A cathode material for lithium iron phosphate batteries and a preparation method thereof

Abstract

The present invention discloses a cathode material for a lithium iron phosphate battery and a preparation method thereof. The cathode material for the lithium iron phosphate battery comprises lithium iron phosphate and modified nano carbon black, and the weight ratio of the modified nano carbon black to the lithium iron phosphate is 0.1-5:100; the modified nano carbon black is 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano carbon black. The nano carbon black modified by hydroxyl reacts with metallic sodium to form sodium alkoxide, and the sodium alkoxide reacts with 1-halo-4-methyl-5-trifluoro-2-pentene to form alkyl nano carbon black containing vinyl, and then 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano carbon black is obtained through polymerization reaction, separation and purification. The modified nano carbon black prepared by the present invention forms a three-dimensional conductive network for wrapping the lithium iron phosphate. Due to the action of the alkyl polymerized long chain, the properties of the carbon black are changed, the flexibility of the nano carbon black is enhanced, the wrapping property of the nano carbon black is increased, the conductivity is correspondingly improved, and the stability is also significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a cathode material for a lithium iron phosphate battery and a preparation method thereof. Background Art

[0002] Lithium iron phosphate batteries use lithium iron phosphate as the cathode material. During charging, lithium ions in the lithium iron phosphate battery are removed, transferred through the electrolyte to the negative electrode, and embedded in the negative electrode carbon material; at the same time, electrons are released from the positive electrode and reach the negative electrode through the external circuit to maintain chemical reaction balance. During discharging, lithium ions are removed from the negative electrode, reach the positive electrode through the electrolyte, and at the same time the negative electrode releases electrons, which reach the positive electrode through the external circuit, so that energy can be provided. The advantages of lithium iron phosphate batteries are high working voltage, large energy density and good safety performance.

[0003] Nano carbon black has excellent electrical conductivity. In the prior art, attempts have been made to dope or combine nano carbon black with lithium iron phosphate to improve the electrical conductivity of lithium iron phosphate and thus improve its performance. However, the existing nano carbon black has strong rigidity. When it directly wraps lithium iron phosphate, its wrapping property is insufficient, so that its improvement effect on electrical conductivity is limited and its stability is also insufficient. Summary of the Invention

[0004] Aiming at the problems of insufficient wrapping property of nano carbon black, limited improvement effect on lithium iron phosphate materials and insufficient stability in the prior art, the present invention provides a cathode material for a lithium iron phosphate battery and a preparation method thereof, and the modified nano carbon black can be better applied to lithium iron phosphate battery materials.

[0005] The present invention is realized through the following technical solutions:

[0006] A cathode material for a lithium iron phosphate battery, comprising lithium iron phosphate and modified nano carbon black, and the weight ratio of the modified nano carbon black to lithium iron phosphate is 0.1-5:100; the modified nano carbon black is 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano carbon black, and its preparation method is as follows: the hydroxy-modified nano carbon black reacts with sodium metal to form sodium alkoxide, and the sodium alkoxide reacts with 1-halo-4-methyl-5-trifluoro-2-pentene to form an alkyl nano carbon black containing vinyl, and then the modified nano carbon black is obtained through polymerization reaction and separation and purification. The reaction formula is as Figure 1 shown, where n represents the polymerization molecular weight;

[0007] The carbon content of the hydroxy-modified nano carbon black is more than 95%.

[0008] Further, the molar ratio of the hydroxy-modified nano carbon black to sodium metal is 1:1-1:1.5, and the reaction conditions are reaction under normal temperature and pressure.

[0009] Further, the molar ratio of the hydroxyl-modified nano carbon black to 1-halo-4-methyl-5-trifluoro-2-pentene is 1:1 to 1:1.5, and the reaction solvent of the hydroxyl-modified nano carbon black and 1-halo-4-methyl-5-trifluoro-2-pentene is ethanol.

[0010] Further, the conditions of the polymerization reaction are as follows: in the presence of a tin catalyst, the reaction temperature is 90-110 °C， The reaction pressure is 2-5 MPa, and the polymerization reaction time is 3-5 h.

[0011] Further, the polymerization molecular weight of the 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano carbon black is 5000-40000, preferably 20000-30000.

[0012] Further, the 1-halo-4-methyl-5-trifluoro-2-pentene is 1-chloro-4-methyl-5-trifluoro-2-pentene.

[0013] In the present invention, the preparation method of the cathode material for a lithium iron phosphate battery includes the following steps:

[0014] (1) The hydroxyl-modified nano carbon black reacts with metallic sodium to form sodium alkoxide, and the sodium alkoxide reacts with 1-halo-4-methyl-5-trifluoro-2-pentene to form vinyl-containing alkyl nano carbon black, and then through polymerization reaction and separation and purification, modified nano carbon black is obtained;

[0015] (2) The modified nano carbon black, lithium iron phosphate and water prepared in step (1) are mixed and stirred, and then ground and granulated to obtain a precursor, and then calcined to obtain the cathode material for a lithium iron phosphate battery.

[0016] Further, in step (2), the weights of the modified nano carbon black, lithium iron phosphate and water are 0.1-5:100:50-200.

[0017] Further, the calcination conditions are 500-800 °C The calcination time is 3-5 h.

[0018] Beneficial effects

[0019] The modified nano carbon black prepared by the present invention forms a three-dimensional conductive network space for encapsulating lithium iron phosphate. The properties of the carbon black are changed by the action of the alkyl polymerization long chain. The flexibility of the nano carbon black is enhanced and the encapsulation property is increased by the action of the alkyl polymerization long chain. Accordingly, the conductivity is improved and the stability is also significantly improved. Brief description of the drawings

[0020] Figure 1 It is a synthesis schematic diagram of the modified nano carbon black of the present invention, showing the polymerization molecular weight.

[0021] Figure 2 Scanning electron microscope image of the cathode material of the lithium iron phosphate battery prepared in Example 1. Detailed implementation manners

[0022] The embodiments of the present invention will be described in detail below. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0023] The synthesis schematic diagram of the modified nano-carbon black prepared in the embodiment of the present invention is as Figure 1 shown, where n represents the polymerization molecular weight;

[0024] The nano-carbon black modified with hydroxyl groups used in the embodiment of the present invention is purchased from Xin Hong Chemical Co., Ltd. in Taicang City, and the carbon content is 95%.

[0025] Example 1

[0026] (1) React the nano-carbon black modified with hydroxyl groups with metallic sodium to form sodium alkoxide. The reaction molar ratio of the nano-carbon black modified with hydroxyl groups to metallic sodium is 1:1.2; then react with 1-halo-4-methyl-5-trifluoro-2-pentene to form alkyl nano-carbon black containing vinyl groups (the solvent is ethanol). The molar ratio of the nano-carbon black modified with hydroxyl groups to 1-halo-4-methyl-5-trifluoro-2-pentene is 1:1. Then carry out a polymerization reaction. The polymerization reaction conditions are as follows: using a tin catalyst, at a temperature of 95 °C and a pressure of 2 MPa, and the polymerization reaction time is 3 h. After the reaction is completed, the modified nano-carbon black with a polymerization molecular weight of 5000 - 10000 (3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano-carbon black) is obtained through separation and purification;

[0027] (2) Mix and stir the modified nano-carbon black, lithium iron phosphate and water prepared in step (1). The mass ratio of the modified nano-carbon black, lithium iron phosphate and water is 1:100:100. After mixing and stirring, grind and granulate to obtain a precursor, and then calcine at 500 °C for 4 hours to obtain the cathode material of the lithium iron phosphate battery. The scanning electron microscope image of the cathode material of the lithium iron phosphate battery is as Figure 1 shown, and the regular appearance of the encapsulated lithium iron phosphate can be observed.

[0028] Example 2

[0029] (1)The molar ratio of the hydroxyl-modified nano-carbon black to sodium metal in the reaction is 1:1.2, and the molar ratio of the hydroxyl-modified nano-carbon black to 1-halo-4-methyl-5-trifluoro-2-pentene is 1:1.1. The polymerization reaction temperature is 90 °C, the polymerization reaction pressure is 3 MPa, and the polymerization reaction time is 4 h. The rest is the same as in step (1) of Example 1. After separation and purification, modified nano-carbon black with a polymerization molecular weight of 10,000 - 20,000 is obtained;

[0030] (2)The preparation method of the positive electrode material for the lithium iron phosphate battery is the same as that in Example 1.

[0031] Example 3

[0032] (1)The molar ratio of the hydroxyl-modified nano-carbon black to sodium metal in the reaction is 1:1.1, and the molar ratio of the hydroxyl-modified nano-carbon black to 1-halo-4-methyl-5-trifluoro-2-pentene is 1:1.2. The polymerization reaction temperature is 95 °C, the polymerization reaction pressure is 2 MPa, and the polymerization reaction time is 4 h. The rest is the same as in step (1) of Example 1. After separation and purification, modified nano-carbon black with a polymerization molecular weight of 20,000 - 30,000 is obtained;

[0033] (2)The preparation method of the positive electrode material for the lithium iron phosphate battery is the same as that in Example 1.

[0034] Example 4

[0035] (1)The molar ratio of the hydroxyl-modified nano-carbon black to sodium metal in the reaction is 1:1.2, and the molar ratio of the hydroxyl-modified nano-carbon black to 1-halo-4-methyl-5-trifluoro-2-pentene is 1:1. The polymerization reaction temperature is 95 °C, the polymerization reaction pressure is 2 MPa, and the polymerization reaction time is 4 h. The rest is the same as in step (1) of Example 1. After separation and purification, modified nano-carbon black with a polymerization molecular weight of 30,000 - 40,000 is obtained.

[0036] (2)The preparation method of the positive electrode material for the lithium iron phosphate battery is the same as that in Example 1.

[0037] Comparative Example 1

[0038] Mix ordinary carbon black without hydroxylation, lithium iron phosphate and water and stir (the ratio is the same as in step (2) of Example 1), then grind and granulate to obtain a precursor, and then calcine to obtain the positive electrode material for the lithium iron phosphate battery.

[0039] Electrochemical performance test

[0040] The initial Coulombic efficiency (%) and the Coulombic efficiency (%) after 100 cycles of the cathode materials of lithium iron phosphate batteries in Examples 1-4 and Comparative Example 1 were tested. The Coulombic efficiency refers to the percentage of the charge discharged during the battery discharge process (unit: ampere-hour) to the charge input during the charging process (unit: ampere-hour). The test results are shown in Table 1 below:

[0041] Table 1 Test Results of Electrochemical Performance of Cathode Materials of Lithium Iron Phosphate Batteries

[0042]

[0043] As can be seen from Table 1, the initial Coulombic efficiencies in Examples 1-4 are all higher than those in the control example, indicating that the conductivity of the cathode materials of lithium iron phosphate batteries wrapped by the action of alkyl-polymerized long-chain modified carbon black has been enhanced, and the efficiency value has been correspondingly improved. Moreover, the efficiencies in Examples 3 and 4 reached the highest, that is, the conductivity reached the optimal when the polymerization molecular weight value of polyethylene was 20,000-30,000 or 30,000-40,000. Considering the economic cost, the polymerization molecular weight value of polyethylene is best at 20,000 to 30,000. In addition, after the charge and discharge cycle reached 100 times and the Coulombic efficiency test was carried out again, the efficiency stability of Examples 1-4 remained at a relatively high level.

Claims

1. A cathode material for lithium iron phosphate battery, characterized in that, It includes lithium iron phosphate and modified nano-carbon black, and the weight ratio of the modified nano-carbon black to lithium iron phosphate is 0.1 - 5:100; The modified nano-carbon black is 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano-carbon black, and its preparation method is as follows: The nano-carbon black modified with hydroxyl reacts with sodium metal to form sodium alkoxide, and the sodium alkoxide reacts with 1-halo-4-methyl-5-trifluoro-2-pentene to form vinyl-containing alkyl nano-carbon black, and then the modified nano-carbon black is obtained through polymerization reaction, separation and purification; The carbon content of the nano-carbon black modified with hydroxyl is more than 95%; The conditions of the polymerization reaction are that in the presence of a tin catalyst, the reaction temperature is 90 - 110 °C, the reaction pressure is 2 - 5 MPa, and the polymerization reaction time is 3 - 5 h; The polymerization molecular weight of the 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano-carbon black is 5000 - 40000.

2. The cathode material for lithium iron phosphate battery according to claim 1, characterized in that, The molar ratio of the nano-carbon black modified with hydroxyl to sodium metal is 1:1 - 1:1.5, and the reaction conditions are at normal temperature and pressure.

3. The cathode material for lithium iron phosphate battery according to claim 1, characterized in that The molar ratio of the nano-carbon black modified with hydroxyl to 1-halo-4-methyl-5-trifluoro-2-pentene is 1:1 - 1:1.5, and the reaction solvent of the nano-carbon black modified with hydroxyl and 1-halo-4-methyl-5-trifluoro-2-pentene is ethanol.

4. The cathode material for lithium iron phosphate battery according to claim 1, wherein The polymerization molecular weight of the 3-oxo-5-polyethylene-7-methyl-8-trifluoroalkyl nano-carbon black is 20000 - 30000.

5. The cathode material of the lithium iron phosphate battery according to claim 1, characterized in that, The 1-halo-4-methyl-5-trifluoro-2-pentene is 1-chloro-4-methyl-5-trifluoro-2-pentene.

6. The preparation method of the lithium iron phosphate battery cathode material according to any one of claims 1 to 5, characterized in that, It includes the following steps: (1) The nano-carbon black modified with hydroxyl reacts with sodium metal to form sodium alkoxide, and the sodium alkoxide reacts with 1-halo-4-methyl-5-trifluoro-2-pentene to form vinyl-containing alkyl nano-carbon black, and then the modified nano-carbon black is obtained through polymerization reaction, separation and purification; (2) The modified nano-carbon black, lithium iron phosphate and water prepared in step (1) are mixed and stirred, and then ground and granulated to obtain a precursor, and then calcined to obtain the positive electrode material of the lithium iron phosphate battery.

7. The preparation method of the cathode material of the lithium iron phosphate battery according to claim 6, characterized in that, In step (2), the weights of the modified nano-carbon black, lithium iron phosphate and water are 0.1 - 5:100:50 - 200.

8. The preparation method of the cathode material for lithium iron phosphate batteries according to claim 6, characterized in that, The calcination conditions are 500 - 800 °C, and the calcination time is 3 - 5 h.

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