A low-temperature lithium-ion battery negative electrode material and preparation method thereof

Abstract

The invention discloses a low-temperature lithium-ion battery negative electrode material and a preparation method thereof, wherein the low-temperature lithium-ion battery negative electrode material preparation method comprises: S1, preparing N-doped porous carbon; S2, Sn doping; S3, preparing TiO2 coated with a carbon coating; S4, preparing carbon-coated Li4Ti5O 12 / Sn / N doped composite negative electrode material; by coating the raw material TiO2 with a carbon coating, the Li4Ti5O 12 The particle agglomeration and enrichment during the material preparation process, and the Sn metal doping of N-doped porous carbon materials further improved the Li4Ti5O 12 The material's transfer rate of lithium ions and electrons improves the existing Li4Ti5O 12 The negative electrode material has large migration impedance and low conductivity at low temperatures.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a low-temperature lithium-ion battery negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, transportation, aerospace and other important fields due to their high energy density, long cycle life and light weight and portability. The characteristics of lithium-ion power batteries are significantly affected by the ambient temperature, especially in low temperature environments, where their available energy and power decay more seriously. Long-term use in low temperature environments will accelerate the aging of power batteries and shorten their service life.

[0003] Due to safety and cycle stability considerations, Li4Ti5O 12 Anode materials are very promising for high rate and low temperature operation of lithium-ion batteries. However, Li4Ti5O 12 The electronic and lithium ion conductivity of the material itself is not high, and its low conductivity leads to slow electrode reaction kinetics; in addition, the existing Li4Ti5O 12 Li4Ti5O prepared by negative electrode material preparation method 12 The material particles are relatively coarse, and the coarse Li4Ti5O 12 It exhibits a large electrode polarization resistance at low temperatures, resulting in poor low-temperature performance of the battery. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a low-temperature lithium-ion battery negative electrode material and a preparation method thereof, aiming to solve the problems of low initial charge and discharge efficiency, poor cycle performance, and poor low-temperature performance of current lithium-ion battery negative electrode materials.

[0005] To achieve the above object, the present invention provides a low-temperature power battery negative electrode material, comprising the following steps: A method for preparing a low-temperature lithium-ion battery negative electrode material, characterized in that it comprises the following steps:

[0006] S1. Preparation of N-doped porous carbon: weigh chitosan powder and add it to an aqueous solution containing 5% (wt) acetic acid, stir at room temperature to form solution A; weigh Zn(NO3)2·6H2O and dissolve it in deionized water to form solution B; add the solution B dropwise into the solution A with a dropper, and continue stirring at room temperature to form solution C; freeze the solution C and dry it using a vacuum freeze-drying method; place the solid powder obtained after the vacuum freeze-drying in a high-temperature tube furnace protected by a nitrogen atmosphere for high-temperature carbonization treatment; pickle the carbonized product obtained by the high-temperature carbonization treatment with a hydrochloric acid solution, filter the solution obtained by the pickling using a vacuum filtration method, and continuously wash the powder sample obtained after filtration with deionized water until the pH value of the filtrate is neutral; dry the filtered sample to obtain the N-doped porous carbon;

[0007] S2, Sn doping: a layer of Sn metal coating is deposited on the surface of N-doped porous carbon by physical vapor deposition;

[0008] S3, preparing TiO2 coated with a carbon coating: mixing TiO2 and glucose in an ethanol-water mixed solvent and stirring, and then drying in an air circulation oven to obtain a mixture; heating the mixture at a high temperature under a N2 atmosphere to obtain TiO2 coated with a carbon coating;

[0009] S4: Preparation of carbon-coated Li4Ti5O 12 / Sn / N doped composite negative electrode material: Sn / N doped porous carbon, Li2CO3 and carbon coated TiO2 are dispersed in a hexamethylene solvent and then mixed by ball milling; the slurry obtained by ball milling is dried to remove the solvent and calcined in a N2 atmosphere to obtain carbon coated Li4Ti5O 12 / Sn / N doped composite negative electrode materials.

[0010] Optionally, the mass ratio of chitosan powder to Zn(NO3)2·6H2O in S1 is 1:1-1:3; the stirring time for forming solution A is 20-35 min, and the stirring time for forming solution C is 4.5-5.5 h;

[0011] Optionally, the freezing treatment in S1 is to place the solution C in a freezer for 6-10 hours at a freezing temperature of -20°C to -10°C;

[0012] Optionally, the high temperature carbonization treatment in S1 is 500-700°C, the heating rate is 5-8°C / min, and the carbonization time is 2-4h;

[0013] Optionally, the drying treatment in S1 is to place the filtered sample in an oven at 80° C. for 20-28 hours;

[0014] Optionally, the thickness of the Sn metal coating in S2 is 40-50 nm;

[0015] Optionally, in S3, the heating temperature is 500-700°C, the heating time is 3-5h, and the mass ratio of TiO2 to glucose is 5:1-4:1;

[0016] Optionally, in S4, the molar ratio of Li2CO3 to carbon-coated TiO2 is 2:5, and the mass ratio of Sn / N-doped porous carbon to the sum of the mass of Li2CO3 and carbon-coated TiO2 is 1:15-1:12;

[0017] Optionally, in S4, the calcination temperature is 700-800° C., the calcination time is 11-13 h, and the ball milling time is 3-4 h;

[0018] In order to achieve the above object, the present invention also provides a low-temperature lithium-ion battery negative electrode material prepared by the above method.

[0019] In order to achieve the above object, the present invention also provides a low-temperature lithium-ion battery negative electrode, comprising the above-mentioned low-temperature lithium-ion battery negative electrode material.

[0020] Beneficial effects of the present invention: The present invention limits the Li4Ti5O 12 The particles aggregate and agglomerate during high temperature calcination, thus reducing the Li4Ti5O 12 The particle size of the particles is small, and the carbon coating on the surface of TiO2 also helps to 12 The particles and N-doped porous carbon particles are bonded together to improve the Li4Ti5O 12 The conductivity of the particles is further improved by depositing a thin Sn metal layer on the surface of the N-doped porous carbon. 12 / Sn / N doped composites for lithium ion and electron transport rates; carbon-coated Li4Ti5O 12 The Sn / N-doped composite material has high transport properties for both lithium ions and electrons, thus achieving good low-temperature performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The carbon-coated Li4Ti5O 12 Flow chart of the preparation of / Sn / N doped composite negative electrode materials. DETAILED DESCRIPTION

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

[0023] Example 1

[0024] Weigh 1g chitosan powder and add it to 30ml aqueous solution containing 5% (wt) acetic acid, stir at room temperature for 20min to form a light yellow viscous solution A; weigh 3g Zn(NO3)2·6H2O and dissolve it in 35ml deionized water to form solution B; add solution B dropwise to solution A and continue stirring at room temperature for 5h to form solution C; place solution C in the freezer of a refrigerator, freeze it at -30℃ for 8h, and then use vacuum freeze drying to dry it to remove moisture; place the solid powder obtained after freeze drying in a high-temperature tube furnace protected by nitrogen atmosphere, and carbonize it at 600℃, respectively, and set the heating rate to 5℃min -1 , the carbonization time is 3h; the carbonized product is acid-washed with a 10% (vol) hydrochloric acid solution for 24h, the solution is filtered by vacuum filtration and the powder sample obtained after filtration is continuously washed with deionized water until the pH value of the filtrate is neutral; the filtered sample is placed in an oven at 80°C and dried for 24h to obtain N-doped porous carbon;

[0025] A 50nm Sn metal coating is deposited on the N-doped porous carbon by physical vapor deposition. The physical vapor deposition metal coating method is common knowledge in the art and will not be described in detail here.

[0026] Anatase TiO2 and glucose in a weight ratio of 4:1 were mixed in an ethanol-water mixed solvent, wherein the volume ratio of ethanol to water was 10:1, stirred for 2 h, and then dried in an air circulation oven at 100 °C for 10 h. The mixture was heated at 600 °C for 5 h under a nitrogen atmosphere to obtain a carbon-coated TiO2;

[0027] According to the molar ratio of Li2CO3 to carbon-coated TiO2 of 2:5, Sn / N-doped porous carbon, Li2CO3 and carbon-coated TiO2 were dispersed in a hexamethylene solvent at a mass ratio of 1:15, and then mixed by ball milling. The ball milling was carried out in a planetary ball mill at a speed of 200 rpm for 4 h. The slurry obtained by ball milling was dried and further calcined at 800 °C for 12 h in a nitrogen atmosphere to obtain carbon-coated Li4Ti5O 12 / Sn / N doped porous carbon composite anode material.

[0028] Preparation of negative electrode sheet: Add PVDF binder and solvent into a stirrer, stir until the binder is completely dissolved, then add conductive agent and carbon-coated Li4Ti5O prepared in Example 1 above. 12 / Sn / N doped porous carbon composite material is stirred to obtain negative electrode slurry, the negative electrode slurry is evenly coated on aluminum foil as a negative electrode current collector, and negative electrode sheets are obtained after rolling and slicing; the negative electrode active material in the negative electrode material accounts for 98.5% of the total weight, the weight ratio of the binder is 1%, and the weight ratio of the conductive agent is 0.5%; the binder is PVDF, and the conductive agent is carbon black.

[0029] Positive electrode slurry and positive electrode sheet are prepared according to a ratio of 1% by weight of the binder, 2% by weight of the conductive agent, and 97% by weight of the positive electrode active material. The positive electrode active material is lithium iron phosphate, the binder is PVDF, and the conductive agent is carbon black. The preparation method of the positive electrode slurry and the positive electrode sheet is common knowledge in the art and will not be elaborated here.

[0030] The positive electrode sheet, negative electrode sheet and separator are prepared into a battery cell 1. The preparation method of the battery cell is common knowledge in the art and will not be described in detail here.

[0031] Example 2

[0032] A battery cell 2 was prepared according to the battery cell preparation method described in Example 1, except that the weight ratio of anatase TiO2 to glucose was 5:1.

[0033] Comparative Example 1

[0034] The prepared N-doped porous carbon was replaced with a common commercially available graphite negative electrode (model LG35-99), and the remaining steps were the same as those in Example 1, thereby preparing a battery cell 3.

[0035] Comparative Example 2

[0036] N-doped porous carbon was prepared according to the steps of Example 1, and the Sn-doping preparation process was omitted. The remaining steps were the same as those of Example 1, thereby preparing a battery cell 4.

[0037] Comparative Example 3

[0038] According to the preparation method described in Example 1, N-doped porous carbon was prepared and a 50 nm Sn metal coating was deposited on the N-doped porous carbon. The step of preparing the carbon-coated TiO2 was omitted, and Li4Ti5O was prepared according to the step of S4 using TiO2 without carbon coating. 12 / Sn / N doped porous carbon composite negative electrode material, thereby preparing battery cell 5.

[0039] The battery cells 1-5 prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to low temperature performance tests. Low temperature performance tests are common knowledge in the art and will not be described in detail herein. The test results are shown in the following table:

[0040]

[0041]

[0042] By comparing the results of the low temperature performance test of Example 1 with those of Comparative Examples 1-3, it can be seen that the carbon coating on the surface of TiO2 reduces the Li4Ti5O 12 The particle size of Li4Ti5O 12 The particles and N-doped porous carbon particles are bonded together, which greatly improves the conductivity of the negative electrode material to lithium ions and electrons, and greatly improves the low-temperature performance of the battery.

[0043] By comparing the results of the low temperature performance test of Example 1 and Example 2, it can be seen that due to the reduction in carbon content, the carbon coating cannot completely cover the TiO2 surface, which affects the improvement of the low temperature performance of the battery.

[0044] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material for a low-temperature lithium-ion battery, characterized in that: The following steps are involved: S1. Preparation of N-doped porous carbon: weigh an appropriate amount of chitosan powder and add it to an aqueous solution containing 5% (wt) acetic acid, and stir at room temperature to form solution A; weigh Zn(NO3)2·6H2O and dissolve it in deionized water to form solution B; add the solution B dropwise into the solution A with a dropper, and continue stirring at room temperature to form solution C; After freezing the solution C, it is dried by vacuum freeze drying; the solid powder obtained by vacuum freeze drying is placed in a high-temperature tube furnace protected by nitrogen atmosphere for high-temperature carbonization; the carbonized product obtained by the high-temperature carbonization is pickled with hydrochloric acid solution, the pickled solution is filtered by vacuum filtration, and the powder sample obtained after filtration is continuously washed with deionized water until the pH value of the filtrate is neutral; the filtered sample is dried to obtain the N-doped porous carbon; S2, Sn doping: a layer of Sn metal coating is deposited on the surface of N-doped porous carbon by physical vapor deposition; S3, preparing TiO2 coated with a carbon coating: mixing TiO2 and glucose in an ethanol-water mixed solvent and stirring, and then drying in an air circulation oven to obtain a mixture; heating the mixture at a high temperature under a N2 atmosphere to obtain TiO2 coated with a carbon coating; S4: Preparation of carbon-coated Li4Ti5O 12 / N / Sn doped composite negative electrode material: N / Sn doped porous carbon, Li2CO3 and carbon coated TiO2 are dispersed in a hexamethylene solvent and then mixed by ball milling; the slurry obtained by ball milling is dried to remove the solvent and calcined in a N2 atmosphere to obtain carbon coated Li4Ti5O 12 / N / Sn doped composite negative electrode materials.

2. The preparation method according to claim 1, characterized in that: The mass ratio of chitosan powder to Zn(NO3)2·6H2O in S1 is 1:1-1:3; the stirring time for forming solution A is 20-35 minutes, and the stirring time for forming solution C is 4.5-5.5 hours.

3. The preparation method according to claim 1, characterized in that: The freezing treatment in S1 is to place the solution C in a freezing chamber for 6-10 hours at a freezing temperature of -20°C to -10°C.

4. The preparation method according to claim 1, characterized in that: The temperature of the high temperature carbonization treatment in S1 is 500-700°C, the heating rate is 5-8°C / min, the carbonization time is 2-4h, and the drying treatment is to place the filtered sample in an oven at 80°C and dry it for 20-28h.

5. The preparation method according to claim 1, characterized in that: The thickness of the Sn metal coating in S2 is 40-50 nm.

6. The preparation method according to claim 1, characterized in that: In S3, the heating temperature is 500-700°C, the heating time is 3-5h, and the mass ratio of TiO2 to glucose is 15:1-20:

1.

7. The preparation method according to claim 1, characterized in that: In the S4, the molar ratio of Li2CO3 to carbon-coated TiO2 is 2:5, and the mass ratio of N / Sn-doped porous carbon to Li2CO3 and carbon-coated TiO2 is 1:15-1:

10.

8. The preparation method according to claim 1, characterized in that: In S4, the calcination temperature is 700-800° C., the calcination time is 11-13 h, and the ball milling time is 3-4 h.

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