Secondary battery and battery module

Abstract

A secondary battery includes: a first positive electrode group in which first positive electrodes are stacked adjacent to each other, the first positive electrodes including a first positive electrode current collector and a first positive electrode active material layer formed on the first positive electrode current collector; and a second positive electrode group in which second positive electrodes including a second positive electrode current collector and a second positive electrode active material layer are stacked adjacent to each other, a second positive electrode active material layer formed on the second positive electrode current collector and having an active material composition different from that of the first positive electrode active material layer or a laminated structure different from that of the first positive electrode active material layer; and the negative electrode is arranged opposite to the first positive electrode or the second positive electrode.

Description

Technical Field

[0001] Embodiments of the present invention relate to a secondary battery and a battery assembly. In more detail, embodiments of the present invention relate to a secondary battery including a plurality of positive electrode structures and a battery assembly including the secondary battery. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, secondary batteries are widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook computers. In addition, in recent years, battery packs including secondary batteries are being developed and used as a power source for environmentally friendly vehicles such as electric vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and light weight, and therefore are actively being researched and developed.

[0004] As the positive electrode active material of lithium secondary batteries, NCM-based active materials containing nickel, cobalt and manganese are used. As the application range of lithium secondary batteries expands to large devices such as electric vehicles, high-nickel (High-Ni)-based lithium oxides with increased nickel content are known to be positive electrode active materials for ensuring high capacity of lithium secondary batteries.

[0005] However, as the nickel content in the positive electrode active material increases, the stability of the chemical structure and crystal structure of the active material particles may decrease. For example, in a high state of charge (SOC) state during repeated charge and discharge, a large amount of gas may be generated due to side reactions.

[0006] In addition, as the nickel content increases, the capacity characteristics can be improved, but the rate characteristics such as fast charging performance may decrease. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] A technical problem of the present invention is to provide a secondary battery having improved stability and charge / discharge characteristics.

[0009] A technical problem of the present invention is to provide a battery assembly having improved stability and charge / discharge characteristics.

[0010] (II) Technical solution

[0011] The secondary battery includes: a first positive electrode group, which is formed by stacking first positive electrodes adjacent to each other, the first positive electrode including a first positive electrode collector and a first positive electrode active material layer, the first positive electrode active material layer being formed on the first positive electrode collector; a second positive electrode group, which is formed by stacking second positive electrodes adjacent to each other, the second positive electrode including a second positive electrode collector and a second positive electrode active material layer, the second positive electrode active material layer being formed on the second positive electrode collector and having an active material composition different from that of the first positive electrode active material layer or a different stacking structure; and a negative electrode, the negative electrode being arranged opposite to the first positive electrode or the second positive electrode.

[0012] In some embodiments, the first positive active material layer may include a first lithium-nickel-based metal oxide, and the second positive active material layer may include a second lithium-nickel-based metal oxide having a molar ratio of nickel less than that of the first lithium-nickel-based metal oxide.

[0013] In some embodiments, a mole fraction of nickel in elements other than lithium and oxygen in the first lithium-nickel-based metal oxide may be 0.9 or more.

[0014] In some embodiments, a mole fraction of nickel in elements other than lithium and oxygen in the second lithium-nickel-based metal oxide may be 0.8 or more and less than 0.9.

[0015] In some embodiments, the second lithium-nickel-based metal oxide may include large-size particles and small-size particles having average particle sizes different from each other.

[0016] In some embodiments, the large-size particles may have a secondary particle shape, and the small-size particles may have a single particle shape.

[0017] In some embodiments, the first positive active material layer may have a single-layer structure, and the second positive active material layer may have a multi-layer structure.

[0018] In some embodiments, the second positive electrode active material layer may include a lower positive electrode active material layer and an upper positive electrode active material layer sequentially stacked from the surface of the second positive electrode current collector and each including a second lithium-nickel-based metal oxide and a binder. The upper positive electrode active material layer and the lower positive electrode active material layer may have different binder contents from each other.

[0019] In some embodiments, the content of the binder included in the upper positive active material layer on a wt % basis may be less than the content of the binder included in the lower positive active material layer on a wt % basis.

[0020] In some embodiments, the first positive electrode collector may include a first positive electrode ear portion, and the second positive electrode collector may include a second positive electrode ear portion that is spaced apart from and protrudes from the first positive electrode ear portion in a horizontal direction.

[0021] In some embodiments, the secondary battery may further include a positive electrode lead fused with the first positive electrode tab portion and the second positive electrode tab portion.

[0022] In some embodiments, the secondary battery may further include a first positive lead fused to the first positive electrode tab and a second positive lead fused to the second positive electrode tab and separated from the first positive lead.

[0023] In some embodiments, the electrode assembly may be defined by stacking the first positive electrode group, the second positive electrode group, and the negative electrode, the first positive electrode group may be disposed at an upper portion of the electrode assembly, and the second positive electrode group may be disposed at a lower portion of the electrode assembly.

[0024] The battery assembly may include a plurality of battery cells, and the battery cells may each include the secondary battery of the above-described embodiment.

[0025] In some embodiments, the battery assembly may further include: a first positive module terminal, the first positive module terminal is connected to the first positive current collector included in the first positive electrode group; and a second positive module terminal, the second positive module terminal is connected to the second positive current collector included in the second positive electrode group.

[0026] In some embodiments, the first positive module terminal and the second positive module terminal may be independently detachable.

[0027] (III) Beneficial effects

[0028] The secondary battery according to the above embodiment may include a first positive electrode and a second positive electrode having different compositions and stacking structures from each other. The first positive electrode can more effectively achieve high capacity characteristics, and the second positive electrode can more effectively improve high rate characteristics and fast charging characteristics.

[0029] The first positive electrode can be assembled to form a first positive electrode group, and the second positive electrode can be assembled to form a second positive electrode group. In some embodiments, the first positive electrode group and the second positive electrode group can be operated independently of each other according to the application object of the secondary battery or battery module. Therefore, different current / capacity characteristics can be achieved from one battery or module. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 and Figure 2 is a schematic cross-sectional view showing a positive electrode included in a secondary battery according to an exemplary embodiment.

[0031] Figure 3 is a schematic cross-sectional view showing a negative electrode included in a secondary battery according to an exemplary embodiment.

[0032] Figure 4 is a schematic plan view showing a secondary battery according to an exemplary embodiment.

[0033] Figure 5 and Figure 6 is a schematic cross-sectional view showing a secondary battery according to an exemplary embodiment.

[0034] Figure 7 is a schematic plan view showing a secondary battery according to an exemplary embodiment.

[0035] Figure 8 and Fig. 9 1 and 2 are schematic cross-sectional views and plan views, respectively, for explaining a battery assembly according to an exemplary embodiment. DETAILED DESCRIPTION

[0036] According to the embodiment disclosed in the present invention, a secondary battery including different types of positive electrodes is provided. In addition, a battery assembly including the secondary battery is provided.

[0037] The secondary battery according to the embodiment of the present invention can be widely used in green technology fields such as electric vehicles using batteries, battery charging stations, solar power generation, wind power generation, etc. In addition, the secondary battery according to the embodiment of the present invention can be used for eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0038] By referring to the accompanying drawings, the exemplary embodiments are described in more detail. However, the drawings and embodiments of this specification are only used to further understand the technical concept of the present invention, and therefore should not be interpreted as the present invention being limited to the contents recorded in these drawings and embodiments.

[0039] The terms "upper part", "upper layer", "lower part", "lower layer" and the like used in the present invention do not specify absolute positions, but are used in a relative sense. For example, the terms are relatively used to specify different areas relative to a specific reference plane.

[0040] Figure 1 and Figure 2 is a schematic cross-sectional view showing a positive electrode included in a secondary battery according to an exemplary embodiment.

[0041] Reference Figure 1 and Figure 2 , the secondary battery may include a first positive electrode 103 and a second positive electrode 105 .

[0042] The first positive electrode 103 may include a first positive electrode collector 112 and a first positive active material layer 120 formed on a surface of the first positive electrode collector 112 .

[0043] The first positive electrode current collector 112 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. In one embodiment, the first positive electrode current collector 112 may include aluminum or an aluminum alloy.

[0044] The first positive active material layer 120 may be formed on the upper or lower surface of the first positive current collector 112. In one embodiment, the first positive active material layer 120 may be formed on the upper and lower surfaces of the first positive current collector 112, and the first positive electrode 103 may have a double-sided coating structure.

[0045] The first positive active material layer 120 may include a first positive active material, and a first lithium-nickel-based metal oxide may be used as the first positive active material. The secondary battery may be a lithium secondary battery using a lithium-nickel-based positive active material.

[0046] According to an exemplary embodiment, a mole fraction of nickel in metals other than lithium and oxygen included in the first lithium-nickel-based metal oxide may be 0.8 or more.

[0047] In some embodiments, the mole fraction of nickel in the first lithium-nickel-based metal oxide may be greater than 0.85. In one embodiment, the mole fraction of nickel in the first lithium-nickel-based metal oxide may be greater than 0.88, greater than 0.9, or greater than 0.92.

[0048] In some embodiments, the mole fraction of nickel in the first lithium-nickel-based metal oxide may be less than 0.98. For example, the mole fraction of nickel in the first lithium-nickel-based metal oxide may be 0.8 to 0.98, 0.85 to 0.98, 0.88 to 0.98, 0.9 to 0.98, or 0.92 to 0.98.

[0049] The first lithium-nickel-based metal oxide may further include at least one of cobalt (Co) and manganese (Mn). In some embodiments, the first lithium-nickel-based metal oxide may further include cobalt and manganese, and may be provided as a Ni-Co-Mn (NCM)-based lithium oxide.

[0050] Ni can be provided as a transition metal related to the power and capacity of a lithium secondary battery. Therefore, as described above, by adopting a high-content (high-Ni) composition in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0051] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or secondary battery may be relatively reduced. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while life stability and capacity retention characteristics can be improved by Mn.

[0052] The first lithium-nickel-based metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1.

[0053] [Chemical formula 1]

[0054] Li x Ni a M b O 2+z

[0055] In Chemical Formula 1, 0.9≤x≤1.2, 0.8≤a≤0.98, 0.02≤b≤0.2, and -0.5≤z≤0.1 may be satisfied. As described above, M may include Co and / or Mn.

[0056] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained in the layered structure or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and Mn may be provided together with Ni as the main active element of the positive electrode active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active elements, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0057] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary element may be mixed together into the layered structure / crystal structure to form a bond, and it should be understood that this case is also included in the chemical structure represented by Chemical Formula 1.

[0058] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may function as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0059] For example, the first lithium-nickel-based metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1-1.

[0060] [Chemical formula 1-1]

[0061] Li x Ni a M1 b1 M2 b2 O 2+z

[0062] In Chemical Formula 1-1, M1 may include Co and / or Mn. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.8≤a≤0.98, 0.02≤b1+b2≤0.2, and -0.5≤z≤0.1 may be selected.

[0063] The first lithium-nickel-based metal oxide may account for 50% by weight or more of the total weight of the first positive electrode active material. In an exemplary embodiment, the first lithium-nickel-based metal oxide may account for 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more of the total weight of the first positive electrode active material.

[0064] In one embodiment, the first positive electrode active material may consist essentially of the first lithium-nickel-based metal oxide.

[0065] According to an exemplary embodiment, the first lithium-nickel-based metal oxide particles may be prepared by reacting a nickel-containing precursor and a lithium precursor. The nickel-containing precursor may further contain, for example, manganese and / or cobalt.

[0066] In some embodiments, the nickel-containing precursor can be prepared in the form of a Ni-Co-Mn precursor (e.g., (NCM)-hydroxide). For example, the nickel-containing precursor can be prepared by reacting a nickel source, a cobalt source, and a manganese source together using a coprecipitation method. The nickel source, the cobalt source, and the manganese source can contain hydroxides, sulfates, carbonates, acetates, and nitrates of nickel, cobalt, and manganese, respectively.

[0067] The first lithium-nickel-based metal oxide may be prepared by reacting the nickel-containing precursor and the lithium precursor (eg, lithium hydroxide or lithium carbonate) using, for example, a co-precipitation method.

[0068] In order to promote the coprecipitation reaction, a precipitant and / or a chelating agent may be used. The precipitant may include alkaline compounds such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). The chelating agent may include, for example, ammonia water, ammonium carbonate, etc.

[0069] In some embodiments, in addition to nickel, cobalt and manganese, a source of doping elements selected from the above auxiliary elements may be reacted together. Thus, the first lithium-nickel-based metal oxide may include dopants mixed into the internal crystal structure / layered structure.

[0070] According to an exemplary embodiment, two or more elements of the auxiliary element may be included by doping. Through the doping, the first lithium-nickel-based metal oxide may have relatively high high temperature stability, and even if charging / discharging is repeated at high temperature, the generation of gas due to a side reaction with an electrolyte may be suppressed, and an improved capacity retention rate may be provided.

[0071] In addition, the first lithium-nickel-based metal oxide may have a relatively increased Ni content and may simultaneously provide high capacity characteristics.

[0072] In some embodiments, after preparing the first lithium-nickel-based metal oxide particles, a calcination process may be further performed. For example, the calcination process may be performed at a temperature of about 600-1000° C. Through the calcination process, the layered structure of the first lithium-nickel-based metal oxide particles may be stabilized, and the doping element may be fixed.

[0073] In some embodiments, the process of washing the first lithium-nickel-based metal oxide with water (pure water) can be omitted. Therefore, surface damage and oxidation of the first lithium-nickel-based metal oxide caused by the washing process can be prevented. Therefore, the high temperature stability of the first lithium-nickel-based metal oxide can be further enhanced.

[0074] For example, the first positive active material may be mixed and stirred with a binder, a conductive material and / or a dispersing material in a solvent to prepare a slurry, which may be coated on the first positive current collector 112 and then dried and rolled to manufacture the first positive electrode 103 .

[0075] The binder may include an organic binder such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or a water-based binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0076] For example, as a binder for forming the positive electrode, a PVDF-based binder can be used. In this case, the amount of the binder used to form the first positive active material layer 120 can be reduced, and the amount of the positive active material can be relatively increased, so the power and capacity of the secondary battery can be improved.

[0077] The conductive material may be included to promote electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0078] According to an exemplary embodiment, the first positive active material layer 120 included in the first positive electrode 103 may have a single layer structure. The term "single layer structure" used in the present invention refers to a structure in which a single active material layer is formed based on one side of a current collector.

[0079] As described above, by including the first positive electrode 103 using the first lithium-nickel-based metal oxide having an increased nickel content and the first positive active material layer 120 having a single-layer structure, high capacity characteristics may be effectively implemented.

[0080] Furthermore, as described above, the first lithium-nickel-based metal oxide that has not been subjected to water washing treatment is used, so that the surface stability and high-temperature stability of the active material particles can be enhanced.

[0081] The second positive electrode 105 may include a second positive electrode collector 115 and a second positive active material layer 130 formed on a surface of the second positive electrode collector 115 .

[0082] The second positive electrode collector 115 may include substantially the same metal or alloy as the first positive electrode collector 112 .

[0083] The second positive active material layer 130 may be formed on the upper or lower surface of the second positive current collector 115. In one embodiment, the second positive active material layer 130 may be formed on the upper and lower surfaces of the second positive current collector 115, and the second positive electrode 105 may have a double-sided coating structure.

[0084] According to an embodiment of the present invention, the second positive active material layer 130 may include a positive active material having a different composition from that of the first positive active material layer 120 , or may have a different stacked structure.

[0085] The second positive electrode active material layer 130 may include a second positive electrode active material, and a second lithium-nickel-based metal oxide may be used as the second positive electrode active material. According to an exemplary embodiment, the mole fraction of nickel in the metals other than lithium and oxygen included in the second lithium-nickel-based metal oxide may be less than the mole fraction of nickel in the first lithium-nickel-based metal oxide.

[0086] According to an exemplary embodiment, the mole fraction of nickel in the metals other than lithium and oxygen included in the first lithium-nickel-based metal oxide may be 0.8 or more.

[0087] In some embodiments, the mole fraction of nickel in the second lithium-nickel-based metal oxide may be 0.80 or more and less than 0.90. In one embodiment, the mole fraction of nickel in the second lithium-nickel-based metal oxide may be 0.85 or more and less than 0.90.

[0088] The second lithium-nickel-based metal oxide may further include at least one of cobalt (Co) and manganese (Mn). In some embodiments, the second lithium-nickel-based metal oxide may further include cobalt and manganese and may be provided as a Ni-Co-Mn (NCM)-based lithium oxide.

[0089] The second lithium-nickel-based metal oxide may include a layered structure or a crystal structure represented by Chemical Formula 2 below.

[0090] [Chemical Formula 2]

[0091] Li x Ni a L b O 2+z

[0092] In Chemical Formula 2, 0.9 ≤ x ≤ 1.2, 0.8 ≤ a < 0.9, 0.1 < b ≤ 0.2, -0.5 ≤ z ≤ 0.1. As described above, L may include Co and / or Mn.

[0093] The second lithium-nickel-based metal oxide may further include the above-described auxiliary elements, and the auxiliary elements may be provided as a surface coating.

[0094] For example, the second lithium-nickel-based metal oxide may include a layered structure or a crystal structure represented by Chemical Formula 2-1 below.

[0095] [Chemical Formula 2-1]

[0096] Li x Ni a L1 b1 L2 b2 O 2+z

[0097] In Chemical Formula 2-1, L1 may include Co and / or Mn. L2 may include the auxiliary elements described above. In Chemical Formula 2-1, 0.9≤x≤1.2, 0.8≤a<0.9, 0.1 <b1+b2≤0.2、-0.5≤z≤0.1。

[0098] The amount of the second lithium-nickel-based metal oxide may be 50 wt % or more of the total weight of the second positive electrode active material. In an exemplary embodiment, the amount of the second lithium-nickel-based metal oxide may be 60 wt % or more, 70 wt % or more, 80 wt % or more, or 90 wt % or more of the total weight of the second positive electrode active material.

[0099] In one embodiment, the second positive electrode active material may consist essentially of the second lithium-nickel-based metal oxide.

[0100] The second lithium-nickel-based metal oxide may be prepared by reacting the nickel-containing precursor and the lithium precursor. According to an exemplary embodiment, after the reaction, a surface coating layer including the auxiliary element may be formed.

[0101] For example, a primary lithium-nickel-based metal oxide may be formed by reacting a nickel-containing precursor with a lithium precursor. The primary lithium-nickel-based metal oxide may be mixed and reacted with an auxiliary element source to form the surface coating. The auxiliary element source may include oxides of auxiliary elements such as titanium oxide, zirconium oxide, and aluminum oxide.

[0102] In some embodiments, the second lithium-nickel-based metal oxide may have a bimodal particle size distribution including large particle size particles and small particle size particles. The large particle size particles may have a secondary particle form in which a plurality of primary particles are aggregated. The small particle size particles may have a single particle form rather than a secondary particle form.

[0103] In one embodiment, the average particle size (D50) of the large-size particles based on the volume cumulative distribution may be 10 μm to 20 μm, and the average particle size (D50) of the small-size particles based on the volume cumulative distribution may be 1 μm to 9 μm.

[0104] By adopting the second lithium-nickel-based metal oxide with a bimodal distribution, the positive electrode density and energy density in the second positive electrode active material layer 130 can be increased, and the rate characteristics and fast charging characteristics can be improved by the second positive electrode 105. In addition, the second lithium-nickel-based metal oxide can have a relatively lower nickel content than the first lithium-nickel-based metal oxide, but the content of other active elements such as cobalt can be increased. Therefore, the rate characteristics and power characteristics can be improved at the same time by the second lithium-nickel-based metal oxide.

[0105] According to an exemplary embodiment, the second positive active material layer 130 may have a multi-layer structure based on one surface of the second positive current collector 115. The second positive active material layer 130 may include a lower positive active material layer 132 and an upper positive active material layer 134 sequentially stacked from the surface of the second positive current collector 115.

[0106] The lower positive active material layer 132 may be in direct contact with the surface of the second positive current collector 115. The upper positive active material layer 134 may be in direct contact with the surface of the lower positive active material layer 132.

[0107] According to an exemplary embodiment, a lower slurry and an upper slurry including the second lithium-nickel-based metal oxide and the above-mentioned binder may be prepared. The lower slurry and the upper slurry may each further include the above-mentioned conductive material and / or dispersion material.

[0108] The lower slurry and the upper slurry may be sequentially coated on the second positive electrode collector 115 , and then dried and rolled to form a second positive electrode active material layer 130 including a lower positive electrode active material layer 132 and an upper positive electrode active material layer 134 .

[0109] The content of the binder contained in the lower positive electrode active material layer 132 (the content of the binder in the total weight of the lower positive electrode active material layer 132) may be greater than the content of the binder contained in the upper positive electrode active material layer 134 (the content of the binder in the total weight of the upper positive electrode active material layer 134).

[0110] By relatively increasing the amount of the binder in the lower positive electrode active material layer 132, the adhesion to the second positive electrode collector 115 can be increased. In the upper positive electrode active material layer 134, the amount of the binder can be relatively reduced, and the amount of the second lithium-nickel-based metal oxide can be increased. Therefore, the high rate / fast charge / high power characteristics at the surface of the second positive electrode 105 can be stably achieved.

[0111] In some embodiments, in the total weight of the upper positive electrode active material layer 134, the content of the binder may be less than 1 wt%, and in the total weight of the lower positive electrode active material layer 132, the content of the binder may be from 1 wt% to 2 wt%. In one embodiment, in the total weight of the upper positive electrode active material layer 134, the content of the binder may be from 0.3 wt% to less than 0.9 wt%, and in the total weight of the lower positive electrode active material layer 132, the content of the binder may be from 1 wt% to 1.5 wt%.

[0112] Figure 3 is a schematic cross-sectional view showing a negative electrode included in a secondary battery according to an exemplary embodiment.

[0113] Referring to Figure 3 , the negative electrode 150 may include a negative electrode current collector 155 and a negative electrode active material layer 153.

[0114] The negative electrode current collector 155 may include the metal or alloy mentioned in the positive electrode current collector. In some embodiments, the negative electrode current collector 155 may include copper or a copper alloy.

[0115] The negative electrode active material layer 153 may be formed on the upper surface and / or the bottom surface of the negative electrode current collector 155. The negative electrode active material layer 153 may be respectively formed on the upper surface and the bottom surface of the negative electrode current collector 155.

[0116] The negative electrode active material layer 153 may contain a negative electrode active material and a negative electrode binder.

[0117] The negative electrode active material may use carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; lithium alloys; silicon (Si)-based compounds or tin, etc.

[0118] As an example of the amorphous carbon, hard carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. may be cited.

[0119] As an example of the crystalline carbon, graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. may be cited.

[0120] As the elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. may be cited.

[0121] The silicon-based compound may contain, for example, silicon (Si), silicon oxide (e.g., SiOx, 0 < x < 2) and / or a silicon-carbon composite compound containing silicon carbide (SiC).

[0122] For example, the negative electrode active material may be mixed and stirred with the binder, conductive material, thickener, etc. in a solvent to prepare a negative electrode slurry. The negative electrode slurry may be coated on at least one side of the negative electrode collector 155 , dried, and rolled to manufacture the negative electrode 150 .

[0123] The binder and the conductive material may use materials that are substantially the same as or similar to those used in the positive electrode active material layer (120, 130). In some embodiments, for compatibility with the carbon-based active material, the negative electrode binder may include a water-based binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0124] Figure 4 is a schematic plan view showing a secondary battery according to an exemplary embodiment. Figure 5 and Figure 6 is a schematic cross-sectional view showing a secondary battery according to an exemplary embodiment. For ease of explanation, Figure 4 The illustration of the housing 90 is omitted. Figure 5 The illustration of the housing 90 and the diaphragm 140 is omitted. Figure 6 Only the positive electrode lugs (112a, 115a) in the structure of the positive electrode are shown.

[0125] Reference Figures 4 to 6 The lithium secondary battery may include an electrode assembly EA accommodated in a case 90 .

[0126] The case 90 may include an outer packaging material of a soft pack type, a can type, a prismatic type, etc. In one embodiment, the case 90 may be formed as a soft pack type outer packaging material, and the electrode assembly EA may be manufactured as a jelly roll type.

[0127] The electrode assembly EA may include a positive electrode (103, 105) and a negative electrode 150. The electrode assembly EA may further include a separator 140 interposed between the positive electrode (103, 105) and the negative electrode 150.

[0128] A plurality of positive electrodes (103, 105) and negative electrodes 150 may be alternately and repeatedly stacked with separators 140 sandwiched between the positive electrodes (103, 105) and the negative electrodes 150 to form an electrode assembly EA. Figure 6 , the separator 140 is shown in a form in which each layer is separated and stacked, but the separator 140 may have a form in which it is continuously wound in a zigzag folded form.

[0129] The separator 140 may include a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The separator 140 may also include a non-woven fabric formed of high melting point glass fiber, polyethylene terephthalate fiber, etc.

[0130] According to an embodiment of the present invention, the electrode assembly EA may include a first positive electrode 103 and a second positive electrode 105. According to an exemplary embodiment, the electrode assembly EA may include an upper layer portion UP and a lower layer portion LP. The upper layer portion UP may include a first positive electrode 103 and a negative electrode 150, and the lower layer portion LP may include a second positive electrode 105 and a negative electrode 150.

[0131] In some embodiments, the positive electrode of the upper part UP may consist of the first positive electrode 103, and the positive electrode of the lower part LP may consist of the second positive electrode 105. Therefore, a first positive electrode group in which a plurality of first positive electrodes 103 are assembled adjacent to each other may be defined, and a second positive electrode group in which a plurality of second positive electrodes 105 are assembled adjacent to each other may be defined.

[0132] In some embodiments, the upper layer portion UP and the lower layer portion LP may include the negative electrode 150 having substantially the same active material and stack structure.

[0133] One side of the first positive current collector 112 included in the first positive electrode 103 may form a first positive electrode ear portion 112a, and one side of the second positive current collector 115 included in the second positive electrode 105 may form a second positive electrode ear portion 115a. The positive electrode ears (112a, 115a) may not be coated with a positive active material layer.

[0134] The first positive electrode tab portions 112a may be aligned so as to overlap each other in a thickness direction or a height direction when viewed in a plan view. The first positive electrode tab portion 112a may be fused or welded with the positive electrode lead 160 at one side of the electrode assembly EA.

[0135] The second positive electrode tab portion 115a may be aligned so as to overlap each other in a thickness direction or a height direction when viewed in a plan view. The second positive electrode tab portion 115a may be fused or welded with the positive electrode lead 160 at one side of the electrode assembly EA.

[0136] According to an exemplary embodiment, Figure 4 As shown, when viewed in a plane, the first positive electrode ear portion 112a and the second positive electrode ear portion 115a can be separated in the horizontal direction (width direction) on the same side of the electrode assembly EA. In some embodiments, the first positive electrode ear portion 112a and the second positive electrode ear portion 115a can be connected or fused together with the positive lead 160.

[0137] A portion of the positive lead 160 may be fused with the terminal end of the positive electrode ear portion (112a, 115a) in the case 90. For example, the portion of the positive lead 160 may be sealed with the terminal end of the positive electrode ear portion (112a, 115a) in the case 90. The remaining portion of the positive lead 160 may protrude to the outside of the case 90.

[0138] In some embodiments, a negative electrode ear portion 155a may be formed on one side of the negative electrode current collector 155. The negative electrode ear portion 155a may not be coated with the negative electrode active material layer 153. The negative electrode ear portions 155a protruding from each negative electrode 150 may be aligned so as to overlap each other in the thickness direction or the height direction when viewed in a plane from the other side of the electrode assembly EA.

[0139] The plurality of negative electrode tabs 155 a may be welded or fused together with the negative electrode lead 170 .

[0140] A portion of the negative electrode lead 170 may be fused with the terminal portion of the negative electrode tab portion 155a in the case 90. For example, the portion of the negative electrode lead 170 may be sealed with the terminal portion of the negative electrode tab portion 155a in the case 90. The remaining portion of the negative electrode lead 170 may protrude to the outside of the case 90.

[0141] The electrolyte may be injected into the interior of the case 90 to impregnate the electrode assembly EA. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0142] The non-aqueous electrolyte may include a lithium salt and an organic solvent. The lithium salt may be, for example, Li + X - As the anion of the lithium salt (X - ), you can use F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N- CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - 、(CF3CF2SO2)2N - wait.

[0143] As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, cyclopentane, γ-butyrolactone, propylene sulfite and tetrahydrofuran can be used. These can be used alone or in combination of two or more.

[0144] According to the above embodiment, the first positive electrode 103 having improved high capacity characteristics and a single positive active material layer structure / higher nickel (Higher-Ni) composition and the second positive electrode 105 having a multi-layer positive active material layer structure and improved high rate characteristics can be spatially separated into different positive electrode groups.

[0145] Since the first positive electrode group and the second positive electrode group are included in one electrode assembly EA, a lithium secondary battery that simultaneously improves high rate characteristics / high capacity characteristics and provides high temperature stability / capacity retention can be realized.

[0146] Figure 7 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment. Figures 1 to 6 The configurations and structures described are substantially the same or similar to the detailed description of the configurations and structures.

[0147] Reference Figure 7 The first positive electrode ear portion 112 a and the second positive electrode ear portion 115 a may be connected or fused to the first positive electrode lead 163 and the second positive electrode lead 165 , respectively.

[0148] Therefore, a first positive electrode connection structure including a first positive electrode ear portion 112a and a first positive electrode lead 163 and a second positive electrode connection structure including a second positive electrode ear portion 115a and a second positive electrode lead 165 can be defined. The first positive electrode connection structure can be provided as an external connection structure of the first positive electrode group, and the second positive electrode connection structure can be provided as an external connection structure of the second positive electrode group.

[0149] According to an exemplary embodiment, the first positive electrode connection structure and the second positive electrode connection structure may be separated / operated independently of each other. The first positive electrode connection structure and the second positive electrode connection structure may be physically separated and / or electrically separated.

[0150] In some embodiments, the negative electrode tabs may also be separated. Figure 7 As shown, the negative electrode tab portion may be divided into a first negative electrode tab portion 152a included in the negative electrode 150 included in the upper portion UP of the electrode assembly EA and a second negative electrode tab portion 154a included in the negative electrode 150 included in the lower portion LP of the electrode assembly EA.

[0151] The first negative electrode ear portion 152a may be aligned so as to overlap in the thickness direction when viewed in a plan view, and may be welded or fused together with the first negative electrode lead 173. The second negative electrode ear portion 154a may be aligned so as to overlap in the thickness direction when viewed in a plan view, and may be welded or fused together with the second negative electrode lead 175.

[0152] Through the above-mentioned electrode connection structure or electrode lead design, independent charge / discharge operation of the upper part UP and the lower part LP can be achieved. For example, in an operating environment requiring high capacity / high temperature stability, charging / discharging can be achieved through the upper part UP. In an environment requiring high rate / high power operation, charging / discharging can be achieved through the lower part LP.

[0153] Figure 8 and Fig. 9 1 and 2 are schematic cross-sectional views and plan views respectively for illustrating a battery assembly according to an exemplary embodiment. Figure 8 and Fig. 9 The illustration of the casing of each battery cell is omitted.

[0154] Reference Figure 8 A plurality of battery cells (C1 to Cn) may be stacked to form a battery assembly. According to an exemplary embodiment, the battery assembly may be manufactured in the form of a battery module. Each battery cell (C1 to Cn) may include an electrode assembly (EA1 to EAn).

[0155] As described above, the positive electrode of the electrode assembly EA may be divided into first and second positive electrode groups respectively included in the upper layer portion UP and the lower layer portion LP, and the first and second positive electrode groups may be connected to the first and second positive electrode leads 163 and 165, respectively.

[0156] Reference Fig. 9 The plurality of first positive leads 163 belonging to each battery cell may be aligned so as to overlap in the thickness direction or height direction of the battery module when viewed in a plan view. The plurality of second positive leads 165 belonging to each battery cell may be aligned so as to overlap in the thickness direction or height direction of the battery module when viewed in a plan view.

[0157] The first positive lead 163 may be connected or fused together and connected to the first positive module terminal 183. The second positive lead 165 may be connected or fused together and connected to the second positive module terminal 185. The first positive module terminal 183 and the second positive module terminal 185 may be formed outside the module case.

[0158] In one embodiment, the lead fixing part 180 may be provided in the module case to merge the first positive lead 163 and the second positive lead 165 , respectively, and may lead out the first positive module terminal 183 and the second positive module terminal 185 .

[0159] In some embodiments, the negative lead may also be Figure 7 As shown, the cathode is separated to form a first negative module terminal and a second negative module terminal.

[0160] According to an exemplary embodiment, independent charge / discharge operation can be achieved by selecting the upper portion UP and the lower portion LP of the electrode assembly included in each battery cell. For example, in an operating environment requiring high capacity / high temperature stability, the charging / discharging of the module unit can be achieved through the upper portion UP. In an environment requiring high rate / high power operation, the charging / discharging of the module unit can be achieved through the lower portion LP.

[0161] In order to help the understanding of the present invention, specific embodiments are proposed below. However, these embodiments are only used to illustrate the present invention and are not used to limit the claims. Various changes and modifications can be made to the embodiments within the scope of the scope and technical concept of the present invention. This is obvious to those skilled in the art, and it is natural that such variations and modifications fall within the scope of the claims.

[0162] Examples and Comparative Examples

[0163] Positive electrodes of Examples and Comparative Examples having the layered structures and active material layer compositions shown in Table 1 were produced.

[0164] Specifically, as the positive electrode active material, Li[Ni 0.92 Co 0.05 Mn 0.03 O2 (denoted as Ni92) or Li[Ni 0.88 Co 0.09 Mn 0.03 O2 (denoted as Ni88) is used.

[0165] When manufacturing the first electrode group, commonly, a mixture is prepared by mixing 98.08 wt% of the positive electrode active material, multi-walled carbon nanotubes (MWCNT) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 98.08:0.72:1.2. N-methylpyrrolidone (NMP) is added to the mixture to prepare a slurry, which is then uniformly coated on an aluminum substrate with a thickness of 12 μm, dried, and rolled to a density of 3.6 g / cm³ (cc), thereby manufacturing the positive electrode. Approximately 20 wt% of the total weight of MWCNT consists of carbon nanotube (CNT) dispersion materials.

[0166] In the second electrode group, the same conductive material is used, but the positive electrode active material and polyvinylidene fluoride (PVDF) as the binder are used according to the contents recorded in Table 1.

[0167] In a mixture containing 81.45 wt% of artificial graphite (D50: 17 μm) as the graphite-based active material, 15.0 wt% of SiOx (0 < x < 2) as the silicon-based active material, 0.25 wt% of single-walled carbon nanotubes (SWCNT) as the conductive material, 1.3 wt% of carboxymethyl cellulose (CMC) as the thickener, and 2.0 wt% of styrene-butadiene rubber (SBR) as the binder (the total amount of solids is 100 wt%), water is added to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper substrate with a thickness of 8 μm, dried, and rolled to a density of 1.6 g / cm³, thereby manufacturing the negative electrode. Approximately 60 wt% of the content of SWCNT consists of CNT dispersion materials.

[0168] The negative electrode is similarly applied to the first electrode group and the second electrode group of the examples and comparative examples.

[0169] The positive electrode and the negative electrode are respectively cut (Notching) into specified sizes, and a separator (polyethylene, thickness 15 μm) is disposed between the positive electrode and the negative electrode and laminated. The positive electrode and the negative electrode are laminated in the same number of layers in the first electrode group and the second electrode group, thereby manufacturing an electrode assembly.

[0170] The electrode assembly is placed in a soft bag and three surfaces except the electrolyte injection surface are sealed. At this time, the portion with the pole ear is included in the sealing portion. The electrolyte is injected through the electrolyte injection surface and the electrolyte injection surface is sealed, and then immersed for more than 12 hours.

[0171] In order to prepare the electrolyte, a 1.1M LiPF6 solution was prepared using a mixed solvent of EC / EMC (25 / 75; volume ratio). To the solution, 8 wt% of fluoroethylene carbonate (FEC), 0.5 wt% of 1,3-propylene sultone (PRS), 0.5 wt% of 1,3-propane sultone (PS) and 0.5 wt% of vinyl sulfate (ESA) were added to the total weight of the electrolyte to prepare the electrolyte.

[0172] Then, heat press pre-charging was performed for 60 minutes at a current corresponding to an average of 0.5C. After stabilization for more than 12 hours, degassing was performed, and aging was performed for more than 24 hours, followed by formation charge and discharge (charging conditions: CC-CV, 0.25C, 4.2V, 0.05C, CUT-OFF; discharging conditions: CC, 0.25C, 2.5V, CUT-OFF).

[0173] Then, standard charge and discharge were performed (charge conditions: CC-CV, 0.33C, 4.2V, 0.05C, cut-off; discharge conditions: CC, 0.33C, 2.5V, cut-off).

[0174] [Table 1]

[0175]

[0176] Experimental example

[0177] (1) Evaluation of energy density

[0178] The lithium secondary batteries of Examples and Comparative Examples were charged (CC / CV 0.3C 4.2V 0.05C cutoff) and discharged (CC 0.3C 2.5V cutoff), and the discharge capacity (Ah) and energy (Wh) were measured.

[0179] The volume of each battery was measured in a charged state of 4.2 V, and the volume-energy density was calculated.

[0180] (2) Measurement of high temperature capacity retention

[0181] For the lithium secondary batteries of the embodiments and comparative examples, at a temperature of 45°C, they were charged at 0.3C under constant current / constant voltage (CC / CV) conditions to a voltage corresponding to SOC 98%, and then cut off at 0.05C. Then, under constant current (CC) conditions, they were discharged at 0.5C to a voltage corresponding to SOC 4%, and the discharge capacity was measured. The above charging and discharging was regarded as 1 cycle, and repeated 1000 cycles. The capacity retention rate was calculated as the percentage of the discharge capacity after the 1000th cycle divided by the discharge capacity of the 1st cycle.

[0182] (3) Evaluation of fast charging characteristics

[0183] At a temperature of 25°C, the lithium secondary batteries of the embodiments and comparative examples were charged at C-rates of 3.0C / 2.75C / 2.5C / 2.25C / 2.0C / 1.75C / 1.5C / 1.25C / 1.0C / 0.75C / 0.5C according to a step charging method to reach a depth of discharge (DOD) of 72% within 25 minutes, and then discharged at 0.5C.

[0184] The above charge and discharge was regarded as one cycle, and was repeated 300 times. The capacity retention rate was calculated as the percentage of the value of the discharge capacity after the 300th cycle divided by the discharge capacity after the 1st cycle.

[0185] (4) Evaluation of high temperature storage characteristics

[0186] The lithium secondary batteries of Examples and Comparative Examples were left at 60° C. for 35 weeks, and the time point at which outgassing occurred was measured.

[0187] The evaluation results are shown in Table 2 below.

[0188] [Table 2]

[0189]

[0190] Referring to Table 2, in the embodiments where the first electrode group and the second electrode group have different active material compositions or stacked structures from each other, high temperature capacity, high temperature stability, and fast charging characteristics are achieved in a balanced manner while maintaining energy density.

Claims

1. A secondary battery comprising: a first positive electrode group, wherein the first positive electrode group is formed by stacking first positive electrodes adjacent to each other, wherein the first positive electrode comprises a first positive electrode current collector and a first positive electrode active material layer, and the first positive electrode active material layer is formed on the first positive electrode current collector; a second positive electrode group, wherein the second positive electrode group is formed by stacking second positive electrodes adjacent to each other, the second positive electrode comprising a second positive electrode current collector and a second positive electrode active material layer, the second positive electrode active material layer being formed on the second positive electrode current collector and having an active material composition different from that of the first positive electrode active material layer or a different stacking structure; and A negative electrode is arranged opposite to the first positive electrode or the second positive electrode.

2. The secondary battery according to claim 1, wherein The first positive electrode active material layer includes a first lithium-nickel-based metal oxide, and the second positive electrode active material layer includes a second lithium-nickel-based metal oxide having a molar ratio of nickel smaller than that of the first lithium-nickel-based metal oxide.

3. The secondary battery according to claim 2, wherein: The mole fraction of nickel in the elements other than lithium and oxygen in the first lithium-nickel-based metal oxide is 0.9 or more.

4. The secondary battery according to claim 2, wherein The mole fraction of nickel in the elements other than lithium and oxygen in the second lithium-nickel-based metal oxide is 0.8 or more and less than 0.

9.

5. The secondary battery according to claim 2, wherein The second lithium-nickel-based metal oxide includes large-size particles and small-size particles having average particle sizes different from each other.

6. The secondary battery according to claim 5, wherein The large-diameter particles have a secondary particle shape, and the small-diameter particles have a single particle shape.

7. The secondary battery according to claim 1, wherein The first positive electrode active material layer has a single-layer structure, and the second positive electrode active material layer has a multi-layer structure.

8. The secondary battery according to claim 7, wherein The second positive electrode active material layer includes a lower positive electrode active material layer and an upper positive electrode active material layer which are sequentially stacked from the surface of the second positive electrode collector and each contain a second lithium-nickel-based metal oxide and a binder, and the upper positive electrode active material layer and the lower positive electrode active material layer have different binder contents from each other.

9. The secondary battery according to claim 8, wherein The content of the binder contained in the upper positive electrode active material layer on a weight % basis is smaller than the content of the binder contained in the lower positive electrode active material layer on a weight % basis.

10. The secondary battery according to claim 1, wherein The first positive electrode current collector includes a first positive electrode ear portion, and the second positive electrode current collector includes a second positive electrode ear portion that is spaced apart from and protrudes from the first positive electrode ear portion in a horizontal direction.

11. The secondary battery according to claim 10, wherein The secondary battery further includes a positive electrode lead fused with the first positive electrode tab portion and the second positive electrode tab portion.

12. The secondary battery according to claim 10, wherein The secondary battery further includes a first positive electrode lead fused to the first positive electrode tab portion and a second positive electrode lead fused to the second positive electrode tab portion and separated from the first positive electrode lead.

13. The secondary battery according to claim 1, wherein An electrode assembly is defined by stacking the first positive electrode group, the second positive electrode group, and the negative electrode, wherein the first positive electrode group is disposed at an upper layer portion of the electrode assembly and the second positive electrode group is disposed at a lower layer portion of the electrode assembly. 14 . A battery assembly comprising a plurality of battery cells, each of the battery cells comprising the secondary battery according to claim 1 .

15. The battery assembly according to claim 14, wherein: The battery assembly further comprises: a first positive electrode module terminal connected to the first positive electrode collector included in the first positive electrode group; and a second positive electrode module terminal connected to the second positive electrode current collector included in the second positive electrode group, Wherein, the first positive module terminal and the second positive module terminal are independently separated.

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