Lithium secondary battery

Abstract

A lithium secondary battery comprises a positive electrode comprising a first positive electrode active material comprising a lithium-nickel-transition metal composite oxide as a positive electrode active material and a second positive electrode active material comprising a lithium-nickel oxide having a molar ratio of lithium to nickel greater than 1 and less than 2, a negative electrode comprising a silicon-based active material as a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode. Through the second positive electrode active material, expansion of the lithium secondary battery can be suppressed and high-temperature stability can be improved.

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery. More specifically, it relates to a lithium secondary battery comprising a lithium metal oxide-based positive electrode active material. Background Technology

[0002] Rechargeable batteries are batteries capable of repeated charging and discharging, and with the advancement of the information and communication and display industries, they are widely applied as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Furthermore, recently, battery packs containing rechargeable batteries are being developed and applied as power sources for eco-friendly vehicles, such as hybrid cars.

[0003] Examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-hydrogen batteries; among these, active research and development is being conducted on lithium-ion batteries due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0004] A lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an outer casing, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0005] Lithium metal oxides can be used as active materials for the positive electrode of a lithium secondary battery. Nickel-based lithium metal oxides can be cited as examples of the lithium metal oxides. In addition, carbon-based active materials such as graphite can be used as active materials for the negative electrode of a lithium secondary battery.

[0006] As the application range of lithium-ion batteries expands, there is a growing demand for longer lifespan, higher capacity, and operational stability. Accordingly, the development of cathode and anode active materials capable of providing higher capacity is underway. However, when cathode and anode active materials capable of providing high capacity are used, chemical and mechanical stability may be compromised, potentially leading to a deterioration in the lifespan characteristics of the secondary battery.

[0007] For example, Korean Registered Patent No. 10-0548988 discloses a method for manufacturing a positive electrode active material for a lithium secondary battery, but there are limitations in ensuring sufficient lifespan characteristics and stability. Prior art literature

[0008] Korean Registered Patent No. 10-0548988 The problem to be solved

[0009] One objective of the present invention is to provide a lithium secondary battery having improved capacity and lifespan stability. means of solving the problem

[0010] A lithium secondary battery according to exemplary embodiments comprises a positive electrode comprising a first positive electrode active material comprising a lithium-nickel-transition metal composite oxide as a positive electrode active material and a second positive electrode active material comprising a lithium-nickel oxide having a molar ratio of lithium to nickel greater than 1 and less than 2, a negative electrode comprising a silicon-based active material as a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode.

[0011] In some embodiments, the lithium-nickel oxide is LixNiO2(1 <x<2)로 표시될 수 있다.

[0012] In some embodiments, the second positive active material may include a surface coating or surface doping comprising Al, Ti, Ba, Zr, Si, B, Mg, P, V, W, alloys thereof and / or oxides thereof.

[0013] In some embodiments, the first positive active material may include a compound represented by the following chemical formula 1.

[0014] [Chemical Formula 1]

[0015] Li 1+a Ni 1-(x+y) Co x M y O2

[0016] In Chemical Formula 1, -0.05≤α≤0.15, 0.01≤x≤0.3, 0.01≤y≤0.3, and M is one or more selected elements selected from Mn, Mg, Sr, Ba, B, Al, Si, Ti, Zr, P, or W.

[0017] In some embodiments, the first positive electrode active material comprises a nickel-cobalt-manganese-based lithium oxide, and the molar ratio of nickel among the nickel, cobalt, and manganese included in the first positive electrode active material may be 0.6 to 0.9.

[0018] In some embodiments, the content of the second positive active material among the positive active materials may be 1 to 10 weight percent.

[0019] In some embodiments, the negative electrode active material may include a mixture of the silicon-based active material and the carbon-based active material.

[0020] In some embodiments, the content of the silicon-based active material in the total weight of the negative electrode active material may be 5 to 30 weight percent.

[0021] In some embodiments, the amount of LiOH remaining on the surface of the second positive active material may be 20,000 ppm or less, and the amount of Li2CO3 remaining on the surface of the second positive active material may be 8,000 ppm or less.

[0022] In some embodiments, the amount of LiOH remaining on the surface of the second positive active material may be 15,000 ppm or less, and the amount of Li2CO3 remaining on the surface of the second positive active material may be 5,000 ppm or less.

[0023] A lithium secondary battery according to exemplary embodiments comprises a positive electrode comprising a first positive electrode active material comprising a nickel-cobalt-manganese-based lithium oxide having a molar ratio of nickel among nickel, cobalt, and manganese of 0.6 to 0.9, and a second positive electrode active material comprising a lithium-nickel oxide having a molar ratio of lithium to nickel greater than 1, a negative electrode comprising a silicon-based active material as a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode. The amount of LiOH remaining on the surface of the second positive electrode active material is 15,000 ppm or less, and the amount of Li2CO3 remaining on the surface of the second positive electrode active material is 5,000 ppm or less.

[0024] In some embodiments, the amount of LiOH remaining on the surface of the second positive active material may be 20,000 ppm or less, and the amount of Li2CO3 remaining on the surface of the second positive active material may be 8,000 ppm or less.

[0025] In some embodiments, the second positive electrode active material may include a surface coating or surface doping comprising at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, V, W, alloys thereof and oxides thereof.

[0026] In some embodiments, the molar ratio of nickel in the nickel-cobalt-manganese-based lithium oxide of the first positive electrode active material may be 0.8 to 0.9. Effects of the invention

[0027] According to embodiments of the present invention, the positive electrode of a lithium secondary battery comprises, for example, a first positive electrode active material comprising nickel-cobalt-manganese-based lithium oxide, LixNiO2 (1 <x<2)로 표시된 제2 양극 활물질을 함께 사용할 수 있다.

[0028] The lifespan stability of the lithium secondary battery can be improved by suppressing the excessive shrinkage / expansion of the electrode that occurs when using a silicon-based negative electrode active material through the above-mentioned second positive active material.

[0029] In addition, residual lithium impurities can be effectively removed from the second positive electrode active material through a washing process, thereby improving the high-temperature stability and high-temperature capacity characteristics of the lithium secondary battery. Brief explanation of the drawing

[0030] FIGS. 1 and FIGS. 2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments. Figures 3 and 4 are graphs showing the changes in cycle characteristics at room temperature (25°C) and high temperature (45°C), respectively, for the lithium secondary batteries of the examples and comparative examples. Specific details for implementing the invention

[0031] According to embodiments of the present invention, a lithium secondary battery comprising a silicon-based negative electrode active material and a plurality of lithium-nickel-based positive electrode active materials is provided.

[0032] Embodiments of the present invention will be described in more detail below with reference to the drawings. However, the following drawings attached to this specification are intended to illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the aforementioned description; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0033] FIGS. 1 and FIGS. 2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments.

[0034] Referring to FIGS. 1 and 2, a lithium secondary battery may include an electrode assembly comprising a positive electrode (100), a negative electrode (130), and a separator (140) interposed between the positive electrode and the negative electrode, and the electrode assembly may be impregnated and contained together with an electrolyte in a case (160).

[0035] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed by coating a negative electrode active material onto the negative electrode current collector (125).

[0036] According to exemplary embodiments, the negative electrode active material may include a silicon-based active material. The silicon-based active material is SiO₂ X (0 <x<2) 또는 리튬 화합물이 포함된 SiOx(0<x<2)를 포함할 수 있다.

[0037] SiOx containing a lithium compound may be SiOx containing lithium silicate. Lithium silicate is SiOx(0 <x<2) 입자의 적어도 일부에 존재할 수 있으며, 예를 들면, SiOx(0<x<2) 입자의 내부 및 / 또는 표면에 존재할 수 있다. 일 실시예에 있어서, 리튬 실리케이트는 Li2SiO3, Li2Si2O5, Li4SiO4, Li4Si3O8등을 포함할 수 있다.

[0038] In some embodiments, the negative electrode active material may include a silicon-carbon-based active material. The silicon-carbon-based active material may include, for example, silicon carbide (SiC) or silicon-carbon particles having a core-shell structure. The silicon-carbon particles may be formed, for example, by depositing a silicon layer on the surface of a graphite core. In one embodiment, the silicon-carbon particles may be formed by coating a silicon layer on commercially available graphite particles through a chemical vapor deposition (CVD) process using a silicon precursor compound, such as a silane-based compound.

[0039] Conventionally, carbon-based active materials such as graphite have been mainly used as the negative electrode active material, and the theoretical capacity of the carbon-based material is limited to about 370 mAh / g. However, according to exemplary embodiments, by using the silicon-based active material and / or silicon-carbon-based active material as the negative electrode active material, the output and capacity characteristics of the secondary battery can be significantly improved beyond the theoretical capacity limit of the carbon-based active material.

[0040] In some embodiments, the negative electrode active material may further include a carbon-based active material together with the silicon-based active material.

[0041] The above carbon-based active material may include, for example, crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0042] Examples of the above-mentioned amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF). Examples of the above-mentioned crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0043] Preferably, the negative electrode active material may include natural graphite or artificial graphite together with the silicon-based active material. More preferably, a mixture of natural graphite and artificial graphite may be used as the carbon-based active material.

[0044] In some embodiments, the content of the carbon-based active material in the total weight of the negative electrode active material may be greater than the content of the silicon-based active material. Accordingly, while securing capacity amplification through the silicon-based active material, excessive electrode shrinkage / expansion caused by the silicon-based active material can be suppressed as described below.

[0045] In a preferred embodiment, the carbon-based active material may be included in a range of about 70 to 95 weight% and the silicon-based active material in a range of about 5 to 30 weight% of the total weight of the negative electrode active material.

[0046] For example, the above-mentioned cathode active material can be prepared in the form of a slurry by mixing and stirring it together with a binder, conductive material, thickener, etc. in a solvent. The cathode (130) can be prepared by coating the slurry onto at least one surface of a cathode current collector (125), and then drying and compressing it.

[0047] The negative current collector (125) may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include copper or a copper alloy.

[0048] The above binder may include, for example, organic binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, and polymethylmethacrylate, or water-based binders such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0049] Preferably, as a binder for the cathode, a water-based binder such as styrene-butadiene rubber (SBR) may be used for compatibility with carbon-based active materials, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0050] In one embodiment, an acrylic binder may be used together with an SBR-based binder to suppress electrode expansion caused by the silicon-based active material. For example, the acrylic binder may include polyacrylic acid (PAA) and / or polyacrylamide.

[0051] The above conductive material may be included to promote electron transfer between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0052] The positive electrode (100) may include a positive electrode active material layer (110) formed by applying a positive electrode active material to a positive electrode current collector (105). The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0053] In exemplary embodiments, the positive electrode active material may comprise a first positive electrode active material comprising a lithium-nickel-transition metal composite oxide and a second positive electrode active material comprising a lithium-nickel oxide (LNO).

[0054] For example, the first positive electrode active material may further include at least one of cobalt (Co) or manganese (Mn) as a transition metal. Preferably, the first positive electrode active material may include a Ni-Co-Mn (NCM) based lithium oxide.

[0055] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by employing a high-nickel (High-Ni) composition in the first cathode active material, a high-output cathode and a high-output lithium secondary battery can be provided.

[0056] However, as the Ni content increases, the long-term storage stability and lifespan stability of the anode or secondary battery may relatively decrease. However, according to exemplary embodiments, lifespan stability and capacity retention characteristics can be improved through Mn while maintaining electrical conductivity by including Co.

[0057] In some embodiments, the positive electrode active material or the lithium-transition metal composite oxide particles may further include a coating element or a doping element. For example, the coating element or doping element may include Al, Ti, Ba, Zr, Si, B, Mg, P, W, alloys thereof, or oxides thereof. These may be used alone or in combination of two or more. The positive electrode active material particles may be passivated by the coating or doping element, thereby further improving stability against penetration by external objects and lifespan.

[0058] For example, the first positive active material can be represented by the following chemical formula 1.

[0059] [Chemical Formula 1]

[0060] Li 1+a Ni 1-(x+y) Co x M y O2

[0061] In the above chemical formula 1, -0.05≤α≤0.15, 0.01≤x≤0.3, 0.01≤y≤0.3, and M may be one or more selected elements selected from Mn, Mg, Sr, Ba, B, Al, Si, Ti, Zr, P, or W.

[0062] Preferably, in Formula 1, the molar ratio of nickel (1-(x+y)) may be 0.6 to 0.9, more preferably 0.8 to 0.9.

[0063] As described above, the second positive electrode active material may include lithium-nickel oxide (LNO). According to exemplary embodiments, the molar ratio of lithium to nickel in the lithium-nickel oxide may be greater than 1.

[0064] In some embodiments, the molar ratio of lithium to nickel in the lithium-nickel oxide may be greater than 1 and less than 2. In this case, for example, the second positive electrode active material is LixNiO2(1 <x<2)로 표시되는 리튬-니켈 산화물을 포함할 수 있다.

[0065] The first positive electrode active material may be included as a main positive electrode active material related to the output and capacity of the lithium secondary battery. The second positive electrode active material may be included as a sub-positive electrode active material that improves the high-temperature stability of the lithium secondary battery.

[0066] As described above, when a silicon-based active material is used as the negative electrode active material, the shrinkage / expansion of the electrode is intensified, which may lead to the consumption of the electrolyte and gas generation due to cracks in the active material particles. For example, when discharging a lithium secondary battery, the voltage in the silicon-based active material increases rapidly, which may lead to electrode shrinkage / expansion and electrolyte consumption at the end of the discharge.

[0067] However, according to exemplary embodiments, the positive voltage at the discharge end can be rapidly reduced by the second positive active material, thereby suppressing the rise in negative voltage. Thus, the action of the silicon-based active material at the discharge end can be reduced, and the reuse of the silicon-based active material can be reduced, thereby effectively suppressing electrode shrinkage / expansion.

[0068] In addition, the self-active capacity of the second positive active material can compensate for the decrease in energy density caused by the limitation of silicon-based active material operation at the discharge end. Therefore, a lithium secondary battery with improved charge / discharge cycle characteristics and energy characteristics can be realized.

[0069] In some embodiments, the second positive electrode active material may be used after removing or reducing unreacted lithium residue remaining on the surface through a washing process. Accordingly, gas generation during high-temperature operation caused by the unreacted lithium residue can be suppressed.

[0070] In some embodiments, the second positive active material may further include surface doping or coating. For example, the surface doping or coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, V, W, alloys thereof, or oxides thereof. These may be used alone or in combination of two or more.

[0071] As described above, lithium impurities remaining on the surface of the second positive electrode active material can be reduced through a washing process. During the washing process, as the lithium impurities are removed or separated, damage such as cracks may occur on the surface of the second positive electrode active material, or the active sites may be excessively exposed.

[0072] In this case, leaching of lithium or transition metals may occur from the exposed damaged area or active site. Consequently, alteration of the active material particle structure or crystal structure may occur, and adverse reactions with the electrolyte due to repeated charge / discharge cycles may be accelerated.

[0073] However, as described above, by introducing doping or coating to the surface of the second positive active material, damage propagation on the particle surface can be blocked, and the leaching of transition metals and deformation of the particle structure can be prevented.

[0074] Therefore, it is possible to achieve high capacity characteristics through the removal of lithium impurities, as well as lifespan stability and side reaction suppression effects through particle surface protection.

[0075] In addition, as described above, to secure high energy density as the first positive active material, for example, a lithium-nickel-transition metal composite oxide with a high-Ni composition having a nickel molar ratio of 0.6 or higher or 0.8 or higher may be used. As the nickel content in the first positive active material increases, the lifespan characteristics may deteriorate due to surface instability caused by an increase in impurities on the surface of the first positive active material.

[0076] However, a second positive active material with a suppressed amount of surface impurities according to exemplary embodiments can be used together to buffer the reduction in operational stability resulting from the adoption of a High-Ni composition. In addition, as described above, since the positive voltage at the discharge end can be rapidly reduced by using the second positive active material together, the shrinkage / expansion of the electrode can be effectively suppressed.

[0077] For example, the first and second positive electrode active materials can be prepared by reacting a lithium salt with a transition metal precursor, such as a nickel precursor, a manganese precursor, or a cobalt precursor. The transition metal precursor may include transition metal halides, hydroxides, acid salts, etc.

[0078] The above lithium salt may include, for example, lithium hydroxide (LiOH) or lithium carbonate (Li2CO3). As a transition metal precursor for the production of the first cathode active material, for example, a Ni-Co-Mn-based oxide or hydroxide may be used. As a transition metal precursor for the production of the second cathode active material, nickel oxide, nickel hydroxide, nickel sulfate, etc. may be used.

[0079] A preliminary positive electrode active material can be obtained by reacting the lithium salt and the transition metal precursor in a wet (e.g., solution precipitation reaction) or dry (e.g., solid-state mixing / grinding reaction). Unreacted lithium salt (LiOH or Li2CO3) may remain on the surface of the preliminary positive electrode active material. Accordingly, the preliminary positive electrode active material can be washed with water to at least partially remove the unreacted lithium residue.

[0080] The above-described first positive active material or second positive active material can be obtained by drying or heat-treating the above-described preliminary positive active material that has been washed.

[0081] According to exemplary embodiments, the amount of LiOH remaining on the surface of the second positive active material may be about 20,000 ppm or less, preferably about 15,000 ppm or less. The amount of Li2CO3 remaining on the surface of the second positive active material may be about 8,000 ppm or less, preferably about 5,000 ppm or less.

[0082] For example, as the preliminary cathode active material for forming the second cathode active material is washed, lithium impurities are removed, and the molar ratio of Li to Ni can be reduced to less than 2. The washed particles can be mixed with a compound containing the aforementioned doping or coating element and heat-treated to introduce doping or coating onto the surface of the second cathode active material.

[0083] In some embodiments, the content of the second positive active material among the positive active materials may be about 1 to 10 weight%, preferably about 1 to 5 weight%. Within this range, voltage reduction at the discharge end is prevented, and electrode shrinkage / expansion caused by the silicon-based active material can be effectively suppressed.

[0084] A slurry can be prepared by mixing and stirring the above positive active material with a binder, a conductive material and / or a dispersant, etc., in a solvent. After coating the slurry onto a positive current collector (105), a positive active material layer (110) can be prepared by compressing and drying.

[0085] The positive current collector (105) may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include aluminum or an aluminum alloy.

[0086] The aforementioned materials used when forming the cathode may be used as the binder and conductive material. In some embodiments, a PVDF-based binder may be used as the anode binder. In this case, the amount of binder for forming the anode active material layer can be reduced, and the amount of the anode active material can be relatively increased, thereby improving the output and capacity of the secondary battery.

[0087] A separator (140) may be interposed between the anode (100) and the cathode (130). The separator (140) may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. The separator (140) may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0088] In some embodiments, the area (e.g., the contact area with the separator (140)) and / or volume of the negative electrode (130) may be larger than that of the positive electrode (100). Accordingly, lithium ions generated from the positive electrode (100) can move smoothly to the negative electrode (130) without precipitating in the middle, for example. Thus, the effect of capacity and output improvement due to the adoption of the silicon-based negative electrode active material described above can be more easily realized.

[0089] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of electrode 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, laminating, folding, etc., of the separator (140).

[0090] A lithium secondary battery can be defined by housing an electrode assembly (150) together with an electrolyte within a case (160). According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0091] The non-aqueous electrolyte comprises a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - It is expressed as and the anion (X) of the above lithium salt - As 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 - Examples of the back can be given.

[0092] Examples of the above organic solvents may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used individually or in combination of two or more.

[0093] As illustrated in FIG. 1, electrode tabs (positive tabs and negative tabs) may protrude from the positive current collector (105) and negative current collector (125) belonging to each electrode cell, respectively, and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (170) to form electrode leads (positive lead (107) and negative lead (127)) that extend or are exposed to the outside of the case (170).

[0094] The above lithium secondary battery can be manufactured in, for example, a cylindrical, prismatic, pouch, or coin type using a can.

[0095] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, these embodiments are merely illustrative of the invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0096] Example 1

[0097] Li[Ni as the first positive active material 0.8 Co 0.1 Mn0.1 ]O296 wt%, water-washed LixNiO2 as the second positive active material (1 <x<2) 4중량%를 혼합한 양극 활물질을 준비하였다. 상기 양극 활물질 , A slurry was prepared by mixing carbon nanotubes (CNT) as a conductive material and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 98.08:0.72:1.2. The slurry was uniformly coated onto an aluminum foil 12 μm thick and vacuum dried at 130°C to produce a positive electrode for a lithium secondary battery.

[0098] 87 wt% of a 9:1 weight ratio mixture of artificial graphite and natural graphite and SiO₂ as the cathode active material x (0 <x<2) 13중량% 혼합된 블렌드를 사용하였다. 상기 음극 활물질 96.25중량%, 도전재로 SWCNT 0.25중량%, 바인더로 스티렌-부타디엔 러버(SBR) 2.0중량% 및 증점제로 카르복시메틸 셀룰로오스(CMC) 1.5중량%를 포함하는 음극 슬러리를 제조하였다. 상기 음극 슬러리를 구리 기재 위에 코팅, 프레스 및 건조를 실시하여 음극을 제조하였다.

[0099] The anode and cathode manufactured as described above were each laminated by performing a predetermined notching, and a separator (polyethylene, thickness 15 μm) was interposed between the anode and cathode to form an electrode cell, after which the tab portions of the anode and cathode were welded. The welded combination of anode / separator / cathode was placed inside a pouch, and three sides excluding the surface for electrolyte injection were sealed. At this time, the portion containing the electrode tabs was included in the sealing portion. Electrolyte was injected through the remaining surfaces excluding the sealing portion, and after sealing the remaining surfaces, the mixture was impregnated for at least 12 hours.

[0100] The electrolyte used was prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), and then adding 5 wt% FEC (Florinated Ethylene Carbonate), 0.5 wt% PS (Propane Sulfone), and 0.5 wt% ESA (ethylene sulfate).

[0101] For the secondary battery manufactured as described above, pre-charging was subsequently performed for 49 minutes at a current (20A) corresponding to 0.25C. After 12 hours, degasing was performed, and after aging for more than 24 hours, formation charge and discharge were performed (charging conditions CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharging conditions CC 0.2C 2.5V CUT-OFF).

[0102] Example 2

[0103] LixNiO2 (1 containing a boron (B) coating as a second positive active material <x<2)가 사용된 것을 제외하고는 실시예 1과 동일한 방법으로 리튬 이차 전지를 제조하고, 화성 충방전을 실시하였다.

[0104] Specifically, LixNiO2(1 <x<2) 입자들을 0분간 교반하며 수세 후, 150℃ 진공 오븐에서 24시간 건조하였다. 건조된 활물질과 H3BO3400ppm을 건식 고속 혼합기에 투입하고 5분 동안 균일하게 혼합하였다. 상기 혼합물을 소성로에서 300℃에서 5시간 동안 열처리하여 붕소 코팅된 제2 양극 활물질을 제조하였다.

[0105] Comparative Example 1

[0106] Li[Ni as a positive electrode active material 0.88 Co 0.1 Mn 0.02 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 100 wt% of ]O2 was used, and a formation charge and discharge were performed.

[0107] Comparative Example 2

[0108] A lithium secondary battery was manufactured in the same manner as in Example 1, except that Li2NiO2 was used as the second positive active material, and a charging and discharging process was performed.

[0109] Comparative Example 3

[0110] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNiO2 was used as the second positive active material, and a charging and discharging process was performed.

[0111] Experimental Example

[0112] (1) Recharge / Discharge Capacity

[0113] For the secondary batteries according to the examples and comparative examples, the initial charge and discharge capacities were measured after performing the formation charge and discharge as described above. The measurement results are shown in Table 1 below.

[0114] Mars charging capacity (mAh / g) Mars discharge capacity (mAh / g) Example 1 234.3 201.9 Example 2 233.9 201.4 Comparative Example 1 228.0 198.5 Comparative Example 2 234.0 201.6 Comparative Example 3 229.3 199.7

[0115] Referring to Table 1, a relatively lower conversion charge capacity was measured in Comparative Example 1, where the first positive electrode active material was used alone, compared to the examples.

[0116] (2) Evaluation of room temperature (25℃) and high temperature (45℃) cycle characteristics

[0117] For the lithium secondary batteries according to the examples and comparative examples, cycle characteristics (change in discharge capacity) were confirmed by repeatedly performing charge / discharge with 1 / 3C charge and 0.5C discharge as one cycle.

[0118] FIGS. 3 and FIGS. 4 are graphs showing the changes in cycle characteristics at room temperature (25°C) and high temperature (45°C), respectively, for the lithium secondary batteries of the examples and comparative examples.

[0119] Referring to FIGS. 3 and 4, in Comparative Example 1, where the first positive electrode active material was used alone, the cycle characteristics at room temperature were significantly degraded. In Comparative Example 2, where Li2NiO2 was used as the second positive electrode active material, the cycle characteristics at high temperature were significantly degraded. In Comparative Example 3, where LiNiO2 was used as the second positive electrode active material, the cycle characteristics at room temperature were significantly degraded.

[0120] (3) Evaluation of high-temperature (60℃) storage characteristics

[0121] For the secondary batteries of the examples and comparative examples, the SOC was charged to 96% (CC-CV 1.0 C 4.2V 0.05C CUT-OFF), stored in a 60-degree chamber, and the week in which cell venting occurred was measured, and the discharge capacity retention rate (%) at the time adjacent to when cell venting occurred was evaluated relative to the initial discharge capacity.

[0122] The evaluation results are shown in Table 2 below.

[0123] Cell venting occurs Capacity retention rate (%) at the time of cell venting Example 1 13 weeks 12 weeks, 90.8% Example 2 17 weeks 16 weeks, 91.5% Comparative Example 1 17 weeks 16%, 91.6% Comparative Example 2 8 weeks 8 weeks, 90.1% Comparative Example 3 15 weeks 12 weeks, 91.1%

[0124] Additionally, for the secondary batteries of the examples and comparative examples, the amount of gas (mL) generated inside the chamber until cell venting appeared was measured at regular intervals. The evaluation results are shown in Table 3 below.

[0125] 4 weeks 8 weeks 12 weeks 14 weeks 16 weeks Example 1 180 285 380 - - Example 2 156 248 324 360 395 Comparative Example 1 130 225 308 350 388 Comparative Example 2 220 350 (7 weeks later) - - - Comparative Example 3 140 245 330 380 -

[0126] Referring to Tables 2 and 3, LixNiO2 (1 <x<2) 대신 Li2NiO2가 사용된 비교예 2에서 고온 안정성이 실시예들에 비해 현저히 열화되었다.

[0127] Meanwhile, in the case of Example 2, in which a boron coping was introduced into the second cathode active material, improved high-temperature capacity and gas generation suppression characteristics were secured.

[0128] From the results of the experimental examples described above, LixNiO2(1 <x<2)을 제2 양극 활물질로 도입함에 따라, 향상된 상온 용량 특성을 확보하면서 안정적인 고온 저장 특성이 유지되었다. 또한, 보론 코팅 도입을 통해 고온 저장 특성 역시 추가적으로 향상되었다.

[0129] (4) Measurement of residual lithium in the second positive electrode active material

[0130] In a 250 mL flask, the second positive active material (LixNiO2 (1) of Example 1 <x<2)) 및 비교예 2 및 3의 제2 양극 활물질(Li2NiO2) 5.0g을 각각 정량 하고 탈이온수 100g을 넣은 후, 마그네틱 바를 넣고 4 rpm의 속도로 10분간 교반하였다. 이 후 감압 플라스크를 이용하여 필터링 후 50g을 분취하였다. 분취한 용액을 자동 측정기(Auto titrator) 용기에 넣고 Wader Method를 참고하여 0.1N HCl로 자동 적정하여 용액 내 LiOH 및 Li2CO3값을 측정하였다.

[0131] The measurement results are shown in Table 4 below.

[0132] LiOH Li2CO3 Example 1 12,860 ppm 4,356 ppm Comparative Example 2 34,586 ppm 9,675 ppm Comparative Example 3 7,660 ppm 2,240 ppm

[0133] Referring to Table 4, the unreacted lithium residue in the second cathode active material used in the example was significantly reduced. In the case of Comparative Example 2, the high-temperature cycle characteristics were significantly degraded as shown in Figure 4 due to the increase in unreacted lithium residue.

[0134] (5) ICP analysis

[0135] The molar ratio of Li to metal (Ni) was measured through elemental analysis of the second cathode active material used in Example 1 and Comparative Examples 2 and 3 using a high-frequency inductively coupled plasma (HFP) apparatus, and the results are shown in Table 5 below. That is, in Example 1, Comparative Example 2, and Comparative Example 3, LixNiO2(1 <x<2), Li2NiO2및 LiNiO2가 사용되었음을 확인하였다.

[0136] Li / Ni measured molar ratio Example 1 1.898 Comparative Example 2 2.098 Comparative Example 3 1.00 Explanation of the symbols

[0137] 100: Anode 105: Anode current collector 110: Positive electrode active material layer 120: Negative electrode active material layer 125: Cathode current collector 130: Cathode 140: Separator 150: Electrode assembly 160: Case

Claims

Claim 1 A first positive active material comprising a compound represented by the following chemical formula 1, comprising a lithium-nickel-transition metal complex oxide as a positive active material, and LixNiO2(1 <x<2)로 표시되는 리튬-니켈 산화물을 포함하는 제2 양극 활물질을 포함하는 양극;음극 활물질로서 규소계 활물질을 포함하는 음극; 및상기 양극 및 음극 사이에 배치된 분리막을 포함하고,상기 제2 양극 활물질 표면에 잔류하는 LiOH의 양은 15,000ppm 이하이고, 상기 제2 양극 활물질 표면에 잔류하는 Li2CO3의 양은 5,000 ppm 이하인, 리튬 이차 전지:[화학식 1]Li 1+a Ni 1-(x+y) Co x M y O2 (of Chemical Formula 1, -0.05≤α≤0.15, 0.01≤x≤0.3, 0.01≤y≤0.3, and M is one or more elements selected from Mn, Mg, Sr, Ba, B, Al, Si, Ti, Zr, P, or W). Claim 2 delete Claim 3 A lithium secondary battery according to claim 1, wherein the second positive active material comprises a surface coating or surface doping comprising at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, V, W, alloys thereof, and oxides thereof. Claim 4 delete Claim 5 A lithium secondary battery according to claim 1, wherein the first positive electrode active material comprises a nickel-cobalt-manganese-based lithium oxide, and the molar ratio of nickel among the nickel, cobalt, and manganese included in the first positive electrode active material is 0.6 to 0.

9. Claim 6 A lithium secondary battery according to claim 1, wherein the content of the second positive active material among the positive active materials is 1 to 10 weight%. Claim 7 A lithium secondary battery according to claim 1, wherein the negative electrode active material comprises a mixture of the silicon-based active material and the carbon-based active material. Claim 8 A lithium secondary battery according to claim 7, wherein the content of the silicon-based active material in the total weight of the negative electrode active material is 5 to 30 weight%. Claim 9 delete Claim 10 delete Claim 11 A first positive active material comprising a nickel-cobalt-manganese-based lithium oxide having a molar ratio of nickel among nickel, cobalt, and manganese of 0.6 to 0.9 as a positive active material, and LixNiO2(1 <x<2)로 표시되는 리튬-니켈 산화물을 포함하는 제2 양극 활물질을 포함하는 양극; 및상기 양극에 대향하도록 배치되고 음극 활물질로서 규소계 활물질을 포함하는 음극; 및상기 양극 및 음극 사이에 배치된 분리막을 포함하고,상기 제2 양극 활물질 표면에 잔류하는 LiOH의 양은 15,000ppm 이하이고, 상기 제2 양극 활물질 표면에 잔류하는 Li2CO3의 양은 5,000 ppm 이하인, 리튬 이차 전지. Claim 12 delete Claim 13 A lithium secondary battery according to claim 11, wherein the second positive active material comprises a surface coating or surface doping comprising at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, V, W, alloys thereof and oxides thereof. Claim 14 A lithium secondary battery according to claim 11, wherein the molar ratio of nickel in the nickel-cobalt-manganese-based lithium oxide of the first positive electrode active material is 0.8 to 0.9.

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