CN102709587B - A kind of lithium ion battery and cathode current collector thereof - Google Patents

Abstract

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a cathode current collector for improving the safety performance of the lithium ion battery and a lithium ion battery comprising the cathode current collector. Including the cathode current collector body, the surface of the cathode current collector body is also covered with a treatment layer, and the treatment layer is composed of 70-80 wt% of a conjugated large π bond conductive polymer, 19.4-29.8 wt% of a viscous Binder and 0.2-0.6wt% oxalic acid. Compared with the prior art, the present invention utilizes the electrochemically active characteristics of conductive polymers and uses them in the treatment layer of the cathode current collector, thereby improving the anti-overcharge and overdischarge characteristics of lithium-ion batteries and improving the safety performance of the batteries. effect. In addition, the present invention is simple to implement and convenient for industrialization. In addition, the invention also discloses a lithium ion battery comprising the cathode current collector.

Description

A kind of lithium ion battery and cathode current collector thereof

technical field

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a cathode current collector for improving the safety performance of the lithium ion battery and a lithium ion battery comprising the cathode current collector.

Background technique

In 1991, Japan's Sony (Sony) took the lead in commercializing lithium-ion batteries. Due to its advantages of high energy density, high voltage, low self-discharge rate and light weight, it has been widely used in various fields. With the intensification of the global energy crisis and the emphasis on environmental protection, lithium-ion batteries have attracted much attention as a green energy source. In recent years, lithium-ion batteries have been gradually used in wind power storage systems and electric vehicles (EV, HEV, PHEV )middle. In these applications, people pay special attention to the safety performance of the battery.

For lithium-ion batteries, whether it is a single battery or assembled into a battery pack, there will be problems such as overcharging and over-discharging during use. These problems are a great test for the cycle life and safety performance of the battery. Because the electrical energy is stored in the form of LiC ₆ at the anode during the charging process, the safety performance of the system continues to decrease as the charging continues.

When overcharging occurs, it is easy to cause the electrolyte to be decomposed, and the battery generates a lot of heat, causing the battery to catch fire or even explode, which brings serious safety hazards to the use of the battery/battery pack. The current measures to protect the battery from overcharging include adding a positive temperature coefficient thermistor (PTC) on the protective plate or performing special treatment on the isolation film. When the battery is overcharged and the temperature exceeds a certain value due to overcharging, the protective device will start to work. These two measures can effectively improve overcharge safety, but their mechanism of action is slightly different: the mechanism of PTC is that the resistance of the protection module increases sharply with the rise of temperature, but the temperature at which it works is relatively high. The high temperature has a bad negative impact on the battery; and the mechanism of dealing with the anti-overcharge of the separator is that the high temperature generated by the heating of the battery causes the diaphragm to close the pores, so that the overcharge cannot continue, thus playing a protective role. But at this time, the diaphragm has closed pores, causing permanent damage to the battery, making subsequent charging and discharging of the battery difficult.

On the other hand, when the battery is over-discharged, the potential of the anode rises. When the potential is higher than a certain value, the anode current collector oxidizes and dissolves, resulting in deterioration of battery performance and seriously affecting the subsequent electrochemical performance of the battery. At present, the means of preventing over-discharge is mainly through external electronic circuit monitoring, which plays a very good role in protecting the single battery, but if a circuit module is to be developed in the battery pack to monitor each battery, it will not only greatly increase the battery life. cost, and it cannot effectively improve the over-discharge prevention performance of each battery in the battery pack.

In view of this, it is necessary to provide a lithium-ion battery that can significantly improve the anti-overcharge and over-discharge characteristics of the lithium-ion battery system without affecting the normal electrochemical performance of the lithium-ion battery, thereby effectively improving the safety performance of the battery. A battery cathode collector and a lithium ion battery comprising the cathode collector.

Contents of the invention

One of the purposes of the present invention is to: address the deficiencies of the prior art, and provide a lithium-ion battery system that can significantly improve the anti-overcharge and over-discharge characteristics of the lithium-ion battery system without affecting the normal electrochemical performance of the lithium-ion battery, thereby effectively A lithium-ion battery cathode current collector for improving battery safety performance.

In order to achieve the above object, the present invention adopts following technical scheme:

A lithium ion battery cathode current collector, comprising a cathode current collector body, the surface of the cathode current collector body is also covered with a treatment layer, and the treatment layer is composed of 70 to 80 wt% of conjugated large π bonds with high conductivity Molecules, 19.4-29.8 wt% binder and 0.2-0.6 wt% oxalic acid.

The cathode current collector treated with this treatment layer, a small amount of oxalic acid etches the cathode current collector body during the treatment process, increasing the surface roughness of the cathode current collector, which is conducive to improving the bonding ability between the treatment layer and the cathode current collector body, The weight percentage of oxalic acid is selected as 0.2-0.6wt%, because if the oxalic acid content is too small, the corrosion effect on the cathode current collector body is not enough, resulting in insufficient roughness of the cathode current collector body, which is not conducive to the cathode current collector body and the treatment layer. If the oxalic acid content is too large, the body of the cathode current collector may be corroded, which is not conducive to the preparation of the battery; the adhesive will bond the oxalic acid in the treatment layer and the conjugated large π bond conductive polymer particles to the together, and the whole treatment layer is bonded on the surface of the cathode current collector, the weight percentage of the binder is selected as 19.4～29.8wt% because: if the content of the binder is too low, the bonding effect between the particles is not strong, It is easy to cause problems such as powder falling, and if the content of the binder is too large, the battery performance will be deteriorated because the binder itself is not conductive; the conjugated large π bond conductive polymer can only be used in certain specific electrochemical windows. It plays the role of electronic conduction. When the cathode potential is too high (or too low) and exceeds the specific electrochemical window, the resistance of the treatment layer increases sharply to play the role of electronic insulation, and the battery circuit is disconnected inside the cathode, which is very good It has the characteristics of preventing overcharge and overdischarge, and plays a very good role in protecting the battery. When the potential decreases (or increases) and returns to its electrochemical active window, the treatment layer can conduct electrons again, and the battery resumes normal operation. The present invention utilizes the electrochemical activity characteristics of the conductive polymer and uses it in the treatment layer of the cathode current collector, thereby improving the anti-overcharge and overdischarge characteristics of the lithium-ion battery and improving the safety performance of the battery. In addition, the invention is easy to implement, easy to industrialize, and protects the battery without damaging the battery system and battery performance, and solves the technical problem of improving the safety performance of the battery/battery pack without damaging the battery.

As an improvement of the lithium ion battery cathode current collector of the present invention, the conjugated large π bond conductive polymer is polyaniline, poly-2,5-dimethoxyaniline, poly-m-methoxyaniline and poly-o- At least one of toluidine, the electrochemical active potential of these conductive polymers relative to the Li ⁺ /Li electrode is 2.9V ~ 3.8V, when the potential is between 2.9V ~ 3.8V, the treatment layer is a good electronic conductor, The handle layer is an insulator when the potential is lower than 2.9V or higher than 3.8V.

As an improvement of the lithium ion battery cathode current collector of the present invention, the binder is at least one of polyvinylidene fluoride and polytetrafluoroethylene.

As an improvement of the lithium ion battery cathode collector of the present invention, the treatment layer is covered on the surface of the cathode collector body by extrusion coating.

As an improvement of the lithium ion battery cathode collector of the present invention, the treatment layer is covered on the surface of the cathode collector body by electrostatic printing.

As an improvement of the lithium ion battery cathode current collector of the present invention, the thickness of the treatment layer is less than 5um. If the thickness of the treatment layer is too large, the overall thickness of the battery will increase, thereby affecting the energy density of the battery.

As an improvement of the lithium ion battery cathode current collector of the present invention, the thickness of the treatment layer is 3um.

As an improvement of the lithium ion battery cathode collector of the present invention, the cathode collector body is aluminum foil or stainless steel sheet.

Another object of the present invention is to provide a lithium ion battery comprising the above-mentioned cathode collector, a lithium ion battery comprising a cathode collector and a cathode active material layer coated on the cathode collector, an anode collector and An anode active material layer, a separator, and an electrolyte coated on the anode current collector, and the cathode current collector is the lithium ion battery cathode current collector described in the above paragraph.

As an improvement of the lithium ion battery of the present invention, the cathode active material layer includes lithium iron phosphate (LiFePO ₄ ), because the reversible lithium iron phosphate lithium deintercalation potential is 3.45V, just in the polyaniline and its derivatives. Within the electrochemical activity window (2.9V ~ 3.8V).

Compared with the prior art, the lithium-ion battery of the present invention has good safety characteristics under the premise of maintaining battery performance due to the introduction of conjugated large π-bond conductive polymers into the treatment layer of the cathode current collector.

Description of drawings

Fig. 1 is the curves of different voltages and internal resistances of the batteries of Examples 1 to 6 of the present invention and Comparative Example 1 at normal temperature;

Fig. 2 is the logarithmic curves of different voltages and internal resistances of the batteries of Examples 1 to 6 of the present invention and Comparative Example 1 at room temperature.

detailed description

The present invention will be further described below in conjunction with specific implementation methods and accompanying drawings.

Example 1

Preparation of cathode current collector treatment layer slurry:

Add oxalic acid (C ₂ H ₂ O ₄ ), conductive polyaniline (PANI) and binder polyvinylidene fluoride (PVDF) into N-methylpyrrolidone (NMP) in a weight ratio of 0.2:70:29.8 and stir evenly. NMP accounts for 80wt% of the total weight of the slurry. The uniformly stirred slurry is filtered with a 200-mesh stainless steel screen to obtain the required cathode collector treatment layer slurry.

Preparation of cathode current collector:

Using 12um aluminum foil as the cathode current collector body, the above-mentioned cathode current collector treatment layer slurry was evenly printed on both sides of the aluminum foil with a gravure printing machine, the printing speed was 2m/min, and the drying temperature was 55°C. The thickness of the printed layer on one side was obtained. 3um processing current collector.

Preparation of the cathode sheet:

Add lithium iron phosphate (LiFePO ₄ ), superconducting carbon (Super-P) and polyvinylidene fluoride (PVDF) into N-methylpyrrolidone (NMP) in a weight ratio of 93:2:5 and stir evenly to obtain a certain flow Then, the cathode slurry is coated on the above-mentioned treated cathode current collector, blown and dried, and then cold-pressed with a roller press, cut and other processes to obtain the cathode sheet.

Preparation of the anode sheet:

Add graphite, superconducting carbon (Super-P), and polyvinylidene fluoride (PVDF) into NMP in a weight ratio of 96:1:3 and mix and stir evenly to obtain an anode slurry with certain fluidity; then, the anode slurry Coated on a 9um copper foil current collector, air-dried, and then cold-pressed with a roller press, cut and other processes to obtain the anode sheet.

Assembly of the battery:

Weld conductive lugs on the cathode and anode pole pieces, and stack them neatly in the order of the positive pole piece, the separator and the negative pole piece, and the separator is a polypropylene (PP)/polyethylene (PE) composite with a thickness of 20um isolation film. After stacking neatly, wind it into a square shape, then pack it with aluminum-plastic film, and inject non-aqueous electrolyte. The electrolyte of the battery is 1mol/L LiPF ₆ solution, and the solvent is ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC), the volume ratio of the three is 40:20:20. After packaging the aluminum-plastic film, the formation and aging tests of the battery were carried out to obtain a square soft-packed battery with a length, width, and thickness of 109mm×101mm×3mm.

Example 2

The difference from Example 1 is that in the cathode collector treatment layer slurry, the weight ratio of oxalic acid (C ₂ H ₂ O ₄ ), conductive polyaniline (PANI) and binder polytetrafluoroethylene (PTFE) is 0.3 :72:27.7, the solvent N-methylpyrrolidone (NMP) accounts for 90wt% of the total weight of the slurry.

The body of the cathode current collector is a stainless steel sheet with a thickness of 10 μm, and the cathode current collector treatment layer slurry is coated on both sides of the stainless steel sheet by extrusion coating, and the thickness of one side of the treatment layer obtained after drying is 1 μm.

The rest are the same as in Embodiment 1, and will not be repeated here.

Example 3

The difference from Example 1 is that in the cathode current collector treatment layer slurry, oxalic acid (C ₂ H ₂ O ₄ ), poly-2,5-dimethoxyaniline and binder polytetrafluoroethylene (PTFE) The weight ratio of polyvinylidene fluoride (PVDF) is 0.4:74:20:5.6, and the solvent N-methylpyrrolidone (NMP) accounts for 70wt% of the total weight of the slurry.

The body of the cathode current collector is a stainless steel sheet with a thickness of 12 μm, and the cathode current collector treatment layer slurry is coated on both sides of the stainless steel sheet by extrusion coating, and the thickness of one side of the treatment layer obtained after drying is 5um.

The rest are the same as in Embodiment 1, and will not be repeated here.

Example 4

The difference from Example 1 is that in the cathode collector treatment layer slurry, the weight ratio of oxalic acid (C ₂ H ₂ O ₄ ), poly-m-methoxyaniline and binder polyvinylidene fluoride (PVDF) is 0.5 :76:23.5, the solvent N-methylpyrrolidone (NMP) accounts for 75wt% of the total weight of the slurry.

The slurry was coated on an aluminum foil with a thickness of 12 μm by a gravure printing machine, and the thickness of one side of the treatment layer obtained after drying was 4 μm.

The rest are the same as in Embodiment 1, and will not be repeated here.

Example 5

The difference from Example 1 is that in the cathode current collector treatment layer slurry, oxalic acid (C ₂ H ₂ O ₄ ), poly-o-toluidine and binders polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF ) in a weight ratio of 0.55:78:21.45, and the solvent N-methylpyrrolidone (NMP) accounts for 85wt% of the total weight of the slurry.

The body of the cathode current collector is a stainless steel sheet with a thickness of 12 μm, and the cathode current collector treatment layer slurry is coated on both sides of the stainless steel sheet by extrusion coating, and the thickness of one side of the treatment layer obtained after drying is 2um.

The rest are the same as in Embodiment 1, and will not be repeated here.

Example 6

The difference from Example 1 is that in the cathode current collector treatment layer slurry, oxalic acid (C ₂ H ₂ O ₄ ), poly-m-methoxyaniline, conductive polyaniline (PANI) and binder polyvinylidene fluoride ( The weight ratio of PVDF) is 0.6:10:70:19.4, and the solvent N-methylpyrrolidone (NMP) accounts for 87wt% of the total weight of the slurry.

The slurry was coated on an aluminum foil with a thickness of 12 μm by a gravure printing machine, and the thickness of one side of the treatment layer obtained after drying was 2.5 μm.

The rest are the same as in Embodiment 1, and will not be repeated here.

Comparative example 1

The difference from Example 1 is that the cathode current collector adopts an aluminum foil current collector that has not been processed by the present invention, that is, only the current collector body is used as the cathode current collector, and the rest is the same as that of Embodiment 1, and will not be repeated here.

The cathode pole piece that above-mentioned embodiment 1 to 6 and comparative example 1 are made carry out bonding performance test and resistance test, and the results are shown in the following table:

Table 1 Adhesive performance and resistance test data of different current collector cathode electrodes

It can be seen from Table 1 that after the cathode current collector body is covered with a treatment layer, the cathode sheet itself has stronger adhesion and smaller internal resistance of the diaphragm. This is because compared with the cathode current collector without surface treatment, the treatment layer of the current collector of the present invention contains an adhesive, which can play a better bonding effect with the active material layer. At the same time, the treatment layer contains oxalic acid , oxalic acid can have a certain corrosion effect on the current collector itself, and can enhance the roughness of the current collector body, thereby enhancing the adhesion between the current collector and the treatment layer. In addition, since polyaniline and its derivatives have good electrical conductivity, the internal resistance of the cathode sheet can be reduced.

The batteries prepared in the above Examples 1 to 6 and Comparative Example 1 were charged and discharged at room temperature, the initial capacity of the battery was calculated, and the number of charge and discharge cycles when the capacity of the battery dropped to 80% of the initial capacity was recorded. Cycle life test comparison, the results are shown in Table 2:

Table 2 battery capacity, cycle life test data

It can be seen from Table 2 that the capacity and cycle life of the lithium ion battery of the present invention are not affected.

In addition, the batteries prepared in Examples 1 to 6 and Comparative Example 1 were subjected to charge and discharge tests at room temperature, and their corresponding internal resistance values at different voltages were recorded. The results are shown in FIGS. 1 and 2 .

It can be seen from Figure 1 and Figure 2 that the internal resistance of the battery is different at different voltages. Compared with Comparative Example 1 in Examples 1 to 6, when the voltage is higher than 3.8V, the internal resistance of the battery increases sharply, because the conductive polymer on the current collector is oxidized at a high potential, causing it to lose its ability to conduct electrons And it becomes a non-conductive layer, so that the internal resistance of the battery increases sharply, so that the battery will not be overcharged, and the overcharge prevention characteristics of the battery are improved. When the voltage is lower than 2.4V, the conductive macromolecules in Examples 1 to 6 are reduced at a low potential to lose electrochemical activity and become a non-conductive layer, so that the internal resistance of the battery increases sharply, making the battery There will be no over-discharge phenomenon, which improves the anti-over-discharge characteristics of the battery. Therefore, the cathode current collector of the present invention can simultaneously solve the problem of preventing overcharge and overdischarge of the battery.

In summary, the lithium ion battery cathode current collector of the present invention can significantly improve the anti-overcharge and overdischarge characteristics of the lithium ion battery system without affecting the normal electrochemical performance of the lithium ion battery, thereby effectively improving the safety performance of the battery .

According to the disclosure and teaching of the above specification, those skilled in the art to which the present invention pertains can also make appropriate changes and modifications to the above embodiment. For example, those skilled in the art to which the present invention belongs can also assemble the single lithium ion battery in the embodiment into a battery pack according to the prior art. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention (such as assembling a single battery of the present invention into a battery pack) should also fall within the protection scope of the claims of the present invention . In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims (9)

1. a lithium ion battery cathode collector, including cathode current collector body, it is characterised in that: described cathode current collector is originally Surface is also covered with processing layer, and by weight percentage, described process layer is conducted electricity high by the conjugation big π key of 70～80wt% The binding agent of molecule, 19.4～29.8wt% and the oxalic acid composition of 0.2～0.6wt%；Described conjugation big π key conduction height Molecule is poly-2, at least one in 5-dimethoxyaniline, poly-m-anisidine.

2. according to the lithium ion battery cathode collector described in claim 1, it is characterised in that: described binding agent is for poly-inclined At least one in PVF and polytetrafluoroethylene (PTFE).

3. according to the lithium ion battery cathode collector described in claim 1, it is characterised in that: described process layer is by squeezing Extrusion mode for cloth covers at described cathode current collector body surface.

4. according to the lithium ion battery cathode collector described in claim 1, it is characterised in that: described process layer is by quiet Electricity mode of printing covers at described cathode current collector body surface.

5. according to the lithium ion battery cathode collector described in claim 1, it is characterised in that: described process layer thickness is little In 5 m.

6. according to the lithium ion battery cathode collector described in claim 5, it is characterised in that: described process layer thickness is 3 µm。

7. according to the lithium ion battery cathode collector described in claim 1, it is characterised in that: described cathode current collector is originally Body is aluminium foil or stainless steel substrates.

8. a lithium ion battery, including cathode current collector and the cathode active material layer being coated on described cathode current collector, Anode collector and the anode active material layer being coated in described anode collector, barrier film, and electrolyte, its feature exists In: described cathode current collector is the lithium ion battery cathode collector described in any one of claim 1 to 7.

Lithium ion battery the most described, it is characterised in that: described cathode active material layer includes ferric phosphate Lithium (LiFePO₄)。