Nitrate-metal oxide / carbon composite material lithium ion battery electrode material and preparation method thereof

Abstract

The invention relates to a nitrate-metal oxide / carbon composite lithium ion battery electrode material and a preparation method thereof, and a nitrate-metal oxide / carbon nanofiber is prepared by etching a metal oxide carbon nanofiber with HNO3. The preparation method specifically comprises the following steps: sequentially adding a certain amount of nitrate and polyacrylonitrile into N, N-dimethylformamide (DMF), uniformly stirring to obtain a transparent solution, then carrying out electrostatic spinning, collecting obtained woven cloth, drying the collected woven cloth in a constant-temperature blast drying oven, then sintering in an N2 atmosphere to obtain an MxOy (at) C fiber composite material, and carrying out ultrasonic treatment in an HNO3 solution to obtain the M (NO3) y-MxOy (at) C fiber composite material. The MxOy (at) C nanofiber is converted into the M (NO3) y-MxOy (at) C nanofiber in situ through HNO3 etching, the technical barrier that the nitrate material is difficult to perform carbon compounding is broken through, the problem that the shape of the nitrate material is difficult to regulate and control is solved, and the cycling stability of the electrode material is improved. According to the invention, M (NO3) y-MxOy (at) C is prepared through HNO3 etching for the first time, and M (NO3) y-MxOy (at) C is used as a lithium ion battery negative electrode material and shows excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a novel preparation method for preparing nitrate-metal oxide / carbon composite lithium-ion battery electrode materials by HNO 3 etching. Background Art

[0002] With the increasing demand in the portable electronics market and electric vehicles, there is an urgent need to develop lithium-ion batteries with higher energy density and longer cycle life. Over the past few decades, various novel electrode materials with high lithium storage capacity and stable cycling performance have been proposed and designed. Among many candidate anode materials, metal nitrates (such as Cu(NO 3 ), 2 ·xH 2 O, Pb(NO 3 ), 2 and [Bi 6 O 4 (OH) 4 (NO 3 ), 6 ·4H 2 O) have attracted extensive attention and research due to their large reversible capacity. Metal nitrates bring high theoretical capacity due to the combined effects of conversion reactions and alloying / dealloying "dual mechanisms", but the volume expansion stress during the alloying / dealloying process leads to unsatisfactory cycling performance. Carbon composite can effectively relieve the volume stress and stabilize the electrode structure. However, metal nitrates have a low thermal decomposition temperature and are prone to hydrolysis, making it difficult to prepare nitrate / carbon composites by conventional methods. The commonly used solvothermal preparation method usually has problems with poor binding between salts and carbon materials due to the relatively mild experimental temperature conditions required for nitrates. Metal oxides, due to their high thermal stability, are more easily operable in terms of their combination with carbon and morphology regulation compared to the corresponding nitrates, and can be used as effective precursors for preparing nitrate / carbon composites.

[0003] This patent first proposed the method of HNO 3 etching to prepare a new type of M(NO 3 ) y -M x O y @C fiber composite anode materials. HNO 3 etching in-situ transforms M x O y @C nanofibers into M(NO 3 ) y -MxOy@C nanofibers, and carbon fibers convert M(NO 3 ) yLimitations: Among them, the volume expansion is effectively alleviated, and combined with the electrochemical stability of metal oxides, the cycling performance of the electrode material is improved. HNO 3 Etching converts part of the oxide into nitrate, achieving a tight composite of metal oxide and its corresponding nitrate. On the one hand, NO in the nitrate 3 - is an important component of the solid electrolyte interface (SEI), which can effectively improve the reversibility of the electrode reaction. On the other hand, nitrate has higher ionic conductivity. The present invention develops a method for preparing nitrate-metal oxide / carbon composite materials by HNO 3 etching. Using M(NO 3 ) y -M x O y @C as the anode material of lithium-ion batteries shows excellent electrochemical performance and has great potential application value. Summary of the Invention

[0004] The present invention aims to develop a simple and efficient class of nitrate-metal oxide / carbon composite materials and a preparation method. To this end, by HNO 3 etching M x O y @C nanofibers, M(NO 3 ) y -M x O y @C nanofiber composite materials are successfully prepared. The specific technical solutions are as follows: A preparation method for a simple and efficient class of nitrate-metal oxide / carbon composite materials. Take nitrate and PAN and dissolve them in DMF, stir to form a uniform transparent solution, transfer the obtained solution to an electrospinning syringe for electrospinning, then dry the obtained spun cloth in an oven, and perform pre-sintering and sintering under N 2 atmosphere to obtain M x O y @C composite materials. Finally, use HNO 3 to etch M x O y @C composite materials, filter by suction and dry in a vacuum oven to obtain M(NO3)y-MxOy@C composite materials.

[0005] In the precursor solution, the mass ratio of nitrate to PAN is 0.55-1.0:1.

[0006] The nitrate in the precursor solution is selected from any one of salts such as iron nitrate, cobalt nitrate, and gallium nitrate, and the corresponding metal oxide can react with HNO 3 to regenerate nitrate.

[0007] The spinning conditions are as follows: voltage is 18 - 23 kV, time is 5 - 10 h, temperature is 35 - 55 °C, relative humidity is 20 - 35%, and distance is 20 - 30 cm.

[0008] The fabric drying conditions are as follows: drying temperature is 60 - 80 °C, and drying time is 10 - 12 h.

[0009] The sintering conditions are as follows: under nitrogen atmosphere, pre - sintering temperature is 200 - 300 °C, time is 2 - 5 h, sintering temperature is 400 - 700 °C, time is 5 - 8 h, and the heating rate during the whole process is 1 - 3 °C / min.

[0010] The vacuum drying conditions are as follows: drying temperature is 40 - 60 °C, and drying time is 8 - 12 h.

[0011] A novel type of M(NO 3 ) y -M x O y @C is used as the anode material for lithium - ion batteries.

[0012] In the present invention, firstly, taking advantage of electrospinning, polymer droplets are stretched into fibers in a strong electric field, and then annealed under nitrogen atmosphere to obtain metal - oxide carbon nanofibers. The obtained metal - oxide carbon composite is etched by HNO 3 to generate the corresponding nitrate - metal - oxide / carbon composite. The carbon fibers confine M(NO 3 ) y therein, effectively alleviating volume expansion. Coupled with the electrochemical stability of the metal oxide, the cycle stability of the electrode material is improved. The HNO 3 etching converts part of the oxide into nitrate, realizing the tight combination of the metal oxide and the corresponding nitrate. On the one hand, NO 3 - in the nitrate is an important component of the solid - electrolyte interface (SEI), which can effectively improve the reversibility of the electrode reaction. On the other hand, the introduction of nitrate brings higher ionic conductivity. M(NO 3 ) y -M x O y @C, as the anode material for lithium - ion batteries, shows excellent electrochemical performance and has great potential application value.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Low production cost, green and pollution - free, and environmentally friendly.

[0014] (2) Innovative concept, using HNO3 A method for preparing a nitrate / carbon composite electrode by etching, with a simple and efficient synthesis method. Description of the Drawings

[0015] Figure 1 Optical photograph during the preparation of the sample in Example 1: (a) Ga 3 O@C material before etching, (b) Ga(NO 2 O 3 ) 3 -Ga 3 O 2 O@C material obtained after etching. 3

[0016] Figure 2 XRD pattern of the sample prepared in Example 1.

[0017] Figure 3 XPS pattern of the sample prepared in Example 1.

[0018] Figure 4 SEM image of the sample prepared in Example 1.

[0019] Figure 5 Charge and discharge curves and cycling performance graphs of the sample prepared in Example 1 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance graph.

[0020] Figure 6 Charge and discharge curves and cycling performance graphs of the sample prepared in Example 2 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance graph.

[0021] Figure 7 Charge and discharge curves and cycling performance graphs of the sample prepared in Example 3 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance graph.

[0022] Figure 8 Charge and discharge curves and cycling performance graphs of the sample prepared in Example 4 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance graph.

[0023] Figure 9 Charge and discharge curves and cycling performance graphs of the sample prepared in Example 5 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance graph.

[0024] Figure 10 Charge and discharge curves and cycling performance graphs of the sample prepared in Example 6 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance graph.

[0025] Figure 11Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 7 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram.

[0026] Figure 12 Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 8 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram.

[0027] Figure 13 Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 9 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram.

[0028] Figure 14 Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 10 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram.

[0029] Figure 15 Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 11 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram.

[0030] Figure 16 Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 12 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram.

[0031] Figure 17 Charge and discharge curves and cycling performance diagrams of the samples prepared in Example 13 for the first three cycles: (a) Charge and discharge curves for the first three cycles, (b) Cycling performance diagram. Detailed implementation method

[0032] Example 1 Weigh 0.4475 g of Ga(NO 3 ) 3 ·xH 2 O and add it to 10 mL of DMF, stir for half an hour. After complete dissolution, add 0.6500 g of PAN and stir for 36 h to mix them evenly. Transfer the resulting homogeneous solution to a syringe and perform electrospinning for 8 h under the conditions of a voltage of 21 kV, a temperature of 50 °C, a relative humidity of about 30%, and a pushing speed of 0.030 mm / min. After electrospinning, collect the obtained material, transfer it to a constant-temperature blast drying oven, dry it at 80 °C for 12 h, and then pre-sinter the dried material at 200 °C for 2 h in an N 2 atmosphere with a heating rate of 2 °C / min, and sinter it at 600 °C for 5 h with a heating rate of 3 °C / min to obtain the Ga 2 O 3 @C composite material ( Figure 1a). Ultrasonic for 10 min in 10% HNO 3 solution, filter by suction, and dry in a vacuum oven at 40 °C for 12 h to obtain Ga(NO 3 ) 3 -Ga 2 O 3 @C composite material ( Figure 1 b). Through XRD pattern analysis, the obtained material is an amorphous material ( Figure 2 ). Through XPS spectrum analysis, the Ga 2p spectrum ( Figure 3 a) can be fitted into two peaks at 1118.3 eV and 1145.1 eV, respectively pointing to Ga 2p 2 / 3 , Ga 2p 1 / 2 . The Ga 3d spectrum is as shown in Figure 3 b, and the peaks at 20.3 eV and 25.1 eV correspond to Ga 3+ and O 1s, respectively. As shown in Figure 3 c, three peaks can be observed in the N 1s spectrum: 398.3 eV, 400.1 eV, and 406.1 eV, corresponding to Ga-N, C-N, and NO 3 - , respectively. XPS spectrum analysis proves the successful preparation of Ga(NO 3 ) 3 . Through SEM, it can be seen that the overall material presents an intertwined fiber network morphology ( Figure 4 ).

[0033] The material is made into a battery by the following method: Mix the prepared sample with acetylene black and polyvinylidene fluoride in a weight ratio of 8:1:1, make a slurry with N-methylpyrrolidone as the solvent, coat it on a copper foil with a thickness of 10 μm, dry at 120 °C for 10 h, and then cut it into circular pieces with a diameter of 14 mm. Use a lithium metal sheet as the counter electrode, a Celgard membrane as the separator, and an EC+DMC+DEC (volume ratio of 1:1:1) solution dissolved with LiPF 6 (1 mmol L -1 ) as the electrolyte, and assemble it into a CR2025 type battery in a glove box protected by argon. After the battery is assembled, let it stand for 8 h, and then perform constant current charge and discharge tests with a CT3001 battery test system. The test voltage is 0.01~3 V, and the current density is 500 mA g -1 . Figure 4 For the first three charge and discharge curves and cycling performance graph of the prepared Ga(NO 3 ) 3 -Ga 2 O 3 @C composite material lithium ion battery. The initial charge and discharge specific capacities are 972.1 and 1465.1 mAh g-1 The specific charge and discharge capacities of the second cycle are 1057.3 and 1102.8 mAh g respectively -1 , and there are obvious charge and discharge platforms ( Figure 5 a), compared with the unetched electrode material ( Figure 6 a), there is no obvious side reaction platform at 2.5 - 3.0 V, which benefits from the fact that HNO 3 generates the corresponding nitrate after etching, enhancing the ionic conductivity of the electrode material. At the same time, NO in the nitrate 3 - is an important component of SEI, effectively improving the reversibility of the electrode reaction. After 50 cycles, the charge and discharge specific capacities are 981.8 and 987.9 mAh g respectively -1 ( Figure 5 b), showing excellent electrochemical performance and cycle stability.

[0034] Example 2 Omit the HNO 3 etching step in Example 1, that is, do not perform HNO 3 etching, and keep other conditions unchanged to obtain Ga 2 O 3 @C composite material. Make a battery according to the method in Example 1, and the initial charge and discharge specific capacities are 851.7 and 1395.1 mAh g respectively -1 ( Figure 6 a), and the slope at 2.5 - 3.0 V comes from the formation of SEI and other side reactions. After 50 cycles, the charge and discharge specific capacities are 583.0 and 587.4 mAh g respectively -1 ( Figure 6 b). Compared with Example 1, the unetched electrode material shows poorer reversibility and lower specific capacity.

[0035] Example 3 Take Ga(NO 3 ) 3 ·xH 2 O and acetylene black and polyvinylidene fluoride are mixed in a weight ratio of 7:2:1, made into a slurry with N-methylpyrrolidone as the solvent, and then made into a battery according to the method in Example 1. The initial charge and discharge specific capacities are 1018.3 and 2024.8 mAh g respectively -1 ( Figure 7 a), and the slope at 2.5 - 3.0 V comes from the formation of SEI and other side reactions. After 50 cycles, the charge and discharge specific capacities are 717.8 and 719.1 mAh g respectively -1 ( Figure 7 b). Compared with Example 1, Ga(NO3 ) 3 The electrode exhibits poor reversibility and low specific capacity.

[0036] Example 4 After adjusting the concentration of HNO in Example 1 from 10 wt% to 5 wt%, other conditions remain unchanged. A battery is made according to the method of Example 1, and the initial charge and discharge specific capacities are 740.3 and 1035.1 mAh g 3 respectively. -1 ( Figure 8 a), There are obvious charge and discharge platforms. After 50 cycles, the charge and discharge specific capacities are 586.6 and 589.7 mAh g -1 ( Figure 8 b). Compared with Example 1, the specific capacity is lower, but it still exhibits excellent electrochemical performance.

[0037] Example 5 After adjusting the concentration of HNO in Example 1 from 10 wt% to 20 wt%, other conditions remain unchanged. A battery is made according to the method of Example 1, and the initial charge and discharge specific capacities are 810.9 and 1168.1 mAh g 3 respectively. -1 ( Figure 9 a), There are obvious charge and discharge platforms. After 50 cycles, the charge and discharge specific capacities are 690.0 and 694.1 mAh g -1 ( Figure 9 b). Compared with Example 1, the specific capacity decreases, but it still exhibits excellent electrochemical performance.

[0038] Example 6 After adjusting the concentration of HNO in Example 1 from 10 wt% to 30 wt%, other conditions remain unchanged. A battery is made according to the method of Example 1, and the initial charge and discharge specific capacities are 580.4 and 1090.3 mAh g 3 respectively. -1 ( Figure 10 a), After 50 cycles, the charge and discharge specific capacities are 671.2 and 674.8 mAh g -1 ( Figure 10 b). After several cycles, the specific capacity shows obvious fluctuations up and down. It can be seen that 30 wt% HNO 3 is not a suitable etching concentration.

[0039] Example 7 After adjusting the concentration of HNO in Example 1 3After the concentration was adjusted from 10 wt% to 40 wt% and other conditions remained unchanged, a battery was fabricated according to the method of Example 1. The initial charge and discharge specific capacities were 469.5 and 1034.3 mAh g -1 ( Figure 11 a), respectively. After 50 cycles, the charge and discharge specific capacities were 703.8 and 706.7 mAh g -1 ( Figure 11 b). During the entire cycling process, the specific capacity showed significant fluctuations up and down and could not be maintained stably. It can be seen that 40 wt% HNO 3 is not a suitable etching concentration.

[0040] Example 8 Replace 0.4475 g of Ga(NO 3 ) 3 ·xH 2 O in Example 1 with 0.7070 g of Fe(NO 3 ) 3 ·9H 2 O, and other conditions remained unchanged. A battery was fabricated according to the method of Example 1. The initial charge and discharge specific capacities were 843.9 and 1400.4 mAh g -1 ( Figure 12 a), respectively. There were obvious charge and discharge plateaus. After 50 cycles, the charge and discharge specific capacities were 882.9 and 894.1 mAh g -1 ( Figure 12 b). Even when the type of nitrate was changed, the obtained electrode still exhibited excellent electrochemical performance.

[0041] Example 9 Replace 0.4475 g of Ga(NO 3 ) 3 ·xH 2 O in Example 1 with 0.5091 g of Co(NO 3 ) 2 ·6H 2 O, and other conditions remained unchanged. A battery was fabricated according to the method of Example 1. The initial charge and discharge specific capacities were 739.5 and 1162.7 mAh g -1 ( Figure 13 a), respectively. There were obvious charge and discharge plateaus. After 50 cycles, the charge and discharge specific capacities were 615.8 and 617.7 mAh g -1 ( Figure 13 b). Even when the type of nitrate was changed, the obtained electrode still exhibited excellent electrochemical performance.

[0042] Example 10 Take 0.4475 g of Ga(NO3 ) 3 ·xH 2 O and 0.0448 g of carbon nanotubes (CNT) were added to 80 mL of absolute ethanol, ultrasonicated for 1 h, stirred for 4 h, and after thorough mixing, added to a polytetrafluoroethylene reaction kettle for ethanol solvothermal reaction under the reaction conditions of 70 °C for 15 h. After filtration and drying, Ga(NO 3 ) 3 / CNT composite materials were obtained. The battery was fabricated according to the method of Example 1, and the initial charge and discharge specific capacities were 940.8 and 1618.5 mAh g -1 respectively. After 50 cycles, the charge and discharge specific capacities were 412.2 and 414.7 mAh g -1 ( Figure 14 b). Using the solvothermal preparation method, the combination of nitrate and carbon nanotubes is poor, resulting in poor specific capacity and cycling performance of the obtained electrode.

[0043] Example 11 Ga(NO 3 ) 3 ·xH 2 O was not added to the solution A in Example 1, and other conditions remained unchanged, then PAN carbon nanofiber materials were obtained. The battery was fabricated according to the method of Example 1, and the initial charge and discharge specific capacities were 105 and 152 mAh g -1 ( Figure 15 a). There is a discharge platform at ~1.7 V, which is different from that in Example 1 (1.9 - 2.0 V). After 50 cycles, the charge and discharge specific capacities were 157 and 150 mAh g -1 ( Figure 15 b). It can be seen that the addition of carbon materials mainly plays a role in increasing the cycling stability of the electrode.

[0044] Example 12 The Ga 2 O 3 @C materials obtained in Example 1 were etched with 10 wt% H 2 SO 4 under other unchanged conditions. The battery was fabricated according to the method of Example 1, and the initial charge and discharge specific capacities were 576.3 and 1312.1 mAh g -1 respectively. The charge and discharge specific capacities of the second cycle were 576.6 and 632.3 mAh g -1 respectively. There is a discharge platform at ~1.4 V, which is different from that in Example 1 (1.9 - 2.0 V) ( Figure 16 a). After 50 cycles, the charge and discharge specific capacities were 391.8 and 394.4 mAh g -1 (Figure 16 b), H 2 SO 4 Etching causes the specific capacity of the original Ga 2 O 3 @C electrode material to decrease, possibly due to H 2 SO 4 having too strong etching ability, resulting in poor effect.

[0045] Example 13 The Ga 2 O 3 @C material obtained in Example 1 was etched with 10 wt% H 3 PO 4 under other unchanged conditions. It was made into a battery according to the method of Example 1. The initial charge and discharge specific capacities were 633.0 and 1143.2 mAh g -1 respectively, and there were two discharge platforms at ~1.2 V and ~1.4 V, which were different from those in Example 1 (1.9 - 2.0 V) ( Figure 17 a). After 50 cycles, the charge and discharge specific capacities were 482.7 and 487.6 mAh g -1 respectively ( Figure 17 b), H 3 PO 4 etching had little effect on the performance of the original Ga 2 O 3 @C electrode material, resulting in poor effect.

Claims

1. A nitrate-metal oxide / carbon composite lithium ion battery electrode material and preparation method, characterized in that: The method comprises the following steps: (1) Dissolve nitrate and PAN in DMF and stir to form a uniform transparent solution; (2) transferring the transparent solution obtained in step (1) into an electrospinning syringe for electrospinning; (3) drying the woven fabric obtained in step (2), placing it in a nitrogen atmosphere, and heating it to obtain M x O y @C nanofiber; (4) Substitute the M obtained in step (3) x O y @C nanofibers were ultrasonicated in HNO3 solution, filtered and dried in an oven to obtain M(NO3) y -M x O y @C nanofibers.

2. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: In step (1), the mass ratio of nitrate to PAN in the precursor solution is 0.55-1.0:

1.

3. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: In step (1), the nitrate in the precursor solution is selected from any one of salts such as iron nitrate, cobalt nitrate, gallium nitrate, etc., and is characterized in that the corresponding metal oxide can react with HNO3 to regenerate nitrate.

4. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: The spinning conditions in step (2) are: voltage of 18-22 kV, electrospinning time of 5-10 h, temperature of 35-55° C., relative humidity of 20-35%, and receiving distance of 20-30 cm.

5. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: In step (4), the drying temperature is 60-80°C and the drying time is 10-12 h.

6. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: In step (4), under a nitrogen atmosphere, the pre-sintering temperature is 200-300°C for 2-5 h, the sintering temperature is 400-700°C for 5-8 h, and the heating rate of the whole process is 1-3°C / min.

7. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: The mass concentration of HNO3 is 5-20 wt%, and the ultrasonic time is 5-20 min.

8. The method for preparing the nitrate-metal oxide / carbon composite lithium ion battery electrode material according to claim 1, characterized in that: After filtration, dry in a vacuum oven at a temperature of 40-60°C and a drying time of 8-12 h.

9. A negative electrode material for a lithium ion battery, characterized in that: The accessory material is a nitrate-metal oxide / carbon composite material lithium ion battery electrode prepared by the method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The negative electrode material for a lithium-ion battery comprises the negative electrode material of claim 9.

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