A composite lithium supplement, a preparation method and application thereof

Abstract

The application discloses a composite lithium supplementing agent and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries, and the composite lithium supplementing agent comprises an organic lithium supplementing agent and a catalyst, the catalyst is a metal oxide cluster dispersed on a carbon material, and the lithium supplementing agent is dispersed on the surface of the catalyst. The composite lithium supplementing agent is obtained by compounding the catalyst and the lithium supplementing agent through recrystallization and freeze-drying. The porous conductive network of the carrier and the highly dispersed active sites in the catalyst significantly reduce the oxidative decomposition potential of the lithium supplementing agent, and the theoretical capacity of the lithium supplementing agent is released at a low potential. The composite lithium supplementing agent increases the cycle stability of the battery, improves the first charge capacity of the battery, and can effectively achieve the purpose of supplementing lithium for the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a composite lithium supplementing agent and a preparation method and application thereof. BACKGROUND

[0002] Under the background of clean energy transformation, lithium ion batteries with high energy density and environmental friendly characteristics have become the core of modern energy storage systems and are widely used in portable electronic devices and electric vehicle fields. With the continuous improvement of battery performance requirements in these application scenarios, developing lithium ion batteries with higher energy density has become the key research direction. During the first cycle of the battery, the formation of the solid electrolyte interface film and the side reactions lead to irreversible active lithium loss, which seriously restricts the actual available capacity of the battery. The pre-lithiation technology introduces additional active lithium sources into the electrode material or electrolyte during the battery manufacturing stage, which can effectively compensate for the initial lithium loss, significantly improve the initial efficiency and energy density of the battery, and become the key strategy to solve this problem.

[0003] Lithium supplementing agents mainly include negative electrode lithium supplementing agents such as metal lithium powder, lithium foil and lithium alloy, positive electrode lithium supplementing agents such as lithium-rich compounds Li5FeO4, Li2O, electrolyte lithium supplementing additives and organic lithium supplementing agents. At present, the lithium supplementing technology still faces many challenges in commercial application. Metal lithium lithium supplementing agents have high safety risk and complex process; the lithium supplementing capacity of electrolyte additives is limited; and lithium-rich positive electrode lithium supplementing agents face high decomposition potential and low lithium supplementing efficiency.

[0004] Although the organic lithium supplementing agent solves some of the above problems to some extent, it also has some shortcomings. For example, some organic lithium supplementing agents have poor conductivity and high oxidation decomposition potential, which are difficult to match with low-voltage positive electrode materials. In addition, the solubility and dispersibility of some organic lithium supplementing agents need to be improved, which may lead to uneven lithium supplementing process and affect the consistency of the overall performance of the battery.

[0005] Therefore, developing a new lithium supplementing agent system that is efficient, stable, safe and controllable and compatible with existing battery production processes, and optimizing its application process, has become a key technical problem to be broken through in the current lithium ion battery field, and is of great significance for promoting the commercial application of high-energy-density lithium ion batteries. SUMMARY

[0006] The purpose of the present application is to provide a composite lithium supplementing agent and a preparation method and application thereof to solve the problem of poor lithium supplementing effect of organic lithium supplementing agents.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] The first aspect of the present application provides a composite lithium supplementing agent, which comprises an organic lithium supplementing agent and a catalyst, wherein the catalyst comprises a carbon material and a metal oxide cluster supported on the carbon material, and the lithium supplementing agent is dispersed on the surface of the catalyst; the chemical general formula of the lithium supplementing agent is Li2C x O y , wherein 2≤x≤6 and 4≤y≤6, and the lithium supplementing agent comprises at least one of Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6 and Li2C6O6.

[0009] In some possible implementation manners, the catalyst is prepared by taking one or more Anderson-type polyoxometalates as a precursor, combining with the carbon material through electrostatic interaction, and then performing heat treatment.

[0010] In some possible implementation manners, the Anderson-type polyoxometalate has a general formula of [XM6O 24 ] n- , wherein X is one of Fe, Co, Ni, Cu, Zn, Pt and Rh, and M is one of V, Mo, W, Nb and Ta.

[0011] In some possible implementation manners, the carbon material is one or more of porous carbon (Ketjen black), graphene oxide and carbon nanotube.

[0012] In some possible implementation manners, the catalyst accounts for 12.5 wt% to 50.0 wt% of the composite lithium supplementing agent.

[0013] In some possible implementation manners, the particle size of the composite lithium supplementing agent is 10 μm to 20 μm.

[0014] The second aspect of the present application provides a preparation method of a composite lithium supplementing agent, which comprises the following steps:

[0015] The lithium supplementing agent and the catalyst are mixed, and then recrystallized in deionized water and ethanol, and the crystalline product is vacuum freeze-dried to obtain the composite lithium supplementing agent.

[0016] In some possible implementation manners, the volume ratio of the deionized water to the ethanol is 1: (1-5).

[0017] In some possible implementation manners, the recrystallization temperature is 60-80℃, and the vacuum freeze-drying condition is 1.0-10 Pa.

[0018] The third aspect of the present application provides an application of the composite lithium supplementing agent in a lithium ion battery. The lithium ion battery comprises a positive electrode material, a separator and a negative electrode material.

[0019] In some possible implementation manners, the positive electrode material comprises the composite lithium supplementing agent.

[0020] In some possible implementation manners, the separator comprises the composite lithium supplementing agent.

[0021] Advantages of the present application:

[0022] The present application provides a composite lithium supplementing agent, which comprises an organic lithium supplementing agent and a catalyst, wherein the catalyst is a metal oxide cluster supported on a carbon material, and the lithium supplementing agent is dispersed on the surface of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0023] The present application will be further described below in conjunction with the drawings.

[0024] Figure 1 is a TEM image of the catalyst PtMo6@N-RGO and the cluster in the carbon nanopore in Example 1 of the present application;

[0025] Figure 2 is a SEM image of the composite lithium supplementing agent in Example 1 of the present application;

[0026] Figure 3 is a TEM image of the catalyst Pt / FeMo6@N-RGO and the cluster in the carbon nanopore in Example 2 of the present application;

[0027] Figure 4 is a comparison schematic diagram of the first charge curve of the composite lithium supplementing agent provided in Example 1 and Comparative Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5 in the positive electrode application system.

[0028] Figure 5 is a comparison schematic diagram of the oxidative decomposition potential of the composite lithium supplementing agent provided in Example 1 and Comparative Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5 in the positive electrode application system. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative work fall within the protection scope of the present application.

[0030] The experimental methods in the following examples are all conventional methods, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained commercially, unless otherwise specified.

[0031] The following is a detailed description of a composite lithium supplement, a preparation method and application thereof according to an embodiment of the present application.

[0032] Example 1

[0033] This embodiment provides a composite lithium supplement, which is prepared by the following steps:

[0034] First step, dissolve square acid and lithium carbonate in deionized water respectively according to 1:1 molar ratio, after stirring and dissolving, add the square acid solution into the lithium carbonate solution, after heating and stirring reaction, spin off Li2C4O4 crystals at 60℃, grind to obtain the lithium supplement Li2C4O4.

[0035] Second step, add 200mg graphene oxide and 200mg polyethyleneimine (PEI, Mw~600) into 100mL deionized water, ultrasonic dispersion for 1 hour, then add 200μL hydrazine hydrate, reflux under NH3 atmosphere at 95℃ for 12h, after cooling to room temperature, filter and wash, freeze-drying; take 50mg of the above sample and 30mg Na6[H5PtMo6O 24 ]·29H2O, disperse in 30mL deionized water, stir for 6 hours, filter and wash, then freeze-dry to obtain the catalyst PtMo6@N-RGO. The TEM images of the catalyst PtMo6@N-RGO and the clusters in carbon nanoholes are shown in Figure 1 .

[0036] Third step, mix PtMo6@N-RGO and Li2C4O4 according to 2:6 mass ratio, add 40mL deionized water and 80mL ethanol to it, spin at 80℃, vacuum freeze-dry the spin product to obtain the composite lithium supplement. The pressure range of vacuum freeze-drying is 1.0~10Pa. The SEM image of the composite lithium supplement is shown in Figure 2 , and the particle size of the composite lithium supplement is 10-20μm.

[0037] Example 2

[0038] This embodiment provides a composite lithium supplement, which is different from Example 1 in that the second step is different: add Na6[H5PtMo6O 24 ]·29H2O and (NH4)3[FeMo6O 18(OH)6]·7H2O to synthesize the catalyst Pt / FeMo6@N-RGO. The TEM images of the catalyst Pt / FeMo6@N-RGO and the clusters in the carbon nanoholes are shown in FIG. 1, and the particle size of the composite lithium supplement agent is 10-20 μm. Figure 3

[0039] The remaining raw materials and preparation process are the same as in Example 1.

[0040] Example 3

[0041] This example provides a composite lithium supplement agent, which differs from Example 1 in that the second step is different.

[0042] 200 mg of Ketjen black is used instead of 200 mg of graphene oxide in the second step to synthesize the catalyst PtMo6@N-KJ.

[0043] The remaining raw materials and preparation process are the same as in Example 1, and the particle size of the composite lithium supplement agent is 10-20 μm.

[0044] Example 4

[0045] This example provides a composite lithium supplement agent, which differs from Example 3 in that the second step is different: 200 mg of carbon nanotubes is used instead of 200 mg of graphene oxide in the second step to synthesize the catalyst PtMo6@N-CNT.

[0046] The remaining raw materials and preparation process are the same as in Example 1, and the particle size of the composite lithium supplement agent is 10-20 μm.

[0047] Example 5

[0048] This example provides a composite lithium supplement agent, which differs from Example 1 in that Li2C2O4 is used instead of Li2C4O4 synthesized in the first and third steps, and the mass ratio of PtMo6@N-RGO and Li2C2O4 is 3:5. The remaining raw materials and preparation process are the same as in Example 1, and the particle size of the composite lithium supplement agent is 10-20 μm.

[0049] Example 6

[0050] This example provides a composite lithium supplement agent, which differs from Example 2 in that Li2C2O4 is used instead of Li2C4O4 synthesized in the first and third steps, and the mass ratio of Pt / FeMo6@N-RGO and Li2C2O4 is 3:5.

[0051] The remaining raw materials and preparation process are the same as in Example 2, and the particle size of the composite lithium supplement agent is 10-20 μm.

[0052] Example 7​

[0053] The embodiment provides a composite lithium supplementing agent, compared with the embodiment 3, the difference lies in that Li2C4O4 synthesized in the first step and the third step is replaced by Li2C2O4, and the mass ratio of the catalyst PtMo6@N-KJ and Li2C2O4 is 3:5.

[0054] The remaining raw materials and the preparation process are the same as those in the embodiment 3, and the particle size of the composite lithium supplementing agent is 10-20 μm.

[0055] Embodiment 8

[0056] The embodiment provides a composite lithium supplementing agent, compared with the embodiment 4, the difference lies in that Li2C4O4 synthesized in the first step and the third step is replaced by Li2C2O4, and the mass ratio of the catalyst PtMo6@N-CNT and Li2C2O4 is 3:5, the remaining raw materials and the preparation process are the same as those in the embodiment 4, and the particle size of the composite lithium supplementing agent is 10-20 μm.

[0057] Comparative example 1

[0058] The comparative example is compared with the embodiment 1, the difference lies in that no catalyst is added, and the remaining raw materials and the preparation process are the same as those in the embodiment 1.

[0059] Comparative example 2

[0060] The comparative example is compared with the embodiment 5, the difference lies in that no catalyst is added, and the remaining raw materials and the preparation process are the same as those in the embodiment 5.

[0061] Comparative example 3

[0062] The comparative example is compared with the embodiment 1, the difference lies in that the recrystallization temperature of PtMo6@N-RGO and Li2C4O4 is 100 DEG C, the remaining raw materials and the preparation process are the same as those in the embodiment 1, and the particle size of the obtained composite lithium supplementing agent is greater than 20 μm.

[0063] Comparative example 4

[0064] The comparative example is compared with the embodiment 1, the difference lies in that the proportion of the catalyst in the composite lithium supplementing agent is 10%, and the remaining raw materials and the preparation process are the same as those in the embodiment 1.

[0065] Comparative example 5

[0066] The comparative example is compared with the embodiment 1, the difference lies in that the proportion of the catalyst in the composite lithium supplementing agent is 50%, and the remaining raw materials and the preparation process are the same as those in the embodiment 1.

[0067] Comparative example 6

[0068] The difference between this comparative example and Example 1 is that in the second step of catalyst preparation, 50 mg of graphene oxide, 9 mg of H2PtCl6·6H2O, and 24 mg of Na2MoO4·2H2O were dispersed in 30 mL of deionized water, stirred for 6 hours, filtered, washed, and then freeze-dried to obtain the catalyst Pt-Mo@RGO. The remaining raw materials and preparation process remained the same as in Example 1.

[0069] Application Examples 1-8 and Comparative Application Examples 1-6

[0070] Preparation of composite lithium supplement electrode: The lithium supplement, lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) from Examples 1-8 and Comparative Examples 1-6 were mixed evenly in 1.5g of solvent N-methylpyrrolidone (NMP) at a mass ratio of 1:79:10:10 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on the surface of carbon-coated aluminum foil, vacuum dried at 60°C overnight, and rolled to obtain a composite lithium supplement electrode.

[0071] The composite lithium supplements provided in the above embodiments and comparative examples were assembled into lithium-ion batteries according to the following methods:

[0072] Negative electrode: commercially available lithium sheet; Electrolyte: commercially available LB-008; The battery case is of model CR 2032, and the coin cell is assembled in the following order: negative electrode case, spring, gasket, lithium sheet, electrolyte, separator, electrolyte, positive electrode sheet, and positive electrode case.

[0073] Electrochemical performance testing: The prepared coin cells were charged to 4.5V at a constant current of 0.02C in the first cycle, and then discharged to 2.5V at a constant current. The relevant performance test results are shown in Table 1 below.

[0074] Table 1

[0075]

[0076] A comparative schematic diagram of the first charge curves of the composite lithium replenishing agents provided in Example 1 and Comparative Examples 1, 3, 4, and 5 in the cathode application system is shown below. Figure 4 As shown in the diagram; a comparative schematic diagram of the oxidation decomposition potential of the composite lithium supplement provided in Example 1 and Comparative Examples 1, 3, 4, and 5 in the cathode application system is shown in the diagram. Figure 5 As shown.

[0077] Application Examples 9-16 and Comparative Application Examples 7-12

[0078] The positive electrode application was replaced by a separator application, and the operation method was to mix 80% of the lithium supplement in Examples 1-8 and Comparative Examples 1-6, 10% of conductive carbon black (SP), and 10% of polyvinylidene fluoride (PVDF) synthetic slurry in N-methyl pyrrolidone (NMP), and the obtained slurry was coated on a commercial Gelgard 2400 using a coating machine, with a coating thickness of 200 μm, and a surface loading of the lithium supplement of 0.43 mg / cm 2 and dried overnight in a vacuum oven at 60°C.

[0079] Table 2

[0080]

[0081] The data in Tables 1, 2, Figure 4 and Figure 5 were analyzed, and it was found that, according to the application examples 1-4 and 9-12, and the comparative application examples 1 and 7, under the action of the catalyst, the specific capacity of the lithium supplement reached 440 mAh / g at a low voltage of 4.0 V, which was due to the synergistic catalytic effect of the cluster catalyst metal sites in the composite lithium supplement, which promoted the decomposition of the lithium supplement, and the three-dimensional conductive network of the carbon carrier significantly improved the conductivity of the lithium supplement, thereby reducing its decomposition potential and increasing its decomposition capacity. According to application examples 1 and 3, and application examples 9 and 9, the particle size of the composite lithium supplement in application examples 1 and 9 was 10-20 μm, and the particle size of the composite lithium supplement in comparative examples 3 and 9 was >20 μm, it was found that when the recrystallization temperature of the composite lithium supplement was higher than 80°C, the particle size of the composite lithium supplement increased, thereby increasing the oxidation decomposition potential of the lithium supplement and reducing its decomposition capacity. According to application examples 1 and 4, 5, and application examples 9 and 10, 11, it was found that when the proportion of the catalyst in the composite lithium supplement was higher than 50% or lower than 10%, the oxidation decomposition potential of the lithium supplement increased and its decomposition capacity decreased, which was due to the fact that when the amount of catalyst was too small, the contact between the catalyst and the lithium supplement was limited, and the decomposition of the lithium supplement was also limited; when the amount of catalyst was too high, it increased the risk of catalytic electrolyte decomposition, and finally increased the polarization of the battery, thereby increasing the oxidation potential of the lithium supplement and reducing its decomposition capacity. According to application examples 1 and 6, and application examples 9 and 12, it was found that when the cluster in the catalyst was replaced by a metal compound, the catalyst did not have a high catalytic effect on the lithium supplement, and only improved the conductivity of the lithium supplement. According to application examples 13-16, the theoretical specific capacity of lithium oxalate reached 525 mAh / g at a voltage of <4.5 V, and the analysis principle was the same as that of the lithium formate. According to the data of application examples 1-4, 5-8, comparative examples 1 and 2, it was found that the four kinds of catalysts listed could reduce the oxidation decomposition potential of lithium formate and lithium oxalate.

[0082] It has to be noted that, in the present document, the terms "first", "second", etc. merely serve to identify different entities or actions from each other, without necessarily requiring or implying any actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0083] While embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, combinations, and variations of the embodiments can be undertaken without departing from the spirit and scope of the present application, which is defined by the appended claims and their equivalents.

Claims

1. A composite lithium supplement, characterized by comprising: The lithium supplement agent and the catalyst, wherein the catalyst comprises a carbon material and metal oxide clusters supported on the carbon material, the lithium supplement agent is dispersed on the surface of the catalyst, the chemical formula of the lithium supplement agent is Li2C x O y , wherein 2≤x≤6, 4≤y≤6; the catalyst accounts for 12.5wt%-37.5wt% of the composite lithium supplement agent; the particle size of the composite lithium supplement agent is 10μm-20μm; The composite lithium supplement agent is prepared by the following steps: The carbon material and polyethylene imine are added into deionized water, ultrasonic dispersion, then hydrazine hydrate is added for reflux, cooling, filtration, washing, and freeze drying; the above sample and Anderson type polyoxometalate are dispersed in deionized water, stirring, filtration, washing, and freeze drying to obtain a catalyst; The lithium supplement agent and the catalyst are mixed, added into deionized water and ethanol for recrystallization, and the crystalline product is vacuum freeze-dried to obtain the composite lithium supplement agent, and the recrystallization temperature is 60-80℃.

2. The composite lithium supplement according to claim 1, characterized in that, The lithium supplement agent comprises at least one of Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, and Li2C6O6.

3. The composite lithium supplement of claim 1, wherein the lithium supplement is characterized by, The Anderson-type polyoxometalate has a general formula of [XM6O 24 ] n- ; wherein X is one of Fe, Co, Ni, Cu, Zn, Pt, and Rh; and M is one of V, Mo, W, Nb, and Ta.

4. The lithium supplement of claim 1, wherein the lithium supplement is a composite lithium supplement. The carbon material is at least one of porous carbon, graphene oxide, and carbon nanotube.

5. A method for preparing a composite lithium supplement for preparing the composite lithium supplement according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: The carbon material and polyethylene imine are added into deionized water, ultrasonic dispersion, then hydrazine hydrate is added for reflux, cooling, filtration, washing, and freeze drying; the above sample and Anderson type polyoxometalate are dispersed in deionized water, stirring, filtration, washing, and freeze drying to obtain a catalyst; The lithium supplement agent and the catalyst are mixed, added into deionized water and ethanol for recrystallization, and the crystalline product is vacuum freeze-dried to obtain the composite lithium supplement agent.

6. The method for preparing a composite lithium supplement according to claim 5, characterized in that, The volume ratio of the deionized water and ethanol is 1: (1-5); and / or, the vacuum freeze-drying condition is 1.0-10 Pa.

7. Application of the composite lithium supplement agent of any one of claims 1-4 in a lithium ion battery.

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