KR20110118225A - Method for activating high capacity lithium secondary battery - Google Patents

Abstract

The present invention relates to a method for activating a lithium secondary battery comprising a lithium compound having a layered structure represented by the following [Formula 1] as a cathode active material.
Unlike other cathode materials, the cathode active material has a characteristic flat level voltage region in a 4.5V to 4.8V range, and is a special material that is activated only after a formation step at a high voltage above the flat level region to express a high capacity. This material can maintain high capacity even when it is operated at high voltage above the flat level region even after formation, but there are problems that can cause long-term performance degradation such as electrolyte side reactions. However, even in this case, the problem of "electrolyte side reaction during formation" cannot be solved.
Accordingly, the present invention is to provide a method that can realize a high capacity by activating the material while minimizing the side reaction of the electrolyte by forming a cell "at a low voltage" below the flat level unlike the conventional "at a high temperature" of 40 ~ 65 ℃ In particular, when using the infiltration process through high temperature storage, high capacity can be expressed without any additional process, and afterwards, it is operated at a low voltage, resulting in long-term performance by suppressing electrolyte side reaction during formation and electrolyte side reaction at the same time. Can contribute to
[Formula 1] Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z
Wherein 0 <x <0.5, 0.6 <y <1.1, 0 ≦ y '<0.2, 0 ≦ z <0.2;
M includes Mn and at least one member selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn and Ti;
M 'is one or more selected from the group consisting of Al, Mg and B,
A is at least one member selected from the group consisting of F, S and N.)

Description

Activation method of high capacity lithium secondary battery {METHOD FOR ACTIVATING HIGH CAPACITY LITHIUM SECONDARY BATTERY}

The present invention relates to a method for activating a lithium secondary battery comprising a lithium compound having a layered structure represented by the following [Formula 1] as a cathode active material.

Unlike other cathode materials, the cathode active material has a characteristic flat level voltage region in a 4.5V to 4.8V range, and is a special material that is activated only after a formation step at a high voltage above the flat level region to express a high capacity. This material can maintain high capacity even when it is operated at high voltage above the flat level region even after formation, but there are problems that can cause long-term performance degradation such as electrolyte side reactions. However, even in this case, the problem of "electrolyte side reaction during formation" cannot be solved.

Accordingly, the present invention is to provide a method that can realize a high capacity by activating the material while minimizing the side reaction of the electrolyte by forming a cell "at a low voltage" below the flat level unlike the conventional "at a high temperature" of 40 ~ 65 ℃ In particular, when using the infiltration process through high temperature storage, high capacity can be expressed without any additional process, and afterwards, it is operated at a low voltage, resulting in long-term performance by suppressing electrolyte side reaction during formation and electrolyte side reaction at the same time. Can contribute to

[Formula 1] Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z

Wherein 0 <x <0.5, 0.6 <y <1.1, 0 ≦ y '<0.2, 0 ≦ z <0.2;

M includes Mn and at least one member selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn and Ti;

M 'is one or more selected from the group consisting of Al, Mg and B,

A is at least one member selected from the group consisting of F, S and N.)

Recently, as a lithium secondary battery is used as a driving power source of a vehicle as well as a portable electronic device such as a mobile phone, a PDA, a laptop computer, researches for improving the capacity of such a lithium secondary battery have been actively conducted. In particular, as the energy consumption increases due to the multifunctionalization of portable electronic devices, the demand for increasing the capacity of lithium secondary batteries is increasing, and the SOC used together with high output for use as a power source for medium and large devices such as HEV, PHEV, and EV There is a continuous demand for the development of high capacity lithium secondary batteries capable of stably maintaining output in the field.

Although lithium metal, sulfur compounds, etc. are also considered as a negative electrode active material of the lithium secondary battery, carbon materials are mostly used for safety reasons, and in this case, the capacity of the lithium secondary battery is determined by the capacity of the positive electrode, that is, the positive electrode active material. It is determined by the amount of lithium ions contained.

In general, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a cathode active material, and lithium-containing manganese oxides such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, and lithium-containing nickel oxide (LiNiO _2). ) Has been considered.

Among the cathode active materials, LiCoO ₂ is the most used because of its excellent life characteristics and high-speed charging and discharging efficiency, but it is inferior in price competitiveness and mass production because cobalt used as a raw material is inferior in high temperature safety and structural safety. It has a disadvantage.

On the other hand, lithium-containing nickel oxide (LiNiO ₂ ) is relatively inexpensive and exhibits a high discharge capacity of battery characteristics, but when the volume change accompanying the charge and discharge cycle shows a sharp phase transition of the crystal structure, and when exposed to air and moisture There is a problem that the safety is sharply lowered.

Accordingly, lithium-containing manganese oxide has been proposed as a cathode active material. In particular, lithium-containing manganese oxide having a spinel structure has advantages of excellent thermal safety, low cost, and easy synthesis. However, the capacity is small, there is a deterioration in the life characteristics due to side reactions, the cycle characteristics and the high temperature characteristics are disadvantageous.

As a result, a layered lithium-containing manganese oxide has been proposed to compensate for the low capacity of spinel and to ensure excellent thermal safety of the manganese-based active material. In particular, Li (Li _x M _{y - y '} M' _{y '} ) O _{2 -z} A _{z, which} has a layered structure in which Mn content is higher than that of other transition metal (s), has a disadvantage in that its initial irreversible capacity is rather large, but high voltage Overexpresses very large doses. In other words, when overcharged at a high voltage of 4.5 V or more (preferably 4.55 V or more) based on the anode potential during initial charging, the flat level range is 4.5 V to 4.8 V, and an excessive amount of oxygen gas reaches about 250 mAh / g. Seems large capacity.

In conclusion, in order to apply Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z of a layered structure as a cathode active material, a high-cycle cycle at high voltage is required. It is essential. However, when the battery is operated by charging / discharging at a high voltage above the flat level, the reaction of the electrode active material and the electrolyte (eg, electrolyte decomposition) adversely affects the performance of the battery.

Therefore, the development of electrolyte and other units will be required for stable operation at high voltage, but there is a difficulty in maintaining a stable cycle at this high voltage with a general-purpose electrolyte solution developed to date.

In order to solve this problem, in Korean Patent Publication Nos. 10-2007-0012213 and 10-2007-0021955, the formation is performed at a high voltage during the first cycle, and then a gas is removed through a degassing process. When the battery was charged and discharged by lowering the voltage to a level capable of operating stably (below 4.4V), it was confirmed that a relatively large capacity was expressed, although not as a case of rotating the cycle at a high voltage of 4.5V or more.

However, even in this case, since the formation at high voltage must proceed, side reactions such as electrolyte decomposition occurring in the formation step cannot be avoided.

Accordingly, in a lithium secondary battery including a layered lithium-containing manganese oxide Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z as a positive electrode active material, a low voltage band capable of suppressing side reactions of an electrolyte solution There is an urgent need for the development of processing technology that can realize high capacity by activating materials.

The present invention has been made to solve the above-mentioned demands and conventional problems, the inventors of the present application after the in-depth research and various experiments, the method for activating a high capacity lithium secondary battery as described later. With this activation method, the development of electrolytes and other units for stable operation at high voltage is not completed, and the high capacity can be realized by activating the material while suppressing the electrolyte side reactions that are essential for high voltage activation. It was confirmed.

The present invention is to solve the above problems,

In the activation method of a lithium secondary battery comprising a lithium compound having a layered structure represented by the following [Formula 1] as a positive electrode active material,

It relates to a method for activating a lithium secondary battery, characterized in that the cell is formed at a voltage below the flat level at a temperature of 40 ~ 65 ℃.

[Formula 1] Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z

Wherein 0 <x <0.5, 0.6 <y <1.1, 0 ≦ y '<0.2, 0 ≦ z <0.2;

M includes Mn and at least one member selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn and Ti;

M 'is one or more selected from the group consisting of Al, Mg and B,

A is at least one member selected from the group consisting of F, S and N.)

In addition, the flat level may be 4.5 ~ 4.8V based on the anode potential.

The formation may be performed at a voltage below the flat level at a temperature of 45 to 60 ° C., or at a voltage of 4.3 to 4.5 V based on the anode potential at a temperature of 40 to 65 ° C. FIG.

Specifically, the formation may be performed at a voltage of 4.3 to 4.5V based on the anode potential at a temperature of 45 ~ 60 ℃.

In addition, the formation may be performed using a high temperature storage step for wetting of the separator.

In addition, oxygen may be generated from the cathode active material in the flat level section during the formation.

Here, after the formation, it may further comprise the step of removing the oxygen generated from the cathode active material.

In addition, the content of Mn in the lithium compound of the layered structure represented by the above [Formula 1] may be 50 to 80 mol% based on the total amount of the metals except lithium.

In addition, the cathode active material is a lithium compound having a layered structure represented by the above [Formula 1], lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt- nickel oxide, lithium cobalt- manganese oxide, lithium manganese- nickel oxide , Lithium cobalt-nickel-manganese oxide, lithium-containing olivine-type phosphate and any one or two or more lithium-containing metal oxide selected from the group consisting of an oxide substituted or doped with the ellipsoid (s) may be mixed, such The lithium-containing metal oxide is preferably contained within 50% by weight of the total cathode active material.

Here, the ellipsoid (s) may be any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or two or more elements.

According to the present invention, in a lithium secondary battery comprising a lithium compound Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z having a layered structure as a cathode active material, a cell is heated at a high temperature of 40 to 65 ° C. By forming a voltage at or below the flat level at, it is advantageous to minimize the side reactions that are essential when the high voltage is activated and to realize a high capacity by activating the material.

1 is a graph of a charge and discharge cycle of a lithium secondary battery according to an embodiment of the present invention.
2 is a graph showing a charge and discharge cycle of a lithium secondary battery according to a comparative example of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention is for solving the above problems,

In the activation method of a lithium secondary battery comprising a lithium compound having a layered structure represented by the following [Formula 1] as a positive electrode active material,

It relates to a method for activating a lithium secondary battery, characterized in that the cell is formed at a voltage below the flat level at a temperature of 40 ~ 65 ℃.

[Formula 1] Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z

Wherein 0 <x <0.5, 0.6 <y <1.1, 0 ≦ y '<0.2, 0 ≦ z <0.2;

M includes Mn and at least one member selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn and Ti;

M 'is one or more selected from the group consisting of Al, Mg and B,

A is at least one member selected from the group consisting of F, S and N.)

The lithium compound of the layered structure represented by [Formula 1] includes Mn as an essential transition metal, the content of Mn is higher than the content of other metals except lithium, and large through activation (generally performed by overcharging at high voltage). It is a lithium transition metal oxide that expresses a capacity. On the other hand, it is a material that provides lithium ions consumed in the initial irreversible reaction on the surface of the negative electrode, and then lithium ions that were not used for the irreversible reaction on the negative electrode move to the positive electrode to provide additional lithium soot.

Preferably, the lithium compound of the layered structure represented by the above [Formula 1] may be one containing essentially Fe in addition to Mn as a transition metal.

Mn included as an essential transition metal in the layered lithium compound is higher than the content of other metals (except lithium), and is preferably 50 to 80 mol% based on the total amount of metals except lithium. If the amount of Mn is too small, safety may decrease and manufacturing cost may increase, and it may be difficult to exhibit unique characteristics of the lithium compound having a layered structure represented by the above [Formula 1]. On the contrary, too much Mn content may result in poor cycle stability.

In addition, the lithium compound having a layered structure represented by the above [Formula 1] has a flat level of a certain period above the oxidation / reduction potential indicated by the oxidation number change of the components in the positive electrode active material. Specifically, when the overcharge at a high voltage of 4.5V or more based on the anode potential has a flat level section in the vicinity of 4.5V ~ 4.8V.

In such a flat level section, as lithium is released, gas (oxygen) is released to balance the oxidation / reduction. That is, two lithium ions, that is 2Li ^{+ +} 2e occurring while oxygen is released ^- is let this + 1 / 2O ₂ type of reaction.

Therefore, in order to activate the lithium compound having a layered structure represented by the above [Formula 1] and utilize it at a high capacity according to the purpose, it is recognized that the cell must be overcharged at a high voltage above the flat level in the formation step.

However, when the formation is performed at a high voltage above the flat level, side reactions such as decomposition of the electrolyte inevitably occur, which adversely affects the performance of the battery. Regarding suppression of the side reaction of the electrolyte during battery operation, a method of forming a battery at a high voltage and then lowering the voltage to a level (4.4 V or less) that does not burden the electrolyte is disclosed. Since high voltage formation is an essential step, electrolyte side reactions in the activation step were inevitable.

On the other hand, when the formation is performed at a low voltage to suppress side reactions of the electrolyte, it becomes difficult to activate the cells themselves. In other words, the suppression of the side reaction of the electrolyte in the formation step and the activation of the cell can be said to be a trade-off relationship.

Thus, in the present invention, the cell is formed at a high temperature of 40 to 65 ° C. to a voltage below the flat level (hereinafter, referred to as 'high temperature / low voltage formation'), thereby satisfying both conditions of suppression of electrolyte side reaction and cell activation. To help.

The high temperature / low voltage formation is a step for realizing a high capacity by reflecting the characteristics of the lithium compound of the layered structure represented by the above [Formula 1], and having a low voltage below the flat level at 40 to 65 ° C. higher than room temperature (eg, Charge to 4.4V) to activate the cell.

When forming at a temperature below 40 ° C, cell activation may not be possible due to deactivation of the positive electrode active material, etc., and formation at too high a temperature above 65 ° C may put a burden on the electrode material. May cause side reactions. Preferably, the high temperature / low voltage formation is performed at a voltage below the flat level at a temperature of 45 to 60 ° C.

Specifically, the low voltage below the flat level may be in the range of 4.3 to 4.5V based on the anode potential. That is, the high temperature / low voltage formation may be performed at a voltage of about 4.3 to 4.5V based on the anode potential at a temperature of 40 to 65 ° C. Preferably at a temperature of 45 ~ 60 ℃ is carried out with a voltage of 4.3 ~ 4.5V based on the anode potential.

The method of performing the high temperature / low voltage formation is not particularly limited except that the high temperature / low voltage formation is performed at a voltage below the flat level at a high temperature of 40 to 65 ° C. That is, a method known in the art may be used as a method of activating a cell through formation.

Preferably, by performing the high temperature / low voltage formation using a high temperature storage step for wetting the separator, a more economical and simple process can be provided.

The inventors of the present application confirmed that the cell is activated faster after the high temperature storage through the experiment, and based on this, the existing membrane infiltration step as described above can be used as a high temperature / low voltage formation step.

That is, when the high temperature storage step performed for the infiltration of the separator and the like in the current battery manufacturing process is used as the time for performing the high temperature / low voltage formation, the high capacity lithium secondary battery can be activated without a separate high voltage cycle.

In addition, the activation process of the cell through the high temperature / low voltage formation may be performed once or repeatedly performed two or more times. Such processing is generally performed before shipment charge, but the circuit is designed to automatically activate the cell through the high temperature / low voltage formation during a certain number of charge / discharge cycles after the initial charge after shipment. It is also possible.

On the other hand, in the formation step, it is common that a large amount of gas such as oxygen is generated from the lithium compound of the layered structure represented by the above [Formula 1] and shows a flat level section. Therefore, in this case, a degassing step for removing gas such as generated oxygen is required. The method for degassing is not particularly limited and may be a method known in the art.

The cathode active material according to the present invention is a lithium compound having a layered structure represented by the above [Formula 1],

Lithium Cobalt Oxide, Lithium Nickel Oxide, Lithium Manganese Oxide, Lithium Cobalt-Nickel Oxide, Lithium Cobalt-Manganese Oxide, Lithium Manganese-Nickel Oxide, Lithium Cobalt-Nickel-Manganese Oxide, Lithium-containing Olivine Phosphate and Ellipsium (s) ) May be a mixture of any one or two or more lithium-containing metal oxide selected from the group consisting of substituted or doped oxide. Here, the ellipsoid (s) may be any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or two or more elements. The lithium-containing metal oxide is preferably contained within 50% by weight relative to the total weight of the positive electrode active material in view of the effect exhibited in the present invention.

On the other hand, the lithium compound of the layered structure represented by the above [Formula 1] in the present invention may be a complex with the conductive material. This is to increase the conductivity to further improve cycle stability and lifespan.

The conductive material is not particularly limited as long as the conductive material is excellent in electrical conductivity and does not cause side reactions in the internal environment of the lithium secondary battery, but a carbon-based material having high conductivity is particularly preferable. Preferred examples of such highly conductive carbon-based materials include materials in which the crystal structure includes graphene or graphite. In some cases, a conductive polymer having high conductivity is also possible. In addition, the precursor of the conductive material may be used without particular limitation as long as it is a material that is converted into a conductive material in the process of baking at a relatively low temperature in an atmosphere containing oxygen, for example, an air atmosphere.

The activation method of the present invention is applied to a lithium secondary battery.

In general, a lithium secondary battery includes a positive electrode composed of a positive electrode mixture and a current collector, a negative electrode composed of a negative electrode mixture and a current collector, and a separator capable of blocking electron conduction and conducting lithium ions between the positive electrode and the negative electrode. The void of the membrane material contains an electrolyte for conducting lithium ions.

The positive electrode and the negative electrode are usually prepared by applying a mixture of an electrode active material, a conductive agent and a binder on a current collector and then drying, and a filler may be further added to the mixture as necessary.

The lithium secondary battery to which the present invention is applied can be manufactured according to a conventional method in the art. Specifically, it can be prepared by putting a porous separator between the positive electrode and the negative electrode, the non-aqueous electrolyte.

When applying the activation method according to the present invention, the material is activated even when charging at about 4.4V without the high voltage formation, it is possible to provide a high capacity lithium secondary battery in which the side reaction of the electrolyte caused by the high voltage formation is suppressed.

Such a lithium secondary battery may be preferably used as a unit cell of a medium-large battery module including a plurality of battery cells as well as a battery cell used as a power source of a small device.

Hereinafter, the content of the present invention through the specific examples will be described in more detail.

Example

Manufacture of anode

Li (Li0.2Mn0.55Ni0.15Co0.1) O ₂ was used as a cathode active material, which was 87% by weight of the total cathode mixture, 7% by weight of denca black as a conductive agent, and 6% by weight of PVDF as a binder were added to NMP. A slurry was made. This was coated on aluminum (Al) foil, which is a positive electrode current collector, and rolled and dried to prepare a positive electrode for a lithium secondary battery.

Of lithium secondary battery  Produce

A coin-type lithium secondary battery was manufactured by interposing a separator of porous polyethylene between the positive electrode and the metal lithium negative electrode prepared as described above, and injecting a lithium electrolyte.

battery Formation  And cycle progress

In the formation step, the coin-type lithium secondary battery was charged to CC / CV at a cathode potential of 4.4V at 50 ° C., and then discharged to 2V (C-rate = 0.1C). The cycle was then operated at 4.4V to 3V.

Comparative example

Except that the battery was formed at room temperature other than 50 ℃ for the manufactured lithium secondary battery is the same as the embodiment.

The charge and discharge of the half cell lithium secondary batteries prepared by the above Examples and Comparative Examples were repeated under 0.1C conditions, and the change in capacity according to the cycle was measured, respectively, and the results are shown in FIGS. 1 and 2, respectively. Shown in

Referring to these drawings, the lithium secondary battery of the embodiment, when compared with the lithium secondary battery of the comparative example, the material is effectively activated even at a voltage of 4.4V to realize a high capacity, and the capacity decreases even when the cycle is increased, and 3V ~ It can be seen that the profile is even without a sudden drop in voltage over 4.4V.

That is, the activation method of the lithium secondary battery according to the present invention is Li (Li _x M _{y -y '} M' _{y '} of a layered structure even at a low voltage (for example, 4.4V or less) that can suppress the side reaction of the electrolyte It was confirmed that O _{2 -z} A _z can be effectively activated.

※ Unless otherwise defined, the voltage values described herein refer to the anode potential in a half cell, and are about 0.05 to 0.1V lower depending on the cathode potential in a full cell. For example, 4.6V for half cell (although it depends on the cathode) is about 4.5 ~ 4.55V at full cell voltage when graphite cathode is used.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, the protection scope of the present invention should be interpreted by the following claims and all technical spirits within the equivalent scope thereof. Should be construed as being included in the scope of the present invention.

Claims (12)

In the activation method of a lithium secondary battery comprising a lithium compound having a layered structure represented by the following [Formula 1] as a positive electrode active material,
A method of activating a lithium secondary battery, wherein the cell is formed at a voltage below the flat level at a temperature of 40 to 65 ° C.
[Formula 1] Li (Li _x M _{y - y '} M' _{y '} ) O _{2- z} A _z
Wherein 0 <x <0.5, 0.6 <y <1.1, 0 ≦ y '<0.2, 0 ≦ z <0.2;
M includes Mn and at least one member selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn and Ti;
M 'is one or more selected from the group consisting of Al, Mg and B,
A is at least one member selected from the group consisting of F, S and N.)
The method of claim 1,
The flat level is a method of activating a lithium secondary battery, characterized in that 4.5 ~ 4.8V on the basis of the anode potential.
The method of claim 1,
The formation is a method of activating a lithium secondary battery, characterized in that performed at a voltage below the flat level at a temperature of 45 ~ 60 ℃.
The method of claim 1,
The formation is a method of activating a lithium secondary battery, characterized in that carried out at a voltage of 4.3 ~ 4.5V based on the anode potential at a temperature of 40 ~ 65 ℃.
The method of claim 1,
The formation is a method of activating a lithium secondary battery, characterized in that performed at a voltage of 4.3 ~ 4.5V based on the cathode potential at a temperature of 45 ~ 60 ℃.
The method of claim 1,
The formation is a method of activating a lithium secondary battery, characterized in that performed using a high temperature storage step for wetting of the separator.
The method of claim 1,
The method of activating the lithium secondary battery, characterized in that oxygen is generated from the cathode active material in the flat level section during the formation.
The method of claim 7, wherein
And after the formation, removing the oxygen generated from the cathode active material.
The method of claim 1,
Mn content of the lithium compound of the layered structure represented by the [Formula 1] is 50 to 80 mol% based on the total amount of metals except lithium, characterized in that the activation method of the lithium secondary battery.
The method of claim 1,
The positive electrode active material is lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium to the lithium compound of the layered structure represented by the above [Formula 1] Lithium secondary battery, characterized in that any one or two or more lithium-containing metal oxide selected from the group consisting of cobalt-nickel-manganese oxide, lithium-containing olivine-type phosphate and oxides substituted or doped with ellipsoid (s) Activation method.
The method of claim 10,
The lithium-containing metal oxide is a method of activating a lithium secondary battery, characterized in that contained within 50% by weight of the total cathode active material.
The method of claim 10,
The ellipsoid (s) is any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or an activation method of a lithium secondary battery, characterized in that two or more elements.

Images