CN115939664A - Lithium ion battery diaphragm modified by metal nano oxide and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the field of lithium ion batteries, and particularly relates to a lithium ion battery diaphragm modified by metal nano-oxides, and a preparation method and application thereof. The thickness of the metal nano oxide modification layer on the surface of the lithium ion battery diaphragm is 5-100nm, and one side or two sides of the diaphragm can be modified, and the preparation method comprises the following steps: firstly, preparing a metal layer on at least one surface of the diaphragm, then completely immersing the diaphragm in deionized water, heating the diaphragm in the presence of oxygen-containing atmosphere to enable the metal layer on the surface to fully react and synthesize metal oxide in situ, and drying the metal oxide modified diaphragm to obtain the metal nano oxide modified diaphragm. The metal nano oxide modification layer can improve the contact of an interface, strengthen the mechanical property and the thermal stability of the diaphragm, has flame retardance and good wettability, and can improve the cycle life and the safety of a lithium battery; and has excellent interfacial contact and adhesion. The method has simple and efficient preparation process and great commercialization potential.

Description

Lithium ion battery diaphragm modified by metal nano oxide and preparation method and application thereof

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to a lithium ion battery diaphragm modified by metal nano-oxides, and a preparation method and application thereof.

Background

In recent years, the development of energy storage systems has become necessary due to the increasingly worsening environmental problems and the irreversible consumption of non-renewable fossil energy. Lithium ion batteries are widely used in the fields of electronic devices, electric vehicles and aerospace engineering due to their excellent overall properties, such as low self-discharge rate, excellent cycle life and high operating voltage. The lithium ion battery mainly comprises three parts: positive electrode, negative electrode, and separator. Wherein the diaphragm is sandwiched between the positive and negative electrodes, and plays the roles of preventing internal short circuit, ensuring the conduction of lithium ions through the interconnected microporous structure, and avoiding thermal runaway of the lithium ion battery under the condition of abnormal heating.

Commercial separators made from polyolefin materials (e.g., polyethylene and polypropylene) are the first choice for commercial lithium batteries due to their excellent performance and low cost. However, the inherently hydrophobic surface properties resulting from the low surface energy of polyolefins, impairs affinity for carbonate electrolytes, which impairs lithium ion transport, further impairing the overall performance of lithium ion batteries; polyolefins have poor thermal stability and tend to shrink at elevated temperatures, causing potential safety hazards such as internal short circuits and even explosions. In order to improve the mechanical properties and the thermal stability of the separator, many studies have been made so far to modify the surface of the separator, such as coating the surface with a ceramic material, grafting functional groups on the surface, coating nanoparticles, and the like. The method for coating the nano inorganic particles on the surface of the diaphragm is proved to be a method capable of improving the thermal stability, the flame retardance and the mechanical property enhancement of the diaphragm.

In the description of the related literature, for example, patent CN110400898A, a polyolefin-based separator coated with inorganic particle coating with porous core-shell structure is proposed, the invention optimizes the wettability and thermal stability of the separator to the electrolyte, but the process greatly increases the thickness (25%) of the separator; similarly, CN106221480A, which discloses a coating filler with a polymer-coated silica core-shell structure, proposes that the complex process and time-consuming characteristics of preparing the core-shell structure are contradictory to the principle requirements of large-scale and low-cost commercial manufacturing. In addition, patent CN108819393A proposes a sandwich structure (polysulfone amide/titanium dioxide/polysulfone amide) lithium battery separator based on the combination of electrostatic spinning technology and electrostatic spraying technology, wherein the polysulfone amide thin film is prepared on the outer layer by using an electrostatic spinning method, and the nano titanium dioxide thin layer is prepared on the middle layer by using electrostatic spraying, so as to form a composite separator with a sandwich structure. In addition, patent CN104269509A proposes a ceramic-coated separator, i.e. a ceramic protective layer structure is coated on a separator substrate by using an aqueous ceramic coating slurry, which has the disadvantage of high ceramic cost, and at the same time, the coating method increases the weight of the separator from 16 μm to 20 μm, and greatly increases the weight of the separator, which easily results in the reduction of the energy density of the lithium battery.

Therefore, a low-cost, low-technology barrier smart manufacturing technology is a necessary condition for producing a separator having excellent electrolyte affinity, high strength, and high flame retardancy.

Disclosure of Invention

Aiming at the problems of poor wettability, poor thermal stability and poor flame retardance of a lithium battery diaphragm, high cost of a diaphragm modification technology, high technical barrier and the like in the prior art, the invention provides a lithium battery diaphragm modified by metal nano oxide, and a preparation method and application thereof, so that an ultrathin nano oxide layer is obtained, the mechanical property of the diaphragm is enhanced, the thermal stability is excellent, the diaphragm has flame retardance and good wettability, and the cycle life and the safety of a lithium battery can be improved; in addition, the method has simple and efficient preparation process and huge commercial potential and market application prospect.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a lithium ion battery diaphragm modified by metal nano oxides is characterized in that a layer of ultrathin metal layer is deposited on the surface of at least one side of the diaphragm by adopting a physical vapor deposition method; completely immersing the obtained diaphragm with the metal layer deposited on the surface into water, heating, and completely oxidizing the metal layer on the surface of the diaphragm into a metal oxide layer in the presence of oxygen-containing atmosphere; and drying the obtained diaphragm to obtain the lithium ion battery diaphragm modified by the metal nano oxide.

Preferably, the water is deionized water.

Preferably, the oxygen-containing atmosphere is oxygen.

Preferably, the preparation method specifically comprises the following steps:

s1, depositing an ultrathin metal layer on the surface of at least one side of a diaphragm by adopting a physical vapor deposition method;

s2, completely immersing the diaphragm with the surface deposited with the metal layer obtained in the step S1 into water, carrying out heat treatment, introducing a certain amount of oxygen-containing atmosphere, and completely oxidizing the metal layer on the surface of the diaphragm into a metal oxide layer after a certain time;

and S3, drying the diaphragm obtained in the step S2 to obtain the lithium ion battery diaphragm modified by the metal nano oxide.

Preferably, the physical vapor deposition method in step S1 is to use magnetron sputtering method to plate a metal layer on the surface of both sides (or one side) of the lithium battery separator, and more preferably, the thickness is 5-100nm, but not limited to the recited values, and other values in the range of the recited values are also applicable.

Preferably, in the process of carrying out magnetron sputtering, the pressure is 0.4-1.2Pa, more preferably 0.7-0.9Pa, the sputtering power is 40-80W, the sputtering time is 5-30min, and the atmosphere is inert atmosphere, more preferably at least one of argon or nitrogen; but are not limited to the recited values and other values not recited within the numerical range are equally applicable.

Preferably, the separator in step S1 is at least one of a polyethylene separator, a polypropylene separator, a polyimide film, and a polyacrylonitrile film, but is not limited to the above-mentioned ones, and others are not listed in this range and are also applicable.

Preferably, the thickness of the separator in step S1 is 10 to 30 μm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the metal in step S1 is at least one of aluminum, tin and indium, but not limited to the listed metals, and other metals not listed in the scope are also applicable.

Preferably, the heat treatment condition of step S2 is 60-100 ℃ heat preservation for 2-12 hours. The thin metal layer is less likely to undergo an oxidation reaction with oxygen at normal temperature, and therefore, it is preferable to perform the reaction more efficiently at that temperature. But are not limited to the recited values and other values not recited within the numerical range are equally applicable.

Preferably, the oxygen-containing atmosphere in step S2 is oxygen, and more preferably, the oxygen is introduced at a rate of 3-10mL/min, but not limited to the recited values, and other values not recited in the above range are also applicable. By the technical scheme, the reaction can be further completed; when the oxygen introducing rate is higher, the metal surface can be quickly oxidized to form metal oxide, and the internal metal is difficult to contact with the oxygen to react; meanwhile, when the oxygen rate is lower, the metal at the outside thereof is preferentially oxidized, and when the external reaction is complete, the metal at the inside is difficult to contact oxygen to cause the reaction.

Preferably, the drying in step S3 is to make the water content of the diaphragm meet the requirement of a common lithium battery diaphragm, and more preferably, the drying is performed until the water content is 200-350ppm.

Preferably, the drying condition in step S3 is 60-80 ℃ for 8-12 hours, but is not limited to the recited values, and other unrecited values in the range of the values are also applicable.

The invention also aims to provide the lithium ion battery diaphragm modified by the metal nano oxide prepared by any one of the preparation methods.

The invention further aims to provide application of the lithium ion battery diaphragm modified by the metal nano oxide in the field of lithium ion batteries.

According to the lithium ion battery diaphragm modified by the metal nano oxide, the metal nano oxide modification layer can improve interface contact, strengthen the mechanical property and the thermal stability of the diaphragm, has flame retardance and good wettability, and can prolong the cycle life and improve the safety of a lithium battery; and, it is synthesized in situ by chemical conversion reaction, thus having excellent interfacial contact and adhesion.

Compared with the prior art, the invention has the following beneficial effects:

(1) The lithium ion battery diaphragm prepared by the invention introduces the inorganic metal oxide nano layer, and has higher strength, equivalent safety and better electrolyte wettability compared with the traditional lithium ion battery diaphragm; the structure is simple, the weight of the battery is not influenced, the cost is low, the large-scale processing is easy, and the wide market application prospect is realized;

(2) The method avoids violent chemical reaction in the reaction process of preparing the inorganic metal oxide nano layer, and adopts a low-temperature heat treatment method to synthesize the inorganic metal oxide nano layer on the surface of the diaphragm in situ through chemical conversion reaction, so that the inorganic metal oxide nano layer has excellent interface contact and adhesive force and is suitable for industrial large-scale application.

Drawings

Fig. 1 is a schematic structural diagram of a lithium ion battery separator modified by metal nano-oxides according to the present invention.

Figure 2 is the membrane XRD pattern obtained from example 1.

Fig. 3 is a stress-strain relationship between the PP separator prepared in example 1 and a pure PP separator.

Fig. 4 is a graph comparing the thermal stability at 80 ℃ of the PP separator prepared in example 1 (right panel) with the pure PP separator (left panel).

Fig. 5 is a graph of cycle number-discharge capacity at 0.5C rate of the PP separator-assembled lithium iron phosphate-lithium button cell prepared in example 1.

Detailed Description

The technical solution of the present invention is further specifically described below by way of specific examples in conjunction with the accompanying drawings.

Example 1:

firstly, adopting magnetron sputtering technology, sputtering two sides of a polypropylene (PP) diaphragm with the diameter of 19mm for 5min at the power of 50W under the condition of 0.7Pa to respectively obtain a layer of metal aluminum layer (Al @ PP) with the diameter of 15nm, then completely soaking the obtained Al @ PP into deionized water, heating to 60 ℃, preserving heat for 6h, and simultaneously introducing oxygen at the speed of 3mL/min to ensure that the nano metal aluminum layer on the surface of the PP diaphragm is completely oxidized into a nano aluminum oxide layer to obtain the PP diaphragm (Al @ PP) coated with aluminum oxide ₂ O ₃ @ PP), taking out after the reaction is finished, transferring the obtained diaphragm to a 70 ℃ oven for heat preservation for 8 hours to ensure that the moisture is completely removed, and completely drying to obtain the lithium ion battery diaphragm modified by the metal nano oxide.

Figure 2 is the XRD pattern of the membrane prepared in this example.

Fig. 3 is a graph of stress-strain relationship between the PP separator prepared in example 1 and a pure PP separator (comparative example 1). Wherein, the mechanical property of the modified diaphragm is better than that of an unmodified pure PP diaphragm.

Fig. 4 is a graph comparing the thermal stability at 80 ℃ of the PP separator prepared in example 1 (right side of the figure) and a pure PP separator (left side of the figure, comparative example 1). The modified diaphragm does not curl within 40 minutes at 80 ℃, while the unmodified pure PP diaphragm is easy to curl at 80 ℃, and the large-amplitude curl occurs within about 5 minutes.

Fig. 5 is a graph of cycle number versus discharge capacity at 0.5C rate for the PP separator prepared in example 1 and the unmodified separator (pure PP separator) of comparative example 1 for a lithium iron phosphate-lithium button cell. Wherein, the unmodified diaphragm has happened the short circuit in 680 circles, and the battery after modifying still does not short circuit after circulating 700 circles, and, discharge capacity and capacity retention rate are superior to half-cell that unmodified diaphragm prepared gets.

The preparation steps of the lithium-lithium button cell in the embodiment are as follows: sequentially placing the gasket and the positive pole piece into a 2032 positive shell; placing a corresponding diaphragm above the positive plate, and absorbing electrolyte by using a rubber head dropper to wet the surface of the diaphragm; and placing the lithium plate in the center of the diaphragm, placing the gasket on the lithium plate to align, and covering the negative electrode shell matched with the positive electrode shell. Further, the button cell is placed on a cell sealing machine, and the pressure (generally 500 Pa) is adjusted to press for 5 seconds to complete the assembly and prepare the button cell.

The material types of the positive electrode sheet are shown in table 1.

Example 2:

firstly, adopting magnetron sputtering technology, sputtering for 5min at 60W on one side of a Polyethylene (PE) diaphragm under the condition of 0.8Pa to obtain a 30nm metallic tin layer (Sn @ PE), then completely soaking the obtained Sn @ PE into deionized water, heating to 80 ℃, preserving heat for 10h, and simultaneously introducing oxygen at the speed of 5mL/min to ensure that the nano metallic tin layer on the surface of the PE diaphragm is completely oxidized into a nano tin oxide layer to obtain the PE diaphragm (SnO) ₂ @ PE), taking out after the reaction is finished, transferring the obtained diaphragm to an oven with the temperature of 80 ℃ for heat preservation for 12 hours to ensure that the moisture is completely removed, and completely drying to obtain the lithium ion battery diaphragm modified by the metal nano oxide. .

Assembling the obtained separator into a lithium nickel cobalt manganese oxide (811) -lithium button cell, wherein one side of tin oxide corresponds to one side of lithium nickel cobalt manganese oxide (metallic lithium)Readily reacted with tin oxide) at 0.5C and an initial discharge capacity of 182mAhg ^-1 The capacity still maintained 82% of the discharge capacity after 100 cycles.

Example 3:

firstly, respectively sputtering two sides of a Polyimide (PI) diaphragm for 10min by adopting a magnetron sputtering technology at the power of 80W under the condition of 0.7Pa to obtain a layer of metal indium layer (In @ PI) with the thickness of 40nm, then completely soaking the obtained In @ PI into deionized water, heating to 100 ℃, preserving heat for 10h, and simultaneously introducing oxygen at the speed of 10mL/min to ensure that the nano metal indium layer on the surface of the polyimide diaphragm is completely oxidized into a nano indium oxide layer to obtain the PI diaphragm (In coated with indium oxide) (In @ PI) ₂ O ₃ @ PI), taking out after the reaction is finished, transferring the obtained diaphragm to an oven with the temperature of 80 ℃ for heat preservation for 10 hours to ensure that moisture is completely removed, and completely drying to obtain the lithium ion battery diaphragm modified by the metal nano oxide. .

The obtained diaphragm is assembled into a lithium iron phosphate-lithium button cell, and the initial discharge capacity at 0.2C is 157mAh g ^-1 The capacity still maintained 94% of the discharge capacity after 100 cycles.

Example 4:

firstly, adopting magnetron sputtering technology, sputtering a Polyacrylonitrile (PAN) diaphragm for 10min at the power of 50W under the condition of 0.7Pa to obtain a metal aluminum layer (Al @ PAN) with the thickness of 30nm, then completely immersing the obtained Al @ PAN into deionized water, heating to 60 ℃, preserving heat for 12h, and simultaneously introducing oxygen at the speed of 3mL/min to ensure that the nano metal aluminum layer on the surface of the PAN diaphragm is completely oxidized into a nano aluminum oxide layer to obtain the PAN diaphragm (Al @ PAN) coated by aluminum oxide ₂ O ₃ @ PAN), taking out after the reaction is finished, transferring the obtained diaphragm to an oven with the temperature of 80 ℃ for heat preservation for 8 hours to ensure that the moisture is completely removed, and completely drying to obtain the lithium ion battery diaphragm modified by the metal nano oxide.

The obtained diaphragm is assembled into a lithium nickel manganese oxide (64) -lithium button cell battery, and the initial discharge capacity at 0.2C is 170mAh g ^-1 The capacity still maintains 82% of the discharge capacity after 50 cycles.

Example 5:

first, adoptMagnetron sputtering technology, under the condition of 0.7Pa, sputtering a PP/PE double-layer diaphragm for 15min at the power of 50W to obtain a metal aluminum layer (Al @ PP/PE) with the thickness of 45nm, then completely soaking the Al @ PP/PE into deionized water, heating to 70 ℃, preserving heat for 8h, and simultaneously introducing oxygen at the speed of 4mL/min to ensure that the nano metal aluminum layer on the surface of the PP/PE diaphragm is completely oxidized into a nano aluminum oxide layer to obtain the PP/PE diaphragm (Al @ PP/PE) coated with aluminum oxide ₂ O ₃ @ PP/PE), taking out after the reaction is finished, transferring the obtained diaphragm to an oven with the temperature of 80 ℃ for heat preservation for 8 hours to ensure that moisture is completely removed, and completely drying to obtain the lithium ion battery diaphragm modified by the metal nano oxide.

The obtained diaphragm is assembled into a lithium iron phosphate-lithium button cell, and the initial discharge capacity at 1C is 140mA h g ^-1 The capacity still maintained 89% of the discharge capacity after 100 cycles.

Example 6: the preparation method is basically the same as that of the embodiment 1, except that the radio frequency magnetron sputtering time is 20 minutes, and a metal aluminum layer with the thickness of 60nm is obtained.

Example 7: the preparation method is basically the same as that of the example 1, except that the radio frequency magnetron sputtering time is 25 minutes, and a 75nm thick metal aluminum layer is obtained.

Example 8: the preparation method is basically the same as that of the embodiment 1, except that the radio frequency magnetron sputtering time is 30 minutes, and a metal aluminum layer with the thickness of 90nm is obtained.

Example 9: the preparation method is basically the same as that of example 1, except that the metal aluminum layer with the thickness of 15nm is prepared on one side of the diaphragm by radio frequency magnetron sputtering.

Comparative example 1: the polypropylene (PP) separator of example 1 was used without any treatment.

Comparative example 2: compared with example 1, the PP membrane modified by the conventional alumina ceramic is adopted.

Comparative example 3: compared to example 1, a conventional Lithium Lanthanum Zirconium Oxygen (LLZO) ceramic modified PP separator was used.

Test example 1:

the membranes obtained in examples 1-9 and comparative examples 1-3 are assembled into button lithium ion batteries, and the preparation method of the button lithium ion batteries is shown in the preparation method of the lithium-lithium button batteries in example 1; respectively using constant current densities with different multiplying powers to carry out charge and discharge performance tests on the assembled battery, and acquiring time, voltage and capacity in the charge and discharge processes of the assembled battery to obtain a charge and discharge curve and charge and discharge capacity, wherein in the test, the charge and discharge interval of the battery taking lithium iron phosphate as the positive electrode is 2.5-3.8V, the charge and discharge interval of the battery taking nickel cobalt lithium manganate as the positive electrode is 2.5-4.2V, and a test instrument is a Shenzhen New Willebell battery performance tester).

Table 1 table for testing battery performance of each example and comparative example

/>

In summary, according to the lithium ion battery separator modified by the metal nano oxide and the preparation method thereof provided by the invention, the metal layer on the surface of the separator is fully subjected to chemical conversion reaction through simple heating to synthesize the metal oxide in situ, so that the contact of an interface can be improved, the adhesive force between the metal oxide and the separator is improved, the mechanical property and the thermal stability of the separator are enhanced, the lithium ion battery separator has the advantages of flame retardance, good wettability, improved interface stability, prolonged cycle life and improved safety of a lithium battery. The method has simple and efficient preparation process and great commercialization potential.

The above-described embodiments are merely preferred embodiments of the present invention, which is not intended to be limiting in any way, and other variations and modifications are possible without departing from the scope of the invention as set forth in the appended claims.

Claims (10)

1. A preparation method of a lithium ion battery diaphragm modified by metal nano oxides is characterized in that a metal layer is deposited on the surface of at least one side of the diaphragm by adopting a vapor deposition method; immersing the obtained diaphragm into water, and completely oxidizing the metal layer on the surface of the diaphragm into a metal oxide layer under the heating condition and in the presence of an oxygen-containing atmosphere; and drying to obtain the lithium ion battery diaphragm modified by the metal nano oxide.

2. The method for preparing a lithium ion battery separator modified by metal nano-oxide according to claim 1, wherein the thickness of the metal layer is 5-100nm.

3. The preparation method of the metal nano-oxide modified lithium ion battery separator according to claim 1, wherein the vapor deposition method is a magnetron sputtering method for depositing a metal layer, and during the magnetron sputtering process, the pressure is 0.4-1.2Pa, the sputtering power is 40-80W, and the sputtering time is 5-30min.

4. The method for preparing the metal nano-oxide modified lithium ion battery separator according to claim 1, wherein the separator is at least one of a polyethylene separator, a polypropylene separator, a polyimide film and a polyacrylonitrile film.

5. The method for preparing a lithium ion battery separator modified by metal nano-oxide according to claim 1, wherein the metal is at least one of aluminum, tin and indium.

6. The preparation method of the metal nano-oxide modified lithium ion battery separator according to claim 1, wherein the heating condition is 60-100 ℃ and the temperature is kept for 2-12 hours.

7. The method for preparing the lithium ion battery separator modified by the metal nano-oxide according to claim 1, wherein the introduction condition of the oxygen-containing atmosphere is 3-10mL/min.

8. The method for preparing the lithium ion battery diaphragm modified by the metal nano oxide according to claim 1, wherein the drying means that the water content of the diaphragm meets the requirement of a common lithium battery diaphragm.

9. The lithium ion battery separator modified by the metal nano-oxide prepared by the preparation method according to any one of claims 1 to 8.

10. The use of the metal nano-oxide modified lithium ion battery separator of claim 9 in the field of lithium ion batteries.

Images