CN112928275B - Method for preparing lithium ion carbon anode material by organophosphorus modification on carbon black surface - Google Patents

Abstract

The invention relates to a method for preparing a lithium ion carbon negative electrode material by modifying the surface of carbon black with organophosphorus. Methane; drop thionyl chloride into the two-necked flask, the mole number of which is 0.5-3 times the mole number of triethyl phosphite, and react for 0.5-24 hours at 25-65°C; carbon black is dispersed in dichloromethane In the methane solvent, then add it to the two-necked flask in step 3), then add triethylamine, and continue to react at 25-65 ° C for 0.5-48 hours; Washed and dried under vacuum. The advantages are: the present invention introduces an organic phosphorus functional group on the surface of the carbon black, compared with the original carbon black, the carbon black modified by the organic phosphorus functional group is reversible in the first circle, and the lithium storage capacity is increased to 950mAh/g.

Description

Method for preparing lithium ion carbon anode material by organophosphorus modification on carbon black surface

technical field

The invention relates to the field of carbon-based negative electrode materials for lithium ion batteries, in particular to a method for preparing a lithium ion carbon negative electrode material by modifying the surface of carbon black with organic phosphorus.

Background technique

In recent years, great progress has been made in the research of anode materials for lithium-ion secondary batteries, among which graphite anode materials have been successfully commercialized. Safety performance and rate performance put forward higher requirements. Graphite materials can no longer meet the needs of future lithium-ion batteries due to their low rate performance. New anode materials, such as new carbon materials, metals, metal oxides and their sulfides, are gradually moving from the laboratory to industrial production. Among them, hard carbon The material has become the most potential electrode material for commercialization due to its advantages of low price, easy preparation, and low environmental harm.

Hard carbon materials have an amorphous structure with more lithium storage sites. Li ions are mainly stored through diffusion-controlled intercalation behavior, but their cycle/rate performance is often poor due to kinetic limitations. Carbon black (CB) is a typical hard carbon material with good electrical conductivity and low price. At present, it is mainly used as an additive in the production of rubber and in the production of dyes and other low value-added products. Its application is relatively simple, but its good electrical conductivity gives its potential as a high value-added electrode material. In 2020, Wang et al. published "Enhanced Li Ion Storage Performances of Carbon Black by Introducing Organosulfur Groups on Surface" in "Electrochemistry", which effectively improved the performance of carbon black by introducing organic functional groups such as -COSR and -CSR on the surface of carbon black. However, the improvement of its lithium storage capacity is not obvious, which limits the application of modified carbon black in the production of practical electrode materials.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a lithium ion carbon negative electrode material by organophosphorus modification on the surface of carbon black, utilizing the reactivity of functional groups such as hydroxyl and carboxyl groups on the surface of carbon black, on the surface of carbon black. The introduction of organophosphorus functional groups improves the lithium storage capacity and cycle stability of carbon black.

To achieve the above object, the present invention is achieved through the following technical solutions:

The method for preparing a lithium ion carbon negative electrode material by organophosphorus modification on the surface of carbon black comprises the following steps:

1) Use the Boemh titration method to measure the hydroxyl and carboxyl functional groups on the surface of carbon black;

2) get the triethyl phosphite of carbon black hydroxyl and carboxyl molar total multiples respectively and join in the two-necked flask, and add anhydrous dichloromethane;

3) drop thionyl chloride into the two-necked flask, the mole number of which is 0.5-3 times of the mole number of triethyl phosphite, and reacts at 25-65 ° C for 0.5-24 hours;

4) Disperse the carbon black in the dichloromethane solvent, then add it to the two-necked flask in step 3), then add triethylamine, and continue the reaction at 25-65 ° C for 0.5-48 hours; The mass concentration in methane is 1g/1000mL-100g/mL; the amount of triethylamine added is 1-5 times the total molar amount of carbon black hydroxyl and carboxyl groups;

5) after the reaction finishes, the carbon black after the reaction is washed with chloroform, and vacuum-dried;

The reaction equation for the above process is:

The gas generated during the reaction of step 3) is introduced into the saturated sodium bicarbonate solution.

The mass concentration of methylene chloride in the methylene chloride solvent described in step 4) is 98%-100%.

Compared with the prior art, the beneficial effects of the present invention are:

Compared with the original carbon black, the carbon black modified by the organic phosphorus functional group is reversible in the first circle, and the lithium storage capacity is increased from 301mAh/g to 950mAh/g, so that it can become a High energy density battery negative electrode material, so the use of organic phosphorus modified carbon black to prepare lithium ion battery carbon negative electrode material has broad market application prospects.

Description of drawings

Figure 1 is a flow chart of the production process of organophosphorus modified carbon black.

Figure 2 is a diagram of a lithium-ion battery assembly process.

3 is the infrared spectrum of CB and 7P-CB of Example 1.

In Figure 3: (a) is the infrared spectrum of CB; (b) is the infrared spectrum of 7P-CB.

4 is an adsorption/desorption isotherm plot of CB and 7P-CB of Example 1. FIG.

FIG. 5 is a pore size distribution diagram of CB and 7P-CB of Example 1. FIG.

Fig. 6 is the cycle performance test chart of the battery when CB and 7P-CB of Example 1 are used as lithium ion negative electrode materials.

In Figure 6, (a) is the cycle performance test chart of CB; (b) is the cycle performance test chart of 7P-CB.

7 is a test chart of the rate performance of the battery when CB and 7P-CB of Example 1 are used as lithium ion negative electrode materials.

In Figure 7 (a) is the rate capability test chart of CB; (b) is the rate capability test chart of 7P-CB.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings, but it should be pointed out that the implementation of the present invention is not limited to the following embodiments.

Referring to Figure 1 and Figure 2, the method for preparing a lithium ion carbon anode material by organophosphorus modification on the surface of carbon black includes the following steps:

1) The hydroxyl and carboxyl functional groups on the surface of carbon black were determined by Boemh titration.

2) Take triethyl phosphite with a certain multiple of the total number of moles of carbon black hydroxyl and carboxyl groups, respectively, and add it to the two-necked flask, and add anhydrous dichloromethane.

3) drop thionyl chloride into the two-necked flask, its mole number is 0.5-3 times of triethyl phosphite mole number, and react 0.5-24 hour at 25-65 ℃; The gas that produces in the reaction process is imported into a saturated solution of sodium bicarbonate.

4) Disperse the carbon black in the dichloromethane solvent, then add it to the two-necked flask in step 3), then add triethylamine, and continue the reaction at 25-65 ° C for 0.5-48 hours; The mass concentration in methane is 1g/1000mL-100g/mL; the amount of triethylamine added is 1-5 times the total molar amount of carbon black hydroxyl and carboxyl groups; wherein, the methylene chloride mass concentration in the dichloromethane solvent is 98%- 100%.

5) After the reaction, the carbon black after the reaction was washed with chloroform and dried under vacuum.

The equation for the above reaction is:

Example 1

Example 1

a. The content of hydroxyl and carboxyl functional groups on the surface of carbon black was determined by Boemh titration, and the total moles of hydroxyl and carboxyl groups on the surface of carbon black were 2.54×10 ^-4 mol/g;

b. Take triethyl phosphite with 7 times the total molar amount of hydroxyl and carboxyl groups on the carbon black surface and add it to the two-necked flask, and add anhydrous dichloromethane;

c. Drop thionyl chloride into the two-necked flask, the mole number of which is 0.5 times the mole number of triethyl phosphite, react at 40 ° C for 2 hours, and the gas generated during the reaction is introduced into the saturated sodium bicarbonate solution middle;

d. Add 2g of carbon black and 55mL of dichloromethane into the three-necked flask, then add triethylamine with 5 times the total number of moles of hydroxyl and carboxyl groups on the surface of the carbon black, and continue the reaction at 40°C for 24 hours;

e. After the reaction is completed, the reacted carbon black is washed with chloroform, and then vacuum-dried. The final product is named 7P-CB, and the raw carbon black is named CB, which is used as a negative electrode material for lithium ion batteries to prepare electrode sheets. And assembled lithium-ion batteries to test their electrochemical performance.

Example 2

a. The content of hydroxyl and carboxyl functional groups on the surface of carbon black was determined by Boemh titration, and the total moles of hydroxyl and carboxyl groups on the surface of carbon black were 2.54×10 ^-4 mol/g;

b. Take triethyl phosphite with 7 times the total molar amount of hydroxyl and carboxyl groups on the carbon black surface and add it to the two-necked flask, and add anhydrous dichloromethane;

c. Drop thionyl chloride into the two-necked flask, the mole number of which is 1.5 times the mole number of triethyl phosphite, react at 40 ° C for 2 hours, and the gas generated during the reaction is introduced into the saturated sodium bicarbonate solution middle;

d. Add 2g of carbon black and 55mL of dichloromethane into the three-necked flask, then add triethylamine with 5 times the total number of moles of hydroxyl and carboxyl groups on the surface of the carbon black, and continue the reaction at 40°C for 24 hours;

e. After the reaction is completed, the reacted carbon black is washed with chloroform, and then vacuum-dried. The final product is named 7P-CB, and the raw carbon black is named CB, which is used as a negative electrode material for lithium ion batteries to prepare electrode sheets. And assembled lithium-ion batteries to test their electrochemical performance.

Example 3

a. The content of hydroxyl and carboxyl functional groups on the surface of carbon black was determined by Boemh titration, and the total moles of hydroxyl and carboxyl groups on the surface of carbon black were 2.54×10 ^-4 mol/g;

b. Take triethyl phosphite with 7 times the total molar amount of hydroxyl and carboxyl groups on the carbon black surface and add it to the two-necked flask, and add anhydrous dichloromethane;

c. Drop thionyl chloride into the two-necked flask, the mole number of which is 3 times the mole number of triethyl phosphite, react at 40 ° C for 2 hours, and the gas generated during the reaction is introduced into the saturated sodium bicarbonate solution middle;

d. Add 2g of carbon black and 55mL of dichloromethane into the three-necked flask, then add triethylamine with 5 times the total number of moles of hydroxyl and carboxyl groups on the surface of the carbon black, and continue the reaction at 40°C for 24 hours;

e. After the reaction is completed, the reacted carbon black is washed with chloroform, and then vacuum-dried. The final product is named 7P-CB, and the raw carbon black is named CB, which is used as a negative electrode material for lithium ion batteries to prepare electrode sheets. And assembled lithium-ion batteries to test their electrochemical performance.

The assembly process of the lithium-ion battery includes the preparation of electrode sheets and the process of assembling the lithium-ion battery, as follows:

The preparation of electrode sheets can be summarized into the following steps:

(1) Dry grinding: The electrode material, conductive agent (acetylene black, SP), and binder (polyvinylidene fluoride, PVDF) are uniformly ground in an agate mortar in a mass ratio of 8:1:1.

(2) Wet grinding: nitrogen methyl pyrrolidone (NMP) was added dropwise to an agate mortar, and ground to a uniform viscous slurry.

(3) Smear: first, wipe the copper foil to be used clean with alcohol, place the ground slurry on the surface of the copper foil after drying, and use an automatic film applicator to evenly coat the slurry on the copper foil.

(4) Drying: The electrode sheet was placed in the air, preliminarily dried at 80 °C to remove most of the NMP, and then transferred to a vacuum drying oven for drying at 120 °C for 12 h to completely remove NMP.

(5) Cut sheet: Use a punching machine to cut the electrode sheet into a circular sheet with a diameter of 11 mm.

After the preparation of the above electrode sheets, the lithium ion battery was assembled in a vacuum glove box (water concentration < 0.1 ppm, oxygen concentration < 0.1 ppm) using a CR2032 button battery case. The counter electrode of the lithium ion battery is a lithium sheet, and the specific assembly sequence is negative electrode shell, lithium sheet, separator, 100ul electrolyte, electrode sheet, steel sheet, shrapnel, and positive electrode shell. After the battery is assembled, the electrochemical performance is tested after standing for 12 hours. .

It can be seen from Figure 3(b) that 7P-CB has obvious characteristic peaks at 2922cm ^-1 and 2853cm ^-1 , which correspond to the -CH ₂ - asymmetric stretching vibration and the symmetric stretching vibration in triethyl phosphite, respectively. It indicated that triethyl phosphite was successfully modified to the surface of carbon black.

See Fig. 4 and Fig. 5, according to the calculation of BET equation, the specific surface area of CB is 66.5m ² /g, and the specific surface area of 7P-CB is 60.4m ² /g. It can be seen from Figure 5 that compared with CB, 7P-CB has the most obvious attenuation trend of the pore volume corresponding to the pore size in the range of 11.1nm to 36.2nm, which indicates that due to steric hindrance, it is difficult for the reactants to enter below 11.1nm. The reactants in the organophosphorus modification reaction are mainly concentrated in the pores of 11.1 nm to 36.2 nm for the reaction.

As can be seen from Figure 6, the first-round discharge specific capacity of the raw carbon black CB is 561.7mAh/g, the charging capacity is 301.1mAh/g, and the Coulomb efficiency is 53.60%; the first-round discharge specific capacity of 7P-CB is 1183mAh/g, charging The capacity is 950.2mAh/g, and the coulombic efficiency is 80.32%. During the first cycle of charge and discharge, the reversible capacity of the material was significantly attenuated, which was mainly due to the irreversible capacity generated by the formation of the SEI film. Black CB. In addition, 7P-CB still has a capacity of 711.1 mAh/g after 40 cycles, which is almost twice that of carbon black, and its capacity is significantly improved.

It can be seen from Figure 7 that with the increase of the current density, the capacity of the sample decreases significantly. After 10 cycles, at a current density of 100 mA/g, the capacities of the CB and 7P-CB samples are 290 mAh/g and 825.7 mAh/g, respectively. After 20 cycles, at a current density of 200 mA/g, the capacities of the CB and 7P-CB samples were 273 mAh/g and 754.8 mAh/g, respectively. After 60 cycles, the capacities of the CB and 7P-CB samples were 41 mAh/g and 104.2 mAh/g, respectively, at a current density of 5 A/g. When the current density returned to 100 mA/g again, the sample capacities of CB and 7P-CB were 222 mAh/g and 824 mAh/g, respectively, which indicated that when CB was charged and discharged with a large current and then returned to a small current charge and discharge, its capacity had increased. Significant attenuation, while the capacity of 7P-CB has almost no change, indicating that the rate performance of carbon black after phosphorus modification is significantly improved.

Claims (3)

1. the method for preparing lithium ion carbon negative electrode material by organophosphorus modification on carbon black surface, is characterized in that, comprises the following steps: 1) Use the Boemh titration method to measure the hydroxyl and carboxyl functional groups on the surface of carbon black; 2) get the triethyl phosphite of carbon black hydroxyl and carboxyl molar total multiples respectively and join in the two-necked flask, and add anhydrous dichloromethane; 3) drop thionyl chloride into the two-necked flask, the mole number of which is 0.5-3 times of the mole number of triethyl phosphite, and reacts at 25-65 ° C for 0.5-24 hours; 4) Disperse the carbon black in the dichloromethane solvent, then add it to the two-necked flask in step 3), then add triethylamine, and continue the reaction at 25-65 ° C for 0.5-48 hours; The mass concentration in methane is 1g/1000mL-100g/mL; the amount of triethylamine added is 1-5 times the total molar amount of carbon black hydroxyl and carboxyl groups; 5) after the reaction finishes, the carbon black after the reaction is washed with chloroform, and vacuum-dried; The reaction equation for the above process is:

2. The method for preparing lithium ion carbon negative electrode material by organophosphorus modification on the surface of carbon black according to claim 1, wherein the gas generated during the reaction of step 3) is introduced into the saturated sodium bicarbonate solution. 3. the method for preparing lithium ion carbon anode material by organophosphorus modification on carbon black surface according to claim 1, is characterized in that, in the dichloromethane solvent described in step 4), the methylene chloride mass concentration is 98% -100%.

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