Positive electrode and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode in which a positive electrode composite layer containing a single-particle positive electrode active material and a point-like conductive material is arranged on a current collector, and the Rolling Index, which is determined by the degree of single-particle formation of the single-particle lithium nickel oxide, the bulk density of the point-like conductive material, the BET specific surface area, and the oil absorption amount, is 0.01 to 1.00. Because the positive electrode has a low porosity and a high rolling density, it is possible to provide a lithium secondary battery with excellent energy density.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery containing the same, and more particularly to a positive electrode with low porosity and high rolling density and a lithium secondary battery containing the same. [Background technology]

[0002] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode contain an active material that allows for the insertion and deintercalation of lithium ions.

[0003] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Of these, lithium cobalt oxide has the advantage of a high operating voltage and excellent capacity characteristics, but the high price of cobalt, the raw material, and the unstable supply make it difficult to commercially apply to high-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifespan characteristics. On the other hand, lithium manganese oxide has excellent stability but suffers from poor capacity characteristics. Therefore, in order to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone, lithium nickel-based oxides containing two or more transition metals have been developed, and among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0004] On the other hand, in order to manufacture batteries with high energy density, it is important to apply a positive electrode active material with high capacity characteristics, but the materials contained in the positive electrode can also act as an important factor. For this reason, research is being conducted in order to maximize the proportion of active material and minimize the content of conductive material and binder. Typically, when using carbon nanotubes (CNTs) as a conductive material, CNTs are linear and located between the active materials, making it easy to ensure conductivity even in small amounts, and offering the advantage of maximizing the loading amount of active material.

[0005] However, in the case of CNTs, there is a problem that if the pressure exceeds a certain level during electrode rolling, it damages the active material. If the rolling density is reduced to prevent damage to the active material and space is created so that linear CNTs exist between the active materials, the electrode thickness increases, the porosity increases, and there is a problem that the energy density cannot be increased.

[0006] Therefore, research is needed to create a cathode that reduces porosity and increases rolling density without damaging the active material. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems by using a point-like conductive material such as carbon black, and in particular by applying a point-like conductive material with a large specific surface area and excellent secondary structure together with a single-particle positive electrode active material, thereby providing a positive electrode with excellent rolling density and low porosity.

[0008] Furthermore, the present invention provides a lithium secondary battery in which the energy density is improved by including the positive electrode. [Means for solving the problem]

[0009] [1] In one aspect of the present invention, a positive electrode composite layer including a single-particle type positive electrode active material and a dot-shaped conductive material is disposed on a current collector, and a positive electrode is provided in which a rolling index represented by the following formula 1 is 0.01 to 1.00. [Formula 1] RI = [(D 50 , 50 , , 50 , , 2 , , 3 ,

[0011] ,

[0012] , , , c , , mean , mean ,

[0013] , c , c , , ,

[0010] / D mean ) × B c / (S c × O c ) × 10 5 In the formula 1, the D mean is the average particle diameter (μm) of nodules measured from a scanning electron microscope image with respect to the single-particle type positive electrode active material, and the D 50 is the average particle diameter (μm) at 50% volume accumulation of the particle size distribution graph obtained by the laser diffraction method with respect to the single-particle type positive electrode active material. The B c is the bulk density of carbon black, which is the unitless number of the bulk density in g / cm 3 . The S c is the BET specific surface area of carbon black, which is the unitless number of the specific surface area in m 2 / g. The O c is the oil absorption number (OAN) of carbon black, which is the unitless number of the oil absorption number in ml / 100g.

[0010] [2] In the positive electrode of [1], the single-particle type positive electrode active material may have D 50 of 2.0 μm to 6.0 μm.

[0011] [3] In the positive electrode of [1] and / or [2], the single-particle type positive electrode active material may have D mean of 0.2 μm to 3.0 μm.

[0012] [4] In at least one of the positive electrodes of [1] to [3], the single-particle type positive electrode active material may have D 50 / D[[ID=​​​​[5] In at least one of the positive electrodes of [1] to [4] above, the point conductive material has a BET specific surface area of ​​300 m 2 / g~1300m 2 / g is also acceptable.

[0014] [6] In at least one of the positive electrodes of [1] to [5] above, the point conductive material may have an oil absorption number of 250 ml / 100 g to 500 ml / 100 g.

[0015] [7] In at least one of the positive electrodes of [1] to [6] above, the point conductive material has a bulk density of 0.05 cm 3 / g~0.14cm 3 / g is also acceptable.

[0016] [8] In at least one of the positive electrodes described in [1] to [7] above, the positive electrode active material comprises one or more selected from the group consisting of lithium nickel oxides and lithium metal phosphate compounds, wherein the lithium nickel oxide has a composition represented by the following chemical formula 1, and the lithium metal phosphate compound may have a composition represented by the following chemical formula 2. [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e In the above chemical formula 1, M 1 It includes one or more selected from Mn and Al, and M 2 x includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X includes one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 <b≦0.35、0<c≦0.35、0≦d≦0.05および0≦e≦0.05である。 [Chemical formula 2] Li 1+x [Fe 1-y M y]PO4 In the above chemical formula 2, M comprises one or more elements selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

[0017] [9] In at least one of the positive electrodes of [1] to [8] above, the point conductive material may be carbon black.

[0018]

[10] In at least one of the positive electrodes described in [1] to [9] above, the porosity of the positive electrode may be 12.0% to 22.0%.

[0019]

[11] In at least one of the positive electrodes of [1] to

[10] , the single-particle lithium nickel oxide may be present in an amount of 93.0% to 99.0% by weight relative to the total weight of the positive electrode composite layer.

[0020]

[12] In at least one of the positive electrodes of [1] to

[11] , the positive electrode composite layer may further include a binder.

[0021]

[13] In another aspect of the present invention, a lithium secondary battery comprising the positive electrode according to the present invention is provided. [Effects of the Invention]

[0022] The positive electrode according to the present invention utilizes a single-particle type positive electrode active material in the form of a single particle and / or pseudo-single particle, which has excellent particle strength. By applying this together with a point-like conductive material that has a large specific surface area and excellent secondary structure, even when rolled at high pressure, the external force applied to the active material particles is dispersed, resulting in less particle cracking and fracture, a smaller amount of fine particles, and a lower porosity.

[0023] Furthermore, as described above, the lithium secondary battery according to the present invention has a positive electrode with high rolling density and low porosity, which improves energy density, reduces cracking and fracture phenomena of the active material particles, reduces side reactions with the electrolyte, reduces the amount of gas generated as a result, and has excellent lifespan characteristics. [Modes for carrying out the invention]

[0024] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0025] In this specification, terms such as “includes,” “equip,” or “have” specify the presence of an implemented feature, figure, step, component, or combination thereof, and should be understood not to preclude the existence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0026] In this invention, "single-particle type" refers to a particle form consisting of 30 or fewer nodules, and the concept of single-particle type particles includes single particles consisting of one nodule and pseudo-single particles which are composites of 2 to 30 nodules.

[0027] The aforementioned "nodule" is a lower particle unit that constitutes a single particle or a pseudo-single particle, and may be a single crystal without crystalline grain boundaries, or a polycrystalline material in which no grain boundaries appear to exist when observed with a scanning electron microscope at a field of view of 5,000 to 20,000 times magnification.

[0028] In this invention, "secondary particle" refers to a particle formed by the aggregation of several tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles.

[0029] The term "particle" as used in this invention may include one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0030] In the present invention, "D mean This method involves imaging the positive electrode active material particles with a scanning electron microscope (SEM), determining the particle size of each nodule for approximately 30 particles containing one or more nodules, and then taking the average value.

[0031] In the present invention, "D 50 " refers to the particle size at the 50% reference level of the volume cumulative particle size distribution of the positive electrode active material powder. The average particle size D 50 This can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, the device is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves at approximately 28 kHz are irradiated at an output of 60 W. After obtaining a volume-cumulative particle size distribution graph, the particle size corresponding to 50% of the volume-cumulative amount can be determined.

[0032] In this invention, "specific surface area (m²) 2 The value of " / g)" was measured using the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using the BELSORP-mini II manufactured by BEL Japan.

[0033] In this invention, "bulk density (g / cm³) 3 )" is the volume (cm³) occupied by the point conductive material. 3 This is the ratio of the mass (g) of the point conductive material to the mass (g), and can be calculated under conditions where no external force is applied.

[0034] In the present invention, the "oil absorption number" of the point conductive material is a value obtained by using DBP (dibutyl phthalate) as the oil and measuring the value by the method described in JIS K6221 Method B, and then converting that value to a value equivalent to JIS K6217-4:2008 using the following formula (a).

[0035] [Formula (a)] DBP absorption amount = (A - 10.974) / 0.7833

[0036] In formula (a), A represents the value of the DBP absorption amount measured by the method described in Method B of JIS K6221.

[0037] The present invention will be described in more detail below.

[0038] The positive electrode and lithium secondary battery according to the present invention include at least one of the configurations described below, and may include any combination of technically possible configurations from the following.

[0039] positive electrode The positive electrode according to the present invention is characterized in that a positive electrode composite layer containing a single-particle positive electrode active material and a point-like conductive material is arranged on a current collector, and the rolling index represented by the following formula 1 is 0.01 to 1.00.

[0040] [Formula 1] RI=[(D 50 / D mean ) × B c ] / (S c ×O c ) × 10 5

[0041] In formula 1, the D mean This is the average particle size (μm) of nodules measured from scanning electron microscope images for single-particle type positive electrode active material, and the above D 50 This is the average particle size (μm) at 50% volume accumulation in the particle size distribution graph obtained by laser diffraction for a single-particle type positive electrode active material, and the above B c This is the bulk density of point-type conductive material, and its unit is g / cm³. 3 It is a unitless number of bulk densities, and the above S c This is the BET specific surface area of ​​the point-type conductive material, in units of m 2 The unitless number of specific surface area is / g, and the above O c This is the oil absorption number (OAN) of the point-type conductive material, and is a unitless number of oil absorption numbers with a unit of ml / 100g.

[0042] Rolling index According to one embodiment of the present invention, the positive electrode is characterized in that a positive electrode composite layer containing a single-particle positive electrode active material and a point-like conductive material is disposed on a current collector, and the rolling index represented by formula 1 is 0.01 to 1.00. The rolling index is characterized in that the physical properties of the single-particle positive electrode active material and the point-like conductive material contained in the positive electrode are factors, and the rolling index is composed of factors that affect the rolling density and porosity of the positive electrode among the physical properties of each material.

[0043] Specifically, to achieve a high-energy-density cathode, it is common to increase the loading amount of active material. Conventionally, it was common to reduce the amount of conductive material used and increase the amount of active material by using carbon nanotubes, which can ensure conductivity even when used in small amounts. However, in this case, controlling the electrode thickness is not easy due to the length characteristics of the carbon nanotubes, and damage to the active material inevitably occurs when the rolling pressure is increased. Therefore, although it is possible to achieve a high-loading cathode, the effect of improving energy density is insufficient.

[0044] However, the positive electrode according to one embodiment of the present invention uses a positive electrode active material in the form of a single particle or pseudo-single particle together with a point-like conductive material with a large specific surface area, and by investigating the relationship between specific factors among the characteristics of each material, it is possible to realize a positive electrode with improved energy density without damage to the active material particles.

[0045] Specifically, the rolling index is expressed by the following formula 1 and is characterized by being between 0.01 and 1.00.

[0046] [Formula 1] RI=[(D 50 / D mean ) × B c ] / (S c ×O c ) × 10 5

[0047] In formula 1, the D meanThis is the average particle size (μm) of nodules measured from scanning electron microscope images for single-particle type positive electrode active material, and the above D 50 This is the average particle size (μm) at 50% volume accumulation in the particle size distribution graph obtained by laser diffraction for a single-particle type positive electrode active material, and the above B c This is the bulk density of point-type conductive material, and its unit is g / cm³. 3 It is a unitless number of bulk densities, and the above S c This is the BET specific surface area of ​​the point-type conductive material, in units of m 2 The unitless number of specific surface area is / g, and the above O c This is the oil absorption number (OAN) of the point-type conductive material, and is a unitless number of oil absorption numbers with a unit of ml / 100g.

[0048] D, which was included as a factor in the rolling index. 50 / D mean This can be called the degree of single-particle formation, and it is used to describe the particle characteristics of a single-particle type positive electrode active material, indicating that it is not in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles. The smaller the ratio, the closer the positive electrode active material can be to a single particle or pseudo-single particle form, and as the particle strength increases, it can withstand high rolling pressures without being damaged.

[0049] Furthermore, the bulk density and oil absorption number of the point-shaped conductive material are characteristics related to the secondary structure of the point-shaped conductive material. A smaller bulk density means that its shape is more uniform and bulky, while a larger oil absorption number means that it has a higher ability to replenish the electrolyte and may indicate a larger secondary structure. In other words, the characteristics of the secondary structure of the point-shaped conductive material are ultimately a measure of how well the point-shaped conductive material is arranged between the particles of the single-particle positive electrode active material and how well the voids can be minimized. The smaller the bulk density and the larger the oil absorption number, the better the secondary structure of the point-shaped conductive material can be.

[0050] Furthermore, the specific surface area of ​​the point-like conductive material may represent the number of point-like conductive materials per unit mass, and a larger number of point-like conductive materials may mean that they are better positioned to find voids within the positive electrode.

[0051] The rolling index according to one embodiment of the present invention was derived considering the relationships of the factors described above. While a larger number of point-like conductive materials per unit mass is advantageous for filling voids, a larger number of point-like conductive materials per unit mass may indirectly affect the size of the secondary structure. Even if the secondary structure of the point-like conductive materials is bulky, if it is not densely formed, the bulk density may be small, but the ability to hold electrolyte may be poor, and the oil absorption number may be small. In other words, the present invention derives the rolling index by considering the characteristics of point-like conductive materials that have such complex relationships.

[0052] Furthermore, even when such point-like conductive materials satisfy all conditions and the relationship is well established, if an active material that cannot withstand high rolling pressure and is easily damaged is used, it may be difficult to realize an electrode with high energy density. Therefore, the relationship is completed by reflecting the particle size characteristics of the active material, i.e., the single-particle type cathode active material, in the rolling index.

[0053] The rolling index derived from formula 1 in this way is 0.01 to 1.00, preferably 0.03 or more, 0.05 or more, 0.08 or more, 0.10 or more, 0.15 or more, or 0.20 or more, and may be 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, 0.65 or less, or 0.60 or less.

[0054] If the rolling index is less than 0.01, the bulk density of the point-like conductive material and the secondary structure due to the oil absorption number may be excessively bulky, and the conductive material itself may have a high porosity. This means that it may not be well-positioned in the voids that can be formed within the positive electrode, and even if it is well-positioned, it may have a structure that makes it difficult to fill even the fine voids. In fact, it may not be possible to reduce the porosity of the electrode, and therefore the energy density may not be improved. On the other hand, if the rolling index is greater than 1.00, the specific surface area of ​​the point-like conductive material is insufficient, and the rolling density cannot be increased, making it difficult to reduce the porosity of the electrode. The conductive material particles may not be well-positioned between the single-particle positive electrode active material particles, and the assurance of conductivity may not be smooth. On the other hand, the particle size characteristics of the positive electrode active material become closer to secondary particles than single particles, and problems such as an increase in differential amount and a decrease in volume may occur due to particle damage at high rolling pressure.

[0055] The following explains each of the factors included in the aforementioned rolling index relation.

[0056] positive electrode active material According to one embodiment of the present invention, the single-particle type cathode active material has a degree of single-particle formation (D 50 / D mean ) may be 1 to 10. Single-particle positive electrode active materials have higher particle strength compared to conventional secondary particle positive electrode active materials in which tens to hundreds of primary particles are aggregated, resulting in less particle cracking during rolling. In addition, in the case of the single-particle positive electrode active material, the number of lower-component elements (i.e., nodules) that make up the particle is small, so there is less change due to volume expansion and contraction of the primary particles during charging and discharging, and as a result the occurrence of cracks inside the particle is also significantly reduced.

[0057] The smaller the degree of single-particle formation, the more likely it is that the particles are in the form of single particles or in the form of pseudo-single particles composed of a small number of nodules. Thus, the degree of single-particle formation is preferably 1 to 8, 1 to 7, 1 to 6, or 1 to 5. When this range is met, the degree of particle fracture can be reduced, the rolling density can be improved, and improvements in both lifetime characteristics and energy density can be expected.

[0058] According to one embodiment of the present invention, the D of the single-particle type cathode active material 50 The particle size may be between 2.0 μm and 6.0 μm.

[0059] The single-particle type positive electrode active material has an average particle size of 2.0 μm to 6.0 μm at 50% of the cumulative volume of particles, preferably 2.3 μm or more, 2.5 μm or more, 2.7 μm or more, 3.0 μm or more, or 3.5 μm or more, and may be 6.0 μm or less, 5.8 μm or less, 5.5 μm or less, or 5.0 μm or less. 50 If the above range is met, there is the advantage that the rolling density can be increased without damaging the active material particles.

[0060] According to one embodiment of the present invention, the average particle size (D) of the nodules of the single-particle type positive electrode active material. mean The particle size may be 0.2 μm to 3.0 μm, and the average particle size of the nodule may preferably be 0.5 μm or more, 0.7 μm or more, or 1.0 μm or more, and may also be 2.8 μm or less, 2.5 μm or less, or 2.0 μm or less. When the above range is satisfied, the range of single-particle degree can be satisfied, and the effects thereon can be expected.

[0061] The single-particle positive electrode active material according to the present invention may include one or more selected from the group consisting of lithium nickel oxides and lithium metal phosphate compounds.

[0062] For example, the lithium nickel oxide may have a composition represented by the following chemical formula 1.

[0063] [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0064] In the above chemical formula 1, M 1 It includes one or more selected from Mn and Al, and M 2 x includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X includes one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 <b≦0.35、0<c≦0.35、0≦d≦0.05および0≦e≦0.05である。

[0065] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, M 2 This is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 While elements are not essential, if present in appropriate amounts, they can promote grain growth during calcination or improve crystal structure stability. Furthermore, X is an anion substituted at the oxygen site and can include N, P, S, F, or Cl.

[0066] The aforementioned 1+x represents the molar ratio of lithium in the lithium nickel oxide, and may be 0≦x≦0.1, 0≦x≦0.08, 0≦x≦0.05, 0≦x≦0.03, or 0≦x≦0.02.

[0067] The above-mentioned a represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based oxide, and 0.50 ≦ a < 1.00, 0.60 ≦ a ≦ 0.99, 0.70 ≦ a ≦ 0.99, or 0.75 ≦ a ≦ 0.99, 0.80 ≦ a ≦ 0.99, 0.82 ≦ a ≦ 0.99, 0.84 ≦ a ≦ 0.99, or 0.86 ≦ a ≦ 0.99 may be satisfied.

[0068] The above-mentioned b represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based oxide, and 0 < b ≦ 0.35, 0.01 ≦ b ≦ 0.34, 0.01 ≦ b ≦ 0.30, 0.01 ≦ b ≦ 0.25, 0.01 ≦ b ≦ 0.20, or 0.01 ≦ b ≦ 0.15 may be satisfied.

[0069] The above-mentioned c represents the molar ratio of M 1 among all metals other than lithium in the lithium nickel-based oxide, and 0 < c ≦ 0.35, 0.01 ≦ c ≦ 0.34, 0.01 ≦ c ≦ 0.30, 0.01 ≦ c ≦ 0.25, 0.01 ≦ c ≦ 0.20, or 0.01 ≦ c ≦ 0.15 may be satisfied.

[0070] The above-mentioned d represents the molar ratio of the M 2 element among all metals other than lithium in the lithium nickel-based oxide, and 0 ≦ d ≦ 0.05, 0 ≦ d ≦ 0.02, or 0 ≦ d ≦ 0.01 may be satisfied.

[0071] The above-mentioned e represents the molar ratio of the X element among all non-metals other than oxygen in the lithium nickel-based oxide, and 0 ≦ e ≦ 0.05, 0 ≦ e ≦ 0.02, or 0 ≦ e ≦ 0.01 may be satisfied.

[0072] On the other hand, the lithium nickel-based oxide may further include a coating layer containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S on the surface of the particles.

[0073] When a coating layer is present on the surface of single-particle lithium nickel oxide particles, the coating layer suppresses contact between the electrolyte and the single-particle lithium nickel oxide, thereby reducing the elution of transition metals and the generation of gases due to side reactions with the electrolyte.

[0074] Preferably, the coating layer may contain Co as a coating element. When a coating layer containing Co is formed on the surface of single-particle lithium nickel oxide particles, an effect of suppressing side reactions with the electrolyte and an effect of improving output can be obtained.

[0075] Furthermore, the lithium metal phosphate compound may have a composition represented by the following chemical formula 2.

[0076] [Chemical formula 2] Li 1+x [Fe 1-y M y ]PO4

[0077] In the above chemical formula 2, M comprises one or more elements selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

[0078] The lithium metal phosphate compound can be doped with M. In this case, the lattice structure and distance within the olivine crystal structure, which is the crystalline structure, change, increasing the diffusivity of lithium ions, and as a result, the electrochemical properties of the battery containing the positive electrode active material can be improved.

[0079] The aforementioned x may be -0.5 to 0.5, preferably -0.3 or greater, -0.1 or greater, or 0 or greater, and may also be 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0080] The aforementioned y may be 0 or greater, less than 1, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.20 or less, 0.10 or less, or 0.05 or less.

[0081] The lithium metal phosphate compound may be, for example, LiFePO4.

[0082] The lithium metal phosphate compound according to the present invention may be in the form of a single particle consisting of only one primary particle, or in the form of amorphous secondary particles consisting of 2 to 50 primary particles. Furthermore, the lithium metal phosphate compound may contain an olivine structure, and more specifically, may consist solely of an olivine structure. The coating layer according to the present invention may be formed not only on the secondary particles but also on the primary particles. That is, the coating layer according to the present invention can be uniformly present on the surface of primary particles that exist inside the secondary particles.

[0083] The coating layer may include a carbon coating layer with a graphite structure, and the thickness of the coating layer may be 0.5 nm to 5 nm. When the thickness of the coating layer is within the above range, there is an advantage in that electrical conductivity is improved and the movement of lithium ions is not hindered. Specifically, the thickness of the coating layer may be 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, or 3.0 nm or more, and may be 5.0 nm or less.

[0084] The coating layer may be uniformly coated on the surface of the lithium metal phosphate compound. That is, the coating layer may be in the form of a thin film. The coating layer can improve the ionic conductivity and electronic conductivity during charging and discharging of the battery containing the positive electrode active material. In addition to carbon, the coating layer may contain trace amounts of impurities such as nitrogen, oxygen, and hydrogen.

[0085] The coating layer can be contained in an amount of 0.5 wt% to 3 wt% based on the total weight of the lithium metal phosphate-based compound so as to improve the electric conductivity and not to prevent the entry and exit of lithium ions.

[0086] Dot-shaped conductive material The positive electrode according to an embodiment of the present invention includes a dot-shaped conductive material, and the dot-shaped conductive material can include carbon black, and the carbon black may be, for example, one or more selected from the group consisting of acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Generally, for a single-particle positive electrode active material, since the particle strength is high and even if only a small amount is used to increase the loading amount, carbon nanotubes that can easily ensure conductivity are used. However, as described above, carbon nanotubes are not suitable for the positive electrode to be realized in the present invention because they cause damage even with a high rolling pressure even if the particle strength of a single particle is strong. Therefore, the positive electrode of the present invention may not include carbon nanotubes.

[0087] According to an embodiment of the present invention, the dot-shaped conductive material is a material that has a great influence on the setting of the relationship of the rolling index, and as described above, the BET specific surface area, bulk density, and oil absorption number may be the main factors.

[0088] The BET specific surface area of the dot-shaped conductive material may be 290 m 2 / g to 1300 m 2 / g, which is measured by the BET method. Specifically, it can be calculated from the nitrogen gas adsorption amount at a liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan. Preferably, 300 m 2 / g or more, 330 m 2 / g or more, 370 m 2 / g or more, 400 m 2 / g or more, 420 m 2 / g or more, 440 m 2 / g or more, 460 m 2 / g or more, 480 m 2 / g or more, or 500 m2 It may be more than / g, and also 1200m 2 / g or less, 1100m 2 / g or less, 1000m 2 / g or less, 950m 2 / g or less, 900m 2 / g or less, or 880m 2 It may be less than / g.

[0089] The specific surface area is a factor that greatly influences the determination of the rolling index, and it is preferable to apply the largest possible specific surface area. Typically, point conductive materials have a specific surface area of ​​100 m². 2 / g~200m 2 The value per gram applies, and the maximum value is 250m 2 It is common to use point-like conductive materials with a specific surface area of ​​1 / g, and when attempting to use conductive materials with a high specific surface area, it is generally considered common to use linear conductive materials such as carbon nanotubes, considering the conductivity that can be ensured relative to the content. However, the rolling index according to one embodiment of the present invention can be realized when a point-like conductive material with a large specific surface area is used instead of a linear conductive material, and can be a factor that can minimize the voids in the positive electrode.

[0090] Furthermore, the bulk density of the point-shaped conductive material is 0.05 cm². 3 / g~0.14cm 3 It may also be / g, and the volume occupied by the point conductive material (cm³ 3 This is the ratio of the mass (g) of the point conductive material to the ), and can be calculated under conditions where no external force is applied. Preferably, 0.06 cm 3 / g or more, 0.08cm 3 / g or more, 0.09cm 3 / g or more, or 0.10cm 3 It may be 0.135 cm or more, and also 0.135 cm 3 / g or less, 0.132cm 3 / g or less, 0.13cm 3It may be less than / g. When the bulk density satisfies the above range, the point conductive material can be considered to have a secondary structure in which it can be positioned between the active material particles, which can help reduce porosity and increase rolling density.

[0091] Furthermore, the oil absorption number of the point-shaped conductive material may be 250 ml / 100 g to 500 ml / 100 g, and the value measured using DBP (dibutyl phthalate) as the oil, according to the method of Method B of JIS K6221, is shown as the value converted to a value equivalent to JIS K6217-4:2008 using the following formula (a).

[0092] [Formula (a)] DBP absorption amount = (A - 10.974) / 0.7833

[0093] In formula (a), A represents the value of the DBP absorption amount measured by the method described in JIS K62.

[0094] The oil absorption number is preferably 260 ml / 100g or more, 270 ml / 100g or more, 280 ml / 100g or more, 290 ml / 100g or more, or 300 ml / 100g or more, and may also be 495 ml / 100g or less, 490 ml / 100g or less, 485 ml / 100g or less, or 480 ml / 100g or less. When the above range is satisfied, the conditions for density and bulkiness of the secondary structure can be met, thereby not only the ability to hold the electrolyte but also the effect of dispersing the external force acting on the active material particles under high rolling pressure can be obtained.

[0095] Positive electrode and others As described above, the positive electrode according to the present invention comprises a single-particle positive electrode active material and a point-like conductive material, and may further comprise a binder. The positive electrode active material, the point-like conductive material, and the binder constitute a positive electrode composite layer, and the positive electrode composite layer can be formed on a positive electrode current collector.

[0096] Here, the positive electrode active material may be included in an amount of 90% to 99% by weight, more specifically 93% or more by weight, 95% or more by weight, 96% or more by weight, or 97% or more by weight, with a content of 98.5% or less by weight, or 98% or less by weight, and when included within the above content range, it can exhibit excellent capacity characteristics.

[0097] Furthermore, the point-shaped conductive material may be included in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode composite layer, preferably 0.3% or more by weight, 0.5% or more by weight, 0.7% or more by weight, or 1.0% or more by weight, and may also be 9.0% or less by weight, 8.5% or less by weight, 8.0% or less by weight, 7.5% or less by weight, 7.0% or less by weight, or 6.5% or less by weight.

[0098] Furthermore, according to one embodiment of the present invention, the positive electrode may further contain a binder. The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode composite layer, preferably 0.3% or more by weight, 0.5% or more by weight, 0.7% or more by weight, or 1.0% or more by weight, and may also be 9.0% or less by weight, 8.5% or less by weight, 8.0% or less by weight, 7.5% or less by weight, 7.0% or less by weight, or 6.5% or less by weight.

[0099] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode composite layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on its surface to enhance the adhesion of the positive electrode active material. It can be used in various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0100] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material powder is used. Specifically, the positive electrode slurry composition, which is prepared by dissolving or dispersing the positive electrode active material powder and, if necessary, a binder, a conductive material, and a dispersant in a solvent, is applied to a positive electrode current collector, followed by drying and rolling.

[0101] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0102] Alternatively, the positive electrode can also be manufactured by casting the positive electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0103] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described. The lithium secondary battery according to the present invention includes the positive electrode of the present invention as described above.

[0104] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes. As the positive electrode is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0105] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0106] In the lithium secondary battery described above, the negative electrode may include a negative electrode current collector and a negative electrode composite layer located on the negative electrode current collector, and the negative electrode composite layer may include a negative electrode active material, a binder, and a conductive material.

[0107] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used.

[0108] The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, preferably 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities can also be formed on the surface of the current collector to strengthen the bonding force with the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven bodies, etc.

[0109] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. For example, carbon materials such as artificial graphite, natural graphite, kish graphite, pyrolytic carbon, meso-carbon microbeads, mesophase pitches, petroleum / coal tar pitch derived cokes, mesophase pitch based carbon fiber, graphitized carbon fiber, amorphous carbon, softened carbon, or hardened carbon; (semi) metallic materials capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO b (0 < b ≤ 2), (semi) metallic oxide materials such as SnO2, vanadium oxides, lithium vanadium oxides, which can be doped and undoped with lithium; heterogeneous composite materials such as Si-C composites or Sn-C composites; or metal lithium thin films, etc. One or a mixture of two or more of these can be used.

[0110] Preferably, the negative electrode active material can include one or more selected from the group consisting of silicon-based active materials, carbon-based active materials, and silicon-carbon composite active materials. More preferably, the carbon-based active material can include one or more selected from the group consisting of artificial graphite, natural graphite, softened carbon, and hardened carbon, and the silicon-based active material can include pure Si particles and / or SiO b(0 < b ≤ 2) can be included, and the silicon-carbon composite active material can include a Si-C composite. Further, as the negative electrode active material, a mixed active material in which two or more of the above substances are mixed may be applied.

[0111] The negative electrode active material can be contained in an amount of 60% to 99% by weight based on the total weight of the negative electrode composite material layer, preferably 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, and can also be contained in an amount of 98% by weight or less, 97% by weight or less, 95% by weight or less.

[0112] The binder is a component that helps to bond the conductive material, active material, and current collector, and can usually be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode composite layer, and can be present in amounts of 0.2% or more by weight, 0.3% or more by weight, or 0.5% or more by weight, and can also be present in amounts of 8% or less by weight, or 5% or less by weight. Examples of such binders include one or more selected from the group consisting of styrene-butadiene copolymer, acrylate-styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, and polyvinyl alcohol. In particular, it may include one or more selected from the group consisting of styrene-butadiene copolymer, acrylate-styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, diacetylcellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylfuran, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, and cyanoethylsucrose. Preferably, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, or mixtures thereof are used. The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less, relative to the total weight of the negative electrode composite layer, and may also be included in amounts of 0.01% by weight or more, 0.05% by weight or more, 0.08% by weight or more, 0.1% by weight or more, or 0.3% by weight or more.Such conductive materials are not particularly limited as long as they do not cause chemical changes in the battery and are conductive. Examples of usable conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0113] The negative electrode composite layer can be manufactured by applying a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and, selectively, a binder and a conductive material in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0114] In the lithium secondary battery described above, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0115] Examples of electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0116] The electrolyte may include an organic solvent and a lithium salt.

[0117] The organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0118] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of the following, and the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0119] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Here, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0120] Examples Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0121] Examples 1-6 and Comparative Examples 1-5 As a single-particle lithium nickel oxide having the particle size characteristics shown in Table 1 below, LiNi 0.6 Co 0.1 Mn 0.3 A material having an O2 composition was applied as the positive electrode active material, and carbon black having the properties described in Table 1 below was used to manufacture the positive electrodes of Examples 1-6 and Comparative Examples 1-5.

[0122] The positive electrode was manufactured by mixing the positive electrode active material, carbon black, and PVDF binder in an N-methylpyrrolidone solvent in a weight ratio of 97.0:1.2:1.8 to produce a positive electrode slurry (5,000 mPa.s), applying this slurry to one surface of an aluminum current collector, drying it at 130°C, and rolling it at a linear pressure of 2,000 kgf / cm.

[0123] [Table 1]

[0124] Examples 7-10 and Comparative Examples 6-8 A single-particle lithium iron phosphate with the particle size characteristics shown in Table 2 below, having a LiFePO4 composition, was used as the positive electrode active material, and carbon black with the characteristics shown in Table 2 below was applied to produce the positive electrodes of Examples 7-10 and Comparative Examples 6-8.

[0125] The positive electrode was manufactured by mixing the positive electrode active material, carbon black, and PVDF binder in an N-methylpyrrolidone solvent in a weight ratio of 97.0:1.2:1.8 to produce a positive electrode slurry (approximately 15,000 mPa.s), applying this slurry to one surface of an aluminum current collector, drying it at 130°C, and rolling it at a linear pressure of 2,000 kgf / cm.

[0126] [Table 2]

[0127] The particle size characteristics of the positive electrode active material and the physical properties of the carbon black were measured by the following method.

[0128] 1) D mean The particle size (μm) was determined by scanning electron microscopy (SEM) at a magnification of 5.0K for positive electrode active material particles. For approximately 30 particles containing one or more nodules, the particle size of each nodule was determined, and then the average value was taken.

[0129] 2) D 50 The particle size (μm) was determined by dispersing the positive electrode active material powder in a dispersion medium, introducing it into a laser diffraction particle size analyzer (Microtrac MT 3000), irradiating it with ultrasound at approximately 28 kHz at an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume-cumulative amount.

[0130] 3) Specific surface area (m 2The amount ( / g) was measured using the BET method, calculated from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using a BELSORP-mino II manufactured by BEL Japan.

[0131] 4) Bulk density (g / cm³) 3 ) is the volume (cm³) occupied by the point conductive material. 3 This is the ratio of the mass (g) of the point conductive material to the mass (g), calculated under conditions where no external force is applied.

[0132] 5) The oil absorption amount was measured using DBP (dibutyl phthalate) as the oil, according to the method described in JIS K6221 Method B, and the value was converted to a value equivalent to JIS K6217-4:2008 using the following formula (a).

[0133] [Formula (a)] DBP absorption amount = (A - 10.974) / 0.7833

[0134] In formula (a), A represents the value of the DBP absorption amount measured by the method described in JIS K6221 Method B.

[0135] Experimental Example 1: Electrode Characteristic Evaluation (Porosity and Rolling Density) The rolling density of the mixed powders of the positive electrode active material and carbon black from the above examples and comparative examples was measured using a density measuring instrument (Caver Pellet Press). Specifically, 3 g of the mixed powders of the positive electrode active material and carbon black from the above examples and comparative examples were divided into smaller portions, filled tightly into a cylindrical holder with a diameter of 13 mm, and then rolled using a force of 9 tonf to measure the rolling density (g / cc).

[0136] The porosity was calculated using the following formula 1.

[0137] [Formula 1] Porosity of the cathode composite layer after rolling (%) = {1 - (electrode density of the cathode composite layer after rolling / true density of the cathode composite layer)} × 100

[0138] In the above formula 1, the true density of the positive electrode composite layer is the density of the positive electrode composite layer measured when the positive electrode composite layer is taken in a predetermined size and pressed with a press device until the thickness of the positive electrode composite layer no longer changes, and the electrode density of the positive electrode composite layer after rolling is the density of the positive electrode composite layer measured when the positive electrode composite layer is taken in a predetermined size after rolling.

[0139] [Table 3]

[0140] [Table 4]

[0141] Referring to Table 3 above, it can be confirmed that in Examples 1 to 6, which satisfy the rolling index, the rolling density is excellent, and the porosity is also considerably low because the carbon black is well arranged in the voids between the positive electrode active material particles.

[0142] On the other hand, referring to Comparative Examples 1 to 5, in which the rolling index is either less than 0.01 or greater than 1.00, it can be confirmed that the properties of the carbon black are not appropriate in relation to the positive electrode active material particles; that is, the specific surface area, OAN, and bulk density cannot be properly related, resulting in low rolling density and high porosity.

[0143] Referring to Table 4, it can be confirmed that, similar to the results in Table 3, Examples 7-10 have lower porosity and higher rolling density compared to Comparative Examples 6-8.

[0144] Experiment Example 2: Battery Performance Evaluation An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and the negative electrode of the above-mentioned examples and comparative examples. After positioning this assembly inside a case, an electrolyte solution was injected to manufacture a lithium secondary battery.

[0145] Here, the electrolyte was prepared by dissolving 1M LiPF6 in an organic solvent in a volume ratio of 3:4:4 as ethylene carbonate / ethyl methyl carbonate / diethyl carbonate, and the negative electrode was prepared as follows.

[0146] The anode slurry was prepared by adding artificial graphite as a graphite-based active material, carbon black as a conductive material, and CMC:SBR as a binder to distilled water in a weight ratio of 95.6:1.0:1.1:2.3 to a solid content concentration of 45% by weight. In this process, the conductive material and binder were dispersed in water using a homomixer at 2500 rpm for 30 minutes (min), and then the anode active material was added and dispersed again at 2500 rpm for 30 minutes (min) to prepare the anode slurry.

[0147] As the negative electrode current collector, a copper current collector (thickness: 8 μm) is coated with the negative electrode slurry at a concentration of 10.0 mg / cm³. 2 The negative electrode was manufactured by coating it with the specified loading amount, rolling it (roll press), and drying it in a vacuum oven at 130°C for 10 hours.

[0148] The lithium secondary battery was charged at 4.2V with a C-rate of 0.1C, then discharged to 2.5V, and an activation process was performed.

[0149] Each lithium secondary battery manufactured as described above was charged in CCCV mode to 0.2C and 4.25V (termination current 1 / 20C). Subsequently, at 45°C, it was charged to 4.25V with a constant current of 0.33C and discharged to 2.5V with a constant current of 0.33C, with each cycle being considered one unit. The charge and discharge capacities were measured while performing 100 charge-discharge cycles. Using the measurement results, the capacity retention rate was calculated as follows and is shown in Tables 5 and 6 below.

[0150] Capacity retention rate (%) = (Discharge capacity after 100 cycles) / (Discharge capacity after 1 cycle) × 100

[0151] [Table 5]

[0152] [Table 6]

[0153] Referring to Table 5 above, it can be confirmed that Examples 1 to 6, which satisfy the rolling index, have low porosity, and despite the increased energy density, side reactions due to cracking of active material particles are significantly reduced, resulting in excellent life characteristics.

[0154] However, in the case of Comparative Examples 1-3, which have a high rolling index, the number of conductive materials is relatively smaller compared to the example, and therefore the number of conductive paths formed is also smaller. In the case of Comparative Examples 4 and 5, which have a low rolling index, the porosity of the conductive material itself and the porosity of the electrodes increased due to the inability to reduce the fine pores within the electrodes, resulting in longer conductive paths compared to the example. Consequently, comparative examples with fewer or longer conductive paths compared to the example may experience faster battery degradation, which can be confirmed by the low capacity retention rate.

[0155] Furthermore, referring to Table 6, it can be confirmed that the results show the same trend as those of the examples and comparative examples in Table 5.

[0156] In other words, when a positive electrode is manufactured by applying a positive electrode active material and a conductive material to satisfy the rolling index according to one embodiment of the present invention, it can be confirmed that the porosity of the electrode can be reduced, rolling can be performed at a high rolling density, the conductive path is short and densely formed, and the life characteristics can be improved. As a result, the resistance characteristics of the electrode are improved, and it can be expected that the output of the battery can also be improved.

Claims

1. A positive electrode composite layer containing a single-particle positive electrode active material and a point-like conductive material is arranged on the current collector. A positive electrode having a rolling index (Rolling Index) of 0.01 to 1.00, as expressed by formula 1 below. [Formula 1] RI = [(D ５０ / D ｍｅａｎ ) × B ｃ ] / ( S ｃ ×O ｃ ) × 10 ５ In the above formula 1, The aforementioned D ｍｅａｎ This is the average particle size (μm) of nodules measured from scanning electron microscope images for single-particle type cathode active material. The aforementioned D ５０ This is the average particle size (μm) at 50% volume accumulation in the particle size distribution graph obtained by laser diffraction for single-particle type cathode active material. Said B ｃ is the bulk density of carbon black, and is the unitless number of the bulk density in g / cm ３ and is the unitless number of the bulk density, The aforementioned S ｃ This is the BET specific surface area of ​​carbon black, in units of m². ２ It is a unitless number of specific surface area, where / g is the value of the specific surface area. The aforementioned O ｃ This is the oil absorption number (OAN) of carbon black, and is a unitless number of oil absorption numbers with a unit of ml / 100g.

2. The aforementioned single-particle positive electrode active material is D ５０ The positive electrode according to claim 1, wherein the particle size is 2.0 μm to 6.0 μm.

3. The aforementioned single-particle positive electrode active material is D ｍｅａｎ The positive electrode according to claim 1, wherein the particle size is 0.2 μm to 3.0 μm.

4. The aforementioned single-particle positive electrode active material is D ５０ / D ｍｅａｎ The positive electrode according to claim 1, wherein the value is 1 to 10.

5. The aforementioned point-shaped conductive material has a BET specific surface area of ​​300 m². ２ / g ~ 1300m ２ The positive electrode according to claim 1, wherein the value is / g.

6. The positive electrode according to claim 1, wherein the point-shaped conductive material has an oil absorption number of 250 ml / 100 g to 500 ml / 100 g.

7. The aforementioned point-shaped conductive material has a bulk density of 0.05 cm³. ３ / g ~ 0.14cm ３ The positive electrode according to claim 1, wherein the value is / g.

8. The single-particle positive electrode active material comprises one or more selected from the group consisting of lithium nickel oxides and lithium metal phosphate compounds. The lithium nickel oxide has the composition represented by the following chemical formula 1, The positive electrode according to claim 1, wherein the lithium metal phosphate compound has a composition represented by the following chemical formula 2. [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２－ｅ X ｅ In the above chemical formula 1, M １ It includes one or more selected from Mn and Al, and M ２ x includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and x includes one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 < b ≤ 0.35, 0 < c ≤ 0.35, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.

05. [Chemical formula 2] Li １＋ｘ [Fe １－ｙ M ｙ ]PO ４ In the above chemical formula 2, M includes one or more elements selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

9. The positive electrode according to claim 1, wherein the point-shaped conductive material includes carbon black.

10. The positive electrode according to claim 1, wherein the positive electrode has a porosity of 12.0% to 22.0%.

11. The positive electrode according to claim 1, wherein the single-particle lithium nickel oxide is present in an amount of 93.0% to 99.0% by weight relative to the total weight of the positive electrode composite layer.

12. The positive electrode according to claim 1, wherein the positive electrode composite layer further comprises a binder.

13. A lithium secondary battery comprising the positive electrode described in claim 1.

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