Modified lithium iron manganese phosphate positive electrode material and preparation method thereof

Abstract

The invention belongs to the field of lithium ion battery positive electrode materials, and particularly relates to a modified lithium iron manganese phosphate positive electrode material and a preparation method thereof. By utilizing the unique advantages of Cu9S5 and lithium manganese iron phosphate, Cu9S5 and lithium manganese iron phosphate are prepared into a novel composite positive electrode material with a specific conductive network, and the conductivity and lithium ion diffusion rate of lithium manganese iron phosphate are expected to be improved, so that the composite positive electrode material is applied to a high-performance lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion battery positive electrode materials, and specifically relates to a modified lithium manganese iron phosphate positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are a very important energy storage device in modern new energy technologies and are widely used in electric vehicles, portable electronic devices, and renewable energy storage. The commercialized cathode material lithium iron phosphate is widely used due to its high theoretical capacity and good cycle stability, but it cannot meet the use requirements of high-capacity lithium-ion batteries due to its relatively low operating voltage. Lithium manganese iron phosphate (LMFP) combines the properties of manganese and iron and has a higher energy density than LFP. Due to its excellent performance, it is gradually being used in electric vehicles (EVs), energy storage systems, and portable electronic devices. Especially in the field of electric vehicles, with the emphasis on safety and cost, lithium manganese iron phosphate has become a promising alternative material.

[0003] However, lithium manganese iron phosphate also has its own structural defects, such as low intrinsic conductivity, high Li + Diffusion barrier, Mn under Jahn-Teller effect 3+ Disproportionation reaction occurs to generate Mn 4+ and Mn 2+ In the later stage of discharge, the disproportionation reaction intensifies under the catalysis of the electrolyte, resulting in partial dissolution of Mn and destruction of the structure, which directly affects the electrochemical performance of the material. In response to these problems, researchers have done a lot of work, and the current research direction is mainly to start from ion doping, morphology control and surface coating. Carbon coating on its surface is also considered to be one of the most effective and direct methods to improve electronic conductivity. However, traditional carbon coating on the surface is a point-to-point method, which limits high-rate performance and even hinders the migration and diffusion of lithium ions between the particle surface and the electrolyte, increasing the charge transfer resistance.

[0004] Therefore, the present invention proposes a Cu 9 S 5 Method for coating modified lithium manganese iron phosphate positive electrode material, Cu 9 S 5 The coating layer has high electronic conductivity, which effectively enhances the electronic conductivity of the material, so that the composite material exhibits excellent electrochemical properties. Summary of the invention

[0005] In order to improve the electrochemical performance of lithium manganese iron phosphate, the present invention utilizes Cu 9 S 5The unique advantages of lithium iron manganese phosphate and lithium iron manganese phosphate are combined to form a new type of composite positive electrode material with a specific conductive network, which is expected to improve the electrical conductivity and lithium ion diffusion rate of lithium iron manganese phosphate, and thus be applied to high-performance lithium-ion batteries.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A modified lithium manganese iron phosphate positive electrode material, the modified positive electrode material is a lithium storage positive electrode material with a sulfide layer coated on the surface, and the sulfide is Cu 9 S 5 The content of the sulfide coating layer is 0.5-2%, and the lithium storage positive electrode material is LiFe x Mn y PO 4 / C, where x+y=1, 0<x<1, 0<y<1.

[0008] A method for preparing a modified lithium manganese iron phosphate positive electrode material comprises the following steps:

[0009] (1) Synthesis of LMFP by sol-gel method: lithium source, manganese source, iron source, phosphorus source and carbon source are mixed and dissolved in proportion to obtain a liquid slurry, which is then dehydrated and crushed to obtain a powdery precursor, which is then sintered and crushed to obtain LMFP;

[0010] (2)Cu 9 S 5 Coated LMFP material: LMFP is dispersed in a copper source solution, a sulfur source solution is added, the solution is mixed evenly, transferred to a reactor for reaction, and then washed, dried, and heat-treated to obtain the sulfide-coated positive electrode material.

[0011] In the step (1), the carbon sources are citric acid and ethylene glycol, and the molar ratio of citric acid to metal cation is 1.5:1, and the molar ratio of ethylene glycol to citric acid is 1:1.

[0012] In the step (1), the copper source is one of copper nitrate, copper sulfate or copper chloride; the sulfur source is at least one of thioacetamide, 3-mercaptopropionic acid ester, ammonium thiocyanate or tetramethylthiourea; and the solvent is one or more of methanol, ethanol, propanol, NMP or DMF.

[0013] In the step (1), the phosphorus source is one of ammonium phosphate, diammonium hydrogen phosphate, monoammonium hydrogen phosphate, and phosphoric acid.

[0014] In the step (1), the calcination temperature is 600-750° C. and the calcination time is 6-15 hours.

[0015] In the step (2), the reaction temperature of the reactor is 100-150° C., and the reaction time is 10-20 h.

[0016] The heat treatment temperature in step (2) is 400-600° C., and the heat treatment time is 1-5 hours.

[0017] The lithium source, manganese source and iron source mainly include metal salts containing Li, Mn, Fe, etc. The types of metal salts are mainly nitrates, oxalates, sulfates and halides.

[0018] Compared with the prior art, the preparation method of the present invention has the following beneficial effects:

[0019] The present invention introduces Cu 9 S 5 The coating layer is used to modify the surface of lithium manganese iron phosphate to solve the problems of interface side reactions and material structural instability caused by direct contact between the electrolyte solution and the electrode material. 9 S 5 The coating layer has high electronic conductivity, which effectively enhances the electronic conductivity of the material, thereby significantly improving its electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The Cu prepared in Example 1 9 S 5 EDS diagram of elements in @LMFP: Mn, Fe, P, S, Cu. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] Example 1

[0023] (1) According to LiMn 0.6 Fe 0.4 PO 4 Lithium carbonate, phosphoric acid, ferric nitrate, and manganese nitrate were weighed in a stoichiometric ratio and added to deionized water in a certain order, and citric acid and ethylene glycol were added. Among them, the molar ratio of citric acid to metal cations was 1.5:1, and the molar ratio of ethylene glycol to citric acid was 1:1. The above solution was stirred overnight, then the solvent was evaporated at 100°C and dried at 200°C for 4h. The dried sample was placed in a tubular atmosphere furnace, high-purity nitrogen (≥99.999%) was introduced, and it was heated to 450°C at a heating rate of 3°C / min and kept warm for 6h, and then heated to 650°C again and kept warm for 12h. After cooling in the furnace, it was air flow crushed and graded to obtain lithium manganese iron phosphate positive electrode material.

[0024] (2) Disperse 4.5 kg LMFP into a solution containing 104.2 g Cu(NO 3 ) 245.9 g of thioacetamide was weighed and dissolved in ethanol. The two solutions were mixed evenly, transferred to a reactor and reacted at 120 ° C for 12 hours, washed and vacuum dried at 100 ° C to obtain an intermediate product. The intermediate product was transferred to a sealed box furnace and heated to 500 ° C for 2 hours to obtain Cu 9 S 5 Coated lithium manganese iron phosphate material.

[0025] Example 2

[0026] The difference from Example 1 is that in step (2), by adjusting Cu(NO 3 ) 2 and thioacetamide dosage, Cu 9 S 5 The addition amount of is adjusted from 1% to 2%, and the rest is the same as in Example 1.

[0027] Example 3

[0028] The difference from Example 1 is that in step (2), by adjusting Cu(NO 3 ) 2 and thioacetamide dosage, Cu 9 S 5 The addition amount of is adjusted from 1% to 0.5%, and the rest is the same as in Example 1.

[0029] Example 4

[0030] The difference from Example 1 is that in step (2), the calcination temperature in the box furnace is 600°C.

[0031] Example 5

[0032] The difference from Example 1 is that in step (2), the calcination time in the box furnace is 4 hours.

[0033] Comparative Example 1

[0034] The positive electrode material of this comparative example directly uses the lithium manganese iron phosphate material prepared in step (1) of Example 1.

[0035] The positive electrode material, conductive carbon black, and PVDF were mixed and stirred in a mass ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent to form a slurry. The slurry was then coated on an aluminum foil and made into a positive electrode sheet after being fully dried. The battery was assembled in an argon protection glove box, and the assembled battery was left to stand for 24 hours before charge and discharge tests were performed in a Blue Electric electrochemical tester. The test results are shown in Table 1 below.

[0036] Table 1 Performance test results

[0037]

[0038]

[0039] Figure 1 The element distribution of the sample prepared in Example 1 was analyzed by energy dispersive X-ray spectroscopy (EDS). The elements Mn, Fe, P, S and Cu in the material were clearly visible and evenly distributed in the material.

[0040] From the examples and comparative examples in Table 1, it can be seen that the sulfide coating layer is crucial to the capacity and cycle stability of the lithium manganese iron phosphate positive electrode material. 9 S 5 The coating layer has high electronic conductivity, which effectively enhances the electronic conductivity of the material and greatly improves the positive electrode capacity.

[0041] The above content describes the technical principles, beneficial effects and features of the present invention. It should be pointed out that the above is only a preferred implementation mode of the present invention, but is not limited to the above embodiments. For technicians in the technical field to which the present invention belongs, some improvements and optimizations can be made without departing from the content of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A modified lithium manganese iron phosphate positive electrode material, characterized in that: The modified positive electrode material is a lithium storage positive electrode material with a sulfide layer coated on the surface, the sulfide is Cu9S5, the content of the sulfide coating layer is 0.5-2%, and the lithium storage positive electrode material is LiFe x Mn y PO4 / C, where x+y=1, 0<x<1, 0<y<1.

2. A method for preparing the modified lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The steps include: (1) Synthesis of LMFP by sol-gel method: lithium source, manganese source, iron source, phosphorus source and carbon source are mixed and dissolved in proportion to obtain a liquid slurry, which is then dehydrated and crushed to obtain a powdered precursor, which is then sintered and crushed to obtain LMFP; (2) Cu9S5-coated LMFP material: LMFP is dispersed in a copper source solution, a sulfur source solution is added, the solution is mixed evenly, and the solution is transferred to a reactor for reaction, and then washed, dried, and heat treated to obtain the sulfide-coated positive electrode material.

3. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 2, characterized in that: In the step (1), the carbon sources are citric acid and ethylene glycol, and the molar ratio of citric acid to metal cation is 1.5:1, and the molar ratio of ethylene glycol to citric acid is 1:

1.

4. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 2, characterized in that: In step (1), the copper source is one of copper nitrate, copper sulfate or copper chloride; the sulfur source is at least one of thioacetamide, 3-mercaptopropionic acid ester, ammonium thiocyanate or tetramethylthiourea; and the solvent is one or more of methanol, ethanol, propanol, NMP or DMF.

5. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 2, characterized in that: In the step (1), the phosphorus source is one of ammonium phosphate, diammonium hydrogen phosphate, monoammonium hydrogen phosphate, and phosphoric acid.

6. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 2, characterized in that: In the step (1), the calcination temperature is 600-750° C. and the calcination time is 6-15 hours.

7. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 2, characterized in that: In the step (2), the reaction temperature of the reactor is 100-150° C., and the reaction time is 10-20 hours.

8. The method for preparing the modified lithium iron manganese phosphate positive electrode material according to claim 2, characterized in that: The heat treatment temperature in step (2) is 400-600° C. and the heat treatment time is 1-5 hours.

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