Modified lithium-rich lithium iron phosphate and preparation method thereof, positive electrode lithium supplementing material and application

Abstract

The application provides a modified lithium-rich lithium iron phosphate, a preparation method of the modified lithium-rich lithium iron phosphate, a positive electrode lithium supplement material and application, and the preparation method of the modified lithium-rich lithium iron phosphate comprises the following steps: S1, taking an iron source in a solvent A to obtain a solution A; S2, taking a lithium source in a solvent B to obtain a solution B; S3, spraying the solution A to the surface of the solution B through a spraying device, so that the system is subjected to a precipitation reaction to obtain a precursor; and S4, performing sintering treatment on the precursor to obtain the modified lithium-rich lithium iron phosphate; wherein the lithium source is an organic lithium compound, and the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents. The modified lithium-rich lithium iron phosphate prepared by the application has high structural regularity, and the ion conductivity and structural stability are relatively good; meanwhile, the lithium ion transmission efficiency and the rate performance of the modified lithium-rich lithium iron phosphate are greatly improved, the lithium supplement capacity is relatively high, and the comprehensive performance is relatively good.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium battery additives, in particular to a modified lithium-rich lithium iron phosphate, a preparation method thereof, a positive electrode lithium supplementing material and application. BACKGROUND

[0002] During the formation process of lithium ion batteries, the formation of the negative electrode SEI film will consume part of the active lithium, thereby causing the battery capacity to decrease and the cycle performance to decrease. Therefore, supplementing active lithium becomes an effective means to solve this problem. At present, the lithium supplementing method is divided into positive electrode lithium supplementing and negative electrode lithium supplementing, however, due to the need to use lithium powder and other active metals for negative electrode lithium supplementing, the operation environment and equipment requirements are strict and difficult to perform. Positive electrode lithium supplementing is simple and easy to operate, a small amount of lithium supplementing agent can be added during the preparation of the positive electrode sheet to achieve lithium supplementing, and the lithium supplementing process is safe and has strong operability, which has broad application prospects.

[0003] As a positive electrode lithium supplementing additive, lithium-rich lithium iron phosphate (Li5FeO4) is considered to be the most commercially promising positive electrode lithium supplementing additive due to its good compatibility with batteries, low production cost, non-toxicity and high lithium supplementing capacity. However, the application of lithium-rich lithium iron phosphate still encounters some problems. Mainly due to the following points: first, lithium-rich lithium iron phosphate itself is unstable, extremely sensitive to H2O and CO2 in the environment, and easily reacts with them to generate lithium compound impurities, thereby causing performance deterioration. Second, the preparation of lithium-rich lithium iron phosphate is difficult, usually prepared by high-temperature sintering, which has high requirements for the particle size and uniformity of the reactants, and the size of the product particles is large, controllability is poor, which further affects the path density of ions and electrons, resulting in low rate performance, and it is difficult to play its high lithium supplementing capacity to meet the demand of high-power batteries.

[0004] In summary, the lithium-rich lithium iron phosphate (Li5FeO4) in the prior art is prone to sintering and agglomeration during preparation, thereby causing problems such as low lithium ion transmission efficiency, poor rate performance or low lithium supplementing capacity. Therefore, the present application provides a new modified lithium-rich lithium iron phosphate and a preparation method thereof to solve the above problems. SUMMARY

[0005] The main purpose of the present application is to provide a modified lithium-rich lithium iron phosphate and a preparation method thereof, a positive electrode lithium supplementing material and application, to solve the problem of low lithium ion transmission efficiency, poor rate performance or low lithium supplementing capacity of the lithium-rich lithium iron phosphate in the prior art.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, there is provided a preparation method of modified lithium-rich lithium-iron oxide, comprising: step S1, taking an iron source in a solvent A to obtain a solution A; step S2, taking a lithium source in a solvent B to obtain a solution B; step S3, spraying the solution A to the surface of the solution B through a spraying device, so that the system is subjected to a precipitation reaction to obtain a precursor; and step S4, sintering the precursor to obtain the modified lithium-rich lithium-iron oxide; wherein the lithium source is an organic lithium compound, and the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents.

[0007] Further, the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents with a molecular dipole moment of 0.00-5.00 Cm; preferably, the solvent A and the solvent B are independently selected from C1-C20 alkanes or mixtures thereof; preferably, the solvent A and the solvent B are independently selected from petroleum ether and / or o-xylene; preferably, the spraying pressure of the spraying device is 0.1-0.3 MPa, the spraying flow rate is 3-5 mL / min, and the average droplet diameter is 0.3-1.0 μm.

[0008] Further, the lithium source is selected from alkyl organolithium and / or allyl organolithium; preferably, the lithium source is lithium 1,2-hydroxystearate and / or lithium octadecanoate; preferably, the sintering is performed in an inert atmosphere, and the inert gas is preferably nitrogen and / or argon; preferably, the sintering temperature is 600-900 °C, and the sintering time is 4-8 h.

[0009] Further, after the spraying treatment, the sintering treatment is preceded by a standing treatment of the sprayed material to perform the precipitation reaction; preferably, the standing temperature is 20-40 °C, and the standing time is 2-4 h.

[0010] Further, after the standing treatment, step S3 further comprises sequentially performing a settling treatment and a drying treatment on the standing material to obtain the precursor; preferably, the settling treatment is performed in a centrifuge; preferably, the drying treatment is performed in a vacuum drying machine; further preferably, the drying treatment temperature is 80-120 °C, the treatment time is 8-12 h, and the vacuum degree is 0-0.02 MPa.

[0011] Further, the iron source is selected from one or more of ferric nitrate, ferric chloride or ferric acetate; preferably, the weight content of the iron source added in the solvent A is 10-30 wt%; preferably, the weight content of the lithium source added in the solvent B is 10-30 wt%; and preferably, the molar ratio of lithium in the lithium source to iron in the iron source is (5.5-6.0):1.

[0012] In order to achieve the above-mentioned purpose, according to one aspect of the present application, there is provided a modified lithium-rich lithium-iron oxide obtained by the above-mentioned preparation method of modified lithium-rich lithium-iron oxide.

[0013] Further, the modified lithium-rich lithium iron phosphate is in a granular form, preferably the average size of the granules of the modified lithium-rich lithium iron phosphate is 200-500 nm.

[0014] According to another aspect of the present application, there is provided a use of the modified lithium-rich lithium iron phosphate as a positive electrode lithium supplement material.

[0015] According to another aspect of the present application, there is provided a lithium ion battery comprising the positive electrode lithium supplement material, which is the modified lithium-rich lithium iron phosphate.

[0016] The modified lithium-rich lithium iron phosphate obtained by the technical solution of the present application has a high structural regularity, and has a high ion conductivity and structural stability. The lithium ion transmission efficiency and rate performance of the modified lithium-rich lithium iron phosphate are greatly improved, and the modified lithium-rich lithium iron phosphate has a high lithium supplement capacity and a high comprehensive performance. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and are used in the explanation of the preferred embodiments of the present application together with the specification. The accompanying drawings include the following drawings:

[0018] Figure 1 FIG. 1 shows a SEM image of the modified lithium-rich lithium iron phosphate obtained in Example 1 of the present application (magnification 50,000 times);

[0019] Figure 2 FIG. 5 shows a SEM image of the modified lithium-rich lithium iron phosphate obtained in Comparative Example 1 of the present application (magnification 50,000 times);

[0020] Figure 3 FIG. 8 shows a SEM image of the modified lithium-rich lithium iron phosphate obtained in Comparative Example 4 of the present application (magnification 10,000 times). DETAILED DESCRIPTION

[0021] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] As described in the background section of the present application, the prior art lithium-rich lithium iron oxide exists in the low lithium ion transmission efficiency or poor rate performance or low lithium supplement capacity. The present application provides a preparation method of modified lithium-rich lithium iron oxide, the preparation method comprising: step S1, taking an iron source in a solvent A to obtain a solution A; step S2, taking a lithium source in a solvent B to obtain a solution B; step S3, spraying the solution A to the surface of the solution B by a spraying device, so that the system performs a precipitation reaction to obtain a precursor; step S4, sintering the precursor to obtain the modified lithium-rich lithium iron oxide. Wherein the lithium source is an organic lithium compound, and the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents.

[0023] Based on the prior art lithium-rich lithium iron oxide (Li5FeO4), it is usually prepared by sintering a lithium source (such as lithium oxide or lithium hydroxide) and an iron source (iron oxide) at high temperature. However, due to the high requirement of high temperature sintering on the particle size and the uniformity of the mixture, it is easy to cause the particle size of the generated lithium-rich lithium iron oxide to be large, thereby reducing the ion conductivity and affecting its application. The present application provides a preparation method of modified lithium-rich lithium iron oxide. First, an iron source is taken in a solvent A to obtain a solution A, and a lithium source is taken in a solvent B to obtain a solution B, obtaining two uniform and stable reactant solutions, so as to avoid the influence of the particle size of the reactants being too large or the mixture being non-uniform on the physical properties of the product, and further affecting the electrochemical performance of the lithium-rich lithium iron oxide. Then, the present application creatively sprays the solution A to the surface of the solution B by a spraying device, so that the system performs a precipitation reaction to obtain a precursor. On the one hand, by using the spraying treatment, the solution A can be dispersed into fine droplets in the solution B, so that the solution A is more uniformly dispersed, and the above operation is simple, easy to scale up, and has industrialization prospect; on the other hand, the solution A which is more uniformly dispersed can be further contacted with the solution B to promote the liquid phase reaction to proceed fully, improve the reaction rate, and also improve the structural stability of the product lithium-rich lithium iron oxide. Finally, the precursor is sintered to obtain the modified lithium-rich lithium iron oxide. Sintering the precursor can promote the ordered arrangement of the precursor structure, make it form a crystalline phase, and also make the organic carbon chain in the lithium source sintered into a carbon layer, coated on the outer surface of the lithium-rich lithium iron oxide, thereby improving its ion conductivity and structural stability.

[0024] Especially important is that the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents. The present application is just by virtue of the weak polarity of the solvent A and the solvent B, which has a lower surface tension, so that the two reactant materials are in full contact, especially can make the carbon chain in the iron source and the organic lithium compound self-assemble through electrostatic force, so as to further form the product precursor small particles with relatively regular shape, thereby reducing the product aggregation degree, improving the structural regularity of the lithium-rich lithium iron oxide, and improving its conductivity. Moreover, the lithium source used in the present application is an organic lithium compound, which can provide lithium source and carbon source. In the sintering process, the excess organic lithium compound can generate a surface carbon coating in situ, thereby further inhibiting the aggregation of product particles, reducing the particle size, stabilizing the product structure, and further improving the transmission efficiency of ions and electrons, and improving the electrochemical performance.

[0025] In a preferred embodiment, the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents with a molecular dipole moment of 0.00-5.00 Cm, and further preferably the solvent A and the solvent B are independently selected from C1-C20 alkanes and mixtures thereof, which have lower polarity and smaller surface tension, so that the two reactant material solutions can be in full contact, thereby better promoting the self-assembly between the reactants to obtain more structured product precursors. Further preferably, the solvent A and the solvent B are independently selected from petroleum ether and / or o-xylene.

[0026] In order to make the solution A more uniformly dispersed, and to make the spraying of the solution A to the surface of the solution B more uniform and with a wider spraying area, the spraying pressure of the spraying device is preferably 0.1-0.3 MPa, the spraying flow rate is 3-5 mL / min, and the average droplet diameter is 0.3-1.0 μm, thereby further increasing the spraying distance and spraying range, promoting the precipitation reaction to proceed fully, improving the reaction efficiency, and further promoting the self-assembly of the carbon chain in the iron source and the organic lithium compound through electrostatic force, thereby further forming product precursor small particles with relatively regular shape, thereby reducing the product aggregation degree, improving the structural regularity of the lithium-rich lithium iron oxide, and improving its conductivity.

[0027] In a preferred embodiment, in order to further exert the dual role of the lithium source, which provides both the lithium source and the carbon source for coating, the lithium source is preferably selected from alkyl organolithium and / or allyl organolithium, and further preferably the lithium source is lithium 1,2-hydroxystearate and / or lithium octadecanoate.

[0028] In order to reduce the side reaction of oxygen component in air and reactant in the sintering process, thereby affecting the performance of the positive electrode lithium supplement agent, preferably, the sintering is carried out in an inert atmosphere, and further preferably, the inert gas is nitrogen and / or argon. In order to promote the structure arrangement of the positive electrode lithium supplement agent to be more ordered, and to generate a surface carbon coating layer in situ for the excess organic lithium compound, thereby further inhibiting the agglomeration of the product particles, reducing the particle size, stabilizing the product structure, and further improving the rate performance of the positive electrode lithium supplement agent. Preferably, the sintering treatment temperature is 600-900℃, and the treatment time is 4-8h.

[0029] In order to promote the spraying treatment of solution A on solution B to be more sufficient, and to make the mist droplets sprayed out of the spraying equipment to be more uniform, thereby further improving the structure regularity of the positive electrode lithium supplement agent, reducing the product particle size, and improving the ionic conductivity, after the spraying treatment, the sintering treatment is required before the standing treatment of the sprayed material to carry out the precipitation reaction. Preferably, the standing temperature is 20-40℃, and the standing time is 2-4h.

[0030] In a preferred embodiment, the step S3 further comprises sequentially carrying out the settling and drying treatment on the standing material. The settling treatment is carried out in a centrifuge to obtain the precipitate, and the drying treatment is carried out in a vacuum dryer, thereby further removing the solvent and the remaining impurities, thereby reducing the influence of the subsequent sintering process on the formation of the regular structure of the positive electrode lithium supplement agent, and thereby improving the electrochemical performance in the application process. Further preferably, the drying treatment temperature is 80-120℃, the treatment time is 8-12h, and the vacuum degree is 0-0.02MPa.

[0031] In a preferred embodiment, the iron source is selected from one or more of ferric nitrate, ferric chloride or ferric acetate, and the molar ratio of lithium element in the lithium source to iron element in the iron source is (5.5-6.0):1. The molar ratio of lithium element in the lithium source to iron element in the iron source is preferably within the above range, so that compared with the solution B containing an excess of lithium source, the solution A containing a small amount of iron source can be more uniformly dispersed, thereby further promoting the full reaction of the liquid phase reaction, improving the reaction rate. Further preferably, the weight content of the iron source added in the solvent A is 10-30wt%, and the weight content of the lithium source added in the solvent B is 10-30wt%.

[0032] Another aspect of the present application also provides a modified lithium-rich lithium iron phosphate, which is obtained by the above-mentioned preparation method of the modified lithium-rich lithium iron phosphate, and the crystal lattice structure of the modified lithium-rich lithium iron phosphate is ordered and has high regularity, thereby having high ionic conductivity.

[0033] In a preferred embodiment, the modified lithium-rich lithium-iron-oxide is in the form of particles, preferably the average size of the modified lithium-rich lithium-iron-oxide particles is 200-500 nm, so that the agglomeration degree of the modified lithium-rich lithium-iron-oxide particles is reduced, the particle size is reduced, the internal crystal lattice structure is regular, and the ion transfer efficiency is higher.

[0034] Another aspect of the present application also provides a use of the modified lithium-rich lithium-iron-oxide as a positive electrode lithium supplement material. The modified lithium-rich lithium-iron-oxide has a higher lithium supplement capacity as a positive electrode lithium supplement agent.

[0035] Another aspect of the present application also provides a lithium ion battery comprising the above-mentioned positive electrode lithium supplement material. The lithium ion battery has a higher electrical conductivity, excellent rate cycling performance and stability.

[0036] The present application will be further described in detail below in combination with specific examples, which should not be understood as limiting the scope of the present application.

[0037] Example 1

[0038] Take 10 g of ferric nitrate (0.0413 mol) and add it to 75.8 mL of hexane (molecular dipole distance is 0.06 Cm) to obtain a solution A. Take 67.24 g of lithium octadecanoate and add it to 312.5 mL of petroleum ether (molecular dipole distance is 0.1 Cm) to obtain a solution B. Place the solution A in a spraying device, the spraying pressure is 0.1 MPa, the average droplet diameter is 0.5 μm, and spray it into the solution B at a rate of 3 mL / min. Let it stand at room temperature for 4 h. Then centrifuge the material after standing to obtain a precipitate. Dry the precipitate in a vacuum drying machine, the drying temperature is 80℃, the vacuum degree is 0.02 MPa, and the drying time is 12 h. Then place the dried material in an atmospheric box furnace for sintering, the nitrogen atmosphere, the sintering temperature is 600℃, the sintering time is 8 h, and the modified lithium-rich lithium-iron-oxide is obtained. The SEM image of the modified lithium-rich lithium-iron-oxide is shown in Figure 1

[0039] Example 2

[0040] ​Take 10 g of iron chloride (0.0616 mol) into 58.6 mL of heptane (molecular dipole moment 0.2 Cm), uniformly dispersed to obtain solution A, take 105.8 g of lithium 12-hydroxystearate (0.345 mol) into 466.7 mL of naphtha (molecular dipole moment 0 Cm), uniformly mixed to obtain solution B. Solution A is placed in a spraying device, the spraying pressure is 0.2 MPa, the average diameter of the liquid droplets is 0.6 μm, sprayed into solution B at a rate of 5 mL / min, and left to stand at room temperature for 2 h. Then the material after standing is centrifuged to obtain a precipitate. The precipitate is dried in a vacuum drying machine, the drying temperature is 120°C, the vacuum degree is 0.02 MPa, and the drying time is 12 h. Then the dried material is placed in a tube furnace for sintering, in a nitrogen atmosphere, the sintering temperature is 900°C, the sintering time is 4 h, and a modified lithium-rich lithium ferrite is obtained.

[0041] Example 3

[0042] Take 10 g of iron nitrate (0.0413 mol) into 47.9 mL of n-pentane (molecular dipole moment 0 Cm), uniformly dispersed to obtain solution A, take 69.6 g of lithium octadecanoate (0.240 mol) into 770.6 mL of toluene (molecular dipole moment 2.4 Cm), uniformly mixed to obtain solution B. Solution A is placed in a spraying device, the spraying pressure is 0.3 MPa, the average diameter of the liquid droplets is 0.3 μm, sprayed into solution B at a rate of 3 mL / min, and left to stand at room temperature for 4 h. Then the material after standing is centrifuged to obtain a precipitate. The precipitate is dried in a vacuum drying machine, the drying temperature is 100°C, the vacuum degree is 0.02 MPa, and the drying time is 10 h. Then the dried material is placed in a gas atmosphere box furnace for sintering, in a nitrogen atmosphere, the sintering temperature is 900°C, the sintering time is 6 h, and a modified lithium-rich lithium ferrite is obtained.

[0043] Example 4

[0044] Take 10 g of iron nitrate (0.0413 mol) into 47.9 mL of n-pentane (molecular dipole moment 0 Cm), uniformly dispersed to obtain solution A, take 69.6 g of lithium octadecanoate (0.240 mol) into 770.6 mL of toluene (molecular dipole moment 2.4 Cm), uniformly mixed to obtain solution B. Solution A is placed in a spraying device, the spraying pressure is 0.3 MPa, the average diameter of the liquid droplets is 0.3 μm, sprayed into solution B at a rate of 3 mL / min, and left to stand at room temperature for 4 h. Then the material after standing is centrifuged to obtain a precipitate. The precipitate is dried in a vacuum drying machine, the drying temperature is 100°C, the vacuum degree is 0.02 MPa, and the drying time is 10 h. Then the dried material is placed in a gas atmosphere box furnace for sintering, in a nitrogen atmosphere, the sintering temperature is 900°C, the sintering time is 6 h, and a modified lithium-rich lithium ferrite is obtained.

[0045] Example 5

[0046] Take 10 g of iron chloride (0.0616 mol) and add to 72.4 mL of isooctane (molecular dipole moment 0.1 Cm) to uniformly disperse to obtain solution A. Take 100.2 g of lithium octadecanoate (0.345 mol) and add to 468.8 mL of petroleum ether (molecular dipole moment 0.1 Cm) to uniformly mix to obtain solution B. Solution A is placed in a spraying device and sprayed into solution B at a rate of 3 mL / min, the spraying pressure is 0.2 MPa, the average droplet diameter is 0.6 μm, and the material is left to stand at room temperature for 4 h. The material after standing is then centrifuged to obtain a precipitate. The precipitate is dried in a vacuum drying machine, the drying temperature is 80 °C, the vacuum degree is 0.02 MPa, and the drying time is 12 h. The dried material is then placed in an atmospheric box furnace to sinter, the nitrogen atmosphere, the sintering temperature is 600 °C, the sintering time is 8 h, and the modified lithium-rich lithium iron oxide is obtained.

[0047] Example 6

[0048] The difference from Example 1 is only that solvent A is hexane (molecular dipole moment is 0.06 Cm) and solvent B is isopropyl alcohol (molecular dipole moment is 4.3 Cm).

[0049] Example 7

[0050] The difference from Example 1 is only that the lithium source is lithium hydroxide.

[0051] Example 8

[0052] The difference from Example 1 is only that the spraying flow rate is 1 mL / min.

[0053] Example 9

[0054] The difference from Example 1 is only that the spraying flow rate is 8 mL / min.

[0055] Example 10

[0056] The difference from Example 1 is only that the average droplet diameter of the spraying device is 0.1 μm.

[0057] Example 11

[0058] The difference from Example 1 is only that the average droplet diameter of the spraying device is 1.5 μm.

[0059] Comparative Example 1

[0060] The difference from Example 1 is only that there is no spraying device, but solution A is directly poured into solution B.

[0061] Comparative Example 2

[0062] The difference from Example 1 is only that there is no spraying device, but 200 g of lithium octadecanoate is directly added to solution A.

[0063] Comparative Example 3

[0064] The difference from Example 1 is only that solution B is sprayed into solution A.

[0065] Comparative Example 4

[0066] The difference from Example 1 is only that there is no solvent, and 10 g of iron oxide is directly mixed with 200 g of lithium octadecanoate by grinding and then sintering.

[0067] Performance test:

[0068] The positive electrode lithium supplement prepared above is mixed with carbon black and PVDF at a mass ratio of 8:1:1, and then scraped on an aluminum foil as a lithium ion battery positive electrode, and a button cell with a model number of CR2032 is assembled in an argon-filled glove box. The battery negative electrode is a metal lithium sheet, the separator is a polypropylene microporous membrane, and the electrolyte is a 1 mol / L LiPF6 solution, and the solvent of the electrolyte is EC:DMC:EMC=1:1:1(v / v / v). The voltage range of the button cell measurement is 2-4.5V, and the charge and discharge current is 0.05C and 0.1C.

[0069] The lithium ion batteries prepared in the above examples and comparative examples are tested, and the results are shown in Table 1 below.

[0070] Table 1

[0071]

[0072] From the above description, it can be seen that the above-mentioned examples of the present application achieve the following technical effects:

[0073] From the test results of Example 1 and Comparative Examples 1 and 2, it can be found that when the modified lithium-rich lithium iron oxide is prepared by the preparation method of the present application, especially by mixing the iron source solution and the lithium source solution through the spraying device for further treatment, the lithium-rich lithium iron oxide has a small particle size and a more stable structure due to more uniform dispersion and ordered arrangement of the structure, and exhibits excellent electrochemical performance as a lithium supplement material. When the lithium-rich lithium iron oxide prepared without using the spraying device is directly mixed, the SEM image of the modified lithium-rich lithium iron oxide obtained in Comparative Example 1 is shown in Figure 2 , and its particle size is obviously larger, so its ionic conductivity is also poor.

[0074] From the test results of Example 1 and Comparative Example 3, it can be found that when the preparation method of modified lithium-rich lithium-iron oxide in the present application is adopted, the solution A is sprayed onto the surface of the solution B by a spraying device, the system is allowed to carry out a precipitation reaction, and then the lithium-rich lithium-iron oxide product is obtained by further processing the precursor. The ion conductivity of the lithium-rich lithium-iron oxide product is high. Compared with the operation step of spraying the solution B into the solution A in Comparative Example 3, the Li + content in the B spraying solution is higher than the Fe 3+ content in the A spraying solution, and the ratio of the Li

[0075] content in the B spraying solution to the Fe Figure 3 content in the A spraying solution is (5.5-6.0):1. If the A spraying solution is taken as the basis, the number of nucleation sites provided by the A spraying solution is lower than that of the B spraying solution, which is easy to cause aggregation and make the precipitated particles larger, so that the average particle size of the lithium-rich lithium-iron oxide is large, and the electrochemical performance is poor.

[0076] From the test results of Example 1, 2, 3, 4, 5, 6 and Comparative Example 4, it can be found that the lithium-rich lithium-iron oxide prepared by directly mixing a lithium source and an iron source and then sintering in a conventional method, the SEM image of the modified lithium-rich lithium-iron oxide obtained in Comparative Example 4 is shown in Figure 3 , the particle size is large, and the electrochemical performance is poor. The modified lithium-rich lithium-iron oxide prepared by the preparation method of the present application exhibits high ion and electron transfer efficiency and structural stability.

[0076] From the test results of Example 1 and Example 7, it can be found that the carbon chain in the iron source and the organic lithium compound can be self-assembled by electrostatic force by using the organic lithium source in the present application, so as to further form a product precursor small particle with relatively regular shape, thereby reducing the degree of product agglomeration, improving the structural regularity of the lithium-rich lithium-iron oxide, and improving the conductivity performance.

[0077] From the test results of Example 1 and Example 8, 9, 10, it can be found that when the spraying device in the present application is adopted, the spraying pressure of the spraying device is preferably 0.1-0.3 MPa, the spraying flow rate is 3-5 mL / min, and the average droplet diameter is 0.3-1.0 μm, which can further make the solution A and the solution B in the dispersion more uniform, promote the liquid phase reaction to proceed fully, improve the reaction rate, and also improve the structural stability of the product lithium-rich lithium-iron oxide, so that the modified lithium-rich lithium-iron oxide prepared by the present application has excellent electrochemical performance and structural stability.

[0078] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a modified lithium-rich lithium-iron-phosphate, characterized in that, The preparation method comprises: Step S1, taking an iron source in a solvent A to obtain a solution A; Step S2, taking a lithium source in a solvent B to obtain a solution B; Step S3, spraying the solution A to the surface of the solution B through a spraying device, so that the system performs a precipitation reaction to obtain a precursor; Step S4, performing a sintering treatment on the precursor to obtain the modified lithium-rich lithium iron phosphate; The lithium source is an organic lithium compound, and the solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents.

2. The production method according to claim 1, characterized by, The solvent A and the solvent B are independently selected from non-polar and / or weakly polar organic solvents with a molecular dipole moment of 0.00-5.00 Cm.

3. The preparation method according to claim 2, characterized in that, The solvent A and the solvent B are independently selected from C1-C20 alkanes or mixtures thereof.

4. The production method according to claim 2, characterized by, The solvent A and the solvent B are independently selected from petroleum ether and / or o-xylene.

5. The preparation method according to claim 2, characterized in that, The spraying pressure of the spraying device is 0.1-0.3 MPa, the spraying flow rate is 3-5 mL / min, and the average droplet diameter is 0.3-1.0 μm.

6. The production method according to claim 1 or 2, characterized by, The lithium source is selected from alkyl lithium and / or allyl lithium.

7. The production method according to claim 6, wherein The lithium source is lithium 1,2-hydroxystearate and / or lithium octadecanoate.

8. The preparation method according to claim 6, characterized in that, The sintering is performed in an inert atmosphere.

9. The preparation method according to claim 8, characterized in that, The inert atmosphere is a nitrogen atmosphere and / or an argon atmosphere.

10. The method of claim 6, wherein, The sintering temperature is 600-900°C, and the sintering time is 4-8 h.

11. The production method according to claim 1 or 2, characterized by, After the spraying treatment, a standing treatment is further required on the sprayed material before the sintering treatment to perform the precipitation reaction.

12. The method of claim 11, wherein, The standing temperature is 20-40°C, and the standing time is 2-4 h.

13. The preparation method according to claim 11, characterized in that, After the standing treatment, the step S3 further comprises sequentially performing a sedimentation treatment and a drying treatment on the material after standing to obtain the precursor.

14. The method of claim 13, wherein, The sedimentation treatment is performed in a centrifuge.

15. The preparation method according to claim 13, characterized in that, The drying treatment is performed in a vacuum drying machine.

16. The method of claim 15, wherein, The drying treatment temperature is 80-120°C, the treatment time is 8-12 h, and the vacuum degree is 0-0.02 MPa.

17. The method of making according to claim 1 or 2, wherein, The iron source is selected from one or more of ferric nitrate, ferric chloride, or ferric acetate.

18. The method of claim 17, wherein, The weight content of the iron source added in the solvent A is 10-30 wt%.

19. The method of claim 17, wherein, The weight content of the lithium source added in the solvent B is 10-30 wt%.

20. The method of claim 17, wherein, The molar ratio of lithium in the lithium source to iron in the iron source is (5.5-6.0):

1.

21. A modified lithium-rich lithium-iron-phosphate, characterized in that, The modified lithium-rich lithium iron phosphate is obtained by the preparation method of the modified lithium-rich lithium iron phosphate according to any one of claims 1-20.

22. The modified lithium-rich lithium-iron-phosphate of claim 21, wherein, The modified lithium-rich lithium iron phosphate is in a granular form.

23. The modified lithium-rich lithium-iron-phosphate of claim 22, wherein, The average particle size of the modified lithium-rich lithium iron phosphate is 200-500 nm.

24. Use of the modified lithium-rich lithium iron phosphate according to any one of claims 21-23 as a positive electrode lithium supplement material.

25. A lithium-ion battery comprising a positive electrode lithiation- supplementing material, characterized in that, The positive electrode lithium supplement material is the modified lithium-rich lithium iron phosphate according to any one of claims 21-23.

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