KR102010015B1 - Lithium secondary battery and operating method thereof - Google Patents

Abstract

The present invention relates to a lithium secondary battery and a driving method thereof having improved life characteristics while suppressing capacity degradation.
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 the problem that the output decreases due to the increase in the resistance while decreasing the electrical conductivity in the low SOC region, as in the case of the general three-component layered cathode active material. There is a limit to the SOC interval. In addition, the initial irreversibility is large (depending on the formulation, composition, coating, activation conditions, etc., but generally shows an initial efficiency of 70-90%). 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 cathode 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 conceived to solve the conventional problems described above, inventors of the present application are at the end of extensive research and various experiments in depth, the positive electrode active material of aLi ₂ MnO _{3 -} Composition of (1-a) LiMO _2, By appropriately controlling the formation voltage and the operation voltage, it is possible to provide a driving method capable of improving life characteristics while suppressing capacity deterioration due to an increase in the number of cycles.

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 the anode potential, and has an upper limit of operating voltage of 4.40V or less and has a peak in the graph of dQ / dV vs. voltage (V) after 100 to 500 cycle processes. do:

<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 dQ / dV represents the derivative value in the voltage (V) -capacity (Q) graph.

According to one embodiment, the activation voltage is in the range of 4.35V or less.

According to one embodiment, the activation voltage ranges from 4.20V to 4.40V.

According to one embodiment, the upper limit of the operating voltage is 4.35V or less.

According to one embodiment, the upper limit of the operating voltage is 4.20V to 4.40V.

According to one embodiment, the operating voltage ranges from 2.50V to 4.35V.

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 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

Controlling the upper limit of the operating voltage to 4.40V or less;

A method of driving a lithium secondary battery having a peak in a graph of dQ / dV vs. voltage (V) after 100 to 500 cycles is provided:

<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 dQ / dV represents the derivative value in the voltage (V) -capacity (Q) graph.

According to one aspect, the lithium secondary battery may be used as a unit cell of the battery module which is the power source of the 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 It is possible to increase the life of the cell while suppressing capacity degradation.

1 is a graph showing capacity retention rates according to cycles of lithium batteries obtained in Example 1, Comparative Examples 1 and 2. FIG.
2 shows voltage (V)-dQ / dV graphs of Experimental Examples 1 and 2, Example 1, and Comparative Examples 1 and 2. FIG.

Hereinafter, the present invention will be described in detail.

In general, increasing the charge upper limit voltage of the lithium secondary battery increases capacity but accelerates life deterioration. However, in the case of a lithium secondary battery including the layered lithium compound of Chemical Formula 1, the composition, activation voltage, and operating voltage of the material may be increased. By appropriately adjusting, it is possible to increase the life of the battery while suppressing capacity deterioration due to the increase in the number of cycles. That is, in the case of a lithium secondary battery having a positive electrode including the layered lithium compound of Chemical Formula 1, durability at an upper limit charging voltage of 4.1 V to 4.2 V is also excellent, and capacity deterioration occurs due to an increase in cycle number, thereby causing the upper limit. Even if the charging voltage is increased from 4.3V to 4.4V, the capacity can be maintained for a considerable period. This is due to the characteristics of the compound Li ₂ MnO ₃ , the drive voltage of 4.1V to 4.2V helps to stabilize the structure does not participate in the reaction, while in the 4.3V to 4.4V little by little participate in the reaction to deteriorate the capacity of the battery Because it compensates.

However, when the layered structure lithium compound of Formula 1 is activated and cycled at a high voltage of 4.6 V or more, the Li ₂ MnO ₃ part participates in the reaction and thereafter, cannot contribute to the structure stabilization. As a result, the peak disappears from the dQ / dV graph, which is the derivative of the capacitance versus voltage. Therefore, the composition, activation voltage, and operating voltage of the lithium compound may be properly controlled to confirm the presence of Li ₂ MnO ₃ even after activation and a constant cycle process, which is a dQ / dV graph that is a derivative value of capacity versus voltage. This can be confirmed by the presence of a peak at.

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 a peak in a graph of dQ / dV vs. voltage (V) after 00 to 500 cycle processes.

<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 simultaneously applied. dQ / dV represents the derivative value in the voltage (V) -capacity (Q) graph.

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 . In addition, even after 100 to 500 cycles, the peak of Li ₂ MnO ₃ remains, thereby suppressing the deterioration of the battery to maintain the capacity for a long time to improve the life 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, unlike other conventional cathode active materials, the lithium compound having a layered structure has a certain level of flatness over an oxidation / reduction potential caused by a change in oxidation number of a component 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 large capacity of more than 250mAh / g will be 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 activated by charging at an upper voltage of 4.40V or less, for example, 4.20V to 4.40V. 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 between 4.20V and 4.40V. 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 operating voltage may range from 2.50V to 4.35V.

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 positive electrode 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 conductive material is preferably contained in 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). 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 the upper limit of the operating voltage to 4.40V or less, and providing a method of driving a lithium secondary battery having a peak in a graph of dQ / dV vs. voltage (V) after 100 to 500 cycle processes:

<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 simultaneously applied. dQ / dV represents the derivative value in the voltage (V) -capacity (Q) graph.

The positive electrode active material layer including the positive electrode active material, the activation step, the upper limit of the operating voltage, the peaks in the graph of dQ / dV, and the like are already described above.

In general, a lithium secondary battery is composed of 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. The void of the electrode and the separator material contains an electrolyte solution for conduction of 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 the cathode mixture 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. The negative electrode active material may include at least one selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (The Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth Element or a combination thereof, not Si), Sn-Y alloy (Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element or combination thereof, and not Sn. ) And the like. As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO 2, SiO x (0 <x <2), or the like.

The carbonaceous material may be crystalline carbon, amorphous carbon or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low temperature calcined carbon) or hard carbon (hard). carbon, mesophase pitch carbide, calcined coke, and the like.

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 polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. 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.

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 or large battery pack including a plurality of unit cells stacked and packaged, or a medium and large battery pack including such a medium and 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 1

-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

A half cell was manufactured by using the positive electrode prepared as described above, a lithium metal counter electrode, a separator (Celgard 2400), and EC / DMC (1: 1 v / v) of 1M LiPF ₆ .

The half battery produced above was charged to 4.35V based on the potential of the cathode, and then discharged to activate the battery. (C-rate = 0.1C)

Capacity retention was measured by setting the operating voltage range from 4.35V to 2.5V and performing a cycle to measure each capacity. The measurement result is shown in FIG.

As shown in FIG. 1, it can be seen that the capacity retention rate is maintained at a very high value during 400 cycles. Therefore, it can be seen that the life characteristics are improved.

 Comparative Example 1

The same process as in Example 1 was performed except that the activation voltage was changed from 4.35V to 4.60V, and the capacity retention rate is shown in FIG. 1.

As shown in FIG. 1, the deterioration of the capacity was continuously generated due to the high activation voltage, and the capacity dropped sharply in about 270 cycles.

Comparative Example 2

0.15Li ₂ MnO ₃ 0.85LiMn _{0 . 33} Ni _{0 . 33} Co _{0 .} LiMn ₀ instead of ₃₃ O _{2 . 33} Ni _{0 . 33} Co _{0 .} Except for using the ₃₃ O ₂ lithium compound was carried out the same process as in Example 1, the capacity retention results are shown in FIG.

As shown in FIG. 1, it can be seen that the degeneration of the dose continuously occurred.

Experimental Example 1

Except for changing the activation voltage and cycle voltage to 4.60V, dQ / dV with respect to the voltage was measured and shown in FIG.

Experimental Example 2

A half cell was subjected to the same process as in Example 1 except that LiMn _0.33 Ni _0.33 Co _0.33 O ₂ lithium compound was used in the same manner as in Comparative Example 2, and the activation voltage and cycle voltage were changed to 4.60V. The dQ / dV versus the voltage were measured and shown in FIG. 2.

In FIG. 2, dotted lines show the results measured in Experimental Example 1 and Experimental Example 2, and it can be seen that the presence of a peak of Li ₂ MnO ₃ is determined according to the composition and activation process of the lithium compound. In addition, the results of the half cell after performing the cycle process in Examples 1, Comparative Examples 1 and 2 also shown in Figure 2, only the half cell of Example 1 remained Li ₂ MnO ₃ peak value It can be seen that.

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;
Lithium secondary, activated at a voltage of 4.20 V to 4.35 V based on the anode potential, with an upper operating limit of 4.40 V or less, and having a peak in the graph of dQ / dV versus voltage (V) after 100 to 500 cycles battery:
<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 dQ / dV represents the derivative value in the voltage (V) -capacity (Q) graph. The method of claim 1,
The upper limit of the initial operating voltage is 4.35V or less lithium secondary battery. The method of claim 1,
The upper limit of the initial operating voltage is a lithium secondary battery of 4.20V to 4.40V. delete delete The method of claim 1,
The lithium secondary battery of the operating voltage is 2.50V to 4.35V. 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 4.20 V to 4.35 V based on the anode potential; And
Controlling the upper limit of the operating voltage to 4.40V or less;
Method for driving a lithium secondary battery having a peak in the graph of dQ / dV versus voltage (V) after 100 to 500 cycles:
<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 dQ / dV represents the derivative value in the voltage (V) -capacity (Q) graph. The method according to any one of claims 1 to 3, and 6 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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