Lithium secondary battery

Abstract

A lithium secondary battery according to an embodiment of the present invention comprises: a positive electrode comprising a positive electrode active material layer containing a positive electrode active material, the positive electrode active material comprising lithium-nickel-based metal oxide particles; and a negative electrode provided opposite to the positive electrode, in which peaks of the (101) plane, the (102) plane, the (104) plane, the (105) plane, and the (107) plane of the lithium-nickel-based metal oxide particles are measured by XRD analysis of the positive electrode active material layer, and the peaks of the (101) plane, the (102) plane, the (104) plane, the (105) plane, and the (107) plane of the lithium-nickel-based metal oxide particles are measured. The lattice strain (epsilon) of the lithium-nickel-based metal oxide particles as calculated by applying a Williamson-Hall method defined by a prescribed formula to the measured peaks of the (101) plane, the (102) plane, the (104) plane, the (105) plane, and the (107) plane of the lithium-nickel-based metal oxide particles is 0.2 to 0.4. Consequently, the capacity characteristics and lifetime characteristics of the lithium secondary battery are improved.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery. More specifically, the present invention relates to a positive electrode including a positive electrode active material containing lithium-nickel-based metal oxide particles and a lithium secondary battery including the positive electrode. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communications and display industries, they are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. Battery packs containing secondary batteries are also used as power sources 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 these, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and weight reduction.

[0004] For example, a lithium secondary battery may include an electrode assembly and an electrolyte impregnated with the electrode assembly, wherein the electrode assembly includes a positive electrode, a negative electrode, and a separator (separator). The lithium secondary battery may further include an outer packaging material for accommodating the electrode assembly and the electrolyte, such as an outer packaging material in the form of a soft pack.

[0005] Lithium secondary batteries store electrical energy through the difference in chemical potential when lithium ions are intercalated and deintercalated between the positive and negative electrodes. Therefore, lithium secondary batteries can use materials that allow lithium ions to be reversibly intercalated and deintercalated as positive and negative active materials.

[0006] For example, as the positive electrode active material, a lithium-metal composite oxide can be used. An example of the lithium-metal composite oxide is a lithium-nickel-based metal oxide. In the lithium-nickel-based metal oxide, the nickel content can be increased to achieve high energy density. Summary of the Invention

[0007] (1) Technical issues to be resolved

[0008] A technical problem of the present invention is to provide a lithium secondary battery having improved capacity characteristics and lifespan characteristics.

[0009] (2) Technical solution

[0010] A lithium secondary battery according to an exemplary embodiment may include: a positive electrode, the positive electrode including a positive electrode active material layer including a positive electrode active material, the positive electrode active material including lithium-nickel-based metal oxide particles; and a negative electrode, the negative electrode being arranged opposite to the positive electrode, wherein the lattice strain (ε) of the lithium-nickel-based metal oxide particles calculated by applying the Williamson-Hall method defined by Formula 1 to the peaks of the (101) plane, (102) plane, (104) plane, (105) plane, and (107) plane of the lithium-nickel-based metal oxide particles measured by performing XRD analysis on the positive electrode active material layer may be 0.2 to 0.4.

[0011] [Formula 1]

[0012]

[0013] In Formula 1, β may be the full width at half maximum (radians (rad)) of the corresponding peak obtained by XRD analysis, θ may be the diffraction angle (radians), ε may be the lattice strain (dimensionless number), λ may be the X-ray wavelength (Å), and D may be the crystallite size (Å).

[0014] In some embodiments, the lattice strain of the lithium-nickel-based metal oxide particles can be the slope of a straight line obtained as follows: obtaining the half-maximum full width of the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane appearing through the XRD analysis, substituting the obtained half-maximum full width into the formula 1, and plotting with sinθ as the horizontal axis and βcosθ as the vertical axis to obtain a straight line.

[0015] In some embodiments, the lattice strain of the lithium-nickel-based metal oxide particles may be 0.25 to 0.38.

[0016] In some embodiments, the lithium-nickel-based metal oxide particles may have a structure represented by the following Chemical Formula 1.

[0017] [Chemical Formula 1]

[0018] Li x Ni 1-y M y O 2+z

[0019] In Chemical Formula 1, x may be 0.95≤x≤1.1, y may be 0≤y≤0.7, z may be −0.1≤z≤0.1, and M may be at least one element of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

[0020] In some embodiments, in Chemical Formula 1, (1-y) may be 0.6 to 1.

[0021] In some embodiments, in Chemical Formula 1, M may include Mn.

[0022] In some embodiments, the lithium-nickel-based metal oxide particles may have a structure represented by the following Chemical Formula 2.

[0023] [Chemical Formula 2]

[0024] Li a Ni 1-b-c-d Co b Mn c J d O 2+e

[0025] In Chemical Formula 2, a may be 0.95≤a≤1.1, b may be 0≤b≤0.1, c may be 0≤c≤0.4, d may be 0≤d≤0.2, e may be -0.1≤e≤0.1, and J may be at least one element of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

[0026] In some embodiments, in Chemical Formula 2, (1-bcd) may be 0.6 to 1.

[0027] In some embodiments, in Chemical Formula 2, b may be 0 to 0.02.

[0028] In some embodiments, in Chemical Formula 2, c may be 0.05 to 0.35.

[0029] In some embodiments, in Chemical Formula 2, c may be 0.2 to 0.33.

[0030] In some embodiments, in Chemical Formula 2, (1-bcd) / c may be greater than 1.

[0031] (3) Beneficial effects

[0032] In a lithium secondary battery according to an exemplary embodiment, the positive electrode may include a positive electrode active material containing lithium-nickel-based metal oxide particles having a lattice strain of 0.2 to 0.4 calculated by applying the Williamson-Hall method defined by a specific formula to a predetermined XRD peak measured by XRD analysis. Therefore, the capacity characteristics and life characteristics of the lithium secondary battery can be improved.

[0033] In some embodiments, the lithium-nickel-based metal oxide particles may have a low cobalt content and high nickel and manganese contents. When the lattice strain is controlled to be 0.2 to 0.4, the manganese contained in the lithium-nickel-based metal oxide particles can be electrochemically activated, thereby improving the discharge capacity of the battery.

[0034] The positive electrode active material can be widely used in electric vehicles, battery charging stations, and other green technology fields such as solar power generation and wind power generation using batteries. The lithium secondary battery can be used in eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 and Figure 2 1 and 2 are respectively a schematic plan view and a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment.

[0036] Figures 3a to 3d The figures respectively show the slopes of Example 3, Example 4, Comparative Example 1 and Comparative Example 2 obtained as follows: the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane of the lithium-nickel-based metal oxide particles were obtained by performing XRD analysis on the positive electrode active material layers according to Example 3, Example 4, Comparative Example 1 and Comparative Example 2, the Williamson-Hall method was applied to the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane of the obtained lithium-nickel-based metal oxide particles, and the slopes were obtained by linear regression analysis.

[0037] Figure 4 Graph showing capacity retention rates of lithium secondary batteries according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0038] Description of reference numerals:

[0039] 100: positive electrode; 105: positive electrode current collector

[0040] 108: positive electrode lead; 110: positive electrode active material layer

[0041] 120: negative electrode active material layer; 125: negative electrode current collector

[0042] 128: negative lead; 130: negative electrode

[0043] 140: diaphragm; 150: electrode assembly

[0044] 160: Shell DETAILED DESCRIPTION

[0045] An embodiment of the present invention provides a lithium secondary battery including lithium-nickel-based metal oxide particles having crystallite strain within a specified range as a positive electrode active material.

[0046] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0047] Figure 1 and Figure 2 1 and 2 are respectively a schematic plan view and a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken along line II'.

[0048] Reference Figure 1 and Figure 2 The lithium secondary battery may include a positive electrode 100 and a negative electrode 130 , wherein the negative electrode 130 is disposed opposite to the positive electrode 100 .

[0049] The positive electrode 100 may include a positive active material layer 110 formed by coating a positive active material on a positive current collector 105. The positive active material may include a compound that can reversibly intercalate and deintercalate lithium ions.

[0050] In an exemplary embodiment, the positive active material may include lithium-nickel-based metal oxide particles. For example, the lithium-nickel-based metal oxide particles may further include at least one of cobalt (Co) and manganese (Mn).

[0051] In some embodiments, the lithium-nickel-based metal oxide particles may have a structure represented by the following Chemical Formula 1.

[0052] [Chemical Formula 1]

[0053] Li x Ni 1-y M y O 2+z

[0054] In Chemical Formula 1, x may be 0.95≤x≤1.1, y may be 0≤y≤0.7, z may be −0.1≤z≤0.1, and M may be at least one element of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

[0055] 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 (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.

[0056] 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 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.

[0057] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, 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, for example, together with Co or Mn.

[0058] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially identical to 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.

[0059] The coating element or the doping element may be present on the surface of the lithium-nickel-based metal oxide particle or permeate through the surface of the lithium-nickel-based metal oxide particle and be included in the bonding structure represented by the Chemical Formula 1.

[0060] In some embodiments, the molar ratio or concentration (1-y) of Ni in Chemical Formula 1 may be 0.6 to 1, for example, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.62 to 0.95, 0.65 to 0.9, or 0.7 to 0.85.

[0061] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. 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.

[0062] However, as the Ni content increases, the long-term storage stability and lifespan stability of the positive electrode or secondary battery may be relatively reduced, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain conductivity while the inclusion of Mn can improve lifespan stability and capacity retention characteristics.

[0063] In some embodiments, in Chemical Formula 1, M may include Mn, for example, M may consist of Mn. For example, when the content of expensive Co is reduced, the contents of Ni and Mn may be further increased, thereby improving capacity characteristics, thermal stability, and structural stability.

[0064] In some embodiments, the lithium-nickel-based metal oxide particles may have a structure represented by the following Chemical Formula 2.

[0065] [Chemical Formula 2]

[0066] Li a Ni 1-b-c-d Co b Mn c J d O 2+e

[0067] In Chemical Formula 2, a may be 0.95≤a≤1.1, b may be 0≤b≤0.1, c may be 0≤c≤0.4, d may be 0≤d≤0.2, e may be -0.1≤e≤0.1, and J may be at least one element of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

[0068] In some embodiments, in Chemical Formula 2, the molar ratio or concentration of Ni (1-bcd) may be 0.6 to 1, for example, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.62 to 0.95, 0.65 to 0.9, or 0.7 to 0.85.

[0069] In some embodiments, in Chemical Formula 2, the molar ratio or concentration b of Co may be 0 to 0.02, for example, 0 to 0.01 or 0. Co is a rare and expensive element, so reducing the content of Co can manufacture batteries in a more economical manner.

[0070] In some embodiments, in Chemical Formula 2, the molar ratio or concentration c of Mn may be 0.05 to 0.35, for example, 0.2 to 0.33, 0.22 to 0.32, 0.25 to 0.31, or 0.25 to 0.3.

[0071] For example, while achieving high capacity characteristics with Mn is difficult, electrochemical activation of Mn can improve the initial efficiency and discharge capacity of the battery. Therefore, even if the Co content is reduced, increasing the Mn content can improve lifespan stability and capacity retention.

[0072] In some embodiments, in Chemical Formula 2, the ratio of the molar ratio or concentration of Ni to the molar ratio or concentration of Mn (1-bcd) / c may be greater than 1, for example, greater than 2. Therefore, in the lithium secondary battery, not only high capacity and high power characteristics can be achieved, but also improved thermal stability and structural stability can be achieved.

[0073] In an exemplary embodiment, the lattice strain (ε) of the lithium-nickel-based metal oxide particles calculated as follows may be 0.2 to 0.4, that is, by performing XRD analysis on the positive active material layer to measure the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane of the lithium-nickel-based metal oxide particles, and applying the Williamson-Hall method defined by Formula 1 to the measured peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane of the lithium-nickel-based metal oxide particles, the lattice strain (ε) calculated may be 0.2 to 0.4.

[0074] [Formula 1]

[0075]

[0076] In Formula 1, β may be the full width at half maximum (radians) of the corresponding peak obtained by XRD analysis, θ may be the diffraction angle (radians), ε may be the lattice strain (dimensionless number), λ may be the X-ray wavelength (Å), and D may be the crystallite size (Å).

[0077] For example, by X-ray diffraction (XRD) analysis of the positive electrode active material layer, the XRD peaks of the positive electrode active material particles can be obtained, and the lattice strain of the positive electrode active material particles can be obtained by applying the Williamson-Hall method defined by Formula 1 to the obtained peaks. For example, the XRD peaks can be peaks of the (101) plane, (102) plane, (104) plane, (105) plane, and (107) plane of the lithium-nickel-based metal oxide particles.

[0078] In some embodiments, in Formula 1, β can use the full width at half maximum corrected for the value from the device. In one embodiment, Si can be used as a standard substance reflecting the value from the device. In this case, by plotting the full width at half maximum curve over the entire 2θ range of Si, the full width at half maximum from the device can be expressed as a function of 2θ. Thereafter, the value obtained by subtracting and correcting the full width at half maximum value from the device at the corresponding 2θ obtained from the function can be used as β.

[0079] For example, the XRD analysis can be performed on dry powder of lithium-nickel-based metal oxide particles using Cu Kα rays as a light source and at a scanning rate of 0.0065° / step within a diffraction angle (2θ) range of 10° to 120°.

[0080] For example, after measuring the full width at half maximum of the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane appearing in the above-mentioned diffraction angle range, the obtained measured value is substituted into Formula 1, and the slope is obtained by linear regression analysis, thereby calculating the lattice strain (Williamson-Hall method).

[0081] For example, the lattice strain can be defined as the slope of a straight line obtained by plotting sinθ in Formula 1 on the horizontal axis and βcosθ in Formula 1 on the vertical axis.

[0082] In some embodiments, the lattice strain may be from 0.2 to 0.4.

[0083] For example, when the lattice strain is less than 0.2, the initial structure of the lithium-nickel-based metal oxide particles may change significantly and deteriorate faster, thereby deteriorating the capacity retention rate of the lithium secondary battery.

[0084] For example, when the lattice strain is greater than 0.4, Mn contained in the lithium-nickel-based metal oxide particles may not be sufficiently electrochemically activated, and thus, the initial efficiency and discharge capacity of the lithium secondary battery may be deteriorated.

[0085] In some embodiments, the lattice strain of the lithium-nickel-based metal oxide particles can be 0.25 to 0.38, 0.28 to 0.38, 0.32 to 0.36, or 0.3 to 0.38. Within the above range, Mn can be electrochemically activated and can delay the degradation of the positive electrode active material. Therefore, the capacity characteristics and life characteristics of the lithium secondary battery can be improved.

[0086] In one embodiment, the lithium secondary battery can be subjected to a formation process, wherein the formation process is to impart electrical characteristics by charging and discharging the lithium secondary battery multiple times, for example, 2 to 5 times of charging and discharging. The lithium secondary battery that has undergone the formation process can be subjected to a driving process, wherein the driving process is to charge and discharge the lithium secondary battery that has undergone the formation process multiple times, for example, 3 to 5 times of charging and discharging.

[0087] In some embodiments, the formation voltage applied to the lithium secondary battery during the formation process may be higher than the driving voltage applied to the lithium secondary battery during the driving process. For example, the formation voltage may be 0.03V to 0.15V, 0.03V to 0.13V, or 0.05V to 0.1V higher than the driving voltage.

[0088] Within the above-mentioned difference range between the formation voltage and the driving voltage, the lattice strain can be easily adjusted to the above-mentioned range by changing the crystallite size (Å) in Formula 1.

[0089] The properties (e.g., lattice strain) of the lithium-nickel-based metal oxide particles according to embodiments of the present invention do not necessarily depend on the above conditions. For example, the crystallite size (Å) in Formula 1 may also vary depending on other factors including the charging and discharging speeds (current rates) of the lithium secondary battery, the temperature during the formation process, and the like, and thus the lattice strain value may vary.

[0090] In an exemplary embodiment, the lithium-nickel-based metal oxide particles may be formed by reacting a lithium precursor and a transition metal precursor (eg, a Ni—Co—Mn precursor).

[0091] For example, the transition metal precursor can be prepared by coprecipitation of metal salts, which may include nickel salts, manganese salts, and cobalt salts.

[0092] Examples of the nickel salt include nickel sulfate, nickel nitrate, nickel acetate, and hydrates thereof. Examples of the manganese salt include manganese sulfate, manganese acetate, and hydrates thereof. Examples of the cobalt salt include cobalt sulfate, cobalt nitrate, cobalt carbonate, and hydrates thereof.

[0093] The metal salts may be mixed with a precipitant and / or a chelating agent in a ratio satisfying the content or concentration ratio of each metal described with reference to Chemical Formulas 1 and 2 to prepare an aqueous solution. The aqueous solution may be co-precipitated in a reactor to prepare a transition metal precursor.

[0094] The precipitant may include alkaline compounds such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). The chelating agent may include, for example, ammonia water (eg, NH3.H2O), ammonium carbonate (eg, (NH4)2CO3), and the like.

[0095] The temperature of the coprecipitation reaction can be adjusted, for example, within a range of about 40° C. to 60° C. The reaction time can be adjusted within a range of about 24 hours to 72 hours.

[0096] For example, a transition metal precursor can be reacted with a lithium precursor and a doping element source containing a doping element to prepare lithium-nickel-based metal oxide particles. The lithium precursor compound can include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, etc. These can be used alone or in combination of two or more.

[0097] For example, the doping element source may include titanium dioxide, titanium butoxide, manganese sulfate hydrate, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, zirconium dioxide, yttria-stabilized zirconia, tungsten oxide, etc. These may be used alone or in combination of two or more.

[0098] Subsequently, a heat treatment (calcination) process may be performed to fix the metal particles or improve crystallinity. In one embodiment, the heat treatment temperature may be in the range of about 600°C to 1000°C.

[0099] The positive electrode active material comprising the lithium-nickel-based metal oxide particles can be mixed with a binder, a conductive material, and / or a dispersant in a solvent and stirred to prepare a slurry. The slurry can be coated on at least one side of the positive electrode current collector 105, dried, and rolled to produce the positive electrode 100.

[0100] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector is not limited thereto, but may be, for example, 10 μm to 50 μm.

[0101] The coating process can be performed by gravure coating, slot die coating, multi-layer simultaneous die coating, stamping, doctor blade coating, dip coating, bar coating, casting, and the like, but is not limited thereto. The positive electrode mixture may further include a binder and may optionally further include a conductive material, a thickener, and the like.

[0102] Non-limiting examples of the solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like.

[0103] The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as a positive electrode binder.

[0104] The conductive material may be added to enhance the conductivity and / or lithium ion or electron mobility 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, vapor-grown carbon fiber (VGCF), and carbon fiber, and / or metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0105] As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

[0106] 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 on the negative electrode current collector 125 .

[0107] The negative electrode active material may be any material known in the art that can intercalate and deintercalate lithium ions without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-based compounds; or tin-containing materials may be used.

[0108] Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fibers (MPCF).

[0109] Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0110] The lithium metal may include pure lithium metal or lithium metal formed with a protective layer for suppressing dendrite growth or the like. In one embodiment, the lithium metal-containing layer deposited or coated on the negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, the lithium thin film layer may be used as the negative electrode active material layer.

[0111] Examples of the elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0112] The silicon-based compound may include, for example, silicon (Si), silicon oxide (e.g., SiOx, 0 < x < 2), or silicon-carbon composite compounds such as silicon carbide (SiC).

[0113] For example, the negative electrode active material may be mixed and stirred together with the above-mentioned binder, conductive material, thickener, etc. in a solvent to form a slurry. The slurry may be coated on at least one surface of the negative electrode current collector 125 and then dried and calendered to manufacture the negative electrode 130.

[0114] The coating process may be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, knife coating, dip coating, bar coating, casting, etc., and is not limited thereto.

[0115] For example, non-limiting examples of the negative electrode current collector 125 include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, polymer substrates coated with conductive metals, etc. The negative electrode current collector is not limited thereto, but may be, for example, 10 μm to 50 μm.

[0116] Non-limiting examples of the solvent include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc.

[0117] As the binder, conductive material, and thickener, the above-mentioned substances that can be used in manufacturing the positive electrode may be used.

[0118] In some embodiments, the negative electrode binder may use styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid-based binders, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binders, etc.

[0119] In some embodiments, the negative electrode may further include a negative electrode active material layer in the form of lithium metal formed by a deposition / coating process.

[0120] In one embodiment, a separator 140 may be provided between the positive electrode 100 and the negative electrode 130. The separator can prevent a short circuit between the positive electrode and the negative electrode and maintain the flow of ions. According to the embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present invention is not limited thereto.

[0121] In some embodiments, the area of ​​the negative electrode 130 (eg, the area in contact with the separator 140) may be larger than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 may migrate smoothly to the negative electrode 130 without being precipitated in between.

[0122] For example, the separator 140 may include a porous polymer film made of a polyolefin-based polymer such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer.

[0123] For example, the separator 140 may include non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like.

[0124] For example, a battery cell may be formed by including a positive electrode 100, a negative electrode 130, and a separator 140. In addition, an electrode assembly 150 may be formed by stacking a plurality of battery cells. For example, the electrode assembly 150 may be formed by winding, stacking, zigzag folding, or stack-folding the separator 140.

[0125] The electrode assembly 150 may be housed in the case 160 together with an electrolyte, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0126] The non-aqueous electrolyte may contain a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - Indicates that, as the anion of the lithium salt (X - ), we can exemplify F - 、Cl - Br - , I - 、NO3- 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - 、 CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - wait.

[0127] The organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive in the battery. The organic solvent may include, for example, at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0128] The organic solvent may be propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, ethylpropyl 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), and the like. ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone and propylene sulfite. These can be used alone or in combination of two or more.

[0129] 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.

[0130] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0131] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

[0132] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0133] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0134] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, and the like.

[0135] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0136] The borate-based compound may include lithium bis(oxalate) borate, and the like.

[0137] like Figure 1 As shown, the tabs (positive tabs or negative tabs) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the case 160. The tabs may be fused together and connected to the electrode lead (positive lead 108 or negative lead 128) extending to the outside of the case 160.

[0138] For example, the lithium secondary battery may be manufactured in a cylindrical shape, a prismatic shape, a pouch type, a coin type, or the like using a can.

[0139] The following further describes the embodiments of the present invention with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are intended only to illustrate the present invention and are not intended to limit the scope of the claims. Various changes and modifications to the embodiments may be made within the scope and technical concept of the present invention, which will be apparent to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0140] Example 1

[0141] (1) Preparation of lithium-nickel-based metal oxide particles

[0142] Using distilled water that had been bubbled with N2 for 24 hours to remove dissolved oxygen, NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.75:0:0.25. The above solution was added to a reactor at 50°C, and NaOH and NH3·H2O were used as precipitants and chelating agents for a co-precipitation reaction for 72 hours to obtain Ni as a transition metal precursor. 0.75 Mn 0.25 The obtained precursor was dried at 100° C. for 12 hours and then dried again at 120° C. for 10 hours.

[0143] Lithium hydroxide and the transition metal precursor are added to a dry high-speed mixer at a ratio of 1.02:1 and mixed evenly for 5 minutes. The mixture is placed in a calcining furnace, heated to 730°C to 780°C at a rate of 2°C / min, and maintained at 730°C to 780°C for 10 hours. During the heating and holding process, oxygen is continuously introduced at a flow rate of 20L / min. After the calcination is completed, it is naturally cooled to room temperature, and crushed and classified to obtain LiNi 0.75 Mn 0.25 Lithium-nickel based metal oxide particles composed of O2.

[0144] (2) Manufacturing of lithium secondary batteries

[0145] The obtained lithium-nickel-based metal oxide particles are used as a positive electrode active material to prepare a lithium secondary battery.

[0146] Specifically, the positive electrode active material, acetylene black (Denka Black) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 97:2:1 to prepare a positive electrode mixture. The prepared positive electrode mixture was coated on an aluminum current collector, dried, and rolled to produce a positive electrode.

[0147] A negative electrode slurry was prepared, comprising 93% by weight of natural graphite as the negative electrode active material, 5% by weight of a flake-type conductive material (KS6) as the conductive material, 1% by weight of styrene-butadiene rubber (SBR) as the binder, and 1% by weight of carboxymethyl cellulose (CMC) as the thickener. The negative electrode slurry was coated on a copper substrate, dried, and rolled to produce a negative electrode.

[0148] The positive electrode and negative electrode prepared as described above are respectively cut (notching) and stacked, and a separator (polyethylene, 12 μm thick) is set between the positive electrode and the negative electrode to form a battery cell, and then the tab parts of the positive electrode and the negative electrode are welded respectively. The welded positive electrode / separator / negative electrode assembly is placed in a soft bag, and the three surfaces except the electrolyte injection surface are sealed. At this time, the portion with the tab is included in the sealing portion. The electrolyte is injected through the non-sealed portion, the remaining surfaces mentioned above are pressed, and immersed for more than 12 hours.

[0149] The electrolyte used was a solution of 1 M LiPF6 dissolved in a mixed solvent of EC / EMC (20 / 80; volume ratio).

[0150] Subsequently, the secondary battery prepared as described above was pre-charged for 50 minutes with a current (5A) corresponding to 0.24C. ​​After about 12 hours, degassing was performed and the battery was aged for more than 24 hours. The battery was then subjected to formation charge-discharge (charging condition CC-CV 0.24C 4.30V 0.05C cut-off (CUT-OFF), and discharge condition CC 0.24C 2.5V cut-off). The secondary battery was then further transported and charged (charging condition CC-CV 0.24C 4.30V SOC 30% cut-off). The secondary battery transported after the formation process was driven under the following charge-discharge conditions (charging condition CC-CV 0.1C to 1C 4.25V 0.05C cut-off, and discharge condition CC 0.1C to 1C 2.5V cut-off).

[0151] Example 2

[0152] Lithium-nickel-based metal oxide particles and a lithium secondary battery were obtained by the same method as in Example 1, except that the formation charge and discharge conditions were changed (charge condition CC-CV 0.24C 4.35V 0.05C cut-off, discharge condition CC 0.24C 2.5V cut-off).

[0153] Example 3

[0154] A lithium secondary battery was obtained by the same method as in Example 1, except that the mixing ratio of NiSO4, CoSO4, and MnSO4 was changed so that the composition of the prepared lithium-nickel-based metal oxide particles was LiNi 0.76 Co 0.02 Mn 0.22 O2.

[0155] Example 4

[0156] A lithium secondary battery was obtained by the same method as in Example 1, except that the mixing ratio of NiSO4, CoSO4, and MnSO4 was changed so that the composition of the prepared lithium-nickel-based metal oxide particles was LiNi 0.62 Co 0.07 Mn 0.31 O2.

[0157] Comparative Example 1

[0158] Lithium-nickel-based metal oxide particles and a lithium secondary battery were obtained by the same method as in Example 1, except that the formation charge and discharge conditions were changed (charge condition CC-CV 0.24C 4.25V 0.05C cutoff, discharge condition CC 0.24C 2.5V cutoff).

[0159] Comparative Example 2

[0160] A lithium secondary battery was obtained by the same method as in Example 1, except that the mixing ratio of NiSO4, CoSO4, and MnSO4 was changed so that the composition of the prepared lithium-nickel-based metal oxide particles was LiNi 0.64 Co 0.06 Mn 0.30 O2, and change the conditions during formation charge and discharge (charging conditions CC-CV 0.24C 4.45V 0.05C cut-off, discharging conditions CC 0.24C2.5V cut-off).

[0161] The compositions of the lithium-nickel-based metal oxide particles of the above examples and comparative examples and the difference between the voltage during formation charge and discharge and the voltage during driving charge and discharge are shown in Table 1 below.

[0162] [Table 1]

[0163]

[0164] Experimental example

[0165] (1) XRD analysis and lattice strain measurement

[0166] The lithium secondary batteries of the examples and comparative examples were disassembled to obtain positive electrodes. XRD analysis was performed on the positive electrode active material layer included in the positive electrodes to measure peaks at the (101) plane, (102) plane, (104) plane, (105) plane, and (107) plane of the lithium-nickel-based metal oxide particles.

[0167] The Williamson-Hall method defined by Formula 1 was applied to the peaks of the obtained (101) plane, (102) plane, (104) plane, (105) plane, and (107) plane to calculate the lattice strain of the lithium-nickel-based metal oxide particles. The calculation results are recorded in Table 3 below.

[0168] [Formula 1]

[0169]

[0170] (In Formula 1, β is the full width at half maximum of the corresponding peak obtained by XRD analysis (radians), θ is the diffraction angle (radians), ε is the lattice strain (a dimensionless number), λ is the X-ray wavelength (Å), and D is the crystallite size (Å).)

[0171] Figures 3a to 3d A graph showing the slope obtained as follows is recorded in the text: According to the above method, XRD analysis was performed on the positive electrode active material layers of Example 3, Example 4, Comparative Example 1 and Comparative Example 2 to obtain the peaks of the (101) surface, (102) surface, (104) surface, (105) surface and (107) surface of the lithium-nickel-based metal oxide particles, and the Williamson-Hall method was applied to the peaks of the (101) surface, (102) surface, (104) surface, (105) surface and (107) surface of the obtained lithium-nickel-based metal oxide particles, and the slope was obtained by linear regression analysis.

[0172] In addition, specific XRD analysis equipment and conditions are described in Table 2 below.

[0173] [Table 2]

[0174]

[0175] (2) Measurement of discharge capacity

[0176] The lithium secondary batteries of Examples and Comparative Examples were driven to be charged and discharged, and the battery capacity after discharge (discharge capacity) was measured. The measurement results are shown in Table 3 below.

[0177] (3) Evaluation of high temperature life characteristics (45°C)

[0178] The lithium secondary batteries of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were repeatedly driven to charge and discharge 500 times, and the capacity retention rate was evaluated by dividing the discharge capacity of the 100th, 200th, 300th, 400th and 500th times by the percentage of the value of the discharge capacity of the first time.

[0179] The capacity retention ratio at 500 cycles is described in Table 3 below, and a graph showing the capacity retention ratios of the lithium secondary batteries according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2 is described in Figure 4 middle.

[0180] [Table 3]

[0181]

[0182] 1) 45℃

[0183] Referring to Table 3, the discharge capacity of the batteries of Examples 1 to 4 using the lithium-nickel-based metal oxide particles having a lattice strain of 0.2 to 0.4 was high, and the capacity retention rate of the batteries of Examples 1 and 2 was high.

[0184] The discharge capacity of the battery of Comparative Example 1 using lithium-nickel-based metal oxide particles having a lattice strain greater than 0.4 was lower than the discharge capacities of the batteries of Examples 1 to 4.

[0185] The capacity retention rate of the battery of Comparative Example 2 using lithium-nickel-based metal oxide particles having a lattice strain of less than 0.2 was lower than the capacity retention rates of the batteries of Examples 1 and 2.

Claims

1. A lithium secondary battery comprising: A positive electrode comprising a positive electrode active material layer containing a positive electrode active material, wherein the positive electrode active material comprises lithium-nickel-based metal oxide particles; as well as a negative electrode, the negative electrode being arranged opposite to the positive electrode, wherein the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane of the lithium-nickel-based metal oxide particles are measured by performing XRD analysis on the positive electrode active material layer, and the lattice strain ε of the lithium-nickel-based metal oxide particles calculated by applying the Williamson-Hall method defined by Formula 1 to the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane of the measured lithium-nickel-based metal oxide particles is 0.2 to 0.4, [Formula 1] In Formula 1, β is the full width at half maximum of the corresponding peak obtained by XRD analysis and the unit is radian, θ is the diffraction angle and the unit is radian, ε is the lattice strain and is a dimensionless number, λ is the X-ray wavelength and the unit is Å, and D is the crystallite size and the unit is Å.

2. The lithium secondary battery according to claim 1, wherein The lattice strain of the lithium-nickel-based metal oxide particles is the slope of a straight line obtained as follows: obtaining the full width at half maximum of the peaks of the (101) plane, (102) plane, (104) plane, (105) plane and (107) plane appearing in the XRD analysis, substituting the obtained full width at half maximum into the formula 1, and plotting with sinθ as the horizontal axis and βcosθ as the vertical axis to obtain a straight line.

3. The lithium secondary battery according to claim 1, wherein The lattice strain of the lithium-nickel-based metal oxide particles is 0.25 to 0.

38.

4. The lithium secondary battery according to claim 1, wherein The lithium-nickel-based metal oxide particles have a structure represented by the following Chemical Formula 1: [Chemical Formula 1] Li x Ni 1-y M y O 2+z In Chemical Formula 1, x is 0.95≤x≤1.1, y is 0≤y≤0.7, z is −0.1≤z≤0.1, and M is at least one element selected from the group consisting of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

5. The lithium secondary battery according to claim 4, wherein In Chemical Formula 1, (1-y) is 0.6 to 1.

6. The lithium secondary battery according to claim 4, wherein In Chemical Formula 1, M includes Mn.

7. The lithium secondary battery according to claim 1, wherein The lithium-nickel-based metal oxide particles have a structure represented by the following Chemical Formula 2: [Chemical Formula 2] Li a Ni 1-b-c-d Co b Mr c J d O 2+e In Chemical Formula 2, a is 0.95≤a≤1.1, b is 0≤b≤0.1, c is 0≤c≤0.4, d is 0≤d≤0.2, e is -0.1≤e≤0.1, and J is at least one element of Na, Mg, Ca, Y, Ti, Sr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

8. The lithium secondary battery according to claim 7, wherein In Chemical Formula 2, (1-bcd) is 0.6 to 1.

9. The lithium secondary battery according to claim 7, wherein In Chemical Formula 2, b is 0 to 0.

02.

10. The lithium secondary battery according to claim 7, wherein In Chemical Formula 2, c is 0.05 to 0.

35.

11. The lithium secondary battery according to claim 7, wherein In Chemical Formula 2, c is 0.2 to 0.

33.

12. The lithium secondary battery according to claim 7, wherein In Chemical Formula 2, (1-bcd) / c is greater than 1.

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