layer; The carbon layer is formed by carbonization after coating the core surface with a polydopamine layer.

[0007] In one or more embodiments of the present invention, the loading amount of the nano-titanium dioxide on the core is 0.5wt%-1.3wt%; And / or, the loading of the nano-silica on the core is 0.3wt%-1.0wt%.

[0008] In one or more embodiments of the present invention, the loading of nano-titanium dioxide on the core surface is greater than the loading of nano-silicon dioxide.

[0009] Another specific embodiment of the present invention provides the following technical solution: A method for preparing a sheet-like composite lithium manganese iron phosphate material includes the following steps: Lithium, manganese, iron, and phosphorus sources are dispersed in a hydrophobic solvent to prepare a mixed solution; Prepare a colloid from the mixed solution; The colloid was sintered to obtain flake-shaped lithium manganese iron phosphate; Nano-titanium dioxide and nano-silica were loaded onto sheet-like lithium manganese iron phosphate to obtain sheet-like lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on the surface. A sheet-like lithium manganese iron phosphate material with nano-titanium dioxide and nano-silica loaded on its surface is coated with a polydopamine layer and then sintered to obtain a sheet-like composite lithium manganese iron phosphate material.

[0010] In one or more embodiments of the present invention, a titanium source and a silicon source are taken, and the titanium source and the silicon source are respectively dissolved in an acidic hydrolysate to obtain a titanium source hydrolysate and a silicon source hydrolysate. Flake-shaped lithium manganese iron phosphate was placed in a titanium source hydrolysate for reaction, and then placed in a silicon source hydrolysate for reaction to obtain flake-shaped lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on the surface.

[0011] In one or more embodiments of the present invention, the reaction conditions of the flake-shaped lithium manganese iron phosphate in the titanium source hydrolysate are: temperature 30℃-70℃, time 3h-6h; And / or, the reaction conditions of the flake-shaped lithium manganese iron phosphate in the silicon source hydrolysate are: temperature 30℃-70℃, time 3h-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.

[0012] In one or more embodiments of the present invention, the operation of coating polydopamine layer is as follows: the sheet-like lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on the surface is mixed with weakly alkaline Tris buffer, then dopamine hydrochloride is added, and centrifuged after reaction to obtain sheet-like lithium manganese iron phosphate coated with polydopamine layer. The amount of dopamine hydrochloride used is 2-3% of the mass of the sheet-like lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on the surface.

[0013] In one or more embodiments of the present invention, the sintering conditions of the sheet-like lithium manganese iron phosphate coated with a polydopamine layer are: under an inert atmosphere, at a temperature of 600℃-700℃, for a time of 2h-3h.

[0014] In one or more embodiments of the present invention, the hydrophobic solvent is at least one of oleic acid, oleylamine, and trioctylphosphine; And / or, the mixed solution is reacted at 40℃-80℃ for 30 min-1 h to prepare a colloid; And / or, the sintering conditions of the colloid are: under an inert atmosphere, at a temperature of 300℃-600℃, for 8h-12h.

[0015] In one or more embodiments of the present invention, 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.

[0016] Compared with the prior art, the present invention optimizes the structural stability of the sheet-like composite lithium manganese iron phosphate material by loading nano-titanium dioxide and nano-silica onto sheet-like lithium manganese iron phosphate and coordinating with carbon layer coating. This not only inhibits the dissolution of manganese ions but also promotes lithium ion transport, resulting in excellent cycle performance and significantly improving the electrochemical performance of the battery. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0018] A specific embodiment of the present invention provides a sheet-like composite lithium manganese iron phosphate material, which has sheet-like lithium manganese iron phosphate as the core, the core surface is loaded with nano-titanium dioxide and nano-silica, and the outermost layer of the core is coated with a carbon layer; wherein, the carbon layer is formed by carbonization after coating the core surface with a polydopamine layer.

[0019] Specifically, the sheet-like structure helps shorten the diffusion path of lithium ions, and the stacking of sheet-like structures helps reduce porosity, increase compaction density, and improve the cycling stability of the material. By loading nano-titanium dioxide and nano-silica onto the core surface, on the one hand, it can block the contact between the electrolyte and manganese ions, reduce manganese ion dissolution, and help maintain cycling stability; on the other hand, it can improve the structural stability of the material and reduce volume expansion during use; moreover, the synergy between nano-titanium dioxide and nano-silica can also improve lithium ion transport efficiency and maintain a high capacity retention rate.

[0020] Finally, a carbon layer is coated onto the core surface to further increase the compaction density and improve conductivity, compensating for the weak conductivity of nano-titanium dioxide and nano-silica, and optimizing the electrochemical performance of the battery. Furthermore, the carbon layer can further suppress manganese ion dissolution and maintain cycle stability.

[0021] Furthermore, the loading amount of nano-titanium dioxide on the core is 0.5wt%-1.3wt%, and the loading amount of nano-silica on the core is 0.3wt%-1.0wt%.

[0022] Specifically, by controlling the loading of nano-titanium dioxide and nano-silica, the dissolution of manganese ions is effectively suppressed without affecting lithium ion transport, and the structural stability is effectively improved, resulting in excellent battery cycle performance.

[0023] Furthermore, the loading of nano-titanium dioxide on the core surface is greater than that of nano-silica.

[0024] Specifically, nano-silica has weaker conductivity than nano-titanium dioxide. The high loading of nano-titanium dioxide can ensure that the sheet-like composite lithium manganese iron phosphate material has high conductivity, which helps to improve the electrochemical performance of the battery.

[0025] Another specific embodiment of the present invention provides a method for preparing a sheet-like composite lithium manganese iron phosphate material, comprising the following steps: Step 1: Prepare flake-shaped lithium manganese iron phosphate.

[0026] Specifically, lithium, manganese, iron, and phosphorus sources are dispersed in a hydrophobic solvent to prepare a mixed solution. The mixed solution is then formulated into a colloid, which is sintered to obtain flake-shaped lithium manganese iron phosphate.

[0027] 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.

[0028] A mixed solution is prepared by selecting the above-mentioned lithium, manganese, iron and phosphorus sources. The mixed solution is reacted at 40℃-80℃ for 30min-1h to form a colloid. Then, under an inert atmosphere such as nitrogen or argon, it is sintered at 300℃-600℃ for 8h-12h. During the sintering process, lithium manganese iron phosphate crystals are directionally grown into a plate-like structure.

[0029] Step 2: Dissolve the titanium source and silicon source in acidic hydrolysate to obtain titanium source hydrolysate and silicon source hydrolysate, respectively.

[0030] Specifically, the silicon source is at least one of tetraethyl or tetrabutyl silicate, and the titanium source is at least one of tetraethyl or tetrabutyl titanate. The silicon and titanium sources are dissolved in an acidic hydrolysate formed by ethanol, acetic acid, and deionized water, with a pH of 3-5. The mass concentration of the titanium source in the hydrolysate is 1%-3%. The mass concentration of the silicon source in the hydrolysate is 1%-3%.

[0031] Step 3: Place the flake-shaped lithium manganese iron phosphate in a titanium source hydrolysate for reaction, then remove it and place it in a silicon source hydrolysate for reaction to obtain flake-shaped lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on the surface.

[0032] Specifically, the loading amounts of nano-titanium dioxide on the core are 0.5wt%-1.3wt%, and the loading amounts of nano-silicon dioxide on the core are 0.3wt%-1.0wt%, which can be calculated based on the molar amounts of titanium and silicon atoms. Flake-shaped lithium manganese iron phosphate is then reacted sequentially in titanium-source hydrolysate and silicon-source hydrolysate. Ultrasonic dispersion can be used to assist the reaction and improve the uniformity of the loading of nano-titanium dioxide and nano-silicon dioxide. The reaction conditions for flake-shaped lithium manganese iron phosphate in titanium-source hydrolysate are: temperature 30℃-70℃, time 3h-6h; the reaction conditions for flake-shaped lithium manganese iron phosphate in silicon-source hydrolysate are: temperature 30℃-70℃, time 3h-6h.

[0033] First, nano-titanium dioxide is loaded, allowing it to preferentially form a stable adhesion layer on the surface of flake-shaped lithium manganese iron phosphate. This enhances the inhibition of manganese ion dissolution and facilitates lithium ion transport. Then, nano-silica is loaded. The nano-silica fills the pores between the nano-titanium dioxide particles, increasing density and thus compaction density. Simultaneously, it blocks contact between the electrolyte and manganese ions, further inhibiting manganese ion dissolution.

[0034] Step 4: Coat the sheet-like lithium manganese iron phosphate with a polydopamine layer on the surface loaded with nano-titanium dioxide and nano-silica, and then sinter to obtain sheet-like composite lithium manganese iron phosphate material.

[0035] Specifically, after loading nano-titanium dioxide and nano-silica onto the surface of sheet-like manganese iron phosphate, the polydopamine layer can be uniformly coated on the surface. The carbon layer formed after sintering, in conjunction with the nano-titanium dioxide, improves the conductivity of the material and enhances the electrochemical performance of the battery.

[0036] Further, the process of coating with a polydopamine layer is as follows: Sheet-shaped lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on its surface is mixed with a weakly alkaline Tris buffer solution, then dopamine hydrochloride is added. After the reaction, the mixture is centrifuged to obtain sheet-shaped lithium manganese iron phosphate coated with a polydopamine layer. The amount of dopamine hydrochloride used is 2-3% of the mass of the sheet-shaped lithium manganese iron phosphate with nano-titanium dioxide and nano-silica loaded on its surface.

[0037] Furthermore, the sintering conditions in step 4 are: under an inert atmosphere such as nitrogen, at a temperature of 600℃-700℃, for a time of 2h-3h.

[0038] The present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, all reagents used in the present invention are commercially available.

[0039] Preparation Example 1 The preparation of flake-shaped lithium manganese iron phosphate is as follows: Take 0.1 mol of lithium carbonate and disperse it in 40 ml of oleylamine to obtain a lithium carbonate dispersion; take 0.04 mol of manganese acetate and disperse it in 20 ml of oleic acid to obtain a manganese acetate dispersion; take 0.16 mol of ferrous oxalate and disperse it in 30 ml of trioctylphosphine to obtain a ferrous oxalate dispersion; take 0.2 mol of ammonium dihydrogen phosphate and disperse it in 40 ml of oleylamine to obtain an ammonium dihydrogen phosphate dispersion.

[0040] Mix the above dispersions, stir and heat to 40°C for 50 minutes to prepare a colloid.

[0041] The colloid was sintered at 450°C for 12 hours under a nitrogen atmosphere to obtain flake-shaped lithium manganese iron phosphate.

[0042] Example 1 An acidic hydrolysate was prepared by mixing deionized water, ethanol, and acetic acid in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0043] The flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added to the titanium source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysate used was calculated based on a loading of 0.5 wt% of nano-titanium dioxide on the flake-shaped lithium manganese iron phosphate.

[0044] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide was then added to the silicon source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amount of silicon source hydrolysate used was calculated based on a nano-silica loading of 0.3 wt% on the flake-shaped lithium manganese iron phosphate.

[0045] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 2% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 600℃ for 3 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0046] Example 2 An acidic hydrolysate was prepared by mixing ethanol, acetic acid, and deionized water in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0047] The flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added to the titanium source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 50°C for 4 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysate used was calculated based on a loading of 0.8 wt% of nano-titanium dioxide on the flake-shaped lithium manganese iron phosphate.

[0048] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide was then added to the silicon source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 50°C for 4 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amount of silicon source hydrolysate used was calculated based on a nano-silica loading of 0.5 wt% on the flake-shaped lithium manganese iron phosphate.

[0049] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 3% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 700℃ for 2 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0050] Example 3 An acidic hydrolysate was prepared by mixing ethanol, acetic acid, and deionized water in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0051] The flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added to the titanium source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysate used was calculated based on a loading of 1.0 wt% of nano-titanium dioxide on the flake-shaped lithium manganese iron phosphate.

[0052] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide was then added to the silicon source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amount of silicon source hydrolysate used was calculated based on a nano-silica loading of 0.8 wt% on the flake-shaped lithium manganese iron phosphate.

[0053] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 2% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 600℃ for 3 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0054] Example 4 An acidic hydrolysate was prepared by mixing ethanol, acetic acid, and deionized water in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0055] The flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added to the titanium source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysate used was calculated based on a loading of 1.3 wt% of nano-titanium dioxide on the flake-shaped lithium manganese iron phosphate.

[0056] Next, flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide was added to the silicon source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonic dispersion, and reacted at 60℃ for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amount of silicon source hydrolysate used was calculated based on a nano-silica loading of 1.0 wt% on the flake-shaped lithium manganese iron phosphate.

[0057] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 2% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 600℃ for 3 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0058] Example 5 An acidic hydrolysate was prepared by mixing ethanol, acetic acid, and deionized water in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0059] The flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added to the titanium source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysate used was calculated based on a loading of 1.0 wt% of nano-titanium dioxide on the flake-shaped lithium manganese iron phosphate.

[0060] Next, flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide was added to the silicon source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonic dispersion, and reacted at 60℃ for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amount of silicon source hydrolysate used was calculated based on a nano-silica loading of 1.0 wt% on the flake-shaped lithium manganese iron phosphate.

[0061] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 2% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 600℃ for 3 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0062] Example 6 An acidic hydrolysate was prepared by mixing ethanol, acetic acid, and deionized water in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0063] The flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added to the titanium source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide. The amount of titanium source hydrolysate used was calculated based on a loading of 0.5 wt% of nano-titanium dioxide on the flake-shaped lithium manganese iron phosphate.

[0064] Next, flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide was added to the silicon source hydrolysate. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonic dispersion, and reacted at 60℃ for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amount of silicon source hydrolysate used was calculated based on a nano-silica loading of 1.0 wt% on the flake-shaped lithium manganese iron phosphate.

[0065] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 2% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 600℃ for 3 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0066] Example 7 An acidic hydrolysate was prepared by mixing ethanol, acetic acid, and deionized water in a mass ratio of 39:60:1. Tetraethyl titanate was then dispersed in the acidic hydrolysate at a mass concentration of 1%, thus preparing a titanium-source hydrolysate. Separately, a silicon-source hydrolysate was prepared by dispersing tetraethyl silicate in the acidic hydrolysate at a mass concentration of 1%.

[0067] The titanium-source hydrolysate and silicon-source hydrolysate were mixed, and then the flake-shaped lithium manganese iron phosphate from Preparation Example 1 was added. The flake-shaped lithium manganese iron phosphate was uniformly dispersed by ultrasonication and reacted at 60°C for 3 hours. The flake-shaped lithium manganese iron phosphate was collected by centrifugation, washed with deionized water, and dried to obtain flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. The amounts of titanium-source hydrolysate and silicon-source hydrolysate were calculated based on a loading of 0.5 wt% for nano-titanium dioxide and 0.3 wt% for nano-silica on the flake-shaped lithium manganese iron phosphate.

[0068] Flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica was added to Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride. The mixture was stirred continuously for 2 hours, and the precipitate was collected by centrifugation. The amount of dopamine hydrochloride used was 2% of the mass of the flake-shaped lithium manganese iron phosphate loaded with nano-titanium dioxide and nano-silica. Finally, the mixture was sintered at 600℃ for 3 hours under a nitrogen atmosphere to obtain the flake-shaped composite lithium manganese iron phosphate material.

[0069] Comparative Example 1 The only difference between this comparative example and Example 1 is that the surface of the sheet-like lithium manganese iron phosphate is loaded with only nano-titanium dioxide.

[0070] Comparative Example 2 The only difference between this comparative example and Example 1 is that the surface of the sheet-like lithium manganese iron phosphate is loaded with only nano-silica.

[0071] Comparative Example 3 The only difference between this comparative example and Example 1 is that the sheet-like lithium manganese iron phosphate has nano-titanium dioxide and nano-silica loaded on its surface, but is not coated with a polydopamine layer.

[0072] Performance testing The sheet-like composite lithium manganese iron phosphate materials from each embodiment and comparative example were assembled into coin cells, and their compaction density and discharge performance were tested.

[0073] A slurry was prepared by mixing sheet-like composite lithium manganese iron phosphate material, conductive carbon black, and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 90:5:5. The slurry was then coated onto a 20μm thick aluminum foil, dried, rolled, die-cut, and punched into positive electrode sheets. A coin cell was assembled using lithium sheets as the negative electrode, a polypropylene separator, and a 1mol / L LiPF6 electrolyte (EC:DMC=1:1).

[0074] (1) Compacted density: First calculate the surface density of the positive electrode sheet, surface density = (electrode sheet mass - aluminum foil mass) / electrode sheet area, then measure the thickness of the electrode sheet and aluminum foil after rolling, compacted density = surface density / (electrode sheet thickness - aluminum foil thickness).

[0075] (2) Set the test voltage to 2.0-4.5V and the test temperature to 25℃, and test the capacity retention rate of the battery after 300 cycles at 1C rate.

[0076] Table 1 Performance Test Results Compared with Comparative Examples 1 and 2, the sheet-like composite lithium manganese iron phosphate material in the embodiments of the present invention exhibits high compaction density and high stable cycle performance, indicating that the present invention optimizes the compaction density and cycle performance of the sheet-like composite lithium manganese iron phosphate material by loading nano-titanium dioxide and nano-silica onto the surface of the sheet-like lithium manganese iron phosphate and coating it with a carbon layer, which helps to improve the electrochemical performance of the battery.

[0077] Comparative Examples 1 and 2 show that the carbon layer helps improve the conductivity of the material, optimizes the negative impact of loaded nano-titanium dioxide and nano-silica on conductivity, and enables the sheet-like composite lithium manganese iron phosphate material to exhibit excellent cycle stability.

[0078] As can be seen from Examples 1-6, the loading of nano-titanium dioxide on the surface of sheet-like lithium manganese iron phosphate is higher than that of nano-silica, which is more conducive to improving the electrochemical performance of the battery.

[0079] Combining Examples 1 and 7, it is evident that the method of first loading nano-titanium dioxide and then nano-silica in Example 1 is more conducive to improving the electrochemical performance of the battery. Analysis suggests that when nano-titanium dioxide and nano-silica are simultaneously loaded onto the surface of the sheet-like lithium manganese iron phosphate, the nano-silica may adhere to the surface of the sheet-like lithium manganese iron phosphate first, hindering the adhesion of nano-titanium dioxide to the surface. This reduces the conductivity of the sheet-like composite lithium manganese iron phosphate material to some extent and also reduces the inhibition effect on manganese ion dissolution. However, loading nano-titanium dioxide first ensures uniform loading on the surface of the sheet-like lithium manganese iron phosphate, guaranteeing the inhibition effect on manganese ion dissolution. Simultaneously, the combination with the carbon layer ensures the excellent conductivity of the sheet-like composite lithium manganese iron phosphate material. When nano-silica is loaded later, the nano-silica fills the pores between the nano-titanium dioxide, improving density and inhibiting manganese ion dissolution while having a smaller impact on conductivity. This ensures the high conductivity of the sheet-like composite lithium manganese iron phosphate material, thus exhibiting excellent electrochemical performance of the battery.

[0080] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.

[0081] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A flaky composite lithium iron manganese phosphate material, characterized in that, The flaky composite manganese iron lithium phosphate material takes flaky manganese iron lithium 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. The carbon layer is formed by carbonization after coating a polydopamine layer on the surface of the core. 2.The flaky composite lithium iron manganese phosphate material of claim 1, characterized in that, 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%. 3.The flaky composite lithium iron manganese phosphate material of claim 1, characterized in that, 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.

4. A method for preparing a sheet-shaped composite lithium iron manganese phosphate material, characterized in that, The method comprises the following steps: Take a lithium source, a manganese source, an iron source and a phosphorus source, disperse them in a hydrophobic solvent to prepare a mixed solution; Prepare a colloid from the mixed solution; Sinter the colloid to obtain flaky manganese iron lithium phosphate; Load nano titanium dioxide and nano silicon dioxide on the flaky manganese iron lithium phosphate to obtain flaky manganese iron lithium phosphate loaded with nano titanium dioxide and nano silicon dioxide; Coat a polydopamine layer on the flaky manganese iron lithium phosphate loaded with nano titanium dioxide and nano silicon dioxide, then sinter to obtain the flaky composite manganese iron lithium phosphate material.

5. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 4, characterized in that, Take a titanium source and a silicon source, dissolve 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; Put the flaky manganese iron lithium phosphate in the titanium source hydrolysis solution for reaction, take it out and then put it in the silicon source hydrolysis solution for reaction to obtain flaky manganese iron lithium phosphate loaded with nano titanium dioxide and nano silicon dioxide.

6. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 5, characterized in that, The reaction conditions of the flaky manganese iron lithium phosphate in the titanium source hydrolysis solution are: temperature 30-70℃, time 3-6h; And / or, the reaction conditions of the flaky manganese iron lithium phosphate in the silicon source hydrolysis solution are: temperature 30-70℃, time 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.

7. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 4, characterized in that, The operation of coating the polydopamine layer is: mix the flaky manganese iron lithium phosphate loaded with nano titanium dioxide and nano silicon dioxide with a weak alkaline Tris buffer solution, then add hydrochloric acid dopamine, centrifuge after reaction to obtain flaky manganese iron lithium phosphate coated with a polydopamine layer; The amount of hydrochloric acid dopamine is 2-3% of the mass of the flaky manganese iron lithium phosphate loaded with nano titanium dioxide and nano silicon dioxide.

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

9. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 4, 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 conditions of the colloid are: inert atmosphere, temperature 300-600℃, sintering time 8-12h.

10. The method for preparing the sheet-like composite lithium manganese iron phosphate material according to claim 4, 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, potassium monohydrogen phosphate. And / or, the phosphorus source is at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate.

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