A lithium supplement composite separator and its preparation method and application

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium-supplementing composite separator and its preparation method and application. The lithium-supplementing composite separator provided by the present invention can form a primary battery by contacting the negative electrode through a solid electrolyte without waiting until after liquid injection, and can spontaneously react to carry out lithium intercalation to achieve the lithium-supplementing effect, which can improve the first charge-discharge efficiency and discharge capacity of the battery cell, reduce the lithium-supplementing static time, and improve the production efficiency. In addition, when the lithium reaction is complete, a porous solid electrolyte separator can be formed. This separator has good porosity, which is helpful for lithium-ion transmission, and the solid electrolyte separator can inhibit the precipitation of lithium dendrites and improve the safety performance of the battery cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a lithium - supplementing composite separator and a preparation method and application thereof. Background Art

[0002] Due to advantages such as high working voltage, high energy density, long cycle life, and no memory effect, lithium - ion batteries are widely used in laptop computers, digital products, mobile communications, etc. However, lithium - ion batteries also have a fatal drawback, that is, as the number of uses increases, their capacity will also decline accordingly. This is because during the first charge - discharge process of lithium - ion batteries, a reaction occurs between the electrode material and the electrolyte at the solid - liquid interface to form a passivation layer covering the surface of the electrode material, namely the solid electrolyte interface (SEI) and the cathode electrolyte interface (CEI) film, consuming some lithium ions and reducing the charge - discharge efficiency of the electrode material.

[0003] Therefore, in order to improve the initial efficiency and capacity of the battery cell, a lithium - supplementing process is needed to supplement the irreversible capacity loss. For example, the prior art discloses a method of spreading lithium powder on the surface of the electrode sheet and performing prelithiation after rolling. However, metallic lithium powder has strong activity and its safety is difficult to control. There is also a patent document that discloses a method for prelithiation of an electrode sheet and a device for prelithiation of an electrode sheet, which uses two roller mechanisms to roll two lithium foils. However, in this method, the time for the electrolyte to infiltrate the lithium foil and the electrode sheet is relatively long, and the amount of lithium supplementation is difficult to control, affecting production efficiency. There is also a patent document that discloses a lithium - supplementing composite film for the negative electrode of a lithium - ion battery and a preparation method and application thereof. In this method, the lithium - supplementing composite film is prepared by compounding an organic binder and metallic lithium to form a lithium - supplementing composite film. However, in this method, the organic matter is a non - conductive substance, covering the surface of the negative electrode sheet, which will increase the impedance of the battery cell and seriously affect the electrochemical performance of the battery cell. There is also a patent document that discloses a prelithiated electrode sheet, a prelithiated separator of a lithium - ion battery, and a preparation method thereof. Using the method of high - temperature heating and melting makes the safety of metallic lithium even more difficult to control. In addition, compared with solid electrolytes, inorganic materials have poor conductivity, which will affect the electrical performance of the battery cell.

[0004] In view of this, there is an urgent need to develop a lithium - supplementing separator that is safe, has good lithium - supplementing effect, and does not affect the electrochemical performance of the battery cell. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the above - mentioned defects existing in the lithium - supplementing methods in the prior art, and thus provide a lithium - supplementing composite separator and a preparation method and application thereof.

[0006] To this end, the present invention provides the following technical solutions:

[0007] The present invention provides a lithium - supplementing composite separator, comprising a base film and a lithium - supplementing layer coated on at least one surface of the base film.

[0008] The lithium supplement layer comprises components in the following parts by weight: 70-100 parts of a solid electrolyte; 5-30 parts of lithium powder; 1-5 parts of a binder.

[0009] Optionally, the particle size of the solid electrolyte is 0.1-2 μm; the particle size of the lithium powder is below 200 nm;

[0010] and / or, the particle size of the binder is below 500 nm.

[0011] Optionally, the solid electrolyte is at least one of an oxide solid electrolyte and / or a sulfide solid electrolyte;

[0012] Optionally, the oxide solid electrolyte is Li 7 La 3 Zr 2 O 12 (LLZO), Li 3x La 2 / 3-x TiO 3 (LLTO), Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP), Li 1+x Al x Ge 2-x (PO 4 ) 3 (LAGP), etc., where 0 < x ≤ 2;

[0013] Optionally, the sulfide solid electrolyte is Li x (A y )P z S q , where A is at least one of Ge, Sn, and Si, and x, y, z, q are corresponding stoichiometric numbers, 0 < x ≤ 4, 0 < y ≤ 2, 0 < z ≤ 2, 4 < q ≤ 8.

[0014] Typically and non-limitingly, the sulfide solid electrolyte can be Li 10 SnP 2 S 12 、Li 7 P 2 S 8 I、Li 7 P 3 S 11 、Li 3.25 Ge 0.25 P 0.75 S 4 、LPSI, etc.

[0015] Optionally, the binder is at least one of polyvinylidene fluoride (PVDF) or polymethyl methacrylate (PMMA);

[0016] And / or, the base film is a polyethylene film, a polypropylene film or a polyethylene - polypropylene composite film.

[0017] Optionally, the thickness of the base film is 1 - 15 μm;

[0018] And / or, the thickness of the lithium - supplement composite separator is 1 μm - 20 μm.

[0019] The present invention also provides a method for preparing the above - mentioned lithium - supplement composite separator, which comprises the following steps:

[0020] S1, mix lithium powder, binder and solid electrolyte according to different ratios to obtain a mixed material;

[0021] S2, spray the mixed material on the base film by powder electrostatic spraying to obtain the lithium - supplement composite separator.

[0022] Optionally, the voltage of the powder electrostatic spraying is 5 - 20 KV, the spraying distance is 10 - 20 cm, and the carrier gas is nitrogen or an inert gas.

[0023] Optionally, step S1 is carried out under a vacuum state for mixing.

[0024] The selection of the above - mentioned carrier gas and vacuum conditions is to ensure production safety.

[0025] The present invention also provides a battery, which includes the above - mentioned lithium - supplement composite separator or the lithium - supplement composite separator prepared by the above - mentioned preparation method.

[0026] The battery provided by the present invention can be a lithium - ion battery, and its composition and preparation method are both conventional compositions and methods in the art. Typically and non - restrictively, the lithium - ion battery further includes a positive electrode and a negative electrode.

[0027] The positive electrode may include lithium nickel cobalt manganese oxide: conductive carbon black: binder PVDF = 96:2:2.

[0028] The negative electrode may include graphite: silicon: conductive carbon black: dispersant (sodium carboxymethyl cellulose CMC): binder (styrene - butadiene rubber latex SBR) = 86.5:10:1:1:1.5.

[0029] The electrolyte used can be prepared by oneself or obtained through commercial channels. For example, the electrolyte can be grade A60 purchased from Capchem.

[0030] The preparation method of the battery may include:

[0031] The above positive and negative electrode materials are mixed together in proportion, stirred and dispersed fully to form a slurry, and evenly coated on the current collector (aluminum foil or copper foil, etc.) with a specified thickness, and dried to obtain the corresponding positive and negative electrodes. The battery assembly is in the order of positive electrode sheet-diaphragm-negative electrode sheet-diaphragm from top to bottom, and wound into a battery core, and then injected with electrolyte, sealed and other processes to complete the battery assembly process and make a finished battery.

[0032] The technical solution of the present invention has the following advantages:

[0033] The lithium-supplementing composite isolation membrane provided by the present invention comprises a base membrane and a lithium-supplementing layer coated on the surface of the base membrane, wherein the lithium-supplementing layer comprises the following components in parts by weight: 70-100 parts of solid electrolyte; 5-30 parts of lithium powder; 1-5 parts of binder. Among them, the solid electrolyte plays a structural support role in the lithium-supplementing composite isolation membrane, and the binder and the metal lithium powder are evenly embedded in the solid electrolyte powder. The lithium-supplementing layer of the obtained lithium-supplementing composite isolation membrane has the advantages of being dense, having strong adhesion, and being safe and controllable. The lithium-supplementing composite isolation membrane provided by the present invention can form a primary battery through the contact of the solid electrolyte with the negative electrode without waiting for liquid injection, and spontaneously reacts to insert lithium to achieve the lithium-supplementing effect, which can improve the initial charge and discharge efficiency and discharge capacity of the battery cell, reduce the lithium-supplementing standing time, and improve production efficiency; in addition, when the lithium reaction is complete, a porous solid electrolyte isolation membrane can also be formed, and this isolation membrane has good porosity, which is conducive to lithium ion transmission, and the solid electrolyte isolation membrane can inhibit the precipitation of lithium branched crystals and improve the safety performance of the battery cell.

[0034] The lithium-supplementing composite isolation membrane provided by the present invention can enable the solid electrolyte to more comprehensively wrap the lithium powder and the binder by limiting the particle size of each component, thereby improving the safety during the preparation process.

[0035] According to the preparation method of the lithium-supplementing composite isolation membrane provided by the present invention, various materials can be directly coated on the surface of the base membrane in the form of powder, and the operation is simple, the preparation is convenient, and it is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 It is a schematic structural diagram of one side of the lithium-supplementing composite isolation membrane provided by the present invention;

[0038] Reference numerals:

[0039] 1. Base film; 2. Solid electrolyte; 3. Lithium powder; 4. Binder. Detailed implementation manners

[0040] The following embodiments are provided to better understand the present invention further. They are not limited to the best implementation manners, and do not constitute limitations on the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other existing technologies falls within the protection scope of the present invention.

[0041] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0042] Example 1

[0043] This example provides a lithium - supplement composite separator membrane, as Figure 1 shown, including a base film 1 and a lithium - supplement layer coated on the surface of the base film 1. Calculated by the total mass of the lithium - supplement layer, it consists of 20% by mass of metallic lithium powder 3 and 78% of solid electrolyte 2 (Li 0.5 La 0.5 TiO 3 ) and 2% of polyvinylidene fluoride (binder 4) (manufacturer: Arkema, model: HSV900).

[0044] The preparation method of the lithium - supplement composite separator membrane is as follows:

[0045] (1) Place metallic lithium powder with a particle size of 20 nm, solid electrolyte with a particle size of 2 μm, and polyvinylidene fluoride with a particle size of 50 nm in a centrifugal stirrer, and dry - mix them evenly at 2000 rad / s for 60 min in a vacuum environment to obtain a mixed material.

[0046] (2) In an inert environment, use electrostatic spraying to coat the mixed material on both sides of a 7 - μm base film (PP film, manufacturer: Enjie). The voltage between the gun of the powder electrostatic spraying device and the base film is 10 KV; the distance between the powder gun and the base film is controlled at 15 cm; the carrier gas used by the powder gun is argon; the spraying thickness is 2 μm, and an 11 - μm lithium - supplement composite separator membrane can be obtained.

[0047] Example 2

[0048] This example provides a lithium - supplement composite separator membrane, as Figure 1 shown, including a base film 1 and a lithium - supplement layer coated on the surface of the base film 1. Calculated by the total mass of the lithium - supplement layer, it consists of 5% by mass of metallic lithium powder 3 and 93% of solid electrolyte 2 (Li 0.5 La0.5 TiO 3 and 2% polyvinylidene fluoride (from the same source).

[0049] The preparation method of the lithium - supplementing composite separator is as follows:

[0050] (1) Put the metal lithium powder with a particle size of 50 nm, the solid electrolyte with a particle size of 4 μm, and the polyvinylidene fluoride with a particle size of 50 nm into a centrifugal mixer, and dry - mix them evenly at 2000 rad / s for 60 min in a vacuum environment to obtain a mixed material.

[0051] (2) In an inert environment, use electrostatic spraying to coat the mixed material on both sides of a 7 - μm base film (from the same source). The voltage between the spray gun of the powder electrostatic spraying device and the base film is 10 KV; the distance between the powder spray gun and the base film is controlled at 15 cm; the carrier gas used by the powder spray gun is argon; the spraying thickness is 2 μm, and a 11 - μm lithium - supplementing composite separator can be obtained.

[0052] Example 3

[0053] This example provides a lithium - supplementing composite separator, as Figure 1 shown, including a base film 1 and a lithium - supplementing layer coated on the surface of the base film 1. Calculated by the total mass of the lithium - supplementing layer, it is composed of 20% by mass of metal lithium powder 3, 78% of solid electrolyte 2 (Li 05 La 05 TiO 3 ) and 2% polyvinylidene fluoride (from the same source).

[0054] The preparation method of the lithium - supplementing composite separator is as follows:

[0055] (1) Put the metal lithium powder with a particle size of 20 nm, the solid electrolyte with a particle size of 2 μm, and the polyvinylidene fluoride with a particle size of 50 nm into a centrifugal mixer, and dry - mix them evenly at 2000 rad / s for 60 min in a vacuum environment to obtain a mixed material.

[0056] (2) In an inert environment, use electrostatic spraying to coat the mixed material on one side surface of a 15 - μm base film (from the same source). The voltage between the spray gun of the powder electrostatic spraying device and the base film is 10 KV; the distance between the powder spray gun and the base film is controlled at 5 cm; the carrier gas used by the powder spray gun is argon; the spraying thickness is 6 μm, and a 21 - μm lithium - supplementing composite separator can be obtained.

[0057] Example 4

[0058] This example provides a lithium - supplementing composite separator. Different from Example 1, the solid electrolyte is Li 7 La 3 Zr 2 O12 .

[0059] Example 5

[0060] This example provides a lithium - supplemented composite separator. The difference compared with Example 1 is that the solid electrolyte is Li 7 P 3 S 11 .

[0061] Comparative Example 1

[0062] This comparative example provides a lithium - supplemented composite separator. The difference compared with Example 1 is that it does not include a binder.

[0063] Comparative Example 2

[0064] This comparative example provides a lithium - supplemented composite separator. The difference compared with Example 1 is that it uses metal oxide TiO 2 to replace the solid electrolyte.

[0065] Comparative Example 3

[0066] This comparative example provides a lithium - supplemented composite separator. The difference compared with Example 1 is that it does not include lithium powder.

[0067] Comparative Example 4

[0068] This comparative example provides a lithium - supplemented composite separator. The difference compared with Example 1 is that the content of the solid electrolyte accounts for 65%, the lithium powder accounts for 33%, and the binder accounts for 2%.

[0069] Test Example

[0070] 1. Test the compactness, uniformity, and adhesion of the lithium - supplemented composite separators provided in each example and comparative example. The specific test method is as follows: The compactness and uniformity are observed by magnifying with a metallographic microscope to check whether the diaphragm coating is uniform and the compactness; the adhesion is tested using a 180 °C peeling machine. Stick the separator on a stainless - steel plate with double - sided tape and attach a tape to the other end of the separator; fix the stainless - steel plate and the separator on the two clamps of a peel - force tester, and then conduct a 180 - degree peeling test at a speed of 10 mm / min with a load of 10 N. The force detected when the tape is completely peeled off is the peel force. The specific test results are shown in the following table:

[0071] Table 1

[0072]

[0073]

[0074] From the data in the table, it can be seen that adding a binder can significantly improve the stripping force of the coating and extend its service life; in addition, by controlling the ratio of lithium powder and solid electrolyte, the density of the diaphragm coating can be significantly improved.

[0075] 2. Electrical performance test

[0076] The lithium-supplementing composite isolation membranes provided in the embodiments and comparative examples are assembled into a lithium-ion battery, the specific composition of which is as follows:

[0077] The positive electrode includes lithium nickel cobalt manganese oxide: conductive carbon black: binder PVDF = 96:2:2.

[0078] The negative electrode includes graphite: silicon: conductive carbon black: dispersant (sodium carboxymethyl cellulose CMC): binder (styrene-butadiene rubber latex SBR) = 86.5:10:1:1:1.5.

[0079] The electrolyte is purchased from Xinzhoubang with brand A60.

[0080] The preparation method of the battery is as follows:

[0081] The above positive and negative electrode materials are mixed with the solvent (NMP) in proportion, stirred and dispersed to form a slurry, and evenly coated on the current collector (aluminum foil for positive electrode and copper foil for negative electrode) with a specified thickness, and dried. The assembly is arranged in the order of positive electrode sheet-diaphragm-negative electrode sheet-diaphragm from top to bottom, and wound into a battery cell, and then injected with 6g electrolyte, sealed and other processes to complete the battery assembly process and make a 2Ah finished battery. The battery cell internal resistance, discharge capacity, 500-cycle capacity retention rate, and needle puncture test of each battery cell were tested. The specific test methods are as follows: the discharge capacity and cycle capacity retention rate were both tested using a Ruineng test cabinet. In a 25°C normal temperature environment, the upper limit cutoff voltage was set to 4.4V, the lower limit voltage was set to 2.8V, and the current was set to 660mAh for charge and discharge tests; the battery cell internal resistance was tested using a voltage resistance tester; the needle puncture test method was to place the battery cell connected to a thermocouple in an explosion-proof cabinet, and pierce the battery cell with a 2mm diameter steel needle at a speed of 20mm / s, and hold for 5s. See the table below for specific test results:

[0082] Table 2

[0083]

[0084] It can be seen from the data in the table that the lithium-supplementing composite isolation membrane provided by the present invention can reduce the internal resistance of the battery cell while improving the discharge capacity and cycle capacity retention rate of the battery cell. In addition, the introduced solid electrolyte isolation membrane can also greatly improve the safety performance of the battery cell.

[0085] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A lithium - supplementing composite separator, characterized in that, it is composed of a base film and a lithium - supplementing layer coated on at least one surface of the base film, the lithium - supplementing layer comprises the following components in parts by weight: 70 - 100 parts of solid electrolyte; 5 - 30 parts of lithium powder; 1 - 5 parts of binder; the particle size of the solid electrolyte is 0.1 - 2μm; the particle size of the lithium powder is below 200nm; the particle size of the binder is below 500nm.

2. The composite separator according to claim 1, characterized in that, the solid electrolyte is at least one of oxide solid electrolyte and / or sulfide solid electrolyte.

3. The composite separator according to claim 2, characterized in that, The oxide solid electrolyte is Li 7 La 3 Zr 2 O 12 (LLZO), Li 3x La 2 / 3-x TiO 3 (LLTO), Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP), Li 1+x Al x Ge 2-x (PO 4 ) 3 (LAGP), where 0 < x ≤ 2; and / or, the sulfide solid electrolyte is Li x (A y )P z S q , where A is at least one of Ge, Sn, and Si, and x, y, z, and q are corresponding stoichiometric coefficients, 0 < x ≤ 4, 0 < y ≤ 2, 0 < z ≤ 2, 4 < q ≤ 8.

4. The composite separator according to claim 3, characterized in that, the binder is at least one of polyvinylidene fluoride or polymethyl methacrylate; and / or, the base film is a polyethylene film, a polypropylene film or a polyethylene - polypropylene composite film.

5. The composite separator according to any one of claims 1 - 4, characterized in that, the thickness of the base film is 1 - 15μm; and / or, the thickness of the lithium - supplementing composite separator is 1μm - 20μm.

6. A preparation method of the lithium - supplementing composite separator according to any one of claims 1 - 5, characterized in that, it comprises the following steps: S1, mixing lithium powder, binder and solid electrolyte according to different ratios to obtain a mixed material; S2, spraying the mixed material on the base film by powder electrostatic spraying to obtain the lithium - supplementing composite separator.

7. The preparation method of the composite separator according to claim 6, characterized in that, the voltage of the powder electrostatic spraying is 5 - 20KV, the spraying distance is 10 - 20cm, and the carrier gas is nitrogen or inert gas.

8. The preparation method of the composite separator according to any one of claims 6 - 7, characterized in that, step S1 is carried out for mixing under a vacuum state.

9. A battery, characterized in that, it comprises the lithium - supplementing composite separator according to any one of claims 1 - 5 or the lithium - supplementing composite separator prepared by the preparation method according to any one of claims 6 - 8.

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