Negative electrode and rechargeable lithium battery comprising the same

Abstract

Disclosed are a negative active material for a rechargeable lithium battery and a rechargeable lithium battery including the same. A negative electrode for a rechargeable lithium battery includes a current collector and a negative active material layer disposed on the current collector, wherein the negative active material layer includes a first region in contact with the current collector and including a first negative active material, and a second region disposed on the first region and including a second negative active material, each of the first negative active material and the second negative active material has an average particle diameter (D50) of 9 µm to 22 µm, the morphology of the first negative active material and the second negative active material is different from each other, the porosity of the second region is higher than the porosity of the first region, and the ratio of the porosity of the second region to the porosity of the first region is in the range of 110% to 190%.

Description

TECHNICAL FIELD

[0001] Disclosed is a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. BACKGROUND

[0002] Portable information devices such as cellular phones, laptop computers, smart phones, etc. or electric vehicles have used rechargeable lithium batteries having high energy density and easy portability as a driving power source. Recently, research has been actively conducted to use rechargeable lithium batteries having high energy density as a driving power source or a power storage power source of a hybrid electric vehicle or an electric vehicle.

[0003] Such rechargeable lithium batteries require high-capacity electrodes, but there is a limit to increasing the capacity of the active material itself, and thus the amount of active material needs to be increased and the electrode is thus made thicker. As the electrode plate is thicker, the resistance of lithium ions within the pores of the electrode plate becomes more important to the performance of the electrode than the resistance of lithium ions intercalating into the active material. However, since this internal resistance can vary greatly depending on the structure of the electrode plate, various research is being conducted to reduce the resistance by improving the structure of the electrode plate. SUMMARY

[0004] Provided is a negative electrode for a rechargeable lithium battery, which is a thick film electrode maximizing capacity, capable of alleviating unevenness of resistance, improving output characteristics, improving capacity retention at high rates, and maintaining a high cycle life even during rapid charging and discharging, and a rechargeable lithium battery including the same.

[0005] An embodiment provides a negative electrode for a rechargeable lithium battery, the negative electrode including a current collector and a negative active material layer disposed on the current collector, wherein the negative active material layer includes a first region in contact with the current collector and including a first negative active material, and a second region disposed on the first region and including a second negative active material, each of the first negative active material and the second negative active material has an average particle diameter (D50) of 9 μm to 22 μm, the morphology of the first negative active material and the second negative active material are different from each other, the porosity of the second region is higher than the porosity of the first region, and the ratio of the porosity of the second region to the porosity of the first region is in the range of about 110% to about 190%.

[0006] Another embodiment provides a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte.

[0007] The negative electrode manufactured according to the embodiment and the rechargeable lithium battery including the same alleviate unevenness of resistance in a thick film electrode, improve output characteristics and capacity retention at high rates, and achieve a high cycle life even during rapid charging and discharging while achieving high capacity. Attached Figure Description

[0008] Figure 1 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment.

[0009] Figure 2 It is a scanning electron microscope image of the first negative electrode active material according to Example 1.

[0010] Figure 3 The image is a scanning electron microscope photograph of the second negative electrode active material according to Example 1.

[0011] Figure 4 It is a scanning electron microscope image of the cross-section of the negative electrode according to Example 1.

[0012] Figure 5 This is a graph showing the porosity of the negative electrode active material layers of Example 1, Comparative Example 1, and Comparative Example 2 as measured by nanocomputation tomography.

[0013] Figure 6 This is a graph showing the discharge rate of the battery cells according to Example 1, Comparative Example 1, and Comparative Example 2 at the C-rate.

[0014] Figure 7 This is a graph showing the amount of lithium deposition at the C-rate of the battery cell according to Comparative Example 1.

[0015] Figure 8 This is a graph showing the amount of lithium deposition at the C-rate of the battery cell according to Example 1.

[0016] Figure 9 It is a scanning electron microscope image of the cross-section of the negative electrode according to Example 2.

[0017] Figure 10 It is a scanning electron microscope image of the cross-section of the negative electrode according to Example 3.

[0018] Figure 11 It is a scanning electron microscope image of the cross-section of the negative electrode of Comparative Example 3. Detailed Implementation

[0019] Specific embodiments will be described in detail below, enabling those skilled in the art to readily implement them. However, this disclosure may be embodied in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0020] The terminology used herein is for describing embodiments only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0021] As used herein, "combination thereof" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, and the like.

[0022] Here, it should be understood that terms such as "include," "comprise," or "have" are intended to indicate existence of the features, numbers, steps, actions, elements, or combinations thereof described in the specification, but do not exclude the possibility of existence or addition of one or more other features, numbers, steps, actions, elements, or combinations thereof.

[0023] In the drawings, the thickness of layers, films, panels, regions, and the like, are exaggerated for clarity, and throughout the specification, like reference numerals refer to like elements. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0024] In addition, "layer" herein includes not only a shape formed on the entire surface when viewed from a plan view, but also a shape formed on a partial surface.

[0025] In addition, the average particle diameter can be measured by a method well known to those skilled in the art, for example, can be measured by a particle size analyzer, or can be measured by a transmission electron micrograph or a scanning electron micrograph. Alternatively, it is possible to measure by using a dynamic light scattering method, perform data analysis, count the number of particles for each particle size range, and obtain an average particle diameter value from the calculation. Unless otherwise defined, the average particle diameter is measured by a particle size analyzer, and can represent the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution (D50).

[0026] Negative electrode

[0027] In an embodiment, a negative electrode for a rechargeable lithium battery includes a current collector and a negative active material layer disposed on the current collector, wherein the negative active material layer includes a first region in contact with the current collector and including a first negative active material, and a second region disposed on the first region and including a second negative active material. Here, each of the first negative active material and the second negative active material has an average particle diameter (D50) of about 9 μm to about 22 μm, and the morphology of the first negative active material and the second negative active material is different from each other. In addition, the porosity of the second region is higher than the porosity of the first region, and the ratio of the porosity of the second region to the porosity of the first region is about 110% to about 190%.

[0028] The negative electrode for a rechargeable lithium-ion battery can be a thick-film electrode plate that maximizes capacity. As the electrode plate thickens, lithium ions become more difficult to embed into the current collector during charging, resulting in resistance concentration on the surface of the electrode plate and causing resistance non-uniformity, which is further exacerbated in high-rate batteries. An embodiment can provide a negative electrode for a rechargeable lithium-ion battery by coating a negative electrode active material with different morphologies in a first region (lower) and a second region (upper), and by making the electrode plate thicker to increase capacity. This negative electrode has a second region with a higher porosity than the first region. This reduces the resistance on the electrode plate surface and improves the battery's output characteristics.

[0029] In an embodiment, the ratio of the porosity of the second region to the porosity of the first region can be in the range of about 110% to about 190% (or, for example, about 120% to about 190%). A negative electrode of a rechargeable lithium battery that meets this range can mitigate resistance inhomogeneities and exhibit excellent output characteristics while achieving high capacity. Porosity can be measured using nano-computed tomography (nano-CT), scanning electron microscopy (SEM), or other general methods. The ratio of the porosity of the second region to the porosity of the first region is calculated according to the equation {(porosity of the second region) / (porosity of the first region) × 100%}.

[0030] The porosity of the first region, measured by nanocomputed tomography, can be greater than or equal to about 5% and less than about 16% (e.g., about 5% to about 15.5%, about 7% to about 15.5%, about 9% to about 15.5%, about 10% to about 15.5%, or about 12% to about 15%). Additionally, the porosity of the second region, measured by nanocomputed tomography, can be greater than or equal to about 16% and less than about 25% (e.g., about 16% to about 24%, about 16% to about 22%, about 16% to about 20%, or about 17% to about 19%). When the first and second regions meet these porosity ranges, the resistivity non-uniformity of the electrode plate can be mitigated, and output characteristics and cycle life characteristics can be improved. However, the porosity can vary depending on the type of negative electrode active material and the composition of the negative electrode active material layer slurry.

[0031] The porosity of the first region, measured by scanning electron microscopy, can be greater than or equal to about 5% and less than about 13% (e.g., about 5% to about 12.5%, about 7% to about 12.5%, about 9% to about 12.5%, or about 10% to about 12%), and the porosity of the second region can be greater than or equal to about 13% and less than about 25% (e.g., about 13% to about 24%, about 13% to about 22%, about 14% to about 20%, or about 15% to about 19%). When the first and second regions meet this porosity range, the resistivity non-uniformity of the electrode plate can be reduced, and the output characteristics and cycle life characteristics can be improved. However, the porosity can vary depending on the type of negative electrode active material and the composition of the negative electrode active material layer slurry.

[0032] The first negative electrode active material coated onto the first region and the second negative electrode active material coated onto the second region can have the same average particle size but different morphologies. For example, the first negative electrode active material can be spherical, and the second negative electrode active material can be amorphous. Here, spherical shape includes a shape similar to a sphere, and refers to a circular shape without angles. The first negative electrode active material has a near-spherical morphology and is easily compressed during compression. The first region composed of these components has a high internal density and relatively low porosity. The second negative electrode active material has a non-uniform morphology with a specific surface area higher than that of a spherical shape. The second region composed of these components can have relatively high porosity.

[0033] Both the first and second negative electrode active materials can include carbon-based active materials. Carbon-based active materials can include crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include flake, sheet, spherical, or fibrous graphite, and the graphite can be natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0034] The average particle size (D50) of the first negative electrode active material and the average particle size (D50) of the second negative electrode active material can be similar to each other, and can be in the range of about 9 μm to about 22 μm, respectively. The average particle size of the first negative electrode active material and the average particle size of the second negative electrode active material can be in the range of, for example, about 10 μm to about 21 μm, about 10 μm to about 20 μm, about 11 μm to about 19 μm, or about 12 μm to about 18 μm, respectively. When the first and second negative electrode active materials meet these particle size ranges, high capacity can be achieved, and excellent output characteristics and cycle life characteristics can be exhibited.

[0035] The tapped density of the first negative electrode active material can be greater than that of the second negative electrode active material. For example, the tapped density of the first negative electrode active material can be in the range of about 1.2 g / cc to about 1.5 g / cc, and the tapped density of the second negative electrode active material can be in the range of about 0.8 g / cc to about 1.4 g / cc. Optionally, the first negative electrode active material can have a tapped density of about 1.25 g / cc to about 1.5 g / cc, and the second negative electrode active material can have a tapped density of about 1.0 g / cc to about 1.24 g / cc. When the tapped densities of both the first negative electrode active material and the second negative electrode active material satisfy these ranges, the porosity of the second region can be designed to be higher than that of the first region, thereby reducing the non-uniformity of resistance and improving the output characteristics and cycle life characteristics of the battery. The tapped density can be measured by filling a 100 cc graduated cylinder with 50 cc of the negative electrode active material, performing 1000 taps at a height of 3 mm per second, and then dividing the mass by the volume.

[0036] The BET specific surface area of the first negative electrode active material can be greater than that of the second negative electrode active material. For example, the BET specific surface area of the first negative electrode active material can be in the range of about 1.4 m 2 ² / g to about 2.0 m 2 / ² / g, and the specific surface area of the second negative electrode active material can be in the range of about 1.0 m 2 ² / g to about 1.8 m 2 ² / g. Optionally, the BET specific surface area of the first negative electrode active material can be in the range of about 1.5 m 2 ² / g to about 2.0 m 2 ² / g, and the specific surface area of the second negative electrode active material can be in the range of about 1.0 m 2 ² / g to about 1.7 m 2 ² / g. When both the first negative electrode active material and the second negative electrode active material have BET specific surface areas that satisfy these ranges, the second region can be designed to have a higher porosity than that of the first region, thereby reducing the resistance non-uniformity and improving the output characteristics and cycle life characteristics of the battery.

[0037] Meanwhile, the first region and / or the second region can further include a silicon-based active material. When a silicon-based active material is further included, a rechargeable lithium battery with a higher capacity can be achieved. The silicon-based negative electrode active material can include silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (where Q is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, but not Si).

[0038] The silicon-carbon composite can be, for example, a silicon-carbon composite comprising a core containing crystalline carbon and silicon particles, and an amorphous carbon coating disposed on the surface of the core. The crystalline carbon can be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon precursor can be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or polymer resins (such as phenolic resins, furan resins, or polyimide resins). In this case, the silicon content can be from about 10 wt% to about 50 wt% based on the total weight of the silicon-carbon composite. Additionally, the crystalline carbon content can be from about 10 wt% to about 70 wt% based on the total weight of the silicon-carbon composite, and the amorphous carbon content can be from about 20 wt% to about 40 wt% based on the total weight of the silicon-carbon composite. Furthermore, the thickness of the amorphous carbon coating can be from about 5 nm to about 100 nm. The average particle size (D50) of the silicon particles can be from about 10 nm to about 200 nm. Silicon particles can exist in an oxidized form, and in this case, the atomic ratio of Si:O in the silicon particles, which indicates the degree of oxidation, can be from about 99:1 to about 33:66. The silicon particles can be SiO₂. x Particles, and in this case, SiO x The range of x in the equation can be greater than approximately 0 and less than approximately 2.

[0039] The average particle size (D50) of the silicon-based active material can range from about 1 μm to about 20 μm (or, for example, from about 5 μm to about 15 μm). The silicon-based active material can have a tap density of about 0.3 g / cc to about 1.1 g / cc (for example, from about 0.5 g / cc to about 1.0 g / cc). Additionally, the silicon-based active material can have a particle size of about 1.9 μm. 2 / g to approximately 2.7m 2 / g (for example, about 2.0m 2 / g to approximately 2.5m 2 The BET specific surface area is (g). Silicon-based active materials can be in various forms, such as spherical shapes, irregular shapes (e.g., near-spherical shapes), etc. When the properties of the silicon-based active material meet this range, the negative electrode containing this silicon-based active material can improve cycle life characteristics and general battery performance such as charge and discharge efficiency.

[0040] When the first and / or second regions also include silicon-based active materials, the content of the silicon-based active materials can be from about 1 wt% to about 15 wt% based on the total weight of each region, or for example from about 5 wt% to about 14 wt%. When silicon-based active materials are included in this range, rechargeable lithium batteries can exhibit excellent output characteristics and cycle life characteristics while achieving high capacity.

[0041] The negative electrode for a rechargeable lithium battery according to an embodiment can be a thickened negative electrode to maximize capacity; therefore, the thickness of each of the first and second regions can be in the range of about 30 μm to about 100 μm (e.g., about 30 μm to about 80 μm, or about 40 μm to about 70 μm). The total thickness of the negative electrode active material layer including the first and second regions can be in the range of about 60 μm to about 200 μm (e.g., about 70 μm to about 150 μm, or about 80 μm to about 140 μm). When the negative electrode active material layer is formed on both surfaces of the current collector, the negative electrode can have a total thickness of about 120 μm to about 400 μm, about 130 μm to about 400 μm (e.g., about 150 μm to about 300 μm, or about 160 μm to about 250 μm). When the thickness of each region and the negative electrode meets the stated range, very high capacity can be achieved, and according to an embodiment, the porosity of the first and second regions can be adjusted to achieve excellent output characteristics and cycle life characteristics at that thickness. Alternatively, the thickness of each region can be the thickness of the compressed electrode plate.

[0042] In the negative electrode active material layer, the content of the negative electrode active material can be from about 90 wt% to about 99.9 wt% based on the total weight of the negative electrode active material layer, or from about 95 wt% to about 99 wt%.

[0043] In embodiments, the negative electrode active material layer may further include a binder and may optionally further include a conductive material. The binder content in the negative electrode active material layer may be from about 0.5 wt% to about 5 wt% based on the total weight of the negative electrode active material layer, or from about 1 wt% to about 3 wt%. Additionally, when further including a conductive material, the negative electrode active material layer may include about 90 wt% to about 98 wt% of the negative electrode active material, about 1 wt% to about 5 wt% of the binder, and about 1 wt% to about 5 wt% of the conductive material.

[0044] Both the first and second regions in the negative electrode active material layer can include a binder, wherein the binder content can be from about 0.5 wt% to about 5 wt% based on the total weight of each region. Additionally, in embodiments, the binder in the first region and the binder in the second region can be used in a weight ratio of about 60:40 to about 95:5 (e.g., about 70:30 to about 90:10). When the weight ratio of the binder in the first and second regions meets this range, a stable electrode plate can be obtained despite increased thickness, and the battery's output characteristics and cycle life characteristics can be improved.

[0045] Adhesives are used to ensure good adhesion between particles of negative electrode active material, and also to adhere negative electrode active material to current collectors. Adhesives can be non-water-soluble adhesives, water-soluble adhesives, or combinations thereof.

[0046] Examples of non-water-soluble adhesives include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0047] Water-soluble adhesives may include rubber adhesives or polymeric resin adhesives. Rubber adhesives may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. Polymeric resin adhesives may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0048] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As a cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts may be mixed and used. As an alkali metal, Na, K, or Li may be used. The amount of thickener may be from about 0.1 parts by weight to about 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0049] Conductive materials are included to provide electrode conductivity. Any electrically conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.; metal-based materials containing metal powders or fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0050] The current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0051] On the other hand, in the negative electrode according to the embodiment, the second region can be formed after the first region is formed in the current collector, or the first region and the second region can be formed simultaneously by using a coating device such as a dual-groove mold, and then dried and compressed.

[0052] Positive electrode

[0053] The positive electrode for a rechargeable lithium battery may include a current collector and a layer of positive electrode active material disposed on the current collector. The positive electrode active material layer may include a positive electrode active material, and may also include a binder and / or a conductive material.

[0054] Positive electrode active materials can include lithiation compounds that reversibly insert and deintercalate lithium ions. Examples of positive electrode active materials include compounds represented by any of the following chemical formulas:

[0055] Li a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5);

[0056] Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);

[0057] Li a E 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);

[0058] Li a E 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);

[0059] Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2);

[0060] Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2);

[0061] Li a Ni 1-b-c Co b X c O2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0062] Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α≤2);

[0063] Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0064] Li a Ni 1-b-c Mr b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0065] Li a Ni b HAVE BEEN c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);

[0066] Li a Ni b Co c Mr d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);

[0067] Li a NiG b O2(0.90≤a≤1.8,0.001≤b≤0.1);

[0068] Li a CoG b O2(0.90≤a≤1.8,0.001≤b≤0.1);

[0069] Li a Mr 1-b G bO2(0.90≤a≤1.8, 0.001≤b≤0.1);

[0070] Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1);

[0071] Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5);

[0072] QO2; QS2; LiQS2;

[0073] V₂O₅; LiV₂O₅;

[0074] LiZO2;

[0075] LiNiVO4;

[0076] Li (3-f) J2(PO4)3(0≤f≤2);

[0077] Li (3-f) Fe2(PO4)3 (0≤f≤2); and

[0078] Li a FePO4 (0.90≤a≤1.8).

[0079] In the above chemical formulas, A is selected from Ni, Co, Mn and their combinations; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and their combinations; D is selected from O, F, S, P and their combinations; E is selected from Co, Mn and their combinations; T is selected from F, S, P and their combinations; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and their combinations; Q is selected from Ti, Mo, Mn and their combinations; Z is selected from Cr, V, Fe, Sc, Y and their combinations; and J is selected from V, Cr, Mn, Co, Ni, Cu and their combinations.

[0080] The compound may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from oxides, hydroxides, hydroxyoxides, oxycarbonates, and hydroxycarbonates of the coating element. The compound used for the coating may be amorphous or crystalline. The coating element included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or combinations thereof. The method of forming the coating may be a method that does not adversely affect the physical properties of the positive electrode active material (e.g., spraying, dipping, dry coating, atomic deposition, evaporation, etc.).

[0081] The positive electrode active material can be, for example, at least one of lithium composite oxides represented by chemical formula 11.

[0082] [Chemical Formula 11]

[0083] Li a M 11 1-y11-z11 M 12 y11 M 13 z11 O2

[0084] In chemical formula 11, 0.9 ≤ a ≤ 1.8, 0 ≤ y11 ≤ 1, 0 ≤ z11 ≤ 1, 0 ≤ y11 + z11 < 1, and M 11 M 12 and M 13 Each of them independently consists of Ni, Co, Mn, Al, Mg, Ti, Fe, or a combination thereof.

[0085] For example, M 11 It can be Ni, and M 12 and M 13 Each of these can be an independent metal, such as Co, Mn, Al, Mg, Ti, or Fe. As a specific example, M... 11 It can be Ni or M 12 It can be Co, and M 13 It can be Mn or Al, but this disclosure is not limited thereto.

[0086] In a specific embodiment, the positive electrode active material can be a lithium nickel-based oxide represented by chemical formula 12.

[0087] [Chemical Formula 12]

[0088] Li a12 Ni x12 M 14 y12 M 15 1-x12-y12 O2

[0089] In chemical formula 12, 0.9 ≤ a12 ≤ 1.8, 0.3 ≤ x12 ≤ 1, 0 ≤ y12 ≤ 0.7, M 14 and M 15 Each of them independently consists of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or combinations thereof.

[0090] Positive electrode active materials may include, for example, compounds of chemical formula 13.

[0091] [Chemical Formula 13]

[0092] Li a13 Ni x13 Co y13 M 16 1-x13-y13 O2

[0093] In chemical formula 13, 0.9 ≤ a13 ≤ 1.8, 0.3 ≤ x13 ≤ 1, 0 ≤ y13 ≤ 0.7, and M 16 It is Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or combinations thereof.

[0094] The content of the positive electrode active material can be from about 90 wt% to about 98 wt% (e.g., from about 90 wt% to about 95 wt%) based on the total weight of the positive electrode active material layer. The respective contents of the binder and conductive material can be from about 1 wt% to about 5 wt% based on the total weight of the positive electrode active material layer.

[0095] The adhesive improves the adhesion properties between the positive electrode active material particles and between them and the current collector. Examples of adhesives may include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0096] Conductive materials are used to impart conductivity to electrodes, and any material can be used as long as it does not cause a chemical change in the battery to be constructed and is electronically conductive. Examples of conductive materials can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.; metal-based materials containing metal powders or fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0097] The current collector may include, but is not limited to, aluminum foil.

[0098] Rechargeable lithium battery

[0099] Another embodiment provides a rechargeable lithium battery including a positive electrode, a negative electrode, a separator disposed therebetween, and an electrolyte.

[0100] Figure 1 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment. (Refer to...) Figure 1 According to an embodiment, a rechargeable lithium battery 100 includes a battery cell, a battery housing 120 housing the battery cell, and a sealing member 140 sealing the battery housing 120. The battery cell includes a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 between the positive electrode 114 and the negative electrode 112, and an electrolyte for the rechargeable lithium battery that impregnates the positive electrode 114, the negative electrode 112, and the separator 113.

[0101] Electrolytes include non-aqueous organic solvents and lithium salts.

[0102] Non-aqueous organic solvents are used as media for transporting ions involved in the electrochemical reactions of a battery. Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, or aprotic solvents. Examples of carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). Examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, mevalonolactone, and caprolactone. Ether solvents can be dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and ketone solvents can be cyclohexanone, etc. In addition, alcohol solvents can be ethanol, isopropanol, etc., and aprotic solvents can be nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may include double bonds, aromatic rings or ether bonds), amides such as dimethylformamide, dioxolane such as 1,3-dioxolane, sulfolane, etc.

[0103] Non-aqueous organic solvents can be used alone or in mixtures. When organic solvents are used in mixtures, the mixing ratio can be controlled according to the desired battery performance.

[0104] Alternatively, in the case of carbonate solvents, a mixture of cyclic carbonates and linear (chain) carbonates can be used. In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte can exhibit excellent performance.

[0105] In addition to carbonate solvents, non-aqueous organic solvents may also include aromatic organic solvents. In this case, carbonate solvents and aromatic organic solvents can be mixed in a volume ratio of about 1:1 to about 30:1.

[0106] As an aromatic solvent, aromatic compounds represented by chemical formula I can be used.

[0107] [Chemical Formula I]

[0108]

[0109] In chemical formula I, R 4 To R 9 The same or different, and selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl and combinations thereof.

[0110] Specific examples of aromatic solvents may be selected from 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, and fluorotoluene. 2,3-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.

[0111] Electrolytes may also include vinylene carbonate or compounds of the ethylene carbonate class of formula II to improve battery cycle life.

[0112] [Chemical Formula II]

[0113]

[0114] In chemical formula II, R 10 and R 11Same or different, and selected from hydrogen, halogen, cyano, nitro and fluorinated C1 to C5 alkyl groups, provided that R 10 and R 11 At least one of them is selected from halogen, cyano, nitro and fluorinated C1 to C5 alkyl groups, but R 10 and R 11 Neither of them is hydrogen.

[0115] Examples of ethylene carbonate compounds may be difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of additives used to improve cycle life may be used within appropriate limits.

[0116] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in the battery, enabling basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes.

[0117] Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide):LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers, for example, integers in the range of 1 to 20), lithium difluoro(bis(oxalate)phosphate), LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalate)borate, LiBOB), and at least one supporting salt of lithium difluoro(oxalate)borate (LiDFOB).

[0118] Lithium salts can be used at concentrations ranging from about 0.1 M to about 2.0 M. When lithium salts are used in concentration ranges including those mentioned above, the electrolyte can exhibit excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0119] Separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a transport channel for lithium ions. It can be any commonly used separator in lithium-ion batteries. In other words, separator 113 can have low ion transport resistance and excellent electrolyte impregnation. For example, the separator can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof. The separator can be in the form of nonwoven or woven fabric. For example, in lithium-ion batteries, separators made of polyolefin polymers (such as polyethylene and polypropylene) are mainly used. To ensure heat resistance or mechanical strength, a separator coated with ceramic components or polymer materials can be used. Optionally, the separator can have a single-layer or multi-layer structure.

[0120] Based on the presence of a separator and the type of electrolyte used therein, rechargeable lithium batteries can be classified as lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries. Rechargeable lithium batteries can have various shapes and sizes, including cylindrical, prismatic, coin-shaped, or pouch-shaped batteries, and can be thin-film batteries or quite large in size. The structures and manufacturing methods of the lithium-ion batteries included in this disclosure are well known in the art.

[0121] Due to its high capacity, excellent storage stability at high temperatures, cycle life characteristics, and high rate performance, the rechargeable lithium battery according to the embodiment can be used in IT mobile devices and the like.

[0122] Examples and comparative examples of this disclosure are described below. However, it will be understood that these examples are for illustrative purposes and should not be construed as limiting this disclosure.

[0123] Example 1

[0124] Manufacture of negative electrode

[0125] First region

[0126] The sample consisted of 93 wt% particles with a spherical shape, an average particle size (D50) of 16.0 μm, a tap density of 1.27 g / cc, and a BET specific surface area of ​​1.8 m². 2 The negative electrode active material was prepared by mixing 96.38 wt% of graphite-based first negative electrode active material with 7 wt% of silicon-based active material. The silicon-based active material is a silicon-carbon composite in the form of a core comprising artificial graphite and silicon particles and soft carbon coated on the surface of the core, and has an average particle size (D50) of 10.2 μm and a spherical shape. The first region composition was prepared by mixing 96.38 wt% of the prepared negative electrode active material, 2.72 wt% of styrene-butadiene rubber, and 0.9 wt% of carboxymethyl cellulose in distilled water.

[0127] Second region

[0128] The sample consisted of 93 wt% of irregularly shaped particles with an average particle size (D50) of 14.5 μm, a tap density of 1.22 g / cc, and a BET specific surface area of ​​1.3 m². 2 The negative electrode active material was prepared by mixing 98.42 wt% of graphite-based second negative electrode active material with 7 wt% of silicon-based active material. The silicon-based active material was the same as that used in the first region. The second region composition was prepared by mixing 98.42 wt% of the prepared negative electrode active material, 0.68 wt% of styrene-butadiene rubber, and 0.9 wt% of carboxymethyl cellulose in distilled water.

[0129] The first region composition and the second region composition are simultaneously coated onto the current collector using a dual-groove mold coater, such that the first region and the second region are sequentially located on the current collector, and then dried and compressed.

[0130] Figure 2 This is a scanning electron microscope image of the first negative electrode active material. Figure 3 This is a scanning electron microscope image of the second negative electrode active material. (Comparison) Figure 2 and Figure 3 The first and second negative electrode active materials have different forms. Figure 4 This is a scanning electron microscope image of a cross-section of the negative electrode plate, showing the formation of negative electrode active material layers on both surfaces of the current collector. The negative electrode active material layer on one surface has a thickness of approximately 100 μm, with a first region having a thickness of approximately 50 μm and a second region having a thickness of approximately 50 μm.

[0131] Manufacture of battery cell

[0132] A coin half-cell was manufactured by placing a separator with a polyethylene-polypropylene multilayer structure between a prepared negative electrode and a lithium metal counter electrode, and then injecting an electrolyte solution containing 1.0 M LiPF6 lithium salt into a solvent prepared by mixing ethylene carbonate and diethyl carbonate in a 50:50 volume ratio.

[0133] Comparative Example 1

[0134] The negative electrode and battery were manufactured in the same manner as in Example 1, except that the second region composition was prepared by mixing 98.42 wt% of the negative electrode active material of the first region, 0.68 wt% of styrene-butadiene rubber, and 0.9 wt% of carboxymethyl cellulose. Thus, a negative electrode with the same morphology and properties as the first and second regions but including different proportions of binder was manufactured.

[0135] Comparison Example 2

[0136] The negative electrode and battery are manufactured in the same manner as in Example 1, except that the negative electrode active material in the first region is prepared by mixing 86 wt% of the first negative electrode active material and 14 wt% of the silicon-based active material, and the negative electrode active material in the second region uses 100 wt% of the first negative electrode active material. According to Comparative Example 2, the negative electrode active material layer has a structure in which the silicon-based active material is present in the lower part (first region), and has substantially the same morphology in the upper and lower parts.

[0137] Evaluation Example 1: Evaluation of porosity of negative electrode

[0138] The porosity of the negative electrode active material layer of Example 1 and Comparative Examples 1 and 2 was measured using nano-computed tomography (nano-CT), and the results show... Figure 5 Measurements were performed using a device manufactured by Carl Zeiss XRadia 510 Versa at 80 kV, 7 W, obj: 20X, binning: 1, and exposure: 20 s. The cross-section of the negative electrode is shown. Figure 4 In this study, the upper surface with the white current collector in the middle is arbitrarily referred to as surface A, and the lower surface is referred to as surface B. Its analytical range (thickness) is approximately 75 μm.

[0139] As a result of the measurements, in surface A of Comparative Example 1, the first region exhibited a porosity of 16.6%, while the second region had a porosity of 17.4%. Therefore, the ratio of the porosity of the second region to that of the first region was 104%. In surface B of Comparative Example 1, the first region exhibited a porosity of 17.2%, while the second region exhibited a porosity of 17.2%. Therefore, the ratio of the porosity of the second region to that of the first region was 100%. This confirms that the porosity of the first region and the porosity of the second region are at the same level.

[0140] Additionally, refer to Figure 5 In comparing surfaces A and B of Example 2, the second region exhibits a higher porosity than the first region. Conversely, in surface A of Example 1, the porosity of the second region is 18.4% (higher than the 14.8% porosity of the first region), where the ratio of the porosity of the second region to that of the first region is approximately 124%. Similarly, in surface B of Example 1, the porosity of the second region is 18.3% (higher than the 14.8% porosity of the first region), where the ratio of the porosity of the second region to that of the first region is approximately 124%.

[0141] Evaluation Example 2: Evaluation of battery cell

[0142] The batteries of Example 1, along with Comparative Examples 1 and 2, were charged at a constant current of 0.33C to the upper limit voltage of 4.25V and then disconnected at a constant voltage mode at a rate of 0.05C at 25°C. Subsequently, the batteries were discharged to 2.8V at 0.33C, 0.5C, 0.7C, 1.0C, 1.5C, 2.0C, and 2.5C, and the discharge rate at each rate was evaluated. The results are shown in […]. Figure 6 As shown in the image. (Refer to...) Figure 6 Example 1 shows improved capacity retention at high-rate discharge at 1.5C, 2.0C and 2.5C.

[0143] Additionally, the lithium deposition of the batteries in Example 1 and Comparative Example 1 during fast charging was evaluated by charging the batteries to the upper limit voltage of 4.25V at 0.5C, 0.7C, 1.0C, 1.3C, 1.5C, and 1.7C, respectively. The results for Comparative Example 1 are... Figure 7 As shown in [the diagram], and the results of Example 1 are in [the diagram]. Figure 8 As shown in [the image]. Figure 7 In the comparison example 1, lithium deposition was 1.03% during fast charging at 1.7C. Conversely, in... Figure 8 Even during fast charging at 1.7C, Example 1 exhibited a lithium deposition of 0.51% (less than 1%). Lower lithium deposition results in better cycle life characteristics at high rates, and excellent cycle life characteristics are achieved during fast charging and discharging when lithium deposition is kept below 1% (as in Example 1).

[0144] Example 2

[0145] The negative electrode and battery of Example 1 were manufactured in the same manner as in Example 1, except that the negative electrode active material in the first region was prepared by using 86 wt% of the first negative electrode active material and 14 wt% of the silicon-based active material, and 100 wt% of the second negative electrode active material was used in the second region. Figure 9 This is a scanning electron microscope showing a cross-section of the negative electrode according to Example 2. (Refer to...) Figure 9 In the negative electrode of Example 2, the silicon-based active material exists only in the first region, and the first and second regions exhibit different morphologies.

[0146] Example 3

[0147] The negative electrode and battery were manufactured in the same manner as in Example 1, except that the negative electrode active material in the first region was prepared by mixing 86 wt% of a first negative electrode active material and 14 wt% of a silicon-based active material, and the negative electrode active material in the second region used 100 wt% of a graphite-based second negative electrode active material, which had an irregular shape, an average particle size (D50) of about 11 μm, a tap density of about 1.00 g / cc, and a particle size of about 1.70 μm. 2 / g BET specific surface area. Figure 10 This is a scanning electron microscope image of the cross-section of the negative electrode according to Example 3. (Refer to...) Figure 10 In the negative electrode of Example 3, the silicon-based active material exists only in the first region, and the first region and the second region have different morphologies.

[0148] Comparative Example 3

[0149] The negative electrode and battery were manufactured in the same manner as in Example 1, except that the negative electrode active material of the first region was prepared by mixing 43 wt% of the first negative electrode active material of Example 1, 43 wt% of the second negative electrode active material of Example 1, and 14 wt% of the silicon-based active material of Example 1. The negative electrode active material of the second region was prepared by mixing 50 wt% of the first negative electrode active material of Example 1 and 50 wt% of the second negative electrode active material of Example 1. Figure 11 This is a scanning electron microscope image of the cross-section of the negative electrode in Comparative Example 3. (Refer to...) Figure 11 In the negative electrode active material layer of Comparative Example 3, the silicon-based active material exists only in the lower part, and the upper and lower parts have essentially the same morphology.

[0150] Evaluation Example 3: Evaluation of porosity of negative electrode

[0151] The porosity of the negative electrode active material layer in Examples 2 and 3, and in Comparative Example 3, was measured by scanning electron microscopy (SEM). The results are shown in Table 1. Measurements were performed using a scanning electron microscope manufactured by Magellan (FEI), and analyses were conducted at 3 keV, 0.8 nA BSE and 5 keV, 3.2 nA EDS. The cross-section of the negative electrode is shown in the table. Figure 9 In the above, the upper surface with the white current collector in the middle is called surface A, and the lower surface is called surface B.

[0152] (Table 1)

[0153]

[0154] Referring to Table 1, Comparative Example 3 shows almost no difference in porosity between the first region (lower part) and the second region (upper part). In contrast, Examples 2 and 3 show higher porosity in the second region than in the first region, and the ratio of porosity in the second region to porosity in the first region is 135%, 142%, 143%, 173%, etc.

[0155] Although this disclosure has been described in conjunction with exemplary embodiments now considered practical, it should be understood that the invention is not limited to the disclosed embodiments. Rather, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0156] <Description of reference numerals>

[0157] 100: Rechargeable lithium battery; 112: Negative electrode

[0158] 113: Diaphragm 114: Positive electrode

[0159] 120: Battery casing; 140: Sealing component

Claims

1. A negative electrode for a rechargeable lithium battery, the negative electrode comprising a current collector and a negative electrode active material layer disposed on the current collector, in, The negative electrode active material layer includes a first region in contact with the current collector and comprising a first negative electrode active material, and a second region disposed on the first region and comprising a second negative electrode active material. Each of the first and second negative electrode active materials has an average particle size of 9 μm to 22 μm. The first negative electrode active material and the second negative electrode active material have different morphologies. The porosity of the second region is higher than that of the first region. The ratio of the porosity of the second region to that of the first region is in the range of 110% to 190%. The second region is in contact with the first region. The first negative electrode active material and the second negative electrode active material are carbon-based active materials, and the first region and / or the second region also include silicon-based active materials dispersed in the respective carbon-based active materials, and the content of the silicon-based active materials is 1 wt% to 15 wt% based on the total weight of the first region and / or the second region, respectively.

2. The negative electrode according to claim 1, wherein, The first negative electrode active material is spherical, and the second negative electrode active material is irregularly shaped.

3. The negative electrode according to claim 1, wherein, The tap density of the first negative electrode active material is in the range of 1.2 g / cc to 1.5 g / cc, and the tap density of the second negative electrode active material is in the range of 0.8 g / cc to 1.4 g / cc.

4. The negative electrode according to claim 1, wherein, The specific surface area of ​​the first negative electrode active material is 1.4 m². 2 / g to 2.0m 2 The specific surface area of ​​the second negative electrode active material is within the range of / g, and the specific surface area is within 1.0m². 2 / g to 1.8m 2 Within the range of / g.

5. The negative electrode according to claim 1, wherein, The average particle size of the silicon-based active material is in the range of 5 μm to 15 μm.

6. The negative electrode according to claim 1, wherein, The thickness of the first region and the thickness of the second region are each in the range of 30 μm to 100 μm.

7. The negative electrode according to claim 1, wherein, The first region and the second region also include an adhesive, and The weight ratio of the adhesive in the first region to the adhesive in the second region is in the range of 60:40 to 95:

5.

8. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode, positive electrode, and electrolyte for a rechargeable lithium battery according to any one of claims 1 to 7.

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