Negative electrode active material for secondary battery and secondary battery including same

Abstract

A negative electrode active material for a lithium secondary battery according to an exemplary embodiment comprises: a core particle; a crown ether coating layer, the crown ether coating layer being formed on the core particle, and the crown ether coating layer comprising a crown ether; and a conductive particle formed on or within the crown ether coating layer. Stability can be improved and electrical resistance can be reduced by a crown ether coating containing a crown ether compound, and power characteristics can be improved by conductive particles.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material for a secondary battery and a secondary battery including the negative electrode active material. More specifically, the present invention relates to a negative electrode active material for a secondary battery having a core-shell structure and a secondary battery including the negative electrode active material. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of information communication and display industries, secondary batteries are widely used in portable electronic communication devices such as camcorders, mobile phones, and laptop computers. Secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in charging speed and light weight. Therefore, lithium secondary batteries are actively developed and applied.

[0003] The lithium secondary battery may include, for example, an electrode assembly including a positive electrode, a negative electrode and a separator (separation membrane); and an electrolyte impregnated with the electrode assembly. The lithium secondary battery may also include an outer packaging material containing the electrode assembly and the electrolyte, such as a soft pack outer packaging material.

[0004] For example, the negative electrode may use carbon-based active material particles or silicon-based active material particles as the negative electrode active material. In the case of repeated charge / discharge, side reactions may occur due to contact between the active material particles and the electrolyte, and mechanical damage such as cracks of the particles and chemical damage may occur.

[0005] When the composition and structure of the negative electrode active material are changed in order to improve the stability of the active material particles, the conductivity may be reduced, and thus the power of the secondary battery may be reduced. Therefore, it is necessary to develop a negative electrode active material that can ensure life stability and power / capacity characteristics.

[0006] For example, Korean Patent Publication No. 2017-0099748 discloses an electrode assembly for a lithium secondary battery and a lithium secondary battery including the electrode assembly. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] A technical problem of the present invention is to provide a negative electrode active material for a secondary battery having improved stability and electrical characteristics.

[0009] A technical problem of the present invention is to provide a secondary battery with improved stability and electrical characteristics.

[0010] (II) Technical solution

[0011] A negative active material for a secondary battery according to an exemplary embodiment includes: a core particle; a crown ether coating layer formed on the core particle and including a crown ether compound; and conductive particles formed on the crown ether coating layer.

[0012] In some embodiments, the core particle may include a graphite-based substance, an amorphous carbon-based substance, a silicon-based active substance, or a mixture of two or more thereof.

[0013] In some embodiments, the core particle may include at least one of natural graphite and artificial graphite.

[0014] In some embodiments, the crown ether coating may have a thickness of 1 nm to 100 nm.

[0015] In some embodiments, the crown ether compound may include a nitrogen atom (N) or a sulfur atom (S).

[0016] In some embodiments, the crown ether compound may include 10-crown-3, 11-crown-3, aza-11-crown-3, 12-crown-3, aza-12-crown-3, 12-crown-4, benzo-12-crown-4, tetrathia-12-crown-4, aza-12-crown-4, diaza-12-crown-4, 14-crown-4, tetrathia-14-crown-4, benzo-14-crown-4, dibenzo-14-crown-4, di(decahydronaphthalene) At least one of didecalino-14-crown-4, decalino-14-crown-4, 15-crown-5, aza-15-crown-5, diaza-15-crown-5, benzo-15-crown-5, dibenzo-15-crown-5, cyclohexanedo-15-crown-5, 16-crown-4, 16-crown-5, 18-crown-6, hexathia-18-crown-6, aza-18-crown-6, diaza-18-crown-6, benzo-18-crown-6 and dibenzo-18-crown-6.

[0017] In some embodiments, the content of the crown ether compound may be 0.01 wt % to 5 wt % relative to the total weight of the core particle.

[0018] In some embodiments, the crown ether coating can consist essentially of the crown ether compound.

[0019] In some embodiments, the conductive particles may cover the entire crown ether coating.

[0020] In some embodiments, at least a portion of the conductive particles may be embedded in the interior of the crown ether coating and protrude outside the surface of the crown ether coating.

[0021] In some embodiments, the conductive particles may not be in contact with the core particles.

[0022] In some embodiments, at least a portion of the conductive particles may extend through the crown ether coating.

[0023] In some embodiments, the conductive particles may include at least one of lithium titanate (LTO), Super P, carbon black, acetylene black, Ketjen black, flaky carbon, activated carbon, graphene, carbon nanotubes (CNTs), carbon nanofibers (CNFs), metal fibers, and metal particles.

[0024] In some embodiments, the negative electrode active material for a lithium secondary battery may further include a carbon coating layer, the carbon coating layer being disposed between the core particle and the crown ether coating layer, and the carbon coating layer covering the core particle.

[0025] In one embodiment, the carbon coating may include an amorphous carbon-based substance.

[0026] In one embodiment, the ratio of the thickness of the crown ether coating layer to the thickness of the carbon coating layer may be greater than 0 and 5 or less.

[0027] A lithium secondary battery according to an exemplary embodiment includes: a negative electrode including the negative electrode active material for a secondary battery according to the above embodiment; and a positive electrode disposed opposite to the negative electrode.

[0028] (III) Beneficial effects

[0029] A crown ether coating containing a crown ether compound can be formed on the core particles of the negative electrode active material. Through the crown ether compound, a channel for lithium ions can be formed in the crown ether coating, thereby preventing the increase in resistance caused by the crown ether coating. Therefore, the ionic conductivity of the negative electrode active material can be improved, and the power characteristics and fast charging characteristics of the secondary battery can be improved.

[0030] In addition, the crown ether coating can suppress side reactions and damage such as cracks on the outer surface of the core particles that provide negative electrode activity, thereby improving life stability.

[0031] Conductive particles may be disposed on or within the crown ether coating. The electronic conductivity of the negative electrode active material may be increased by the conductive particles. For example, migration channels for electrons and ions may be formed between adjacent negative electrode active material particles by the conductive particles. Therefore, the power reduction caused by the crown ether coating may be prevented, and the activity of the negative electrode active material may be increased.

[0032] The negative electrode active material may further include a carbon coating layer. Therefore, even in the case of repeated charge and discharge, the life of the core particles can be increased, and the high capacity and high rate characteristics of the negative electrode active material can be maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic cross-sectional view showing a negative electrode active material for a secondary battery according to an exemplary embodiment.

[0034] Figure 2 is a schematic plan view showing a secondary battery according to an exemplary embodiment.

[0035] Figure 3 is a schematic cross-sectional view showing a secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION

[0036] An embodiment of the present invention provides a negative electrode active material for a secondary battery, the negative electrode active material for a secondary battery including a core particle, a crown ether coating layer formed on the core particle, and conductive particles.

[0037] Furthermore, an embodiment of the present invention provides a secondary battery including the negative electrode active material for a secondary battery.

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments exemplarily described.

[0039] <Negative electrode active material for secondary battery>

[0040] Figure 1 : is a schematic cross-sectional view showing a negative electrode active material for a secondary battery (hereinafter, may be simply referred to as a negative electrode active material) according to an exemplary embodiment. For example, Figure 1 1 is a schematic cross-sectional view showing a shape in which negative electrode active materials are gathered on the negative electrode collector 125 .

[0041] Reference Figure 1 The negative electrode active material 50 may include core particles 60 , crown ether coatings 70 and conductive particles 80 .

[0042] The core particle 60 may be provided as a main particle providing substantial negative electrode activity. For example, the core particle 60 may include an amorphous carbon-based active material, a graphite-based active material, or a silicon-based active material, etc. These may be included alone or in combination of two or more.

[0043] In some embodiments, the core particle 60 may include a graphite-based active material such as natural graphite and / or artificial graphite.

[0044] In one embodiment, the core particle 60 may include artificial graphite. Compared with natural graphite, artificial graphite may have relatively high chemical stability and thermal stability. Therefore, by using artificial graphite as the core particle 60, the high-temperature storage characteristics or high-temperature life characteristics of the secondary battery can be improved. In addition, even if the core particle 60 includes artificial graphite, the power and capacity can be sufficiently increased by the conductive particle 80.

[0045] In some embodiments, the core particle 60 may include a silicon-based active material. The silicon-based active material may include silicon (Si), SiO x (0 < x < 2) or SiO containing a lithium compound or a magnesium compound x (0 < x < 2), etc.

[0046] In one embodiment, the SiO containing a lithium compound or a magnesium compound x may be SiO pretreated with lithium or magnesium x . For example, the SiO containing a lithium compound or a magnesium compound x may include lithium silicate or magnesium silicate, etc.

[0047] In some embodiments, the core particle 60 may further include a silicon-carbon-based active material. The silicon-carbon-based active material may include, for example, silicon carbide (SiC) or silicon-carbon particles having a core-shell structure.

[0048] The silicon-carbon particles may be formed, for example, by depositing a silicon layer on the surface of a graphite core. In one embodiment, a silicon layer may be coated on commercial graphite particles by a chemical vapor deposition (CVD) process using a silicon precursor compound such as a silane-based compound to form the silicon-carbon particles.

[0049] In some embodiments, the core particle 60 may further include an amorphous carbon-based active material derived from hard carbon, coke, pitch, etc. In one embodiment, the core particle 60 may include a mixture of two or more of the above-mentioned graphite-based active material, silicon-based active material, or amorphous carbon-based active material.

[0050] According to an exemplary embodiment, the average particle diameter (D 50 ) of the core particle 60 may be 1 μm to 100 μm. D 50 refers to the particle diameter at a volume fraction of 50% in the cumulative particle size distribution. For example, the average particle diameter (D 50 ) of the core particle 60 may be 3 μm to 20 μm.

[0051] In some embodiments, a carbon coating layer may be formed on the surface of the core particle 60. For example, the carbon coating layer may be formed on the surface of the core particle 60 to cover the outer surface of the core particle 60.

[0052] In one embodiment, the carbon coating layer may also be partially formed on the outer surface of the core particle 60 .

[0053] In one embodiment, the carbon coating layer may include an amorphous carbon-based substance. For example, the core particle 60 and the carbon coating layer may have a core-shell structure in which at least a portion of the outer surface of the graphite-based active substance or the silicon-based active substance is coated with the amorphous carbon-based substance.

[0054] The thermal stability and mechanical physical properties of the negative electrode active material 50 can be further improved by forming a carbon coating layer containing an amorphous carbon-based substance on the surface of the core particle 60. In addition, the amorphous carbon-based substance can react before the core particle 60 in a relatively high reaction potential region, thereby suppressing the degradation of the core particle 60 due to repeated charge and discharge.

[0055] Therefore, the negative electrode activity of the core particle 60 can be maintained for a long time, and the negative electrode active material 50 having high power and high capacity can be provided.

[0056] In some embodiments, the thickness of the carbon coating layer may be 1 nm to 1000 nm, for example, 5 nm to 300 nm. Within the above range, heat resistance and stability may be further improved without reducing the power and capacity of the lithium secondary battery.

[0057] The crown ether coating 70 may be formed on the surface of the core particle 60. In some embodiments, the entire outer surface of the core particle 60 may be substantially surrounded by the crown ether coating 70.

[0058] Therefore, it is possible to reduce or prevent side reactions, oxidation, corrosion, cracks, etc. on the surface of the core particle 60. For example, with repeated charge / discharge of the secondary battery, the surface of the core particle 60 may be mechanically and chemically damaged. In addition, when the surface of the core particle 60 contacts the electrolyte, gas may be generated due to side reactions.

[0059] According to an exemplary embodiment, the crown ether coating 70 protects the surface of the core particle 60, thereby suppressing direct exposure to the electrolyte and the damage caused thereby. In addition, the crown ether coating 70 can also act as an elastic body to alleviate the expansion of the core particle 60. Therefore, the generation of cracks in the core particle 60 caused by repeated charge and discharge can be suppressed.

[0060] In one embodiment, the crown ether coating 70 may also be partially formed on the outer surface of the core particle 60. In this case, for example, the crown ether coating 70 may cover more than 50% of the outer surface area of ​​the core particle 60.

[0061] In some embodiments, when a carbon coating layer is formed on the outer surface of the core particle 60 , the crown ether coating layer 70 may be formed on the outer surface of the carbon coating layer.

[0062] The crown ether coating layer 70 may include a crown ether compound. The crown ether compound has high conductivity to lithium ions, and thus can supplement the ion conductivity of the negative electrode active material.

[0063] For example, the crown ether compound can function as a host substance for guest ions (eg, lithium ions). Therefore, the crown ether compound can selectively bind and release lithium ions, thereby improving the mobility of ions within the crown ether coating 70.

[0064] Therefore, an increase in resistance caused by the crown ether coating layer 70 can be prevented, so that the power and capacity of the lithium secondary battery can be improved.

[0065] In one embodiment, the crown ether compound may be present in the crown ether coating layer 70 in a dispersed or mixed form. For example, a polymer matrix including the crown ether compound may be coated on the core particle 60 to form the crown ether coating layer 70.

[0066] In some embodiments, the crown ether compound may contain a macrocyclic ring in its molecular structure, for example, the macrocyclic ring may have a repeating unit of -R1-R2-O- structure. R1 and R2 may each independently be a single bond, an alkylene group having 1 to 6 carbon atoms, a cycloalkylene group having 3 to 12 carbon atoms, a bicycloalkylene group having 4 to 12 carbon atoms, an arylene group having 6 to 12 carbon atoms, a carbonyl group, an ester group or an amide group, etc.

[0067] For example, the crown ether compound can be represented by "n-crown-m". n represents the total number of atoms contained in the macrocycle, and m represents the number of oxygen atoms contained in the macrocycle. n and m can each independently be an integer greater than 2.

[0068] In some embodiments, the crown ether compound may contain a nitrogen atom (N) or a sulfur atom (S). For example, at least one of the oxygen atoms contained in the macrocycle may be substituted with a nitrogen atom or a sulfur atom. For example, at least one of the oxygen atoms of the crown ether compound represented by "n-crown-m" may be substituted with a nitrogen atom or a sulfur atom.

[0069] The macrocycle of the crown ether compound can play the role of a cavity for accommodating guest ions (e.g., lithium ions). For example, in the case of a crown ether compound, due to the multiple heteroatoms contained in the macrocycle, the crown ether compound can have a strong binding force or affinity for cations.

[0070] For example, since the heteroatoms contained in the macrocyclic ring have unshared electron pairs, the crown ether compound can carry a strong negative charge inside the ring. Therefore, electron-deficient metal cations can easily coordinate and bind to the crown ether compound to form a complex. Therefore, the crown ether compound can provide a migration path for lithium ions within the crown ether coating.

[0071] In some embodiments, the crown ether compound may include a macrocycle with an atomic number of 10 to 18. For example, the crown ether compound may include n-crown-m with n being 10 to 18 and m being 1 or more. Within the above range, the crown ether compound can be prevented from becoming too bulky. Therefore, the structural stability of the crown ether coating 70 can be further improved, and the ionic conductivity and electronic conductivity can be further improved.

[0072] In some embodiments, the crown ether compound may contain a carbonyl group, an ester group or an amide group in its molecular structure. For example, at least one of the carbon atoms of the crown ether compound may be substituted or connected by a carbonyl group, an ester group or an amide group.

[0073] In some embodiments, the crown ether compound can include 10-crown-3, 11-crown-3, aza-11-crown-3, 12-crown-3, aza-12-crown-3, 12-crown-4, benzo-12-crown-4, tetrathia-12-crown-4, aza-12-crown-4, diaza-12-crown-4, 14-crown-4, tetrathia-14-crown-4, benzo-14-crown-4, dibenzo-14-crown-4, di(decahydronaphthalene)-1 -14-crown-4, decahydronaphtho-14-crown-4, 15-crown-5, aza-15-crown-5, diaza-15-crown-5, benzo-15-crown-5, dibenzo-15-crown-5, cyclohexanedo-15-crown-5, 16-crown-4, 16-crown-5, 18-crown-6, hexathia-18-crown-6, aza-18-crown-6, diaza-18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6, etc. These can be used alone or in combination of two or more.

[0074] In some embodiments, the content of the crown ether compound may be about 0.05 wt % to 5 wt % relative to the total weight of the core particle 60. When the content of the crown ether compound is less than 0.05 wt %, the content of the crown ether compound may be relatively small relative to the dissolved lithium ions, and the ionic conductivity may be reduced. When the content of the crown ether compound exceeds 5 wt %, the resistance may be relatively increased, and side reactions caused by the crown ether compound may occur.

[0075] In one embodiment, the content of the crown ether compound may be 0.5 wt % to 3 wt %. Within the above range, a sufficient ion conductive path may be ensured without hindering the negative electrode activity of the core particle 60 .

[0076] In some embodiments, the crown ether compounds can be polymerized or cross-linked to form a film. For example, a solution of a monomer, oligomer or polymer in which a crown ether compound is dissolved can be applied to the core particle 60 and then heated to form the crown ether coating 70. Therefore, the polymerization and cross-linking of the above substances can be performed on the surface of the core particle 60. In this case, the crown ether polymer can form the skeleton of the crown ether coating 70.

[0077] In some embodiments, the crown ether compound in the form of a monomer or oligomer may be present in the form of being dispersed in the crown ether coating 70. Therefore, the crown ether compound in the form of a monomer or oligomer may be uniformly distributed inside the crown ether coating 70 and have mobility, thereby further increasing the electron / ion migration path caused by the crown ether compound.

[0078] In some embodiments, the crown ether coating 70 may only contain crown ether compounds. Therefore, the electronic conductivity and ionic conductivity of the crown ether coating 70 can be further improved. For example, when other polymer substances are included in the crown ether coating 70, the internal resistance of the negative electrode may be relatively increased due to the low conductivity of the polymer substance. In addition, due to the volume occupied by the polymer substance, the mass energy density or volume capacity may be relatively reduced.

[0079] In one embodiment, the crown ether coating 70 is substantially composed of a crown ether compound, so electrons and ions can more easily migrate into and out of the crown ether coating 70. Therefore, the internal resistance of the negative electrode active material can be reduced, and the power characteristics and fast charging characteristics of the lithium secondary battery can be improved.

[0080] In some embodiments, the weight average molecular weight (Mw) of the polymer substance (e.g., crown ether polymer) included in the crown ether coating 70 may be less than 500000 g / mol. In one embodiment, the weight average molecular weight of the polymer substance included in the crown ether coating 70 may be 50000 g / mol or more and less than 500000 g / mol, for example, 50000 g / mol to 300000 g / mol. Within the above range, the crown ether coating 70 may further suppress swelling and expansion of the core particles 60, while ensuring flexibility in which the conductive particles 80 may be embedded.

[0081] In some embodiments, the content of the crown ether coating 70 may be about 0.01 wt % to 5 wt % or 0.1 wt % to 3 wt % relative to the total weight of the core particle 60 .

[0082] In some embodiments, the crown ether coating 70 may have a thickness of 1 nm to 100 nm, 10 nm to 100 nm, or 10 nm to 80 nm. Within the above range, the mechanical stability / chemical stability can be further improved without deteriorating the negative electrode activity of the core particle 60 and the charge and discharge capacity of the lithium secondary battery.

[0083] In some embodiments, when a carbon coating layer is formed on the core particle 60 , a ratio of a thickness of the crown ether coating layer 70 to a thickness of the carbon coating layer may be greater than 0 and less than 5 or 0.3 to 3.

[0084] Within the above range, an increase in internal resistance and a decrease in power can be prevented, while swelling, expansion, and collapse of the core particles 60 due to repeated charge / discharge can be further suppressed.

[0085] The conductive particles 80 may increase or supplement the electronic conductivity of the crown ether coating 70 or the negative electrode active material 50 .

[0086] The conductive particles 80 may be formed on the crown ether coating 70 or embedded in the crown ether coating 70. For example, the conductive particles 80 may be attached to the surface of the crown ether coating 70. For example, at least a portion of the conductive particles 80 may be embedded in the interior of the crown ether coating 70.

[0087] In some embodiments, the conductive particles 80 may be distributed discontinuously on the surface of the crown ether coating 70. For example, the conductive particles 80 may exist in a local area of ​​the outer surface of the crown ether coating 70 in the form of separate islands.

[0088] In some embodiments, the conductive particles 80 may be continuously and evenly distributed on the surface of the crown ether coating 70. For example, the conductive particles 80 may exist in the form of a film covering at least a portion of the surface of the crown ether coating 70. In one embodiment, the conductive particles 80 may surround the entire outer surface of the crown ether coating 70 and substantially form a single layer coating.

[0089] In some embodiments, the conductive particles 80 may not be in physical contact with the core particles 60. For example, the conductive particles 80 may be formed only on the crown ether coating 70, or may exist within the crown ether coating 70 without contacting the core particles 60.

[0090] Since the crown ether coating layer 70 includes the crown ether compound, the conductive particles 80 can have high ionic conductivity even if they are not in contact with the core particles 60. In addition, since the core particles 60 are not in physical contact with the conductive particles 80, cracks and physical damage to the core particles 60 that may occur when the conductive particles 80 are attached can be prevented.

[0091] In one embodiment, when the crown ether coating 70 is partially formed on the outer surface of the core particle 60, at least a portion of the conductive particles 80 may be attached to the region of the outer surface of the core particle 60 where the crown ether coating 70 is not formed. For example, a portion of the conductive particles 80 may be disposed on the crown ether coating 70, and the remaining portion may be disposed on the core particle 60.

[0092] In some embodiments, at least a portion of the conductive particles 80 may be embedded in the crown ether coating 70. For example, at least a portion of the conductive particles 80 may be embedded in the crown ether coating 70 and protrude outside the surface of the crown ether coating 70.

[0093] In one embodiment, at least a portion of the conductive particles 80 may penetrate the crown ether coating 70 and contact the surface of the core particle 60. For example, at least a portion of the conductive particles 80 may be embedded in the crown ether coating 70 and contact the surface of the core particle 60.

[0094] Furthermore, at least a portion of the conductive particles 80 may be embedded in the core particle 60 while being embedded in the crown ether coating layer 70 .

[0095] The high power characteristics and high capacity characteristics of the negative electrode active material can be ensured by the conductive particles 80. For example, since the conductive particles 80 are embedded in the crown ether coating 70, the conductive particles 80 can contact the crown ether compound inside the crown ether coating 70. Therefore, additional ion / electron migration paths can be provided by the conductive particles 80 inside the crown ether coating 70, so that the power / capacity of the lithium secondary battery can be further enhanced.

[0096] The conductive particles 80 may include lithium titanate (LTO), Super P, carbon black, acetylene black, Ketjen black, flaky carbon, activated carbon, graphene, carbon nanotubes, carbon nanofibers, metal fibers, etc. These may be used alone or in combination of two or more.

[0097] In some embodiments, the weight of the conductive particles 80 may be 0.01 wt % to 5 wt % or 0.03 wt % to 2 wt % relative to the total weight of the core particles 60. Within the above range, a sufficient conductive path may be provided without hindering the negative electrode activity of the core particles 60.

[0098] In one embodiment, the average particle size of the conductive particles 80 may be greater than or equal to the thickness of the crown ether coating 70. For example, the average particle size of the conductive particles 80 may be greater than the thickness of the crown ether coating 70. For example, the average particle size of the conductive particles 80 may be an average value calculated by selecting a specified number (e.g., more than 100) of particles in the SEM cross-sectional image of the negative electrode active material layer 120 and actually measuring the particle size of each particle.

[0099] For example, the ratio of the thickness of the crown ether coating layer 70 to the average particle size of the conductive particles 80 may be about 0.001 or more. When the ratio is less than 0.001, a substantially uniform protective film may not be formed, and a sufficient side reaction suppression effect may not be obtained.

[0100] According to the exemplary embodiment, the negative active material 50 may be prepared by the method and process described below.

[0101] For example, the core particle 60 including the above-mentioned graphite-based active material or silicon-based active material may be prepared. Thereafter, the crown ether coating layer 70 may be formed on the core particle 60 .

[0102] The crown ether coating 70 can be formed by a wet coating method. For example, a coating solution containing a crown ether compound can be mixed with the core particles 60 and then stirred at a first speed. Thereafter, the polymer material can be fixed by heat treatment or drying to form the crown ether coating 70.

[0103] After the crown ether coating 70 is formed, the conductive particles 80 may be formed by wet surface treatment or dry surface treatment. For example, the conductive particles 80 may be wet mixed or dry mixed with the core particles 60 formed with the crown ether coating 70, and stirred at a second rotation speed so that the conductive particles 80 are attached to the crown ether coating 70.

[0104] The dry surface treatment can be performed by, for example, a ball mill, a roller mill, a high energy mill, a stirred mill, a planetary mill, a vibration mill, a Nobilta mill, mechanofusion, high speed mixing, etc.

[0105] The wet surface treatment may be performed by, for example, spraying, coprecipitation, dipping, stirring, extrusion, or the like.

[0106] The second rotation speed may be greater than the first rotation speed. For example, the second rotation speed may be in the range of about 1000 rpm to 2000 rpm, and the first rotation speed may be in the range of about 10 rpm to 100 rpm.

[0107] In the above rotation speed range, the conductive particles 80 can be distributed in the form of separate islands without damaging the crown ether coating layer 70 formed in the form of a thin film.

[0108] <Secondary Battery>

[0109] Figure 2 and Figure 3 are respectively a schematic plan view and a schematic cross-sectional view showing a secondary battery according to an exemplary embodiment. Figure 3 is along Figure 2 The illustrated cross-sectional view is taken along line II' in the thickness direction of the lithium secondary battery.

[0110] Reference Figure 2 and Figure 3 According to an exemplary embodiment, the secondary battery may include an electrode assembly 150 and a case 160 accommodating the electrode assembly 150. The electrode assembly 150 may include a positive electrode 100, a negative electrode 130, and a separator 140.

[0111] The positive electrode 100 may include a positive electrode collector 105 and a positive electrode active material layer 110 formed on at least one side of the positive electrode collector 105. According to an exemplary embodiment, the positive electrode active material layer 110 may be formed on both sides (e.g., the upper side and the lower side) of the positive electrode collector 105. For example, the positive electrode active material layer 110 may be coated on the upper side and the lower side of the positive electrode collector 105, respectively, and may be directly coated on the surface of the positive electrode collector 105.

[0112] The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably may include aluminum or an aluminum alloy.

[0113] The positive active material layer 110 may include lithium metal oxide as a positive active material, and according to an exemplary embodiment, may include lithium (Li)-nickel (Ni)-based oxide.

[0114] In some embodiments, the lithium metal oxide included in the positive active material layer 110 may be represented by the following Chemical Formula 1.

[0115] [Chemical formula 1]

[0116] Li 1+a Ni 1-(x+y) Co x M y O2

[0117] In the chemical formula 1, -0.05≤a≤0.15, 0.01≤x≤0.2, 0≤y≤0.2 may be satisfied, and M may be one or more elements selected from Mg, Sr, Ba, B, Al, Si, Mn, Ti, Zr, and W. In one embodiment, 0.01≤x≤0.20, 0.01≤y≤0.15 may be satisfied.

[0118] In one embodiment, in Chemical Formula 1, M may be manganese (Mn). In this case, a nickel-cobalt-manganese (NCM)-based lithium oxide may be used as the positive active material.

[0119] For example, nickel (Ni) can be provided as a metal related to the capacity of a lithium secondary battery. The higher the content of nickel, the more the capacity of the lithium secondary battery can be improved, but when the content of nickel is excessively increased, the life span may be reduced, and it may be disadvantageous in terms of mechanical stability and electrical stability. For example, cobalt (Co) can be a metal related to the conductivity or resistance and power of a lithium secondary battery. In one embodiment, M may include manganese (Mn), and Mn can be provided as a metal related to the mechanical stability and electrical stability of a lithium secondary battery.

[0120] Through the interaction of nickel, cobalt, and manganese, the capacity, power, low resistance, and life stability of the positive electrode active material layer 110 can be simultaneously improved.

[0121] For example, the positive active material may be mixed and stirred with a binder, a conductive material and / or a dispersing material in a solvent to prepare a slurry, which is coated on the positive current collector 105 and then compressed and dried to form the positive active material layer 110 .

[0122] The adhesive may include, for example, an organic adhesive such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a water-based adhesive such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0123] For example, a PVDF-based adhesive can be used as an adhesive for forming a positive electrode. In this case, the amount of the adhesive for forming the positive electrode active material layer 110 can be reduced, and the amount of the positive electrode active material or lithium metal oxide particles can be relatively increased, so the power and capacity of the secondary battery can be further improved.

[0124] The conductive material may be included to promote electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0125] In some embodiments, the electrode density of the positive electrode 100 may be 3.0 g / cubic centimeter (cc) to 3.9 g / cc, for example, 3.2 g / cc to 3.8 g / cc.

[0126] The negative electrode 130 may include a negative electrode collector 125 and a negative electrode active material layer 120 formed on at least one side of the negative electrode collector 125. According to an exemplary embodiment, the negative electrode active material layer 120 may be formed on both sides of the negative electrode collector 125. For example, the negative electrode active material layer 120 may be coated on the upper and lower surfaces of the negative electrode collector 125, respectively, and may directly contact the surface of the negative electrode collector 125.

[0127] The negative electrode current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably may include copper or a copper alloy.

[0128] According to an exemplary embodiment, the negative active material layer 120 may include the negative active material according to the above embodiment. For example, the content of the negative active material may be 80 wt % to 99 wt % or 90 wt % to 98 wt % relative to the total weight of the negative active material layer 120 .

[0129] For example, the negative electrode active material may be mixed and stirred with a binder, a conductive material and / or a dispersing material in a solvent to prepare a negative electrode slurry, which is coated (applied) on the negative electrode collector 125 , and then compressed (calendered) and dried to form the negative electrode active material layer 120 .

[0130] As the binder and the conductive material, a material substantially the same as or similar to that used when forming the positive electrode 100 may be used. In some embodiments, for example, for compatibility with a graphite-based active material, the binder used to form the negative electrode 130 may include styrene-butadiene rubber (SBR) or an acrylic-based binder, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0131] In an exemplary embodiment, the density of the negative active material layer 120 may be 1.4 g / cm 3 to 1.9 g / cm 3 .

[0132] In some embodiments, the area (e.g., contact area with the separator 140) and / or volume of the negative electrode 130 may be greater than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 may migrate smoothly to the negative electrode 130 without, for example, being precipitated in the middle, thereby further improving power characteristics and capacity characteristics.

[0133] A separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. The separator may also include a non-woven fabric formed of a high melting point glass fiber, a polyethylene terephthalate fiber, and the like.

[0134] The separator 140 may extend along the second direction between the positive electrode 100 and the negative electrode 130 and may be folded and wound along the thickness direction of the lithium secondary battery. Therefore, a plurality of positive electrodes 100 and negative electrodes 130 may be stacked along the thickness direction via the separator 140 .

[0135] According to an exemplary embodiment, a battery cell may be defined by a positive electrode 100, a negative electrode 130, and a separator 140, and a plurality of battery cells may be stacked to form, for example, an electrode assembly 150 in the form of a jelly roll. For example, the electrode assembly 150 may be formed by winding, lamination, folding, etc., of the separator 140.

[0136] The electrode assembly 150 may be accommodated in the case 160, and an electrolyte may be injected together into the case 160. The case 160 may include, for example, a pouch, a can, and the like.

[0137] According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0138] The non-aqueous electrolyte may include a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - Indicates that, as the anion of the lithium salt (X - ), we can exemplify F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - wait.

[0139] The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These may be used alone or in combination of two or more.

[0140] like Figure 2 As shown, the tabs (positive tabs and negative tabs) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the case 160. The tabs may be fused to the one side of the case 160 and connected to the electrode leads (positive lead 107 and negative lead 127) extending to the outside of the case 160 or exposed to the outside of the case 160.

[0141] Figure 2 Although the positive electrode lead 107 and the negative electrode lead 127 are shown to be formed on the same side of the lithium secondary battery or the case 160 , they may be formed on opposite sides to each other.

[0142] For example, the positive electrode lead 107 may be formed on one side of the case 160 , and the negative electrode lead 127 may be formed on the other side of the case 160 .

[0143] The lithium secondary battery can be manufactured in a cylindrical shape using a can, a prismatic shape, a pouch shape, a coin shape, or the like, for example.

[0144] In order to help understand the present invention, experimental examples including specific embodiments and comparative examples are proposed below. However, this is only used to illustrate the present invention and is not used to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept. This is obvious to those skilled in the art, and it is natural that such variations and modifications fall within the scope of the claims.

[0145] Examples and Comparative Examples

[0146] Example 1

[0147] (1) Manufacturing of negative electrode

[0148] 100g of artificial graphite particles (D 50 : 10 μm) and 4 g of a mixed solution of 18-crown-6-ether and ethanol were added to a mixer (manufactured by INOUE), mixed at a stirring speed of 20 Hz for 2 hours, and then dried at 60° C. under vacuum.

[0149] 0.5 wt % of Super P (average particle size: 150 nm) was added to the artificial graphite active material having a crown ether coating (coating thickness: 50 nm) based on the artificial graphite, and high-speed surface treatment was performed at a stirring speed of 1100 rpm for 10 minutes using a Nobilta mill.

[0150] The negative electrode active material prepared as described above, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) were mixed in a weight ratio of 97.3:1.2:1.5 to prepare a negative electrode slurry. The negative electrode slurry was coated on a Cu foil, and then dried and rolled to manufacture a negative electrode having a mixture density of 10 mg / cm2 and 1.7 g / cubic centimeter.

[0151] (2) Manufacturing of positive electrode

[0152] LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 92:5:3 to prepare a positive electrode slurry, and then the positive electrode slurry was coated on an aluminum substrate, dried and rolled to form a positive electrode.

[0153] (3) Manufacturing of secondary batteries

[0154] A polyethylene (PE) separator (13 μm) is provided between the positive electrode and the negative electrode manufactured as described above to form a battery cell, and the battery cells are stacked to form an electrode assembly. The electrode assembly is contained in a soft pack, and the tab portion is fused. Thereafter, an electrolyte containing a mixed solvent of 1M LiPF6 and ethylene carbonate / ethyl methyl carbonate (EC / EMC, 3 / 7; volume ratio) is injected and sealed to manufacture a secondary battery.

[0155] Example 2

[0156] A secondary battery was manufactured by the same method as in Example 1, except that 10 g of 18-crown-6-ether was included when preparing the negative electrode active material.

[0157] Example 3

[0158] A secondary battery was manufactured by the same method as in Example 1, except that 0.5 g of 18-crown-6-ether was included when preparing the negative electrode active material.

[0159] Example 4

[0160] A secondary battery was manufactured by the same method as in Example 1, except that 0.1 g of 18-crown-6-ether was included when preparing the negative electrode active material.

[0161] Example 5

[0162] A secondary battery was manufactured by the same method as in Example 1, except that 4 g of 12-crown-4-ether was included instead of 18-crown-6-ether when the negative electrode active material was prepared.

[0163] Example 6

[0164] A secondary battery was manufactured by the same method as in Example 1, except that the crown ether coating layer was formed to have a thickness of 200 nm when preparing the negative electrode active material.

[0165] Comparative Example 1

[0166] A secondary battery was manufactured by the same method as in Example 1, except that artificial graphite without the crown ether coating layer and Super-P was used as the negative electrode active material.

[0167] Comparative Example 2

[0168] A secondary battery was manufactured by the same method as in Example 1, except that no crown ether coating layer was formed when preparing the negative electrode active material.

[0169] Comparative Example 3

[0170] A secondary battery was manufactured by the same method as in Example 1, except that 4 g of LiOH was included instead of 18-crown-6-ether of the crown ether coating layer when preparing the negative electrode active material.

[0171] Comparative Example 4

[0172] A secondary battery was manufactured by the same method as in Example 1, except that the formation of Super-P was omitted when preparing the negative electrode active material.

[0173] Experimental example

[0174] (1) Evaluation of initial efficiency

[0175] The secondary batteries of Examples and Comparative Examples were charged (CC / CV 0.5C 4.2V 0.05C CUT-OFF) and discharged (CC 0.5C 2.5V CUT-OFF), and the initial charge capacity and the initial discharge capacity (CC: Constant Current, CV: Constant Voltage) were measured.

[0176] Thereafter, the initial efficiency was evaluated by the percentage of the value obtained by dividing the initial discharge capacity by the initial charge capacity.

[0177] (2) Evaluation of capacity retention rate

[0178] At 25° C., for the secondary batteries of the embodiments and comparative examples, charging (CC / CV, 0.5C, 4.2V, 0.05C cut-off) and discharging (CC, 0.5C, 2.5V cut-off) were repeated for 500 cycles of charging / discharging as one cycle. Thereafter, the capacity retention rate was evaluated by dividing the discharge capacity of the 500th cycle by the percentage of the value obtained by the discharge capacity of the 1st cycle.

[0179] (3) Fast charging performance characteristics

[0180] At 25°C, the secondary batteries of the embodiments and comparative examples were charged (CC / CV, 0.3C, 4.2V, 0.05C cut-off) and discharged (CC, 0.3C, 2.5V cut-off), and the initial discharge capacity A was measured. After that, at 25°C, within the range of 1.25C to 3.0C, fast charging was performed to SOC 80% at the current value of each stage, and discharge was performed to SOC 8% at 0.3C, and the above process was repeated 150 times as one cycle.

[0181] After 150 cycles, charge (CC / CV, 0.3C, 4.2V, 0.05C cutoff) and discharge (CC, 0.3C, 2.5V cutoff) were performed to measure the discharge capacity B. The rapid charge characteristics were evaluated by the percentage of the value obtained by dividing the discharge capacity B by the initial discharge capacity A.

[0182] The evaluation results are shown together in Table 1 below.

[0183] [Table 1]

[0184]

[0185] Referring to Table 1, the embodiment includes a negative electrode active material formed with a crown ether coating layer including a crown ether and conductive particles, and the initial efficiency, lifespan and fast charging performance are improved. On the other hand, the initial efficiency, lifespan and fast charging performance of the comparative example are reduced compared with the embodiment.

Claims

1. A negative electrode active material for a lithium secondary battery, comprising: nuclear particles; a crown ether coating layer formed on the core particle, wherein the crown ether coating layer comprises a crown ether compound; and Conductive particles are formed on or within the crown ether coating.

2. The negative electrode active material for lithium secondary battery according to claim 1, wherein The core particles include a graphite-based active material, an amorphous carbon-based active material, a silicon-based active material, or a mixture of two or more thereof.

3. The negative electrode active material for lithium secondary battery according to claim 1, wherein The core particles include at least one of natural graphite and artificial graphite.

4. The negative electrode active material for lithium secondary battery according to claim 1, wherein The thickness of the crown ether coating is 1 nm to 100 nm.

5. The negative electrode active material for lithium secondary battery according to claim 1, wherein The crown ether compound includes a nitrogen atom (N) or a sulfur atom (S).

6. The negative electrode active material for lithium secondary battery according to claim 1, wherein The crown ether compound comprises 10-crown-3, 11-crown-3, aza-11-crown-3, 12-crown-3, aza-12-crown-3, 12-crown-4, benzo-12-crown-4, tetrathia-12-crown-4, aza-12-crown-4, diaza-12-crown-4, 14-crown-4, tetrathia-14-crown-4, benzo-14-crown-4, dibenzo-14-crown-4, di(decahydronaphthalene)-14-crown-4 , decahydronaphtho-14-crown-4, 15-crown-5, aza-15-crown-5, diaza-15-crown-5, benzo-15-crown-5, dibenzo-15-crown-5, cyclohexaneda-15-crown-5, 16-crown-4, 16-crown-5, 18-crown-6, hexathia-18-crown-6, aza-18-crown-6, diaza-18-crown-6, benzo-18-crown-6 and at least one of dibenzo-18-crown-6.

7. The negative electrode active material for lithium secondary battery according to claim 1, wherein The content of the crown ether compound is 0.01 wt % to 5 wt % relative to the total weight of the core particle.

8. The negative electrode active material for lithium secondary battery according to claim 1, wherein The crown ether coating consists of the crown ether compound.

9. The negative electrode active material for lithium secondary battery according to claim 1, wherein The conductive particles cover the entire crown ether coating.

10. The negative electrode active material for lithium secondary battery according to claim 1, wherein At least a portion of the conductive particles are embedded in the crown ether coating and protrude outside the surface of the crown ether coating.

11. The negative electrode active material for lithium secondary battery according to claim 1, wherein The conductive particles are not in contact with the core particles.

12. The negative electrode active material for lithium secondary battery according to claim 1, wherein At least a portion of the conductive particles penetrate the crown ether coating.

13. The negative electrode active material for lithium secondary battery according to claim 1, wherein The conductive particles include at least one of lithium titanate (LTO), Super P, carbon black, acetylene black, Ketjen black, flaky carbon, activated carbon, graphene, carbon nanotubes (CNT), carbon nanofibers (CNF), metal fibers and metal particles.

14. The negative electrode active material for lithium secondary battery according to claim 1, wherein The negative electrode active material for a lithium secondary battery further includes a carbon coating layer formed between the core particle and the crown ether coating layer, and the carbon coating layer covers an outer surface of the core particle.

15. The negative electrode active material for lithium secondary battery according to claim 14, wherein The carbon coating layer includes an amorphous carbon-based substance.

16. The negative electrode active material for lithium secondary battery according to claim 14, wherein The ratio of the thickness of the crown ether coating layer to the thickness of the carbon coating layer is greater than 0 and less than 5.

17. A lithium secondary battery comprising: positive electrode; as well as A negative electrode is disposed opposite to the positive electrode, and the negative electrode comprises the negative electrode active material for a lithium secondary battery according to claim 1.

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