Modified lithium iron manganese phosphate, preparation method and application thereof, and positive electrode material containing same

Abstract

This invention discloses a modified lithium iron manganese phosphate, its preparation method and application, and a cathode material containing the same. The preparation method of the modified lithium iron manganese phosphate includes the following steps: S1. A mixture of a silver source, a manganese source, an iron source, a phosphorus source, and a lithium-containing source solution is subjected to a hydrothermal reaction to obtain an intermediate; the molar ratio of the lithium source to the silver source is 1:(0.010~0.230); S2. The intermediate is mixed with a carbon source and then subjected to ball milling and heat treatment. The preparation method provided by this invention is simple to operate, low in cost, and yields modified lithium iron manganese phosphate with improved ion migration performance and increased electron transport rate, thus improving rate performance while maintaining high charge / discharge capacity.

Description

Technical Field

[0001] This invention relates to a modified lithium iron manganese phosphate, its preparation method and application, and cathode materials containing it. Background Technology

[0002] CN108832119A uses carbon doping and spray drying to prepare carbon-doped lithium iron manganese phosphate, which improves the low electronic conductivity, but does not significantly improve the ion transport performance.

[0003] Existing technologies achieve structural stability, improved cycle life, and discharge capacity by doping lithium iron manganese phosphate (LMP) materials with metal ions. For example, CN113224278A discloses a modified LMP material comprising a magnesium-doped LMP core layer and a boron-containing coating layer on the surface of the magnesium-doped LMP core layer; CN111276693A describes LMP doping with metals such as Mg, Ca, Co, Ni, Cu, Zn, Al, Ga, Sc, Y, La, Ti, Zr, V, Nb, Cr, and Mo. However, these technologies do not fundamentally solve the problems of low electronic conductivity and poor ion transport performance of LMP, resulting in no significant improvement in rate performance. Summary of the Invention

[0004] The technical problem this invention aims to solve is to overcome the poor rate performance of lithium iron manganese phosphate cathode materials in the prior art. This invention provides a modified lithium iron manganese phosphate, its preparation method and applications, and cathode materials containing it. The preparation method provided by this invention is simple to operate and low in cost. The modified lithium iron manganese phosphate obtained has improved ion migration performance and increased electron transport rate, thus improving rate performance while maintaining high charge and discharge capacity.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention provides a method for preparing modified lithium iron manganese phosphate, which includes the following steps:

[0007] S1. A mixture of silver source, manganese source, iron source, phosphorus source and lithium source solution is subjected to hydrothermal reaction to obtain an intermediate; the molar ratio of the lithium source and the silver source is 1:(0.010~0.230);

[0008] S2. The intermediate is mixed with a carbon source and then subjected to ball milling and heat treatment.

[0009] In S1, the silver source can be a conventional silver-containing compound solution, preferably silver nitrate or silver sulfate, such as silver nitrate.

[0010] In S1, the molar ratio of the lithium source to the silver source is preferably 1:(0.026 to 0.230), more preferably 1:(0.040 to 0.230), for example 1:0.041, 1:0.128, 0.025 or 1:0.222.

[0011] In S1, the type of manganese source can be conventional in the art, preferably MnSO4 H2O or Mn(CH3COO)2 4H2O, such as MnSO4 H2O.

[0012] In S1, the molar ratio of the lithium source to the manganese source can be 1:(1.010 to 1.120), for example 1:1.020, 1:1.064 or 1:1.111.

[0013] In S1, the type of iron source can be conventional in the art, preferably Fe(NO3)3, FeSO4 7H2O or Fe(CH3COO)2, such as FeSO4 7H2O.

[0014] In S1, the molar ratio of the lithium source to the iron source can be 1:(1.010 to 1.120), for example 1:1.020, 1:1.064 or 1:1.111.

[0015] In S1, the phosphorus source can be any conventional source in the art, preferably H3PO4 or NH4H2PO4, such as H3PO4.

[0016] In S1, the molar ratio of the lithium source to the phosphorus source can be 1:(2.020~2.240), for example 1:2.040, 1:2.128 or 1:2.222.

[0017] In S1, the lithium source in the lithium source solution can be of the conventional type in the art, preferably Li2CO3, LiOH or CH3COOLi, such as Li2CO3.

[0018] In S1, the solvent in the lithium source solution can be deionized water and alcohols.

[0019] The alcohol is preferably ethylene glycol. Ethylene glycol can improve the crystallinity of the particles, which is beneficial to particle dispersibility.

[0020] The volume ratio of the deionized water to the alcohol can be 1:1.

[0021] In S1, preferably, the mixture is prepared by the following steps: adding the phosphorus source dropwise to the lithium source solution and stirring until a white suspension is obtained; then adding the manganese source, the iron source and the silver source and stirring.

[0022] The dripping rate can be 50 to 70 drops / minute, for example, 60 drops / minute.

[0023] The stirring speed can be 800-1200 r / min, for example 1000 r / min.

[0024] In S1, the temperature of the hydrothermal reaction can be conventional in the art, preferably 160-200°C, for example 200°C.

[0025] In S1, the hydrothermal reaction time can be conventional in the art, preferably 15 to 20 hours, for example 20 hours.

[0026] In S1, after the hydrothermal reaction, conventional operations in the art, such as centrifugation to separate the precipitate, washing, and drying, can also be performed.

[0027] The washing operation can be conventional in the art, and preferably involves alternating washing with deionized water and ethanol.

[0028] The drying temperature can be conventional in the art, preferably 60-100°C, for example 80°C.

[0029] In S2, the carbon source can be of a type conventional in the art, preferably one or more of glucose, lactose, sucrose, maltose, phenolic resin, graphite, carbon nanotubes, graphene, polyethylene glycol and epoxy resin, such as glucose.

[0030] In S2, the mass ratio of the intermediate to the carbon source can be conventional in the art, preferably 10:(1-5), for example 10:3.

[0031] In S2, the rotation speed of the ball milling reaction can be conventional in the art, preferably 200 to 300 rpm, for example 250 rpm.

[0032] In S2, the ball milling reaction time can be conventional in the art, preferably 10 to 14 hours, for example 12 hours.

[0033] In S2, the ball milling reaction can be carried out in a ball mill conventional in the art.

[0034] In S2, the process prior to heat treatment may also include a drying operation.

[0035] The drying temperature can be conventional in the art, preferably 60-100°C, for example 80°C.

[0036] In S2, preferably, the heat treatment is carried out under the protection of an inert atmosphere; the inert atmosphere generally refers to an atmosphere formed by gases that do not participate in the system reaction, and is not limited to inert gases, but can also be nitrogen. For example, the gas in the inert atmosphere can be one or more of nitrogen, helium, argon, and helium, and argon is another example;

[0037] In S2, the temperature of the heat treatment can be 500-600°C, for example 550°C.

[0038] In S2, the heat treatment time can be 5 to 10 hours, for example, 5 hours.

[0039] In S2, the heat treatment may further include crushing and sieving operations.

[0040] The mesh size of the sieve can be 80 to 120 mesh, for example, 100 mesh.

[0041] The present invention also provides a modified lithium iron manganese phosphate, which is prepared by the above-described preparation method.

[0042] The present invention also provides an application of the above-mentioned modified lithium iron manganese phosphate in cathode materials.

[0043] The present invention also provides a cathode material comprising the above-described modified lithium iron manganese phosphate.

[0044] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0045] The reagents and raw materials used in this invention are all commercially available.

[0046] The positive and progressive effects of this invention are as follows:

[0047] This invention increases the ion diffusion channels in the lithium iron manganese phosphate lattice by substituting some Li sites with Ag, thereby improving ion migration performance. Simultaneously, Ag doping also induces volume changes, enhancing electron transport rates and further increasing the conductivity of the resulting modified lithium iron manganese phosphate product. This improves rate performance while maintaining high charge / discharge capacity. Furthermore, the preparation method proposed in this invention is simple to operate, low in cost, easy to implement, and has the potential for large-scale production. Detailed Implementation

[0048] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0049] Example 1

[0050] (1) Dissolve 0.49 mol Li2CO3 in 100 mL of a mixed solvent of deionized water and ethylene glycol (volume ratio 1:1) and stir vigorously.

[0051] (2) Slowly add 1 mol of H3PO4 to the above mixed liquid while stirring continuously to obtain a white suspension;

[0052] (3) Add 0.5 mol MnSO4 H2O, 0.5 mol FeSO4 7H2O and 0.02 mol AgNO3 to the above liquid in sequence, and stir vigorously to disperse the liquid evenly;

[0053] (4) After transferring the obtained liquid into a hydrothermal reactor with a polytetrafluoroethylene liner, it is kept at 200°C for 20 hours.

[0054] (5) After the reaction time is complete, the hydrothermal reactor is cooled to room temperature. The reactor is opened and the precipitate is collected by centrifugation. The precipitate is washed five times alternately with deionized water and ethanol. The resulting product is then dried in an oven at 80°C to obtain Li. 0.98 Ag 0.02 Fe 0.5 Mn 0.5 PO4.

[0055] (6) The obtained Li 0.98 Ag 0.02 Fe 0.5 Mn 0.5 PO4 and glucose were mixed at a mass ratio of 10:3, and an appropriate amount of anhydrous ethanol was added. The mixture was then placed in a ball mill and ball-milled at 250 rpm for 12 hours.

[0056] (7) After the ball-milled product is dried in an oven at 80°C, the sample is placed in an atmosphere furnace and Ar atmosphere is introduced as a protective gas. The sample is then sintered at 550°C for 5 hours.

[0057] (8) Collect the obtained sample, grind it, and sieve it through a 100-mesh sieve to finally obtain Li. 0.98 Ag 0.02 Fe 0.5 Mn 0.5 PO4 / C composite material, namely modified lithium iron manganese phosphate.

[0058] Example 2

[0059] Compared with Example 1, the difference is the addition of 0.47 mol Li2CO3 and 0.06 mol AgNO3, while all other operations and conditions are the same as in Example 1.

[0060] Example 3

[0061] Compared with Example 1, the difference is the addition of 0.45 mol Li2CO3 and 0.10 mol AgNO3, while all other operations and conditions are the same as in Example 1.

[0062] Comparative Example 1

[0063] Compared with Example 1, the difference is that 0.50 mol of Li2CO3 was added and AgNO3 was not added, while all other operations and conditions were the same as in Example 1.

[0064] Example 1

[0065] The modified lithium iron manganese phosphate from Examples 1-3 and the lithium iron manganese phosphate from Comparative Example 1 were stirred with SP, PVDF, and graphene to form a uniformly dispersed positive electrode slurry with a ratio of 96.8:0.5:2:0.7. The negative electrode used a lithium metal sheet, a Celgard 2400 microporous polypropylene membrane as the separator, ethylene carbonate (EC) / dimethyl carbonate (DMC) with a solvent volume ratio of 1:1, and 1 mol / L LiPF6 as the electrolyte. The cells were assembled into a 2032-type button cell in a glove box filled with dry, high-purity argon gas.

[0066] Test conditions: Charge and discharge were performed using a Landian tester (CT2001A, Wuhan Landian Electronics Co., Ltd.). 10 mg of lithium iron manganese phosphate was weighed to prepare the above-mentioned 2032 type button battery. The theoretical capacity of the battery is 1.7 mAh. At 25℃, it was charged at 0.1C to 3.75V, then switched to constant voltage charging to 0.05C, and allowed to stand for 30 min. It was then discharged to 2.0V at different rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C for testing.

[0067] Table 1 shows the discharge capacity of the products prepared in Examples 1-3 and Comparative Example 1 at different rates.

[0068] Table 1

[0069]

[0070] Table 2 shows the capacity retention rates of the products prepared in Examples 1-3 and Comparative Example 1 at different expansion rates.

[0071] Table 2

[0072] 0.2C / 0.1C Capacity Retention Rate / % 97.1 97.4 97.5 96.1 0.5C / 0.1C Capacity Retention Rate / % 94.8 95.0 95.1 93.7 1C / 0.1C capacity retention rate (%) 91.6 91.8 92.2 89.3 2C / 0.1C capacity retention rate (%) 86.0 86.5 87.0 78.3 5C / 0.1C capacity retention rate (%) 80.8 81.1 82.0 58.3

[0073] From Table 1 and Table 2, we can see that:

[0074] ① Comparing Example 1 and Comparative Example 1, although a comparable charge-discharge capacity can be achieved at 0.1C without the addition of a silver source, the discharge capacity of the product prepared in Comparative Example 1 drops sharply as the rate increases; the capacity retention rate of Comparative Example 1 at different rates is also lower than that of Example 1.

[0075] ② In Examples 1-3, the molar ratios of lithium source to silver source were 1:0.041, 1:0.128, and 1:0.222, respectively. With the increase in silver source, the discharge capacity decreased to some extent within a certain range, while the rate performance gradually improved. This indicates that in order to balance capacity and rate performance, the ratio of lithium source to silver source needs to be controlled.

Claims

1. A method for preparing modified lithium iron manganese phosphate, characterized by, It includes the following steps: S1. A mixture of silver source, manganese source, iron source, phosphorus source and lithium-containing source solution is subjected to hydrothermal reaction to obtain an intermediate; the molar ratio of the lithium source to the silver source is 1:(0.010~0.230); the temperature of the hydrothermal reaction is 160~200℃; the time of the hydrothermal reaction is 15~20h; S2. The intermediate is mixed with a carbon source and then subjected to ball milling and heat treatment.

2. The method of claim 1, wherein the modified lithium manganese iron phosphate is prepared by the steps of: In S1, the silver source is either silver nitrate or silver sulfate; ​ And / or, in S1, the molar ratio of the lithium source to the silver source is 1:(0.026~0.230). and / or, in S1, the kind of the manganese source is MnS04 H20 or Mn(CH3COO)2 4H20; And / or, in S1, the molar ratio of the lithium source to the manganese source is 1:(1.010~1.120). And / or, in S1, the type of iron source is Fe(NO3)3 or FeSO4. 7H2O or Fe(CH3COO)2; And / or, in S1, the molar ratio of the lithium source to the iron source is 1:(1.010~1.120). And / or, in S1, the phosphorus source is H3PO4 or NH4H2PO4; And / or, in S1, the molar ratio of the lithium source to the phosphorus source is 1:(2.020~2.240).

3. The method of claim 2, wherein the modified lithium manganese iron phosphate is prepared by the steps of: mixing lithium hydroxide, manganese sulfate, and iron sulfate in a solution; and adding an acid to the solution to precipitate the modified lithium manganese iron phosphate. In S1, the silver source is silver nitrate; And / or, in S1, the molar ratio of the lithium source to the silver source is 1:(0.040~0.230). and / or, in S1, the kind of the manganese source is MnS04 H20; And / or, in S1, the molar ratio of the lithium source to the manganese source is 1:1.020, 1:1.064, or 1:1.111; And / or, in S1, the type of iron source is FeSO4. 7H2O; And / or, in S1, the molar ratio of the lithium source to the iron source is 1:1.020, 1:1.064, or 1:1.111; And / or, in S1, the phosphorus source is H3PO4; And / or, in S1, the molar ratio of the lithium source to the phosphorus source is 1:2.040, 1:2.128, or 1:2.

222.

4. The method for preparing modified lithium iron manganese phosphate as described in claim 2, characterized in that, In S1, the molar ratio of the lithium source to the silver source is 1:0.041, 1:0.128, or 1:0.

222.

5. The method for preparing modified lithium iron manganese phosphate as described in claim 1, characterized in that, In S1, the lithium source in the lithium source solution is Li2CO3, LiOH, or CH3COOLi; And / or, in S1, the solvent in the lithium source solution is deionized water and alcohols; And / or, in S1, the mixture is prepared by the following steps: adding the phosphorus source dropwise to the lithium source solution and stirring until a white suspension is obtained; then adding the manganese source, the iron source and the silver source and stirring.

6. The method for preparing modified lithium iron manganese phosphate as described in claim 5, characterized in that, In S1, the alcohol is ethylene glycol; And / or, the dripping rate is 50-70 drops / minute.

7. The method of claim 5, wherein the modified lithium manganese iron phosphate is prepared by the steps of: mixing lithium hydroxide, manganese sulfate, and iron sulfate in a solution; adding a base to the solution; and precipitating the modified lithium manganese iron phosphate. In S1, the volume ratio of the deionized water to the alcohol is 1:1; And / or, the dripping rate is 60 drops / minute.

8. The method for preparing modified lithium iron manganese phosphate as described in claim 5, characterized in that, In S1, the stirring speed is 800~1200 r / min.

9. The method for preparing modified lithium iron manganese phosphate as described in claim 5, characterized in that, In S1, the stirring speed is 1000 r / min.

10. The method for preparing modified lithium iron manganese phosphate as described in claim 1, characterized in that, In S1, after the hydrothermal reaction, centrifugation to separate the precipitate, washing, and drying are also performed.

11. The method for preparing modified lithium iron manganese phosphate as described in claim 10, characterized in that, In S1, the temperature of the hydrothermal reaction is 200°C; And / or, in S1, the hydrothermal reaction time is 20 hours; And / or, in S1, the washing operation is to alternately wash with deionized water and ethanol.

12. The method of claim 10, wherein the modified lithium manganese iron phosphate is prepared by the steps of: In S1, the drying temperature is 60~100℃. ​ 13. The method for preparing modified lithium iron manganese phosphate as described in claim 10, characterized in that, In S1, the drying temperature is 80°C.

14. The method for preparing modified lithium iron manganese phosphate as described in claim 1, characterized in that, In S2, the carbon source is one or more of glucose, lactose, sucrose, maltose, phenolic resin, graphite, carbon nanotubes, graphene, polyethylene glycol, and epoxy resin. And / or, in S2, the mass ratio of the intermediate to the carbon source is 10:(1~5).

15. The method for preparing modified lithium iron manganese phosphate as described in claim 14, characterized in that, In S2, the carbon source is glucose; And / or, in S2, the mass ratio of the intermediate to the carbon source is 10:

3.

16. The method for preparing modified lithium iron manganese phosphate as described in claim 1, characterized in that, In S2, the rotation speed of the ball milling reaction is 200~300 rpm; And / or, in S2, the ball milling reaction time is 10~14h; And / or, in S2, the heat treatment is further preceded by a drying operation; the drying temperature is 60~100℃.

17. The method for preparing modified lithium iron manganese phosphate as described in claim 16, characterized in that, In S2, the rotation speed of the ball milling reaction is 250 rpm; And / or, in S2, the ball milling reaction time is 12 hours; And / or, in S2, the drying temperature is 80°C.

18. The method of claim 1, wherein the modified lithium manganese iron phosphate is prepared by the steps of: In S2, the heat treatment is carried out under the protection of an inert atmosphere; ​ And / or, in S2, the temperature of the heat treatment is 500~600℃; And / or, in S2, the heat treatment time is 5~10h; And / or, in S2, the heat treatment further includes crushing and sieving operations.

19. The method for preparing modified lithium iron manganese phosphate as described in claim 18, characterized in that, In S2, the gas in the inert atmosphere is one or more of nitrogen, helium, argon, and helium; And / or, in S2, the temperature of the heat treatment is 550°C; And / or, in S2, the heat treatment time is 5 hours; And / or, in S2, the mesh size of the sieve is 80~120 mesh.

20. The method of claim 18, wherein the modified lithium iron manganese phosphate is prepared by the steps of: In S2, the gas in the inert atmosphere is argon. ​ And / or, in S2, the mesh size of the sieve is 100 mesh.

21. A modified lithium iron manganese phosphate characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 20.

22. The application of the modified lithium iron manganese phosphate as described in claim 21 in cathode materials.

23. A positive electrode material, characterized in that, It includes the modified lithium iron manganese phosphate as described in claim 21.

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