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

Abstract

A lithium secondary battery according to an exemplary embodiment includes: a battery case; and an electrode assembly accommodated inside the battery case, in which the electrode assembly includes a unit cell stack in which n (n is an integer of 2 or more) unit cells each including a positive electrode and a negative electrode are arranged in the thickness direction, the unit cell stack including a first unit cell including a first positive electrode and a second unit cell including a second negative electrode, and a positive electrode active material of the first positive electrode is configured from a first positive electrode active material represented by the following Chemical Formula 1. [Chemical Formula 1] LipFe (1-q) M1qO4 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 are 5 < = p < = 7 and 0 < = q < = 0.5, respectively.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0084840, filed on June 27, 2024, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to a lithium secondary battery, as well as a battery module and battery pack comprising the same. Background Technology

[0003] In recent years, the demand for lithium-ion batteries has grown in various fields such as electric vehicles, smartphones and wearable devices, but there is a continued demand for devices with higher energy in a limited space.

[0004] To improve the electrochemical capacity of lithium secondary batteries, there are methods to improve the performance of the cathode material or to minimize the amount of lithium ions consumed by the formation of SEI at the anode.

[0005] On the other hand, various techniques exist to compensate for the lithium ions consumed during SEI formation, such as pre-lithiation and Li alloying, but their industrial application is limited due to process difficulties. Therefore, a method has been researched and proposed to compensate for the consumed lithium ions by adding lithium-based additives to the cathode material as a sacrificial cathode material.

[0006] (Patent Document 1) Korean pending patent publication No. 10-2021-00655655 Summary of the Invention

[0007] Technical issues

[0008] The problem that this invention aims to solve is to provide a lithium secondary battery with improved initial efficiency and energy density.

[0009] Technical solution

[0010] According to an exemplary embodiment of the present invention, in order to solve the above-mentioned problems, a lithium secondary battery is provided. The lithium secondary battery includes: a battery casing; and an electrode assembly housed inside the battery casing. The electrode assembly comprises a stack of n (n is an integer greater than or equal to 2) unit cells, each containing a positive electrode and a negative electrode, arranged in the thickness direction. The cell stack comprises a first cell and a second cell. The first cell includes a first positive electrode, and The positive electrode active material of the first positive electrode is composed of the first positive electrode active material represented by the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012] Li p Fe (1-q) M 1 q O4

[0013] In chemical formula 1, M 1 It 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 are 5≤p≤7 and 0≤q≤0.5, respectively.

[0014] In an exemplary embodiment, the second cell includes a second positive electrode, and the second positive electrode may include a second positive electrode active material of a different type than the first positive electrode active material as the positive electrode active material.

[0015] In an exemplary embodiment, the second cell includes a second positive electrode, and the second positive electrode may include lithium iron phosphate with an olivine structure containing iron as the positive electrode active material.

[0016] In an exemplary embodiment, the second positive electrode does not contain the first positive electrode active material as the positive electrode active material.

[0017] In an exemplary embodiment, the first cell may be disposed at the center of the cell stack along the thickness direction (Z direction).

[0018] In an exemplary embodiment, in chemical formula 1, M 1 It can be any one of Ti, Zr, Al, Y, Sc, Nb, and Mg, and p and q can be 5.5≤p≤6.5 and 0≤q≤0.2, respectively.

[0019] In an exemplary embodiment, the first cell and / or the second cell can be any one of a single cell having a separator / negative electrode / separator / positive electrode structure, a dual cell having a separator / negative electrode / separator / positive electrode / separator / negative electrode structure, and a dual cell having a separator / positive electrode / separator / negative electrode / separator / positive electrode structure.

[0020] In an exemplary embodiment, the electrode assembly may further include a half-cell having a separator / negative electrode / separator structure or a half-cell having a separator / positive electrode / separator structure.

[0021] In an exemplary embodiment, the half-cell may be disposed at the outermost part of the electrode assembly based on the thickness direction (Z direction).

[0022] In an exemplary embodiment, the ratio of the number of first cell cells to the total number of cell cells in the cell stack can be less than 20%.

[0023] In an exemplary embodiment, the ratio of the thickness of the first cell to the total thickness of the cell stack can be less than 20%.

[0024] In an exemplary embodiment, the first cell may be disposed at each of the lower, central, and upper portions of the cell stack based on the thickness direction (Z direction).

[0025] In an exemplary embodiment, the electrode assembly can be any of the following types: stacked, stacked folded, and layered stacked.

[0026] According to other embodiments of the present invention, a battery module including the lithium secondary battery is provided.

[0027] According to another embodiment of the present invention, a battery pack comprising the lithium secondary battery is provided.

[0028] Beneficial effects

[0029] According to an exemplary embodiment of the present invention, by changing the configuration of the electrode assembly, it is possible to improve the battery capacity and energy density while maintaining excellent initial efficiency.

[0030] The technical effects achievable in the exemplary embodiments of the present invention are not limited to those described above, and those skilled in the art can clearly deduce and understand other effects not mentioned from the following description. In other words, those skilled in the art can also deduce unintended effects from implementing the exemplary embodiments of the present invention. Attached Figure Description

[0031] Figure 1 This is an exploded perspective view of a lithium secondary battery according to an exemplary embodiment.

[0032] Figure 2 This is a cross-sectional view of an electrode assembly according to an exemplary embodiment.

[0033] Figure 3 This is a cross-sectional view of the first cell according to an exemplary embodiment.

[0034] Figure 4 This is a cross-sectional view of the second cell according to an exemplary embodiment.

[0035] Figure 5 This is a cross-sectional view of an electrode assembly according to other embodiments.

[0036] Figure 6This is a cross-sectional view of an electrode assembly according to other embodiments.

[0037] [Explanation of reference numerals in the attached figures]

[0038] 100: Lithium secondary battery

[0039] 110, 210, 310: Electrode assemblies

[0040] 120: Battery casing

[0041] UCS: Cell Stack

[0042] UC1: First unit battery

[0043] UC2: Second unit battery

[0044] HC: Half-cell

[0045] 130: Electrode tabs

[0046] 140: Electrode lead

[0047] 150: Lead film

[0048] 111, 111': Positive electrode

[0049] 112: Diaphragm

[0050] 113: Negative electrode Detailed Implementation

[0051] The present invention will be described in more detail below to aid in understanding it.

[0052] The terms or words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings, but rather as meanings and concepts consistent with the technical idea of ​​the invention, based on the principle that the inventors are able to appropriately define the concepts of the terms in order to best describe their invention.

[0053] The terminology used in this specification is for describing exemplary embodiments only and is not intended to limit the invention. Unless the context clearly specifies otherwise, singular expressions include plural expressions.

[0054] The terms “comprising,” “including,” or “having” as used herein specify the presence of the features, figures, steps, constituent elements, or combinations thereof described in the specification, and should be understood not to preclude the possibility of the presence or addition of one or more other features, figures, steps, constituent elements, or combinations thereof.

[0055] In this specification, the term "combination thereof" included in the Markush-type representation means a mixture or combination of more than one of the constituent elements described in the Markush-type representation, and means including more than one of the constituent elements.

[0056] In this specification, the description of "A and / or B" means "A or B or both".

[0057] In this specification, unless otherwise expressly stated, “%” represents weight.

[0058] In this specification, the first positive electrode is defined as the positive electrode contained in the first cell, and the second positive electrode is defined as the positive electrode contained in the second cell.

[0059] Figure 1 This is an exploded perspective view of a lithium secondary battery according to an exemplary embodiment.

[0060] Figure 2 This is a cross-sectional view of an electrode assembly according to an exemplary embodiment.

[0061] Figure 3 This is a cross-sectional view of the first cell according to an exemplary embodiment.

[0062] Figure 4 This is a cross-sectional view of the second cell according to an exemplary embodiment.

[0063] refer to Figure 1 A lithium secondary battery 100 according to an exemplary embodiment includes a battery casing 120 and an electrode assembly 110, wherein the electrode assembly 110 is housed within receiving portions 120a and 120b of the battery casing. In an exemplary embodiment, the lithium secondary battery 100 can be manufactured by accommodating the electrode assembly 110 in the battery casing 120, injecting an electrolyte (not shown), and then sealing it.

[0064] In an exemplary embodiment, the electrode assembly 110 can be any of a stacked type, a stacked-folded type, and a layered-stacked type. A stacked electrode assembly is an electrode assembly having a structure in which a predetermined number of cell units are stacked, or a positive electrode, a separator, and a negative electrode are stacked in sequence. A stacked-folded electrode assembly is an electrode assembly having a structure in which cell units are placed side-by-side on a folded separator and then folded from one side. A layered-stacked electrode assembly is an electrode assembly having a structure in which a predetermined number of cell units are stacked (where the separator and electrodes are combined).

[0065] refer to Figure 2The electrode assembly 110 according to an exemplary embodiment includes a cell stack body UCS. The cell stack body UCS has a structure in which a plurality of cell cells UC1, UC2 are stacked in the thickness direction (Z direction). The cell cells UC1, UC2 may have a structure in which they are simply stacked or the cell cells are sequentially folded and stacked by means of a folded separator (not shown).

[0066] refer to Figure 2 According to an exemplary embodiment, a cell stack UCS includes a first cell UC1 and a second cell UC2. The cell stack UCS may have a structure in which the first cell UC1 and the second cell UC2 are arranged in the thickness direction (Z direction).

[0067] refer to Figure 3 The first unit battery UC1 may include a first positive electrode 111, a negative electrode 113 and a separator 112.

[0068] refer to Figure 4 The second cell UC2 may include a second positive electrode 111', a negative electrode 113, and a separator 112. The cell stack UCS may have the form in which n (n is an integer greater than 2) first cell UC1 and second cell UC2 are arranged in the thickness direction.

[0069] According to an exemplary embodiment, at least one cell in the cell stack UCS is a first cell UC1. The first 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.

[0070] [Chemical Formula 1]

[0071] Li p Fe (1-q) M 1 q O4

[0072] In chemical formula 1, M 1 It 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

[0073] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0074] In an exemplary embodiment, M in chemical formula 1 1 It can be any of Ti, Zr, Al, Y, Sc, Nb, and Mg. Partially doped with M. 1The first positive electrode active material of the metal is preferred because the crystal structure is stabilized, thereby minimizing the degradation caused by repeated charge-discharge cycles.

[0075] The first positive electrode active material represented by chemical formula 1 may include Li5FeO4, Li6FeO4, and Li6Fe 0.8 Mg 0.2 O4, Li 5.5 Fe 0.9 Al 0.1 O4, Li6Fe 0.7 Ti 0.3 One or more of O4.

[0076] In an exemplary embodiment, p and q in Formula 1 can be in the ranges of 5.5 ≤ p ≤ 6.5 and 0 ≤ q ≤ 0.2, respectively. When p and q are within these ranges, it is preferred because the risk of electrolyte decomposition can be reduced.

[0077] The theoretical charge capacity of the positive electrode active material of Chemical Formula 1 is known to be approximately 700 mAh / g, and the theoretical discharge capacity is approximately 40 mAh / g. Therefore, during the initial charging period, it releases lithium ions in greater quantities than typical positive electrode materials, and subsequently, during discharge, the positive electrode active material exhibits irreversible properties, enabling it to compensate for the irreversible capacity loss of the negative electrode. Therefore, in related technical fields, a small amount of a compound of Chemical Formula 1 is added to the positive electrode to improve its capacity and the initial efficiency of the battery.

[0078] When a battery contains a positive electrode in which a small amount of a compound of Formula 1 is added at a weight level of 2 to 3% as the positive electrode active material, the measured values ​​of charging capacity and discharging capacity are less than the theoretical charging capacity and theoretical discharging capacity, respectively. The inventors of this invention have discovered that when a battery contains a positive electrode in which 100% of the compound of Formula 1 is used as the positive electrode active material, the measured values ​​of charging capacity and discharging capacity are equal to or similar to the theoretical charging capacity and theoretical discharging capacity, respectively. When the compound of Formula 1 is mixed with different types of positive electrode active materials, the capacity expression rate of the compound of Formula 1 is significantly reduced, but when 100% of the positive electrode active material is the compound of Formula 1, 100% of the capacity is expressed.

[0079] Therefore, by preparing a first cell UC1 containing a first positive electrode 111 (to which 100% of the positive electrode active material of Formula 1 is applied), and including at least one first cell UC1 in a cell stack UCS, the present invention achieves the effects of using the positive electrode active material of Formula 1, namely, increased positive electrode capacity, increased battery energy density, and increased initial efficiency. When assuming the total weight of the first positive electrode active material represented by Formula 1 in the cell stack is the same, the battery according to the present invention has superior initial capacity and initial efficiency compared to a battery in which all positive electrodes of the cell contain a predetermined range of the first positive electrode active material represented by Formula 1 as the positive electrode active material. Furthermore, the present invention can maximize the capacity expression of the first positive electrode active material represented by Formula 1, thereby enabling a corresponding reduction in the content of the first positive electrode active material and an increase in the content of the positive electrode active material that achieves 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.

[0080] It is sufficient for the cell stack UCS to contain at least one first cell UC1. The cell stack UCS may contain one first cell, two first cells, or three first cells. Because the first cell UC1 primarily supplies lithium ions to the second cell UC2 during the initial charging period and is used to compensate for irreversible lithium loss at the negative electrode, it is sufficient if the cell stack UCS contains a predetermined number of first cells UC1.

[0081] If the cell stack UCS consists only of the first cell UC1, it may degrade due to repeated charge-discharge cycles due to the material properties of the positive electrode active material of Formula 1. Therefore, the first cell UC1 can be included in the range of 20% or less, preferably 15% or less, more preferably 0.5% to 10%, and most preferably 1% to 7%, relative to the total number of cells included in the cell stack. When the number of first cells UC1 is within the above range, a battery with excellent initial capacity and initial efficiency can be achieved while preventing side effects caused by the degradation of the first cell. Furthermore, in the cell stack, the ratio of the thickness of the first cell to the total thickness of the cell stack can be 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 cell refers to the total thickness of the first cells when there are multiple first cells. When the thickness ratio of the first cells is within the above range, a battery with high energy density and excellent initial capacity and initial efficiency can be achieved.

[0082] refer to Figure 3 The first unit battery UC1 includes a first positive electrode 111, a negative electrode 113 and a separator 112, and may have a structure in which the separator 112 is located between the positive electrode 111 and the negative electrode 113.

[0083] The first positive electrode 111 can be manufactured, for example, by coating a first positive electrode slurry onto a positive electrode current collector, then drying and calendering it.

[0084] The first positive electrode slurry includes a first positive electrode active material and a positive electrode binder, and may also include one or more of the following: a positive electrode conductive material, a dispersant, and other additives.

[0085] The first positive electrode active material is as described above.

[0086] A positive electrode binder is used to bond positive electrode active materials, positive electrode additives, and conductive materials together, and can be used without particular limitations, as long as it has this function. Specifically, the binder may include one or more resins selected from: polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0087] In addition, based on the weight of the positive electrode active material 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.

[0088] Positive electrode conductive materials are used to improve the electrical properties of the positive electrode, and materials commonly used in the art can be applied. However, specifically, positive electrode conductive materials may include one or more of the following substances: natural graphite, artificial graphite, carbon black, acetylene black, Danka black, Ketjen black, Super-P, channel black, furnace black, lamp black, thermal cracking black, graphene, and carbon nanotubes.

[0089] Furthermore, based on the weight of the positive electrode active material layer, the content of the positive electrode conductive material can be 0.1 to 10 parts by weight, specifically 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.

[0090] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause chemical changes in the battery. It can be made of materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector can typically range from 3 to 500 μm, and the adhesion of the positive electrode active material can be enhanced by forming micro-protrusions on the surface of the current collector. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0091] The negative electrode 113 can be manufactured, for example, by coating a negative electrode slurry onto a negative electrode current collector, then drying and calendering it.

[0092] The negative electrode slurry contains negative electrode active material and negative electrode binder, and may also contain one or more of negative electrode conductive material, dispersant and other additives.

[0093] There are no particular restrictions on the negative electrode active material, and compounds capable of reversibly inserting and deintercalating lithium can generally be used. Specific examples include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon, and highly crystalline carbon; (semi-metallic) materials capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; or composites containing (semi-metallic) materials and carbonaceous materials. Furthermore, examples of low-crystallinity carbon include soft carbon and hard carbon, and examples of highly crystalline carbon include high-temperature calcined carbon such as natural graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch. One of these materials can be used alone, or a mixture of two or more can be used, and thin films of metallic lithium can also be used as the negative electrode active material.

[0094] A negative electrode binder is used to improve the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include: polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and may be used alone or in mixtures of two or more thereof. Based on the total weight of the negative electrode active material layer, the content of the negative electrode binder may be 1 to 30% by weight, specifically 1 to 20% by weight, more specifically 1 to 10% by weight.

[0095] Negative electrode conductive materials are used to impart conductivity to the electrode and can be used without particular restrictions, as long as they do not cause chemical changes in the battery and are electronically conductive. Specific examples include: graphite such as natural or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, carbon fibers, and carbon nanotubes; metal powders or 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 can be used alone or in mixtures of two or more. Based on the total weight of the negative electrode active material layer, the content of the negative electrode conductive material can typically be 1 to 30% by weight, specifically 1 to 20% by weight, and more specifically 1 to 10% by weight.

[0096] On the other hand, there are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery, and it can be, for example: copper; stainless steel; aluminum; nickel; titanium; calcined carbon; materials with surface treatments of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel; aluminum-cadmium alloys, etc.

[0097] Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, the adhesion of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the negative electrode current collector. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0098] The separator 112 can be any porous substrate used as a separator in a lithium secondary battery, and can be, for example, a polyolefin porous membrane or a nonwoven fabric, but is not particularly limited thereto. In particular, it is preferred that the separator has low resistance to the movement of electrolyte ions and excellent electrolyte retention capacity.

[0099] Examples of polyolefin porous membranes include membranes formed individually or as mixtures thereof from polyolefin polymers such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene), polypropylene, polybutene, and polypentene.

[0100] Besides polyolefin-based nonwoven fabrics, examples of nonwoven fabrics also include those formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate, either individually or as mixtures thereof. The structure of the nonwoven fabric can be spunbond nonwoven fabric or meltblown nonwoven fabric composed of long fibers.

[0101] There are no particular restrictions on the thickness of the porous substrate, but it can be 5 to 50 μm. There are also no particular restrictions on the pore size and porosity present in the porous substrate, but they can be 0.01 to 50 μm and 10% to 95%, respectively.

[0102] On the other hand, in order to improve the mechanical strength of the diaphragm made of porous substrate and suppress short circuits between the positive and negative electrodes, a porous coating comprising inorganic particles and binder polymers may be further included on at least one surface of the porous substrate.

[0103] As described above, the first cell provides sufficient lithium ions for the second cell (described later) during charging and compensates for irreversible capacity loss during discharging. As also described above, the lithium secondary battery according to the invention achieves increased energy density by altering the configuration of the electrode assembly.

[0104] refer to Figure 2 The cell stack UCS includes a second cell UC2 in addition to the first cell UC1. The second cell UC2 includes a second positive electrode 111', and the second positive electrode 111' contains a second positive electrode active material of a different type than the first positive electrode active material. Because the first positive electrode active material is rich in lithium but has low lithium-ion irreversibility, the capacity of the first positive electrode of the first cell rapidly decreases due to repeated charge-discharge cycles. Because the electrode assembly according to the present invention includes a second cell UC2 in addition to the first cell UC1, it can have the capacity and capacity retention rate required for a secondary battery.

[0105] In an exemplary embodiment, when the cell stack UCS includes a plurality of second cell UC2, the positive electrode, negative electrode and separator of each second cell UC2 may have the same material and the same composition.

[0106] The second unit battery UC2 includes a second positive electrode 111', a negative electrode 113 and a separator 112, and may have a structure in which the separator 112 is located between the second positive electrode 111' and the negative electrode 113.

[0107] In an exemplary embodiment, the second cell UC2 does not contain the first positive electrode active material as the positive electrode active material of the second positive electrode 111'. As can be seen above, when the first positive electrode active material is mixed with different types of positive electrode active materials, the capacity expression rate decreases. Therefore, it is preferable that the second positive electrode 111' of the second cell UC2 does not contain the first positive electrode active material as the positive electrode active material.

[0108] In the exemplary embodiment, there is no particular limitation on the type of the second positive electrode active material, as long as it is different from the type of the first positive electrode active material. That is, as the second positive electrode active material, compounds known in the art can be used as compounds capable of reversibly inserting and deintercalating lithium.

[0109] In an exemplary embodiment, the second positive electrode active material may be one or more of the following substances: layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or compounds replaced by one or more transition metals; lithium manganese oxide such as Li 1+x Mn 2-x O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5 or Cu2V2O7; and 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); by chemical formula LiMn 2- x M x Lithium manganese composite oxides represented by 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); and LiNi x Mn 2-x O4 represents lithium manganese composite oxides with a spinel structure; LiMn2O4, wherein part of the Li in the chemical formula is replaced by alkaline earth metal ions; disulfide compounds; lithium iron phosphate represented by LiFePO4; or Fe2(MoO4)3.

[0110] Since the first positive electrode active material contains iron, it is preferable that the second positive electrode active material comprises lithium iron phosphate with an olivine structure containing iron to maximize the efficiency of the present invention.

[0111] In an exemplary embodiment, the lithium iron phosphate having an olivine structure can be a compound represented by the following chemical formula 2.

[0112] [Chemical Formula 2]

[0113] LiFe x M 2 y PO4

[0114] In chemical formula 2, M 2It is one or more 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. x is 1-y, and y is 0≤y≤0.8.

[0115] In an exemplary embodiment, the lithium nickel oxide can be a lithium transition metal oxide with a high Ni content, represented by the following chemical formula 3. Lithium transition metal oxides represented by the following chemical formula 3 are preferred for improving energy density.

[0116] [Chemical Formula 3]

[0117] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O 2-y A y

[0118] In the above chemical formula, M is selected from at least one of Cu, Ti, Mg, Al, Pt, and Zr. A is an oxygen-substituted halogen, and 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.

[0119] The detailed description of the negative electrode and separator contained in the second cell UC2 is the same as that of the negative electrode and separator contained in the first cell, so redundant descriptions are omitted.

[0120] refer to Figure 2 The first cell UC1 can be located at the center of the cell stack UCS in the thickness direction (Z direction). The electrode tab of the cell located at the center of the cell stack has a shorter length compared to the electrode tab of the cell located at the outermost part of the cell stack in the thickness direction. Since the first cell is used to provide sufficient lithium ions for the second cell, the effect of increasing the energy density of the battery can be further maximized when the first cell is located at the center.

[0121] Figure 5 This is a cross-sectional view of an electrode assembly according to other embodiments.

[0122] refer to Figure 5The first cell UC1 can be disposed at each of the lower, central, and upper portions of the cell stack UCS based on the thickness direction (Z direction). Since the first cell is used to provide sufficient lithium ions for the second cell, it is advantageous to uniformly dispose the first cell at the lower, central, and upper portions to reduce the deviation in the amount of lithium ions provided due to positional deviations in the thickness direction of the second cell.

[0123] Figure 6 This is a cross-sectional view of an electrode assembly according to other embodiments.

[0124] refer to Figure 6 The electrode assembly 310 may further include a half-cell HC having a separator 112 / negative electrode 113 / separator 112 structure. However, the structure of the half-cell is not limited to this, and the half-cell may have a separator / positive electrode / separator structure. The half-cell HC may be disposed at the outermost part of the electrode assembly 310 based on the thickness direction (Z direction).

[0125] The electrolyte contained in the lithium secondary battery of the present invention will be described in detail below.

[0126] In an exemplary embodiment, the electrolyte may contain commonly used organic solvents and lithium salts, and there are no particular limitations.

[0127] As organic solvents, any solvent capable of serving as a medium through which ions participating in the battery electrochemical reaction can move can be used without particular limitation. Specifically, as organic solvents, the following can be used: 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; and carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0128] Preferably, a carbonate solvent is used; more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge-discharge performance of the battery and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is used.

[0129] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Preferably, the lithium salt is contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0130] To improve battery life characteristics, suppress battery capacity degradation, and improve battery discharge capacity, in addition to the electrolyte component, the electrolyte may contain one or more additives, such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine, N,N-substituted imidazolidine, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of additives can be from 0.1 to 5% by weight, based on the total weight of the electrolyte.

[0131] Unlike the lithium secondary battery described above, the lithium secondary battery according to another embodiment of the present invention can be an all-solid-state battery.

[0132] The battery case can be a battery case commonly used in this field, and its appearance is not limited depending on the purpose of the battery. For example, it can be a cylindrical, prismatic, pouch-shaped, or coin-shaped case.

[0133] On the other hand, the present invention provides a battery module and a battery pack that include the secondary battery in one of the above embodiments as a unit battery.

[0134] Battery packs can be used as power sources for medium to large-sized devices that require high-temperature stability, long cycle life, and high rate capability. Specific examples of such devices include: power tools driven by electric motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles, including electric bicycles and electric scooters; electric golf carts; energy storage systems, and more specifically, hybrid electric vehicles (HEVs), but not limited thereto.

[0135] The present invention will be described in more detail below through embodiments. However, the following embodiments are used to illustrate the present invention, and the scope of the present invention is not limited thereto.

[0136] Example 1

[0137] (Manufacturing of the first cell)

[0138] A positive electrode slurry was prepared by mixing Li5FeO4 (as the first positive electrode active material), polyvinylidene fluoride (PVdF) (as a binder), and carbon black (as a conductive material) in N-methylpyrrolidone at a weight ratio of 94:3:3 and stirring. The positive electrode slurry was then coated onto aluminum foil, dried, and calendered to manufacture the first positive electrode.

[0139] A negative electrode slurry was prepared by mixing artificial graphite (particle size: 20 μm) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carbon black as the conductive material in water at a weight ratio of 90:5:5 and stirring. The negative electrode slurry was then coated onto copper foil, dried, and calendered to manufacture the negative electrode.

[0140] Prepare a porous polyethylene separator (20 μm thick) and stack the separator / first positive electrode / separator / negative electrode in sequence to manufacture the first unit cell.

[0141] (Manufacturing of the second cell)

[0142] A positive electrode slurry was prepared by mixing LiFeO4 (as the second positive electrode active material), polyvinylidene fluoride (PVdF) (as a binder), and carbon black (as a conductive material) in N-methylpyrrolidone at a weight ratio of 94:3:3 and stirring. The positive electrode slurry was then coated onto aluminum foil, dried, and calendered to manufacture the second positive electrode.

[0143] A negative electrode slurry was prepared by mixing artificial graphite (particle size: 20 μm) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carbon black as the conductive material in water at a weight ratio of 90:5:5 and stirring. The negative electrode slurry was then coated onto copper foil, dried, and calendered to manufacture the negative electrode.

[0144] The separator / second positive electrode / separator / negative electrode are stacked in sequence to manufacture the second cell.

[0145] (Battery manufacturing)

[0146] Prepare a first cell and 19 second cells. Place the first cell at the bottom and stack the 19 second cells on it in the thickness direction to manufacture the electrode assembly.

[0147] The electrode assembly is housed in a pouch-shaped battery case, electrolyte is injected, and then the pouch-shaped battery case is sealed to complete the battery manufacturing process.

[0148] Example 2

[0149] Except that in the manufacture of the battery in Example 1, the first cell is placed at the 10th position from the bottom, the battery is manufactured in the same manner as in Example 1.

[0150] Comparative example

[0151] (Manufacturing of a single cell)

[0152] A positive electrode slurry was prepared by using a mixture of LiFePO4 and Li5FeO4 in a weight ratio of 95:5 as the positive electrode active material, and by mixing polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material in N-methylpyrrolidone and stirring. At this point, the weight ratio of the positive electrode active material, binder, and conductive material in the solids of the positive electrode slurry was 94:3:3. The positive electrode slurry was coated onto aluminum foil, dried, and calendered to manufacture the positive electrode.

[0153] A negative electrode slurry was prepared by mixing artificial graphite (particle size: 20 μm) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carbon black as the conductive material in water at a weight ratio of 90:5:5 and stirring. The negative electrode slurry was then coated onto copper foil, dried, and calendered to manufacture the negative electrode.

[0154] Prepare a porous polyethylene separator (20 μm thick) and stack the separator / positive electrode / separator / negative electrode in sequence to manufacture a cell.

[0155] (Battery manufacturing)

[0156] Prepare 20 cell units and stack them sequentially in the thickness direction to manufacture an electrode assembly. Place the electrode assembly in a pouch-shaped battery case, inject electrolyte, and then seal the pouch-shaped battery case to complete battery manufacturing.

[0157] Experiment Example 1: Measurement of Capacity

[0158] The batteries of Examples 1 to 2 and the Comparative Examples were charged at 0.1C in a charge-discharge chamber at 25°C until they reached 3.65 V, and then discharged to 2.5 V. At this point, the discharge capacity was measured, and the results are shown in Table 1.

[0159] Experimental Example 2: Initial Efficiency of the Battery

[0160] The batteries of Examples 1 to 2 and the Comparative Examples were charged to 4.0 V at 25°C and 0.1C to confirm the charging capacity. They were then discharged to 2.5 V at the same temperature and 0.1C to confirm the discharging capacity. Furthermore, the percentage of the discharging capacity relative to the charging capacity at this point was calculated as the initial efficiency, and the results are shown in Table 1.

[0161] [Table 1]

[0162] Referring to Table 1, it can be confirmed that the battery according to the embodiment has superior capacity and initial efficiency compared to the battery according to the comparative example. In the battery according to the embodiment, because there is a first cell to which the first positive electrode active material is applied at 100%, the capacity expression rate of the first positive electrode active material is 100%, while the battery of the comparative example is composed of a cell containing a positive electrode in which the first positive electrode active material and the second positive electrode active material are mixed, and it has been determined that this is a result of a significant decrease in the capacity expression rate of the first positive electrode active material.

[0163] As described above, the present invention has been described in more detail with reference to the accompanying drawings and embodiments. However, it should be understood that the configurations described in the drawings or the embodiments described in this specification are merely one embodiment of the present invention and do not represent the entirety of the technical concept of the present invention. Therefore, at the time of filing this application, there may be various equivalents and variations that can replace these.

Claims

1. A lithium secondary battery, the lithium secondary battery comprising: a battery casing; and an electrode assembly housed inside the battery casing, in, The electrode assembly includes a stack of cell cells containing positive and negative electrodes, wherein n (n is an integer greater than or equal to 2) are arranged in the thickness direction. The cell stack includes a first cell and a second cell. The first cell includes a first positive electrode, and The positive electrode active material of the first positive electrode is composed of the 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 chemical formula 1, M 1 It 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 are 5≤p≤7 and 0≤q≤0.5, respectively.

2. The lithium secondary battery according to claim 1, wherein the second 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. The lithium secondary battery according to claim 1, wherein the second cell includes a second positive electrode, and the second positive electrode includes lithium iron phosphate with an olivine structure containing iron as the positive electrode active material.

4. The lithium secondary battery according to claim 2 or 3, wherein the second positive electrode does not contain the first positive electrode active material as the positive electrode active material.

5. The lithium secondary battery according to claim 1, wherein the first cell is disposed at the center of the cell stack in the thickness direction (Z direction).

6. The lithium secondary battery according to claim 1, wherein in the chemical formula 1, M 1 It is any one of Ti, Zr, Al, Y, Sc, Nb, and Mg, and p and q are 5.5≤p≤6.5 and 0≤q≤0.2, respectively.

7. The lithium secondary battery according to claim 1, wherein the first unit battery and / or the second unit battery is any one of a single battery having a separator / negative electrode / separator / positive electrode structure, a dual battery having a separator / negative electrode / separator / positive electrode / separator / negative electrode structure, and a dual battery having a separator / positive electrode / separator / negative electrode / separator / positive electrode structure.

8. The lithium secondary battery according to claim 1, wherein the electrode assembly further comprises a half-cell having a separator / negative electrode / separator structure or a half-cell having a separator / positive electrode / separator structure, and The half-cell is located at the outermost part of the electrode assembly in the thickness direction (Z direction).

9. The lithium secondary battery according to claim 1, wherein in the cell stack, the ratio of the number of the first cell to the total number of cell units is 20% or less.

10. The lithium secondary battery according to claim 1, wherein in the cell stack, the ratio of the thickness of the first cell to the total thickness of the cell stack is 20% or less.

11. The lithium secondary battery of claim 1, wherein the first cell is disposed at each of the lower, central and upper portions of the cell stack in the thickness direction (Z direction).

12. The lithium secondary battery according to claim 1, wherein the electrode assembly is any one of stacked, stacked folded, and layered stacked types.

13. A battery module comprising the lithium secondary battery of claim 1.

14. A battery pack comprising the lithium secondary battery of claim 1.

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