Rechargeable lithium battery

Abstract

A rechargeable lithium battery is disclosed, comprising: an electrode stack, comprising a positive electrode having a positive electrode current collector and a positive electrode active material layer disposed thereon, a negative electrode having a negative electrode current collector, a negative electrode active material layer disposed thereon, and a negative electrode functional layer disposed on the negative electrode active material layer, and a separator, wherein a ratio of a height (which is a length along a protruding direction of an electrode terminal) to a width (which is perpendicular to the protruding direction of the electrode terminal and parallel to a stacking surface) of the electrode stack is about 1.1 to about 2.3, the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material, the first positive electrode active material comprises at least one of a composite oxide of a metal selected from cobalt, manganese, nickel, and a combination thereof and lithium, and the second positive electrode active material comprises a Li a Fe 1‑x1 M x1 The compound is represented by PO (0.90≤a≤1.8, 0≤x1≤0.7, M is Mn, Co, Ni or a combination thereof), the negative electrode functional layer includes flaky polyethylene particles, and the operating voltage is greater than or equal to about 4.3V.

Description

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0052570 filed on May 3, 2019, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to rechargeable lithium batteries. Background Art

[0003] Portable information devices or electric vehicles such as cellular phones, laptop computers, smart phones, etc. have used rechargeable lithium batteries with high energy density and easy portability as driving power sources. In addition, research has recently been actively conducted on using rechargeable lithium batteries as power sources or power storage for hybrid or electric vehicles by utilizing high energy density characteristics.

[0004] One of the main research tasks of such rechargeable lithium batteries is to improve the safety of rechargeable lithium batteries. For example, if the rechargeable lithium battery releases heat due to internal short circuit, overcharge and over discharge, etc., and electrolyte decomposition reaction and thermal runaway phenomenon occur, the internal pressure inside the battery may rise rapidly and cause the battery to explode. Among these, when an internal short circuit of a rechargeable lithium battery occurs, there is a high risk of explosion because the high electrical energy stored in each electrode is conducted in the short-circuited positive and negative electrodes.

[0005] In addition to the damage to the rechargeable lithium battery, the explosion may also cause fatal harm to the user. Therefore, it is urgent to develop a technology that can improve the stability of the rechargeable lithium battery.

[0006] On the other hand, LFP is used as a low heat generation safety material, but its average potential is relatively low, accompanied by a decrease in capacity during discharge. Therefore, technical development is required to improve these problems. Summary of the invention

[0007] Provided is a rechargeable lithium battery capable of operating at a high voltage and having high capacity and high stability.

[0008] An embodiment provides a rechargeable lithium battery, the rechargeable lithium battery comprising an electrode stack, the electrode stack comprising: a positive electrode, comprising a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector; a negative electrode, comprising a negative electrode collector, a negative electrode active material layer disposed on the negative electrode collector, and a negative electrode functional layer disposed on the negative electrode active material layer; and a separator, wherein a ratio (L / W) of a height (L) to a width (W) of the electrode stack is from about 1.1 to about 2.3, the height (L) is the length in a protruding direction of the electrode terminal, the width (W) is perpendicular to the protruding direction of the electrode terminal and parallel to the stacking surface, the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material, the first positive electrode active material comprises at least one of a composite oxide of a metal selected from cobalt, manganese, nickel and combinations thereof and lithium, the second positive electrode active material comprises a compound represented by Chemical Formula 1, the negative electrode functional layer comprises flaky polyethylene particles, and an operating voltage is greater than or equal to about 4.3V.

[0009] [Chemical formula 1]

[0010] Li a Fe 1-x1 M x1 PO4

[0011] In Chemical Formula 1, 0.90≤a≤1.8, 0≤x1≤0.7, and M is Mn, Co, Ni, or a combination thereof.

[0012] As a rechargeable lithium battery that can operate at high voltage without reducing capacity, safety can be achieved by realizing the early closure function. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The structure of a rechargeable lithium battery according to an embodiment of the present disclosure is schematically shown.

[0014] Figure 2 is a schematic diagram of an electrode stack according to an embodiment of the present disclosure.

[0015] Figure 3 The heat transfer simulation results over time of the rechargeable lithium battery cells during the puncture safety evaluation according to Examples 1 and 2 of the present disclosure are shown.

[0016] Figure 4 The heat transfer simulation results of the rechargeable lithium battery cells according to Comparative Examples 1 and 2 over time during the puncture safety evaluation are shown.

[0017] Figure 5 is a SEM photograph of polyethylene particles of the negative electrode functional layer according to the example.

[0018] Figure 6is a SEM photograph of a negative electrode composition according to an example. DETAILED DESCRIPTION

[0019] Hereinafter, embodiments of the present disclosure are described in detail with reference to the accompanying drawings. In the following description of the present disclosure, well-known functions or constructions will not be described in order to clarify the present disclosure.

[0020] In order to clearly illustrate the present disclosure, descriptions and relationships are omitted, and the same or similar structural elements are represented by the same reference numerals throughout the disclosure. Moreover, since the size and thickness of each structure shown in the drawings are arbitrarily shown for better understanding and ease of description, the present disclosure is not necessarily limited thereto.

[0021] According to the types of separators and electrolytes, rechargeable lithium batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries. According to the shape, rechargeable lithium batteries can also be classified into cylindrical, prismatic, coin-shaped, bag-shaped, etc. In addition, according to the size, rechargeable lithium batteries can be block-shaped and thin-film-shaped. The structure and manufacturing method of the lithium ion battery disclosed in the present invention are well known in the art.

[0022] Hereinafter, as an example of a rechargeable lithium battery, for example, a pouch-type rechargeable lithium battery is described. Figure 1 The structure of a rechargeable lithium battery according to an embodiment is schematically shown. Figure 1 The rechargeable lithium battery 1 according to an embodiment of the present disclosure may include a case 20, an electrode stack 10 inserted into the case 20, and a positive terminal 40 and a negative terminal 50 electrically connected to the electrode stack. The positive terminal 40 and the negative terminal 50 may be led out of the case 20 through tabs, respectively, and each is insulated from the case 20 by an insulating member 60.

[0023] like Figure 1 As shown in the figure, the electrode stack 10 has a structure in which a positive electrode 11 and a negative electrode 12 in a rectangular sheet shape having a predetermined size and a separator 13 disposed therebetween are stacked and wound in one direction (jelly roll type). Alternatively, although not shown, a plate-shaped positive electrode, a plate-shaped negative electrode, and a plate-shaped separator having a predetermined size may be laminated, and the positive electrode and the negative electrode may be formed into a stacked (laminated) structure in which separators are alternately stacked.

[0024] The electrode stack 10 may include at least one positive electrode, at least one negative electrode, and at least one separator.

[0025] The case 20 may include a lower case 22 and an upper case 21 , and the electrode stack 10 may be accommodated in an inner space 221 of the lower case 22 .

[0026] After the electrode stack 10 is accommodated in the case 20 , a sealing material is applied to the sealing portion 222 provided at the edge of the lower case 22 to seal the upper case 21 and the lower case 22 .

[0027] In addition, the positive electrode 11 , the negative electrode 12 , and the separator 13 may be immersed in an electrolyte.

[0028] The positive electrode 11 may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a positive electrode binder, and optionally a conductive material.

[0029] Hereinafter, a detailed configuration of the rechargeable lithium battery 1 according to an embodiment of the present disclosure is described.

[0030] A rechargeable lithium battery according to an embodiment of the present disclosure includes an electrode stack, the electrode stack including a positive electrode, a negative electrode and a separator, and a ratio (L / W) of a height (L) to a width (W) of the electrode stack is about 1.1 to about 2.3, the height (L) is the length in a protruding direction of the electrode terminal, and the width (W) is perpendicular to the protruding direction of the electrode terminal and parallel to the stacking surface.

[0031] To define the width and height of the electrode stack, Figure 2 A schematic diagram of an electrode stack is shown in FIG.

[0032] Figure 2 is a schematic diagram of an electrode stack according to an embodiment of the present disclosure.

[0033] according to Figure 2 , the width (W) of the electrode stack refers to the length perpendicular to the protruding direction of the electrode terminal and parallel to the stacking surface in the packaged electrode stack. That is, in the packaged electrode stack, it refers to the length of the surface in the direction along which the positive electrode, the negative electrode and the separator are stacked and in the direction perpendicular to the protruding direction of the electrode terminal.

[0034] In addition, the height (L) of the electrode stack refers to the length of the electrode terminals in the packaged electrode stack in the protruding direction, and in this case, the length extending from the electrode terminals (ie, the negative electrode terminal and the positive electrode terminal) is excluded.

[0035] When the ratio of the height to the width (L / W) of the electrode stack satisfies 1.1 to 2.3, safety may be ensured when operating at a high voltage of about 4.3V or more.

[0036] The positive electrode includes a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector, wherein the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material.

[0037] The first positive active material may include at least one of a composite oxide of a metal selected from the group consisting of cobalt, manganese, nickel, and a combination thereof and lithium, and the second positive active material may include a compound represented by Chemical Formula 1.

[0038] [Chemical formula 1]

[0039] Li a Fe 1-x1 M x1 PO4

[0040] In Chemical Formula 1, 0.90≤a≤1.8, 0≤x1≤0.7, and M is Mn, Co, Ni, or a combination thereof.

[0041] The first positive electrode active material is a high capacity material having a high energy density per unit amount, and thus can minimize capacity degradation during operation at a high voltage of about 4.3 V or more, and the second positive electrode active material is a low heat generation stability material, and thus can ensure stability. In other words, the first positive electrode active material and the second positive electrode active material are used together, and thus a rechargeable lithium battery with high capacity and high stability can be realized.

[0042] Specifically, the rechargeable lithium battery according to the embodiment includes a positive electrode including a first positive active material, and thus may minimize capacity degradation during operation at a high voltage of greater than or equal to about 4.3 V and thereby improve cycle-life characteristics.

[0043] The first positive active material may be included in an amount of about 80 wt % to about 97 wt %, specifically about 80 wt % to about 95 wt %, for example about 85 wt % to about 95 wt % or about 85 wt % to about 94 wt %, based on the total weight of the positive active material layer.

[0044] The positive electrode active material layer may further include a positive electrode functional layer disposed on the positive electrode active material layer.

[0045] For example, the first positive electrode active material may be included in the positive electrode active material layer, and the second positive electrode active material may be included in the positive electrode functional layer.

[0046] In this case, the first positive active material and the second positive active material may be included in a weight ratio of about 97:3 to about 80:20 or a weight ratio of about 95:5 to about 80:20.

[0047] For example, the first positive electrode active material may be included in the positive electrode active material layer, and the second positive electrode active material may be included in the positive electrode active material layer and the positive electrode functional layer, respectively.

[0048] In this case, the first positive active material and the second positive active material may be included in a weight ratio of about 94:6 to about 85:15.

[0049] In this case, the second positive active material of the positive electrode functional layer may be included in about 20 parts by weight to about 120 parts by weight based on 100 parts by weight of the second positive active material of the positive active material layer.

[0050] When the first positive electrode active material and the second positive electrode active material satisfy the above range, high capacity and safety can be ensured.

[0051] The first positive electrode active material may specifically include LiCoO2, Li b M 1 1-y1-z1 M 2 y1 M 3 z1 O2(0.9≤b≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1≤1, M 1 、M 2 and M 3 Independently one of metal Ni, Co, Mn, Al, Sr, Mg or La) and combinations thereof.

[0052] For example, the first positive active material may include LiCoO 2 , but is not limited thereto.

[0053] For example, M 1 Can be Ni, M 2 and M 3 It may independently be a metal such as Co, Mn, Al, Sr, Mg or La.

[0054] More specifically, M 1 Can be Ni, M 2 It can be Co, M 3 It may be Mn or Al, but is not limited thereto.

[0055] The second positive active material may include LiFePO 4 .

[0056] The negative electrode may include a negative electrode collector, a negative electrode active material layer disposed on the negative electrode collector, and a negative electrode functional layer disposed on the negative electrode active material layer, and the negative electrode functional layer may include flake-shaped polyethylene particles.

[0057] When the flake polyethylene particles are used, a large area can be effectively blocked at the shutdown temperature (or current cutoff temperature) compared to the spherical polyethylene particles. Therefore, a negative electrode having a negative electrode functional layer including the flake polyethylene particles can also be included to more effectively achieve the closed-cell function and thereby prevent additional chemical reactions, resulting in a rechargeable battery with further improved safety.

[0058] Polyethylene is usually HDPE (high density polyethylene, density: about 0.94 g / cc to about 0.965 g / cc), MDPE (medium density polyethylene, density: about 0.925 g / cc to about 0.94 g / cc), LDPE (low density polyethylene, density: about 0.91 g / cc to about 0.925 g / cc), VLDPE (very low density polyethylene, density: about 0.85 g / cc to about 0.91 g / cc), etc.

[0059] The flaky polyethylene particles may be used alone or in combination of two or more polyethylene polymers such as HDPE, MDPE or LDPE.

[0060] The average particle diameter (D50) of the sheet-like polyethylene particles included in the negative electrode functional layer disposed on the negative electrode active material layer may be about 1 μm to about 8 μm, specifically about 2 μm to about 6 μm.

[0061] As used herein, when no additional definition is provided, the average particle size (D50) can be measured by methods known to those of ordinary skill in the art, for example, by a particle size analyzer or from a TEM or SEM photograph. Alternatively, a dynamic light scattering measurement device is used to perform data analysis, and the number of particles in each particle size range is counted. Thus, the D50 value can be easily obtained by calculation.

[0062] More precisely, the particle size of the flake polyethylene particles can be determined by dynamic light scattering measurements. Specifically, the size can be measured by analysis of the light scattering properties of the particles via ISO 13320. For non-spherical particles, a size distribution is reported where the predicted scattering pattern for the volume sum of spherical particles matches the measured scattering pattern.

[0063] On the other hand, the ratio of the major axis length to the minor axis length of the flaky polyethylene particles may be about 1 to about 5, specifically about 1.1 to about 4.5, for example about 1.2 to about 3.5.

[0064] In addition, the thickness of the sheet-like polyethylene particles may be about 0.2 μm to about 4 μm, specifically, about 0.3 μm to about 2.5 μm, for example, about 0.3 μm to about 1.5 μm.

[0065] like Figure 5 As seen in FIG. 1 , the polyethylene particles according to the present disclosure are flaky and the average particle size can be defined as above (D50).

[0066] When the size and thickness of the flaky polyethylene particles are within the above range, the ion channels can be effectively closed even in a small amount. When a negative electrode functional layer including flaky polyethylene particles is provided, the reaction rate can be increased according to the temperature under the same reaction conditions compared with the case where spherical polyethylene particles are included, thereby improving the stability improvement effect of the rechargeable lithium battery. In the case of the flaky polyethylene particles before melting, the area covering the holes is thinner and wider than the area covering the holes of the spherical polyethylene particles before melting. When the polyethylene particles are melted at a predetermined temperature or higher to close the ion channels, the reaction rate is faster because the flaky polyethylene particles have an area larger than the area of ​​the electrode plate closed by the melted spherical polyethylene particles.

[0067] That is, the polyethylene particles included in the negative electrode functional layer melt during thermal runaway of the battery to close the ion channels, thereby restricting the movement of ions to achieve a closed-pore function that can prevent additional electrochemical reactions.

[0068] For example, Figure 6 As shown in , since the flaky polyethylene particles according to the embodiment are disposed on the pores in the composition for a negative electrode functional layer in a thin and wide shape, the flaky polyethylene particles melt more rapidly during thermal runaway due to thermal / physical shock, thereby inhibiting the passage of ions.

[0069] On the other hand, the electrode stack may have a volume of about 17.5 cc to about 30 cc, but may be manufactured as a unit cell having a volume of about 30 cc or more depending on the purpose.

[0070] In addition, the electrode stack may have an energy density of about 600 Wh / L to about 750 Wh / L.

[0071] The energy density corresponds to the capacity of a rechargeable battery and can be obtained by dividing the energy (Wh) of the rechargeable battery under standard charge and discharge conditions (eg, charge at 0.5C / discharge at 0.2C) by the volume (L) of the rechargeable battery and then normalizing the quotient.

[0072] For example, the energy density of the electrode stack may be in a range of about 630 Wh / L to about 720 Wh / L or about 650 Wh / L to about 690 Wh / L.

[0073] The rechargeable battery according to the embodiment includes an electrode stack having an energy density within the aforementioned range, and thus may achieve high voltage and high capacity.

[0074] The rechargeable battery according to the embodiment may have an operating voltage of about 4.3V to about 4.5V, for example.

[0075] The positive electrode active material layer may further optionally include a positive electrode conductive material and a positive electrode binder.

[0076] The amount of the positive conductive material and the positive binder may be about 1 wt % to about 7 wt %, respectively, based on the total weight of the positive active material layer.

[0077] The positive electrode conductive material is used to impart conductivity to the positive electrode, and can be used as long as it is an electronic conductive material that does not cause chemical changes in the battery. Examples of the conductive material may include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0078] The positive electrode binder is well bonded to the positive electrode active material particles, and is also used to well bond the positive electrode active material to the current collector. Examples thereof may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0079] As the positive electrode current collector, aluminum, nickel, etc. can be used, but it is not limited thereto.

[0080] The electrolyte includes a nonaqueous organic solvent and a lithium salt.

[0081] The nonaqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0082] The non-aqueous organic solvent may include carbonates, esters, ethers, ketones, alcohols or aprotic solvents. Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc., and ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and ketone solvents may include cyclohexanone, etc. Alcohol solvents include ethanol, isopropanol, etc., and examples of aprotic solvents include nitriles such as R-CN (wherein R is a C2 to C20 straight chain hydrocarbon, branched hydrocarbon or cyclic hydrocarbon, and may include a double bond, an aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, cyclopentane, etc.

[0083] The nonaqueous organic solvent may be used alone or in a mixture of two or more. When the organic solvent is used in a mixture, the mixing ratio may be controlled according to desired battery performance.

[0084] The carbonate-based solvent may include a mixture of a cyclic carbonate and a linear carbonate. The cyclic carbonate and the linear carbonate are mixed together in a volume ratio of about 1:1 to about 1:9, and when the mixture is used as an electrolyte, electrolyte performance may be enhanced.

[0085] In addition to the carbonate-based solvent, the non-aqueous organic solvent of the present disclosure may further include an aromatic hydrocarbon-based organic solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0086] As the aromatic hydrocarbon organic solvent, the aromatic hydrocarbon compound of Chemical Formula 2 may be used.

[0087] [Chemical formula 2]

[0088]

[0089] In Chemical Formula 2, R1 to R6 are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, halogenated alkyl, and combinations thereof.

[0090] Specific examples of the aromatic hydrocarbon organic solvent may include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, 2,4-fluorotoluene, and the like. 3-Difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene and combinations thereof, but are not limited thereto.

[0091] The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of Chemical Formula 3 to improve the cycle life of the battery.

[0092] [Chemical formula 3]

[0093]

[0094] In Chemical Formula 3, R7 and R8 may be the same or different and may be selected from hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2) and a fluorinated C1 to C5 alkyl group, wherein at least one of R7 and R8 is selected from a halogen group, a cyano group (CN), a nitro group (NO2) and a fluorinated C1 to C5 alkyl group, with the proviso that R7 and R8 are not both hydrogen.

[0095] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the cycle life improving additive may be used within a suitable range.

[0096] Lithium salts dissolved in organic solvents supply lithium ions to the battery, essentially making the rechargeable lithium battery work, and improve the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F2y+1 SO2) (wherein x and y are natural numbers), LiCl, LiI, and at least one supporting salt of LiB(C2O4)2 (lithium bis(oxalato)borate, LiBOB). The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0097] The negative electrode functional layer may further include inorganic particles and a binder.

[0098] The total weight of the flaky polyethylene particles and the inorganic particles: the weight of the binder (i.e., the ratio of the total weight of the flaky polyethylene particles and the inorganic particles to the weight of the binder) can be a weight ratio of about 80:20 to about 99:1, specifically, a weight ratio of about 85:15 to about 97:3.

[0099] The flake polyethylene particles and the inorganic particles may be included in a weight ratio of about 95:5 to about 10:90, specifically, in a weight ratio of about 70:30 to about 30:70.

[0100] When the amounts of the flake-like polyethylene particles and the inorganic particles are within the above ranges, the cycle life characteristics and output characteristics of the battery can be ensured.

[0101] Inorganic particles may include, for example, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, but are not limited thereto. In addition to the inorganic particles, organic particles such as acrylic compounds, imide compounds, amide compounds, or a combination thereof may also be included, but the organic particles are not limited thereto.

[0102] The inorganic particles may be spherical, flaky, cubic or amorphous. The average particle size (D50) of the inorganic particles may be from about 1 nm to about 2500 nm, for example, from about 100 nm to about 2000 nm, from about 200 nm to about 1500 nm or from about 300 nm to about 1500 nm. The average particle size of the inorganic particles may be the average particle size (D50) when the volume ratio is 50% in the cumulative size distribution curve.

[0103] The thickness of the negative electrode functional layer may be about 1 μm to about 10 μm, specifically about 3 μm to about 10 μm.

[0104] In addition, a ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode functional layer may be about 50:1 to about 10:1, specifically about 30:1 to about 10:1.

[0105] When the thickness of the negative electrode functional layer is within the above range, thermal stability may be significantly improved while maintaining excellent cycle-life characteristics.

[0106] Specifically, when the ratio of the thickness of the negative electrode functional layer is included in the above range, thermal safety may be improved while minimizing a decrease in energy density.

[0107] The negative electrode current collector may include one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0108] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0109] Examples of materials capable of reversibly intercalating / deintercalating lithium ions may include carbonaceous materials, i.e., carbon-based negative electrode active materials commonly used in rechargeable lithium batteries. Examples of carbon-based negative electrode active materials may be crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flaky, spherical, or fibrous form, and amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, fired coke, and the like.

[0110] Lithium metal alloys include alloys of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn.

[0111] The material capable of being doped / dedoped with lithium can be a silicon-based material or a tin-based material, such as Si, SiO x(0 < x < 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Si), Si-C composite, Sn, SnO2, Sn-R alloy (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Sn), Sn-C composite, etc. At least one of these materials can be mixed with SiO2. The element Q and the element R can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0112] The transition metal oxide can include lithium titanium oxide.

[0113] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the negative electrode active material is about 95 wt% to about 99 wt%.

[0114] The negative electrode active material layer can also optionally include a negative electrode conductive material and a negative electrode binder.

[0115] Based on the total weight of the negative electrode active material layer, the respective amounts of the negative electrode conductive material and the negative electrode binder can be about 1 wt% to about 5 wt%.

[0116] The negative electrode conductive material is used to impart conductivity to the negative electrode, and the type of the negative electrode conductive material is the same as the type of the above-mentioned positive electrode conductive material.

[0117] The negative electrode binder improves the adhesion properties between the negative electrode active material particles and the adhesion properties between the negative electrode active material particles and the current collector. The negative electrode binder can be a water-insoluble binder, a water-soluble binder, an amphiphilic binder (water-soluble / water-insoluble binder), or a combination thereof.

[0118] The water-insoluble binder can be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0119] The water-soluble binder may be styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and C2 to C8 olefin, a copolymer of (meth)acrylic acid and alkyl (meth)acrylate, or a combination thereof.

[0120] The amphiphilic adhesive may be an acrylated styrene-based rubber.

[0121] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may also be used as a thickener to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, about 0.1 parts by weight to about 3 parts by weight of the thickener may be included.

[0122] The rechargeable lithium battery according to an embodiment of the present disclosure simultaneously includes a positive electrode active material layer having a first positive electrode active material and a second positive electrode active material and a negative electrode functional layer including flaky polyethylene particles and disposed on a negative electrode, thereby minimizing capacity degradation and reducing the heat increase rate due to thermal / physical shock and thereby effectively presenting a closed-cell effect.

[0123] On the other hand, the separator 13 can be arranged between the positive electrode 11 and the negative electrode 12 as described above. The separator 13 can be selected, for example, from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene or a combination thereof. It can have the form of a non-woven fabric or a woven fabric. For example, in a rechargeable lithium battery, polyolefin polymer separators such as polyethylene and polypropylene are mainly used. In order to ensure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material can be used. Alternatively, it can have a single-layer structure or a multi-layer structure.

[0124] Hereinafter, the above aspects of the present disclosure are described in more detail with reference to examples. However, these examples are exemplary and the present disclosure is not limited thereto.

[0125] (Manufacturing of rechargeable lithium battery cells)

[0126] Example 1:

[0127] 95 wt% of a positive electrode active material, 3 wt% of a polyvinylidene fluoride binder, and 2 wt% of a Ketjen black conductive material were mixed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry, wherein the positive electrode active material was prepared by mixing LiCoO2 / LiFePO4 as a first positive electrode active material / a second positive electrode active material at a weight ratio of 9:1. The positive electrode active material slurry was coated on an aluminum current collector, and then dried and compressed to manufacture a positive electrode having a positive electrode active material layer.

[0128] 98 wt% of graphite, 0.8 wt% of carboxymethyl cellulose and 1.2 wt% of styrene-butadiene rubber were mixed in pure water to prepare a negative active material slurry. The negative active material slurry was coated on both surfaces of a copper current collector, and then dried and compressed to manufacture a negative electrode having a negative active material layer.

[0129] 48 wt% of 2 μm flaky PE particles (major axis length / minor axis length = about 2, thickness = about 0.6 μm), 47 wt% of alumina (average particle size (D50) = 1.2 μm), and 5 wt% of an acrylated styrene-based rubber binder were mixed in an alcohol solvent to prepare a PE / alumina slurry.

[0130] The PE / alumina slurry was coated on both surfaces of the negative electrode, which was then dried and compressed, thereby manufacturing a negative electrode having a coating layer including flaky PE particles.

[0131] Negative electrode / separator / positive electrode / separator were stacked to form a jelly-roll type electrode stack (L / W of the electrode stack = 2.3).

[0132] The jelly-roll type electrode stack and electrolyte (1.0 M LiPF6 in EC / DEC=50:50 v / v) were placed in a battery case and sealed, thereby manufacturing a bag-shaped cell.

[0133] Example 2

[0134] A rechargeable lithium battery cell was manufactured according to the same method as Example 1 except that the L / W of the electrode stack was changed to 1.1.

[0135] Comparative Example 1

[0136] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the L / W of the electrode stack was changed to 2.5.

[0137] Comparative Example 2

[0138] A rechargeable lithium battery cell was manufactured according to the same method as Example 1 except that the L / W of the electrode stack was changed to 1.

[0139] Evaluation Example: Piercing Safety Assessment

[0140] Ten rechargeable battery cells each according to Examples 1 and 2 and Comparative Examples 1 and 2 were manufactured, and their puncture safety evaluation was performed.

[0141] The puncture safety evaluation was performed by charging the rechargeable lithium battery cells of Examples 1 and 2 and Comparative Examples 1 and 2 at 0.5C and 4.3V at a cutoff of 0.05C and after one hour, puncturing at 80 mm / sec using a pin with a diameter of 3 mm, and the results were examined.

[0142] While performing a puncture safety assessment, a heat transfer simulation of a rechargeable lithium battery cell was performed, and the results are shown in Figure 3 and Figure 4 middle.

[0143] Figure 3 The heat transfer simulation results over time of the rechargeable lithium battery cells during the puncture safety evaluation according to Examples 1 and 2 of the present disclosure are shown.

[0144] Figure 4 The heat transfer simulation results of the rechargeable lithium battery cells according to Comparative Examples 1 and 2 over time during the puncture safety evaluation are shown.

[0145] Reference Figure 3 , in a rechargeable lithium battery cell having an L / W in the range of 1.1 to 2.3, heat transfer is smoothly performed during puncture and causes early closure before explosion / fire of the battery cell, so puncture safety can be ensured.

[0146] On the contrary, refer to Figure 4 , in a rechargeable lithium battery cell with L / W less than 1.1 or L / W greater than 2.3, heat transfer is not smoothly performed, and may lead to early cell closure failure and cause explosion / fire of the battery cell. In other words, when L / W does not meet the range of 1.1 to 2.3, heat transfer is not smoothly performed, and thus safety cannot be ensured.

[0147] On the other hand, the puncture safety evaluation results of the rechargeable lithium battery cells of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1. In Table 1, the numbers refer to the number of battery cells that did not catch fire, smoked, and caught fire.

[0148] (Table 1)

[0149] L / W No fire smoke Fire Example 1 2.3 10 0 0 Example 2 1.1 10 0 0 Comparative Example 1 2.5 5 2 3 Comparative Example 2 1.0 5 2 3

[0150] As shown in Table 1, for the battery cells of Examples 1 and 2 having an aspect ratio (L / W) of the electrode stack in the range of 1.1 to 2.3, heat transfer was performed throughout the electrode stack in the puncture test, thus ensuring excellent safety.

[0151] However, the battery cells of Comparative Examples 1 and 2 do not satisfy L / W of 1.1 to 2.3, and it is difficult to ensure puncture safety, and therefore, Examples 1 and 2 exhibit very excellent safety compared to the battery cells of Comparative Examples 1 and 2.

[0152] In the above, certain embodiments of the present disclosure have been described and illustrated, however, it is clear to those skilled in the art that the present disclosure is not limited to the described embodiments, and various modifications and variations may be made without departing from the spirit and scope of the present disclosure. Therefore, the modified or varied embodiments are not to be understood separately from the technical ideas and aspects of the present disclosure, and the modified embodiments are within the scope of the claims of the present disclosure.

[0153] <Description of symbols>

[0154] 1: Rechargeable lithium battery 11: Positive electrode

[0155] 12: Negative electrode 13: Separator

[0156] 10: Electrode stack 20: Case

[0157] 21: Upper shell 22: Lower shell

[0158] 40: Positive terminal 50: Negative terminal

[0159] 60: Insulating member 221: Internal space of the lower housing

[0160] 222: Sealing part

Claims

1. A rechargeable lithium battery, the rechargeable lithium battery include: The electrode stack comprises: a positive electrode, comprising a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; a negative electrode, comprising a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector and a negative electrode functional layer disposed on the negative electrode active material layer; and a separator, The ratio L / W of the height L and the width W of the electrode stack is 1.1 to 2.3, the height L is the length in the protruding direction of the electrode terminal, and the width W is perpendicular to the protruding direction of the electrode terminal and parallel to the stacking surface. The positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material includes at least one of a composite oxide of a metal selected from cobalt, manganese, nickel and a combination thereof and lithium, and the second positive electrode active material includes a compound represented by Chemical Formula 1, The negative electrode functional layer includes flaky polyethylene particles, wherein the ratio of the major axis length to the minor axis length of the flaky polyethylene particles is 1.1 to 4.5, The working voltage is greater than or equal to 4.3V, [Chemical formula 1] Li a Fe 1-x1 M x1 P.O. 4 In Chemical Formula 1, 0.90≤a≤1.8, 0≤x1≤0.7, and M is Mn, Co, Ni, or a combination thereof.

2. The rechargeable lithium battery according to claim 1, in, The electrode stack has a volume of 17.5 cc to 30 cc.

3. The rechargeable lithium battery according to claim 1, in, The electrode stack has an energy density of 600 Wh / L to 750 Wh / L.

4. The rechargeable lithium battery according to claim 1, in, The operating voltage is 4.3V to 4.5V.

5. The rechargeable lithium battery according to claim 1, in, The first positive active material is included in an amount of 80 wt % to 97 wt % based on the total weight of the positive active material layer.

6. The rechargeable lithium battery according to claim 1, in, The first positive electrode active material and the second positive electrode active material are included in a weight ratio of 97:3 to 80:

20.

7. The rechargeable lithium battery according to claim 1, in, The positive electrode active material layer further includes a positive electrode functional layer disposed on the positive electrode active material layer.

8. The rechargeable lithium battery according to claim 7, in, The first positive electrode active material is included in the positive electrode active material layer, and The second positive electrode active material is included in at least one of the positive electrode active material layer and the positive electrode functional layer.

9. The rechargeable lithium battery according to claim 1, in, The first positive electrode active material includes a material selected from LiCoO 2 , Li b M 1 1-y1-z1 M 2 y1 M 3 z1 O 2 and a combination thereof, wherein 0.9≤b≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1≤1, M 1 、M 2 and M 3 Independently, it is metal Ni, Co, Mn, Al, Sr, Mg or La.

10. The rechargeable lithium battery according to claim 1, in, The second positive electrode active material includes LiFePO 4 .

11. The rechargeable lithium battery according to claim 1, in, The average particle diameter D50 of the flaky polyethylene particles is 1 μm to 8 μm.

12. The rechargeable lithium battery according to claim 1, in, The thickness of the flaky polyethylene particles is 0.2 μm to 4 μm.

13. The rechargeable lithium battery according to claim 1, in, The negative electrode functional layer further includes inorganic particles and a binder.

14. The rechargeable lithium battery according to claim 13, in, The weight ratio of the total weight of the flaky polyethylene particles and the inorganic particles to the weight of the binder is 80:20 to 99:

1.

15. The rechargeable lithium battery according to claim 13, in, The flaky polyethylene particles and the inorganic particles are included in a weight ratio of 95:5 to 10:

90.

16. The rechargeable lithium battery according to claim 1, in, The negative electrode functional layer has a thickness of 1 μm to 10 μm.

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