KR20060073436A - Cathod for lithium secondary batteries having improved cathode coating nature and lithium secondary batteries using the same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery, wherein the slurry contains a polymerization inhibitor. According to the configuration of the positive electrode for a lithium secondary battery according to the present invention by increasing the adhesion of the positive electrode by preventing the gelation of the slurry (Slurry) that can occur when manufacturing the positive electrode to improve the coating properties, also improves the ease of coating Can kill.

Polymerization inhibitor, lithium secondary battery, positive electrode, slurry, gelation

Description

Cathode for Lithium secondary batteries having improved cathode coating nature And Lithium secondary batteries using the same

   The present invention relates to a positive electrode for a lithium secondary battery having an improved positive electrode coating property, and more particularly, for a lithium secondary battery having an improved positive electrode coating property by preventing gelation of a slurry that may occur in manufacturing a positive electrode of a battery. It is about a positive electrode.

In general, lithium metal oxide (LiMO ₂ ) used as a positive electrode active material is a powder having a spherical or pseudo-spherical shape, in order to facilitate electron conduction, a good adhesion between particles is used.

    The material used for this purpose is called a binder, and polyvinylidene fluoride (PVdF) is mainly used. PVdF is composed of fluorine (F), which has the highest electronegativity, and hydrogen (H), which has the lowest electronegativity.It is a polymer composed of monomers with a molecular structure with a large dipole moment. .

     PVdF, which is mainly used as a plate binder of lithium ion batteries and lithium polymer batteries, forms a chain having a number average molecular weight of about 130,000 to 220,000. PVdF produced in the PVdF manufacturing process is a mixture of α and ß form. However, when the solution casting (solvent casting), it is a general structure that the α phase has a distortion (γ) phase.

   In general, a method of injecting a PVdF binder into a positive electrode dissolves a PVdF binder in a solvent, N-methyl-pyrrolidone, to form a solution, and adds an active material thereto to mix the same. As such, a state in which the active material, the conductive material, the binder, and the NMP are evenly dispersed is referred to as a slurry, and when the slurry is coated on a current collector to a certain thickness and dried, a positive electrode of a coated solid is produced on the current collector.

    The adhesive force of the positive electrode is changed into a solid phase as the slurry is dried in a liquid binder, and at this time, the binder is present as a solid phase between particles and particles or between the current collector and the particles to have an adhesive force. At this time, PVdF is changed to ß or γ-PVdF. In the PVdF structure, since the fluorine atoms are arranged in one direction, the dipole moment is greatly increased to form many hydrogen molecular bonds.

    Due to this polarity, hydrogen ions are particularly vulnerable to cations in the solvent. At this time, if an alkaline component such as Li + ion of the positive electrode active material approaches, hydrogen bonds with fluorine by its polarity and is released in the form of hydrofluoric acid (HF), and carbons which lose ions share electrons to form a double bond. Done.

   The double bonds formed as described above undergo crosslinking by compounds that promote oxygen, moisture and other crosslinking, resulting in gelation of the slurry. This gelation makes it impossible for the slurry to be uniformly coated on the current collector and, even when coated, reduces the adhesion between the particles and the particles or between the particles and the current collector.

    Lack of adhesion between the particles and the particles facilitates the dropping of the particles from the surface of the positive electrode, resulting in deterioration of battery safety. That is, the particles of the positive electrode dropped due to insufficient adhesive force may generate microshort inside the battery, thereby degrading the performance of the battery, and when the short is large, a fire due to a short circuit may occur.

   In addition, if the adhesion between the particles and the current collector is reduced, the resistance of the electrons from the particles to the current collector is reduced, and the electron conduction speed is reduced, and as a result, high-rate characteristics and lifetime characteristics can be reduced.

     In addition, when the slurry coating is completed, the particles coated on the current collector hundreds of micrometers (㎛) is subjected to a pressing process, the surface adhesion or overpressure due to the adhesion of the particles to the continuous rotation (roll) Since the negative electrode of the electrode plate is applied to reduce the adhesion between the particles and the current collector, the yield of the battery manufacturing process also decreases.

Accordingly, the present invention is invented to solve the above problems of the prior art to prevent the gelation that may occur during the production of the positive electrode of the battery to enable the coating of the slurry on the current collector, between the particles and the particles or between the particles and the collector The purpose is to provide a positive electrode having excellent adhesion.

     In order to achieve the above object, the present invention provides a positive electrode for a lithium secondary battery, wherein the slurry contains a polymerization inhibitor in a slurry coated positive electrode including an active material, a binder, and a solvent.

The polymerization inhibitor is characterized in that the catechols of the formula (1).

[Formula 1]

 (Wherein R 1, R 2, R 3, and R 4 are each independently hydrogen or an alkyl group)

The catechols of the formula (1) is characterized in that 4-tert-butyl-catechol (4-tert-butyl-catechol) of the formula (2).

[Formula 2]

The polymerization inhibitor is characterized in that the derivative compound of catechols.

The slurry is characterized in that it comprises 0.01 to 10 parts by weight of the polymerization inhibitor, 80 to 99 parts by weight of the active material, 0.3 to 10 parts by weight of polyvinylidene fluoride (PVdF) binder.

In addition, the present invention provides a positive electrode for a lithium secondary battery, further comprising 0.1 to 10 parts by weight of acetylene black or graphite as a conductive material.

In addition, the active material in the present invention provides a lithium secondary battery positive electrode, characterized in that the lithium transition metal composite oxide.

The present invention provides a lithium secondary battery, wherein the lithium secondary battery positive electrode is used.

Hereinafter, the components of the lithium secondary battery positive electrode of the present invention and the manufacturing process thereof will be described in detail.

The polymerization inhibitor of the present invention is a substance added to prevent gelation of the slurry.

It is preferable to use the catechols of the following general formula (1) as a polymerization inhibitor, and it is more preferable to use 4-tert-butyl-catechol of the following chemical formula (2).

[Formula 1]

(Wherein R 1, R 2, R 3, and R 4 are each independently hydrogen or an alkyl group)

[Formula 2]

     When catechols or derivatives thereof are added as a polymerization inhibitor, not only the coating is possible by inhibiting gelation during mixing or slurry coating of the slurry, but also adhesion is increased.

   In addition, when phenols or cresols are used as polymerization inhibitors, there are less hydroxy groups that can act as polymerization inhibitors per unit molecule than catechols. Therefore, a larger amount should be added to achieve the same effect. After assembling, the initial discharge efficiency during charging and discharging decreases, and at high rates, the battery characteristics deteriorate.

    It is preferable to add a polymerization inhibitor at the time of manufacturing a slurry, and it is more preferable to use it, melt | dissolving in a solvent. To this end, a) 80 to 99 parts by weight of the active material, preferably 92 to 96 parts by weight b) 0.3 to 10 parts by weight, preferably 1 to 6 parts by weight of PVdF binder, and c) 0.01 parts by weight to catechols or derivatives thereof. 10 parts by weight, preferably 0.05 parts by weight to 2 parts by weight of a solvent is prepared by dissolving and dispersing it in a positive electrode slurry, which is then coated on a current collector of each positive electrode and dried to produce a positive electrode.

      In addition, the positive electrode slurry may further include 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight of acetylene black or graphite as the conductive material.

  The solvent may be at least one selected from the group consisting of an organic solvent such as N-methylpyrrolidone, acetone, dimethylacetamide, or dimethylformaldehyde and an inorganic solvent such as water.

   The amount of the solvent used is sufficient to dissolve and disperse the active material, the conductive material, the positive electrode binder, and the gelling agent in consideration of the coating thickness and production yield of the positive electrode slurry. These solvents are removed by drying after coating the positive electrode slurry.

The adhesion promoting additive of the present invention can be used for both the positive electrode and the negative electrode of a general lithium ion battery or a lithium polymer battery.

As the positive electrode, a lithium transition metal composite oxide (Li _a MO ₂ ) may be used.

(However, M is at least one selected from the group consisting of Co, Ni, Mn, Al, Mg, Sr, Ca, P, Pb, Y, Zr, and 0.9≤a≤1.1.)

      In addition, acetylene black or graphite may be further used as the conductive material used for the purpose of improving conductivity.

As the electrolyte solution of the battery including the positive electrode of the present invention, a lithium salt such as LiClO ₄ , LiPF ₆ or the like dissolved in a non-hydrogen organic solvent is used as the electrolyte solution of a general secondary battery.

      Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

<Example 1>

      (Manufacture of Slurry)

      96 wt% of the active material powder was mixed with 2 wt% of the conductive material and 2 wt% of the PVDF, 4-tert-butyl-catechol was prepared from 5 wt% NMP aqueous solution, and then 0.01 wt% of the active material was added. The slurry was added as much as possible, and an appropriate amount of NMP was further added. The slurry was left to stand at a temperature of 22 ° C. and a relative humidity of 50% to observe the gelation time.

      (Manufacture of Anode)

 The slurry prepared by the above method was coated and dried on an aluminum foil having a thickness of 20 μm using a doctor blade to prepare a plate.

      (Production of battery)

A 2016 type coin cell was fabricated in a glove box in an Ar atmosphere using lithium metal as a negative electrode and 1.15M of LiPF ₆ EC / DMC / DEC solvent as an electrolyte. The produced battery was aged for 12 hours to stabilize the initial voltage (OCV), and then the charge and discharge test was conducted in the voltage range of 4.3 to 3.0 V with a current density of 0.150 mA / _{cm 2} . The discharge capacity (initial capacity) of the first cycle is shown in Table 1.

<Example 2>

The slurry was prepared in the same manner as in Example 1 except for changing the amount of 4-tert-butyl-catechol added to the slurry and the positive electrode to 0.03 wt% of the active material. And batteries were prepared.

<Example 3>

The slurry was prepared in the same manner as in Example 1 except for changing the amount of 4-tert-butyl-catechol added to the slurry and the positive electrode to 0.05 wt% of the active material. And batteries were prepared.

<Example 4>

 The slurry was prepared in the same manner as in Example 1, except that the amount of 4-tert-butyl-catechol added to the slurry and the cathode was changed to 0.07 wt% of the active material. And batteries were prepared.

Example 5

  The slurry was prepared in the same manner as in Example 1, except that the amount of 4-tert-butyl-catechol added in the preparation of the slurry and the positive electrode was changed to 0.1 wt% of the active material. And batteries were prepared.

<Example 6>

  The slurry was prepared in the same manner as in Example 1, except that the amount of 4-tert-butyl-catechol added to the slurry and the cathode was changed to 0.2 wt% of the active material. And batteries were prepared.

<Example 7>

  The slurry was prepared in the same manner as in Example 1, except that the amount of 4-tert-butyl-catechol added to the slurry and the cathode was changed to 0.3 wt% of the active material. And batteries were prepared.

Comparative Example 1

  A slurry and a battery were prepared in the same manner as in Example 1, except that 4-tert-butyl-catechol, a polymerization inhibitor, was not added when preparing the slurry and the positive electrode.

Comparative Example 2

  The same method as in Example 1, except that 0.5 wt% of phenol was added instead of 4-tert-butyl-catechol, which is an antigelling agent, in preparing the slurry and the positive electrode. Slurries and batteries were prepared.

0.1C discharge (mAh / g) 0.1C efficiency (%) 1.0C discharge (mAh / g) 1.0C / 0.1C (%) Gel time (hr) Example 1 191.0 93.7 171.3 89.7 1 hr Example 2 191.7 94.2 172.1 89.8 4 hr Example 3 190.4 93.9 170.8 89.7 9 hr Example 4 188.7 93.2 167.8 88.9 12 hr Example 5 187.5 91.3 168.2 89.7 20 hr Example 6 190.5 89.0 167.6 87.9 63 hr Example 7 190.4 87.7 164.7 86.6 112 hr Comparative Example 1 190.2 92.5 167.5 88.1 0.3 hr Comparative Example 2 180.5 84.2 155.7 86.3 43 hr

      The battery manufactured according to the present invention has excellent initial discharge efficiency and high battery characteristics at high rate during charge and discharge after battery assembly, and significantly suppresses gelation that may occur during slurry production of a positive electrode active material, thereby enabling production of a pole plate. In addition, the excellent coating properties of the slurry improved the characteristics of the battery.

Claims (8)

      A positive electrode for a lithium secondary battery coated with a slurry containing an active material, a binder, and a solvent, wherein the slurry contains a polymerization inhibitor.  The positive electrode for a lithium secondary battery according to claim 1, wherein the polymerization inhibitor is catechols of the following Chemical Formula 1. [Formula 1]

 (Wherein R 1, R 2, R 3, and R 4 are each independently hydrogen or an alkyl group) The cathode of claim 2, wherein the catechols of Chemical Formula 1 are 4-tert-butyl-catechol of Chemical Formula 2 below. [Formula 2]

The positive electrode for a lithium secondary battery according to claim 1, wherein the polymerization inhibitor is a derivative compound of catechols. The positive electrode of claim 1, wherein the slurry comprises 0.01 to 10 parts by weight of a polymerization inhibitor, 80 to 99 parts by weight of an active material, and 0.3 to 10 parts by weight of a polyvinylidene fluoride (PVdF) binder. The cathode for a lithium secondary battery according to claim 5, further comprising 0.1 to 10 parts by weight of acetylene black or graphite as a conductive material. The positive electrode for a lithium secondary battery according to claim 1, wherein the active material is a lithium transition metal composite oxide. The lithium secondary battery using the positive electrode for lithium secondary batteries in any one of Claims 1-7.