Lithium secondary battery, and battery module and battery pack comprising same

Abstract

A lithium secondary battery according to exemplary embodiments comprises: a battery case; and an electrode assembly accommodated in the battery case, wherein the electrode assembly comprises a unit cell stack in which n unit cells (n is an integer of 2 or more), each comprising a positive electrode and a negative electrode, are arranged in the thickness direction, wherein the unit cell stack comprises a first unit cell and a second unit cell, the first unit cell comprises a first positive electrode, and a positive electrode active material of the first positive electrode is composed of a first positive electrode active material represented by chemical formula 1. [Chemical formula 1] LipFe(1-q)M1 qO4 In chemical formula 1, M1 is any one of W, Cu, 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 satisfy 5≤p≤7 및 0≤q≤0.5, respectively.

Description

Lithium secondary battery, battery module and battery pack including the same

[0001] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0084840, filed on June 27, 2024.

[0002] The present invention relates to a lithium secondary battery, a battery module including the same, and a battery pack.

[0003]

[0004] Recently, demand for lithium secondary batteries has been increasing in various fields such as electric vehicles, smartphones, and wearable devices, but there is a continuous need for devices with higher energy within limited spaces.

[0005] In order to increase the electrochemical capacity in lithium secondary batteries, there are methods to improve the performance of the cathode material or to minimize the amount of lithium ions consumed by SEI formation generated at the cathode.

[0006] Meanwhile, various technologies exist to compensate for lithium ion consumption, such as lithium pre-lithiation and lithium alloying, due to process difficulties. However, their industrial application is limited. Therefore, a method to compensate for lithium ion consumption by adding a sacrificial lithium additive to the cathode material has been studied and proposed.

[0007] (Patent Document 1) Republic of Korea Patent Publication No. 10-2021-00655655

[0008]

[0009] The technical idea of ​​the present invention aims to solve a problem by providing a lithium secondary battery with improved initial efficiency and energy density.

[0010]

[0011] According to exemplary embodiments of the present invention for solving the above-described problem, a lithium secondary battery is provided. The lithium secondary battery includes: a battery case; and an electrode assembly housed inside the battery case; wherein the electrode assembly includes a unit cell stack in which n (n is an integer greater than or equal to 2) unit cells including a positive electrode and a negative electrode are arranged in a thickness direction, and the unit cell stack includes a first unit cell and a second unit cell, and the first unit cell includes a first positive electrode, and a positive electrode active material of the first positive electrode is composed of a first positive electrode active material represented by the following Chemical Formula 1.

[0012] [Chemical Formula 1]

[0013] Li p Fe (1-q) M 1 q O4

[0014] In the above chemical formula 1, M 1 is any one of W, Cu, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0015] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0016] In exemplary embodiments, the second unit cell includes a second positive electrode, and the second positive electrode may include a second positive electrode active material of a different type from the first positive electrode active material as the positive electrode active material.

[0017] In exemplary embodiments, the second unit cell may include a second positive electrode, and the second positive electrode may include lithium iron phosphate having an olivine structure including iron element as a positive electrode active material.

[0018] In exemplary embodiments, the second positive electrode does not include the first positive electrode active material as the positive electrode active material.

[0019] In exemplary embodiments, the first unit cell may be positioned centrally in the thickness direction (Z direction) of the unit cell stack.

[0020] In exemplary embodiments, in the above chemical formula 1, M 1 is any one of Ti, Zr, Al, Y, Sc, Nb, and Mg, and P and q may be 5.5≤p≤6.5 and 0≤q≤0.2, respectively.

[0021] In exemplary embodiments, the first unit cell and / or the second unit cell,

[0022] It can be any one of a mono cell with a membrane / cathode / membrane / anode structure, a bi cell with a membrane / cathode / membrane / anode / membrane / anode structure, and a bi cell with a membrane / anode / membrane / cathode / membrane / anode structure.

[0023] In exemplary embodiments, the electrode assembly may further include a half-cell having a separator / cathode / separator structure or a half-cell having a separator / anode / separator structure.

[0024] In exemplary embodiments, the half-cell may be arranged on the outermost side of the electrode assembly in the thickness direction (Z direction).

[0025] In exemplary embodiments, the unit cell stack may have a ratio of the number of the first unit cells to the total number of unit cells of 20% or less.

[0026] In exemplary embodiments, the unit cell stack may have a thickness ratio of the first unit cell to the total thickness of the unit cell stack of 20% or less.

[0027] In exemplary embodiments, the first unit cell may be arranged at the bottom, center, and top, respectively, based on the thickness direction (Z direction) of the unit cell stack.

[0028] In exemplary embodiments, the electrode assembly may be any one of a stack type, a stack and folding type, and a lamination and stack type.

[0029] According to other embodiments of the present invention, a battery module including the lithium secondary battery is provided.

[0030] According to further embodiments of the present invention, a battery pack including the lithium secondary battery is provided.

[0031]

[0032] According to exemplary embodiments of the present invention, by changing the configuration of the electrode assembly, there is an effect of improving the capacity and energy density of the battery while providing excellent initial efficiency.

[0033] The effects that can be obtained from the exemplary embodiments of the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly derived and understood by those skilled in the art to which the exemplary embodiments of the present disclosure pertain from the following description. In other words, unintended effects resulting from practicing the exemplary embodiments of the present disclosure can also be derived from the exemplary embodiments of the present disclosure by those skilled in the art.

[0034]

[0035] FIG. 1 is an exploded perspective view of a lithium secondary battery according to exemplary embodiments.

[0036] Figure 2 is a cross-sectional view of an electrode assembly according to exemplary embodiments.

[0037] FIG. 3 is a cross-sectional view of a first unit cell according to exemplary embodiments.

[0038] FIG. 4 is a cross-sectional view of a second unit cell according to exemplary embodiments.

[0039] Figure 5 is a cross-sectional view of an electrode assembly according to other embodiments.

[0040] Figure 6 is a cross-sectional view of an electrode assembly according to other embodiments.

[0041]

[0042] [Explanation of symbols]

[0043] 100: Lithium secondary battery

[0044] 110, 210, 310: Electrode assembly

[0045] 120: Battery case

[0046] UCS: Unit Cell Stack

[0047] UC1: First unit cell

[0048] UC2: Second unit cell

[0049] HC: Half Cell

[0050] 130: Electrode tab

[0051] 140: Electrode lead

[0052] 150: Lead Film

[0053] 111, 111': positive pole

[0054] 112: Membrane

[0055] 113: Cathode

[0056]

[0057] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0058] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0059] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0060] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0061] In this specification, the term “combination(s) thereof” included in the surface of the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Makushi format, and means including one or more selected from the group consisting of the above components.

[0062] In this specification, the description of “A and / or B” means “A or B or both.”

[0063] In this specification, “%” means weight percent unless explicitly indicated otherwise.

[0064] In this specification, the first anode is defined as an anode included in the first unit cell, and the second anode is defined as an anode included in the second unit cell.

[0065]

[0066] FIG. 1 is an exploded perspective view of a lithium secondary battery according to exemplary embodiments. FIG. 2 is a cross-sectional view of an electrode assembly according to exemplary embodiments. FIG. 3 is a cross-sectional view of a first unit cell according to exemplary embodiments. FIG. 4 is a cross-sectional view of a second unit cell according to exemplary embodiments.

[0067] Referring to FIG. 1, a lithium secondary battery (100) according to exemplary embodiments includes a battery case (120); and an electrode assembly (110), wherein the electrode assembly (110) is housed within a housing portion (120a, 120b) of the battery case. In exemplary embodiments, the lithium secondary battery (100) can be manufactured by housing the electrode assembly (110) within the battery case (120), injecting an electrolyte (not shown), and then sealing the battery.

[0068] In exemplary embodiments, the electrode assembly (110) may be one of a stack type, a stack-and-fold type, and a lamination-and-stack type. The stack-type electrode assembly is an electrode assembly having a structure in which a predetermined number of unit cells are stacked, or in which a cathode, a separator, and anode are repeatedly stacked one by one. The stack-and-fold type electrode assembly is an electrode assembly having a structure in which unit cells are placed side by side on a folding separator and then folded from one side. The lamination-and-stack type electrode assembly is an electrode assembly having a structure in which a predetermined number of unit cells in which a separator and an electrode are joined are stacked.

[0069] Referring to FIG. 2, an electrode assembly (110) according to exemplary embodiments includes a unit cell stack (UCS). The unit cell stack (UCS) has a structure in which a plurality of unit cells (UC1, UC2) are stacked in the thickness direction (Z direction). The unit cells (UC1, UC2) may be simply stacked, or may have a structure in which the unit cells are sequentially folded and stacked by a folding separator (not shown).

[0070] Referring to FIG. 2, a unit cell stack (UCS) according to exemplary embodiments includes a first unit cell (UC1) and a second unit cell (UC2). The unit cell stack (UCS) may have a structure in which the first and second unit cells (UC1, UC2) are arranged in the thickness direction (Z direction). Referring to FIG. 3, the first unit cell (UC1) may include a first anode (111), a cathode (113), and a separator (112). Referring to FIG. 4, the second unit cell (UC2) may include a second anode (111'), a cathode (113), and a separator (112). The unit cell stack (UCS) may have a structure in which n (n is an integer greater than or equal to 2) of the first and second unit cells (UC1, UC2) are arranged in the thickness direction.

[0071] According to exemplary embodiments, at least one unit cell in the unit cell stack (UCS) is a first unit cell (UC1). The first unit cell (UC1) includes a first positive electrode (111), and the positive electrode active material of the first positive electrode (111) is composed of a first positive electrode active material represented by the following chemical formula 1.

[0072] [Chemical Formula 1]

[0073] Li p Fe (1-q) M 1 q O4

[0074] In the above chemical formula 1, M 1 is any one of W, Cu, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0075] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0076] In exemplary embodiments, M of the above chemical formula 1 1 M may be any one of Ti, Zr, Al, Y, Sc, Nb and Mg. 1The first cathode active material partially doped with a metal is preferable because it has a stabilized lattice structure and can minimize deterioration due to repeated charge and discharge.

[0077] The first positive electrode active material represented by the above chemical formula 1 is Li5FeO4, Li6FeO4, Li6Fe 0.8 Mg 0.2 O4, Li 5.5 Fe 0.9 Al 0.1 O4, Li6Fe 0.7 Ti 0.3 It may contain one or more of O4.

[0078] In exemplary embodiments, P and q of the above chemical formula 1 may be in the ranges of 5.5≤p≤6.5 and 0≤q≤0.2, respectively. When P and q are in the above ranges, the risk of electrolyte decomposition can be reduced, which is preferable.

[0079] The positive electrode active material of the above chemical formula 1 is known to have a theoretical charge capacity of about 700 mAh / g and a theoretical discharge capacity of about 40 mAh / g. Therefore, during the initial charge, lithium ions are released in larger quantities than those of general positive electrode materials, and during subsequent discharge, it has irreversible characteristics, which can compensate for the irreversible capacity loss of the negative electrode. Therefore, in the past, a small amount of the compound of the above chemical formula 1 was added to the positive electrode for the purpose of increasing the capacity of the positive electrode and improving the initial efficiency of the battery.

[0080] In the case of a battery including a positive electrode to which the compound of the above chemical formula 1 is added in a small amount of 2 to 3 wt% as a positive electrode active material, the measured values ​​of the charge capacity and the measured values ​​of the discharge capacity are smaller than the theoretical charge capacity and the theoretical discharge capacity, respectively. The inventors of the present invention have found that in the case of a battery including a positive electrode to which the compound of the above chemical formula 1 is applied 100% as a positive electrode active material, the measured values ​​of the charge capacity and the measured values ​​of the discharge capacity are the same as or similar to the theoretical charge capacity and the theoretical discharge capacity, respectively. When the compound of the above chemical formula 1 is mixed with a different type of positive electrode active material, the capacity development rate of the compound of the above chemical formula 1 is significantly reduced, but when 100% of the positive electrode active material is the compound of the above chemical formula 1, 100% capacity is developed.

[0081] Accordingly, by preparing a first unit cell (UC1) including a first positive electrode (111) to which the positive electrode active material of the chemical formula 1 is 100% applied, and including the first unit cell (UC1) in at least one unit cell stack (UCS), the present invention has achieved the effects of using the positive electrode active material of the chemical formula 1, namely, increased positive electrode capacity, increased energy density of the battery, and increased initial efficiency. The battery according to the present invention has superior initial capacity and initial efficiency, as compared to a battery in which all positive electrodes of the unit cells include the first positive electrode active material represented by the chemical formula 1 as the positive electrode active material in a predetermined range, assuming that the total weight of the first positive electrode active material represented by the chemical formula 1 in the unit cell stack is the same. In addition, the present invention can maximize the capacity development rate of the first positive electrode active material represented by the chemical formula 1, thereby reducing the content of the first positive electrode active material and increasing the content of the positive electrode active material that realizes high energy density. Therefore, the lithium secondary battery according to the present invention has the effect of increasing the energy density of the battery by changing the configuration of the electrode assembly.

[0082] The unit cell stack (UCS) above sufficiently includes at least one first unit cell (UC1). The unit cell stack (UCS) may include one first unit cell, or may include two first unit cells, or may include three first unit cells. Since the first unit cell (UC1) mainly provides lithium ions to the second unit cell (UC2) during initial charging, thereby compensating for irreversible lithium loss of the negative electrode, it is sufficient if the unit cell stack (UCS) includes a predetermined number of the first unit cells.

[0083] If the unit cell stack (UCS) is composed only of the first unit cells (UC1), it may deteriorate with repeated charge and discharge due to the material properties of the positive electrode active material of Chemical Formula 1. Therefore, the first unit cells (UC1) may be included in an amount of 20% or less, preferably 15% or less, more preferably 0.5 to 10%, and most preferably 1 to 7%, of the total number of unit cells included in the unit cell stack. When the number ratio of the first unit cells (UC1) is in the above range, a battery having excellent initial capacity and initial efficiency can be implemented while preventing side effects due to deterioration of the first unit cells. In addition, the unit cell stack may have a thickness ratio of the first unit cells to the total thickness of the unit cell stack of 20% or less, preferably 15% or less, more preferably 0.5 to 10%, and most preferably 1 to 7%. Here, the thickness of the first unit cell refers to the total thickness of the first unit cells when there are multiple first unit cells. When the thickness ratio of the first unit cells is within the above range, a battery having high energy density, excellent initial capacity, and excellent initial efficiency can be realized.

[0084] Referring to FIG. 3, the first unit cell (UC1) includes a first anode (111), a cathode (113), and a separator (112), and may have a structure in which the separator (112) is interposed between the anode (111) and the cathode (113).

[0085] The above first positive electrode (111) can be manufactured, for example, by applying the first positive electrode slurry on a positive electrode current collector, followed by drying and rolling.

[0086] The above first positive electrode slurry includes the first positive electrode active material, the positive electrode binder, and may additionally include one or more of a positive electrode conductive material, a dispersant, and other additives.

[0087] The above first positive electrode active material is as described above.

[0088] The above-mentioned positive electrode binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0089] In addition, the binder may be included in an amount of 1 to 10 parts by weight based on the weight of the positive electrode active material layer, specifically 2 to 8 parts by weight; or 1 to 5 parts by weight.

[0090] The above-mentioned positive electrode conductive material is used to improve the electrical performance of the positive electrode, and may be applied to materials commonly used in the art, but specifically may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

[0091] In addition, the positive electrode conductive material may be included in an amount of 0.1 to 10 parts by weight based on the weight of the positive electrode active material layer, and specifically, may be included in an amount of 0.1 to 5 parts by weight; 0.5 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.

[0092] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0093] The above-mentioned negative electrode (113) can be manufactured, for example, by applying negative electrode slurry on a negative electrode current collector, followed by drying and rolling.

[0094] The above negative electrode slurry includes a negative electrode active material, a negative electrode binder, and may additionally include one or more of a negative electrode conductive agent, a dispersant, and other additives.

[0095] The negative electrode active material is not particularly limited, and a compound capable of reversible intercalation and deintercalation of lithium can be typically used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, and highly crystalline carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; or a composite including a metallic compound and a carbonaceous material. In addition, examples of low-crystalline carbon include soft carbon and hard carbon, and examples of high-crystalline carbon include natural graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes. One of these may be used alone or a mixture of two or more thereof, and a metallic lithium thin film may also be used as the negative electrode active material.

[0096] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above negative electrode binder may be included in an amount of 1 to 30 wt%, specifically 1 to 20 wt%, and more specifically 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0097] The above-described negative electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The negative electrode conductive material may typically be included in an amount of 1 to 30 wt%, specifically 1 to 20 wt%, and more specifically 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0098] Meanwhile, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0099] In addition, the negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, may have fine irregularities formed on the surface of the negative electrode current collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0100] The above separator (112) can be any porous substrate used as a separator in a lithium secondary battery. For example, a polyolefin porous membrane or non-woven fabric can be used, but is not particularly limited thereto. In particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable.

[0101] Examples of the above polyolefin porous membrane include a membrane formed from a single or mixed polymer of polyolefin polymers such as polyethylene, polypropylene, polybutylene, polypentene, etc., such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

[0102] The above nonwoven fabric may include, in addition to polyolefin-based nonwoven fabrics, nonwoven fabrics formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either singly or in combination. The structure of the nonwoven fabric may be a spunbond nonwoven fabric composed of long fibers or a meltblown nonwoven fabric.

[0103] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and pore content present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0104] Meanwhile, in order to improve the mechanical strength of the separator composed of the porous substrate and to suppress short circuits between the anode and cathode, a porous coating layer including inorganic particles and a binder polymer may be further included on at least one side of the porous substrate.

[0105] As described above, the first unit cell serves to sufficiently supply lithium ions to the second unit cell described below during charging, and to compensate for irreversible capacity during discharge. As described above, the lithium secondary battery according to the present invention has the effect of increasing the energy density of the battery by changing the configuration of the electrode assembly.

[0106] Referring to FIG. 2, the unit cell stack (UCS) further includes a second unit cell (UC2) in addition to the first unit cell (UC1). The second unit cell (UC2) includes a second positive electrode (111'), and the second positive electrode (111') includes a second positive electrode active material of a different type from the first positive electrode active material as a positive electrode active material. The first positive electrode active material is rich in lithium, but the irreversibility of lithium ions is low, so that the capacity of the first positive electrode of the first unit cell rapidly decreases with repeated charge and discharge. Since the electrode assembly according to the present invention includes the second unit cell (UC2) in addition to the first unit cell (UC1), it can have the capacity and capacity retention rate required for a secondary battery.

[0107] In exemplary embodiments, when the unit cell stack (UCS) includes a plurality of second unit cells (UC2), each anode, each cathode, and each separator of the second unit cells (UC2) may have the same material and the same composition.

[0108] The above second unit cell (UC2) may include a second anode (111'), a cathode (113), and a separator (112), and may have a structure in which the separator (112) is interposed between the second anode (111') and the cathode (113).

[0109] In exemplary embodiments, the second unit cell (UC2) does not include the first positive electrode active material as the positive electrode active material of the second positive electrode (111'). As previously described, when the first positive electrode active material is mixed with another type of positive electrode active material, the capacity development rate decreases, so it is preferable that the second positive electrode (111') of the second unit cell (UC2) does not include the first positive electrode active material as the positive electrode active material.

[0110] In exemplary embodiments, the type of the second positive electrode active material is not particularly limited, as long as it is of a different type from the first positive electrode active material. That is, the second positive electrode active material may be a compound known in the art as a compound capable of reversible intercalation and deintercalation of lithium.

[0111] In exemplary embodiments, the second positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); LiV3O8, LiV3O4, V2O5, Cu2V2O Vanadium oxide, chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides expressed as O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x It may be one or more selected from the group consisting of a lithium manganese composite oxide having a spinel structure represented by O4; LiMn2O4 in which a part of the Li in the chemical formula is replaced by an alkaline earth metal ion; a disulfide compound; a lithium iron phosphate represented by LiFePO4; a disulfide compound; and Fe2(MoO4)3.

[0112] Since the first positive electrode active material contains an iron element, it is preferable for the second positive electrode active material to contain lithium iron phosphate having an olivine structure containing an iron element in order to maximize the efficiency of the present invention.

[0113] In exemplary embodiments, the lithium iron phosphate having the olivine structure may be a compound represented by the following chemical formula 2.

[0114] [Chemical Formula 2]

[0115] LiFe x M 2 y PO4

[0116] In the above chemical formula 2, M 2 is at least one of Ni, Co, Mn, W, Cu, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0117] x is 1-y, and y is 0≤y≤0.8.

[0118] In exemplary embodiments, the lithium nickel oxide may be a lithium transition metal oxide having a high Ni content represented by the following chemical formula 3. A lithium transition metal oxide represented by the following chemical formula 3 is preferable in terms of increasing energy density.

[0119] [Chemical Formula 3]

[0120] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O 2-y A y

[0121] In the above formula,

[0122] M is at least one selected from the group consisting of Cu, Ti, Mg, Al, Pt, and Zr,

[0123] A is an oxygen-substituting halogen,

[0124] 0≤x≤0.5, 0.8≤a≤1, 0≤b≤0.2, 0≤c≤0.2, 0.9≤a+b+c≤1, and 0≤y≤0.001.

[0125] The details of the cathode and separator included in the second unit cell (UC2) are the same as those of the cathode and separator included in the first unit cell, so duplicate descriptions are omitted.

[0126] Referring to FIG. 2, the first unit cell (UC1) may be arranged at the center of the unit cell stack (UCS) in the thickness direction (Z direction). The electrode tab of the unit cell arranged at the center of the unit cell stack is shorter than the electrode tab of the unit cell arranged at the outermost end in the thickness direction of the unit cell stack, and the first unit cell plays a role in sufficiently providing lithium ions to the second unit cell. Therefore, when the first unit cell is arranged at the center, the effect of increasing the energy density of the battery can be further maximized.

[0127] Figure 5 is a cross-sectional view of an electrode assembly according to other embodiments.

[0128] Referring to Fig. 5, the first unit cells (UC1) can be respectively arranged at the bottom, center, and top in the thickness direction (Z direction) of the unit cell stack (UCS). Since the first unit cells play a role in sufficiently providing lithium ions to the second unit cells, if the first unit cells are evenly arranged at the bottom, center, and top, there is an advantage in that the deviation in the amount of lithium ions provided due to the deviation in the thickness direction position of the second unit cells can be reduced.

[0129] Figure 6 is a cross-sectional view of an electrode assembly according to other embodiments.

[0130] Referring to FIG. 6, the electrode assembly (310) may further include a half-cell (HC) having a separator (112) / cathode (113) / separator (112) structure. However, the structure of the half-cell is not limited thereto, and the half-cell may also have a separator / anode / separator structure. The half-cell (HC) may be arranged on the outermost side based on the thickness direction (Z direction) of the electrode assembly (310).

[0131] Below, the electrolyte included in the lithium secondary battery of the present invention is described in detail.

[0132] In exemplary embodiments, the electrolyte may include an organic solvent and a lithium salt commonly used in the electrolyte, but is not particularly limited thereto.

[0133] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC) can be used.

[0134] Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0135] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the lithium salt be included in the electrolyte at a concentration of approximately 0.6 mol% to 2 mol%.

[0136] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0137] Unlike the lithium secondary battery described above, a lithium secondary battery according to another embodiment of the present invention may be an all-solid-state battery.

[0138] The above battery case can be adopted as one commonly used in the field, and there is no limitation on the external shape according to the use of the battery. For example, it can be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0139] Meanwhile, the present invention provides a battery module and a battery pack including the secondary battery described above as a unit battery in one embodiment.

[0140] The above battery pack can be used as a power source for medium- to large-sized devices that require high-temperature stability, long cycle characteristics, and high-rate characteristics, and specific examples of such medium- to large-sized devices include, but are not limited to, power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); electric golf carts; and power storage systems, and more specifically, hybrid electric vehicles (HEVs) are exemplified, but are not limited thereto.

[0141]

[0142] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0143]

[0144] Example 1

[0145] (Manufacturing of the first unit cell)

[0146] A positive electrode slurry was prepared by mixing and stirring Li5FeO4 as a first positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material in a weight ratio of 94:3:3 in N-methylpyrrolidone. The positive electrode slurry was applied to aluminum foil, dried, and rolled to prepare a first positive electrode.

[0147] An anode slurry was prepared by mixing and stirring artificial graphite (particle size: 20 μm) as an anode active material, styrene butadiene rubber (SBR) as a binder, and carbon black as a conductive material in a weight ratio of 90:5:5 in water. The anode slurry was applied to a copper foil, dried, and rolled to prepare an anode.

[0148] A polyethylene porous separator (20 μm thick) was prepared, and the separator / the first anode / the separator / the cathode were sequentially laminated to manufacture a first unit cell.

[0149] (Manufacturing of the second unit cell)

[0150] A cathode slurry was prepared by mixing and stirring LiFePO4 as a second cathode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material in a weight ratio of 94:3:3 in N-methylpyrrolidone. The cathode slurry was applied to aluminum foil, dried, and rolled to prepare a second cathode.

[0151] An anode slurry was prepared by mixing and stirring artificial graphite (particle size: 20 μm) as an anode active material, styrene butadiene rubber (SBR) as a binder, and carbon black as a conductive material in a weight ratio of 90:5:5 in water. The anode slurry was applied to a copper foil, dried, and rolled to prepare an anode.

[0152] A second unit cell was manufactured by sequentially stacking the above separator / the second anode / the above separator / the above cathode.

[0153] (Battery manufacturing)

[0154] One first unit cell and nineteen second unit cells were prepared, the first unit cell was placed at the bottom, and nineteen second unit cells were stacked on top of it in the thickness direction to manufacture an electrode assembly.

[0155] The above electrode assembly was housed in a pouch-type battery case, an electrolyte was injected, and the pouch-type battery case was sealed to complete the manufacture of the battery.

[0156]

[0157] Example 2

[0158] In the above Example 1, a battery was manufactured in the same manner as in the above Example 1, except that the first unit cell was placed 10th from the bottom during the manufacture of the battery.

[0159]

[0160] Comparative example

[0161] (Manufacturing of unit cells)

[0162] A mixture of LiFePO4 and Li5FeO4 in a weight ratio of 95:5 was used as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material was mixed and stirred in N-methylpyrrolidone to prepare a positive electrode slurry. At this time, among the solid content of the positive electrode slurry, the positive electrode active material, binder, and conductive material were mixed in a weight ratio of 94:3:3. The positive electrode slurry was applied to aluminum foil, dried, and rolled to prepare a positive electrode.

[0163] An anode slurry was prepared by mixing and stirring artificial graphite (particle size: 20 μm) as an anode active material, styrene butadiene rubber (SBR) as a binder, and carbon black as a conductive material in a weight ratio of 90:5:5 in water. The anode slurry was applied to a copper foil, dried, and rolled to prepare an anode.

[0164] A polyethylene porous separator (20 μm thick) was prepared, and the separator / the anode / the separator / the cathode were sequentially laminated to manufacture a unit cell.

[0165] (Battery manufacturing)

[0166] Twenty of the above unit cells were prepared, and the 20 unit cells were sequentially stacked in the thickness direction to manufacture an electrode assembly. The electrode assembly was housed in a pouch-type battery case, an electrolyte was injected, and the pouch-type battery case was sealed to complete the manufacture of the battery.

[0167]

[0168] Experimental Example 1: Measurement of Capacity

[0169] Each battery of Examples 1 to 2 and Comparative Example was charged to 3.65 V at a current of 0.1 C in a charge / discharge chamber at 25°C, and then discharged to 2.5 V. At this time, the discharge capacity was measured, and the results are shown in Table 1.

[0170]

[0171] Experimental Example 2: Initial Efficiency of the Battery

[0172] Each battery of Examples 1-2 and Comparative Example was charged to 4.0 V under 0.1 C charging conditions at 25°C to check the charge capacity, and then discharged to 2.5 V under 0.1 C discharging conditions at the same temperature to check the discharge capacity. In addition, the percentage of discharge capacity compared to charge capacity at this time was calculated as the initial efficiency, and the results are shown in Table 1.

[0173] Discharge capacity (Ah) Initial efficiency (%) Example 129.189 Example 231.090 Comparative example 28.985

[0174]

[0175] Referring to Table 1, it can be confirmed that the batteries according to the Examples have better capacity and initial efficiency compared to the batteries according to the Comparative Examples. It is believed that the batteries according to the Examples have a capacity development rate of 100% of the first positive electrode active material due to the presence of a first unit cell to which 100% of the first positive electrode active material is applied, whereas the batteries of the Comparative Examples are composed of unit cells including a positive electrode in which the first positive electrode active material and the second positive electrode active material are mixed, resulting in a significantly lower capacity development rate of the first positive electrode active material.

[0176]

[0177] The present invention has been described in more detail through drawings and examples. However, the configurations described in the drawings or examples described in this specification are merely embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

Claims

1. A lithium secondary battery comprising a battery case; and an electrode assembly housed inside the battery case. The above electrode assembly, A unit cell laminate comprising n (n is an integer greater than or equal to 2) unit cells including an anode and a cathode arranged in the thickness direction, The above unit cell stack includes a first unit cell and a second unit cell, The first unit cell includes a first positive electrode, A lithium secondary battery characterized in that the positive electrode active material of the first positive electrode is composed of a first positive electrode active material represented by the following chemical formula 1: [Chemical Formula 1] Li p Fe (1-q) M 1 q O4 In the above chemical formula 1, M 1 is any one of W, Cu, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

2. In paragraph 1, A lithium secondary battery, characterized in that the second unit cell includes a second positive electrode, and the second positive electrode includes a second positive electrode active material of a different type from the first positive electrode active material as a positive electrode active material.

3. In paragraph 1, A lithium secondary battery characterized in that the second unit cell includes a second positive electrode, and the second positive electrode includes lithium iron phosphate having an olivine structure including an iron element as a positive electrode active material.

4. In paragraph 2 or 3, A lithium secondary battery characterized in that the second positive electrode is a positive electrode active material and does not contain the first positive electrode active material.

5. In paragraph 1, A lithium secondary battery, characterized in that the first unit cell is arranged centrally in the thickness direction (Z direction) of the unit cell stack.

6. In paragraph 1, In the above chemical formula 1, M 1 is any one of Ti, Zr, Al, Y, Sc, Nb and Mg, P and q are 5.5≤p≤6.5 and 0≤q≤0.2, respectively.

7. In paragraph 1, The first unit cell and / or the second unit cell, A lithium secondary battery characterized by any one of a mono-cell having a separator / cathode / separator / anode structure, a bi-cell having a separator / cathode / separator / anode / separator / anode structure, and a bi-cell having a separator / anode / separator / anode / separator / anode / separator / anode structure.

8. In paragraph 1, The above electrode assembly further includes a half-cell having a separator / cathode / separator structure or a half-cell having a separator / anode / separator structure, A lithium secondary battery, characterized in that the above half-cell is arranged on the outermost side based on the thickness direction (Z direction) of the electrode assembly.

9. In paragraph 1, A lithium secondary battery, characterized in that the unit cell stack has a ratio of the number of the first unit cells to the total number of unit cells of 20% or less.

10. In paragraph 1, A lithium secondary battery, characterized in that the unit cell stack has a thickness ratio of the first unit cell to the total thickness of the unit cell stack of 20% or less.

11. In paragraph 1, A lithium secondary battery, characterized in that the first unit cells are arranged at the bottom, center, and top, respectively, based on the thickness direction (Z direction) of the unit cell stack.

12. In paragraph 1, A lithium secondary battery characterized in that the electrode assembly is one of a stack type, a stack and folding type, and a lamination and stack type.

13. A battery module including the lithium secondary battery of paragraph 1.

14. A battery pack including the lithium secondary battery of paragraph 1.

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