Positive electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery containing the same. The positive electrode is manufactured using a pre-dispersion liquid containing a positive electrode additive represented by Chemical Formula 1 as an irreversible additive in a positive electrode mixture layer, and by adjusting the electrode thin film resistivity according to the use of the positive electrode additive to satisfy a specific range, there are advantages that not only the amount of oxygen generated during charging / discharging can be reduced, but also the charging / discharging efficiency of the lithium secondary battery can be easily improved.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0002] This application claims the priority and benefit of Korean Patent Application No. 10-2021-0071877, filed on June 3, 2021, the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] In recent years, the demand for secondary batteries as an energy source has increased rapidly. Among these secondary batteries, lithium secondary batteries having high energy density, high working potential, long cycle life, and low self-discharge rate have been widely studied, commercialized, and used in various fields.

[0004] Although graphite is mainly used as the negative electrode material of a lithium secondary battery, it is difficult to increase the capacity of the lithium secondary battery because the capacity per unit mass of graphite is small, 372 mAh / g. Therefore, high-capacity lithium secondary batteries have been developed, which use non-carbon negative electrode materials having higher energy density than graphite, such as negative electrode materials that form intermetallic compounds with lithium, such as silicon, tin, and their oxides. However, such non-carbon negative electrode materials have a large capacity but low initial efficiency, resulting in a large amount of lithium consumption during initial charge / discharge and a large irreversible capacity loss.

[0005] In this regard, a method for overcoming the irreversible capacity loss of the negative electrode has been proposed, which uses a material that can provide a lithium ion source or storage for the positive electrode material and exhibits electrochemical activity after the first cycle, without deteriorating the overall performance of the battery. Specifically, it is known to apply an oxide containing excess lithium, such as Li6CoO4, to the positive electrode as a sacrificial positive electrode material or an irreversible additive (or over-discharge inhibitor).

[0006] On the other hand, conventional irreversible additives such as Li6CoO4 are usually prepared by reacting a metal oxide such as cobalt oxide with excess lithium oxide. The irreversible additive prepared as described above has an unstable structure and generates a large amount of oxygen (O2) as charging progresses. And during the initial charge of the secondary battery, that is, the activation of the battery, when the irreversible additive does not react completely and remains, it may react during subsequent charge / discharge processes, causing side reactions in the battery or generating a large amount of oxygen. The oxygen generated as described above may cause volume expansion of the electrode assembly, which is one of the main factors leading to deterioration of battery performance.

[0007]

[0008] In addition, conventionally, because there is a two-dimensional penetration network, the commonly used irreversible additives exhibit no more than 10-11 a very low powder conductivity of S / cm, which is almost close to that of an insulator. This low powder conductivity increases the resistance of the positive electrode. In this case, although a large capacity of over 200 mAh / g is shown at a low C rate, when the C rate increases, as charging / discharging progresses, due to the large resistance, the performance rapidly deteriorates, and thus there are limitations in that the charging / discharging capacity of the battery decreases and it is difficult to charge / discharge at high speed.

[0009] Therefore, there is a need to develop a lithium secondary battery having excellent electrical properties and improved battery safety.

[0010] Related technical literature

[0011] [Patent literature]

[0012] Korean Unexamined Patent Application Publication No. 10-2019-0064423 Summary of the Invention

[0013] [Technical problem]

[0014] Therefore, an object of the present invention is to provide a positive electrode for a lithium secondary battery, which effectively improves the electrical properties of the lithium secondary battery and improves safety, and the present invention also relates to a lithium secondary battery including the same.

[0015] [Technical solution]

[0016] To solve the above problems,

[0017] One aspect of the present invention provides a positive electrode for a lithium secondary battery, the positive electrode comprising:

[0018] a positive electrode current collector; and

[0019] a positive electrode mixture layer provided on the positive electrode current collector and containing a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a conductive material, and a binder,

[0020] wherein the following arithmetic expression 1 is 1.55 or less,

[0021] [Chemical Formula 1]

[0022] Li p Co (1-q) M 1 q O4

[0023] In Chemical Formula 1,

[0024] M 1is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0025] p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.5, respectively;

[0026] [Formula 1]

[0027] R LCZO / R0

[0028] In Formula 1,

[0029] R LCZO represents the sheet resistance of the electrode thin layer when the positive electrode additive shown in Chemical Formula 1 is contained in the positive electrode mixture layer, and

[0030] R0 represents the sheet resistance of the electrode thin layer when the positive electrode additive shown in Chemical Formula 1 is not contained in the positive electrode mixture layer.

[0031] Specifically, in the case of the positive electrode for a lithium secondary battery, Formula 1 can be satisfied to be 1.3 or less.

[0032] In addition, the positive electrode additive can have a tetragonal structure with a space group of P42 / nmc.

[0033] In addition, the content of the positive electrode additive can be 0.1 to 10 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

[0034] In addition, the positive electrode active material can be a lithium metal composite oxide shown in Chemical Formula 2:

[0035] [Chemical Formula 2]

[0036] Li x [Ni y Co z Mn w M 2 v O u

[0037] In Chemical Formula 2,

[0038] M 2 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0039] x, y, z, w, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

[0040] In addition, the conductive material may include one or more selected from the following: activated carbon, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, Vulcan XC-72R, Super-P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0041] In addition, the content of the conductive material may be 0.1 to 5 parts by weight with respect to 100 parts by weight of the positive electrode mixture layer.

[0042] In addition, another aspect of the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, the method including the following steps:

[0043] Preparing a pre-dispersion liquid by mixing a positive electrode additive represented by Chemical Formula 1 below, a conductive material, and a binder;

[0044] Preparing a positive electrode paste by mixing the pre-dispersion liquid, a positive electrode active material, and a binder; and

[0045] Forming a positive electrode mixture layer by coating the positive electrode paste on a positive electrode current collector,

[0046] wherein, for the manufactured positive electrode, the following Formula 1 is 1.55 or less,

[0047] [Chemical Formula 1]

[0048] Li p Co (1-q) M 1 q O4

[0049] In Chemical Formula 1,

[0050] M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0051] p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.5, respectively;

[0052] [Formula 1]

[0053] R LCZO / R0

[0054] In Formula 1,

[0055] RLCZO represents the sheet resistance of the electrode when the positive electrode additive shown in Chemical Formula 1 is contained in the positive electrode mixture layer, and

[0056] R0 represents the sheet resistance of the electrode when the positive electrode additive shown in Chemical Formula 1 is not contained in the positive electrode mixture layer.

[0057] Herein, the preparation of the predispersion can be carried out under a relative humidity condition of 10% or less.

[0058] In addition, another aspect of the present invention provides a lithium secondary battery, which includes: a positive electrode according to the present invention; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0059] Herein, the negative electrode may include a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, wherein the negative electrode mixture layer contains a negative electrode active material, and wherein the negative electrode active material may contain a carbon material and a silicon material.

[0060] In addition, the silicon material may include one or more of silicon (Si) particles and silicon oxide (SiOx, 1≤x≤2) particles, and the content of the silicon material may be 1 to 20 parts by weight based on 100 parts by weight of the negative electrode mixture layer.

[0061] [Advantageous Effects]

[0062] The positive electrode for a lithium secondary battery according to the present invention is manufactured using a predispersion containing a positive electrode additive shown in Chemical Formula 1 as an irreversible additive in the positive electrode mixture layer, and the sheet resistivity of the electrode is adjusted according to the use of the positive electrode additive to meet a specific range, thereby having the advantages of not only being able to reduce the amount of oxygen generated during charging / discharging, but also being able to easily improve the charging / discharging efficiency of the lithium secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 is a graph showing the sheet resistance of the positive electrodes manufactured in Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0064] The present invention can have various variations and various examples, and thus specific examples are shown in the drawings and described in detail in the detailed description.

[0065] However, it should be understood that the present invention is not limited to specific embodiments, but includes all variations, equivalents or alternatives within the spirit and technical scope of the present invention.

[0066] As used herein, the terms "comprising", "including" and "having" denote the presence of the features, quantities, steps, actions, components or elements or combinations thereof described in the specification, but it should be understood that these terms do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, actions, components, elements or combinations thereof.

[0067] In addition, when a part of a layer, film, region or plate is disposed "above" another part, this includes not only the case where a part is disposed "directly" above another part, but also the case where other parts are inserted therebetween. Conversely, when a part of a layer, film, region or plate is disposed "below" another part, this includes not only the case where a part is disposed "directly" below another part, but also the case where other parts are inserted therebetween. In addition, in this application, "above" includes not only the case of being disposed above the upper part, but also the case of being disposed above the lower part.

[0068] In addition, the "main component" used herein may be a component having a content of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more or 97.5% by weight or more relative to the total weight of the composition or a specific component, and in some cases, when the main component constitutes the entire composition or a specific component, its content may be 100% by weight.

[0069] In addition, the term "Ah" used herein refers to the capacity unit of a lithium secondary battery, also known as "ampere-hour", which refers to the current flow per hour. For example, when the battery capacity is "3000 mAh", this means that the battery can discharge at a current of 3000 mA for 1 hour.

[0070] Hereinafter, the present invention will be described in more detail.

[0071] Positive electrode for lithium secondary battery

[0072] In one embodiment of the present invention, the positive electrode for a lithium secondary battery comprises:

[0073] a positive electrode current collector; and

[0074] a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material, a positive electrode additive, a conductive material and a binder.

[0075] The positive electrode for a lithium secondary battery according to the present invention comprises a positive electrode mixture layer prepared by coating a positive electrode paste on a positive electrode current collector, drying and pressing, and the positive electrode mixture layer has a structure containing a positive electrode active material, a positive electrode additive, a conductive material and a binder.

[0076] Here, the positive electrode additive can be a lithium cobalt oxide represented by the following Chemical Formula 1:

[0077] [Chemical Formula 1]

[0078] Li p Co (1-q) M 1 q O4

[0079] In Chemical Formula 1,

[0080] M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0081] p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.5, respectively.

[0082] The positive electrode additive can contain an excessive amount of lithium, thereby providing lithium for the consumption of lithium caused by irreversible chemical and physical reactions occurring at the negative electrode during the initial charging, i.e., activation. Thereby, the charging capacity is increased, the irreversible capacity is reduced, and the life characteristics are improved.

[0083] In the positive electrode additive, the lithium ion content of the positive electrode additive represented by Chemical Formula 1 can be higher than the lithium ion content of nickel-containing oxides commonly used in the art. Thereby, the lithium ions lost due to irreversible reactions during the initial activation of the battery are supplemented, and thus the charging / discharging capacity of the battery can be significantly improved. In addition, compared with iron-containing and / or manganese-containing oxides commonly used in the art, no side reactions caused by the dissolution of transition metals occur during the charging / discharging process of the battery, thereby exhibiting excellent stability of the battery. Examples of the lithium cobalt oxide represented by Chemical Formula 1 can include Li6CoO4, Li6Co 0.5 Zn 0.5 O4 and Li6Co 0.7 Zn 0.3 O4.

[0084] In addition, the lithium cobalt oxide represented by Chemical Formula 1 may have a tetragonal crystal structure, and in the tetragonal crystal structure, it may be included in the P42 / nmc space group having a distorted tetrahedral structure composed of cobalt element and oxygen element. Since the cathode additive has a distorted tetrahedral structure composed of cobalt element and oxygen element, and this structure is unstable, when the amount of the cathode additive relative to 100 parts by weight of the cathode mixture layer is 5 parts by weight during the manufacture of the cathode, side reactions may occur with moisture or oxygen in the air during the mixing process of the cathode slurry. However, the advantage of the present invention is that by using a composition in which the cathode additive is pre-dispersed with the conductive material when preparing the cathode slurry, side reactions of the cathode additive with moisture or oxygen in the air can be prevented.

[0085] In addition, the content of the cathode additive may be 0.1 to 10 parts by weight, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 1 to 10 parts by weight, 2 to 10 parts by weight, 5 to 10 parts by weight, 2 to 8 parts by weight, 3 to 7 parts by weight, or 4 to 5.5 parts by weight relative to 100 parts by weight of the cathode mixture layer. In the present invention, by adjusting the content of the cathode additive within the above range, it is possible to prevent a decrease in charge / discharge capacity caused by insufficient replenishment of lithium ions lost due to an irreversible reaction caused by a low content of the cathode additive, and it is possible to prevent a large amount of oxygen from being generated due to an excessive amount of the cathode additive during the charge / discharge process of the battery.

[0086] In addition, the cathode for a lithium secondary battery can exhibit a low electrode sheet resistance even when containing the cathode additive represented by Chemical Formula 1, and thus excellent performance can be achieved during the charge / discharge of the battery.

[0087] Specifically, the irreversible additive commonly used in the art has a significantly low conductivity of about 10 -11 S / cm, resulting in a problem of high resistance imparted to the electrode during the charge / discharge of the battery. However, even when the cathode additive represented by Chemical Formula 1 is included in the cathode mixture layer, the cathode for a lithium secondary battery according to the present invention can exhibit a low sheet resistance within a predetermined range.

[0088] In one example, the cathode may satisfy the following formula 1 to be 1.55 or less, specifically 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 0.2 to 1.5, 0.5 to 1.5, 0.8 to 1.5, or 0.8 to 1.3. Formula 1 represents the ratio (R LCZO ) of the electrode sheet resistance (R LCZO ) of the cathode containing the cathode additive represented by Chemical Formula 1 to the electrode sheet resistance (R0) of the cathode not containing the cathode additive represented by Chemical Formula 1 (R LCZO / R0):

[0089] [Formula 1]

[0090] R LCZO / R0

[0091] In Equation 1,

[0092] R LCZO represents the sheet resistance of the electrode when the positive electrode additive shown in Chemical Formula 1 is contained in the positive electrode mixture layer, and

[0093] R0 represents the sheet resistance of the electrode when the positive electrode additive shown in Chemical Formula 1 is not contained in the positive electrode mixture layer.

[0094] On the other hand, the positive electrode active material is a positive electrode active material capable of reversibly inserting and extracting, and may include a lithium metal composite oxide shown in the following Chemical Formula 2 as a main component:

[0095] [Chemical Formula 2]

[0096] Li x [Ni y Co z Mn w M 2 v O u

[0097] In Chemical Formula 2,

[0098] M 2 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0099] x, y, z, w, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

[0100] The lithium metal composite oxide shown in Chemical Formula 2 is a composite metal oxide containing lithium and nickel, and may include selected from LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 One or more compounds in O2.

[0101] In addition, relative to 100 parts by weight of the positive electrode mixture layer, the content of the positive electrode active material can be 85 to 95 parts by weight, 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight.

[0102] In addition, the conductive material can be used to improve the electrical properties of the positive electrode, and common conductive materials in the art can be applied. Specifically, one or more selected from the following can be applied: activated carbon, natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, thermal cracking carbon black, graphene, and carbon nanotubes.

[0103] For example, as the conductive material, carbon black or Denka black can be used alone or in combination.

[0104] In addition, relative to 100 parts by weight of the positive electrode mixture layer, the content of the conductive material can be 0.1 to 5 parts by weight, specifically 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight.

[0105] In addition, the binder serves to bond the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having the above functions can be used without particular limitation. Specifically, as the binder, one or more resins selected from polyvinylidene fluoride - hexafluoropropylene copolymer (PVdF - co - HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and their copolymers can be included. In one example, the binder can include polyvinylidene fluoride.

[0106] In addition, relative to 100 parts by weight of the positive electrode mixture layer, the content of the binder can be 1 to 10 parts by weight, specifically 2 to 8 parts by weight or 1 to 5 parts by weight.

[0107] In addition, the average thickness of the positive electrode mixture layer is not particularly limited, but specifically can be 50 to 300 μm, more specifically 100 to 200 μm, 80 to 150 μm, 120 to 170 μm, 150 to 300 μm, 200 to 300 μm, or 150 to 190 μm.

[0108] In addition, in the positive electrode, a material having high conductivity and not causing chemical changes in the battery can be used as the positive electrode current collector. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can be used as the positive electrode current collector, and in the case of aluminum or stainless steel, aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver can also be used. In addition, the positive electrode current collector may have fine irregularities formed on its surface to improve the adhesion of the positive electrode active material, and can be formed in various shapes such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabric bodies. In addition, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the current collector can be appropriately applied within 3 to 500 μm.

[0109] Method for manufacturing positive electrode for lithium secondary battery

[0110] In addition, an embodiment of the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, the method including the following steps:

[0111] Preparing a pre-dispersion liquid by mixing a positive electrode additive, a conductive material, and a binder represented by Chemical Formula 1 below;

[0112] Preparing a positive electrode paste by mixing the prepared pre-dispersion liquid, a positive electrode active material, and a binder; and

[0113] Forming a positive electrode mixture layer by coating the positive electrode paste on a positive electrode current collector,

[0114] wherein, for the manufactured positive electrode, the following Formula 1 is 1.55 or less,

[0115] [Chemical Formula 1]

[0116] Li p Co (1-q) M 1 q O4

[0117] In Chemical Formula 1,

[0118] M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0119] p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.5, respectively;

[0120] [Formula 1]

[0121] R LCZO / R0

[0122] In Equation 1,

[0123] R LCZO represents the sheet resistance of the electrode when the positive electrode additive shown in Chemical Formula 1 is contained in the positive electrode mixture layer, and

[0124] R0 represents the sheet resistance of the electrode when the positive electrode additive shown in Chemical Formula 1 is not contained in the positive electrode mixture layer.

[0125] The method for manufacturing a positive electrode for a lithium secondary battery according to the present invention may include: preparing a pre-dispersion liquid by first mixing a positive electrode additive, a conductive material, and a binder shown in Chemical Formula 1; preparing a positive electrode slurry by further mixing the prepared pre-dispersion liquid with a positive electrode active material and a binder; and forming a positive electrode mixture layer by coating the positive electrode slurry on a positive electrode current collector and drying the positive electrode slurry.

[0126] Here, the preparation of the pre-dispersion liquid is a step of mixing a positive electrode additive, a conductive material, and a binder, and can be carried out by a conventional method for preparing a slurry in the art. For example, the preparation of the pre-dispersion liquid is carried out by putting various components into a homogenizer and stirring the obtained product at 1000 to 5000 rpm for 30 to 600 minutes, and the viscosity can be controlled by adding a solvent during stirring. In one example, the pre-dispersion liquid for the positive electrode according to the present invention can be prepared by putting the positive electrode additive, the conductive material, and the binder shown in Chemical Formula 1 into a homogenizer and mixing the components at 3000 rpm for 60 minutes while injecting an N-methylpyrrolidone solvent to adjust the viscosity at 25 ± 1 °C to 7500 ± 300 cps.

[0127] In addition, the preparation of the pre-dispersion liquid can be carried out under temperature and / or humidity conditions that satisfy a specific range to prevent decomposition and / or damage of the positive electrode additive with unstable structure.

[0128] Specifically, the preparation of the pre-dispersion liquid can be carried out at a temperature of 40 °C or lower, more specifically at a temperature condition of 10 to 40 °C, 10 to 35 °C, 10 to 30 °C, 10 to 25 °C, 10 to 20 °C, 15 to 40 °C, 20 to 40 °C, 15 to 35 °C, or 18 to 30 °C.

[0129] In addition, the preparation of the pre-dispersion liquid can be carried out under a relative humidity (RH) condition of 10% or lower, more specifically 9% or lower, 8% or lower, 7% or lower, 6% or lower, 5% or lower, 4% or lower, 3% or lower, 2% or lower, or 1% or lower.

[0130] In the present invention, by controlling the temperature and / or humidity conditions during the preparation of the predispersion liquid as described above, it is possible to prevent a decrease in irreversible activity caused by side reactions with moisture and / or oxygen in the air that may occur during the mixing of the fine particle type cathode additive and the conductive material, and a low sheet resistance of the cathode mixture layer is achieved.

[0131] Lithium secondary battery

[0132] In addition, an embodiment of the present invention provides a lithium secondary battery, which includes:

[0133] The above-mentioned cathode, anode, and separator interposed between the cathode and the anode according to the present invention.

[0134] The lithium secondary battery according to the present invention includes the above-mentioned cathode of the present invention, and thus not only generates a small amount of oxygen during charging / discharging, but also exhibits excellent charging / discharging performance.

[0135] The lithium secondary battery of the present invention has a structure including a cathode, an anode, and a separator interposed between the cathode and the anode.

[0136] Here, the anode can be manufactured by coating an anode active material on an anode current collector, drying, and pressing, and may further selectively include a conductive material, an organic binder polymer, or an additive as needed like the cathode.

[0137] In addition, the anode active material may include, for example, a carbon material and a silicon material. The carbon material refers to a carbon material containing carbon atoms as the main component, and examples of these carbon materials may include: graphite having a completely layered crystalline structure such as natural graphite, soft carbon having a layered crystalline structure with low crystallinity (graphene structure; a structure of a hexagonal honeycomb planar layer arrangement of carbon), and hard carbon in which the above structure is mixed with an amorphous part, artificial graphite, expanded graphite, carbon nanofibers, non-graphitized carbon, carbon black, acetylene black, Ketjen black, carbon nanotubes, fullerenes, activated carbon, and graphene, preferably one or more selected from natural graphite, artificial graphite, and carbon nanotubes. More preferably, the carbon material includes natural graphite and / or artificial graphite, and in addition to natural graphite and / or artificial graphite, it may further include any one or more of carbon black and carbon nanotubes. In this case, relative to a total of 100 parts by weight of the carbon material, the carbon material may contain 0.1 to 10 parts by weight, more specifically 0.1 to 5 parts by weight or 0.1 to 2 parts by weight of carbon black and / or carbon nanotubes.

[0138] In addition, the silicon material is particles containing (semi) metallic component silicon (Si) as the main component, and may include silicon (Si) particles and silicon oxide (SiO X, one or more of the particles where 1 ≤ X ≤ 2). In one instance, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture thereof.

[0139] In addition, the silicon material may have a form in which crystalline particles and amorphous particles are mixed, and with respect to a total of 100 parts by weight of the silicon material, the proportion of the amorphous particles may be 50 to 100 parts by weight, specifically 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight. In the present invention, by controlling the proportion of the amorphous particles contained in the silicon material within the above range, the thermal stability and flexibility can be improved without degrading the electrical properties of the electrode.

[0140] In addition, the content of the silicon material with respect to 100 parts by weight of the negative electrode mixture layer may be 1 to 20 parts by weight, particularly 5 to 20 parts by weight, 3 to 10 parts by weight, 8 to 15 parts by weight, 13 to 18 parts by weight, or 2 to 7 parts by weight.

[0141] In the present invention, by adjusting the contents of the carbon material and the silicon material contained in the negative electrode active material to the above ranges, the consumption of lithium and the irreversible capacity loss during the initial charge / discharge process of the battery can be reduced, and the charge capacity per unit mass can also be improved.

[0142] In one instance, with respect to 100 parts by weight of the negative electrode mixture layer, the negative electrode active material may include: 95 ± 2 parts by weight of graphite; and 5 ± 2 parts by weight of a mixture in which silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles are uniformly mixed. In the present invention, by adjusting the contents of the carbon material and the silicon material contained in the negative electrode active material to the above ranges, the consumption of lithium and the irreversible capacity loss during the initial charge / discharge process of the battery can be reduced, and the charge capacity per unit mass can also be improved.

[0143] In addition, the average thickness of the negative electrode mixture layer may be 100 to 200 μm, specifically 100 to 180 μm, 100 to 150 μm, 120 to 200 μm, 140 to 200 μm, or 140 to 160 μm.

[0144] In addition, there is no particular limitation on the negative electrode current collector as long as it does not cause chemical changes in the battery and has high electrical conductivity. For example, copper, stainless steel, nickel, titanium, or calcined carbon can be used. In the case of copper or stainless steel, copper or stainless steel with its surface treated with carbon, nickel, titanium, or silver can be used. In addition, similar to the positive electrode current collector, the negative electrode current collector has fine irregularities on its surface to enhance the adhesion of the negative electrode active material and can be formed in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies. In addition, considering the electrical conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector can be appropriately applied in the range of 3 to 500 μm.

[0145] In addition, as the separator, an insulating film is used, which is interposed between the positive electrode and the negative electrode and has high ion permeability and mechanical strength. There is no particular limitation on the separator as long as it is commonly used in the art. Specifically, a sheet or non-woven fabric made of polypropylene, glass fiber, or polyethylene with chemical resistance and hydrophobicity can be used. In some cases, a composite separator in which a porous polymer substrate such as a sheet or non-woven fabric is coated with inorganic particles / organic particles using an organic binder polymer can be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as the separator. In addition, the average pore diameter of the separator can be 0.01 to 10 μm, and the average thickness can be 5 to 300 μm.

[0146] On the other hand, the positive electrode and the negative electrode can be wound in the shape of a roll and housed in a cylindrical, prismatic, or pouch-type battery, or can be housed in a pouch-type battery in a folded or stacked and folded form, but the present invention is not limited thereto.

[0147] In addition, the electrolyte containing a lithium salt according to the present invention can be composed of an electrolyte and a lithium salt. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte can be used.

[0148] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl citrate, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate can be used.

[0149] As an organic solid electrolyte, a polymer such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a polylysine alginate, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, and a polymer containing an ion dissociating group can be used, for example.

[0150] As an inorganic solid electrolyte, a nitride, a halide, or a sulfate of lithium such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, or Li3PO4-Li2S-SiS2 can be used, for example.

[0151] The lithium salt is a material that is soluble in a non-aqueous electrolyte, and can be, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, a lithium salt of a lower aliphatic carboxylic acid, lithium tetraphenylborate, or a lithium imide.

[0152] Furthermore, in order to improve the charge / discharge characteristics and the flame retardancy, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, a (poly)glycol dimethyl ether, hexamethylphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imide dye, an N-substituted oxazolidone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride can be added to the electrolyte. In some cases, in order to impart nonflammability, the electrolyte may further contain a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene, and in order to improve the high-temperature storage characteristics, carbon dioxide gas may also be contained, and fluoroethylene carbonate (FEC) or propene sultone (PRS) may also be contained.

[0153] Preferred Embodiments

[0154] Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples.

[0155] However, the following Examples and Experimental Examples are only for illustrating the present invention, and the content of the present invention is not limited to the following Examples and Experimental Examples.

[0156] Example 1. Manufacture of a Positive Electrode for a Lithium Secondary Battery

[0157] By injecting N-methylpyrrolidone into a homogenizing mixer, 5 parts by weight of a positive electrode additive Li6Co is added relative to 100 parts by weight of the solid content of the positive electrode paste0.7 Zn 0.3 O4, 2 parts by weight of conductive material carbon black, and 1 part by weight of binder PVdF, and primary mixing was carried out at 2000 rpm for 30 minutes to prepare a pre-dispersion liquid for manufacturing a positive electrode. Here, in the preparation of the pre-dispersion liquid, the temperature and humidity were adjusted to 20 to 25 °C and 3%, respectively.

[0158] Subsequently, 91 parts by weight of positive electrode active material LiNi was added to a homogenizer containing the prepared pre-dispersion liquid with respect to 100 parts by weight of the solid content of the positive electrode paste 0.6 Co 0.2 Mn 0.2 O2 and 1 part by weight of binder PVdF, and secondary mixing was carried out at 2500 rpm for 30 minutes to prepare a positive electrode paste for a lithium secondary battery.

[0159] A positive electrode was manufactured by coating the prepared positive electrode paste on one surface of an aluminum current collector, drying the paste at 100 °C, and roll-pressing the obtained product. Here, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the manufactured positive electrode was about 200 μm.

[0160] Comparative Example 1. Manufacture of a positive electrode for a lithium secondary battery

[0161] A positive electrode for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode additive used in Example 1 was not used.

[0162] Comparative Example 2. Manufacture of a positive electrode for a lithium secondary battery

[0163] N-methylpyrrolidone was injected into a homogenizer, and 91 parts by weight of positive electrode active material LiNi was added with respect to 100 parts by weight of the solid content of the positive electrode paste 0.6 Co 0.2 Mn 0.2 O2, 5 parts by weight of positive electrode additive Li6Co 0.7 Zn 0.3 O4, 2 parts by weight of conductive material carbon black, and 2 parts by weight of binder PVdF, and it was mixed at 2000 rpm for 60 minutes to prepare a positive electrode paste for a lithium secondary battery. Here, during the mixing, the temperature and humidity were adjusted to 20 to 25 °C and 3%, respectively.

[0164] A positive electrode was manufactured by coating the prepared positive electrode paste on one surface of an aluminum current collector, drying the paste at 100 °C, and roll-pressing the obtained product. Here, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the manufactured positive electrode was about 200 μm.

[0165] Comparative Example 3. Fabrication of the positive electrode for a lithium secondary battery

[0166] N-methylpyrrolidone was injected into a homogenizer, and 5 parts by weight of the positive electrode additive Li6Co 0.7 Zn 0.3 O4 and 1 part by weight of the binder PVdF were added thereto, and the mixture was mixed at 2000 rpm for 30 minutes to prepare a pre-dispersion liquid for fabricating the positive electrode. Here, during the preparation of the pre-dispersion liquid, the temperature and humidity were adjusted to 20 to 25 °C and 3%, respectively.

[0167] Subsequently, 91 parts by weight of the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2, 2 parts by weight of the conductive material carbon black, and 1 part by weight of the binder PVdF were added to the homogenizer containing the prepared pre-dispersion liquid, and secondary mixing was performed at 2500 rpm for 30 minutes to prepare a positive electrode paste for a lithium secondary battery.

[0168] The positive electrode was fabricated by coating the prepared positive electrode paste on one surface of an aluminum current collector, drying the paste at 100 °C, and roll-pressing the obtained product. Here, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the fabricated positive electrode was about 200 μm.

[0169] Comparative Examples 4 and 5. Fabrication of the positive electrode for a lithium secondary battery

[0170] The positive electrode for a lithium secondary battery was fabricated in the same manner as in Example 1, except that the temperature and humidity were adjusted as shown in the following table during the preparation of the pre-dispersion liquid.

[0171] [Table 1]

[0172] Temperature Relative humidity Comparative Example 4 50℃ 3％ Comparative Example 5 20～25℃ 50％

[0173] Examples 2 and Comparative Examples 6 to 10. Fabrication of a lithium secondary battery

[0174] Natural graphite and silicon (SiOx, 1 ≤ x ≤ 2) particles as the negative electrode active material and styrene-butadiene rubber (SBR) as the binder were prepared, and a negative electrode paste was prepared in the same manner as the positive electrode paste. Here, the graphite used for preparing the negative electrode mixture layer was natural graphite (average particle size: 0.01 to 0.5 μm), and the average particle size of the silicon (SiOx) particles was 0.9 to 1.1 μm. The negative electrode was fabricated by coating the prepared negative electrode paste on one surface of a copper current collector, drying the obtained product at 100 °C, and roll-pressing it. Here, the total thickness of the negative electrode mixture layer was 150 μm, and the total thickness of the fabricated negative electrode was about 250 μm.

[0175] A full cell was fabricated by stacking a separator (thickness: approximately 16 μm) composed of a porous polyethylene (PE) membrane between the negative electrode and a positive electrode fabricated in Example 1 and Comparative Examples 1 to 5, and injecting E2DVC as the electrolyte.

[0176] Herein, "E2DVC" refers to a carbonate-based electrolyte which is a mixed solution obtained by adding lithium hexafluorophosphate (LiPF6, 1.0 M) and vinylene carbonate (VC, 2 wt%) to a mixture of ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0177] [Table 2]

[0178] Positive electrode for lithium secondary battery Lithium secondary battery Example 1 Example 2 Comparative Example 1 Comparative Example 6 Comparative Example 2 Comparative Example 7 Comparative Example 3 Comparative Example 8 Comparative Example 4 Comparative Example 9 Comparative Example 5 Comparative Example 10

[0179] Experimental Examples

[0180] In order to evaluate the performance of the positive electrode for a lithium secondary battery according to the present invention, the following experiments were conducted.

[0181] a) Evaluation of electrode thin-film resistance

[0182] The sheet resistance of various positive electrodes fabricated in Example 1 and Comparative Examples 1 to 5 was measured by the four-point probe method, and the results are shown in Table 3 below and Figure 1 in.

[0183] b) Evaluation of oxygen degassing amount during charge / discharge

[0184] For the lithium secondary batteries fabricated in Example 2 and Comparative Examples 6 to 10, initial charging (formation) was performed at 55 °C under the conditions of 3.5 V and 1.0 C, and the content of oxygen generated during the initial charging was analyzed by degassing the gas generated from the positive electrode while performing the initial charging. Then, by repeating charging / discharging 50 times at 45 °C under the condition of 0.3 C, the oxygen content at each charging / discharging was further analyzed. The analysis results are shown in Table 3 below.

[0185] c) Evaluation of charge / discharge capacity and retention rate

[0186] The various lithium secondary batteries fabricated in Example 2 and Comparative Examples 6 to 10 were charged at a charging current of 0.1 C at 25 °C until the charging cut-off voltage of 4.2 to 4.25 V, and were activated. Subsequently, the secondary batteries were discharged at a discharging current of 0.1 C to a discharging cut-off voltage of 2 V, and the initial charging / discharging capacity per unit mass was measured.

[0187] Then, during charging / discharging, the secondary battery was repeatedly charged / discharged 50 times at 0.3C at 45°C to measure the capacity. After 50 charge / discharge cycles, the charge / discharge capacity retention rate was calculated. The results are shown in Table 3 below.

[0188] [Table 3]

[0189]

[0190] Referring to Table 3 and Figure 1 , in the case of the positive electrode for a lithium secondary battery of an embodiment manufactured according to the present invention, although the positive electrode additive shown in Chemical Formula 1 is contained in the positive electrode mixture layer, the sheet resistance of the electrode is low, so there is no significant difference from the sheet resistance (R0) of the positive electrode without the positive electrode additive, and the R LCZO / R0 value is less than 1.5. The lithium secondary battery including the positive electrode has not only a high initial charge / discharge capacity of 102 Ah or more but also a high capacity retention rate of 91% or more. In addition, it was confirmed that the lithium secondary battery has high safety because the amount of oxygen generated after the initial charge / discharge is significantly reduced.

[0191] Based on the above results, a positive electrode for a lithium secondary battery according to the present invention was manufactured by using a pre-dispersion liquid containing the positive electrode additive shown in Chemical Formula 1 as an irreversible additive in the positive electrode mixture layer, and by adjusting the sheet resistivity of the electrode to meet a specific range according to the use of the positive electrode additive, there are advantages that not only the amount of oxygen generated during charging / discharging can be reduced but also the charge / discharge efficiency of the lithium secondary battery can be easily improved.

[0192] In the above, although the present invention has been described with reference to exemplary embodiments, those skilled in the art or those of ordinary skill in the art should understand that various improvements and changes can be made to the present invention without departing from the spirit and technical scope of the present invention described in the claims.

[0193] Therefore, the technical scope of the present invention is not limited to the content described in the detailed description of the specification, but should be defined by the claims.

Claims

1. A positive electrode for a lithium secondary battery, the positive electrode comprising: A positive electrode current collector; and A positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a conductive material, and a binder, wherein the following Arithmetic Formula 1 is 1.55 or less, [Chemical Formula 1] Li p Co (1-q) M 1 q O4 In Chemical Formula 1, M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are 5 ≤ p ≤ 7 and 0 < q ≤ 0.5, respectively; [Arithmetic Formula 1] R LCZO / R0 In Arithmetic Formula 1, R LCZO represents the thin-film resistance of the electrode when a cathode additive represented by Chemical Formula 1 is contained in the cathode mixture layer, and R0 represents the electrode thin layer resistance when the positive electrode additive represented by Chemical Formula 1 is not contained in the positive electrode mixture layer.

2. The positive electrode according to claim 1, wherein the Arithmetic Formula 1 is 1.3 or less.

3. The positive electrode according to claim 1, wherein the positive electrode additive has a tetragonal structure with a space group of P42 / nmc.

4. The positive electrode according to claim 1, wherein the content of the positive electrode additive is 0.1 part by weight to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer.

5. The positive electrode according to claim 1, wherein the positive electrode active material is a lithium metal composite oxide represented by Chemical Formula 2: [Chemical Formula 2] Li x [Ni y Co z Mn w M 2 v O u In Chemical Formula 2, M 2 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

6. The positive electrode according to claim 1, wherein the conductive material includes one or more selected from the following: activated carbon, natural graphite, artificial graphite, acetylene black, Degussa black, Ketjen black, Super-P, channel black, furnace black, lamp black, thermal cracking carbon black, graphene, and carbon nanotubes.

7. The positive electrode according to claim 6, wherein the content of the conductive material is 0.1 part by weight to 5 parts by weight based on 100 parts by weight of the positive electrode mixture layer.

8. A method for manufacturing a positive electrode for a lithium secondary battery, the method comprising the following steps: Preparing a pre-dispersion liquid by mixing a positive electrode additive represented by the following Chemical Formula 1, a conductive material, and a binder; Preparing a positive electrode slurry by mixing the prepared pre-dispersion liquid, a positive electrode active material, and a binder; and Forming a positive electrode mixture layer by coating the positive electrode slurry on a positive electrode current collector, wherein the preparation of the pre-dispersion liquid is carried out under a relative humidity condition of 10% or less and a temperature condition of 40°C or less, Among them, for the manufactured positive electrode, the following Arithmetic Formula 1 is 1.55 or less, [Chemical Formula 1] Li p Co (1-q) M 1 q O4 In Chemical Formula 1, M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.5, respectively; [Arithmetic Formula 1] R LCZO / R0 In Arithmetic Formula 1, R LCZO represents the thin-film resistance of the electrode when a cathode additive represented by Chemical Formula 1 is contained in the cathode mixture layer, and R0 represents the electrode thin layer resistance when the positive electrode additive represented by Chemical Formula 1 is not contained in the positive electrode mixture layer.

9. A lithium secondary battery, the lithium secondary battery comprising: The positive electrode according to claim 1; A negative electrode; and A separator disposed between the positive electrode and the negative electrode.

10. The lithium secondary battery according to claim 9, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector and containing a negative electrode active material, The negative electrode active material contains a carbon material and a silicon material.

11. The lithium secondary battery according to claim 10, wherein the silicon material includes one or more of silicon Si particles and silicon oxide SiOx particles, where 1 ≤ x ≤ 2.

12. The lithium secondary battery according to claim 10, wherein the content of the silicon material is 1 to 20 parts by weight with respect to 100 parts by weight of the negative electrode mixture layer.

Images