Negative electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

A negative electrode active material for a lithium secondary battery according to an embodiment of the present invention comprises composite particles, the composite particles comprising: carbon-based particles comprising pores; and a silicon-containing coating layer formed on the surface of the carbon-based particles, in which the conversion porosity of the composite particles is 5% to 25.1%.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery containing the negative electrode active material. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, secondary batteries are widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook computers. In addition, in recent years, battery packs including secondary batteries are being developed and used as a power source for environmentally friendly vehicles such as electric vehicles.

[0003] Examples of 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 terms of charging speed and light weight, and therefore are being actively developed and used.

[0004] In recent years, as the application of lithium secondary batteries has expanded, lithium secondary batteries with higher capacity and power have been developed. For example, high-capacity silicon and carbon can be combined and used as negative electrode active materials.

[0005] However, due to the large difference in volume expansion rate of the silicon-carbon composite negative electrode active material, repeated charge and discharge may cause cracks in the negative electrode active material and expose it to the electrolyte. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] According to one aspect of the present invention, a negative electrode active material for a lithium secondary battery having improved life characteristics can be provided.

[0008] According to another aspect of the present invention, a lithium secondary battery having improved lifespan characteristics can be provided.

[0009] (II) Technical solution

[0010] According to an embodiment of the present invention, a negative electrode active material for a lithium secondary battery includes composite particles, the composite particles including: carbon-based particles, the carbon-based particles including pores; and a silicon-containing coating formed on the surface of the carbon-based particles, wherein the composite particles have a converted porosity defined by the following formula 1 of 5% to 25.1%.

[0011] [Formula 1]

[0012]

[0013] In formula 1, D 碳(carbon) is the density of carbon (g / cm 3), D Si is the density of silicon (g / cm 3 ), D P is the density (g / cm2) of the composite particles measured using a helium pycnometer. 3 ), W Si is the weight (g) of silicon contained in the composite particles, W 碳 is the weight (g) of carbon contained in the composite particles.

[0014] In some embodiments, W Si It can be calculated by the following formula 2.

[0015] [Formula 2]

[0016]

[0017] In formula 2, R Si is the ratio of the weight of silicon contained in the silicon-containing coating to the total weight of the composite particles measured by inductively coupled plasma (ICP) analysis, W 碳 is the weight (g) of carbon contained in the composite particles.

[0018] In some embodiments, D 碳 Can be 2.1g / cm 3 , D Si Can be 2.33g / cm 3 .

[0019] In some embodiments, the carbon-based particles may comprise an amorphous structure.

[0020] In some embodiments, the silicon included in the silicon-containing coating may include an amorphous structure.

[0021] In some embodiments, the internal deposition index of the composite particle represented by the following Formula 3 may be 1.0 to 2.0.

[0022] [Formula 3]

[0023]

[0024] In Formula 3, V t is the specific volume of the pores of the carbon-based particles (cm 3 / g), D 碳 is the density of carbon (g / cm 3 ), D Si is the density of silicon (g / cm 3 ), D Pis the density of the composite particles measured using a helium pycnometer (g / cm 3 ), W Si is the weight (g) of silicon contained in the composite particles, W 碳 is the weight (g) of carbon contained in the composite particles.

[0025] In some embodiments, W Si It can be calculated by the following formula 2.

[0026] [Formula 2]

[0027]

[0028] In formula 2, R Si is the ratio of the weight of silicon contained in the silicon-containing coating to the total weight of the composite particles measured by inductively coupled plasma (ICP) analysis, W 碳 is the weight (g) of carbon contained in the composite particles.

[0029] In some embodiments, D 碳 Can be 2.1g / cm 3 , D Si Can be 2.33g / cm 3 .

[0030] In some embodiments, V t The measurement can be performed by nitrogen adsorption-desorption method.

[0031] In some embodiments, the composite particles may further include a carbon coating formed on the silicon-containing coating.

[0032] In some embodiments, the pores may include a shape that curves from the outermost portion of the carbon-based particle toward the inner portion of the carbon-based particle.

[0033] In some embodiments, the pores may include closed pores separated from the exterior of the carbon-based particle by the silicon-containing coating.

[0034] A lithium secondary battery according to an embodiment of the present invention includes: a negative electrode including a negative electrode active material for a lithium secondary battery; and a positive electrode disposed opposite to the negative electrode.

[0035] (III) Beneficial effects

[0036] According to one embodiment of the present invention, the volume expansion of silicon can be sufficiently suppressed. In addition, the energy density, power characteristics, and life characteristics of the negative electrode active material can be improved.

[0037] According to one embodiment of the present invention, the content of silicon formed on the inner surface of the pores can be increased, and the content of silicon deposited on the outside of the carbon-based particles can be reduced. In addition, the efficiency of the binder can be improved. Therefore, the life characteristics can be improved.

[0038] The negative electrode active material for lithium secondary batteries of the present invention and the lithium secondary batteries containing the negative electrode active material can be widely used in electric vehicles, battery charging stations, other green technology fields such as solar power generation and wind power generation using batteries. The negative electrode active material for lithium secondary batteries of the present invention and the lithium secondary batteries containing the negative electrode active material can be used for eco-friendly electric vehicles, hybrid vehicles, etc. that suppress air pollution and greenhouse gas emissions to prevent climate change. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic cross-sectional view showing a composite particle according to an exemplary embodiment.

[0040] Figure 2 and Figure 3 1 and 2 are a schematic plan view and a schematic cross-sectional view, respectively, showing a lithium secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION

[0041] The present invention provides a negative electrode active material for a lithium secondary battery (hereinafter referred to as "negative electrode active material") containing composite particles. In addition, a lithium secondary battery (hereinafter referred to as "secondary battery") containing the negative electrode active material is provided.

[0042] Hereinafter, embodiments of the present invention will be described in detail, however, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0043] Figure 1 is a schematic cross-sectional view showing a composite particle according to an exemplary embodiment.

[0044] For ease of explanation, Figure 1 The shape of the composite particles is schematically shown in FIG. 1 , but the structure / shape of the composite particles of the present invention is not limited to Figure 1 The structure / shape shown in FIG. For example, the cross-section of the carbon-based particles can be randomly changed from a circle. In addition, the silicon-containing coating can be partially formed on the pores and surfaces of the carbon-based particles, and can also be formed as a discontinuous plurality of islands or patterns.

[0045] Reference Figure 1 , the composite particle 50 may include a carbon-based particle 60 and a silicon (Si)-containing coating 70 .

[0046] In an exemplary embodiment of the present invention, the carbon-based particle 60 may include pores 65. For example, the carbon-based particle 60 may be a porous particle including a plurality of pores.

[0047] In some embodiments, the carbon-based particles 60 may include activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, pyrolysis cryogel, pyrolysis xerogel, pyrolysis aerogel, etc. These may be used alone or in combination of two or more.

[0048] In some embodiments, the carbon-based particles 60 may include an amorphous structure or a crystalline structure.

[0049] According to one embodiment, the carbon-based particles 60 may include an amorphous structure. Therefore, the durability of the negative electrode active material may be increased, thereby suppressing the generation of cracks during charge and discharge or external impact. Therefore, the life characteristics of the secondary battery may be improved.

[0050] A silicon-containing coating 70 may be formed on the surface of the carbon-based particles 60 including the pores 65. For example, the volume expansion of silicon contained in the silicon-containing coating 70 may be alleviated by the pores 65. Therefore, the relatively high capacity characteristics of silicon may be utilized, while cracks caused by the difference in the volume expansion rate of carbon (e.g., about 150% by volume or less) and the volume expansion rate of silicon (e.g., about 400% by volume or more) during the charge and discharge of the battery may be prevented. Therefore, the generation of gas caused by the side reactions of the negative electrode active material and the electrolyte may be suppressed, and the life characteristics of the secondary battery may be improved.

[0051] In some embodiments, the silicon-containing coating 70 may include silicon, and may optionally further include SiO x (0 <x<2)。

[0052] In some embodiments, silicon included in the silicon-containing coating layer 70 may include an amorphous structure. Therefore, structural stability may be improved, and life characteristics in a high temperature environment or during repeated charge and discharge may be improved.

[0053] The pores 65 of the carbon-based particles 60 may include a shape bent from the outermost portion of the carbon-based particles 60 toward the inside of the carbon-based particles 60. For example, the pores 65 may include pores (open pores) open to the outside of the carbon-based particles 60.

[0054] The terms “surface of carbon-based particles” and / or “surface of carbon-based particles 60 ” used in this specification may refer to the outer surface 62 of the carbon-based particles 60 , the inner surface 67 of the pores 65 , or the outer surface 62 of the carbon-based particles 60 and the inner surface 67 of the pores 65 .

[0055] For example, the silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particle 60 .

[0056] For example, the silicon-containing coating 70 may be formed on at least a portion of the inner surface 67 of the pores 65 of the carbon-based particles 60 .

[0057] For example, the silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particle 60 and on at least a portion of the inner surface 67 of the pore 65 .

[0058] The carbon-based particle 60 may be formed with closed pores 65a inside. For example, the closed pores 65a may exist inside the carbon-based particle 60 in a form separated from the outside.

[0059] For example, the pores 65 may include closed pores 65a separated from the outside of the carbon-based particle 60 by the silicon-containing coating 70. For example, the closed pores 65a may be voids inside the carbon-based particle 60 formed by closing pores open to the outside by the silicon-containing coating 70.

[0060] In some embodiments, the size of the pores 65 may be 0.1 nm to 10 nm, 0.5 nm to 8 nm, or 1 nm to 5 nm. Within the above range, excessive deposition of silicon can be prevented, thereby further suppressing the generation of cracks in the negative electrode active material during charge and discharge of the secondary battery.

[0061] The size of the pore 65 may refer to a diameter of an entrance of the pore 65 formed at a surface portion of the carbon-based particle 60 .

[0062] According to an exemplary embodiment of the present invention, the composite particle 50 may have a converted porosity defined by the following Formula 1, which may be 5% to 25.1%, and in some embodiments, may be 8.5% to 22.6%.

[0063] [Formula 1]

[0064]

[0065] In formula 1, D 碳 is the density of carbon (g / cm 3 ), D Si is the density of silicon (g / cm 3 ), D P is the density (g / cm2) of the composite particle 50 measured using a helium pycnometer 3 ), WSi is the weight (g) of silicon contained in the composite particle 50, W 碳 is the weight (g) of carbon contained in the composite particle 50.

[0066] The converted porosity can be calculated by the difference between the volume of the composite particle converted from the density measured using a helium pycnometer and the volume of the actual composite particle. Therefore, the volume of the pores including the closed pores 65a inside the composite particle 50 can be reflected in the converted porosity. Therefore, the porosity (e.g., converted porosity) of the composite particle 50 can be accurately measured.

[0067] In the above-mentioned converted porosity range, the volume expansion of silicon contained in the silicon-containing coating layer 70 can be sufficiently suppressed, and the energy density, power characteristics, and life characteristics of the negative electrode active material can be improved.

[0068] When the converted porosity is less than 5%, the volume expansion of silicon may not be sufficiently alleviated, and thus the life characteristics may be degraded.

[0069] When the converted porosity exceeds 25.1%, the density of the negative electrode active material decreases, and the resistance increases, so that the energy density and / or life characteristics may decrease.

[0070] According to one embodiment, in Formula 1, D 碳 Can be 2.1g / cm 3 , D Si Can be 2.33g / cm 3 In some embodiments, W of Formula 1 Si It can be calculated by the following formula 2.

[0071] [Formula 2]

[0072]

[0073] In formula 2, R Si is the ratio of the weight of silicon contained in the silicon-containing coating 70 to the total weight of the composite particles 50 measured by inductively coupled plasma (ICP) analysis, W 碳 R is the weight (g) of carbon contained in the composite particle 50. Si Is a dimensionless number.

[0074] W Si By measuring through ICP analysis, it is possible to accurately convert the volume of silicon in the composite particle 50. Therefore, the measurement accuracy and reliability of the converted porosity and the internal deposition index of Formula 3 can be improved.

[0075] In some embodiments, the internal deposition index of the composite particle 50 represented by the following Formula 3 may be 1.0 to 2.0, and in one embodiment, may be 1.01 to 1.55.

[0076] [Formula 3]

[0077]

[0078] In Formula 3, V t is the specific volume (cm2) of the pores 65 of the carbon-based particles 60 3 / g), D 碳 is the density of carbon (g / cm 3 ), D Si is the density of silicon (g / cm 3 ), D P is the density (g / cm2) of the composite particle 50 measured using a helium pycnometer 3 ), W Si is the weight (g) of silicon contained in the composite particle 50, W 碳 is the weight (g) of carbon contained in the composite particle 50. The internal deposition index is a dimensionless number.

[0079] D of Formula 3 碳 , D Si , D P and W Si can be interpreted as D 碳 , D Si , D P and W Si For example, W in Formula 3 Si It can be calculated by the formula 2. According to one embodiment, in formula 3, D 碳 Can be 2.1g / cm 3 , D Si Can be 2.33g / cm 3 .

[0080] The internal deposition index may represent the ratio of the total volume of pores in which silicon may be deposited to the actual volume of silicon. The total volume of pores in which silicon may be deposited may represent the total pore volume (V t ×W 碳 ) and the volume of the closed pores 65a. The volume of the closed pores 65a can be calculated by the difference between the volume of the composite particles converted from the density measured using a helium pycnometer and the actual volume of the composite particles. Therefore, it is possible to quantify whether the region in which silicon can be deposited in the composite particles 50 is sufficient relative to the volume of silicon contained in the composite particles 50.

[0081] In the above-mentioned inner deposition index range, the content of silicon formed on the inner surface 67 of the pore 65 can be increased, and the content of silicon deposited outside the carbon-based particle 60 can be reduced. Therefore, the lifespan characteristics can be improved.

[0082] In the above-mentioned internal deposition index range, the specific surface area of ​​the composite particles 50 can be maintained within an appropriate range, and thus the efficiency of the binder included in the negative electrode can be improved. Therefore, the life characteristics can be improved.

[0083] In some embodiments, V of Formula 3 t The total pore volume of carbon-based particles can be measured by nitrogen (N2) adsorption-desorption method. Therefore, the reliability and accuracy of the total pore volume measurement of carbon-based particles can be improved.

[0084] For example, the nitrogen adsorption desorption method can be performed by adsorbing and desorbing nitrogen on the carbon-based particles 60 according to ISO 15901-2 and ISO 15901-3 of the International Organization for Standardization (ISO). For example, the nitrogen adsorption desorption method can be performed using ASAP manufactured by Micromeritics. TM 2420 equipment to carry out.

[0085] For ease of calculation, in equations 1 to 3, W 碳 It can be assumed to be 1g.

[0086] In some embodiments, the converted porosity may be 8.5% to 22.6%, and the internal deposition index may be 1.01 to 1.55. Within the above range, the converted porosity and the internal deposition index may be controlled simultaneously, so that an appropriate amount of silicon is formed on the inner surface of the pores, thereby further improving the capacity retention rate.

[0087] The converted porosity and the internal deposition index can be obtained by calculating the specific volume (V t ), the concentration of silane gas in the silicon-containing coating source, the pressure during silicon deposition, etc. are compound controlled to adjust. For example, by compound adjusting all of the above factors without relying on any of the above factors, the converted porosity range and the internal deposition index range according to the embodiment of the present invention can be met.

[0088] In some embodiments, the composite particle 50 may further include a carbon coating layer (not shown) formed on the silicon-containing coating layer 70. Therefore, the surface of the composite particle 50 may be protected, and the electrical conductivity may be increased, so that the life characteristics and the power characteristics may be improved.

[0089] In some embodiments, the carbon coating layer may also be formed on a portion of the surface of the carbon-based particle 60 where the silicon-containing coating layer 70 is not formed. For example, the carbon coating layer may entirely cover the carbon-based particle 60 and the silicon-containing coating layer 70. Therefore, the mechanical stability and chemical stability of the negative active material may be improved.

[0090] In one embodiment, the carbon coating may include at least one of carbon and a conductive polymer. For example, the conductive polymer may include polyacetylene, polyaniline, polypyrrole, polythiophene, and the like.

[0091] Hereinafter, a preparation method of the negative electrode active material for a lithium secondary battery according to an exemplary embodiment is provided.

[0092] In an exemplary embodiment, carbon-based particles 60 including pores 65 may be prepared.

[0093] In some embodiments, an inert gas may be added to the primary carbon-based particles and a first calcination may be performed, and water vapor may be added and a second calcination may be performed for activation.

[0094] For example, the primary carbon-based particles may include at least one selected from the group consisting of glucose, sucrose, cellulose, petroleum-based asphalt, coal-based asphalt, biomass (coconut shell, wood, etc.), and resol oligomers.

[0095] For example, the first calcination may be performed at about 600° C. to 900° C. for 1 to 6 hours. Therefore, the size and / or volume of the pores 65 may be appropriately controlled. For example, the inert gas may be nitrogen, and the first calcination may be performed under a nitrogen atmosphere.

[0096] For example, the second calcination may be performed at about 800° C. to 1000° C. for 1 to 6 hours. Therefore, the size and / or volume of the pores 65 may be appropriately controlled. The specific volume (V) of the pores 65 of the carbon-based particles 60 may be adjusted by changing the temperature and time of the second calcination. t ).

[0097] In some embodiments, the activated primary carbon-based particles may be cooled, crushed, and classified to prepare carbon-based particles 60 including pores 65 .

[0098] In an exemplary embodiment, the carbon-based particles 60 and the silicon-containing gas (silicon source) may be calcined together (e.g., the third calcination) to form composite particles 50, the composite particles 50 including the silicon-containing coating 70 formed on the surface of the carbon-based particles 60. For example, the silicon-containing gas may include silane (SiH4) gas and an inert gas. For example, the inert gas may include nitrogen or argon (Ar) gas.

[0099] For example, the volume of the silane gas relative to the total volume of the silicon-containing gas may be 10 vol % to 70 vol % or 30 vol % to 50 vol %. Thus, silicon may be further deposited on the inner surface 67 of the hole 65 .

[0100] For example, the third calcination may be performed at 400° C. to 600° C. for 1 hour to 6 hours. Thus, silicon may be further deposited on the inner surface 67 of the pore 65 .

[0101] For example, the third calcination may be performed under a low pressure environment, for example, the third calcination may be performed under a pressure of 50 Torr to 500 Torr.

[0102] The converted porosity of the composite particle 50 formed by the above method may be 5% to 25.1%.

[0103] Figure 2 and Figure 3 1 and 2 are schematic plan views and schematic cross-sectional views respectively showing a lithium secondary battery according to an exemplary embodiment. Figure 3 It is along Figure 2 A cross-sectional view taken along the thickness direction along the line II'.

[0104] Figure 2 and Figure 3 The structure shown in FIG. 1 is an example for convenience of description, and the structure of the lithium secondary battery according to the embodiment of the present invention is not limited thereto.

[0105] The lithium secondary battery may include a negative electrode 130 including the negative electrode active material described above and a positive electrode 100 disposed opposite to the negative electrode 130 .

[0106] 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 .

[0107] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector 105 may be 10 μm to 50 μm.

[0108] The positive electrode active material layer 110 may include a positive electrode active material. The positive electrode active material may include a compound that can reversibly intercalate and deintercalate lithium ions.

[0109] According to an exemplary embodiment, the positive active material may include lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0110] In some embodiments, the positive active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1.

[0111] [Chemical formula 1]

[0112] Li x Ni a M b O 2+z

[0113] In Chemical Formula 1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.5, and -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0114] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained in the layered structure or crystal structure of the positive active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active elements, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0115] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary element may be mixed together into the layered structure / crystal structure to form a bond, and it should be understood that this case is also included in the chemical structure represented by Chemical Formula 1.

[0116] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may function as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0117] For example, the positive active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1-1.

[0118] [Chemical formula 1-1]

[0119] Li x Ni a M1 b1 M2 b2 O 2+z

[0120] In Chemical Formula 1-1, M1 may include Co, Mn and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.5, and -0.5≤z≤0.1 may be selected.

[0121] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially the same as or similar to the auxiliary element may be used as the coating element or the doping element. For example, one or a combination of two or more of the above elements may be used as the coating element or the doping element.

[0122] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particle or permeate through the surface of the lithium-nickel metal oxide particle and be included in the bonding structure represented by the Chemical Formula 1 or Chemical Formula 1-1.

[0123] The positive active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, the NCM-based lithium oxide having an increased nickel content may be used.

[0124] Ni can be provided as a transition metal related to the power and capacity of a lithium secondary battery. Therefore, as described above, by using a high-content (high-nickel (High-Ni)) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0125] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or secondary battery may be relatively reduced, and the side reaction with the electrolyte may also increase. However, according to an exemplary embodiment, the conductivity can be maintained by including Co, while the life stability and capacity retention characteristics can be improved by Mn.

[0126] The content of Ni in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt and manganese) may be greater than 0.5, greater than 0.6, greater than 0.7 or greater than 0.8. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95 or 0.88 to 0.95.

[0127] In some embodiments, the positive electrode active material may also include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (eg, LiFePO 4 ).

[0128] In some embodiments, the positive electrode active material may include, for example, a Li rich layered oxide (LLO) / OverLithiated Oxide (OLO) based active material having a chemical structure or crystal structure represented by Chemical Formula 2, an Mn-rich based active material, a Co-less based active material, etc. These may be used alone or in combination of two or more.

[0129] [Chemical Formula 2]

[0130] p[Li2MnO3]·(1-p)[Li q JO2]

[0131] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element among Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0132] The positive electrode active material may be mixed in a solvent to prepare a positive electrode paste. The positive electrode paste may be coated on at least one surface of the positive electrode current collector 105 and then dried and calendered to prepare the positive electrode active material layer 110. The coating may include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc. The positive electrode active material layer 110 may further include a binder, and may optionally further include a conductive material, a thickener, etc.

[0133] As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. may be used.

[0134] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethylmethacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0135] In one embodiment, a PVDF-based binder may be used as a positive electrode binder. In this case, the amount of the binder used to form the positive electrode active material layer 110 may be reduced, and the amount of the positive electrode active material may be relatively increased. Therefore, the power characteristics and capacity characteristics of the secondary battery may be improved.

[0136] The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode active material layer 110. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes (CNT), vapor-grown carbon fiber (VGCF), carbon fiber, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These may be used alone or in combination of two or more.

[0137] The positive electrode slurry may further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0138] 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 .

[0139] For example, the negative electrode current collector 125 may include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 125 may be 10 μm to 50 μm.

[0140] The negative electrode active material layer 120 may include a negative electrode active material including the composite particles 50. For example, the negative electrode active material may include a plurality of composite particles 50.

[0141] In some embodiments, the negative electrode active material may include composite particles 50 and a graphite-based active material. For example, the graphite-based active material may include artificial graphite and / or natural graphite.

[0142] In the total weight of the negative electrode active material (for example, the total weight of multiple composite particles 50 and the graphite-based active material), the content of the composite particles 50 can be more than 3 weight %, more than 5 weight %, more than 10 weight %, more than 15 weight %, more than 20 weight %, more than 25 weight %, more than 30 weight %, more than 35 weight %, more than 40 weight % or more than 45 weight %.

[0143] The content of the composite particles in the total weight of the negative electrode active material may be 90 wt % or less, 85 wt % or less, 80 wt % or less, 75 wt % or less, 70 wt % or less, 65 wt % or less, 60 wt % or less, 55 wt % or less or 50 wt % or less.

[0144] In one embodiment, the negative electrode active material may consist essentially of the composite particles 50 and the graphite-based active material.

[0145] The negative electrode active material may be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry may be coated / deposited on a negative electrode current collector 125 and then dried and rolled to prepare a negative electrode active material layer 120. The coating may include gravure coating, slot extrusion coating, multi-layer simultaneous die coating, stamping, blade coating, dip coating, rod coating, casting, and the like. The negative electrode active material layer 120 may further include a binder, and may optionally further include a conductive material, a thickener, and the like.

[0146] The solvent contained in the negative electrode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propyl alcohol, tert-butyl alcohol, etc. These may be used alone or in combination of two or more.

[0147] As the binder, the conductive material, and the thickener, the above-mentioned substances that can be used when manufacturing the positive electrode 100 can be used.

[0148] In some embodiments, the negative electrode binder can use styrene-butadiene-rubber (SBR) based binder, carboxymethyl cellulose (CMC), polyacrylic acid based binder, polyethylene dioxythiophene (poly (3,4-ethylenedioxythiophene)) (poly (3,4-ethylenedioxythiophene)), PEDOT) based binder, etc. These can be used alone or in combination of two or more.

[0149] In an exemplary embodiment, the separator 140 may be disposed between the cathode 100 and the anode 130. The separator 140 may be provided to prevent a short circuit between the cathode 100 and the anode 130 and to generate a flow of ions. For example, the separator may have a thickness of 10 μm to 20 μm.

[0150] For example, the separator 140 may include a porous polymer film or a porous nonwoven fabric.

[0151] The porous polymer film may include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, which may be used alone or in combination of two or more.

[0152] The porous nonwoven fabric may include high melting point glass fiber, polyethylene terephthalate fiber, and the like.

[0153] The separator 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer film to improve heat resistance.

[0154] The separator 140 may have a single-layer or multi-layer structure including the above-mentioned polymer film and / or non-woven fabric.

[0155] According to an exemplary embodiment, a battery cell is 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, stacking, z-folding, stack-folding, etc., of the separator 140.

[0156] The electrode assembly 150 is accommodated in the case 160 together with an electrolyte, so that a lithium secondary battery may be defined. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0157] 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 - etc.

[0158] As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DME), ether, DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, cyclopentane, γ-butyrolactone and propylene sulfite, etc. These can be used alone or in combination of two or more.

[0159] The non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, cyclic sulfite-based compounds, phosphate-based compounds, and borate-based compounds, etc. These may be used alone or in combination of two or more.

[0160] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0161] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

[0162] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0163] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0164] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, and the like.

[0165] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0166] The borate-based compound may include lithium bis(oxalate) borate and the like.

[0167] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery may be made into an all-solid-state battery. In addition, a solid electrolyte layer may be provided between the positive electrode 100 and the negative electrode 130 instead of the separator 140.

[0168] The solid electrolyte may include a sulfide-based electrolyte. As non-limiting examples, the sulfide-based electrolyte may include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m Sn (m and n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2), etc. These can be used alone or in combination of two or more.

[0169] In one embodiment, the solid electrolyte may also include an oxide-based amorphous solid electrolyte such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0170] like Figure 3 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 shell 160. The tabs may be fused with the one side of the shell 160 to form electrode leads (positive lead 107 and negative lead 127) extending to the outside of the shell 160 or exposed to the outside of the shell 160.

[0171] The lithium secondary battery may be manufactured in, for example, a cylindrical shape using a can, a prismatic shape, a pouch type, a coin shape, or the like.

[0172] The embodiments of the present invention are further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only used to illustrate the present invention and are not used to limit the claims. Various modifications and variations can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art, and it is natural that such modifications and variations belong to the scope of the claims.

[0173] Example 1

[0174] Preparation of carbon-based particles

[0175] The coconut shell charcoal was put into a thermal chamber and first calcined at 800° C. for 2 hours while adding nitrogen, and then second calcined at 900° C. for 2 hours while adding water vapor into the thermal chamber for activation.

[0176] The activated coconut shell carbon was cooled to room temperature and pulverized and classified to prepare carbon-based particles containing pores (D50: 8 μm).

[0177] The specific volume (V) of the pores of the carbon-based particles was measured by the method described in the following Experimental Example (1) 3). t ).

[0178] Formation of Silicon-Containing Coating

[0179] A silicon-containing gas comprising silane gas and nitrogen is injected into a CVD coater at a flow rate of 50 mL / min to 100 mL / min. The content of silane gas relative to the total volume of the silicon-containing gas is 10 volume %. The temperature is raised to 550° C. at a heating rate of 5° C. / min to 20° C. / min, and then maintained for about 120 minutes, thereby preparing composite particles comprising a silicon-containing coating. The pressure of the CVD coater is maintained at 100 Torr.

[0180] The silicon-containing coating layer was formed with a silicon content of 50% by weight relative to the total weight of the composite particles as a target.

[0181] Negative electrode formation

[0182] 95.5 wt % of a negative electrode active material prepared by mixing 15 wt % of the composite particles and 80.5 wt % of artificial graphite, 1 wt % of carbon nanotubes (CNT) as a conductive material, 2 wt % of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt % of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0183] The negative electrode slurry is coated on a copper substrate and dried and rolled to manufacture a negative electrode.

[0184] Manufacturing of Li-half cell

[0185] A lithium half-cell is manufactured, which includes the negative electrode and uses lithium metal (Li metal) as a counter electrode (positive electrode).

[0186] Specifically, a separator (polyethylene, 20 μm thick) was provided between the negative electrode and lithium metal (1 mm thick) to produce a lithium coin half-cell of CR2016 (20 mm in diameter, 1.6 mm in thickness).

[0187] The lithium metal / separator / negative electrode assembly is placed in a coin cell plate and injected with electrolyte, and then covered with a cap and clamped. The electrolyte is a 1M LiPF6 solution formed by using a mixed solvent of EC / EMC (3:7; volume ratio) and 2.0 volume % of fluoroethylene carbonate (FEC) is added relative to the total volume of the electrolyte. After clamping, it is immersed for 3 to 24 hours, and then charged and discharged at 0.1C for 3 cycles (charging conditions: CC-CV 0.1C 0.01V 0.01C cut-off (CUT-OFF), discharge conditions: CC 0.1C 1.5V cut-off).

[0188] Example 2

[0189] Composite particles, a negative electrode, and a lithium half-cell were manufactured by the same method as in Example 1, except that a second calcination was performed at 900° C. for 1 hour.

[0190] Example 5

[0191] Composite particles, a negative electrode, and a lithium half-cell were manufactured by the same method as in Example 1, except that a second calcination was performed at 800° C. for 2 hours.

[0192] Example 3, Example 4, Example 6 to Example 8 and Comparative Examples 1 to Comparative Examples 4

[0193] Composite particles, a negative electrode and a lithium half-cell were manufactured by the same method as in Example 1, except that the content of the silane gas relative to the total volume of the silicon-containing gas and the pressure of the CVD coater were adjusted as shown in Table 1 below.

[0194] Example 9

[0195] The carbon-based particles formed with the silicon-containing coating layer are placed in a thermal chemical vapor deposition (thermal CVD) chamber and heat-treated at less than 600° C. while supplying a mixed gas of ethylene gas and argon gas, thereby preparing composite particles having a carbon coating layer formed on the silicon-containing coating layer.

[0196] Composite particles, a negative electrode, and a lithium half-cell were manufactured by the same method as in Example 1 except for the above contents.

[0197] Comparative Example 5

[0198] Composite particles, a negative electrode, and a lithium half-cell were manufactured by the same method as in Example 1, except that a second calcination was performed at 1000° C. for 6 hours.

[0199] Experimental example

[0200] (1) Evaluation of converted porosity and internal deposition index

[0201] 1) Density of composite particles (D P )

[0202] A sample of known weight of the composite particles prepared according to the above examples and comparative examples was dried at 130°C for more than 5 hours and a 10 cm 3 A sample of 70% by volume of the battery was placed in the battery.

[0203] The density of the sample was measured at room temperature using an AccPyc II instrument from Micromeritics Instruments. The purge frequency was set to 10 times, and the measurement was repeated 100 times. The average value was evaluated as the density of the composite particles (D P ).

[0204] 2) The ratio of the weight of silicon to the total weight of the composite particles (R Si )

[0205] 0.05g of the powder of the composite particles of the above-mentioned embodiments and comparative examples was added to a 50mL polypropylene tube (PPtube). Nitric acid was added to the polypropylene tube and placed at room temperature for 5 minutes. Hydrofluoric acid was added to the polypropylene tube, and the polypropylene tube was sealed with a parafilm, then dissolved at room temperature for 1 hour and placed in a refrigerator for 12 hours. Afterwards, 45mL of distilled water was added to the polypropylene tube and cooled in a refrigerator for 30 minutes. Saturated boric acid solution was added to the polypropylene tube and stirred at 60rpm for 60 minutes to neutralize the boric acid. The sample was prepared by removing undissolved components with a 0.45μm syringe filter (SyringeFilter).

[0206] The sample was placed in an inductively coupled plasma-optical emission spectrometer (ICP-OES Optima 8300DV, Perkin Elmer) and analyzed to measure the ratio of the weight of silicon to the total weight of the composite particles (R Si ).

[0207] 3) The specific volume of the pores of the carbon-based particles (V t )

[0208] For the carbon-based particles of the above-mentioned Examples and Comparative Examples, nitrogen was adsorbed and desorbed to measure the specific volume (V t ).

[0209] Specifically, the carbon-based particles were pretreated at 180°C for 8 hours and then placed in an ASAP TM 2420 device. The isothermal adsorption curve and desorption curve of nitrogen adsorption and desorption at 77K are measured by the device, and the specific volume (V t ).

[0210] 4) Calculation of converted porosity and internal deposition index

[0211] W 碳 Assume 1g, D 碳 Set to 2.1 g / cm 3 , D Si Set to 2.33 g / cm 3 , the D measured for each embodiment and comparative example P , R Si and V t Substituting into equations 1 to 3, the converted porosity and internal deposition index are calculated.

[0212] (2) Evaluation of capacity retention rate

[0213] The lithium half cells of Examples and Comparative Examples were charged (CC / CV 0.5C 0.01V 0.01C cutoff) and discharged (CC 0.1C 3.0V cutoff) 50 times, and the capacity retention was evaluated by dividing the 50th discharge capacity by the 1st discharge capacity.

[0214] The measurement results and evaluation results are shown in Tables 1 and 2 below.

[0215] [Table 1]

[0216]

[0217] [Table 2]

[0218]

[0219] Referring to Table 1 and Table 2, the capacity retention rate of the examples having a converted porosity of 5% to 25.1% is improved compared with the comparative example.

[0220] The capacity retention rates of Examples 1 to 4 and 9, which have a converted porosity of 8.5% to 22.6% and an internal deposition index of 1.01 to 1.55, are relatively improved.

[0221] The capacity retention rates of Examples 5 to 8, in which the internal deposition index is outside the range of 1.0 to 2.0, are relatively reduced.

[0222] The capacity retention rate of Example 9 including the carbon coating layer is relatively improved.

Claims

1. A negative electrode active material for a lithium secondary battery, the negative electrode active material for a lithium secondary battery comprising composite particles, the composite particles comprising: a carbon-based particle comprising pores; and a silicon-containing coating formed on the surface of the carbon-based particles, in, The composite particles have a converted porosity of 5% to 25.1% as defined by the following formula 1: [Formula 1] In formula 1, D 碳 is the density of carbon and is expressed in g / cm 3 , D Si is the density of silicon and is expressed in g / cm 3 , D P is the density of the composite particles measured using a helium pycnometer and is expressed in g / cm 3 , W Si is the weight of silicon contained in the composite particles and is expressed in g, W 碳 is the weight of carbon contained in the composite particles and the unit is g.

2. The negative electrode active material for lithium secondary battery according to claim 1, wherein W in formula 1 Si Calculated by the following formula 2: [Formula 2] In formula 2, R Si is the ratio of the weight of silicon contained in the silicon-containing coating to the total weight of the composite particles measured by inductively coupled plasma (ICP) analysis, W 碳 is the weight of carbon contained in the composite particles and the unit is g.

3. The negative electrode active material for lithium secondary battery according to claim 1, wherein D 碳 2.1g / cm 3 , D Si 2.33 g / cm 3 .

4. The negative electrode active material for lithium secondary battery according to claim 1, wherein The carbon-based particles comprise an amorphous structure.

5. The negative electrode active material for lithium secondary battery according to claim 1, wherein Silicon contained in the silicon-containing coating layer includes an amorphous structure.

6. The negative electrode active material for lithium secondary battery according to claim 1, wherein The internal deposition index of the composite particles represented by the following Formula 3 is 1.0 to 2.0: [Formula 3] In Formula 3, V t is the specific volume of the pores of the carbon-based particles and is expressed in cm 3 / g,D 碳 is the density of carbon and is expressed in g / cm 3 , D Si is the density of silicon and is expressed in g / cm 3 , D P is the density of the composite particles measured using a helium pycnometer and is expressed in g / cm 3 , W Si is the weight of silicon contained in the composite particles and is expressed in g, W 碳 is the weight of carbon contained in the composite particles and the unit is g.

7. The negative electrode active material for lithium secondary battery according to claim 6, wherein W in Formula 3 Si Calculated by the following formula 2: [Formula 2] In formula 2, R Si is the ratio of the weight of silicon contained in the silicon-containing coating to the total weight of the composite particles measured by inductively coupled plasma (ICP) analysis, W 碳 is the weight of carbon contained in the composite particles and the unit is g.

8. The negative electrode active material for lithium secondary battery according to claim 6, wherein D 碳 2.1g / cm 3 , D Si 2.33 g / cm 3 .

9. The negative electrode active material for lithium secondary battery according to claim 6, wherein V t The measurement was performed by the nitrogen adsorption-desorption method.

10. The negative electrode active material for lithium secondary battery according to claim 1, wherein The composite particle further includes a carbon coating formed on the silicon-containing coating.

11. The negative electrode active material for lithium secondary battery according to claim 1, wherein The pores include a shape bent from the outermost portion of the carbon-based particle toward the inner portion of the carbon-based particle.

12. The negative electrode active material for lithium secondary battery according to claim 1, wherein The pores include closed cells separated from the exterior of the carbon-based particle by the silicon-containing coating.

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

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