CN114420940A - Current collector for lithium ion secondary battery and preparation method and system thereof - Google Patents

Abstract

The invention relates to the field of battery current collectors, in particular to a current collector for lithium ion secondary batteries and a preparation method and system thereof. The preparation method specifically includes: electrospinning a polymer melt to obtain polymer fibers, and then preparing the polymer fibers into fiber aggregates; then performing pre-oxidation and carbonization on the fiber aggregates in sequence to obtain The current collector; wherein, in the electrospinning, the temperature is 180-230° C., the speed is 10-30 m/min; the diameter of the polymer fiber is 0.2-0.4 μm. The present invention also provides a processing system for a current collector for a lithium ion secondary battery. The current collector prepared by the present invention has strong bonding force with the pole piece, and the electrode resistance is low; the lithium ion secondary battery prepared by using the current collector of the present invention has low internal resistance of the battery, and can improve the charging performance of the lithium ion secondary battery. Discharge performance and rate performance.

Description

Current collector for lithium ion secondary battery and preparation method and system thereof

technical field

The invention relates to the field of battery current collectors, in particular to a current collector for lithium ion secondary batteries and a preparation method and system thereof.

Background technique

Aluminum foil is the positive current collector of lithium ion secondary battery, but there are the following problems: the interface between aluminum foil and positive electrode active material has contact resistance, which leads to excessive polarization and heavy heating during charging and discharging; aluminum foil sticks to active material and conductive agent. The bonding force is weak. With the progress of charging and discharging, the volume of the active material continues to collide and shrink, and the active material is peeled off from the aluminum foil, which accelerates the decay of capacity and life; moreover, the reaction between the electrolyte and the aluminum foil also accelerates the decay of battery life.

In order to solve the above problems, a lot of modification research on aluminum foil has been carried out in recent years, such as chemical etching, corona treatment, surface carbon coating, etc. Among them, carbon-coated aluminum foil (referred to as carbon-coated aluminum foil) has been widely used. The contact resistance between the positive electrode current collector and the active material is reduced, the polarization is reduced, and the charge-discharge performance and rate performance of the battery are improved to a certain extent.

In carbon-coated aluminum foil, the commonly used conductive carbon materials mainly include carbon black, carbon nanotubes, etc. These conductive carbon materials have poor dispersibility in water, so in the process of preparing carbon-coated aluminum foil, it is difficult to make the coating uniform during coating. , Delicately coated on the aluminum foil, reducing the bonding strength of the coating and the aluminum foil and the stability of the current collector, the lithium-ion secondary battery made of this type of carbon-coated aluminum foil is prone to cycle diving during the cycle.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a method for preparing a current collector, which specifically includes:

The polymer melt is electrospun to obtain polymer fibers, and then the polymer fibers are made into fiber aggregates; then the fiber aggregates are sequentially pre-oxidized and carbonized to obtain the current collector;

Wherein, in the electrospinning, the temperature is 180-230° C., the speed is 10-30 m/min; the diameter of the polymer fiber is 0.2-0.4 μm.

The current collector prepared by the above method has strong adhesion to the pole piece, and the resistance of the pole piece is low; the lithium ion secondary battery prepared by using the above current collector has a low internal resistance of the battery, which can improve the charging and discharging of the lithium ion secondary battery. performance and rate capability.

As a preferred embodiment of the present invention, the polymer melt is any one or more melts of polypropylene, polyacrylic acid, and polyacrylonitrile.

As a preferred embodiment of the present invention, the porosity of the fiber aggregate is 40-85%.

It is found in the present invention that under the above porosity, the positive electrode active material can enter the pores of the current collector and fully contact the current collector, thereby improving the bonding strength between the positive electrode active material and the current collector, and reducing the contact resistance between the positive electrode active material and the current collector. .

As a preferred embodiment of the present invention, the preparation of the fiber aggregates specifically includes:

The polymer fibers are collected under a pressure of -0.1 to -0.01 MPa and a voltage of 20 to 50 kV to obtain the fiber aggregate.

By collecting under the above conditions, the porosity of the fiber aggregate can be controlled to 40-85%, which is beneficial to maximize the performance of the current collector.

Preferably, the collection can be carried out in an electrostatic adsorption element; in the electrostatic adsorption element, the electrostatic pendulum voltage is 20-50 kV, and the adsorption wind pressure is -0.1--0.01 MPa.

As a preferred embodiment of the present invention, the temperature of the pre-oxidation is 200-400°C; the temperature of the carbonization is 1500-1800°C.

At the above pre-oxidation temperature and carbonization temperature, the porosity of the obtained current collector can be controlled to 30-70%, the bonding strength between the positive electrode active material and the current collector can be further improved, and the contact resistance between the positive electrode active material and the current collector can be further reduced , thereby improving the performance of the prepared battery.

The second object of the present invention is to provide a current collector prepared by the above preparation method.

By using the current collector of the present invention, no conductive agent is added to the electrodes, and the internal resistance of the prepared battery is comparable to that of the battery prepared by using carbon-coated aluminum foil, thereby reducing the material cost.

Preferably, the porosity of the current collector is 30-70%, and/or the thickness is 10-20 μm.

The third object of the present invention is to provide an electrode made of the current collector and electrode active material prepared by the present invention.

The fourth object of the present invention is to provide a lithium battery, the electrode of which includes the current collector prepared by the above preparation method.

The lithium battery prepared by using the current collector of the present invention has lower internal resistance of the battery, and can improve the charge-discharge performance and rate performance of the lithium battery.

The fifth object of the present invention is to provide a processing system for realizing the above-mentioned current collector preparation method, comprising a fiber weaving device, a preoxidation device and a carbonization device connected in sequence;

Wherein, the fiber weaving device includes a spinning unit and a fiber aggregate preparation unit;

The spinning unit is used for spinning the polymer melt to obtain polymer fibers;

The fiber aggregate preparation unit is used to make the polymer fibers into a fiber aggregate.

The outlet of the spinning unit is connected to the inlet of the fiber aggregate preparation unit;

The outlet of the fiber aggregate preparation unit is connected to the inlet of the preoxidation device.

The processing system of the present invention can continuously and completely realize the processing and preparation of the current collector, which is convenient for popularization and application in the industry. Polymer fiber aggregates with suitable porosity are first prepared by a fiber weaving device, and then a current collector with better performance in all aspects is obtained through a pre-oxidation device and a carbonization device.

Preferably, the fiber aggregate preparation unit contains an electrostatic adsorption element, and the electrostatic adsorption element is used to make the polymer fiber into a fiber aggregate by electrostatic action and adsorption action.

Preferably, the fiber weaving device further comprises a melting unit, the melting unit is used to make the polymer into a polymer melt;

The outlet of the melting unit is connected to the inlet of the spinning unit.

In particular embodiments, a melt spinning machine may be employed to perform the functions of the melting unit and the spinning unit.

Preferably, the above-mentioned processing system further includes a cooling device and a winding shaft device; at the outlet of the carbonization device, the cooling device and the winding shaft device are connected and arranged in sequence.

The beneficial effects of the present invention are as follows: the current collector prepared by the present invention has strong adhesion force with the pole piece, and the resistance of the pole piece is low; the lithium ion secondary battery prepared by using the current collector of the present invention has low internal resistance of the battery, and can Improve the charge-discharge performance and rate performance of lithium-ion secondary batteries. In addition, by using the current collector of the present invention, no conductive agent is added to the electrode, and the internal resistance of the prepared battery is comparable to that of the battery prepared by using carbon-coated aluminum foil, thereby reducing the material cost.

Description of drawings

FIG. 1 is a schematic diagram of the connection relationship of the processing system of Example 5. FIG.

In Fig. 1: 1. Fiber weaving device; 2. Pre-oxidation device; 3. Carbonization device; 4. Cooling device; adsorption element.

Detailed ways

The following examples are intended to illustrate the present invention, but not to limit the scope of the present invention.

If no specific technique or condition is indicated in the examples, it is performed by conventional method or according to the technique or condition described in the literature in this field, or according to the product specification. The reagents and instruments used without the manufacturer's indication are all conventional products that can be purchased through formal channels.

Example 1

The present embodiment provides a current collector, and the specific steps of its preparation method are as follows:

(1) Polypropylene fibers are obtained after the polypropylene is melt-spun in the fiber weaving device; wherein, in the fiber weaving device, the temperature of the melt spinning unit is set to 210° C., the spinning speed is set to 15 m/min, and the control The diameter of polypropylene fibers is 0.2-0.4 μm;

After the polypropylene fibers are subjected to the electrostatic effect, adsorption effect and self-temperature effect of the electrostatic adsorption unit, a polypropylene fiber aggregate with a porosity of 82.3% and a thickness of 22 μm is formed; wherein, in the electrostatic adsorption unit, the electrostatic wobble voltage is controlled. It is 45kV, and the adsorption wind size is -0.02MPa;

(2) transferring the polypropylene fiber aggregates from the fiber weaving device to the pre-oxidizing device for treatment; wherein, the treatment temperature is 350° C., and the treatment time is 3 minutes;

(3) After pre-oxidation, the polypropylene fiber aggregates are sent to the carbonization device for carbonization treatment; wherein, the carbonization temperature is 1600 ° C, the treatment time is 8 minutes, after carbonization, a current collector is formed, and the formed current collector has a porosity of 65.4 %, the thickness is 17.2μm;

(4) The current collector prepared in step (3) is sent to a cooling device to cool down to room temperature, and then collected into a roll through a winding shaft device.

Further, this embodiment also provides a lithium ion secondary battery containing the above current collector, and the specific preparation process is as follows: coating the lithium iron phosphate positive electrode slurry on the above current collector, drying at 95 ° C, rolling, slitting , After winding, a 26650 cylindrical lithium-ion secondary battery with a capacity of 4Ah was obtained. Among them, the ratio of the positive electrode pieces is as follows: in terms of mass fraction, lithium iron phosphate is 94%, Super P is 3%, PVDF is 3%, and the compaction density is 2.45g/cm ³ .

Example 2

The present embodiment provides a current collector, and the specific steps of its preparation method are as follows:

(1) Polypropylene fibers are obtained after the polypropylene is melt-spun in the fiber weaving device; wherein, in the fiber weaving device, the temperature of the melt spinning unit is set to 220° C., the spinning speed is set to 10 m/min, and the control The diameter of polypropylene fibers is 0.2-0.4 μm;

After the polypropylene fiber is subjected to the electrostatic action, adsorption action and its own temperature action of the electrostatic adsorption unit, a polypropylene fiber aggregate with a porosity of 65.8% and a thickness of 15 μm is formed; in which, in the electrostatic adsorption unit, the electrostatic pendulum voltage is controlled. It is 45kV, and the adsorption wind size is -0.06MPa;

(2) Transfer the polypropylene fiber aggregates from the fiber weaving device to the pre-oxidation device for treatment; wherein, the treatment temperature is 350° C., and the treatment time is 5 minutes;

(3) After pre-oxidation, the polypropylene fiber aggregates are sent to the carbonization device for carbonization treatment; wherein the carbonization temperature is 1600 ° C, and the treatment time is 8 minutes. After carbonization, a current collector is formed, and the porosity of the formed current collector is 46.1 %, the thickness is 10.6μm;

(4) The current collector prepared in step (3) is sent to a cooling device to cool down to room temperature, and then collected into a roll through a winding shaft device.

Further, this embodiment also provides a lithium ion secondary battery containing the above current collector, and the specific preparation process is as follows: coating the lithium iron phosphate positive electrode slurry on the above current collector, drying at 95 ° C, rolling, slitting , After winding, a 26650 cylindrical lithium-ion secondary battery with a capacity of 4Ah was obtained. Among them, the ratio of the positive electrode pieces is as follows: in terms of mass fraction, lithium iron phosphate is 94%, Super P is 3%, PVDF is 3%, and the compaction density is 2.45g/cm ³ .

Example 3

The present embodiment provides a current collector, and the specific steps of its preparation method are as follows:

(1) Polypropylene fibers are obtained after the polypropylene is melt-spun in the fiber weaving device; wherein, in the fiber weaving device, the temperature of the melt spinning unit is set to 210° C., the spinning speed is set to 18 m/min, and the control The diameter of polypropylene fibers is 0.2-0.4 μm;

After the polypropylene fiber is subjected to the electrostatic action, adsorption action and its own temperature action of the electrostatic adsorption unit, a polypropylene fiber aggregate with a porosity of 42.3% and a thickness of 20 μm is formed; in which, in the electrostatic adsorption unit, the electrostatic wobble voltage is controlled. It is 45kV, and the adsorption wind size is -0.09MPa;

(2) Transfer the polypropylene fiber aggregates from the fiber weaving device to the pre-oxidation device for treatment; wherein, the treatment temperature is 350° C., and the treatment time is 5 minutes;

(3) After pre-oxidation, the polypropylene fiber aggregates are sent to the carbonization device for carbonization treatment; wherein, the carbonization temperature is 1800 ° C, and the treatment time is 8 minutes. After carbonization, a current collector is formed, and the formed current collector has a porosity of 30.7 %, the thickness is 15.2μm;

(4) The current collector prepared in step (3) is sent to a cooling device to cool down to room temperature, and then collected into a roll through a winding shaft device.

Further, this embodiment also provides a lithium ion secondary battery containing the above current collector, and the specific preparation process is as follows: coating the lithium iron phosphate positive electrode slurry on the above current collector, drying at 95 ° C, rolling, slitting , After winding, a 26650 cylindrical lithium-ion secondary battery with a capacity of 4Ah was obtained. Among them, the ratio of the positive electrode pieces is as follows: in terms of mass fraction, lithium iron phosphate is 94%, Super P is 3%, PVDF is 3%, and the compaction density is 2.45g/cm ³ .

Example 4

The present embodiment provides a current collector, and the specific steps of its preparation method are as follows:

(1) Polypropylene fibers are obtained after the polypropylene is melt-spun in the fiber weaving device; wherein, in the fiber weaving device, the temperature of the melt spinning unit is set to 210° C., the spinning speed is set to 15 m/min, and the control The diameter of polypropylene fibers is 0.2-0.4 μm;

After the polypropylene fibers are subjected to the electrostatic effect, adsorption effect and self-temperature effect of the electrostatic adsorption unit, a polypropylene fiber aggregate with a porosity of 82.3% and a thickness of 22 μm is formed; wherein, in the electrostatic adsorption unit, the electrostatic wobble voltage is controlled. It is 45kV, and the adsorption wind size is -0.02MPa;

(2) transferring the polypropylene fiber aggregates from the fiber weaving device to the pre-oxidizing device for treatment; wherein, the treatment temperature is 350° C., and the treatment time is 3 minutes;

(3) After pre-oxidation, the polypropylene fiber aggregates are sent to the carbonization device for carbonization treatment; wherein, the carbonization temperature is 1600 ° C, the treatment time is 8 minutes, after carbonization, a current collector is formed, and the formed current collector has a porosity of 65.4 %, the thickness is 17.2μm;

(4) The current collector prepared in step (3) is sent to a cooling device to cool down to room temperature, and then collected into a roll through a winding shaft device.

Further, this embodiment also provides a lithium ion secondary battery containing the above current collector, and the specific preparation process is as follows: coating the lithium iron phosphate positive electrode slurry on the above current collector, drying at 95 ° C, rolling, slitting , After winding, a 26650 cylindrical lithium-ion secondary battery with a capacity of 4Ah was obtained. Among them, the proportion of the positive electrode piece is as follows: in terms of mass fraction, lithium iron phosphate is 97%, PVDF is 3%, and the compaction density is 2.45 g/cm ³ .

Example 5

A processing system for a current collector for a lithium ion secondary battery (a schematic diagram of the connection relationship is shown in Figure 1), comprising a fiber weaving device 1, a preoxidation device 2, a carbonization device 3, a cooling device 4 and a winding shaft connected in sequence device 5.

Wherein, the fiber weaving device 1 includes: a melt spinning unit 11 and a fiber aggregate preparation unit 12;

The melt spinning unit 11 is used to melt and spin polymers to obtain polymer fibers;

The fiber aggregate preparation unit 12 is used to make polymer fibers into fiber aggregates; in the fiber aggregate preparation unit 12, an electrostatic adsorption element 121 is included, and the electrostatic adsorption element 121 is used to prepare polymer fibers through electrostatic action and adsorption. Fibroblast aggregates;

The outlet of the melt-spinning unit 11 is connected to the inlet of the fiber aggregate preparation unit 12;

The outlet of the fiber aggregate preparation unit 12 is connected with the inlet of the pre-oxidation device 2;

The outlet of the pre-oxidation device 2 is connected with the inlet of the carbonization device 3;

At the outlet of the carbonization device 3, the cooling device 4 and the winding shaft device 5 are connected in sequence;

Wherein, the cooling device 4 cools the prepared high-temperature current collector to room temperature, and finally collects the cooled current collector into a roll through the winding shaft device 5 .

Comparative Example 1

This comparative example provides a lithium ion secondary battery, and the specific preparation process is as follows: coating the lithium iron phosphate positive electrode slurry on an ordinary carbon-coated aluminum foil current collector, drying at 95°C, rolling, slitting, winding Afterwards, a 26650 cylindrical lithium-ion secondary battery with a capacity of 4Ah was obtained. Among them, the ratio of the positive electrode pieces is as follows: in terms of mass fraction, lithium iron phosphate is 94%, Super P is 3%, PVDF is 3%, and the compaction density is 2.45g/cm ³ .

Comparative Example 2

This comparative example provides a lithium ion secondary battery, and the specific preparation process is as follows: coating the lithium iron phosphate positive electrode slurry on an ordinary aluminum foil current collector, drying at 95°C, rolling, slitting, and winding to obtain A 26650 cylindrical lithium-ion secondary battery with a capacity of 4Ah. Among them, the proportion of the positive electrode piece is as follows: in terms of mass fraction, lithium iron phosphate is 94%, Super P is 3%, and PVDF is 3%, and the compaction density is 2.45 g/cm ³ .

Test example

The performances of the lithium ion secondary batteries prepared in the above examples and comparative examples were tested, and the results are shown in Table 1.

Among them, the test method of the adhesion of the pole piece: cut the pole piece after rolling into a size of 200*20mm, paste the high temperature tape of the same size on the surface of the pole piece, use a universal testing machine to peel off at a speed of 1mm/s, peel off The minimum value in the process is the pole piece cohesion.

Pole piece impedance test method: Cut the rolled pole piece into a square size of 4cm*8cm, place the cut pole piece between the probes of the BER2200 tester, apply 5MPa pressure, and read the value.

Battery internal resistance test method: use RJ3563 internal resistance tester to test the battery internal resistance under the condition of 1000Hz.

Table 1 Performance test results

As can be seen from Table 1, compared with the comparative example, the lithium ion secondary battery using the current collector prepared by the present invention, even if no conductive agent is added, the adhesion force of the pole piece is significantly better than that of ordinary carbon coating Aluminum foil and ordinary aluminum foil, and the electrode impedance and battery internal resistance are much lower than those of lithium-ion secondary batteries using ordinary carbon-coated aluminum foil and ordinary aluminum foil as current collectors. It can be seen that the lithium ion secondary battery using the current collector prepared by the present invention has better positive electrode adhesion, electrode resistance and battery internal resistance than commercial carbon-coated aluminum foil and ordinary aluminum foil.

Although the present invention has been described in detail above with general description and specific embodiments, some modifications or improvements can be made on the basis of the present invention, which will be obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention fall within the scope of the claimed protection of the present invention.

Claims (10)

1. a preparation method of current collector, is characterized in that, comprises: The polymer melt is electrospun to obtain polymer fibers, and then the polymer fibers are made into fiber aggregates; then the fiber aggregates are sequentially pre-oxidized and carbonized to obtain the current collector; Wherein, in the electrospinning, the temperature is 180-230° C., the speed is 10-30 m/min; the diameter of the polymer fiber is 0.2-0.4 μm. 2 . The preparation method according to claim 1 , wherein the polymer melt is any one or more melts of polypropylene, polyacrylic acid, and polyacrylonitrile. 3 . 3 . The preparation method according to claim 1 or 2 , wherein the porosity of the fiber aggregate is 40-85%. 4 . The preparation method according to any one of claims 1 to 3, wherein the preparation of the fiber aggregates specifically comprises: The polymer fibers are collected under a pressure of -0.1 to -0.01 MPa and a voltage of 20 to 50 kV to obtain the fiber aggregate. 5 . The preparation method according to claim 1 , wherein the temperature of the pre-oxidation is 200-400° C.; the temperature of the carbonization is 1,500-1,800° C. 6 . 6 . A current collector, characterized in that, it is prepared by the preparation method according to any one of claims 1 to 5 . 7 . The current collector according to claim 6 , wherein the current collector has a porosity of 30-70%, and/or a thickness of 10-20 μm. 8 . 8. An electrode comprising the current collector of claim 6 or 7 and an electrode active material. 9 . A lithium battery, wherein the electrode comprises the current collector according to claim 6 or 7. 10 . 10. A processing system for realizing the preparation method according to any one of claims 1 to 5, characterized in that it comprises a fiber weaving device, a preoxidation device and a carbonization device which are connected in sequence; Wherein, the fiber weaving device includes a spinning unit and a fiber aggregate preparation unit; The spinning unit is used for spinning the polymer melt to obtain polymer fibers; The fiber aggregate preparation unit is used for preparing the polymer fibers into fiber aggregates; The outlet of the spinning unit is connected to the inlet of the fiber aggregate preparation unit; The outlet of the fiber aggregate preparation unit is connected to the inlet of the preoxidation device.

Images