Lithium secondary battery and method for manufacturing the same

Abstract

A lithium secondary battery includes a cathode formed of a cathode active material including first cathode active material particles and second cathode active material particles; an anode; and a separator interposed between the cathode and the anode. The first cathode active material particles include a lithium metal oxide having a continuous concentration gradient in at least one region between a central portion and a surface portion. The second cathode active material particles include a lithium metal oxide including at least two metals other than lithium having a constant concentration from a central portion to a surface, and the second cathode active material particles include an excess of nickel among the metals other than lithium.

Description

[0001] This application is a divisional application of Chinese patent application filed on November 17, 2017, with Chinese patent application number 201711146025.2 and the invention title "Lithium Secondary Battery and Method for Manufacturing the Same".

[0002] Cross-reference and priority claims of related applications

[0003] This application claims priority to Korean Patent Application No. 10-2016-0154284, filed on November 18, 2016 with the Korean Intellectual Property Office (KIPO), and Korean Patent Application No. 10-2017-0120353, filed on September 19, 2017, the entire disclosure of which is incorporated herein by reference. Technical Field

[0004] This invention relates to a lithium secondary battery and a method for manufacturing the same. More specifically, this invention relates to a lithium secondary battery comprising lithium metal oxide and a method for manufacturing the same. Background Technology

[0005] With the development of information and display technologies, rechargeable and dischargeable secondary batteries have been widely used as power sources for mobile electronic devices such as portable cameras, mobile phones, and laptops. Recently, battery packs incorporating secondary batteries have been developed for use as power sources in environmentally friendly vehicles such as hybrid electric vehicles.

[0006] Secondary batteries include, for example, lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Lithium-ion batteries have received significant attention due to their high operating voltage, high energy density per unit weight, high charge rate, and compact size.

[0007] For example, a lithium secondary battery may include an electrode assembly having a cathode, an anode, and a separator layer, as well as an electrolyte immersing the electrode assembly. A lithium secondary battery may also include a casing having, for example, a pouch shape.

[0008] Lithium metal oxides can be used as preferred cathode active materials for lithium secondary batteries, offering high capacity, high power, and long lifespan. Furthermore, due to the expanding industrial applications of lithium secondary batteries, stability of the batteries or cathode active materials under harsh high or low temperature conditions is also required. Additionally, the battery must be resistant to malfunctions such as short circuits, ignition, or explosions when penetrated by external objects.

[0009] However, it is not easy to obtain a cathode active material that possesses all the aforementioned properties. For example, Korean Patent Application No. 10-2017-0093085 discloses a cathode active material comprising a transition metal compound and an ion-adsorbing binder, but this material does not have sufficient lifetime and stability. Summary of the Invention

[0010] According to one aspect of the present invention, there is provided a lithium secondary battery having improved electrical reliability and stability, as well as mechanical reliability and stability.

[0011] According to one aspect of the present invention, there is provided a method for manufacturing a lithium secondary battery having improved electrical reliability and stability, as well as mechanical reliability and stability.

[0012] According to an exemplary embodiment, a lithium secondary battery includes a cathode formed of a cathode active material including first cathode active material particles and second cathode active material particles; an anode; and a separator interposed between the cathode and the anode. The first cathode active material particles include a lithium metal oxide having a continuous concentration gradient in at least one region between a central portion and a surface portion. The second cathode active material particles include a lithium metal oxide including at least two metals other than lithium having a constant concentration from the central portion to the surface, and the second cathode active material particles include an excess of nickel among the metals other than lithium.

[0013] In some embodiments, the first cathode active material particles may include a first metal having a continuously decreasing concentration between a central portion and a surface portion and a second metal having a continuously increasing concentration between the central portion and the surface portion.

[0014] In some embodiments, the first cathode active material particles may further include a third metal having a constant concentration from the central portion to the surface portion.

[0015] In some embodiments, the first cathode active material particles may be represented by the following Chemical Formula 1.

[0016] [Chemical Formula 1]

[0017] Li x M1 a M2 b M3 c O y

[0018] In Chemical Formula 1 above, M1, M2, and M3 may each represent the first metal, the second metal, and the third metal, and may be selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, or B, 0 < x ≤ 1.1, 2 ≤ y ≤ 2.02, 0 < a < 1, 0 < b < 1, 0 < c < 1, and 0 < a + b + c ≤ 1.

[0019] In some implementations, in chemical formula 1, 0.6 ≤ a ≤ 0.95 and 0.05 ≤ b + c ≤ 0.4.

[0020] In some implementations, in chemical formula 1, 0.7 ≤ a ≤ 0.9 and 0.1 ≤ b + c ≤ 0.3.

[0021] In some implementations, the first metal may be nickel (Ni), the second metal may be manganese (Mn), and the third metal may be cobalt (Co).

[0022] In some embodiments, the first cathode active material particles may include a concentration gradient layer formed between the central portion and the surface portion.

[0023] In some embodiments, the concentration gradient layer may include a continuous concentration gradient. The central portion and the surface portion may each have a constant concentration composition, and the central portion and the surface portion may have different concentration compositions from each other through the concentration gradient layer.

[0024] In some implementations, the first cathode active material particles may have a continuous concentration gradient from the central portion to the entire surface region.

[0025] In some implementations, the second cathode active material particles may be represented by the following chemical formula 2.

[0026] [Chemical Formula 2]

[0027] Li x M1' a M2' b M3' c O y ,

[0028] In the above chemical formula 2, M1' can be nickel, and M2' and M3' can be selected from Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, or B. <x≤1.1,2≤y≤2.02,0<a+b+c≤1,0.48≤a≤0.52,0.18≤b≤0.22,0.28≤c≤0.32。

[0029] In some implementations, in chemical formula 2, 0.49 ≤ a ≤ 0.51, 0.19 ≤ b ≤ 0.21, and 0.29 ≤ c ≤ 0.31.

[0030] In some implementations, M2' and M3' can be cobalt (Co) and manganese (Mn), respectively.

[0031] In some implementations, the molar ratio of nickel, cobalt, and manganese in the second cathode active material particles can be 5:2:3.

[0032] In some implementations, the mixing ratio of the first cathode active material particles to the second cathode active material particles can be in the range of 7:3 to 1:9.

[0033] In some implementations, the mixing ratio of the first cathode active material particles to the second cathode active material particles can be in the range of 5:5 to 1:9.

[0034] In some implementations, the average diameter (D) of the second cathode active material particles 50 It can be in the range of 3μm to 15μm.

[0035] In some implementations, the average diameter (D) of the second cathode active material particles 50 It can be in the range of 4.5μm to 15μm.

[0036] According to the exemplary embodiments described above, the cathode active material of a lithium secondary battery may comprise first cathode active material particles with a concentration gradient and second cathode active material particles with a fixed concentration profile. The high capacity and high power of the lithium secondary battery can be achieved by the first cathode active material particles, while the penetration stability and thermal stability of the lithium secondary battery can be obtained by the second cathode active material particles.

[0037] Therefore, both the electrical performance and mechanical stability of lithium secondary batteries can be improved.

[0038] In an exemplary embodiment, the first cathode active material particles and the second cathode active material particles may comprise a lithium metal oxide containing nickel, and the second cathode active material particles may have a lower nickel concentration than the first cathode active material particles. Therefore, the lifespan and penetration stability of the lithium secondary battery can be further improved by combining this with the concentration gradient of the first cathode active material particles.

[0039] In some implementations, the size of the second cathode active material particles can be controlled, or a coating can be formed on the first cathode active material particles, thereby further improving the lifespan and penetration stability of the lithium secondary battery. Attached Figure Description

[0040] Figure 1 A schematic cross-sectional view of a lithium secondary battery according to an exemplary embodiment;

[0041] Figure 2A A cross-sectional schematic diagram showing the measurement location of the concentration gradient of first cathode active material particles prepared according to some exemplary embodiments;

[0042] Figure 2B A schematic diagram illustrating the measurement locations of the concentration gradient of first cathode active material particles prepared according to some exemplary embodiments;

[0043] Figure 3 A cross-sectional schematic diagram showing the measurement location of the concentration gradient of first cathode active material particles prepared according to some exemplary embodiments;

[0044] Figure 4 A cross-sectional image of first cathode active material particles prepared according to an exemplary embodiment; and

[0045] Figure 5 A cross-sectional image of the lithium metal oxide used in the comparative example. Detailed Implementation Plan

[0046] According to an exemplary embodiment of the present invention, a lithium secondary battery with improved electrical performance and mechanical stability is provided. The lithium secondary battery may include a cathode active material comprising first cathode active material particles having a concentration gradient and second cathode active material particles having a fixed concentration distribution. According to an exemplary embodiment, a method for manufacturing a lithium secondary battery or a cathode active material is also provided.

[0047] The invention will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will recognize that this description of embodiments with reference to the drawings is intended to further understand the spirit of the invention and is not intended to limit the subject matter to be protected as disclosed in the detailed specification and appended claims.

[0048] The terms “first” and “second” used in this article are not intended to specify the number or order of objects, but are only used to identify different elements or objects.

[0049] Figure 1 This is a schematic cross-sectional view of a lithium secondary battery according to an exemplary embodiment.

[0050] refer to Figure 1 A lithium secondary battery may include a cathode 130, an anode 140, and a separator layer between the cathode 130 and the anode 140.

[0051] The cathode may include a cathode current collector 110 and a cathode active material layer 115 formed by coating the cathode current collector 110 with a cathode active material. In an exemplary embodiment, the cathode active material may include first cathode active material particles and second cathode active material particles.

[0052] The first cathode active material particles may comprise lithium metal oxide having a continuous concentration gradient from the center of the particle to the particle surface. In some embodiments, the first cathode active material particles may have a full concentration gradient (FCG) structure, wherein a concentration gradient can be formed substantially throughout the entire particle.

[0053] In some embodiments, the first cathode active material particles may comprise lithium metal oxide and may have a continuous concentration gradient in at least one region between the central portion and the surface portion of the first cathode active material particles. For example, the first cathode active material particles may include a concentration gradient layer formed between the central portion and the surface portion.

[0054] In some implementations, the concentrations of lithium and oxygen can be substantially constant throughout the entire region of the particle, and at least one element other than lithium and oxygen can have a continuous concentration gradient.

[0055] The term "continuous concentration gradient" as used in this article can refer to a concentration distribution that can change with a uniform trend or tendency between the central and surface portions. A uniform trend can include either an increasing trend or a decreasing trend.

[0056] As used herein, the term "central portion" may include the center point of an active material particle, or it may include a region within a predetermined diameter from the center point. For example, "central portion" may include a region within a diameter of approximately 0.2 μm or approximately 0.1 μm from the center point of the active material particle.

[0057] As used herein, the term "surface portion" can include the outermost surface of the active material particles, and may also include a region within a predetermined thickness from the outermost surface. For example, "surface portion" can include a region within approximately 0.2 μm or approximately 0.1 μm of the outermost surface of the active material particles.

[0058] In some implementations, continuous concentration particles may include a linear concentration distribution or a curvilinear concentration distribution. In a curvilinear concentration distribution, the concentration may change with a uniform trend without any inflection points.

[0059] In one embodiment, the at least one metal other than lithium contained in the first cathode active material particles may have a continuously increasing concentration gradient, and the at least one metal other than lithium contained in the first cathode active material particles may have a continuously decreasing concentration gradient.

[0060] In one embodiment, the concentration of at least one metal other than lithium contained in the first cathode active material particles may be substantially constant from the central portion to the surface.

[0061] In an exemplary embodiment, the first cathode active material particles may comprise a nickel-containing lithium metal oxide, and nickel may have a continuous concentration gradient throughout the entire region of the particles or in a specific region between the central portion and the surface portion. In an exemplary embodiment, the concentration (or molar ratio) of nickel may continuously decrease between the central portion and the surface portion of the first cathode active material particles.

[0062] In one embodiment, the metals other than lithium contained in the first cathode active material particles may include a first metal M1 and a second metal M2. The first metal M1 may have a concentration gradient that continuously decreases from the central portion to the surface. The second metal M2 has a concentration gradient that continuously increases from the central portion to the surface.

[0063] In one embodiment, the metals other than lithium contained in the first cathode active material particles may further include a third metal M3. The third metal M3 may have a substantially constant concentration from the central portion to the surface.

[0064] As used herein, the term "concentration" may refer to, for example, the molar ratio of the first metal to the third metal.

[0065] For example, the first cathode active material particles may be represented by the following Chemical Formula 1.

[0066] [Chemical Formula 1]

[0067] Li x M1 a M2 b M3 c O y

[0068] In Chemical Formula 1 above, M1, M2, and M3 may be selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, or B, and 0 < x ≤ 1.1, 2 ≤ y ≤ 2.02, 0 < a < 1, 0 < b < 1, 0 < c < 1, and 0 < a + b + c ≤ 1.

[0069] In some embodiments, M1, M2, and M3 of Chemical Formula 1 may be nickel (Ni), manganese (Mn), and cobalt (Co), respectively.

[0070] For example, nickel may be used as the metal related to the capacity of the lithium secondary battery. When the amount of nickel increases, the capacity and power of the lithium secondary battery can be improved. However, an excessive amount of nickel will reduce the life characteristics of the battery and is disadvantageous in terms of the mechanical stability and electrical stability of the battery. For example, when the amount of nickel increases excessively, defects such as fire or short circuit caused by the penetration of an external object cannot be sufficiently suppressed.

[0071] However, according to an exemplary embodiment, nickel may be included as the first metal M1. Therefore, the amount of nickel at the central portion can be relatively high to improve the capacity and power of the lithium secondary battery, and the nickel concentration can be reduced from the central portion to the surface to prevent defects and shortened lifespan caused by penetration.

[0072] For example, manganese (Mn) can be used as a metal related to the mechanical and electrical stability of lithium secondary batteries. In an exemplary embodiment, the amount of Mn can be increased from the center to the surface, thereby suppressing or reducing defects caused by penetration of the surface, such as fires or short circuits, and also improving the lifespan of the lithium secondary battery.

[0073] For example, cobalt (Co) can be used as a metal related to the conductivity or resistance of lithium secondary batteries. In an exemplary embodiment, the concentration of cobalt can be fixed or uniformly maintained throughout the entire area of ​​the first cathode active material particles. Therefore, the current or charge flow passing through the first cathode active material particles can be uniformly maintained while increasing the battery's conductivity and maintaining low resistance.

[0074] In some embodiments, in Formula 1, the first metal M1 may be nickel, and for example, 0.6 ≤ a ≤ 0.95 and 0.05 ≤ b + c ≤ 0.4. For example, the concentration (or molar ratio) of nickel may continuously decrease from about 0.95 to about 0.6. In one embodiment, a concentration gradient layer with a concentration gradient region may be formed between the central portion and the surface portion, and the concentration (or molar ratio) of nickel in the concentration gradient layer may continuously decrease from about 0.95 to about 0.6.

[0075] If the lower limit of nickel concentration (e.g., surface concentration) is less than about 0.6, the capacity and power at the surface of the first cathode active material particles will be excessively degraded. If the upper limit of nickel concentration (e.g., center concentration) exceeds about 0.95, the lifetime and mechanical stability at the center will be excessively reduced.

[0076] Preferably, in chemical formula 1, 0.7 ≤ a ≤ 0.9 and 0.1 ≤ b + c ≤ 0.3. In this case, both the capacity and stability of the battery can be improved. In one embodiment, 0.77 ≤ a ≤ 0.83, 0.07 ≤ b ≤ 0.13 and 0.07 ≤ c ≤ 0.13, preferably 0.79 ≤ a ≤ 0.81, 0.09 ≤ b ≤ 0.11 and 0.09 ≤ c ≤ 0.11.

[0077] According to the exemplary embodiment described above, the first cathode active material particles may include a continuous concentration gradient between the central portion and the surface.

[0078] In some embodiments, the first cathode active material particles may have an FCG structure comprising a concentration gradient over substantially their entire region. In this case, for example, the Ni concentration may continuously decrease from the center to the surface, and the Mn concentration may continuously increase from the center to the surface. The Co concentration may be substantially constant from the center to the surface.

[0079] In some embodiments, the first cathode active material particles may include a concentration gradient layer located in a specific region between a central portion and a surface portion. In the concentration gradient layer, the concentration of Ni may continuously decrease, the concentration of Mn may continuously increase, and the concentration of Co may remain substantially constant.

[0080] In this configuration, the elemental composition of the first cathode active material particles can be uniform in both the central and surface portions. For example, the concentrations of Ni and Mn can be constant in both the central and surface portions. Through the concentration gradient layer, the Ni concentration can become relatively high in the central portion, and the Mn concentration can become relatively high in the surface portion. The Co concentration can be substantially uniform or constant throughout the central portion, the concentration gradient layer, and the surface portion.

[0081] In some embodiments, the first cathode active material particles may further comprise a coating on their surface. For example, the coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, alloys thereof, or oxides thereof. These may be used alone or in mixtures thereof. The first cathode active material particles may be passivated by the coating, thereby further improving the cell's penetration stability and lifespan.

[0082] In one embodiment, the elements, alloys, or oxides of the coating may be added as dopants to the particles of the first cathode active material.

[0083] In some embodiments, the first cathode active material particles can be formed from rod-shaped primary particles. The average diameter of the first cathode active material particles can be in the range of about 3 μm to about 25 μm.

[0084] The cathode active material may comprise second cathode active material particles mixed with the first cathode active material particles. In an exemplary embodiment, the second cathode active material particles may have a substantially constant or fixed concentration throughout the entire region of the particles.

[0085] The second cathode active material particles may comprise lithium metal oxide. In an exemplary embodiment, the second cathode active material particles may comprise nickel-containing lithium metal oxide. The nickel concentration in the second cathode active material particles may be lower than the nickel concentration in the first cathode active material particles. In one embodiment, the nickel concentration in the second cathode active material particles may be fixed to be lower than the nickel concentration at the surface of the first cathode active material particles.

[0086] In some embodiments, the second cathode active material particles may include at least two metals other than lithium. The concentration of the metals other than lithium may be kept constant from the center of the particle to the particle surface.

[0087] In some embodiments, the second cathode active material particles may include a first metal M1', a second metal M2', and a third metal M3'. For example, the first metal M1', the second metal M2', and the third metal M3' may be nickel (Ni), cobalt (Co), and manganese (Mn), respectively.

[0088] As described above, the concentrations or molar ratios of Ni, Co, and Mn can be uniform or constant throughout the entire region of the second cathode active material particles. In some embodiments, the second cathode active material particles may include an excess of nickel, while the concentrations of nickel, manganese, and cobalt may decrease sequentially, taking into account the capacity and stability of the lithium secondary battery. In an exemplary embodiment, the Ni:Co:Mn concentration ratio in the second cathode active material particles may be substantially 5:2:3.

[0089] The term "excess" as used in this article can refer to an excess of a metal element having the highest concentration or molar ratio among metal elements other than lithium in the cathode active material particles.

[0090] For example, the particles of the second cathode active material can be represented by the following chemical formula 2.

[0091] [Chemical Formula 2]

[0092] Li x M1' a M2' b M3' c O y

[0093] In the above chemical formula 2, M1', M2', and M3' can be selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, or B, and 0 <x≤1.1,2≤y≤2.02,0<a+b+c≤1。

[0094] In some embodiments, in the above chemical formula 2, 0.48≤a≤0.52, 0.18≤b≤0.22, 0.28≤c≤0.32, preferably 0.49≤a≤0.51, 0.19≤b≤0.21 and 0.29≤c≤0.31.

[0095] In some implementations, as described above, the first metal M1', the second metal M2', and the third metal M3' can be Ni, Co, and Mn, respectively.

[0096] In an exemplary embodiment, the thermal stability of the lithium secondary battery or cathode can be improved by mixing the second cathode active material particles with the first cathode active material particles. Throughout the entire region of the particles, the nickel concentration or molar ratio of the second cathode active material particles is lower than that of the first cathode active material particles, and Mn is uniformly distributed throughout the second cathode active material particles.

[0097] Therefore, it can prevent fires or explosions caused by penetration by external objects, and also improves heat resistance during repeated charging and discharging, thereby significantly improving the operational uniformity and lifespan of lithium secondary batteries.

[0098] Furthermore, the cobalt concentration can be constant throughout the entire region of the second cathode active material particles, thereby uniformly maintaining the conductivity and resistance of the entire cathode.

[0099] In some embodiments, the nickel concentration can be greater than that of other metals (e.g., manganese and cobalt) in the second cathode active material particles, and the nickel concentration in the second cathode active material particles can be less than that in the first cathode active material particles. Therefore, capacity reduction due to the inclusion of second cathode active material particles can be suppressed, while improving the lifespan and penetration stability of the lithium-ion secondary battery.

[0100] In some implementations, the average diameter (D) of the second cathode active material particles 50 The particle size can be in the range of approximately 3 μm to approximately 15 μm. Within this range, the lifespan and stability of the lithium secondary battery or cathode can be improved without the electroactivity of the first cathode active material particles being interfered with by the second cathode active material particles. Preferably, the average diameter (D) of the second cathode active material particles is... 50 The size can be approximately 4.5 μm to approximately 15 μm.

[0101] If the average diameter of the particles of the second cathode active material (D) 50 If the particle size is less than approximately 3 μm, the particle size will be excessively reduced, making it impossible to achieve and control the desired composition, activity, and stability. If the average diameter (D) of the second cathode active material particles is less than approximately 3 μm, the particle size will be excessively reduced, making it impossible to achieve and control the desired composition, activity, and stability. 50If the particle size exceeds approximately 15 μm, excessive heat will be required to form the particles, thereby reducing process efficiency.

[0102] In an exemplary embodiment, the mixing ratio of the first cathode active material particles to the second cathode active material particles can be, for example, 7:3 to 1:9, preferably 5:5 to 1:9. Within the above range, the second cathode active material particles can more effectively achieve improved thermal stability and prevent fires caused by penetration.

[0103] The first and second cathode active material particles can be prepared separately and then mixed to obtain the cathode active material.

[0104] When forming the first cathode active material, metal precursor solutions of different concentrations can be prepared. The metal precursor solutions may include precursors of metals that can be contained in the cathode active material. For example, metal precursors may include metal halides, hydroxides, acid salts, etc.

[0105] For example, metal precursors may include lithium precursors (e.g., lithium oxide), nickel precursors, manganese precursors, and cobalt precursors.

[0106] In an exemplary embodiment, a first precursor solution having a target composition at the central portion (e.g., the concentrations of nickel, manganese, and cobalt at the central portion) and a second precursor solution having a target composition at the surface or surface portion (e.g., the concentrations of nickel, manganese, and cobalt at the surface) can be prepared respectively.

[0107] Subsequently, the first precursor solution and the second precursor solution can be mixed, and a precipitate can be formed by co-precipitation. In some embodiments, the mixing ratio can be continuously varied to create a continuous concentration gradient of the target composition from the central portion to the surface portion. In some embodiments, the mixing ratio can be varied over a specific time period to create a concentration gradient layer between the central and surface portions. Therefore, the precipitate can include a concentration gradient of the metal contained therein.

[0108] In some embodiments, a chelating agent and a basic agent (e.g., an alkaline agent) may be added simultaneously with the formation of the precipitate. In some embodiments, the precipitate may be heat-treated, and then the lithium salt may be mixed in and heat-treated again.

[0109] Second cathode active material particles can be formed by precipitation using a metal precursor solution with a single target composition.

[0110] In an exemplary embodiment, first cathode active material particles and second cathode active material particles may be mixed to form a cathode active material. The cathode active material may be mixed and stirred with a binder, conductive additives and / or dispersing additives in a solvent to form a slurry. The slurry may be coated onto cathode current collector 110, pressed and dried to obtain cathode 130.

[0111] The cathode current collector 110 may comprise stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. Preferably, aluminum or alloys thereof may be used.

[0112] Adhesives may include organic adhesives such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based adhesives such as styrene-butadiene rubber (SBR), which may be used with thickeners such as carboxymethyl cellulose (CMC)

[0113] For example, a PVDF-based binder can be used as the cathode binder. In this case, the amount of binder used to form the cathode active material layer 115, as well as the amount of the first cathode active material particles and the second cathode active material particles, can be appropriately increased. Therefore, the capacity and power of the lithium secondary battery can be further improved.

[0114] Conductive additives can be added to improve electron mobility between active material particles. For example, conductive additives may include carbon-based materials such as graphite, carbon black, graphene, carbon nanotubes, and / or metal-based materials such as tin, tin oxide, titanium oxide, perovskite materials (e.g., LaSrCoO3 or LaSrMnO3).

[0115] In an exemplary embodiment, the electrode density of the cathode 130 can be in the range of about 3.0 g / cc to about 3.9 g / cc, preferably in the range of about 3.2 g / cc to about 3.8 g / cc.

[0116] In an exemplary embodiment, the anode 140 may include an anode current collector 120 and an anode active material layer 125 formed by coating the anode current collector 120 with an anode active material.

[0117] Anode active materials can include materials capable of adsorbing and ejecting lithium ions. For example, carbon-based materials (such as crystalline carbon, amorphous carbon, carbon complexes, or carbon fibers), lithium alloys, silicon, tin, etc., can be used. Amorphous carbon can include hard carbon, coke, mesophase carbon microspheres (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fibers (MPCF), ETC, etc. Crystalline carbon can include graphite-based materials, such as natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. Lithium alloys can also include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0118] The anode current collector 120 may include gold, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, and preferably may include copper or copper alloys.

[0119] In some embodiments, the anolyte active material can be mixed with a binder, conductive additives, and / or dispersing additives in a solvent and stirred to form a slurry. The slurry can be coated onto the anolyte current collector 120, pressed, and dried to obtain the anolyte 140.

[0120] Adhesives and conductive additives that are substantially the same or similar to those described above can be used. In some embodiments, the adhesive for the anode 140 may include an aqueous adhesive, such as styrene-butadiene rubber (SBR), which can be used with a thickener such as carboxymethyl cellulose (CMC), thereby improving compatibility with carbon-based active materials.

[0121] A diaphragm 150 can be inserted between the cathode 130 and the anode 140. The diaphragm 150 may comprise a porous polymer membrane, which is prepared from, for example, a polyolefin-based polymer (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc.). The diaphragm 150 may also be formed from a nonwoven fabric containing high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0122] In some embodiments, the area and / or volume of the anode 140 (e.g., the contact area with the diaphragm 150) can be larger than the area and / or volume of the cathode 130. Therefore, lithium ions generated from the cathode 130 can be readily transferred to the anode 140 without loss due to, for example, precipitation or deposition. Thus, improved power and stability can be effectively achieved through the combination of first and second cathode active material particles.

[0123] In an exemplary embodiment, electrode unit 160 may be defined by cathode 130, anode 140, and diaphragm 150, and multiple electrode units 160 may be stacked to form an electrode assembly having, for example, a jelly roll shape. For example, the electrode assembly may be formed by winding, laminating, or folding diaphragm 150.

[0124] The electrode assembly can be housed together with the electrolyte in the housing 170 to form a lithium secondary battery. In an exemplary embodiment, the electrolyte may include a non-aqueous electrolyte solution.

[0125] Non-aqueous electrolyte solutions can include lithium salts and organic solvents. Lithium salts can be derived from Li... + X - This indicates that the lithium salt anion X - It can include, for example, 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.

[0126] Organic solvents may include propylene carbonate, 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, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These can be used alone or in combination.

[0127] An electrode tab can be formed from each of the cathode current collector 110 and the anode current collector 120 to extend to one end of the housing 170. The electrode tab can be welded to one end of the housing 170 to form an electrode lead exposed to the outside of the housing 170.

[0128] Lithium-ion batteries can be manufactured into cylindrical, prismatic, pouch-shaped, coin-shaped, and other shapes using cans.

[0129] Preferred embodiments are presented below to describe the invention in more detail. However, the following examples are merely illustrative, and those skilled in the art must clearly understand that various changes and modifications can be made within the scope and spirit of the invention. The appended claims appropriately encompass such changes and modifications.

[0130] Experimental Example 1: A first cathode active material including a concentration gradient layer in the middle of the particles and a fixed concentration of... Second cathode active material mixing

[0131] Manufacturing of lithium secondary batteries

[0132] (1) Cathode

[0133] Figure 2A and 2B This is a schematic diagram illustrating the measurement location of the concentration gradient of first cathode active material particles prepared according to some exemplary embodiments.

[0134] The first cathode active material particles having a concentration gradient layer formed between the central portion and the surface portion are prepared as follows.

[0135] Lithium metal oxide (CAM10a) is used as the first cathode active material (first lithium metal oxide). The overall composition of the first lithium metal oxide is Li. 1.0 Ni 0.80 Co 0.11 Mn 0.09 O2, the central part (positions numbered 1 to 12 in Table 1 below) is composed of Li 1.0 Ni 0.80 2Co 0.11 Mn 0.088 O2, the surface portion (numbered 12-5 to 13 in Table 1 below) is composed of Li 1.0 Ni 0.77 Co 0.11 Mn 0.12 O2. A concentration gradient layer with nickel and manganese concentration gradients is formed between the central portion and the surface portion (positions numbered 12 to 12-4).

[0136] Specifically, as shown in Table 1 below, a concentration gradient of the first lithium metal oxide is formed (the concentration is measured from the center of the first lithium metal oxide to the surface). Figure 2B The image shows the location of the concentration gradient layer and the location where the concentration was measured.

[0137] In a first lithium metal oxide particle with a center-to-surface distance of 4.8 μm, the molar ratio of each metal contained in the first lithium metal oxide particle was measured at positions numbered 1 to 12 at intervals of 0.4 μm away from the center. Between positions numbered 12 and 13, the molar ratio of each metal was measured at positions numbered 12-1, 12-2, 12-3, 12-4, 12-5, 12-6, 12-7, 12-8, and 12-9 at intervals of 0.04 μm (40 nm).

[0138] Having Li 1.0 Ni 1 / 2 Co 1 / 5 Mn 3 / 10 A second lithium metal oxide with a fixed total composition of O2 (NCM523) is used as the second cathode active material particles. The mixing ratio of the first lithium metal oxide and the second lithium metal oxide is adjusted as listed in the table below to form the cathode active material.

[0139] Denka Black was used as the conductive additive, and PVDF was used as the binder. The cathode active material, conductive additive, and binder were mixed in a weight ratio of 92:5:3 to form a positive electrode slurry. The positive electrode slurry was coated, dried, and pressed onto an aluminum substrate to form the cathode. The density of the pressed cathode was 3.3 g / cc.

[0140] Table 1

[0141] Location number molar ratio of Ni molar ratio of Co The molar ratio of Mn 1 0.802 0.110 0.088 2 0.801 0.111 0.088 3 0.802 0.110 0.088 4 0.802 0.110 0.088 5 0.803 0.111 0.086 6 0.802 0.110 0.088 7 0.802 0.110 0.088 8 0.802 0.109 0.089 9 0.801 0.110 0.089 10 0.802 0.110 0.088 11 0.802 0.108 0.090 12 0.800 0.110 0.090 12-1 0.794 0.110 0.096 12-2 0.789 0.109 0.102 12-3 0.782 0.110 0.108 12-4 0.777 0.110 0.113 12-5 0.770 0.110 0.120 12-6 0.771 0.110 0.119 12-7 0.770 0.110 0.120 12-8 0.769 0.111 0.120 12-9 0.770 0.109 0.121 13 0.770 0.110 0.120

[0142] (2) Anode

[0143] An anode slurry was prepared by mixing 93 wt% natural graphite as the anode active material, 5 wt% flake conductive additive KS6, 1 wt% SBR as a binder, and 1 wt% CMC as a thickener. The anode slurry was coated, dried, and pressed onto a copper substrate to form an anode.

[0144] (3) Lithium secondary battery

[0145] The cathode and anode obtained as described above are cut to appropriate sizes and stacked, with a diaphragm (polyethylene, thickness: 25 μm) inserted between them to form an electrode unit. Each tab portion of the cathode and anode is welded. The welded cathode / diaphragm / anode assembly is inserted into a bag, sealing three sides of the bag (e.g., except for the electrolyte injection side). The tab portions are also included in the sealed portion. Electrolyte is injected via the electrolyte injection side, which is then also sealed. The structure is then impregnated for more than 12 hours.

[0146] The method involves dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), followed by the addition of 1 wt% vinylene carbonate, 0.5 wt% 1,3-propensultone (PRS), and 0.5 wt% lithium bis(oxalato)borate (LiBOB).

[0147] The lithium secondary battery manufactured as described above was precharged for 36 minutes by applying a precharge current (2.5A) corresponding to 0.25C. After 1 hour, the battery was degassed and aged for more than 24 hours, followed by formation charging-discharging (charging conditions: constant current-constant voltage (CC-CV) 0.2C 4.2V 0.05C cut-off; discharging conditions: constant current (CC) 0.2C 2.5V cut-off). Then, standard charge-discharge was performed (charging conditions: constant current-constant voltage 0.5C 4.2V 0.05C cut-off; discharging conditions: constant current 0.5C 2.5V cut-off).

[0148] Examples and Comparative Examples

[0149] In the examples, a mixture of cathode active material particles CAM10a and NCM523 was used. In the comparative examples, LiNi with a uniform composition throughout the entire particle region was used. 0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as CAM20, see...) Figure 5 (Image) as the cathode active material.

[0150] Apart from the cathode active material particles, the methods for forming the cathode, anode, and lithium secondary battery in the examples and comparative examples are the same.

[0151] (1-1) Experimental Example 1-1: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 3μm (3μm)

[0152] The battery cells prepared as described in Table 2 below were repeatedly charged (constant current-constant voltage 2.0C 4.2V 0.05C cutoff) and discharged (constant current 2.0C 2.75V cutoff) 500 times. Then the percentage (%) of the discharge capacity of the 500th cycle relative to the discharge capacity of the first cycle was calculated to measure the lifetime characteristics at room temperature.

[0153] In addition, the battery cells of the embodiments and comparative examples were charged (1C 4.2V 0.1C cutoff), and then a 3mm diameter nail was used to penetrate the battery cell at a speed of 80mm / second to check whether a fire or explosion occurred (O: fire or explosion occurred, X: no fire or explosion).

[0154] The results are shown in Table 2 below.

[0155] Table 2

[0156]

[0157] (1-2) Experimental Example 1-2: According to NCM523(D 50 The lifetime and penetration stability were evaluated using a mixing ratio of 4.5 μm.

[0158] The lifetime characteristics and penetration stability of battery cells with the compositions described in Table 3 below were evaluated using the same method as in Experimental Example 1-1.

[0159] Table 3

[0160]

[0161] (1-3) Experimental Example 1-3: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 7μm.

[0162] The lifetime characteristics and penetration stability of battery cells with the composition described in Table 4 below were evaluated using the same method as in Experimental Example 1-1.

[0163] Table 4

[0164]

[0165]

[0166] (1-4) Experimental Example 1-4: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 10 μm.

[0167] The lifetime characteristics and penetration stability of battery cells with the composition described in Table 5 below were evaluated using the same method as in Experimental Example 1-1.

[0168] Table 5

[0169]

[0170]

[0171] (1-5) Experimental Example 1-5: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 15μm (15μm)

[0172] The lifetime characteristics and penetration stability of battery cells with the compositions described in Table 6 below were evaluated using the same method as in Experimental Example 1-1.

[0173] Table 6

[0174]

[0175]

[0176] Referring to Tables 2 to 6 above, the batteries in the embodiments exhibit improved lifespan characteristics and penetration stability compared to the batteries in the comparative examples.

[0177] Regarding the particle size (D) of the second lithium metal oxide 50 The lifetime characteristics and penetration stability of experimental examples 1-1 to 1-5 were generally improved.

[0178] In an embodiment, when the mixing ratio of the first lithium metal oxide and the second lithium metal oxide is from about 50:50 to about 10:90, essentially in D 50 Penetration stability was improved in all regions.

[0179] When the particle size of the second lithium metal oxide (D) 50 When the thickness is 4.5μm to 15μm, the range of mixing ratios of the first lithium metal oxide and the second lithium metal oxide that will not cause fire or explosion due to penetration is greatly expanded.

[0180] Experimental Example 2: A first cathode active material with an FCG structure and a second cathode active material with a fixed concentration were used. Material mixing

[0181] Manufacturing of lithium secondary batteries

[0182] (1) Cathode

[0183] By continuously changing the mixing ratio of the precursors to form a precipitate, a LiNi alloy is formed. 0.8 Co 0.1 Mn 0.1 The overall composition of O2, and has properties derived from LiNi 0.84 Co 0.11 Mn 0.05 The central composition of O2 to LiNi 0.78 Co 0.10 Mn 0.12 The first cathode active material particles (hereinafter referred to as CAM10b, see also O2) form a continuous concentration gradient on the surface. Figure 4 (Image). In addition, a second cathode active material particle (hereinafter referred to as NCM523) with uniform nickel, manganese and cobalt concentrations (or molar ratios) from the center to the surface was prepared.

[0184] The mixing ratio of the first cathode active material particles and the second cathode active material particles was adjusted according to the table below to form the cathode active material. The cathode active material, Denka Black as a conductive additive, and PVDF as a binder were mixed at a weight ratio of 92:5:3 to form a positive electrode slurry. The positive electrode slurry was coated, dried, and pressed onto an aluminum current collector to form the cathode. The density of the pressed cathode was 3.3 g / cc.

[0185] Figure 3 This is a schematic cross-sectional view showing the measurement locations of the concentration gradient of first cathode active material particles prepared according to some exemplary embodiments. (Reference) Figure 3 The concentration was measured at intervals of 5 μm, from the center of the first cathode active material particle to the surface. The results are listed in Table 7 below.

[0186] Table 7

[0187] Location number molar ratio of Ni molar ratio of Co The molar ratio of Mn 1 77.97 10.07 11.96 2 80.98 9.73 9.29 3 82.68 10.32 7 4 82.6 10 7.4 5 82.55 10.37 7.07 6 83.24 10.86 5.9 7 84.33 10.83 4.84

[0188] (2) Anode

[0189] The anode was manufactured using the same method as in Experimental Example 1.

[0190] (3) Lithium secondary battery

[0191] Using the cathode and anode prepared as described above, a lithium secondary battery was manufactured by the same method as in Experimental Example 1.

[0192] Examples and Comparative Examples

[0193] In the examples, a mixture of cathode active material particles CAM10b and NCM523 was used. In the comparative examples, LiNi with a uniform composition throughout the particle region was used. 0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as CAM20, see...) Figure 5 (Image) as the cathode active material.

[0194] Apart from the cathode active material particles, the methods for forming the cathode, anode, and lithium secondary battery in the examples and comparative examples are the same.

[0195] (2-1) Experimental Example 2-1: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 3μm (3μm)

[0196] The battery cells prepared as described in Table 8 were repeatedly charged (1C 4.2V 0.1C cutoff) and discharged (1C 3.0V cutoff) 500 times. The percentage (%) of the discharge capacity of the 500th cycle relative to the discharge capacity of the first cycle was then calculated to measure the lifetime characteristics.

[0197] In addition, the battery cells of the embodiments and comparative examples were charged (1C 4.2V 0.1C cutoff), and then a 3mm diameter nail was used to penetrate the battery cell at a speed of 80mm / s to check for fire or explosion (O: fire or explosion occurred, X: no fire or explosion).

[0198] The results are shown in Table 8 below.

[0199] Table 8

[0200]

[0201]

[0202] (2-2) Experimental Example 2-2: According to NCM523(D 50 The lifetime and penetration stability were evaluated using a mixing ratio of 4.5 μm.

[0203] The lifetime characteristics and penetration stability of battery cells with the compositions described in Table 9 below were evaluated using the same method as in Experimental Example 2-1.

[0204] Table 9

[0205]

[0206]

[0207] (2-3) Experimental Example 2-3: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 7μm.

[0208] The lifetime characteristics and penetration stability of battery cells with the compositions described in Table 10 below were evaluated using the same method as in Experimental Example 2-1.

[0209] Table 10

[0210]

[0211]

[0212] (2-4) Experimental Example 2-4: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 10 μm.

[0213] The lifetime characteristics and penetration stability of battery cells with the composition described in Table 11 below were evaluated using the same method as in Experimental Example 2-1.

[0214] Table 11

[0215]

[0216]

[0217] (2-5) Experimental Example 2-5: According to NCM523(D 50 Evaluation of lifetime and penetration stability using a mixing ratio of 15μm (15μm)

[0218] The lifetime characteristics and penetration stability of battery cells with the composition described in Table 12 below were evaluated using the same method as in Experimental Example 2-1.

[0219] Table 12

[0220]

[0221]

[0222] Referring to Tables 8 to 12 above, compared with the comparative examples, the batteries in the examples using a mixture of first cathode active material particles (CAM10b) with a concentration gradient and second cathode active material particles (NCM523) with a fixed composition showed improved lifetime characteristics and penetration stability.

[0223] The comparative battery cells generally exhibited reduced lifespan characteristics and penetration stability, and only failed to catch fire when containing excessive amounts of NCM523.

[0224] In Examples 2-1 to 2-5, when the mixing ratio of the first cathode active material particles to the second cathode active material particles is about 50:40 to about 10:90, no fire or explosion will occur due to penetration.

[0225] When the particle size of the second lithium metal oxide (NCM523) is (D 50 When the particle size is 4.5μm to 15μm, the mixing ratio of the first cathode active material particles and the second cathode active material particles is greatly increased so that they will not ignite or explode due to penetration.

Claims

1. A lithium secondary battery comprising: a cathode formed of a cathode active material including first cathode active material particles and second cathode active material particles; an anode; and a separator interposed between the cathode and the anode, wherein the first cathode active material particles include a lithium metal oxide having a continuous concentration gradient in at least one region between a central portion and a surface portion, wherein the second cathode active material particles include a lithium metal oxide including at least two metals other than lithium having a constant concentration from a central portion to a surface, and the second cathode active material particles include an excess of nickel among the metals other than lithium, wherein a mixing ratio of the first cathode active material particles to the second cathode active material particles is 5:5 to 1:

9. 2.The lithium secondary battery according to claim 1, wherein the first cathode active material particles include a first metal having a continuously decreasing concentration between the central portion and the surface portion and a second metal having a continuously increasing concentration between the central portion and the surface portion. 3.The lithium secondary battery according to claim 2, wherein the first cathode active material particles further include a third metal having a constant concentration from the central portion to the surface portion. 4.The lithium secondary battery according to claim 3, wherein the first cathode active material particles are represented by the following Chemical Formula 1: [Chemical Formula 1] wherein in the above Chemical Formula 1, M1, M2, and M3 each represent the first metal, the second metal, and the third metal, and each is selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, or B, and Li x M1 a M2 b M3 c O y , 0 < x ≤ 1.1, 2 ≤ y ≤ 2.02, 0 < a < 1, 0 < b < 1, 0 < c < 1, and 0 < a + b + c ≤ 1. 5.The lithium secondary battery according to claim 4, wherein in Chemical Formula 1, 0.6 ≤ a ≤ 0.95 and 0.05 ≤ b + c ≤ 0.

4. 6.The lithium secondary battery according to claim 4, wherein in Chemical Formula 1, 0.7 ≤ a ≤ 0.9 and 0.1 ≤ b + c ≤ 0.

3. 7.The lithium secondary battery according to claim 4, wherein the first metal is nickel (Ni), the second metal is manganese (Mn), and the third metal is cobalt (Co). 8.The lithium secondary battery according to claim 1, wherein the first cathode active material particles include a concentration gradient layer formed between the central portion and the surface portion. 9.The lithium secondary battery according to claim 8, wherein the concentration gradient layer includes a continuous concentration gradient, wherein the central portion and the surface portion each have a constant concentration composition, and the central portion and the surface portion have different concentration compositions from each other through the concentration gradient layer. 10.The lithium secondary battery according to claim 1, wherein the first cathode active material particles have a continuous concentration gradient in all regions from the central portion to the surface thereof. ​ 11.The lithium secondary battery according to claim 1, wherein the second cathode active material particle is represented by the following Chemical Formula 2: [Chemical Formula 2] Li x M1' a M2' b M3' c O y , wherein in the above Chemical Formula 2, M1' is nickel, M2' and M3' are selected from Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, or B, and 0 < x ≤ 1.1, 2 ≤ y ≤ 2.02, 0 < a + b + c ≤ 1, 0.48 ≤ a ≤ 0.52, 0.18 ≤ b ≤ 0.22, 0.28 ≤ c ≤ 0.

32. 12.The lithium secondary battery according to claim 11, wherein in Chemical Formula 2, 0.49 ≤ a ≤ 0.51, 0.19 ≤ b ≤ 0.21, and 0.29 ≤ c ≤ 0.

31. 13.The lithium secondary battery according to claim 11, wherein M2' and M3' are cobalt (Co) and manganese (Mn), respectively. 14.The lithium secondary battery according to claim 13, wherein the molar ratio of nickel, cobalt, and manganese in the second cathode active material particle is 5:2:

3.

15. The lithium secondary battery according to claim 1, wherein the average diameter (D 50 ) of the second cathode active material particles is 3-15 μm.

16. The lithium secondary battery according to claim 1, wherein the average diameter (D 50 ) of the second cathode active material particles is 4.5-15 μm.

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