KR102010014B1 - Lithium secondary battery and operating method thereof - Google Patents

Abstract

The present invention relates to a lithium secondary battery and a driving method thereof, which maintain a high capacity while suppressing capacity deterioration and improving life characteristics.
The positive electrode active material of _{aLi 2 MnO 3 - (1-} a) by properly controlling the composition of the LiMO _2, activation (formation) voltage, and the operation (operation) voltage to improve the life characteristics while suppressing the capacity degradation of the cycle increased number It is possible to provide a driving method that can.

Description

Lithium secondary battery and driving method thereof

The present invention relates to a lithium secondary battery and a driving method thereof having improved life characteristics while suppressing capacity degradation.

Recently, as the lithium secondary battery is used as a driving power source of a vehicle as well as portable electronic devices such as a mobile phone, a PDA, a laptop computer, and 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 multifunction of portable electronic devices, the demand for increasing the capacity of lithium secondary batteries is increasing, and the SOC used together with the 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 a high capacity lithium secondary battery that can maintain a stable output in the (state of charge) section.

Although lithium metal, sulfur compounds, and the like 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 positive electrode 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 positive electrode 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 oxides have been proposed as positive electrode active materials. 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, and the disadvantages of poor cycle characteristics and high temperature characteristics.

As a result, a layered lithium-containing manganese oxide has been proposed to compensate for the low-volume problem of spinel and to secure excellent thermal safety of the manganese-based active material. In particular, the layered aLi ₂ MnO _3- (1-a) LiMO ₂ with a higher Mn content than the other transition metal (s) has a disadvantage in that its initial irreversible capacity is rather large, but the voltage above 4.5 V based on the anode potential When filled in, very large doses are expressed. In other words, when charging at a relatively high voltage of 4.5 V or more (preferably 4.55 V or more) based on the anode potential during initial charging, a flat level range of 4.5 V to 4.8 V is shown, and 250 mAh / g with excess oxygen gas Seems to have a greater capacity.

However, the aLi ₂ MnO _3- (1-a) LiMO ₂ has a problem in that the output decreases due to the increase in the resistance while decreasing the electrical conductivity in the low SOC section like the general three-component layered cathode active material, and thus the available SOC There is a limit to the interval. In addition, the initial irreversibility is large (depending on the formula, composition, coating, activation conditions, etc., but generally shows an initial efficiency of 70 to 90%). There is a problem that this becomes smaller.

Therefore, in a lithium secondary battery comprising a layered lithium-containing manganese oxide aLi ₂ MnO _3- (1-a) LiMO ₂ as a positive electrode active material, a method for improving life characteristics while suppressing capacity deterioration with increasing cycles It's time for development.

The present invention has been made to solve the above-described conventional problems, the inventors of the present application, after repeated studies and various experiments, the composition of the positive electrode active material aLi ₂ MnO _3- (1-a) LiMO ₂ , Properly control the formation voltage and the operation voltage to suppress the capacity decay with increasing cycle number while providing a wide operating SOC section due to high output characteristics and providing a driving method that can improve the lifetime characteristics. You can do it.

As to solve the above problems, the present invention

A positive electrode comprising a lithium compound having a layered structure represented by the following <Formula 1> as a positive electrode active material; And a cathode;

It provides a lithium secondary battery that is activated at a voltage of 4.40V or less on the basis of its anode potential and has an upper limit of operating voltage of 4.40V or less:

<Formula 1>

aLi ₂ MnO _3- (1-a) LiMO ₂

In the formula,

a is 0.1 <a <0.2,

M is any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or two or more elements are applied at the same time.

According to one embodiment, the upper limit of the operating voltage is 4.20V or less.

According to one embodiment, the upper limit of the operating voltage is 4.10V to 4.20V.

According to one embodiment, the cathode active material is lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide including lithium manganese spinel, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium cobalt-nickel- One or more lithium-containing metal oxides selected from the group consisting of manganese oxides, lithium-containing olivine-type phosphates, and oxides in which ellipsoid (s) are substituted or doped may be additionally mixed. Here, the ellipsoid is selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi. It may be one or more.

According to one embodiment, the lithium-containing metal oxide may be included within 50 parts by weight based on 100 parts by weight of the lithium compound of the layered structure represented by the <Formula 1>.

According to one embodiment, the anode may further include a conductive material.

According to one embodiment, the content of the conductive material may be 0.5 to 15 parts by weight with respect to 100 parts by weight of the lithium compound of the layered structure represented by the <Formula 1>.

According to one embodiment, the negative electrode may be a graphite-based negative electrode.

According to one embodiment, the negative electrode may include at least 85% by weight of one or more selected from natural graphite and artificial graphite.

According to one embodiment, the ratio of the weight per positive electrode area to the weight per negative electrode area may be 1.8 to 2.0.

According to the sun,

A positive electrode comprising a lithium compound having a layered structure represented by the following <Formula 1> as a positive electrode active material; And a negative electrode;

Activating at a voltage of 4.40V or less based on the anode potential; And

It provides a method of driving a lithium secondary battery comprising the step of controlling the upper limit of the operating voltage to 4.40V or less:

<Formula 1>

aLi ₂ MnO _3- (1-a) LiMO ₂

In the formula,

a is 0.1 <a <0.2,

M is any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or two or more elements are applied at the same time.

According to one embodiment, the lithium secondary battery may be used as a unit cell of a battery module that is a power source of medium and large devices. Here, the medium-large device includes a power tool; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric two-wheeled vehicles including E-bikes and E-scooters; Electric Golf Carts; Electric trucks; Electric commercial vehicles; Or it may be a system for power storage.

According to the present invention, in a lithium secondary battery positive electrode comprising a layered lithium-containing manganese oxide aLi ₂ MnO _3- (1-a) LiMO ₂ , according to the increase in the number of cycles by appropriately controlling the composition, activation voltage and operating voltage A large operating SOC section is achieved due to the high level of high capacity and high output characteristics while suppressing capacity degradation.

1 is a graph showing discharge capacity during 500 cycles of a lithium battery obtained in Example 1 and Comparative Examples 1 to 3 and 5. FIG.

Hereinafter, the present invention will be described in detail.

In general, increasing the charge upper limit voltage of the lithium secondary battery increases the capacity, but accelerates the life deterioration. In addition, lowering the operating voltage requires an excess cathode that can accommodate large activation capacities to improve lifetime, while the actual reversible capacity is not large, resulting in poor energy density and economy. If the activation process itself is performed at a low voltage, the capacity under the voltage that can cause activation of the material having the structure of Formula 1 is not large. In addition, when the operating voltage is increased to increase the capacity, deterioration due to the collapse of the structure of the anode occurs, which lowers the endurance life.

However, in the case of the lithium secondary battery including the layered lithium compound of Chemical Formula 1, it is possible to increase the life of the battery while suppressing capacity deterioration due to the increase in the number of cycles by appropriately adjusting the composition, activation voltage and operating voltage of the material. .

To this end, in one embodiment of the present invention, a positive electrode including a lithium compound having a layered structure represented by the following <Formula 1> as a positive electrode active material; And a negative electrode, which is activated at a voltage of 4.40 V or less on the basis of the positive electrode potential, and has an upper limit of an operating voltage of 4.40 V or less.

<Formula 1>

aLi ₂ MnO _3- (1-a) LiMO ₂

In formula, a is 0.1 <a <0.2, M is Al, Mg, Mn, Ni, Co, Cr, V, Fe, any one element chosen from the group, or two or more elements are applied simultaneously.

The lithium secondary battery limits the activation (formation) voltage to 4.40V or less, and limits the upper limit (upper charge voltage) of the operating voltage to 4.40V or less to suppress the structural change of the compound due to the reaction of Li ₂ MnO ₃ . Improved stability prevents battery degeneration, resulting in a wide operating SOC section due to high capacity of 170mAh / g, long life over 1000 cycles, and high output characteristics.

The lithium compound having a layered structure represented by Chemical Formula 1 includes Mn as an essential transition metal, and the content of Mn is higher than that of other metals except lithium, and a lithium transition metal oxide expressing a large capacity through activation.

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.

In addition, the lithium compound of the layered structure, unlike other conventional cathode active materials, has a certain level of flatness above the oxidation / reduction potential caused by the oxidation number change of the components in the cathode active material. 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 of the layered structure and use it at a high capacity according to the purpose, the cell should be charged at a high voltage above the flat level in the activation step, and in this case, a capacity of 170 mAh / g is exhibited.

In the present invention, the lithium secondary battery including the lithium compound of Formula 1 as the positive electrode active material for the above activation can be performed by charging by activating at an upper voltage of 4.40V or less, for example, 4.15V to 4.35V. Will be.

As described above, the lithium secondary battery according to an embodiment has an operating voltage having an upper limit of 4.40V or less, for example, a value of 4.35V or less, or 4.15V to 4.35V. In such a range, the structural change of the compound due to the reaction of Li ₂ MnO ₃ is suppressed, and as a result, an increase in resistance in the low SOC section is prevented.

According to one embodiment, the positive electrode active material, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide including lithium manganese spinel, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium cobalt-nickel One or more lithium-containing metal oxides selected from the group consisting of manganese oxides, lithium-containing olivine-type phosphates and oxides in which ellipsoid (s) are substituted or doped may be further mixed. Here, the ellipsoid is selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi. It may be one or more kinds.

According to one embodiment, the lithium-containing metal oxide may be included within 50 parts by weight based on 100 parts by weight of the lithium compound of the layered structure represented by the formula (1).

In addition, the anode may further include a conductive material in addition to the composite.

By applying an appropriate conductive system, the output characteristics of the battery can be further improved by increasing the overall conductivity of the cathode active material layer. The method of including the conductive material is not particularly limited, and conventional methods known in the art, such as coating on the positive electrode active material, may be adopted.

The content of the conductive material is preferably 0.5 to 15 parts by weight based on 100 parts by weight of the lithium compound having a layered structure represented by Chemical Formula 1. When the content of the conductive material satisfies this range, the effect of applying the conductive system can be expected, and the amount of the positive electrode active material can be relatively reduced, thereby preventing the problem of decreasing capacity.

The conductive material is not particularly limited as long as the conductive material has excellent electrical conductivity and does not cause side reactions in the internal environment of the lithium secondary battery. However, graphite or a highly conductive carbon-based material is particularly preferable. In some cases, of course, 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 the material 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 graphite and the conductive carbon are also not particularly limited as long as they have excellent electrical conductivity and have conductivity without causing side reactions in the internal environment of the lithium secondary battery or causing chemical changes in the battery.

Specifically, the graphite is not limited to natural graphite or artificial graphite, and the conductive carbon is preferably a highly conductive carbon-based material, specifically, carbon black, acetylene black, Ketjen black, channel black, furnace black, Carbon black, such as lamp black, summer black, or a mixture of one or more selected from the group consisting of a material having a crystal structure including graphene or graphite may be used.

According to one embodiment, a positive electrode including a lithium compound having a layered structure represented by the following formula (1) as a positive electrode active material; And a negative electrode, comprising: activating at a voltage of 4.40V or less based on a positive electrode potential; And controlling an upper limit value of the operating voltage to 4.40 V or less.

<Formula 1>

aLi ₂ MnO _3- (1-a) LiMO ₂

In formula, a is 0.1 <a <0.2, M is Al, Mg, Mn, Ni, Co, Cr, V, Fe, any one element chosen from the group, or two or more elements are applied simultaneously.

The cathode active material layer including the cathode active material, the activation step, the upper limit of the operating voltage, and the like have been described above.

The lithium secondary battery includes a positive electrode composed of a positive electrode active material layer and a current collector, a negative electrode composed of a negative electrode active material layer and a current collector, and a separator capable of blocking electron conduction and conducting lithium ions between the positive electrode and the negative electrode. And 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 material and a binder on a current collector and then drying, and a filler may be further added to the mixture as necessary.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Conductive fibers such as carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and summer black, carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. In some cases, addition of the conductive material may be omitted by adding a conductive second coating layer to the positive electrode active material.

The binder is a component that assists the bonding of the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

The filler is optionally used as a component for inhibiting the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention also provides a cathode in which a cathode active material layer including the cathode active material is included on a current collector.

For example, the secondary battery positive electrode is dried and rolled after applying a slurry prepared by mixing a positive electrode mixture such as a positive electrode active material, a conductive material, a binder, and a filler to a solvent such as NMP on a positive electrode current collector on a negative electrode current collector. Can be prepared.

The positive electrode current collector is generally made to a thickness of 3 to 500㎛. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver, or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric.

The present invention also provides a lithium secondary battery composed of the positive electrode, the negative electrode, the separator, and the lithium salt-containing nonaqueous electrolyte.

For example, the negative electrode may be manufactured by applying and drying a negative electrode mixture including a negative electrode active material on a negative electrode current collector, and the negative electrode mixture may further include components as described above as necessary.

As the negative electrode, a graphite negative electrode may be used, and for example, one or more of natural graphite and artificial graphite may be used. In this case, their content may be about 85% by weight to 100% by weight based on the total weight of the negative electrode.

The negative electrode current collector is generally made of a thickness of 3 to 500㎛. The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel , Surface treated with nickel, titanium, silver, or the like, an aluminum-cadnium alloy, or the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The separator is interposed between the cathode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polyethylene and polypropylene; Porous substrates such as films, sheets or nonwovens made of glass fibers or polyethylene terephthalate are used. In addition, a porous coating layer including inorganic particles and a binder polymer may be formed on at least one surface of the porous substrate. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The said lithium salt containing non-aqueous electrolyte solution consists of a nonaqueous electrolyte solution and a lithium salt. As the nonaqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dime Methoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, pyrion An aprotic organic solvent such as methyl acid or ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 C l1 0, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, _{LiAsF 6, LiSbF 6, LiAlCl 4} , CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide Can be.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

According to one embodiment, in the lithium secondary battery employing a positive electrode and a graphite-based negative electrode comprising a lithium compound of the layered structure represented by the formula (1), the ratio of the weight per positive electrode area to the weight per negative electrode area is about 1.7 to about 2.2, For example, in the range from about 1.8 to about 2.0. In this case, when the ratio of the weight per positive electrode area to the weight per negative electrode area is greater than 2.2, the energy density of the secondary battery may be low, and when it is less than 1.7, the life characteristics of the secondary battery may be reduced.

In the present invention, a secondary battery may be used as a single unit, and a secondary battery according to the present invention may be used as a unit cell, and a medium / large battery pack including a plurality of unit cells stacked and packaged, or a medium / large battery pack including such a medium / large module. Can be.

In particular, the secondary battery according to the present invention may be preferably used in a high output large capacity battery requiring a long life and excellent durability, or a medium-large battery module or a medium-large battery pack including a plurality of such cells as a unit cell.

The medium-large battery pack includes a power tool; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric two-wheeled vehicles including E-bikes and E-scooters; Electric golf carts; Electric trucks; It can be used as a power source for electric commercial vehicles.

Since the structure and manufacturing method of such a medium-large battery module or a medium-large battery pack are well known in the art, a detailed description thereof will be omitted herein.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, which are merely illustrative and are not intended to limit the present invention.

Example

-Manufacture of anodes

805% by weight of a layered lithium compound having a composition of 0.15Li ₂ MnO ₃ .0.85LiMn _0.33 Ni _0.33 Co _0.33 O ₂ , 7% by weight graphite and 7% by weight Ketjenblack was formed to form a composite, followed by PVDF 6% by weight. A positive electrode active material slurry was prepared by mixing in NMP solvent.

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.

-Manufacturing of Lithium Secondary Battery

The coin cell was manufactured using the anode prepared as described above, the graphite counter electrode, the separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ . The ratio of the weight per positive electrode area to the weight per negative electrode area was 1.9.

The coin battery prepared above was charged to 4.35V based on the potential of the cathode, and then discharged to perform formation. (C-rate = 0.1C)

The capacity was measured by setting the upper limit of the operating voltage to 4.35V and performing cycles in the voltage range of 4.35V to 2.5V up to 500 times. The measurement result is shown in FIG.

At the initial charge capacity of 185 mAh / g, the initial discharge capacity was 170 mAh / g, and the reversible capacity was 170 mAh / g. There was no significant change over 500 cycles thereafter. Therefore, it can be seen that the endurance life characteristics are improved.

Comparative Example 1

-Manufacture of anodes

0.5Li ₂ MnO ₃ 0.5LiMn _0.33 Ni _0.33 Co _0.33 O ₂ 80% by weight of the layered lithium compound, 7% by weight of graphite and 7% by weight of ketjenblack to form a composite, followed by 6% by weight of PVDF A positive electrode active material slurry was prepared by mixing in NMP solvent.

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.

-Manufacturing of Lithium Secondary Battery

The coin cell was manufactured using the anode prepared as described above, the graphite counter electrode, the separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ . The ratio of the weight per positive electrode area to the weight per negative electrode area was 1.2.

The coin battery prepared above was charged to 4.60V based on the positive electrode potential, and then discharged to perform formation. (C-rate = 0.1C)

The capacity was measured by setting the upper limit of the operating voltage to 4.60V and performing cycles in the voltage range of 4.6V to 2.5V up to 150 times. The measurement result is shown in FIG.

The initial discharge capacity was 250mAh / g and the reversible capacity was 250mAh / g at the initial charge capacity of 300mAh / g. The initial dose was very high, but then the dose dropped sharply.

Comparative Example 2

-Manufacture of anodes

_{0.5Li 2 MnO 3 · 0.5LiMn 0 .33} Ni 0 .33 _{0 .33} after the formation of the Co ₂ O composition having a layered structure of lithium compound to 80% by weight, 7% by weight graphite, and Ketjen black composite material by milling a 7% by weight, A positive electrode active material slurry was prepared by mixing in 6% by weight of PVDF in an NMP solvent.

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.

-Manufacturing of Lithium Secondary Battery

The coin cell was manufactured using the anode prepared as described above, the graphite counter electrode, the separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ . The ratio of the weight per positive electrode area to the weight per negative electrode area was 1.5.

The coin battery prepared above was charged to 4.60V based on the positive electrode potential, and then discharged to perform formation. (C-rate = 0.1C)

The capacity was measured by setting the upper limit of the operating voltage to 4.35V and performing cycles in the voltage range of 4.35V to 2.5V up to 300 times. The measurement result is shown in FIG.

The initial discharge capacity was 250mAh / g and the reversible capacity was 210mAh / g at the initial charge capacity of 300mAh / g. Initial capacity was very high, but the capacity dropped sharply after 250 cycles.

Comparative Example 3

-Manufacture of anodes

0.5Li ₂ MnO ₃ 0.5LiMn _0.33 Ni _0.33 Co _0.33 O ₂ 80% by weight of the layered lithium compound, 7% by weight of graphite and 7% by weight of ketjenblack to form a composite, followed by 6% by weight of PVDF A positive electrode active material slurry was prepared by mixing in NMP solvent.

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.

-Manufacturing of Lithium Secondary Battery

The coin cell was manufactured using the anode prepared as described above, the graphite counter electrode, the separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ . The ratio of weight per positive electrode area to weight per negative electrode area was 2.5.

The coin battery prepared above was charged to 4.35V based on the potential of the cathode, and then discharged to perform formation. (C-rate = 0.1C)

The capacity was measured by setting the upper limit of the operating voltage to 4.35V and performing cycles in the voltage range of 4.35V to 2.5V up to 200 times. The measurement result is shown in FIG.

The initial discharge capacity was 120mAh / g and the reversible capacity was 120mAh / g at the initial charge capacity of 130mAh / g. Initial dose showed low levels.

Comparative Example 4

-Manufacture of anodes

80% by weight of the layered lithium compound having a composition of LiMn _0.33 Ni _0.33 Co _0.33 O ₂ , 7% by weight of graphite, and 7% by weight of ketjen black were formed to form a composite, and then mixed with 6% by weight of PVDF in an NMP solvent to form a cathode active material. Slurry was prepared.

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.

-Manufacturing of Lithium Secondary Battery

The coin cell was manufactured using the anode prepared as described above, the graphite counter electrode, the separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ . The ratio of the weight per positive electrode area to the weight per negative electrode area was 2.2.

The coin battery prepared above was charged to 4.15V based on the anode potential, and then discharged to perform formation. (C-rate = 0.1C)

The capacity was measured by setting the upper limit of the operating voltage to 4.15V and performing cycles in the voltage range of 4.15V to 2.5V up to 200 times. The initial discharge capacity was 145 mAh / g at 165 mAh / g and the reversible capacity was 145 mAh / g. Initial dose showed low levels.

Comparative Example 5

-Manufacture of anodes

80% by weight of the layered lithium compound having a composition of LiMn _0.33 Ni _0.33 Co _0.33 O ₂ , 7% by weight of graphite, and 7% by weight of ketjen black were formed to form a composite, and then mixed with 6% by weight of PVDF in an NMP solvent to form a cathode active material. Slurry was prepared.

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.

-Manufacturing of Lithium Secondary Battery

The coin cell was manufactured using the anode prepared as described above, the graphite counter electrode, the separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ . The ratio of the weight per positive electrode area to the weight per negative electrode area was 1.9.

The coin battery prepared above was charged to 4.35V based on the potential of the cathode, and then discharged to perform formation. (C-rate = 0.1C)

The capacity was measured by setting the upper limit of the operating voltage to 4.35V and performing cycles in the voltage range of 4.35V to 2.5V up to 400 times. The measurement result is shown in FIG.

At the initial charge capacity of 185 mAh / g, the initial discharge capacity was 170 mAh / g, and the reversible capacity was 170 mAh / g. Dose decay was observed rapidly as the cycle progressed at the initial dose.

As can be seen from the above results, it can be seen that in Example 1, an initial capacity of an appropriate level was obtained by limiting the composition, activation voltage, and operating voltage of the cathode active material, and at the same time, the durability life characteristics were improved.

On the contrary, in Comparative Examples 1 to 5, it can be seen that the capacity retention rate is drastically reduced due to high activation voltage, high or low operating voltage, or improper composition of the positive electrode active material.

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 are intended to be described. It should be interpreted as being included in the scope of the present invention.

Claims (15)

A cathode including a lithium compound having a layered structure represented by the following Chemical Formula 1 as a cathode active material; And a cathode;
A lithium secondary battery activated at a voltage of 4.15 V to 4.35 V based on the anode potential and having an upper limit of operating voltage of 4.40 V or less:
<Formula 1>
aLi ₂ MnO _3- (1-a) LiMO ₂
In the formula,
a is 0.1 <a <0.2,
M is any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or two or more elements are applied at the same time. The method of claim 1,
The upper limit of the operating voltage is 4.15V to 4.35V lithium secondary battery. The method of claim 1,
Lithium secondary battery wherein the negative electrode is a graphite negative electrode. The method of claim 1,
Lithium secondary battery wherein the negative electrode comprises at least one of natural graphite and artificial graphite. The method of claim 4, wherein
At least one of the natural graphite and artificial graphite content of more than 85% by weight based on the weight of the negative electrode lithium secondary battery. The method of claim 1,
A lithium secondary battery having a ratio of the weight per positive electrode area to the weight per negative electrode area of 1.8 to 2.0. The method of claim 1,
The cathode active material may be 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 One or more lithium-containing metal oxides selected from the group consisting of substituted or doped oxides of other elements are additionally mixed, and the ellipses are Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B And at least one member selected from the group consisting of Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi. The method of claim 7, wherein
Lithium secondary battery that the lithium-containing metal oxide is contained within 50 parts by weight based on 100 parts by weight of the lithium compound of the layered structure represented by the formula (1). The method of claim 1,
Lithium secondary battery that the positive electrode further comprises a conductive material. The method of claim 9,
Lithium secondary battery that the content of the conductive material is 0.5 to 15 parts by weight based on 100 parts by weight of the lithium compound of the layered structure represented by the formula (1). The method of claim 1,
Lithium secondary battery further comprises a separator interposed between the positive electrode and the negative electrode. The method of claim 1,
A lithium secondary battery further comprising a lithium salt-containing non-aqueous electrolyte. A cathode including a lithium compound having a layered structure represented by the following Chemical Formula 1 as a cathode active material; And a negative electrode;
Activating at a voltage of 4.15 V to 4.35 V based on the anode potential; And
Controlling the upper limit of the initial operating voltage to 4.40V or less; driving method of a lithium secondary battery comprising:
<Formula 1>
aLi ₂ MnO _3- (1-a) LiMO ₂
In the formula,
a is 0.1 <a <0.2,
M is any one element selected from the group consisting of Al, Mg, Mn, Ni, Co, Cr, V, Fe, or two or more elements are applied at the same time. The method according to any one of claims 1 to 12,
The lithium secondary battery is used as a unit cell of the battery module which is the power source of the medium and large devices. The method of claim 14,
The medium-to-large size device includes a power tool; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric two-wheeled vehicles including E-bikes and E-scooters; Electric Golf Carts; Electric trucks; Electric commercial vehicles; Or a lithium secondary battery that is a system for power storage.

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