KR101650568B1 - Pre-treatment method of cathode active material - Google Patents

Abstract

More particularly, the present invention relates to a method for pretreatment of a cathode active material. More particularly, it is necessary to formulate the cathode active material at a high voltage for initial activation. In the activation process, a large irreversible capacity and a large amount of gas are generated. A method of pretreating a cathode active material which enables activation of a Mn-rich material at a low voltage, reduces an initial irreversible capacity, and improves capacity and lifetime characteristics by performing a Li decontamination treatment, To a lithium secondary battery.

Description

PRE-TREATMENT METHOD OF CATHODE ACTIVE MATERIAL [0002]

More particularly, the present invention relates to a method for pretreatment of a cathode active material. More particularly, it is necessary to formulate the cathode active material at a high voltage for initial activation. In the activation process, a large irreversible capacity and a large amount of gas are generated. A method of pretreating a cathode active material which enables activation of a Mn-rich material at a low voltage, reduces an initial irreversible capacity, and improves capacity and lifetime characteristics by performing a Li decontamination treatment, To a lithium secondary battery.

2. Description of the Related Art In recent years, lithium secondary batteries have been used in many fields including portable electronic devices such as mobile phones, PDAs, and laptop computers. Especially, as the interest in environmental problems grows, it is one of the main causes of air pollution. As a driving source of electric vehicles that can replace fossil fuel vehicles such as gasoline vehicles and diesel vehicles, lithium secondary batteries Research on batteries has been actively conducted, and some of them are in the commercialization stage. On the other hand, in order to use lithium secondary battery as a driving source of such electric vehicles, it is necessary to maintain a stable output in a wide range of state of charge (SOC) in addition to a high output.

LiCoO ₂ , which is a typical positive electrode material as a cathode material of a high capacity lithium secondary battery, has reached the practical limit of an increase in energy density and output characteristics. Especially, when it is used in a high energy density application field, State, it releases oxygen in the structure and generates an exothermic reaction with the electrolyte in the cell, thereby becoming the main cause of the explosion of the battery. In order to solve the safety problem of LiCoO ₂ , a lithium-containing manganese oxide such as a layered crystal structure of LiMnO ₂ , a spinel crystal structure of LiMn ₂ O ₄ and LiNiO ₂ (Mn) is added to the layered lithium manganese oxide as a necessary transition metal in a larger amount than other transition metals (excluding lithium). (Hereinafter also referred to as "Mn-rich"

Formula 1

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

In order for the Mn-rich to exhibit a high capacity, a formation process through overcharging at a high voltage is indispensably required. That is, the Mn-rich has a flat level at a certain level above the oxidation / reduction potential represented by the oxidation number of the constituent components in the cathode active material. Specifically, when overcharging at a high voltage of 4.45 V or more based on the cathode potential, And has a flat level section in the range of 4.45 to 4.8V.

Li ₂ MnO ₃ - &^gt; ₂ Li ⁺ MnO ₃ ^- + e ^- // MnO ₃ ^- - > 1 / 2O ₂ + MnO ₂ + e ^-

MnO ₂ + Li ⁺ + e ^- - > LiMnO ₂

However, when the Mn-rich is activated through the formation at high voltage, the cathode is excessively designed for balancing with the anode due to the low initial efficiency of Mn-rich (i.e., large irreversible charging capacity) And side reactions such as oxidation of electrolytic solution may occur at a high voltage and gas such as oxygen and carbon dioxide is generated from the Mn-rich, which makes it difficult to obtain a stable service life thereafter.

In order to solve this problem, a method of leaching out Li ₂ O by treating Mn-rich powder with a strong acid has been proposed. However, in this case, material is greatly damaged, and Li-H exchange Side reactions may occur during the cycle.

Accordingly, Mn-rich material, which has been attracting attention as a cathode material of a lithium secondary battery, can be effectively and stably pretreated to enable Mn-rich to be activated at a relatively low voltage and to reduce initial irreversible capacity, It is time to develop a technology that can control overuse and improve capacity and lifetime characteristics.

Korean Patent Laid-Open No. 10-2009-0006897

It is an object of the present invention to solve the above-mentioned problems and to solve the conventional problems. It is an object of the present invention to solve the problems of a Mn-rich material in which a large amount of irreversible charging capacity is generated along with a large irreversible capacity during the initial activation process, And to provide a cathode material.

In order to accomplish the above object, the present invention provides a pretreatment method for a positive electrode active material represented by the following Chemical Formula 1, characterized in that it includes a reduction treatment and a Li consumption treatment at the same time:

Formula 1

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

In Formula 1,

0 &lt; x < 1,

0.9? Y? 1.2,

M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,

According to another aspect of the present invention, there is provided a cathode active material represented by Chemical Formula 1, which is pretreated by the above method.

According to still another aspect of the present invention, there is provided a lithium secondary battery comprising the cathode active material.

The lithium secondary battery including the Mn-rich pretreated according to the present invention can be activated at a relatively low voltage and the initial irreversible capacity is reduced and excessive use of a cathode (for example, a graphite-based cathode) for balancing with an anode And the capacity and lifetime characteristics and rate characteristics of the battery are greatly improved.

In addition, a passivation film may be formed on the surface of the cathode active material to improve the performance of the battery.

1 to 3 are graphs showing cell characteristics of a lithium secondary battery according to the present invention.

Hereinafter, the present invention will be described in detail.

Cathode active material  Pretreatment method

The pretreatment method of the present invention is a pretreatment of a layered positive electrode active material (Mn-rich) represented by the following general formula (1), and includes reduction treatment and Li consumption treatment at the same time.

Formula 1

xLi ₂ MnO ₃ (1-x) Li _y MO ₂

Wherein M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg and < RTI ID = 0.0 &gt; B. &lt; / RTI &gt;

The layered manganese oxide (Mn-rich) represented by the above formula (1) contains Mn as an essential transition metal. The content of Mn is larger than the content of other metals except lithium, and a large capacity when overcharged at a high voltage It is a type of lithium transition metal oxide that is expressed.

Mn contained as an essential transition metal in the lithium manganese oxide of the layered structure is contained in a larger amount than other metals (excluding lithium), and it is preferably 50 to 80 mol% based on the total amount of metals except lithium Do. If the content of Mn is too small, the safety may be lowered and the manufacturing cost may increase, and it may be difficult to exhibit the unique characteristics of the Mn-rich. Conversely, if the content of Mn is too large, the cycle stability may be deteriorated.

In order for the Mn-rich to exhibit a high capacity, a formation process through overcharging at a high voltage is indispensably required. That is, the Mn-rich has a flat level at a certain level above the oxidation / reduction potential due to the change in the oxidation number of constituent components in the cathode active material. Specifically, in the region of 4.45 ~ 4.8V overcharging at a high voltage of 4.45V or more based on the anode potential, And has a flat level section.

However, when the Mn-rich is activated through the formation at high voltage, the cathode is excessively designed for balancing with the anode due to the low initial efficiency of Mn-rich (i.e., large irreversible charging capacity) And side reactions such as oxidation of electrolytic solution may occur at a high voltage and gas such as oxygen and carbon dioxide is generated from the Mn-rich, which makes it difficult to obtain a stable service life thereafter.

In order to solve this problem, a method of leaching out Li ₂ O by treating Mn-rich powder with a strong acid has been proposed. However, in this case, material is greatly damaged and Li-H exchange ), Side reactions may occur during the cycle.

In view of the above, the present invention can be applied to Mn-rich simultaneously with reduction treatment and Li-consumption treatment, without depending on the conventional acid treatment method, so that Mn-rich can be activated at a relatively low voltage and the initial irreversible capacity is reduced, For example, a graphite-based cathode), and to improve capacity and lifetime characteristics.

The pretreatment method of the present invention is capable of effectively extracting Li ₂ O from Mn-rich without depending on an acid treatment method, and provides a result similar to the chemical activation of Mn-rich. As a result, In addition, the amount of gas generated during formation can be minimized.

In the present invention, the "reduction treatment" is a step of extracting and removing some oxygen (O) in the Mn-rich structure. As a result, the transition metal constituting the Mn-rich is reduced (decreased in oxidation number) ) Characteristics are also improved.

The method for reducing Mn-rich is not particularly limited, and methods known in the art such as treatment with a reducing gas can be used.

In one embodiment, the reduction treatment may be performed at 150 to 250 ° C by at least one gas selected from the group consisting of H ₂ and N ₂ . More specifically, the Mn-rich material is exposed to H ₂ / N ₂ It can be treated with gas to extract oxygen (O) in the Mn-rich structure and reduce the transition metal.

In another embodiment, at least one gas selected from the group consisting of Ar and N ₂ (for example, Ar / N ₂ Gas) can be performed. The present inventors have found that when the Mn-rich is reduced at a high temperature, the capacity, cycle characteristics and lifetime characteristics are greatly improved. To prove this fact, Mn-rich is converted to air and argon When the reduction treatment was performed for 12 hours, the characteristics of each cell were measured and shown in Figs. 1 to 3, respectively.

"Li-consuming process" in the invention is Mn-rich some Li in the structure as the process of extracting, removing, conclusion, Li ₂ O, some extracted from the first structure via a combination of the above-mentioned reduction treatment, the removed form Mn -rich can be obtained. In addition, in the present invention, the reduction treatment and the Li consumption treatment are performed in parallel to control the stoichiometry or the unbalanced oxidation caused by the removal of some oxygen (O) in the Mn-rich structure through reduction treatment. Specifically, since Mn-rich in which some oxygen (O) is removed can receive oxygen again when exposed to air, it is possible to pretreat Mn-rich more stably and effectively by applying the Li reduction treatment together with the reduction treatment have.

The irreversible capacity generated when the Mn-rich is used is reduced through the Li dissipation process, thereby controlling excessive design of the cathode. At the same time, a passivation film is formed directly on the surface of the Mn-rich material, such as LiF, And can enjoy the surface protection (passivation) effect of the material.

There is no particular limitation on the method for treating the Mn-rich with Li, and methods for extracting or removing Li from the cathode material for the lithium secondary battery such as the F treatment and the S treatment can be freely used.

In one embodiment, Li consumption treatment can be performed by at least one selected from F ₂ gas and (NH ₄ ) ₂ SO ₄ . Among them, when F ₂ gas is used, a LiF film is formed as a passivation film on the surface of the material. (NH ₄ ) ₂ SO ₄ is used, a Li ₂ SO ₄ film is formed as a passivation film, and it is more preferable that some spinel structure can be formed on the surface of the material.

The reduction treatment and the Li consumption treatment can be performed simultaneously or sequentially, and the order of treatment is not necessarily limited.

Cathode active material  And Lithium secondary battery

The cathode active material of the present invention is a Mn-rich cathode active material represented by the above formula (1), which is pretreated by the above-mentioned method. Specifically, the cathode active material of the present invention has a form in which Li ₂ O is partially extracted from the original structure through the reduction treatment and the Li consumption treatment described above, and unlike the conventional Mn-rich material which is not subjected to the pretreatment, You can.

In addition, the cathode active material of the present invention has a very small amount of generated gas such as oxygen and carbon dioxide during the activation process, thereby significantly improving lifetime characteristics of the cell.

In addition, the positive electrode active material of the present invention can realize a higher capacity than the same active material not subjected to the pretreatment.

The negative electrode material including the positive electrode active material according to the present invention and a negative electrode material including a negative electrode active material to be described later may further include a conductive material for improving electrical conductivity.

The conductive material is not particularly limited as long as it does not cause side reactions in the internal environment of the lithium secondary battery and does not cause chemical change in the battery, and has excellent electrical conductivity. Typically, graphite or conductive carbon can be used.

For example, graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, black black, thermal black, channel black, furnace black, lamp black, and summer black; A carbon-based material whose crystal structure is graphene or graphite; Conductive fibers such as carbon fiber and metal fiber; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And polyphenylene derivatives may be used singly or in combination of two or more, but the present invention is not limited thereto.

The conductive material is usually added in an amount of 0.5 to 50 parts by weight, specifically 1 to 15 parts by weight, more specifically 3 to 10 parts by weight, based on 100 parts by weight of the total weight of the electrode material including the active material. If the content of the conductive material is less than 0.5 parts by weight, the effect of improving electrical conductivity may not be expected or the electrochemical characteristics of the battery may deteriorate. If the content of the conductive material exceeds 50 parts by weight, The capacity and the energy density may be lowered.

The method of including the conductive material in the electrode material is not particularly limited, and conventional methods known in the art such as coating on the active material can be used. In some cases, the conductive second coating layer is added to the active material, so that the conductive material may be added instead.

The electrode material may further include a binder as a component for assisting in bonding of the active material and the conductive material and bonding to the current collector.

Examples of the binder include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene (Meth) acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polyvinyl pyrrolidone, styrene Butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluorine rubber, carboxymethylcellulose (CMC), starch, hydroxypropyl At least one selected from the group consisting of celluloses, regenerated celluloses, and mixtures thereof may be used. However, It is not.

The binder is usually added in an amount of 1 to 50 parts by weight, more specifically 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the electrode material including the active material. If the content of the binder is less than 1 part by weight, the adhesive force between the active material and the current collector may be insufficient. If the amount of the binder is more than 50 parts by weight, the adhesive strength may be improved, but the content of the active material may be decreased.

A filler may be optionally added to the electrode material as a component for suppressing the expansion of the electrode.

The filler is not particularly limited as long as it can inhibit the expansion of the electrode without causing chemical change in the battery, and includes, for example, an olefin polymer such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers; Etc. may be used.

The lithium secondary battery of the present invention includes a Mn-rich cathode active material pretreated by the above method. Specifically, the lithium secondary battery of the present invention includes a positive electrode including Mn-rich pretreated through reduction treatment and Li dissolution treatment; And a negative electrode including a negative electrode active material.

Generally, a lithium secondary battery is composed of a positive electrode composed of a positive electrode material and a current collector, a negative electrode composed of a negative electrode material and a current collector, and a separator for blocking electrical contact between the positive electrode and the negative electrode and moving lithium ions, Includes an electrolyte solution for conducting lithium ions.

The positive electrode and the negative electrode may be produced by a conventional method known in the art. For example, a slurry is prepared by dispersing and mixing one or more kinds of a cathode active material or a negative electrode active material, a conductive material, a binder, and a filler (if necessary) in a dispersion medium (solvent) An anode and a cathode can be manufactured.

As the cathode active material, a mixture of Mn-rich or other cathode materials pretreated according to the method of the present invention may be used.

Examples of the negative electrode active material include lithium metal, a lithium alloy (e.g., an alloy of lithium and aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium), amorphous carbon, crystalline carbon, And SnO ₂ may be used, but are not limited thereto. Specifically, a carbon-based material such as graphite can be used as the negative electrode active material.

The dispersion medium may be N-methyl-2-pyrrolidone (DMF), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water or mixtures thereof.

The current collector may include at least one of platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS) (SnO ₂ ), FTO (F doped SnO ₂ ), and the like, and a metal oxide such as copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten Or a surface treated with carbon (C), nickel (Ni), titanium (Ti) or silver (Ag) on the surface of aluminum (Al), copper (Cu) or stainless steel. But the present invention is not limited thereto. Specifically, aluminum is used for the positive electrode collector and copper is used for the negative electrode collector. The current collector may be in the form of a foil, a film, a sheet, a punched, a porous body, a foam or the like.

The separation membrane is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and to provide a movement path of lithium ions.

As the separation membrane, an olefin-based polymer such as polyethylene or polypropylene, glass fiber or the like may be used in the form of a sheet, a multilayer, a microporous film, a woven fabric and a nonwoven fabric, but is not limited thereto. On the other hand, when a solid electrolyte such as a polymer (for example, an organic solid electrolyte, an inorganic solid electrolyte or the like) is used as the electrolyte, the solid electrolyte may also serve as a separation membrane. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally in the range of 0.01 to 10 mu m, and the thickness may generally be in the range of 5 to 300 mu m.

As the electrolyte solution, carbonate, ester, ether, or ketone may be used alone or as a mixture of two or more of them as a non-aqueous liquid electrolyte (non-aqueous organic solvent), but the present invention is not limited thereto.

Examples of the solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylenecarbonate, butylene carbonate, gamma-butylolactone, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydroxyfurfane, 2-methyltetrahydrofuran Dimethylformamide, dioxolane and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dioxolane, Dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used. However, It is not.

(Lithium salt-containing non-aqueous electrolyte solution), and the lithium salt may be a known one which is soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO _{4 , LiBF 4, LiB 10 Cl 10} , LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiPF 3 (CF 2 CF 3) 3, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, imide, and the like, but not always limited thereto.

The above (non-aqueous) electrolytic solution may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The lithium secondary battery of the present invention can be produced by a conventional method in the art. For example, a porous separator may be interposed between the prepared anode and cathode, and a non-aqueous electrolyte may be added.

In one embodiment, the step of pretreating the lithium secondary battery of the present invention is a simultaneous application of Mn-rich to reduction treatment and Li consumption treatment; Preparing an anode comprising pretreated Mn-rich; A negative electrode comprising a negative electrode active material (e.g., carbon-based); Forming a battery unit with a separator interposed between the positive electrode and the negative electrode, and injecting the battery unit into the battery case; Injecting an electrolyte into the battery case and activating the electrolyte solution; And a degassing step.

The lithium secondary battery of the present invention can be activated at a relatively low voltage and can lower the initial irreversible capacity by including the Mn-rich pretreated as described above as a cathode active material. The capacity, lifetime and rate characteristics of the battery Greatly improved.

Therefore, the lithium secondary battery of the present invention can be suitably used as a unit cell of a battery module, which is a power source of a medium and large-sized device as well as a battery cell used as a power source of a small device. The medium and large devices include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); An electric motorcycle including an E-bike and an E-scooter; Electric golf cart; Electric truck; Electric commercial vehicle; And a system for power storage; , But the present invention is not limited thereto.

In this respect, the present invention also provides a battery module in which the lithium secondary battery 2 or more is connected in series or in parallel. It is needless to say that the number of lithium secondary batteries included in the battery module may be variously controlled in consideration of the use and capacity of the battery module. Further, the present invention provides a battery pack in which the battery module is electrically connected according to a conventional technique.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. The scope of the present invention should be interpreted based on the scope of the following claims and all technical ideas within the scope of equivalents thereof are to be construed as being included in the scope of the present invention. It is to be understood that the invention is not limited thereto.

Claims (10)

A reduction treatment and a Li consumption treatment at the same time,
The reduction treatment is performed by at least one gas selected from the group consisting of Ar and N ₂ at a temperature of 900 ° C or higher,
A method for pretreating a cathode active material represented by the following formula (1), wherein the Li dissolution treatment is performed by (NH ₄ ) ₂ SO ₄ :
Formula 1
xLi ₂ MnO ₃ (1-x) Li _y MO ₂
In Formula 1,
0 &lt; x < 1,
0.9? Y? 1.2,
M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,
The method according to claim 1,
Wherein the reduction treatment and the Li consumption treatment are performed simultaneously or sequentially.
delete delete delete A pretreatment method as claimed in claim 1 or 2,
A passivation film is formed on the surface of the positive electrode active material,
The cathode active material according to claim 1, wherein the passivation film is a Li ₂ SO ₄ film.
Formula 1
xLi ₂ MnO ₃ (1-x) Li _y MO ₂
In Formula 1,
0 &lt; x < 1,
0.9? Y? 1.2,
M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al,
The method according to claim 6,
Wherein the cathode active material has a form in which a part of Li ₂ O is extracted from the original structure.
delete delete A lithium secondary battery comprising the cathode active material according to claim 6.

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