Negative electrode and lithium secondary battery

Abstract

The present invention relates to a negative electrode for lithium secondary batteries and a lithium secondary battery, the negative electrode comprising: a current collector; a first layer provided on the current collector and including a carbon-based active material; a second layer provided on the first layer and including a silicon-based active material; and a third layer provided on the second layer and including aluminum or an aluminum-containing compound, wherein the thickness of the third layer is greater than 0 but not exceeding 1 / 20 of the combined thickness of the first and second layers.

Description

Cathode and lithium secondary battery

[0001] This specification claims the benefit of the filing dates of Korean Patent Application No. 10-2023-0118377, filed with the Korean Intellectual Property Office on September 6, 2023, and Korean Patent Application No. 10-2024-0120050, filed with the Korean Intellectual Property Office on September 4, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a negative electrode and a lithium secondary battery, and a battery module and battery pack including the same.

[0003] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting attention as power sources for portable devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, etc. In addition, an active material layer including a positive electrode active material and a negative electrode active material may be formed on a current collector on the positive electrode and the negative electrode, respectively. In general, a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 is used as a positive electrode active material for the positive electrode, and a carbon-based active material or a silicon-based active material that does not contain lithium is used as an negative electrode active material for the negative electrode.

[0005] Among negative active materials, silicon-based materials have higher capacities than carbon-based materials, making them attractive as high-capacity secondary battery materials. However, silicon-based materials suffer from poor cycle life and swelling characteristics due to side reactions with the electrolyte. Therefore, the development of technologies that utilize silicon-based materials while minimizing these drawbacks is necessary.

[0006] The present invention relates to a negative electrode for a lithium secondary battery that can provide a high-capacity battery by using a silicon-based active material as a negative electrode active material while improving the disadvantages of the aforementioned silicon-based active material, and to a lithium secondary battery including the same.

[0007] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, comprising: a current collector; a first layer including a carbon-based active material provided on the current collector; a second layer provided on the first layer and including a silicon-based active material; and a third layer provided on the second layer and including aluminum or an aluminum-containing compound, wherein the thickness of the third layer is greater than 0 and less than or equal to 1 / 20 of the sum of the thicknesses of the first and second layers.

[0008] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode for a lithium secondary battery according to the above-described embodiment; a separator and a positive electrode, wherein a third layer of the negative electrode is provided to face the separator.

[0009] One embodiment of the present invention provides a battery module including a lithium secondary battery according to the above-described embodiment.

[0010] One embodiment of the present invention provides a battery pack including a lithium secondary battery according to the above-described embodiment.

[0011] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment.

[0012] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery includes a silicon-based active material, and includes a silicon-based active material in an upper layer of a two-layer active material structure, and a layer including aluminum or an aluminum-containing compound is disposed on a surface facing a separator, thereby significantly improving cycle characteristics, lifespan, and swelling characteristics. Specifically, an inorganic layer containing relatively hard aluminum can suppress changes in volume expansion of an active material layer including a silicon-based active material with high swelling, thereby improving cycle characteristics, lifespan, and swelling.

[0013] Hereinafter, the present specification will be described in more detail.

[0014] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0015] In this specification, when it is said that a member is located “on” another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0016] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0017] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0018] In this specification, the description referred to only as “negative electrode active material layer” without the expressions first and second can be applied to both the first layer and the second layer.

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0020]

[0021] <Cathode>

[0022] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery comprises: a current collector; a first layer comprising a carbon-based active material provided on the current collector; and a second layer provided on the first layer and comprising a silicon-based active material. In addition, the negative electrode for a lithium secondary battery comprises a third layer provided on the second layer and comprising aluminum or an aluminum-containing compound, and the thickness of the third layer is characterized in that it is greater than 0 and less than or equal to 1 / 20 of the sum of the thicknesses of the first and second layers.

[0023] According to the above embodiment, there is an advantage in that the detachment phenomenon of the current collector and the active material due to the silicon-based active material having a large volume change can be suppressed due to the laminated structure of the first layer and the second layer. By additionally laminating the third layer on the surface of the laminated structure including the active material, the relatively hard aluminum-containing inorganic layer suppresses the volume expansion change of the active material layer including the silicon-based active material having a large volume change, thereby improving the battery life and swelling characteristics.

[0024] According to one embodiment, the first layer includes a carbon-based active material as an active material and does not include a silicon-based active material. According to one example, the carbon-based active material may be graphite, and the graphite may be natural graphite, graphite graphite, or a mixture thereof. The content of the carbon-based active material in the first layer may be 80 parts by weight to 100 parts by weight, for example, 90 parts by weight to 100 parts by weight, or 95 parts by weight to 100 parts by weight, based on 100 parts by weight of the active material in the first layer.

[0025] According to one embodiment, the silicon-based active material of the second layer includes at least one of silicon (Si), silicon oxide, metal-doped silicon oxide, silicon carbon composite, and silicon metal alloy. The content of the silicon-based active material of the second layer may be 0.1 parts by weight to 40 parts by weight, for example, 1 part by weight to 20 parts by weight or 5 parts by weight to 12 parts by weight, based on 100 parts by weight of the active material in the second layer.

[0026] When the content of the silicon-based active material of the second layer satisfies the above range based on 100 parts by weight of the active material of the second layer, the capacity of the negative electrode can be increased, and the electrode can be manufactured thinner, thereby improving the lifespan and swelling characteristics of the battery. Specifically, when the content of the silicon-based active material of the second layer is 0.1 parts by weight or more, it is advantageous for increasing the capacity of the negative electrode, and the negative electrode can be formed relatively thin to implement excellent capacity, thereby improving the lifespan and swelling characteristics. In addition, when the silicon-based content of the second layer is 40 parts by weight or less, the Si content is not too high and the swelling characteristics of Si are improved within an appropriate range, thereby improving the lifespan and swelling characteristics.

[0027] If necessary, the second layer may further include a carbon-based active material. The carbon-based active material in the second layer may be natural graphite, graphite, or a mixture thereof. The content of the carbon-based active material in the second layer may be 60 to 99.9 parts by weight based on 100 parts by weight of the active material in the second layer.

[0028] The above silicon-based active material is SiO x It may be an active material containing (0≤x<2), which is SiO x (0 <x<2) 및 기공을 포함하는 실리콘계 복합 입자일 수 있다.

[0029] The above SiO x The active material containing (0≤x<2) is SiO x(0 <x<2) 및 기공을 포함하는 실리콘 산화물 입자일 수 있다.

[0030] The above SiO x (0 <x<2)는 상기 실리콘 산화물 입자 내에서 매트릭스(matrix)에 해당한다. 상기 SiO x (0 <x<2)는 Si 및 SiO2가 포함된 형태일 수 있으며, 상기 Si는 상(phase)을 이루고 있을 수도 있다. 즉, 상기 x는 상기 SiO x (0 <x<2) 내에 포함된 Si에 대한 O의 개수비에 해당한다. 상기 실리콘 산화물 입자가 상기 SiO x (0 <x<2)를 포함하는 경우, 이차 전지의 방전 용량이 개선될 수 있다.

[0031] The silicon oxide particles may further include at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon oxide particles.

[0032] The above Mg compound and / or Li compound is SiO x (0 <x<2)의 내부 및 / 또는 표면에 존재할 수 있다. 상기 Mg 화합물 및 / 또는 Li 화합물에 의해 전지의 초기 효율이 개선될 수 있다.

[0033] The above Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0034] In one embodiment of the present specification, the Mg element may be included in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 15 wt%, based on 100 wt% of the total silicon oxide particles. Specifically, the Mg element may be included in an amount of 0.5 wt% to 10 wt% or 0.8 wt% to 10 wt%. When the above range is satisfied, the Mg compound can be included in an appropriate amount in the silicon oxide particles, so that volume changes of the silicon oxide particles during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0035] The Li compound may include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0036] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate may include Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)로 표시되며, 결정질 리튬 실리케이트와 비정질 리튬 실리케이트로 구분될 수 있다. 상기 결정질 리튬 실리케이트는 상기 실리콘 산화물 입자 내에서 Li2SiO3, Li4SiO4및 Li2Si2O5로 이루어진 군에서 선택된 적어도 1종의 리튬 실리케이트의 형태로 존재할 수 있으며, 비정질 리튬 실리케이트는 Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)의 형태일 수 있고, 상기 형태에 한정되지는 않는다.

[0037] In one embodiment of the present specification, the Li element may be included in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 15 wt%, based on 100 wt% of the total silicon oxide particles. Specifically, the Li element may be included in an amount of 0.5 wt% to 10 wt%, and more specifically, may be included in an amount of 0.5 wt% to 10 wt%. When the above range is satisfied, the Li compound may be included in an appropriate amount in the silicon oxide particles, so that volume change of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0038] The content of the above Mg element or Li element can be confirmed through ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative electrode active material is precisely aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Thereafter, an inductively coupled plasma electroluminescence spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of the standard solution prepared using a standard solution (5 mg / kg) at the wavelength unique to the Mg element or Li element, thereby creating a reference calibration curve. Thereafter, the pretreated sample solution and blank sample are introduced into the device, and the respective intensities are measured to calculate the actual intensity, and the concentration of each component is calculated against the created calibration curve, and then the content of the Mg element or Li element of the manufactured silicon oxide particles can be analyzed by converting so that the sum of the entire values ​​becomes the theoretical value.

[0039] In one embodiment of the present invention, the silicon oxide particles may include additional metal atoms. The metal atoms may be present in the silicon oxide particles in the form of at least one of a metal atom, a metal silicate, a metal silicide, and a metal oxide. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Accordingly, the initial efficiency of the negative electrode active material may be improved.

[0040] In one embodiment of the present invention, the silicon oxide particle has a carbon layer on at least a portion of its surface. In this case, the carbon layer may be partially coated on at least a portion of the surface, i.e., the particle surface, or may be coated on the entire particle surface. The carbon layer provides conductivity to the negative electrode active material, and the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery can be improved.

[0041] In one embodiment of the present invention, the carbon layer includes amorphous carbon. In addition, the carbon layer may additionally include crystalline carbon.

[0042] The above crystalline carbon can further improve the conductivity of the negative electrode active material. The above crystalline carbon can include at least one selected from the group consisting of fluorene, carbon nanotubes, and graphene.

[0043] The amorphous carbon can appropriately maintain the strength of the carbon layer, thereby suppressing expansion of the silicon-based particles. The amorphous carbon can be a carbon-based material formed using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source for chemical vapor deposition.

[0044] The above-mentioned other organic carbonates may be carbonates of organic carbonates selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or kedohexose and combinations thereof.

[0045] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0046] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0047] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on 100 parts by weight of the total silicon-based particles. More specifically, it may be included in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0048] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, volume change of the negative electrode active material is easily suppressed, and side reactions between the electrolyte and the negative electrode active material are suppressed, thereby improving the initial efficiency and / or lifespan of the battery.

[0049] Specifically, the carbon layer can be formed by a chemical vapor deposition (CVD) method using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0050] In the present invention, the crystallinity of the carbon layer can be confirmed by calculating the D / G band ratio according to Raman spectroscopy. Specifically, the measurement can be performed using a Renishaw 2000 Raman microscope system and a 532 nm laser excitation, and a 100x optical lens with a low laser power density and an exposure time of 30 seconds to avoid laser thermal effects. In order to reduce positional deviation, a total of 25 points are measured for a 5 μm x 5 μm area, and the calculation can be performed by calculating the average values ​​of the D band and G band after fitting using a Lorentzian function.

[0051] The above silicon-based active material may be a silicon carbon composite, which may be a Si / C-based active material.

[0052] In this specification, the silicon carbon composite is a composite of Si and C, and is distinguished from silicon carbide, denoted as SiC.

[0053] The above silicon-carbon composite may be a composite of silicon and graphite, and may form a structure in which a core composed of silicon and graphite is surrounded by graphene or amorphous carbon. The silicon in the silicon-carbon composite may be nano silicon.

[0054] According to one embodiment, the silicon carbon composite includes porous carbon particles and silicon located on the surface or internal pores of the porous carbon particles.

[0055] According to one embodiment, the silicon carbon composite has a pore volume of 0.005 cm by the BET method. 3 / g to 0.03 cm 3 / g, and the pore size by the BET method may be 10 to 20 nm. The silicon carbon composite has a pore volume of 0.005 to 0.03 cm as measured by the mercury penetration method. 3 / g could be.

[0056] According to one embodiment, the silicon carbon composite can be manufactured by a method including a step of forming silicon on the surface and internal pores of porous carbon particles.

[0057] The porous carbon particles can be manufactured using methods known in the art, and for example, can be obtained by carbonizing organic materials, such as petroleum-based materials, polymers, etc., or by carbonizing naturally occurring materials, such as palm tree shells, after chemically treating them. As another example, the porous carbon particles can be obtained by a method including a step of etching carbon particles contained in internal pores to expand the internal pores of the carbon particles.

[0058] The step of expanding the internal pores of the above carbon particles can be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, or an air atmosphere. Specifically, the flow rate of the oxygen (O2) or the air containing the oxygen can be controlled to 0.1 L / min to 10 L / min.

[0059] The step of expanding the internal pores of the above carbon particles can be performed at a temperature range of 400°C to 1200°C for 30 minutes to 4 hours.

[0060] Depending on the conditions for expanding the internal pores of the above carbon particles, the pore characteristics of the obtained porous carbon particles may vary.

[0061] The step of forming the above silicon can be performed using a chemical vapor deposition method. In this case, silicon nanoparticles are deposited on the surface and / or in the internal pores of the carbon particles with expanded internal pores, thereby forming silicon in the form of a film, an island, or a mixture of these.

[0062] The above silicon nanoparticles may be crystalline, quasi-crystalline, amorphous, or a combination thereof.

[0063] The above silicon-based active material may be a silicon metal alloy, and for example, the silicon metal alloy (Si-alloy) may be an alloy of Si with one or more metals selected from the group consisting of Zn, Al, Mn, Ti, Fe, and Sn, and may include, but is not limited to, a solid solution, an intermetallic compound, a eutectic alloy, etc. with these.

[0064] In this specification, the average particle diameter (D50) can be defined as the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The average particle diameter (D50) can be measured using, for example, a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0065] The average particle diameter (D50) of the above silicon-based active material may be 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be ensured, the problem of increased volume expansion / contraction due to excessively large particle diameters can be prevented, and the problem of decreased initial efficiency due to excessively small particle diameters can be prevented.

[0066] The first layer and the second layer each additionally contain a binder and a conductive material, and may further contain a thickener and / or a conductive material as needed.

[0067] The first layer and the second layer may be formed by applying a negative electrode slurry containing the above-described active material, binder, thickener, and / or conductive material to at least one surface of a current collector, drying, and rolling. The first layer and the second layer may be sequentially formed on the current collector. The thicknesses of the first layer and the second layer may be the same, and the ratio of the thickness of the second layer to the first layer may be 0.7 to 1.3.

[0068] The above negative electrode slurry may further include an additional negative electrode active material.

[0069] As the above additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 < β < 2), SnO2, vanadium oxide, lithium titanium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0070] According to one embodiment of the present invention, the pH of the negative electrode slurry at 25°C may be 7 to 11. When the pH of the negative electrode slurry satisfies the above range, there is an effect of stabilizing the rheological properties of the slurry. On the other hand, when the pH of the negative electrode slurry is less than 7 or the pH of the negative electrode slurry exceeds 11, decomposition of carboxymethyl cellulose (CMC) used as a thickener occurs, resulting in a decrease in the viscosity of the slurry, and there is a problem of a decrease in the dispersion of the active material contained in the slurry.

[0071] The negative current collector may be any conductive material that does not cause chemical changes in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that readily absorbs carbon, such as copper or nickel, may be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0072] The above binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and materials in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0073] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0074] The above thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the present technical field may be appropriately employed.

[0075] In one embodiment of the present invention, the total negative electrode active material included in the negative electrode slurry may be included in an amount of 60 parts by weight to 99 parts by weight, specifically 70 parts by weight to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0076] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0077] In one embodiment of the present invention, the conductive material may be included in an amount of 0.0.1 to 25 parts by weight, specifically 0.05 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0078] In one embodiment of the present invention, the thickener may be included in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, and more specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0079] The cathode slurry according to one embodiment of the present invention may further include a solvent for forming the cathode slurry. Specifically, the solvent for forming the cathode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of the components.

[0080] In one embodiment of the present invention, the solid content weight of the cathode slurry may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the total cathode slurry.

[0081] In the present invention, the third layer includes aluminum or an aluminum-containing compound, and the thickness of the third layer is greater than 0 and less than or equal to 1 / 20 of the sum of the thicknesses of the first and second layers. The thickness of the third layer refers to the thickness of the third layer at the portion where the third layer exists. In other words, the third layer may completely cover one side of the second layer, but may only cover a portion of one side of the second layer, in which case, the thickness of the third layer refers to the thickness of the third layer at the area where the third layer covers the second layer. The thickness and thickness ratio of each layer can be obtained by a method of measuring the thickness with a SEM of a cross-section of an electrode. The measurement of the thickness can be performed at any one of the following points of time: before electrolyte impregnation, after impregnation, or after the battery cycle. When the ratio of the thickness calculated from the thickness measured at any one point of time is within the scope of the present invention, the effects of the present invention can be achieved. In the case of the above material, the third layer containing relatively hard aluminum has the advantage of improving cycle characteristics, lifespan, and swelling by suppressing changes in volume expansion of the active material layer containing a silicon-based active material with high swelling, and when the above thickness range is satisfied, there is the advantage of suppressing volume expansion without reducing the conductivity of the negative electrode.

[0082] According to one embodiment, the third layer is provided to cover only a portion of the second layer or to cover the entire second layer. When the third layer covers only a portion of the second layer, it may cover at least 30%, at least 50%, at least 70%, or at least 90% of the second layer.

[0083] According to one embodiment, the third layer may further include a binder in addition to aluminum or an aluminum-containing compound. In this case, the binder may be included in an amount of 1 to 20 parts by weight, for example, 5 to 15 parts by weight, based on 100 parts by weight of the third layer.

[0084] According to one embodiment, the third layer can be manufactured by the following method. First, a dispersion is manufactured by dispersing at least one of aluminum and an aluminum-containing compound by mixing a solvent and a polymer binder. Then, the dispersion is manufactured by applying and coating the second layer among the laminated structures of the first and second layers described above. Here, the laminated structures of the first and second layers may be in a rolled state. If necessary, a drying process may be additionally performed. According to one embodiment of the present invention, the dispersion of aluminum or an aluminum-containing compound may further include a solvent for forming the dispersion. Specifically, the solvent for forming the dispersion may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, distilled water, in terms of facilitating dispersion of the components.

[0085] The polymer binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and materials in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0086] According to one embodiment, the aluminum-containing compound of the third layer includes at least one of aluminum oxide and Al(OH)3.

[0087] According to one embodiment, based on 100 parts by weight of the third layer composition, the content of the aluminum or aluminum-containing compound is 90 parts by weight to 100 parts by weight, for example, 90 parts by weight to 95 parts by weight.

[0088] When the above range is satisfied, the lifespan and swelling characteristics of the battery can be improved. Specifically, when the content of aluminum or an aluminum compound in the third layer is within the above range, the content of the polymer binder in the third layer composition does not increase to more than 10 parts by weight, thereby preventing the polymer binder from acting as a resistive layer and reducing electrical conductivity, thereby improving the lifespan characteristics.

[0089]

[0090] Secondary battery

[0091] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode according to the aforementioned embodiments; a separator; and a positive electrode, wherein the inorganic layer of the negative electrode is provided so as to face the separator. In this case, a third layer of the negative electrode is provided so as to face the separator. When the third layer comes into contact with the separator, the bonding strength with the separator is increased, which is advantageous for battery manufacturing.

[0092] According to one embodiment of the present application, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and including the positive electrode active material.

[0093] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0094] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0095] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0096] In addition, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0097] The positive electrode binder may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the positive electrode active material layer, for example, preferably 0.3 to 35 parts by weight, more preferably 0.5 to 20 parts by weight.

[0098] The conductive material included in the above-described positive electrode active material layer is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical changes within the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0099] Specifically, in one embodiment, the conductive material may include at least one of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the composition for the positive electrode active material layer, for example, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight.

[0100] A secondary battery according to one embodiment of the present invention includes the above-described negative electrode, positive electrode, and a separator interposed between the positive electrode and negative electrode, and may additionally include an electrolyte.

[0101] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0102] According to one embodiment of the present invention, the separation membrane may be an SRS (Safety Reinforced Separator) separation membrane.

[0103] Examples of the above electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0104] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0105] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0106] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte having high electrical conductivity can be produced, so that they can be used even more preferably.

[0107] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - , Cl - , I - , NO3 -, N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0108] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, difluoroethylene carbonate and other haloalkylene carbonate compounds, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0109] According to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0110] According to another embodiment of the present invention, a battery pack including the lithium secondary battery is provided.

[0111] According to another embodiment of the present invention, a battery pack including the battery module is provided.

[0112] The above battery module and battery pack include the lithium secondary battery having high capacity, high rate characteristics and cycle characteristics, and thus can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0113] <Examples and Comparative Examples>

[0114] Example 1

[0115] A composition for forming a first layer was prepared, which included 96.3 parts by weight of graphite, 2.55 parts by weight of SBR (styrene butadiene rubber) as a binder, 1 part by weight of CMC (carboxymethyl cellulose) based on 100 parts by weight of the first layer, and a CNT pre-dispersion liquid containing 0.1 parts by weight of a dispersant and 0.05 parts by weight of single-wall CNT. At this time, the graphite was prepared to a size of D50=17㎛ by an airflow grinding method. The composition for forming the first layer was coated on a copper foil having a thickness of 15㎛ so that the first layer had a thickness of 50㎛ in a dry state.

[0116] A second layer-forming composition was prepared, which included 97.7 parts by weight of graphite (90 parts by weight based on 100 parts by weight of the negative electrode active material) and 10 parts by weight of silicon oxide active material carbon-coated by methane CVD (10 parts by weight based on 100 parts by weight of the negative electrode active material), 1.15 parts by weight of SBR (styrene butadiene rubber) as a binder, 1 part by weight of CMC (carboxymethyl cellulose), and, in addition, 0.1 parts by weight of a dispersant and 0.05 parts by weight of a single-wall CNT. At this time, the carbon-coated silicon oxide active material was prepared by an airflow grinding method to have a D50=6㎛ size, and the graphite was prepared to have a D50=17㎛ size. The second layer-forming composition was coated on the first layer to have a thickness of 100 ㎛ in a dry state.

[0117] The first and second layers were coated on the negative electrode, and the electrode was manufactured by rolling to have a thickness of 60 μm. Next, alumina (Al2O3) as an inorganic material and SBR and CMC as binders were mixed in a ratio of 90:6:4, dissolved in water, and then the inorganic particles were crushed and dispersed using a ball mill method for more than 12 hours to manufacture an aluminum compound dispersion. The dispersion was applied on the second layer of the negative electrode coated with the first and second layers, and the negative electrode was manufactured so that the sum of the thicknesses of the first to third layers in a dry state was 62 μm.

[0118]

[0119] Example 2

[0120] A negative electrode was manufactured in the same manner as in Example 1, except that a Mg-doped carbon-coated silicon oxide active material was used instead of a carbon-coated silicon oxide active material.

[0121]

[0122] Example 3

[0123] A negative electrode was manufactured in the same manner as in Example 1, except that a Li-doped carbon-coated silicon oxide active material was used instead of a carbon-coated silicon oxide active material.

[0124]

[0125] Example 4

[0126] A negative electrode was manufactured in the same manner as in Example 1, except that a silicon carbon composite (Si / C) was used instead of the carbon-coated silicon oxide active material.

[0127]

[0128] Example 5

[0129] A negative electrode was manufactured in the same manner as in Example 1, except that Si-alloy (Si6Cu3Sn1) was used instead of the carbon-coated silicon oxide active material.

[0130]

[0131] Example 6

[0132] A negative electrode was manufactured in the same manner as in Example 1, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 61 μm.

[0133]

[0134] Example 7

[0135] A negative electrode was manufactured in the same manner as in Example 1, except that graphite (50 parts by weight based on 100 parts by weight of the negative electrode active material) and silicon oxide active material coated with carbon by methane CVD (50 parts by weight based on 100 parts by weight of the negative electrode active material) were included based on 100 parts by weight of the negative electrode active material of the second layer.

[0136]

[0137] Example 8

[0138] A negative electrode was manufactured in the same manner as Example 1, except that the inorganic material, alumina (Al2O3), and the binder, SBR and CMC, were used in a ratio of 50:30:20 based on 100 parts by weight of the third layer composition.

[0139]

[0140] Comparative Example 1

[0141] A cathode was manufactured in the same manner as in Example 1, except that the third layer was not applied.

[0142] Comparative Example 2

[0143] A cathode was manufactured in the same manner as in Example 2, except that the third layer was not applied.

[0144]

[0145] Comparative Example 3

[0146] A cathode was manufactured in the same manner as in Example 3, except that the third layer was not applied.

[0147]

[0148] Comparative Example 4

[0149] A cathode was manufactured in the same manner as in Example 4, except that the third layer was not applied.

[0150]

[0151] Comparative Example 5

[0152] A cathode was manufactured in the same manner as in Example 5, except that the third layer was not applied.

[0153]

[0154] Comparative Example 6

[0155] A negative electrode was manufactured in the same manner as in Example 1, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0156]

[0157] Comparative Example 7

[0158] A negative electrode was manufactured in the same manner as in Example 2, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0159]

[0160] Comparative Example 8

[0161] A negative electrode was manufactured in the same manner as in Example 3, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0162]

[0163] Comparative Example 9

[0164] A negative electrode was manufactured in the same manner as in Example 4, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0165]

[0166] Comparative Example 10

[0167] A negative electrode was manufactured in the same manner as in Example 5, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0168]

[0169] Comparative Example 11

[0170] A negative electrode was manufactured in the same manner as in Example 1, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 64.6 μm.

[0171]

[0172] Experimental Example 1

[0173] The above cathode was dried in a vacuum oven at 130°C for 12 hours.

[0174] The manufactured negative electrode and a lithium (Li) metal thin film cut into a circle of 1.7671㎠ were used as the positive electrode. A porous polyethylene separator was interposed between the positive and negative electrodes, and 0.5 parts by weight of vinylene carbonate was dissolved in a mixed solution of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) having a volume ratio of 7:3, and an electrolyte solution containing 1M LiPF6 was injected to manufacture a lithium coin half-cell.

[0175]

[0176] Charge and discharge were performed on the manufactured battery to evaluate the capacity retention rate and electrode expansion rate, which are listed in Table 1 below.

[0177] The 1st and 2nd cycles were charged and discharged at 0.1C, and from the 3rd to the 49th cycles, the charging and discharging was performed at 0.5C. The 50th cycle was terminated in a charged state (with lithium in the negative electrode).

[0178] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0179] Discharge conditions: CC (constant current) condition 1.5 V

[0180] Based on the results of one charge / discharge cycle, the capacity retention rate was derived by the following calculations.

[0181] Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0182] The electrode expansion ratio was derived by the following calculation.

[0183] Electrode expansion ratio (%) = (electrode thickness after 50 cycles / initial electrode thickness) × 100

[0184] Si active material 2 layer / 1 layer thickness ratio 1 layer + 2 layer thickness 3 layer thickness 3 layer / (1 layer + 2 layer) thickness ratio 49th capacity retention rate 50th electrode expansion rate Example 1 Silicon oxide 16021 / 308540 Example 2 Mg-silicon oxide 16021 / 308440 Example 3 Li-silicon oxide 16021 / 308540 Example 4 Si / C 16021 / 309040 Example 5 Si-alloy 16021 / 308145 Example 6 Silicon oxide 16011 / 608440 Example 7 Silicon oxide 16021 / 307941 Example 8 Silicon oxide 16021 / 307941 Comparative example 1 Silicon oxide 160007547 Comparative example 2Mg-silicon oxide 160007347Comparative example 3Li-silicon oxide 160007348Comparative example 4Si / C 160008047Comparative example 5Si-alloy 160006953Comparative example 6Silicon oxide 16051 / 127741Comparative example 7Mg-silicon oxide 16051 / 127741Comparative example 8Li-silicon oxide 16051 / 127841Comparative example 9Si / C 16051 / 128041Comparative example 10Si-alloy 16051 / 127547Comparative example 11Silicon oxide 1604.61 / 137741

[0185] As shown in Table 1 above, it was confirmed that the batteries manufactured in Examples 1 to 6 in which the thickness of the third layer was greater than 0 and less than or equal to 1 / 20 of the sum of the thicknesses of the first and second layers had significantly higher capacity retention rates and significantly reduced electrode expansion rates compared to Comparative Examples 1 to 5 in which the third layer was not formed. In addition, in Comparative Examples 6 to 11 in which the third layer was formed thicker than in the above examples, the electrode expansion rates could be reduced to some extent, but the electrode expansion rates were relatively greater than those in Examples in which the third layer was formed thinner compared to those in which the third layer was formed thicker. In addition, Comparative Examples 6 to 11 showed inferior capacity retention rates because the third layer was thick.

[0186] The battery manufactured in Example 7, in which the silicon-based active material in the second layer was 50 parts by weight based on 100 parts by weight of the active material in the second layer, had a higher capacity retention rate than that in Comparative Example 1, but had a lower capacity retention rate than that in Example 1, in which the silicon-based active material in the second layer was 0.4 to 40 parts by weight based on 100 parts by weight of the active material in the second layer.

[0187] In addition, the battery manufactured in Example 8, in which the content of the aluminum-containing compound was 50 parts by weight based on 100 parts by weight of the third layer composition, had a higher capacity ratio than that of Comparative Example 1, but a lower capacity retention ratio than that of Example 1, in which the content of the aluminum compound was 90 parts by weight based on 100 parts by weight of the third layer composition.

Claims

1. Whole house; A first layer comprising a carbon-based active material provided on the above-mentioned collector, A second layer provided on the first layer and including a silicon-based active material, and A third layer is provided on the second layer and includes aluminum or an aluminum-containing compound, A negative electrode for a lithium secondary battery, wherein the thickness of the third layer is greater than 0 and less than or equal to 1 / 20 of the sum of the thicknesses of the first and second layers.

2. A negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based active material of the first layer is graphite.

3. A negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based active material of the first layer is 80 to 100 parts by weight based on 100 parts by weight of the active material in the first layer.

4. A negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material of the second layer includes at least one of silicon (Si), silicon oxide, metal-doped silicon oxide, silicon carbon composite, and silicon metal alloy.

5. A negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material of the second layer is 0.1 to 40 parts by weight based on 100 parts by weight of the active material in the second layer.

6. A negative electrode for a lithium secondary battery according to claim 1, wherein the aluminum-containing compound of the third layer includes at least one of aluminum oxide and Al(OH)3.

7. A negative electrode for a lithium secondary battery according to claim 1, wherein the content of aluminum or an aluminum compound in the third layer is 90 to 100 parts by weight based on 100 parts by weight of the third layer composition.

8. A negative electrode for a lithium secondary battery according to claim 1, wherein the third layer is provided to cover only a part of or all of the second layer.

9. A negative electrode for a lithium secondary battery according to claim 1, wherein the first layer and the second layer each additionally include a binder and a conductive material.

10. A lithium secondary battery comprising a cathode according to any one of claims 1 to 9; a separator and a cathode, wherein the third layer of the cathode is provided to face the separator.

11. A lithium secondary battery according to claim 10, wherein the separator is a Safety Reinforced Separator (SRS) separator.

12. A battery module including a lithium secondary battery according to claim 11.

13. A battery pack comprising a lithium secondary battery according to claim 11.

14. A battery pack comprising the battery module of claim 12.