Lithium manganese iron phosphate precursor, and preparation method therefor and use thereof

Abstract

A lithium manganese iron phosphate precursor, and a preparation method therefor and the use thereof. The general chemical formula of the lithium manganese iron phosphate precursor is MnxFeyM1-x-yPO7 / 2, wherein x is 0.5-0.7, y is 0.3-0.5, and M is a doped metal element. The lithium manganese iron phosphate precursor has a relatively small particle size, uniform composition and a high tap density, can solve the problem of the generation of a large amount of ammonia gas during the blending and sintering of a lithium manganese iron phosphate precursor and lithium due to the fact that the precursor has a large particle size and a low tap density and contains an ammonium radical component, thereby significantly improving the compaction density and electrochemical performance of the lithium manganese iron phosphate positive electrode material.

Description

A lithium manganese iron phosphate precursor and its preparation method and application Technical Field

[0001] The present application relates to the field of battery technology, for example, a lithium manganese iron phosphate precursor and its preparation method and application. Background Art

[0002] LFP (LiFePO4) is widely used in power tools and energy storage due to its safety, environmental friendliness, long cycle life, and wide operating temperature range. However, its low capacity and operating voltage result in low energy density. Therefore, there is an urgent need for a material with higher energy density and comparable cycle performance to LFP. Lithium manganese iron phosphate is a good choice. It partially replaces Fe with Mn, increasing the discharge platform voltage (from 3.4V to 4.1V) and energy density (15%-20%). It also offers advantages such as long cycle life, high thermal stability, and strong safety.

[0003] Lithium manganese iron phosphate and lithium iron phosphate are both polyanionic phosphates with similar preparation processes. The solid-phase method is simpler and more suitable for industrial production, while the liquid-phase method is more complex but offers better product performance. However, LFP already has a mature FePO4 precursor process, while the LFMP industry is still in its early stages and lacks a precursor, raising technical barriers.

[0004] For example, CN115974681A discloses a method for cyclically preparing manganese iron oxalate, in which manganese and iron sulfates are co-precipitated with oxalate to obtain a manganese iron oxalate precursor, which is then sand-milled, sprayed, and sintered with a phosphorus source, a lithium source, and a carbon source to obtain a lithium manganese iron phosphate positive electrode material. However, this method produces severe gas, resulting in a low compaction density of the material.

[0005] CN111268664A discloses a ferromanganese phosphate intermediate, lithium ferromanganese phosphate and their manufacturing methods. The preparation method of the ferromanganese phosphate intermediate is to simultaneously add a ferromanganese mixed solution, a phosphorus source, a nitrogen source and a pH regulator to a reactor for precipitation. This method adds a variety of chemical reagents, which easily introduces impurities during precipitation. The prepared precursor is flaky, has a large particle size, and has a low tap density. In addition, ammonia is generated during the lithium sintering process, resulting in too low a compacted density of the LFMP.

[0006] Moreover, due to the K of Fe3(PO4)2 sp =10 -36 , K of Mn3(PO4)2 sp =1.3×10 -32 , Fe 2+ and Mn 2+ With PO4 3-The solubility product constants of Fe and Fe are very small and differ by four orders of magnitude, which makes it difficult to precipitate Fe with phosphate. 2+ and Mn 2+ When the precipitate is not proportional, it is easy to precipitate out of proportion, and often due to high supersaturation, it leads to problems such as excessive growth rate and large particle size.

[0007] Based on the above research, it is necessary to provide a lithium iron manganese phosphate precursor, which has a high tap density. When the precursor is sintered with lithium, less gas is produced, and the prepared lithium iron manganese phosphate has a high compaction density.

[0008] Summary of the Invention

[0009] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0010] The present application provides a lithium iron manganese phosphate precursor and its preparation method and application. The lithium iron manganese phosphate precursor has a small particle size, uniform composition and high tap density, which can solve the problem that the lithium iron manganese phosphate precursor has large particle size, low tap density and contains ammonium radical components, resulting in a large amount of ammonia gas generated during sintering of the precursor with lithium, thereby significantly improving the compaction density of the lithium iron manganese phosphate positive electrode material.

[0011] In the first aspect, the present application provides a lithium manganese iron phosphate precursor, the chemical formula of the lithium manganese iron phosphate precursor is Mn x Fe y M 1-x-y PO 7 / 2 , where x is 0.5-0.7, y is 0.3-0.5, and M is the doped metal element.

[0012] The lithium iron phosphate precursor described in the present application is manganese iron pyrophosphate rather than ammonium iron manganese phosphate, which can avoid the generation of reducing gas in the preparation process of the lithium iron manganese phosphate positive electrode material. Since lithium iron manganese phosphate is easily sintered in a reducing atmosphere to produce magnetic foreign matter such as Fe2P and Mn2P, which is harmful to battery performance, the precursor of the present application has uniform composition, high tap density, and does not contain ammonium ions, thereby avoiding the generation of reducing gases such as ammonia during sintering of the precursor material, thereby improving the compaction density and electrochemical performance of the lithium iron manganese phosphate positive electrode material.

[0013] The x is 0.5-0.7, for example, 0.5, 0.6 or 0.7, and the y is 0.3-0.5, for example, 0.3, 0.4 or 0.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In one embodiment, the M includes any one or a combination of at least two of Mg, Ti, Nb, Zr or Cu.

[0015] In a second aspect, the present application provides a method for preparing the lithium manganese iron phosphate precursor as described in the first aspect, the preparation method comprising the following steps:

[0016] (1) feeding a metal salt solution, a pH regulator, and a phosphate solution into a bottom liquid to perform a coprecipitation reaction to obtain an intermediate product;

[0017] The metal salt solution includes manganese salt and iron salt, or manganese salt, iron salt and M salt;

[0018] (2) Sintering the intermediate product of step (1) to obtain the lithium manganese iron phosphate precursor.

[0019] The present application first prepares the intermediate product ammonium manganese iron phosphate through a coprecipitation reaction, and then sintering it to prepare manganese iron pyrophosphate. In the sintering stage of step (2), NH3 and H2O are removed to avoid gas production during the preparation stage of the lithium manganese iron phosphate positive electrode material, which affects its compaction density and electrochemical performance.

[0020] In one embodiment, during the feeding process of step (1), the pH of the coprecipitation reaction system gradually decreases.

[0021] In one embodiment, the pH of the base solution in step (1) is 7-8, for example, 7, 7.2, 7.4, 7.6, 7.8 or 8, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] The coprecipitation reaction of the present application is not carried out at a fixed pH, but under gradually decreasing pH conditions. The initial pH of the coprecipitation system is the pH of the base liquid. As the feeding proceeds, the pH of the system is gradually reduced by controlling the feeding rate of the pH regulator. The purpose is to make the pH of the initial coprecipitation reaction 7-8, which can promote the ionization of phosphates such as NH4H2PO4 to PO4 3- and NH 4+ , so that a large amount of nucleation is formed at the beginning of the reaction, and the pH is gradually reduced during the reaction to reduce the ionized PO4 3- The amount of crystalline solids can be increased to reduce the growth rate of the crystal nucleus and avoid the problem of excessive growth rate and large particle size.

[0023] In one embodiment, after the feeding in step (1) is completed, the pH of the coprecipitation reaction system is 5-6, for example, 5, 5.5 or 6, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] After feeding, the pH of the material needs to be controlled in a weakly acidic environment of less than 7, so as to promote the ionization of the pH regulator ammonia water, increase the concentration of ammonium ions in the system, participate in coprecipitation, and promote the precipitation of ions in equal proportions. However, it is not suitable to coprecipitate in an overly acidic environment (pH < 5), otherwise it will cause Fe 2+ Preferential precipitation produces Fe3(PO4)2·8H2O impurity phase.

[0025] In one embodiment, the time to complete the feeding of step (1) is 2-4 hours, for example, 2.5 hours, 3.0 hours or 3.5 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In one embodiment, after the feeding in step (1) is completed, aging, washing and vacuum drying are performed to obtain the intermediate product.

[0027] In one embodiment, the number of washings is 3-5 times, for example, 3 times, 4 times or 5 times, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] In one embodiment, the vacuum drying temperature is 60-80°C, for example, 60°C, 70°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] In one embodiment, the coprecipitation reaction in step (1) is carried out in a reactor, and the amount of the bottom liquid added to the reactor accounts for 1 / 3-2 / 3 of the volume of the reactor.

[0030] In one embodiment, the base liquid in step (1) comprises water.

[0031] The base liquid in step (1) of the present application is mainly water, and ammonium dihydrogen phosphate, a chelating agent and ammonia water are also added.

[0032] The bottom liquid of the present application mainly includes water. The ratio of the bottom liquid in the reactor is the ratio of the water in the bottom liquid in the reactor. Therefore, the present application adds water accounting for one-third to two-thirds of the volume of the reactor, which can dilute the concentration of ions during coprecipitation and reduce the growth rate of crystal nuclei. The complexing agent in the bottom liquid can prevent Fe from forming under weakly acidic conditions. 2+ and Mn 2+ Oxidation, but also with Fe 2+ and Mn 2+ Contact complexation forms an intermediate, which is then desorbed to form a precipitate under the action of phosphate ions, reducing the growth rate.

[0033] In one embodiment, the concentration of phosphate in the base solution of step (1) is 0-0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] In one embodiment, the concentration of the complexing agent in the base solution of step (1) is 0-0.1 mol / L, for example, 0.01 mol / L, 0.05 mol / L or 0.1 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] In one embodiment, the complexing agent includes any one of ammonium citrate, ammonium tartrate, ammonium ethylenediaminetetraacetate or ammonium oxalate, or a combination of at least two thereof, and may be ammonium citrate and / or ammonium tartrate.

[0036] In one embodiment, the pH of the metal salt solution in step (1) is 1-4, for example, 1, 2, 3 or 4, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] The pH of the metal salt solution of this application is within the range of 1-4, which can prevent Fe 2+ Hydrolysis generates Fe(OH)2, thus preventing the problem of uneven product composition.

[0038] In one embodiment, the concentration of total metal ions in the metal salt solution of step (1) is 0.5-4 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] In one embodiment, the concentration of the phosphate solution in step (1) is 0.5-3 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L or 3 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] In one embodiment, the concentration of the pH adjuster in step (1) is 10-28%, for example, 10%, 15%, 20%, 25% or 28%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] In one embodiment, the phosphate solution in step (1) includes any one of NH4H2PO4, (NH4)2HPO4 or (NH4)3PO4 or a combination of at least two thereof, and NH4H2PO4 may be selected.

[0042] In one embodiment, the pH adjuster in step (1) includes any one of ammonia water, urea or ammonium carbonate, or a combination of at least two of them, and ammonia water can be selected.

[0043] The pH regulator of the present application can be ammonia water. Since ammonia water is not only a pH regulator, under the weakly acidic coprecipitation conditions of the present application, the NH 4+ Also involved in precipitation, NH 4+ Always keep excess, and Fe 2+ and Mn 2+ Co-precipitation can not only slow down the precipitation rate, but also allow Fe 2+ and Mn 2+ The mixture is uniformly precipitated in proportion, and therefore, the ammonia water and the weakly acidic co-precipitation conditions of the present application play a cooperative role.

[0044] In one embodiment, the manganese salt in step (1) includes any one of MnSO4, MnCl2, Mn(NO3)2 or Mn(CH3COO)2, or a combination of at least two thereof, and MnSO4 may be selected.

[0045] In one embodiment, the iron salt in step (1) includes any one of FeSO4, FeCl2, Fe(NO3)2 or Fe(CH3COO)2 or a combination of at least two thereof, and FeSO4 may be selected.

[0046] In one embodiment, the M salt in step (1) includes any one of MgSO4, TiOSO4, Nb2O4SO4, Zr(SO4)2 or CuSO4, or a combination of at least two thereof.

[0047] In one embodiment, the coprecipitation reaction in step (1) is carried out in a nitrogen atmosphere, wherein the flow rate of nitrogen is 1-3 L / min, for example, 1 L / min, 2 L / min or 3 L / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] In one embodiment, the coprecipitation reaction in step (1) is carried out under stirring, and the stirring speed is 300-600 r / min, for example, it can be 300 r / min, 400 r / min, 500 r / min or 600 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] In one embodiment, the temperature of the coprecipitation reaction in step (1) is 20-60°C, for example, 20°C, 40°C or 60°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] The present application does not impose any specific limitation on the feed rate of the raw materials. Those skilled in the art can make reasonable choices based on the desired morphology. For example, using room temperature as the co-precipitation temperature is beneficial to reducing the size of the precipitated product particles. When preferential oriented growth is required, the temperature can be appropriately increased. When secondary spherical particles are required, the feed rate can be reduced, and the stirring rate and oxidation degree can be increased.

[0051] In one embodiment, the sintering temperature in step (2) is 500-600°C, for example, 500°C, 550°C or 600°C, and the sintering time is 2-4h, for example, 2h, 3h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] In one embodiment, the sintering in step (2) is performed in a nitrogen atmosphere.

[0053] In one embodiment, the preparation method comprises the following steps:

[0054] (1) feeding a metal salt solution having a total metal ion concentration of 0.5-4 mol / L and a pH of 1-4, a pH regulator having a concentration of 10-28%, and a phosphate solution having a concentration of 0.5-3 mol / L into the bottom liquid at a nitrogen flow rate of 1-3 L / min, a stirring speed of 300-600 r / min, and a temperature of 20-60° C., so that the pH of the coprecipitation reaction system is gradually reduced from 7-8. After the feeding is completed, the pH of the coprecipitation reaction system is reduced to 5-6. After the feeding is completed within 2-4 hours, the feeding is aged, washed 3-5 times, and vacuum dried at 60-80° C. to obtain an intermediate product;

[0055] The coprecipitation reaction is carried out in a reactor, and the amount of the bottom liquid added to the reactor accounts for 1 / 3-2 / 3 of the volume of the reactor; the pH of the bottom liquid is 7-8, and it includes water, ammonium dihydrogen phosphate, a complexing agent and ammonia water;

[0056] The metal salt solution includes manganese salt, iron salt and M salt;

[0057] (2) Sintering the intermediate product of step (1) at a temperature of 500-600° C. for 2-4 hours in a nitrogen atmosphere to obtain the lithium manganese iron phosphate precursor.

[0058] In a third aspect, the present application provides a lithium iron manganese phosphate positive electrode material, which is prepared using a lithium source and the lithium iron manganese phosphate precursor as described in the first aspect.

[0059] In a fourth aspect, the present application provides a battery, comprising the lithium manganese iron phosphate positive electrode material as described in the first aspect.

[0060] Compared with the related art, this application has the following beneficial effects:

[0061] The present application uses ferromanganese pyrophosphate instead of ammonium ferromanganese phosphate as the precursor of lithium iron manganese phosphate, thereby avoiding the generation of reducing gas in the preparation process of the lithium iron manganese phosphate positive electrode material, thereby avoiding the generation of impurities such as magnetic foreign matter Fe2P and Mn2P. Therefore, the precursor of the present application has uniform composition, high tap density, and does not contain ammonium ions, thereby avoiding the generation of reducing gas such as ammonia during sintering of the precursor material, thereby improving the compaction density and electrochemical performance of the lithium iron manganese phosphate positive electrode material.

[0062] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0064] FIG1 is a SEM image of the intermediate product described in Example 1 of the present application;

[0065] FIG2 is an XRD pattern of the intermediate product described in Example 1 of the present application;

[0066] FIG3 is a thermogravimetric curve of the intermediate product described in Example 1 of the present application;

[0067] FIG4 is an XRD pattern of the lithium manganese iron phosphate precursor described in Example 1 of the present application;

[0068] FIG5 is a SEM image of the intermediate product described in Example 2 of the present application;

[0069] FIG6 is an XRD pattern of the intermediate product described in Example 2 of the present application;

[0070] FIG7 is a SEM image of the intermediate product described in Example 3 of the present application;

[0071] FIG8 is an XRD pattern of the intermediate product described in Example 3 of the present application;

[0072] FIG9 is a SEM image of the intermediate product described in Example 4 of the present application;

[0073] FIG10 is an XRD pattern of the intermediate product described in Example 4 of the present application;

[0074] FIG11 is a SEM image of lithium manganese iron phosphate prepared using the lithium manganese iron phosphate precursor described in Example 1 of the present application;

[0075] FIG12 is an XRD pattern of lithium manganese iron phosphate prepared using the lithium manganese iron phosphate precursor described in Example 1 of the present application;

[0076] FIG13 is a charge-discharge curve diagram of a battery prepared using the lithium manganese iron phosphate precursor described in Example 1 of the present application during rate cycling. DETAILED DESCRIPTION

[0077] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0078] Example 1

[0079] This embodiment provides a lithium manganese iron phosphate precursor, which is Mn 0.59 Fe 0.395 Mg 0.015 PO 7 / 2 ;

[0080] The preparation method of the lithium manganese iron phosphate precursor comprises the following steps:

[0081] (1) At a nitrogen flow rate of 2 L / min, a stirring speed of 400 r / min and a temperature of 25°C, a metal salt solution with a total metal ion concentration of 1.8 mol / L, an ammonia solution with a concentration of 12.5% ​​and a phosphate solution with a concentration of 1.8 mol / L were fed into the bottom liquid in parallel. The injection rate of the metal salt solution and the phosphate solution was set to 12 mL / min. The pH of the coprecipitation reaction system was gradually reduced from 7 to 5.5 by adjusting the flow rate of the ammonia solution. After the feeding was completed within 3 hours, the mixture was aged for 1 hour, washed 4 times and vacuum dried at 70°C to obtain an intermediate product (NH4Mn 0.59 Fe 0.395 Mg 0.015 PO4·H2O);

[0082] The SEM image of the intermediate product is shown in FIG1 . The particles in FIG1 are disc-shaped, with a thickness of about 5 μm and a length and width of about 20 μm. The XRD pattern of the intermediate product is shown in FIG2 . The peak is sharp and the sample has high crystallinity. The thermogravimetric curve of the intermediate product is shown in FIG3 . The thermogravimetric curve under nitrogen at a heating rate of 5°C / min shows the weight loss mechanism:

[0083] From 50℃ to 350℃,

[0084] 2NH4Mn 0.59 Fe 0.395 Mg 0.015 PO4.H2O(s)→2Mn 0.59 Fe 0.395 Mg 0.015 HPO4(s)+2NH3(g)+2H2O(g),

[0085] From 350℃ to 550℃,

[0086] 2Mn 0.59 Fe 0.395 Mg 0.015 HPO4(s)→2Mn 0.59 Fe 0.395 Mg 0.015 PO 7 / 2 (s)+H2O(g);

[0087] The coprecipitation reaction is carried out in a reactor, and the amount of the base liquid added to the reactor accounts for 1 / 3 of the volume of the reactor; the pH of the base liquid is 7, and it includes water, wherein the concentration of phosphate in the base liquid is 0.33 mol / L, and the concentration of the complexing agent is 0.05 mol / L;

[0088] The metal salt solution is prepared by mixing MnSO4·H2O, FeSO4·7H2O and MgSO4·H2O in a certain amount, and the pH value of the metal salt solution is adjusted to 2 by using sulfuric acid;

[0089] The phosphate is NH4H2PO4, and the complexing agent is ammonium citrate;

[0090] (2) The intermediate product of step (1) was sintered at 550° C. for 3 h in a nitrogen atmosphere to obtain the lithium iron manganese phosphate precursor. The XRD pattern of the lithium iron manganese phosphate precursor is shown in FIG4 , confirming that it is ferromanganese pyrophosphate. The SEM image of the lithium iron manganese phosphate prepared from the lithium iron manganese phosphate precursor is shown in FIG11 , and the primary particle size is about 200 nm. The XRD pattern is shown in FIG12 , and there is no impurity peak. The charge and discharge curve of the battery prepared from the lithium iron manganese phosphate precursor during rate cycling is shown in FIG13 , and the rate cycle is cycled from 0.1C→0.2C→0.5C→1C→1C→….

[0091] Example 2

[0092] This embodiment provides a lithium manganese iron phosphate precursor, which is Mn 0.59 Fe 0.395 Mg 0.015 PO 7 / 2 ;

[0093] The preparation method of the lithium manganese iron phosphate precursor comprises the following steps:

[0094] (1) At a nitrogen flow rate of 2 L / min, a stirring speed of 600 r / min and a temperature of 45°C, a metal salt solution with a total metal ion concentration of 1.8 mol / L, an ammonia solution with a concentration of 12.5% ​​and a phosphate solution with a concentration of 1.8 mol / L were fed into the bottom liquid in parallel. The injection rate of the metal salt solution and the phosphate solution was set to 1.5 mL / min. The pH of the coprecipitation reaction system was gradually reduced from 7 to 5.5 by adjusting the flow rate of the ammonia solution. After the feeding was completed within 3 hours, the mixture was aged for 1 hour, washed 5 times and vacuum dried at 80°C to obtain an intermediate product (NH4Mn 0.59 Fe 0.395 Mg 0.015 PO4·H2O);

[0095] The SEM image of the intermediate product is shown in FIG5 , in which the primary particles are small flakes and the secondary particles are nearly spherical; the XRD pattern of the intermediate product is shown in FIG6 , in which the peak is sharp, the sample has a higher crystallinity, and has a preferred orientation compared to FIG2 ;

[0096] The coprecipitation reaction is carried out in a reactor, wherein the amount of the base liquid added to the reactor accounts for 2 / 3 of the volume of the reactor; the pH of the base liquid is 7, and the base liquid comprises water, wherein the concentration of phosphate in the base liquid is 0.04 mol / L, and the concentration of the complexing agent is 0.05 mol / L;

[0097] The metal salt solution is prepared by mixing MnSO4·H2O, FeSO4·7H2O and MgSO4·H2O in a certain amount, and the pH value of the metal salt solution is adjusted to 4 by using sulfuric acid;

[0098] The phosphate is NH4H2PO4, and the complexing agent is ammonium tartrate;

[0099] (2) The intermediate product of step (1) is sintered at 530° C. for 4 h in a nitrogen atmosphere to obtain the lithium manganese iron phosphate precursor.

[0100] Example 3

[0101] This embodiment provides a lithium manganese iron phosphate precursor, which is Mn 0.59 Fe 0.395 Mg 0.015 PO 7 / 2 ;

[0102] The preparation method of the lithium manganese iron phosphate precursor comprises the following steps:

[0103] (1) At a nitrogen flow rate of 2 L / min, a stirring speed of 300 r / min and a temperature of 45°C, a metal salt solution with a total metal ion concentration of 1.8 mol / L, an ammonia solution with a concentration of 12.5% ​​and a phosphate solution with a concentration of 1.8 mol / L were fed into the bottom liquid in parallel. The injection rate of the metal salt solution and the phosphate solution was set to 12 mL / min. The pH of the coprecipitation reaction system was gradually reduced from 7 to 5.5 by adjusting the flow rate of the ammonia solution. After the feeding was completed within 3 hours, the mixture was aged for 1 hour, washed 3 times and vacuum dried at 70°C to obtain an intermediate product (NH4Mn 0.59 Fe 0.395 Mg 0.015 PO4·H2O);

[0104] The SEM image of the intermediate product is shown in FIG7 , and the XRD pattern is shown in FIG8 ;

[0105] The coprecipitation reaction is carried out in a reactor, and the amount of the base liquid added to the reactor accounts for 1 / 3 of the volume of the reactor; the pH of the base liquid is 7, and it includes water, wherein the concentration of phosphate in the base liquid is 0.5 mol / L, and the concentration of the complexing agent is 0.05 mol / L;

[0106] The metal salt solution is prepared by mixing MnSO4·H2O, FeSO4·7H2O and MgSO4·H2O in a certain amount, and the pH value of the metal salt solution is adjusted to 1 by using sulfuric acid;

[0107] The phosphate is NH4H2PO4, and the complexing agent is ammonium citrate;

[0108] (2) The intermediate product of step (1) was sintered at 570° C. for 3 h in a nitrogen atmosphere to obtain the lithium manganese iron phosphate precursor.

[0109] Example 4

[0110] This embodiment provides a lithium manganese iron phosphate precursor, which is Mn 0.59 Fe 0.395 Mg 0.015 PO 7 / 2 ;

[0111] The preparation method of the lithium manganese iron phosphate precursor comprises the following steps:

[0112] (1) At a stirring speed of 600 r / min and a temperature of 60° C., a metal salt solution with a total metal ion concentration of 1.8 mol / L, an ammonia solution with a concentration of 12.5%, and a phosphate solution with a concentration of 1.8 mol / L are fed into the bottom liquid in parallel, and the injection rate of the metal salt solution and the phosphate solution is set to 3 mL / min. The pH of the coprecipitation reaction system is gradually maintained between 5.9 and 6.1 by adjusting the flow rate of the ammonia solution. After the feeding is completed within 3 hours, the mixture is aged for 1 hour, washed 5 times, and vacuum-dried at 70° C. to obtain an intermediate product;

[0113] The SEM image of the intermediate product is shown in FIG9 . Under the conditions of oxidation and high temperature, the primary particles are coarser, and the XRD pattern is shown in FIG10 .

[0114] The coprecipitation reaction is carried out in a reactor, and the amount of the bottom liquid added to the reactor accounts for 1 / 3 of the volume of the reactor; the pH of the bottom liquid is 7, and it includes water and phosphate, wherein the concentration of phosphate in the bottom liquid is 0.33 mol / L;

[0115] The metal salt solution is prepared by mixing MnSO4·H2O, FeSO4·7H2O and MgSO4·H2O in a certain amount, and the pH value of the metal salt solution is adjusted to 2 by using sulfuric acid;

[0116] The phosphate is NH4H2PO4;

[0117] (2) The intermediate product of step (1) is sintered at 580° C. for 2 h in a nitrogen atmosphere to obtain the lithium manganese iron phosphate precursor.

[0118] Example 5

[0119] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the pH of the base liquid in step (1) is 7.5 and the pH of the coprecipitation reaction system is reduced from 7.5 to 6, so that the lithium iron manganese phosphate precursor changes accordingly.

[0120] Example 6

[0121] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the pH of the coprecipitation reaction system in step (1) is maintained at 7 to change the lithium iron manganese phosphate precursor accordingly.

[0122] Example 7

[0123] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the pH of the coprecipitation reaction system in step (1) is maintained at 8 to change the lithium iron manganese phosphate precursor accordingly.

[0124] Example 8

[0125] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the pH of the coprecipitation reaction system in step (1) is reduced from 7 to 5, causing the lithium iron manganese phosphate precursor to change accordingly.

[0126] Example 9

[0127] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the pH of the coprecipitation reaction system in step (1) is reduced from 7 to 4, causing the lithium iron manganese phosphate precursor to change accordingly.

[0128] Example 10

[0129] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the amount of the bottom liquid added to the reactor in step (1) accounts for 1 / 5 of the volume of the reactor, which changes the lithium iron manganese phosphate precursor accordingly.

[0130] Example 11

[0131] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the amount of the bottom liquid added to the reactor in step (1) accounts for 5 / 6 of the volume of the reactor, which changes the lithium iron manganese phosphate precursor accordingly.

[0132] Example 12

[0133] This embodiment provides a lithium iron manganese phosphate precursor. The preparation method of the lithium iron manganese phosphate precursor is the same as that of Example 1, except that the base solution in step (1) does not include a complexing agent, which causes a corresponding change in the lithium iron manganese phosphate precursor.

[0134] Example 13

[0135] This embodiment provides a lithium manganese iron phosphate precursor, which is Mn 0.5 Fe 0.485 Mg 0.015 PO 7 / 2 ;

[0136] The preparation method of the lithium manganese iron phosphate precursor is the same as that of Example 1 except that the raw materials in the metal salt solution are changed according to the formula amount.

[0137] Example 14

[0138] This embodiment provides a lithium manganese iron phosphate precursor, which is Mn 0.7 Fe 0.3 PO 7 / 2 ;

[0139] The preparation method of the lithium manganese iron phosphate precursor is the same as that of Example 1 except that the raw materials in the metal salt solution are changed according to the formula amount.

[0140] Comparative Example 1

[0141] This comparative example provides a lithium iron manganese phosphate precursor, the chemical formula of which is NH4Mn 0.59 Fe 0.395 Mg 0.015 PO4·H2O;

[0142] The preparation method of the lithium manganese iron phosphate precursor is the same as that of Example 1 except that step (2) is not performed.

[0143] The lithium manganese iron phosphate precursor obtained in the above examples and comparative examples was mixed with lithium carbonate and glucose at a ratio of Li:(Mn+Fe+Mg)=1.02, with the addition ratio of glucose being 13.5%. The mixture was dispersed in water and sand-milled to a particle size of D50=300 nm. The mixture was spray-dried with the inlet air temperature set at 220°C and the outlet air temperature maintained at 95°C. The mixture was then calcined at 750°C in a nitrogen atmosphere for 10 hours to obtain lithium manganese iron phosphate with a morphology of primary particle aggregation. The reaction equation is: 2Mn 0.59 Fe 0.395 Mg 0.015 PO 7 / 2 (s)+Li2CO3(s)=2LiMn 0.59 Fe 0.395 Mg 0.015 PO4(s)+CO2(g), and then jet milling to obtain lithium manganese iron phosphate; the lithium manganese iron phosphate is prepared into button batteries and subjected to charge and discharge tests, with the test voltage range being 2.5V-4.5V.

[0144] The ICP test results of the lithium manganese iron phosphate precursors obtained in the above examples and comparative examples, the tap density, and the 1C discharge specific capacity of the prepared batteries are shown in Table 1.

[0145] Table 1

[0146] From Table 1 we can see that:

[0147] The lithium iron phosphate precursor provided in this application can obtain a lithium iron phosphate precursor with high tap density and lithium iron phosphate with excellent electrochemical performance, wherein the tap density of the lithium iron phosphate precursor is 1.5g / cm 3 As shown above, the 1C discharge capacity of the battery is above 145 mAh / g. As can be seen from Example 1 and Comparative Example 1, if the sintering in step (2) is not performed, the precursor obtained is ammonium manganese ferrous phosphate with a low tap density, which will affect the battery performance. As can be seen from Example 1 and Examples 6-7, the pH of the coprecipitation reaction of the present application is gradually reduced, thereby reducing the ionized PO4 3- The amount of the bottom solution can affect the uniform precipitation of ions. The complexing agent in the bottom solution can prevent Fe from being precipitated under weak acidic conditions. 2+ and Mn 2+ Oxidation, and can react with Fe 2+ and Mn 2+ Contact complexation forms an intermediate, which is then desorbed and precipitated under the action of phosphate ions, reducing the growth rate and improving the precursor tap density and battery performance.

[0148] In summary, the present application provides a lithium iron manganese phosphate precursor and its preparation method and application. The lithium iron manganese phosphate precursor has a small particle size, uniform composition and high tap density, which can solve the problem that the lithium iron manganese phosphate precursor has large particle size, low tap density and contains ammonium radical components, resulting in a large amount of ammonia gas generated during sintering of the precursor with lithium, thereby significantly improving the compaction density of the lithium iron manganese phosphate positive electrode material.

[0149] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application fall within the protection scope and disclosure scope of the present application.

Claims

1. A lithium manganese iron phosphate precursor, wherein: The general chemical formula of the lithium manganese iron phosphate precursor is Mn x Fe y M 1-x-y PO 7 / 2 , wherein x is 0.5-0.7, y is 0.3-0.5, and M is the doped metal element.

2. The lithium iron manganese phosphate precursor according to claim 1, wherein The M includes any one of Mg, Ti, Nb, Zr or Cu, or a combination of at least two of them.

3. A method for preparing the lithium iron manganese phosphate precursor as claimed in claim 1 or 2, comprising the following steps: (1) feeding a metal salt solution, a pH adjuster and a phosphate solution into a base liquid to carry out a coprecipitation reaction to obtain an intermediate product; The metal salt solution includes a manganese salt and an iron salt, or a manganese salt, an iron salt and an M salt; (2) Sintering the intermediate product of step (1) to obtain the lithium manganese iron phosphate precursor.

4. The preparation method according to claim 3, wherein During the feeding process of step (1), the pH of the coprecipitation reaction system gradually decreases.

5. The preparation method according to claim 3 or 4, wherein The pH of the base solution in step (1) is 7-8.

6. The preparation method according to any one of claims 3 to 5, wherein: After the feeding in step (1) is completed, the pH of the coprecipitation reaction system is 5-6.

7. The preparation method according to any one of claims 3 to 6, wherein: The time to complete the feeding of step (1) is 2-4 hours.

8. The preparation method according to any one of claims 3 to 7, wherein: After the feeding in step (1) is completed, aging, washing and vacuum drying are performed to obtain the intermediate product; Optionally, the washing is performed 3-5 times; Optionally, the vacuum drying temperature is 60-80°C.

9. The preparation method according to any one of claims 3 to 8, wherein: The coprecipitation reaction in step (1) is carried out in a reactor, and the amount of the bottom liquid added to the reactor accounts for 1 / 3-2 / 3 of the volume of the reactor; Optionally, the base liquid in step (1) comprises water; Optionally, in the base solution of step (1), the concentration of phosphate is 0-0.5 mol / L; Optionally, in the base solution of step (1), the concentration of the complexing agent is 0-0.1 mol / L; Optionally, the complexing agent includes any one of ammonium citrate, ammonium tartrate, ammonium ethylenediaminetetraacetate or ammonium oxalate, or a combination of at least two thereof, and may be ammonium citrate and / or ammonium tartrate.

10. The preparation method according to any one of claims 3 to 9, wherein: The pH of the metal salt solution in step (1) is 1-4; Optionally, in the metal salt solution of step (1), the concentration of total metal ions is 0.5-4 mol / L; Optionally, the concentration of the phosphate solution in step (1) is 0.5-3 mol / L; Optionally, the concentration of the pH regulator in step (1) is 10-28%; Optionally, the phosphate solution in step (1) includes any one of NH4H2PO4, (NH4)2HPO4 or (NH4)3PO4, or a combination of at least two thereof, and may be NH4H2PO4; Optionally, the pH adjuster in step (1) includes any one of ammonia water, urea or ammonium carbonate, or a combination of at least two of them, and ammonia water can be selected.

11. The preparation method according to any one of claims 3 to 10, wherein: The coprecipitation reaction in step (1) is carried out in a nitrogen atmosphere, wherein the flow rate of the nitrogen is 1-3 L / min; Optionally, the coprecipitation reaction in step (1) is carried out under stirring at a speed of 300-600 r / min; Optionally, the temperature of the coprecipitation reaction in step (1) is 20-60°C; Optionally, the sintering temperature in step (2) is 500-600° C. and the sintering time is 2-4 h; Optionally, the sintering in step (2) is carried out in a nitrogen atmosphere.

12. The preparation method according to any one of claims 3 to 11, comprising the steps of: (1) feeding a metal salt solution having a total metal ion concentration of 0.5-4 mol / L and a pH of 1-4, a pH regulator having a concentration of 10-28%, and a phosphate solution having a concentration of 0.5-3 mol / L into a bottom liquid at a nitrogen flow rate of 1-3 L / min, a stirring speed of 300-600 r / min, and a temperature of 20-60° C., so that the pH of the coprecipitation reaction system is gradually reduced from 7-8. After the feeding is completed, the pH of the coprecipitation reaction system is reduced to 5-6. After the feeding is completed within 2-4 hours, the feeding is aged, washed 3-5 times, and vacuum dried at 60-80° C. to obtain an intermediate product; The coprecipitation reaction is carried out in a reactor, and the amount of the bottom liquid added to the reactor accounts for 1 / 3-2 / 3 of the volume of the reactor; the pH of the bottom liquid is 7-8, and it includes water; The metal salt solution includes manganese salt, iron salt and M salt; (2) Sintering the intermediate product of step (1) at 500-600° C. for 2-4 hours in a nitrogen atmosphere to obtain the lithium manganese iron phosphate precursor.

13. A lithium manganese iron phosphate positive electrode material, wherein: The lithium iron manganese phosphate positive electrode material is prepared using a lithium source and the lithium iron manganese phosphate precursor as claimed in claim 1 or 2.

14. A battery, wherein: The battery comprises the lithium manganese iron phosphate positive electrode material as claimed in claim 13.

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