A modified battery separator, its preparation method and application

Abstract

This invention discloses a modified battery separator, its preparation method, and its applications. The modified battery separator includes a base separator and a composite layer attached to the base separator. The composite layer comprises a MgB2 layer and a graphene layer stacked sequentially. The modified battery separator of this invention can improve the electrochemical performance of the black phosphorus anode. By constructing a layer-by-layer assembly structure, a highly efficient lithium polyphosphide diffusion barrier layer is formed. The composite layer possesses both good electronic and ionic conductivity, forming an effective upper current collector, improving the utilization rate of active materials, preventing active material loss, and promoting the efficient utilization of soluble lithium polyphosphides.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery separator materials, and particularly relates to a battery modified separator and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of new energy industry and the popularity of various portable electronic products, people's demand for today's mobile electrochemical energy storage devices has intensified, and battery products with high safety, high energy density and fast charging and discharging have also led to a new round of research boom.

[0003] The energy density of the existing commercial lithium ion battery is limited by the low theoretical specific capacity of the positive and negative electrode materials, and it is difficult to develop battery products with ultra-high energy density. Especially the theoretical specific capacity of the commercial graphite negative electrode is only 370 mAh / g, which greatly hinders the improvement of the energy density of the battery. Therefore, the key to developing a battery with high energy density lies in breaking through the theoretical specific capacity of the existing positive and negative active materials. Among them, black phosphorus as a lithium ion battery negative electrode exhibits a theoretical specific capacity of 2560 mAh / g. The layered structure of black phosphorus has good electronic and ionic conductivity, can realize large current fast charging and discharging, and the phosphorus reserves are abundant, becoming one of the most potential high-energy-density battery negative electrode systems. However, black phosphorus negative electrode material faces the same challenge as silicon negative electrode. During the lithium intercalation process, it produces a volume expansion of up to 300%, generating a large internal stress of the electrode, aggravating the pulverization of the active material and the collapse of the electrode structure. In addition, phosphorus will form soluble lithium polyphosphides during the charging and discharging process, dissolve in ester electrolyte, form a shuttle effect, cause the loss of active material, and deteriorate the electrochemical performance of the battery.

[0004] Therefore, the key to developing a phosphorus negative electrode is to inhibit the volume expansion problem and the lithium polyphosphate dissolution and shuttle problem during the charging and discharging process. The separator, as an important barrier to the electronic conductive material of the positive and negative electrodes in the battery, directly faces the shuttle path of lithium polyphosphate.

[0005] Therefore, it is necessary to provide a new modified battery separator. SUMMARY

[0006] To solve the above technical problems, the present application provides a battery modified separator. The battery modified separator inhibits the volume expansion of phosphorus in the electrochemical reaction by modifying the separator, blocks the dissolution and shuttle of lithium polyphosphate, reduces the loss of active material phosphorus during the cycle process, reduces the capacity attenuation of black phosphorus negative electrode, and thus improves the electrochemical performance of the black phosphorus negative electrode.

[0007] Another object of the present application is to provide a preparation method of the above-mentioned battery modified separator.

[0008] The application further provides application of the battery modified diaphragm in a black phosphorus negative electrode lithium battery.

[0009] To achieve the above-mentioned purposes, the specific technical solutions of the application are as follows:

[0010] A battery modified diaphragm comprises a base diaphragm and a composite layer attached to the base diaphragm, wherein the composite layer comprises a MgB2 layer and a graphene layer stacked in sequence.

[0011] The side of the battery modified diaphragm with the composite layer faces the black phosphorus electrode.

[0012] The preparation method of the battery modified diaphragm comprises the following steps:

[0013] 1) dispersing MgB2 and expanded graphite powder in an organic solvent to obtain a dispersion liquid;

[0014] 2) ultrasonic exfoliating the prepared dispersion liquid to obtain an ultrasonic exfoliated solution;

[0015] 3) using the base diaphragm as a filter membrane to perform suction filtration on the ultrasonic exfoliated solution to obtain a diaphragm with the MgB2 layer and the graphene layer attached thereto;

[0016] 4) drying the diaphragm with the MgB2 layer and the graphene layer attached thereto to obtain the battery modified diaphragm.

[0017] As a preferred embodiment in the application, the organic solvent in step 1) is one of NMP or DMF or a mixture of the two, and the mass of the MgB2 and expanded graphite powder to the mass volume ratio of the organic solvent is 0.01-0.05 g / mL.

[0018] As a preferred embodiment in the application, the mass ratio of MgB2 to expanded graphite in step 1) is any ratio, and preferably the mass ratio of MgB2 to expanded graphite is 1:1.

[0019] As a preferred embodiment in the application, the ultrasonic exfoliation conditions in step 2) are as follows: the ultrasonic power is 400-800 W, and the time is 1-2 h.

[0020] As a preferred embodiment in the present application, the amount of the ultrasonic exfoliation dispersion solution used in the vacuum filtration in step 3) is 0.8-1.5 mL / cm. That is, the amount of the dispersion solution is related to the diameter of the filter membrane. If the diameter of the filter membrane is 5 cm, the volume of the ultrasonic exfoliation dispersion solution used in the filtration is 4-7.5 mL.

[0021] As a preferred embodiment in the present application, the base separator film in step 3) includes a polyolefin separator film, a glass fiber separator film and a cellulose separator film.

[0022] As a preferred embodiment in the present application, the drying condition in step 4) is that the drying temperature is 60 ℃ and the drying time is 12 h.

[0023] As a preferred embodiment in the present application, the step of diluting the ultrasonic exfoliation dispersion solution is further included before the filtration, and the concentration of the diluted ultrasonic exfoliation dispersion solution used in the filtration is 0.3-0.8 mg / mL.

[0024] The application of the battery modified separator in a black phosphorus negative lithium ion battery.

[0025] In the present application, the ultrasonic exfoliation preparation of the battery modified separator can provide good electronic conductivity and ionic conductivity for the modified layer, and the composite layer on the base separator film is a MgB2 / graphene layer layer assembly structure. The lamellar structure of the composite layer can better block the shuttling of lithium polyphosphate and strengthen the adsorption and utilization of dissolved lithium polyphosphate. Limiting lithium polyphosphate on the black phosphorus electrode side can effectively prevent the occurrence of the shuttling effect and reduce the loss of active material phosphorus. At the same time, there is a large stress and space gap between the separator and the electrode, which can relieve the volume change on the electrode, stabilize the electrode structure and promote the electrode stability, thereby improving the electrochemical performance of the black phosphorus negative electrode.

[0026] The battery modified separator prepared by the present application is constructed with a stable barrier layer on the surface of the separator, which can isolate the diffusion and shuttling of dissolved lithium polyphosphate to the lithium electrode and reduce the occurrence of side reactions in the battery. The layered structure forms a direct barrier on the diffusion path of lithium polyphosphate, inhibiting the migration of active material to the opposite electrode side. The designed MgB2 / graphene layer layer assembly structure modification structure has high ionic conductivity and electronic conductivity, can realize the reuse of dissolved lithium polyphosphate, effectively reduce the loss of positive active material phosphorus, improve the utilization rate of active material in the electrochemical reaction, and at the same time, the modified layer can effectively relieve the volume change of the positive electrode phosphorus during charging and discharging, maintain the stability of the electrode system, thereby improving the electrochemical performance of the black phosphorus negative electrode.

[0027] Compared with the prior art, the positive effects of the present application are as follows:

[0028] The battery modified diaphragm can improve the electrochemical performance of the black phosphorus negative electrode, form an efficient lithium polyphosphide diffusion barrier layer through the construction of a layer-by-layer assembly structure, and the composite layer (MgB2 / graphene layer layer assembly structure) has good electronic conductivity and ionic conductivity, forms an effective upper current collector, improves the utilization rate of active substances, prevents the loss of active substances, and promotes the efficient use of soluble lithium polyphosphide.

[0029] The layered MgB2 in the composite layer has high reactivity, can effectively improve the adsorption effect of carbon materials on lithium polyphosphide, and can promote the conversion of lithium polyphosphide.

[0030] The battery modified diaphragm has flexibility of the diaphragm, can act as a buffer layer for the volume change of the phosphorus negative electrode during charging and discharging, inhibits the volume change, prevents the collapse and fragmentation of the positive electrode structure during the charging and discharging process, and stabilizes the electrode.

[0031] The battery modified diaphragm can improve the electrochemical performance of the black phosphorus negative electrode, improve its practicability. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 SEM image of the MgB2 / graphene layer layer assembly modified diaphragm material prepared in Example 1;

[0033] Figure 2 SEM image and EDS images of carbon element, magnesium element and boron element of the MgB2 / graphene layer layer assembly modified diaphragm material prepared in Example 1;

[0034] Figure 3 EDS image of boron element in the MgB2 / graphene layer layer assembly modified diaphragm material prepared in Example 1;

[0035] Figure 4 EDS image of carbon element in the MgB2 / graphene layer layer assembly modified diaphragm material prepared in Example 1;

[0036] Figure 5 EDS image of magnesium element in the MgB2 / graphene layer layer assembly modified diaphragm material prepared in Example 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0038] All features disclosed in this specification, and / or all steps of any methods or processes disclosed in this specification, can be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0039] Any feature in the present specification, unless explicitly stated to the contrary, is intended to be an example of an equivalent or similar feature. In other words, in the context of this specification, the use of the word "example" to modify a feature, or the use of language such as "for example", "for instance", "e.g." or "for example only" in relation to a feature, means only one of a number of equivalent or similar features is being discussed, and does not indicate that a feature is preferred over other equivalent or similar features. In other words, the word "example" or the use of language such as "for example", "for instance", "e.g." or "for example only" in relation to a feature does not mean that a feature is preferred or optimal over other equivalent or similar features.

[0040] The features and nature of the present application will become more apparent from the detailed description set forth below, taken in conjunction with the drawings.

[0041] In this application, all raw materials used are commercially available products.

[0042] Example 1

[0043] (1) Take 1.0 g of MgB2 and 1.0 g of expanded graphite powder with an electronic balance, transfer 100 mL of NMP (N-methyl pyrrolidone) solvent into a beaker, add the weighed powder, add a magnetic stirrer, and continuously stir the sample on a magnetic stirrer to obtain a MgB2 and expanded graphite dispersion liquid.

[0044] (2) Transfer the prepared dispersion liquid to an ultrasonic device, turn on the power, set the ultrasonic parameters, ultrasonic power 800 W, ultrasonic time 2 h, and perform ultrasonic peeling to obtain an ultrasonic peeling dispersion liquid (MgB2 / graphene layer-by-layer assembly dispersion liquid).

[0045] (3) Take 5 mL of the ultrasonic peeling dispersion liquid with a concentration of 0.5 mg / mL, select a filter membrane with a diameter of 5 cm, and use a vacuum filtration device with a lithium ion battery polyolefin PP separator as the filter membrane to obtain a modified separator by filtration. The 0.5 mg / mL ultrasonic peeling dispersion liquid in this step is diluted by adding NMP to the ultrasonic peeling dispersion liquid in step 2.

[0046] (4) Dry the modified separator in a vacuum drying oven at a drying temperature of 60 °C for 12 h to obtain a battery modified separator (MgB2 / graphene layer-by-layer assembly modified separator).

[0047] Place the modified separator prepared in Example 1 in a small round piece with a diameter of 16 mm. Assemble the prepared battery modified separator with black phosphorus as the negative electrode into a half-cell to perform 1000 mA / g charge and discharge test, and the specific results are shown in Table 1.

[0048] Referring to Figures 1 to 5 From Figure 1It can be seen that the composite layer formed by the MgB2 layer and the graphene layer stacked in sequence is attached to the base diaphragm. Figures 2 to 5 It can be seen from the elemental map of the diaphragm material that the diaphragm material comprises C, B and Mg elements.

[0049] Example 2:

[0050] (1) 1.0 g of MgB2 and 4.0 g of expanded graphite powder were weighed with an electronic balance, 100 mL of DMF (N,N-dimethylformamide) solvent was transferred to a beaker, the weighed powder was added, a magnetic stirrer was added, and the sample was continuously stirred on a magnetic stirrer to obtain a MgB2 and expanded graphite dispersion liquid.

[0051] (2) The prepared dispersion liquid was transferred to an ultrasonic device, the power was turned on, the ultrasonic parameters were set, the ultrasonic power was 800 W, and the ultrasonic time was 2 h, and the ultrasonic peeling was carried out to obtain a MgB2 / graphene layer layer assembly dispersion liquid.

[0052] (3) 5 mL of the dispersion liquid after ultrasonic peeling with a concentration of 0.5 mg / mL was taken, a filter membrane with a diameter of 5 cm was selected, a vacuum filtration device was used, a lithium ion battery polyolefin PP diaphragm was used as the filter membrane, and a modified diaphragm was obtained by filtration.

[0053] (4) The modified diaphragm was placed in a vacuum drying oven for drying, the drying temperature was 60°C, and the drying time was 12 h, thereby obtaining a MgB2 / graphene layer layer assembly modified diaphragm.

[0054] The battery modified diaphragm prepared in Example 2 was also cut into a small disc with a diameter of 16 mm. The prepared battery modified diaphragm was assembled into a half battery with black phosphorus as the negative electrode, and 1000 mA / g charge-discharge test was carried out, and the specific results are shown in Table 1.

[0055] Example 3:

[0056] (1) 1.0 g of MgB2 and 1.0 g of expanded graphite powder were weighed with an electronic balance, 100 mL of NMP solvent was transferred to a beaker, the weighed powder was added, a magnetic stirrer was added, and the sample was continuously stirred on a magnetic stirrer to obtain a MgB2 and expanded graphite dispersion liquid.

[0057] (2) The prepared dispersion liquid was transferred to an ultrasonic device, the power was turned on, the ultrasonic parameters were set, the ultrasonic power was 400 W, and the ultrasonic time was 1 h, and the ultrasonic peeling was carried out to obtain a MgB2 / graphene layer layer assembly dispersion liquid.

[0058] (3) 5 mL of the dispersion liquid after ultrasonic peeling with a concentration of 0.5 mg / mL was taken, a filter membrane with a diameter of 5 cm was selected, a vacuum filtration device was used, a lithium ion battery polyolefin PP diaphragm was used as the filter membrane, and a modified diaphragm was obtained by filtration.

[0059] (4) Put the modified separator into a vacuum drying oven, dry at 60 ℃ for 12 h to obtain the MgB2 / graphene layer-by-layer assembled modified separator.

[0060] The above MgB2 / graphene layer-by-layer assembled modified separator was cut into a small disc with a diameter of 16 mm. The prepared modified separator was assembled into a half battery with black phosphorus as the negative electrode, and 1000 mA / g charge-discharge test was performed, and the specific results are shown in Table 1.

[0061] Example 4:

[0062] (1) Take 4.0 g of MgB2 and 1.0 g of expanded graphite powder with an electronic balance, transfer 100 mL of NMP solvent into a beaker, add the weighed powder, add a magnetic stirrer, and continuously stir the sample on a magnetic stirrer to obtain a MgB2 and expanded graphite dispersion liquid.

[0063] (2) Transfer the prepared dispersion liquid to an ultrasonic device, turn on the power, set the ultrasonic parameters, ultrasonic power 600W, ultrasonic time 1h, and perform ultrasonic peeling to obtain a MgB2 / graphene layer-by-layer assembled dispersion liquid.

[0064] (3) Take 4 mL of the dispersion liquid after ultrasonic peeling with a concentration of 0.3 mg / mL, select a filter membrane with a diameter of 5 cm, and use a vacuum filtration device with a lithium ion battery polyolefin PP separator as the filter membrane to obtain a modified separator by filtration.

[0065] (4) Put the modified separator into a vacuum drying oven, dry at room temperature for 12 h to obtain the MgB2 / graphene layer-by-layer assembled modified separator.

[0066] Example 5:

[0067] (1) Take 1.0 g of MgB2 and 5.0 g of expanded graphite powder with an electronic balance, transfer 100 mL of NMP solvent into a beaker, add the weighed powder, add a magnetic stirrer, and continuously stir the sample on a magnetic stirrer to obtain a MgB2 and expanded graphite dispersion liquid.

[0068] (2) Transfer the prepared dispersion liquid to an ultrasonic device, turn on the power, set the ultrasonic parameters, ultrasonic power 600W, ultrasonic time 1h, and perform ultrasonic peeling to obtain a MgB2 / graphene layer-by-layer assembled dispersion liquid.

[0069] (3) Take 5 mL of the dispersion liquid after ultrasonic peeling with a concentration of 0.8 mg / mL, select a filter membrane with a diameter of 5 cm, and use a vacuum filtration device with a lithium ion battery polyolefin PP separator as the filter membrane to obtain a modified separator by filtration.

[0070] (4) Put the modified separator into a vacuum drying oven, dry at 40 °C for 12 h to obtain the MgB2 / graphene layer assembly modified separator.

[0071] Comparative Example 1:

[0072] (1) Take 2.0 g of expanded graphite powder with an electronic balance, transfer 100 mL of NMP solvent into a beaker, add the weighed powder, add a magnetic stirrer, and continuously stir the sample on a magnetic stirrer to obtain an expanded graphite dispersion.

[0073] (2) Transfer the prepared dispersion to an ultrasonic device, turn on the power, set the ultrasonic parameters, ultrasonic power 800 W, ultrasonic time 2 h, and perform ultrasonic peeling to obtain a graphene assembly dispersion.

[0074] (3) Take 5 mL of the dispersion after ultrasonic peeling with a concentration of 0.5 mg / mL, select a filter membrane with a diameter of 5 cm, and use a lithium ion battery polyolefin PP separator as the filter membrane to obtain a modified separator by vacuum filtration.

[0075] (4) Put the modified separator into a vacuum drying oven, dry at 60 °C for 12 h to obtain a graphene assembly modified separator.

[0076] Place the modified separator obtained in Comparative Example 1 in a small disc with a diameter of 16 mm. Assemble a half-cell by using the prepared modified separator as the negative electrode and black phosphorus as the negative electrode, and perform 1000 mA / g charge-discharge test. The specific results are shown in Table 1.

[0077] Comparative Example 2:

[0078] (1) Take 2.0 g of MgB2 with an electronic balance, transfer 100 mL of NMP solvent into a beaker, add the weighed powder, add a magnetic stirrer, and continuously stir the sample on a magnetic stirrer to obtain an MgB2 dispersion.

[0079] (2) Transfer the prepared dispersion to an ultrasonic device, turn on the power, set the ultrasonic parameters, ultrasonic power 800 W, ultrasonic time 2 h, and perform ultrasonic peeling to obtain an MgB2 assembly dispersion.

[0080] (3) Take 5 mL of the dispersion after ultrasonic peeling with a concentration of 0.5 mg / mL, select a filter membrane with a diameter of 5 cm, and use a lithium ion battery polyolefin PP separator as the filter membrane to obtain a modified separator by vacuum filtration.

[0081] (4) The modified diaphragm is placed in a vacuum drying oven for drying, the drying temperature is 60 DEG C, and the drying time is 12 h, to obtain the MgB2 assembled modified diaphragm.

[0082] The modified diaphragm obtained in Comparative Example 2 is cut into a small disc with a diameter of 16 mm. The prepared modified diaphragm is assembled into a half battery with black phosphorus as a negative electrode, and 1000 mA / g charge-discharge test is carried out, and the specific results are shown in Table 1.

[0083] Table 1: Detection results of the performance of the prepared black phosphorus negative electrode

[0084]

[0085] From the data in Table 1, it can be seen that the performance of the diaphragm material with the composite layer of the MgB2 layer and the graphene layer is better than that of the MgB2 layer and the graphene layer alone.

[0086] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0087] The part of the present application not described in detail belongs to the known technology in the art. The above examples are provided only for the purpose of describing the present application, and are not intended to limit the scope of the present application. The scope of the present application is defined by the appended claims. Any equivalent replacement and modification made without departing from the spirit and principle of the present application shall be included in the scope of the present application.

Claims

1. A modified separator for black phosphorus negative lithium-ion batteries, characterized by, The modified diaphragm comprises a base diaphragm and a composite layer attached to the base diaphragm, and the composite layer comprises a layered structure of a MgB2 layer and a graphene layer.

2. The method of producing a modified separator according to claim 1, characterized by, The method comprises the following steps: 1) dispersing MgB2 and expanded graphite powder with an organic solvent to obtain a dispersion liquid; 2) performing ultrasonic exfoliation on the prepared dispersion liquid to obtain an ultrasonic exfoliation dispersion liquid; 3) using a base diaphragm as a filter membrane to perform suction filtration on the ultrasonic exfoliation dispersion liquid to obtain a diaphragm with MgB2 and graphene layers attached thereto; 4) drying the diaphragm with MgB2 and graphene layers attached thereto to obtain a modified diaphragm.

3. The method of claim 2, wherein: The organic solvent in step 1) is one of NMP or DMF or a mixture of the two, and the mass ratio of the MgB2 and expanded graphite powder to the mass volume of the organic solvent is 0.01-1.5 g / mL.

4. The method of claim 2, wherein: The mixing ratio of MgB2 and expanded graphite in step 1) is any ratio.

5. The method of claim 2, wherein: The ultrasonic exfoliation conditions in step 2) are as follows: ultrasonic power is 400-800 W, and time is 1-2 h.

6. The method of claim 2, wherein: The amount of ultrasonic exfoliation dispersion liquid used in vacuum suction filtration in step 3) is 0.8-1.5 mL / cm.

7. The method of claim 2, wherein: The base diaphragm in step 3) comprises a polyolefin diaphragm, a glass fiber diaphragm, and a cellulose diaphragm.

8. The method of claim 2, wherein: The drying conditions in step 4) are as follows: drying temperature is 20-60 ℃, and drying time is 1-12 h.

9. The method of claim 2, wherein: The method further comprises a step of diluting the ultrasonic exfoliation dispersion liquid before suction filtration, and the concentration of the diluted ultrasonic exfoliation dispersion liquid used in suction filtration is 0.3-0.8 mg / mL.

10. Application of the modified diaphragm of claim 1 in a black phosphorus negative lithium ion battery.

Images