A modified iron phosphate material, a lithium iron phosphate material, and a preparation method and application thereof

Abstract

The application discloses a modified iron phosphate material, a lithium iron phosphate material and a preparation method and application thereof, and belongs to the technical field of lithium iron phosphate materials. The modified iron phosphate material is in a sheet shape as a whole, and the modified iron phosphate material comprises zirconium phosphate with a sheet structure, the zirconium phosphate is loaded with elemental silver and lithium oxide between layers, and the outer surface of the zirconium phosphate is formed with iron phosphate. The modified iron phosphate material can be further prepared into the lithium iron phosphate material and applied to a battery, so that the rate performance, coulomb efficiency, capacity and conductivity of the battery can be improved. The preparation method of the modified iron phosphate material and the lithium iron phosphate material is simple and can be used for industrial production.

Description

Technical Field

[0001] This disclosure relates to the field of lithium iron phosphate materials technology, and more specifically, to a modified iron phosphate material, lithium iron phosphate materials, their preparation methods and applications. Background Technology

[0002] Lithium-ion batteries, due to their high specific energy, long lifespan, and pollution-free characteristics, have experienced rapid popularization and development since their invention. Their applications have gradually shifted from traditional digital products to power supply fields, maintaining a strong growth trend. The performance of the cathode material directly affects the performance of lithium-ion batteries, and its cost directly determines the battery's overall cost. Therefore, the research and development of lithium battery cathode materials is of great significance for improving lithium battery performance.

[0003] The low electronic conductivity and ion mobility of LiFePO4 limit its large-scale application in high-power and low-temperature environments. Furthermore, batteries currently made from lithium iron phosphate exhibit poor performance in terms of initial coulombic efficiency and capacity.

[0004] In view of this, this disclosure is hereby made. Summary of the Invention

[0005] The purpose of this disclosure is to provide a modified iron phosphate material, a lithium iron phosphate material, a preparation method thereof, and its application, in order to solve or improve the above-mentioned technical problems.

[0006] This disclosure can be implemented as follows:

[0007] In a first aspect, this disclosure provides a modified iron phosphate material, which is generally in the form of a sheet. The modified iron phosphate material includes zirconium phosphate with a layered structure, with elemental silver and lithium oxide loaded between the layers of zirconium phosphate, and iron phosphate formed on the outer surface of zirconium phosphate.

[0008] In an optional embodiment, the modified iron phosphate material has at least one of the following characteristics:

[0009] Feature 1: The diameter of the modified iron phosphate material is 1μm-2μm;

[0010] Feature 2: The thickness of the modified iron phosphate material is 180nm-220nm.

[0011] Secondly, this disclosure provides a method for preparing a modified iron phosphate material as described in the foregoing embodiments, comprising the following steps: mixing and reacting a zirconium phosphate precursor loaded with silver and organolithium in the interlayer with an iron source and a phosphate source in a solution system to obtain iron phosphate with zirconium phosphate as the core; calcining the iron phosphate in a reducing atmosphere to obtain the modified iron phosphate material.

[0012] In an optional embodiment, the ratio of zirconium phosphate precursor to iron source is from 2 g:1 mol to 5 g:1 mol; and / or, the molar ratio of phosphate ions in the phosphate source to iron ions in the iron source is from 0.98:1 to 1.05:1.

[0013] In an optional implementation, the iron ions in the iron source are ferric ions (Fe3+).

[0014] In an optional embodiment, the iron source includes at least one of ferric nitrate and ferric chloride.

[0015] In an optional embodiment, the phosphate source includes at least one of ammonium hydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate.

[0016] In an optional implementation, the mixing reaction includes at least one of the following features:

[0017] Feature 1: The reaction pH value is 1.2-2.2;

[0018] Feature 2: The reaction temperature is 60℃-90℃;

[0019] Feature 3: The reaction time is 2-5 hours;

[0020] Feature 4: The reaction is carried out under stirring conditions.

[0021] In an optional embodiment, the pH adjuster used to adjust the pH value includes at least one of ammonia, NaOH, and urea.

[0022] And / or, the stirring speed is 500rpm-900rpm.

[0023] In an optional embodiment, the preparation of the zirconium phosphate precursor includes: mixing and reacting silver-loaded zirconium phosphate with organolithium under acidic conditions.

[0024] In an optional embodiment, the molar ratio of organolithium to silver-supported zirconium phosphate is 5:100 to 10:100.

[0025] In an optional embodiment, the organic lithium includes at least one of lithium hydroxypyruvate hydrate, lithium citrate, lithium salicylate, and lithium octanoate.

[0026] In an optional implementation, the acidic conditions are provided by hydrochloric acid.

[0027] In an optional embodiment, the preparation of silver-loaded zirconium phosphate includes mixing a silver source, layered zirconium phosphate, and an interstitial conditioner under acidic conditions.

[0028] In an optional embodiment, the layered zirconium phosphate has at least one of the following characteristics:

[0029] Feature 1: The diameter of layered zirconium phosphate is 200nm-600nm;

[0030] Feature 2: The thickness of the layered zirconium phosphate is 20nm-50nm.

[0031] In an optional embodiment, the mass ratio of the silver source to layered zirconium phosphate is 0.1:100 to 3:100.

[0032] In an optional implementation, the molar ratio of the gap conditioner to the silver element in the silver source is 3:1 to 6:1.

[0033] In an optional embodiment, the gap conditioner includes at least one selected from methylamine, ethylamine, butylamine, and tetrabutylammonium bromide.

[0034] In an optional embodiment, the acidic conditions in the preparation of silver-loaded zirconium phosphate are provided by nitric acid.

[0035] In an optional embodiment, the calcination temperature is 500℃-800℃; and / or the calcination time is 3h-6h.

[0036] Thirdly, this disclosure provides a lithium iron phosphate material, the raw materials for which include the modified iron phosphate material of the aforementioned embodiments.

[0037] In an optional embodiment, the lithium iron phosphate material is carbon-coated lithium iron phosphate.

[0038] Fourthly, this disclosure provides a method for preparing lithium iron phosphate material as described in the foregoing embodiments, comprising the following steps: mixing modified iron phosphate material, lithium source, and carbon source, and calcining.

[0039] In an optional embodiment, the modified iron phosphate material is mixed with a lithium source and a carbon source and then calcined.

[0040] Fifthly, this disclosure provides a battery whose raw materials include the lithium iron phosphate material described in the aforementioned embodiments.

[0041] The beneficial effects of this disclosure include:

[0042] In this disclosure, the sheet-like modified iron phosphate material can shorten the lithium-ion transport path. By introducing silver and lithium into the interlayer of zirconium phosphate, elemental silver can improve the activity of lithium oxide as a lithium supplement, and at the same time, due to the good conductivity of elemental silver, the conductivity of the material can be improved. In addition, the layered structure of the zirconium phosphate itself is conducive to lithium-ion transport, increasing the lithium-ion transport rate, and the layered structure also helps to induce the formation of sheet-like iron phosphate. By placing lithium oxide in the intercalation of zirconium phosphate, this disclosure not only effectively utilizes the interlayer voids of zirconium phosphate, but also forms iron phosphate on the outer surface of zirconium phosphate, thereby effectively preventing the lithium oxide in the layer from contacting the air, which helps to reduce the generation of residual alkali byproducts.

[0043] By preparing lithium iron phosphate from the above-mentioned modified iron phosphate material and further preparing it into a battery, the performance of the battery in terms of first-cycle coulombic efficiency and battery capacity can be improved. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a SEM image of the modified iron phosphate material prepared in Example 1 of this disclosure. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0047] The modified iron phosphate materials, lithium iron phosphate materials, their preparation methods, and applications disclosed herein will be described in detail below.

[0048] This disclosure proposes a modified iron phosphate material, which is in the form of a sheet. The modified iron phosphate material includes zirconium phosphate with a layered structure, with elemental silver and lithium oxide loaded between the layers of zirconium phosphate, and iron phosphate formed on the outer surface of zirconium phosphate.

[0049] The aforementioned elemental silver can improve the conductivity of modified iron phosphate materials; furthermore, the aforementioned elemental silver can also promote the role of lithium oxide as a lithium replenishing agent, thereby improving the lithium replenishment capacity of the material.

[0050] In some implementations, elemental silver is nanoscale.

[0051] In this disclosure, the sheet-like modified iron phosphate material can shorten the lithium-ion transport path. By introducing silver and lithium into the interlayer of zirconium phosphate, elemental silver can improve the activity of lithium oxide as a lithium supplement, and at the same time, due to the good conductivity of elemental silver, the conductivity of the material can be improved. In addition, the layered structure of the zirconium phosphate itself is conducive to lithium-ion transport, increasing the lithium-ion transport rate, and the layered structure also helps to induce the formation of sheet-like iron phosphate. It should be noted that lithium oxide, as a lithium supplement for binary lithium compounds, easily absorbs moisture and CO2 in the air, thus deteriorating into LiOH and Li2CO3. When in contact with water, it generates strongly alkaline lithium hydroxide. Therefore, when lithium oxide is used as a lithium supplement, it usually needs to be isolated from the air by means of carbon layers, etc. In this disclosure, by placing it in the interlayer of zirconium phosphate, not only is the interlayer void of zirconium phosphate effectively utilized, but also iron phosphate is formed on the outer surface of zirconium phosphate, thereby effectively preventing the lithium oxide in the layer from contacting the air, which is beneficial to reducing the generation of residual alkali byproducts.

[0052] In some embodiments, the diameter of the modified iron phosphate material can be 1μm-2μm, such as 1μm, 1.5μm, or 2μm. In some embodiments, the thickness of the modified iron phosphate material can be 180nm-220nm, such as 180nm, 190nm, 200nm, 210nm, or 220nm.

[0053] Accordingly, this disclosure also provides a method for preparing the above-mentioned modified iron phosphate material, which may include the following steps: mixing and reacting a zirconium phosphate precursor loaded with silver and organolithium in the interlayer with an iron source and a phosphate source in a solution system to obtain iron phosphate with zirconium phosphate as the core; and then calcining it in a reducing atmosphere to obtain the modified iron phosphate material.

[0054] In this disclosure, the preparation of the zirconium phosphate precursor may include: mixing and reacting silver-loaded zirconium phosphate with organolithium under acidic conditions.

[0055] The preparation of silver-loaded zirconium phosphate may include mixing a silver source, layered zirconium phosphate, and an interstitial conditioner under acidic conditions.

[0056] The diameter of the aforementioned layered zirconium phosphate can be 200nm-600nm, such as 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, or 600nm. The thickness of the layered zirconium phosphate can be 20nm-50nm, such as 20nm, 25nm, 30nm, 35nm, 40nm, or 50nm.

[0057] The mass ratio of silver source to layered zirconium phosphate can be from 0.1:100 to 3:100, such as 0.1:100, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100 or 3:100, or any other value within the range of 0.1:100 to 3:100.

[0058] The molar ratio of the gap conditioner to silver in the silver source can be from 3:1 to 6:1, such as 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, or 6:1, or any other value within the range of 3:1 to 6:1. The gap conditioner used may, by way of example but not by way of limitation, include at least one of methylamine, ethylamine, butylamine, and tetrabutylammonium bromide.

[0059] In some embodiments, the acidic conditions in the above-described process for preparing silver-loaded zirconium phosphate can be provided by a nitric acid solution, the concentration of which is exemplarily 1 mol / L. In other embodiments, other acidic substances may also be used.

[0060] In some specific embodiments, the preparation of silver-loaded zirconium phosphate can be carried out at room temperature by mixing silver and layered zirconium phosphate in a 1 mol / L nitric acid solution at a predetermined mass ratio, adding a predetermined amount of gap conditioner, stirring for 2 hours, filtering, washing, and drying to obtain silver-loaded zirconium phosphate.

[0061] As mentioned above, zirconium phosphate has abundant hydroxyl groups in its layered structure. When mixed with silver in solution and under stirring conditions, silver ions can undergo ion exchange with the hydroxyl groups in zirconium phosphate. That is, hydrogen in the hydroxyl groups is replaced by silver ions, thereby obtaining zirconium phosphate loaded with silver ions.

[0062] In this disclosure, during the preparation of the zirconium phosphate precursor, the molar ratio of organolithium to silver-supported zirconium phosphate can be from 5:100 to 10:100, such as 5:100, 5.5:100, 6:100, 6.5:100, 7:100, 7.5:100, 8:100, 8.5:100, 9:100, 9.5:100, or 10:100, or any other value within the range of 5:100 to 10:100.

[0063] The aforementioned organic lithium may, by way of example but not limitation, include at least one of lithium hydroxypyruvate hydrate, lithium citrate, lithium salicylate and lithium octanoate.

[0064] In some embodiments, the acidic conditions in the preparation process of the zirconium phosphate precursor can be provided by hydrochloric acid, and the concentration of the hydrochloric acid solution can be, for example, 1 mol / L. In other embodiments, other acidic substances may also be used.

[0065] In some specific embodiments, the zirconium phosphate precursor can be prepared by placing silver-loaded zirconium phosphate in deionized water, adding 1 mol / L hydrochloric acid, adding organic lithium, stirring continuously for 1 hour, filtering, and washing to obtain the zirconium phosphate precursor.

[0066] Continuing from the above, when organolithium is reacted with silver-loaded zirconium phosphate, the organolithium can interact or attract with the interlayer hydroxyl groups of zirconium phosphate, thereby introducing them into the interlayer of zirconium phosphate, so that the interlayer of zirconium phosphate contains both silver ions and organolithium.

[0067] In this disclosure, the ratio of zirconium phosphate precursor to iron source can be from 2g:1mol to 5g:1mol, such as 2g:1mol, 2.5g:1mol, 3g:1mol, 3.5g:1mol, 4g:1mol, 4.5g:1mol or 5g:1mol, or any other value within the range of 2g:1mol to 5g:1mol.

[0068] The molar ratio of phosphate ions in the phosphate source to iron ions in the iron source can be from 0.98:1 to 1.05:1, such as 0.98:1, 0.99:1, 1.00:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1 or 1.05:1, or any other value within the range of 0.98:1 to 1.05:1.

[0069] In some embodiments, the iron ions in the iron source can be ferric ions (Fe3+). In other embodiments, the iron ions in the iron source can be ferrous ions (Fe2+). If ferrous ions are used, an oxidizing agent is required to oxidize them to ferric ions. In some specific embodiments, the iron source can, by way of example but not by limitation, be at least one of ferric nitrate and ferric chloride.

[0070] Phosphate sources may include, by example but not by limitation, at least one of ammonium hydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate.

[0071] In some embodiments, the iron source can be prepared into an iron source solution and the phosphate source can be prepared into a phosphate solution. Then, the zirconium phosphate precursor loaded with silver and organolithium in the interlayer can be mixed and reacted with the iron source solution and the phosphate solution.

[0072] The concentration of the iron source solution is, but not limited to, 1 mol / L. The concentration of the phosphate solution is also, but not limited to, 1 mol / L. It should be noted that the concentrations of the iron source solution and the phosphate solution can be adjusted according to actual conditions, and are not specified here.

[0073] For reference, the pH value of the reaction between the zirconium phosphate precursor loaded with silver and organolithium in the interlayer and the iron source and phosphate source can be 1.2-2.2, such as 1.2, 1.4, 1.6, 1.8, 2.0, or 2.2, or any other value within the range of 1.2-2.2. Exemplarily, the pH adjuster used to adjust the pH value may include at least one of ammonia, NaOH, and urea. In some specific embodiments, ammonia may be used to adjust the pH value. The concentration of the ammonia used may be, for example, 1 mol / L, and may also be adjusted as needed.

[0074] The reaction temperature of the zirconium phosphate precursor loaded with silver and organolithium in the interlayer with the iron source and phosphate source can be 60℃-90℃, such as 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃, or any other value in the range of 60℃-90℃.

[0075] The reaction temperature of the zirconium phosphate precursor loaded with silver and organolithium in the interlayer with the iron source and phosphate source can be 2h-5h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, or any other value in the range of 2h-5h.

[0076] In some embodiments, the reaction of the zirconium phosphate precursor loaded with silver and organolithium in the interlayer with the iron source and the phosphate source is carried out under stirring conditions. The stirring speed can be, for example, 500 rpm to 900 rpm, such as 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm or 900 rpm.

[0077] After the reaction is complete, iron phosphate with zirconium phosphate as the core can be obtained by filtration, washing and drying.

[0078] Continuing from the above, due to the high negative charge density on the surface of zirconium phosphate, it can adsorb ferric ions and induce phosphate ions to react with it to form iron phosphate, which can form iron phosphate with zirconium phosphate core loaded with silver and organolithium in the interlayer.

[0079] In this disclosure, the calcination temperature can be 500℃-800℃, such as 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, or any other value within the range of 500℃-800℃.

[0080] The calcination time can be 3h-6h, such as 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, or any other value within the range of 3h-6h.

[0081] The reducing atmosphere used for calcination can be, by way of example but not limited to, a carbon monoxide atmosphere or a hydrogen atmosphere.

[0082] Continuing from the above, through the calcination treatment, silver ions in zirconium phosphate are reduced to elemental silver in situ, and organolithium is calcined to obtain lithium oxide, thus forming elemental silver and lithium oxide between the zirconium phosphate layers. The metallic silver nanoparticles formed by the calcination treatment are small enough to enable lithium oxide to play its role as a lithium supplement agent, improving the lithium supplementation capacity; at the same time, metallic silver can also improve the conductivity of the material.

[0083] In addition, this disclosure also provides a lithium iron phosphate material, the raw materials for which the above-mentioned modified iron phosphate material is included.

[0084] In some embodiments, the lithium iron phosphate material is carbon-coated lithium iron phosphate.

[0085] Accordingly, this disclosure also provides a method for preparing the above-mentioned lithium iron phosphate material, which may include, for example, the following steps: mixing modified iron phosphate material, carbon source and lithium source, and calcining.

[0086] When lithium iron phosphate materials have a carbon coating layer, the modified lithium iron phosphate material is mixed with a lithium source and a carbon source and then calcined during preparation.

[0087] For reference, the lithium source described above may, but is not limited to, be lithium carbonate, and the carbon source may, but is not limited to, be glucose, etc.

[0088] In some specific embodiments, lithium iron phosphate materials can be prepared by referring to the following method: The modified iron phosphate material provided in this disclosure is mixed with Li2CO3 at a molar ratio of 1.02:1, and glucose is added, along with anhydrous ethanol. The glucose content is 5% of the total mass of the modified iron phosphate material and Li2CO3. After ball milling for 4 hours, the mixture is dried at 80°C for 12 hours. After being removed and ground uniformly again, it is placed under nitrogen protection and calcined at 650°C for 6 hours to obtain carbon-coated lithium iron phosphate material. It should be noted that in other embodiments, commonly used lithium sources, carbon sources, and solvents for preparing lithium iron phosphate materials can also be used, and the process conditions can be adjusted according to actual conditions.

[0089] Furthermore, this disclosure also provides a battery whose raw materials include the aforementioned lithium iron phosphate material.

[0090] It should be noted that the battery fabrication process can refer to the conventional technology for battery fabrication using lithium iron phosphate as the cathode material, and will not be elaborated or limited here.

[0091] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0092] Example 1

[0093] This embodiment provides a modified iron phosphate material, the preparation process of which includes:

[0094] S1: In a 1 mol / L nitric acid solution, silver and layered zirconium phosphate were mixed at a mass ratio of 1:100. Ethylamine was added as an interstitial regulator. The molar ratio of ethylamine to silver was 4:1. The mixture was stirred at room temperature for 2 hours. After filtration, washing, and drying, silver-loaded zirconium phosphate was obtained.

[0095] S2: Place the above-mentioned silver-loaded zirconium phosphate in deionized water, add 1 mol / L hydrochloric acid, mix lithium salicylate and silver-loaded zirconium phosphate at a molar ratio of 7:100, stir continuously for 1 hour, and obtain a zirconium phosphate precursor with interlayer silver and organolithium after filtration, washing and drying.

[0096] S3: The zirconium phosphate precursor loaded with silver and organolithium was placed in water, and 1 mol / L ferric nitrate solution was added. The molar ratio of zirconium phosphate to ferric nitrate was 4 g: 1 mol. After stirring evenly, 1 mol / L ammonium hydrogen phosphate solution was added, while ensuring that the molar ratio of phosphate to ferric iron was 1:1. The pH was adjusted to 1.2-2.2 with ammonia water. The reaction was carried out at a stirring speed of 700 rpm and a reaction temperature of 85℃ for 4 h. The precipitate was filtered, washed, and dried to obtain ferric phosphate with zirconium phosphate as the core.

[0097] S4: The above-mentioned zirconium phosphate-based iron phosphate was calcined at 700℃ in a hydrogen atmosphere for 6 hours to obtain the modified iron phosphate material. Its SEM image is shown below. Figure 1 As shown.

[0098] The modified iron phosphate material has a diameter of approximately 1.5 μm and a thickness of approximately 200 nm.

[0099] Example 2

[0100] The difference between this embodiment and Embodiment 1 is that in S1, the mass ratio of silver to layered zirconium phosphate is 3:100. In S2, the molar ratio of lithium salicylate to silver-loaded zirconium phosphate is 5:100.

[0101] The remaining steps and conditions are the same as in Example 1.

[0102] Example 3

[0103] The difference between this embodiment and Embodiment 1 is that: in S1, the mass ratio of silver to layered zirconium phosphate is 0.1:100. In S2, the molar ratio of lithium salicylate to silver-loaded zirconium phosphate is 10:100.

[0104] The remaining steps and conditions are the same as in Example 1.

[0105] Example 4

[0106] The difference between this embodiment and Example 1 is that in S3, the molar ratio of zirconium phosphate to ferric nitrate is 2g:1mol.

[0107] The remaining steps and conditions are the same as in Example 1.

[0108] Example 5

[0109] The difference between this embodiment and Example 1 is that in S3, the molar ratio of zirconium phosphate to ferric nitrate is 5g:1mol.

[0110] The remaining steps and conditions are the same as in Example 1.

[0111] Example 6

[0112] This embodiment provides a modified iron phosphate material, the preparation process of which includes:

[0113] S1: In a 1 mol / L nitric acid solution, silver and layered zirconium phosphate were mixed in a mass ratio of 1.5:100. Tetrabutylammonium bromide was added as an interstitial regulator. The molar ratio of tetrabutylammonium bromide to silver was 3:1. The mixture was stirred at room temperature for 2 hours. After filtration, washing, and drying, silver-loaded zirconium phosphate was obtained.

[0114] S2: Place the above-mentioned silver-loaded zirconium phosphate in deionized water, add 1 mol / L hydrochloric acid, mix lithium citrate and silver-loaded zirconium phosphate at a molar ratio of 5:100, stir continuously for 1 hour, and obtain a zirconium phosphate precursor with interlayer silver and organolithium after filtration, washing and drying.

[0115] S3: The zirconium phosphate precursor loaded with silver and organolithium was placed in water, and a 1 mol / L ferric chloride solution was added. The molar ratio of zirconium phosphate to ferric chloride was 3.5 g: 1 mol. After stirring evenly, a 1 mol / L ammonium phosphate solution was added, while ensuring that the molar ratio of phosphate to ferric iron was 0.98:1. The pH was adjusted to 1.2-2.2 with NaOH solution. The reaction was carried out at a stirring speed of 500 rpm and a reaction temperature of 60℃ for 5 h. The precipitate was filtered, washed, and dried to obtain ferric phosphate with zirconium phosphate as the core.

[0116] S4: The above-mentioned iron phosphate with zirconium phosphate as the core was calcined in a carbon monoxide atmosphere at 500°C for 6 hours to obtain the modified iron phosphate material.

[0117] Example 7

[0118] This embodiment provides a modified iron phosphate material, the preparation process of which includes:

[0119] S1: In a 1 mol / L nitric acid solution, silver and layered zirconium phosphate were mixed at a mass ratio of 2:100. Butylamine was added as an interstitial regulator. The molar ratio of butylamine to silver was 6:1. The mixture was stirred at room temperature for 2 hours. After filtration, washing, and drying, silver-loaded zirconium phosphate was obtained.

[0120] S2: Place the above-mentioned silver-loaded zirconium phosphate in deionized water, add 1 mol / L hydrochloric acid, mix lithium octoate and silver-loaded zirconium phosphate at a molar ratio of 10:100, stir continuously for 1 hour, and obtain a zirconium phosphate precursor with interlayer silver and organolithium after filtration, washing and drying.

[0121] S3: The zirconium phosphate precursor loaded with silver and organolithium was placed in water, and a 1 mol / L ferric chloride solution was added. The molar ratio of zirconium phosphate to ferric chloride was 4.5 g: 1 mol. After stirring evenly, a 1 mol / L ammonium dihydrogen phosphate solution was added, while ensuring that the molar ratio of phosphate to ferric iron was 1.05:1. The pH was adjusted to 1.2-2.2 with urea solution. The reaction was carried out at a stirring speed of 900 rpm and a reaction temperature of 90℃ for 2 h. The precipitate was filtered, washed, and dried to obtain ferric phosphate with zirconium phosphate as the core.

[0122] S4: The above-mentioned iron phosphate with zirconium phosphate as the core is calcined in a hydrogen atmosphere at 800°C for 6 hours to obtain the modified iron phosphate material.

[0123] Example 8

[0124] This embodiment provides a carbon-coated lithium iron phosphate material, the preparation process of which is as follows: The modified iron phosphate material provided in Example 1 is mixed with Li2CO3 at a molar ratio of 1.02:1 and glucose is added, and anhydrous ethanol is added. The glucose is 5% of the total mass of the modified iron phosphate material and Li2CO3. After ball milling for 4 hours, it is dried at 80°C for 12 hours. After being taken out and ground evenly again, it is placed under nitrogen protection and calcined at 650°C for 6 hours.

[0125] Comparative Example 1

[0126] The difference between this comparative example and Example 1 is as follows:

[0127] S1: Silver and layered zirconium phosphate were mixed in a 1 mol / L nitric acid solution at a mass ratio of 1:100 and stirred at room temperature for 2 h. After filtration, washing and drying, silver-loaded zirconium phosphate was obtained.

[0128] S2: Same as Example 1.

[0129] S3: Same as Example 1.

[0130] S4: Same as Example 1.

[0131] That is, no gap conditioner was used in this comparative example.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is as follows:

[0134] S1: None.

[0135] S2: None.

[0136] S3: Mix 1 mol / L ferric nitrate solution and 1 mol / L ammonium hydrogen phosphate solution to ensure that the molar ratio of phosphate to ferric iron is 1:1. Adjust the pH to 1.2-2.2 with ammonia water. React for 4 hours with a stirring speed of 700 rpm and a reaction temperature of 85℃. Filter, wash and dry the precipitate.

[0137] S4: Same as Example 1.

[0138] That is, zirconium phosphate was not used in this comparative example.

[0139] Comparative Example 3

[0140] The difference between this comparative example and Example 1 is as follows:

[0141] S1: None.

[0142] S2: Place the nano-layered zirconium phosphate in deionized water, add 1 mol / L hydrochloric acid, mix lithium salicylate and zirconium phosphate at a molar ratio of 7:100, stir continuously for 1 h, and obtain the zirconium phosphate precursor with interlayer loaded with organic lithium after filtration, washing and drying.

[0143] S3 is the same as in Example 1.

[0144] S4 is the same as in Example 1.

[0145] That is, no silver was used in this comparative example.

[0146] Comparative Example 4

[0147] The difference between this comparative example and Example 1 is as follows:

[0148] S1: Same as Example 1.

[0149] S2: None.

[0150] S3: Place the silver-loaded zirconium phosphate in water, then add a 1 mol / L ferric nitrate solution. The molar ratio of zirconium phosphate to ferric nitrate is 4 g: 1 mol. After stirring evenly, add a 1 mol / L ammonium hydrogen phosphate solution, while ensuring that the molar ratio of phosphate to ferric iron is 1:1. Adjust the pH to 1.2-2.2 with ammonia water. Stir at 700 rpm and at a reaction temperature of 85℃ for 4 hours.

[0151] S4: Same as Example 1.

[0152] That is, no organic lithium was used in this comparative example.

[0153] Test case

[0154] The modified iron phosphate materials of Examples 1-7 and the iron phosphate materials of Comparative Examples 1-4 were all prepared into carbon-coated lithium iron phosphate materials according to the method and conditions of Example 8, and further prepared into coin cells by the following methods: the binder (polyvinylidene fluoride), the conductive agent (acetylene black) and LiFePO4 were mixed in a mass ratio of 1:1:8, N-methylpyrrolidone was added to make a slurry, which was uniformly coated on aluminum foil, and after vacuum drying, it was taken out, rolled and punched into a circular electrode sheet, and assembled into coin cells in a glove box.

[0155] For the constant current charge-discharge cycle test of the above-mentioned button batteries, the charge-discharge voltage was 2.5 to 4.2V.

[0156] In addition, the rate specific capacity at 1C, 3C and 10C, as well as the first discharge specific capacity and first coulombic efficiency at 1C, were tested; and the conductivity of the material was tested by direct voltammetry.

[0157] The test results are shown in Table 1.

[0158] Table 1 Test Results

[0159]

[0160] Comparing Examples 1 and 2, it can be seen that increasing the silver loading of zirconium phosphate improves conductivity, but reduces the lithium replenishment effect due to the reduced organic lithium loading, resulting in a relative decrease in coulombic efficiency and battery capacity in the first week.

[0161] Comparing Examples 1 and 3, it can be seen that reducing the silver loading of zirconium phosphate will relatively reduce the conductivity, but due to the increased loading of organic lithium, the lithium replenishment effect is improved, resulting in a relative increase in the first-week coulombic efficiency and battery capacity.

[0162] A comparison of Examples 1 and 4 shows that a decrease in zirconium phosphate content leads to a relative decrease in conductivity and lithium replenishment effect.

[0163] A comparison of Examples 1 and 5 shows that increasing the zirconium phosphate content will reduce the capacity.

[0164] By comparing Example 1 and Comparative Example 1, it can be seen that the absence of gap conditioner leads to a reduction in interlayer intercalation material, resulting in poor battery performance.

[0165] By comparing Example 1 and Comparative Example 2, it can be seen that the battery performance is poor without the use of zirconium phosphate.

[0166] Comparing Example 1 and Comparative Example 3, it can be seen that without the use of silver, the conductivity is low and the lithium replenishment effect is poor.

[0167] By comparing Example 1 and Comparative Example 4, it can be seen that although the conductivity is better when only silver ions are used and no organic lithium is added, the initial coulombic efficiency is poor.

[0168] Industrial applicability

[0169] The sheet-like modified iron phosphate material disclosed herein possesses high conductivity and lithium-ion transport speed, and can reduce the generation of residual alkali. Using this modified iron phosphate material to prepare a lithium iron phosphate cathode material and further fabricating a battery can improve the battery's performance in terms of first-cycle coulombic efficiency and battery capacity.

Claims

1. A modified iron phosphate material, characterized in that, The modified iron phosphate material is in the form of a sheet, and includes zirconium phosphate with a layered structure. Elemental silver and lithium oxide are loaded between the layers of the zirconium phosphate, and iron phosphate is formed on the outer surface of the zirconium phosphate. The preparation of the modified iron phosphate material includes: mixing and reacting a zirconium phosphate precursor with interlayer silver and organolithium with an iron source and a phosphate source in a solution system to obtain iron phosphate with zirconium phosphate as the core; calcining the iron phosphate with zirconium phosphate as the core in a reducing atmosphere to obtain the modified iron phosphate material; the preparation of the zirconium phosphate precursor with interlayer silver and organolithium includes: mixing and reacting the silver-loaded zirconium phosphate and organolithium under acidic conditions; the preparation of the silver-loaded zirconium phosphate includes: mixing the silver source, layered zirconium phosphate, and interstitial regulator under acidic conditions.

2. The modified iron phosphate material according to claim 1, characterized in that, The modified iron phosphate material has at least one of the following characteristics: Feature 1: The diameter of the modified iron phosphate material is 1μm-2μm; Feature 2: The thickness of the modified iron phosphate material is 180nm-220nm.

3. A method for preparing the modified iron phosphate material as described in claim 1 or 2, characterized in that, Includes the following steps: Zirconium phosphate precursor with silver and organolithium loaded in the interlayer is mixed and reacted with iron source and phosphate source in solution system to obtain iron phosphate with zirconium phosphate core; the iron phosphate with zirconium phosphate core is calcined in reducing atmosphere to obtain the modified iron phosphate material. The preparation of the zirconium phosphate precursor loaded with silver and organolithium in the interlayer comprises: mixing and reacting the silver-loaded zirconium phosphate and organolithium under acidic conditions; the preparation of the silver-loaded zirconium phosphate comprises: mixing the silver source, layered zirconium phosphate and interstitial regulator under acidic conditions.

4. The preparation method according to claim 3, characterized in that, The ratio of the zirconium phosphate precursor to the iron source is from 2 g:1 mol to 5 g:1 mol; and / or, the molar ratio of phosphate ions in the phosphate source to iron ions in the iron source is from 0.98:1 to 1.05:

1.

5. The preparation method according to claim 3 or 4, characterized in that, The iron ions in the iron source are ferric ions (Fe3+).

6. The preparation method according to claim 5, characterized in that, The iron source includes at least one of ferric nitrate and ferric chloride.

7. The preparation method according to claim 3, characterized in that, The phosphate source includes at least one of ammonium hydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate.

8. The preparation method according to claim 3, characterized in that, Mixed reactions include at least one of the following characteristics: Feature 1: The reaction pH value is 1.2-2.2; Feature 2: The reaction temperature is 60℃-90℃; Feature 3: The reaction time is 2-5 hours; Feature 4: The reaction is carried out under stirring conditions.

9. The preparation method according to claim 8, characterized in that, pH adjusters used to adjust pH value include at least one of ammonia, NaOH, and urea. And / or, the stirring speed is 500rpm-900rpm.

10. The preparation method according to claim 3, characterized in that, The molar ratio of the organolithium to the silver-loaded zirconium phosphate is 5:100 to 10:

100.

11. The preparation method according to claim 3, characterized in that, The organolithium compounds include at least one of lithium hydroxypyruvate hydrate, lithium citrate, lithium salicylate, and lithium octanoate.

12. The preparation method according to claim 3, characterized in that, The acidic conditions are provided by hydrochloric acid.

13. The preparation method according to claim 3, characterized in that, The layered zirconium phosphate has at least one of the following characteristics: Feature 1: The diameter of the layered zirconium phosphate is 200nm-600nm; Feature 2: The thickness of the layered zirconium phosphate is 20nm-50nm.

14. The preparation method according to claim 3, characterized in that, The mass ratio of the silver source to the layered zirconium phosphate is from 0.1:100 to 3:

100.

15. The preparation method according to claim 3, characterized in that, The molar ratio of the gap conditioner to the silver element in the silver source is 3:1 to 6:

1.

16. The preparation method according to claim 3, characterized in that, The gap conditioner includes at least one of methylamine, ethylamine, butylamine, and tetrabutylammonium bromide.

17. The preparation method according to claim 3, characterized in that, The acidic conditions in the preparation of silver-loaded zirconium phosphate are provided by nitric acid.

18. The preparation method according to claim 3, characterized in that, The calcination temperature is 500℃-800℃; and / or the calcination time is 3h-6h.

19. A lithium iron phosphate material, characterized in that, The raw materials for preparing the lithium iron phosphate material include the modified iron phosphate material as described in claim 1 or 2.

20. The lithium iron phosphate material according to claim 19, characterized in that, The lithium iron phosphate material is carbon-coated lithium iron phosphate.

21. A method for preparing lithium iron phosphate material as described in claim 19 or 20, characterized in that, Includes the following steps: The modified iron phosphate material was mixed with a lithium source and then calcined.

22. The preparation method according to claim 21, characterized in that, The modified iron phosphate material was mixed with a lithium source and a carbon source and then calcined.

23. A battery, characterized in that, The raw materials for preparing the battery include the lithium iron phosphate material as described in claim 19 or 20.

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