KR20120133409A - Separator and lithium secondary battery - Google Patents

Abstract

PURPOSE: A separator for a secondary battery is provided to have electric stability by forming a lithium carbonate layer and to have thermal stability by forming an aluminum oxide layer, thereby being capable of improving the performance of a battery. CONSTITUTION: A separator(30) for a secondary battery comprises: a substrate(31); and a first inorganic material layer(32) and a second inorganic layer(33) which have different properties from each other and spread on the both sides of the substrate respectively. The material of the first inorganic material layer is lithium carbonate. The first inorganic layer is comprised between a separator and a positive electrode. The material of the second inorganic layer is an aluminum oxide and/or barium titanium oxide. The content of the first inorganic layer is 0.01-1.0 weight% and the content of the second inorganic based on an electrode active material. A lithium secondary battery comprises a positive electrode, a negative electrode, the separator, and an electrolyte.

Description

Separator for secondary battery and lithium secondary battery including same {Separator and lithium secondary battery}

The present invention relates to a lithium secondary battery that has enhanced safety by applying different inorganic materials between the separator and the electrode.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the field attracting the most attention in this respect, and among them, the development of a secondary battery capable of charging and discharging has become a focus of attention. In recent years, research and development on the design of new electrodes and batteries have been proceeding in order to improve capacity density and specific energy in developing such batteries.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, such a lithium secondary battery has safety problems such as ignition and explosion when using an organic electrolytic solution, and it is disadvantageous in that it is difficult to manufacture.

It is very important that the safety evaluation and safety of the battery as described above. The most important consideration is that the battery should not injure the user in case of malfunction, and the battery safety standard strictly regulates the ignition and smoke in the battery. Therefore, many solutions are proposed to solve the safety problem.

As a more fundamental problem, a lithium secondary battery, which is currently being produced, uses a polyolefin-based separator to prevent a short circuit between the positive electrode and the negative electrode. However, since the separation membrane is usually subjected to a stretching process for controlling the pore size and porosity for use as a separation membrane as well as using a polymer component melted at a temperature of 200 ° C or lower, ). Therefore, when the battery rises to a high temperature by internal / external stimulation, the anode and the cathode are likely to be short-circuited due to shrinkage or melting of the separator, etc., Lt; / RTI > Therefore, it is essential to develop a separator which does not cause thermal shrinkage at high temperature.

In order to improve the problems of the polyolefin-based separators as described above, many attempts have been made to develop electrolytes to which inorganic substances can be substituted for conventional separators.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a secondary battery separator and a lithium secondary battery, which enables the thermal shrinkage problem of the separator and the electrical safety of the secondary battery.

In order to solve the above problems, the present invention is a membrane substrate; There is provided a separator for a secondary battery including a first inorganic material layer and a second inorganic material layer having different properties applied to both surfaces of the substrate, respectively.

The material of the first inorganic layer is lithium carbonate, and is included between the separator and the positive electrode.

The material of the second inorganic layer is any one or a mixture of aluminum oxide and barium titanium oxide, and is included between the separator and the cathode.

The thickness of the first inorganic layer and the second inorganic layer is 1 ~ 5㎛.

The content of the first inorganic layer and the second inorganic layer is 0.01 to 1.0% by weight relative to the electrode active material.

The present invention also provides a lithium secondary battery including a first inorganic layer and a second inorganic layer having different properties, respectively, applied to both surfaces of the separator in a lithium secondary battery including a cathode, an anode, a separator, and an electrolyte. do.

The material of the electrolyte is characterized in that the carbonate compound.

The content of the electrolyte is characterized in that 20 to 25% by weight based on the total weight of the battery cell.

As described above, by forming a lithium carbonate layer to induce electrical safety and an aluminum oxide layer to induce thermal safety, respectively, on both sides of the separator which is a component of the lithium secondary battery, safety in various states rather than a specific one is improved. At the same time, the performance of the battery can be further improved.

1 is a schematic view showing the structure of a lithium secondary battery according to the present invention.

Hereinafter, a preferred embodiment of a separator for a secondary battery according to the present invention and a lithium secondary battery including the same will be described in detail.

As shown in FIG. 1, the secondary battery separator 30 according to the present invention includes a separator substrate 31 and a first inorganic layer 32 and a second inorganic layer 33 formed on both surfaces of the substrate, respectively. Include.

As the separator, a conventional porous separator known in the art may be used. For example, a polyolefin-based porous separator such as polypropylene and polyethylene may be used, and the separator may be formed of a single layer or a multilayer structure of two or more layers. This is all applicable.

Existing lithium secondary batteries are overcharged over a specified operating voltage range, or when the exothermic reaction between the charged electrode and the electrolyte is stored for a long time at high temperature, the reactivity of the positive electrode and the electrolyte increases, resulting in degradation of the surface of the positive electrode. And oxidation reaction of the electrolyte occurs. In addition, there is a problem of lack of battery stability, such as lithium dendrite growth and the resulting membrane destruction, rapid exothermic reaction, explosion.

In view of this, in the past, the inorganic particles may be used as a constituent or coating component of the separator to improve the safety of the battery. However, the non-porous inorganic particles are mainly used to increase the overall weight of the secondary battery. Furthermore, by applying the inorganic layer or the inorganic particles of the same property on one side or both sides of the separator may be effective in improving any one specific stability of the secondary battery, but the improvement of the stability of various properties and the improvement of the function according to the facing electrode There was a problem.

On the contrary, in the present invention, the first inorganic layer 32 for electrical stability and the second inorganic layer 33 for thermal stability are respectively applied to both sides of the separator to induce stability improvement of various properties.

That is, the separator substrate of the present invention is coated with lithium carbonate for electrical stability of the secondary battery as a first inorganic layer on one surface thereof. The first inorganic layer is interposed at the interface between the positive electrode and the separator of the electrode of the secondary battery to prompt the increase of the internal pressure due to the generation of gas during overcharging of the secondary battery to reduce the time until the short circuit of the current blocking device (CID) to reduce the secondary battery Can prevent overheating and explosion.

In addition, the separator substrate of the present invention is coated with a mixture of any one or two of aluminum oxide, barium titanium oxide for the thermal stability of the secondary battery as the second inorganic layer. The second inorganic layer may be interposed at an interface between the negative electrode and the separator among the electrodes of the secondary battery to prevent thermal contraction of the separator.

On the other hand, the content of each inorganic layer is not particularly limited, in particular 0.01 to 1.0% by weight relative to the electrode active material is preferred. When the amount is less than 0.01 wt%, the effect of improving the safety and performance of the battery generated by the addition of the inorganic layer is insignificant, and when the amount exceeds 1.0 wt%, the capacity and performance of the battery are reduced due to the addition of the additive. Similarly, the first inorganic material layer and the second inorganic material layer are each formed to a thickness of 1 ~ 5㎛. If the thickness is less than 1㎛ less than expected for each specific stability, if it exceeds 5㎛ may cause a lack of space inside the battery cell.

A method of interposing the first inorganic layer or the second inorganic layer is not particularly limited, and a known coating method may be used.

The present invention also provides a lithium secondary battery including the separator described above. That is, the lithium secondary battery of the present invention, as shown in FIG. 1, includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte, and interposes a porous separator between the positive electrode and the negative electrode. It may be prepared by injecting an electrolyte after assembly.

The lithium secondary battery is capable of charging and discharging because lithium ions, which are discharged from the positive electrode active material by the first charge, transfer energy while reciprocating both electrodes such as being inserted into a negative electrode active material, such as carbon particles, and detached again during discharge. do.

Here, the carbonate compound is used as the electrolyte, the content is preferably 5 to 20% by weight based on the total weight of the battery cell. If the content of the electrolyte is less than 5% by weight it may not be able to fully perform its role, if it exceeds 20% by weight may lead to an increase in the weight of the battery cell.

As the carbonate compound used as the electrolyte, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxy Dissolved or dissociated in an organic solvent consisting of ethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone (GBL) or mixtures thereof There is, but is not limited to this.

As described above, in the lithium secondary battery of the present invention, the first inorganic layer and the second inorganic layer are coated on both surfaces of the separator, thereby improving electrical safety and thermal stability, and consequently, improving the performance of the secondary battery. have.

That is, the separator formed with the second inorganic layer of the present invention can improve the thermal safety of the battery by suppressing side reactions with the electrolyte during overcharging or during high temperature storage for a long time.

In addition, since the conventional polyolefin-based separator has a melting point of 120 ~ 140 ℃ heat shrink occurs at a high temperature, the porous separator formed with the first inorganic layer does not occur high temperature heat shrink due to the heat resistance of the first inorganic layer. Therefore, in the lithium secondary battery using the porous separator, even if the separator ruptures inside the battery due to excessive conditions due to internal or external factors such as high temperature, overcharge, external impact, etc., it is difficult for both electrodes to be completely shorted by the first inorganic layer. Even if a short circuit occurs, the enlargement of the short-circuited area is suppressed significantly, and the safety of the battery can be improved.

On the other hand, unlike the conventional separator or polymer electrolyte prepared in the form of a free standing film (assembled together with the electrode), since the porous separator of the present invention is formed by coating directly on the polyolefin-based separator, the polyolefin-based separator substrate The pores on the surface and the active layer are present in an angular form (anchoring), so that the active layer and the porous substrate are physically firmly bonded. Accordingly, the mechanical properties such as brittleness can be improved, and the interface resistance between the polyolefin-based separator substrate and the active layer is excellent, thereby reducing the interface resistance.

[Example]

1-1. Anode manufacturing

A positive electrode mixture slurry was prepared by adding 89 wt% of LiCoO 2 as a cathode active material, 4 wt% of carbon black as a conductive agent, and 4 wt% of PVdF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of 20 μm, and the positive electrode was manufactured by drying, and then roll press was performed.

1-2. Cathode manufacturing

The negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive agent at 96% by weight to N-methyl-2 pyrrolidone (NMP) as a solvent. Was prepared. The negative electrode mixture slurry was applied to a copper (Cu) thin film having a thickness of 10 μm, and a negative electrode was prepared by drying, followed by roll pressing.

1-3. Battery manufacturing

1 mole of lithium hexafluorophosphate after interposing a separator in which 0.1 wt% of lithium carbonate and aluminum oxide are formed on both sides of the electrode active material, respectively, between the positive electrodes prepared in Examples 1-1 and 1-2. An electrolyte solution, a mixed solution of ethylene carbonate / propylene carbonate / diethyl carbonate (EC: PC: DEC = 30: 20: 50 wt%) in which (LiPF6) was dissolved, was injected to complete a battery.

[Comparative Example]

Manufacture of lithium secondary battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a separator in which lithium carbonate and aluminum oxide was not applied was used.

[Experimental Example]

Overcharge Test of Lithium Secondary Battery

In order to evaluate the safety of the lithium secondary battery having an electrode prepared from an electrode slurry containing inorganic particles having lithium ion transfer capability according to the present invention, the following experiment was carried out.

A lithium secondary battery including a positive electrode prepared in Examples and Comparative Examples was used, and each battery was overcharged under conditions of 10 V / 1 A, and then the state of the battery was described in Table 1 below.

As a result of the experiment, the battery of the comparative example rapidly increased the temperature of the battery due to overcharging, and eventually ignition and explosion of the battery occurred. In contrast, the battery of the present invention having an electrode prepared from an electrode slurry containing inorganic particles having lithium ion transfer capability showed a stable state (see Table 1). As a result, it can be seen that electrical safety and thermal safety are satisfied due to lithium carbonate and aluminum oxide applied to the separator.

battery Fire explosion Acting Example One × × × Comparative example One O O O

10; anode
20; cathode
30; Membrane
31; materials
32; 1st inorganic layer
33; 2nd inorganic layer

Claims (20)

Separator substrate;
Separation membrane for a secondary battery, characterized in that it comprises a first inorganic material layer and a second inorganic material layer of different properties, respectively applied to both sides of the substrate.
The method of claim 1,
The material of the first inorganic layer is a secondary battery separator, characterized in that the lithium carbonate.
The method of claim 2,
The first inorganic layer is a separator for a secondary battery, characterized in that included between the separator and the positive electrode.
The method of claim 1,
The material of the second inorganic layer is a secondary battery separator, characterized in that any one or a mixture of aluminum oxide, barium titanium oxide.
5. The method of claim 4,
The second inorganic layer is a secondary battery separator, characterized in that included between the separator and the negative electrode.
The method of claim 1,
Separator for a secondary battery, characterized in that the thickness of the first inorganic layer is 1 ~ 5㎛.
The method of claim 1,
Separation membrane for a secondary battery, characterized in that the thickness of the second inorganic layer is 1 ~ 5㎛.
The method of claim 1,
The amount of the first inorganic layer is a secondary battery separator, characterized in that 0.01 to 1.0% by weight relative to the electrode active material.
The method of claim 1,
The amount of the second inorganic layer is a secondary battery separator, characterized in that 0.01 to 1.0% by weight relative to the electrode active material.
In a lithium secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte solution,
Lithium secondary battery characterized in that it comprises a first inorganic material layer and a second inorganic material layer of different properties respectively applied to both surfaces of the separator.
The method of claim 10,
The material of the first inorganic layer is a lithium secondary battery, characterized in that the lithium carbonate.
The method of claim 11,
The first inorganic layer is a lithium secondary battery, characterized in that included between the separator and the positive electrode.
The method of claim 10,
The material of the second inorganic layer is a lithium secondary battery, characterized in that any one or a mixture of aluminum oxide, barium titanium oxide.
The method of claim 13,
The second inorganic layer is a lithium secondary battery, characterized in that included between the separator and the negative electrode.
The method of claim 10,
The thickness of the second inorganic layer is a lithium secondary battery, characterized in that 1 ~ 5㎛.
The method of claim 10,
The thickness of the second inorganic layer is a lithium secondary battery, characterized in that 1 ~ 5㎛.
The method of claim 10,
The content of the first inorganic layer is a lithium secondary battery, characterized in that 0.01 to 1.0% by weight relative to the electrode active material.
The method of claim 10,
The content of the second inorganic layer is a lithium secondary battery, characterized in that 0.01 to 1.0% by weight relative to the electrode active material.
The method of claim 10,
The material of the electrolyte is a lithium secondary battery, characterized in that the carbonate compound.
The method of claim 10,
The amount of the electrolyte is a lithium secondary battery, characterized in that 5 to 20% by weight based on the total weight of the battery cell.

Images