Low-temperature lithium battery negative electrode material and preparation method thereof

Abstract

This invention discloses a method for preparing a low-temperature lithium battery anode material, comprising the following steps: 1) mixing manganese, manganese tetroxide, and lithium hydride to obtain a first mixture; 2) weighing europium nitrate hexahydrate and dissolving it in anhydrous ethanol, then adding the first mixture, adjusting the pH to 9 while stirring, reacting for 1-1.5 hours, rotary evaporation, drying, and pulverizing to obtain a second mixture; 3) mixing the second mixture with NH4F, grinding the mixture, and then subjecting it to high-temperature heat treatment to obtain a third mixture; 4) mixing the third mixture, expanded graphite, and surfactant uniformly in anhydrous ethanol, then stirring and heating at 80-90°C for 0.5-1 hours, followed by rotary evaporation to obtain a composite material; 5) sintering; 6) pulverizing and sieving: pulverizing the sintered material at high speed and sieving to obtain the low-temperature lithium battery anode material. This method can effectively improve the electrochemical performance of lithium battery anode materials at low temperatures and expand the application range of lithium batteries in low-temperature environments.

Description

Technical Field

[0001] This invention relates to the field of lithium battery anode material preparation technology, and in particular to a low-temperature lithium battery anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries have been widely used in mobile communications, electronic devices, and electric vehicles due to their advantages such as high voltage, high specific energy, long cycle life, and good safety performance. In lithium-ion batteries, electrode materials are a key factor determining performance. Although the cost of the negative electrode material in the battery system is relatively low, it has a significant impact on the battery's cycle life.

[0003] Currently, graphite is generally used as the anode active material. Graphite has advantages such as high specific capacity, flat charge-discharge curve, and low price, making it an ideal anode material for lithium-ion batteries. For example, patent application CN2012103090617 discloses a carbon anode material for lithium-ion batteries, including core-shell structured composite particles. The core-shell structured composite particles include a matrix, a matrix coating layer, and carbon nanotubes embedded in the matrix and matrix coating layer. The matrix is ​​natural graphite, and the matrix coating layer is an organic pyrolytic carbon coating layer. The preparation method includes mixing the organic pyrolytic carbon coating layer raw material with a solvent, heating and melting it, and then adding carbon nanotubes to form a uniform dispersion system; adding natural graphite, mixing and stirring in an oil bath, evaporating and drying, and then crushing and granulating; and then performing the following treatments in a non-oxidizing atmosphere: removal of small molecules, organic pyrolytic carbon pyrolysis and free radicalization, thermal polymerization, high-temperature carbonization, and microcrystallization.

[0004] This anode material exhibits good charge-discharge performance at room temperature, but its charge-discharge performance and cycle performance both decline sharply at low temperatures, showing significant performance degradation. However, as the application of lithium-ion batteries in extreme environments such as deep sea, deep space, and extremely cold regions gradually expands, lithium-ion batteries need to maintain good electrochemical performance even below zero degrees Celsius. Therefore, it is urgent to solve the problem of poor electrochemical performance of lithium battery anode materials at low temperatures. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a low-temperature lithium battery anode material and its preparation method. The method can effectively improve the electrochemical performance of the lithium battery anode material at low temperatures and expand the application range of lithium batteries in low-temperature environments.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for preparing a low-temperature lithium battery anode material, comprising the following steps: 1) mixing manganese, manganese tetroxide, and lithium hydride in a mass ratio of 1:(1-2):(0.05-1) to obtain a first mixture; 2) weighing europium nitrate hexahydrate and dissolving it in anhydrous ethanol, then adding the first mixture, adjusting the pH to 9 while stirring, reacting for 1-1.5 hours, rotary evaporating, drying and pulverizing to obtain a second mixture; 3) uniformly mixing the second mixture with NH4F, grinding the mixture, and then subjecting it to high-temperature heat treatment to obtain a third mixture; 4) uniformly mixing the third mixture, expanded graphite, and surfactant in anhydrous ethanol, then stirring and heating at 80-90°C for 0.5-1 hours, rotary evaporating to obtain a composite material; 5) sintering; 6) pulverizing and sieving: pulverizing the sintered material at high speed and sieving to obtain a low-temperature lithium battery anode material.

[0007] Furthermore, in step 2), the ratio of europium nitrate hexahydrate to anhydrous ethanol is 1:(10-20), and its mass ratio to the first mixture is 1:(0.5-0.8).

[0008] Furthermore, in step 3), the mass ratio of the second mixture to NH4F is 100:(10-15).

[0009] Furthermore, the temperature of the high-temperature heat treatment is 100-120℃.

[0010] Furthermore, the expanded graphite was subjected to thermal expansion treatment before being mixed with the third mixture and the surfactant.

[0011] Furthermore, the temperature of the thermal expansion treatment is 800-900℃, and the thermal expansion time is 5-10 minutes.

[0012] Furthermore, the mass ratio of the third mixture, expanded graphite, and surfactant is 1:(5-10):(3-5), and the ratio of the total mass of the third mixture, expanded graphite, and surfactant to the volume of anhydrous ethanol is 1:(10-20).

[0013] Furthermore, the temperature of rotary evaporation in steps 2) and 4) is 90-100℃.

[0014] Furthermore, the sintering temperature is 800-900℃, and the sintering time is 5-6h.

[0015] The present invention also provides a low-temperature lithium battery anode material, which is prepared by the method described above.

[0016] The beneficial effects of the low-temperature lithium battery anode material and its preparation method of the present invention are as follows: The preparation method of the present invention is simple. In the preparation process, a combination of adding europium hexahydrate nitrate + fluorination treatment + expanded graphite + heating oxidation treatment is adopted, so that the anode material not only does not contain europium but also contains europium oxide-expanded graphite phase change material. When used in a low-temperature environment, the combined effect of the doped europium itself and europium oxide-expanded graphite can significantly improve the discharge specific capacitance and cycle performance of the anode material at low temperatures, improve the stability of the anode material at low temperatures, and expand the application range of the anode material. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments, but these specific embodiments do not limit the scope of protection of the present invention in any way.

[0018] Example 1

[0019] A method for preparing a low-temperature lithium battery anode material includes the following steps:

[0020] 1) Manganese, manganese tetroxide, and lithium hydride are mixed in a mass ratio of 1:1.5:0.08 to obtain the first mixture;

[0021] 2) Weigh europium nitrate hexahydrate and dissolve it in anhydrous ethanol. The ratio of europium nitrate hexahydrate to anhydrous ethanol is 1:15. Then add the first mixture. The mass ratio of europium nitrate hexahydrate to the first mixture is 1:0.6. While stirring, adjust the pH to 9 and react for 1.2 hours. Then, evaporate the mixture by rotary evaporation at 95°C, dry and pulverize it to obtain the second mixture.

[0022] 3) The second mixture and NH4F are mixed evenly at a mass ratio of 100:12. After mixing, the mixture is ground and then subjected to high-temperature heat treatment at 110℃ for 1.5h to obtain the third mixture.

[0023] 4) Heat treatment of expanded graphite: Place the expanded graphite at a temperature of 850℃ for 8 minutes to expand it.

[0024] 5) The third mixture, thermally expanded graphite, and glycerol ester (surfactant) are mixed evenly in anhydrous ethanol at a mass ratio of 1:8:4. The ratio of the total mass of the third mixture, expanded graphite, and glycerol ester to the volume of anhydrous ethanol is 1:15. The mixture is then stirred and heated at 85°C for 0.6 h, and then rotary evaporated at 95°C to obtain the composite material.

[0025] 6) Sintering: The composite material is sintered at a high temperature of 850℃ for 6 hours;

[0026] 7) Crushing and sieving: The sintered material is crushed at a high speed of 2400 R / min and sieved through a 270 mesh sieve to obtain the low-temperature lithium battery anode material.

[0027] Example 2

[0028] A method for preparing a low-temperature lithium battery anode material includes the following steps:

[0029] 1) Manganese, manganese tetroxide, and lithium hydride are mixed in a mass ratio of 1:1:0.05 to obtain the first mixture;

[0030] 2) Weigh europium nitrate hexahydrate and dissolve it in anhydrous ethanol. The ratio of europium nitrate hexahydrate to anhydrous ethanol is 1:10. Then add the first mixture. The mass ratio of europium nitrate hexahydrate to the first mixture is 1:0.5. While stirring, adjust the pH to 9 and react for 1 hour. Then, evaporate the mixture by rotary evaporation at 90°C, dry and pulverize to obtain the second mixture.

[0031] 3) Mix the second mixture with NH4F at a mass ratio of 100:10, grind the mixture, and then heat-treat it at 100℃ for 1 hour to obtain the third mixture.

[0032] 4) Heat treatment of expanded graphite: Place the expanded graphite at a temperature of 800℃ for 5 minutes to expand it.

[0033] 5) The third mixture, thermally expanded graphite and glycerol ester were mixed evenly in anhydrous ethanol at a mass ratio of 1:5:3. The ratio of the total mass of the third mixture, expanded graphite and surfactant to the volume of anhydrous ethanol was 1:10. The mixture was then stirred and heated at 80°C for 0.5 h, and then rotary evaporated at 90°C to obtain the composite material.

[0034] 6) Sintering: The composite material is sintered at a high temperature of 800℃ for 5 hours;

[0035] 7) Crushing and sieving: The sintered material is crushed at a high speed of 2400 R / min and sieved through a 270 mesh sieve to obtain the low-temperature lithium battery anode material.

[0036] Example 3

[0037] A method for preparing a low-temperature lithium battery anode material includes the following steps:

[0038] 1) Manganese, manganese tetroxide, and lithium hydride are mixed in a mass ratio of 1:2:1 to obtain the first mixture;

[0039] 2) Weigh europium nitrate hexahydrate and dissolve it in anhydrous ethanol. The ratio of europium nitrate hexahydrate to anhydrous ethanol is 1:20. Then add the first mixture. The mass ratio of europium nitrate hexahydrate to the first mixture is 1:0.8. While stirring, adjust the pH to 9 and react for 1.5 hours. Then, evaporate the mixture by rotary evaporation at 100°C, dry and pulverize it to obtain the second mixture.

[0040] 3) The second mixture and NH4F are mixed evenly at a mass ratio of 100:15. After mixing, the mixture is ground and then subjected to high-temperature heat treatment at 120℃ for 2 hours to obtain the third mixture.

[0041] 4) Heat treatment of expanded graphite: Place the expanded graphite at a temperature of 900℃ for 10 minutes to allow it to expand.

[0042] 5) The third mixture, thermally expanded graphite and glycerol ester were mixed evenly in anhydrous ethanol at a mass ratio of 1:10:5. The ratio of the total mass of the third mixture, expanded graphite and surfactant to the volume of anhydrous ethanol was 1:20. The mixture was then stirred and heated at 90°C for 1 hour and then rotary evaporated at 100°C to obtain the composite material.

[0043] 6) Sintering: The composite material is sintered at a high temperature of 900℃ for 6 hours;

[0044] 7) Crushing and sieving: The sintered material is crushed at a high speed of 2400 R / min and sieved through a 270 mesh sieve to obtain the low-temperature lithium battery anode material.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that steps 2)-5) are not included, and the first mixture obtained in step 1) is directly sintered and then crushed and sieved.

[0047] Comparative Example 2

[0048] The difference between this comparative example and Example 1 is that it does not include steps 2), 4) and 5). In step 3), the first mixture is mixed with NH4F and then ground and subjected to high-temperature heat treatment. The resulting third mixture is then directly sintered, crushed and sieved.

[0049] Comparative Example 3

[0050] The difference between this comparative example and Example 1 is that it does not include step 2). In step 3), the first mixture NH4F is mixed. The other steps are the same as in Example 1.

[0051] Comparative Example 4

[0052] The difference between this comparative example and Example 1 is that it does not include steps 3) and 5), where the second mixture, thermally expanded graphite, and glycerol ester are mixed evenly in anhydrous ethanol at a mass ratio of 1:10:5. All other steps are the same as in Example 1.

[0053] Comparative Example 5

[0054] The difference between this comparative example and Example 1 is that it does not include steps 4) and 5), and directly sinters the third mixture obtained in step 3) and then crush and sieve it.

[0055] Comparative Example 6

[0056] The difference between this comparative example and Example 1 is that in step 5), the mixture is stirred and mixed evenly at room temperature.

[0057] The differences in the steps for preparing low-temperature lithium battery anode materials between Example 1 and Comparative Examples 1-6 are shown in Table 1:

[0058] Table 1. Differences in the steps for preparing low-temperature lithium battery anode materials between Example 1 and Comparative Examples 1-6

[0059]

[0060]

[0061] Experiment 1: Electrochemical performance of batteries made using the low-temperature lithium-ion battery anode materials prepared in Examples 1-3 and Comparative Examples 1-6 at room temperature was determined.

[0062] This experiment investigated the electrochemical performance (discharge specific capacity and cycle performance) of batteries made using the low-temperature lithium-ion battery anode materials prepared in Examples 1-3 and Comparative Examples 1-6. The testing method involved characterizing the batteries using button cells. The negative electrode active material of the button cells was the same as that prepared in Examples 1-3 and Comparative Examples 1-6. The positive electrode used the same material. Acetylene black was used as the conductive agent, polyvinylidene fluoride as the binder, and Celgard 2325 composite membrane as the separator. The electrolyte was a 2 mol / L ZnSO4 + 0.1 mol / L MnSO4 solution. The mass ratio of the low-temperature lithium-ion battery anode material, conductive agent, and binder was 95:2:3. The button cells were assembled in a glove box with an argon protective atmosphere. The electrochemical performance of the button cells was tested using a Blue Electric test cabinet with constant current charge-discharge testing. The test voltage range was set from 0.8V to 2V, and the test conditions were 25±2℃. The results are shown in Table 1-2.

[0063] Table 1. Discharge specific capacity (mAh·g) of low-temperature lithium battery anode materials prepared in Examples 1-3 at room temperature -1 )

[0064]

[0065] As shown in the table above, the low-temperature lithium battery anode materials prepared in Examples 1-3 exhibit discharge specific capacities exceeding 520 mAh·g at discharge rates of 0.2C and 0.5C when used at room temperature. -1 The discharge specific capacity at 1C is higher than 510 mAh·g. -1 Furthermore, the positive electrode materials of Examples 1-3 showed that the discharge specific capacity retention rates after 200 and 4000 cycles at a discharge rate of 1C were higher than 97% and 94%, respectively, indicating that the low-temperature lithium battery negative electrode materials prepared by the method of the present invention have excellent discharge specific capacitance and cycle performance.

[0066] Table 2. Discharge specific capacity (mAh·g) of low-temperature lithium battery anode materials prepared in Examples 1 and Comparative Examples 1-6 at room temperature -1 )

[0067]

[0068] As shown in the table above, the discharge specific capacitance of the low-temperature lithium battery anode materials prepared in Comparative Examples 1-6 is significantly lower than that of Example 1 when used at room temperature at different discharge rates. Furthermore, the reduction in discharge specific capacitance after 200 and 4000 cycles at 1C is also significantly lower than that of Example 1. This indicates that only the combined process of "adding europium nitrate hexahydrate + fluorination treatment + expanded graphite + heating oxidation treatment" of this invention can improve the electrochemical performance of low-temperature lithium batteries under room temperature conditions.

[0069] Experimental Example 2: Determination of the electrochemical performance at low temperatures of batteries fabricated using the low-temperature lithium-ion battery anode materials prepared in Examples 1-3 and Comparative Examples 1-6.

[0070] In this experimental example, the same detection method as in Experiment 1 was used to determine the electrochemical performance under test conditions of -20℃±2℃. The results are shown in Table 3-4:

[0071] Table 3. Discharge specific capacity (mAh·g) of the low-temperature lithium battery anode materials prepared in Examples 1-3 at -20℃ -1 )

[0072]

[0073] As shown in Tables 1 and 3, when the low-temperature lithium battery anode materials prepared in Examples 1-3 are used in a low-temperature environment (-20℃±2℃), the reduction in discharge specific capacitance at discharge rates of 0.2C, 0.5C, and 1C compared to the room temperature environment (25±2℃) is less than 21 mAh·g. -131mAh·g -1 and 46mAh·g -1 Furthermore, the discharge specific capacity retention rates after 200 and 4000 cycles at a discharge rate of 1C are higher than 95% and 88%, respectively, which is less than 8% compared to the retention rate reduction under normal temperature conditions. This indicates that the low-temperature lithium battery prepared by this invention can maintain good discharge specific capacity and cycle performance under low-temperature conditions.

[0074] Table 4. Discharge specific capacity (mAh·g) of the low-temperature lithium battery anode materials prepared in Example 1 and Comparative Examples 1-6 at -20°C -1 )

[0075]

[0076] As shown in the table above, the discharge specific capacitance of the low-temperature lithium battery anode materials prepared in Comparative Examples 1-6 is significantly lower than that of Example 1 at different discharge rates when used in a low-temperature environment. Furthermore, the reduction in discharge specific capacitance after 200 and 4000 cycles at 1C is also significantly lower than that of Example 1. This indicates that only the combined process of "adding europium nitrate hexahydrate + fluorination treatment + expanded graphite + heating oxidation treatment" in this invention can improve the electrochemical performance of low-temperature lithium batteries under low-temperature environmental testing.

[0077] Furthermore, the low-temperature lithium battery anode material prepared in Example 1 retains 88.9% of its discharge specific capacity after 4000 cycles at 1C when used in a low-temperature environment, which is only 6% lower than when used in a normal temperature environment.

[0078] Compared to Comparative Example 1, Comparative Example 1, when used in a low-temperature environment, showed a discharge specific capacity retention rate of 12.8% after 4000 cycles at 1C, which was 72% lower than that when used in a normal-temperature environment. This indicates that the combination of "adding europium nitrate hexahydrate + fluorination treatment + expanded graphite + heating oxidation treatment" used in this invention can significantly improve the cycle performance of the negative electrode material in a low-temperature environment compared to the blank group (Comparative Example 1).

[0079] Compared with Comparative Example 2, Comparative Example 2, when used in a low-temperature environment, had a discharge specific capacity retention rate of 37.6% after 4000 cycles at 1C, which was 48% lower than that when used in a normal temperature environment. This indicates that although fluorination treatment can improve the electrochemical performance of the negative electrode material to a certain extent at normal temperature, it cannot enable the negative electrode material to maintain good electrochemical performance at low temperatures.

[0080] Compared to Comparative Example 3, Comparative Example 3, when used in a low-temperature environment, showed a discharge specific capacity retention rate of 96.2% after 4000 cycles at 1C, which was 20% lower than when used in a normal-temperature environment. This indicates that the absence of the "addition of europium hexahydrate" step in the "addition of europium nitrate hexahydrate + fluorination treatment + expanded graphite + heating oxidation treatment" process also significantly reduces the electrochemical performance of the negative electrode material at low temperatures. This may be because the europium oxide-expanded graphite phase change material cannot be formed during the preparation process, thus failing to effectively utilize the phase change material to maintain the lithium battery temperature under low-temperature conditions, which in turn significantly affects the electrochemical performance of the negative electrode material at low temperatures.

[0081] Compared with Comparative Example 4, Comparative Example 4, when used in a low-temperature environment, retained 74.5% of its discharge specific capacity after 4000 cycles at 1C, which was 15% lower than that when used in a normal-temperature environment. However, its discharge specific capacity after 4000 cycles at 1C in a low-temperature environment was significantly higher than that of other comparative examples, indicating that the lack of fluorination treatment affected the negative electrode material when used in a low-temperature environment. However, the degree of impact was significantly less than that of "adding europium nitrate hexahydrate + expanded graphite + heating oxidation treatment".

[0082] Compared with Comparative Example 5, Comparative Example 5, when used in a low-temperature environment, showed a discharge specific capacity retention rate of 50.9% after 4000 cycles at 1C, which was 36% lower than that when used in a normal temperature environment. This indicates that the absence of the "expanded graphite + heated oxidation treatment" step in the "addition of europium nitrate hexahydrate + fluorination treatment + expanded graphite + heated oxidation treatment" process significantly reduces the electrochemical performance of the negative electrode material at low temperatures. Furthermore, the cycle performance of Comparative Example 5 and Comparative Example 6 showed no significant difference, indicating that the "heated oxidation treatment" can only maintain good electrochemical performance at low temperatures when combined with both "addition of europium nitrate hexahydrate" and "expanded graphite".

[0083] Based on the above analysis, the various operational steps in the "addition of europium nitrate hexahydrate + fluorination treatment + expanded graphite + heating oxidation treatment" of the present invention are interconnected and work together. Only when all these operational steps are included can the prepared low-temperature lithium battery anode material have excellent discharge specific capacitance and cycle performance.

[0084] The working principle and usage of a low-temperature lithium battery anode material and its preparation method are as follows:

[0085] First, europium nitrate hexahydrate is added to the first mixture to obtain a europium-doped second mixture. Then, the second mixture is fluorinated to form a europium-fluorine-based porous network structure. Finally, expanded graphite is added and subjected to heating oxidation. During the heating oxidation process, europium is oxidized to form europium oxide. The expanded graphite and europium oxide further combine to form europium oxide-expanded graphite phase change material. Finally, after sintering and sieving, a negative electrode material containing not only europium doping but also europium oxide-expanded graphite phase change material is obtained. This phase change material can play a heat preservation role when the low-temperature lithium battery negative electrode is used in a low-temperature environment, effectively maintaining the electrochemical performance of the negative electrode material in a low-temperature environment.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a low-temperature lithium battery anode material, characterized in that, Includes the following steps: 1) Manganese, manganese tetroxide, and lithium hydride are mixed in a mass ratio of 1:(1-2):(0.05-1) to obtain the first mixture; 2) Europium nitrate hexahydrate is weighed and dissolved in anhydrous ethanol, then the first mixture is added, and the pH is adjusted to 9 while stirring. The reaction is carried out for 1-1.5 hours, followed by rotary evaporation, drying, and pulverization to obtain the second mixture; 3) The second mixture is uniformly mixed with NH4F, ground, and then subjected to high-temperature heat treatment to obtain the third mixture; 4) The third mixture, expanded graphite, and surfactant are uniformly mixed in anhydrous ethanol, then stirred and heated at 80-90℃ for 0.5-1 hours for oxidation, followed by rotary evaporation to obtain the composite material; 5) Sintering; 6) Pulverization and sieving: The sintered material is pulverized at high speed and sieved to obtain the low-temperature lithium battery anode material; The expanded graphite was also subjected to thermal expansion treatment before being mixed with the third mixture and the surfactant; The temperature of the thermal expansion treatment is 800-900℃, and the thermal expansion time is 5-10 minutes.

2. The method for preparing a low-temperature lithium battery anode material as described in claim 1, characterized in that, In step 2), the ratio of europium nitrate hexahydrate to anhydrous ethanol is 1:(10-20), and the mass ratio of europium nitrate hexahydrate to the first mixture is 1:(0.5-0.8).

3. The method for preparing a low-temperature lithium battery anode material as described in claim 1, characterized in that, In step 3), the mass ratio of the second mixture to NH4F is 100:(10-15).

4. The method for preparing a low-temperature lithium battery anode material as described in claim 1, characterized in that, The high-temperature heat treatment temperature is 100-120℃.

5. The method for preparing a low-temperature lithium battery anode material as described in claim 1, characterized in that, The mass ratio of the third mixture, expanded graphite and surfactant is 1:(5-10):(3-5), and the ratio of the total mass of the third mixture, expanded graphite and surfactant to the volume of anhydrous ethanol is 1:(10-20).

6. The method for preparing a low-temperature lithium battery anode material as described in claim 1, characterized in that, The rotary evaporation temperature in steps 2) and 4) is 90-100℃.

7. The method for preparing a low-temperature lithium battery anode material as described in claim 1, characterized in that, The sintering temperature is 800-900℃, and the sintering time is 5-6h.

8. A low-temperature lithium battery anode material, characterized in that, It is prepared by any one of the preparation methods described in claims 1-7.

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