Preparation method of lithium vanadate / carbon composite material, negative electrode and lithium ion capacitor

Abstract

The present application embodiment provides a preparation method of a lithium vanadate / carbon composite material, a negative electrode and a lithium ion capacitor, the method comprising: preparing a precursor mixed solution; spraying and rapidly drying the precursor mixed solution, collecting and obtaining a precursor material; subjecting the precursor material to high temperature heat treatment to obtain a lithium vanadate / carbon composite material. The lithium vanadate / carbon composite material prepared by the spray drying method in the present application embodiment has a small sphere size, which can shorten the lithium ion diffusion path and improve the ion conductivity of the material. The composite with the carbon material can improve the electronic conductivity of the material. The two together constitute an ion / electronic mixed conductor with excellent performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium ion capacitors, and in particular to a preparation method of a lithium vanadate / carbon composite material, a negative electrode and a lithium ion capacitor. Background Art

[0002] Among common electrochemical energy storage systems, lithium-ion batteries have a high energy density (150-200Wh kg -1 ) and a wider operating voltage (3-4V), but with low power density (<1kwkg -1 ) and poor lifespan (<10 3 In contrast, supercapacitors are widely used in power-type devices because of their high power density and long cycle life.

[0003] With the continuous development of science and technology, people are in urgent need of a new type of energy storage device with high energy density, high power density and long life. Lithium-ion capacitors have the characteristics of both lithium-ion batteries and supercapacitors, with high energy density and power density, and long service life, making them the most promising devices. However, the ion diffusion rate of the battery-type negative electrode is much lower than the ion adsorption / desorption rate of the capacitor-type positive electrode. Therefore, the development and design of promising fast-charging negative electrode materials is a huge challenge and is of great significance. Summary of the invention

[0004] In view of this, the present application provides a preparation method of a lithium vanadate / carbon composite material, a negative electrode and a lithium ion capacitor, so as to help solve the problem in the prior art that the ion diffusion rate of the battery-type negative electrode is much lower than the ion adsorption / desorption rate of the capacitor-type positive electrode, resulting in poor performance of the lithium ion capacitor.

[0005] In a first aspect, the present application provides a method for preparing a lithium vanadate / carbon composite material, comprising:

[0006] preparing a precursor mixed solution;

[0007] The precursor mixed solution is sprayed and quickly dried, and the precursor material is collected and obtained;

[0008] The precursor material is subjected to high temperature heat treatment to obtain a lithium vanadate / carbon composite material.

[0009] In a possible implementation, the preparing of the precursor mixed solution includes:

[0010] Lithium salt, vanadium pentoxide, germanium oxide and a small molecule carbon source are dissolved in water at an ion concentration ratio of 3-3.1:0.9-0.95:0.5-0.1:1-2 and stirred fully to obtain a precursor mixed solution.

[0011] In a possible implementation, the lithium salt includes lithium hydroxide, lithium oxalate and / or lithium carbonate.

[0012] In a possible implementation, the small molecule carbon source includes glucose, sucrose and / or tartaric acid.

[0013] In a possible implementation, spraying and rapidly drying the precursor mixed solution, and collecting and obtaining the precursor material, comprises:

[0014] The precursor mixed solution is sprayed and dried at a temperature of 250-350° C. to collect and obtain the precursor material.

[0015] In a possible implementation, spraying and rapidly drying the precursor mixed solution, and collecting and obtaining the precursor material, comprises:

[0016] The precursor mixed solution is sprayed at a feed rate of 200 to 800 mL / h and quickly dried to collect and obtain the precursor material.

[0017] In a possible implementation, the step of subjecting the precursor material to high-temperature heat treatment to obtain a lithium vanadate / carbon composite material comprises:

[0018] The precursor material is heat treated at 750-900° C. for 3-8 hours under a protective atmosphere to obtain a lithium vanadate / carbon composite material.

[0019] In a possible implementation, the protective atmosphere includes argon, nitrogen and / or carbon dioxide.

[0020] In a second aspect, an embodiment of the present application provides a negative electrode for a lithium ion capacitor, comprising:

[0021] A carrier, wherein the carrier is in sheet form;

[0022] A coating layer is uniformly coated on the carrier, and the coating layer comprises a conductive agent and a lithium vanadate / carbon composite material prepared by the method described in any one of the first aspects.

[0023] In a third aspect, an embodiment of the present application provides a lithium ion capacitor, comprising the lithium ion capacitor negative electrode described in the second aspect.

[0024] The lithium vanadate / carbon composite material prepared by the spray drying method in the embodiment of the present application has a small sphere size, which can shorten the lithium ion diffusion path and improve the ionic conductivity of the material. The composite with the carbon material can improve the electronic conductivity of the material. The two together constitute an ion / electron mixed conductor with excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 A schematic diagram of a preparation method of a lithium vanadate / carbon composite material provided in an embodiment of the present application;

[0027] Figure 2 XRD diagram of the lithium vanadate / carbon material provided in the embodiment of the present application;

[0028] Figure 3 This is a SEM image of the lithium vanadate / carbon material provided in the examples of the present application;

[0029] Figure 4 A rate performance diagram of a lithium vanadate / carbon composite material provided in an embodiment of the present application;

[0030] Figure 5 This is a cycle performance diagram of another lithium vanadate / carbon composite material provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0032] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0033] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0034] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] Lithium vanadate material has the advantages of low discharge platform, large theoretical specific capacity, good cycle stability, etc. It is a very promising fast-charging negative electrode material. The reduction of particle size can effectively reduce the diffusion path of ions, thereby improving the kinetic rate of negative electrode reaction. At the same time, the composite with carbon material can construct an ion / electron mixed conductor, which makes up for the disadvantage of low electronic conductivity of lithium vanadate material itself, and makes the overall electrochemical performance of the material better. It is described in detail in conjunction with specific embodiments below.

[0036] See also Figure 1 , is a schematic diagram of a preparation method of a lithium vanadate / carbon composite material provided in an embodiment of the present application. Figure 1 As shown, it mainly includes the following steps.

[0037] Step S101: preparing a precursor mixed solution.

[0038] In a specific implementation, lithium salt, vanadium pentoxide, germanium oxide and a small molecule carbon source can be dissolved in water at an ion concentration ratio of 3-3.1:0.9-0.95:0.5-0.1:1-2 and stirred thoroughly to obtain a precursor mixed solution.

[0039] In a possible implementation, the lithium salt includes lithium hydroxide, lithium oxalate, lithium carbonate, or a mixture of any two or more thereof. Of course, those skilled in the art may also select other water-soluble lithium salts according to actual needs, and the embodiments of the present application make specific restrictions on this.

[0040] In a possible implementation, the small molecule carbon source includes glucose, sucrose, tartaric acid, or a mixture of any two or more thereof, etc. Of course, those skilled in the art can also select other water-soluble small molecule carbon sources according to actual needs, and the embodiments of the present application make specific restrictions on this.

[0041] Step S102: spraying and rapidly drying the precursor mixed solution, collecting and obtaining the precursor material.

[0042] In one possible implementation, the feed rate of the spray in this step is 200-800mL / h, for example 200mL / h, 300mL / h, 400mL / h, 500mL / h, 600mL / h, 700mL / h, 800mL / h, etc. Those skilled in the art can make adaptive selections within this range according to actual needs. It should be pointed out that if the feed rate of the spray is too low, for example, lower than 200mL / h, the spray precursor will be too loose, resulting in the inability to form particles, affecting the particle structure after subsequent heat treatment; if the feed rate of the spray is too high, for example, higher than 800mL / h, the size of the spray precursor will be too large, affecting the electrochemical properties of the material after heat treatment.

[0043] In one possible implementation, the temperature for rapid drying in this step is 250-350°C, for example, 250°C, 280°C, 320°C, 350°C, etc. Technical personnel in this field can make adaptive selections within this range according to actual needs. Within this temperature limit range, the material particles can be well aggregated and a carbon layer with suitable thickness and stable structure can be formed on the surface of the particles.

[0044] Step S103: subjecting the precursor material to high-temperature heat treatment to obtain a lithium vanadate / carbon composite material.

[0045] In a possible implementation, the heating rate of calcination in the above steps is 1°C / min to 5°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, etc., and those skilled in the art can make adaptive selections within this range according to actual needs. It should be pointed out that if the heating rate of calcination is too low, for example, lower than 1°C / min, the overall calcination time will be too long, resulting in agglomeration and growth of the particles; if the heating rate of calcination is too fast, for example, higher than 5°C / min, the spherical structure of the material will be destroyed. The lithium vanadate / carbon composite material prepared at this heating rate is a spherical particle with a well-maintained morphology.

[0046] In one possible implementation, the calcination time in the above step is 3 to 8 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc., and those skilled in the art can make adaptive selections within this range according to actual needs. Within the limited calcination time, the material can be guaranteed to have good crystallinity and uniformity.

[0047] In a possible implementation, the calcination temperature in the above steps is 750-900°C, 750°C, 790°C, 800°C, 820°C, 850°C, 900°C, etc., and those skilled in the art can make an adaptive selection within this range according to actual needs. It should be pointed out that if the calcination temperature is too low, for example, below 750°C, the germanium ions cannot be doped into the lithium vanadate lattice, resulting in a lower ionic conductivity of the material; if the calcination temperature is too high, for example, above 900°C, the material particles will agglomerate to form larger particle clusters.

[0048] In a possible implementation, the protective atmosphere in the above steps may be argon, nitrogen, or a mixture of the two, and this embodiment of the present application does not impose any specific limitation on this.

[0049] The lithium vanadate / carbon composite material prepared by the preparation method of the lithium vanadate / carbon composite material provided in the embodiment of the present application has a well-preserved spherical morphology, high crystallinity, and a complete crystal phase structure. In addition, the method has low preparation cost, simple preparation process operation, easy controllable conditions, and the materials required in the reaction process are low-toxic and harmless.

[0050] Based on the above-mentioned lithium vanadate / carbon composite material, an embodiment of the present application also provides a lithium ion capacitor negative electrode, including a carrier, the carrier is in sheet form; a coating layer, the coating layer is uniformly coated on the carrier, and the coating layer includes a conductive agent and a lithium vanadate / carbon composite material prepared by the method of the above embodiment.

[0051] In a possible implementation, the carrier may be copper foil, carbon-coated copper foil or carbon paper. Of course, those skilled in the art may select other conductive sheets as carriers according to actual needs, and the present application embodiment does not impose specific restrictions on this.

[0052] In one possible implementation, the mass ratio of the conductive agent to the lithium vanadate / carbon composite material is 0.8:9 to 0.3:9, for example, 0.3:9, 0.4:9, 0.5:9, 0.6:9, 0.7:9 or 0.8:9, etc., and those skilled in the art can make an adaptive selection within this range according to actual needs.

[0053] In one possible implementation, the conductive agent is acetylene black, and the loading amount of the carrier in the negative electrode of the lithium ion capacitor is 0.3-0.5 mg / cm 2 , for example 0.3 mg / cm 2 , 0.4mg / cm 2 , 0.5mg / cm 2 The technical personnel in this field can make an adaptive selection within this range according to actual needs, and this range can ensure that the overall performance of the lithium ion capacitor device is good.

[0054] Corresponding to the above embodiment, the present application also provides a lithium ion capacitor, which includes the lithium ion capacitor negative electrode prepared in the above embodiment. The lithium ion capacitor can achieve high-capacity charging and discharging and has excellent cycle performance.

[0055] For ease of understanding, the technical solution provided in this application is described in detail below in conjunction with specific embodiments.

[0056] Embodiment 1:

[0057] Lithium carbonate, vanadium pentoxide, germanium oxide and glucose were dissolved in water at an ion concentration ratio of 3:0.9:0.1:2, and stirred at room temperature. The mixed solution was sealed and stirred for 30 minutes. After the solution was fully stirred, it was transferred to an ultrasonic generator for spraying. Under an argon atmosphere, the feed rate was controlled to 300mL / h and the drying temperature was 280℃ for rapid drying. The dried precursor material was collected, vacuum dried and transferred to a tube furnace, heated to 800℃ at a heating rate of 2℃ / min and kept warm for 4h to obtain a lithium vanadate / carbon composite material.

[0058] See also Figure 2 , is the XRD diagram of the lithium vanadate / carbon material provided in the embodiment of the present application. Figure 2 As shown, the XRD spectrum of the lithium vanadate / carbon composite material prepared in Example 1 is consistent with the lithium vanadate standard card, proving that the lithium vanadate material is successfully synthesized.

[0059] See also Figure 3 , is a SEM image of the lithium vanadate / carbon material provided in the embodiment of the present application. Figure 3 As shown, the lithium vanadate / carbon composite material prepared in Example 1 is particles with a well-maintained spherical morphology.

[0060] Weigh 180 mg of lithium vanadate / carbon composite material, 10 mg of acetylene black, and 200 mg of binder PVDF (5% mass fraction solution), fully mix the three materials into slurry, and evenly apply it on a copper foil with a diameter of 1.2 cm. The copper foil loaded with active materials is used as the negative electrode of the lithium ion capacitor.

[0061] See also Figure 4 , is a rate performance diagram of a lithium vanadate / carbon composite material provided in an embodiment of the present application; see Figure 5 , is another cycle performance diagram of lithium vanadate / carbon composite material provided in the embodiment of the present application. Figure 4 Combined with Figure 5 As shown, the specific capacity of the lithium vanadate / carbon composite material can reach 330mAh / g at 0.1A / g; after 1500 cycles at a current density of 1A / g, the capacity retention rate is as high as 89%, and the capacity retention rate is about 70% after 3500 cycles, proving that the lithium vanadate / carbon composite material has excellent electrochemical properties as a negative electrode material for lithium ion capacitors.

[0062] Embodiment 2:

[0063] The difference between this embodiment and embodiment 1 is that the feed rate is 200 mL / h.

[0064] Embodiment 3:

[0065] The difference between this embodiment and embodiment 1 is that the feed rate is 800 mL / h.

[0066] Embodiment 4:

[0067] The difference between this embodiment and embodiment 1 is that the rapid drying temperature is 250°C.

[0068] Embodiment 5:

[0069] The difference between this embodiment and embodiment 1 is that the rapid drying temperature is 350°C.

[0070] Embodiment 6:

[0071] The difference between this embodiment and embodiment 1 is that the calcination temperature for preparing the lithium vanadate / carbon composite material is 750°C.

[0072] Embodiment 7:

[0073] The difference between this embodiment and embodiment 1 is that the calcination temperature for preparing the lithium vanadate / carbon composite material is 900°C.

[0074] Embodiment 8:

[0075] The difference between this embodiment and embodiment 1 is that the heating rate is 1° C. / min.

[0076] Embodiment 9:

[0077] The difference between this embodiment and embodiment 1 is that the heating rate is 5° C. / min.

[0078] Comparative Example 1:

[0079] The difference between this embodiment and embodiment 1 is that no additional carbon source is added to the precursor solution, and a single lithium vanadate material is used as the negative electrode.

[0080] The negative electrode prepared in the above embodiment was assembled with a lithium sheet into a button-type battery and the following electrochemical performance test was performed to obtain the test results shown in Table 1.

[0081] (1) Cycle performance test: The prepared battery was tested on the LAND battery test system at room temperature, with a charge and discharge voltage range of 0.2 to 3 V. The test battery was charged and discharged at a constant current density of 0.1 A / g.

[0082] (2) Rate performance test: Under room temperature conditions, the prepared batteries were tested on a LAND battery testing system, and the specific capacities of the batteries were tested at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 0.8 A / g, 1 A / g, 2 A / g, 5 A / g, 10 A / g, and 20 A / g.

[0083] Table 1:

[0084]

[0085] As shown in Table 1, using the lithium vanadate / carbon composite material prepared in Example 1 as the negative electrode of a lithium ion capacitor can obtain better rate performance, cycle performance and first charge and discharge efficiency.

[0086] The above are only specific implementations of the present application. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. The protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a lithium vanadate / carbon composite material, characterized in that: include: Dissolve lithium salt, vanadium pentoxide, germanium oxide and a small molecule carbon source in water at an ion concentration ratio of 3-3.1:0.9-0.95:0.5-0.1:1-2 and stir thoroughly to obtain a precursor mixed solution; The precursor mixed solution is sprayed at a feed rate of 300 mL / h and quickly dried at a drying temperature of 280° C., and a precursor material is collected and obtained; The precursor material is heated to 800° C. at a heating rate of 2° C. / min under a protective atmosphere and kept warm for 4 hours to obtain a lithium vanadate / carbon composite material, which is used for a negative electrode of a lithium ion capacitor.

2. The method according to claim 1, characterized in that The lithium salt includes lithium hydroxide, lithium oxalate and / or lithium carbonate.

3. The method according to claim 1, characterized in that The small molecule carbon source includes glucose, sucrose and / or tartaric acid.

4. The method according to claim 1, characterized in that: The protective atmosphere includes argon, nitrogen and / or carbon dioxide.

5. A negative electrode for a lithium ion capacitor, characterized in that: include: A carrier, wherein the carrier is in sheet form; A coating layer is uniformly coated on the carrier, and the coating layer comprises a conductive agent and a lithium vanadate / carbon composite material prepared by the method described in any one of claims 1 to 4.

6. A lithium ion capacitor, characterized in that: The invention comprises the negative electrode of the lithium ion capacitor as claimed in claim 5.

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