KR20210037657A - Negative active material for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery and to a lithium secondary battery comprising the same. The negative electrode active material includes: primary particles of a crystalline carbon-based material; and secondary particles to which the primary particles are assembled, wherein the ratio of the average particle diameter (D50) of the secondary particles to the average particle diameter (D50) of the primary particles (average particle diameter (D50) of the secondary particles/average particle diameter (D50) of the primary particles) is 1.5 to 5, and the aspect ratio of the primary particles is 1 to 7.

Description

Anode active material for lithium secondary batteries and lithium secondary batteries including the same {NEGATIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING SAME}

It relates to a negative active material for a lithium secondary battery and a lithium secondary battery including the same.

Lithium secondary batteries are mainly used as a driving power source for mobile information terminals such as mobile phones, notebook computers, and smart phones, or electric vehicles.

The lithium secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte. At this time, the cathode active material of the positive electrode is composed of lithium and a transition metal having a structure capable of intercalating lithium ions such as _{LiCoO 2} , LiMn ₂ O ₄ , and LiNi _1-x Co _x O _{2 (0 <x <1).} Oxide is mainly used.

As the negative active material, various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of intercalation/deintercalation of lithium may be mainly used.

In recent years, the miniaturization and weight reduction of mobile information terminals has rapidly progressed, and a higher capacity of a lithium secondary battery, which is a driving power source thereof, has been demanded, and wireless charging and a short charging time are also required. In particular, charging for a long time is the biggest inconvenience that users feel, so a short charging time is the most demanded.

One embodiment is to provide a negative active material for a lithium secondary battery excellent in charge rate characteristics and discharge rate characteristics.

Another embodiment is to provide a lithium secondary battery including the negative active material.

One embodiment of the present invention includes primary particles of a crystalline carbon-based material and secondary particles in which the primary particles are assembled, and the average particle diameter of the secondary particles relative to the average particle diameter (D50) of the primary particles (D50) ratio (average particle diameter of the secondary particles (D50)/average particle diameter of the primary particles (D50)) is 1.5 to 5, and the aspect ratio of the primary particles is 1 to 7 lithium secondary It provides a negative active material for batteries.

The average particle diameter (D50) of the primary particles may be 3 μm to 10 μm, and may be 5 μm to 10 μm.

The average particle diameter (D50) of the secondary particles may be 10 μm to 25 μm.

The crystalline carbonaceous material may be artificial graphite, natural graphite, or a combination thereof. According to another embodiment, the crystalline carbon-based material may be artificial graphite, and may be a needle-cokes type or a mosaic-cokes type artificial graphite.

_{In the X-ray diffraction pattern of the negative active material, I (002)} /I _{(110), which} is an X-ray diffraction intensity ratio of the (002) plane and the (110) plane, may be 50 to 270.

The negative active material may further include a Si-based or Sn-based material.

_{In the X-ray diffraction pattern of the negative electrode active material, I (002)} /I ₍₁₁₀₎ , which is the ratio of the X-ray diffraction intensity of the (002) plane and the (110) plane, and the pellet density of the negative electrode active material are in the following equation 1 It may be to have.

[Equation 1]

29 ≤ [(I ₍₀₀₂₎ /I ₍₁₁₀₎ ) / pellet density (cc/g)] ≤140

In another embodiment, a negative electrode including the negative active material; A positive electrode including a positive electrode active material; And it provides a lithium secondary battery including an electrolyte.

Other specifics of the embodiments of the present invention are included in the detailed description below.

The negative active material for a lithium secondary battery according to an embodiment may exhibit excellent electrolyte impregnation properties, charge rate and discharge rate characteristics, particularly high rate charge/discharge characteristics.

1 is a schematic view showing the structure of a rechargeable lithium battery according to an embodiment of the present invention.
Figure 2 is a graph showing by measuring the electrolyte impregnation characteristics of the slurry pellets of Examples 4 to 13 and Comparative Examples 4 to 12.
3 is a graph showing X-ray diffraction characteristics measured for the powder pellets of Examples 14 to 19 and Comparative Examples 13 to 20.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

The negative active material for a lithium secondary battery according to an embodiment of the present invention includes primary particles of a crystalline carbon-based material and secondary particles in which the primary particles are assembled.

Unless otherwise defined herein, the average particle diameter (D50) refers to the diameter of particles having a cumulative volume of 50% by volume in a particle size distribution.

In addition, the ratio of the average particle diameter (D50) of the secondary particles to the average particle diameter (D50) of the primary particles, that is, the average particle diameter of the secondary particles (D50) / the average particle diameter of the primary particles (D50) is 1.5 To 5 may be. When the average particle diameter (D50) of the secondary particles / the average particle diameter (D50) of the primary particles is 1.5 to 5, there may be an advantage in terms of difficult orientation (難配向性, random-orientation). That is, if the degree of disorder is increased due to excellent difficult orientation, lithium ions can be easily inserted into the negative active material during charging, which is appropriate.

The aspect ratio of the primary particles may be 1 to 7 and may be 1 to 5.

When the aspect ratio of the primary particles is out of 1 to 7, the negative electrode active material has a reduced orientation property, and thus rate characteristics are deteriorated, which is not appropriate.

As described above, in the negative active material according to an embodiment, the average particle diameter (D50) of the secondary particles / the average particle diameter (D50) of the primary particles is 1.5 to 5, and the average aspect ratio of the primary particles is 1 to 7 As a result, as the degree of disorder of the particles increases as the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) and the aspect ratio of the primary particles are adjusted within the above range, the electrolyte impregnation property can be improved. In addition, charging and discharging characteristics may be improved to exhibit excellent charging and discharging rate characteristics. In addition, the negative active material may have improved swelling characteristics.

If even one of the average particle diameter of the secondary particles (D50) / the average particle diameter of the primary particles (D50) and the aspect ratio of the primary particles does not satisfy the above range, electrolyte impregnation and difficult orientation are reduced. It is not appropriate in terms of rate characteristics.

In addition, the average particle diameter (D50) of the primary particles may be 3 μm to 10 μm, and may be 5 μm to 10 μm. When the average particle diameter (D50) of the primary particles is out of the above range, the rate characteristics are deteriorated as the poor orientation and impregnating properties of the electrolyte are reduced, which is not appropriate.

The average particle diameter (D50) of the secondary particles may be 10 μm to 25 μm. When the average particle diameter (D50) of the secondary particles is out of the above range, the rate characteristics are deteriorated as the non-alignment property and the impregnating property of the electrolyte solution decrease, and thus it is not appropriate.

The crystalline carbonaceous material may be artificial graphite, natural graphite, or a combination thereof. According to another embodiment, the crystalline carbon-based material may be artificial graphite, for example, needle-cokes type or mosaic-cokes type artificial graphite. In the case of using artificial graphite, particularly needle coke artificial graphite or mosaic coke artificial graphite as the crystalline carbon-based material, a higher charge/discharge capacity can be obtained, which is appropriate. The needle coke-type artificial graphite refers to artificial graphite produced by graphitizing and heat-treating needle coke, and the mosaic coke-type artificial graphite refers to artificial graphite produced by graphitizing and heat-treating mosaic coke.

In addition, the negative active material may further include a Si-based or Sn-based material. When the Si-based or Sn-based material is further included, the mixing ratio of the crystalline carbon-based material and the Si-based or Sn-based material may be 99.9:0.1 to 20:80 by weight. When the mixing ratio of the crystalline carbon-based material and the Si-based or Sn-based material is included in the above range, the expansion problem due to further inclusion of the Si-based and Sn-based material is reduced, and battery charging/discharging efficiency can be further improved, It is suitable because it can further increase the lifespan.

As the Si-based or Sn-based material, Si, Si-C composite, SiO _x (0 <x <2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 It is an element selected from the group consisting of elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Si), Sn, SnO ₂ , Sn-R alloy (where R is an alkali metal, alkaline earth metal, group 13 An element selected from the group consisting of an element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and combinations thereof, and not Sn), and the like. Further, at least one of these and SiO ₂ may be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, What is selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

_{In the X-ray diffraction pattern of the negative active material, I (002)} /I _{(110), which} is an X-ray diffraction intensity ratio of the (002) plane and the (110) plane, may be 50 to 270, and may be 50 to 230. have. The X-ray diffraction pattern is measured using CuKα rays unless specifically limited. In addition, the peak intensity ratio represents the height ratio of the peak.

_{In particular, when adjusting the X-ray diffraction intensity ratio (I (002)} /I ₍₁₁₀₎ ) of the (002) plane and the (110) plane according to the pellet density of the negative active material, the tendency for each pellet density can be identified. , More appropriate properties can be obtained depending on the pellet density, More appropriate. An appropriate ratio of the X-ray diffraction intensity of the (002) plane and the (110) plane, I ₍₀₀₂₎ /I ₍₁₁₀₎ ]/pellet density may have a relationship of Equation 1 below.

[Equation 1]

29 ≤ [(I ₍₀₀₂₎ /I ₍₁₁₀₎ ) / pellet density (cc/g)] ≤140

Following an embodiment, the I ₍₀₀₂₎ /I ₍₁₁₀₎ ) / pellet density may be 29 to 125.

The pellet density may be a slurry pellet density. Slurry pellets are prepared by mixing an active material and a binder in a solvent to prepare a negative electrode active material slurry, drying the slurry, pulverizing, and applying a certain pressure to the powder. This is generally known in the art. Even if the details are omitted, it is clear that the contents can be easily understood by those in the field. When preparing the negative active material slurry, a conductive material may be further added.

When the X-ray diffraction property of the negative active material according to the embodiment is included in the above range, it can be seen that the degree of difficult orientation is improved.

The negative active material according to the exemplary embodiment of the present invention may be manufactured by a general negative active material manufacturing process well known in the art, and this will be briefly described.

Primary particles having an average particle diameter (D50) of 3 μm to 10 μm, preferably 5 μm to 10 μm are prepared. This primary particle may be a crystalline carbon-based material.

The primary particles and the binder are mixed and assembled to form secondary particles.

The ratio of the average particle diameter (D50) of the secondary particles to be formed may be 1.5 to 5 with respect to the average particle diameter (D50) of the primary particles (that is, the average particle diameter of the secondary particles (D50)/ The average particle diameter (D50) of the primary particles is 1.5 to 5). The average particle diameter (D50) of the secondary particles may be 10 μm to 25 μm.

The binder may be a coal-based pitch or a petroleum-based pitch. The mixing ratio of the primary particles and the binder may be 5: 5 to 9.9: 0.1 weight ratio. When the mixing ratio of the primary particles and the binder is included in the above range, secondary particles having an average particle diameter (D50) of a desired size may be formed.

The mixing and granulation process may be performed under general granulation process conditions in which secondary particles are formed using primary particles.

Another embodiment of the present invention provides a lithium secondary battery including a negative electrode including the negative electrode active material, a positive electrode including the positive electrode active material, and an electrolyte.

The negative electrode includes a negative active material layer including the negative active material, and a current collector supporting the negative active material.

In the negative active material layer, the content of the negative active material may be 95% to 99% by weight based on the total weight of the negative active material layer.

In one embodiment of the present invention, the negative active material layer includes a binder, and may optionally further include a conductive material. The content of the binder in the negative active material layer may be 1% to 5% by weight based on the total weight of the negative active material layer. In addition, when a conductive material is further included, 90 to 98% by weight of the negative active material, 1 to 5% by weight of the binder, and 1 to 5% by weight of the conductive material may be used.

The binder serves to attach the negative active material particles well to each other, and also serves to attach the negative active material to the current collector well. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

As the water-insoluble binder, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluorine rubber, and combinations thereof. The polymer resin binder is polypropylene, ethylene propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, poly It may be one selected from ester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more types of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K or Li may be used as the alkali metal. The content of the thickener may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

The conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, any material may be used as long as it does not cause chemical change and is an electron conductive material. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

The current collector may be selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

The positive electrode includes a positive electrode active material layer and a current collector supporting the positive electrode active material. In the positive electrode active material layer, the amount of the positive electrode active material may be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

In one embodiment of the present invention, the positive active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1% to 5% by weight, respectively, based on the total weight of the positive electrode active material layer.

As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (reitiated intercalation compound) may be used.

Specifically, it is possible to use one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. As a more specific example, a compound represented by any one of the following formulas may be used. Li _a A _1-b X _b D ₂ (0.90≦a≦1.8, 0≦b≦0.5); Li _a A _1-b X _b O _2-c D _c (0.90 <a <1.8, 0 <b <0.5, 0 <c <0.05); Li _a E _1-b X _b O _2-c D _c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); Li _a E _2-b X _b O _4-c D _c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 <α ≤ 2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Co _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b X _c O _2-α T ₂ (0.90 <a <1.8, 0 <b <0.5, 0 <c <0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li _a NiG _b O ₂ (0.90 <a <1.8, 0.001 <b <0.1) Li _a CoG _b O ₂ (0.90 <a <1.8, 0.001 <b <0.1); Li _a Mn _1-b G _b O ₂ (0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn _1-g G _g PO ₄ (0.90≦a≦1.8, 0≦g≦0.5); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦f≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦f≦2); Li _a FePO ₄ (0.90 ≤ a ≤ 1.8)

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Of course, one having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer contains at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. I can. The compound constituting these coating layers may be amorphous or crystalline. As a coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. The coating layer forming process may be any coating method as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (e.g., spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the relevant field, detailed description will be omitted.

The content of the positive active material may be 90% to 98% by weight based on the total weight of the positive active material layer.

In one embodiment of the present invention, the positive active material layer may include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1% to 5% by weight, respectively, based on the total weight of the positive electrode active material layer.

The binder adheres well the positive electrode active material particles to each other, and also plays a role in attaching the positive electrode active material to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, and polyvinyl Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any material can be used as long as it does not cause chemical change and is an electronic conductive material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen Carbon-based materials such as black and carbon fiber; Metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

As the current collector, an aluminum foil, a nickel foil, or a combination thereof may be used, but the present invention is not limited thereto.

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of a battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used.

As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, and caprolactone. Etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like may be used. In addition, cyclohexanone or the like may be used as the ketone-based solvent. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms) as the aprotic solvent. , A double bonded aromatic ring or an ether bond), such as nitriles, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used. .

The organic solvent may be used alone or as a mixture of one or more, and the mixing ratio in the case of using one or more mixtures may be appropriately adjusted according to the desired battery performance, which may be widely understood by those engaged in the field. have.

In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the electrolyte may exhibit excellent performance.

The organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound of Formula 1 may be used.

[Formula 1]

(In Formula 1, R ₁ to R ₆ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.)

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 ,2,4-trichlorobenzene, iodobenzene, 1,2-diaiodobenzene, 1,3-diaiodobenzene, 1,4-diaiodobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-diaiodotoluene, 2,4-diaiodotoluene, 2,5-diaiodotoluene, 2,3,4-triiodotoluene, 2,3 It is selected from the group consisting of, 5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of Formula 2 as a life-improving additive in order to improve battery life.

[Formula 2]

(In Formula 2, R ₇ and R ₈ are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms. , _{At least one of R 7} and R ₈ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that both _{R 7} and R _{8 are} It is not hydrogen.)

Representative examples of the ethylene-based carbonate-based compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. Can be lifted. In the case of further use of the life-improving additive, the amount of the additive can be appropriately adjusted.

The lithium salt is a material that is dissolved in an organic solvent and acts as a source of lithium ions in the battery, enabling the operation of a basic lithium secondary battery, and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers, for example It is an integer of 1 to 20), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (supporting one or two or more selected from the group consisting of lithium bis(oxalato) borate: LiBOB) It is included as an electrolytic salt It is preferable to use the lithium salt concentration within the range of 0.1M to 2.0 M. If the concentration of the lithium salt falls within the above range, the electrolyte has an appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited, Lithium ions can move effectively.

Depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. Polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used as such a separator, and a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, a polypropylene/polyethylene/poly It goes without saying that a mixed multilayer film such as a three-layer propylene separator may be used.

1 shows an exploded perspective view of a rechargeable lithium battery according to an embodiment of the present invention. A lithium secondary battery according to an embodiment is described as an example of a prismatic shape, but the present invention is not limited thereto, and may be applied to various types of batteries such as a cylindrical shape and a pouch type.

Referring to FIG. 1, a rechargeable lithium battery 100 according to an embodiment includes an electrode assembly 40 wound between a positive electrode 10 and a negative electrode 20 through a separator 30, and the electrode assembly 40. ) May include a built-in case 50. The anode 10, the cathode 20, and the separator 30 may be impregnated with an electrolyte (not shown).

Hereinafter, examples and comparative examples of the present invention will be described. The following examples are only examples of the present invention, and the present invention is not limited to the following examples.

(Example 1)

Primary particles having an average particle diameter (D50) of 9.0 µm and an aspect ratio of 1 to 5, formed of needle-coke artificial graphite, were mixed with a binder pitch in a ratio of 9:1 by weight and assembled, so that the average particle diameter (D50) was 20.5 µm. A phosphorus secondary particle negative active material was prepared. In the prepared negative active material, the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) was 2.28.

(Example 2)

Primary particles having an average particle diameter (D50) of 5.0 µm and an aspect ratio of 1 to 5, formed of needle-coke type artificial graphite, were mixed with a binder pitch in a weight ratio of 8:2 and assembled, and the average particle diameter (D50) was 13.5 µm. A phosphorus secondary particle negative active material was prepared. In the prepared negative active material, the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) was 2.70.

(Example 3)

Primary particles having an average particle diameter (D50) of 9.0 µm and an aspect ratio of 1 to 5, formed of needle-coke artificial graphite, were mixed with a binder pitch in a ratio of 9:1 by weight and assembled, and the average particle diameter (D50) was 18.4 µm. A phosphorus secondary particle negative active material was prepared. In the prepared negative active material, the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) was 2.04.

(Comparative Example 1)

Primary particles having an average particle diameter (D50) of 9.0 μm and an aspect ratio of 1 to 5, formed of needle-coke artificial graphite, were mixed with a binder pitch in a weight ratio of 9:1 and assembled, and the average particle diameter (D50) was 13.3 μm. A phosphorus secondary particle negative active material was prepared. In the prepared negative active material, the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) was 1.48.

(Comparative Example 2)

A secondary particle negative electrode having an average particle diameter (D50) of 15.2 μm by mixing and assembling primary particles having an average particle diameter (D50) of 12.0 μm and an aspect ratio of 1 to 5 with a binder pitch, formed of needle-coke artificial graphite An active material was prepared. In the prepared negative active material, the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) was 1.27.

(Comparative Example 3)

Secondary particle negative electrode having an average particle diameter (D50) of 18.0 μm by mixing and assembling primary particles having an average particle diameter (D50) of 8.0 μm and an aspect ratio of 8 to 9 with a binder pitch, formed of needle-coke artificial graphite An active material was prepared. In the prepared negative active material, the average particle diameter of the secondary particles (D50)/the average particle diameter of the primary particles (D50) was 2.25.

* Electrolyte impregnation experiment

A negative active material slurry was prepared by mixing 97.5% by weight of an anode active material prepared according to Examples 1 to 3 and Comparative Examples 1 to 3, 1.0% by weight of carboxymethylcellulose, and 1.5% by weight of styrene-butadiene rubber in a water solvent. A slurry pellet made of an active material and a binder was prepared by applying the pressure shown in Table 1 to the prepared slurry. The prepared slurry pellets were named Examples 4 to 13 and Comparative Examples 4 to 12.

Negative active material Pressure(ton) Slurry pellet density (g/cc) Comparative Example 4 Comparative Example 1 0.52 1.33 Comparative Example 5 Comparative Example 1 0.76 1.42 Comparative Example 6 Comparative Example 1 1.10 1.53 Comparative Example 7 Comparative Example 1 1.79 1.65 Example 4 Example 1 1.20 1.38 Example 5 Example 1 1.50 1.43 Example 6 Example 1 2.00 1.50 Example 7 Example 1 3.00 1.59 Example 8 Example 1 4.60 1.66 Example 9 Example 2 2.00 1.52 Example 10 Example 2 3.00 1.71 Example 11 Example 3 1.00 1.54 Example 12 Example 3 1.50 1.68 Example 13 Example 3 2.00 1.79 Comparative Example 8 Comparative Example 2 0.75 1.45 Comparative Example 9 Comparative Example 2 1.00 1.56 Comparative Example 10 Comparative Example 2 1.50 1.67 Comparative Example 11 Comparative Example 3 0.75 1.47 Comparative Example 12 Comparative Example 3 1.00 1.58

Thereafter, _{50 µl of a mixed solvent of ethylene carbonate and dimethyl carbonate in which 1M LiPF 6} was dissolved (3:7 volume ratio) was carefully added dropwise onto the pellet, and the lid was covered to prevent evaporation of the electrolyte, and the time until the electrolyte was completely moistened. Was measured. The results are shown in FIG. 2. As shown in FIG. 2, the slurry pellets of Examples 4 to 13 using the negative active material of Examples 1 to 3 were subjected to electrolytic solution impregnation compared to the slurry pellets of Comparative Examples 4 to 12 using the negative active material of Comparative Examples 1 to 3. You can see that the time is very short. Therefore, since the electrolyte solution impregnation rate (movement speed) of the negative electrode active materials of Examples 1 to 3 is much shorter than that of the negative electrode active materials of Comparative Examples 1 to 3, the internal resistance of the battery decreases, and as a result, it can be predicted that it is advantageous in terms of life retention rate have.

According to this result, the average particle diameter (D50) of the secondary particles / the average particle diameter (D50) of the primary particles deviate from 1.5 to 5 (Comparative Examples 4 to 10), or the aspect ratio of the primary particles is 1-7. If it deviates (Comparative Examples 11 and 12), it can be seen that the electrolyte impregnation property is deteriorated.

* X-ray diffraction property evaluation

A negative active material slurry was prepared by mixing 97.5% by weight of an anode active material prepared according to Examples 1 to 3 and Comparative Examples 1 to 3, 1.0% by weight of carboxymethylcellulose, and 1.5% by weight of styrene-butadiene rubber in a water solvent. A slurry pellet made of an active material and a binder was prepared by applying the pressure shown in Table 2 below to the prepared slurry. The prepared slurry pellets were named Examples 14 to 19 and Comparative Examples 13 to 20.

Negative active material Pressure(ton) Slurry pellet density (g/cc) Comparative Example 13 Comparative Example 1 1.1 1.36 Comparative Example 14 Comparative Example 1 1.79 1.43 Comparative Example 15 Comparative Example 1 2.10 1.55 Example 14 Example 1 1.50 1.43 Example 15 Example 1 4.60 1.66 Example 16 Example 2 3.00 1.71 Example 17 Example 2 4.00 1.83 Example 18 Example 3 1.00 1.54 Example 19 Example 3 1.50 1.68 Comparative Example 16 Comparative Example 2 0.75 1.45 Comparative Example 17 Comparative Example 2 1.00 1.56 Comparative Example 18 Comparative Example 2 1.50 1.67 Comparative Example 19 Comparative Example 3 0.75 1.47 Comparative Example 20 Comparative Example 3 1.00 1.58

The prepared powder pellets were subjected to X-ray diffraction (XRD) using CuKα rays to obtain the intensity of the (002) plane and the (110) plane. From this result, the peak intensity ratio I ₍₀₀₂₎ /I ₍₁₁₀₎ was obtained, and the results are shown in Table 3 and Fig. 3 below. In addition, using the measured peak intensity ratio I ₍₀₀₂₎ /I ₍₁₁₀₎ and the slurry pellet density value shown in Table 2, (I ₍₀₀₂₎ /I ₍₁₁₀₎ ) / slurry pellet density value was obtained, and the following It is shown in Table 3.

Negative active material I ₍₀₀₂₎ /I ₍₁₁₀₎ [I ₍₀₀₂₎ /I ₍₁₁₀₎ ]/Slurry pellet density, (cc/g) Comparative Example 13 Comparative Example 1 200 147.06 Comparative Example 14 Comparative Example 1 230 160.84 Comparative Example 15 Comparative Example 1 249 160.65 Example 14 Example 1 80 55.94 Example 15 Example 1 110 66.27 Example 16 Example 2 155 90.64 Example 17 Example 2 220 120.22 Example 18 Example 3 75 48.70 Example 19 Example 3 77 45.83 Comparative Example 16 Comparative Example 2 210 144.83 Comparative Example 17 Comparative Example 2 252 161.54 Comparative Example 18 Comparative Example 2 270 161.68 Comparative Example 19 Comparative Example 3 267 181.63 Comparative Example 20 Comparative Example 3 290 183.54

As shown in Figure 3, the peak intensity ratio I (002) / I (110) of the pellets of Examples 14 to 19 using the negative active material of Examples 1 to 3 is 77 to 220, [I ₍₀₀₂₎ /I ₍₁₁₀₎ ]/Slurry pellet density is 45.83cc/g to 120.22cc/g, whereas the peak intensity ratio I(002)/I(110) of the pellets of Comparative Examples 13 to 20 using the negative electrode active material of Comparative Examples 1 to 3 ) Is 200 to 290, and [I ₍₀₀₂₎ /I ₍₁₁₀₎ ]/slurry pellet density is 144.83cc/g to 183.54cc/g. According to this result, the negative electrode active materials of Examples 1 to 3 It can be seen that the difficulty of orientation is excellent, that is, the degree of disorder increases. In particular, it can be seen that the negative electrode active material of Example 3 has the most excellent non-alignment properties. In addition, according to this result, the average particle diameter of the secondary particles (D50) / the average particle diameter of the primary particles (D50) deviated from 1.5 to 5 (Comparative Examples 13 to 18), or the aspect ratio of the primary particles was 1 to 7 When it deviates from (Comparative Examples 19 and 20), it can be seen that the poor orientation is lowered.

* Rate characteristics evaluation

A negative active material composition was prepared by mixing 97.5% by weight of the negative active material of Examples 1 to 3 and Comparative Examples 1 to 2, 1.0% by weight of carboxymethylcellulose, and 1.5% by weight of styrene-butadiene rubber in a water solvent. This negative electrode active material composition was applied to a Cu current collector to prepare a negative electrode.

Using the prepared negative electrode, a lithium metal counter electrode, and an electrolyte, a coin-shaped half-cell was manufactured by a conventional method. As the electrolyte, a mixed solvent (50:50 volume ratio) of ethylene carbonate and diethyl carbonate in which _{1.0M LiPF 6 was dissolved was used.} The prepared half-cells were named Examples 20 to 22 and Comparative Examples 21 and 23.

The prepared half-cell was charged and discharged once at 25°C and 0.2C, and the discharge capacity was measured. The measured discharge capacity is shown in Table 4 below.

In addition, the prepared half-cell was charged and discharged once at 25°C at 0.2C, once at 0.5C, once at 1.0C, once at 2.0C, and once at 3.0C to measure the charge/discharge capacity. . The 0.5C charging capacity ratio to the 0.2C charging capacity, the 1.0C charging capacity ratio to the 0.2C charging capacity, and the 2.0C charging capacity ratio to the 0.2C charging capacity were calculated, and the results are shown in Table 4 below. In addition, 1.0C discharge capacity ratio to 0.2C discharge capacity, 2.0C discharge capacity ratio to 0.2C discharge capacity, and 3.0C discharge capacity ratio to 0.2C discharge capacity were calculated, and the results are shown in Table 4 below.

Negative active material Pressure(ton) Slurry pellet density (g/cc) Comparative Example 13 Comparative Example 1 1.1 1.36 Comparative Example 14 Comparative Example 1 1.79 1.43 Comparative Example 15 Comparative Example 1 2.10 1.55 Example 14 Example 1 1.50 1.43 Example 15 Example 1 4.60 1.66 Example 16 Example 2 3.00 1.71 Example 17 Example 2 4.00 1.83 Example 18 Example 3 1.00 1.54 Example 19 Example 3 1.50 1.68 Comparative Example 16 Comparative Example 2 0.75 1.45 Comparative Example 17 Comparative Example 2 1.00 1.56 Comparative Example 18 Comparative Example 2 1.50 1.67 Comparative Example 19 Comparative Example 3 0.75 1.47 Comparative Example 20 Comparative Example 3 1.00 1.58

As shown in Table 4, the charge/discharge rate characteristics of the half-cells of Examples 20 to 22 using the negative active materials of Examples 1 to 3 were compared to the half-cells of Comparative Examples 21 to 23 using the negative active materials of Comparative Examples 1 to 3 It can be seen that it is superior compared to In particular, it can be seen that the high-rate characteristics of the half-cells of Examples 21 to 22 are much better than those of Comparative Examples 21 to 23. In addition, according to this result, the average particle diameter of the secondary particles (D50) / the average particle diameter of the primary particles (D50) deviated from 1.5 to 5 (Comparative Examples 21 and 22), or the aspect ratio of the primary particles was 1-7 It can be seen that the charge/discharge rate characteristics, particularly the high rate characteristics, are deteriorated in the case of deviating from (Comparative Example 23). Although a preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and the claims and invention It is possible to carry out various modifications within the scope of the detailed description and the accompanying drawings, and it is natural that this also falls within the scope of the present invention.

Claims (9)

Including primary particles of a crystalline carbon-based material and secondary particles in which the primary particles are assembled,
The ratio of the average particle diameter (D50) of the secondary particles to the average particle diameter (D50) of the primary particles (average particle diameter of the secondary particles (D50)/average particle diameter of the primary particles (D50)) is 1.5 to 5 ego,
The aspect ratio of the primary particles is 1 to 5
As a negative active material for lithium secondary batteries,
_{In the X-ray diffraction pattern of the negative active material, I (002)} /I _{(110), which} is an X-ray diffraction intensity ratio of the (002) plane and the (110) plane, is 50 to 230,
_{In the X-ray diffraction pattern of the negative active material, I (002)} / I ₍₁₁₀₎ , which is the ratio of the X-ray diffraction intensity of the (002) plane and the (110) plane, and the pellet density of the negative active material are the relationship of the following equation 1 Having a negative active material for a lithium secondary battery.
[Equation 1]
29 ≤ [(I ₍₀₀₂₎ /I ₍₁₁₀₎ )/pellet density (cc/g)] ≤ 140. The method of claim 1,
The average particle diameter (D50) of the primary particles is 3㎛ to 10㎛ negative active material for a lithium secondary battery. The method of claim 1,
The average particle diameter (D50) of the primary particles is 5㎛ to 10㎛ negative active material for a lithium secondary battery. The method of claim 1,
The negative active material for a lithium secondary battery having an average particle diameter (D50) of 10 μm to 25 μm of the secondary particles. The method of claim 1,
The crystalline carbon-based material is artificial graphite, natural graphite, or a combination thereof, a negative active material for a lithium secondary battery. The method of claim 1,
The crystalline carbon-based material is an artificial graphite negative active material for a lithium secondary battery. The method of claim 1,
The crystalline carbon-based material is a needle coke type or mosaic coke type artificial graphite negative active material for a lithium secondary battery. The method of claim 1,
The negative active material is a negative active material for a lithium secondary battery further comprising a Si-based or Sn-based material. A negative electrode comprising the negative active material of any one of claims 1 to 8;
A positive electrode including a positive electrode active material; And
Electrolyte
Lithium secondary battery comprising a.

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