CN115172750A

CN115172750A - Flexible fibrous braided lithium ion battery cathode and preparation and application thereof

Info

Publication number: CN115172750A
Application number: CN202210671294.5A
Authority: CN
Inventors: 王兵杰; 江海波; 彭慧胜; 陈培宁; 孙雪梅
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2022-06-14
Filing date: 2022-06-14
Publication date: 2022-10-11

Abstract

The invention relates to a flexible fibrous braided lithium ion battery cathode and preparation and application thereof, wherein the preparation method comprises the following steps: firstly, coating and depositing primer slurry on the surface of a fibrous negative current collector, and drying to obtain a negative current collector with a conductive primer; wherein the priming paint comprises a conductive material, polyvinylidene fluoride and N-methyl pyrrolidone, the mass ratio of the conductive material to the priming paint is (1-3) to (0.5-2) to (100-200); and then coating and depositing the negative electrode slurry, and drying to obtain negative electrode fibers, namely the flexible fibrous braided lithium ion battery negative electrode. Compared with the prior art, the flexible fibrous weaveable lithium ion battery prepared by assembling the cathode prepared by the invention has obviously improved internal resistance, multiplying power and the like, and provides better prospect for later application.

Description

Flexible fibrous braided lithium ion battery cathode and preparation and application thereof

Technical Field

The invention belongs to the technical field of manufacturing processes of flexible braided lithium ion batteries, and relates to a flexible fibrous braided lithium ion battery cathode and a preparation method and application thereof.

Background

The invention and the application of the chemical power supply serving as a device for converting chemical energy into electric energy lay a foundation for the development of storage batteries and the like, and people always seek to open up a new direction as a lithium ion battery system which develops the fastest and best. With diversification of application scenes of the lithium ion battery, the flexible fibrous braided lithium ion battery gradually appears in the visual field of people.

The most important part of the battery is the positive and negative electrode performance of the battery, the positive and negative electrode performance is similar to the positive electrode, the negative electrode is always the key for improving a series of electrical properties such as energy density and the like in the field of lithium ion batteries, and the contact tightness degree of a negative electrode active substance and a current collector plays a non-negligible role in the overall performance of the battery. The traditional current collector of the flexible fibrous braided lithium ion battery cathode has poor contact tightness with active substances, so that the internal resistance is high, and the performances of the battery such as multiplying power and the like are greatly influenced.

Disclosure of Invention

The invention aims to overcome the defect that the traditional current collector of the negative electrode of the existing flexible fibrous weaveable lithium ion battery has poor contact tightness with an active substance, so that the internal resistance is higher, and provides a flexible fibrous weaveable lithium ion battery negative electrode, and preparation and application thereof, which are used for improving the contact tightness between the negative current collector and the active substance and reducing the internal resistance, thereby improving the multiplying power and other performances of the battery, and providing a new possibility for the development of the flexible fibrous weaveable lithium ion battery.

The purpose of the invention can be realized by the following technical scheme:

a preparation method of a flexible fibrous braided lithium ion battery cathode comprises the following steps:

s1: coating and depositing a primary coating slurry on the surface of the fibrous negative current collector, and drying to obtain a negative current collector with a conductive primary coating; wherein the priming paint comprises a conductive material, polyvinylidene fluoride and N-methylpyrrolidone (NMP) according to the mass ratio of (1-3) to (0.5-2) to (100-200); the contact tightness between the active substance and the current collector is increased through the conductive material, so that the conductivity is improved;

s2: coating and depositing the cathode slurry, and drying to obtain cathode fibers, namely the flexible fibrous braided lithium ion battery cathode.

Further, in step S1, the fibrous negative electrode current collector includes a copper wire.

Further, in step S1, the conductive material includes at least one of conductive carbon black, carbon nanotubes, or graphene.

Further, in step S1, the drying temperature is 80 to 120 ℃.

Further, in the step S1, the thickness of the conductive base coat is 1-10 μm.

Further, in the step S2, the negative electrode slurry comprises a negative electrode material, a conductive agent and a binder, wherein the mass ratio of the negative electrode material to the conductive agent is (90-95) to (2-4) to (3-6);

the negative electrode material comprises at least one of graphite, a silicon carbon material or lithium titanate; the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon nanotubes or graphene; the adhesive comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose or styrene butadiene rubber.

The flexible fibrous braided lithium ion battery cathode is prepared by the method.

The application of the flexible fibrous braided lithium ion battery negative electrode specifically comprises the step of using negative electrode fibers for preparing the flexible fibrous braided lithium ion battery, wherein the preparation method comprises the following steps:

winding a diaphragm on the negative electrode fiber in a wrapping mode, and then twisting the diaphragm with the positive electrode fiber to obtain a battery cell; and then assembling the electric core on a flexible fiber tube, and then sequentially carrying out switching, drying, liquid injection and sealing to obtain the flexible fibrous braided lithium ion battery.

Furthermore, in the process of winding the diaphragm, the included angle between the used wrapping tape and the negative fiber is 10-90 degrees;

the packaging temperature is 200-400 ℃; the drying temperature is 60-85 ℃, and the drying time is 12-72h; in the electrolyte, the solvent comprises one of Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) or Ethyl Methyl Carbonate (EMC), and the solute is lithium hexafluorophosphate with concentration of 1mol/L.

Compared with the prior art, the invention has the following characteristics:

1) On the basis of the traditional cathode copper wire, a layer of priming coating material is added between the copper wire and an active substance (namely cathode slurry), and the material mainly comprises carbon conductive agents such as conductive carbon black, conductive graphite or other conductive materials and the like, so that the contact tightness between the active substance and a current collector can be improved, and the conductivity is improved. The primer coating material is prepared by mixing a conductive agent, polyvinylidene fluoride and N-methyl pyrrolidone (NMP) according to a certain proportion, wherein the N-methyl pyrrolidone, also called NMP, has the capability of having affinity with a carbon material, so the primer coating material can be used for dispersing the carbon material, and meanwhile, the polyvinylidene fluoride, also called PVDF, provides cohesiveness. The conductive agent is mainly a carbon material and has good dispersibility in NMP, so that the contact tightness of a negative current collector and an active substance is greatly improved, the problem of an interface between the negative material and the current collector is solved, the negative material and the current collector are combined more tightly, the internal resistance of the interface is reduced, the internal resistance can be reduced by 60 percent, the conductivity is improved, the rate capability is improved, and the rate capability of the battery is improved by about 32 percent;

2) The preparation process is simple and quick, and is convenient for industrial application;

3) The prepared cathode and the anode are assembled into a battery, wherein the anode takes a commercial aluminum wire as a cathode current collector, cathode slurry is uniformly dip-coated on the surface of the cathode current collector, and the cathode is dried to obtain a cathode electrode; after the negative electrode is dried, the diaphragm is wound in a winding mode (the diaphragm can be a traditional winding belt), the included angle between the winding belt and the negative electrode fiber (namely copper wire for dip-coating negative electrode slurry) is 10-90 degrees, on one hand, the electrode material can be fully covered, short circuit is avoided, on the other hand, the negative electrode and the positive electrode cannot be too thick and increase the obstruction of ion transmission, and the battery core is manufactured in a stranded wire mode, packaged, dried and injected with liquid, and then the battery is assembled, so that the multiplying power performance and other performances of the battery can be improved.

Drawings

FIG. 1 is a photomicrograph taken before and after the copper wire is under-coated in example 1, wherein a is the photomicrograph taken before the copper wire is under-coated and b is the photomicrograph taken after the copper wire is under-coated;

FIG. 2 is SEM pictures of the copper wire before and after priming of the copper wire in example 1, wherein a is the SEM picture of the copper wire before priming and b is the SEM picture of the copper wire after priming;

fig. 3 is a graph comparing the internal resistance and rate performance of the primed negative electrode battery and unprimed negative electrode battery prepared in example 1.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

m1: placing the negative current collector in a degreaser at 50-80 ℃, ultrasonically cleaning for 10-30min, and drying to remove surface oil stains and obtain a fibrous negative current collector; the negative current collector is preferably a copper wire, the purity of the copper wire is not less than 99%, and other metal wires with corresponding purity can be adopted;

m2: mixing a conductive material, polyvinylidene fluoride and N-methyl pyrrolidone in water according to a mass ratio of (1-3) to (0.5-2) to (100-200) to obtain a primer slurry; wherein the conductive material comprises at least one of conductive carbon black, carbon nanotubes or graphene;

and M3: uniformly dip-coating the priming paint on the surface of the fibrous negative current collector, and drying at 80-120 ℃ to obtain the negative current collector with the conductive priming paint; wherein, the thickness of the conductive base coat is preferably 1-10 μm;

m4: mixing a negative electrode material, a conductive agent and an adhesive in a mass ratio of (90-95) to (2-4) to (3-6) to obtain a primer slurry; the cathode material comprises at least one of graphite, a silicon carbon material or lithium titanate; the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon nanotubes or graphene; the adhesive comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose or styrene butadiene rubber;

m5: uniformly dipping the negative electrode slurry on the surface of a negative electrode current collector with conductive bottom coating, and drying to obtain negative electrode fibers, namely the flexible fibrous braided lithium ion battery negative electrode; wherein the thickness of the negative electrode slurry coating is 50-80 μm.

The application of the flexible fibrous braided lithium ion battery negative electrode comprises the step of using negative electrode fibers for preparing the flexible fibrous braided lithium ion battery, wherein the preparation method comprises the following steps:

n1: pretreating the positive current collector by adopting the method in the same step M1 to obtain a fibrous positive current collector; the anode current collector is preferably an aluminum wire, the purity is not lower than 99%, and other metal wires with corresponding purity can be adopted;

n2: mixing a positive electrode material, a conductive agent and a binder in water according to the preferred mass ratio of (90-95.5) to (2-4.5) to (2.5-5.5) to obtain positive electrode slurry; the anode material comprises at least one of lithium cobaltate, lithium iron phosphate or a ternary anode material; the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon nanotubes or graphene; the adhesive comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose or styrene butadiene rubber;

n3: uniformly dip-coating the anode slurry on the surface of a fibrous anode current collector, and drying to obtain anode fibers; wherein the thickness of the positive electrode slurry coating is 50-80 μm;

n4: winding a diaphragm on the negative electrode fiber in a wrapping mode, and twisting the diaphragm and the positive electrode fiber oppositely to obtain a battery cell; wherein, in the process of winding the diaphragm, the included angle between the used lapping tape and the negative pole fiber is 10-90 degrees;

n5: assembling the electric core in a polymer flexible fiber pipe with the inner diameter of 0.5-2mm and the outer diameter of 2-4mm by a pipe forming extruder, namely aligning the electric core to the orifice of the extruded flexible fiber pipe, and synchronously completing the automatic penetration of the electric core in the flexible fiber pipe along with the continuous extrusion of the flexible fiber pipe; then, carrying out tab connection by a laser welding machine, wherein the positive electrode is connected with an aluminum wire in a switching way, and the negative electrode is connected with a copper wire in a switching way, or connected with other metals according to electrochemical stability; drying, and then injecting and packaging by high-pressure injection sealing equipment to finally obtain the flexible fibrous lithium ion battery;

wherein, the polymer pipe material flexible fiber pipe comprises one of a polypropylene pipe material, a polyethylene terephthalate pipe material or a polytetrafluoroethylene pipe material; the drying temperature is 60-85 ℃, and the drying time is 12-72h; in the electrolyte, a solvent is one of Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) or Ethyl Methyl Carbonate (EMC), and a solute is lithium hexafluorophosphate with the concentration of 1mol/L; the packaging temperature is 200-400 ℃.

Preferably, the diameter of each of the negative electrode fibers and the positive electrode fibers is 300 to 500 μm.

The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

Example 1:

a flexible fibrous weaveable lithium ion battery, the preparation method of which comprises the following steps:

1) Placing aluminum wires and copper wires with the diameter of about 200 mu m in a degreaser at 50 ℃ for ultrasonic cleaning for 30min, and drying to remove surface oil stains to obtain a fibrous positive current collector (aluminum) and a fibrous negative current collector (copper);

2) Mixing conductive carbon black, polyvinylidene fluoride and N-methyl pyrrolidone in water according to the mass ratio of 2.5;

3) Uniformly dip-coating the primary coating slurry on the surface of the fibrous negative current collector, and drying to obtain a negative current collector with conductive primary coating;

as shown in fig. 1, which is an optical microscope photograph of a bare copper wire (a) and a negative current collector (b) with a conductive primer, it can be seen that the diameter of the bare copper wire is about 200 μm, the diameter of the primed copper wire is about 215 μm, and the average thickness of the conductive primer is about 7.5 μm;

as shown in fig. 2, which is an SEM image of a bare copper wire (a) and a negative current collector (b) with a conductive undercoat, the magnification is 200 times, and it can be seen that the undercoat on the surface of the copper wire is mostly uniformly distributed, containing a small amount of non-uniformly dispersed flake conductive carbon black, which is mainly related to the dispersion degree of the undercoat slurry;

4) Mixing graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene butadiene rubber in water according to a mass ratio of 95.5; mixing lithium cobaltate, conductive carbon black and polyvinylidene fluoride in N-methyl pyrrolidone according to a mass ratio of 95;

5) Uniformly dipping the cathode slurry on the surface of a cathode current collector with a conductive bottom coat, uniformly dipping the cathode slurry on the surface of a fibrous cathode current collector, and drying together to respectively prepare cathode fibers and cathode fibers; wherein the positive and negative electrode paste coating layers are respectively about 50 μm;

6) Winding a diaphragm on the negative fiber in a wrapping mode, and then twisting the diaphragm and the positive fiber oppositely (the winding angle is 45 degrees), so as to obtain a battery cell;

7) Assembling a battery cell in a polypropylene flexible fiber tube with the inner diameter of about 1.9mm and the outer diameter of about 2.0mm by a tube forming extruder, then carrying out tab connection by a laser welding machine, transferring an aluminum wire to the positive electrode, transferring a copper wire to the negative electrode, drying, and then carrying out liquid injection and packaging by high-pressure liquid injection sealing equipment to obtain a flexible fibrous lithium ion battery;

wherein the drying temperature is 80 ℃, and the drying time is 36h; in the electrolyte, a solvent is Ethylene Carbonate (EC)/diethyl carbonate (DEC)/dimethyl carbonate (DMC) according to a volume ratio of 1:1:1 proportion, wherein the solute is lithium hexafluorophosphate, and the concentration is 1mol/L; the encapsulation temperature was 400 ℃.

Example 2:

compared with the embodiment 1, the preparation method of the flexible fibrous weaveable lithium ion battery only differs from the embodiment 1 in that:

in the step 1), the positive current collector is a stainless steel wire, the cleaning temperature is 80 ℃, and the cleaning time is 10min;

in the step 2), the priming slurry is prepared by mixing conductive graphite, polyvinylidene fluoride and N-methyl pyrrolidone in water according to the mass ratio of 1;

in the step 4), the negative electrode slurry is prepared by mixing graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene butadiene rubber in water according to the mass ratio of 90; the positive electrode slurry is prepared by mixing lithium oxide, conductive carbon black and polyvinylidene fluoride in N-methyl pyrrolidone in a mass ratio of 90.

The rest is the same as example 1.

Example 3:

in the step 1), the current collector of the negative electrode is a stainless steel wire;

in the step 2), mixing the priming paint with graphene, polyvinylidene fluoride and N-methyl pyrrolidone in water according to a mass ratio of 3;

in the step 4), the negative electrode slurry is prepared by mixing graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene butadiene rubber in water according to the mass ratio of 95.5; the positive electrode slurry was obtained by mixing lithium oxide, conductive carbon black, and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 95.

The rest is the same as example 1.

The application example is as follows:

this example was used to examine the effect of conductive undercoats on the performance of flexible fibrous, weaveable lithium ion batteries, including:

experimental groups: examples 1 to 3;

control group: compared with example 1, the difference is only that: step 2) -3) is not included, namely the negative electrode fiber is not subjected to primary coating slurry dip coating;

and (3) performance detection:

1. detecting internal resistance performance, and performing EIS test by using CHI660D type electrochemical workstation of Shanghai Chen Hua;

2. detecting the multiplying power performance, namely, adopting a blue point tester to change the current density for testing, specifically, testing the charge and discharge test according to GB/T18287-2013, wherein the specific charge and discharge test condition is 0.2/0.2C for charge and discharge, and subsequently changing the current density, namely increasing the discharge current, and increasing the 0.2/0.2C to 0.2/1C; the results are shown in Table 1.

TABLE 1 Performance of different flexible, knittable lithium ion batteries

	Example 1	Example 2	Example 3	Control group
					Internal resistance of	29.4Ω	29.7Ω	27.6Ω	74.3Ω
Multiplying power	95.1％	94.5％	96.2％	72.0％

Fig. 3 is a comparison of internal resistance and rate performance of the batteries assembled from the primed negative electrodes prepared in example 1 and the batteries without primed negative electrodes, and in combination with table 1 above, it can be seen that, taking the battery with a capacity of about 4mAh as an example, the internal resistance of the primed battery is reduced by about 60% on average compared with the battery without primed battery; in the aspect of multiplying power, the discharging multiplying power of the primed battery at 1C is improved by about 32% compared with the discharging multiplying power of the unprimed battery, and the effect is obvious.

The embodiments described above are intended to facilitate a person of ordinary skill in the art in understanding and using the invention. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims

1. A preparation method of a flexible fibrous braided lithium ion battery cathode is characterized by comprising the following steps:

s1: coating and depositing a primary coating slurry on the surface of the fibrous negative current collector, and drying to obtain a negative current collector with a conductive primary coating; wherein the priming paint comprises a conductive material, polyvinylidene fluoride and N-methylpyrrolidone, wherein the mass ratio of the conductive material to the priming paint is (1-3) to (0.5-2) to (100-200);

s2: coating and depositing the negative electrode slurry, and drying to obtain the negative electrode fiber, namely the flexible fibrous braided lithium ion battery negative electrode.

2. The method according to claim 1, wherein in step S1, the fibrous negative electrode current collector comprises copper wire.

3. The method according to claim 1, wherein in step S1, the conductive material comprises at least one of conductive carbon black, carbon nanotubes or graphene.

4. The method for preparing the flexible fibrous braided lithium ion battery negative electrode according to claim 1, characterized in that in step S1, the drying temperature is 80-120 ℃.

5. The method for preparing the flexible fibrous braided lithium ion battery negative electrode according to claim 1, wherein in step S1, the thickness of the conductive primer coating is 1-10 μm.

6. The method as claimed in claim 1, wherein in step S2, the negative electrode slurry comprises a negative electrode material, a conductive agent and a binder in a mass ratio of (90-95) - (2-4) - (3-6);

wherein the negative electrode material comprises at least one of graphite, a silicon-carbon material or lithium titanate; the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon nanotubes or graphene; the adhesive comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose or styrene butadiene rubber.

7. A flexible fibrous, woven lithium ion battery negative electrode prepared by the method of any one of claims 1 to 6.

8. Use of a flexible fibrous lithium ion battery negative electrode capable of being woven according to claim 7, for a flexible fibrous lithium ion battery capable of being woven.

9. The use of the flexible fibrous lithium ion battery negative electrode according to claim 8, wherein the flexible fibrous lithium ion battery is prepared by a method comprising:

10. The application of the flexible fibrous braided lithium ion battery negative electrode of claim 9, wherein in the process of winding the diaphragm, the included angle between the used wrapping tape and the negative electrode fiber is 10-90 degrees;

the packaging temperature is 200-400 ℃; the drying temperature is 60-85 ℃, and the drying time is 12-72h; in the electrolyte, the solvent comprises one of ethylene carbonate, diethyl carbonate, dimethyl carbonate or ethyl methyl carbonate, and the solute is lithium hexafluorophosphate with the concentration of 1mol/L.